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godot VisualScriptComment VisualScriptComment
===================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A Visual Script node used to annotate the script.
Description
-----------
A Visual Script node used to display annotations in the script, so that code may be documented.
Comment nodes can be resized so they encompass a group of nodes.
Properties
----------
| | | |
| --- | --- | --- |
| [String](class_string#class-string) | [description](#class-visualscriptcomment-property-description) | `""` |
| [Vector2](class_vector2#class-vector2) | [size](#class-visualscriptcomment-property-size) | `Vector2( 150, 150 )` |
| [String](class_string#class-string) | [title](#class-visualscriptcomment-property-title) | `"Comment"` |
Property Descriptions
---------------------
### [String](class_string#class-string) description
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_description(value) |
| *Getter* | get\_description() |
The text inside the comment node.
### [Vector2](class_vector2#class-vector2) size
| | |
| --- | --- |
| *Default* | `Vector2( 150, 150 )` |
| *Setter* | set\_size(value) |
| *Getter* | get\_size() |
The comment node's size (in pixels).
### [String](class_string#class-string) title
| | |
| --- | --- |
| *Default* | `"Comment"` |
| *Setter* | set\_title(value) |
| *Getter* | get\_title() |
The comment node's title.
godot Semaphore Semaphore
=========
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A synchronization semaphore.
Description
-----------
A synchronization semaphore which can be used to synchronize multiple [Thread](class_thread#class-thread)s. Initialized to zero on creation. Be careful to avoid deadlocks. For a binary version, see [Mutex](class_mutex#class-mutex).
Tutorials
---------
* [Using multiple threads](https://docs.godotengine.org/en/3.5/tutorials/performance/threads/using_multiple_threads.html)
Methods
-------
| | |
| --- | --- |
| [Error](class_%40globalscope#enum-globalscope-error) | [post](#class-semaphore-method-post) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [try\_wait](#class-semaphore-method-try-wait) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [wait](#class-semaphore-method-wait) **(** **)** |
Method Descriptions
-------------------
### [Error](class_%40globalscope#enum-globalscope-error) post ( )
Lowers the `Semaphore`, allowing one more thread in.
**Note:** This method internals' can't possibly fail, but an error code is returned for backwards compatibility, which will always be [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok).
### [Error](class_%40globalscope#enum-globalscope-error) try\_wait ( )
Like [wait](#class-semaphore-method-wait), but won't block, so if the value is zero, fails immediately and returns [@GlobalScope.ERR\_BUSY](class_%40globalscope#class-globalscope-constant-err-busy). If non-zero, it returns [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok) to report success.
### [Error](class_%40globalscope#enum-globalscope-error) wait ( )
Waits for the `Semaphore`, if its value is zero, blocks until non-zero.
**Note:** This method internals' can't possibly fail, but an error code is returned for backwards compatibility, which will always be [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok).
godot PoolColorArray PoolColorArray
==============
A pooled array of [Color](class_color#class-color)s.
Description
-----------
An array specifically designed to hold [Color](class_color#class-color). Optimized for memory usage, does not fragment the memory.
**Note:** This type is passed by value and not by reference. This means that when *mutating* a class property of type `PoolColorArray` or mutating a `PoolColorArray` within an [Array](class_array#class-array) or [Dictionary](class_dictionary#class-dictionary), changes will be lost:
```
var array = [PoolColorArray()]
array[0].push_back(Color(0.1, 0.2, 0.3, 0.4))
print(array) # [[]] (empty PoolColorArray within an Array)
```
Instead, the entire `PoolColorArray` property must be *reassigned* with `=` for it to be changed:
```
var array = [PoolColorArray()]
var pool_array = array[0]
pool_array.push_back(Color(0.1, 0.2, 0.3, 0.4))
array[0] = pool_array
print(array) # [[(0.1, 0.2, 0.3, 0.4)]] (PoolColorArray with 1 element inside an Array)
```
Methods
-------
| | |
| --- | --- |
| [PoolColorArray](#class-poolcolorarray) | [PoolColorArray](#class-poolcolorarray-method-poolcolorarray) **(** [Array](class_array#class-array) from **)** |
| void | [append](#class-poolcolorarray-method-append) **(** [Color](class_color#class-color) color **)** |
| void | [append\_array](#class-poolcolorarray-method-append-array) **(** [PoolColorArray](#class-poolcolorarray) array **)** |
| [int](class_int#class-int) | [count](#class-poolcolorarray-method-count) **(** [Color](class_color#class-color) value **)** |
| [bool](class_bool#class-bool) | [empty](#class-poolcolorarray-method-empty) **(** **)** |
| void | [fill](#class-poolcolorarray-method-fill) **(** [Color](class_color#class-color) color **)** |
| [int](class_int#class-int) | [find](#class-poolcolorarray-method-find) **(** [Color](class_color#class-color) value, [int](class_int#class-int) from=0 **)** |
| [bool](class_bool#class-bool) | [has](#class-poolcolorarray-method-has) **(** [Color](class_color#class-color) value **)** |
| [int](class_int#class-int) | [insert](#class-poolcolorarray-method-insert) **(** [int](class_int#class-int) idx, [Color](class_color#class-color) color **)** |
| void | [invert](#class-poolcolorarray-method-invert) **(** **)** |
| void | [push\_back](#class-poolcolorarray-method-push-back) **(** [Color](class_color#class-color) color **)** |
| void | [remove](#class-poolcolorarray-method-remove) **(** [int](class_int#class-int) idx **)** |
| void | [resize](#class-poolcolorarray-method-resize) **(** [int](class_int#class-int) idx **)** |
| [int](class_int#class-int) | [rfind](#class-poolcolorarray-method-rfind) **(** [Color](class_color#class-color) value, [int](class_int#class-int) from=-1 **)** |
| void | [set](#class-poolcolorarray-method-set) **(** [int](class_int#class-int) idx, [Color](class_color#class-color) color **)** |
| [int](class_int#class-int) | [size](#class-poolcolorarray-method-size) **(** **)** |
| void | [sort](#class-poolcolorarray-method-sort) **(** **)** |
Method Descriptions
-------------------
### [PoolColorArray](#class-poolcolorarray) PoolColorArray ( [Array](class_array#class-array) from )
Constructs a new `PoolColorArray`. Optionally, you can pass in a generic [Array](class_array#class-array) that will be converted.
### void append ( [Color](class_color#class-color) color )
Appends an element at the end of the array (alias of [push\_back](#class-poolcolorarray-method-push-back)).
### void append\_array ( [PoolColorArray](#class-poolcolorarray) array )
Appends a `PoolColorArray` at the end of this array.
### [int](class_int#class-int) count ( [Color](class_color#class-color) value )
Returns the number of times an element is in the array.
### [bool](class_bool#class-bool) empty ( )
Returns `true` if the array is empty.
### void fill ( [Color](class_color#class-color) color )
Assigns the given value to all elements in the array. This can typically be used together with [resize](#class-poolcolorarray-method-resize) to create an array with a given size and initialized elements.
### [int](class_int#class-int) find ( [Color](class_color#class-color) value, [int](class_int#class-int) from=0 )
Searches the array for a value and returns its index or `-1` if not found. Optionally, the initial search index can be passed. Returns `-1` if `from` is out of bounds.
### [bool](class_bool#class-bool) has ( [Color](class_color#class-color) value )
Returns `true` if the array contains the given value.
**Note:** This is equivalent to using the `in` operator.
### [int](class_int#class-int) insert ( [int](class_int#class-int) idx, [Color](class_color#class-color) color )
Inserts a new element at a given position in the array. The position must be valid, or at the end of the array (`idx == size()`).
### void invert ( )
Reverses the order of the elements in the array.
### void push\_back ( [Color](class_color#class-color) color )
Appends a value to the array.
### void remove ( [int](class_int#class-int) idx )
Removes an element from the array by index.
### void resize ( [int](class_int#class-int) idx )
Sets the size of the array. If the array is grown, reserves elements at the end of the array. If the array is shrunk, truncates the array to the new size.
### [int](class_int#class-int) rfind ( [Color](class_color#class-color) value, [int](class_int#class-int) from=-1 )
Searches the array in reverse order. Optionally, a start search index can be passed. If negative, the start index is considered relative to the end of the array. If the adjusted start index is out of bounds, this method searches from the end of the array.
### void set ( [int](class_int#class-int) idx, [Color](class_color#class-color) color )
Changes the [Color](class_color#class-color) at the given index.
### [int](class_int#class-int) size ( )
Returns the number of elements in the array.
### void sort ( )
Sorts the elements of the array in ascending order.
godot AudioEffectNotchFilter AudioEffectNotchFilter
======================
**Inherits:** [AudioEffectFilter](class_audioeffectfilter#class-audioeffectfilter) **<** [AudioEffect](class_audioeffect#class-audioeffect) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Adds a notch filter to the Audio bus.
Description
-----------
Attenuates frequencies in a narrow band around the [AudioEffectFilter.cutoff\_hz](class_audioeffectfilter#class-audioeffectfilter-property-cutoff-hz) and cuts frequencies outside of this range.
godot Tree Tree
====
**Inherits:** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Control to show a tree of items.
Description
-----------
This shows a tree of items that can be selected, expanded and collapsed. The tree can have multiple columns with custom controls like text editing, buttons and popups. It can be useful for structured displays and interactions.
Trees are built via code, using [TreeItem](class_treeitem#class-treeitem) objects to create the structure. They have a single root but multiple roots can be simulated if a dummy hidden root is added.
```
func _ready():
var tree = Tree.new()
var root = tree.create_item()
tree.set_hide_root(true)
var child1 = tree.create_item(root)
var child2 = tree.create_item(root)
var subchild1 = tree.create_item(child1)
subchild1.set_text(0, "Subchild1")
```
To iterate over all the [TreeItem](class_treeitem#class-treeitem) objects in a `Tree` object, use [TreeItem.get\_next](class_treeitem#class-treeitem-method-get-next) and [TreeItem.get\_children](class_treeitem#class-treeitem-method-get-children) after getting the root through [get\_root](#class-tree-method-get-root). You can use [Object.free](class_object#class-object-method-free) on a [TreeItem](class_treeitem#class-treeitem) to remove it from the `Tree`.
**Incremental search:** Like [ItemList](class_itemlist#class-itemlist) and [PopupMenu](class_popupmenu#class-popupmenu), `Tree` supports searching within the list while the control is focused. Press a key that matches the first letter of an item's name to select the first item starting with the given letter. After that point, there are two ways to perform incremental search: 1) Press the same key again before the timeout duration to select the next item starting with the same letter. 2) Press letter keys that match the rest of the word before the timeout duration to match to select the item in question directly. Both of these actions will be reset to the beginning of the list if the timeout duration has passed since the last keystroke was registered. You can adjust the timeout duration by changing [ProjectSettings.gui/timers/incremental\_search\_max\_interval\_msec](class_projectsettings#class-projectsettings-property-gui-timers-incremental-search-max-interval-msec).
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [allow\_reselect](#class-tree-property-allow-reselect) | `false` |
| [bool](class_bool#class-bool) | [allow\_rmb\_select](#class-tree-property-allow-rmb-select) | `false` |
| [bool](class_bool#class-bool) | [column\_titles\_visible](#class-tree-property-column-titles-visible) | `false` |
| [int](class_int#class-int) | [columns](#class-tree-property-columns) | `1` |
| [int](class_int#class-int) | [drop\_mode\_flags](#class-tree-property-drop-mode-flags) | `0` |
| [FocusMode](class_control#enum-control-focusmode) | focus\_mode | `2` (overrides [Control](class_control#class-control-property-focus-mode)) |
| [bool](class_bool#class-bool) | [hide\_folding](#class-tree-property-hide-folding) | `false` |
| [bool](class_bool#class-bool) | [hide\_root](#class-tree-property-hide-root) | `false` |
| [bool](class_bool#class-bool) | rect\_clip\_content | `true` (overrides [Control](class_control#class-control-property-rect-clip-content)) |
| [SelectMode](#enum-tree-selectmode) | [select\_mode](#class-tree-property-select-mode) | `0` |
Methods
-------
| | |
| --- | --- |
| void | [clear](#class-tree-method-clear) **(** **)** |
| [TreeItem](class_treeitem#class-treeitem) | [create\_item](#class-tree-method-create-item) **(** [Object](class_object#class-object) parent=null, [int](class_int#class-int) idx=-1 **)** |
| [bool](class_bool#class-bool) | [edit\_selected](#class-tree-method-edit-selected) **(** **)** |
| void | [ensure\_cursor\_is\_visible](#class-tree-method-ensure-cursor-is-visible) **(** **)** |
| [int](class_int#class-int) | [get\_button\_id\_at\_position](#class-tree-method-get-button-id-at-position) **(** [Vector2](class_vector2#class-vector2) position **)** const |
| [int](class_int#class-int) | [get\_column\_at\_position](#class-tree-method-get-column-at-position) **(** [Vector2](class_vector2#class-vector2) position **)** const |
| [String](class_string#class-string) | [get\_column\_title](#class-tree-method-get-column-title) **(** [int](class_int#class-int) column **)** const |
| [int](class_int#class-int) | [get\_column\_width](#class-tree-method-get-column-width) **(** [int](class_int#class-int) column **)** const |
| [Rect2](class_rect2#class-rect2) | [get\_custom\_popup\_rect](#class-tree-method-get-custom-popup-rect) **(** **)** const |
| [int](class_int#class-int) | [get\_drop\_section\_at\_position](#class-tree-method-get-drop-section-at-position) **(** [Vector2](class_vector2#class-vector2) position **)** const |
| [TreeItem](class_treeitem#class-treeitem) | [get\_edited](#class-tree-method-get-edited) **(** **)** const |
| [int](class_int#class-int) | [get\_edited\_column](#class-tree-method-get-edited-column) **(** **)** const |
| [Rect2](class_rect2#class-rect2) | [get\_item\_area\_rect](#class-tree-method-get-item-area-rect) **(** [Object](class_object#class-object) item, [int](class_int#class-int) column=-1 **)** const |
| [TreeItem](class_treeitem#class-treeitem) | [get\_item\_at\_position](#class-tree-method-get-item-at-position) **(** [Vector2](class_vector2#class-vector2) position **)** const |
| [TreeItem](class_treeitem#class-treeitem) | [get\_next\_selected](#class-tree-method-get-next-selected) **(** [Object](class_object#class-object) from **)** |
| [int](class_int#class-int) | [get\_pressed\_button](#class-tree-method-get-pressed-button) **(** **)** const |
| [TreeItem](class_treeitem#class-treeitem) | [get\_root](#class-tree-method-get-root) **(** **)** |
| [Vector2](class_vector2#class-vector2) | [get\_scroll](#class-tree-method-get-scroll) **(** **)** const |
| [TreeItem](class_treeitem#class-treeitem) | [get\_selected](#class-tree-method-get-selected) **(** **)** const |
| [int](class_int#class-int) | [get\_selected\_column](#class-tree-method-get-selected-column) **(** **)** const |
| void | [scroll\_to\_item](#class-tree-method-scroll-to-item) **(** [Object](class_object#class-object) item **)** |
| void | [set\_column\_expand](#class-tree-method-set-column-expand) **(** [int](class_int#class-int) column, [bool](class_bool#class-bool) expand **)** |
| void | [set\_column\_min\_width](#class-tree-method-set-column-min-width) **(** [int](class_int#class-int) column, [int](class_int#class-int) min\_width **)** |
| void | [set\_column\_title](#class-tree-method-set-column-title) **(** [int](class_int#class-int) column, [String](class_string#class-string) title **)** |
Theme Properties
----------------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [custom\_button\_font\_highlight](#class-tree-theme-color-custom-button-font-highlight) | `Color( 0.94, 0.94, 0.94, 1 )` |
| [Color](class_color#class-color) | [drop\_position\_color](#class-tree-theme-color-drop-position-color) | `Color( 1, 0.3, 0.2, 1 )` |
| [Color](class_color#class-color) | [font\_color](#class-tree-theme-color-font-color) | `Color( 0.69, 0.69, 0.69, 1 )` |
| [Color](class_color#class-color) | [font\_color\_selected](#class-tree-theme-color-font-color-selected) | `Color( 1, 1, 1, 1 )` |
| [Color](class_color#class-color) | [guide\_color](#class-tree-theme-color-guide-color) | `Color( 0, 0, 0, 0.1 )` |
| [Color](class_color#class-color) | [relationship\_line\_color](#class-tree-theme-color-relationship-line-color) | `Color( 0.27, 0.27, 0.27, 1 )` |
| [Color](class_color#class-color) | [title\_button\_color](#class-tree-theme-color-title-button-color) | `Color( 0.88, 0.88, 0.88, 1 )` |
| [int](class_int#class-int) | [button\_margin](#class-tree-theme-constant-button-margin) | `4` |
| [int](class_int#class-int) | [draw\_guides](#class-tree-theme-constant-draw-guides) | `1` |
| [int](class_int#class-int) | [draw\_relationship\_lines](#class-tree-theme-constant-draw-relationship-lines) | `0` |
| [int](class_int#class-int) | [hseparation](#class-tree-theme-constant-hseparation) | `4` |
| [int](class_int#class-int) | [item\_margin](#class-tree-theme-constant-item-margin) | `12` |
| [int](class_int#class-int) | [scroll\_border](#class-tree-theme-constant-scroll-border) | `4` |
| [int](class_int#class-int) | [scroll\_speed](#class-tree-theme-constant-scroll-speed) | `12` |
| [int](class_int#class-int) | [vseparation](#class-tree-theme-constant-vseparation) | `4` |
| [Font](class_font#class-font) | [font](#class-tree-theme-font-font) | |
| [Font](class_font#class-font) | [title\_button\_font](#class-tree-theme-font-title-button-font) | |
| [Texture](class_texture#class-texture) | [arrow](#class-tree-theme-icon-arrow) | |
| [Texture](class_texture#class-texture) | [arrow\_collapsed](#class-tree-theme-icon-arrow-collapsed) | |
| [Texture](class_texture#class-texture) | [checked](#class-tree-theme-icon-checked) | |
| [Texture](class_texture#class-texture) | [select\_arrow](#class-tree-theme-icon-select-arrow) | |
| [Texture](class_texture#class-texture) | [unchecked](#class-tree-theme-icon-unchecked) | |
| [Texture](class_texture#class-texture) | [updown](#class-tree-theme-icon-updown) | |
| [StyleBox](class_stylebox#class-stylebox) | [bg](#class-tree-theme-style-bg) | |
| [StyleBox](class_stylebox#class-stylebox) | [bg\_focus](#class-tree-theme-style-bg-focus) | |
| [StyleBox](class_stylebox#class-stylebox) | [button\_pressed](#class-tree-theme-style-button-pressed) | |
| [StyleBox](class_stylebox#class-stylebox) | [cursor](#class-tree-theme-style-cursor) | |
| [StyleBox](class_stylebox#class-stylebox) | [cursor\_unfocused](#class-tree-theme-style-cursor-unfocused) | |
| [StyleBox](class_stylebox#class-stylebox) | [custom\_button](#class-tree-theme-style-custom-button) | |
| [StyleBox](class_stylebox#class-stylebox) | [custom\_button\_hover](#class-tree-theme-style-custom-button-hover) | |
| [StyleBox](class_stylebox#class-stylebox) | [custom\_button\_pressed](#class-tree-theme-style-custom-button-pressed) | |
| [StyleBox](class_stylebox#class-stylebox) | [selected](#class-tree-theme-style-selected) | |
| [StyleBox](class_stylebox#class-stylebox) | [selected\_focus](#class-tree-theme-style-selected-focus) | |
| [StyleBox](class_stylebox#class-stylebox) | [title\_button\_hover](#class-tree-theme-style-title-button-hover) | |
| [StyleBox](class_stylebox#class-stylebox) | [title\_button\_normal](#class-tree-theme-style-title-button-normal) | |
| [StyleBox](class_stylebox#class-stylebox) | [title\_button\_pressed](#class-tree-theme-style-title-button-pressed) | |
Signals
-------
### button\_pressed ( [TreeItem](class_treeitem#class-treeitem) item, [int](class_int#class-int) column, [int](class_int#class-int) id )
Emitted when a button on the tree was pressed (see [TreeItem.add\_button](class_treeitem#class-treeitem-method-add-button)).
### cell\_selected ( )
Emitted when a cell is selected.
### column\_title\_pressed ( [int](class_int#class-int) column )
Emitted when a column's title is pressed.
### custom\_popup\_edited ( [bool](class_bool#class-bool) arrow\_clicked )
Emitted when a cell with the [TreeItem.CELL\_MODE\_CUSTOM](class_treeitem#class-treeitem-constant-cell-mode-custom) is clicked to be edited.
### empty\_rmb ( [Vector2](class_vector2#class-vector2) position )
Emitted when the right mouse button is pressed in the empty space of the tree.
### empty\_tree\_rmb\_selected ( [Vector2](class_vector2#class-vector2) position )
Emitted when the right mouse button is pressed if right mouse button selection is active and the tree is empty.
### item\_activated ( )
Emitted when an item's label is double-clicked.
### item\_collapsed ( [TreeItem](class_treeitem#class-treeitem) item )
Emitted when an item is collapsed by a click on the folding arrow.
### item\_custom\_button\_pressed ( )
Emitted when a custom button is pressed (i.e. in a [TreeItem.CELL\_MODE\_CUSTOM](class_treeitem#class-treeitem-constant-cell-mode-custom) mode cell).
### item\_double\_clicked ( )
Emitted when an item's icon is double-clicked.
### item\_edited ( )
Emitted when an item is edited.
### item\_rmb\_edited ( )
Emitted when an item is edited using the right mouse button.
### item\_rmb\_selected ( [Vector2](class_vector2#class-vector2) position )
Emitted when an item is selected with the right mouse button.
### item\_selected ( )
Emitted when an item is selected.
### multi\_selected ( [TreeItem](class_treeitem#class-treeitem) item, [int](class_int#class-int) column, [bool](class_bool#class-bool) selected )
Emitted instead of `item_selected` if `select_mode` is [SELECT\_MULTI](#class-tree-constant-select-multi).
### nothing\_selected ( )
Emitted when a left mouse button click does not select any item.
Enumerations
------------
enum **SelectMode**:
* **SELECT\_SINGLE** = **0** --- Allows selection of a single cell at a time. From the perspective of items, only a single item is allowed to be selected. And there is only one column selected in the selected item.
The focus cursor is always hidden in this mode, but it is positioned at the current selection, making the currently selected item the currently focused item.
* **SELECT\_ROW** = **1** --- Allows selection of a single row at a time. From the perspective of items, only a single items is allowed to be selected. And all the columns are selected in the selected item.
The focus cursor is always hidden in this mode, but it is positioned at the first column of the current selection, making the currently selected item the currently focused item.
* **SELECT\_MULTI** = **2** --- Allows selection of multiple cells at the same time. From the perspective of items, multiple items are allowed to be selected. And there can be multiple columns selected in each selected item.
The focus cursor is visible in this mode, the item or column under the cursor is not necessarily selected.
enum **DropModeFlags**:
* **DROP\_MODE\_DISABLED** = **0** --- Disables all drop sections, but still allows to detect the "on item" drop section by [get\_drop\_section\_at\_position](#class-tree-method-get-drop-section-at-position).
**Note:** This is the default flag, it has no effect when combined with other flags.
* **DROP\_MODE\_ON\_ITEM** = **1** --- Enables the "on item" drop section. This drop section covers the entire item.
When combined with [DROP\_MODE\_INBETWEEN](#class-tree-constant-drop-mode-inbetween), this drop section halves the height and stays centered vertically.
* **DROP\_MODE\_INBETWEEN** = **2** --- Enables "above item" and "below item" drop sections. The "above item" drop section covers the top half of the item, and the "below item" drop section covers the bottom half.
When combined with [DROP\_MODE\_ON\_ITEM](#class-tree-constant-drop-mode-on-item), these drop sections halves the height and stays on top / bottom accordingly.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) allow\_reselect
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_allow\_reselect(value) |
| *Getter* | get\_allow\_reselect() |
If `true`, the currently selected cell may be selected again.
### [bool](class_bool#class-bool) allow\_rmb\_select
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_allow\_rmb\_select(value) |
| *Getter* | get\_allow\_rmb\_select() |
If `true`, a right mouse button click can select items.
### [bool](class_bool#class-bool) column\_titles\_visible
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_column\_titles\_visible(value) |
| *Getter* | are\_column\_titles\_visible() |
If `true`, column titles are visible.
### [int](class_int#class-int) columns
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_columns(value) |
| *Getter* | get\_columns() |
The number of columns.
### [int](class_int#class-int) drop\_mode\_flags
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_drop\_mode\_flags(value) |
| *Getter* | get\_drop\_mode\_flags() |
The drop mode as an OR combination of flags. See [DropModeFlags](#enum-tree-dropmodeflags) constants. Once dropping is done, reverts to [DROP\_MODE\_DISABLED](#class-tree-constant-drop-mode-disabled). Setting this during [Control.can\_drop\_data](class_control#class-control-method-can-drop-data) is recommended.
This controls the drop sections, i.e. the decision and drawing of possible drop locations based on the mouse position.
### [bool](class_bool#class-bool) hide\_folding
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_hide\_folding(value) |
| *Getter* | is\_folding\_hidden() |
If `true`, the folding arrow is hidden.
### [bool](class_bool#class-bool) hide\_root
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_hide\_root(value) |
| *Getter* | is\_root\_hidden() |
If `true`, the tree's root is hidden.
### [SelectMode](#enum-tree-selectmode) select\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_select\_mode(value) |
| *Getter* | get\_select\_mode() |
Allows single or multiple selection. See the [SelectMode](#enum-tree-selectmode) constants.
Method Descriptions
-------------------
### void clear ( )
Clears the tree. This removes all items.
### [TreeItem](class_treeitem#class-treeitem) create\_item ( [Object](class_object#class-object) parent=null, [int](class_int#class-int) idx=-1 )
Creates an item in the tree and adds it as a child of `parent`, which can be either a valid [TreeItem](class_treeitem#class-treeitem) or `null`.
If `parent` is `null`, the root item will be the parent, or the new item will be the root itself if the tree is empty.
The new item will be the `idx`th child of parent, or it will be the last child if there are not enough siblings.
### [bool](class_bool#class-bool) edit\_selected ( )
Edits the selected tree item as if it was clicked. The item must be set editable with [TreeItem.set\_editable](class_treeitem#class-treeitem-method-set-editable). Returns `true` if the item could be edited. Fails if no item is selected.
### void ensure\_cursor\_is\_visible ( )
Makes the currently focused cell visible.
This will scroll the tree if necessary. In [SELECT\_ROW](#class-tree-constant-select-row) mode, this will not do horizontal scrolling, as all the cells in the selected row is focused logically.
**Note:** Despite the name of this method, the focus cursor itself is only visible in [SELECT\_MULTI](#class-tree-constant-select-multi) mode.
### [int](class_int#class-int) get\_button\_id\_at\_position ( [Vector2](class_vector2#class-vector2) position ) const
Returns the button id at `position`, or -1 if no button is there.
### [int](class_int#class-int) get\_column\_at\_position ( [Vector2](class_vector2#class-vector2) position ) const
Returns the column index at `position`, or -1 if no item is there.
### [String](class_string#class-string) get\_column\_title ( [int](class_int#class-int) column ) const
Returns the column's title.
### [int](class_int#class-int) get\_column\_width ( [int](class_int#class-int) column ) const
Returns the column's width in pixels.
### [Rect2](class_rect2#class-rect2) get\_custom\_popup\_rect ( ) const
Returns the rectangle for custom popups. Helper to create custom cell controls that display a popup. See [TreeItem.set\_cell\_mode](class_treeitem#class-treeitem-method-set-cell-mode).
### [int](class_int#class-int) get\_drop\_section\_at\_position ( [Vector2](class_vector2#class-vector2) position ) const
Returns the drop section at `position`, or -100 if no item is there.
Values -1, 0, or 1 will be returned for the "above item", "on item", and "below item" drop sections, respectively. See [DropModeFlags](#enum-tree-dropmodeflags) for a description of each drop section.
To get the item which the returned drop section is relative to, use [get\_item\_at\_position](#class-tree-method-get-item-at-position).
### [TreeItem](class_treeitem#class-treeitem) get\_edited ( ) const
Returns the currently edited item. Can be used with [item\_edited](#class-tree-signal-item-edited) to get the item that was modified.
```
func _ready():
$Tree.connect("item_edited", self, "on_Tree_item_edited")
func on_Tree_item_edited():
print($Tree.get_edited()) # This item just got edited (e.g. checked).
```
### [int](class_int#class-int) get\_edited\_column ( ) const
Returns the column for the currently edited item.
### [Rect2](class_rect2#class-rect2) get\_item\_area\_rect ( [Object](class_object#class-object) item, [int](class_int#class-int) column=-1 ) const
Returns the rectangle area for the specified [TreeItem](class_treeitem#class-treeitem). If `column` is specified, only get the position and size of that column, otherwise get the rectangle containing all columns.
### [TreeItem](class_treeitem#class-treeitem) get\_item\_at\_position ( [Vector2](class_vector2#class-vector2) position ) const
Returns the tree item at the specified position (relative to the tree origin position).
### [TreeItem](class_treeitem#class-treeitem) get\_next\_selected ( [Object](class_object#class-object) from )
Returns the next selected [TreeItem](class_treeitem#class-treeitem) after the given one, or `null` if the end is reached.
If `from` is `null`, this returns the first selected item.
### [int](class_int#class-int) get\_pressed\_button ( ) const
Returns the last pressed button's index.
### [TreeItem](class_treeitem#class-treeitem) get\_root ( )
Returns the tree's root item, or `null` if the tree is empty.
### [Vector2](class_vector2#class-vector2) get\_scroll ( ) const
Returns the current scrolling position.
### [TreeItem](class_treeitem#class-treeitem) get\_selected ( ) const
Returns the currently focused item, or `null` if no item is focused.
In [SELECT\_ROW](#class-tree-constant-select-row) and [SELECT\_SINGLE](#class-tree-constant-select-single) modes, the focused item is same as the selected item. In [SELECT\_MULTI](#class-tree-constant-select-multi) mode, the focused item is the item under the focus cursor, not necessarily selected.
To get the currently selected item(s), use [get\_next\_selected](#class-tree-method-get-next-selected).
### [int](class_int#class-int) get\_selected\_column ( ) const
Returns the currently focused column, or -1 if no column is focused.
In [SELECT\_SINGLE](#class-tree-constant-select-single) mode, the focused column is the selected column. In [SELECT\_ROW](#class-tree-constant-select-row) mode, the focused column is always 0 if any item is selected. In [SELECT\_MULTI](#class-tree-constant-select-multi) mode, the focused column is the column under the focus cursor, and there are not necessarily any column selected.
To tell whether a column of an item is selected, use [TreeItem.is\_selected](class_treeitem#class-treeitem-method-is-selected).
### void scroll\_to\_item ( [Object](class_object#class-object) item )
Causes the `Tree` to jump to the specified [TreeItem](class_treeitem#class-treeitem).
### void set\_column\_expand ( [int](class_int#class-int) column, [bool](class_bool#class-bool) expand )
If `true`, the column will have the "Expand" flag of [Control](class_control#class-control). Columns that have the "Expand" flag will use their "min\_width" in a similar fashion to [Control.size\_flags\_stretch\_ratio](class_control#class-control-property-size-flags-stretch-ratio).
### void set\_column\_min\_width ( [int](class_int#class-int) column, [int](class_int#class-int) min\_width )
Sets the minimum width of a column. Columns that have the "Expand" flag will use their "min\_width" in a similar fashion to [Control.size\_flags\_stretch\_ratio](class_control#class-control-property-size-flags-stretch-ratio).
### void set\_column\_title ( [int](class_int#class-int) column, [String](class_string#class-string) title )
Sets the title of a column.
Theme Property Descriptions
---------------------------
### [Color](class_color#class-color) custom\_button\_font\_highlight
| | |
| --- | --- |
| *Default* | `Color( 0.94, 0.94, 0.94, 1 )` |
Text [Color](class_color#class-color) for a [TreeItem.CELL\_MODE\_CUSTOM](class_treeitem#class-treeitem-constant-cell-mode-custom) mode cell when it's hovered.
### [Color](class_color#class-color) drop\_position\_color
| | |
| --- | --- |
| *Default* | `Color( 1, 0.3, 0.2, 1 )` |
[Color](class_color#class-color) used to draw possible drop locations. See [DropModeFlags](#enum-tree-dropmodeflags) constants for further description of drop locations.
### [Color](class_color#class-color) font\_color
| | |
| --- | --- |
| *Default* | `Color( 0.69, 0.69, 0.69, 1 )` |
Default text [Color](class_color#class-color) of the item.
### [Color](class_color#class-color) font\_color\_selected
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
Text [Color](class_color#class-color) used when the item is selected.
### [Color](class_color#class-color) guide\_color
| | |
| --- | --- |
| *Default* | `Color( 0, 0, 0, 0.1 )` |
[Color](class_color#class-color) of the guideline.
### [Color](class_color#class-color) relationship\_line\_color
| | |
| --- | --- |
| *Default* | `Color( 0.27, 0.27, 0.27, 1 )` |
[Color](class_color#class-color) of the relationship lines.
### [Color](class_color#class-color) title\_button\_color
| | |
| --- | --- |
| *Default* | `Color( 0.88, 0.88, 0.88, 1 )` |
Default text [Color](class_color#class-color) of the title button.
### [int](class_int#class-int) button\_margin
| | |
| --- | --- |
| *Default* | `4` |
The horizontal space between each button in a cell.
### [int](class_int#class-int) draw\_guides
| | |
| --- | --- |
| *Default* | `1` |
Draws the guidelines if not zero, this acts as a boolean. The guideline is a horizontal line drawn at the bottom of each item.
### [int](class_int#class-int) draw\_relationship\_lines
| | |
| --- | --- |
| *Default* | `0` |
Draws the relationship lines if not zero, this acts as a boolean. Relationship lines are drawn at the start of child items to show hierarchy.
### [int](class_int#class-int) hseparation
| | |
| --- | --- |
| *Default* | `4` |
The horizontal space between item cells. This is also used as the margin at the start of an item when folding is disabled.
### [int](class_int#class-int) item\_margin
| | |
| --- | --- |
| *Default* | `12` |
The horizontal margin at the start of an item. This is used when folding is enabled for the item.
### [int](class_int#class-int) scroll\_border
| | |
| --- | --- |
| *Default* | `4` |
The maximum distance between the mouse cursor and the control's border to trigger border scrolling when dragging.
### [int](class_int#class-int) scroll\_speed
| | |
| --- | --- |
| *Default* | `12` |
The speed of border scrolling.
### [int](class_int#class-int) vseparation
| | |
| --- | --- |
| *Default* | `4` |
The vertical padding inside each item, i.e. the distance between the item's content and top/bottom border.
### [Font](class_font#class-font) font
[Font](class_font#class-font) of the item's text.
### [Font](class_font#class-font) title\_button\_font
[Font](class_font#class-font) of the title button's text.
### [Texture](class_texture#class-texture) arrow
The arrow icon used when a foldable item is not collapsed.
### [Texture](class_texture#class-texture) arrow\_collapsed
The arrow icon used when a foldable item is collapsed.
### [Texture](class_texture#class-texture) checked
The check icon to display when the [TreeItem.CELL\_MODE\_CHECK](class_treeitem#class-treeitem-constant-cell-mode-check) mode cell is checked.
### [Texture](class_texture#class-texture) select\_arrow
The arrow icon to display for the [TreeItem.CELL\_MODE\_RANGE](class_treeitem#class-treeitem-constant-cell-mode-range) mode cell.
### [Texture](class_texture#class-texture) unchecked
The check icon to display when the [TreeItem.CELL\_MODE\_CHECK](class_treeitem#class-treeitem-constant-cell-mode-check) mode cell is unchecked.
### [Texture](class_texture#class-texture) updown
The updown arrow icon to display for the [TreeItem.CELL\_MODE\_RANGE](class_treeitem#class-treeitem-constant-cell-mode-range) mode cell.
### [StyleBox](class_stylebox#class-stylebox) bg
Default [StyleBox](class_stylebox#class-stylebox) for the `Tree`, i.e. used when the control is not being focused.
### [StyleBox](class_stylebox#class-stylebox) bg\_focus
[StyleBox](class_stylebox#class-stylebox) used when the `Tree` is being focused.
### [StyleBox](class_stylebox#class-stylebox) button\_pressed
[StyleBox](class_stylebox#class-stylebox) used when a button in the tree is pressed.
### [StyleBox](class_stylebox#class-stylebox) cursor
[StyleBox](class_stylebox#class-stylebox) used for the cursor, when the `Tree` is being focused.
### [StyleBox](class_stylebox#class-stylebox) cursor\_unfocused
[StyleBox](class_stylebox#class-stylebox) used for the cursor, when the `Tree` is not being focused.
### [StyleBox](class_stylebox#class-stylebox) custom\_button
Default [StyleBox](class_stylebox#class-stylebox) for a [TreeItem.CELL\_MODE\_CUSTOM](class_treeitem#class-treeitem-constant-cell-mode-custom) mode cell.
### [StyleBox](class_stylebox#class-stylebox) custom\_button\_hover
[StyleBox](class_stylebox#class-stylebox) for a [TreeItem.CELL\_MODE\_CUSTOM](class_treeitem#class-treeitem-constant-cell-mode-custom) mode cell when it's hovered.
### [StyleBox](class_stylebox#class-stylebox) custom\_button\_pressed
[StyleBox](class_stylebox#class-stylebox) for a [TreeItem.CELL\_MODE\_CUSTOM](class_treeitem#class-treeitem-constant-cell-mode-custom) mode cell when it's pressed.
### [StyleBox](class_stylebox#class-stylebox) selected
[StyleBox](class_stylebox#class-stylebox) for the selected items, used when the `Tree` is not being focused.
### [StyleBox](class_stylebox#class-stylebox) selected\_focus
[StyleBox](class_stylebox#class-stylebox) for the selected items, used when the `Tree` is being focused.
### [StyleBox](class_stylebox#class-stylebox) title\_button\_hover
[StyleBox](class_stylebox#class-stylebox) used when the title button is being hovered.
### [StyleBox](class_stylebox#class-stylebox) title\_button\_normal
Default [StyleBox](class_stylebox#class-stylebox) for the title button.
### [StyleBox](class_stylebox#class-stylebox) title\_button\_pressed
[StyleBox](class_stylebox#class-stylebox) used when the title button is being pressed.
| programming_docs |
godot OmniLight OmniLight
=========
**Inherits:** [Light](class_light#class-light) **<** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Omnidirectional light, such as a light bulb or a candle.
Description
-----------
An Omnidirectional light is a type of [Light](class_light#class-light) that emits light in all directions. The light is attenuated by distance and this attenuation can be configured by changing its energy, radius, and attenuation parameters.
**Note:** By default, only 32 OmniLights may affect a single mesh *resource* at once. Consider splitting your level into several meshes to decrease the likelihood that more than 32 lights will affect the same mesh resource. Splitting the level mesh will also improve frustum culling effectiveness, leading to greater performance. If you need to use more lights per mesh, you can increase [ProjectSettings.rendering/limits/rendering/max\_lights\_per\_object](class_projectsettings#class-projectsettings-property-rendering-limits-rendering-max-lights-per-object) at the cost of shader compilation times.
Tutorials
---------
* [3D lights and shadows](https://docs.godotengine.org/en/3.5/tutorials/3d/lights_and_shadows.html)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [omni\_attenuation](#class-omnilight-property-omni-attenuation) | `1.0` |
| [float](class_float#class-float) | [omni\_range](#class-omnilight-property-omni-range) | `5.0` |
| [ShadowDetail](#enum-omnilight-shadowdetail) | [omni\_shadow\_detail](#class-omnilight-property-omni-shadow-detail) | `1` |
| [ShadowMode](#enum-omnilight-shadowmode) | [omni\_shadow\_mode](#class-omnilight-property-omni-shadow-mode) | `1` |
Enumerations
------------
enum **ShadowMode**:
* **SHADOW\_DUAL\_PARABOLOID** = **0** --- Shadows are rendered to a dual-paraboloid texture. Faster than [SHADOW\_CUBE](#class-omnilight-constant-shadow-cube), but lower-quality.
* **SHADOW\_CUBE** = **1** --- Shadows are rendered to a cubemap. Slower than [SHADOW\_DUAL\_PARABOLOID](#class-omnilight-constant-shadow-dual-paraboloid), but higher-quality. Only supported on GPUs that feature support for depth cubemaps.
enum **ShadowDetail**:
* **SHADOW\_DETAIL\_VERTICAL** = **0** --- Use more detail vertically when computing the shadow.
* **SHADOW\_DETAIL\_HORIZONTAL** = **1** --- Use more detail horizontally when computing the shadow.
Property Descriptions
---------------------
### [float](class_float#class-float) omni\_attenuation
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
The light's attenuation (drop-off) curve. A number of presets are available in the **Inspector** by right-clicking the curve.
### [float](class_float#class-float) omni\_range
| | |
| --- | --- |
| *Default* | `5.0` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
The light's radius. Note that the effectively lit area may appear to be smaller depending on the [omni\_attenuation](#class-omnilight-property-omni-attenuation) in use. No matter the [omni\_attenuation](#class-omnilight-property-omni-attenuation) in use, the light will never reach anything outside this radius.
### [ShadowDetail](#enum-omnilight-shadowdetail) omni\_shadow\_detail
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_shadow\_detail(value) |
| *Getter* | get\_shadow\_detail() |
See [ShadowDetail](#enum-omnilight-shadowdetail).
### [ShadowMode](#enum-omnilight-shadowmode) omni\_shadow\_mode
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_shadow\_mode(value) |
| *Getter* | get\_shadow\_mode() |
The shadow rendering mode to use for this `OmniLight`. See [ShadowMode](#enum-omnilight-shadowmode).
**Note:** In GLES2, [SHADOW\_CUBE](#class-omnilight-constant-shadow-cube) is only supported on GPUs that feature support for depth cubemaps. Old GPUs such as the Radeon HD 4000 series don't support cubemap shadows and will fall back to dual paraboloid shadows as a result.
godot Image Image
=====
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Image datatype.
Description
-----------
Native image datatype. Contains image data which can be converted to an [ImageTexture](class_imagetexture#class-imagetexture) and provides commonly used *image processing* methods. The maximum width and height for an `Image` are [MAX\_WIDTH](#class-image-constant-max-width) and [MAX\_HEIGHT](#class-image-constant-max-height).
An `Image` cannot be assigned to a `texture` property of an object directly (such as [Sprite](class_sprite#class-sprite)), and has to be converted manually to an [ImageTexture](class_imagetexture#class-imagetexture) first.
**Note:** The maximum image size is 16384×16384 pixels due to graphics hardware limitations. Larger images may fail to import.
Tutorials
---------
* [Importing images](https://docs.godotengine.org/en/3.5/tutorials/assets_pipeline/importing_images.html)
Properties
----------
| | | |
| --- | --- | --- |
| [Dictionary](class_dictionary#class-dictionary) | [data](#class-image-property-data) | `{"data": PoolByteArray( ),"format": "Lum8","height": 0,"mipmaps": false,"width": 0}` |
Methods
-------
| | |
| --- | --- |
| void | [blend\_rect](#class-image-method-blend-rect) **(** [Image](#class-image) src, [Rect2](class_rect2#class-rect2) src\_rect, [Vector2](class_vector2#class-vector2) dst **)** |
| void | [blend\_rect\_mask](#class-image-method-blend-rect-mask) **(** [Image](#class-image) src, [Image](#class-image) mask, [Rect2](class_rect2#class-rect2) src\_rect, [Vector2](class_vector2#class-vector2) dst **)** |
| void | [blit\_rect](#class-image-method-blit-rect) **(** [Image](#class-image) src, [Rect2](class_rect2#class-rect2) src\_rect, [Vector2](class_vector2#class-vector2) dst **)** |
| void | [blit\_rect\_mask](#class-image-method-blit-rect-mask) **(** [Image](#class-image) src, [Image](#class-image) mask, [Rect2](class_rect2#class-rect2) src\_rect, [Vector2](class_vector2#class-vector2) dst **)** |
| void | [bumpmap\_to\_normalmap](#class-image-method-bumpmap-to-normalmap) **(** [float](class_float#class-float) bump\_scale=1.0 **)** |
| void | [clear\_mipmaps](#class-image-method-clear-mipmaps) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [compress](#class-image-method-compress) **(** [CompressMode](#enum-image-compressmode) mode, [CompressSource](#enum-image-compresssource) source, [float](class_float#class-float) lossy\_quality **)** |
| void | [convert](#class-image-method-convert) **(** [Format](#enum-image-format) format **)** |
| void | [copy\_from](#class-image-method-copy-from) **(** [Image](#class-image) src **)** |
| void | [create](#class-image-method-create) **(** [int](class_int#class-int) width, [int](class_int#class-int) height, [bool](class_bool#class-bool) use\_mipmaps, [Format](#enum-image-format) format **)** |
| void | [create\_from\_data](#class-image-method-create-from-data) **(** [int](class_int#class-int) width, [int](class_int#class-int) height, [bool](class_bool#class-bool) use\_mipmaps, [Format](#enum-image-format) format, [PoolByteArray](class_poolbytearray#class-poolbytearray) data **)** |
| void | [crop](#class-image-method-crop) **(** [int](class_int#class-int) width, [int](class_int#class-int) height **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [decompress](#class-image-method-decompress) **(** **)** |
| [AlphaMode](#enum-image-alphamode) | [detect\_alpha](#class-image-method-detect-alpha) **(** **)** const |
| void | [expand\_x2\_hq2x](#class-image-method-expand-x2-hq2x) **(** **)** |
| void | [fill](#class-image-method-fill) **(** [Color](class_color#class-color) color **)** |
| void | [fill\_rect](#class-image-method-fill-rect) **(** [Rect2](class_rect2#class-rect2) rect, [Color](class_color#class-color) color **)** |
| void | [fix\_alpha\_edges](#class-image-method-fix-alpha-edges) **(** **)** |
| void | [flip\_x](#class-image-method-flip-x) **(** **)** |
| void | [flip\_y](#class-image-method-flip-y) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [generate\_mipmaps](#class-image-method-generate-mipmaps) **(** [bool](class_bool#class-bool) renormalize=false **)** |
| [PoolByteArray](class_poolbytearray#class-poolbytearray) | [get\_data](#class-image-method-get-data) **(** **)** const |
| [Format](#enum-image-format) | [get\_format](#class-image-method-get-format) **(** **)** const |
| [int](class_int#class-int) | [get\_height](#class-image-method-get-height) **(** **)** const |
| [int](class_int#class-int) | [get\_mipmap\_offset](#class-image-method-get-mipmap-offset) **(** [int](class_int#class-int) mipmap **)** const |
| [Color](class_color#class-color) | [get\_pixel](#class-image-method-get-pixel) **(** [int](class_int#class-int) x, [int](class_int#class-int) y **)** const |
| [Color](class_color#class-color) | [get\_pixelv](#class-image-method-get-pixelv) **(** [Vector2](class_vector2#class-vector2) src **)** const |
| [Image](#class-image) | [get\_rect](#class-image-method-get-rect) **(** [Rect2](class_rect2#class-rect2) rect **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_size](#class-image-method-get-size) **(** **)** const |
| [Rect2](class_rect2#class-rect2) | [get\_used\_rect](#class-image-method-get-used-rect) **(** **)** const |
| [int](class_int#class-int) | [get\_width](#class-image-method-get-width) **(** **)** const |
| [bool](class_bool#class-bool) | [has\_mipmaps](#class-image-method-has-mipmaps) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_compressed](#class-image-method-is-compressed) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_empty](#class-image-method-is-empty) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_invisible](#class-image-method-is-invisible) **(** **)** const |
| [Error](class_%40globalscope#enum-globalscope-error) | [load](#class-image-method-load) **(** [String](class_string#class-string) path **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [load\_bmp\_from\_buffer](#class-image-method-load-bmp-from-buffer) **(** [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [load\_jpg\_from\_buffer](#class-image-method-load-jpg-from-buffer) **(** [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [load\_png\_from\_buffer](#class-image-method-load-png-from-buffer) **(** [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [load\_tga\_from\_buffer](#class-image-method-load-tga-from-buffer) **(** [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [load\_webp\_from\_buffer](#class-image-method-load-webp-from-buffer) **(** [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer **)** |
| void | [lock](#class-image-method-lock) **(** **)** |
| void | [normalmap\_to\_xy](#class-image-method-normalmap-to-xy) **(** **)** |
| void | [premultiply\_alpha](#class-image-method-premultiply-alpha) **(** **)** |
| void | [resize](#class-image-method-resize) **(** [int](class_int#class-int) width, [int](class_int#class-int) height, [Interpolation](#enum-image-interpolation) interpolation=1 **)** |
| void | [resize\_to\_po2](#class-image-method-resize-to-po2) **(** [bool](class_bool#class-bool) square=false, [Interpolation](#enum-image-interpolation) interpolation=1 **)** |
| [Image](#class-image) | [rgbe\_to\_srgb](#class-image-method-rgbe-to-srgb) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [save\_exr](#class-image-method-save-exr) **(** [String](class_string#class-string) path, [bool](class_bool#class-bool) grayscale=false **)** const |
| [Error](class_%40globalscope#enum-globalscope-error) | [save\_png](#class-image-method-save-png) **(** [String](class_string#class-string) path **)** const |
| [PoolByteArray](class_poolbytearray#class-poolbytearray) | [save\_png\_to\_buffer](#class-image-method-save-png-to-buffer) **(** **)** const |
| void | [set\_pixel](#class-image-method-set-pixel) **(** [int](class_int#class-int) x, [int](class_int#class-int) y, [Color](class_color#class-color) color **)** |
| void | [set\_pixelv](#class-image-method-set-pixelv) **(** [Vector2](class_vector2#class-vector2) dst, [Color](class_color#class-color) color **)** |
| void | [shrink\_x2](#class-image-method-shrink-x2) **(** **)** |
| void | [srgb\_to\_linear](#class-image-method-srgb-to-linear) **(** **)** |
| void | [unlock](#class-image-method-unlock) **(** **)** |
Enumerations
------------
enum **Format**:
* **FORMAT\_L8** = **0** --- Texture format with a single 8-bit depth representing luminance.
* **FORMAT\_LA8** = **1** --- OpenGL texture format with two values, luminance and alpha each stored with 8 bits.
* **FORMAT\_R8** = **2** --- OpenGL texture format `RED` with a single component and a bitdepth of 8.
**Note:** When using the GLES2 backend, this uses the alpha channel instead of the red channel for storage.
* **FORMAT\_RG8** = **3** --- OpenGL texture format `RG` with two components and a bitdepth of 8 for each.
* **FORMAT\_RGB8** = **4** --- OpenGL texture format `RGB` with three components, each with a bitdepth of 8.
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_RGBA8** = **5** --- OpenGL texture format `RGBA` with four components, each with a bitdepth of 8.
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_RGBA4444** = **6** --- OpenGL texture format `RGBA` with four components, each with a bitdepth of 4.
* **FORMAT\_RGBA5551** = **7** --- OpenGL texture format `GL_RGB5_A1` where 5 bits of depth for each component of RGB and one bit for alpha.
* **FORMAT\_RF** = **8** --- OpenGL texture format `GL_R32F` where there's one component, a 32-bit floating-point value.
* **FORMAT\_RGF** = **9** --- OpenGL texture format `GL_RG32F` where there are two components, each a 32-bit floating-point values.
* **FORMAT\_RGBF** = **10** --- OpenGL texture format `GL_RGB32F` where there are three components, each a 32-bit floating-point values.
* **FORMAT\_RGBAF** = **11** --- OpenGL texture format `GL_RGBA32F` where there are four components, each a 32-bit floating-point values.
* **FORMAT\_RH** = **12** --- OpenGL texture format `GL_R32F` where there's one component, a 16-bit "half-precision" floating-point value.
* **FORMAT\_RGH** = **13** --- OpenGL texture format `GL_RG32F` where there are two components, each a 16-bit "half-precision" floating-point value.
* **FORMAT\_RGBH** = **14** --- OpenGL texture format `GL_RGB32F` where there are three components, each a 16-bit "half-precision" floating-point value.
* **FORMAT\_RGBAH** = **15** --- OpenGL texture format `GL_RGBA32F` where there are four components, each a 16-bit "half-precision" floating-point value.
* **FORMAT\_RGBE9995** = **16** --- A special OpenGL texture format where the three color components have 9 bits of precision and all three share a single 5-bit exponent.
* **FORMAT\_DXT1** = **17** --- The [S3TC](https://en.wikipedia.org/wiki/S3_Texture_Compression) texture format that uses Block Compression 1, and is the smallest variation of S3TC, only providing 1 bit of alpha and color data being premultiplied with alpha.
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_DXT3** = **18** --- The [S3TC](https://en.wikipedia.org/wiki/S3_Texture_Compression) texture format that uses Block Compression 2, and color data is interpreted as not having been premultiplied by alpha. Well suited for images with sharp alpha transitions between translucent and opaque areas.
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_DXT5** = **19** --- The [S3TC](https://en.wikipedia.org/wiki/S3_Texture_Compression) texture format also known as Block Compression 3 or BC3 that contains 64 bits of alpha channel data followed by 64 bits of DXT1-encoded color data. Color data is not premultiplied by alpha, same as DXT3. DXT5 generally produces superior results for transparent gradients compared to DXT3.
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_RGTC\_R** = **20** --- Texture format that uses [Red Green Texture Compression](https://www.khronos.org/opengl/wiki/Red_Green_Texture_Compression), normalizing the red channel data using the same compression algorithm that DXT5 uses for the alpha channel.
* **FORMAT\_RGTC\_RG** = **21** --- Texture format that uses [Red Green Texture Compression](https://www.khronos.org/opengl/wiki/Red_Green_Texture_Compression), normalizing the red and green channel data using the same compression algorithm that DXT5 uses for the alpha channel.
* **FORMAT\_BPTC\_RGBA** = **22** --- Texture format that uses [BPTC](https://www.khronos.org/opengl/wiki/BPTC_Texture_Compression) compression with unsigned normalized RGBA components.
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_BPTC\_RGBF** = **23** --- Texture format that uses [BPTC](https://www.khronos.org/opengl/wiki/BPTC_Texture_Compression) compression with signed floating-point RGB components.
* **FORMAT\_BPTC\_RGBFU** = **24** --- Texture format that uses [BPTC](https://www.khronos.org/opengl/wiki/BPTC_Texture_Compression) compression with unsigned floating-point RGB components.
* **FORMAT\_PVRTC2** = **25** --- Texture format used on PowerVR-supported mobile platforms, uses 2-bit color depth with no alpha. More information can be found [here](https://en.wikipedia.org/wiki/PVRTC).
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_PVRTC2A** = **26** --- Same as [PVRTC2](https://en.wikipedia.org/wiki/PVRTC), but with an alpha component.
* **FORMAT\_PVRTC4** = **27** --- Similar to [PVRTC2](https://en.wikipedia.org/wiki/PVRTC), but with 4-bit color depth and no alpha.
* **FORMAT\_PVRTC4A** = **28** --- Same as [PVRTC4](https://en.wikipedia.org/wiki/PVRTC), but with an alpha component.
* **FORMAT\_ETC** = **29** --- [Ericsson Texture Compression format 1](https://en.wikipedia.org/wiki/Ericsson_Texture_Compression#ETC1), also referred to as "ETC1", and is part of the OpenGL ES graphics standard. This format cannot store an alpha channel.
* **FORMAT\_ETC2\_R11** = **30** --- [Ericsson Texture Compression format 2](https://en.wikipedia.org/wiki/Ericsson_Texture_Compression#ETC2_and_EAC) (`R11_EAC` variant), which provides one channel of unsigned data.
* **FORMAT\_ETC2\_R11S** = **31** --- [Ericsson Texture Compression format 2](https://en.wikipedia.org/wiki/Ericsson_Texture_Compression#ETC2_and_EAC) (`SIGNED_R11_EAC` variant), which provides one channel of signed data.
* **FORMAT\_ETC2\_RG11** = **32** --- [Ericsson Texture Compression format 2](https://en.wikipedia.org/wiki/Ericsson_Texture_Compression#ETC2_and_EAC) (`RG11_EAC` variant), which provides two channels of unsigned data.
* **FORMAT\_ETC2\_RG11S** = **33** --- [Ericsson Texture Compression format 2](https://en.wikipedia.org/wiki/Ericsson_Texture_Compression#ETC2_and_EAC) (`SIGNED_RG11_EAC` variant), which provides two channels of signed data.
* **FORMAT\_ETC2\_RGB8** = **34** --- [Ericsson Texture Compression format 2](https://en.wikipedia.org/wiki/Ericsson_Texture_Compression#ETC2_and_EAC) (`RGB8` variant), which is a follow-up of ETC1 and compresses RGB888 data.
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_ETC2\_RGBA8** = **35** --- [Ericsson Texture Compression format 2](https://en.wikipedia.org/wiki/Ericsson_Texture_Compression#ETC2_and_EAC) (`RGBA8`variant), which compresses RGBA8888 data with full alpha support.
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_ETC2\_RGB8A1** = **36** --- [Ericsson Texture Compression format 2](https://en.wikipedia.org/wiki/Ericsson_Texture_Compression#ETC2_and_EAC) (`RGB8_PUNCHTHROUGH_ALPHA1` variant), which compresses RGBA data to make alpha either fully transparent or fully opaque.
**Note:** When creating an [ImageTexture](class_imagetexture#class-imagetexture), an sRGB to linear color space conversion is performed.
* **FORMAT\_MAX** = **37** --- Represents the size of the [Format](#enum-image-format) enum.
enum **Interpolation**:
* **INTERPOLATE\_NEAREST** = **0** --- Performs nearest-neighbor interpolation. If the image is resized, it will be pixelated.
* **INTERPOLATE\_BILINEAR** = **1** --- Performs bilinear interpolation. If the image is resized, it will be blurry. This mode is faster than [INTERPOLATE\_CUBIC](#class-image-constant-interpolate-cubic), but it results in lower quality.
* **INTERPOLATE\_CUBIC** = **2** --- Performs cubic interpolation. If the image is resized, it will be blurry. This mode often gives better results compared to [INTERPOLATE\_BILINEAR](#class-image-constant-interpolate-bilinear), at the cost of being slower.
* **INTERPOLATE\_TRILINEAR** = **3** --- Performs bilinear separately on the two most-suited mipmap levels, then linearly interpolates between them.
It's slower than [INTERPOLATE\_BILINEAR](#class-image-constant-interpolate-bilinear), but produces higher-quality results with far fewer aliasing artifacts.
If the image does not have mipmaps, they will be generated and used internally, but no mipmaps will be generated on the resulting image.
**Note:** If you intend to scale multiple copies of the original image, it's better to call [generate\_mipmaps](#class-image-method-generate-mipmaps)] on it in advance, to avoid wasting processing power in generating them again and again.
On the other hand, if the image already has mipmaps, they will be used, and a new set will be generated for the resulting image.
* **INTERPOLATE\_LANCZOS** = **4** --- Performs Lanczos interpolation. This is the slowest image resizing mode, but it typically gives the best results, especially when downscalng images.
enum **AlphaMode**:
* **ALPHA\_NONE** = **0** --- Image does not have alpha.
* **ALPHA\_BIT** = **1** --- Image stores alpha in a single bit.
* **ALPHA\_BLEND** = **2** --- Image uses alpha.
enum **CompressMode**:
* **COMPRESS\_S3TC** = **0** --- Use S3TC compression.
* **COMPRESS\_PVRTC2** = **1** --- Use PVRTC2 compression.
* **COMPRESS\_PVRTC4** = **2** --- Use PVRTC4 compression.
* **COMPRESS\_ETC** = **3** --- Use ETC compression.
* **COMPRESS\_ETC2** = **4** --- Use ETC2 compression.
enum **CompressSource**:
* **COMPRESS\_SOURCE\_GENERIC** = **0** --- Source texture (before compression) is a regular texture. Default for all textures.
* **COMPRESS\_SOURCE\_SRGB** = **1** --- Source texture (before compression) is in sRGB space.
* **COMPRESS\_SOURCE\_NORMAL** = **2** --- Source texture (before compression) is a normal texture (e.g. it can be compressed into two channels).
* **COMPRESS\_SOURCE\_LAYERED** = **3** --- Source texture (before compression) is a [TextureLayered](class_texturelayered#class-texturelayered).
Constants
---------
* **MAX\_WIDTH** = **16384** --- The maximal width allowed for `Image` resources.
* **MAX\_HEIGHT** = **16384** --- The maximal height allowed for `Image` resources.
Property Descriptions
---------------------
### [Dictionary](class_dictionary#class-dictionary) data
| | |
| --- | --- |
| *Default* | `{"data": PoolByteArray( ),"format": "Lum8","height": 0,"mipmaps": false,"width": 0}` |
Holds all the image's color data in a given format. See [Format](#enum-image-format) constants.
Method Descriptions
-------------------
### void blend\_rect ( [Image](#class-image) src, [Rect2](class_rect2#class-rect2) src\_rect, [Vector2](class_vector2#class-vector2) dst )
Alpha-blends `src_rect` from `src` image to this image at coordinates `dest`, clipped accordingly to both image bounds. This image and `src` image **must** have the same format. `src_rect` with not positive size is treated as empty.
### void blend\_rect\_mask ( [Image](#class-image) src, [Image](#class-image) mask, [Rect2](class_rect2#class-rect2) src\_rect, [Vector2](class_vector2#class-vector2) dst )
Alpha-blends `src_rect` from `src` image to this image using `mask` image at coordinates `dst`, clipped accordingly to both image bounds. Alpha channels are required for both `src` and `mask`. `dst` pixels and `src` pixels will blend if the corresponding mask pixel's alpha value is not 0. This image and `src` image **must** have the same format. `src` image and `mask` image **must** have the same size (width and height) but they can have different formats. `src_rect` with not positive size is treated as empty.
### void blit\_rect ( [Image](#class-image) src, [Rect2](class_rect2#class-rect2) src\_rect, [Vector2](class_vector2#class-vector2) dst )
Copies `src_rect` from `src` image to this image at coordinates `dst`, clipped accordingly to both image bounds. This image and `src` image **must** have the same format. `src_rect` with not positive size is treated as empty.
### void blit\_rect\_mask ( [Image](#class-image) src, [Image](#class-image) mask, [Rect2](class_rect2#class-rect2) src\_rect, [Vector2](class_vector2#class-vector2) dst )
Blits `src_rect` area from `src` image to this image at the coordinates given by `dst`, clipped accordingly to both image bounds. `src` pixel is copied onto `dst` if the corresponding `mask` pixel's alpha value is not 0. This image and `src` image **must** have the same format. `src` image and `mask` image **must** have the same size (width and height) but they can have different formats. `src_rect` with not positive size is treated as empty.
### void bumpmap\_to\_normalmap ( [float](class_float#class-float) bump\_scale=1.0 )
Converts a bumpmap to a normalmap. A bumpmap provides a height offset per-pixel, while a normalmap provides a normal direction per pixel.
### void clear\_mipmaps ( )
Removes the image's mipmaps.
### [Error](class_%40globalscope#enum-globalscope-error) compress ( [CompressMode](#enum-image-compressmode) mode, [CompressSource](#enum-image-compresssource) source, [float](class_float#class-float) lossy\_quality )
Compresses the image to use less memory. Can not directly access pixel data while the image is compressed. Returns error if the chosen compression mode is not available. See [CompressMode](#enum-image-compressmode) and [CompressSource](#enum-image-compresssource) constants.
### void convert ( [Format](#enum-image-format) format )
Converts the image's format. See [Format](#enum-image-format) constants.
### void copy\_from ( [Image](#class-image) src )
Copies `src` image to this image.
### void create ( [int](class_int#class-int) width, [int](class_int#class-int) height, [bool](class_bool#class-bool) use\_mipmaps, [Format](#enum-image-format) format )
Creates an empty image of given size and format. See [Format](#enum-image-format) constants. If `use_mipmaps` is `true` then generate mipmaps for this image. See the [generate\_mipmaps](#class-image-method-generate-mipmaps).
### void create\_from\_data ( [int](class_int#class-int) width, [int](class_int#class-int) height, [bool](class_bool#class-bool) use\_mipmaps, [Format](#enum-image-format) format, [PoolByteArray](class_poolbytearray#class-poolbytearray) data )
Creates a new image of given size and format. See [Format](#enum-image-format) constants. Fills the image with the given raw data. If `use_mipmaps` is `true` then loads mipmaps for this image from `data`. See [generate\_mipmaps](#class-image-method-generate-mipmaps).
### void crop ( [int](class_int#class-int) width, [int](class_int#class-int) height )
Crops the image to the given `width` and `height`. If the specified size is larger than the current size, the extra area is filled with black pixels.
### [Error](class_%40globalscope#enum-globalscope-error) decompress ( )
Decompresses the image if it is compressed. Returns an error if decompress function is not available.
### [AlphaMode](#enum-image-alphamode) detect\_alpha ( ) const
Returns [ALPHA\_BLEND](#class-image-constant-alpha-blend) if the image has data for alpha values. Returns [ALPHA\_BIT](#class-image-constant-alpha-bit) if all the alpha values are stored in a single bit. Returns [ALPHA\_NONE](#class-image-constant-alpha-none) if no data for alpha values is found.
### void expand\_x2\_hq2x ( )
Stretches the image and enlarges it by a factor of 2. No interpolation is done.
### void fill ( [Color](class_color#class-color) color )
Fills the image with `color`.
### void fill\_rect ( [Rect2](class_rect2#class-rect2) rect, [Color](class_color#class-color) color )
Fills `rect` with `color`.
### void fix\_alpha\_edges ( )
Blends low-alpha pixels with nearby pixels.
### void flip\_x ( )
Flips the image horizontally.
### void flip\_y ( )
Flips the image vertically.
### [Error](class_%40globalscope#enum-globalscope-error) generate\_mipmaps ( [bool](class_bool#class-bool) renormalize=false )
Generates mipmaps for the image. Mipmaps are precalculated lower-resolution copies of the image that are automatically used if the image needs to be scaled down when rendered. They help improve image quality and performance when rendering. This method returns an error if the image is compressed, in a custom format, or if the image's width/height is `0`.
**Note:** Mipmap generation is done on the CPU, is single-threaded and is *always* done on the main thread. This means generating mipmaps will result in noticeable stuttering during gameplay, even if [generate\_mipmaps](#class-image-method-generate-mipmaps) is called from a [Thread](class_thread#class-thread).
### [PoolByteArray](class_poolbytearray#class-poolbytearray) get\_data ( ) const
Returns a copy of the image's raw data.
### [Format](#enum-image-format) get\_format ( ) const
Returns the image's format. See [Format](#enum-image-format) constants.
### [int](class_int#class-int) get\_height ( ) const
Returns the image's height.
### [int](class_int#class-int) get\_mipmap\_offset ( [int](class_int#class-int) mipmap ) const
Returns the offset where the image's mipmap with index `mipmap` is stored in the `data` dictionary.
### [Color](class_color#class-color) get\_pixel ( [int](class_int#class-int) x, [int](class_int#class-int) y ) const
Returns the color of the pixel at `(x, y)` if the image is locked. If the image is unlocked, it always returns a [Color](class_color#class-color) with the value `(0, 0, 0, 1.0)`. This is the same as [get\_pixelv](#class-image-method-get-pixelv), but two integer arguments instead of a Vector2 argument.
### [Color](class_color#class-color) get\_pixelv ( [Vector2](class_vector2#class-vector2) src ) const
Returns the color of the pixel at `src` if the image is locked. If the image is unlocked, it always returns a [Color](class_color#class-color) with the value `(0, 0, 0, 1.0)`. This is the same as [get\_pixel](#class-image-method-get-pixel), but with a Vector2 argument instead of two integer arguments.
### [Image](#class-image) get\_rect ( [Rect2](class_rect2#class-rect2) rect ) const
Returns a new image that is a copy of the image's area specified with `rect`.
### [Vector2](class_vector2#class-vector2) get\_size ( ) const
Returns the image's size (width and height).
### [Rect2](class_rect2#class-rect2) get\_used\_rect ( ) const
Returns a [Rect2](class_rect2#class-rect2) enclosing the visible portion of the image, considering each pixel with a non-zero alpha channel as visible.
### [int](class_int#class-int) get\_width ( ) const
Returns the image's width.
### [bool](class_bool#class-bool) has\_mipmaps ( ) const
Returns `true` if the image has generated mipmaps.
### [bool](class_bool#class-bool) is\_compressed ( ) const
Returns `true` if the image is compressed.
### [bool](class_bool#class-bool) is\_empty ( ) const
Returns `true` if the image has no data.
### [bool](class_bool#class-bool) is\_invisible ( ) const
Returns `true` if all the image's pixels have an alpha value of 0. Returns `false` if any pixel has an alpha value higher than 0.
### [Error](class_%40globalscope#enum-globalscope-error) load ( [String](class_string#class-string) path )
Loads an image from file `path`. See [Supported image formats](https://docs.godotengine.org/en/3.5/tutorials/assets_pipeline/importing_images.html#supported-image-formats) for a list of supported image formats and limitations.
**Warning:** This method should only be used in the editor or in cases when you need to load external images at run-time, such as images located at the `user://` directory, and may not work in exported projects.
See also [ImageTexture](class_imagetexture#class-imagetexture) description for usage examples.
### [Error](class_%40globalscope#enum-globalscope-error) load\_bmp\_from\_buffer ( [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer )
Loads an image from the binary contents of a BMP file.
**Note:** Godot's BMP module doesn't support 16-bit per pixel images. Only 1-bit, 4-bit, 8-bit, 24-bit, and 32-bit per pixel images are supported.
### [Error](class_%40globalscope#enum-globalscope-error) load\_jpg\_from\_buffer ( [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer )
Loads an image from the binary contents of a JPEG file.
### [Error](class_%40globalscope#enum-globalscope-error) load\_png\_from\_buffer ( [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer )
Loads an image from the binary contents of a PNG file.
### [Error](class_%40globalscope#enum-globalscope-error) load\_tga\_from\_buffer ( [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer )
Loads an image from the binary contents of a TGA file.
### [Error](class_%40globalscope#enum-globalscope-error) load\_webp\_from\_buffer ( [PoolByteArray](class_poolbytearray#class-poolbytearray) buffer )
Loads an image from the binary contents of a WebP file.
### void lock ( )
Locks the data for reading and writing access. Sends an error to the console if the image is not locked when reading or writing a pixel.
### void normalmap\_to\_xy ( )
Converts the image's data to represent coordinates on a 3D plane. This is used when the image represents a normalmap. A normalmap can add lots of detail to a 3D surface without increasing the polygon count.
### void premultiply\_alpha ( )
Multiplies color values with alpha values. Resulting color values for a pixel are `(color * alpha)/256`.
### void resize ( [int](class_int#class-int) width, [int](class_int#class-int) height, [Interpolation](#enum-image-interpolation) interpolation=1 )
Resizes the image to the given `width` and `height`. New pixels are calculated using the `interpolation` mode defined via [Interpolation](#enum-image-interpolation) constants.
### void resize\_to\_po2 ( [bool](class_bool#class-bool) square=false, [Interpolation](#enum-image-interpolation) interpolation=1 )
Resizes the image to the nearest power of 2 for the width and height. If `square` is `true` then set width and height to be the same. New pixels are calculated using the `interpolation` mode defined via [Interpolation](#enum-image-interpolation) constants.
### [Image](#class-image) rgbe\_to\_srgb ( )
Converts a standard RGBE (Red Green Blue Exponent) image to an sRGB image.
### [Error](class_%40globalscope#enum-globalscope-error) save\_exr ( [String](class_string#class-string) path, [bool](class_bool#class-bool) grayscale=false ) const
Saves the image as an EXR file to `path`. If `grayscale` is `true` and the image has only one channel, it will be saved explicitly as monochrome rather than one red channel. This function will return [@GlobalScope.ERR\_UNAVAILABLE](class_%40globalscope#class-globalscope-constant-err-unavailable) if Godot was compiled without the TinyEXR module.
**Note:** The TinyEXR module is disabled in non-editor builds, which means [save\_exr](#class-image-method-save-exr) will return [@GlobalScope.ERR\_UNAVAILABLE](class_%40globalscope#class-globalscope-constant-err-unavailable) when it is called from an exported project.
### [Error](class_%40globalscope#enum-globalscope-error) save\_png ( [String](class_string#class-string) path ) const
Saves the image as a PNG file to `path`.
### [PoolByteArray](class_poolbytearray#class-poolbytearray) save\_png\_to\_buffer ( ) const
### void set\_pixel ( [int](class_int#class-int) x, [int](class_int#class-int) y, [Color](class_color#class-color) color )
Sets the [Color](class_color#class-color) of the pixel at `(x, y)` if the image is locked. Example:
```
var img = Image.new()
img.create(img_width, img_height, false, Image.FORMAT_RGBA8)
img.lock()
img.set_pixel(x, y, color) # Works
img.unlock()
img.set_pixel(x, y, color) # Does not have an effect
```
### void set\_pixelv ( [Vector2](class_vector2#class-vector2) dst, [Color](class_color#class-color) color )
Sets the [Color](class_color#class-color) of the pixel at `(dst.x, dst.y)` if the image is locked. Note that the `dst` values must be integers. Example:
```
var img = Image.new()
img.create(img_width, img_height, false, Image.FORMAT_RGBA8)
img.lock()
img.set_pixelv(Vector2(x, y), color) # Works
img.unlock()
img.set_pixelv(Vector2(x, y), color) # Does not have an effect
```
### void shrink\_x2 ( )
Shrinks the image by a factor of 2.
### void srgb\_to\_linear ( )
Converts the raw data from the sRGB colorspace to a linear scale.
### void unlock ( )
Unlocks the data and prevents changes.
| programming_docs |
godot BoxContainer BoxContainer
============
**Inherits:** [Container](class_container#class-container) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
**Inherited By:** [ColorPicker](class_colorpicker#class-colorpicker), [HBoxContainer](class_hboxcontainer#class-hboxcontainer), [VBoxContainer](class_vboxcontainer#class-vboxcontainer)
Base class for box containers.
Description
-----------
Arranges child controls vertically or horizontally, and rearranges the controls automatically when their minimum size changes.
Tutorials
---------
* [GUI containers](https://docs.godotengine.org/en/3.5/tutorials/ui/gui_containers.html)
Properties
----------
| | | |
| --- | --- | --- |
| [AlignMode](#enum-boxcontainer-alignmode) | [alignment](#class-boxcontainer-property-alignment) | `0` |
| [MouseFilter](class_control#enum-control-mousefilter) | mouse\_filter | `1` (overrides [Control](class_control#class-control-property-mouse-filter)) |
Methods
-------
| | |
| --- | --- |
| void | [add\_spacer](#class-boxcontainer-method-add-spacer) **(** [bool](class_bool#class-bool) begin **)** |
Enumerations
------------
enum **AlignMode**:
* **ALIGN\_BEGIN** = **0** --- Aligns children with the beginning of the container.
* **ALIGN\_CENTER** = **1** --- Aligns children with the center of the container.
* **ALIGN\_END** = **2** --- Aligns children with the end of the container.
Property Descriptions
---------------------
### [AlignMode](#enum-boxcontainer-alignmode) alignment
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_alignment(value) |
| *Getter* | get\_alignment() |
The alignment of the container's children (must be one of [ALIGN\_BEGIN](#class-boxcontainer-constant-align-begin), [ALIGN\_CENTER](#class-boxcontainer-constant-align-center) or [ALIGN\_END](#class-boxcontainer-constant-align-end)).
Method Descriptions
-------------------
### void add\_spacer ( [bool](class_bool#class-bool) begin )
Adds a control to the box as a spacer. If `true`, `begin` will insert the spacer control in front of other children.
godot Room Room
====
**Inherits:** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Room node, used to group objects together locally for [Portal](class_portal#class-portal) culling.
Description
-----------
The [Portal](class_portal#class-portal) culling system requires levels to be built using objects grouped together by location in areas called `Room`s. In many cases these will correspond to actual rooms in buildings, but not necessarily (a canyon area may be treated as a room).
Any [VisualInstance](class_visualinstance#class-visualinstance) that is a child or grandchild of a `Room` will be assigned to that room, if the `portal_mode` of that [VisualInstance](class_visualinstance#class-visualinstance) is set to `STATIC` (does not move) or `DYNAMIC` (moves only within the room).
Internally the room boundary must form a **convex hull**, and by default this is determined automatically by the geometry of the objects you place within the room.
You can alternatively precisely specify a **manual bound**. If you place a [MeshInstance](class_meshinstance#class-meshinstance) with a name prefixed by `Bound_`, it will turn off the bound generation from geometry, and instead use the vertices of this MeshInstance to directly calculate a convex hull during the conversion stage (see [RoomManager](class_roommanager#class-roommanager)).
In order to see from one room into an adjacent room, [Portal](class_portal#class-portal)s must be placed over non-occluded openings between rooms. These will often be placed over doors and windows.
Properties
----------
| | | |
| --- | --- | --- |
| [PoolVector3Array](class_poolvector3array#class-poolvector3array) | [points](#class-room-property-points) | `PoolVector3Array( )` |
| [float](class_float#class-float) | [room\_simplify](#class-room-property-room-simplify) | `0.5` |
| [bool](class_bool#class-bool) | [use\_default\_simplify](#class-room-property-use-default-simplify) | `true` |
Methods
-------
| | |
| --- | --- |
| void | [set\_point](#class-room-method-set-point) **(** [int](class_int#class-int) index, [Vector3](class_vector3#class-vector3) position **)** |
Property Descriptions
---------------------
### [PoolVector3Array](class_poolvector3array#class-poolvector3array) points
| | |
| --- | --- |
| *Default* | `PoolVector3Array( )` |
| *Setter* | set\_points(value) |
| *Getter* | get\_points() |
If `points` are set, the `Room` bounding convex hull will be built from these points. If no points are set, the room bound will either be derived from a manual bound ([MeshInstance](class_meshinstance#class-meshinstance) with name prefix `Bound_`), or from the geometry within the room.
Note that you can use the `Generate Points` editor button to get started. This will use either the geometry or manual bound to generate the room hull, and save the resulting points, allowing you to edit them to further refine the bound.
### [float](class_float#class-float) room\_simplify
| | |
| --- | --- |
| *Default* | `0.5` |
| *Setter* | set\_room\_simplify(value) |
| *Getter* | get\_room\_simplify() |
The `simplify` value determines to what degree room hulls (bounds) are simplified, by removing similar planes. A value of 0 gives no simplification, 1 gives maximum simplification.
### [bool](class_bool#class-bool) use\_default\_simplify
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_use\_default\_simplify(value) |
| *Getter* | get\_use\_default\_simplify() |
The room hull simplification can either use the default value set in the [RoomManager](class_roommanager#class-roommanager), or override this and use the per room setting.
Method Descriptions
-------------------
### void set\_point ( [int](class_int#class-int) index, [Vector3](class_vector3#class-vector3) position )
Sets individual points. Primarily for use by the editor.
godot Transform2D Transform2D
===========
2D transformation (2×3 matrix).
Description
-----------
2×3 matrix (2 rows, 3 columns) used for 2D linear transformations. It can represent transformations such as translation, rotation, or scaling. It consists of three [Vector2](class_vector2#class-vector2) values: [x](#class-transform2d-property-x), [y](#class-transform2d-property-y), and the [origin](#class-transform2d-property-origin).
For more information, read the "Matrices and transforms" documentation article.
Tutorials
---------
* [Math tutorial index](https://docs.godotengine.org/en/3.5/tutorials/math/index.html)
* [Matrices and transforms](https://docs.godotengine.org/en/3.5/tutorials/math/matrices_and_transforms.html)
* [Matrix Transform Demo](https://godotengine.org/asset-library/asset/584)
* [2.5D Demo](https://godotengine.org/asset-library/asset/583)
Properties
----------
| | | |
| --- | --- | --- |
| [Vector2](class_vector2#class-vector2) | [origin](#class-transform2d-property-origin) | `Vector2( 0, 0 )` |
| [Vector2](class_vector2#class-vector2) | [x](#class-transform2d-property-x) | `Vector2( 1, 0 )` |
| [Vector2](class_vector2#class-vector2) | [y](#class-transform2d-property-y) | `Vector2( 0, 1 )` |
Methods
-------
| | |
| --- | --- |
| [Transform2D](#class-transform2d) | [Transform2D](#class-transform2d-method-transform2d) **(** [Transform](class_transform#class-transform) from **)** |
| [Transform2D](#class-transform2d) | [Transform2D](#class-transform2d-method-transform2d) **(** [Vector2](class_vector2#class-vector2) x\_axis, [Vector2](class_vector2#class-vector2) y\_axis, [Vector2](class_vector2#class-vector2) origin **)** |
| [Transform2D](#class-transform2d) | [Transform2D](#class-transform2d-method-transform2d) **(** [float](class_float#class-float) rotation, [Vector2](class_vector2#class-vector2) position **)** |
| [Transform2D](#class-transform2d) | [affine\_inverse](#class-transform2d-method-affine-inverse) **(** **)** |
| [Vector2](class_vector2#class-vector2) | [basis\_xform](#class-transform2d-method-basis-xform) **(** [Vector2](class_vector2#class-vector2) v **)** |
| [Vector2](class_vector2#class-vector2) | [basis\_xform\_inv](#class-transform2d-method-basis-xform-inv) **(** [Vector2](class_vector2#class-vector2) v **)** |
| [Vector2](class_vector2#class-vector2) | [get\_origin](#class-transform2d-method-get-origin) **(** **)** |
| [float](class_float#class-float) | [get\_rotation](#class-transform2d-method-get-rotation) **(** **)** |
| [Vector2](class_vector2#class-vector2) | [get\_scale](#class-transform2d-method-get-scale) **(** **)** |
| [Transform2D](#class-transform2d) | [interpolate\_with](#class-transform2d-method-interpolate-with) **(** [Transform2D](#class-transform2d) transform, [float](class_float#class-float) weight **)** |
| [Transform2D](#class-transform2d) | [inverse](#class-transform2d-method-inverse) **(** **)** |
| [bool](class_bool#class-bool) | [is\_equal\_approx](#class-transform2d-method-is-equal-approx) **(** [Transform2D](#class-transform2d) transform **)** |
| [Transform2D](#class-transform2d) | [orthonormalized](#class-transform2d-method-orthonormalized) **(** **)** |
| [Transform2D](#class-transform2d) | [rotated](#class-transform2d-method-rotated) **(** [float](class_float#class-float) angle **)** |
| [Transform2D](#class-transform2d) | [scaled](#class-transform2d-method-scaled) **(** [Vector2](class_vector2#class-vector2) scale **)** |
| [Transform2D](#class-transform2d) | [translated](#class-transform2d-method-translated) **(** [Vector2](class_vector2#class-vector2) offset **)** |
| [Variant](class_variant#class-variant) | [xform](#class-transform2d-method-xform) **(** [Variant](class_variant#class-variant) v **)** |
| [Variant](class_variant#class-variant) | [xform\_inv](#class-transform2d-method-xform-inv) **(** [Variant](class_variant#class-variant) v **)** |
Constants
---------
* **IDENTITY** = **Transform2D( 1, 0, 0, 1, 0, 0 )** --- The identity `Transform2D` with no translation, rotation or scaling applied. When applied to other data structures, [IDENTITY](#class-transform2d-constant-identity) performs no transformation.
* **FLIP\_X** = **Transform2D( -1, 0, 0, 1, 0, 0 )** --- The `Transform2D` that will flip something along the X axis.
* **FLIP\_Y** = **Transform2D( 1, 0, 0, -1, 0, 0 )** --- The `Transform2D` that will flip something along the Y axis.
Property Descriptions
---------------------
### [Vector2](class_vector2#class-vector2) origin
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
The origin vector (column 2, the third column). Equivalent to array index `2`. The origin vector represents translation.
### [Vector2](class_vector2#class-vector2) x
| | |
| --- | --- |
| *Default* | `Vector2( 1, 0 )` |
The basis matrix's X vector (column 0). Equivalent to array index `0`.
### [Vector2](class_vector2#class-vector2) y
| | |
| --- | --- |
| *Default* | `Vector2( 0, 1 )` |
The basis matrix's Y vector (column 1). Equivalent to array index `1`.
Method Descriptions
-------------------
### [Transform2D](#class-transform2d) Transform2D ( [Transform](class_transform#class-transform) from )
Constructs the transform from a 3D [Transform](class_transform#class-transform).
* [Transform2D](#class-transform2d) **Transform2D** **(** [Vector2](class_vector2#class-vector2) x\_axis, [Vector2](class_vector2#class-vector2) y\_axis, [Vector2](class_vector2#class-vector2) origin **)**
Constructs the transform from 3 [Vector2](class_vector2#class-vector2) values representing [x](#class-transform2d-property-x), [y](#class-transform2d-property-y), and the [origin](#class-transform2d-property-origin) (the three column vectors).
* [Transform2D](#class-transform2d) **Transform2D** **(** [float](class_float#class-float) rotation, [Vector2](class_vector2#class-vector2) position **)**
Constructs the transform from a given angle (in radians) and position.
### [Transform2D](#class-transform2d) affine\_inverse ( )
Returns the inverse of the transform, under the assumption that the transformation is composed of rotation, scaling and translation.
### [Vector2](class_vector2#class-vector2) basis\_xform ( [Vector2](class_vector2#class-vector2) v )
Returns a vector transformed (multiplied) by the basis matrix.
This method does not account for translation (the origin vector).
### [Vector2](class_vector2#class-vector2) basis\_xform\_inv ( [Vector2](class_vector2#class-vector2) v )
Returns a vector transformed (multiplied) by the inverse basis matrix.
This method does not account for translation (the origin vector).
### [Vector2](class_vector2#class-vector2) get\_origin ( )
Returns the transform's origin (translation).
### [float](class_float#class-float) get\_rotation ( )
Returns the transform's rotation (in radians).
### [Vector2](class_vector2#class-vector2) get\_scale ( )
Returns the scale.
### [Transform2D](#class-transform2d) interpolate\_with ( [Transform2D](#class-transform2d) transform, [float](class_float#class-float) weight )
Returns a transform interpolated between this transform and another by a given `weight` (on the range of 0.0 to 1.0).
### [Transform2D](#class-transform2d) inverse ( )
Returns the inverse of the transform, under the assumption that the transformation is composed of rotation and translation (no scaling, use [affine\_inverse](#class-transform2d-method-affine-inverse) for transforms with scaling).
### [bool](class_bool#class-bool) is\_equal\_approx ( [Transform2D](#class-transform2d) transform )
Returns `true` if this transform and `transform` are approximately equal, by calling `is_equal_approx` on each component.
### [Transform2D](#class-transform2d) orthonormalized ( )
Returns the transform with the basis orthogonal (90 degrees), and normalized axis vectors (scale of 1 or -1).
### [Transform2D](#class-transform2d) rotated ( [float](class_float#class-float) angle )
Returns a copy of the transform rotated by the given `angle` (in radians), using matrix multiplication.
### [Transform2D](#class-transform2d) scaled ( [Vector2](class_vector2#class-vector2) scale )
Returns a copy of the transform scaled by the given `scale` factor, using matrix multiplication.
**Note:** Negative X scales in 2D are not decomposable from the transformation matrix. Due to the way scale is represented with transformation matrices in Godot, negative scales on the X axis will be changed to negative scales on the Y axis and a rotation of 180 degrees when decomposed.
### [Transform2D](#class-transform2d) translated ( [Vector2](class_vector2#class-vector2) offset )
Returns a copy of the transform translated by the given `offset`, relative to the transform's basis vectors.
Unlike [rotated](#class-transform2d-method-rotated) and [scaled](#class-transform2d-method-scaled), this does not use matrix multiplication.
### [Variant](class_variant#class-variant) xform ( [Variant](class_variant#class-variant) v )
Transforms the given [Vector2](class_vector2#class-vector2), [Rect2](class_rect2#class-rect2), or [PoolVector2Array](class_poolvector2array#class-poolvector2array) by this transform.
### [Variant](class_variant#class-variant) xform\_inv ( [Variant](class_variant#class-variant) v )
Inverse-transforms the given [Vector2](class_vector2#class-vector2), [Rect2](class_rect2#class-rect2), or [PoolVector2Array](class_poolvector2array#class-poolvector2array) by this transform, under the assumption that the transformation is composed of rotation and translation (no scaling). Equivalent to calling `inverse().xform(v)` on this transform. For affine transformations (e.g. with scaling) see [affine\_inverse](#class-transform2d-method-affine-inverse) method.
godot VisualShaderNodeGlobalExpression VisualShaderNodeGlobalExpression
================================
**Inherits:** [VisualShaderNodeExpression](class_visualshadernodeexpression#class-visualshadernodeexpression) **<** [VisualShaderNodeGroupBase](class_visualshadernodegroupbase#class-visualshadernodegroupbase) **<** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A custom global visual shader graph expression written in Godot Shading Language.
Description
-----------
Custom Godot Shader Language expression, which is placed on top of the generated shader. You can place various function definitions inside to call later in [VisualShaderNodeExpression](class_visualshadernodeexpression#class-visualshadernodeexpression)s (which are injected in the main shader functions). You can also declare varyings, uniforms and global constants.
godot TabContainer TabContainer
============
**Inherits:** [Container](class_container#class-container) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Tabbed container.
Description
-----------
Arranges [Control](class_control#class-control) children into a tabbed view, creating a tab for each one. The active tab's corresponding [Control](class_control#class-control) has its `visible` property set to `true`, and all other children's to `false`.
Ignores non-[Control](class_control#class-control) children.
**Note:** The drawing of the clickable tabs themselves is handled by this node. Adding [Tabs](class_tabs#class-tabs) as children is not needed.
Tutorials
---------
* [GUI containers](https://docs.godotengine.org/en/3.5/tutorials/ui/gui_containers.html)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [all\_tabs\_in\_front](#class-tabcontainer-property-all-tabs-in-front) | `false` |
| [int](class_int#class-int) | [current\_tab](#class-tabcontainer-property-current-tab) | `0` |
| [bool](class_bool#class-bool) | [drag\_to\_rearrange\_enabled](#class-tabcontainer-property-drag-to-rearrange-enabled) | `false` |
| [TabAlign](#enum-tabcontainer-tabalign) | [tab\_align](#class-tabcontainer-property-tab-align) | `1` |
| [bool](class_bool#class-bool) | [tabs\_visible](#class-tabcontainer-property-tabs-visible) | `true` |
| [bool](class_bool#class-bool) | [use\_hidden\_tabs\_for\_min\_size](#class-tabcontainer-property-use-hidden-tabs-for-min-size) | `false` |
Methods
-------
| | |
| --- | --- |
| [Control](class_control#class-control) | [get\_current\_tab\_control](#class-tabcontainer-method-get-current-tab-control) **(** **)** const |
| [Popup](class_popup#class-popup) | [get\_popup](#class-tabcontainer-method-get-popup) **(** **)** const |
| [int](class_int#class-int) | [get\_previous\_tab](#class-tabcontainer-method-get-previous-tab) **(** **)** const |
| [Control](class_control#class-control) | [get\_tab\_control](#class-tabcontainer-method-get-tab-control) **(** [int](class_int#class-int) tab\_idx **)** const |
| [int](class_int#class-int) | [get\_tab\_count](#class-tabcontainer-method-get-tab-count) **(** **)** const |
| [bool](class_bool#class-bool) | [get\_tab\_disabled](#class-tabcontainer-method-get-tab-disabled) **(** [int](class_int#class-int) tab\_idx **)** const |
| [bool](class_bool#class-bool) | [get\_tab\_hidden](#class-tabcontainer-method-get-tab-hidden) **(** [int](class_int#class-int) tab\_idx **)** const |
| [Texture](class_texture#class-texture) | [get\_tab\_icon](#class-tabcontainer-method-get-tab-icon) **(** [int](class_int#class-int) tab\_idx **)** const |
| [int](class_int#class-int) | [get\_tab\_idx\_at\_point](#class-tabcontainer-method-get-tab-idx-at-point) **(** [Vector2](class_vector2#class-vector2) point **)** const |
| [String](class_string#class-string) | [get\_tab\_title](#class-tabcontainer-method-get-tab-title) **(** [int](class_int#class-int) tab\_idx **)** const |
| [int](class_int#class-int) | [get\_tabs\_rearrange\_group](#class-tabcontainer-method-get-tabs-rearrange-group) **(** **)** const |
| void | [set\_popup](#class-tabcontainer-method-set-popup) **(** [Node](class_node#class-node) popup **)** |
| void | [set\_tab\_disabled](#class-tabcontainer-method-set-tab-disabled) **(** [int](class_int#class-int) tab\_idx, [bool](class_bool#class-bool) disabled **)** |
| void | [set\_tab\_hidden](#class-tabcontainer-method-set-tab-hidden) **(** [int](class_int#class-int) tab\_idx, [bool](class_bool#class-bool) hidden **)** |
| void | [set\_tab\_icon](#class-tabcontainer-method-set-tab-icon) **(** [int](class_int#class-int) tab\_idx, [Texture](class_texture#class-texture) icon **)** |
| void | [set\_tab\_title](#class-tabcontainer-method-set-tab-title) **(** [int](class_int#class-int) tab\_idx, [String](class_string#class-string) title **)** |
| void | [set\_tabs\_rearrange\_group](#class-tabcontainer-method-set-tabs-rearrange-group) **(** [int](class_int#class-int) group\_id **)** |
Theme Properties
----------------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [font\_color\_bg](#class-tabcontainer-theme-color-font-color-bg) | `Color( 0.69, 0.69, 0.69, 1 )` |
| [Color](class_color#class-color) | [font\_color\_disabled](#class-tabcontainer-theme-color-font-color-disabled) | `Color( 0.9, 0.9, 0.9, 0.2 )` |
| [Color](class_color#class-color) | [font\_color\_fg](#class-tabcontainer-theme-color-font-color-fg) | `Color( 0.94, 0.94, 0.94, 1 )` |
| [int](class_int#class-int) | [hseparation](#class-tabcontainer-theme-constant-hseparation) | `4` |
| [int](class_int#class-int) | [label\_valign\_bg](#class-tabcontainer-theme-constant-label-valign-bg) | `2` |
| [int](class_int#class-int) | [label\_valign\_fg](#class-tabcontainer-theme-constant-label-valign-fg) | `0` |
| [int](class_int#class-int) | [side\_margin](#class-tabcontainer-theme-constant-side-margin) | `8` |
| [int](class_int#class-int) | [top\_margin](#class-tabcontainer-theme-constant-top-margin) | `24` |
| [Font](class_font#class-font) | [font](#class-tabcontainer-theme-font-font) | |
| [Texture](class_texture#class-texture) | [decrement](#class-tabcontainer-theme-icon-decrement) | |
| [Texture](class_texture#class-texture) | [decrement\_highlight](#class-tabcontainer-theme-icon-decrement-highlight) | |
| [Texture](class_texture#class-texture) | [increment](#class-tabcontainer-theme-icon-increment) | |
| [Texture](class_texture#class-texture) | [increment\_highlight](#class-tabcontainer-theme-icon-increment-highlight) | |
| [Texture](class_texture#class-texture) | [menu](#class-tabcontainer-theme-icon-menu) | |
| [Texture](class_texture#class-texture) | [menu\_highlight](#class-tabcontainer-theme-icon-menu-highlight) | |
| [StyleBox](class_stylebox#class-stylebox) | [panel](#class-tabcontainer-theme-style-panel) | |
| [StyleBox](class_stylebox#class-stylebox) | [tab\_bg](#class-tabcontainer-theme-style-tab-bg) | |
| [StyleBox](class_stylebox#class-stylebox) | [tab\_disabled](#class-tabcontainer-theme-style-tab-disabled) | |
| [StyleBox](class_stylebox#class-stylebox) | [tab\_fg](#class-tabcontainer-theme-style-tab-fg) | |
Signals
-------
### pre\_popup\_pressed ( )
Emitted when the `TabContainer`'s [Popup](class_popup#class-popup) button is clicked. See [set\_popup](#class-tabcontainer-method-set-popup) for details.
### tab\_changed ( [int](class_int#class-int) tab )
Emitted when switching to another tab.
### tab\_selected ( [int](class_int#class-int) tab )
Emitted when a tab is selected, even if it is the current tab.
Enumerations
------------
enum **TabAlign**:
* **ALIGN\_LEFT** = **0** --- Align the tabs to the left.
* **ALIGN\_CENTER** = **1** --- Align the tabs to the center.
* **ALIGN\_RIGHT** = **2** --- Align the tabs to the right.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) all\_tabs\_in\_front
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_all\_tabs\_in\_front(value) |
| *Getter* | is\_all\_tabs\_in\_front() |
If `true`, all tabs are drawn in front of the panel. If `false`, inactive tabs are drawn behind the panel.
### [int](class_int#class-int) current\_tab
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_current\_tab(value) |
| *Getter* | get\_current\_tab() |
The current tab index. When set, this index's [Control](class_control#class-control) node's `visible` property is set to `true` and all others are set to `false`.
### [bool](class_bool#class-bool) drag\_to\_rearrange\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_drag\_to\_rearrange\_enabled(value) |
| *Getter* | get\_drag\_to\_rearrange\_enabled() |
If `true`, tabs can be rearranged with mouse drag.
### [TabAlign](#enum-tabcontainer-tabalign) tab\_align
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_tab\_align(value) |
| *Getter* | get\_tab\_align() |
The alignment of all tabs in the tab container. See the [TabAlign](#enum-tabcontainer-tabalign) constants for details.
### [bool](class_bool#class-bool) tabs\_visible
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_tabs\_visible(value) |
| *Getter* | are\_tabs\_visible() |
If `true`, tabs are visible. If `false`, tabs' content and titles are hidden.
### [bool](class_bool#class-bool) use\_hidden\_tabs\_for\_min\_size
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_use\_hidden\_tabs\_for\_min\_size(value) |
| *Getter* | get\_use\_hidden\_tabs\_for\_min\_size() |
If `true`, children [Control](class_control#class-control) nodes that are hidden have their minimum size take into account in the total, instead of only the currently visible one.
Method Descriptions
-------------------
### [Control](class_control#class-control) get\_current\_tab\_control ( ) const
Returns the child [Control](class_control#class-control) node located at the active tab index.
### [Popup](class_popup#class-popup) get\_popup ( ) const
Returns the [Popup](class_popup#class-popup) node instance if one has been set already with [set\_popup](#class-tabcontainer-method-set-popup).
**Warning:** This is a required internal node, removing and freeing it may cause a crash. If you wish to hide it or any of its children, use their [CanvasItem.visible](class_canvasitem#class-canvasitem-property-visible) property.
### [int](class_int#class-int) get\_previous\_tab ( ) const
Returns the previously active tab index.
### [Control](class_control#class-control) get\_tab\_control ( [int](class_int#class-int) tab\_idx ) const
Returns the [Control](class_control#class-control) node from the tab at index `tab_idx`.
### [int](class_int#class-int) get\_tab\_count ( ) const
Returns the number of tabs.
### [bool](class_bool#class-bool) get\_tab\_disabled ( [int](class_int#class-int) tab\_idx ) const
Returns `true` if the tab at index `tab_idx` is disabled.
### [bool](class_bool#class-bool) get\_tab\_hidden ( [int](class_int#class-int) tab\_idx ) const
Returns `true` if the tab at index `tab_idx` is hidden.
### [Texture](class_texture#class-texture) get\_tab\_icon ( [int](class_int#class-int) tab\_idx ) const
Returns the [Texture](class_texture#class-texture) for the tab at index `tab_idx` or `null` if the tab has no [Texture](class_texture#class-texture).
### [int](class_int#class-int) get\_tab\_idx\_at\_point ( [Vector2](class_vector2#class-vector2) point ) const
Returns the index of the tab at local coordinates `point`. Returns `-1` if the point is outside the control boundaries or if there's no tab at the queried position.
### [String](class_string#class-string) get\_tab\_title ( [int](class_int#class-int) tab\_idx ) const
Returns the title of the tab at index `tab_idx`. Tab titles default to the name of the indexed child node, but this can be overridden with [set\_tab\_title](#class-tabcontainer-method-set-tab-title).
### [int](class_int#class-int) get\_tabs\_rearrange\_group ( ) const
Returns the `TabContainer` rearrange group id.
### void set\_popup ( [Node](class_node#class-node) popup )
If set on a [Popup](class_popup#class-popup) node instance, a popup menu icon appears in the top-right corner of the `TabContainer`. Clicking it will expand the [Popup](class_popup#class-popup) node.
### void set\_tab\_disabled ( [int](class_int#class-int) tab\_idx, [bool](class_bool#class-bool) disabled )
If `disabled` is `true`, disables the tab at index `tab_idx`, making it non-interactable.
### void set\_tab\_hidden ( [int](class_int#class-int) tab\_idx, [bool](class_bool#class-bool) hidden )
If `hidden` is `true`, hides the tab at index `tab_idx`, making it disappear from the tab area.
### void set\_tab\_icon ( [int](class_int#class-int) tab\_idx, [Texture](class_texture#class-texture) icon )
Sets an icon for the tab at index `tab_idx`.
### void set\_tab\_title ( [int](class_int#class-int) tab\_idx, [String](class_string#class-string) title )
Sets a title for the tab at index `tab_idx`. Tab titles default to the name of the indexed child node.
### void set\_tabs\_rearrange\_group ( [int](class_int#class-int) group\_id )
Defines rearrange group id, choose for each `TabContainer` the same value to enable tab drag between `TabContainer`. Enable drag with [drag\_to\_rearrange\_enabled](#class-tabcontainer-property-drag-to-rearrange-enabled).
Theme Property Descriptions
---------------------------
### [Color](class_color#class-color) font\_color\_bg
| | |
| --- | --- |
| *Default* | `Color( 0.69, 0.69, 0.69, 1 )` |
Font color of inactive tabs.
### [Color](class_color#class-color) font\_color\_disabled
| | |
| --- | --- |
| *Default* | `Color( 0.9, 0.9, 0.9, 0.2 )` |
Font color of disabled tabs.
### [Color](class_color#class-color) font\_color\_fg
| | |
| --- | --- |
| *Default* | `Color( 0.94, 0.94, 0.94, 1 )` |
Font color of the currently selected tab.
### [int](class_int#class-int) hseparation
| | |
| --- | --- |
| *Default* | `4` |
Horizontal separation between tabs.
### [int](class_int#class-int) label\_valign\_bg
| | |
| --- | --- |
| *Default* | `2` |
### [int](class_int#class-int) label\_valign\_fg
| | |
| --- | --- |
| *Default* | `0` |
### [int](class_int#class-int) side\_margin
| | |
| --- | --- |
| *Default* | `8` |
The space at the left and right edges of the tab bar.
### [int](class_int#class-int) top\_margin
| | |
| --- | --- |
| *Default* | `24` |
### [Font](class_font#class-font) font
The font used to draw tab names.
### [Texture](class_texture#class-texture) decrement
Icon for the left arrow button that appears when there are too many tabs to fit in the container width. When the button is disabled (i.e. the first tab is visible), it appears semi-transparent.
### [Texture](class_texture#class-texture) decrement\_highlight
Icon for the left arrow button that appears when there are too many tabs to fit in the container width. Used when the button is being hovered with the cursor.
### [Texture](class_texture#class-texture) increment
Icon for the right arrow button that appears when there are too many tabs to fit in the container width. When the button is disabled (i.e. the last tab is visible) it appears semi-transparent.
### [Texture](class_texture#class-texture) increment\_highlight
Icon for the right arrow button that appears when there are too many tabs to fit in the container width. Used when the button is being hovered with the cursor.
### [Texture](class_texture#class-texture) menu
The icon for the menu button (see [set\_popup](#class-tabcontainer-method-set-popup)).
### [Texture](class_texture#class-texture) menu\_highlight
The icon for the menu button (see [set\_popup](#class-tabcontainer-method-set-popup)) when it's being hovered with the cursor.
### [StyleBox](class_stylebox#class-stylebox) panel
The style for the background fill.
### [StyleBox](class_stylebox#class-stylebox) tab\_bg
The style of inactive tabs.
### [StyleBox](class_stylebox#class-stylebox) tab\_disabled
The style of disabled tabs.
### [StyleBox](class_stylebox#class-stylebox) tab\_fg
The style of the currently selected tab.
| programming_docs |
godot ColorPickerButton ColorPickerButton
=================
**Inherits:** [Button](class_button#class-button) **<** [BaseButton](class_basebutton#class-basebutton) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Button that pops out a [ColorPicker](class_colorpicker#class-colorpicker).
Description
-----------
Encapsulates a [ColorPicker](class_colorpicker#class-colorpicker) making it accessible by pressing a button. Pressing the button will toggle the [ColorPicker](class_colorpicker#class-colorpicker) visibility.
See also [BaseButton](class_basebutton#class-basebutton) which contains common properties and methods associated with this node.
**Note:** By default, the button may not be wide enough for the color preview swatch to be visible. Make sure to set [Control.rect\_min\_size](class_control#class-control-property-rect-min-size) to a big enough value to give the button enough space.
Tutorials
---------
* [GUI Drag And Drop Demo](https://godotengine.org/asset-library/asset/133)
* [2D GD Paint Demo](https://godotengine.org/asset-library/asset/517)
Properties
----------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [color](#class-colorpickerbutton-property-color) | `Color( 0, 0, 0, 1 )` |
| [bool](class_bool#class-bool) | [edit\_alpha](#class-colorpickerbutton-property-edit-alpha) | `true` |
| [bool](class_bool#class-bool) | toggle\_mode | `true` (overrides [BaseButton](class_basebutton#class-basebutton-property-toggle-mode)) |
Methods
-------
| | |
| --- | --- |
| [ColorPicker](class_colorpicker#class-colorpicker) | [get\_picker](#class-colorpickerbutton-method-get-picker) **(** **)** |
| [PopupPanel](class_popuppanel#class-popuppanel) | [get\_popup](#class-colorpickerbutton-method-get-popup) **(** **)** |
Theme Properties
----------------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [font\_color](#class-colorpickerbutton-theme-color-font-color) | `Color( 1, 1, 1, 1 )` |
| [Color](class_color#class-color) | [font\_color\_disabled](#class-colorpickerbutton-theme-color-font-color-disabled) | `Color( 0.9, 0.9, 0.9, 0.3 )` |
| [Color](class_color#class-color) | [font\_color\_focus](#class-colorpickerbutton-theme-color-font-color-focus) | `Color( 1, 1, 1, 1 )` |
| [Color](class_color#class-color) | [font\_color\_hover](#class-colorpickerbutton-theme-color-font-color-hover) | `Color( 1, 1, 1, 1 )` |
| [Color](class_color#class-color) | [font\_color\_pressed](#class-colorpickerbutton-theme-color-font-color-pressed) | `Color( 0.8, 0.8, 0.8, 1 )` |
| [int](class_int#class-int) | [hseparation](#class-colorpickerbutton-theme-constant-hseparation) | `2` |
| [Font](class_font#class-font) | [font](#class-colorpickerbutton-theme-font-font) | |
| [Texture](class_texture#class-texture) | [bg](#class-colorpickerbutton-theme-icon-bg) | |
| [StyleBox](class_stylebox#class-stylebox) | [disabled](#class-colorpickerbutton-theme-style-disabled) | |
| [StyleBox](class_stylebox#class-stylebox) | [focus](#class-colorpickerbutton-theme-style-focus) | |
| [StyleBox](class_stylebox#class-stylebox) | [hover](#class-colorpickerbutton-theme-style-hover) | |
| [StyleBox](class_stylebox#class-stylebox) | [normal](#class-colorpickerbutton-theme-style-normal) | |
| [StyleBox](class_stylebox#class-stylebox) | [pressed](#class-colorpickerbutton-theme-style-pressed) | |
Signals
-------
### color\_changed ( [Color](class_color#class-color) color )
Emitted when the color changes.
### picker\_created ( )
Emitted when the [ColorPicker](class_colorpicker#class-colorpicker) is created (the button is pressed for the first time).
### popup\_closed ( )
Emitted when the [ColorPicker](class_colorpicker#class-colorpicker) is closed.
Property Descriptions
---------------------
### [Color](class_color#class-color) color
| | |
| --- | --- |
| *Default* | `Color( 0, 0, 0, 1 )` |
| *Setter* | set\_pick\_color(value) |
| *Getter* | get\_pick\_color() |
The currently selected color.
### [bool](class_bool#class-bool) edit\_alpha
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_edit\_alpha(value) |
| *Getter* | is\_editing\_alpha() |
If `true`, the alpha channel in the displayed [ColorPicker](class_colorpicker#class-colorpicker) will be visible.
Method Descriptions
-------------------
### [ColorPicker](class_colorpicker#class-colorpicker) get\_picker ( )
Returns the [ColorPicker](class_colorpicker#class-colorpicker) that this node toggles.
**Warning:** This is a required internal node, removing and freeing it may cause a crash. If you wish to hide it or any of its children, use their [CanvasItem.visible](class_canvasitem#class-canvasitem-property-visible) property.
### [PopupPanel](class_popuppanel#class-popuppanel) get\_popup ( )
Returns the control's [PopupPanel](class_popuppanel#class-popuppanel) which allows you to connect to popup signals. This allows you to handle events when the ColorPicker is shown or hidden.
**Warning:** This is a required internal node, removing and freeing it may cause a crash. If you wish to hide it or any of its children, use their [CanvasItem.visible](class_canvasitem#class-canvasitem-property-visible) property.
Theme Property Descriptions
---------------------------
### [Color](class_color#class-color) font\_color
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
Default text [Color](class_color#class-color) of the `ColorPickerButton`.
### [Color](class_color#class-color) font\_color\_disabled
| | |
| --- | --- |
| *Default* | `Color( 0.9, 0.9, 0.9, 0.3 )` |
Text [Color](class_color#class-color) used when the `ColorPickerButton` is disabled.
### [Color](class_color#class-color) font\_color\_focus
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
Text [Color](class_color#class-color) used when the `ColorPickerButton` is focused. Only replaces the normal text color of the button. Disabled, hovered, and pressed states take precedence over this color.
### [Color](class_color#class-color) font\_color\_hover
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
Text [Color](class_color#class-color) used when the `ColorPickerButton` is being hovered.
### [Color](class_color#class-color) font\_color\_pressed
| | |
| --- | --- |
| *Default* | `Color( 0.8, 0.8, 0.8, 1 )` |
Text [Color](class_color#class-color) used when the `ColorPickerButton` is being pressed.
### [int](class_int#class-int) hseparation
| | |
| --- | --- |
| *Default* | `2` |
The horizontal space between `ColorPickerButton`'s icon and text.
### [Font](class_font#class-font) font
[Font](class_font#class-font) of the `ColorPickerButton`'s text.
### [Texture](class_texture#class-texture) bg
The background of the color preview rect on the button.
### [StyleBox](class_stylebox#class-stylebox) disabled
[StyleBox](class_stylebox#class-stylebox) used when the `ColorPickerButton` is disabled.
### [StyleBox](class_stylebox#class-stylebox) focus
[StyleBox](class_stylebox#class-stylebox) used when the `ColorPickerButton` is focused. It is displayed over the current [StyleBox](class_stylebox#class-stylebox), so using [StyleBoxEmpty](class_styleboxempty#class-styleboxempty) will just disable the focus visual effect.
### [StyleBox](class_stylebox#class-stylebox) hover
[StyleBox](class_stylebox#class-stylebox) used when the `ColorPickerButton` is being hovered.
### [StyleBox](class_stylebox#class-stylebox) normal
Default [StyleBox](class_stylebox#class-stylebox) for the `ColorPickerButton`.
### [StyleBox](class_stylebox#class-stylebox) pressed
[StyleBox](class_stylebox#class-stylebox) used when the `ColorPickerButton` is being pressed.
godot VisualShaderNodeOutput VisualShaderNodeOutput
======================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Represents the output shader parameters within the visual shader graph.
Description
-----------
This visual shader node is present in all shader graphs in form of "Output" block with multiple output value ports.
godot CollisionObject2D CollisionObject2D
=================
**Inherits:** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
**Inherited By:** [Area2D](class_area2d#class-area2d), [PhysicsBody2D](class_physicsbody2d#class-physicsbody2d)
Base node for 2D collision objects.
Description
-----------
CollisionObject2D is the base class for 2D physics objects. It can hold any number of 2D collision [Shape2D](class_shape2d#class-shape2d)s. Each shape must be assigned to a *shape owner*. The CollisionObject2D can have any number of shape owners. Shape owners are not nodes and do not appear in the editor, but are accessible through code using the `shape_owner_*` methods.
**Note:** Only collisions between objects within the same canvas ([Viewport](class_viewport#class-viewport) canvas or [CanvasLayer](class_canvaslayer#class-canvaslayer)) are supported. The behavior of collisions between objects in different canvases is undefined.
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [collision\_layer](#class-collisionobject2d-property-collision-layer) | `1` |
| [int](class_int#class-int) | [collision\_mask](#class-collisionobject2d-property-collision-mask) | `1` |
| [bool](class_bool#class-bool) | [input\_pickable](#class-collisionobject2d-property-input-pickable) | `true` |
Methods
-------
| | |
| --- | --- |
| void | [\_input\_event](#class-collisionobject2d-method-input-event) **(** [Object](class_object#class-object) viewport, [InputEvent](class_inputevent#class-inputevent) event, [int](class_int#class-int) shape\_idx **)** virtual |
| [int](class_int#class-int) | [create\_shape\_owner](#class-collisionobject2d-method-create-shape-owner) **(** [Object](class_object#class-object) owner **)** |
| [bool](class_bool#class-bool) | [get\_collision\_layer\_bit](#class-collisionobject2d-method-get-collision-layer-bit) **(** [int](class_int#class-int) bit **)** const |
| [bool](class_bool#class-bool) | [get\_collision\_mask\_bit](#class-collisionobject2d-method-get-collision-mask-bit) **(** [int](class_int#class-int) bit **)** const |
| [RID](class_rid#class-rid) | [get\_rid](#class-collisionobject2d-method-get-rid) **(** **)** const |
| [float](class_float#class-float) | [get\_shape\_owner\_one\_way\_collision\_margin](#class-collisionobject2d-method-get-shape-owner-one-way-collision-margin) **(** [int](class_int#class-int) owner\_id **)** const |
| [Array](class_array#class-array) | [get\_shape\_owners](#class-collisionobject2d-method-get-shape-owners) **(** **)** |
| [bool](class_bool#class-bool) | [is\_shape\_owner\_disabled](#class-collisionobject2d-method-is-shape-owner-disabled) **(** [int](class_int#class-int) owner\_id **)** const |
| [bool](class_bool#class-bool) | [is\_shape\_owner\_one\_way\_collision\_enabled](#class-collisionobject2d-method-is-shape-owner-one-way-collision-enabled) **(** [int](class_int#class-int) owner\_id **)** const |
| void | [remove\_shape\_owner](#class-collisionobject2d-method-remove-shape-owner) **(** [int](class_int#class-int) owner\_id **)** |
| void | [set\_collision\_layer\_bit](#class-collisionobject2d-method-set-collision-layer-bit) **(** [int](class_int#class-int) bit, [bool](class_bool#class-bool) value **)** |
| void | [set\_collision\_mask\_bit](#class-collisionobject2d-method-set-collision-mask-bit) **(** [int](class_int#class-int) bit, [bool](class_bool#class-bool) value **)** |
| [int](class_int#class-int) | [shape\_find\_owner](#class-collisionobject2d-method-shape-find-owner) **(** [int](class_int#class-int) shape\_index **)** const |
| void | [shape\_owner\_add\_shape](#class-collisionobject2d-method-shape-owner-add-shape) **(** [int](class_int#class-int) owner\_id, [Shape2D](class_shape2d#class-shape2d) shape **)** |
| void | [shape\_owner\_clear\_shapes](#class-collisionobject2d-method-shape-owner-clear-shapes) **(** [int](class_int#class-int) owner\_id **)** |
| [Object](class_object#class-object) | [shape\_owner\_get\_owner](#class-collisionobject2d-method-shape-owner-get-owner) **(** [int](class_int#class-int) owner\_id **)** const |
| [Shape2D](class_shape2d#class-shape2d) | [shape\_owner\_get\_shape](#class-collisionobject2d-method-shape-owner-get-shape) **(** [int](class_int#class-int) owner\_id, [int](class_int#class-int) shape\_id **)** const |
| [int](class_int#class-int) | [shape\_owner\_get\_shape\_count](#class-collisionobject2d-method-shape-owner-get-shape-count) **(** [int](class_int#class-int) owner\_id **)** const |
| [int](class_int#class-int) | [shape\_owner\_get\_shape\_index](#class-collisionobject2d-method-shape-owner-get-shape-index) **(** [int](class_int#class-int) owner\_id, [int](class_int#class-int) shape\_id **)** const |
| [Transform2D](class_transform2d#class-transform2d) | [shape\_owner\_get\_transform](#class-collisionobject2d-method-shape-owner-get-transform) **(** [int](class_int#class-int) owner\_id **)** const |
| void | [shape\_owner\_remove\_shape](#class-collisionobject2d-method-shape-owner-remove-shape) **(** [int](class_int#class-int) owner\_id, [int](class_int#class-int) shape\_id **)** |
| void | [shape\_owner\_set\_disabled](#class-collisionobject2d-method-shape-owner-set-disabled) **(** [int](class_int#class-int) owner\_id, [bool](class_bool#class-bool) disabled **)** |
| void | [shape\_owner\_set\_one\_way\_collision](#class-collisionobject2d-method-shape-owner-set-one-way-collision) **(** [int](class_int#class-int) owner\_id, [bool](class_bool#class-bool) enable **)** |
| void | [shape\_owner\_set\_one\_way\_collision\_margin](#class-collisionobject2d-method-shape-owner-set-one-way-collision-margin) **(** [int](class_int#class-int) owner\_id, [float](class_float#class-float) margin **)** |
| void | [shape\_owner\_set\_transform](#class-collisionobject2d-method-shape-owner-set-transform) **(** [int](class_int#class-int) owner\_id, [Transform2D](class_transform2d#class-transform2d) transform **)** |
Signals
-------
### input\_event ( [Node](class_node#class-node) viewport, [InputEvent](class_inputevent#class-inputevent) event, [int](class_int#class-int) shape\_idx )
Emitted when an input event occurs. Requires [input\_pickable](#class-collisionobject2d-property-input-pickable) to be `true` and at least one `collision_layer` bit to be set. See [\_input\_event](#class-collisionobject2d-method-input-event) for details.
### mouse\_entered ( )
Emitted when the mouse pointer enters any of this object's shapes. Requires [input\_pickable](#class-collisionobject2d-property-input-pickable) to be `true` and at least one `collision_layer` bit to be set.
### mouse\_exited ( )
Emitted when the mouse pointer exits all this object's shapes. Requires [input\_pickable](#class-collisionobject2d-property-input-pickable) to be `true` and at least one `collision_layer` bit to be set.
Property Descriptions
---------------------
### [int](class_int#class-int) collision\_layer
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_collision\_layer(value) |
| *Getter* | get\_collision\_layer() |
The physics layers this CollisionObject2D is in. Collision objects can exist in one or more of 32 different layers. See also [collision\_mask](#class-collisionobject2d-property-collision-mask).
**Note:** A contact is detected if object A is in any of the layers that object B scans, or object B is in any layers that object A scans. See [Collision layers and masks](https://docs.godotengine.org/en/3.5/tutorials/physics/physics_introduction.html#collision-layers-and-masks) in the documentation for more information.
### [int](class_int#class-int) collision\_mask
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_collision\_mask(value) |
| *Getter* | get\_collision\_mask() |
The physics layers this CollisionObject2D scans. Collision objects can scan one or more of 32 different layers. See also [collision\_layer](#class-collisionobject2d-property-collision-layer).
**Note:** A contact is detected if object A is in any of the layers that object B scans, or object B is in any layers that object A scans. See [Collision layers and masks](https://docs.godotengine.org/en/3.5/tutorials/physics/physics_introduction.html#collision-layers-and-masks) in the documentation for more information.
### [bool](class_bool#class-bool) input\_pickable
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_pickable(value) |
| *Getter* | is\_pickable() |
If `true`, this object is pickable. A pickable object can detect the mouse pointer entering/leaving, and if the mouse is inside it, report input events. Requires at least one [collision\_layer](#class-collisionobject2d-property-collision-layer) bit to be set.
Method Descriptions
-------------------
### void \_input\_event ( [Object](class_object#class-object) viewport, [InputEvent](class_inputevent#class-inputevent) event, [int](class_int#class-int) shape\_idx ) virtual
Accepts unhandled [InputEvent](class_inputevent#class-inputevent)s. Requires [input\_pickable](#class-collisionobject2d-property-input-pickable) to be `true`. `shape_idx` is the child index of the clicked [Shape2D](class_shape2d#class-shape2d). Connect to the `input_event` signal to easily pick up these events.
### [int](class_int#class-int) create\_shape\_owner ( [Object](class_object#class-object) owner )
Creates a new shape owner for the given object. Returns `owner_id` of the new owner for future reference.
### [bool](class_bool#class-bool) get\_collision\_layer\_bit ( [int](class_int#class-int) bit ) const
Returns whether or not the specified `bit` of the [collision\_layer](#class-collisionobject2d-property-collision-layer) is set.
### [bool](class_bool#class-bool) get\_collision\_mask\_bit ( [int](class_int#class-int) bit ) const
Returns whether or not the specified `bit` of the [collision\_mask](#class-collisionobject2d-property-collision-mask) is set.
### [RID](class_rid#class-rid) get\_rid ( ) const
Returns the object's [RID](class_rid#class-rid).
### [float](class_float#class-float) get\_shape\_owner\_one\_way\_collision\_margin ( [int](class_int#class-int) owner\_id ) const
Returns the `one_way_collision_margin` of the shape owner identified by given `owner_id`.
### [Array](class_array#class-array) get\_shape\_owners ( )
Returns an [Array](class_array#class-array) of `owner_id` identifiers. You can use these ids in other methods that take `owner_id` as an argument.
### [bool](class_bool#class-bool) is\_shape\_owner\_disabled ( [int](class_int#class-int) owner\_id ) const
If `true`, the shape owner and its shapes are disabled.
### [bool](class_bool#class-bool) is\_shape\_owner\_one\_way\_collision\_enabled ( [int](class_int#class-int) owner\_id ) const
Returns `true` if collisions for the shape owner originating from this `CollisionObject2D` will not be reported to collided with `CollisionObject2D`s.
### void remove\_shape\_owner ( [int](class_int#class-int) owner\_id )
Removes the given shape owner.
### void set\_collision\_layer\_bit ( [int](class_int#class-int) bit, [bool](class_bool#class-bool) value )
If `value` is `true`, sets the specified `bit` in the [collision\_layer](#class-collisionobject2d-property-collision-layer).
If `value` is `false`, clears the specified `bit` in the [collision\_layer](#class-collisionobject2d-property-collision-layer).
### void set\_collision\_mask\_bit ( [int](class_int#class-int) bit, [bool](class_bool#class-bool) value )
If `value` is `true`, sets the specified `bit` in the [collision\_mask](#class-collisionobject2d-property-collision-mask).
If `value` is `false`, clears the specified `bit` in the [collision\_mask](#class-collisionobject2d-property-collision-mask).
### [int](class_int#class-int) shape\_find\_owner ( [int](class_int#class-int) shape\_index ) const
Returns the `owner_id` of the given shape.
### void shape\_owner\_add\_shape ( [int](class_int#class-int) owner\_id, [Shape2D](class_shape2d#class-shape2d) shape )
Adds a [Shape2D](class_shape2d#class-shape2d) to the shape owner.
### void shape\_owner\_clear\_shapes ( [int](class_int#class-int) owner\_id )
Removes all shapes from the shape owner.
### [Object](class_object#class-object) shape\_owner\_get\_owner ( [int](class_int#class-int) owner\_id ) const
Returns the parent object of the given shape owner.
### [Shape2D](class_shape2d#class-shape2d) shape\_owner\_get\_shape ( [int](class_int#class-int) owner\_id, [int](class_int#class-int) shape\_id ) const
Returns the [Shape2D](class_shape2d#class-shape2d) with the given id from the given shape owner.
### [int](class_int#class-int) shape\_owner\_get\_shape\_count ( [int](class_int#class-int) owner\_id ) const
Returns the number of shapes the given shape owner contains.
### [int](class_int#class-int) shape\_owner\_get\_shape\_index ( [int](class_int#class-int) owner\_id, [int](class_int#class-int) shape\_id ) const
Returns the child index of the [Shape2D](class_shape2d#class-shape2d) with the given id from the given shape owner.
### [Transform2D](class_transform2d#class-transform2d) shape\_owner\_get\_transform ( [int](class_int#class-int) owner\_id ) const
Returns the shape owner's [Transform2D](class_transform2d#class-transform2d).
### void shape\_owner\_remove\_shape ( [int](class_int#class-int) owner\_id, [int](class_int#class-int) shape\_id )
Removes a shape from the given shape owner.
### void shape\_owner\_set\_disabled ( [int](class_int#class-int) owner\_id, [bool](class_bool#class-bool) disabled )
If `true`, disables the given shape owner.
### void shape\_owner\_set\_one\_way\_collision ( [int](class_int#class-int) owner\_id, [bool](class_bool#class-bool) enable )
If `enable` is `true`, collisions for the shape owner originating from this `CollisionObject2D` will not be reported to collided with `CollisionObject2D`s.
### void shape\_owner\_set\_one\_way\_collision\_margin ( [int](class_int#class-int) owner\_id, [float](class_float#class-float) margin )
Sets the `one_way_collision_margin` of the shape owner identified by given `owner_id` to `margin` pixels.
### void shape\_owner\_set\_transform ( [int](class_int#class-int) owner\_id, [Transform2D](class_transform2d#class-transform2d) transform )
Sets the [Transform2D](class_transform2d#class-transform2d) of the given shape owner.
| programming_docs |
godot BakedLightmap BakedLightmap
=============
**Inherits:** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Prerendered indirect light map for a scene.
Description
-----------
Baked lightmaps are an alternative workflow for adding indirect (or baked) lighting to a scene. Unlike the [GIProbe](class_giprobe#class-giprobe) approach, baked lightmaps work fine on low-end PCs and mobile devices as they consume almost no resources in run-time.
**Procedural generation:** Lightmap baking functionality is only available in the editor. This means `BakedLightmap` is not suited to procedurally generated or user-built levels. For procedurally generated or user-built levels, use [GIProbe](class_giprobe#class-giprobe) instead.
**Note:** Due to how lightmaps work, most properties only have a visible effect once lightmaps are baked again.
Tutorials
---------
* [Baked lightmaps](https://docs.godotengine.org/en/3.5/tutorials/3d/baked_lightmaps.html)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [atlas\_generate](#class-bakedlightmap-property-atlas-generate) | `true` |
| [int](class_int#class-int) | [atlas\_max\_size](#class-bakedlightmap-property-atlas-max-size) | `4096` |
| [float](class_float#class-float) | [bias](#class-bakedlightmap-property-bias) | `0.005` |
| [float](class_float#class-float) | [bounce\_indirect\_energy](#class-bakedlightmap-property-bounce-indirect-energy) | `1.0` |
| [int](class_int#class-int) | [bounces](#class-bakedlightmap-property-bounces) | `3` |
| [float](class_float#class-float) | [capture\_cell\_size](#class-bakedlightmap-property-capture-cell-size) | `0.5` |
| [bool](class_bool#class-bool) | [capture\_enabled](#class-bakedlightmap-property-capture-enabled) | `true` |
| [float](class_float#class-float) | [capture\_propagation](#class-bakedlightmap-property-capture-propagation) | `1.0` |
| [BakeQuality](#enum-bakedlightmap-bakequality) | [capture\_quality](#class-bakedlightmap-property-capture-quality) | `1` |
| [float](class_float#class-float) | [default\_texels\_per\_unit](#class-bakedlightmap-property-default-texels-per-unit) | `16.0` |
| [Color](class_color#class-color) | [environment\_custom\_color](#class-bakedlightmap-property-environment-custom-color) | |
| [float](class_float#class-float) | [environment\_custom\_energy](#class-bakedlightmap-property-environment-custom-energy) | |
| [Sky](class_sky#class-sky) | [environment\_custom\_sky](#class-bakedlightmap-property-environment-custom-sky) | |
| [Vector3](class_vector3#class-vector3) | [environment\_custom\_sky\_rotation\_degrees](#class-bakedlightmap-property-environment-custom-sky-rotation-degrees) | |
| [Color](class_color#class-color) | [environment\_min\_light](#class-bakedlightmap-property-environment-min-light) | `Color( 0, 0, 0, 1 )` |
| [EnvironmentMode](#enum-bakedlightmap-environmentmode) | [environment\_mode](#class-bakedlightmap-property-environment-mode) | `0` |
| [Vector3](class_vector3#class-vector3) | [extents](#class-bakedlightmap-property-extents) | `Vector3( 10, 10, 10 )` |
| [String](class_string#class-string) | [image\_path](#class-bakedlightmap-property-image-path) | |
| [BakedLightmapData](class_bakedlightmapdata#class-bakedlightmapdata) | [light\_data](#class-bakedlightmap-property-light-data) | |
| [BakeQuality](#enum-bakedlightmap-bakequality) | [quality](#class-bakedlightmap-property-quality) | `1` |
| [bool](class_bool#class-bool) | [use\_color](#class-bakedlightmap-property-use-color) | `true` |
| [bool](class_bool#class-bool) | [use\_denoiser](#class-bakedlightmap-property-use-denoiser) | `true` |
| [bool](class_bool#class-bool) | [use\_hdr](#class-bakedlightmap-property-use-hdr) | `true` |
Methods
-------
| | |
| --- | --- |
| [BakeError](#enum-bakedlightmap-bakeerror) | [bake](#class-bakedlightmap-method-bake) **(** [Node](class_node#class-node) from\_node=null, [String](class_string#class-string) data\_save\_path="" **)** |
Enumerations
------------
enum **BakeQuality**:
* **BAKE\_QUALITY\_LOW** = **0** --- The lowest bake quality mode. Fastest to calculate.
* **BAKE\_QUALITY\_MEDIUM** = **1** --- The default bake quality mode.
* **BAKE\_QUALITY\_HIGH** = **2** --- A higher bake quality mode. Takes longer to calculate.
* **BAKE\_QUALITY\_ULTRA** = **3** --- The highest bake quality mode. Takes the longest to calculate.
enum **BakeError**:
* **BAKE\_ERROR\_OK** = **0** --- Baking was successful.
* **BAKE\_ERROR\_NO\_SAVE\_PATH** = **1** --- Returns if no viable save path is found. This can happen where an [image\_path](#class-bakedlightmap-property-image-path) is not specified or when the save location is invalid.
* **BAKE\_ERROR\_NO\_MESHES** = **2** --- Currently unused.
* **BAKE\_ERROR\_CANT\_CREATE\_IMAGE** = **3** --- Returns when the baker cannot save per-mesh textures to file.
* **BAKE\_ERROR\_LIGHTMAP\_SIZE** = **4** --- The size of the generated lightmaps is too large.
* **BAKE\_ERROR\_INVALID\_MESH** = **5** --- Some mesh contains UV2 values outside the `[0,1]` range.
* **BAKE\_ERROR\_USER\_ABORTED** = **6** --- Returns if user cancels baking.
* **BAKE\_ERROR\_NO\_LIGHTMAPPER** = **7** --- Returns if lightmapper can't be created. Unless you are using a custom lightmapper, please report this as bug.
* **BAKE\_ERROR\_NO\_ROOT** = **8** --- There is no root node to start baking from. Either provide `from_node` argument or attach this node to a parent that should be used as root.
enum **EnvironmentMode**:
* **ENVIRONMENT\_MODE\_DISABLED** = **0** --- No environment is used during baking.
* **ENVIRONMENT\_MODE\_SCENE** = **1** --- The baked environment is automatically picked from the current scene.
* **ENVIRONMENT\_MODE\_CUSTOM\_SKY** = **2** --- A custom sky is used as environment during baking.
* **ENVIRONMENT\_MODE\_CUSTOM\_COLOR** = **3** --- A custom solid color is used as environment during baking.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) atlas\_generate
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_generate\_atlas(value) |
| *Getter* | is\_generate\_atlas\_enabled() |
If `true`, the lightmapper will merge the textures for all meshes into one or several large layered textures. If `false`, every mesh will get its own lightmap texture, which is less efficient.
**Note:** Atlas lightmap rendering is only supported in GLES3, *not* GLES2. Non-atlas lightmap rendering is supported by both GLES3 and GLES2. If [ProjectSettings.rendering/quality/driver/fallback\_to\_gles2](class_projectsettings#class-projectsettings-property-rendering-quality-driver-fallback-to-gles2) is `true`, consider baking lightmaps with [atlas\_generate](#class-bakedlightmap-property-atlas-generate) set to `false` so that the resulting lightmap is visible in both GLES3 and GLES2.
### [int](class_int#class-int) atlas\_max\_size
| | |
| --- | --- |
| *Default* | `4096` |
| *Setter* | set\_max\_atlas\_size(value) |
| *Getter* | get\_max\_atlas\_size() |
Maximum size of each lightmap layer, only used when [atlas\_generate](#class-bakedlightmap-property-atlas-generate) is enabled.
### [float](class_float#class-float) bias
| | |
| --- | --- |
| *Default* | `0.005` |
| *Setter* | set\_bias(value) |
| *Getter* | get\_bias() |
Raycasting bias used during baking to avoid floating point precision issues.
### [float](class_float#class-float) bounce\_indirect\_energy
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_bounce\_indirect\_energy(value) |
| *Getter* | get\_bounce\_indirect\_energy() |
The energy multiplier for each bounce. Higher values will make indirect lighting brighter. A value of `1.0` represents physically accurate behavior, but higher values can be used to make indirect lighting propagate more visibly when using a low number of bounces. This can be used to speed up bake times by lowering the number of [bounces](#class-bakedlightmap-property-bounces) then increasing [bounce\_indirect\_energy](#class-bakedlightmap-property-bounce-indirect-energy). Unlike [BakedLightmapData.energy](class_bakedlightmapdata#class-bakedlightmapdata-property-energy), this property does not affect direct lighting emitted by light nodes, emissive materials and the environment.
**Note:** [bounce\_indirect\_energy](#class-bakedlightmap-property-bounce-indirect-energy) only has an effect if [bounces](#class-bakedlightmap-property-bounces) is set to a value greater than or equal to `1`.
### [int](class_int#class-int) bounces
| | |
| --- | --- |
| *Default* | `3` |
| *Setter* | set\_bounces(value) |
| *Getter* | get\_bounces() |
Number of light bounces that are taken into account during baking. See also [bounce\_indirect\_energy](#class-bakedlightmap-property-bounce-indirect-energy).
### [float](class_float#class-float) capture\_cell\_size
| | |
| --- | --- |
| *Default* | `0.5` |
| *Setter* | set\_capture\_cell\_size(value) |
| *Getter* | get\_capture\_cell\_size() |
Grid size used for real-time capture information on dynamic objects.
### [bool](class_bool#class-bool) capture\_enabled
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_capture\_enabled(value) |
| *Getter* | get\_capture\_enabled() |
When enabled, an octree containing the scene's lighting information will be computed. This octree will then be used to light dynamic objects in the scene.
### [float](class_float#class-float) capture\_propagation
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_capture\_propagation(value) |
| *Getter* | get\_capture\_propagation() |
Bias value to reduce the amount of light propagation in the captured octree.
### [BakeQuality](#enum-bakedlightmap-bakequality) capture\_quality
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_capture\_quality(value) |
| *Getter* | get\_capture\_quality() |
Bake quality of the capture data.
### [float](class_float#class-float) default\_texels\_per\_unit
| | |
| --- | --- |
| *Default* | `16.0` |
| *Setter* | set\_default\_texels\_per\_unit(value) |
| *Getter* | get\_default\_texels\_per\_unit() |
If a baked mesh doesn't have a UV2 size hint, this value will be used to roughly compute a suitable lightmap size.
### [Color](class_color#class-color) environment\_custom\_color
| | |
| --- | --- |
| *Setter* | set\_environment\_custom\_color(value) |
| *Getter* | get\_environment\_custom\_color() |
The environment color when [environment\_mode](#class-bakedlightmap-property-environment-mode) is set to [ENVIRONMENT\_MODE\_CUSTOM\_COLOR](#class-bakedlightmap-constant-environment-mode-custom-color).
### [float](class_float#class-float) environment\_custom\_energy
| | |
| --- | --- |
| *Setter* | set\_environment\_custom\_energy(value) |
| *Getter* | get\_environment\_custom\_energy() |
The energy scaling factor when when [environment\_mode](#class-bakedlightmap-property-environment-mode) is set to [ENVIRONMENT\_MODE\_CUSTOM\_COLOR](#class-bakedlightmap-constant-environment-mode-custom-color) or [ENVIRONMENT\_MODE\_CUSTOM\_SKY](#class-bakedlightmap-constant-environment-mode-custom-sky).
### [Sky](class_sky#class-sky) environment\_custom\_sky
| | |
| --- | --- |
| *Setter* | set\_environment\_custom\_sky(value) |
| *Getter* | get\_environment\_custom\_sky() |
The [Sky](class_sky#class-sky) resource to use when [environment\_mode](#class-bakedlightmap-property-environment-mode) is set o [ENVIRONMENT\_MODE\_CUSTOM\_SKY](#class-bakedlightmap-constant-environment-mode-custom-sky).
### [Vector3](class_vector3#class-vector3) environment\_custom\_sky\_rotation\_degrees
| | |
| --- | --- |
| *Setter* | set\_environment\_custom\_sky\_rotation\_degrees(value) |
| *Getter* | get\_environment\_custom\_sky\_rotation\_degrees() |
The rotation of the baked custom sky.
### [Color](class_color#class-color) environment\_min\_light
| | |
| --- | --- |
| *Default* | `Color( 0, 0, 0, 1 )` |
| *Setter* | set\_environment\_min\_light(value) |
| *Getter* | get\_environment\_min\_light() |
Minimum ambient light for all the lightmap texels. This doesn't take into account any occlusion from the scene's geometry, it simply ensures a minimum amount of light on all the lightmap texels. Can be used for artistic control on shadow color.
### [EnvironmentMode](#enum-bakedlightmap-environmentmode) environment\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_environment\_mode(value) |
| *Getter* | get\_environment\_mode() |
Decides which environment to use during baking.
### [Vector3](class_vector3#class-vector3) extents
| | |
| --- | --- |
| *Default* | `Vector3( 10, 10, 10 )` |
| *Setter* | set\_extents(value) |
| *Getter* | get\_extents() |
Size of the baked lightmap. Only meshes inside this region will be included in the baked lightmap, also used as the bounds of the captured region for dynamic lighting.
### [String](class_string#class-string) image\_path
| | |
| --- | --- |
| *Setter* | set\_image\_path(value) |
| *Getter* | get\_image\_path() |
Deprecated, in previous versions it determined the location where lightmaps were be saved.
### [BakedLightmapData](class_bakedlightmapdata#class-bakedlightmapdata) light\_data
| | |
| --- | --- |
| *Setter* | set\_light\_data(value) |
| *Getter* | get\_light\_data() |
The calculated light data.
### [BakeQuality](#enum-bakedlightmap-bakequality) quality
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_bake\_quality(value) |
| *Getter* | get\_bake\_quality() |
Determines the amount of samples per texel used in indirect light baking. The amount of samples for each quality level can be configured in the project settings.
### [bool](class_bool#class-bool) use\_color
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_use\_color(value) |
| *Getter* | is\_using\_color() |
Store full color values in the lightmap textures. When disabled, lightmap textures will store a single brightness channel. Can be disabled to reduce disk usage if the scene contains only white lights or you don't mind losing color information in indirect lighting.
### [bool](class_bool#class-bool) use\_denoiser
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_use\_denoiser(value) |
| *Getter* | is\_using\_denoiser() |
When enabled, a lightmap denoiser will be used to reduce the noise inherent to Monte Carlo based global illumination.
### [bool](class_bool#class-bool) use\_hdr
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_use\_hdr(value) |
| *Getter* | is\_using\_hdr() |
If `true`, stores the lightmap textures in a high dynamic range format (EXR). If `false`, stores the lightmap texture in a low dynamic range PNG image. This can be set to `false` to reduce disk usage, but light values over 1.0 will be clamped and you may see banding caused by the reduced precision.
**Note:** Setting [use\_hdr](#class-bakedlightmap-property-use-hdr) to `true` will decrease lightmap banding even when using the GLES2 backend or if [ProjectSettings.rendering/quality/depth/hdr](class_projectsettings#class-projectsettings-property-rendering-quality-depth-hdr) is `false`.
Method Descriptions
-------------------
### [BakeError](#enum-bakedlightmap-bakeerror) bake ( [Node](class_node#class-node) from\_node=null, [String](class_string#class-string) data\_save\_path="" )
Bakes the lightmap, scanning from the given `from_node` root and saves the resulting [BakedLightmapData](class_bakedlightmapdata#class-bakedlightmapdata) in `data_save_path`. If no root node is provided, parent of this node will be used as root instead. If no save path is provided it will try to match the path from the current [light\_data](#class-bakedlightmap-property-light-data).
godot VisualScriptSubCall VisualScriptSubCall
===================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Calls a method called `_subcall` in this object.
Description
-----------
`VisualScriptSubCall` will call method named `_subcall` in the current script. It will fail if the method doesn't exist or the provided arguments are wrong.
Methods
-------
| | |
| --- | --- |
| [Variant](class_variant#class-variant) | [\_subcall](#class-visualscriptsubcall-method-subcall) **(** [Variant](class_variant#class-variant) arguments **)** virtual |
Method Descriptions
-------------------
### [Variant](class_variant#class-variant) \_subcall ( [Variant](class_variant#class-variant) arguments ) virtual
Called by this node.
godot CSGPolygon CSGPolygon
==========
**Inherits:** [CSGPrimitive](class_csgprimitive#class-csgprimitive) **<** [CSGShape](class_csgshape#class-csgshape) **<** [GeometryInstance](class_geometryinstance#class-geometryinstance) **<** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Extrudes a 2D polygon shape to create a 3D mesh.
Description
-----------
An array of 2D points is extruded to quickly and easily create a variety of 3D meshes. See also [CSGMesh](class_csgmesh#class-csgmesh) for using 3D meshes as CSG nodes.
**Note:** CSG nodes are intended to be used for level prototyping. Creating CSG nodes has a significant CPU cost compared to creating a [MeshInstance](class_meshinstance#class-meshinstance) with a [PrimitiveMesh](class_primitivemesh#class-primitivemesh). Moving a CSG node within another CSG node also has a significant CPU cost, so it should be avoided during gameplay.
Tutorials
---------
* [Prototyping levels with CSG](https://docs.godotengine.org/en/3.5/tutorials/3d/csg_tools.html)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [depth](#class-csgpolygon-property-depth) | `1.0` |
| [Material](class_material#class-material) | [material](#class-csgpolygon-property-material) | |
| [Mode](#enum-csgpolygon-mode) | [mode](#class-csgpolygon-property-mode) | `0` |
| [bool](class_bool#class-bool) | [path\_continuous\_u](#class-csgpolygon-property-path-continuous-u) | |
| [float](class_float#class-float) | [path\_interval](#class-csgpolygon-property-path-interval) | |
| [PathIntervalType](#enum-csgpolygon-pathintervaltype) | [path\_interval\_type](#class-csgpolygon-property-path-interval-type) | |
| [bool](class_bool#class-bool) | [path\_joined](#class-csgpolygon-property-path-joined) | |
| [bool](class_bool#class-bool) | [path\_local](#class-csgpolygon-property-path-local) | |
| [NodePath](class_nodepath#class-nodepath) | [path\_node](#class-csgpolygon-property-path-node) | |
| [PathRotation](#enum-csgpolygon-pathrotation) | [path\_rotation](#class-csgpolygon-property-path-rotation) | |
| [float](class_float#class-float) | [path\_simplify\_angle](#class-csgpolygon-property-path-simplify-angle) | |
| [float](class_float#class-float) | [path\_u\_distance](#class-csgpolygon-property-path-u-distance) | |
| [PoolVector2Array](class_poolvector2array#class-poolvector2array) | [polygon](#class-csgpolygon-property-polygon) | `PoolVector2Array( 0, 0, 0, 1, 1, 1, 1, 0 )` |
| [bool](class_bool#class-bool) | [smooth\_faces](#class-csgpolygon-property-smooth-faces) | `false` |
| [float](class_float#class-float) | [spin\_degrees](#class-csgpolygon-property-spin-degrees) | |
| [int](class_int#class-int) | [spin\_sides](#class-csgpolygon-property-spin-sides) | |
Enumerations
------------
enum **Mode**:
* **MODE\_DEPTH** = **0** --- The [polygon](#class-csgpolygon-property-polygon) shape is extruded along the negative Z axis.
* **MODE\_SPIN** = **1** --- The [polygon](#class-csgpolygon-property-polygon) shape is extruded by rotating it around the Y axis.
* **MODE\_PATH** = **2** --- The [polygon](#class-csgpolygon-property-polygon) shape is extruded along the [Path](class_path#class-path) specified in [path\_node](#class-csgpolygon-property-path-node).
enum **PathRotation**:
* **PATH\_ROTATION\_POLYGON** = **0** --- The [polygon](#class-csgpolygon-property-polygon) shape is not rotated.
**Note:** Requires the path's Z coordinates to continually decrease to ensure viable shapes.
* **PATH\_ROTATION\_PATH** = **1** --- The [polygon](#class-csgpolygon-property-polygon) shape is rotated along the path, but it is not rotated around the path axis.
**Note:** Requires the path's Z coordinates to continually decrease to ensure viable shapes.
* **PATH\_ROTATION\_PATH\_FOLLOW** = **2** --- The [polygon](#class-csgpolygon-property-polygon) shape follows the path and its rotations around the path axis.
enum **PathIntervalType**:
* **PATH\_INTERVAL\_DISTANCE** = **0** --- When [mode](#class-csgpolygon-property-mode) is set to [MODE\_PATH](#class-csgpolygon-constant-mode-path), [path\_interval](#class-csgpolygon-property-path-interval) will determine the distance, in meters, each interval of the path will extrude.
* **PATH\_INTERVAL\_SUBDIVIDE** = **1** --- When [mode](#class-csgpolygon-property-mode) is set to [MODE\_PATH](#class-csgpolygon-constant-mode-path), [path\_interval](#class-csgpolygon-property-path-interval) will subdivide the polygons along the path.
Property Descriptions
---------------------
### [float](class_float#class-float) depth
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_depth(value) |
| *Getter* | get\_depth() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_DEPTH](#class-csgpolygon-constant-mode-depth), the depth of the extrusion.
### [Material](class_material#class-material) material
| | |
| --- | --- |
| *Setter* | set\_material(value) |
| *Getter* | get\_material() |
Material to use for the resulting mesh. The UV maps the top half of the material to the extruded shape (U along the the length of the extrusions and V around the outline of the [polygon](#class-csgpolygon-property-polygon)), the bottom-left quarter to the front end face, and the bottom-right quarter to the back end face.
### [Mode](#enum-csgpolygon-mode) mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_mode(value) |
| *Getter* | get\_mode() |
The [mode](#class-csgpolygon-property-mode) used to extrude the [polygon](#class-csgpolygon-property-polygon).
### [bool](class_bool#class-bool) path\_continuous\_u
| | |
| --- | --- |
| *Setter* | set\_path\_continuous\_u(value) |
| *Getter* | is\_path\_continuous\_u() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_PATH](#class-csgpolygon-constant-mode-path), by default, the top half of the [material](#class-csgpolygon-property-material) is stretched along the entire length of the extruded shape. If `false` the top half of the material is repeated every step of the extrusion.
### [float](class_float#class-float) path\_interval
| | |
| --- | --- |
| *Setter* | set\_path\_interval(value) |
| *Getter* | get\_path\_interval() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_PATH](#class-csgpolygon-constant-mode-path), the path interval or ratio of path points to extrusions.
### [PathIntervalType](#enum-csgpolygon-pathintervaltype) path\_interval\_type
| | |
| --- | --- |
| *Setter* | set\_path\_interval\_type(value) |
| *Getter* | get\_path\_interval\_type() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_PATH](#class-csgpolygon-constant-mode-path), this will determine if the interval should be by distance ([PATH\_INTERVAL\_DISTANCE](#class-csgpolygon-constant-path-interval-distance)) or subdivision fractions ([PATH\_INTERVAL\_SUBDIVIDE](#class-csgpolygon-constant-path-interval-subdivide)).
### [bool](class_bool#class-bool) path\_joined
| | |
| --- | --- |
| *Setter* | set\_path\_joined(value) |
| *Getter* | is\_path\_joined() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_PATH](#class-csgpolygon-constant-mode-path), if `true` the ends of the path are joined, by adding an extrusion between the last and first points of the path.
### [bool](class_bool#class-bool) path\_local
| | |
| --- | --- |
| *Setter* | set\_path\_local(value) |
| *Getter* | is\_path\_local() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_PATH](#class-csgpolygon-constant-mode-path), if `true` the [Transform](class_transform#class-transform) of the `CSGPolygon` is used as the starting point for the extrusions, not the [Transform](class_transform#class-transform) of the [path\_node](#class-csgpolygon-property-path-node).
### [NodePath](class_nodepath#class-nodepath) path\_node
| | |
| --- | --- |
| *Setter* | set\_path\_node(value) |
| *Getter* | get\_path\_node() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_PATH](#class-csgpolygon-constant-mode-path), the location of the [Path](class_path#class-path) object used to extrude the [polygon](#class-csgpolygon-property-polygon).
### [PathRotation](#enum-csgpolygon-pathrotation) path\_rotation
| | |
| --- | --- |
| *Setter* | set\_path\_rotation(value) |
| *Getter* | get\_path\_rotation() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_PATH](#class-csgpolygon-constant-mode-path), the [PathRotation](#enum-csgpolygon-pathrotation) method used to rotate the [polygon](#class-csgpolygon-property-polygon) as it is extruded.
### [float](class_float#class-float) path\_simplify\_angle
| | |
| --- | --- |
| *Setter* | set\_path\_simplify\_angle(value) |
| *Getter* | get\_path\_simplify\_angle() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_PATH](#class-csgpolygon-constant-mode-path), extrusions that are less than this angle, will be merged together to reduce polygon count.
### [float](class_float#class-float) path\_u\_distance
| | |
| --- | --- |
| *Setter* | set\_path\_u\_distance(value) |
| *Getter* | get\_path\_u\_distance() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_PATH](#class-csgpolygon-constant-mode-path), this is the distance along the path, in meters, the texture coordinates will tile. When set to 0, texture coordinates will match geometry exactly with no tiling.
### [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon
| | |
| --- | --- |
| *Default* | `PoolVector2Array( 0, 0, 0, 1, 1, 1, 1, 0 )` |
| *Setter* | set\_polygon(value) |
| *Getter* | get\_polygon() |
The point array that defines the 2D polygon that is extruded. This can be a convex or concave polygon with 3 or more points. The polygon must *not* have any intersecting edges. Otherwise, triangulation will fail and no mesh will be generated.
**Note:** If only 1 or 2 points are defined in [polygon](#class-csgpolygon-property-polygon), no mesh will be generated.
### [bool](class_bool#class-bool) smooth\_faces
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_smooth\_faces(value) |
| *Getter* | get\_smooth\_faces() |
If `true`, applies smooth shading to the extrusions.
### [float](class_float#class-float) spin\_degrees
| | |
| --- | --- |
| *Setter* | set\_spin\_degrees(value) |
| *Getter* | get\_spin\_degrees() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_SPIN](#class-csgpolygon-constant-mode-spin), the total number of degrees the [polygon](#class-csgpolygon-property-polygon) is rotated when extruding.
### [int](class_int#class-int) spin\_sides
| | |
| --- | --- |
| *Setter* | set\_spin\_sides(value) |
| *Getter* | get\_spin\_sides() |
When [mode](#class-csgpolygon-property-mode) is [MODE\_SPIN](#class-csgpolygon-constant-mode-spin), the number of extrusions made.
| programming_docs |
godot SceneState SceneState
==========
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A script interface to a scene file's data.
Description
-----------
Maintains a list of resources, nodes, exported, and overridden properties, and built-in scripts associated with a scene.
This class cannot be instantiated directly, it is retrieved for a given scene as the result of [PackedScene.get\_state](class_packedscene#class-packedscene-method-get-state).
Methods
-------
| | |
| --- | --- |
| [Array](class_array#class-array) | [get\_connection\_binds](#class-scenestate-method-get-connection-binds) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_connection\_count](#class-scenestate-method-get-connection-count) **(** **)** const |
| [int](class_int#class-int) | [get\_connection\_flags](#class-scenestate-method-get-connection-flags) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_connection\_method](#class-scenestate-method-get-connection-method) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_connection\_signal](#class-scenestate-method-get-connection-signal) **(** [int](class_int#class-int) idx **)** const |
| [NodePath](class_nodepath#class-nodepath) | [get\_connection\_source](#class-scenestate-method-get-connection-source) **(** [int](class_int#class-int) idx **)** const |
| [NodePath](class_nodepath#class-nodepath) | [get\_connection\_target](#class-scenestate-method-get-connection-target) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_node\_count](#class-scenestate-method-get-node-count) **(** **)** const |
| [PoolStringArray](class_poolstringarray#class-poolstringarray) | [get\_node\_groups](#class-scenestate-method-get-node-groups) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_node\_index](#class-scenestate-method-get-node-index) **(** [int](class_int#class-int) idx **)** const |
| [PackedScene](class_packedscene#class-packedscene) | [get\_node\_instance](#class-scenestate-method-get-node-instance) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_node\_instance\_placeholder](#class-scenestate-method-get-node-instance-placeholder) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_node\_name](#class-scenestate-method-get-node-name) **(** [int](class_int#class-int) idx **)** const |
| [NodePath](class_nodepath#class-nodepath) | [get\_node\_owner\_path](#class-scenestate-method-get-node-owner-path) **(** [int](class_int#class-int) idx **)** const |
| [NodePath](class_nodepath#class-nodepath) | [get\_node\_path](#class-scenestate-method-get-node-path) **(** [int](class_int#class-int) idx, [bool](class_bool#class-bool) for\_parent=false **)** const |
| [int](class_int#class-int) | [get\_node\_property\_count](#class-scenestate-method-get-node-property-count) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_node\_property\_name](#class-scenestate-method-get-node-property-name) **(** [int](class_int#class-int) idx, [int](class_int#class-int) prop\_idx **)** const |
| [Variant](class_variant#class-variant) | [get\_node\_property\_value](#class-scenestate-method-get-node-property-value) **(** [int](class_int#class-int) idx, [int](class_int#class-int) prop\_idx **)** const |
| [String](class_string#class-string) | [get\_node\_type](#class-scenestate-method-get-node-type) **(** [int](class_int#class-int) idx **)** const |
| [bool](class_bool#class-bool) | [is\_node\_instance\_placeholder](#class-scenestate-method-is-node-instance-placeholder) **(** [int](class_int#class-int) idx **)** const |
Enumerations
------------
enum **GenEditState**:
* **GEN\_EDIT\_STATE\_DISABLED** = **0** --- If passed to [PackedScene.instance](class_packedscene#class-packedscene-method-instance), blocks edits to the scene state.
* **GEN\_EDIT\_STATE\_INSTANCE** = **1** --- If passed to [PackedScene.instance](class_packedscene#class-packedscene-method-instance), provides inherited scene resources to the local scene.
**Note:** Only available in editor builds.
* **GEN\_EDIT\_STATE\_MAIN** = **2** --- If passed to [PackedScene.instance](class_packedscene#class-packedscene-method-instance), provides local scene resources to the local scene. Only the main scene should receive the main edit state.
**Note:** Only available in editor builds.
* **GEN\_EDIT\_STATE\_MAIN\_INHERITED** = **3** --- If passed to [PackedScene.instance](class_packedscene#class-packedscene-method-instance), it's similar to [GEN\_EDIT\_STATE\_MAIN](#class-scenestate-constant-gen-edit-state-main), but for the case where the scene is being instantiated to be the base of another one.
**Note:** Only available in editor builds.
Method Descriptions
-------------------
### [Array](class_array#class-array) get\_connection\_binds ( [int](class_int#class-int) idx ) const
Returns the list of bound parameters for the signal at `idx`.
### [int](class_int#class-int) get\_connection\_count ( ) const
Returns the number of signal connections in the scene.
The `idx` argument used to query connection metadata in other `get_connection_*` methods in the interval `[0, get_connection_count() - 1]`.
### [int](class_int#class-int) get\_connection\_flags ( [int](class_int#class-int) idx ) const
Returns the connection flags for the signal at `idx`. See [ConnectFlags](class_object#enum-object-connectflags) constants.
### [String](class_string#class-string) get\_connection\_method ( [int](class_int#class-int) idx ) const
Returns the method connected to the signal at `idx`.
### [String](class_string#class-string) get\_connection\_signal ( [int](class_int#class-int) idx ) const
Returns the name of the signal at `idx`.
### [NodePath](class_nodepath#class-nodepath) get\_connection\_source ( [int](class_int#class-int) idx ) const
Returns the path to the node that owns the signal at `idx`, relative to the root node.
### [NodePath](class_nodepath#class-nodepath) get\_connection\_target ( [int](class_int#class-int) idx ) const
Returns the path to the node that owns the method connected to the signal at `idx`, relative to the root node.
### [int](class_int#class-int) get\_node\_count ( ) const
Returns the number of nodes in the scene.
The `idx` argument used to query node data in other `get_node_*` methods in the interval `[0, get_node_count() - 1]`.
### [PoolStringArray](class_poolstringarray#class-poolstringarray) get\_node\_groups ( [int](class_int#class-int) idx ) const
Returns the list of group names associated with the node at `idx`.
### [int](class_int#class-int) get\_node\_index ( [int](class_int#class-int) idx ) const
Returns the node's index, which is its position relative to its siblings. This is only relevant and saved in scenes for cases where new nodes are added to an instanced or inherited scene among siblings from the base scene. Despite the name, this index is not related to the `idx` argument used here and in other methods.
### [PackedScene](class_packedscene#class-packedscene) get\_node\_instance ( [int](class_int#class-int) idx ) const
Returns a [PackedScene](class_packedscene#class-packedscene) for the node at `idx` (i.e. the whole branch starting at this node, with its child nodes and resources), or `null` if the node is not an instance.
### [String](class_string#class-string) get\_node\_instance\_placeholder ( [int](class_int#class-int) idx ) const
Returns the path to the represented scene file if the node at `idx` is an [InstancePlaceholder](class_instanceplaceholder#class-instanceplaceholder).
### [String](class_string#class-string) get\_node\_name ( [int](class_int#class-int) idx ) const
Returns the name of the node at `idx`.
### [NodePath](class_nodepath#class-nodepath) get\_node\_owner\_path ( [int](class_int#class-int) idx ) const
Returns the path to the owner of the node at `idx`, relative to the root node.
### [NodePath](class_nodepath#class-nodepath) get\_node\_path ( [int](class_int#class-int) idx, [bool](class_bool#class-bool) for\_parent=false ) const
Returns the path to the node at `idx`.
If `for_parent` is `true`, returns the path of the `idx` node's parent instead.
### [int](class_int#class-int) get\_node\_property\_count ( [int](class_int#class-int) idx ) const
Returns the number of exported or overridden properties for the node at `idx`.
The `prop_idx` argument used to query node property data in other `get_node_property_*` methods in the interval `[0, get_node_property_count() - 1]`.
### [String](class_string#class-string) get\_node\_property\_name ( [int](class_int#class-int) idx, [int](class_int#class-int) prop\_idx ) const
Returns the name of the property at `prop_idx` for the node at `idx`.
### [Variant](class_variant#class-variant) get\_node\_property\_value ( [int](class_int#class-int) idx, [int](class_int#class-int) prop\_idx ) const
Returns the value of the property at `prop_idx` for the node at `idx`.
### [String](class_string#class-string) get\_node\_type ( [int](class_int#class-int) idx ) const
Returns the type of the node at `idx`.
### [bool](class_bool#class-bool) is\_node\_instance\_placeholder ( [int](class_int#class-int) idx ) const
Returns `true` if the node at `idx` is an [InstancePlaceholder](class_instanceplaceholder#class-instanceplaceholder).
godot Mutex Mutex
=====
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A synchronization mutex (mutual exclusion).
Description
-----------
A synchronization mutex (mutual exclusion). This is used to synchronize multiple [Thread](class_thread#class-thread)s, and is equivalent to a binary [Semaphore](class_semaphore#class-semaphore). It guarantees that only one thread can ever acquire the lock at a time. A mutex can be used to protect a critical section; however, be careful to avoid deadlocks.
Tutorials
---------
* [Using multiple threads](https://docs.godotengine.org/en/3.5/tutorials/performance/threads/using_multiple_threads.html)
Methods
-------
| | |
| --- | --- |
| void | [lock](#class-mutex-method-lock) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [try\_lock](#class-mutex-method-try-lock) **(** **)** |
| void | [unlock](#class-mutex-method-unlock) **(** **)** |
Method Descriptions
-------------------
### void lock ( )
Locks this `Mutex`, blocks until it is unlocked by the current owner.
**Note:** This function returns without blocking if the thread already has ownership of the mutex.
### [Error](class_%40globalscope#enum-globalscope-error) try\_lock ( )
Tries locking this `Mutex`, but does not block. Returns [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok) on success, [@GlobalScope.ERR\_BUSY](class_%40globalscope#class-globalscope-constant-err-busy) otherwise.
**Note:** This function returns [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok) if the thread already has ownership of the mutex.
### void unlock ( )
Unlocks this `Mutex`, leaving it to other threads.
**Note:** If a thread called [lock](#class-mutex-method-lock) or [try\_lock](#class-mutex-method-try-lock) multiple times while already having ownership of the mutex, it must also call [unlock](#class-mutex-method-unlock) the same number of times in order to unlock it correctly.
godot RootMotionView RootMotionView
==============
**Inherits:** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Editor-only helper for setting up root motion in [AnimationTree](class_animationtree#class-animationtree).
Description
-----------
*Root motion* refers to an animation technique where a mesh's skeleton is used to give impulse to a character. When working with 3D animations, a popular technique is for animators to use the root skeleton bone to give motion to the rest of the skeleton. This allows animating characters in a way where steps actually match the floor below. It also allows precise interaction with objects during cinematics. See also [AnimationTree](class_animationtree#class-animationtree).
**Note:** `RootMotionView` is only visible in the editor. It will be hidden automatically in the running project, and will also be converted to a plain [Node](class_node#class-node) in the running project. This means a script attached to a `RootMotionView` node *must* have `extends Node` instead of `extends RootMotionView`. Additionally, it must not be a `tool` script.
Tutorials
---------
* [Using AnimationTree - Root motion](https://docs.godotengine.org/en/3.5/tutorials/animation/animation_tree.html#root-motion)
Properties
----------
| | |
| --- | --- |
| [NodePath](class_nodepath#class-nodepath) | [animation\_path](#class-rootmotionview-property-animation-path) |
| [float](class_float#class-float) | [cell\_size](#class-rootmotionview-property-cell-size) |
| [Color](class_color#class-color) | [color](#class-rootmotionview-property-color) |
| [float](class_float#class-float) | [radius](#class-rootmotionview-property-radius) |
| [bool](class_bool#class-bool) | [zero\_y](#class-rootmotionview-property-zero-y) |
Property Descriptions
---------------------
### [NodePath](class_nodepath#class-nodepath) animation\_path
| | |
| --- | --- |
| *Setter* | set\_animation\_path(value) |
| *Getter* | get\_animation\_path() |
Path to an [AnimationTree](class_animationtree#class-animationtree) node to use as a basis for root motion.
### [float](class_float#class-float) cell\_size
| | |
| --- | --- |
| *Setter* | set\_cell\_size(value) |
| *Getter* | get\_cell\_size() |
The grid's cell size in 3D units.
### [Color](class_color#class-color) color
| | |
| --- | --- |
| *Setter* | set\_color(value) |
| *Getter* | get\_color() |
The grid's color.
### [float](class_float#class-float) radius
| | |
| --- | --- |
| *Setter* | set\_radius(value) |
| *Getter* | get\_radius() |
The grid's radius in 3D units. The grid's opacity will fade gradually as the distance from the origin increases until this [radius](#class-rootmotionview-property-radius) is reached.
### [bool](class_bool#class-bool) zero\_y
| | |
| --- | --- |
| *Setter* | set\_zero\_y(value) |
| *Getter* | get\_zero\_y() |
If `true`, the grid's points will all be on the same Y coordinate (*local* Y = 0). If `false`, the points' original Y coordinate is preserved.
godot MultiMeshInstance MultiMeshInstance
=================
**Inherits:** [GeometryInstance](class_geometryinstance#class-geometryinstance) **<** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Node that instances a [MultiMesh](class_multimesh#class-multimesh).
Description
-----------
`MultiMeshInstance` is a specialized node to instance [GeometryInstance](class_geometryinstance#class-geometryinstance)s based on a [MultiMesh](class_multimesh#class-multimesh) resource.
This is useful to optimize the rendering of a high amount of instances of a given mesh (for example trees in a forest or grass strands).
Tutorials
---------
* [Animating thousands of fish with MultiMeshInstance](https://docs.godotengine.org/en/3.5/tutorials/performance/vertex_animation/animating_thousands_of_fish.html)
* [Using MultiMeshInstance](https://docs.godotengine.org/en/3.5/tutorials/3d/using_multi_mesh_instance.html)
* [Optimization using MultiMeshes](https://docs.godotengine.org/en/3.5/tutorials/performance/using_multimesh.html)
Properties
----------
| | |
| --- | --- |
| [MultiMesh](class_multimesh#class-multimesh) | [multimesh](#class-multimeshinstance-property-multimesh) |
Property Descriptions
---------------------
### [MultiMesh](class_multimesh#class-multimesh) multimesh
| | |
| --- | --- |
| *Setter* | set\_multimesh(value) |
| *Getter* | get\_multimesh() |
The [MultiMesh](class_multimesh#class-multimesh) resource that will be used and shared among all instances of the `MultiMeshInstance`.
godot PopupMenu PopupMenu
=========
**Inherits:** [Popup](class_popup#class-popup) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
PopupMenu displays a list of options.
Description
-----------
`PopupMenu` is a [Control](class_control#class-control) that displays a list of options. They are popular in toolbars or context menus.
**Incremental search:** Like [ItemList](class_itemlist#class-itemlist) and [Tree](class_tree#class-tree), `PopupMenu` supports searching within the list while the control is focused. Press a key that matches the first letter of an item's name to select the first item starting with the given letter. After that point, there are two ways to perform incremental search: 1) Press the same key again before the timeout duration to select the next item starting with the same letter. 2) Press letter keys that match the rest of the word before the timeout duration to match to select the item in question directly. Both of these actions will be reset to the beginning of the list if the timeout duration has passed since the last keystroke was registered. You can adjust the timeout duration by changing [ProjectSettings.gui/timers/incremental\_search\_max\_interval\_msec](class_projectsettings#class-projectsettings-property-gui-timers-incremental-search-max-interval-msec).
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [allow\_search](#class-popupmenu-property-allow-search) | `false` |
| [FocusMode](class_control#enum-control-focusmode) | focus\_mode | `2` (overrides [Control](class_control#class-control-property-focus-mode)) |
| [bool](class_bool#class-bool) | [hide\_on\_checkable\_item\_selection](#class-popupmenu-property-hide-on-checkable-item-selection) | `true` |
| [bool](class_bool#class-bool) | [hide\_on\_item\_selection](#class-popupmenu-property-hide-on-item-selection) | `true` |
| [bool](class_bool#class-bool) | [hide\_on\_state\_item\_selection](#class-popupmenu-property-hide-on-state-item-selection) | `false` |
| [float](class_float#class-float) | [submenu\_popup\_delay](#class-popupmenu-property-submenu-popup-delay) | `0.3` |
Methods
-------
| | |
| --- | --- |
| void | [add\_check\_item](#class-popupmenu-method-add-check-item) **(** [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 **)** |
| void | [add\_check\_shortcut](#class-popupmenu-method-add-check-shortcut) **(** [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false **)** |
| void | [add\_icon\_check\_item](#class-popupmenu-method-add-icon-check-item) **(** [Texture](class_texture#class-texture) texture, [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 **)** |
| void | [add\_icon\_check\_shortcut](#class-popupmenu-method-add-icon-check-shortcut) **(** [Texture](class_texture#class-texture) texture, [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false **)** |
| void | [add\_icon\_item](#class-popupmenu-method-add-icon-item) **(** [Texture](class_texture#class-texture) texture, [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 **)** |
| void | [add\_icon\_radio\_check\_item](#class-popupmenu-method-add-icon-radio-check-item) **(** [Texture](class_texture#class-texture) texture, [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 **)** |
| void | [add\_icon\_radio\_check\_shortcut](#class-popupmenu-method-add-icon-radio-check-shortcut) **(** [Texture](class_texture#class-texture) texture, [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false **)** |
| void | [add\_icon\_shortcut](#class-popupmenu-method-add-icon-shortcut) **(** [Texture](class_texture#class-texture) texture, [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false **)** |
| void | [add\_item](#class-popupmenu-method-add-item) **(** [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 **)** |
| void | [add\_multistate\_item](#class-popupmenu-method-add-multistate-item) **(** [String](class_string#class-string) label, [int](class_int#class-int) max\_states, [int](class_int#class-int) default\_state=0, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 **)** |
| void | [add\_radio\_check\_item](#class-popupmenu-method-add-radio-check-item) **(** [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 **)** |
| void | [add\_radio\_check\_shortcut](#class-popupmenu-method-add-radio-check-shortcut) **(** [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false **)** |
| void | [add\_separator](#class-popupmenu-method-add-separator) **(** [String](class_string#class-string) label="", [int](class_int#class-int) id=-1 **)** |
| void | [add\_shortcut](#class-popupmenu-method-add-shortcut) **(** [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false **)** |
| void | [add\_submenu\_item](#class-popupmenu-method-add-submenu-item) **(** [String](class_string#class-string) label, [String](class_string#class-string) submenu, [int](class_int#class-int) id=-1 **)** |
| void | [clear](#class-popupmenu-method-clear) **(** **)** |
| [int](class_int#class-int) | [get\_current\_index](#class-popupmenu-method-get-current-index) **(** **)** const |
| [int](class_int#class-int) | [get\_item\_accelerator](#class-popupmenu-method-get-item-accelerator) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_item\_count](#class-popupmenu-method-get-item-count) **(** **)** const |
| [Texture](class_texture#class-texture) | [get\_item\_icon](#class-popupmenu-method-get-item-icon) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_item\_id](#class-popupmenu-method-get-item-id) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_item\_index](#class-popupmenu-method-get-item-index) **(** [int](class_int#class-int) id **)** const |
| [Variant](class_variant#class-variant) | [get\_item\_metadata](#class-popupmenu-method-get-item-metadata) **(** [int](class_int#class-int) idx **)** const |
| [ShortCut](class_shortcut#class-shortcut) | [get\_item\_shortcut](#class-popupmenu-method-get-item-shortcut) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_item\_submenu](#class-popupmenu-method-get-item-submenu) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_item\_text](#class-popupmenu-method-get-item-text) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_item\_tooltip](#class-popupmenu-method-get-item-tooltip) **(** [int](class_int#class-int) idx **)** const |
| [bool](class_bool#class-bool) | [is\_hide\_on\_window\_lose\_focus](#class-popupmenu-method-is-hide-on-window-lose-focus) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_item\_checkable](#class-popupmenu-method-is-item-checkable) **(** [int](class_int#class-int) idx **)** const |
| [bool](class_bool#class-bool) | [is\_item\_checked](#class-popupmenu-method-is-item-checked) **(** [int](class_int#class-int) idx **)** const |
| [bool](class_bool#class-bool) | [is\_item\_disabled](#class-popupmenu-method-is-item-disabled) **(** [int](class_int#class-int) idx **)** const |
| [bool](class_bool#class-bool) | [is\_item\_radio\_checkable](#class-popupmenu-method-is-item-radio-checkable) **(** [int](class_int#class-int) idx **)** const |
| [bool](class_bool#class-bool) | [is\_item\_separator](#class-popupmenu-method-is-item-separator) **(** [int](class_int#class-int) idx **)** const |
| [bool](class_bool#class-bool) | [is\_item\_shortcut\_disabled](#class-popupmenu-method-is-item-shortcut-disabled) **(** [int](class_int#class-int) idx **)** const |
| void | [remove\_item](#class-popupmenu-method-remove-item) **(** [int](class_int#class-int) idx **)** |
| void | [set\_current\_index](#class-popupmenu-method-set-current-index) **(** [int](class_int#class-int) index **)** |
| void | [set\_hide\_on\_window\_lose\_focus](#class-popupmenu-method-set-hide-on-window-lose-focus) **(** [bool](class_bool#class-bool) enable **)** |
| void | [set\_item\_accelerator](#class-popupmenu-method-set-item-accelerator) **(** [int](class_int#class-int) idx, [int](class_int#class-int) accel **)** |
| void | [set\_item\_as\_checkable](#class-popupmenu-method-set-item-as-checkable) **(** [int](class_int#class-int) idx, [bool](class_bool#class-bool) enable **)** |
| void | [set\_item\_as\_radio\_checkable](#class-popupmenu-method-set-item-as-radio-checkable) **(** [int](class_int#class-int) idx, [bool](class_bool#class-bool) enable **)** |
| void | [set\_item\_as\_separator](#class-popupmenu-method-set-item-as-separator) **(** [int](class_int#class-int) idx, [bool](class_bool#class-bool) enable **)** |
| void | [set\_item\_checked](#class-popupmenu-method-set-item-checked) **(** [int](class_int#class-int) idx, [bool](class_bool#class-bool) checked **)** |
| void | [set\_item\_disabled](#class-popupmenu-method-set-item-disabled) **(** [int](class_int#class-int) idx, [bool](class_bool#class-bool) disabled **)** |
| void | [set\_item\_icon](#class-popupmenu-method-set-item-icon) **(** [int](class_int#class-int) idx, [Texture](class_texture#class-texture) icon **)** |
| void | [set\_item\_id](#class-popupmenu-method-set-item-id) **(** [int](class_int#class-int) idx, [int](class_int#class-int) id **)** |
| void | [set\_item\_metadata](#class-popupmenu-method-set-item-metadata) **(** [int](class_int#class-int) idx, [Variant](class_variant#class-variant) metadata **)** |
| void | [set\_item\_multistate](#class-popupmenu-method-set-item-multistate) **(** [int](class_int#class-int) idx, [int](class_int#class-int) state **)** |
| void | [set\_item\_shortcut](#class-popupmenu-method-set-item-shortcut) **(** [int](class_int#class-int) idx, [ShortCut](class_shortcut#class-shortcut) shortcut, [bool](class_bool#class-bool) global=false **)** |
| void | [set\_item\_shortcut\_disabled](#class-popupmenu-method-set-item-shortcut-disabled) **(** [int](class_int#class-int) idx, [bool](class_bool#class-bool) disabled **)** |
| void | [set\_item\_submenu](#class-popupmenu-method-set-item-submenu) **(** [int](class_int#class-int) idx, [String](class_string#class-string) submenu **)** |
| void | [set\_item\_text](#class-popupmenu-method-set-item-text) **(** [int](class_int#class-int) idx, [String](class_string#class-string) text **)** |
| void | [set\_item\_tooltip](#class-popupmenu-method-set-item-tooltip) **(** [int](class_int#class-int) idx, [String](class_string#class-string) tooltip **)** |
| void | [toggle\_item\_checked](#class-popupmenu-method-toggle-item-checked) **(** [int](class_int#class-int) idx **)** |
| void | [toggle\_item\_multistate](#class-popupmenu-method-toggle-item-multistate) **(** [int](class_int#class-int) idx **)** |
Theme Properties
----------------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [font\_color](#class-popupmenu-theme-color-font-color) | `Color( 0.88, 0.88, 0.88, 1 )` |
| [Color](class_color#class-color) | [font\_color\_accel](#class-popupmenu-theme-color-font-color-accel) | `Color( 0.7, 0.7, 0.7, 0.8 )` |
| [Color](class_color#class-color) | [font\_color\_disabled](#class-popupmenu-theme-color-font-color-disabled) | `Color( 0.4, 0.4, 0.4, 0.8 )` |
| [Color](class_color#class-color) | [font\_color\_hover](#class-popupmenu-theme-color-font-color-hover) | `Color( 0.88, 0.88, 0.88, 1 )` |
| [Color](class_color#class-color) | [font\_color\_separator](#class-popupmenu-theme-color-font-color-separator) | `Color( 0.88, 0.88, 0.88, 1 )` |
| [int](class_int#class-int) | [hseparation](#class-popupmenu-theme-constant-hseparation) | `4` |
| [int](class_int#class-int) | [vseparation](#class-popupmenu-theme-constant-vseparation) | `4` |
| [Font](class_font#class-font) | [font](#class-popupmenu-theme-font-font) | |
| [Font](class_font#class-font) | [font\_separator](#class-popupmenu-theme-font-font-separator) | |
| [Texture](class_texture#class-texture) | [checked](#class-popupmenu-theme-icon-checked) | |
| [Texture](class_texture#class-texture) | [radio\_checked](#class-popupmenu-theme-icon-radio-checked) | |
| [Texture](class_texture#class-texture) | [radio\_unchecked](#class-popupmenu-theme-icon-radio-unchecked) | |
| [Texture](class_texture#class-texture) | [submenu](#class-popupmenu-theme-icon-submenu) | |
| [Texture](class_texture#class-texture) | [unchecked](#class-popupmenu-theme-icon-unchecked) | |
| [StyleBox](class_stylebox#class-stylebox) | [hover](#class-popupmenu-theme-style-hover) | |
| [StyleBox](class_stylebox#class-stylebox) | [labeled\_separator\_left](#class-popupmenu-theme-style-labeled-separator-left) | |
| [StyleBox](class_stylebox#class-stylebox) | [labeled\_separator\_right](#class-popupmenu-theme-style-labeled-separator-right) | |
| [StyleBox](class_stylebox#class-stylebox) | [panel](#class-popupmenu-theme-style-panel) | |
| [StyleBox](class_stylebox#class-stylebox) | [panel\_disabled](#class-popupmenu-theme-style-panel-disabled) | |
| [StyleBox](class_stylebox#class-stylebox) | [separator](#class-popupmenu-theme-style-separator) | |
Signals
-------
### id\_focused ( [int](class_int#class-int) id )
Emitted when user navigated to an item of some `id` using `ui_up` or `ui_down` action.
### id\_pressed ( [int](class_int#class-int) id )
Emitted when an item of some `id` is pressed or its accelerator is activated.
### index\_pressed ( [int](class_int#class-int) index )
Emitted when an item of some `index` is pressed or its accelerator is activated.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) allow\_search
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_allow\_search(value) |
| *Getter* | get\_allow\_search() |
If `true`, allows navigating `PopupMenu` with letter keys.
### [bool](class_bool#class-bool) hide\_on\_checkable\_item\_selection
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_hide\_on\_checkable\_item\_selection(value) |
| *Getter* | is\_hide\_on\_checkable\_item\_selection() |
If `true`, hides the `PopupMenu` when a checkbox or radio button is selected.
### [bool](class_bool#class-bool) hide\_on\_item\_selection
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_hide\_on\_item\_selection(value) |
| *Getter* | is\_hide\_on\_item\_selection() |
If `true`, hides the `PopupMenu` when an item is selected.
### [bool](class_bool#class-bool) hide\_on\_state\_item\_selection
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_hide\_on\_state\_item\_selection(value) |
| *Getter* | is\_hide\_on\_state\_item\_selection() |
If `true`, hides the `PopupMenu` when a state item is selected.
### [float](class_float#class-float) submenu\_popup\_delay
| | |
| --- | --- |
| *Default* | `0.3` |
| *Setter* | set\_submenu\_popup\_delay(value) |
| *Getter* | get\_submenu\_popup\_delay() |
Sets the delay time in seconds for the submenu item to popup on mouse hovering. If the popup menu is added as a child of another (acting as a submenu), it will inherit the delay time of the parent menu item.
Method Descriptions
-------------------
### void add\_check\_item ( [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 )
Adds a new checkable item with text `label`.
An `id` can optionally be provided, as well as an accelerator (`accel`). If no `id` is provided, one will be created from the index. If no `accel` is provided then the default `0` will be assigned to it. See [get\_item\_accelerator](#class-popupmenu-method-get-item-accelerator) for more info on accelerators.
**Note:** Checkable items just display a checkmark, but don't have any built-in checking behavior and must be checked/unchecked manually. See [set\_item\_checked](#class-popupmenu-method-set-item-checked) for more info on how to control it.
### void add\_check\_shortcut ( [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false )
Adds a new checkable item and assigns the specified [ShortCut](class_shortcut#class-shortcut) to it. Sets the label of the checkbox to the [ShortCut](class_shortcut#class-shortcut)'s name.
An `id` can optionally be provided. If no `id` is provided, one will be created from the index.
**Note:** Checkable items just display a checkmark, but don't have any built-in checking behavior and must be checked/unchecked manually. See [set\_item\_checked](#class-popupmenu-method-set-item-checked) for more info on how to control it.
### void add\_icon\_check\_item ( [Texture](class_texture#class-texture) texture, [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 )
Adds a new checkable item with text `label` and icon `texture`.
An `id` can optionally be provided, as well as an accelerator (`accel`). If no `id` is provided, one will be created from the index. If no `accel` is provided then the default `0` will be assigned to it. See [get\_item\_accelerator](#class-popupmenu-method-get-item-accelerator) for more info on accelerators.
**Note:** Checkable items just display a checkmark, but don't have any built-in checking behavior and must be checked/unchecked manually. See [set\_item\_checked](#class-popupmenu-method-set-item-checked) for more info on how to control it.
### void add\_icon\_check\_shortcut ( [Texture](class_texture#class-texture) texture, [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false )
Adds a new checkable item and assigns the specified [ShortCut](class_shortcut#class-shortcut) and icon `texture` to it. Sets the label of the checkbox to the [ShortCut](class_shortcut#class-shortcut)'s name.
An `id` can optionally be provided. If no `id` is provided, one will be created from the index.
**Note:** Checkable items just display a checkmark, but don't have any built-in checking behavior and must be checked/unchecked manually. See [set\_item\_checked](#class-popupmenu-method-set-item-checked) for more info on how to control it.
### void add\_icon\_item ( [Texture](class_texture#class-texture) texture, [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 )
Adds a new item with text `label` and icon `texture`.
An `id` can optionally be provided, as well as an accelerator (`accel`). If no `id` is provided, one will be created from the index. If no `accel` is provided then the default `0` will be assigned to it. See [get\_item\_accelerator](#class-popupmenu-method-get-item-accelerator) for more info on accelerators.
### void add\_icon\_radio\_check\_item ( [Texture](class_texture#class-texture) texture, [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 )
Same as [add\_icon\_check\_item](#class-popupmenu-method-add-icon-check-item), but uses a radio check button.
### void add\_icon\_radio\_check\_shortcut ( [Texture](class_texture#class-texture) texture, [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false )
Same as [add\_icon\_check\_shortcut](#class-popupmenu-method-add-icon-check-shortcut), but uses a radio check button.
### void add\_icon\_shortcut ( [Texture](class_texture#class-texture) texture, [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false )
Adds a new item and assigns the specified [ShortCut](class_shortcut#class-shortcut) and icon `texture` to it. Sets the label of the checkbox to the [ShortCut](class_shortcut#class-shortcut)'s name.
An `id` can optionally be provided. If no `id` is provided, one will be created from the index.
### void add\_item ( [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 )
Adds a new item with text `label`.
An `id` can optionally be provided, as well as an accelerator (`accel`). If no `id` is provided, one will be created from the index. If no `accel` is provided then the default `0` will be assigned to it. See [get\_item\_accelerator](#class-popupmenu-method-get-item-accelerator) for more info on accelerators.
### void add\_multistate\_item ( [String](class_string#class-string) label, [int](class_int#class-int) max\_states, [int](class_int#class-int) default\_state=0, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 )
Adds a new multistate item with text `label`.
Contrarily to normal binary items, multistate items can have more than two states, as defined by `max_states`. Each press or activate of the item will increase the state by one. The default value is defined by `default_state`.
An `id` can optionally be provided, as well as an accelerator (`accel`). If no `id` is provided, one will be created from the index. If no `accel` is provided then the default `0` will be assigned to it. See [get\_item\_accelerator](#class-popupmenu-method-get-item-accelerator) for more info on accelerators.
### void add\_radio\_check\_item ( [String](class_string#class-string) label, [int](class_int#class-int) id=-1, [int](class_int#class-int) accel=0 )
Adds a new radio check button with text `label`.
An `id` can optionally be provided, as well as an accelerator (`accel`). If no `id` is provided, one will be created from the index. If no `accel` is provided then the default `0` will be assigned to it. See [get\_item\_accelerator](#class-popupmenu-method-get-item-accelerator) for more info on accelerators.
**Note:** Checkable items just display a checkmark, but don't have any built-in checking behavior and must be checked/unchecked manually. See [set\_item\_checked](#class-popupmenu-method-set-item-checked) for more info on how to control it.
### void add\_radio\_check\_shortcut ( [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false )
Adds a new radio check button and assigns a [ShortCut](class_shortcut#class-shortcut) to it. Sets the label of the checkbox to the [ShortCut](class_shortcut#class-shortcut)'s name.
An `id` can optionally be provided. If no `id` is provided, one will be created from the index.
**Note:** Checkable items just display a checkmark, but don't have any built-in checking behavior and must be checked/unchecked manually. See [set\_item\_checked](#class-popupmenu-method-set-item-checked) for more info on how to control it.
### void add\_separator ( [String](class_string#class-string) label="", [int](class_int#class-int) id=-1 )
Adds a separator between items. Separators also occupy an index, which you can set by using the `id` parameter.
A `label` can optionally be provided, which will appear at the center of the separator.
### void add\_shortcut ( [ShortCut](class_shortcut#class-shortcut) shortcut, [int](class_int#class-int) id=-1, [bool](class_bool#class-bool) global=false )
Adds a [ShortCut](class_shortcut#class-shortcut).
An `id` can optionally be provided. If no `id` is provided, one will be created from the index.
### void add\_submenu\_item ( [String](class_string#class-string) label, [String](class_string#class-string) submenu, [int](class_int#class-int) id=-1 )
Adds an item that will act as a submenu of the parent `PopupMenu` node when clicked. The `submenu` argument is the name of the child `PopupMenu` node that will be shown when the item is clicked.
An `id` can optionally be provided. If no `id` is provided, one will be created from the index.
### void clear ( )
Removes all items from the `PopupMenu`.
### [int](class_int#class-int) get\_current\_index ( ) const
Returns the index of the currently focused item. Returns `-1` if no item is focused.
### [int](class_int#class-int) get\_item\_accelerator ( [int](class_int#class-int) idx ) const
Returns the accelerator of the item at index `idx`. Accelerators are special combinations of keys that activate the item, no matter which control is focused.
### [int](class_int#class-int) get\_item\_count ( ) const
Returns the number of items in the `PopupMenu`.
### [Texture](class_texture#class-texture) get\_item\_icon ( [int](class_int#class-int) idx ) const
Returns the icon of the item at index `idx`.
### [int](class_int#class-int) get\_item\_id ( [int](class_int#class-int) idx ) const
Returns the id of the item at index `idx`. `id` can be manually assigned, while index can not.
### [int](class_int#class-int) get\_item\_index ( [int](class_int#class-int) id ) const
Returns the index of the item containing the specified `id`. Index is automatically assigned to each item by the engine. Index can not be set manually.
### [Variant](class_variant#class-variant) get\_item\_metadata ( [int](class_int#class-int) idx ) const
Returns the metadata of the specified item, which might be of any type. You can set it with [set\_item\_metadata](#class-popupmenu-method-set-item-metadata), which provides a simple way of assigning context data to items.
### [ShortCut](class_shortcut#class-shortcut) get\_item\_shortcut ( [int](class_int#class-int) idx ) const
Returns the [ShortCut](class_shortcut#class-shortcut) associated with the specified `idx` item.
### [String](class_string#class-string) get\_item\_submenu ( [int](class_int#class-int) idx ) const
Returns the submenu name of the item at index `idx`. See [add\_submenu\_item](#class-popupmenu-method-add-submenu-item) for more info on how to add a submenu.
### [String](class_string#class-string) get\_item\_text ( [int](class_int#class-int) idx ) const
Returns the text of the item at index `idx`.
### [String](class_string#class-string) get\_item\_tooltip ( [int](class_int#class-int) idx ) const
Returns the tooltip associated with the specified index `idx`.
### [bool](class_bool#class-bool) is\_hide\_on\_window\_lose\_focus ( ) const
Returns `true` if the popup will be hidden when the window loses focus or not.
### [bool](class_bool#class-bool) is\_item\_checkable ( [int](class_int#class-int) idx ) const
Returns `true` if the item at index `idx` is checkable in some way, i.e. if it has a checkbox or radio button.
**Note:** Checkable items just display a checkmark or radio button, but don't have any built-in checking behavior and must be checked/unchecked manually.
### [bool](class_bool#class-bool) is\_item\_checked ( [int](class_int#class-int) idx ) const
Returns `true` if the item at index `idx` is checked.
### [bool](class_bool#class-bool) is\_item\_disabled ( [int](class_int#class-int) idx ) const
Returns `true` if the item at index `idx` is disabled. When it is disabled it can't be selected, or its action invoked.
See [set\_item\_disabled](#class-popupmenu-method-set-item-disabled) for more info on how to disable an item.
### [bool](class_bool#class-bool) is\_item\_radio\_checkable ( [int](class_int#class-int) idx ) const
Returns `true` if the item at index `idx` has radio button-style checkability.
**Note:** This is purely cosmetic; you must add the logic for checking/unchecking items in radio groups.
### [bool](class_bool#class-bool) is\_item\_separator ( [int](class_int#class-int) idx ) const
Returns `true` if the item is a separator. If it is, it will be displayed as a line. See [add\_separator](#class-popupmenu-method-add-separator) for more info on how to add a separator.
### [bool](class_bool#class-bool) is\_item\_shortcut\_disabled ( [int](class_int#class-int) idx ) const
Returns `true` if the specified item's shortcut is disabled.
### void remove\_item ( [int](class_int#class-int) idx )
Removes the item at index `idx` from the menu.
**Note:** The indices of items after the removed item will be shifted by one.
### void set\_current\_index ( [int](class_int#class-int) index )
Sets the currently focused item as the given `index`.
Passing `-1` as the index makes so that no item is focused.
### void set\_hide\_on\_window\_lose\_focus ( [bool](class_bool#class-bool) enable )
Hides the `PopupMenu` when the window loses focus.
### void set\_item\_accelerator ( [int](class_int#class-int) idx, [int](class_int#class-int) accel )
Sets the accelerator of the item at index `idx`. Accelerators are special combinations of keys that activate the item, no matter which control is focused.
### void set\_item\_as\_checkable ( [int](class_int#class-int) idx, [bool](class_bool#class-bool) enable )
Sets whether the item at index `idx` has a checkbox. If `false`, sets the type of the item to plain text.
**Note:** Checkable items just display a checkmark, but don't have any built-in checking behavior and must be checked/unchecked manually.
### void set\_item\_as\_radio\_checkable ( [int](class_int#class-int) idx, [bool](class_bool#class-bool) enable )
Sets the type of the item at the specified index `idx` to radio button. If `false`, sets the type of the item to plain text.
### void set\_item\_as\_separator ( [int](class_int#class-int) idx, [bool](class_bool#class-bool) enable )
Mark the item at index `idx` as a separator, which means that it would be displayed as a line. If `false`, sets the type of the item to plain text.
### void set\_item\_checked ( [int](class_int#class-int) idx, [bool](class_bool#class-bool) checked )
Sets the checkstate status of the item at index `idx`.
### void set\_item\_disabled ( [int](class_int#class-int) idx, [bool](class_bool#class-bool) disabled )
Enables/disables the item at index `idx`. When it is disabled, it can't be selected and its action can't be invoked.
### void set\_item\_icon ( [int](class_int#class-int) idx, [Texture](class_texture#class-texture) icon )
Replaces the [Texture](class_texture#class-texture) icon of the specified `idx`.
### void set\_item\_id ( [int](class_int#class-int) idx, [int](class_int#class-int) id )
Sets the `id` of the item at index `idx`.
### void set\_item\_metadata ( [int](class_int#class-int) idx, [Variant](class_variant#class-variant) metadata )
Sets the metadata of an item, which may be of any type. You can later get it with [get\_item\_metadata](#class-popupmenu-method-get-item-metadata), which provides a simple way of assigning context data to items.
### void set\_item\_multistate ( [int](class_int#class-int) idx, [int](class_int#class-int) state )
Sets the state of a multistate item. See [add\_multistate\_item](#class-popupmenu-method-add-multistate-item) for details.
### void set\_item\_shortcut ( [int](class_int#class-int) idx, [ShortCut](class_shortcut#class-shortcut) shortcut, [bool](class_bool#class-bool) global=false )
Sets a [ShortCut](class_shortcut#class-shortcut) for the specified item `idx`.
### void set\_item\_shortcut\_disabled ( [int](class_int#class-int) idx, [bool](class_bool#class-bool) disabled )
Disables the [ShortCut](class_shortcut#class-shortcut) of the specified index `idx`.
### void set\_item\_submenu ( [int](class_int#class-int) idx, [String](class_string#class-string) submenu )
Sets the submenu of the item at index `idx`. The submenu is the name of a child `PopupMenu` node that would be shown when the item is clicked.
### void set\_item\_text ( [int](class_int#class-int) idx, [String](class_string#class-string) text )
Sets the text of the item at index `idx`.
### void set\_item\_tooltip ( [int](class_int#class-int) idx, [String](class_string#class-string) tooltip )
Sets the [String](class_string#class-string) tooltip of the item at the specified index `idx`.
### void toggle\_item\_checked ( [int](class_int#class-int) idx )
Toggles the check state of the item of the specified index `idx`.
### void toggle\_item\_multistate ( [int](class_int#class-int) idx )
Cycle to the next state of a multistate item. See [add\_multistate\_item](#class-popupmenu-method-add-multistate-item) for details.
Theme Property Descriptions
---------------------------
### [Color](class_color#class-color) font\_color
| | |
| --- | --- |
| *Default* | `Color( 0.88, 0.88, 0.88, 1 )` |
The default text [Color](class_color#class-color) for menu items' names.
### [Color](class_color#class-color) font\_color\_accel
| | |
| --- | --- |
| *Default* | `Color( 0.7, 0.7, 0.7, 0.8 )` |
The text [Color](class_color#class-color) used for shortcuts and accelerators that show next to the menu item name when defined. See [get\_item\_accelerator](#class-popupmenu-method-get-item-accelerator) for more info on accelerators.
### [Color](class_color#class-color) font\_color\_disabled
| | |
| --- | --- |
| *Default* | `Color( 0.4, 0.4, 0.4, 0.8 )` |
[Color](class_color#class-color) used for disabled menu items' text.
### [Color](class_color#class-color) font\_color\_hover
| | |
| --- | --- |
| *Default* | `Color( 0.88, 0.88, 0.88, 1 )` |
[Color](class_color#class-color) used for the hovered text.
### [Color](class_color#class-color) font\_color\_separator
| | |
| --- | --- |
| *Default* | `Color( 0.88, 0.88, 0.88, 1 )` |
[Color](class_color#class-color) used for labeled separators' text. See [add\_separator](#class-popupmenu-method-add-separator).
### [int](class_int#class-int) hseparation
| | |
| --- | --- |
| *Default* | `4` |
The horizontal space between the item's name and the shortcut text/submenu arrow.
### [int](class_int#class-int) vseparation
| | |
| --- | --- |
| *Default* | `4` |
The vertical space between each menu item.
### [Font](class_font#class-font) font
[Font](class_font#class-font) used for the menu items.
### [Font](class_font#class-font) font\_separator
[Font](class_font#class-font) used for the labeled separator.
### [Texture](class_texture#class-texture) checked
[Texture](class_texture#class-texture) icon for the checked checkbox items.
### [Texture](class_texture#class-texture) radio\_checked
[Texture](class_texture#class-texture) icon for the checked radio button items.
### [Texture](class_texture#class-texture) radio\_unchecked
[Texture](class_texture#class-texture) icon for the unchecked radio button items.
### [Texture](class_texture#class-texture) submenu
[Texture](class_texture#class-texture) icon for the submenu arrow.
### [Texture](class_texture#class-texture) unchecked
[Texture](class_texture#class-texture) icon for the unchecked checkbox items.
### [StyleBox](class_stylebox#class-stylebox) hover
[StyleBox](class_stylebox#class-stylebox) displayed when the `PopupMenu` item is hovered.
### [StyleBox](class_stylebox#class-stylebox) labeled\_separator\_left
[StyleBox](class_stylebox#class-stylebox) for the left side of labeled separator. See [add\_separator](#class-popupmenu-method-add-separator).
### [StyleBox](class_stylebox#class-stylebox) labeled\_separator\_right
[StyleBox](class_stylebox#class-stylebox) for the right side of labeled separator. See [add\_separator](#class-popupmenu-method-add-separator).
### [StyleBox](class_stylebox#class-stylebox) panel
Default [StyleBox](class_stylebox#class-stylebox) of the `PopupMenu` items.
### [StyleBox](class_stylebox#class-stylebox) panel\_disabled
[StyleBox](class_stylebox#class-stylebox) used when the `PopupMenu` item is disabled.
### [StyleBox](class_stylebox#class-stylebox) separator
[StyleBox](class_stylebox#class-stylebox) used for the separators. See [add\_separator](#class-popupmenu-method-add-separator).
| programming_docs |
godot UndoRedo UndoRedo
========
**Inherits:** [Object](class_object#class-object)
Helper to manage undo/redo operations in the editor or custom tools.
Description
-----------
Helper to manage undo/redo operations in the editor or custom tools. It works by registering methods and property changes inside "actions".
Common behavior is to create an action, then add do/undo calls to functions or property changes, then committing the action.
Here's an example on how to add an action to the Godot editor's own `UndoRedo`, from a plugin:
```
var undo_redo = get_undo_redo() # Method of EditorPlugin.
func do_something():
pass # Put your code here.
func undo_something():
pass # Put here the code that reverts what's done by "do_something()".
func _on_MyButton_pressed():
var node = get_node("MyNode2D")
undo_redo.create_action("Move the node")
undo_redo.add_do_method(self, "do_something")
undo_redo.add_undo_method(self, "undo_something")
undo_redo.add_do_property(node, "position", Vector2(100,100))
undo_redo.add_undo_property(node, "position", node.position)
undo_redo.commit_action()
```
[create\_action](#class-undoredo-method-create-action), [add\_do\_method](#class-undoredo-method-add-do-method), [add\_undo\_method](#class-undoredo-method-add-undo-method), [add\_do\_property](#class-undoredo-method-add-do-property), [add\_undo\_property](#class-undoredo-method-add-undo-property), and [commit\_action](#class-undoredo-method-commit-action) should be called one after the other, like in the example. Not doing so could lead to crashes.
If you don't need to register a method, you can leave [add\_do\_method](#class-undoredo-method-add-do-method) and [add\_undo\_method](#class-undoredo-method-add-undo-method) out; the same goes for properties. You can also register more than one method/property.
Methods
-------
| | |
| --- | --- |
| void | [add\_do\_method](#class-undoredo-method-add-do-method) **(** [Object](class_object#class-object) object, [String](class_string#class-string) method, ... **)** vararg |
| void | [add\_do\_property](#class-undoredo-method-add-do-property) **(** [Object](class_object#class-object) object, [String](class_string#class-string) property, [Variant](class_variant#class-variant) value **)** |
| void | [add\_do\_reference](#class-undoredo-method-add-do-reference) **(** [Object](class_object#class-object) object **)** |
| void | [add\_undo\_method](#class-undoredo-method-add-undo-method) **(** [Object](class_object#class-object) object, [String](class_string#class-string) method, ... **)** vararg |
| void | [add\_undo\_property](#class-undoredo-method-add-undo-property) **(** [Object](class_object#class-object) object, [String](class_string#class-string) property, [Variant](class_variant#class-variant) value **)** |
| void | [add\_undo\_reference](#class-undoredo-method-add-undo-reference) **(** [Object](class_object#class-object) object **)** |
| void | [clear\_history](#class-undoredo-method-clear-history) **(** [bool](class_bool#class-bool) increase\_version=true **)** |
| void | [commit\_action](#class-undoredo-method-commit-action) **(** **)** |
| void | [create\_action](#class-undoredo-method-create-action) **(** [String](class_string#class-string) name, [MergeMode](#enum-undoredo-mergemode) merge\_mode=0 **)** |
| [String](class_string#class-string) | [get\_current\_action\_name](#class-undoredo-method-get-current-action-name) **(** **)** const |
| [int](class_int#class-int) | [get\_version](#class-undoredo-method-get-version) **(** **)** const |
| [bool](class_bool#class-bool) | [has\_redo](#class-undoredo-method-has-redo) **(** **)** const |
| [bool](class_bool#class-bool) | [has\_undo](#class-undoredo-method-has-undo) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_commiting\_action](#class-undoredo-method-is-commiting-action) **(** **)** const |
| [bool](class_bool#class-bool) | [redo](#class-undoredo-method-redo) **(** **)** |
| [bool](class_bool#class-bool) | [undo](#class-undoredo-method-undo) **(** **)** |
Signals
-------
### version\_changed ( )
Called when [undo](#class-undoredo-method-undo) or [redo](#class-undoredo-method-redo) was called.
Enumerations
------------
enum **MergeMode**:
* **MERGE\_DISABLE** = **0** --- Makes "do"/"undo" operations stay in separate actions.
* **MERGE\_ENDS** = **1** --- Makes so that the action's "do" operation is from the first action created and the "undo" operation is from the last subsequent action with the same name.
* **MERGE\_ALL** = **2** --- Makes subsequent actions with the same name be merged into one.
Method Descriptions
-------------------
### void add\_do\_method ( [Object](class_object#class-object) object, [String](class_string#class-string) method, ... ) vararg
Register a method that will be called when the action is committed.
### void add\_do\_property ( [Object](class_object#class-object) object, [String](class_string#class-string) property, [Variant](class_variant#class-variant) value )
Register a property value change for "do".
### void add\_do\_reference ( [Object](class_object#class-object) object )
Register a reference for "do" that will be erased if the "do" history is lost. This is useful mostly for new nodes created for the "do" call. Do not use for resources.
### void add\_undo\_method ( [Object](class_object#class-object) object, [String](class_string#class-string) method, ... ) vararg
Register a method that will be called when the action is undone.
### void add\_undo\_property ( [Object](class_object#class-object) object, [String](class_string#class-string) property, [Variant](class_variant#class-variant) value )
Register a property value change for "undo".
### void add\_undo\_reference ( [Object](class_object#class-object) object )
Register a reference for "undo" that will be erased if the "undo" history is lost. This is useful mostly for nodes removed with the "do" call (not the "undo" call!).
### void clear\_history ( [bool](class_bool#class-bool) increase\_version=true )
Clear the undo/redo history and associated references.
Passing `false` to `increase_version` will prevent the version number to be increased from this.
### void commit\_action ( )
Commit the action. All "do" methods/properties are called/set when this function is called.
### void create\_action ( [String](class_string#class-string) name, [MergeMode](#enum-undoredo-mergemode) merge\_mode=0 )
Create a new action. After this is called, do all your calls to [add\_do\_method](#class-undoredo-method-add-do-method), [add\_undo\_method](#class-undoredo-method-add-undo-method), [add\_do\_property](#class-undoredo-method-add-do-property), and [add\_undo\_property](#class-undoredo-method-add-undo-property), then commit the action with [commit\_action](#class-undoredo-method-commit-action).
The way actions are merged is dictated by the `merge_mode` argument. See [MergeMode](#enum-undoredo-mergemode) for details.
### [String](class_string#class-string) get\_current\_action\_name ( ) const
Gets the name of the current action.
### [int](class_int#class-int) get\_version ( ) const
Gets the version. Every time a new action is committed, the `UndoRedo`'s version number is increased automatically.
This is useful mostly to check if something changed from a saved version.
### [bool](class_bool#class-bool) has\_redo ( ) const
Returns `true` if a "redo" action is available.
### [bool](class_bool#class-bool) has\_undo ( ) const
Returns `true` if an "undo" action is available.
### [bool](class_bool#class-bool) is\_commiting\_action ( ) const
Returns `true` if the `UndoRedo` is currently committing the action, i.e. running its "do" method or property change (see [commit\_action](#class-undoredo-method-commit-action)).
### [bool](class_bool#class-bool) redo ( )
Redo the last action.
### [bool](class_bool#class-bool) undo ( )
Undo the last action.
godot RayCast RayCast
=======
**Inherits:** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Query the closest object intersecting a ray.
Description
-----------
A RayCast represents a line from its origin to its destination position, `cast_to`. It is used to query the 3D space in order to find the closest object along the path of the ray.
RayCast can ignore some objects by adding them to the exception list via `add_exception` or by setting proper filtering with collision layers and masks.
RayCast can be configured to report collisions with [Area](class_area#class-area)s ([collide\_with\_areas](#class-raycast-property-collide-with-areas)) and/or [PhysicsBody](class_physicsbody#class-physicsbody)s ([collide\_with\_bodies](#class-raycast-property-collide-with-bodies)).
Only enabled raycasts will be able to query the space and report collisions.
RayCast calculates intersection every physics frame (see [Node](class_node#class-node)), and the result is cached so it can be used later until the next frame. If multiple queries are required between physics frames (or during the same frame), use [force\_raycast\_update](#class-raycast-method-force-raycast-update) after adjusting the raycast.
Tutorials
---------
* [Ray-casting](https://docs.godotengine.org/en/3.5/tutorials/physics/ray-casting.html)
* [3D Voxel Demo](https://godotengine.org/asset-library/asset/676)
Properties
----------
| | | |
| --- | --- | --- |
| [Vector3](class_vector3#class-vector3) | [cast\_to](#class-raycast-property-cast-to) | `Vector3( 0, -1, 0 )` |
| [bool](class_bool#class-bool) | [collide\_with\_areas](#class-raycast-property-collide-with-areas) | `false` |
| [bool](class_bool#class-bool) | [collide\_with\_bodies](#class-raycast-property-collide-with-bodies) | `true` |
| [int](class_int#class-int) | [collision\_mask](#class-raycast-property-collision-mask) | `1` |
| [Color](class_color#class-color) | [debug\_shape\_custom\_color](#class-raycast-property-debug-shape-custom-color) | `Color( 0, 0, 0, 1 )` |
| [int](class_int#class-int) | [debug\_shape\_thickness](#class-raycast-property-debug-shape-thickness) | `2` |
| [bool](class_bool#class-bool) | [enabled](#class-raycast-property-enabled) | `false` |
| [bool](class_bool#class-bool) | [exclude\_parent](#class-raycast-property-exclude-parent) | `true` |
Methods
-------
| | |
| --- | --- |
| void | [add\_exception](#class-raycast-method-add-exception) **(** [Object](class_object#class-object) node **)** |
| void | [add\_exception\_rid](#class-raycast-method-add-exception-rid) **(** [RID](class_rid#class-rid) rid **)** |
| void | [clear\_exceptions](#class-raycast-method-clear-exceptions) **(** **)** |
| void | [force\_raycast\_update](#class-raycast-method-force-raycast-update) **(** **)** |
| [Object](class_object#class-object) | [get\_collider](#class-raycast-method-get-collider) **(** **)** const |
| [int](class_int#class-int) | [get\_collider\_shape](#class-raycast-method-get-collider-shape) **(** **)** const |
| [bool](class_bool#class-bool) | [get\_collision\_mask\_bit](#class-raycast-method-get-collision-mask-bit) **(** [int](class_int#class-int) bit **)** const |
| [Vector3](class_vector3#class-vector3) | [get\_collision\_normal](#class-raycast-method-get-collision-normal) **(** **)** const |
| [Vector3](class_vector3#class-vector3) | [get\_collision\_point](#class-raycast-method-get-collision-point) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_colliding](#class-raycast-method-is-colliding) **(** **)** const |
| void | [remove\_exception](#class-raycast-method-remove-exception) **(** [Object](class_object#class-object) node **)** |
| void | [remove\_exception\_rid](#class-raycast-method-remove-exception-rid) **(** [RID](class_rid#class-rid) rid **)** |
| void | [set\_collision\_mask\_bit](#class-raycast-method-set-collision-mask-bit) **(** [int](class_int#class-int) bit, [bool](class_bool#class-bool) value **)** |
Property Descriptions
---------------------
### [Vector3](class_vector3#class-vector3) cast\_to
| | |
| --- | --- |
| *Default* | `Vector3( 0, -1, 0 )` |
| *Setter* | set\_cast\_to(value) |
| *Getter* | get\_cast\_to() |
The ray's destination point, relative to the RayCast's `position`.
### [bool](class_bool#class-bool) collide\_with\_areas
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_collide\_with\_areas(value) |
| *Getter* | is\_collide\_with\_areas\_enabled() |
If `true`, collision with [Area](class_area#class-area)s will be reported.
### [bool](class_bool#class-bool) collide\_with\_bodies
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_collide\_with\_bodies(value) |
| *Getter* | is\_collide\_with\_bodies\_enabled() |
If `true`, collision with [PhysicsBody](class_physicsbody#class-physicsbody)s will be reported.
### [int](class_int#class-int) collision\_mask
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_collision\_mask(value) |
| *Getter* | get\_collision\_mask() |
The ray's collision mask. Only objects in at least one collision layer enabled in the mask will be detected. See [Collision layers and masks](https://docs.godotengine.org/en/3.5/tutorials/physics/physics_introduction.html#collision-layers-and-masks) in the documentation for more information.
### [Color](class_color#class-color) debug\_shape\_custom\_color
| | |
| --- | --- |
| *Default* | `Color( 0, 0, 0, 1 )` |
| *Setter* | set\_debug\_shape\_custom\_color(value) |
| *Getter* | get\_debug\_shape\_custom\_color() |
The custom color to use to draw the shape in the editor and at run-time if **Visible Collision Shapes** is enabled in the **Debug** menu. This color will be highlighted at run-time if the `RayCast` is colliding with something.
If set to `Color(0.0, 0.0, 0.0)` (by default), the color set in [ProjectSettings.debug/shapes/collision/shape\_color](class_projectsettings#class-projectsettings-property-debug-shapes-collision-shape-color) is used.
### [int](class_int#class-int) debug\_shape\_thickness
| | |
| --- | --- |
| *Default* | `2` |
| *Setter* | set\_debug\_shape\_thickness(value) |
| *Getter* | get\_debug\_shape\_thickness() |
If set to `1`, a line is used as the debug shape. Otherwise, a truncated pyramid is drawn to represent the `RayCast`. Requires **Visible Collision Shapes** to be enabled in the **Debug** menu for the debug shape to be visible at run-time.
### [bool](class_bool#class-bool) enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_enabled(value) |
| *Getter* | is\_enabled() |
If `true`, collisions will be reported.
### [bool](class_bool#class-bool) exclude\_parent
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_exclude\_parent\_body(value) |
| *Getter* | get\_exclude\_parent\_body() |
If `true`, collisions will be ignored for this RayCast's immediate parent.
Method Descriptions
-------------------
### void add\_exception ( [Object](class_object#class-object) node )
Adds a collision exception so the ray does not report collisions with the specified node.
### void add\_exception\_rid ( [RID](class_rid#class-rid) rid )
Adds a collision exception so the ray does not report collisions with the specified [RID](class_rid#class-rid).
### void clear\_exceptions ( )
Removes all collision exceptions for this ray.
### void force\_raycast\_update ( )
Updates the collision information for the ray. Use this method to update the collision information immediately instead of waiting for the next `_physics_process` call, for example if the ray or its parent has changed state.
**Note:** `enabled` is not required for this to work.
### [Object](class_object#class-object) get\_collider ( ) const
Returns the first object that the ray intersects, or `null` if no object is intersecting the ray (i.e. [is\_colliding](#class-raycast-method-is-colliding) returns `false`).
### [int](class_int#class-int) get\_collider\_shape ( ) const
Returns the shape ID of the first object that the ray intersects, or `0` if no object is intersecting the ray (i.e. [is\_colliding](#class-raycast-method-is-colliding) returns `false`).
### [bool](class_bool#class-bool) get\_collision\_mask\_bit ( [int](class_int#class-int) bit ) const
Returns `true` if the bit index passed is turned on.
**Note:** Bit indices range from 0-19.
### [Vector3](class_vector3#class-vector3) get\_collision\_normal ( ) const
Returns the normal of the intersecting object's shape at the collision point.
### [Vector3](class_vector3#class-vector3) get\_collision\_point ( ) const
Returns the collision point at which the ray intersects the closest object.
**Note:** This point is in the **global** coordinate system.
### [bool](class_bool#class-bool) is\_colliding ( ) const
Returns whether any object is intersecting with the ray's vector (considering the vector length).
### void remove\_exception ( [Object](class_object#class-object) node )
Removes a collision exception so the ray does report collisions with the specified node.
### void remove\_exception\_rid ( [RID](class_rid#class-rid) rid )
Removes a collision exception so the ray does report collisions with the specified [RID](class_rid#class-rid).
### void set\_collision\_mask\_bit ( [int](class_int#class-int) bit, [bool](class_bool#class-bool) value )
Sets the bit index passed to the `value` passed.
**Note:** Bit indexes range from 0-19.
godot VisualScriptReturn VisualScriptReturn
==================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Exits a function and returns an optional value.
Description
-----------
Ends the execution of a function and returns control to the calling function. Optionally, it can return a [Variant](class_variant#class-variant) value.
**Input Ports:**
* Sequence
* Data (variant): `result` (optional)
**Output Ports:**
none
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [return\_enabled](#class-visualscriptreturn-property-return-enabled) | `false` |
| [Variant.Type](class_%40globalscope#enum-globalscope-variant-type) | [return\_type](#class-visualscriptreturn-property-return-type) | `0` |
Property Descriptions
---------------------
### [bool](class_bool#class-bool) return\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_enable\_return\_value(value) |
| *Getter* | is\_return\_value\_enabled() |
If `true`, the `return` input port is available.
### [Variant.Type](class_%40globalscope#enum-globalscope-variant-type) return\_type
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_return\_type(value) |
| *Getter* | get\_return\_type() |
The return value's data type.
godot VisualShaderNodeScalarSmoothStep VisualShaderNodeScalarSmoothStep
================================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Calculates a scalar SmoothStep function within the visual shader graph.
Description
-----------
Translates to `smoothstep(edge0, edge1, x)` in the shader language.
Returns `0.0` if `x` is smaller than `edge0` and `1.0` if `x` is larger than `edge1`. Otherwise the return value is interpolated between `0.0` and `1.0` using Hermite polynomials.
godot RegEx RegEx
=====
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Class for searching text for patterns using regular expressions.
Description
-----------
A regular expression (or regex) is a compact language that can be used to recognise strings that follow a specific pattern, such as URLs, email addresses, complete sentences, etc. For instance, a regex of `ab[0-9]` would find any string that is `ab` followed by any number from `0` to `9`. For a more in-depth look, you can easily find various tutorials and detailed explanations on the Internet.
To begin, the RegEx object needs to be compiled with the search pattern using [compile](#class-regex-method-compile) before it can be used.
```
var regex = RegEx.new()
regex.compile("\\w-(\\d+)")
```
The search pattern must be escaped first for GDScript before it is escaped for the expression. For example, `compile("\\d+")` would be read by RegEx as `\d+`. Similarly, `compile("\"(?:\\\\.|[^\"])*\"")` would be read as `"(?:\\.|[^"])*"`.
Using [search](#class-regex-method-search), you can find the pattern within the given text. If a pattern is found, [RegExMatch](class_regexmatch#class-regexmatch) is returned and you can retrieve details of the results using methods such as [RegExMatch.get\_string](class_regexmatch#class-regexmatch-method-get-string) and [RegExMatch.get\_start](class_regexmatch#class-regexmatch-method-get-start).
```
var regex = RegEx.new()
regex.compile("\\w-(\\d+)")
var result = regex.search("abc n-0123")
if result:
print(result.get_string()) # Would print n-0123
```
The results of capturing groups `()` can be retrieved by passing the group number to the various methods in [RegExMatch](class_regexmatch#class-regexmatch). Group 0 is the default and will always refer to the entire pattern. In the above example, calling `result.get_string(1)` would give you `0123`.
This version of RegEx also supports named capturing groups, and the names can be used to retrieve the results. If two or more groups have the same name, the name would only refer to the first one with a match.
```
var regex = RegEx.new()
regex.compile("d(?<digit>[0-9]+)|x(?<digit>[0-9a-f]+)")
var result = regex.search("the number is x2f")
if result:
print(result.get_string("digit")) # Would print 2f
```
If you need to process multiple results, [search\_all](#class-regex-method-search-all) generates a list of all non-overlapping results. This can be combined with a `for` loop for convenience.
```
for result in regex.search_all("d01, d03, d0c, x3f and x42"):
print(result.get_string("digit"))
# Would print 01 03 0 3f 42
```
**Example of splitting a string using a RegEx:**
```
var regex = RegEx.new()
regex.compile("\\S+") # Negated whitespace character class.
var results = []
for result in regex.search_all("One Two \n\tThree"):
results.push_back(result.get_string())
# The `results` array now contains "One", "Two", "Three".
```
**Note:** Godot's regex implementation is based on the [PCRE2](https://www.pcre.org/) library. You can view the full pattern reference [here](https://www.pcre.org/current/doc/html/pcre2pattern.html).
**Tip:** You can use [Regexr](https://regexr.com/) to test regular expressions online.
Methods
-------
| | |
| --- | --- |
| void | [clear](#class-regex-method-clear) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [compile](#class-regex-method-compile) **(** [String](class_string#class-string) pattern **)** |
| [int](class_int#class-int) | [get\_group\_count](#class-regex-method-get-group-count) **(** **)** const |
| [Array](class_array#class-array) | [get\_names](#class-regex-method-get-names) **(** **)** const |
| [String](class_string#class-string) | [get\_pattern](#class-regex-method-get-pattern) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_valid](#class-regex-method-is-valid) **(** **)** const |
| [RegExMatch](class_regexmatch#class-regexmatch) | [search](#class-regex-method-search) **(** [String](class_string#class-string) subject, [int](class_int#class-int) offset=0, [int](class_int#class-int) end=-1 **)** const |
| [Array](class_array#class-array) | [search\_all](#class-regex-method-search-all) **(** [String](class_string#class-string) subject, [int](class_int#class-int) offset=0, [int](class_int#class-int) end=-1 **)** const |
| [String](class_string#class-string) | [sub](#class-regex-method-sub) **(** [String](class_string#class-string) subject, [String](class_string#class-string) replacement, [bool](class_bool#class-bool) all=false, [int](class_int#class-int) offset=0, [int](class_int#class-int) end=-1 **)** const |
Method Descriptions
-------------------
### void clear ( )
This method resets the state of the object, as if it was freshly created. Namely, it unassigns the regular expression of this object.
### [Error](class_%40globalscope#enum-globalscope-error) compile ( [String](class_string#class-string) pattern )
Compiles and assign the search pattern to use. Returns [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok) if the compilation is successful. If an error is encountered, details are printed to standard output and an error is returned.
### [int](class_int#class-int) get\_group\_count ( ) const
Returns the number of capturing groups in compiled pattern.
### [Array](class_array#class-array) get\_names ( ) const
Returns an array of names of named capturing groups in the compiled pattern. They are ordered by appearance.
### [String](class_string#class-string) get\_pattern ( ) const
Returns the original search pattern that was compiled.
### [bool](class_bool#class-bool) is\_valid ( ) const
Returns whether this object has a valid search pattern assigned.
### [RegExMatch](class_regexmatch#class-regexmatch) search ( [String](class_string#class-string) subject, [int](class_int#class-int) offset=0, [int](class_int#class-int) end=-1 ) const
Searches the text for the compiled pattern. Returns a [RegExMatch](class_regexmatch#class-regexmatch) container of the first matching result if found, otherwise `null`. The region to search within can be specified without modifying where the start and end anchor would be.
### [Array](class_array#class-array) search\_all ( [String](class_string#class-string) subject, [int](class_int#class-int) offset=0, [int](class_int#class-int) end=-1 ) const
Searches the text for the compiled pattern. Returns an array of [RegExMatch](class_regexmatch#class-regexmatch) containers for each non-overlapping result. If no results were found, an empty array is returned instead. The region to search within can be specified without modifying where the start and end anchor would be.
### [String](class_string#class-string) sub ( [String](class_string#class-string) subject, [String](class_string#class-string) replacement, [bool](class_bool#class-bool) all=false, [int](class_int#class-int) offset=0, [int](class_int#class-int) end=-1 ) const
Searches the text for the compiled pattern and replaces it with the specified string. Escapes and backreferences such as `$1` and `$name` are expanded and resolved. By default, only the first instance is replaced, but it can be changed for all instances (global replacement). The region to search within can be specified without modifying where the start and end anchor would be.
| programming_docs |
godot VisualScriptCustomNode VisualScriptCustomNode
======================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A scripted Visual Script node.
Description
-----------
A custom Visual Script node which can be scripted in powerful ways.
Methods
-------
| | |
| --- | --- |
| [String](class_string#class-string) | [\_get\_caption](#class-visualscriptcustomnode-method-get-caption) **(** **)** virtual |
| [String](class_string#class-string) | [\_get\_category](#class-visualscriptcustomnode-method-get-category) **(** **)** virtual |
| [int](class_int#class-int) | [\_get\_input\_value\_port\_count](#class-visualscriptcustomnode-method-get-input-value-port-count) **(** **)** virtual |
| [int](class_int#class-int) | [\_get\_input\_value\_port\_hint](#class-visualscriptcustomnode-method-get-input-value-port-hint) **(** [int](class_int#class-int) idx **)** virtual |
| [String](class_string#class-string) | [\_get\_input\_value\_port\_hint\_string](#class-visualscriptcustomnode-method-get-input-value-port-hint-string) **(** [int](class_int#class-int) idx **)** virtual |
| [String](class_string#class-string) | [\_get\_input\_value\_port\_name](#class-visualscriptcustomnode-method-get-input-value-port-name) **(** [int](class_int#class-int) idx **)** virtual |
| [int](class_int#class-int) | [\_get\_input\_value\_port\_type](#class-visualscriptcustomnode-method-get-input-value-port-type) **(** [int](class_int#class-int) idx **)** virtual |
| [int](class_int#class-int) | [\_get\_output\_sequence\_port\_count](#class-visualscriptcustomnode-method-get-output-sequence-port-count) **(** **)** virtual |
| [String](class_string#class-string) | [\_get\_output\_sequence\_port\_text](#class-visualscriptcustomnode-method-get-output-sequence-port-text) **(** [int](class_int#class-int) idx **)** virtual |
| [int](class_int#class-int) | [\_get\_output\_value\_port\_count](#class-visualscriptcustomnode-method-get-output-value-port-count) **(** **)** virtual |
| [int](class_int#class-int) | [\_get\_output\_value\_port\_hint](#class-visualscriptcustomnode-method-get-output-value-port-hint) **(** [int](class_int#class-int) idx **)** virtual |
| [String](class_string#class-string) | [\_get\_output\_value\_port\_hint\_string](#class-visualscriptcustomnode-method-get-output-value-port-hint-string) **(** [int](class_int#class-int) idx **)** virtual |
| [String](class_string#class-string) | [\_get\_output\_value\_port\_name](#class-visualscriptcustomnode-method-get-output-value-port-name) **(** [int](class_int#class-int) idx **)** virtual |
| [int](class_int#class-int) | [\_get\_output\_value\_port\_type](#class-visualscriptcustomnode-method-get-output-value-port-type) **(** [int](class_int#class-int) idx **)** virtual |
| [String](class_string#class-string) | [\_get\_text](#class-visualscriptcustomnode-method-get-text) **(** **)** virtual |
| [int](class_int#class-int) | [\_get\_working\_memory\_size](#class-visualscriptcustomnode-method-get-working-memory-size) **(** **)** virtual |
| [bool](class_bool#class-bool) | [\_has\_input\_sequence\_port](#class-visualscriptcustomnode-method-has-input-sequence-port) **(** **)** virtual |
| [Variant](class_variant#class-variant) | [\_step](#class-visualscriptcustomnode-method-step) **(** [Array](class_array#class-array) inputs, [Array](class_array#class-array) outputs, [int](class_int#class-int) start\_mode, [Array](class_array#class-array) working\_mem **)** virtual |
Enumerations
------------
enum **StartMode**:
* **START\_MODE\_BEGIN\_SEQUENCE** = **0** --- The start mode used the first time when [\_step](#class-visualscriptcustomnode-method-step) is called.
* **START\_MODE\_CONTINUE\_SEQUENCE** = **1** --- The start mode used when [\_step](#class-visualscriptcustomnode-method-step) is called after coming back from a [STEP\_PUSH\_STACK\_BIT](#class-visualscriptcustomnode-constant-step-push-stack-bit).
* **START\_MODE\_RESUME\_YIELD** = **2** --- The start mode used when [\_step](#class-visualscriptcustomnode-method-step) is called after resuming from [STEP\_YIELD\_BIT](#class-visualscriptcustomnode-constant-step-yield-bit).
Constants
---------
### STEP\_PUSH\_STACK\_BIT = 16777216 --- Hint used by [\_step](#class-visualscriptcustomnode-method-step) to tell that control should return to it when there is no other node left to execute.
This is used by [VisualScriptCondition](class_visualscriptcondition#class-visualscriptcondition) to redirect the sequence to the "Done" port after the `true`/`false` branch has finished execution.
* **STEP\_GO\_BACK\_BIT** = **33554432** --- Hint used by [\_step](#class-visualscriptcustomnode-method-step) to tell that control should return back, either hitting a previous [STEP\_PUSH\_STACK\_BIT](#class-visualscriptcustomnode-constant-step-push-stack-bit) or exiting the function.
* **STEP\_NO\_ADVANCE\_BIT** = **67108864**
* **STEP\_EXIT\_FUNCTION\_BIT** = **134217728** --- Hint used by [\_step](#class-visualscriptcustomnode-method-step) to tell that control should stop and exit the function.
* **STEP\_YIELD\_BIT** = **268435456** --- Hint used by [\_step](#class-visualscriptcustomnode-method-step) to tell that the function should be yielded.
Using this requires you to have at least one working memory slot, which is used for the [VisualScriptFunctionState](class_visualscriptfunctionstate#class-visualscriptfunctionstate).
Method Descriptions
-------------------
### [String](class_string#class-string) \_get\_caption ( ) virtual
Return the node's title.
### [String](class_string#class-string) \_get\_category ( ) virtual
Return the node's category.
### [int](class_int#class-int) \_get\_input\_value\_port\_count ( ) virtual
Return the count of input value ports.
### [int](class_int#class-int) \_get\_input\_value\_port\_hint ( [int](class_int#class-int) idx ) virtual
Return the specified input port's hint. See the [PropertyHint](class_%40globalscope#enum-globalscope-propertyhint) hints.
### [String](class_string#class-string) \_get\_input\_value\_port\_hint\_string ( [int](class_int#class-int) idx ) virtual
Return the specified input port's hint string.
### [String](class_string#class-string) \_get\_input\_value\_port\_name ( [int](class_int#class-int) idx ) virtual
Return the specified input port's name.
### [int](class_int#class-int) \_get\_input\_value\_port\_type ( [int](class_int#class-int) idx ) virtual
Return the specified input port's type. See the [Variant.Type](class_%40globalscope#enum-globalscope-variant-type) values.
### [int](class_int#class-int) \_get\_output\_sequence\_port\_count ( ) virtual
Return the amount of output **sequence** ports.
### [String](class_string#class-string) \_get\_output\_sequence\_port\_text ( [int](class_int#class-int) idx ) virtual
Return the specified **sequence** output's name.
### [int](class_int#class-int) \_get\_output\_value\_port\_count ( ) virtual
Return the amount of output value ports.
### [int](class_int#class-int) \_get\_output\_value\_port\_hint ( [int](class_int#class-int) idx ) virtual
Return the specified output port's hint. See the [PropertyHint](class_%40globalscope#enum-globalscope-propertyhint) hints.
### [String](class_string#class-string) \_get\_output\_value\_port\_hint\_string ( [int](class_int#class-int) idx ) virtual
Return the specified output port's hint string.
### [String](class_string#class-string) \_get\_output\_value\_port\_name ( [int](class_int#class-int) idx ) virtual
Return the specified output port's name.
### [int](class_int#class-int) \_get\_output\_value\_port\_type ( [int](class_int#class-int) idx ) virtual
Return the specified output port's type. See the [Variant.Type](class_%40globalscope#enum-globalscope-variant-type) values.
### [String](class_string#class-string) \_get\_text ( ) virtual
Return the custom node's text, which is shown right next to the input **sequence** port (if there is none, on the place that is usually taken by it).
### [int](class_int#class-int) \_get\_working\_memory\_size ( ) virtual
Return the size of the custom node's working memory. See [\_step](#class-visualscriptcustomnode-method-step) for more details.
### [bool](class_bool#class-bool) \_has\_input\_sequence\_port ( ) virtual
Return whether the custom node has an input **sequence** port.
### [Variant](class_variant#class-variant) \_step ( [Array](class_array#class-array) inputs, [Array](class_array#class-array) outputs, [int](class_int#class-int) start\_mode, [Array](class_array#class-array) working\_mem ) virtual
Execute the custom node's logic, returning the index of the output sequence port to use or a [String](class_string#class-string) when there is an error.
The `inputs` array contains the values of the input ports.
`outputs` is an array whose indices should be set to the respective outputs.
The `start_mode` is usually [START\_MODE\_BEGIN\_SEQUENCE](#class-visualscriptcustomnode-constant-start-mode-begin-sequence), unless you have used the `STEP_*` constants.
`working_mem` is an array which can be used to persist information between runs of the custom node. The size needs to be predefined using [\_get\_working\_memory\_size](#class-visualscriptcustomnode-method-get-working-memory-size).
When returning, you can mask the returned value with one of the `STEP_*` constants.
godot GLTFSkin GLTFSkin
========
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Properties
----------
| | | |
| --- | --- | --- |
| [Skin](class_skin#class-skin) | [godot\_skin](#class-gltfskin-property-godot-skin) | |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [joints](#class-gltfskin-property-joints) | `PoolIntArray( )` |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [joints\_original](#class-gltfskin-property-joints-original) | `PoolIntArray( )` |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [non\_joints](#class-gltfskin-property-non-joints) | `PoolIntArray( )` |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [roots](#class-gltfskin-property-roots) | `PoolIntArray( )` |
| [int](class_int#class-int) | [skeleton](#class-gltfskin-property-skeleton) | `-1` |
| [int](class_int#class-int) | [skin\_root](#class-gltfskin-property-skin-root) | `-1` |
Methods
-------
| | |
| --- | --- |
| [Array](class_array#class-array) | [get\_inverse\_binds](#class-gltfskin-method-get-inverse-binds) **(** **)** |
| [Dictionary](class_dictionary#class-dictionary) | [get\_joint\_i\_to\_bone\_i](#class-gltfskin-method-get-joint-i-to-bone-i) **(** **)** |
| [Dictionary](class_dictionary#class-dictionary) | [get\_joint\_i\_to\_name](#class-gltfskin-method-get-joint-i-to-name) **(** **)** |
| void | [set\_inverse\_binds](#class-gltfskin-method-set-inverse-binds) **(** [Array](class_array#class-array) inverse\_binds **)** |
| void | [set\_joint\_i\_to\_bone\_i](#class-gltfskin-method-set-joint-i-to-bone-i) **(** [Dictionary](class_dictionary#class-dictionary) joint\_i\_to\_bone\_i **)** |
| void | [set\_joint\_i\_to\_name](#class-gltfskin-method-set-joint-i-to-name) **(** [Dictionary](class_dictionary#class-dictionary) joint\_i\_to\_name **)** |
Property Descriptions
---------------------
### [Skin](class_skin#class-skin) godot\_skin
| | |
| --- | --- |
| *Setter* | set\_godot\_skin(value) |
| *Getter* | get\_godot\_skin() |
### [PoolIntArray](class_poolintarray#class-poolintarray) joints
| | |
| --- | --- |
| *Default* | `PoolIntArray( )` |
| *Setter* | set\_joints(value) |
| *Getter* | get\_joints() |
### [PoolIntArray](class_poolintarray#class-poolintarray) joints\_original
| | |
| --- | --- |
| *Default* | `PoolIntArray( )` |
| *Setter* | set\_joints\_original(value) |
| *Getter* | get\_joints\_original() |
### [PoolIntArray](class_poolintarray#class-poolintarray) non\_joints
| | |
| --- | --- |
| *Default* | `PoolIntArray( )` |
| *Setter* | set\_non\_joints(value) |
| *Getter* | get\_non\_joints() |
### [PoolIntArray](class_poolintarray#class-poolintarray) roots
| | |
| --- | --- |
| *Default* | `PoolIntArray( )` |
| *Setter* | set\_roots(value) |
| *Getter* | get\_roots() |
### [int](class_int#class-int) skeleton
| | |
| --- | --- |
| *Default* | `-1` |
| *Setter* | set\_skeleton(value) |
| *Getter* | get\_skeleton() |
### [int](class_int#class-int) skin\_root
| | |
| --- | --- |
| *Default* | `-1` |
| *Setter* | set\_skin\_root(value) |
| *Getter* | get\_skin\_root() |
Method Descriptions
-------------------
### [Array](class_array#class-array) get\_inverse\_binds ( )
### [Dictionary](class_dictionary#class-dictionary) get\_joint\_i\_to\_bone\_i ( )
### [Dictionary](class_dictionary#class-dictionary) get\_joint\_i\_to\_name ( )
### void set\_inverse\_binds ( [Array](class_array#class-array) inverse\_binds )
### void set\_joint\_i\_to\_bone\_i ( [Dictionary](class_dictionary#class-dictionary) joint\_i\_to\_bone\_i )
### void set\_joint\_i\_to\_name ( [Dictionary](class_dictionary#class-dictionary) joint\_i\_to\_name )
godot Path2D Path2D
======
**Inherits:** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Contains a [Curve2D](class_curve2d#class-curve2d) path for [PathFollow2D](class_pathfollow2d#class-pathfollow2d) nodes to follow.
Description
-----------
Can have [PathFollow2D](class_pathfollow2d#class-pathfollow2d) child nodes moving along the [Curve2D](class_curve2d#class-curve2d). See [PathFollow2D](class_pathfollow2d#class-pathfollow2d) for more information on usage.
**Note:** The path is considered as relative to the moved nodes (children of [PathFollow2D](class_pathfollow2d#class-pathfollow2d)). As such, the curve should usually start with a zero vector (`(0, 0)`).
Properties
----------
| | | |
| --- | --- | --- |
| [Curve2D](class_curve2d#class-curve2d) | [curve](#class-path2d-property-curve) | |
| [Color](class_color#class-color) | self\_modulate | `Color( 0.5, 0.6, 1, 0.7 )` (overrides [CanvasItem](class_canvasitem#class-canvasitem-property-self-modulate)) |
Property Descriptions
---------------------
### [Curve2D](class_curve2d#class-curve2d) curve
| | |
| --- | --- |
| *Setter* | set\_curve(value) |
| *Getter* | get\_curve() |
A [Curve2D](class_curve2d#class-curve2d) describing the path.
godot VisualScriptSelf VisualScriptSelf
================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Outputs a reference to the current instance.
Description
-----------
Provides a reference to the node running the visual script.
**Input Ports:**
none
**Output Ports:**
* Data (object): `instance`
godot PlaneShape PlaneShape
==========
**Inherits:** [Shape](class_shape#class-shape) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Infinite plane shape for 3D collisions.
Description
-----------
An infinite plane shape for 3D collisions. Note that the [Plane](class_plane#class-plane)'s normal matters; anything "below" the plane will collide with it. If the `PlaneShape` is used in a [PhysicsBody](class_physicsbody#class-physicsbody), it will cause colliding objects placed "below" it to teleport "above" the plane.
Properties
----------
| | | |
| --- | --- | --- |
| [Plane](class_plane#class-plane) | [plane](#class-planeshape-property-plane) | `Plane( 0, 1, 0, 0 )` |
Property Descriptions
---------------------
### [Plane](class_plane#class-plane) plane
| | |
| --- | --- |
| *Default* | `Plane( 0, 1, 0, 0 )` |
| *Setter* | set\_plane(value) |
| *Getter* | get\_plane() |
The [Plane](class_plane#class-plane) used by the `PlaneShape` for collision.
godot ResourceImporter ResourceImporter
================
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [EditorImportPlugin](class_editorimportplugin#class-editorimportplugin)
Base class for the implementation of core resource importers.
Description
-----------
This is the base class for the resource importers implemented in core. To implement your own resource importers using editor plugins, see [EditorImportPlugin](class_editorimportplugin#class-editorimportplugin).
Tutorials
---------
* [Import plugins](https://docs.godotengine.org/en/3.5/tutorials/plugins/editor/import_plugins.html)
Enumerations
------------
enum **ImportOrder**:
* **IMPORT\_ORDER\_DEFAULT** = **0** --- The default import order.
* **IMPORT\_ORDER\_SCENE** = **100** --- The import order for scenes, which ensures scenes are imported *after* all other core resources such as textures. Custom importers should generally have an import order lower than `100` to avoid issues when importing scenes that rely on custom resources.
godot CameraTexture CameraTexture
=============
**Inherits:** [Texture](class_texture#class-texture) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Texture provided by a [CameraFeed](class_camerafeed#class-camerafeed).
Description
-----------
This texture gives access to the camera texture provided by a [CameraFeed](class_camerafeed#class-camerafeed).
**Note:** Many cameras supply YCbCr images which need to be converted in a shader.
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [camera\_feed\_id](#class-cameratexture-property-camera-feed-id) | `0` |
| [bool](class_bool#class-bool) | [camera\_is\_active](#class-cameratexture-property-camera-is-active) | `false` |
| [int](class_int#class-int) | flags | `0` (overrides [Texture](class_texture#class-texture-property-flags)) |
| [FeedImage](class_cameraserver#enum-cameraserver-feedimage) | [which\_feed](#class-cameratexture-property-which-feed) | `0` |
Property Descriptions
---------------------
### [int](class_int#class-int) camera\_feed\_id
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_camera\_feed\_id(value) |
| *Getter* | get\_camera\_feed\_id() |
The ID of the [CameraFeed](class_camerafeed#class-camerafeed) for which we want to display the image.
### [bool](class_bool#class-bool) camera\_is\_active
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_camera\_active(value) |
| *Getter* | get\_camera\_active() |
Convenience property that gives access to the active property of the [CameraFeed](class_camerafeed#class-camerafeed).
### [FeedImage](class_cameraserver#enum-cameraserver-feedimage) which\_feed
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_which\_feed(value) |
| *Getter* | get\_which\_feed() |
Which image within the [CameraFeed](class_camerafeed#class-camerafeed) we want access to, important if the camera image is split in a Y and CbCr component.
godot EditorResourcePreview EditorResourcePreview
=====================
**Inherits:** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Helper to generate previews of resources or files.
Description
-----------
This object is used to generate previews for resources of files.
**Note:** This class shouldn't be instantiated directly. Instead, access the singleton using [EditorInterface.get\_resource\_previewer](class_editorinterface#class-editorinterface-method-get-resource-previewer).
Methods
-------
| | |
| --- | --- |
| void | [add\_preview\_generator](#class-editorresourcepreview-method-add-preview-generator) **(** [EditorResourcePreviewGenerator](class_editorresourcepreviewgenerator#class-editorresourcepreviewgenerator) generator **)** |
| void | [check\_for\_invalidation](#class-editorresourcepreview-method-check-for-invalidation) **(** [String](class_string#class-string) path **)** |
| void | [queue\_edited\_resource\_preview](#class-editorresourcepreview-method-queue-edited-resource-preview) **(** [Resource](class_resource#class-resource) resource, [Object](class_object#class-object) receiver, [String](class_string#class-string) receiver\_func, [Variant](class_variant#class-variant) userdata **)** |
| void | [queue\_resource\_preview](#class-editorresourcepreview-method-queue-resource-preview) **(** [String](class_string#class-string) path, [Object](class_object#class-object) receiver, [String](class_string#class-string) receiver\_func, [Variant](class_variant#class-variant) userdata **)** |
| void | [remove\_preview\_generator](#class-editorresourcepreview-method-remove-preview-generator) **(** [EditorResourcePreviewGenerator](class_editorresourcepreviewgenerator#class-editorresourcepreviewgenerator) generator **)** |
Signals
-------
### preview\_invalidated ( [String](class_string#class-string) path )
Emitted if a preview was invalidated (changed). `path` corresponds to the path of the preview.
Method Descriptions
-------------------
### void add\_preview\_generator ( [EditorResourcePreviewGenerator](class_editorresourcepreviewgenerator#class-editorresourcepreviewgenerator) generator )
Create an own, custom preview generator.
### void check\_for\_invalidation ( [String](class_string#class-string) path )
Check if the resource changed, if so, it will be invalidated and the corresponding signal emitted.
### void queue\_edited\_resource\_preview ( [Resource](class_resource#class-resource) resource, [Object](class_object#class-object) receiver, [String](class_string#class-string) receiver\_func, [Variant](class_variant#class-variant) userdata )
Queue the `resource` being edited for preview. Once the preview is ready, the `receiver`'s `receiver_func` will be called. The `receiver_func` must take the following four arguments: [String](class_string#class-string) path, [Texture](class_texture#class-texture) preview, [Texture](class_texture#class-texture) thumbnail\_preview, [Variant](class_variant#class-variant) userdata. `userdata` can be anything, and will be returned when `receiver_func` is called.
**Note:** If it was not possible to create the preview the `receiver_func` will still be called, but the preview will be null.
### void queue\_resource\_preview ( [String](class_string#class-string) path, [Object](class_object#class-object) receiver, [String](class_string#class-string) receiver\_func, [Variant](class_variant#class-variant) userdata )
Queue a resource file located at `path` for preview. Once the preview is ready, the `receiver`'s `receiver_func` will be called. The `receiver_func` must take the following four arguments: [String](class_string#class-string) path, [Texture](class_texture#class-texture) preview, [Texture](class_texture#class-texture) thumbnail\_preview, [Variant](class_variant#class-variant) userdata. `userdata` can be anything, and will be returned when `receiver_func` is called.
**Note:** If it was not possible to create the preview the `receiver_func` will still be called, but the preview will be null.
### void remove\_preview\_generator ( [EditorResourcePreviewGenerator](class_editorresourcepreviewgenerator#class-editorresourcepreviewgenerator) generator )
Removes a custom preview generator.
| programming_docs |
godot VisualScriptInputAction VisualScriptInputAction
=======================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A Visual Script node returning a state of an action.
Description
-----------
`VisualScriptInputAction` can be used to check if an action is pressed or released.
Properties
----------
| | | |
| --- | --- | --- |
| [String](class_string#class-string) | [action](#class-visualscriptinputaction-property-action) | `""` |
| [Mode](#enum-visualscriptinputaction-mode) | [mode](#class-visualscriptinputaction-property-mode) | `0` |
Enumerations
------------
enum **Mode**:
* **MODE\_PRESSED** = **0** --- `True` if action is pressed.
* **MODE\_RELEASED** = **1** --- `True` if action is released (i.e. not pressed).
* **MODE\_JUST\_PRESSED** = **2** --- `True` on the frame the action was pressed.
* **MODE\_JUST\_RELEASED** = **3** --- `True` on the frame the action was released.
Property Descriptions
---------------------
### [String](class_string#class-string) action
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_action\_name(value) |
| *Getter* | get\_action\_name() |
Name of the action.
### [Mode](#enum-visualscriptinputaction-mode) mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_action\_mode(value) |
| *Getter* | get\_action\_mode() |
State of the action to check. See [Mode](#enum-visualscriptinputaction-mode) for options.
godot ImmediateGeometry ImmediateGeometry
=================
**Inherits:** [GeometryInstance](class_geometryinstance#class-geometryinstance) **<** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Draws simple geometry from code.
Description
-----------
Draws simple geometry from code. Uses a drawing mode similar to OpenGL 1.x.
See also [ArrayMesh](class_arraymesh#class-arraymesh), [MeshDataTool](class_meshdatatool#class-meshdatatool) and [SurfaceTool](class_surfacetool#class-surfacetool) for procedural geometry generation.
**Note:** ImmediateGeometry3D is best suited to small amounts of mesh data that change every frame. It will be slow when handling large amounts of mesh data. If mesh data doesn't change often, use [ArrayMesh](class_arraymesh#class-arraymesh), [MeshDataTool](class_meshdatatool#class-meshdatatool) or [SurfaceTool](class_surfacetool#class-surfacetool) instead.
**Note:** Godot uses clockwise [winding order](https://learnopengl.com/Advanced-OpenGL/Face-culling) for front faces of triangle primitive modes.
**Note:** In case of missing points when handling large amounts of mesh data, try increasing its buffer size limit under [ProjectSettings.rendering/limits/buffers/immediate\_buffer\_size\_kb](class_projectsettings#class-projectsettings-property-rendering-limits-buffers-immediate-buffer-size-kb).
Methods
-------
| | |
| --- | --- |
| void | [add\_sphere](#class-immediategeometry-method-add-sphere) **(** [int](class_int#class-int) lats, [int](class_int#class-int) lons, [float](class_float#class-float) radius, [bool](class_bool#class-bool) add\_uv=true **)** |
| void | [add\_vertex](#class-immediategeometry-method-add-vertex) **(** [Vector3](class_vector3#class-vector3) position **)** |
| void | [begin](#class-immediategeometry-method-begin) **(** [PrimitiveType](class_mesh#enum-mesh-primitivetype) primitive, [Texture](class_texture#class-texture) texture=null **)** |
| void | [clear](#class-immediategeometry-method-clear) **(** **)** |
| void | [end](#class-immediategeometry-method-end) **(** **)** |
| void | [set\_color](#class-immediategeometry-method-set-color) **(** [Color](class_color#class-color) color **)** |
| void | [set\_normal](#class-immediategeometry-method-set-normal) **(** [Vector3](class_vector3#class-vector3) normal **)** |
| void | [set\_tangent](#class-immediategeometry-method-set-tangent) **(** [Plane](class_plane#class-plane) tangent **)** |
| void | [set\_uv](#class-immediategeometry-method-set-uv) **(** [Vector2](class_vector2#class-vector2) uv **)** |
| void | [set\_uv2](#class-immediategeometry-method-set-uv2) **(** [Vector2](class_vector2#class-vector2) uv **)** |
Method Descriptions
-------------------
### void add\_sphere ( [int](class_int#class-int) lats, [int](class_int#class-int) lons, [float](class_float#class-float) radius, [bool](class_bool#class-bool) add\_uv=true )
Simple helper to draw an UV sphere with given latitude, longitude and radius.
### void add\_vertex ( [Vector3](class_vector3#class-vector3) position )
Adds a vertex in local coordinate space with the currently set color/uv/etc.
### void begin ( [PrimitiveType](class_mesh#enum-mesh-primitivetype) primitive, [Texture](class_texture#class-texture) texture=null )
Begin drawing (and optionally pass a texture override). When done call [end](#class-immediategeometry-method-end). For more information on how this works, search for `glBegin()` and `glEnd()` references.
For the type of primitive, see the [PrimitiveType](class_mesh#enum-mesh-primitivetype) enum.
### void clear ( )
Clears everything that was drawn using begin/end.
### void end ( )
Ends a drawing context and displays the results.
### void set\_color ( [Color](class_color#class-color) color )
The current drawing color.
### void set\_normal ( [Vector3](class_vector3#class-vector3) normal )
The next vertex's normal.
### void set\_tangent ( [Plane](class_plane#class-plane) tangent )
The next vertex's tangent (and binormal facing).
### void set\_uv ( [Vector2](class_vector2#class-vector2) uv )
The next vertex's UV.
### void set\_uv2 ( [Vector2](class_vector2#class-vector2) uv )
The next vertex's second layer UV.
godot PropertyTweener PropertyTweener
===============
**Inherits:** [Tweener](class_tweener#class-tweener) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Interpolates an [Object](class_object#class-object)'s property over time.
Description
-----------
`PropertyTweener` is used to interpolate a property in an object. See [SceneTreeTween.tween\_property](class_scenetreetween#class-scenetreetween-method-tween-property) for more usage information.
**Note:** [SceneTreeTween.tween\_property](class_scenetreetween#class-scenetreetween-method-tween-property) is the only correct way to create `PropertyTweener`. Any `PropertyTweener` created manually will not function correctly.
Methods
-------
| | |
| --- | --- |
| [PropertyTweener](#class-propertytweener) | [as\_relative](#class-propertytweener-method-as-relative) **(** **)** |
| [PropertyTweener](#class-propertytweener) | [from](#class-propertytweener-method-from) **(** [Variant](class_variant#class-variant) value **)** |
| [PropertyTweener](#class-propertytweener) | [from\_current](#class-propertytweener-method-from-current) **(** **)** |
| [PropertyTweener](#class-propertytweener) | [set\_delay](#class-propertytweener-method-set-delay) **(** [float](class_float#class-float) delay **)** |
| [PropertyTweener](#class-propertytweener) | [set\_ease](#class-propertytweener-method-set-ease) **(** [EaseType](class_tween#enum-tween-easetype) ease **)** |
| [PropertyTweener](#class-propertytweener) | [set\_trans](#class-propertytweener-method-set-trans) **(** [TransitionType](class_tween#enum-tween-transitiontype) trans **)** |
Method Descriptions
-------------------
### [PropertyTweener](#class-propertytweener) as\_relative ( )
When called, the final value will be used as a relative value instead. Example:
```
var tween = get_tree().create_tween()
tween.tween_property(self, "position", Vector2.RIGHT * 100, 1).as_relative() #the node will move by 100 pixels to the right
```
### [PropertyTweener](#class-propertytweener) from ( [Variant](class_variant#class-variant) value )
Sets a custom initial value to the `PropertyTweener`. Example:
```
var tween = get_tree().create_tween()
tween.tween_property(self, "position", Vector2(200, 100), 1).from(Vector2(100, 100) #this will move the node from position (100, 100) to (200, 100)
```
### [PropertyTweener](#class-propertytweener) from\_current ( )
Makes the `PropertyTweener` use the current property value (i.e. at the time of creating this `PropertyTweener`) as a starting point. This is equivalent of using [from](#class-propertytweener-method-from) with the current value. These two calls will do the same:
```
tween.tween_property(self, "position", Vector2(200, 100), 1).from(position)
tween.tween_property(self, "position", Vector2(200, 100), 1).from_current()
```
### [PropertyTweener](#class-propertytweener) set\_delay ( [float](class_float#class-float) delay )
Sets the time in seconds after which the `PropertyTweener` will start interpolating. By default there's no delay.
### [PropertyTweener](#class-propertytweener) set\_ease ( [EaseType](class_tween#enum-tween-easetype) ease )
Sets the type of used easing from [EaseType](class_tween#enum-tween-easetype). If not set, the default easing is used from the [SceneTreeTween](class_scenetreetween#class-scenetreetween) that contains this Tweener.
### [PropertyTweener](#class-propertytweener) set\_trans ( [TransitionType](class_tween#enum-tween-transitiontype) trans )
Sets the type of used transition from [TransitionType](class_tween#enum-tween-transitiontype). If not set, the default transition is used from the [SceneTreeTween](class_scenetreetween#class-scenetreetween) that contains this Tweener.
godot int int
===
Integer built-in type.
Description
-----------
Signed 64-bit integer type.
It can take values in the interval `[-2^63, 2^63 - 1]`, i.e. `[-9223372036854775808, 9223372036854775807]`. Exceeding those bounds will wrap around.
`int` is a [Variant](class_variant#class-variant) type, and will thus be used when assigning an integer value to a [Variant](class_variant#class-variant). It can also be enforced with the `: int` type hint.
```
var my_variant = 0 # int, value 0.
my_variant += 4.2 # float, value 4.2.
var my_int: int = 1 # int, value 1.
my_int = 4.2 # int, value 4, the right value is implicitly cast to int.
my_int = int("6.7") # int, value 6, the String is explicitly cast with int.
var max_int = 9223372036854775807
print(max_int) # 9223372036854775807, OK.
max_int += 1
print(max_int) # -9223372036854775808, we overflowed and wrapped around.
```
Methods
-------
| | |
| --- | --- |
| [int](#class-int) | [int](#class-int-method-int) **(** [bool](class_bool#class-bool) from **)** |
| [int](#class-int) | [int](#class-int-method-int) **(** [float](class_float#class-float) from **)** |
| [int](#class-int) | [int](#class-int-method-int) **(** [String](class_string#class-string) from **)** |
Method Descriptions
-------------------
### [int](#class-int) int ( [bool](class_bool#class-bool) from )
Cast a [bool](class_bool#class-bool) value to an integer value, `int(true)` will be equals to 1 and `int(false)` will be equals to 0.
* [int](#class-int) **int** **(** [float](class_float#class-float) from **)**
Cast a float value to an integer value, this method simply removes the number fractions (i.e. rounds `from` towards zero), so for example `int(2.7)` will be equals to 2, `int(0.1)` will be equals to 0 and `int(-2.7)` will be equals to -2. This operation is also called truncation.
* [int](#class-int) **int** **(** [String](class_string#class-string) from **)**
Cast a [String](class_string#class-string) value to an integer value, this method is an integer parser from a string, so calling this method with an invalid integer string will return 0, a valid string will be something like `'1.7'`. This method will ignore all non-number characters, so calling `int('1e3')` will return 13.
godot VisualShaderNodeVectorOp VisualShaderNodeVectorOp
========================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A vector operator to be used within the visual shader graph.
Description
-----------
A visual shader node for use of vector operators. Operates on vector `a` and vector `b`.
Properties
----------
| | | |
| --- | --- | --- |
| [Operator](#enum-visualshadernodevectorop-operator) | [operator](#class-visualshadernodevectorop-property-operator) | `0` |
Enumerations
------------
enum **Operator**:
* **OP\_ADD** = **0** --- Adds two vectors.
* **OP\_SUB** = **1** --- Subtracts a vector from a vector.
* **OP\_MUL** = **2** --- Multiplies two vectors.
* **OP\_DIV** = **3** --- Divides vector by vector.
* **OP\_MOD** = **4** --- Returns the remainder of the two vectors.
* **OP\_POW** = **5** --- Returns the value of the first parameter raised to the power of the second, for each component of the vectors.
* **OP\_MAX** = **6** --- Returns the greater of two values, for each component of the vectors.
* **OP\_MIN** = **7** --- Returns the lesser of two values, for each component of the vectors.
* **OP\_CROSS** = **8** --- Calculates the cross product of two vectors.
* **OP\_ATAN2** = **9** --- Returns the arc-tangent of the parameters.
* **OP\_REFLECT** = **10** --- Returns the vector that points in the direction of reflection. `a` is incident vector and `b` is the normal vector.
* **OP\_STEP** = **11** --- Vector step operator. Returns `0.0` if `a` is smaller than `b` and `1.0` otherwise.
Property Descriptions
---------------------
### [Operator](#enum-visualshadernodevectorop-operator) operator
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_operator(value) |
| *Getter* | get\_operator() |
The operator to be used. See [Operator](#enum-visualshadernodevectorop-operator) for options.
godot EditorInspectorPlugin EditorInspectorPlugin
=====================
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Plugin for adding custom property editors on inspector.
Description
-----------
`EditorInspectorPlugin` allows adding custom property editors to [EditorInspector](class_editorinspector#class-editorinspector).
When an object is edited, the [can\_handle](#class-editorinspectorplugin-method-can-handle) function is called and must return `true` if the object type is supported.
If supported, the function [parse\_begin](#class-editorinspectorplugin-method-parse-begin) will be called, allowing to place custom controls at the beginning of the class.
Subsequently, the [parse\_category](#class-editorinspectorplugin-method-parse-category) and [parse\_property](#class-editorinspectorplugin-method-parse-property) are called for every category and property. They offer the ability to add custom controls to the inspector too.
Finally, [parse\_end](#class-editorinspectorplugin-method-parse-end) will be called.
On each of these calls, the "add" functions can be called.
To use `EditorInspectorPlugin`, register it using the [EditorPlugin.add\_inspector\_plugin](class_editorplugin#class-editorplugin-method-add-inspector-plugin) method first.
Tutorials
---------
* [Inspector plugins](https://docs.godotengine.org/en/3.5/tutorials/plugins/editor/inspector_plugins.html)
Methods
-------
| | |
| --- | --- |
| void | [add\_custom\_control](#class-editorinspectorplugin-method-add-custom-control) **(** [Control](class_control#class-control) control **)** |
| void | [add\_property\_editor](#class-editorinspectorplugin-method-add-property-editor) **(** [String](class_string#class-string) property, [Control](class_control#class-control) editor **)** |
| void | [add\_property\_editor\_for\_multiple\_properties](#class-editorinspectorplugin-method-add-property-editor-for-multiple-properties) **(** [String](class_string#class-string) label, [PoolStringArray](class_poolstringarray#class-poolstringarray) properties, [Control](class_control#class-control) editor **)** |
| [bool](class_bool#class-bool) | [can\_handle](#class-editorinspectorplugin-method-can-handle) **(** [Object](class_object#class-object) object **)** virtual |
| void | [parse\_begin](#class-editorinspectorplugin-method-parse-begin) **(** [Object](class_object#class-object) object **)** virtual |
| void | [parse\_category](#class-editorinspectorplugin-method-parse-category) **(** [Object](class_object#class-object) object, [String](class_string#class-string) category **)** virtual |
| void | [parse\_end](#class-editorinspectorplugin-method-parse-end) **(** **)** virtual |
| [bool](class_bool#class-bool) | [parse\_property](#class-editorinspectorplugin-method-parse-property) **(** [Object](class_object#class-object) object, [int](class_int#class-int) type, [String](class_string#class-string) path, [int](class_int#class-int) hint, [String](class_string#class-string) hint\_text, [int](class_int#class-int) usage **)** virtual |
Method Descriptions
-------------------
### void add\_custom\_control ( [Control](class_control#class-control) control )
Adds a custom control, which is not necessarily a property editor.
### void add\_property\_editor ( [String](class_string#class-string) property, [Control](class_control#class-control) editor )
Adds a property editor for an individual property. The `editor` control must extend [EditorProperty](class_editorproperty#class-editorproperty).
### void add\_property\_editor\_for\_multiple\_properties ( [String](class_string#class-string) label, [PoolStringArray](class_poolstringarray#class-poolstringarray) properties, [Control](class_control#class-control) editor )
Adds an editor that allows modifying multiple properties. The `editor` control must extend [EditorProperty](class_editorproperty#class-editorproperty).
### [bool](class_bool#class-bool) can\_handle ( [Object](class_object#class-object) object ) virtual
Returns `true` if this object can be handled by this plugin.
### void parse\_begin ( [Object](class_object#class-object) object ) virtual
Called to allow adding controls at the beginning of the list.
### void parse\_category ( [Object](class_object#class-object) object, [String](class_string#class-string) category ) virtual
Called to allow adding controls at the beginning of the category.
### void parse\_end ( ) virtual
Called to allow adding controls at the end of the list.
### [bool](class_bool#class-bool) parse\_property ( [Object](class_object#class-object) object, [int](class_int#class-int) type, [String](class_string#class-string) path, [int](class_int#class-int) hint, [String](class_string#class-string) hint\_text, [int](class_int#class-int) usage ) virtual
Called to allow adding property specific editors to the inspector. Usually these inherit [EditorProperty](class_editorproperty#class-editorproperty). Returning `true` removes the built-in editor for this property, otherwise allows to insert a custom editor before the built-in one.
godot Physics2DTestMotionResult Physics2DTestMotionResult
=========================
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Properties
----------
| | | |
| --- | --- | --- |
| [Object](class_object#class-object) | [collider](#class-physics2dtestmotionresult-property-collider) | |
| [int](class_int#class-int) | [collider\_id](#class-physics2dtestmotionresult-property-collider-id) | `0` |
| [RID](class_rid#class-rid) | [collider\_rid](#class-physics2dtestmotionresult-property-collider-rid) | |
| [int](class_int#class-int) | [collider\_shape](#class-physics2dtestmotionresult-property-collider-shape) | `0` |
| [Vector2](class_vector2#class-vector2) | [collider\_velocity](#class-physics2dtestmotionresult-property-collider-velocity) | `Vector2( 0, 0 )` |
| [float](class_float#class-float) | [collision\_depth](#class-physics2dtestmotionresult-property-collision-depth) | `0.0` |
| [Vector2](class_vector2#class-vector2) | [collision\_normal](#class-physics2dtestmotionresult-property-collision-normal) | `Vector2( 0, 0 )` |
| [Vector2](class_vector2#class-vector2) | [collision\_point](#class-physics2dtestmotionresult-property-collision-point) | `Vector2( 0, 0 )` |
| [float](class_float#class-float) | [collision\_safe\_fraction](#class-physics2dtestmotionresult-property-collision-safe-fraction) | `0.0` |
| [float](class_float#class-float) | [collision\_unsafe\_fraction](#class-physics2dtestmotionresult-property-collision-unsafe-fraction) | `0.0` |
| [Vector2](class_vector2#class-vector2) | [motion](#class-physics2dtestmotionresult-property-motion) | `Vector2( 0, 0 )` |
| [Vector2](class_vector2#class-vector2) | [motion\_remainder](#class-physics2dtestmotionresult-property-motion-remainder) | `Vector2( 0, 0 )` |
Property Descriptions
---------------------
### [Object](class_object#class-object) collider
| | |
| --- | --- |
| *Getter* | get\_collider() |
### [int](class_int#class-int) collider\_id
| | |
| --- | --- |
| *Default* | `0` |
| *Getter* | get\_collider\_id() |
### [RID](class_rid#class-rid) collider\_rid
| | |
| --- | --- |
| *Getter* | get\_collider\_rid() |
### [int](class_int#class-int) collider\_shape
| | |
| --- | --- |
| *Default* | `0` |
| *Getter* | get\_collider\_shape() |
### [Vector2](class_vector2#class-vector2) collider\_velocity
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Getter* | get\_collider\_velocity() |
### [float](class_float#class-float) collision\_depth
| | |
| --- | --- |
| *Default* | `0.0` |
| *Getter* | get\_collision\_depth() |
### [Vector2](class_vector2#class-vector2) collision\_normal
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Getter* | get\_collision\_normal() |
### [Vector2](class_vector2#class-vector2) collision\_point
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Getter* | get\_collision\_point() |
### [float](class_float#class-float) collision\_safe\_fraction
| | |
| --- | --- |
| *Default* | `0.0` |
| *Getter* | get\_collision\_safe\_fraction() |
### [float](class_float#class-float) collision\_unsafe\_fraction
| | |
| --- | --- |
| *Default* | `0.0` |
| *Getter* | get\_collision\_unsafe\_fraction() |
### [Vector2](class_vector2#class-vector2) motion
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Getter* | get\_motion() |
### [Vector2](class_vector2#class-vector2) motion\_remainder
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Getter* | get\_motion\_remainder() |
| programming_docs |
godot InputEventScreenTouch InputEventScreenTouch
=====================
**Inherits:** [InputEvent](class_inputevent#class-inputevent) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Input event type for screen touch events.
(only available on mobile devices)
Description
-----------
Stores multi-touch press/release information. Supports touch press, touch release and [index](#class-inputeventscreentouch-property-index) for multi-touch count and order.
Tutorials
---------
* [Using InputEvent](https://docs.godotengine.org/en/3.5/tutorials/inputs/inputevent.html)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [index](#class-inputeventscreentouch-property-index) | `0` |
| [Vector2](class_vector2#class-vector2) | [position](#class-inputeventscreentouch-property-position) | `Vector2( 0, 0 )` |
| [bool](class_bool#class-bool) | [pressed](#class-inputeventscreentouch-property-pressed) | `false` |
Property Descriptions
---------------------
### [int](class_int#class-int) index
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_index(value) |
| *Getter* | get\_index() |
The touch index in the case of a multi-touch event. One index = one finger.
### [Vector2](class_vector2#class-vector2) position
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_position(value) |
| *Getter* | get\_position() |
The touch position.
### [bool](class_bool#class-bool) pressed
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_pressed(value) |
| *Getter* | is\_pressed() |
If `true`, the touch's state is pressed. If `false`, the touch's state is released.
godot AudioEffectDelay AudioEffectDelay
================
**Inherits:** [AudioEffect](class_audioeffect#class-audioeffect) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Adds a delay audio effect to an audio bus. Plays input signal back after a period of time.
Two tap delay and feedback options.
Description
-----------
Plays input signal back after a period of time. The delayed signal may be played back multiple times to create the sound of a repeating, decaying echo. Delay effects range from a subtle echo effect to a pronounced blending of previous sounds with new sounds.
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [dry](#class-audioeffectdelay-property-dry) | `1.0` |
| [bool](class_bool#class-bool) | [feedback/active](#class-audioeffectdelay-property-feedback-active) | `false` |
| [float](class_float#class-float) | [feedback/delay\_ms](#class-audioeffectdelay-property-feedback-delay-ms) | `340.0` |
| [float](class_float#class-float) | [feedback/level\_db](#class-audioeffectdelay-property-feedback-level-db) | `-6.0` |
| [float](class_float#class-float) | [feedback/lowpass](#class-audioeffectdelay-property-feedback-lowpass) | `16000.0` |
| [bool](class_bool#class-bool) | [tap1/active](#class-audioeffectdelay-property-tap1-active) | `true` |
| [float](class_float#class-float) | [tap1/delay\_ms](#class-audioeffectdelay-property-tap1-delay-ms) | `250.0` |
| [float](class_float#class-float) | [tap1/level\_db](#class-audioeffectdelay-property-tap1-level-db) | `-6.0` |
| [float](class_float#class-float) | [tap1/pan](#class-audioeffectdelay-property-tap1-pan) | `0.2` |
| [bool](class_bool#class-bool) | [tap2/active](#class-audioeffectdelay-property-tap2-active) | `true` |
| [float](class_float#class-float) | [tap2/delay\_ms](#class-audioeffectdelay-property-tap2-delay-ms) | `500.0` |
| [float](class_float#class-float) | [tap2/level\_db](#class-audioeffectdelay-property-tap2-level-db) | `-12.0` |
| [float](class_float#class-float) | [tap2/pan](#class-audioeffectdelay-property-tap2-pan) | `-0.4` |
Property Descriptions
---------------------
### [float](class_float#class-float) dry
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_dry(value) |
| *Getter* | get\_dry() |
Output percent of original sound. At 0, only delayed sounds are output. Value can range from 0 to 1.
### [bool](class_bool#class-bool) feedback/active
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feedback\_active(value) |
| *Getter* | is\_feedback\_active() |
If `true`, feedback is enabled.
### [float](class_float#class-float) feedback/delay\_ms
| | |
| --- | --- |
| *Default* | `340.0` |
| *Setter* | set\_feedback\_delay\_ms(value) |
| *Getter* | get\_feedback\_delay\_ms() |
Feedback delay time in milliseconds.
### [float](class_float#class-float) feedback/level\_db
| | |
| --- | --- |
| *Default* | `-6.0` |
| *Setter* | set\_feedback\_level\_db(value) |
| *Getter* | get\_feedback\_level\_db() |
Sound level for `tap1`.
### [float](class_float#class-float) feedback/lowpass
| | |
| --- | --- |
| *Default* | `16000.0` |
| *Setter* | set\_feedback\_lowpass(value) |
| *Getter* | get\_feedback\_lowpass() |
Low-pass filter for feedback, in Hz. Frequencies below this value are filtered out of the source signal.
### [bool](class_bool#class-bool) tap1/active
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_tap1\_active(value) |
| *Getter* | is\_tap1\_active() |
If `true`, `tap1` will be enabled.
### [float](class_float#class-float) tap1/delay\_ms
| | |
| --- | --- |
| *Default* | `250.0` |
| *Setter* | set\_tap1\_delay\_ms(value) |
| *Getter* | get\_tap1\_delay\_ms() |
`tap1` delay time in milliseconds.
### [float](class_float#class-float) tap1/level\_db
| | |
| --- | --- |
| *Default* | `-6.0` |
| *Setter* | set\_tap1\_level\_db(value) |
| *Getter* | get\_tap1\_level\_db() |
Sound level for `tap1`.
### [float](class_float#class-float) tap1/pan
| | |
| --- | --- |
| *Default* | `0.2` |
| *Setter* | set\_tap1\_pan(value) |
| *Getter* | get\_tap1\_pan() |
Pan position for `tap1`. Value can range from -1 (fully left) to 1 (fully right).
### [bool](class_bool#class-bool) tap2/active
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_tap2\_active(value) |
| *Getter* | is\_tap2\_active() |
If `true`, `tap2` will be enabled.
### [float](class_float#class-float) tap2/delay\_ms
| | |
| --- | --- |
| *Default* | `500.0` |
| *Setter* | set\_tap2\_delay\_ms(value) |
| *Getter* | get\_tap2\_delay\_ms() |
**Tap2** delay time in milliseconds.
### [float](class_float#class-float) tap2/level\_db
| | |
| --- | --- |
| *Default* | `-12.0` |
| *Setter* | set\_tap2\_level\_db(value) |
| *Getter* | get\_tap2\_level\_db() |
Sound level for `tap2`.
### [float](class_float#class-float) tap2/pan
| | |
| --- | --- |
| *Default* | `-0.4` |
| *Setter* | set\_tap2\_pan(value) |
| *Getter* | get\_tap2\_pan() |
Pan position for `tap2`. Value can range from -1 (fully left) to 1 (fully right).
godot PoolRealArray PoolRealArray
=============
A pooled array of real numbers ([float](class_float#class-float)).
Description
-----------
An array specifically designed to hold floating-point values. Optimized for memory usage, does not fragment the memory.
**Note:** This type is passed by value and not by reference. This means that when *mutating* a class property of type `PoolRealArray` or mutating a `PoolRealArray` within an [Array](class_array#class-array) or [Dictionary](class_dictionary#class-dictionary), changes will be lost:
```
var array = [PoolRealArray()]
array[0].push_back(12.34)
print(array) # [[]] (empty PoolRealArray within an Array)
```
Instead, the entire `PoolRealArray` property must be *reassigned* with `=` for it to be changed:
```
var array = [PoolRealArray()]
var pool_array = array[0]
pool_array.push_back(12.34)
array[0] = pool_array
print(array) # [[12.34]] (PoolRealArray with 1 element inside an Array)
```
**Note:** Unlike primitive [float](class_float#class-float)s which are 64-bit, numbers stored in `PoolRealArray` are 32-bit floats. This means values stored in `PoolRealArray` have lower precision compared to primitive [float](class_float#class-float)s. If you need to store 64-bit floats in an array, use a generic [Array](class_array#class-array) with [float](class_float#class-float) elements as these will still be 64-bit. However, using a generic [Array](class_array#class-array) to store [float](class_float#class-float)s will use roughly 6 times more memory compared to a `PoolRealArray`.
Methods
-------
| | |
| --- | --- |
| [PoolRealArray](#class-poolrealarray) | [PoolRealArray](#class-poolrealarray-method-poolrealarray) **(** [Array](class_array#class-array) from **)** |
| void | [append](#class-poolrealarray-method-append) **(** [float](class_float#class-float) value **)** |
| void | [append\_array](#class-poolrealarray-method-append-array) **(** [PoolRealArray](#class-poolrealarray) array **)** |
| [int](class_int#class-int) | [count](#class-poolrealarray-method-count) **(** [float](class_float#class-float) value **)** |
| [bool](class_bool#class-bool) | [empty](#class-poolrealarray-method-empty) **(** **)** |
| void | [fill](#class-poolrealarray-method-fill) **(** [float](class_float#class-float) value **)** |
| [int](class_int#class-int) | [find](#class-poolrealarray-method-find) **(** [float](class_float#class-float) value, [int](class_int#class-int) from=0 **)** |
| [bool](class_bool#class-bool) | [has](#class-poolrealarray-method-has) **(** [float](class_float#class-float) value **)** |
| [int](class_int#class-int) | [insert](#class-poolrealarray-method-insert) **(** [int](class_int#class-int) idx, [float](class_float#class-float) value **)** |
| void | [invert](#class-poolrealarray-method-invert) **(** **)** |
| void | [push\_back](#class-poolrealarray-method-push-back) **(** [float](class_float#class-float) value **)** |
| void | [remove](#class-poolrealarray-method-remove) **(** [int](class_int#class-int) idx **)** |
| void | [resize](#class-poolrealarray-method-resize) **(** [int](class_int#class-int) idx **)** |
| [int](class_int#class-int) | [rfind](#class-poolrealarray-method-rfind) **(** [float](class_float#class-float) value, [int](class_int#class-int) from=-1 **)** |
| void | [set](#class-poolrealarray-method-set) **(** [int](class_int#class-int) idx, [float](class_float#class-float) value **)** |
| [int](class_int#class-int) | [size](#class-poolrealarray-method-size) **(** **)** |
| void | [sort](#class-poolrealarray-method-sort) **(** **)** |
Method Descriptions
-------------------
### [PoolRealArray](#class-poolrealarray) PoolRealArray ( [Array](class_array#class-array) from )
Constructs a new `PoolRealArray`. Optionally, you can pass in a generic [Array](class_array#class-array) that will be converted.
### void append ( [float](class_float#class-float) value )
Appends an element at the end of the array (alias of [push\_back](#class-poolrealarray-method-push-back)).
### void append\_array ( [PoolRealArray](#class-poolrealarray) array )
Appends a `PoolRealArray` at the end of this array.
### [int](class_int#class-int) count ( [float](class_float#class-float) value )
Returns the number of times an element is in the array.
### [bool](class_bool#class-bool) empty ( )
Returns `true` if the array is empty.
### void fill ( [float](class_float#class-float) value )
Assigns the given value to all elements in the array. This can typically be used together with [resize](#class-poolrealarray-method-resize) to create an array with a given size and initialized elements.
### [int](class_int#class-int) find ( [float](class_float#class-float) value, [int](class_int#class-int) from=0 )
Searches the array for a value and returns its index or `-1` if not found. Optionally, the initial search index can be passed. Returns `-1` if `from` is out of bounds.
### [bool](class_bool#class-bool) has ( [float](class_float#class-float) value )
Returns `true` if the array contains the given value.
**Note:** This is equivalent to using the `in` operator.
### [int](class_int#class-int) insert ( [int](class_int#class-int) idx, [float](class_float#class-float) value )
Inserts a new element at a given position in the array. The position must be valid, or at the end of the array (`idx == size()`).
### void invert ( )
Reverses the order of the elements in the array.
### void push\_back ( [float](class_float#class-float) value )
Appends an element at the end of the array.
### void remove ( [int](class_int#class-int) idx )
Removes an element from the array by index.
### void resize ( [int](class_int#class-int) idx )
Sets the size of the array. If the array is grown, reserves elements at the end of the array. If the array is shrunk, truncates the array to the new size.
**Note:** Added elements are not automatically initialized to 0 and will contain garbage, i.e. indeterminate values.
### [int](class_int#class-int) rfind ( [float](class_float#class-float) value, [int](class_int#class-int) from=-1 )
Searches the array in reverse order. Optionally, a start search index can be passed. If negative, the start index is considered relative to the end of the array. If the adjusted start index is out of bounds, this method searches from the end of the array.
### void set ( [int](class_int#class-int) idx, [float](class_float#class-float) value )
Changes the float at the given index.
### [int](class_int#class-int) size ( )
Returns the number of elements in the array.
### void sort ( )
Sorts the elements of the array in ascending order.
godot AudioStreamPlayback AudioStreamPlayback
===================
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [AudioStreamPlaybackResampled](class_audiostreamplaybackresampled#class-audiostreamplaybackresampled)
Meta class for playing back audio.
Description
-----------
Can play, loop, pause a scroll through audio. See [AudioStream](class_audiostream#class-audiostream) and [AudioStreamOGGVorbis](class_audiostreamoggvorbis#class-audiostreamoggvorbis) for usage.
Tutorials
---------
* [Audio Generator Demo](https://godotengine.org/asset-library/asset/526)
godot CSGPrimitive CSGPrimitive
============
**Inherits:** [CSGShape](class_csgshape#class-csgshape) **<** [GeometryInstance](class_geometryinstance#class-geometryinstance) **<** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
**Inherited By:** [CSGBox](class_csgbox#class-csgbox), [CSGCylinder](class_csgcylinder#class-csgcylinder), [CSGMesh](class_csgmesh#class-csgmesh), [CSGPolygon](class_csgpolygon#class-csgpolygon), [CSGSphere](class_csgsphere#class-csgsphere), [CSGTorus](class_csgtorus#class-csgtorus)
Base class for CSG primitives.
Description
-----------
Parent class for various CSG primitives. It contains code and functionality that is common between them. It cannot be used directly. Instead use one of the various classes that inherit from it.
**Note:** CSG nodes are intended to be used for level prototyping. Creating CSG nodes has a significant CPU cost compared to creating a [MeshInstance](class_meshinstance#class-meshinstance) with a [PrimitiveMesh](class_primitivemesh#class-primitivemesh). Moving a CSG node within another CSG node also has a significant CPU cost, so it should be avoided during gameplay.
Tutorials
---------
* [Prototyping levels with CSG](https://docs.godotengine.org/en/3.5/tutorials/3d/csg_tools.html)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [invert\_faces](#class-csgprimitive-property-invert-faces) | `false` |
Property Descriptions
---------------------
### [bool](class_bool#class-bool) invert\_faces
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_invert\_faces(value) |
| *Getter* | is\_inverting\_faces() |
Invert the faces of the mesh.
godot PhysicsBody2D PhysicsBody2D
=============
**Inherits:** [CollisionObject2D](class_collisionobject2d#class-collisionobject2d) **<** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
**Inherited By:** [KinematicBody2D](class_kinematicbody2d#class-kinematicbody2d), [RigidBody2D](class_rigidbody2d#class-rigidbody2d), [StaticBody2D](class_staticbody2d#class-staticbody2d)
Base class for all objects affected by physics in 2D space.
Description
-----------
PhysicsBody2D is an abstract base class for implementing a physics body. All \*Body2D types inherit from it.
Tutorials
---------
* [Physics introduction](https://docs.godotengine.org/en/3.5/tutorials/physics/physics_introduction.html)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | input\_pickable | `false` (overrides [CollisionObject2D](class_collisionobject2d#class-collisionobject2d-property-input-pickable)) |
| [int](class_int#class-int) | [layers](#class-physicsbody2d-property-layers) | |
Methods
-------
| | |
| --- | --- |
| void | [add\_collision\_exception\_with](#class-physicsbody2d-method-add-collision-exception-with) **(** [Node](class_node#class-node) body **)** |
| [Array](class_array#class-array) | [get\_collision\_exceptions](#class-physicsbody2d-method-get-collision-exceptions) **(** **)** |
| void | [remove\_collision\_exception\_with](#class-physicsbody2d-method-remove-collision-exception-with) **(** [Node](class_node#class-node) body **)** |
Property Descriptions
---------------------
### [int](class_int#class-int) layers
Both collision\_layer and collision\_mask. Returns collision\_layer when accessed. Updates collision\_layer and collision\_mask when modified.
Method Descriptions
-------------------
### void add\_collision\_exception\_with ( [Node](class_node#class-node) body )
Adds a body to the list of bodies that this body can't collide with.
### [Array](class_array#class-array) get\_collision\_exceptions ( )
Returns an array of nodes that were added as collision exceptions for this body.
### void remove\_collision\_exception\_with ( [Node](class_node#class-node) body )
Removes a body from the list of bodies that this body can't collide with.
godot Node Node
====
**Inherits:** [Object](class_object#class-object)
**Inherited By:** [AnimationPlayer](class_animationplayer#class-animationplayer), [AnimationTree](class_animationtree#class-animationtree), [AnimationTreePlayer](class_animationtreeplayer#class-animationtreeplayer), [AudioStreamPlayer](class_audiostreamplayer#class-audiostreamplayer), [CanvasItem](class_canvasitem#class-canvasitem), [CanvasLayer](class_canvaslayer#class-canvaslayer), [EditorFileSystem](class_editorfilesystem#class-editorfilesystem), [EditorInterface](class_editorinterface#class-editorinterface), [EditorPlugin](class_editorplugin#class-editorplugin), [EditorResourcePreview](class_editorresourcepreview#class-editorresourcepreview), [HTTPRequest](class_httprequest#class-httprequest), [InstancePlaceholder](class_instanceplaceholder#class-instanceplaceholder), [NavigationAgent](class_navigationagent#class-navigationagent), [NavigationAgent2D](class_navigationagent2d#class-navigationagent2d), [NavigationObstacle](class_navigationobstacle#class-navigationobstacle), [NavigationObstacle2D](class_navigationobstacle2d#class-navigationobstacle2d), [ResourcePreloader](class_resourcepreloader#class-resourcepreloader), [SkeletonIK](class_skeletonik#class-skeletonik), [Spatial](class_spatial#class-spatial), [Timer](class_timer#class-timer), [Tween](class_tween#class-tween), [Viewport](class_viewport#class-viewport), [WorldEnvironment](class_worldenvironment#class-worldenvironment)
Base class for all *scene* objects.
Description
-----------
Nodes are Godot's building blocks. They can be assigned as the child of another node, resulting in a tree arrangement. A given node can contain any number of nodes as children with the requirement that all siblings (direct children of a node) should have unique names.
A tree of nodes is called a *scene*. Scenes can be saved to the disk and then instanced into other scenes. This allows for very high flexibility in the architecture and data model of Godot projects.
**Scene tree:** The [SceneTree](class_scenetree#class-scenetree) contains the active tree of nodes. When a node is added to the scene tree, it receives the [NOTIFICATION\_ENTER\_TREE](#class-node-constant-notification-enter-tree) notification and its [\_enter\_tree](#class-node-method-enter-tree) callback is triggered. Child nodes are always added *after* their parent node, i.e. the [\_enter\_tree](#class-node-method-enter-tree) callback of a parent node will be triggered before its child's.
Once all nodes have been added in the scene tree, they receive the [NOTIFICATION\_READY](#class-node-constant-notification-ready) notification and their respective [\_ready](#class-node-method-ready) callbacks are triggered. For groups of nodes, the [\_ready](#class-node-method-ready) callback is called in reverse order, starting with the children and moving up to the parent nodes.
This means that when adding a node to the scene tree, the following order will be used for the callbacks: [\_enter\_tree](#class-node-method-enter-tree) of the parent, [\_enter\_tree](#class-node-method-enter-tree) of the children, [\_ready](#class-node-method-ready) of the children and finally [\_ready](#class-node-method-ready) of the parent (recursively for the entire scene tree).
**Processing:** Nodes can override the "process" state, so that they receive a callback on each frame requesting them to process (do something). Normal processing (callback [\_process](#class-node-method-process), toggled with [set\_process](#class-node-method-set-process)) happens as fast as possible and is dependent on the frame rate, so the processing time *delta* (in seconds) is passed as an argument. Physics processing (callback [\_physics\_process](#class-node-method-physics-process), toggled with [set\_physics\_process](#class-node-method-set-physics-process)) happens a fixed number of times per second (60 by default) and is useful for code related to the physics engine.
Nodes can also process input events. When present, the [\_input](#class-node-method-input) function will be called for each input that the program receives. In many cases, this can be overkill (unless used for simple projects), and the [\_unhandled\_input](#class-node-method-unhandled-input) function might be preferred; it is called when the input event was not handled by anyone else (typically, GUI [Control](class_control#class-control) nodes), ensuring that the node only receives the events that were meant for it.
To keep track of the scene hierarchy (especially when instancing scenes into other scenes), an "owner" can be set for the node with the [owner](#class-node-property-owner) property. This keeps track of who instanced what. This is mostly useful when writing editors and tools, though.
Finally, when a node is freed with [Object.free](class_object#class-object-method-free) or [queue\_free](#class-node-method-queue-free), it will also free all its children.
**Groups:** Nodes can be added to as many groups as you want to be easy to manage, you could create groups like "enemies" or "collectables" for example, depending on your game. See [add\_to\_group](#class-node-method-add-to-group), [is\_in\_group](#class-node-method-is-in-group) and [remove\_from\_group](#class-node-method-remove-from-group). You can then retrieve all nodes in these groups, iterate them and even call methods on groups via the methods on [SceneTree](class_scenetree#class-scenetree).
**Networking with nodes:** After connecting to a server (or making one, see [NetworkedMultiplayerENet](class_networkedmultiplayerenet#class-networkedmultiplayerenet)), it is possible to use the built-in RPC (remote procedure call) system to communicate over the network. By calling [rpc](#class-node-method-rpc) with a method name, it will be called locally and in all connected peers (peers = clients and the server that accepts connections). To identify which node receives the RPC call, Godot will use its [NodePath](class_nodepath#class-nodepath) (make sure node names are the same on all peers). Also, take a look at the high-level networking tutorial and corresponding demos.
Tutorials
---------
* [Nodes and Scenes](../getting_started/step_by_step/nodes_and_scenes)
* [All Demos](https://github.com/godotengine/godot-demo-projects/)
Properties
----------
| | | |
| --- | --- | --- |
| [MultiplayerAPI](class_multiplayerapi#class-multiplayerapi) | [custom\_multiplayer](#class-node-property-custom-multiplayer) | |
| [String](class_string#class-string) | [filename](#class-node-property-filename) | |
| [MultiplayerAPI](class_multiplayerapi#class-multiplayerapi) | [multiplayer](#class-node-property-multiplayer) | |
| [String](class_string#class-string) | [name](#class-node-property-name) | |
| [Node](#class-node) | [owner](#class-node-property-owner) | |
| [PauseMode](#enum-node-pausemode) | [pause\_mode](#class-node-property-pause-mode) | `0` |
| [PhysicsInterpolationMode](#enum-node-physicsinterpolationmode) | [physics\_interpolation\_mode](#class-node-property-physics-interpolation-mode) | `0` |
| [int](class_int#class-int) | [process\_priority](#class-node-property-process-priority) | `0` |
| [bool](class_bool#class-bool) | [unique\_name\_in\_owner](#class-node-property-unique-name-in-owner) | `false` |
Methods
-------
| | |
| --- | --- |
| void | [\_enter\_tree](#class-node-method-enter-tree) **(** **)** virtual |
| void | [\_exit\_tree](#class-node-method-exit-tree) **(** **)** virtual |
| [String](class_string#class-string) | [\_get\_configuration\_warning](#class-node-method-get-configuration-warning) **(** **)** virtual |
| void | [\_input](#class-node-method-input) **(** [InputEvent](class_inputevent#class-inputevent) event **)** virtual |
| void | [\_physics\_process](#class-node-method-physics-process) **(** [float](class_float#class-float) delta **)** virtual |
| void | [\_process](#class-node-method-process) **(** [float](class_float#class-float) delta **)** virtual |
| void | [\_ready](#class-node-method-ready) **(** **)** virtual |
| void | [\_unhandled\_input](#class-node-method-unhandled-input) **(** [InputEvent](class_inputevent#class-inputevent) event **)** virtual |
| void | [\_unhandled\_key\_input](#class-node-method-unhandled-key-input) **(** [InputEventKey](class_inputeventkey#class-inputeventkey) event **)** virtual |
| void | [add\_child](#class-node-method-add-child) **(** [Node](#class-node) node, [bool](class_bool#class-bool) legible\_unique\_name=false **)** |
| void | [add\_child\_below\_node](#class-node-method-add-child-below-node) **(** [Node](#class-node) node, [Node](#class-node) child\_node, [bool](class_bool#class-bool) legible\_unique\_name=false **)** |
| void | [add\_to\_group](#class-node-method-add-to-group) **(** [String](class_string#class-string) group, [bool](class_bool#class-bool) persistent=false **)** |
| [bool](class_bool#class-bool) | [can\_process](#class-node-method-can-process) **(** **)** const |
| [SceneTreeTween](class_scenetreetween#class-scenetreetween) | [create\_tween](#class-node-method-create-tween) **(** **)** |
| [Node](#class-node) | [duplicate](#class-node-method-duplicate) **(** [int](class_int#class-int) flags=15 **)** const |
| [Node](#class-node) | [find\_node](#class-node-method-find-node) **(** [String](class_string#class-string) mask, [bool](class_bool#class-bool) recursive=true, [bool](class_bool#class-bool) owned=true **)** const |
| [Node](#class-node) | [find\_parent](#class-node-method-find-parent) **(** [String](class_string#class-string) mask **)** const |
| [Node](#class-node) | [get\_child](#class-node-method-get-child) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_child\_count](#class-node-method-get-child-count) **(** **)** const |
| [Array](class_array#class-array) | [get\_children](#class-node-method-get-children) **(** **)** const |
| [Array](class_array#class-array) | [get\_groups](#class-node-method-get-groups) **(** **)** const |
| [int](class_int#class-int) | [get\_index](#class-node-method-get-index) **(** **)** const |
| [int](class_int#class-int) | [get\_network\_master](#class-node-method-get-network-master) **(** **)** const |
| [Node](#class-node) | [get\_node](#class-node-method-get-node) **(** [NodePath](class_nodepath#class-nodepath) path **)** const |
| [Array](class_array#class-array) | [get\_node\_and\_resource](#class-node-method-get-node-and-resource) **(** [NodePath](class_nodepath#class-nodepath) path **)** |
| [Node](#class-node) | [get\_node\_or\_null](#class-node-method-get-node-or-null) **(** [NodePath](class_nodepath#class-nodepath) path **)** const |
| [Node](#class-node) | [get\_parent](#class-node-method-get-parent) **(** **)** const |
| [NodePath](class_nodepath#class-nodepath) | [get\_path](#class-node-method-get-path) **(** **)** const |
| [NodePath](class_nodepath#class-nodepath) | [get\_path\_to](#class-node-method-get-path-to) **(** [Node](#class-node) node **)** const |
| [float](class_float#class-float) | [get\_physics\_process\_delta\_time](#class-node-method-get-physics-process-delta-time) **(** **)** const |
| [int](class_int#class-int) | [get\_position\_in\_parent](#class-node-method-get-position-in-parent) **(** **)** const |
| [float](class_float#class-float) | [get\_process\_delta\_time](#class-node-method-get-process-delta-time) **(** **)** const |
| [bool](class_bool#class-bool) | [get\_scene\_instance\_load\_placeholder](#class-node-method-get-scene-instance-load-placeholder) **(** **)** const |
| [SceneTree](class_scenetree#class-scenetree) | [get\_tree](#class-node-method-get-tree) **(** **)** const |
| [Viewport](class_viewport#class-viewport) | [get\_viewport](#class-node-method-get-viewport) **(** **)** const |
| [bool](class_bool#class-bool) | [has\_node](#class-node-method-has-node) **(** [NodePath](class_nodepath#class-nodepath) path **)** const |
| [bool](class_bool#class-bool) | [has\_node\_and\_resource](#class-node-method-has-node-and-resource) **(** [NodePath](class_nodepath#class-nodepath) path **)** const |
| [bool](class_bool#class-bool) | [is\_a\_parent\_of](#class-node-method-is-a-parent-of) **(** [Node](#class-node) node **)** const |
| [bool](class_bool#class-bool) | [is\_displayed\_folded](#class-node-method-is-displayed-folded) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_greater\_than](#class-node-method-is-greater-than) **(** [Node](#class-node) node **)** const |
| [bool](class_bool#class-bool) | [is\_in\_group](#class-node-method-is-in-group) **(** [String](class_string#class-string) group **)** const |
| [bool](class_bool#class-bool) | [is\_inside\_tree](#class-node-method-is-inside-tree) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_network\_master](#class-node-method-is-network-master) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_physics\_interpolated](#class-node-method-is-physics-interpolated) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_physics\_interpolated\_and\_enabled](#class-node-method-is-physics-interpolated-and-enabled) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_physics\_processing](#class-node-method-is-physics-processing) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_physics\_processing\_internal](#class-node-method-is-physics-processing-internal) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_processing](#class-node-method-is-processing) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_processing\_input](#class-node-method-is-processing-input) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_processing\_internal](#class-node-method-is-processing-internal) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_processing\_unhandled\_input](#class-node-method-is-processing-unhandled-input) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_processing\_unhandled\_key\_input](#class-node-method-is-processing-unhandled-key-input) **(** **)** const |
| void | [move\_child](#class-node-method-move-child) **(** [Node](#class-node) child\_node, [int](class_int#class-int) to\_position **)** |
| void | [print\_stray\_nodes](#class-node-method-print-stray-nodes) **(** **)** |
| void | [print\_tree](#class-node-method-print-tree) **(** **)** |
| void | [print\_tree\_pretty](#class-node-method-print-tree-pretty) **(** **)** |
| void | [propagate\_call](#class-node-method-propagate-call) **(** [String](class_string#class-string) method, [Array](class_array#class-array) args=[ ], [bool](class_bool#class-bool) parent\_first=false **)** |
| void | [propagate\_notification](#class-node-method-propagate-notification) **(** [int](class_int#class-int) what **)** |
| void | [queue\_free](#class-node-method-queue-free) **(** **)** |
| void | [raise](#class-node-method-raise) **(** **)** |
| void | [remove\_and\_skip](#class-node-method-remove-and-skip) **(** **)** |
| void | [remove\_child](#class-node-method-remove-child) **(** [Node](#class-node) node **)** |
| void | [remove\_from\_group](#class-node-method-remove-from-group) **(** [String](class_string#class-string) group **)** |
| void | [replace\_by](#class-node-method-replace-by) **(** [Node](#class-node) node, [bool](class_bool#class-bool) keep\_data=false **)** |
| void | [request\_ready](#class-node-method-request-ready) **(** **)** |
| void | [reset\_physics\_interpolation](#class-node-method-reset-physics-interpolation) **(** **)** |
| [Variant](class_variant#class-variant) | [rpc](#class-node-method-rpc) **(** [String](class_string#class-string) method, ... **)** vararg |
| void | [rpc\_config](#class-node-method-rpc-config) **(** [String](class_string#class-string) method, [RPCMode](class_multiplayerapi#enum-multiplayerapi-rpcmode) mode **)** |
| [Variant](class_variant#class-variant) | [rpc\_id](#class-node-method-rpc-id) **(** [int](class_int#class-int) peer\_id, [String](class_string#class-string) method, ... **)** vararg |
| [Variant](class_variant#class-variant) | [rpc\_unreliable](#class-node-method-rpc-unreliable) **(** [String](class_string#class-string) method, ... **)** vararg |
| [Variant](class_variant#class-variant) | [rpc\_unreliable\_id](#class-node-method-rpc-unreliable-id) **(** [int](class_int#class-int) peer\_id, [String](class_string#class-string) method, ... **)** vararg |
| void | [rset](#class-node-method-rset) **(** [String](class_string#class-string) property, [Variant](class_variant#class-variant) value **)** |
| void | [rset\_config](#class-node-method-rset-config) **(** [String](class_string#class-string) property, [RPCMode](class_multiplayerapi#enum-multiplayerapi-rpcmode) mode **)** |
| void | [rset\_id](#class-node-method-rset-id) **(** [int](class_int#class-int) peer\_id, [String](class_string#class-string) property, [Variant](class_variant#class-variant) value **)** |
| void | [rset\_unreliable](#class-node-method-rset-unreliable) **(** [String](class_string#class-string) property, [Variant](class_variant#class-variant) value **)** |
| void | [rset\_unreliable\_id](#class-node-method-rset-unreliable-id) **(** [int](class_int#class-int) peer\_id, [String](class_string#class-string) property, [Variant](class_variant#class-variant) value **)** |
| void | [set\_display\_folded](#class-node-method-set-display-folded) **(** [bool](class_bool#class-bool) fold **)** |
| void | [set\_network\_master](#class-node-method-set-network-master) **(** [int](class_int#class-int) id, [bool](class_bool#class-bool) recursive=true **)** |
| void | [set\_physics\_process](#class-node-method-set-physics-process) **(** [bool](class_bool#class-bool) enable **)** |
| void | [set\_physics\_process\_internal](#class-node-method-set-physics-process-internal) **(** [bool](class_bool#class-bool) enable **)** |
| void | [set\_process](#class-node-method-set-process) **(** [bool](class_bool#class-bool) enable **)** |
| void | [set\_process\_input](#class-node-method-set-process-input) **(** [bool](class_bool#class-bool) enable **)** |
| void | [set\_process\_internal](#class-node-method-set-process-internal) **(** [bool](class_bool#class-bool) enable **)** |
| void | [set\_process\_unhandled\_input](#class-node-method-set-process-unhandled-input) **(** [bool](class_bool#class-bool) enable **)** |
| void | [set\_process\_unhandled\_key\_input](#class-node-method-set-process-unhandled-key-input) **(** [bool](class_bool#class-bool) enable **)** |
| void | [set\_scene\_instance\_load\_placeholder](#class-node-method-set-scene-instance-load-placeholder) **(** [bool](class_bool#class-bool) load\_placeholder **)** |
| void | [update\_configuration\_warning](#class-node-method-update-configuration-warning) **(** **)** |
Signals
-------
### child\_entered\_tree ( [Node](#class-node) node )
Emitted when a child node enters the scene tree, either because it entered on its own or because this node entered with it.
This signal is emitted *after* the child node's own [NOTIFICATION\_ENTER\_TREE](#class-node-constant-notification-enter-tree) and [tree\_entered](#class-node-signal-tree-entered).
### child\_exiting\_tree ( [Node](#class-node) node )
Emitted when a child node is about to exit the scene tree, either because it is being removed or freed directly, or because this node is exiting the tree.
When this signal is received, the child `node` is still in the tree and valid. This signal is emitted *after* the child node's own [tree\_exiting](#class-node-signal-tree-exiting) and [NOTIFICATION\_EXIT\_TREE](#class-node-constant-notification-exit-tree).
### ready ( )
Emitted when the node is ready.
### renamed ( )
Emitted when the node is renamed.
### tree\_entered ( )
Emitted when the node enters the tree.
This signal is emitted *after* the related [NOTIFICATION\_ENTER\_TREE](#class-node-constant-notification-enter-tree) notification.
### tree\_exited ( )
Emitted after the node exits the tree and is no longer active.
### tree\_exiting ( )
Emitted when the node is still active but about to exit the tree. This is the right place for de-initialization (or a "destructor", if you will).
This signal is emitted *before* the related [NOTIFICATION\_EXIT\_TREE](#class-node-constant-notification-exit-tree) notification.
Enumerations
------------
enum **PauseMode**:
* **PAUSE\_MODE\_INHERIT** = **0** --- Inherits pause mode from the node's parent. For the root node, it is equivalent to [PAUSE\_MODE\_STOP](#class-node-constant-pause-mode-stop). Default.
* **PAUSE\_MODE\_STOP** = **1** --- Stops processing when the [SceneTree](class_scenetree#class-scenetree) is paused.
* **PAUSE\_MODE\_PROCESS** = **2** --- Continue to process regardless of the [SceneTree](class_scenetree#class-scenetree) pause state.
enum **PhysicsInterpolationMode**:
* **PHYSICS\_INTERPOLATION\_MODE\_INHERIT** = **0** --- Inherits physics interpolation mode from the node's parent. For the root node, it is equivalent to [PHYSICS\_INTERPOLATION\_MODE\_ON](#class-node-constant-physics-interpolation-mode-on). Default.
* **PHYSICS\_INTERPOLATION\_MODE\_OFF** = **1** --- Turn off physics interpolation in this node and children set to [PHYSICS\_INTERPOLATION\_MODE\_INHERIT](#class-node-constant-physics-interpolation-mode-inherit).
* **PHYSICS\_INTERPOLATION\_MODE\_ON** = **2** --- Turn on physics interpolation in this node and children set to [PHYSICS\_INTERPOLATION\_MODE\_INHERIT](#class-node-constant-physics-interpolation-mode-inherit).
enum **DuplicateFlags**:
* **DUPLICATE\_SIGNALS** = **1** --- Duplicate the node's signals.
* **DUPLICATE\_GROUPS** = **2** --- Duplicate the node's groups.
* **DUPLICATE\_SCRIPTS** = **4** --- Duplicate the node's scripts.
* **DUPLICATE\_USE\_INSTANCING** = **8** --- Duplicate using instancing.
An instance stays linked to the original so when the original changes, the instance changes too.
Constants
---------
### NOTIFICATION\_ENTER\_TREE = 10 --- Notification received when the node enters a [SceneTree](class_scenetree#class-scenetree).
This notification is emitted *before* the related [tree\_entered](#class-node-signal-tree-entered).
* **NOTIFICATION\_EXIT\_TREE** = **11** --- Notification received when the node is about to exit a [SceneTree](class_scenetree#class-scenetree).
This notification is emitted *after* the related [tree\_exiting](#class-node-signal-tree-exiting).
* **NOTIFICATION\_MOVED\_IN\_PARENT** = **12** --- Notification received when the node is moved in the parent.
* **NOTIFICATION\_READY** = **13** --- Notification received when the node is ready. See [\_ready](#class-node-method-ready).
* **NOTIFICATION\_PAUSED** = **14** --- Notification received when the node is paused.
* **NOTIFICATION\_UNPAUSED** = **15** --- Notification received when the node is unpaused.
* **NOTIFICATION\_PHYSICS\_PROCESS** = **16** --- Notification received every frame when the physics process flag is set (see [set\_physics\_process](#class-node-method-set-physics-process)).
* **NOTIFICATION\_PROCESS** = **17** --- Notification received every frame when the process flag is set (see [set\_process](#class-node-method-set-process)).
* **NOTIFICATION\_PARENTED** = **18** --- Notification received when a node is set as a child of another node.
**Note:** This doesn't mean that a node entered the [SceneTree](class_scenetree#class-scenetree).
* **NOTIFICATION\_UNPARENTED** = **19** --- Notification received when a node is unparented (parent removed it from the list of children).
* **NOTIFICATION\_INSTANCED** = **20** --- Notification received when the node is instanced.
* **NOTIFICATION\_DRAG\_BEGIN** = **21** --- Notification received when a drag operation begins. All nodes receive this notification, not only the dragged one.
Can be triggered either by dragging a [Control](class_control#class-control) that provides drag data (see [Control.get\_drag\_data](class_control#class-control-method-get-drag-data)) or using [Control.force\_drag](class_control#class-control-method-force-drag).
Use [Viewport.gui\_get\_drag\_data](class_viewport#class-viewport-method-gui-get-drag-data) to get the dragged data.
* **NOTIFICATION\_DRAG\_END** = **22** --- Notification received when a drag operation ends.
Use [Viewport.gui\_is\_drag\_successful](class_viewport#class-viewport-method-gui-is-drag-successful) to check if the drag succeeded.
* **NOTIFICATION\_PATH\_CHANGED** = **23** --- Notification received when the node's [NodePath](class_nodepath#class-nodepath) changed.
* **NOTIFICATION\_INTERNAL\_PROCESS** = **25** --- Notification received every frame when the internal process flag is set (see [set\_process\_internal](#class-node-method-set-process-internal)).
* **NOTIFICATION\_INTERNAL\_PHYSICS\_PROCESS** = **26** --- Notification received every frame when the internal physics process flag is set (see [set\_physics\_process\_internal](#class-node-method-set-physics-process-internal)).
* **NOTIFICATION\_POST\_ENTER\_TREE** = **27** --- Notification received when the node is ready, just before [NOTIFICATION\_READY](#class-node-constant-notification-ready) is received. Unlike the latter, it's sent every time the node enters tree, instead of only once.
* **NOTIFICATION\_RESET\_PHYSICS\_INTERPOLATION** = **28** --- Notification received when [reset\_physics\_interpolation](#class-node-method-reset-physics-interpolation) is called on the node or parent nodes.
* **NOTIFICATION\_WM\_MOUSE\_ENTER** = **1002** --- Notification received from the OS when the mouse enters the game window.
Implemented on desktop and web platforms.
* **NOTIFICATION\_WM\_MOUSE\_EXIT** = **1003** --- Notification received from the OS when the mouse leaves the game window.
Implemented on desktop and web platforms.
* **NOTIFICATION\_WM\_FOCUS\_IN** = **1004** --- Notification received from the OS when the game window is focused.
Implemented on all platforms.
* **NOTIFICATION\_WM\_FOCUS\_OUT** = **1005** --- Notification received from the OS when the game window is unfocused.
Implemented on all platforms.
* **NOTIFICATION\_WM\_QUIT\_REQUEST** = **1006** --- Notification received from the OS when a quit request is sent (e.g. closing the window with a "Close" button or Alt+F4).
Implemented on desktop platforms.
* **NOTIFICATION\_WM\_GO\_BACK\_REQUEST** = **1007** --- Notification received from the OS when a go back request is sent (e.g. pressing the "Back" button on Android).
Specific to the Android platform.
* **NOTIFICATION\_WM\_UNFOCUS\_REQUEST** = **1008** --- Notification received from the OS when an unfocus request is sent (e.g. another OS window wants to take the focus).
No supported platforms currently send this notification.
* **NOTIFICATION\_OS\_MEMORY\_WARNING** = **1009** --- Notification received from the OS when the application is exceeding its allocated memory.
Specific to the iOS platform.
* **NOTIFICATION\_TRANSLATION\_CHANGED** = **1010** --- Notification received when translations may have changed. Can be triggered by the user changing the locale. Can be used to respond to language changes, for example to change the UI strings on the fly. Useful when working with the built-in translation support, like [Object.tr](class_object#class-object-method-tr).
* **NOTIFICATION\_WM\_ABOUT** = **1011** --- Notification received from the OS when a request for "About" information is sent.
Specific to the macOS platform.
* **NOTIFICATION\_CRASH** = **1012** --- Notification received from Godot's crash handler when the engine is about to crash.
Implemented on desktop platforms if the crash handler is enabled.
* **NOTIFICATION\_OS\_IME\_UPDATE** = **1013** --- Notification received from the OS when an update of the Input Method Engine occurs (e.g. change of IME cursor position or composition string).
Specific to the macOS platform.
* **NOTIFICATION\_APP\_RESUMED** = **1014** --- Notification received from the OS when the app is resumed.
Specific to the Android platform.
* **NOTIFICATION\_APP\_PAUSED** = **1015** --- Notification received from the OS when the app is paused.
Specific to the Android platform.
Property Descriptions
---------------------
### [MultiplayerAPI](class_multiplayerapi#class-multiplayerapi) custom\_multiplayer
| | |
| --- | --- |
| *Setter* | set\_custom\_multiplayer(value) |
| *Getter* | get\_custom\_multiplayer() |
The override to the default [MultiplayerAPI](class_multiplayerapi#class-multiplayerapi). Set to `null` to use the default [SceneTree](class_scenetree#class-scenetree) one.
### [String](class_string#class-string) filename
| | |
| --- | --- |
| *Setter* | set\_filename(value) |
| *Getter* | get\_filename() |
If a scene is instantiated from a file, its topmost node contains the absolute file path from which it was loaded in [filename](#class-node-property-filename) (e.g. `res://levels/1.tscn`). Otherwise, [filename](#class-node-property-filename) is set to an empty string.
### [MultiplayerAPI](class_multiplayerapi#class-multiplayerapi) multiplayer
| | |
| --- | --- |
| *Getter* | get\_multiplayer() |
The [MultiplayerAPI](class_multiplayerapi#class-multiplayerapi) instance associated with this node. Either the [custom\_multiplayer](#class-node-property-custom-multiplayer), or the default SceneTree one (if inside tree).
### [String](class_string#class-string) name
| | |
| --- | --- |
| *Setter* | set\_name(value) |
| *Getter* | get\_name() |
The name of the node. This name is unique among the siblings (other child nodes from the same parent). When set to an existing name, the node will be automatically renamed.
**Note:** Auto-generated names might include the `@` character, which is reserved for unique names when using [add\_child](#class-node-method-add-child). When setting the name manually, any `@` will be removed.
### [Node](#class-node) owner
| | |
| --- | --- |
| *Setter* | set\_owner(value) |
| *Getter* | get\_owner() |
The node owner. A node can have any other node as owner (as long as it is a valid parent, grandparent, etc. ascending in the tree). When saving a node (using [PackedScene](class_packedscene#class-packedscene)), all the nodes it owns will be saved with it. This allows for the creation of complex [SceneTree](class_scenetree#class-scenetree)s, with instancing and subinstancing.
**Note:** If you want a child to be persisted to a [PackedScene](class_packedscene#class-packedscene), you must set [owner](#class-node-property-owner) in addition to calling [add\_child](#class-node-method-add-child). This is typically relevant for [tool scripts](https://docs.godotengine.org/en/3.5/tutorials/plugins/running_code_in_the_editor.html) and [editor plugins](https://docs.godotengine.org/en/3.5/tutorials/plugins/editor/index.html). If [add\_child](#class-node-method-add-child) is called without setting [owner](#class-node-property-owner), the newly added `Node` will not be visible in the scene tree, though it will be visible in the 2D/3D view.
### [PauseMode](#enum-node-pausemode) pause\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_pause\_mode(value) |
| *Getter* | get\_pause\_mode() |
Pause mode. How the node will behave if the [SceneTree](class_scenetree#class-scenetree) is paused.
### [PhysicsInterpolationMode](#enum-node-physicsinterpolationmode) physics\_interpolation\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_physics\_interpolation\_mode(value) |
| *Getter* | get\_physics\_interpolation\_mode() |
Allows enabling or disabling physics interpolation per node, offering a finer grain of control than turning physics interpolation on and off globally.
**Note:** This can be especially useful for [Camera](class_camera#class-camera)s, where custom interpolation can sometimes give superior results.
### [int](class_int#class-int) process\_priority
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_process\_priority(value) |
| *Getter* | get\_process\_priority() |
The node's priority in the execution order of the enabled processing callbacks (i.e. [NOTIFICATION\_PROCESS](#class-node-constant-notification-process), [NOTIFICATION\_PHYSICS\_PROCESS](#class-node-constant-notification-physics-process) and their internal counterparts). Nodes whose process priority value is *lower* will have their processing callbacks executed first.
### [bool](class_bool#class-bool) unique\_name\_in\_owner
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_unique\_name\_in\_owner(value) |
| *Getter* | is\_unique\_name\_in\_owner() |
Sets this node's name as a unique name in its [owner](#class-node-property-owner). This allows the node to be accessed as `%Name` instead of the full path, from any node within that scene.
If another node with the same owner already had that name declared as unique, that other node's name will no longer be set as having a unique name.
Method Descriptions
-------------------
### void \_enter\_tree ( ) virtual
Called when the node enters the [SceneTree](class_scenetree#class-scenetree) (e.g. upon instancing, scene changing, or after calling [add\_child](#class-node-method-add-child) in a script). If the node has children, its [\_enter\_tree](#class-node-method-enter-tree) callback will be called first, and then that of the children.
Corresponds to the [NOTIFICATION\_ENTER\_TREE](#class-node-constant-notification-enter-tree) notification in [Object.\_notification](class_object#class-object-method-notification).
### void \_exit\_tree ( ) virtual
Called when the node is about to leave the [SceneTree](class_scenetree#class-scenetree) (e.g. upon freeing, scene changing, or after calling [remove\_child](#class-node-method-remove-child) in a script). If the node has children, its [\_exit\_tree](#class-node-method-exit-tree) callback will be called last, after all its children have left the tree.
Corresponds to the [NOTIFICATION\_EXIT\_TREE](#class-node-constant-notification-exit-tree) notification in [Object.\_notification](class_object#class-object-method-notification) and signal [tree\_exiting](#class-node-signal-tree-exiting). To get notified when the node has already left the active tree, connect to the [tree\_exited](#class-node-signal-tree-exited).
### [String](class_string#class-string) \_get\_configuration\_warning ( ) virtual
The string returned from this method is displayed as a warning in the Scene Dock if the script that overrides it is a `tool` script.
Returning an empty string produces no warning.
Call [update\_configuration\_warning](#class-node-method-update-configuration-warning) when the warning needs to be updated for this node.
### void \_input ( [InputEvent](class_inputevent#class-inputevent) event ) virtual
Called when there is an input event. The input event propagates up through the node tree until a node consumes it.
It is only called if input processing is enabled, which is done automatically if this method is overridden, and can be toggled with [set\_process\_input](#class-node-method-set-process-input).
To consume the input event and stop it propagating further to other nodes, [SceneTree.set\_input\_as\_handled](class_scenetree#class-scenetree-method-set-input-as-handled) can be called.
For gameplay input, [\_unhandled\_input](#class-node-method-unhandled-input) and [\_unhandled\_key\_input](#class-node-method-unhandled-key-input) are usually a better fit as they allow the GUI to intercept the events first.
**Note:** This method is only called if the node is present in the scene tree (i.e. if it's not an orphan).
### void \_physics\_process ( [float](class_float#class-float) delta ) virtual
Called during the physics processing step of the main loop. Physics processing means that the frame rate is synced to the physics, i.e. the `delta` variable should be constant. `delta` is in seconds.
It is only called if physics processing is enabled, which is done automatically if this method is overridden, and can be toggled with [set\_physics\_process](#class-node-method-set-physics-process).
Corresponds to the [NOTIFICATION\_PHYSICS\_PROCESS](#class-node-constant-notification-physics-process) notification in [Object.\_notification](class_object#class-object-method-notification).
**Note:** This method is only called if the node is present in the scene tree (i.e. if it's not an orphan).
### void \_process ( [float](class_float#class-float) delta ) virtual
Called during the processing step of the main loop. Processing happens at every frame and as fast as possible, so the `delta` time since the previous frame is not constant. `delta` is in seconds.
It is only called if processing is enabled, which is done automatically if this method is overridden, and can be toggled with [set\_process](#class-node-method-set-process).
Corresponds to the [NOTIFICATION\_PROCESS](#class-node-constant-notification-process) notification in [Object.\_notification](class_object#class-object-method-notification).
**Note:** This method is only called if the node is present in the scene tree (i.e. if it's not an orphan).
### void \_ready ( ) virtual
Called when the node is "ready", i.e. when both the node and its children have entered the scene tree. If the node has children, their [\_ready](#class-node-method-ready) callbacks get triggered first, and the parent node will receive the ready notification afterwards.
Corresponds to the [NOTIFICATION\_READY](#class-node-constant-notification-ready) notification in [Object.\_notification](class_object#class-object-method-notification). See also the `onready` keyword for variables.
Usually used for initialization. For even earlier initialization, [Object.\_init](class_object#class-object-method-init) may be used. See also [\_enter\_tree](#class-node-method-enter-tree).
**Note:** [\_ready](#class-node-method-ready) may be called only once for each node. After removing a node from the scene tree and adding it again, `_ready` will not be called a second time. This can be bypassed by requesting another call with [request\_ready](#class-node-method-request-ready), which may be called anywhere before adding the node again.
### void \_unhandled\_input ( [InputEvent](class_inputevent#class-inputevent) event ) virtual
Called when an [InputEvent](class_inputevent#class-inputevent) hasn't been consumed by [\_input](#class-node-method-input) or any GUI [Control](class_control#class-control) item. The input event propagates up through the node tree until a node consumes it.
It is only called if unhandled input processing is enabled, which is done automatically if this method is overridden, and can be toggled with [set\_process\_unhandled\_input](#class-node-method-set-process-unhandled-input).
To consume the input event and stop it propagating further to other nodes, [SceneTree.set\_input\_as\_handled](class_scenetree#class-scenetree-method-set-input-as-handled) can be called.
For gameplay input, this and [\_unhandled\_key\_input](#class-node-method-unhandled-key-input) are usually a better fit than [\_input](#class-node-method-input) as they allow the GUI to intercept the events first.
**Note:** This method is only called if the node is present in the scene tree (i.e. if it's not an orphan).
### void \_unhandled\_key\_input ( [InputEventKey](class_inputeventkey#class-inputeventkey) event ) virtual
Called when an [InputEventKey](class_inputeventkey#class-inputeventkey) hasn't been consumed by [\_input](#class-node-method-input) or any GUI [Control](class_control#class-control) item. The input event propagates up through the node tree until a node consumes it.
It is only called if unhandled key input processing is enabled, which is done automatically if this method is overridden, and can be toggled with [set\_process\_unhandled\_key\_input](#class-node-method-set-process-unhandled-key-input).
To consume the input event and stop it propagating further to other nodes, [SceneTree.set\_input\_as\_handled](class_scenetree#class-scenetree-method-set-input-as-handled) can be called.
For gameplay input, this and [\_unhandled\_input](#class-node-method-unhandled-input) are usually a better fit than [\_input](#class-node-method-input) as they allow the GUI to intercept the events first.
**Note:** This method is only called if the node is present in the scene tree (i.e. if it's not an orphan).
### void add\_child ( [Node](#class-node) node, [bool](class_bool#class-bool) legible\_unique\_name=false )
Adds a child node. Nodes can have any number of children, but every child must have a unique name. Child nodes are automatically deleted when the parent node is deleted, so an entire scene can be removed by deleting its topmost node.
If `legible_unique_name` is `true`, the child node will have a human-readable name based on the name of the node being instanced instead of its type.
**Note:** If the child node already has a parent, the function will fail. Use [remove\_child](#class-node-method-remove-child) first to remove the node from its current parent. For example:
```
if child_node.get_parent():
child_node.get_parent().remove_child(child_node)
add_child(child_node)
```
**Note:** If you want a child to be persisted to a [PackedScene](class_packedscene#class-packedscene), you must set [owner](#class-node-property-owner) in addition to calling [add\_child](#class-node-method-add-child). This is typically relevant for [tool scripts](https://docs.godotengine.org/en/3.5/tutorials/plugins/running_code_in_the_editor.html) and [editor plugins](https://docs.godotengine.org/en/3.5/tutorials/plugins/editor/index.html). If [add\_child](#class-node-method-add-child) is called without setting [owner](#class-node-property-owner), the newly added `Node` will not be visible in the scene tree, though it will be visible in the 2D/3D view.
### void add\_child\_below\_node ( [Node](#class-node) node, [Node](#class-node) child\_node, [bool](class_bool#class-bool) legible\_unique\_name=false )
Adds `child_node` as a child. The child is placed below the given `node` in the list of children.
If `legible_unique_name` is `true`, the child node will have a human-readable name based on the name of the node being instanced instead of its type.
### void add\_to\_group ( [String](class_string#class-string) group, [bool](class_bool#class-bool) persistent=false )
Adds the node to a group. Groups are helpers to name and organize a subset of nodes, for example "enemies" or "collectables". A node can be in any number of groups. Nodes can be assigned a group at any time, but will not be added until they are inside the scene tree (see [is\_inside\_tree](#class-node-method-is-inside-tree)). See notes in the description, and the group methods in [SceneTree](class_scenetree#class-scenetree).
The `persistent` option is used when packing node to [PackedScene](class_packedscene#class-packedscene) and saving to file. Non-persistent groups aren't stored.
**Note:** For performance reasons, the order of node groups is *not* guaranteed. The order of node groups should not be relied upon as it can vary across project runs.
### [bool](class_bool#class-bool) can\_process ( ) const
Returns `true` if the node can process while the scene tree is paused (see [pause\_mode](#class-node-property-pause-mode)). Always returns `true` if the scene tree is not paused, and `false` if the node is not in the tree.
### [SceneTreeTween](class_scenetreetween#class-scenetreetween) create\_tween ( )
Creates a new [SceneTreeTween](class_scenetreetween#class-scenetreetween) and binds it to this node. This is equivalent of doing:
```
get_tree().create_tween().bind_node(self)
```
### [Node](#class-node) duplicate ( [int](class_int#class-int) flags=15 ) const
Duplicates the node, returning a new node.
You can fine-tune the behavior using the `flags` (see [DuplicateFlags](#enum-node-duplicateflags)).
**Note:** It will not work properly if the node contains a script with constructor arguments (i.e. needs to supply arguments to [Object.\_init](class_object#class-object-method-init) method). In that case, the node will be duplicated without a script.
### [Node](#class-node) find\_node ( [String](class_string#class-string) mask, [bool](class_bool#class-bool) recursive=true, [bool](class_bool#class-bool) owned=true ) const
Finds a descendant of this node whose name matches `mask` as in [String.match](class_string#class-string-method-match) (i.e. case-sensitive, but `"*"` matches zero or more characters and `"?"` matches any single character except `"."`). Returns `null` if no matching `Node` is found.
**Note:** It does not match against the full path, just against individual node names.
If `owned` is `true`, this method only finds nodes whose owner is this node. This is especially important for scenes instantiated through a script, because those scenes don't have an owner.
**Note:** As this method walks through all the descendants of the node, it is the slowest way to get a reference to another node. Whenever possible, consider using [get\_node](#class-node-method-get-node) instead. To avoid using [find\_node](#class-node-method-find-node) too often, consider caching the node reference into a variable.
### [Node](#class-node) find\_parent ( [String](class_string#class-string) mask ) const
Finds the first parent of the current node whose name matches `mask` as in [String.match](class_string#class-string-method-match) (i.e. case-sensitive, but `"*"` matches zero or more characters and `"?"` matches any single character except `"."`).
**Note:** It does not match against the full path, just against individual node names.
**Note:** As this method walks upwards in the scene tree, it can be slow in large, deeply nested scene trees. Whenever possible, consider using [get\_node](#class-node-method-get-node) instead. To avoid using [find\_parent](#class-node-method-find-parent) too often, consider caching the node reference into a variable.
### [Node](#class-node) get\_child ( [int](class_int#class-int) idx ) const
Returns a child node by its index (see [get\_child\_count](#class-node-method-get-child-count)). This method is often used for iterating all children of a node.
To access a child node via its name, use [get\_node](#class-node-method-get-node).
### [int](class_int#class-int) get\_child\_count ( ) const
Returns the number of child nodes.
### [Array](class_array#class-array) get\_children ( ) const
Returns an array of references to node's children.
### [Array](class_array#class-array) get\_groups ( ) const
Returns an array listing the groups that the node is a member of.
**Note:** For performance reasons, the order of node groups is *not* guaranteed. The order of node groups should not be relied upon as it can vary across project runs.
**Note:** The engine uses some group names internally (all starting with an underscore). To avoid conflicts with internal groups, do not add custom groups whose name starts with an underscore. To exclude internal groups while looping over [get\_groups](#class-node-method-get-groups), use the following snippet:
```
# Stores the node's non-internal groups only (as an array of Strings).
var non_internal_groups = []
for group in get_groups():
if not group.begins_with("_"):
non_internal_groups.push_back(group)
```
### [int](class_int#class-int) get\_index ( ) const
Returns the node's index, i.e. its position among the siblings of its parent.
### [int](class_int#class-int) get\_network\_master ( ) const
Returns the peer ID of the network master for this node. See [set\_network\_master](#class-node-method-set-network-master).
### [Node](#class-node) get\_node ( [NodePath](class_nodepath#class-nodepath) path ) const
Fetches a node. The [NodePath](class_nodepath#class-nodepath) can be either a relative path (from the current node) or an absolute path (in the scene tree) to a node. If the path does not exist, `null` is returned and an error is logged. Attempts to access methods on the return value will result in an "Attempt to call <method> on a null instance." error.
**Note:** Fetching absolute paths only works when the node is inside the scene tree (see [is\_inside\_tree](#class-node-method-is-inside-tree)).
**Example:** Assume your current node is Character and the following tree:
```
/root
/root/Character
/root/Character/Sword
/root/Character/Backpack/Dagger
/root/MyGame
/root/Swamp/Alligator
/root/Swamp/Mosquito
/root/Swamp/Goblin
```
Possible paths are:
```
get_node("Sword")
get_node("Backpack/Dagger")
get_node("../Swamp/Alligator")
get_node("/root/MyGame")
```
### [Array](class_array#class-array) get\_node\_and\_resource ( [NodePath](class_nodepath#class-nodepath) path )
Fetches a node and one of its resources as specified by the [NodePath](class_nodepath#class-nodepath)'s subname (e.g. `Area2D/CollisionShape2D:shape`). If several nested resources are specified in the [NodePath](class_nodepath#class-nodepath), the last one will be fetched.
The return value is an array of size 3: the first index points to the `Node` (or `null` if not found), the second index points to the [Resource](class_resource#class-resource) (or `null` if not found), and the third index is the remaining [NodePath](class_nodepath#class-nodepath), if any.
For example, assuming that `Area2D/CollisionShape2D` is a valid node and that its `shape` property has been assigned a [RectangleShape2D](class_rectangleshape2d#class-rectangleshape2d) resource, one could have this kind of output:
```
print(get_node_and_resource("Area2D/CollisionShape2D")) # [[CollisionShape2D:1161], Null, ]
print(get_node_and_resource("Area2D/CollisionShape2D:shape")) # [[CollisionShape2D:1161], [RectangleShape2D:1156], ]
print(get_node_and_resource("Area2D/CollisionShape2D:shape:extents")) # [[CollisionShape2D:1161], [RectangleShape2D:1156], :extents]
```
### [Node](#class-node) get\_node\_or\_null ( [NodePath](class_nodepath#class-nodepath) path ) const
Similar to [get\_node](#class-node-method-get-node), but does not log an error if `path` does not point to a valid `Node`.
### [Node](#class-node) get\_parent ( ) const
Returns the parent node of the current node, or `null` if the node lacks a parent.
### [NodePath](class_nodepath#class-nodepath) get\_path ( ) const
Returns the absolute path of the current node. This only works if the current node is inside the scene tree (see [is\_inside\_tree](#class-node-method-is-inside-tree)).
### [NodePath](class_nodepath#class-nodepath) get\_path\_to ( [Node](#class-node) node ) const
Returns the relative [NodePath](class_nodepath#class-nodepath) from this node to the specified `node`. Both nodes must be in the same scene or the function will fail.
### [float](class_float#class-float) get\_physics\_process\_delta\_time ( ) const
Returns the time elapsed (in seconds) since the last physics-bound frame (see [\_physics\_process](#class-node-method-physics-process)). This is always a constant value in physics processing unless the frames per second is changed via [Engine.iterations\_per\_second](class_engine#class-engine-property-iterations-per-second).
### [int](class_int#class-int) get\_position\_in\_parent ( ) const
Returns the node's order in the scene tree branch. For example, if called on the first child node the position is `0`.
### [float](class_float#class-float) get\_process\_delta\_time ( ) const
Returns the time elapsed (in seconds) since the last process callback. This value may vary from frame to frame.
### [bool](class_bool#class-bool) get\_scene\_instance\_load\_placeholder ( ) const
Returns `true` if this is an instance load placeholder. See [InstancePlaceholder](class_instanceplaceholder#class-instanceplaceholder).
### [SceneTree](class_scenetree#class-scenetree) get\_tree ( ) const
Returns the [SceneTree](class_scenetree#class-scenetree) that contains this node.
### [Viewport](class_viewport#class-viewport) get\_viewport ( ) const
Returns the node's [Viewport](class_viewport#class-viewport).
### [bool](class_bool#class-bool) has\_node ( [NodePath](class_nodepath#class-nodepath) path ) const
Returns `true` if the node that the [NodePath](class_nodepath#class-nodepath) points to exists.
### [bool](class_bool#class-bool) has\_node\_and\_resource ( [NodePath](class_nodepath#class-nodepath) path ) const
Returns `true` if the [NodePath](class_nodepath#class-nodepath) points to a valid node and its subname points to a valid resource, e.g. `Area2D/CollisionShape2D:shape`. Properties with a non-[Resource](class_resource#class-resource) type (e.g. nodes or primitive math types) are not considered resources.
### [bool](class_bool#class-bool) is\_a\_parent\_of ( [Node](#class-node) node ) const
Returns `true` if the given node is a direct or indirect child of the current node.
### [bool](class_bool#class-bool) is\_displayed\_folded ( ) const
Returns `true` if the node is folded (collapsed) in the Scene dock.
### [bool](class_bool#class-bool) is\_greater\_than ( [Node](#class-node) node ) const
Returns `true` if the given node occurs later in the scene hierarchy than the current node.
### [bool](class_bool#class-bool) is\_in\_group ( [String](class_string#class-string) group ) const
Returns `true` if this node is in the specified group. See notes in the description, and the group methods in [SceneTree](class_scenetree#class-scenetree).
### [bool](class_bool#class-bool) is\_inside\_tree ( ) const
Returns `true` if this node is currently inside a [SceneTree](class_scenetree#class-scenetree).
### [bool](class_bool#class-bool) is\_network\_master ( ) const
Returns `true` if the local system is the master of this node.
### [bool](class_bool#class-bool) is\_physics\_interpolated ( ) const
Returns `true` if the physics interpolated flag is set for this Node (see [physics\_interpolation\_mode](#class-node-property-physics-interpolation-mode)).
**Note:** Interpolation will only be active if both the flag is set **and** physics interpolation is enabled within the [SceneTree](class_scenetree#class-scenetree). This can be tested using [is\_physics\_interpolated\_and\_enabled](#class-node-method-is-physics-interpolated-and-enabled).
### [bool](class_bool#class-bool) is\_physics\_interpolated\_and\_enabled ( ) const
Returns `true` if physics interpolation is enabled (see [physics\_interpolation\_mode](#class-node-property-physics-interpolation-mode)) **and** enabled in the [SceneTree](class_scenetree#class-scenetree).
This is a convenience version of [is\_physics\_interpolated](#class-node-method-is-physics-interpolated) that also checks whether physics interpolation is enabled globally.
See [SceneTree.physics\_interpolation](class_scenetree#class-scenetree-property-physics-interpolation) and [ProjectSettings.physics/common/physics\_interpolation](class_projectsettings#class-projectsettings-property-physics-common-physics-interpolation).
### [bool](class_bool#class-bool) is\_physics\_processing ( ) const
Returns `true` if physics processing is enabled (see [set\_physics\_process](#class-node-method-set-physics-process)).
### [bool](class_bool#class-bool) is\_physics\_processing\_internal ( ) const
Returns `true` if internal physics processing is enabled (see [set\_physics\_process\_internal](#class-node-method-set-physics-process-internal)).
### [bool](class_bool#class-bool) is\_processing ( ) const
Returns `true` if processing is enabled (see [set\_process](#class-node-method-set-process)).
### [bool](class_bool#class-bool) is\_processing\_input ( ) const
Returns `true` if the node is processing input (see [set\_process\_input](#class-node-method-set-process-input)).
### [bool](class_bool#class-bool) is\_processing\_internal ( ) const
Returns `true` if internal processing is enabled (see [set\_process\_internal](#class-node-method-set-process-internal)).
### [bool](class_bool#class-bool) is\_processing\_unhandled\_input ( ) const
Returns `true` if the node is processing unhandled input (see [set\_process\_unhandled\_input](#class-node-method-set-process-unhandled-input)).
### [bool](class_bool#class-bool) is\_processing\_unhandled\_key\_input ( ) const
Returns `true` if the node is processing unhandled key input (see [set\_process\_unhandled\_key\_input](#class-node-method-set-process-unhandled-key-input)).
### void move\_child ( [Node](#class-node) child\_node, [int](class_int#class-int) to\_position )
Moves a child node to a different position (order) among the other children. Since calls, signals, etc are performed by tree order, changing the order of children nodes may be useful.
### void print\_stray\_nodes ( )
Prints all stray nodes (nodes outside the [SceneTree](class_scenetree#class-scenetree)). Used for debugging. Works only in debug builds.
### void print\_tree ( )
Prints the tree to stdout. Used mainly for debugging purposes. This version displays the path relative to the current node, and is good for copy/pasting into the [get\_node](#class-node-method-get-node) function.
**Example output:**
```
TheGame
TheGame/Menu
TheGame/Menu/Label
TheGame/Menu/Camera2D
TheGame/SplashScreen
TheGame/SplashScreen/Camera2D
```
### void print\_tree\_pretty ( )
Similar to [print\_tree](#class-node-method-print-tree), this prints the tree to stdout. This version displays a more graphical representation similar to what is displayed in the scene inspector. It is useful for inspecting larger trees.
**Example output:**
```
┖╴TheGame
┠╴Menu
┃ ┠╴Label
┃ ┖╴Camera2D
┖╴SplashScreen
┖╴Camera2D
```
### void propagate\_call ( [String](class_string#class-string) method, [Array](class_array#class-array) args=[ ], [bool](class_bool#class-bool) parent\_first=false )
Calls the given method (if present) with the arguments given in `args` on this node and recursively on all its children. If the `parent_first` argument is `true`, the method will be called on the current node first, then on all its children. If `parent_first` is `false`, the children will be called first.
### void propagate\_notification ( [int](class_int#class-int) what )
Notifies the current node and all its children recursively by calling [Object.notification](class_object#id3) on all of them.
### void queue\_free ( )
Queues a node for deletion at the end of the current frame. When deleted, all of its child nodes will be deleted as well. This method ensures it's safe to delete the node, contrary to [Object.free](class_object#class-object-method-free). Use [Object.is\_queued\_for\_deletion](class_object#class-object-method-is-queued-for-deletion) to check whether a node will be deleted at the end of the frame.
**Important:** If you have a variable pointing to a node, it will *not* be assigned to `null` once the node is freed. Instead, it will point to a *previously freed instance* and you should validate it with [@GDScript.is\_instance\_valid](class_%40gdscript#class-gdscript-method-is-instance-valid) before attempting to call its methods or access its properties.
### void raise ( )
Moves this node to the bottom of parent node's children hierarchy. This is often useful in GUIs ([Control](class_control#class-control) nodes), because their order of drawing depends on their order in the tree. The top Node is drawn first, then any siblings below the top Node in the hierarchy are successively drawn on top of it. After using `raise`, a Control will be drawn on top of its siblings.
### void remove\_and\_skip ( )
Removes a node and sets all its children as children of the parent node (if it exists). All event subscriptions that pass by the removed node will be unsubscribed.
### void remove\_child ( [Node](#class-node) node )
Removes a child node. The node is NOT deleted and must be deleted manually.
**Note:** This function may set the [owner](#class-node-property-owner) of the removed Node (or its descendants) to be `null`, if that [owner](#class-node-property-owner) is no longer a parent or ancestor.
### void remove\_from\_group ( [String](class_string#class-string) group )
Removes a node from a group. See notes in the description, and the group methods in [SceneTree](class_scenetree#class-scenetree).
### void replace\_by ( [Node](#class-node) node, [bool](class_bool#class-bool) keep\_data=false )
Replaces a node in a scene by the given one. Subscriptions that pass through this node will be lost.
**Note:** The given node will become the new parent of any child nodes that the replaced node had.
**Note:** The replaced node is not automatically freed, so you either need to keep it in a variable for later use or free it using [Object.free](class_object#class-object-method-free).
### void request\_ready ( )
Requests that `_ready` be called again. Note that the method won't be called immediately, but is scheduled for when the node is added to the scene tree again (see [\_ready](#class-node-method-ready)). `_ready` is called only for the node which requested it, which means that you need to request ready for each child if you want them to call `_ready` too (in which case, `_ready` will be called in the same order as it would normally).
### void reset\_physics\_interpolation ( )
When physics interpolation is active, moving a node to a radically different transform (such as placement within a level) can result in a visible glitch as the object is rendered moving from the old to new position over the physics tick.
This glitch can be prevented by calling `reset_physics_interpolation`, which temporarily turns off interpolation until the physics tick is complete.
[NOTIFICATION\_RESET\_PHYSICS\_INTERPOLATION](#class-node-constant-notification-reset-physics-interpolation) will be received by the node and all children recursively.
**Note:** This function should be called **after** moving the node, rather than before.
### [Variant](class_variant#class-variant) rpc ( [String](class_string#class-string) method, ... ) vararg
Sends a remote procedure call request for the given `method` to peers on the network (and locally), optionally sending all additional arguments as arguments to the method called by the RPC. The call request will only be received by nodes with the same [NodePath](class_nodepath#class-nodepath), including the exact same node name. Behaviour depends on the RPC configuration for the given method, see [rpc\_config](#class-node-method-rpc-config). Methods are not exposed to RPCs by default. See also [rset](#class-node-method-rset) and [rset\_config](#class-node-method-rset-config) for properties. Returns `null`.
**Note:** You can only safely use RPCs on clients after you received the `connected_to_server` signal from the [SceneTree](class_scenetree#class-scenetree). You also need to keep track of the connection state, either by the [SceneTree](class_scenetree#class-scenetree) signals like `server_disconnected` or by checking `SceneTree.network_peer.get_connection_status() == CONNECTION_CONNECTED`.
### void rpc\_config ( [String](class_string#class-string) method, [RPCMode](class_multiplayerapi#enum-multiplayerapi-rpcmode) mode )
Changes the RPC mode for the given `method` to the given `mode`. See [RPCMode](class_multiplayerapi#enum-multiplayerapi-rpcmode). An alternative is annotating methods and properties with the corresponding keywords (`remote`, `master`, `puppet`, `remotesync`, `mastersync`, `puppetsync`). By default, methods are not exposed to networking (and RPCs). See also [rset](#class-node-method-rset) and [rset\_config](#class-node-method-rset-config) for properties.
### [Variant](class_variant#class-variant) rpc\_id ( [int](class_int#class-int) peer\_id, [String](class_string#class-string) method, ... ) vararg
Sends a [rpc](#class-node-method-rpc) to a specific peer identified by `peer_id` (see [NetworkedMultiplayerPeer.set\_target\_peer](class_networkedmultiplayerpeer#class-networkedmultiplayerpeer-method-set-target-peer)). Returns `null`.
### [Variant](class_variant#class-variant) rpc\_unreliable ( [String](class_string#class-string) method, ... ) vararg
Sends a [rpc](#class-node-method-rpc) using an unreliable protocol. Returns `null`.
### [Variant](class_variant#class-variant) rpc\_unreliable\_id ( [int](class_int#class-int) peer\_id, [String](class_string#class-string) method, ... ) vararg
Sends a [rpc](#class-node-method-rpc) to a specific peer identified by `peer_id` using an unreliable protocol (see [NetworkedMultiplayerPeer.set\_target\_peer](class_networkedmultiplayerpeer#class-networkedmultiplayerpeer-method-set-target-peer)). Returns `null`.
### void rset ( [String](class_string#class-string) property, [Variant](class_variant#class-variant) value )
Remotely changes a property's value on other peers (and locally). Behaviour depends on the RPC configuration for the given property, see [rset\_config](#class-node-method-rset-config). See also [rpc](#class-node-method-rpc) for RPCs for methods, most information applies to this method as well.
### void rset\_config ( [String](class_string#class-string) property, [RPCMode](class_multiplayerapi#enum-multiplayerapi-rpcmode) mode )
Changes the RPC mode for the given `property` to the given `mode`. See [RPCMode](class_multiplayerapi#enum-multiplayerapi-rpcmode). An alternative is annotating methods and properties with the corresponding keywords (`remote`, `master`, `puppet`, `remotesync`, `mastersync`, `puppetsync`). By default, properties are not exposed to networking (and RPCs). See also [rpc](#class-node-method-rpc) and [rpc\_config](#class-node-method-rpc-config) for methods.
### void rset\_id ( [int](class_int#class-int) peer\_id, [String](class_string#class-string) property, [Variant](class_variant#class-variant) value )
Remotely changes the property's value on a specific peer identified by `peer_id` (see [NetworkedMultiplayerPeer.set\_target\_peer](class_networkedmultiplayerpeer#class-networkedmultiplayerpeer-method-set-target-peer)).
### void rset\_unreliable ( [String](class_string#class-string) property, [Variant](class_variant#class-variant) value )
Remotely changes the property's value on other peers (and locally) using an unreliable protocol.
### void rset\_unreliable\_id ( [int](class_int#class-int) peer\_id, [String](class_string#class-string) property, [Variant](class_variant#class-variant) value )
Remotely changes property's value on a specific peer identified by `peer_id` using an unreliable protocol (see [NetworkedMultiplayerPeer.set\_target\_peer](class_networkedmultiplayerpeer#class-networkedmultiplayerpeer-method-set-target-peer)).
### void set\_display\_folded ( [bool](class_bool#class-bool) fold )
Sets the folded state of the node in the Scene dock.
### void set\_network\_master ( [int](class_int#class-int) id, [bool](class_bool#class-bool) recursive=true )
Sets the node's network master to the peer with the given peer ID. The network master is the peer that has authority over the node on the network. Useful in conjunction with the `master` and `puppet` keywords. Inherited from the parent node by default, which ultimately defaults to peer ID 1 (the server). If `recursive`, the given peer is recursively set as the master for all children of this node.
### void set\_physics\_process ( [bool](class_bool#class-bool) enable )
Enables or disables physics (i.e. fixed framerate) processing. When a node is being processed, it will receive a [NOTIFICATION\_PHYSICS\_PROCESS](#class-node-constant-notification-physics-process) at a fixed (usually 60 FPS, see [Engine.iterations\_per\_second](class_engine#class-engine-property-iterations-per-second) to change) interval (and the [\_physics\_process](#class-node-method-physics-process) callback will be called if exists). Enabled automatically if [\_physics\_process](#class-node-method-physics-process) is overridden. Any calls to this before [\_ready](#class-node-method-ready) will be ignored.
### void set\_physics\_process\_internal ( [bool](class_bool#class-bool) enable )
Enables or disables internal physics for this node. Internal physics processing happens in isolation from the normal [\_physics\_process](#class-node-method-physics-process) calls and is used by some nodes internally to guarantee proper functioning even if the node is paused or physics processing is disabled for scripting ([set\_physics\_process](#class-node-method-set-physics-process)). Only useful for advanced uses to manipulate built-in nodes' behavior.
**Warning:** Built-in Nodes rely on the internal processing for their own logic, so changing this value from your code may lead to unexpected behavior. Script access to this internal logic is provided for specific advanced uses, but is unsafe and not supported.
### void set\_process ( [bool](class_bool#class-bool) enable )
Enables or disables processing. When a node is being processed, it will receive a [NOTIFICATION\_PROCESS](#class-node-constant-notification-process) on every drawn frame (and the [\_process](#class-node-method-process) callback will be called if exists). Enabled automatically if [\_process](#class-node-method-process) is overridden. Any calls to this before [\_ready](#class-node-method-ready) will be ignored.
### void set\_process\_input ( [bool](class_bool#class-bool) enable )
Enables or disables input processing. This is not required for GUI controls! Enabled automatically if [\_input](#class-node-method-input) is overridden. Any calls to this before [\_ready](#class-node-method-ready) will be ignored.
### void set\_process\_internal ( [bool](class_bool#class-bool) enable )
Enables or disabled internal processing for this node. Internal processing happens in isolation from the normal [\_process](#class-node-method-process) calls and is used by some nodes internally to guarantee proper functioning even if the node is paused or processing is disabled for scripting ([set\_process](#class-node-method-set-process)). Only useful for advanced uses to manipulate built-in nodes' behavior.
**Warning:** Built-in Nodes rely on the internal processing for their own logic, so changing this value from your code may lead to unexpected behavior. Script access to this internal logic is provided for specific advanced uses, but is unsafe and not supported.
### void set\_process\_unhandled\_input ( [bool](class_bool#class-bool) enable )
Enables unhandled input processing. This is not required for GUI controls! It enables the node to receive all input that was not previously handled (usually by a [Control](class_control#class-control)). Enabled automatically if [\_unhandled\_input](#class-node-method-unhandled-input) is overridden. Any calls to this before [\_ready](#class-node-method-ready) will be ignored.
### void set\_process\_unhandled\_key\_input ( [bool](class_bool#class-bool) enable )
Enables unhandled key input processing. Enabled automatically if [\_unhandled\_key\_input](#class-node-method-unhandled-key-input) is overridden. Any calls to this before [\_ready](#class-node-method-ready) will be ignored.
### void set\_scene\_instance\_load\_placeholder ( [bool](class_bool#class-bool) load\_placeholder )
Sets whether this is an instance load placeholder. See [InstancePlaceholder](class_instanceplaceholder#class-instanceplaceholder).
### void update\_configuration\_warning ( )
Updates the warning displayed for this node in the Scene Dock.
Use [\_get\_configuration\_warning](#class-node-method-get-configuration-warning) to setup the warning message to display.
| programming_docs |
godot KinematicBody2D KinematicBody2D
===============
**Inherits:** [PhysicsBody2D](class_physicsbody2d#class-physicsbody2d) **<** [CollisionObject2D](class_collisionobject2d#class-collisionobject2d) **<** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Kinematic body 2D node.
Description
-----------
Kinematic bodies are special types of bodies that are meant to be user-controlled. They are not affected by physics at all; to other types of bodies, such as a character or a rigid body, these are the same as a static body. However, they have two main uses:
**Simulated motion:** When these bodies are moved manually, either from code or from an [AnimationPlayer](class_animationplayer#class-animationplayer) (with [AnimationPlayer.playback\_process\_mode](class_animationplayer#class-animationplayer-property-playback-process-mode) set to "physics"), the physics will automatically compute an estimate of their linear and angular velocity. This makes them very useful for moving platforms or other AnimationPlayer-controlled objects (like a door, a bridge that opens, etc).
**Kinematic characters:** KinematicBody2D also has an API for moving objects (the [move\_and\_collide](#class-kinematicbody2d-method-move-and-collide) and [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) methods) while performing collision tests. This makes them really useful to implement characters that collide against a world, but don't require advanced physics.
Tutorials
---------
* [Kinematic character (2D)](https://docs.godotengine.org/en/3.5/tutorials/physics/kinematic_character_2d.html)
* [Using KinematicBody2D](https://docs.godotengine.org/en/3.5/tutorials/physics/using_kinematic_body_2d.html)
* [2D Kinematic Character Demo](https://godotengine.org/asset-library/asset/113)
* [2D Platformer Demo](https://godotengine.org/asset-library/asset/120)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [collision/safe\_margin](#class-kinematicbody2d-property-collision-safe-margin) | `0.08` |
| [bool](class_bool#class-bool) | [motion/sync\_to\_physics](#class-kinematicbody2d-property-motion-sync-to-physics) | `false` |
| [MovingPlatformApplyVelocityOnLeave](#enum-kinematicbody2d-movingplatformapplyvelocityonleave) | [moving\_platform\_apply\_velocity\_on\_leave](#class-kinematicbody2d-property-moving-platform-apply-velocity-on-leave) | `0` |
Methods
-------
| | |
| --- | --- |
| [float](class_float#class-float) | [get\_floor\_angle](#class-kinematicbody2d-method-get-floor-angle) **(** [Vector2](class_vector2#class-vector2) up\_direction=Vector2( 0, -1 ) **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_floor\_normal](#class-kinematicbody2d-method-get-floor-normal) **(** **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_floor\_velocity](#class-kinematicbody2d-method-get-floor-velocity) **(** **)** const |
| [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d) | [get\_last\_slide\_collision](#class-kinematicbody2d-method-get-last-slide-collision) **(** **)** |
| [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d) | [get\_slide\_collision](#class-kinematicbody2d-method-get-slide-collision) **(** [int](class_int#class-int) slide\_idx **)** |
| [int](class_int#class-int) | [get\_slide\_count](#class-kinematicbody2d-method-get-slide-count) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_on\_ceiling](#class-kinematicbody2d-method-is-on-ceiling) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_on\_floor](#class-kinematicbody2d-method-is-on-floor) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_on\_wall](#class-kinematicbody2d-method-is-on-wall) **(** **)** const |
| [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d) | [move\_and\_collide](#class-kinematicbody2d-method-move-and-collide) **(** [Vector2](class_vector2#class-vector2) rel\_vec, [bool](class_bool#class-bool) infinite\_inertia=true, [bool](class_bool#class-bool) exclude\_raycast\_shapes=true, [bool](class_bool#class-bool) test\_only=false **)** |
| [Vector2](class_vector2#class-vector2) | [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) **(** [Vector2](class_vector2#class-vector2) linear\_velocity, [Vector2](class_vector2#class-vector2) up\_direction=Vector2( 0, 0 ), [bool](class_bool#class-bool) stop\_on\_slope=false, [int](class_int#class-int) max\_slides=4, [float](class_float#class-float) floor\_max\_angle=0.785398, [bool](class_bool#class-bool) infinite\_inertia=true **)** |
| [Vector2](class_vector2#class-vector2) | [move\_and\_slide\_with\_snap](#class-kinematicbody2d-method-move-and-slide-with-snap) **(** [Vector2](class_vector2#class-vector2) linear\_velocity, [Vector2](class_vector2#class-vector2) snap, [Vector2](class_vector2#class-vector2) up\_direction=Vector2( 0, 0 ), [bool](class_bool#class-bool) stop\_on\_slope=false, [int](class_int#class-int) max\_slides=4, [float](class_float#class-float) floor\_max\_angle=0.785398, [bool](class_bool#class-bool) infinite\_inertia=true **)** |
| [bool](class_bool#class-bool) | [test\_move](#class-kinematicbody2d-method-test-move) **(** [Transform2D](class_transform2d#class-transform2d) from, [Vector2](class_vector2#class-vector2) rel\_vec, [bool](class_bool#class-bool) infinite\_inertia=true **)** |
Enumerations
------------
enum **MovingPlatformApplyVelocityOnLeave**:
* **PLATFORM\_VEL\_ON\_LEAVE\_ALWAYS** = **0** --- Add the last platform velocity when you leave a moving platform.
* **PLATFORM\_VEL\_ON\_LEAVE\_UPWARD\_ONLY** = **1** --- Add the last platform velocity when you leave a moving platform, but any downward motion is ignored. It's useful to keep full jump height even when the platform is moving down.
* **PLATFORM\_VEL\_ON\_LEAVE\_NEVER** = **2** --- Do nothing when leaving a platform.
Property Descriptions
---------------------
### [float](class_float#class-float) collision/safe\_margin
| | |
| --- | --- |
| *Default* | `0.08` |
| *Setter* | set\_safe\_margin(value) |
| *Getter* | get\_safe\_margin() |
Extra margin used for collision recovery in motion functions (see [move\_and\_collide](#class-kinematicbody2d-method-move-and-collide), [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide), [move\_and\_slide\_with\_snap](#class-kinematicbody2d-method-move-and-slide-with-snap)).
If the body is at least this close to another body, it will consider them to be colliding and will be pushed away before performing the actual motion.
A higher value means it's more flexible for detecting collision, which helps with consistently detecting walls and floors.
A lower value forces the collision algorithm to use more exact detection, so it can be used in cases that specifically require precision, e.g at very low scale to avoid visible jittering, or for stability with a stack of kinematic bodies.
### [bool](class_bool#class-bool) motion/sync\_to\_physics
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_sync\_to\_physics(value) |
| *Getter* | is\_sync\_to\_physics\_enabled() |
If `true`, the body's movement will be synchronized to the physics frame. This is useful when animating movement via [AnimationPlayer](class_animationplayer#class-animationplayer), for example on moving platforms. Do **not** use together with [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) or [move\_and\_collide](#class-kinematicbody2d-method-move-and-collide) functions.
### [MovingPlatformApplyVelocityOnLeave](#enum-kinematicbody2d-movingplatformapplyvelocityonleave) moving\_platform\_apply\_velocity\_on\_leave
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_moving\_platform\_apply\_velocity\_on\_leave(value) |
| *Getter* | get\_moving\_platform\_apply\_velocity\_on\_leave() |
Sets the behavior to apply when you leave a moving platform. By default, to be physically accurate, when you leave the last platform velocity is applied. See [MovingPlatformApplyVelocityOnLeave](#enum-kinematicbody2d-movingplatformapplyvelocityonleave) constants for available behavior.
Method Descriptions
-------------------
### [float](class_float#class-float) get\_floor\_angle ( [Vector2](class_vector2#class-vector2) up\_direction=Vector2( 0, -1 ) ) const
Returns the floor's collision angle at the last collision point according to `up_direction`, which is `Vector2.UP` by default. This value is always positive and only valid after calling [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) and when [is\_on\_floor](#class-kinematicbody2d-method-is-on-floor) returns `true`.
### [Vector2](class_vector2#class-vector2) get\_floor\_normal ( ) const
Returns the surface normal of the floor at the last collision point. Only valid after calling [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) or [move\_and\_slide\_with\_snap](#class-kinematicbody2d-method-move-and-slide-with-snap) and when [is\_on\_floor](#class-kinematicbody2d-method-is-on-floor) returns `true`.
### [Vector2](class_vector2#class-vector2) get\_floor\_velocity ( ) const
Returns the linear velocity of the floor at the last collision point. Only valid after calling [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) or [move\_and\_slide\_with\_snap](#class-kinematicbody2d-method-move-and-slide-with-snap) and when [is\_on\_floor](#class-kinematicbody2d-method-is-on-floor) returns `true`.
### [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d) get\_last\_slide\_collision ( )
Returns a [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d), which contains information about the latest collision that occurred during the last call to [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide).
### [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d) get\_slide\_collision ( [int](class_int#class-int) slide\_idx )
Returns a [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d), which contains information about a collision that occurred during the last call to [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) or [move\_and\_slide\_with\_snap](#class-kinematicbody2d-method-move-and-slide-with-snap). Since the body can collide several times in a single call to [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide), you must specify the index of the collision in the range 0 to ([get\_slide\_count](#class-kinematicbody2d-method-get-slide-count) - 1).
**Example usage:**
```
for i in get_slide_count():
var collision = get_slide_collision(i)
print("Collided with: ", collision.collider.name)
```
### [int](class_int#class-int) get\_slide\_count ( ) const
Returns the number of times the body collided and changed direction during the last call to [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) or [move\_and\_slide\_with\_snap](#class-kinematicbody2d-method-move-and-slide-with-snap).
### [bool](class_bool#class-bool) is\_on\_ceiling ( ) const
Returns `true` if the body collided with the ceiling on the last call of [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) or [move\_and\_slide\_with\_snap](#class-kinematicbody2d-method-move-and-slide-with-snap). Otherwise, returns `false`.
### [bool](class_bool#class-bool) is\_on\_floor ( ) const
Returns `true` if the body collided with the floor on the last call of [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) or [move\_and\_slide\_with\_snap](#class-kinematicbody2d-method-move-and-slide-with-snap). Otherwise, returns `false`.
### [bool](class_bool#class-bool) is\_on\_wall ( ) const
Returns `true` if the body collided with a wall on the last call of [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) or [move\_and\_slide\_with\_snap](#class-kinematicbody2d-method-move-and-slide-with-snap). Otherwise, returns `false`.
### [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d) move\_and\_collide ( [Vector2](class_vector2#class-vector2) rel\_vec, [bool](class_bool#class-bool) infinite\_inertia=true, [bool](class_bool#class-bool) exclude\_raycast\_shapes=true, [bool](class_bool#class-bool) test\_only=false )
Moves the body along the vector `rel_vec`. The body will stop if it collides. Returns a [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d), which contains information about the collision when stopped, or when touching another body along the motion.
If `test_only` is `true`, the body does not move but the would-be collision information is given.
### [Vector2](class_vector2#class-vector2) move\_and\_slide ( [Vector2](class_vector2#class-vector2) linear\_velocity, [Vector2](class_vector2#class-vector2) up\_direction=Vector2( 0, 0 ), [bool](class_bool#class-bool) stop\_on\_slope=false, [int](class_int#class-int) max\_slides=4, [float](class_float#class-float) floor\_max\_angle=0.785398, [bool](class_bool#class-bool) infinite\_inertia=true )
Moves the body along a vector. If the body collides with another, it will slide along the other body rather than stop immediately. If the other body is a `KinematicBody2D` or [RigidBody2D](class_rigidbody2d#class-rigidbody2d), it will also be affected by the motion of the other body. You can use this to make moving and rotating platforms, or to make nodes push other nodes.
This method should be used in [Node.\_physics\_process](class_node#class-node-method-physics-process) (or in a method called by [Node.\_physics\_process](class_node#class-node-method-physics-process)), as it uses the physics step's `delta` value automatically in calculations. Otherwise, the simulation will run at an incorrect speed.
`linear_velocity` is the velocity vector in pixels per second. Unlike in [move\_and\_collide](#class-kinematicbody2d-method-move-and-collide), you should *not* multiply it by `delta` — the physics engine handles applying the velocity.
`up_direction` is the up direction, used to determine what is a wall and what is a floor or a ceiling. If set to the default value of `Vector2(0, 0)`, everything is considered a wall. This is useful for topdown games.
If `stop_on_slope` is `true`, body will not slide on slopes when you include gravity in `linear_velocity` and the body is standing still.
If the body collides, it will change direction a maximum of `max_slides` times before it stops.
`floor_max_angle` is the maximum angle (in radians) where a slope is still considered a floor (or a ceiling), rather than a wall. The default value equals 45 degrees.
If `infinite_inertia` is `true`, body will be able to push [RigidBody2D](class_rigidbody2d#class-rigidbody2d) nodes, but it won't also detect any collisions with them. If `false`, it will interact with [RigidBody2D](class_rigidbody2d#class-rigidbody2d) nodes like with [StaticBody2D](class_staticbody2d#class-staticbody2d).
Returns the `linear_velocity` vector, rotated and/or scaled if a slide collision occurred. To get detailed information about collisions that occurred, use [get\_slide\_collision](#class-kinematicbody2d-method-get-slide-collision).
When the body touches a moving platform, the platform's velocity is automatically added to the body motion. If a collision occurs due to the platform's motion, it will always be first in the slide collisions.
### [Vector2](class_vector2#class-vector2) move\_and\_slide\_with\_snap ( [Vector2](class_vector2#class-vector2) linear\_velocity, [Vector2](class_vector2#class-vector2) snap, [Vector2](class_vector2#class-vector2) up\_direction=Vector2( 0, 0 ), [bool](class_bool#class-bool) stop\_on\_slope=false, [int](class_int#class-int) max\_slides=4, [float](class_float#class-float) floor\_max\_angle=0.785398, [bool](class_bool#class-bool) infinite\_inertia=true )
Moves the body while keeping it attached to slopes. Similar to [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide).
As long as the `snap` vector is in contact with the ground, the body will remain attached to the surface. This means you must disable snap in order to jump, for example. You can do this by setting `snap` to `(0, 0)` or by using [move\_and\_slide](#class-kinematicbody2d-method-move-and-slide) instead.
### [bool](class_bool#class-bool) test\_move ( [Transform2D](class_transform2d#class-transform2d) from, [Vector2](class_vector2#class-vector2) rel\_vec, [bool](class_bool#class-bool) infinite\_inertia=true )
Checks for collisions without moving the body. Virtually sets the node's position, scale and rotation to that of the given [Transform2D](class_transform2d#class-transform2d), then tries to move the body along the vector `rel_vec`. Returns `true` if a collision would stop the body from moving along the whole path.
Use [move\_and\_collide](#class-kinematicbody2d-method-move-and-collide) instead for detecting collision with touching bodies.
godot AudioEffectFilter AudioEffectFilter
=================
**Inherits:** [AudioEffect](class_audioeffect#class-audioeffect) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [AudioEffectBandLimitFilter](class_audioeffectbandlimitfilter#class-audioeffectbandlimitfilter), [AudioEffectBandPassFilter](class_audioeffectbandpassfilter#class-audioeffectbandpassfilter), [AudioEffectHighPassFilter](class_audioeffecthighpassfilter#class-audioeffecthighpassfilter), [AudioEffectHighShelfFilter](class_audioeffecthighshelffilter#class-audioeffecthighshelffilter), [AudioEffectLowPassFilter](class_audioeffectlowpassfilter#class-audioeffectlowpassfilter), [AudioEffectLowShelfFilter](class_audioeffectlowshelffilter#class-audioeffectlowshelffilter), [AudioEffectNotchFilter](class_audioeffectnotchfilter#class-audioeffectnotchfilter)
Adds a filter to the audio bus.
Description
-----------
Allows frequencies other than the [cutoff\_hz](#class-audioeffectfilter-property-cutoff-hz) to pass.
Tutorials
---------
* [Audio buses](https://docs.godotengine.org/en/3.5/tutorials/audio/audio_buses.html)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [cutoff\_hz](#class-audioeffectfilter-property-cutoff-hz) | `2000.0` |
| [FilterDB](#enum-audioeffectfilter-filterdb) | [db](#class-audioeffectfilter-property-db) | `0` |
| [float](class_float#class-float) | [gain](#class-audioeffectfilter-property-gain) | `1.0` |
| [float](class_float#class-float) | [resonance](#class-audioeffectfilter-property-resonance) | `0.5` |
Enumerations
------------
enum **FilterDB**:
* **FILTER\_6DB** = **0**
* **FILTER\_12DB** = **1**
* **FILTER\_18DB** = **2**
* **FILTER\_24DB** = **3**
Property Descriptions
---------------------
### [float](class_float#class-float) cutoff\_hz
| | |
| --- | --- |
| *Default* | `2000.0` |
| *Setter* | set\_cutoff(value) |
| *Getter* | get\_cutoff() |
Threshold frequency for the filter, in Hz.
### [FilterDB](#enum-audioeffectfilter-filterdb) db
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_db(value) |
| *Getter* | get\_db() |
### [float](class_float#class-float) gain
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_gain(value) |
| *Getter* | get\_gain() |
Gain amount of the frequencies after the filter.
### [float](class_float#class-float) resonance
| | |
| --- | --- |
| *Default* | `0.5` |
| *Setter* | set\_resonance(value) |
| *Getter* | get\_resonance() |
Amount of boost in the frequency range near the cutoff frequency.
godot CullInstance CullInstance
============
**Inherits:** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
**Inherited By:** [VisibilityNotifier](class_visibilitynotifier#class-visibilitynotifier), [VisualInstance](class_visualinstance#class-visualinstance)
Parent of all nodes that can be culled by the Portal system.
Description
-----------
Provides common functionality to nodes that can be culled by the [Portal](class_portal#class-portal) system.
`Static` and `Dynamic` objects are the most efficiently managed objects in the system, but there are some caveats. They are expected to be present initially when [Room](class_room#class-room)s are converted using the [RoomManager](class_roommanager#class-roommanager) `rooms_convert` function, and their lifetime should be the same as the game level (i.e. present until you call `rooms_clear` on the [RoomManager](class_roommanager#class-roommanager). Although you shouldn't create / delete these objects during gameplay, you can manage their visibility with the standard `hide` and `show` commands.
`Roaming` objects on the other hand, require extra processing to keep track of which [Room](class_room#class-room) they are within. This enables them to be culled effectively, wherever they are.
`Global` objects are not culled by the portal system, and use view frustum culling only.
Objects that are not `Static` or `Dynamic` can be freely created and deleted during the lifetime of the game level.
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [allow\_merging](#class-cullinstance-property-allow-merging) | `true` |
| [int](class_int#class-int) | [autoplace\_priority](#class-cullinstance-property-autoplace-priority) | `0` |
| [bool](class_bool#class-bool) | [include\_in\_bound](#class-cullinstance-property-include-in-bound) | `true` |
| [PortalMode](#enum-cullinstance-portalmode) | [portal\_mode](#class-cullinstance-property-portal-mode) | `0` |
Enumerations
------------
enum **PortalMode**:
* **PORTAL\_MODE\_STATIC** = **0** --- Use for instances within [Room](class_room#class-room)s that will **not move** - e.g. walls, floors.
**Note:** If you attempt to delete a `PORTAL_MODE_STATIC` instance while the room graph is loaded (converted), it will unload the room graph and deactivate portal culling. This is because the **room graph** data has been invalidated. You will need to reconvert the rooms using the [RoomManager](class_roommanager#class-roommanager) to activate the system again.
* **PORTAL\_MODE\_DYNAMIC** = **1** --- Use for instances within rooms that will move but **not change room** - e.g. moving platforms.
**Note:** If you attempt to delete a `PORTAL_MODE_DYNAMIC` instance while the room graph is loaded (converted), it will unload the room graph and deactivate portal culling. This is because the **room graph** data has been invalidated. You will need to reconvert the rooms using the [RoomManager](class_roommanager#class-roommanager) to activate the system again.
* **PORTAL\_MODE\_ROAMING** = **2** --- Use for instances that will move **between** [Room](class_room#class-room)s - e.g. players.
* **PORTAL\_MODE\_GLOBAL** = **3** --- Use for instances that will be frustum culled only - e.g. first person weapon, debug.
* **PORTAL\_MODE\_IGNORE** = **4** --- Use for instances that will not be shown at all - e.g. **manual room bounds** (specified by prefix *'Bound\_'*).
Property Descriptions
---------------------
### [bool](class_bool#class-bool) allow\_merging
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_allow\_merging(value) |
| *Getter* | get\_allow\_merging() |
This allows fine control over the mesh merging feature in the [RoomManager](class_roommanager#class-roommanager).
Setting this option to `false` can be used to prevent an instance being merged.
### [int](class_int#class-int) autoplace\_priority
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_portal\_autoplace\_priority(value) |
| *Getter* | get\_portal\_autoplace\_priority() |
When set to `0`, `CullInstance`s will be autoplaced in the [Room](class_room#class-room) with the highest priority.
When set to a value other than `0`, the system will attempt to autoplace in a [Room](class_room#class-room) with the `autoplace_priority`, if it is present.
This can be used to control autoplacement of building exteriors in an outer [RoomGroup](class_roomgroup#class-roomgroup).
### [bool](class_bool#class-bool) include\_in\_bound
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_include\_in\_bound(value) |
| *Getter* | get\_include\_in\_bound() |
When a manual bound has not been explicitly specified for a [Room](class_room#class-room), the convex hull bound will be estimated from the geometry of the objects within the room. This setting determines whether the geometry of an object is included in this estimate of the room bound.
**Note:** This setting is only relevant when the object is set to `PORTAL_MODE_STATIC` or `PORTAL_MODE_DYNAMIC`, and for [Portal](class_portal#class-portal)s.
### [PortalMode](#enum-cullinstance-portalmode) portal\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_portal\_mode(value) |
| *Getter* | get\_portal\_mode() |
When using [Room](class_room#class-room)s and [Portal](class_portal#class-portal)s, this specifies how the `CullInstance` is processed in the system.
| programming_docs |
godot PacketPeerStream PacketPeerStream
================
**Inherits:** [PacketPeer](class_packetpeer#class-packetpeer) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Wrapper to use a PacketPeer over a StreamPeer.
Description
-----------
PacketStreamPeer provides a wrapper for working using packets over a stream. This allows for using packet based code with StreamPeers. PacketPeerStream implements a custom protocol over the StreamPeer, so the user should not read or write to the wrapped StreamPeer directly.
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [input\_buffer\_max\_size](#class-packetpeerstream-property-input-buffer-max-size) | `65532` |
| [int](class_int#class-int) | [output\_buffer\_max\_size](#class-packetpeerstream-property-output-buffer-max-size) | `65532` |
| [StreamPeer](class_streampeer#class-streampeer) | [stream\_peer](#class-packetpeerstream-property-stream-peer) | |
Property Descriptions
---------------------
### [int](class_int#class-int) input\_buffer\_max\_size
| | |
| --- | --- |
| *Default* | `65532` |
| *Setter* | set\_input\_buffer\_max\_size(value) |
| *Getter* | get\_input\_buffer\_max\_size() |
### [int](class_int#class-int) output\_buffer\_max\_size
| | |
| --- | --- |
| *Default* | `65532` |
| *Setter* | set\_output\_buffer\_max\_size(value) |
| *Getter* | get\_output\_buffer\_max\_size() |
### [StreamPeer](class_streampeer#class-streampeer) stream\_peer
| | |
| --- | --- |
| *Setter* | set\_stream\_peer(value) |
| *Getter* | get\_stream\_peer() |
The wrapped [StreamPeer](class_streampeer#class-streampeer) object.
godot InputEventKey InputEventKey
=============
**Inherits:** [InputEventWithModifiers](class_inputeventwithmodifiers#class-inputeventwithmodifiers) **<** [InputEvent](class_inputevent#class-inputevent) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Input event type for keyboard events.
Description
-----------
Stores key presses on the keyboard. Supports key presses, key releases and [echo](#class-inputeventkey-property-echo) events.
Tutorials
---------
* [Using InputEvent](https://docs.godotengine.org/en/3.5/tutorials/inputs/inputevent.html)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [echo](#class-inputeventkey-property-echo) | `false` |
| [int](class_int#class-int) | [physical\_scancode](#class-inputeventkey-property-physical-scancode) | `0` |
| [bool](class_bool#class-bool) | [pressed](#class-inputeventkey-property-pressed) | `false` |
| [int](class_int#class-int) | [scancode](#class-inputeventkey-property-scancode) | `0` |
| [int](class_int#class-int) | [unicode](#class-inputeventkey-property-unicode) | `0` |
Methods
-------
| | |
| --- | --- |
| [int](class_int#class-int) | [get\_physical\_scancode\_with\_modifiers](#class-inputeventkey-method-get-physical-scancode-with-modifiers) **(** **)** const |
| [int](class_int#class-int) | [get\_scancode\_with\_modifiers](#class-inputeventkey-method-get-scancode-with-modifiers) **(** **)** const |
Property Descriptions
---------------------
### [bool](class_bool#class-bool) echo
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_echo(value) |
| *Getter* | is\_echo() |
If `true`, the key was already pressed before this event. It means the user is holding the key down.
### [int](class_int#class-int) physical\_scancode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_physical\_scancode(value) |
| *Getter* | get\_physical\_scancode() |
Key physical scancode, which corresponds to one of the [KeyList](class_%40globalscope#enum-globalscope-keylist) constants. Represent the physical location of a key on the 101/102-key US QWERTY keyboard.
To get a human-readable representation of the `InputEventKey`, use `OS.get_scancode_string(event.physical_scancode)` where `event` is the `InputEventKey`.
### [bool](class_bool#class-bool) pressed
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_pressed(value) |
| *Getter* | is\_pressed() |
If `true`, the key's state is pressed. If `false`, the key's state is released.
### [int](class_int#class-int) scancode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_scancode(value) |
| *Getter* | get\_scancode() |
The key scancode, which corresponds to one of the [KeyList](class_%40globalscope#enum-globalscope-keylist) constants. Represent key in the current keyboard layout.
To get a human-readable representation of the `InputEventKey`, use `OS.get_scancode_string(event.scancode)` where `event` is the `InputEventKey`.
### [int](class_int#class-int) unicode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_unicode(value) |
| *Getter* | get\_unicode() |
The key Unicode identifier (when relevant). Unicode identifiers for the composite characters and complex scripts may not be available unless IME input mode is active. See [OS.set\_ime\_active](class_os#class-os-method-set-ime-active) for more information.
Method Descriptions
-------------------
### [int](class_int#class-int) get\_physical\_scancode\_with\_modifiers ( ) const
Returns the physical scancode combined with modifier keys such as `Shift` or `Alt`. See also [InputEventWithModifiers](class_inputeventwithmodifiers#class-inputeventwithmodifiers).
To get a human-readable representation of the `InputEventKey` with modifiers, use `OS.get_scancode_string(event.get_physical_scancode_with_modifiers())` where `event` is the `InputEventKey`.
### [int](class_int#class-int) get\_scancode\_with\_modifiers ( ) const
Returns the scancode combined with modifier keys such as `Shift` or `Alt`. See also [InputEventWithModifiers](class_inputeventwithmodifiers#class-inputeventwithmodifiers).
To get a human-readable representation of the `InputEventKey` with modifiers, use `OS.get_scancode_string(event.get_scancode_with_modifiers())` where `event` is the `InputEventKey`.
godot Performance Performance
===========
**Inherits:** [Object](class_object#class-object)
Exposes performance-related data.
Description
-----------
This class provides access to a number of different monitors related to performance, such as memory usage, draw calls, and FPS. These are the same as the values displayed in the **Monitor** tab in the editor's **Debugger** panel. By using the [get\_monitor](#class-performance-method-get-monitor) method of this class, you can access this data from your code.
**Note:** A few of these monitors are only available in debug mode and will always return 0 when used in a release build.
**Note:** Many of these monitors are not updated in real-time, so there may be a short delay between changes.
Methods
-------
| | |
| --- | --- |
| [float](class_float#class-float) | [get\_monitor](#class-performance-method-get-monitor) **(** [Monitor](#enum-performance-monitor) monitor **)** const |
Enumerations
------------
enum **Monitor**:
* **TIME\_FPS** = **0** --- Number of frames per second.
* **TIME\_PROCESS** = **1** --- Time it took to complete one frame, in seconds.
* **TIME\_PHYSICS\_PROCESS** = **2** --- Time it took to complete one physics frame, in seconds.
* **MEMORY\_STATIC** = **3** --- Static memory currently used, in bytes. Not available in release builds.
* **MEMORY\_DYNAMIC** = **4** --- Dynamic memory currently used, in bytes. Not available in release builds.
* **MEMORY\_STATIC\_MAX** = **5** --- Available static memory. Not available in release builds.
* **MEMORY\_DYNAMIC\_MAX** = **6** --- Available dynamic memory. Not available in release builds.
* **MEMORY\_MESSAGE\_BUFFER\_MAX** = **7** --- Largest amount of memory the message queue buffer has used, in bytes. The message queue is used for deferred functions calls and notifications.
* **OBJECT\_COUNT** = **8** --- Number of objects currently instanced (including nodes).
* **OBJECT\_RESOURCE\_COUNT** = **9** --- Number of resources currently used.
* **OBJECT\_NODE\_COUNT** = **10** --- Number of nodes currently instanced in the scene tree. This also includes the root node.
* **OBJECT\_ORPHAN\_NODE\_COUNT** = **11** --- Number of orphan nodes, i.e. nodes which are not parented to a node of the scene tree.
* **RENDER\_OBJECTS\_IN\_FRAME** = **12** --- 3D objects drawn per frame.
* **RENDER\_VERTICES\_IN\_FRAME** = **13** --- Vertices drawn per frame. 3D only.
* **RENDER\_MATERIAL\_CHANGES\_IN\_FRAME** = **14** --- Material changes per frame. 3D only.
* **RENDER\_SHADER\_CHANGES\_IN\_FRAME** = **15** --- Shader changes per frame. 3D only.
* **RENDER\_SURFACE\_CHANGES\_IN\_FRAME** = **16** --- Render surface changes per frame. 3D only.
* **RENDER\_DRAW\_CALLS\_IN\_FRAME** = **17** --- Draw calls per frame. 3D only.
* **RENDER\_2D\_ITEMS\_IN\_FRAME** = **18** --- Items or joined items drawn per frame.
* **RENDER\_2D\_DRAW\_CALLS\_IN\_FRAME** = **19** --- Draw calls per frame.
* **RENDER\_VIDEO\_MEM\_USED** = **20** --- The amount of video memory used, i.e. texture and vertex memory combined.
* **RENDER\_TEXTURE\_MEM\_USED** = **21** --- The amount of texture memory used.
* **RENDER\_VERTEX\_MEM\_USED** = **22** --- The amount of vertex memory used.
* **RENDER\_USAGE\_VIDEO\_MEM\_TOTAL** = **23** --- Unimplemented in the GLES2 and GLES3 rendering backends, always returns 0.
* **PHYSICS\_2D\_ACTIVE\_OBJECTS** = **24** --- Number of active [RigidBody2D](class_rigidbody2d#class-rigidbody2d) nodes in the game.
* **PHYSICS\_2D\_COLLISION\_PAIRS** = **25** --- Number of collision pairs in the 2D physics engine.
* **PHYSICS\_2D\_ISLAND\_COUNT** = **26** --- Number of islands in the 2D physics engine.
* **PHYSICS\_3D\_ACTIVE\_OBJECTS** = **27** --- Number of active [RigidBody](class_rigidbody#class-rigidbody) and [VehicleBody](class_vehiclebody#class-vehiclebody) nodes in the game.
* **PHYSICS\_3D\_COLLISION\_PAIRS** = **28** --- Number of collision pairs in the 3D physics engine.
* **PHYSICS\_3D\_ISLAND\_COUNT** = **29** --- Number of islands in the 3D physics engine.
* **AUDIO\_OUTPUT\_LATENCY** = **30** --- Output latency of the [AudioServer](class_audioserver#class-audioserver).
* **MONITOR\_MAX** = **31** --- Represents the size of the [Monitor](#enum-performance-monitor) enum.
Method Descriptions
-------------------
### [float](class_float#class-float) get\_monitor ( [Monitor](#enum-performance-monitor) monitor ) const
Returns the value of one of the available monitors. You should provide one of the [Monitor](#enum-performance-monitor) constants as the argument, like this:
```
print(Performance.get_monitor(Performance.TIME_FPS)) # Prints the FPS to the console
```
godot CylinderMesh CylinderMesh
============
**Inherits:** [PrimitiveMesh](class_primitivemesh#class-primitivemesh) **<** [Mesh](class_mesh#class-mesh) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Class representing a cylindrical [PrimitiveMesh](class_primitivemesh#class-primitivemesh).
Description
-----------
Class representing a cylindrical [PrimitiveMesh](class_primitivemesh#class-primitivemesh). This class can be used to create cones by setting either the [top\_radius](#class-cylindermesh-property-top-radius) or [bottom\_radius](#class-cylindermesh-property-bottom-radius) properties to `0.0`.
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [bottom\_radius](#class-cylindermesh-property-bottom-radius) | `1.0` |
| [float](class_float#class-float) | [height](#class-cylindermesh-property-height) | `2.0` |
| [int](class_int#class-int) | [radial\_segments](#class-cylindermesh-property-radial-segments) | `64` |
| [int](class_int#class-int) | [rings](#class-cylindermesh-property-rings) | `4` |
| [float](class_float#class-float) | [top\_radius](#class-cylindermesh-property-top-radius) | `1.0` |
Property Descriptions
---------------------
### [float](class_float#class-float) bottom\_radius
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_bottom\_radius(value) |
| *Getter* | get\_bottom\_radius() |
Bottom radius of the cylinder. If set to `0.0`, the bottom faces will not be generated, resulting in a conic shape.
### [float](class_float#class-float) height
| | |
| --- | --- |
| *Default* | `2.0` |
| *Setter* | set\_height(value) |
| *Getter* | get\_height() |
Full height of the cylinder.
### [int](class_int#class-int) radial\_segments
| | |
| --- | --- |
| *Default* | `64` |
| *Setter* | set\_radial\_segments(value) |
| *Getter* | get\_radial\_segments() |
Number of radial segments on the cylinder. Higher values result in a more detailed cylinder/cone at the cost of performance.
### [int](class_int#class-int) rings
| | |
| --- | --- |
| *Default* | `4` |
| *Setter* | set\_rings(value) |
| *Getter* | get\_rings() |
Number of edge rings along the height of the cylinder. Changing [rings](#class-cylindermesh-property-rings) does not have any visual impact unless a shader or procedural mesh tool is used to alter the vertex data. Higher values result in more subdivisions, which can be used to create smoother-looking effects with shaders or procedural mesh tools (at the cost of performance). When not altering the vertex data using a shader or procedural mesh tool, [rings](#class-cylindermesh-property-rings) should be kept to its default value.
### [float](class_float#class-float) top\_radius
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_top\_radius(value) |
| *Getter* | get\_top\_radius() |
Top radius of the cylinder. If set to `0.0`, the top faces will not be generated, resulting in a conic shape.
godot Geometry Geometry
========
**Inherits:** [Object](class_object#class-object)
Helper node to calculate generic geometry operations.
Description
-----------
Geometry provides users with a set of helper functions to create geometric shapes, compute intersections between shapes, and process various other geometric operations.
Methods
-------
| | |
| --- | --- |
| [Array](class_array#class-array) | [build\_box\_planes](#class-geometry-method-build-box-planes) **(** [Vector3](class_vector3#class-vector3) extents **)** |
| [Array](class_array#class-array) | [build\_capsule\_planes](#class-geometry-method-build-capsule-planes) **(** [float](class_float#class-float) radius, [float](class_float#class-float) height, [int](class_int#class-int) sides, [int](class_int#class-int) lats, Vector3.Axis axis=2 **)** |
| [Array](class_array#class-array) | [build\_cylinder\_planes](#class-geometry-method-build-cylinder-planes) **(** [float](class_float#class-float) radius, [float](class_float#class-float) height, [int](class_int#class-int) sides, Vector3.Axis axis=2 **)** |
| [PoolVector3Array](class_poolvector3array#class-poolvector3array) | [clip\_polygon](#class-geometry-method-clip-polygon) **(** [PoolVector3Array](class_poolvector3array#class-poolvector3array) points, [Plane](class_plane#class-plane) plane **)** |
| [Array](class_array#class-array) | [clip\_polygons\_2d](#class-geometry-method-clip-polygons-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_a, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_b **)** |
| [Array](class_array#class-array) | [clip\_polyline\_with\_polygon\_2d](#class-geometry-method-clip-polyline-with-polygon-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polyline, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon **)** |
| [PoolVector2Array](class_poolvector2array#class-poolvector2array) | [convex\_hull\_2d](#class-geometry-method-convex-hull-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) points **)** |
| [Array](class_array#class-array) | [exclude\_polygons\_2d](#class-geometry-method-exclude-polygons-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_a, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_b **)** |
| [Vector3](class_vector3#class-vector3) | [get\_closest\_point\_to\_segment](#class-geometry-method-get-closest-point-to-segment) **(** [Vector3](class_vector3#class-vector3) point, [Vector3](class_vector3#class-vector3) s1, [Vector3](class_vector3#class-vector3) s2 **)** |
| [Vector2](class_vector2#class-vector2) | [get\_closest\_point\_to\_segment\_2d](#class-geometry-method-get-closest-point-to-segment-2d) **(** [Vector2](class_vector2#class-vector2) point, [Vector2](class_vector2#class-vector2) s1, [Vector2](class_vector2#class-vector2) s2 **)** |
| [Vector3](class_vector3#class-vector3) | [get\_closest\_point\_to\_segment\_uncapped](#class-geometry-method-get-closest-point-to-segment-uncapped) **(** [Vector3](class_vector3#class-vector3) point, [Vector3](class_vector3#class-vector3) s1, [Vector3](class_vector3#class-vector3) s2 **)** |
| [Vector2](class_vector2#class-vector2) | [get\_closest\_point\_to\_segment\_uncapped\_2d](#class-geometry-method-get-closest-point-to-segment-uncapped-2d) **(** [Vector2](class_vector2#class-vector2) point, [Vector2](class_vector2#class-vector2) s1, [Vector2](class_vector2#class-vector2) s2 **)** |
| [PoolVector3Array](class_poolvector3array#class-poolvector3array) | [get\_closest\_points\_between\_segments](#class-geometry-method-get-closest-points-between-segments) **(** [Vector3](class_vector3#class-vector3) p1, [Vector3](class_vector3#class-vector3) p2, [Vector3](class_vector3#class-vector3) q1, [Vector3](class_vector3#class-vector3) q2 **)** |
| [PoolVector2Array](class_poolvector2array#class-poolvector2array) | [get\_closest\_points\_between\_segments\_2d](#class-geometry-method-get-closest-points-between-segments-2d) **(** [Vector2](class_vector2#class-vector2) p1, [Vector2](class_vector2#class-vector2) q1, [Vector2](class_vector2#class-vector2) p2, [Vector2](class_vector2#class-vector2) q2 **)** |
| [int](class_int#class-int) | [get\_uv84\_normal\_bit](#class-geometry-method-get-uv84-normal-bit) **(** [Vector3](class_vector3#class-vector3) normal **)** |
| [Array](class_array#class-array) | [intersect\_polygons\_2d](#class-geometry-method-intersect-polygons-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_a, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_b **)** |
| [Array](class_array#class-array) | [intersect\_polyline\_with\_polygon\_2d](#class-geometry-method-intersect-polyline-with-polygon-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polyline, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon **)** |
| [bool](class_bool#class-bool) | [is\_point\_in\_circle](#class-geometry-method-is-point-in-circle) **(** [Vector2](class_vector2#class-vector2) point, [Vector2](class_vector2#class-vector2) circle\_position, [float](class_float#class-float) circle\_radius **)** |
| [bool](class_bool#class-bool) | [is\_point\_in\_polygon](#class-geometry-method-is-point-in-polygon) **(** [Vector2](class_vector2#class-vector2) point, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon **)** |
| [bool](class_bool#class-bool) | [is\_polygon\_clockwise](#class-geometry-method-is-polygon-clockwise) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon **)** |
| [Variant](class_variant#class-variant) | [line\_intersects\_line\_2d](#class-geometry-method-line-intersects-line-2d) **(** [Vector2](class_vector2#class-vector2) from\_a, [Vector2](class_vector2#class-vector2) dir\_a, [Vector2](class_vector2#class-vector2) from\_b, [Vector2](class_vector2#class-vector2) dir\_b **)** |
| [Dictionary](class_dictionary#class-dictionary) | [make\_atlas](#class-geometry-method-make-atlas) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) sizes **)** |
| [Array](class_array#class-array) | [merge\_polygons\_2d](#class-geometry-method-merge-polygons-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_a, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_b **)** |
| [Array](class_array#class-array) | [offset\_polygon\_2d](#class-geometry-method-offset-polygon-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon, [float](class_float#class-float) delta, [PolyJoinType](#enum-geometry-polyjointype) join\_type=0 **)** |
| [Array](class_array#class-array) | [offset\_polyline\_2d](#class-geometry-method-offset-polyline-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polyline, [float](class_float#class-float) delta, [PolyJoinType](#enum-geometry-polyjointype) join\_type=0, [PolyEndType](#enum-geometry-polyendtype) end\_type=3 **)** |
| [bool](class_bool#class-bool) | [point\_is\_inside\_triangle](#class-geometry-method-point-is-inside-triangle) **(** [Vector2](class_vector2#class-vector2) point, [Vector2](class_vector2#class-vector2) a, [Vector2](class_vector2#class-vector2) b, [Vector2](class_vector2#class-vector2) c **)** const |
| [Variant](class_variant#class-variant) | [ray\_intersects\_triangle](#class-geometry-method-ray-intersects-triangle) **(** [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) dir, [Vector3](class_vector3#class-vector3) a, [Vector3](class_vector3#class-vector3) b, [Vector3](class_vector3#class-vector3) c **)** |
| [float](class_float#class-float) | [segment\_intersects\_circle](#class-geometry-method-segment-intersects-circle) **(** [Vector2](class_vector2#class-vector2) segment\_from, [Vector2](class_vector2#class-vector2) segment\_to, [Vector2](class_vector2#class-vector2) circle\_position, [float](class_float#class-float) circle\_radius **)** |
| [PoolVector3Array](class_poolvector3array#class-poolvector3array) | [segment\_intersects\_convex](#class-geometry-method-segment-intersects-convex) **(** [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [Array](class_array#class-array) planes **)** |
| [PoolVector3Array](class_poolvector3array#class-poolvector3array) | [segment\_intersects\_cylinder](#class-geometry-method-segment-intersects-cylinder) **(** [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [float](class_float#class-float) height, [float](class_float#class-float) radius **)** |
| [Variant](class_variant#class-variant) | [segment\_intersects\_segment\_2d](#class-geometry-method-segment-intersects-segment-2d) **(** [Vector2](class_vector2#class-vector2) from\_a, [Vector2](class_vector2#class-vector2) to\_a, [Vector2](class_vector2#class-vector2) from\_b, [Vector2](class_vector2#class-vector2) to\_b **)** |
| [PoolVector3Array](class_poolvector3array#class-poolvector3array) | [segment\_intersects\_sphere](#class-geometry-method-segment-intersects-sphere) **(** [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [Vector3](class_vector3#class-vector3) sphere\_position, [float](class_float#class-float) sphere\_radius **)** |
| [Variant](class_variant#class-variant) | [segment\_intersects\_triangle](#class-geometry-method-segment-intersects-triangle) **(** [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [Vector3](class_vector3#class-vector3) a, [Vector3](class_vector3#class-vector3) b, [Vector3](class_vector3#class-vector3) c **)** |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [triangulate\_delaunay\_2d](#class-geometry-method-triangulate-delaunay-2d) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) points **)** |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [triangulate\_polygon](#class-geometry-method-triangulate-polygon) **(** [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon **)** |
Enumerations
------------
enum **PolyBooleanOperation**:
* **OPERATION\_UNION** = **0** --- Create regions where either subject or clip polygons (or both) are filled.
* **OPERATION\_DIFFERENCE** = **1** --- Create regions where subject polygons are filled except where clip polygons are filled.
* **OPERATION\_INTERSECTION** = **2** --- Create regions where both subject and clip polygons are filled.
* **OPERATION\_XOR** = **3** --- Create regions where either subject or clip polygons are filled but not where both are filled.
enum **PolyJoinType**:
* **JOIN\_SQUARE** = **0** --- Squaring is applied uniformally at all convex edge joins at `1 * delta`.
* **JOIN\_ROUND** = **1** --- While flattened paths can never perfectly trace an arc, they are approximated by a series of arc chords.
* **JOIN\_MITER** = **2** --- There's a necessary limit to mitered joins since offsetting edges that join at very acute angles will produce excessively long and narrow "spikes". For any given edge join, when miter offsetting would exceed that maximum distance, "square" joining is applied.
enum **PolyEndType**:
* **END\_POLYGON** = **0** --- Endpoints are joined using the [PolyJoinType](#enum-geometry-polyjointype) value and the path filled as a polygon.
* **END\_JOINED** = **1** --- Endpoints are joined using the [PolyJoinType](#enum-geometry-polyjointype) value and the path filled as a polyline.
* **END\_BUTT** = **2** --- Endpoints are squared off with no extension.
* **END\_SQUARE** = **3** --- Endpoints are squared off and extended by `delta` units.
* **END\_ROUND** = **4** --- Endpoints are rounded off and extended by `delta` units.
Method Descriptions
-------------------
### [Array](class_array#class-array) build\_box\_planes ( [Vector3](class_vector3#class-vector3) extents )
Returns an array with 6 [Plane](class_plane#class-plane)s that describe the sides of a box centered at the origin. The box size is defined by `extents`, which represents one (positive) corner of the box (i.e. half its actual size).
### [Array](class_array#class-array) build\_capsule\_planes ( [float](class_float#class-float) radius, [float](class_float#class-float) height, [int](class_int#class-int) sides, [int](class_int#class-int) lats, Vector3.Axis axis=2 )
Returns an array of [Plane](class_plane#class-plane)s closely bounding a faceted capsule centered at the origin with radius `radius` and height `height`. The parameter `sides` defines how many planes will be generated for the side part of the capsule, whereas `lats` gives the number of latitudinal steps at the bottom and top of the capsule. The parameter `axis` describes the axis along which the capsule is oriented (0 for X, 1 for Y, 2 for Z).
### [Array](class_array#class-array) build\_cylinder\_planes ( [float](class_float#class-float) radius, [float](class_float#class-float) height, [int](class_int#class-int) sides, Vector3.Axis axis=2 )
Returns an array of [Plane](class_plane#class-plane)s closely bounding a faceted cylinder centered at the origin with radius `radius` and height `height`. The parameter `sides` defines how many planes will be generated for the round part of the cylinder. The parameter `axis` describes the axis along which the cylinder is oriented (0 for X, 1 for Y, 2 for Z).
### [PoolVector3Array](class_poolvector3array#class-poolvector3array) clip\_polygon ( [PoolVector3Array](class_poolvector3array#class-poolvector3array) points, [Plane](class_plane#class-plane) plane )
Clips the polygon defined by the points in `points` against the `plane` and returns the points of the clipped polygon.
### [Array](class_array#class-array) clip\_polygons\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_a, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_b )
Clips `polygon_a` against `polygon_b` and returns an array of clipped polygons. This performs [OPERATION\_DIFFERENCE](#class-geometry-constant-operation-difference) between polygons. Returns an empty array if `polygon_b` completely overlaps `polygon_a`.
If `polygon_b` is enclosed by `polygon_a`, returns an outer polygon (boundary) and inner polygon (hole) which could be distinguished by calling [is\_polygon\_clockwise](#class-geometry-method-is-polygon-clockwise).
### [Array](class_array#class-array) clip\_polyline\_with\_polygon\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polyline, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon )
Clips `polyline` against `polygon` and returns an array of clipped polylines. This performs [OPERATION\_DIFFERENCE](#class-geometry-constant-operation-difference) between the polyline and the polygon. This operation can be thought of as cutting a line with a closed shape.
### [PoolVector2Array](class_poolvector2array#class-poolvector2array) convex\_hull\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) points )
Given an array of [Vector2](class_vector2#class-vector2)s, returns the convex hull as a list of points in counterclockwise order. The last point is the same as the first one.
### [Array](class_array#class-array) exclude\_polygons\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_a, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_b )
Mutually excludes common area defined by intersection of `polygon_a` and `polygon_b` (see [intersect\_polygons\_2d](#class-geometry-method-intersect-polygons-2d)) and returns an array of excluded polygons. This performs [OPERATION\_XOR](#class-geometry-constant-operation-xor) between polygons. In other words, returns all but common area between polygons.
The operation may result in an outer polygon (boundary) and inner polygon (hole) produced which could be distinguished by calling [is\_polygon\_clockwise](#class-geometry-method-is-polygon-clockwise).
### [Vector3](class_vector3#class-vector3) get\_closest\_point\_to\_segment ( [Vector3](class_vector3#class-vector3) point, [Vector3](class_vector3#class-vector3) s1, [Vector3](class_vector3#class-vector3) s2 )
Returns the 3D point on the 3D segment (`s1`, `s2`) that is closest to `point`. The returned point will always be inside the specified segment.
### [Vector2](class_vector2#class-vector2) get\_closest\_point\_to\_segment\_2d ( [Vector2](class_vector2#class-vector2) point, [Vector2](class_vector2#class-vector2) s1, [Vector2](class_vector2#class-vector2) s2 )
Returns the 2D point on the 2D segment (`s1`, `s2`) that is closest to `point`. The returned point will always be inside the specified segment.
### [Vector3](class_vector3#class-vector3) get\_closest\_point\_to\_segment\_uncapped ( [Vector3](class_vector3#class-vector3) point, [Vector3](class_vector3#class-vector3) s1, [Vector3](class_vector3#class-vector3) s2 )
Returns the 3D point on the 3D line defined by (`s1`, `s2`) that is closest to `point`. The returned point can be inside the segment (`s1`, `s2`) or outside of it, i.e. somewhere on the line extending from the segment.
### [Vector2](class_vector2#class-vector2) get\_closest\_point\_to\_segment\_uncapped\_2d ( [Vector2](class_vector2#class-vector2) point, [Vector2](class_vector2#class-vector2) s1, [Vector2](class_vector2#class-vector2) s2 )
Returns the 2D point on the 2D line defined by (`s1`, `s2`) that is closest to `point`. The returned point can be inside the segment (`s1`, `s2`) or outside of it, i.e. somewhere on the line extending from the segment.
### [PoolVector3Array](class_poolvector3array#class-poolvector3array) get\_closest\_points\_between\_segments ( [Vector3](class_vector3#class-vector3) p1, [Vector3](class_vector3#class-vector3) p2, [Vector3](class_vector3#class-vector3) q1, [Vector3](class_vector3#class-vector3) q2 )
Given the two 3D segments (`p1`, `p2`) and (`q1`, `q2`), finds those two points on the two segments that are closest to each other. Returns a [PoolVector3Array](class_poolvector3array#class-poolvector3array) that contains this point on (`p1`, `p2`) as well the accompanying point on (`q1`, `q2`).
### [PoolVector2Array](class_poolvector2array#class-poolvector2array) get\_closest\_points\_between\_segments\_2d ( [Vector2](class_vector2#class-vector2) p1, [Vector2](class_vector2#class-vector2) q1, [Vector2](class_vector2#class-vector2) p2, [Vector2](class_vector2#class-vector2) q2 )
Given the two 2D segments (`p1`, `q1`) and (`p2`, `q2`), finds those two points on the two segments that are closest to each other. Returns a [PoolVector2Array](class_poolvector2array#class-poolvector2array) that contains this point on (`p1`, `q1`) as well the accompanying point on (`p2`, `q2`).
### [int](class_int#class-int) get\_uv84\_normal\_bit ( [Vector3](class_vector3#class-vector3) normal )
Used internally by the engine.
### [Array](class_array#class-array) intersect\_polygons\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_a, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_b )
Intersects `polygon_a` with `polygon_b` and returns an array of intersected polygons. This performs [OPERATION\_INTERSECTION](#class-geometry-constant-operation-intersection) between polygons. In other words, returns common area shared by polygons. Returns an empty array if no intersection occurs.
The operation may result in an outer polygon (boundary) and inner polygon (hole) produced which could be distinguished by calling [is\_polygon\_clockwise](#class-geometry-method-is-polygon-clockwise).
### [Array](class_array#class-array) intersect\_polyline\_with\_polygon\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polyline, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon )
Intersects `polyline` with `polygon` and returns an array of intersected polylines. This performs [OPERATION\_INTERSECTION](#class-geometry-constant-operation-intersection) between the polyline and the polygon. This operation can be thought of as chopping a line with a closed shape.
### [bool](class_bool#class-bool) is\_point\_in\_circle ( [Vector2](class_vector2#class-vector2) point, [Vector2](class_vector2#class-vector2) circle\_position, [float](class_float#class-float) circle\_radius )
Returns `true` if `point` is inside the circle or if it's located exactly *on* the circle's boundary, otherwise returns `false`.
### [bool](class_bool#class-bool) is\_point\_in\_polygon ( [Vector2](class_vector2#class-vector2) point, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon )
Returns `true` if `point` is inside `polygon` or if it's located exactly *on* polygon's boundary, otherwise returns `false`.
### [bool](class_bool#class-bool) is\_polygon\_clockwise ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon )
Returns `true` if `polygon`'s vertices are ordered in clockwise order, otherwise returns `false`.
### [Variant](class_variant#class-variant) line\_intersects\_line\_2d ( [Vector2](class_vector2#class-vector2) from\_a, [Vector2](class_vector2#class-vector2) dir\_a, [Vector2](class_vector2#class-vector2) from\_b, [Vector2](class_vector2#class-vector2) dir\_b )
Checks if the two lines (`from_a`, `dir_a`) and (`from_b`, `dir_b`) intersect. If yes, return the point of intersection as [Vector2](class_vector2#class-vector2). If no intersection takes place, returns `null`.
**Note:** The lines are specified using direction vectors, not end points.
### [Dictionary](class_dictionary#class-dictionary) make\_atlas ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) sizes )
Given an array of [Vector2](class_vector2#class-vector2)s representing tiles, builds an atlas. The returned dictionary has two keys: `points` is an array of [Vector2](class_vector2#class-vector2) that specifies the positions of each tile, `size` contains the overall size of the whole atlas as [Vector2](class_vector2#class-vector2).
### [Array](class_array#class-array) merge\_polygons\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_a, [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon\_b )
Merges (combines) `polygon_a` and `polygon_b` and returns an array of merged polygons. This performs [OPERATION\_UNION](#class-geometry-constant-operation-union) between polygons.
The operation may result in an outer polygon (boundary) and multiple inner polygons (holes) produced which could be distinguished by calling [is\_polygon\_clockwise](#class-geometry-method-is-polygon-clockwise).
### [Array](class_array#class-array) offset\_polygon\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon, [float](class_float#class-float) delta, [PolyJoinType](#enum-geometry-polyjointype) join\_type=0 )
Inflates or deflates `polygon` by `delta` units (pixels). If `delta` is positive, makes the polygon grow outward. If `delta` is negative, shrinks the polygon inward. Returns an array of polygons because inflating/deflating may result in multiple discrete polygons. Returns an empty array if `delta` is negative and the absolute value of it approximately exceeds the minimum bounding rectangle dimensions of the polygon.
Each polygon's vertices will be rounded as determined by `join_type`, see [PolyJoinType](#enum-geometry-polyjointype).
The operation may result in an outer polygon (boundary) and inner polygon (hole) produced which could be distinguished by calling [is\_polygon\_clockwise](#class-geometry-method-is-polygon-clockwise).
**Note:** To translate the polygon's vertices specifically, use the [Transform2D.xform](class_transform2d#class-transform2d-method-xform) method:
```
var polygon = PoolVector2Array([Vector2(0, 0), Vector2(100, 0), Vector2(100, 100), Vector2(0, 100)])
var offset = Vector2(50, 50)
polygon = Transform2D(0, offset).xform(polygon)
print(polygon) # prints [Vector2(50, 50), Vector2(150, 50), Vector2(150, 150), Vector2(50, 150)]
```
### [Array](class_array#class-array) offset\_polyline\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polyline, [float](class_float#class-float) delta, [PolyJoinType](#enum-geometry-polyjointype) join\_type=0, [PolyEndType](#enum-geometry-polyendtype) end\_type=3 )
Inflates or deflates `polyline` by `delta` units (pixels), producing polygons. If `delta` is positive, makes the polyline grow outward. Returns an array of polygons because inflating/deflating may result in multiple discrete polygons. If `delta` is negative, returns an empty array.
Each polygon's vertices will be rounded as determined by `join_type`, see [PolyJoinType](#enum-geometry-polyjointype).
Each polygon's endpoints will be rounded as determined by `end_type`, see [PolyEndType](#enum-geometry-polyendtype).
The operation may result in an outer polygon (boundary) and inner polygon (hole) produced which could be distinguished by calling [is\_polygon\_clockwise](#class-geometry-method-is-polygon-clockwise).
### [bool](class_bool#class-bool) point\_is\_inside\_triangle ( [Vector2](class_vector2#class-vector2) point, [Vector2](class_vector2#class-vector2) a, [Vector2](class_vector2#class-vector2) b, [Vector2](class_vector2#class-vector2) c ) const
Returns if `point` is inside the triangle specified by `a`, `b` and `c`.
### [Variant](class_variant#class-variant) ray\_intersects\_triangle ( [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) dir, [Vector3](class_vector3#class-vector3) a, [Vector3](class_vector3#class-vector3) b, [Vector3](class_vector3#class-vector3) c )
Tests if the 3D ray starting at `from` with the direction of `dir` intersects the triangle specified by `a`, `b` and `c`. If yes, returns the point of intersection as [Vector3](class_vector3#class-vector3). If no intersection takes place, an empty [Variant](class_variant#class-variant) is returned.
### [float](class_float#class-float) segment\_intersects\_circle ( [Vector2](class_vector2#class-vector2) segment\_from, [Vector2](class_vector2#class-vector2) segment\_to, [Vector2](class_vector2#class-vector2) circle\_position, [float](class_float#class-float) circle\_radius )
Given the 2D segment (`segment_from`, `segment_to`), returns the position on the segment (as a number between 0 and 1) at which the segment hits the circle that is located at position `circle_position` and has radius `circle_radius`. If the segment does not intersect the circle, -1 is returned (this is also the case if the line extending the segment would intersect the circle, but the segment does not).
### [PoolVector3Array](class_poolvector3array#class-poolvector3array) segment\_intersects\_convex ( [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [Array](class_array#class-array) planes )
Given a convex hull defined though the [Plane](class_plane#class-plane)s in the array `planes`, tests if the segment (`from`, `to`) intersects with that hull. If an intersection is found, returns a [PoolVector3Array](class_poolvector3array#class-poolvector3array) containing the point the intersection and the hull's normal. If no intersecion is found, an the returned array is empty.
### [PoolVector3Array](class_poolvector3array#class-poolvector3array) segment\_intersects\_cylinder ( [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [float](class_float#class-float) height, [float](class_float#class-float) radius )
Checks if the segment (`from`, `to`) intersects the cylinder with height `height` that is centered at the origin and has radius `radius`. If no, returns an empty [PoolVector3Array](class_poolvector3array#class-poolvector3array). If an intersection takes place, the returned array contains the point of intersection and the cylinder's normal at the point of intersection.
### [Variant](class_variant#class-variant) segment\_intersects\_segment\_2d ( [Vector2](class_vector2#class-vector2) from\_a, [Vector2](class_vector2#class-vector2) to\_a, [Vector2](class_vector2#class-vector2) from\_b, [Vector2](class_vector2#class-vector2) to\_b )
Checks if the two segments (`from_a`, `to_a`) and (`from_b`, `to_b`) intersect. If yes, return the point of intersection as [Vector2](class_vector2#class-vector2). If no intersection takes place, returns `null`.
### [PoolVector3Array](class_poolvector3array#class-poolvector3array) segment\_intersects\_sphere ( [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [Vector3](class_vector3#class-vector3) sphere\_position, [float](class_float#class-float) sphere\_radius )
Checks if the segment (`from`, `to`) intersects the sphere that is located at `sphere_position` and has radius `sphere_radius`. If no, returns an empty [PoolVector3Array](class_poolvector3array#class-poolvector3array). If yes, returns a [PoolVector3Array](class_poolvector3array#class-poolvector3array) containing the point of intersection and the sphere's normal at the point of intersection.
### [Variant](class_variant#class-variant) segment\_intersects\_triangle ( [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [Vector3](class_vector3#class-vector3) a, [Vector3](class_vector3#class-vector3) b, [Vector3](class_vector3#class-vector3) c )
Tests if the segment (`from`, `to`) intersects the triangle `a`, `b`, `c`. If yes, returns the point of intersection as [Vector3](class_vector3#class-vector3). If no intersection takes place, an empty [Variant](class_variant#class-variant) is returned.
### [PoolIntArray](class_poolintarray#class-poolintarray) triangulate\_delaunay\_2d ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) points )
Triangulates the area specified by discrete set of `points` such that no point is inside the circumcircle of any resulting triangle. Returns a [PoolIntArray](class_poolintarray#class-poolintarray) where each triangle consists of three consecutive point indices into `points` (i.e. the returned array will have `n * 3` elements, with `n` being the number of found triangles). If the triangulation did not succeed, an empty [PoolIntArray](class_poolintarray#class-poolintarray) is returned.
### [PoolIntArray](class_poolintarray#class-poolintarray) triangulate\_polygon ( [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon )
Triangulates the polygon specified by the points in `polygon`. Returns a [PoolIntArray](class_poolintarray#class-poolintarray) where each triangle consists of three consecutive point indices into `polygon` (i.e. the returned array will have `n * 3` elements, with `n` being the number of found triangles). Output triangles will always be counter clockwise, and the contour will be flipped if it's clockwise. If the triangulation did not succeed, an empty [PoolIntArray](class_poolintarray#class-poolintarray) is returned.
| programming_docs |
godot BitmapFont BitmapFont
==========
**Inherits:** [Font](class_font#class-font) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Renders text using fonts under the [BMFont](https://www.angelcode.com/products/bmfont/) format.
Handles files with the `.fnt` extension.
Description
-----------
Renders text using `*.fnt` fonts containing texture atlases. Supports distance fields. For using vector font files like TTF directly, see [DynamicFont](class_dynamicfont#class-dynamicfont).
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [ascent](#class-bitmapfont-property-ascent) | `0.0` |
| [bool](class_bool#class-bool) | [distance\_field](#class-bitmapfont-property-distance-field) | `false` |
| [BitmapFont](#class-bitmapfont) | [fallback](#class-bitmapfont-property-fallback) | |
| [float](class_float#class-float) | [height](#class-bitmapfont-property-height) | `1.0` |
Methods
-------
| | |
| --- | --- |
| void | [add\_char](#class-bitmapfont-method-add-char) **(** [int](class_int#class-int) character, [int](class_int#class-int) texture, [Rect2](class_rect2#class-rect2) rect, [Vector2](class_vector2#class-vector2) align=Vector2( 0, 0 ), [float](class_float#class-float) advance=-1 **)** |
| void | [add\_kerning\_pair](#class-bitmapfont-method-add-kerning-pair) **(** [int](class_int#class-int) char\_a, [int](class_int#class-int) char\_b, [int](class_int#class-int) kerning **)** |
| void | [add\_texture](#class-bitmapfont-method-add-texture) **(** [Texture](class_texture#class-texture) texture **)** |
| void | [clear](#class-bitmapfont-method-clear) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [create\_from\_fnt](#class-bitmapfont-method-create-from-fnt) **(** [String](class_string#class-string) path **)** |
| [int](class_int#class-int) | [get\_kerning\_pair](#class-bitmapfont-method-get-kerning-pair) **(** [int](class_int#class-int) char\_a, [int](class_int#class-int) char\_b **)** const |
| [Texture](class_texture#class-texture) | [get\_texture](#class-bitmapfont-method-get-texture) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_texture\_count](#class-bitmapfont-method-get-texture-count) **(** **)** const |
Property Descriptions
---------------------
### [float](class_float#class-float) ascent
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_ascent(value) |
| *Getter* | get\_ascent() |
Ascent (number of pixels above the baseline).
### [bool](class_bool#class-bool) distance\_field
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_distance\_field\_hint(value) |
| *Getter* | is\_distance\_field\_hint() |
If `true`, distance field hint is enabled.
### [BitmapFont](#class-bitmapfont) fallback
| | |
| --- | --- |
| *Setter* | set\_fallback(value) |
| *Getter* | get\_fallback() |
The fallback font.
### [float](class_float#class-float) height
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_height(value) |
| *Getter* | get\_height() |
Total font height (ascent plus descent) in pixels.
Method Descriptions
-------------------
### void add\_char ( [int](class_int#class-int) character, [int](class_int#class-int) texture, [Rect2](class_rect2#class-rect2) rect, [Vector2](class_vector2#class-vector2) align=Vector2( 0, 0 ), [float](class_float#class-float) advance=-1 )
Adds a character to the font, where `character` is the Unicode value, `texture` is the texture index, `rect` is the region in the texture (in pixels!), `align` is the (optional) alignment for the character and `advance` is the (optional) advance.
### void add\_kerning\_pair ( [int](class_int#class-int) char\_a, [int](class_int#class-int) char\_b, [int](class_int#class-int) kerning )
Adds a kerning pair to the `BitmapFont` as a difference. Kerning pairs are special cases where a typeface advance is determined by the next character.
### void add\_texture ( [Texture](class_texture#class-texture) texture )
Adds a texture to the `BitmapFont`.
### void clear ( )
Clears all the font data and settings.
### [Error](class_%40globalscope#enum-globalscope-error) create\_from\_fnt ( [String](class_string#class-string) path )
Creates a BitmapFont from the `*.fnt` file at `path`.
### [int](class_int#class-int) get\_kerning\_pair ( [int](class_int#class-int) char\_a, [int](class_int#class-int) char\_b ) const
Returns a kerning pair as a difference.
### [Texture](class_texture#class-texture) get\_texture ( [int](class_int#class-int) idx ) const
Returns the font atlas texture at index `idx`.
### [int](class_int#class-int) get\_texture\_count ( ) const
Returns the number of textures in the BitmapFont atlas.
godot Reference Reference
=========
**Inherits:** [Object](class_object#class-object)
**Inherited By:** [AESContext](class_aescontext#class-aescontext), [ARVRInterface](class_arvrinterface#class-arvrinterface), [ARVRPositionalTracker](class_arvrpositionaltracker#class-arvrpositionaltracker), [AStar](class_astar#class-astar), [AStar2D](class_astar2d#class-astar2d), [AnimationTrackEditPlugin](class_animationtrackeditplugin#class-animationtrackeditplugin), [AudioEffectInstance](class_audioeffectinstance#class-audioeffectinstance), [AudioStreamPlayback](class_audiostreamplayback#class-audiostreamplayback), [CameraFeed](class_camerafeed#class-camerafeed), [CharFXTransform](class_charfxtransform#class-charfxtransform), [ConfigFile](class_configfile#class-configfile), [Crypto](class_crypto#class-crypto), [DTLSServer](class_dtlsserver#class-dtlsserver), [Directory](class_directory#class-directory), [EditorExportPlugin](class_editorexportplugin#class-editorexportplugin), [EditorFeatureProfile](class_editorfeatureprofile#class-editorfeatureprofile), [EditorInspectorPlugin](class_editorinspectorplugin#class-editorinspectorplugin), [EditorResourceConversionPlugin](class_editorresourceconversionplugin#class-editorresourceconversionplugin), [EditorResourcePreviewGenerator](class_editorresourcepreviewgenerator#class-editorresourcepreviewgenerator), [EditorSceneImporter](class_editorsceneimporter#class-editorsceneimporter), [EditorScenePostImport](class_editorscenepostimport#class-editorscenepostimport), [EditorScript](class_editorscript#class-editorscript), [EncodedObjectAsID](class_encodedobjectasid#class-encodedobjectasid), [Expression](class_expression#class-expression), [File](class_file#class-file), [FuncRef](class_funcref#class-funcref), [GDNative](class_gdnative#class-gdnative), [GDScriptFunctionState](class_gdscriptfunctionstate#class-gdscriptfunctionstate), [HMACContext](class_hmaccontext#class-hmaccontext), [HTTPClient](class_httpclient#class-httpclient), [HashingContext](class_hashingcontext#class-hashingcontext), [JSONParseResult](class_jsonparseresult#class-jsonparseresult), [JavaClass](class_javaclass#class-javaclass), [JavaScriptObject](class_javascriptobject#class-javascriptobject), [KinematicCollision](class_kinematiccollision#class-kinematiccollision), [KinematicCollision2D](class_kinematiccollision2d#class-kinematiccollision2d), [MeshDataTool](class_meshdatatool#class-meshdatatool), [MultiplayerAPI](class_multiplayerapi#class-multiplayerapi), [Mutex](class_mutex#class-mutex), [PCKPacker](class_pckpacker#class-pckpacker), [PackedDataContainerRef](class_packeddatacontainerref#class-packeddatacontainerref), [PacketPeer](class_packetpeer#class-packetpeer), [Physics2DShapeQueryParameters](class_physics2dshapequeryparameters#class-physics2dshapequeryparameters), [Physics2DTestMotionResult](class_physics2dtestmotionresult#class-physics2dtestmotionresult), [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters), [PhysicsTestMotionResult](class_physicstestmotionresult#class-physicstestmotionresult), [RandomNumberGenerator](class_randomnumbergenerator#class-randomnumbergenerator), [RegEx](class_regex#class-regex), [RegExMatch](class_regexmatch#class-regexmatch), [Resource](class_resource#class-resource), [ResourceFormatLoader](class_resourceformatloader#class-resourceformatloader), [ResourceFormatSaver](class_resourceformatsaver#class-resourceformatsaver), [ResourceImporter](class_resourceimporter#class-resourceimporter), [ResourceInteractiveLoader](class_resourceinteractiveloader#class-resourceinteractiveloader), [SceneState](class_scenestate#class-scenestate), [SceneTreeTimer](class_scenetreetimer#class-scenetreetimer), [SceneTreeTween](class_scenetreetween#class-scenetreetween), [Semaphore](class_semaphore#class-semaphore), [SkinReference](class_skinreference#class-skinreference), [SpatialGizmo](class_spatialgizmo#class-spatialgizmo), [SpatialVelocityTracker](class_spatialvelocitytracker#class-spatialvelocitytracker), [StreamPeer](class_streampeer#class-streampeer), [SurfaceTool](class_surfacetool#class-surfacetool), [TCP\_Server](class_tcp_server#class-tcp-server), [Thread](class_thread#class-thread), [TriangleMesh](class_trianglemesh#class-trianglemesh), [Tweener](class_tweener#class-tweener), [UDPServer](class_udpserver#class-udpserver), [UPNP](class_upnp#class-upnp), [UPNPDevice](class_upnpdevice#class-upnpdevice), [VisualScriptFunctionState](class_visualscriptfunctionstate#class-visualscriptfunctionstate), [WeakRef](class_weakref#class-weakref), [WebRTCPeerConnection](class_webrtcpeerconnection#class-webrtcpeerconnection), [XMLParser](class_xmlparser#class-xmlparser)
Base class for reference-counted objects.
Description
-----------
Base class for any object that keeps a reference count. [Resource](class_resource#class-resource) and many other helper objects inherit this class.
Unlike other [Object](class_object#class-object) types, References keep an internal reference counter so that they are automatically released when no longer in use, and only then. References therefore do not need to be freed manually with [Object.free](class_object#class-object-method-free).
In the vast majority of use cases, instantiating and using `Reference`-derived types is all you need to do. The methods provided in this class are only for advanced users, and can cause issues if misused.
**Note:** In C#, references will not be freed instantly after they are no longer in use. Instead, garbage collection will run periodically and will free references that are no longer in use. This means that unused references will linger on for a while before being removed.
Tutorials
---------
* [When and how to avoid using nodes for everything](https://docs.godotengine.org/en/3.5/tutorials/best_practices/node_alternatives.html)
Methods
-------
| | |
| --- | --- |
| [bool](class_bool#class-bool) | [init\_ref](#class-reference-method-init-ref) **(** **)** |
| [bool](class_bool#class-bool) | [reference](#class-reference-method-reference) **(** **)** |
| [bool](class_bool#class-bool) | [unreference](#class-reference-method-unreference) **(** **)** |
Method Descriptions
-------------------
### [bool](class_bool#class-bool) init\_ref ( )
Initializes the internal reference counter. Use this only if you really know what you are doing.
Returns whether the initialization was successful.
### [bool](class_bool#class-bool) reference ( )
Increments the internal reference counter. Use this only if you really know what you are doing.
Returns `true` if the increment was successful, `false` otherwise.
### [bool](class_bool#class-bool) unreference ( )
Decrements the internal reference counter. Use this only if you really know what you are doing.
Returns `true` if the decrement was successful, `false` otherwise.
godot AudioStreamPlayer3D AudioStreamPlayer3D
===================
**Inherits:** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Plays positional sound in 3D space.
Description
-----------
Plays a sound effect with directed sound effects, dampens with distance if needed, generates effect of hearable position in space. For greater realism, a low-pass filter is automatically applied to distant sounds. This can be disabled by setting [attenuation\_filter\_cutoff\_hz](#class-audiostreamplayer3d-property-attenuation-filter-cutoff-hz) to `20500`.
By default, audio is heard from the camera position. This can be changed by adding a [Listener](class_listener#class-listener) node to the scene and enabling it by calling [Listener.make\_current](class_listener#class-listener-method-make-current) on it.
See also [AudioStreamPlayer](class_audiostreamplayer#class-audiostreamplayer) to play a sound non-positionally.
**Note:** Hiding an `AudioStreamPlayer3D` node does not disable its audio output. To temporarily disable an `AudioStreamPlayer3D`'s audio output, set [unit\_db](#class-audiostreamplayer3d-property-unit-db) to a very low value like `-100` (which isn't audible to human hearing).
Tutorials
---------
* [Audio streams](https://docs.godotengine.org/en/3.5/tutorials/audio/audio_streams.html)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [area\_mask](#class-audiostreamplayer3d-property-area-mask) | `1` |
| [float](class_float#class-float) | [attenuation\_filter\_cutoff\_hz](#class-audiostreamplayer3d-property-attenuation-filter-cutoff-hz) | `5000.0` |
| [float](class_float#class-float) | [attenuation\_filter\_db](#class-audiostreamplayer3d-property-attenuation-filter-db) | `-24.0` |
| [AttenuationModel](#enum-audiostreamplayer3d-attenuationmodel) | [attenuation\_model](#class-audiostreamplayer3d-property-attenuation-model) | `0` |
| [bool](class_bool#class-bool) | [autoplay](#class-audiostreamplayer3d-property-autoplay) | `false` |
| [String](class_string#class-string) | [bus](#class-audiostreamplayer3d-property-bus) | `"Master"` |
| [DopplerTracking](#enum-audiostreamplayer3d-dopplertracking) | [doppler\_tracking](#class-audiostreamplayer3d-property-doppler-tracking) | `0` |
| [float](class_float#class-float) | [emission\_angle\_degrees](#class-audiostreamplayer3d-property-emission-angle-degrees) | `45.0` |
| [bool](class_bool#class-bool) | [emission\_angle\_enabled](#class-audiostreamplayer3d-property-emission-angle-enabled) | `false` |
| [float](class_float#class-float) | [emission\_angle\_filter\_attenuation\_db](#class-audiostreamplayer3d-property-emission-angle-filter-attenuation-db) | `-12.0` |
| [float](class_float#class-float) | [max\_db](#class-audiostreamplayer3d-property-max-db) | `3.0` |
| [float](class_float#class-float) | [max\_distance](#class-audiostreamplayer3d-property-max-distance) | `0.0` |
| [OutOfRangeMode](#enum-audiostreamplayer3d-outofrangemode) | [out\_of\_range\_mode](#class-audiostreamplayer3d-property-out-of-range-mode) | `0` |
| [float](class_float#class-float) | [pitch\_scale](#class-audiostreamplayer3d-property-pitch-scale) | `1.0` |
| [bool](class_bool#class-bool) | [playing](#class-audiostreamplayer3d-property-playing) | `false` |
| [AudioStream](class_audiostream#class-audiostream) | [stream](#class-audiostreamplayer3d-property-stream) | |
| [bool](class_bool#class-bool) | [stream\_paused](#class-audiostreamplayer3d-property-stream-paused) | `false` |
| [float](class_float#class-float) | [unit\_db](#class-audiostreamplayer3d-property-unit-db) | `0.0` |
| [float](class_float#class-float) | [unit\_size](#class-audiostreamplayer3d-property-unit-size) | `1.0` |
Methods
-------
| | |
| --- | --- |
| [float](class_float#class-float) | [get\_playback\_position](#class-audiostreamplayer3d-method-get-playback-position) **(** **)** |
| [AudioStreamPlayback](class_audiostreamplayback#class-audiostreamplayback) | [get\_stream\_playback](#class-audiostreamplayer3d-method-get-stream-playback) **(** **)** |
| void | [play](#class-audiostreamplayer3d-method-play) **(** [float](class_float#class-float) from\_position=0.0 **)** |
| void | [seek](#class-audiostreamplayer3d-method-seek) **(** [float](class_float#class-float) to\_position **)** |
| void | [stop](#class-audiostreamplayer3d-method-stop) **(** **)** |
Signals
-------
### finished ( )
Emitted when the audio stops playing.
Enumerations
------------
enum **AttenuationModel**:
* **ATTENUATION\_INVERSE\_DISTANCE** = **0** --- Linear dampening of loudness according to distance.
* **ATTENUATION\_INVERSE\_SQUARE\_DISTANCE** = **1** --- Squared dampening of loudness according to distance.
* **ATTENUATION\_LOGARITHMIC** = **2** --- Logarithmic dampening of loudness according to distance.
* **ATTENUATION\_DISABLED** = **3** --- No dampening of loudness according to distance. The sound will still be heard positionally, unlike an [AudioStreamPlayer](class_audiostreamplayer#class-audiostreamplayer). [ATTENUATION\_DISABLED](#class-audiostreamplayer3d-constant-attenuation-disabled) can be combined with a [max\_distance](#class-audiostreamplayer3d-property-max-distance) value greater than `0.0` to achieve linear attenuation clamped to a sphere of a defined size.
enum **OutOfRangeMode**:
* **OUT\_OF\_RANGE\_MIX** = **0** --- Mix this audio in, even when it's out of range. This increases CPU usage, but keeps the sound playing at the correct position if the camera leaves and enters the `AudioStreamPlayer3D`'s [max\_distance](#class-audiostreamplayer3d-property-max-distance) radius.
* **OUT\_OF\_RANGE\_PAUSE** = **1** --- Pause this audio when it gets out of range. This decreases CPU usage, but will cause the sound to restart if the camera leaves and enters the `AudioStreamPlayer3D`'s [max\_distance](#class-audiostreamplayer3d-property-max-distance) radius.
enum **DopplerTracking**:
* **DOPPLER\_TRACKING\_DISABLED** = **0** --- Disables doppler tracking.
* **DOPPLER\_TRACKING\_IDLE\_STEP** = **1** --- Executes doppler tracking in idle step (every rendered frame).
* **DOPPLER\_TRACKING\_PHYSICS\_STEP** = **2** --- Executes doppler tracking in physics step (every simulated physics frame).
Property Descriptions
---------------------
### [int](class_int#class-int) area\_mask
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_area\_mask(value) |
| *Getter* | get\_area\_mask() |
Determines which [Area](class_area#class-area) layers affect the sound for reverb and audio bus effects. Areas can be used to redirect [AudioStream](class_audiostream#class-audiostream)s so that they play in a certain audio bus. An example of how you might use this is making a "water" area so that sounds played in the water are redirected through an audio bus to make them sound like they are being played underwater.
### [float](class_float#class-float) attenuation\_filter\_cutoff\_hz
| | |
| --- | --- |
| *Default* | `5000.0` |
| *Setter* | set\_attenuation\_filter\_cutoff\_hz(value) |
| *Getter* | get\_attenuation\_filter\_cutoff\_hz() |
Dampens audio using a low-pass filter above this frequency, in Hz. To disable the dampening effect entirely, set this to `20500` as this frequency is above the human hearing limit.
### [float](class_float#class-float) attenuation\_filter\_db
| | |
| --- | --- |
| *Default* | `-24.0` |
| *Setter* | set\_attenuation\_filter\_db(value) |
| *Getter* | get\_attenuation\_filter\_db() |
Amount how much the filter affects the loudness, in decibels.
### [AttenuationModel](#enum-audiostreamplayer3d-attenuationmodel) attenuation\_model
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_attenuation\_model(value) |
| *Getter* | get\_attenuation\_model() |
Decides if audio should get quieter with distance linearly, quadratically, logarithmically, or not be affected by distance, effectively disabling attenuation.
### [bool](class_bool#class-bool) autoplay
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_autoplay(value) |
| *Getter* | is\_autoplay\_enabled() |
If `true`, audio plays when the AudioStreamPlayer3D node is added to scene tree.
### [String](class_string#class-string) bus
| | |
| --- | --- |
| *Default* | `"Master"` |
| *Setter* | set\_bus(value) |
| *Getter* | get\_bus() |
The bus on which this audio is playing.
**Note:** When setting this property, keep in mind that no validation is performed to see if the given name matches an existing bus. This is because audio bus layouts might be loaded after this property is set. If this given name can't be resolved at runtime, it will fall back to `"Master"`.
### [DopplerTracking](#enum-audiostreamplayer3d-dopplertracking) doppler\_tracking
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_doppler\_tracking(value) |
| *Getter* | get\_doppler\_tracking() |
Decides in which step the [Doppler effect](https://en.wikipedia.org/wiki/Doppler_effect) should be calculated.
**Note:** Only effective if the current [Camera](class_camera#class-camera)'s [Camera.doppler\_tracking](class_camera#class-camera-property-doppler-tracking) property is set to a value other than [Camera.DOPPLER\_TRACKING\_DISABLED](class_camera#class-camera-constant-doppler-tracking-disabled).
### [float](class_float#class-float) emission\_angle\_degrees
| | |
| --- | --- |
| *Default* | `45.0` |
| *Setter* | set\_emission\_angle(value) |
| *Getter* | get\_emission\_angle() |
The angle in which the audio reaches cameras undampened.
### [bool](class_bool#class-bool) emission\_angle\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_emission\_angle\_enabled(value) |
| *Getter* | is\_emission\_angle\_enabled() |
If `true`, the audio should be dampened according to the direction of the sound.
### [float](class_float#class-float) emission\_angle\_filter\_attenuation\_db
| | |
| --- | --- |
| *Default* | `-12.0` |
| *Setter* | set\_emission\_angle\_filter\_attenuation\_db(value) |
| *Getter* | get\_emission\_angle\_filter\_attenuation\_db() |
Dampens audio if camera is outside of [emission\_angle\_degrees](#class-audiostreamplayer3d-property-emission-angle-degrees) and [emission\_angle\_enabled](#class-audiostreamplayer3d-property-emission-angle-enabled) is set by this factor, in decibels.
### [float](class_float#class-float) max\_db
| | |
| --- | --- |
| *Default* | `3.0` |
| *Setter* | set\_max\_db(value) |
| *Getter* | get\_max\_db() |
Sets the absolute maximum of the soundlevel, in decibels.
### [float](class_float#class-float) max\_distance
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_max\_distance(value) |
| *Getter* | get\_max\_distance() |
Sets the distance from which the [out\_of\_range\_mode](#class-audiostreamplayer3d-property-out-of-range-mode) takes effect. Has no effect if set to 0.
### [OutOfRangeMode](#enum-audiostreamplayer3d-outofrangemode) out\_of\_range\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_out\_of\_range\_mode(value) |
| *Getter* | get\_out\_of\_range\_mode() |
Decides if audio should pause when source is outside of [max\_distance](#class-audiostreamplayer3d-property-max-distance) range.
### [float](class_float#class-float) pitch\_scale
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_pitch\_scale(value) |
| *Getter* | get\_pitch\_scale() |
The pitch and the tempo of the audio, as a multiplier of the audio sample's sample rate.
### [bool](class_bool#class-bool) playing
| | |
| --- | --- |
| *Default* | `false` |
| *Getter* | is\_playing() |
If `true`, audio is playing.
### [AudioStream](class_audiostream#class-audiostream) stream
| | |
| --- | --- |
| *Setter* | set\_stream(value) |
| *Getter* | get\_stream() |
The [AudioStream](class_audiostream#class-audiostream) resource to be played.
### [bool](class_bool#class-bool) stream\_paused
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_stream\_paused(value) |
| *Getter* | get\_stream\_paused() |
If `true`, the playback is paused. You can resume it by setting [stream\_paused](#class-audiostreamplayer3d-property-stream-paused) to `false`.
### [float](class_float#class-float) unit\_db
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_unit\_db(value) |
| *Getter* | get\_unit\_db() |
The base sound level unaffected by dampening, in decibels.
### [float](class_float#class-float) unit\_size
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_unit\_size(value) |
| *Getter* | get\_unit\_size() |
The factor for the attenuation effect. Higher values make the sound audible over a larger distance.
Method Descriptions
-------------------
### [float](class_float#class-float) get\_playback\_position ( )
Returns the position in the [AudioStream](class_audiostream#class-audiostream).
### [AudioStreamPlayback](class_audiostreamplayback#class-audiostreamplayback) get\_stream\_playback ( )
Returns the [AudioStreamPlayback](class_audiostreamplayback#class-audiostreamplayback) object associated with this `AudioStreamPlayer3D`.
### void play ( [float](class_float#class-float) from\_position=0.0 )
Plays the audio from the given position `from_position`, in seconds.
### void seek ( [float](class_float#class-float) to\_position )
Sets the position from which audio will be played, in seconds.
### void stop ( )
Stops the audio.
| programming_docs |
godot CollisionShape CollisionShape
==============
**Inherits:** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Node that represents collision shape data in 3D space.
Description
-----------
Editor facility for creating and editing collision shapes in 3D space. Set the [shape](#class-collisionshape-property-shape) property to configure the shape. **IMPORTANT**: this is an Editor-only helper to create shapes, use [CollisionObject.shape\_owner\_get\_shape](class_collisionobject#class-collisionobject-method-shape-owner-get-shape) to get the actual shape.
You can use this node to represent all sorts of collision shapes, for example, add this to an [Area](class_area#class-area) to give it a detection shape, or add it to a [PhysicsBody](class_physicsbody#class-physicsbody) to create a solid object.
Tutorials
---------
* [Physics introduction](https://docs.godotengine.org/en/3.5/tutorials/physics/physics_introduction.html)
* [3D Kinematic Character Demo](https://godotengine.org/asset-library/asset/126)
* [3D Platformer Demo](https://godotengine.org/asset-library/asset/125)
* [Third Person Shooter Demo](https://godotengine.org/asset-library/asset/678)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [disabled](#class-collisionshape-property-disabled) | `false` |
| [Shape](class_shape#class-shape) | [shape](#class-collisionshape-property-shape) | |
Methods
-------
| | |
| --- | --- |
| void | [make\_convex\_from\_brothers](#class-collisionshape-method-make-convex-from-brothers) **(** **)** |
| void | [resource\_changed](#class-collisionshape-method-resource-changed) **(** [Resource](class_resource#class-resource) resource **)** |
Property Descriptions
---------------------
### [bool](class_bool#class-bool) disabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_disabled(value) |
| *Getter* | is\_disabled() |
A disabled collision shape has no effect in the world.
### [Shape](class_shape#class-shape) shape
| | |
| --- | --- |
| *Setter* | set\_shape(value) |
| *Getter* | get\_shape() |
The actual shape owned by this collision shape.
Method Descriptions
-------------------
### void make\_convex\_from\_brothers ( )
Sets the collision shape's shape to the addition of all its convexed [MeshInstance](class_meshinstance#class-meshinstance) siblings geometry.
### void resource\_changed ( [Resource](class_resource#class-resource) resource )
If this method exists within a script it will be called whenever the shape resource has been modified.
godot Position3D Position3D
==========
**Inherits:** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Generic 3D position hint for editing.
Description
-----------
Generic 3D position hint for editing. It's just like a plain [Spatial](class_spatial#class-spatial), but it displays as a cross in the 3D editor at all times.
godot WebRTCPeerConnection WebRTCPeerConnection
====================
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [WebRTCPeerConnectionGDNative](class_webrtcpeerconnectiongdnative#class-webrtcpeerconnectiongdnative)
Interface to a WebRTC peer connection.
Description
-----------
A WebRTC connection between the local computer and a remote peer. Provides an interface to connect, maintain and monitor the connection.
Setting up a WebRTC connection between two peers from now on) may not seem a trivial task, but it can be broken down into 3 main steps:
* The peer that wants to initiate the connection (`A` from now on) creates an offer and send it to the other peer (`B` from now on).
* `B` receives the offer, generate and answer, and sends it to `A`).
* `A` and `B` then generates and exchange ICE candidates with each other.
After these steps, the connection should become connected. Keep on reading or look into the tutorial for more information.
Methods
-------
| | |
| --- | --- |
| [Error](class_%40globalscope#enum-globalscope-error) | [add\_ice\_candidate](#class-webrtcpeerconnection-method-add-ice-candidate) **(** [String](class_string#class-string) media, [int](class_int#class-int) index, [String](class_string#class-string) name **)** |
| void | [close](#class-webrtcpeerconnection-method-close) **(** **)** |
| [WebRTCDataChannel](class_webrtcdatachannel#class-webrtcdatachannel) | [create\_data\_channel](#class-webrtcpeerconnection-method-create-data-channel) **(** [String](class_string#class-string) label, [Dictionary](class_dictionary#class-dictionary) options={ } **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [create\_offer](#class-webrtcpeerconnection-method-create-offer) **(** **)** |
| [ConnectionState](#enum-webrtcpeerconnection-connectionstate) | [get\_connection\_state](#class-webrtcpeerconnection-method-get-connection-state) **(** **)** const |
| [Error](class_%40globalscope#enum-globalscope-error) | [initialize](#class-webrtcpeerconnection-method-initialize) **(** [Dictionary](class_dictionary#class-dictionary) configuration={ } **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [poll](#class-webrtcpeerconnection-method-poll) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [set\_local\_description](#class-webrtcpeerconnection-method-set-local-description) **(** [String](class_string#class-string) type, [String](class_string#class-string) sdp **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [set\_remote\_description](#class-webrtcpeerconnection-method-set-remote-description) **(** [String](class_string#class-string) type, [String](class_string#class-string) sdp **)** |
Signals
-------
### data\_channel\_received ( [Object](class_object#class-object) channel )
Emitted when a new in-band channel is received, i.e. when the channel was created with `negotiated: false` (default).
The object will be an instance of [WebRTCDataChannel](class_webrtcdatachannel#class-webrtcdatachannel). You must keep a reference of it or it will be closed automatically. See [create\_data\_channel](#class-webrtcpeerconnection-method-create-data-channel).
### ice\_candidate\_created ( [String](class_string#class-string) media, [int](class_int#class-int) index, [String](class_string#class-string) name )
Emitted when a new ICE candidate has been created. The three parameters are meant to be passed to the remote peer over the signaling server.
### session\_description\_created ( [String](class_string#class-string) type, [String](class_string#class-string) sdp )
Emitted after a successful call to [create\_offer](#class-webrtcpeerconnection-method-create-offer) or [set\_remote\_description](#class-webrtcpeerconnection-method-set-remote-description) (when it generates an answer). The parameters are meant to be passed to [set\_local\_description](#class-webrtcpeerconnection-method-set-local-description) on this object, and sent to the remote peer over the signaling server.
Enumerations
------------
enum **ConnectionState**:
* **STATE\_NEW** = **0** --- The connection is new, data channels and an offer can be created in this state.
* **STATE\_CONNECTING** = **1** --- The peer is connecting, ICE is in progress, none of the transports has failed.
* **STATE\_CONNECTED** = **2** --- The peer is connected, all ICE transports are connected.
* **STATE\_DISCONNECTED** = **3** --- At least one ICE transport is disconnected.
* **STATE\_FAILED** = **4** --- One or more of the ICE transports failed.
* **STATE\_CLOSED** = **5** --- The peer connection is closed (after calling [close](#class-webrtcpeerconnection-method-close) for example).
Method Descriptions
-------------------
### [Error](class_%40globalscope#enum-globalscope-error) add\_ice\_candidate ( [String](class_string#class-string) media, [int](class_int#class-int) index, [String](class_string#class-string) name )
Add an ice candidate generated by a remote peer (and received over the signaling server). See [ice\_candidate\_created](#class-webrtcpeerconnection-signal-ice-candidate-created).
### void close ( )
Close the peer connection and all data channels associated with it.
**Note:** You cannot reuse this object for a new connection unless you call [initialize](#class-webrtcpeerconnection-method-initialize).
### [WebRTCDataChannel](class_webrtcdatachannel#class-webrtcdatachannel) create\_data\_channel ( [String](class_string#class-string) label, [Dictionary](class_dictionary#class-dictionary) options={ } )
Returns a new [WebRTCDataChannel](class_webrtcdatachannel#class-webrtcdatachannel) (or `null` on failure) with given `label` and optionally configured via the `options` dictionary. This method can only be called when the connection is in state [STATE\_NEW](#class-webrtcpeerconnection-constant-state-new).
There are two ways to create a working data channel: either call [create\_data\_channel](#class-webrtcpeerconnection-method-create-data-channel) on only one of the peer and listen to [data\_channel\_received](#class-webrtcpeerconnection-signal-data-channel-received) on the other, or call [create\_data\_channel](#class-webrtcpeerconnection-method-create-data-channel) on both peers, with the same values, and the `negotiated` option set to `true`.
Valid `options` are:
```
{
"negotiated": true, # When set to true (default off), means the channel is negotiated out of band. "id" must be set too. "data_channel_received" will not be called.
"id": 1, # When "negotiated" is true this value must also be set to the same value on both peer.
# Only one of maxRetransmits and maxPacketLifeTime can be specified, not both. They make the channel unreliable (but also better at real time).
"maxRetransmits": 1, # Specify the maximum number of attempt the peer will make to retransmits packets if they are not acknowledged.
"maxPacketLifeTime": 100, # Specify the maximum amount of time before giving up retransmitions of unacknowledged packets (in milliseconds).
"ordered": true, # When in unreliable mode (i.e. either "maxRetransmits" or "maxPacketLifetime" is set), "ordered" (true by default) specify if packet ordering is to be enforced.
"protocol": "my-custom-protocol", # A custom sub-protocol string for this channel.
}
```
**Note:** You must keep a reference to channels created this way, or it will be closed.
### [Error](class_%40globalscope#enum-globalscope-error) create\_offer ( )
Creates a new SDP offer to start a WebRTC connection with a remote peer. At least one [WebRTCDataChannel](class_webrtcdatachannel#class-webrtcdatachannel) must have been created before calling this method.
If this functions returns [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok), [session\_description\_created](#class-webrtcpeerconnection-signal-session-description-created) will be called when the session is ready to be sent.
### [ConnectionState](#enum-webrtcpeerconnection-connectionstate) get\_connection\_state ( ) const
Returns the connection state. See [ConnectionState](#enum-webrtcpeerconnection-connectionstate).
### [Error](class_%40globalscope#enum-globalscope-error) initialize ( [Dictionary](class_dictionary#class-dictionary) configuration={ } )
Re-initialize this peer connection, closing any previously active connection, and going back to state [STATE\_NEW](#class-webrtcpeerconnection-constant-state-new). A dictionary of `options` can be passed to configure the peer connection.
Valid `options` are:
```
{
"iceServers": [
{
"urls": [ "stun:stun.example.com:3478" ], # One or more STUN servers.
},
{
"urls": [ "turn:turn.example.com:3478" ], # One or more TURN servers.
"username": "a_username", # Optional username for the TURN server.
"credential": "a_password", # Optional password for the TURN server.
}
]
}
```
### [Error](class_%40globalscope#enum-globalscope-error) poll ( )
Call this method frequently (e.g. in [Node.\_process](class_node#class-node-method-process) or [Node.\_physics\_process](class_node#class-node-method-physics-process)) to properly receive signals.
### [Error](class_%40globalscope#enum-globalscope-error) set\_local\_description ( [String](class_string#class-string) type, [String](class_string#class-string) sdp )
Sets the SDP description of the local peer. This should be called in response to [session\_description\_created](#class-webrtcpeerconnection-signal-session-description-created).
After calling this function the peer will start emitting [ice\_candidate\_created](#class-webrtcpeerconnection-signal-ice-candidate-created) (unless an [Error](class_%40globalscope#enum-globalscope-error) different from [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok) is returned).
### [Error](class_%40globalscope#enum-globalscope-error) set\_remote\_description ( [String](class_string#class-string) type, [String](class_string#class-string) sdp )
Sets the SDP description of the remote peer. This should be called with the values generated by a remote peer and received over the signaling server.
If `type` is `offer` the peer will emit [session\_description\_created](#class-webrtcpeerconnection-signal-session-description-created) with the appropriate answer.
If `type` is `answer` the peer will start emitting [ice\_candidate\_created](#class-webrtcpeerconnection-signal-ice-candidate-created).
godot Particles2D Particles2D
===========
**Inherits:** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
GPU-based 2D particle emitter.
Description
-----------
2D particle node used to create a variety of particle systems and effects. `Particles2D` features an emitter that generates some number of particles at a given rate.
Use the `process_material` property to add a [ParticlesMaterial](class_particlesmaterial#class-particlesmaterial) to configure particle appearance and behavior. Alternatively, you can add a [ShaderMaterial](class_shadermaterial#class-shadermaterial) which will be applied to all particles.
**Note:** `Particles2D` only work when using the GLES3 renderer. If using the GLES2 renderer, use [CPUParticles2D](class_cpuparticles2d#class-cpuparticles2d) instead. You can convert `Particles2D` to [CPUParticles2D](class_cpuparticles2d#class-cpuparticles2d) by selecting the node, clicking the **Particles** menu at the top of the 2D editor viewport then choosing **Convert to CPUParticles2D**.
**Note:** On macOS, `Particles2D` rendering is much slower than [CPUParticles2D](class_cpuparticles2d#class-cpuparticles2d) due to transform feedback being implemented on the CPU instead of the GPU. Consider using [CPUParticles2D](class_cpuparticles2d#class-cpuparticles2d) instead when targeting macOS.
**Note:** After working on a Particles node, remember to update its [visibility\_rect](#class-particles2d-property-visibility-rect) by selecting it, clicking the **Particles** menu at the top of the 2D editor viewport then choose **Generate Visibility Rect**. Otherwise, particles may suddenly disappear depending on the camera position and angle.
**Note:** Unlike [CPUParticles2D](class_cpuparticles2d#class-cpuparticles2d), `Particles2D` currently ignore the texture region defined in [AtlasTexture](class_atlastexture#class-atlastexture)s.
Tutorials
---------
* [Particle systems (2D)](https://docs.godotengine.org/en/3.5/tutorials/2d/particle_systems_2d.html)
* [2D Dodge The Creeps Demo](https://godotengine.org/asset-library/asset/515)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [amount](#class-particles2d-property-amount) | `8` |
| [DrawOrder](#enum-particles2d-draworder) | [draw\_order](#class-particles2d-property-draw-order) | `0` |
| [bool](class_bool#class-bool) | [emitting](#class-particles2d-property-emitting) | `true` |
| [float](class_float#class-float) | [explosiveness](#class-particles2d-property-explosiveness) | `0.0` |
| [int](class_int#class-int) | [fixed\_fps](#class-particles2d-property-fixed-fps) | `0` |
| [bool](class_bool#class-bool) | [fract\_delta](#class-particles2d-property-fract-delta) | `true` |
| [float](class_float#class-float) | [lifetime](#class-particles2d-property-lifetime) | `1.0` |
| [bool](class_bool#class-bool) | [local\_coords](#class-particles2d-property-local-coords) | `true` |
| [Texture](class_texture#class-texture) | [normal\_map](#class-particles2d-property-normal-map) | |
| [bool](class_bool#class-bool) | [one\_shot](#class-particles2d-property-one-shot) | `false` |
| [float](class_float#class-float) | [preprocess](#class-particles2d-property-preprocess) | `0.0` |
| [Material](class_material#class-material) | [process\_material](#class-particles2d-property-process-material) | |
| [float](class_float#class-float) | [randomness](#class-particles2d-property-randomness) | `0.0` |
| [float](class_float#class-float) | [speed\_scale](#class-particles2d-property-speed-scale) | `1.0` |
| [Texture](class_texture#class-texture) | [texture](#class-particles2d-property-texture) | |
| [Rect2](class_rect2#class-rect2) | [visibility\_rect](#class-particles2d-property-visibility-rect) | `Rect2( -100, -100, 200, 200 )` |
Methods
-------
| | |
| --- | --- |
| [Rect2](class_rect2#class-rect2) | [capture\_rect](#class-particles2d-method-capture-rect) **(** **)** const |
| void | [restart](#class-particles2d-method-restart) **(** **)** |
Enumerations
------------
enum **DrawOrder**:
* **DRAW\_ORDER\_INDEX** = **0** --- Particles are drawn in the order emitted.
* **DRAW\_ORDER\_LIFETIME** = **1** --- Particles are drawn in order of remaining lifetime.
Property Descriptions
---------------------
### [int](class_int#class-int) amount
| | |
| --- | --- |
| *Default* | `8` |
| *Setter* | set\_amount(value) |
| *Getter* | get\_amount() |
The number of particles emitted in one emission cycle (corresponding to the [lifetime](#class-particles2d-property-lifetime)).
**Note:** Changing [amount](#class-particles2d-property-amount) will reset the particle emission, therefore removing all particles that were already emitted before changing [amount](#class-particles2d-property-amount).
### [DrawOrder](#enum-particles2d-draworder) draw\_order
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_draw\_order(value) |
| *Getter* | get\_draw\_order() |
Particle draw order. Uses [DrawOrder](#enum-particles2d-draworder) values.
### [bool](class_bool#class-bool) emitting
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_emitting(value) |
| *Getter* | is\_emitting() |
If `true`, particles are being emitted.
### [float](class_float#class-float) explosiveness
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_explosiveness\_ratio(value) |
| *Getter* | get\_explosiveness\_ratio() |
How rapidly particles in an emission cycle are emitted. If greater than `0`, there will be a gap in emissions before the next cycle begins.
### [int](class_int#class-int) fixed\_fps
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_fixed\_fps(value) |
| *Getter* | get\_fixed\_fps() |
The particle system's frame rate is fixed to a value. For instance, changing the value to 2 will make the particles render at 2 frames per second. Note this does not slow down the simulation of the particle system itself.
### [bool](class_bool#class-bool) fract\_delta
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_fractional\_delta(value) |
| *Getter* | get\_fractional\_delta() |
If `true`, results in fractional delta calculation which has a smoother particles display effect.
### [float](class_float#class-float) lifetime
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_lifetime(value) |
| *Getter* | get\_lifetime() |
The amount of time each particle will exist (in seconds).
### [bool](class_bool#class-bool) local\_coords
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_use\_local\_coordinates(value) |
| *Getter* | get\_use\_local\_coordinates() |
If `true`, particles use the parent node's coordinate space. If `false`, they use global coordinates.
### [Texture](class_texture#class-texture) normal\_map
| | |
| --- | --- |
| *Setter* | set\_normal\_map(value) |
| *Getter* | get\_normal\_map() |
Normal map to be used for the [texture](#class-particles2d-property-texture) property.
**Note:** Godot expects the normal map to use X+, Y-, and Z+ coordinates. See [this page](http://wiki.polycount.com/wiki/Normal_Map_Technical_Details#Common_Swizzle_Coordinates) for a comparison of normal map coordinates expected by popular engines.
### [bool](class_bool#class-bool) one\_shot
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_one\_shot(value) |
| *Getter* | get\_one\_shot() |
If `true`, only one emission cycle occurs. If set `true` during a cycle, emission will stop at the cycle's end.
### [float](class_float#class-float) preprocess
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_pre\_process\_time(value) |
| *Getter* | get\_pre\_process\_time() |
Particle system starts as if it had already run for this many seconds.
### [Material](class_material#class-material) process\_material
| | |
| --- | --- |
| *Setter* | set\_process\_material(value) |
| *Getter* | get\_process\_material() |
[Material](class_material#class-material) for processing particles. Can be a [ParticlesMaterial](class_particlesmaterial#class-particlesmaterial) or a [ShaderMaterial](class_shadermaterial#class-shadermaterial).
### [float](class_float#class-float) randomness
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_randomness\_ratio(value) |
| *Getter* | get\_randomness\_ratio() |
Emission lifetime randomness ratio.
### [float](class_float#class-float) speed\_scale
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_speed\_scale(value) |
| *Getter* | get\_speed\_scale() |
Particle system's running speed scaling ratio. A value of `0` can be used to pause the particles.
### [Texture](class_texture#class-texture) texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Particle texture. If `null`, particles will be squares.
### [Rect2](class_rect2#class-rect2) visibility\_rect
| | |
| --- | --- |
| *Default* | `Rect2( -100, -100, 200, 200 )` |
| *Setter* | set\_visibility\_rect(value) |
| *Getter* | get\_visibility\_rect() |
The [Rect2](class_rect2#class-rect2) that determines the node's region which needs to be visible on screen for the particle system to be active.
Grow the rect if particles suddenly appear/disappear when the node enters/exits the screen. The [Rect2](class_rect2#class-rect2) can be grown via code or with the **Particles → Generate Visibility Rect** editor tool.
Method Descriptions
-------------------
### [Rect2](class_rect2#class-rect2) capture\_rect ( ) const
Returns a rectangle containing the positions of all existing particles.
### void restart ( )
Restarts all the existing particles.
| programming_docs |
godot StreamPeerTCP StreamPeerTCP
=============
**Inherits:** [StreamPeer](class_streampeer#class-streampeer) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
TCP stream peer.
Description
-----------
TCP stream peer. This object can be used to connect to TCP servers, or also is returned by a TCP server.
Methods
-------
| | |
| --- | --- |
| [Error](class_%40globalscope#enum-globalscope-error) | [connect\_to\_host](#class-streampeertcp-method-connect-to-host) **(** [String](class_string#class-string) host, [int](class_int#class-int) port **)** |
| void | [disconnect\_from\_host](#class-streampeertcp-method-disconnect-from-host) **(** **)** |
| [String](class_string#class-string) | [get\_connected\_host](#class-streampeertcp-method-get-connected-host) **(** **)** const |
| [int](class_int#class-int) | [get\_connected\_port](#class-streampeertcp-method-get-connected-port) **(** **)** const |
| [Status](#enum-streampeertcp-status) | [get\_status](#class-streampeertcp-method-get-status) **(** **)** |
| [bool](class_bool#class-bool) | [is\_connected\_to\_host](#class-streampeertcp-method-is-connected-to-host) **(** **)** const |
| void | [set\_no\_delay](#class-streampeertcp-method-set-no-delay) **(** [bool](class_bool#class-bool) enabled **)** |
Enumerations
------------
enum **Status**:
* **STATUS\_NONE** = **0** --- The initial status of the `StreamPeerTCP`. This is also the status after disconnecting.
* **STATUS\_CONNECTING** = **1** --- A status representing a `StreamPeerTCP` that is connecting to a host.
* **STATUS\_CONNECTED** = **2** --- A status representing a `StreamPeerTCP` that is connected to a host.
* **STATUS\_ERROR** = **3** --- A status representing a `StreamPeerTCP` in error state.
Method Descriptions
-------------------
### [Error](class_%40globalscope#enum-globalscope-error) connect\_to\_host ( [String](class_string#class-string) host, [int](class_int#class-int) port )
Connects to the specified `host:port` pair. A hostname will be resolved if valid. Returns [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok) on success or [@GlobalScope.FAILED](class_%40globalscope#class-globalscope-constant-failed) on failure.
### void disconnect\_from\_host ( )
Disconnects from host.
### [String](class_string#class-string) get\_connected\_host ( ) const
Returns the IP of this peer.
### [int](class_int#class-int) get\_connected\_port ( ) const
Returns the port of this peer.
### [Status](#enum-streampeertcp-status) get\_status ( )
Returns the status of the connection, see [Status](#enum-streampeertcp-status).
### [bool](class_bool#class-bool) is\_connected\_to\_host ( ) const
Returns `true` if this peer is currently connected or is connecting to a host, `false` otherwise.
### void set\_no\_delay ( [bool](class_bool#class-bool) enabled )
If `enabled` is `true`, packets will be sent immediately. If `enabled` is `false` (the default), packet transfers will be delayed and combined using [Nagle's algorithm](https://en.wikipedia.org/wiki/Nagle%27s_algorithm).
**Note:** It's recommended to leave this disabled for applications that send large packets or need to transfer a lot of data, as enabling this can decrease the total available bandwidth.
godot Container Container
=========
**Inherits:** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
**Inherited By:** [AspectRatioContainer](class_aspectratiocontainer#class-aspectratiocontainer), [BoxContainer](class_boxcontainer#class-boxcontainer), [CenterContainer](class_centercontainer#class-centercontainer), [EditorProperty](class_editorproperty#class-editorproperty), [FlowContainer](class_flowcontainer#class-flowcontainer), [GraphNode](class_graphnode#class-graphnode), [GridContainer](class_gridcontainer#class-gridcontainer), [MarginContainer](class_margincontainer#class-margincontainer), [PanelContainer](class_panelcontainer#class-panelcontainer), [ScrollContainer](class_scrollcontainer#class-scrollcontainer), [SplitContainer](class_splitcontainer#class-splitcontainer), [TabContainer](class_tabcontainer#class-tabcontainer), [ViewportContainer](class_viewportcontainer#class-viewportcontainer)
Base node for containers.
Description
-----------
Base node for containers. A `Container` contains other controls and automatically arranges them in a certain way.
A Control can inherit this to create custom container classes.
Tutorials
---------
* [GUI containers](https://docs.godotengine.org/en/3.5/tutorials/ui/gui_containers.html)
Methods
-------
| | |
| --- | --- |
| void | [fit\_child\_in\_rect](#class-container-method-fit-child-in-rect) **(** [Control](class_control#class-control) child, [Rect2](class_rect2#class-rect2) rect **)** |
| void | [queue\_sort](#class-container-method-queue-sort) **(** **)** |
Signals
-------
### sort\_children ( )
Emitted when sorting the children is needed.
Constants
---------
### NOTIFICATION\_SORT\_CHILDREN = 50 --- Notification for when sorting the children, it must be obeyed immediately.
Method Descriptions
-------------------
### void fit\_child\_in\_rect ( [Control](class_control#class-control) child, [Rect2](class_rect2#class-rect2) rect )
Fit a child control in a given rect. This is mainly a helper for creating custom container classes.
### void queue\_sort ( )
Queue resort of the contained children. This is called automatically anyway, but can be called upon request.
godot RichTextEffect RichTextEffect
==============
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A custom effect for use with [RichTextLabel](class_richtextlabel#class-richtextlabel).
Description
-----------
A custom effect for use with [RichTextLabel](class_richtextlabel#class-richtextlabel).
**Note:** For a `RichTextEffect` to be usable, a BBCode tag must be defined as a member variable called `bbcode` in the script.
```
# The RichTextEffect will be usable like this: `[example]Some text[/example]`
var bbcode = "example"
```
**Note:** As soon as a [RichTextLabel](class_richtextlabel#class-richtextlabel) contains at least one `RichTextEffect`, it will continuously process the effect unless the project is paused. This may impact battery life negatively.
Tutorials
---------
* [BBCode in RichTextLabel](https://docs.godotengine.org/en/3.5/tutorials/ui/bbcode_in_richtextlabel.html)
* <https://github.com/Eoin-ONeill-Yokai/Godot-Rich-Text-Effect-Test-Project>
Methods
-------
| | |
| --- | --- |
| [bool](class_bool#class-bool) | [\_process\_custom\_fx](#class-richtexteffect-method-process-custom-fx) **(** [CharFXTransform](class_charfxtransform#class-charfxtransform) char\_fx **)** virtual |
Method Descriptions
-------------------
### [bool](class_bool#class-bool) \_process\_custom\_fx ( [CharFXTransform](class_charfxtransform#class-charfxtransform) char\_fx ) virtual
Override this method to modify properties in `char_fx`. The method must return `true` if the character could be transformed successfully. If the method returns `false`, it will skip transformation to avoid displaying broken text.
godot PhysicsDirectSpaceState PhysicsDirectSpaceState
=======================
**Inherits:** [Object](class_object#class-object)
Direct access object to a space in the [PhysicsServer](class_physicsserver#class-physicsserver).
Description
-----------
Direct access object to a space in the [PhysicsServer](class_physicsserver#class-physicsserver). It's used mainly to do queries against objects and areas residing in a given space.
Tutorials
---------
* [Physics introduction](https://docs.godotengine.org/en/3.5/tutorials/physics/physics_introduction.html)
* [Ray-casting](https://docs.godotengine.org/en/3.5/tutorials/physics/ray-casting.html)
Methods
-------
| | |
| --- | --- |
| [Array](class_array#class-array) | [cast\_motion](#class-physicsdirectspacestate-method-cast-motion) **(** [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) shape, [Vector3](class_vector3#class-vector3) motion **)** |
| [Array](class_array#class-array) | [collide\_shape](#class-physicsdirectspacestate-method-collide-shape) **(** [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) shape, [int](class_int#class-int) max\_results=32 **)** |
| [Dictionary](class_dictionary#class-dictionary) | [get\_rest\_info](#class-physicsdirectspacestate-method-get-rest-info) **(** [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) shape **)** |
| [Array](class_array#class-array) | [intersect\_point](#class-physicsdirectspacestate-method-intersect-point) **(** [Vector3](class_vector3#class-vector3) point, [int](class_int#class-int) max\_results=32, [Array](class_array#class-array) exclude=[ ], [int](class_int#class-int) collision\_layer=2147483647, [bool](class_bool#class-bool) collide\_with\_bodies=true, [bool](class_bool#class-bool) collide\_with\_areas=false **)** |
| [Dictionary](class_dictionary#class-dictionary) | [intersect\_ray](#class-physicsdirectspacestate-method-intersect-ray) **(** [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [Array](class_array#class-array) exclude=[ ], [int](class_int#class-int) collision\_mask=2147483647, [bool](class_bool#class-bool) collide\_with\_bodies=true, [bool](class_bool#class-bool) collide\_with\_areas=false **)** |
| [Array](class_array#class-array) | [intersect\_shape](#class-physicsdirectspacestate-method-intersect-shape) **(** [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) shape, [int](class_int#class-int) max\_results=32 **)** |
Method Descriptions
-------------------
### [Array](class_array#class-array) cast\_motion ( [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) shape, [Vector3](class_vector3#class-vector3) motion )
Checks how far a [Shape](class_shape#class-shape) can move without colliding. All the parameters for the query, including the shape, are supplied through a [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) object.
Returns an array with the safe and unsafe proportions (between 0 and 1) of the motion. The safe proportion is the maximum fraction of the motion that can be made without a collision. The unsafe proportion is the minimum fraction of the distance that must be moved for a collision. If no collision is detected a result of `[1.0, 1.0]` will be returned.
**Note:** Any [Shape](class_shape#class-shape)s that the shape is already colliding with e.g. inside of, will be ignored. Use [collide\_shape](#class-physicsdirectspacestate-method-collide-shape) to determine the [Shape](class_shape#class-shape)s that the shape is already colliding with.
### [Array](class_array#class-array) collide\_shape ( [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) shape, [int](class_int#class-int) max\_results=32 )
Checks the intersections of a shape, given through a [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) object, against the space. The resulting array contains a list of points where the shape intersects another. Like with [intersect\_shape](#class-physicsdirectspacestate-method-intersect-shape), the number of returned results can be limited to save processing time.
### [Dictionary](class_dictionary#class-dictionary) get\_rest\_info ( [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) shape )
Checks the intersections of a shape, given through a [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) object, against the space. If it collides with more than one shape, the nearest one is selected. The returned object is a dictionary containing the following fields:
`collider_id`: The colliding object's ID.
`linear_velocity`: The colliding object's velocity [Vector3](class_vector3#class-vector3). If the object is an [Area](class_area#class-area), the result is `(0, 0, 0)`.
`normal`: The object's surface normal at the intersection point.
`point`: The intersection point.
`rid`: The intersecting object's [RID](class_rid#class-rid).
`shape`: The shape index of the colliding shape.
If the shape did not intersect anything, then an empty dictionary is returned instead.
### [Array](class_array#class-array) intersect\_point ( [Vector3](class_vector3#class-vector3) point, [int](class_int#class-int) max\_results=32, [Array](class_array#class-array) exclude=[ ], [int](class_int#class-int) collision\_layer=2147483647, [bool](class_bool#class-bool) collide\_with\_bodies=true, [bool](class_bool#class-bool) collide\_with\_areas=false )
Checks whether a point is inside any solid shape. The shapes the point is inside of are returned in an array containing dictionaries with the following fields:
`collider`: The colliding object.
`collider_id`: The colliding object's ID.
`rid`: The intersecting object's [RID](class_rid#class-rid).
`shape`: The shape index of the colliding shape.
The number of intersections can be limited with the `max_results` parameter, to reduce the processing time.
Additionally, the method can take an `exclude` array of objects or [RID](class_rid#class-rid)s that are to be excluded from collisions, a `collision_mask` bitmask representing the physics layers to check in, or booleans to determine if the ray should collide with [PhysicsBody](class_physicsbody#class-physicsbody)s or [Area](class_area#class-area)s, respectively.
### [Dictionary](class_dictionary#class-dictionary) intersect\_ray ( [Vector3](class_vector3#class-vector3) from, [Vector3](class_vector3#class-vector3) to, [Array](class_array#class-array) exclude=[ ], [int](class_int#class-int) collision\_mask=2147483647, [bool](class_bool#class-bool) collide\_with\_bodies=true, [bool](class_bool#class-bool) collide\_with\_areas=false )
Intersects a ray in a given space. The returned object is a dictionary with the following fields:
`collider`: The colliding object.
`collider_id`: The colliding object's ID.
`normal`: The object's surface normal at the intersection point.
`position`: The intersection point.
`rid`: The intersecting object's [RID](class_rid#class-rid).
`shape`: The shape index of the colliding shape.
If the ray did not intersect anything, then an empty dictionary is returned instead.
Additionally, the method can take an `exclude` array of objects or [RID](class_rid#class-rid)s that are to be excluded from collisions, a `collision_mask` bitmask representing the physics layers to check in, or booleans to determine if the ray should collide with [PhysicsBody](class_physicsbody#class-physicsbody)s or [Area](class_area#class-area)s, respectively.
### [Array](class_array#class-array) intersect\_shape ( [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) shape, [int](class_int#class-int) max\_results=32 )
Checks the intersections of a shape, given through a [PhysicsShapeQueryParameters](class_physicsshapequeryparameters#class-physicsshapequeryparameters) object, against the space. The intersected shapes are returned in an array containing dictionaries with the following fields:
`collider`: The colliding object.
`collider_id`: The colliding object's ID.
`rid`: The intersecting object's [RID](class_rid#class-rid).
`shape`: The shape index of the colliding shape.
The number of intersections can be limited with the `max_results` parameter, to reduce the processing time.
godot VisualShaderNodeColorOp VisualShaderNodeColorOp
=======================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A [Color](class_color#class-color) operator to be used within the visual shader graph.
Description
-----------
Applies [operator](#class-visualshadernodecolorop-property-operator) to two color inputs.
Properties
----------
| | | |
| --- | --- | --- |
| [Operator](#enum-visualshadernodecolorop-operator) | [operator](#class-visualshadernodecolorop-property-operator) | `0` |
Enumerations
------------
enum **Operator**:
* **OP\_SCREEN** = **0** --- Produce a screen effect with the following formula:
```
result = vec3(1.0) - (vec3(1.0) - a) * (vec3(1.0) - b);
```
* **OP\_DIFFERENCE** = **1** --- Produce a difference effect with the following formula:
```
result = abs(a - b);
```
* **OP\_DARKEN** = **2** --- Produce a darken effect with the following formula:
```
result = min(a, b);
```
* **OP\_LIGHTEN** = **3** --- Produce a lighten effect with the following formula:
```
result = max(a, b);
```
* **OP\_OVERLAY** = **4** --- Produce an overlay effect with the following formula:
```
for (int i = 0; i < 3; i++) {
float base = a[i];
float blend = b[i];
if (base < 0.5) {
result[i] = 2.0 * base * blend;
} else {
result[i] = 1.0 - 2.0 * (1.0 - blend) * (1.0 - base);
}
}
```
* **OP\_DODGE** = **5** --- Produce a dodge effect with the following formula:
```
result = a / (vec3(1.0) - b);
```
* **OP\_BURN** = **6** --- Produce a burn effect with the following formula:
```
result = vec3(1.0) - (vec3(1.0) - a) / b;
```
* **OP\_SOFT\_LIGHT** = **7** --- Produce a soft light effect with the following formula:
```
for (int i = 0; i < 3; i++) {
float base = a[i];
float blend = b[i];
if (base < 0.5) {
result[i] = base * (blend + 0.5);
} else {
result[i] = 1.0 - (1.0 - base) * (1.0 - (blend - 0.5));
}
}
```
* **OP\_HARD\_LIGHT** = **8** --- Produce a hard light effect with the following formula:
```
for (int i = 0; i < 3; i++) {
float base = a[i];
float blend = b[i];
if (base < 0.5) {
result[i] = base * (2.0 * blend);
} else {
result[i] = 1.0 - (1.0 - base) * (1.0 - 2.0 * (blend - 0.5));
}
}
```
Property Descriptions
---------------------
### [Operator](#enum-visualshadernodecolorop-operator) operator
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_operator(value) |
| *Getter* | get\_operator() |
An operator to be applied to the inputs. See [Operator](#enum-visualshadernodecolorop-operator) for options.
godot Particles Particles
=========
**Inherits:** [GeometryInstance](class_geometryinstance#class-geometryinstance) **<** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
GPU-based 3D particle emitter.
Description
-----------
3D particle node used to create a variety of particle systems and effects. `Particles` features an emitter that generates some number of particles at a given rate.
Use the `process_material` property to add a [ParticlesMaterial](class_particlesmaterial#class-particlesmaterial) to configure particle appearance and behavior. Alternatively, you can add a [ShaderMaterial](class_shadermaterial#class-shadermaterial) which will be applied to all particles.
**Note:** `Particles` only work when using the GLES3 renderer. If using the GLES2 renderer, use [CPUParticles](class_cpuparticles#class-cpuparticles) instead. You can convert `Particles` to [CPUParticles](class_cpuparticles#class-cpuparticles) by selecting the node, clicking the **Particles** menu at the top of the 3D editor viewport then choosing **Convert to CPUParticles**.
**Note:** On macOS, `Particles` rendering is much slower than [CPUParticles](class_cpuparticles#class-cpuparticles) due to transform feedback being implemented on the CPU instead of the GPU. Consider using [CPUParticles](class_cpuparticles#class-cpuparticles) instead when targeting macOS.
**Note:** After working on a Particles node, remember to update its [visibility\_aabb](#class-particles-property-visibility-aabb) by selecting it, clicking the **Particles** menu at the top of the 3D editor viewport then choose **Generate Visibility AABB**. Otherwise, particles may suddenly disappear depending on the camera position and angle.
Tutorials
---------
* [Controlling thousands of fish with Particles](https://docs.godotengine.org/en/3.5/tutorials/performance/vertex_animation/controlling_thousands_of_fish.html)
* [Third Person Shooter Demo](https://godotengine.org/asset-library/asset/678)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [amount](#class-particles-property-amount) | `8` |
| [DrawOrder](#enum-particles-draworder) | [draw\_order](#class-particles-property-draw-order) | `0` |
| [Mesh](class_mesh#class-mesh) | [draw\_pass\_1](#class-particles-property-draw-pass-1) | |
| [Mesh](class_mesh#class-mesh) | [draw\_pass\_2](#class-particles-property-draw-pass-2) | |
| [Mesh](class_mesh#class-mesh) | [draw\_pass\_3](#class-particles-property-draw-pass-3) | |
| [Mesh](class_mesh#class-mesh) | [draw\_pass\_4](#class-particles-property-draw-pass-4) | |
| [int](class_int#class-int) | [draw\_passes](#class-particles-property-draw-passes) | `1` |
| [bool](class_bool#class-bool) | [emitting](#class-particles-property-emitting) | `true` |
| [float](class_float#class-float) | [explosiveness](#class-particles-property-explosiveness) | `0.0` |
| [int](class_int#class-int) | [fixed\_fps](#class-particles-property-fixed-fps) | `0` |
| [bool](class_bool#class-bool) | [fract\_delta](#class-particles-property-fract-delta) | `true` |
| [float](class_float#class-float) | [lifetime](#class-particles-property-lifetime) | `1.0` |
| [bool](class_bool#class-bool) | [local\_coords](#class-particles-property-local-coords) | `true` |
| [bool](class_bool#class-bool) | [one\_shot](#class-particles-property-one-shot) | `false` |
| [float](class_float#class-float) | [preprocess](#class-particles-property-preprocess) | `0.0` |
| [Material](class_material#class-material) | [process\_material](#class-particles-property-process-material) | |
| [float](class_float#class-float) | [randomness](#class-particles-property-randomness) | `0.0` |
| [float](class_float#class-float) | [speed\_scale](#class-particles-property-speed-scale) | `1.0` |
| [AABB](class_aabb#class-aabb) | [visibility\_aabb](#class-particles-property-visibility-aabb) | `AABB( -4, -4, -4, 8, 8, 8 )` |
Methods
-------
| | |
| --- | --- |
| [AABB](class_aabb#class-aabb) | [capture\_aabb](#class-particles-method-capture-aabb) **(** **)** const |
| [Mesh](class_mesh#class-mesh) | [get\_draw\_pass\_mesh](#class-particles-method-get-draw-pass-mesh) **(** [int](class_int#class-int) pass **)** const |
| void | [restart](#class-particles-method-restart) **(** **)** |
| void | [set\_draw\_pass\_mesh](#class-particles-method-set-draw-pass-mesh) **(** [int](class_int#class-int) pass, [Mesh](class_mesh#class-mesh) mesh **)** |
Enumerations
------------
enum **DrawOrder**:
* **DRAW\_ORDER\_INDEX** = **0** --- Particles are drawn in the order emitted.
* **DRAW\_ORDER\_LIFETIME** = **1** --- Particles are drawn in order of remaining lifetime.
* **DRAW\_ORDER\_VIEW\_DEPTH** = **2** --- Particles are drawn in order of depth.
Constants
---------
### MAX\_DRAW\_PASSES = 4 --- Maximum number of draw passes supported.
Property Descriptions
---------------------
### [int](class_int#class-int) amount
| | |
| --- | --- |
| *Default* | `8` |
| *Setter* | set\_amount(value) |
| *Getter* | get\_amount() |
The number of particles emitted in one emission cycle (corresponding to the [lifetime](#class-particles-property-lifetime)).
**Note:** Changing [amount](#class-particles-property-amount) will reset the particle emission, therefore removing all particles that were already emitted before changing [amount](#class-particles-property-amount).
### [DrawOrder](#enum-particles-draworder) draw\_order
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_draw\_order(value) |
| *Getter* | get\_draw\_order() |
Particle draw order. Uses [DrawOrder](#enum-particles-draworder) values.
### [Mesh](class_mesh#class-mesh) draw\_pass\_1
| | |
| --- | --- |
| *Setter* | set\_draw\_pass\_mesh(value) |
| *Getter* | get\_draw\_pass\_mesh() |
[Mesh](class_mesh#class-mesh) that is drawn for the first draw pass.
### [Mesh](class_mesh#class-mesh) draw\_pass\_2
| | |
| --- | --- |
| *Setter* | set\_draw\_pass\_mesh(value) |
| *Getter* | get\_draw\_pass\_mesh() |
[Mesh](class_mesh#class-mesh) that is drawn for the second draw pass.
### [Mesh](class_mesh#class-mesh) draw\_pass\_3
| | |
| --- | --- |
| *Setter* | set\_draw\_pass\_mesh(value) |
| *Getter* | get\_draw\_pass\_mesh() |
[Mesh](class_mesh#class-mesh) that is drawn for the third draw pass.
### [Mesh](class_mesh#class-mesh) draw\_pass\_4
| | |
| --- | --- |
| *Setter* | set\_draw\_pass\_mesh(value) |
| *Getter* | get\_draw\_pass\_mesh() |
[Mesh](class_mesh#class-mesh) that is drawn for the fourth draw pass.
### [int](class_int#class-int) draw\_passes
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_draw\_passes(value) |
| *Getter* | get\_draw\_passes() |
The number of draw passes when rendering particles.
### [bool](class_bool#class-bool) emitting
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_emitting(value) |
| *Getter* | is\_emitting() |
If `true`, particles are being emitted.
### [float](class_float#class-float) explosiveness
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_explosiveness\_ratio(value) |
| *Getter* | get\_explosiveness\_ratio() |
Time ratio between each emission. If `0`, particles are emitted continuously. If `1`, all particles are emitted simultaneously.
### [int](class_int#class-int) fixed\_fps
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_fixed\_fps(value) |
| *Getter* | get\_fixed\_fps() |
The particle system's frame rate is fixed to a value. For instance, changing the value to 2 will make the particles render at 2 frames per second. Note this does not slow down the simulation of the particle system itself.
### [bool](class_bool#class-bool) fract\_delta
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_fractional\_delta(value) |
| *Getter* | get\_fractional\_delta() |
If `true`, results in fractional delta calculation which has a smoother particles display effect.
### [float](class_float#class-float) lifetime
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_lifetime(value) |
| *Getter* | get\_lifetime() |
The amount of time each particle will exist (in seconds).
### [bool](class_bool#class-bool) local\_coords
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_use\_local\_coordinates(value) |
| *Getter* | get\_use\_local\_coordinates() |
If `true`, particles use the parent node's coordinate space. If `false`, they use global coordinates.
### [bool](class_bool#class-bool) one\_shot
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_one\_shot(value) |
| *Getter* | get\_one\_shot() |
If `true`, only `amount` particles will be emitted.
### [float](class_float#class-float) preprocess
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_pre\_process\_time(value) |
| *Getter* | get\_pre\_process\_time() |
Amount of time to preprocess the particles before animation starts. Lets you start the animation some time after particles have started emitting.
### [Material](class_material#class-material) process\_material
| | |
| --- | --- |
| *Setter* | set\_process\_material(value) |
| *Getter* | get\_process\_material() |
[Material](class_material#class-material) for processing particles. Can be a [ParticlesMaterial](class_particlesmaterial#class-particlesmaterial) or a [ShaderMaterial](class_shadermaterial#class-shadermaterial).
### [float](class_float#class-float) randomness
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_randomness\_ratio(value) |
| *Getter* | get\_randomness\_ratio() |
Emission randomness ratio.
### [float](class_float#class-float) speed\_scale
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_speed\_scale(value) |
| *Getter* | get\_speed\_scale() |
Speed scaling ratio. A value of `0` can be used to pause the particles.
### [AABB](class_aabb#class-aabb) visibility\_aabb
| | |
| --- | --- |
| *Default* | `AABB( -4, -4, -4, 8, 8, 8 )` |
| *Setter* | set\_visibility\_aabb(value) |
| *Getter* | get\_visibility\_aabb() |
The [AABB](class_aabb#class-aabb) that determines the node's region which needs to be visible on screen for the particle system to be active.
Grow the box if particles suddenly appear/disappear when the node enters/exits the screen. The [AABB](class_aabb#class-aabb) can be grown via code or with the **Particles → Generate AABB** editor tool.
**Note:** If the [ParticlesMaterial](class_particlesmaterial#class-particlesmaterial) in use is configured to cast shadows, you may want to enlarge this AABB to ensure the shadow is updated when particles are off-screen.
Method Descriptions
-------------------
### [AABB](class_aabb#class-aabb) capture\_aabb ( ) const
Returns the axis-aligned bounding box that contains all the particles that are active in the current frame.
### [Mesh](class_mesh#class-mesh) get\_draw\_pass\_mesh ( [int](class_int#class-int) pass ) const
Returns the [Mesh](class_mesh#class-mesh) that is drawn at index `pass`.
### void restart ( )
Restarts the particle emission, clearing existing particles.
### void set\_draw\_pass\_mesh ( [int](class_int#class-int) pass, [Mesh](class_mesh#class-mesh) mesh )
Sets the [Mesh](class_mesh#class-mesh) that is drawn at index `pass`.
| programming_docs |
godot AnimationNodeTimeSeek AnimationNodeTimeSeek
=====================
**Inherits:** [AnimationNode](class_animationnode#class-animationnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A time-seeking animation node to be used with [AnimationTree](class_animationtree#class-animationtree).
Description
-----------
This node can be used to cause a seek command to happen to any sub-children of the animation graph. Use this node type to play an [Animation](class_animation#class-animation) from the start or a certain playback position inside the [AnimationNodeBlendTree](class_animationnodeblendtree#class-animationnodeblendtree). After setting the time and changing the animation playback, the seek node automatically goes into sleep mode on the next process frame by setting its `seek_position` value to `-1.0`.
```
# Play child animation from the start.
animation_tree.set("parameters/Seek/seek_position", 0.0)
# Alternative syntax (same result as above).
animation_tree["parameters/Seek/seek_position"] = 0.0
# Play child animation from 12 second timestamp.
animation_tree.set("parameters/Seek/seek_position", 12.0)
# Alternative syntax (same result as above).
animation_tree["parameters/Seek/seek_position"] = 12.0
```
Tutorials
---------
* [Using AnimationTree](https://docs.godotengine.org/en/3.5/tutorials/animation/animation_tree.html)
godot BoxShape BoxShape
========
**Inherits:** [Shape](class_shape#class-shape) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Box shape resource.
Description
-----------
3D box shape that can be a child of a [PhysicsBody](class_physicsbody#class-physicsbody) or [Area](class_area#class-area).
Tutorials
---------
* [3D Physics Tests Demo](https://godotengine.org/asset-library/asset/675)
* [3D Kinematic Character Demo](https://godotengine.org/asset-library/asset/126)
* [3D Platformer Demo](https://godotengine.org/asset-library/asset/125)
Properties
----------
| | | |
| --- | --- | --- |
| [Vector3](class_vector3#class-vector3) | [extents](#class-boxshape-property-extents) | `Vector3( 1, 1, 1 )` |
Property Descriptions
---------------------
### [Vector3](class_vector3#class-vector3) extents
| | |
| --- | --- |
| *Default* | `Vector3( 1, 1, 1 )` |
| *Setter* | set\_extents(value) |
| *Getter* | get\_extents() |
The box's half extents. The width, height and depth of this shape is twice the half extents.
godot VideoStreamTheora VideoStreamTheora
=================
**Inherits:** [VideoStream](class_videostream#class-videostream) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
[VideoStream](class_videostream#class-videostream) resource for Ogg Theora videos.
Description
-----------
[VideoStream](class_videostream#class-videostream) resource handling the [Ogg Theora](https://www.theora.org/) video format with `.ogv` extension. The Theora codec is less efficient than [VideoStreamWebm](class_videostreamwebm#class-videostreamwebm)'s VP8 and VP9, but it requires less CPU resources to decode. The Theora codec is decoded on the CPU.
**Note:** While Ogg Theora videos can also have an `.ogg` extension, you will have to rename the extension to `.ogv` to use those videos within Godot.
Methods
-------
| | |
| --- | --- |
| [String](class_string#class-string) | [get\_file](#class-videostreamtheora-method-get-file) **(** **)** |
| void | [set\_file](#class-videostreamtheora-method-set-file) **(** [String](class_string#class-string) file **)** |
Method Descriptions
-------------------
### [String](class_string#class-string) get\_file ( )
Returns the Ogg Theora video file handled by this `VideoStreamTheora`.
### void set\_file ( [String](class_string#class-string) file )
Sets the Ogg Theora video file that this `VideoStreamTheora` resource handles. The `file` name should have the `.ogv` extension.
godot CollisionPolygon2D CollisionPolygon2D
==================
**Inherits:** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Defines a 2D collision polygon.
Description
-----------
Provides a 2D collision polygon to a [CollisionObject2D](class_collisionobject2d#class-collisionobject2d) parent. Polygons can be drawn in the editor or specified by a list of vertices.
Properties
----------
| | | |
| --- | --- | --- |
| [BuildMode](#enum-collisionpolygon2d-buildmode) | [build\_mode](#class-collisionpolygon2d-property-build-mode) | `0` |
| [bool](class_bool#class-bool) | [disabled](#class-collisionpolygon2d-property-disabled) | `false` |
| [bool](class_bool#class-bool) | [one\_way\_collision](#class-collisionpolygon2d-property-one-way-collision) | `false` |
| [float](class_float#class-float) | [one\_way\_collision\_margin](#class-collisionpolygon2d-property-one-way-collision-margin) | `1.0` |
| [PoolVector2Array](class_poolvector2array#class-poolvector2array) | [polygon](#class-collisionpolygon2d-property-polygon) | `PoolVector2Array( )` |
Enumerations
------------
enum **BuildMode**:
* **BUILD\_SOLIDS** = **0** --- Collisions will include the polygon and its contained area.
* **BUILD\_SEGMENTS** = **1** --- Collisions will only include the polygon edges.
Property Descriptions
---------------------
### [BuildMode](#enum-collisionpolygon2d-buildmode) build\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_build\_mode(value) |
| *Getter* | get\_build\_mode() |
Collision build mode. Use one of the [BuildMode](#enum-collisionpolygon2d-buildmode) constants.
### [bool](class_bool#class-bool) disabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_disabled(value) |
| *Getter* | is\_disabled() |
If `true`, no collisions will be detected.
### [bool](class_bool#class-bool) one\_way\_collision
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_one\_way\_collision(value) |
| *Getter* | is\_one\_way\_collision\_enabled() |
If `true`, only edges that face up, relative to `CollisionPolygon2D`'s rotation, will collide with other objects.
**Note:** This property has no effect if this `CollisionPolygon2D` is a child of an [Area2D](class_area2d#class-area2d) node.
### [float](class_float#class-float) one\_way\_collision\_margin
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_one\_way\_collision\_margin(value) |
| *Getter* | get\_one\_way\_collision\_margin() |
The margin used for one-way collision (in pixels). Higher values will make the shape thicker, and work better for colliders that enter the polygon at a high velocity.
### [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon
| | |
| --- | --- |
| *Default* | `PoolVector2Array( )` |
| *Setter* | set\_polygon(value) |
| *Getter* | get\_polygon() |
The polygon's list of vertices. The final point will be connected to the first. The returned value is a clone of the [PoolVector2Array](class_poolvector2array#class-poolvector2array), not a reference.
godot PopupDialog PopupDialog
===========
**Inherits:** [Popup](class_popup#class-popup) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Base class for popup dialogs.
Description
-----------
PopupDialog is a base class for popup dialogs, along with [WindowDialog](class_windowdialog#class-windowdialog).
Theme Properties
----------------
| | |
| --- | --- |
| [StyleBox](class_stylebox#class-stylebox) | [panel](#class-popupdialog-theme-style-panel) |
Theme Property Descriptions
---------------------------
### [StyleBox](class_stylebox#class-stylebox) panel
Sets a custom [StyleBox](class_stylebox#class-stylebox) for the panel of the `PopupDialog`.
godot CurveTexture CurveTexture
============
**Inherits:** [Texture](class_texture#class-texture) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A texture that shows a curve.
Description
-----------
Renders a given [Curve](class_curve#class-curve) provided to it. Simplifies the task of drawing curves and/or saving them as image files.
Properties
----------
| | | |
| --- | --- | --- |
| [Curve](class_curve#class-curve) | [curve](#class-curvetexture-property-curve) | |
| [int](class_int#class-int) | [width](#class-curvetexture-property-width) | `2048` |
Property Descriptions
---------------------
### [Curve](class_curve#class-curve) curve
| | |
| --- | --- |
| *Setter* | set\_curve(value) |
| *Getter* | get\_curve() |
The [Curve](class_curve#class-curve) that is rendered onto the texture.
### [int](class_int#class-int) width
| | |
| --- | --- |
| *Default* | `2048` |
| *Setter* | set\_width(value) |
| *Getter* | get\_width() |
The width of the texture (in pixels). Higher values make it possible to represent high-frequency data better (such as sudden direction changes), at the cost of increased generation time and memory usage.
godot EditorProperty EditorProperty
==============
**Inherits:** [Container](class_container#class-container) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Custom control to edit properties for adding into the inspector.
Description
-----------
This control allows property editing for one or multiple properties into [EditorInspector](class_editorinspector#class-editorinspector). It is added via [EditorInspectorPlugin](class_editorinspectorplugin#class-editorinspectorplugin).
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [checkable](#class-editorproperty-property-checkable) | `false` |
| [bool](class_bool#class-bool) | [checked](#class-editorproperty-property-checked) | `false` |
| [bool](class_bool#class-bool) | [draw\_red](#class-editorproperty-property-draw-red) | `false` |
| [bool](class_bool#class-bool) | [keying](#class-editorproperty-property-keying) | `false` |
| [String](class_string#class-string) | [label](#class-editorproperty-property-label) | `""` |
| [bool](class_bool#class-bool) | [read\_only](#class-editorproperty-property-read-only) | `false` |
Methods
-------
| | |
| --- | --- |
| void | [add\_focusable](#class-editorproperty-method-add-focusable) **(** [Control](class_control#class-control) control **)** |
| void | [emit\_changed](#class-editorproperty-method-emit-changed) **(** [String](class_string#class-string) property, [Variant](class_variant#class-variant) value, [String](class_string#class-string) field="", [bool](class_bool#class-bool) changing=false **)** |
| [Object](class_object#class-object) | [get\_edited\_object](#class-editorproperty-method-get-edited-object) **(** **)** |
| [String](class_string#class-string) | [get\_edited\_property](#class-editorproperty-method-get-edited-property) **(** **)** |
| [String](class_string#class-string) | [get\_tooltip\_text](#class-editorproperty-method-get-tooltip-text) **(** **)** const |
| void | [set\_bottom\_editor](#class-editorproperty-method-set-bottom-editor) **(** [Control](class_control#class-control) editor **)** |
| void | [update\_property](#class-editorproperty-method-update-property) **(** **)** virtual |
Signals
-------
### multiple\_properties\_changed ( [PoolStringArray](class_poolstringarray#class-poolstringarray) properties, [Array](class_array#class-array) value )
Emit it if you want multiple properties modified at the same time. Do not use if added via [EditorInspectorPlugin.parse\_property](class_editorinspectorplugin#class-editorinspectorplugin-method-parse-property).
### object\_id\_selected ( [String](class_string#class-string) property, [int](class_int#class-int) id )
Used by sub-inspectors. Emit it if what was selected was an Object ID.
### property\_changed ( [String](class_string#class-string) property, [Variant](class_variant#class-variant) value, [String](class_string#class-string) field, [bool](class_bool#class-bool) changing )
Do not emit this manually, use the [emit\_changed](#class-editorproperty-method-emit-changed) method instead.
### property\_checked ( [String](class_string#class-string) property, [bool](class_bool#class-bool) checked )
Emitted when a property was checked. Used internally.
### property\_keyed ( [String](class_string#class-string) property )
Emit it if you want to add this value as an animation key (check for keying being enabled first).
### property\_keyed\_with\_value ( [String](class_string#class-string) property, [Variant](class_variant#class-variant) value )
Emit it if you want to key a property with a single value.
### property\_pinned ( [String](class_string#class-string) property, [bool](class_bool#class-bool) pinned )
Emit it if you want to mark (or unmark) the value of a property for being saved regardless of being equal to the default value.
The default value is the one the property will get when the node is just instantiated and can come from an ancestor scene in the inheritance/instancing chain, a script or a builtin class.
### resource\_selected ( [String](class_string#class-string) path, [Resource](class_resource#class-resource) resource )
If you want a sub-resource to be edited, emit this signal with the resource.
### selected ( [String](class_string#class-string) path, [int](class_int#class-int) focusable\_idx )
Emitted when selected. Used internally.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) checkable
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_checkable(value) |
| *Getter* | is\_checkable() |
Used by the inspector, set to `true` when the property is checkable.
### [bool](class_bool#class-bool) checked
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_checked(value) |
| *Getter* | is\_checked() |
Used by the inspector, set to `true` when the property is checked.
### [bool](class_bool#class-bool) draw\_red
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_draw\_red(value) |
| *Getter* | is\_draw\_red() |
Used by the inspector, set to `true` when the property is drawn with the editor theme's warning color. This is used for editable children's properties.
### [bool](class_bool#class-bool) keying
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_keying(value) |
| *Getter* | is\_keying() |
Used by the inspector, set to `true` when the property can add keys for animation.
### [String](class_string#class-string) label
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_label(value) |
| *Getter* | get\_label() |
Set this property to change the label (if you want to show one).
### [bool](class_bool#class-bool) read\_only
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_read\_only(value) |
| *Getter* | is\_read\_only() |
Used by the inspector, set to `true` when the property is read-only.
Method Descriptions
-------------------
### void add\_focusable ( [Control](class_control#class-control) control )
If any of the controls added can gain keyboard focus, add it here. This ensures that focus will be restored if the inspector is refreshed.
### void emit\_changed ( [String](class_string#class-string) property, [Variant](class_variant#class-variant) value, [String](class_string#class-string) field="", [bool](class_bool#class-bool) changing=false )
If one or several properties have changed, this must be called. `field` is used in case your editor can modify fields separately (as an example, Vector3.x). The `changing` argument avoids the editor requesting this property to be refreshed (leave as `false` if unsure).
### [Object](class_object#class-object) get\_edited\_object ( )
Gets the edited object.
### [String](class_string#class-string) get\_edited\_property ( )
Gets the edited property. If your editor is for a single property (added via [EditorInspectorPlugin.parse\_property](class_editorinspectorplugin#class-editorinspectorplugin-method-parse-property)), then this will return the property.
### [String](class_string#class-string) get\_tooltip\_text ( ) const
Must be implemented to provide a custom tooltip to the property editor.
### void set\_bottom\_editor ( [Control](class_control#class-control) editor )
Puts the `editor` control below the property label. The control must be previously added using [Node.add\_child](class_node#class-node-method-add-child).
### void update\_property ( ) virtual
When this virtual function is called, you must update your editor.
godot TCP_Server TCP\_Server
===========
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A TCP server.
Description
-----------
A TCP server. Listens to connections on a port and returns a [StreamPeerTCP](class_streampeertcp#class-streampeertcp) when it gets an incoming connection.
Methods
-------
| | |
| --- | --- |
| [bool](class_bool#class-bool) | [is\_connection\_available](#class-tcp-server-method-is-connection-available) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_listening](#class-tcp-server-method-is-listening) **(** **)** const |
| [Error](class_%40globalscope#enum-globalscope-error) | [listen](#class-tcp-server-method-listen) **(** [int](class_int#class-int) port, [String](class_string#class-string) bind\_address="\*" **)** |
| void | [stop](#class-tcp-server-method-stop) **(** **)** |
| [StreamPeerTCP](class_streampeertcp#class-streampeertcp) | [take\_connection](#class-tcp-server-method-take-connection) **(** **)** |
Method Descriptions
-------------------
### [bool](class_bool#class-bool) is\_connection\_available ( ) const
Returns `true` if a connection is available for taking.
### [bool](class_bool#class-bool) is\_listening ( ) const
Returns `true` if the server is currently listening for connections.
### [Error](class_%40globalscope#enum-globalscope-error) listen ( [int](class_int#class-int) port, [String](class_string#class-string) bind\_address="\*" )
Listen on the `port` binding to `bind_address`.
If `bind_address` is set as `"*"` (default), the server will listen on all available addresses (both IPv4 and IPv6).
If `bind_address` is set as `"0.0.0.0"` (for IPv4) or `"::"` (for IPv6), the server will listen on all available addresses matching that IP type.
If `bind_address` is set to any valid address (e.g. `"192.168.1.101"`, `"::1"`, etc), the server will only listen on the interface with that addresses (or fail if no interface with the given address exists).
### void stop ( )
Stops listening.
### [StreamPeerTCP](class_streampeertcp#class-streampeertcp) take\_connection ( )
If a connection is available, returns a StreamPeerTCP with the connection.
godot HSeparator HSeparator
==========
**Inherits:** [Separator](class_separator#class-separator) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Horizontal separator.
Description
-----------
Horizontal separator. See [Separator](class_separator#class-separator). Even though it looks horizontal, it is used to separate objects vertically.
Theme Properties
----------------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [separation](#class-hseparator-theme-constant-separation) | `4` |
| [StyleBox](class_stylebox#class-stylebox) | [separator](#class-hseparator-theme-style-separator) | |
Theme Property Descriptions
---------------------------
### [int](class_int#class-int) separation
| | |
| --- | --- |
| *Default* | `4` |
The height of the area covered by the separator. Effectively works like a minimum height.
### [StyleBox](class_stylebox#class-stylebox) separator
The style for the separator line. Works best with [StyleBoxLine](class_styleboxline#class-styleboxline).
| programming_docs |
godot VisualShaderNodeVectorCompose VisualShaderNodeVectorCompose
=============================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Composes a [Vector3](class_vector3#class-vector3) from three scalars within the visual shader graph.
Description
-----------
Creates a `vec3` using three scalar values that can be provided from separate inputs.
godot AnimationNodeAnimation AnimationNodeAnimation
======================
**Inherits:** [AnimationRootNode](class_animationrootnode#class-animationrootnode) **<** [AnimationNode](class_animationnode#class-animationnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Input animation to use in an [AnimationNodeBlendTree](class_animationnodeblendtree#class-animationnodeblendtree).
Description
-----------
A resource to add to an [AnimationNodeBlendTree](class_animationnodeblendtree#class-animationnodeblendtree). Only features one output set using the [animation](#class-animationnodeanimation-property-animation) property. Use it as an input for [AnimationNode](class_animationnode#class-animationnode) that blend animations together.
Tutorials
---------
* [AnimationTree](https://docs.godotengine.org/en/3.5/tutorials/animation/animation_tree.html)
* [3D Platformer Demo](https://godotengine.org/asset-library/asset/125)
* [Third Person Shooter Demo](https://godotengine.org/asset-library/asset/678)
Properties
----------
| | | |
| --- | --- | --- |
| [String](class_string#class-string) | [animation](#class-animationnodeanimation-property-animation) | `""` |
Property Descriptions
---------------------
### [String](class_string#class-string) animation
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_animation(value) |
| *Getter* | get\_animation() |
Animation to use as an output. It is one of the animations provided by [AnimationTree.anim\_player](class_animationtree#class-animationtree-property-anim-player).
godot CollisionPolygon CollisionPolygon
================
**Inherits:** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Editor-only class for defining a collision polygon in 3D space.
Description
-----------
Allows editing a collision polygon's vertices on a selected plane. Can also set a depth perpendicular to that plane. This class is only available in the editor. It will not appear in the scene tree at run-time. Creates a [Shape](class_shape#class-shape) for gameplay. Properties modified during gameplay will have no effect.
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [depth](#class-collisionpolygon-property-depth) | `1.0` |
| [bool](class_bool#class-bool) | [disabled](#class-collisionpolygon-property-disabled) | `false` |
| [float](class_float#class-float) | [margin](#class-collisionpolygon-property-margin) | `0.04` |
| [PoolVector2Array](class_poolvector2array#class-poolvector2array) | [polygon](#class-collisionpolygon-property-polygon) | `PoolVector2Array( )` |
Property Descriptions
---------------------
### [float](class_float#class-float) depth
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_depth(value) |
| *Getter* | get\_depth() |
Length that the resulting collision extends in either direction perpendicular to its polygon.
### [bool](class_bool#class-bool) disabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_disabled(value) |
| *Getter* | is\_disabled() |
If `true`, no collision will be produced.
### [float](class_float#class-float) margin
| | |
| --- | --- |
| *Default* | `0.04` |
| *Setter* | set\_margin(value) |
| *Getter* | get\_margin() |
The collision margin for the generated [Shape](class_shape#class-shape). See [Shape.margin](class_shape#class-shape-property-margin) for more details.
### [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon
| | |
| --- | --- |
| *Default* | `PoolVector2Array( )` |
| *Setter* | set\_polygon(value) |
| *Getter* | get\_polygon() |
Array of vertices which define the polygon.
**Note:** The returned value is a copy of the original. Methods which mutate the size or properties of the return value will not impact the original polygon. To change properties of the polygon, assign it to a temporary variable and make changes before reassigning the `polygon` member.
godot ConeTwistJoint ConeTwistJoint
==============
**Inherits:** [Joint](class_joint#class-joint) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
A twist joint between two 3D PhysicsBodies.
Description
-----------
The joint can rotate the bodies across an axis defined by the local x-axes of the [Joint](class_joint#class-joint).
The twist axis is initiated as the X axis of the [Joint](class_joint#class-joint).
Once the Bodies swing, the twist axis is calculated as the middle of the x-axes of the Joint in the local space of the two Bodies. See also [Generic6DOFJoint](class_generic6dofjoint#class-generic6dofjoint).
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [bias](#class-conetwistjoint-property-bias) | `0.3` |
| [float](class_float#class-float) | [relaxation](#class-conetwistjoint-property-relaxation) | `1.0` |
| [float](class_float#class-float) | [softness](#class-conetwistjoint-property-softness) | `0.8` |
| [float](class_float#class-float) | [swing\_span](#class-conetwistjoint-property-swing-span) | `45.0` |
| [float](class_float#class-float) | [twist\_span](#class-conetwistjoint-property-twist-span) | `180.0` |
Methods
-------
| | |
| --- | --- |
| [float](class_float#class-float) | [get\_param](#class-conetwistjoint-method-get-param) **(** [Param](#enum-conetwistjoint-param) param **)** const |
| void | [set\_param](#class-conetwistjoint-method-set-param) **(** [Param](#enum-conetwistjoint-param) param, [float](class_float#class-float) value **)** |
Enumerations
------------
enum **Param**:
* **PARAM\_SWING\_SPAN** = **0** --- Swing is rotation from side to side, around the axis perpendicular to the twist axis.
The swing span defines, how much rotation will not get corrected along the swing axis.
Could be defined as looseness in the `ConeTwistJoint`.
If below 0.05, this behavior is locked.
* **PARAM\_TWIST\_SPAN** = **1** --- Twist is the rotation around the twist axis, this value defined how far the joint can twist.
Twist is locked if below 0.05.
* **PARAM\_BIAS** = **2** --- The speed with which the swing or twist will take place.
The higher, the faster.
* **PARAM\_SOFTNESS** = **3** --- The ease with which the joint starts to twist. If it's too low, it takes more force to start twisting the joint.
* **PARAM\_RELAXATION** = **4** --- Defines, how fast the swing- and twist-speed-difference on both sides gets synced.
* **PARAM\_MAX** = **5** --- Represents the size of the [Param](#enum-conetwistjoint-param) enum.
Property Descriptions
---------------------
### [float](class_float#class-float) bias
| | |
| --- | --- |
| *Default* | `0.3` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
The speed with which the swing or twist will take place.
The higher, the faster.
### [float](class_float#class-float) relaxation
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
Defines, how fast the swing- and twist-speed-difference on both sides gets synced.
### [float](class_float#class-float) softness
| | |
| --- | --- |
| *Default* | `0.8` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
The ease with which the joint starts to twist. If it's too low, it takes more force to start twisting the joint.
### [float](class_float#class-float) swing\_span
| | |
| --- | --- |
| *Default* | `45.0` |
Swing is rotation from side to side, around the axis perpendicular to the twist axis.
The swing span defines, how much rotation will not get corrected along the swing axis.
Could be defined as looseness in the `ConeTwistJoint`.
If below 0.05, this behavior is locked.
### [float](class_float#class-float) twist\_span
| | |
| --- | --- |
| *Default* | `180.0` |
Twist is the rotation around the twist axis, this value defined how far the joint can twist.
Twist is locked if below 0.05.
Method Descriptions
-------------------
### [float](class_float#class-float) get\_param ( [Param](#enum-conetwistjoint-param) param ) const
### void set\_param ( [Param](#enum-conetwistjoint-param) param, [float](class_float#class-float) value )
godot LinkButton LinkButton
==========
**Inherits:** [BaseButton](class_basebutton#class-basebutton) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Simple button used to represent a link to some resource.
Description
-----------
This kind of button is primarily used when the interaction with the button causes a context change (like linking to a web page).
See also [BaseButton](class_basebutton#class-basebutton) which contains common properties and methods associated with this node.
Properties
----------
| | | |
| --- | --- | --- |
| [FocusMode](class_control#enum-control-focusmode) | focus\_mode | `0` (overrides [Control](class_control#class-control-property-focus-mode)) |
| [CursorShape](class_control#enum-control-cursorshape) | mouse\_default\_cursor\_shape | `2` (overrides [Control](class_control#class-control-property-mouse-default-cursor-shape)) |
| [String](class_string#class-string) | [text](#class-linkbutton-property-text) | `""` |
| [UnderlineMode](#enum-linkbutton-underlinemode) | [underline](#class-linkbutton-property-underline) | `0` |
Theme Properties
----------------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [font\_color](#class-linkbutton-theme-color-font-color) | `Color( 0.88, 0.88, 0.88, 1 )` |
| [Color](class_color#class-color) | [font\_color\_focus](#class-linkbutton-theme-color-font-color-focus) | `Color( 0.94, 0.94, 0.94, 1 )` |
| [Color](class_color#class-color) | [font\_color\_hover](#class-linkbutton-theme-color-font-color-hover) | `Color( 0.94, 0.94, 0.94, 1 )` |
| [Color](class_color#class-color) | [font\_color\_pressed](#class-linkbutton-theme-color-font-color-pressed) | `Color( 1, 1, 1, 1 )` |
| [int](class_int#class-int) | [underline\_spacing](#class-linkbutton-theme-constant-underline-spacing) | `2` |
| [Font](class_font#class-font) | [font](#class-linkbutton-theme-font-font) | |
| [StyleBox](class_stylebox#class-stylebox) | [focus](#class-linkbutton-theme-style-focus) | |
Enumerations
------------
enum **UnderlineMode**:
* **UNDERLINE\_MODE\_ALWAYS** = **0** --- The LinkButton will always show an underline at the bottom of its text.
* **UNDERLINE\_MODE\_ON\_HOVER** = **1** --- The LinkButton will show an underline at the bottom of its text when the mouse cursor is over it.
* **UNDERLINE\_MODE\_NEVER** = **2** --- The LinkButton will never show an underline at the bottom of its text.
Property Descriptions
---------------------
### [String](class_string#class-string) text
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_text(value) |
| *Getter* | get\_text() |
The button's text that will be displayed inside the button's area.
### [UnderlineMode](#enum-linkbutton-underlinemode) underline
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_underline\_mode(value) |
| *Getter* | get\_underline\_mode() |
Determines when to show the underline. See [UnderlineMode](#enum-linkbutton-underlinemode) for options.
Theme Property Descriptions
---------------------------
### [Color](class_color#class-color) font\_color
| | |
| --- | --- |
| *Default* | `Color( 0.88, 0.88, 0.88, 1 )` |
Default text [Color](class_color#class-color) of the `LinkButton`.
### [Color](class_color#class-color) font\_color\_focus
| | |
| --- | --- |
| *Default* | `Color( 0.94, 0.94, 0.94, 1 )` |
Text [Color](class_color#class-color) used when the `LinkButton` is focused. Only replaces the normal text color of the button. Disabled, hovered, and pressed states take precedence over this color.
### [Color](class_color#class-color) font\_color\_hover
| | |
| --- | --- |
| *Default* | `Color( 0.94, 0.94, 0.94, 1 )` |
Text [Color](class_color#class-color) used when the `LinkButton` is being hovered.
### [Color](class_color#class-color) font\_color\_pressed
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
Text [Color](class_color#class-color) used when the `LinkButton` is being pressed.
### [int](class_int#class-int) underline\_spacing
| | |
| --- | --- |
| *Default* | `2` |
The vertical space between the baseline of text and the underline.
### [Font](class_font#class-font) font
[Font](class_font#class-font) of the `LinkButton`'s text.
### [StyleBox](class_stylebox#class-stylebox) focus
[StyleBox](class_stylebox#class-stylebox) used when the `LinkButton` is focused. It is displayed over the current [StyleBox](class_stylebox#class-stylebox), so using [StyleBoxEmpty](class_styleboxempty#class-styleboxempty) will just disable the focus visual effect.
godot RandomNumberGenerator RandomNumberGenerator
=====================
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A class for generating pseudo-random numbers.
Description
-----------
RandomNumberGenerator is a class for generating pseudo-random numbers. It currently uses [PCG32](http://www.pcg-random.org/).
**Note:** The underlying algorithm is an implementation detail. As a result, it should not be depended upon for reproducible random streams across Godot versions.
To generate a random float number (within a given range) based on a time-dependant seed:
```
var rng = RandomNumberGenerator.new()
func _ready():
rng.randomize()
var my_random_number = rng.randf_range(-10.0, 10.0)
```
**Note:** The default values of [seed](#class-randomnumbergenerator-property-seed) and [state](#class-randomnumbergenerator-property-state) properties are pseudo-random, and changes when calling [randomize](#class-randomnumbergenerator-method-randomize). The `0` value documented here is a placeholder, and not the actual default seed.
Tutorials
---------
* [Random number generation](https://docs.godotengine.org/en/3.5/tutorials/math/random_number_generation.html)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [seed](#class-randomnumbergenerator-property-seed) | `0` |
| [int](class_int#class-int) | [state](#class-randomnumbergenerator-property-state) | `0` |
Methods
-------
| | |
| --- | --- |
| [float](class_float#class-float) | [randf](#class-randomnumbergenerator-method-randf) **(** **)** |
| [float](class_float#class-float) | [randf\_range](#class-randomnumbergenerator-method-randf-range) **(** [float](class_float#class-float) from, [float](class_float#class-float) to **)** |
| [float](class_float#class-float) | [randfn](#class-randomnumbergenerator-method-randfn) **(** [float](class_float#class-float) mean=0.0, [float](class_float#class-float) deviation=1.0 **)** |
| [int](class_int#class-int) | [randi](#class-randomnumbergenerator-method-randi) **(** **)** |
| [int](class_int#class-int) | [randi\_range](#class-randomnumbergenerator-method-randi-range) **(** [int](class_int#class-int) from, [int](class_int#class-int) to **)** |
| void | [randomize](#class-randomnumbergenerator-method-randomize) **(** **)** |
Property Descriptions
---------------------
### [int](class_int#class-int) seed
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_seed(value) |
| *Getter* | get\_seed() |
Initializes the random number generator state based on the given seed value. A given seed will give a reproducible sequence of pseudo-random numbers.
**Note:** The RNG does not have an avalanche effect, and can output similar random streams given similar seeds. Consider using a hash function to improve your seed quality if they're sourced externally.
**Note:** Setting this property produces a side effect of changing the internal [state](#class-randomnumbergenerator-property-state), so make sure to initialize the seed *before* modifying the [state](#class-randomnumbergenerator-property-state):
```
var rng = RandomNumberGenerator.new()
rng.seed = hash("Godot")
rng.state = 100 # Restore to some previously saved state.
```
**Warning:** the getter of this property returns the previous [state](#class-randomnumbergenerator-property-state), and not the initial seed value, which is going to be fixed in Godot 4.0.
### [int](class_int#class-int) state
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_state(value) |
| *Getter* | get\_state() |
The current state of the random number generator. Save and restore this property to restore the generator to a previous state:
```
var rng = RandomNumberGenerator.new()
print(rng.randf())
var saved_state = rng.state # Store current state.
print(rng.randf()) # Advance internal state.
rng.state = saved_state # Restore the state.
print(rng.randf()) # Prints the same value as in previous.
```
**Note:** Do not set state to arbitrary values, since the random number generator requires the state to have certain qualities to behave properly. It should only be set to values that came from the state property itself. To initialize the random number generator with arbitrary input, use [seed](#class-randomnumbergenerator-property-seed) instead.
Method Descriptions
-------------------
### [float](class_float#class-float) randf ( )
Generates a pseudo-random float between `0.0` and `1.0` (inclusive).
### [float](class_float#class-float) randf\_range ( [float](class_float#class-float) from, [float](class_float#class-float) to )
Generates a pseudo-random float between `from` and `to` (inclusive).
### [float](class_float#class-float) randfn ( [float](class_float#class-float) mean=0.0, [float](class_float#class-float) deviation=1.0 )
Generates a [normally-distributed](https://en.wikipedia.org/wiki/Normal_distribution) pseudo-random number, using Box-Muller transform with the specified `mean` and a standard `deviation`. This is also called Gaussian distribution.
### [int](class_int#class-int) randi ( )
Generates a pseudo-random 32-bit unsigned integer between `0` and `4294967295` (inclusive).
### [int](class_int#class-int) randi\_range ( [int](class_int#class-int) from, [int](class_int#class-int) to )
Generates a pseudo-random 32-bit signed integer between `from` and `to` (inclusive).
### void randomize ( )
Setups a time-based seed to generator.
godot TranslationServer TranslationServer
=================
**Inherits:** [Object](class_object#class-object)
Server that manages all translations.
Description
-----------
Server that manages all translations. Translations can be set to it and removed from it.
Tutorials
---------
* [Internationalizing games](https://docs.godotengine.org/en/3.5/tutorials/i18n/internationalizing_games.html)
* [Locales](https://docs.godotengine.org/en/3.5/tutorials/i18n/locales.html)
Methods
-------
| | |
| --- | --- |
| void | [add\_translation](#class-translationserver-method-add-translation) **(** [Translation](class_translation#class-translation) translation **)** |
| void | [clear](#class-translationserver-method-clear) **(** **)** |
| [Array](class_array#class-array) | [get\_loaded\_locales](#class-translationserver-method-get-loaded-locales) **(** **)** const |
| [String](class_string#class-string) | [get\_locale](#class-translationserver-method-get-locale) **(** **)** const |
| [String](class_string#class-string) | [get\_locale\_name](#class-translationserver-method-get-locale-name) **(** [String](class_string#class-string) locale **)** const |
| void | [remove\_translation](#class-translationserver-method-remove-translation) **(** [Translation](class_translation#class-translation) translation **)** |
| void | [set\_locale](#class-translationserver-method-set-locale) **(** [String](class_string#class-string) locale **)** |
| [String](class_string#class-string) | [translate](#class-translationserver-method-translate) **(** [String](class_string#class-string) message **)** const |
Method Descriptions
-------------------
### void add\_translation ( [Translation](class_translation#class-translation) translation )
Adds a [Translation](class_translation#class-translation) resource.
### void clear ( )
Clears the server from all translations.
### [Array](class_array#class-array) get\_loaded\_locales ( ) const
Returns an array of all loaded locales of the project.
### [String](class_string#class-string) get\_locale ( ) const
Returns the current locale of the project.
See also [OS.get\_locale](class_os#class-os-method-get-locale) and [OS.get\_locale\_language](class_os#class-os-method-get-locale-language) to query the locale of the user system.
### [String](class_string#class-string) get\_locale\_name ( [String](class_string#class-string) locale ) const
Returns a locale's language and its variant (e.g. `"en_US"` would return `"English (United States)"`).
### void remove\_translation ( [Translation](class_translation#class-translation) translation )
Removes the given translation from the server.
### void set\_locale ( [String](class_string#class-string) locale )
Sets the locale of the project. The `locale` string will be standardized to match known locales (e.g. `en-US` would be matched to `en_US`).
If translations have been loaded beforehand for the new locale, they will be applied.
### [String](class_string#class-string) translate ( [String](class_string#class-string) message ) const
Returns the current locale's translation for the given message (key).
| programming_docs |
godot VisualShaderNodeCubeMap VisualShaderNodeCubeMap
=======================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A [CubeMap](class_cubemap#class-cubemap) sampling node to be used within the visual shader graph.
Description
-----------
Translated to `texture(cubemap, vec3)` in the shader language. Returns a color vector and alpha channel as scalar.
Properties
----------
| | | |
| --- | --- | --- |
| [CubeMap](class_cubemap#class-cubemap) | [cube\_map](#class-visualshadernodecubemap-property-cube-map) | |
| [Source](#enum-visualshadernodecubemap-source) | [source](#class-visualshadernodecubemap-property-source) | `0` |
| [TextureType](#enum-visualshadernodecubemap-texturetype) | [texture\_type](#class-visualshadernodecubemap-property-texture-type) | `0` |
Enumerations
------------
enum **Source**:
* **SOURCE\_TEXTURE** = **0** --- Use the [CubeMap](class_cubemap#class-cubemap) set via [cube\_map](#class-visualshadernodecubemap-property-cube-map). If this is set to [source](#class-visualshadernodecubemap-property-source), the `samplerCube` port is ignored.
* **SOURCE\_PORT** = **1** --- Use the [CubeMap](class_cubemap#class-cubemap) sampler reference passed via the `samplerCube` port. If this is set to [source](#class-visualshadernodecubemap-property-source), the [cube\_map](#class-visualshadernodecubemap-property-cube-map) texture is ignored.
enum **TextureType**:
* **TYPE\_DATA** = **0** --- No hints are added to the uniform declaration.
* **TYPE\_COLOR** = **1** --- Adds `hint_albedo` as hint to the uniform declaration for proper sRGB to linear conversion.
* **TYPE\_NORMALMAP** = **2** --- Adds `hint_normal` as hint to the uniform declaration, which internally converts the texture for proper usage as normal map.
Property Descriptions
---------------------
### [CubeMap](class_cubemap#class-cubemap) cube\_map
| | |
| --- | --- |
| *Setter* | set\_cube\_map(value) |
| *Getter* | get\_cube\_map() |
The [CubeMap](class_cubemap#class-cubemap) texture to sample when using [SOURCE\_TEXTURE](#class-visualshadernodecubemap-constant-source-texture) as [source](#class-visualshadernodecubemap-property-source).
### [Source](#enum-visualshadernodecubemap-source) source
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_source(value) |
| *Getter* | get\_source() |
Defines which source should be used for the sampling. See [Source](#enum-visualshadernodecubemap-source) for options.
### [TextureType](#enum-visualshadernodecubemap-texturetype) texture\_type
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_texture\_type(value) |
| *Getter* | get\_texture\_type() |
Defines the type of data provided by the source texture. See [TextureType](#enum-visualshadernodecubemap-texturetype) for options.
godot OptionButton OptionButton
============
**Inherits:** [Button](class_button#class-button) **<** [BaseButton](class_basebutton#class-basebutton) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Button control that provides selectable options when pressed.
Description
-----------
OptionButton is a type button that provides a selectable list of items when pressed. The item selected becomes the "current" item and is displayed as the button text.
See also [BaseButton](class_basebutton#class-basebutton) which contains common properties and methods associated with this node.
Properties
----------
| | | |
| --- | --- | --- |
| [ActionMode](class_basebutton#enum-basebutton-actionmode) | action\_mode | `0` (overrides [BaseButton](class_basebutton#class-basebutton-property-action-mode)) |
| [TextAlign](class_button#enum-button-textalign) | align | `0` (overrides [Button](class_button#class-button-property-align)) |
| [int](class_int#class-int) | [selected](#class-optionbutton-property-selected) | `-1` |
| [bool](class_bool#class-bool) | toggle\_mode | `true` (overrides [BaseButton](class_basebutton#class-basebutton-property-toggle-mode)) |
Methods
-------
| | |
| --- | --- |
| void | [add\_icon\_item](#class-optionbutton-method-add-icon-item) **(** [Texture](class_texture#class-texture) texture, [String](class_string#class-string) label, [int](class_int#class-int) id=-1 **)** |
| void | [add\_item](#class-optionbutton-method-add-item) **(** [String](class_string#class-string) label, [int](class_int#class-int) id=-1 **)** |
| void | [add\_separator](#class-optionbutton-method-add-separator) **(** **)** |
| void | [clear](#class-optionbutton-method-clear) **(** **)** |
| [int](class_int#class-int) | [get\_item\_count](#class-optionbutton-method-get-item-count) **(** **)** const |
| [Texture](class_texture#class-texture) | [get\_item\_icon](#class-optionbutton-method-get-item-icon) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_item\_id](#class-optionbutton-method-get-item-id) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_item\_index](#class-optionbutton-method-get-item-index) **(** [int](class_int#class-int) id **)** const |
| [Variant](class_variant#class-variant) | [get\_item\_metadata](#class-optionbutton-method-get-item-metadata) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_item\_text](#class-optionbutton-method-get-item-text) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_item\_tooltip](#class-optionbutton-method-get-item-tooltip) **(** [int](class_int#class-int) idx **)** const |
| [PopupMenu](class_popupmenu#class-popupmenu) | [get\_popup](#class-optionbutton-method-get-popup) **(** **)** const |
| [int](class_int#class-int) | [get\_selected\_id](#class-optionbutton-method-get-selected-id) **(** **)** const |
| [Variant](class_variant#class-variant) | [get\_selected\_metadata](#class-optionbutton-method-get-selected-metadata) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_item\_disabled](#class-optionbutton-method-is-item-disabled) **(** [int](class_int#class-int) idx **)** const |
| void | [remove\_item](#class-optionbutton-method-remove-item) **(** [int](class_int#class-int) idx **)** |
| void | [select](#class-optionbutton-method-select) **(** [int](class_int#class-int) idx **)** |
| void | [set\_item\_disabled](#class-optionbutton-method-set-item-disabled) **(** [int](class_int#class-int) idx, [bool](class_bool#class-bool) disabled **)** |
| void | [set\_item\_icon](#class-optionbutton-method-set-item-icon) **(** [int](class_int#class-int) idx, [Texture](class_texture#class-texture) texture **)** |
| void | [set\_item\_id](#class-optionbutton-method-set-item-id) **(** [int](class_int#class-int) idx, [int](class_int#class-int) id **)** |
| void | [set\_item\_metadata](#class-optionbutton-method-set-item-metadata) **(** [int](class_int#class-int) idx, [Variant](class_variant#class-variant) metadata **)** |
| void | [set\_item\_text](#class-optionbutton-method-set-item-text) **(** [int](class_int#class-int) idx, [String](class_string#class-string) text **)** |
| void | [set\_item\_tooltip](#class-optionbutton-method-set-item-tooltip) **(** [int](class_int#class-int) idx, [String](class_string#class-string) tooltip **)** |
Theme Properties
----------------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [font\_color](#class-optionbutton-theme-color-font-color) | `Color( 0.88, 0.88, 0.88, 1 )` |
| [Color](class_color#class-color) | [font\_color\_disabled](#class-optionbutton-theme-color-font-color-disabled) | `Color( 0.9, 0.9, 0.9, 0.2 )` |
| [Color](class_color#class-color) | [font\_color\_focus](#class-optionbutton-theme-color-font-color-focus) | `Color( 0.94, 0.94, 0.94, 1 )` |
| [Color](class_color#class-color) | [font\_color\_hover](#class-optionbutton-theme-color-font-color-hover) | `Color( 0.94, 0.94, 0.94, 1 )` |
| [Color](class_color#class-color) | [font\_color\_pressed](#class-optionbutton-theme-color-font-color-pressed) | `Color( 1, 1, 1, 1 )` |
| [int](class_int#class-int) | [arrow\_margin](#class-optionbutton-theme-constant-arrow-margin) | `2` |
| [int](class_int#class-int) | [hseparation](#class-optionbutton-theme-constant-hseparation) | `2` |
| [Font](class_font#class-font) | [font](#class-optionbutton-theme-font-font) | |
| [Texture](class_texture#class-texture) | [arrow](#class-optionbutton-theme-icon-arrow) | |
| [StyleBox](class_stylebox#class-stylebox) | [disabled](#class-optionbutton-theme-style-disabled) | |
| [StyleBox](class_stylebox#class-stylebox) | [focus](#class-optionbutton-theme-style-focus) | |
| [StyleBox](class_stylebox#class-stylebox) | [hover](#class-optionbutton-theme-style-hover) | |
| [StyleBox](class_stylebox#class-stylebox) | [normal](#class-optionbutton-theme-style-normal) | |
| [StyleBox](class_stylebox#class-stylebox) | [pressed](#class-optionbutton-theme-style-pressed) | |
Signals
-------
### item\_focused ( [int](class_int#class-int) index )
Emitted when the user navigates to an item using the `ui_up` or `ui_down` actions. The index of the item selected is passed as argument.
### item\_selected ( [int](class_int#class-int) index )
Emitted when the current item has been changed by the user. The index of the item selected is passed as argument.
Property Descriptions
---------------------
### [int](class_int#class-int) selected
| | |
| --- | --- |
| *Default* | `-1` |
| *Getter* | get\_selected() |
The index of the currently selected item, or `-1` if no item is selected.
Method Descriptions
-------------------
### void add\_icon\_item ( [Texture](class_texture#class-texture) texture, [String](class_string#class-string) label, [int](class_int#class-int) id=-1 )
Adds an item, with a `texture` icon, text `label` and (optionally) `id`. If no `id` is passed, the item index will be used as the item's ID. New items are appended at the end.
### void add\_item ( [String](class_string#class-string) label, [int](class_int#class-int) id=-1 )
Adds an item, with text `label` and (optionally) `id`. If no `id` is passed, the item index will be used as the item's ID. New items are appended at the end.
### void add\_separator ( )
Adds a separator to the list of items. Separators help to group items. Separator also takes up an index and is appended at the end.
### void clear ( )
Clears all the items in the `OptionButton`.
### [int](class_int#class-int) get\_item\_count ( ) const
Returns the amount of items in the OptionButton, including separators.
### [Texture](class_texture#class-texture) get\_item\_icon ( [int](class_int#class-int) idx ) const
Returns the icon of the item at index `idx`.
### [int](class_int#class-int) get\_item\_id ( [int](class_int#class-int) idx ) const
Returns the ID of the item at index `idx`.
### [int](class_int#class-int) get\_item\_index ( [int](class_int#class-int) id ) const
Returns the index of the item with the given `id`.
### [Variant](class_variant#class-variant) get\_item\_metadata ( [int](class_int#class-int) idx ) const
Retrieves the metadata of an item. Metadata may be any type and can be used to store extra information about an item, such as an external string ID.
### [String](class_string#class-string) get\_item\_text ( [int](class_int#class-int) idx ) const
Returns the text of the item at index `idx`.
### [String](class_string#class-string) get\_item\_tooltip ( [int](class_int#class-int) idx ) const
Returns the tooltip of the item at index `idx`.
### [PopupMenu](class_popupmenu#class-popupmenu) get\_popup ( ) const
Returns the [PopupMenu](class_popupmenu#class-popupmenu) contained in this button.
**Warning:** This is a required internal node, removing and freeing it may cause a crash. If you wish to hide it or any of its children, use their [CanvasItem.visible](class_canvasitem#class-canvasitem-property-visible) property.
### [int](class_int#class-int) get\_selected\_id ( ) const
Returns the ID of the selected item, or `-1` if no item is selected.
### [Variant](class_variant#class-variant) get\_selected\_metadata ( ) const
Gets the metadata of the selected item. Metadata for items can be set using [set\_item\_metadata](#class-optionbutton-method-set-item-metadata).
### [bool](class_bool#class-bool) is\_item\_disabled ( [int](class_int#class-int) idx ) const
Returns `true` if the item at index `idx` is disabled.
### void remove\_item ( [int](class_int#class-int) idx )
Removes the item at index `idx`.
### void select ( [int](class_int#class-int) idx )
Selects an item by index and makes it the current item. This will work even if the item is disabled.
Passing `-1` as the index deselects any currently selected item.
### void set\_item\_disabled ( [int](class_int#class-int) idx, [bool](class_bool#class-bool) disabled )
Sets whether the item at index `idx` is disabled.
Disabled items are drawn differently in the dropdown and are not selectable by the user. If the current selected item is set as disabled, it will remain selected.
### void set\_item\_icon ( [int](class_int#class-int) idx, [Texture](class_texture#class-texture) texture )
Sets the icon of the item at index `idx`.
### void set\_item\_id ( [int](class_int#class-int) idx, [int](class_int#class-int) id )
Sets the ID of the item at index `idx`.
### void set\_item\_metadata ( [int](class_int#class-int) idx, [Variant](class_variant#class-variant) metadata )
Sets the metadata of an item. Metadata may be of any type and can be used to store extra information about an item, such as an external string ID.
### void set\_item\_text ( [int](class_int#class-int) idx, [String](class_string#class-string) text )
Sets the text of the item at index `idx`.
### void set\_item\_tooltip ( [int](class_int#class-int) idx, [String](class_string#class-string) tooltip )
Sets the tooltip of the item at index `idx`.
Theme Property Descriptions
---------------------------
### [Color](class_color#class-color) font\_color
| | |
| --- | --- |
| *Default* | `Color( 0.88, 0.88, 0.88, 1 )` |
Default text [Color](class_color#class-color) of the `OptionButton`.
### [Color](class_color#class-color) font\_color\_disabled
| | |
| --- | --- |
| *Default* | `Color( 0.9, 0.9, 0.9, 0.2 )` |
Text [Color](class_color#class-color) used when the `OptionButton` is disabled.
### [Color](class_color#class-color) font\_color\_focus
| | |
| --- | --- |
| *Default* | `Color( 0.94, 0.94, 0.94, 1 )` |
Text [Color](class_color#class-color) used when the `OptionButton` is focused. Only replaces the normal text color of the button. Disabled, hovered, and pressed states take precedence over this color.
### [Color](class_color#class-color) font\_color\_hover
| | |
| --- | --- |
| *Default* | `Color( 0.94, 0.94, 0.94, 1 )` |
Text [Color](class_color#class-color) used when the `OptionButton` is being hovered.
### [Color](class_color#class-color) font\_color\_pressed
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
Text [Color](class_color#class-color) used when the `OptionButton` is being pressed.
### [int](class_int#class-int) arrow\_margin
| | |
| --- | --- |
| *Default* | `2` |
The horizontal space between the arrow icon and the right edge of the button.
### [int](class_int#class-int) hseparation
| | |
| --- | --- |
| *Default* | `2` |
The horizontal space between `OptionButton`'s icon and text.
### [Font](class_font#class-font) font
[Font](class_font#class-font) of the `OptionButton`'s text.
### [Texture](class_texture#class-texture) arrow
The arrow icon to be drawn on the right end of the button.
### [StyleBox](class_stylebox#class-stylebox) disabled
[StyleBox](class_stylebox#class-stylebox) used when the `OptionButton` is disabled.
### [StyleBox](class_stylebox#class-stylebox) focus
[StyleBox](class_stylebox#class-stylebox) used when the `OptionButton` is focused. It is displayed over the current [StyleBox](class_stylebox#class-stylebox), so using [StyleBoxEmpty](class_styleboxempty#class-styleboxempty) will just disable the focus visual effect.
### [StyleBox](class_stylebox#class-stylebox) hover
[StyleBox](class_stylebox#class-stylebox) used when the `OptionButton` is being hovered.
### [StyleBox](class_stylebox#class-stylebox) normal
Default [StyleBox](class_stylebox#class-stylebox) for the `OptionButton`.
### [StyleBox](class_stylebox#class-stylebox) pressed
[StyleBox](class_stylebox#class-stylebox) used when the `OptionButton` is being pressed.
godot GLTFLight GLTFLight
=========
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Description
-----------
**Note:** This class is only compiled in editor builds. Run-time glTF loading and saving is *not* available in exported projects. References to `GLTFLight` within a script will cause an error in an exported project.
Properties
----------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [color](#class-gltflight-property-color) | `Color( 1, 1, 1, 1 )` |
| [float](class_float#class-float) | [inner\_cone\_angle](#class-gltflight-property-inner-cone-angle) | `0.0` |
| [float](class_float#class-float) | [intensity](#class-gltflight-property-intensity) | `1.0` |
| [float](class_float#class-float) | [outer\_cone\_angle](#class-gltflight-property-outer-cone-angle) | `0.785398` |
| [float](class_float#class-float) | [range](#class-gltflight-property-range) | `inf` |
| [String](class_string#class-string) | [type](#class-gltflight-property-type) | `""` |
Property Descriptions
---------------------
### [Color](class_color#class-color) color
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
| *Setter* | set\_color(value) |
| *Getter* | get\_color() |
The [Color](class_color#class-color) of the light. Defaults to white. A black color causes the light to have no effect.
### [float](class_float#class-float) inner\_cone\_angle
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_inner\_cone\_angle(value) |
| *Getter* | get\_inner\_cone\_angle() |
The inner angle of the cone in a spotlight. Must be less than or equal to the outer cone angle.
Within this angle, the light is at full brightness. Between the inner and outer cone angles, there is a transition from full brightness to zero brightness. When creating a Godot [SpotLight](class_spotlight#class-spotlight), the ratio between the inner and outer cone angles is used to calculate the attenuation of the light.
### [float](class_float#class-float) intensity
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_intensity(value) |
| *Getter* | get\_intensity() |
The intensity of the light. This is expressed in candelas (lumens per steradian) for point and spot lights, and lux (lumens per m²) for directional lights. When creating a Godot light, this value is converted to a unitless multiplier.
### [float](class_float#class-float) outer\_cone\_angle
| | |
| --- | --- |
| *Default* | `0.785398` |
| *Setter* | set\_outer\_cone\_angle(value) |
| *Getter* | get\_outer\_cone\_angle() |
The outer angle of the cone in a spotlight. Must be greater than or equal to the inner angle.
At this angle, the light drops off to zero brightness. Between the inner and outer cone angles, there is a transition from full brightness to zero brightness. If this angle is a half turn, then the spotlight emits in all directions. When creating a Godot [SpotLight](class_spotlight#class-spotlight), the outer cone angle is used as the angle of the spotlight.
### [float](class_float#class-float) range
| | |
| --- | --- |
| *Default* | `inf` |
| *Setter* | set\_range(value) |
| *Getter* | get\_range() |
The range of the light, beyond which the light has no effect. GLTF lights with no range defined behave like physical lights (which have infinite range). When creating a Godot light, the range is clamped to 4096.
### [String](class_string#class-string) type
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_type(value) |
| *Getter* | get\_type() |
The type of the light. The values accepted by Godot are "point", "spot", and "directional", which correspond to Godot's [OmniLight](class_omnilight#class-omnilight), [SpotLight](class_spotlight#class-spotlight), and [DirectionalLight](class_directionallight#class-directionallight) respectively.
| programming_docs |
godot AnimationRootNode AnimationRootNode
=================
**Inherits:** [AnimationNode](class_animationnode#class-animationnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [AnimationNodeAnimation](class_animationnodeanimation#class-animationnodeanimation), [AnimationNodeBlendSpace1D](class_animationnodeblendspace1d#class-animationnodeblendspace1d), [AnimationNodeBlendSpace2D](class_animationnodeblendspace2d#class-animationnodeblendspace2d), [AnimationNodeBlendTree](class_animationnodeblendtree#class-animationnodeblendtree), [AnimationNodeStateMachine](class_animationnodestatemachine#class-animationnodestatemachine)
godot AudioServer AudioServer
===========
**Inherits:** [Object](class_object#class-object)
Server interface for low-level audio access.
Description
-----------
`AudioServer` is a low-level server interface for audio access. It is in charge of creating sample data (playable audio) as well as its playback via a voice interface.
Tutorials
---------
* [Audio buses](https://docs.godotengine.org/en/3.5/tutorials/audio/audio_buses.html)
* [Audio Device Changer Demo](https://godotengine.org/asset-library/asset/525)
* [Audio Mic Record Demo](https://godotengine.org/asset-library/asset/527)
* [Audio Spectrum Demo](https://godotengine.org/asset-library/asset/528)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [bus\_count](#class-audioserver-property-bus-count) | `1` |
| [String](class_string#class-string) | [capture\_device](#class-audioserver-property-capture-device) | `"Default"` |
| [String](class_string#class-string) | [device](#class-audioserver-property-device) | `"Default"` |
| [float](class_float#class-float) | [global\_rate\_scale](#class-audioserver-property-global-rate-scale) | `1.0` |
Methods
-------
| | |
| --- | --- |
| void | [add\_bus](#class-audioserver-method-add-bus) **(** [int](class_int#class-int) at\_position=-1 **)** |
| void | [add\_bus\_effect](#class-audioserver-method-add-bus-effect) **(** [int](class_int#class-int) bus\_idx, [AudioEffect](class_audioeffect#class-audioeffect) effect, [int](class_int#class-int) at\_position=-1 **)** |
| [Array](class_array#class-array) | [capture\_get\_device\_list](#class-audioserver-method-capture-get-device-list) **(** **)** |
| [AudioBusLayout](class_audiobuslayout#class-audiobuslayout) | [generate\_bus\_layout](#class-audioserver-method-generate-bus-layout) **(** **)** const |
| [int](class_int#class-int) | [get\_bus\_channels](#class-audioserver-method-get-bus-channels) **(** [int](class_int#class-int) bus\_idx **)** const |
| [AudioEffect](class_audioeffect#class-audioeffect) | [get\_bus\_effect](#class-audioserver-method-get-bus-effect) **(** [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx **)** |
| [int](class_int#class-int) | [get\_bus\_effect\_count](#class-audioserver-method-get-bus-effect-count) **(** [int](class_int#class-int) bus\_idx **)** |
| [AudioEffectInstance](class_audioeffectinstance#class-audioeffectinstance) | [get\_bus\_effect\_instance](#class-audioserver-method-get-bus-effect-instance) **(** [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx, [int](class_int#class-int) channel=0 **)** |
| [int](class_int#class-int) | [get\_bus\_index](#class-audioserver-method-get-bus-index) **(** [String](class_string#class-string) bus\_name **)** const |
| [String](class_string#class-string) | [get\_bus\_name](#class-audioserver-method-get-bus-name) **(** [int](class_int#class-int) bus\_idx **)** const |
| [float](class_float#class-float) | [get\_bus\_peak\_volume\_left\_db](#class-audioserver-method-get-bus-peak-volume-left-db) **(** [int](class_int#class-int) bus\_idx, [int](class_int#class-int) channel **)** const |
| [float](class_float#class-float) | [get\_bus\_peak\_volume\_right\_db](#class-audioserver-method-get-bus-peak-volume-right-db) **(** [int](class_int#class-int) bus\_idx, [int](class_int#class-int) channel **)** const |
| [String](class_string#class-string) | [get\_bus\_send](#class-audioserver-method-get-bus-send) **(** [int](class_int#class-int) bus\_idx **)** const |
| [float](class_float#class-float) | [get\_bus\_volume\_db](#class-audioserver-method-get-bus-volume-db) **(** [int](class_int#class-int) bus\_idx **)** const |
| [Array](class_array#class-array) | [get\_device\_list](#class-audioserver-method-get-device-list) **(** **)** |
| [float](class_float#class-float) | [get\_mix\_rate](#class-audioserver-method-get-mix-rate) **(** **)** const |
| [float](class_float#class-float) | [get\_output\_latency](#class-audioserver-method-get-output-latency) **(** **)** const |
| [SpeakerMode](#enum-audioserver-speakermode) | [get\_speaker\_mode](#class-audioserver-method-get-speaker-mode) **(** **)** const |
| [float](class_float#class-float) | [get\_time\_since\_last\_mix](#class-audioserver-method-get-time-since-last-mix) **(** **)** const |
| [float](class_float#class-float) | [get\_time\_to\_next\_mix](#class-audioserver-method-get-time-to-next-mix) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_bus\_bypassing\_effects](#class-audioserver-method-is-bus-bypassing-effects) **(** [int](class_int#class-int) bus\_idx **)** const |
| [bool](class_bool#class-bool) | [is\_bus\_effect\_enabled](#class-audioserver-method-is-bus-effect-enabled) **(** [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx **)** const |
| [bool](class_bool#class-bool) | [is\_bus\_mute](#class-audioserver-method-is-bus-mute) **(** [int](class_int#class-int) bus\_idx **)** const |
| [bool](class_bool#class-bool) | [is\_bus\_solo](#class-audioserver-method-is-bus-solo) **(** [int](class_int#class-int) bus\_idx **)** const |
| void | [lock](#class-audioserver-method-lock) **(** **)** |
| void | [move\_bus](#class-audioserver-method-move-bus) **(** [int](class_int#class-int) index, [int](class_int#class-int) to\_index **)** |
| void | [remove\_bus](#class-audioserver-method-remove-bus) **(** [int](class_int#class-int) index **)** |
| void | [remove\_bus\_effect](#class-audioserver-method-remove-bus-effect) **(** [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx **)** |
| void | [set\_bus\_bypass\_effects](#class-audioserver-method-set-bus-bypass-effects) **(** [int](class_int#class-int) bus\_idx, [bool](class_bool#class-bool) enable **)** |
| void | [set\_bus\_effect\_enabled](#class-audioserver-method-set-bus-effect-enabled) **(** [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx, [bool](class_bool#class-bool) enabled **)** |
| void | [set\_bus\_layout](#class-audioserver-method-set-bus-layout) **(** [AudioBusLayout](class_audiobuslayout#class-audiobuslayout) bus\_layout **)** |
| void | [set\_bus\_mute](#class-audioserver-method-set-bus-mute) **(** [int](class_int#class-int) bus\_idx, [bool](class_bool#class-bool) enable **)** |
| void | [set\_bus\_name](#class-audioserver-method-set-bus-name) **(** [int](class_int#class-int) bus\_idx, [String](class_string#class-string) name **)** |
| void | [set\_bus\_send](#class-audioserver-method-set-bus-send) **(** [int](class_int#class-int) bus\_idx, [String](class_string#class-string) send **)** |
| void | [set\_bus\_solo](#class-audioserver-method-set-bus-solo) **(** [int](class_int#class-int) bus\_idx, [bool](class_bool#class-bool) enable **)** |
| void | [set\_bus\_volume\_db](#class-audioserver-method-set-bus-volume-db) **(** [int](class_int#class-int) bus\_idx, [float](class_float#class-float) volume\_db **)** |
| void | [swap\_bus\_effects](#class-audioserver-method-swap-bus-effects) **(** [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx, [int](class_int#class-int) by\_effect\_idx **)** |
| void | [unlock](#class-audioserver-method-unlock) **(** **)** |
Signals
-------
### bus\_layout\_changed ( )
Emitted when the [AudioBusLayout](class_audiobuslayout#class-audiobuslayout) changes.
Enumerations
------------
enum **SpeakerMode**:
* **SPEAKER\_MODE\_STEREO** = **0** --- Two or fewer speakers were detected.
* **SPEAKER\_SURROUND\_31** = **1** --- A 3.1 channel surround setup was detected.
* **SPEAKER\_SURROUND\_51** = **2** --- A 5.1 channel surround setup was detected.
* **SPEAKER\_SURROUND\_71** = **3** --- A 7.1 channel surround setup was detected.
Property Descriptions
---------------------
### [int](class_int#class-int) bus\_count
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_bus\_count(value) |
| *Getter* | get\_bus\_count() |
Number of available audio buses.
### [String](class_string#class-string) capture\_device
| | |
| --- | --- |
| *Default* | `"Default"` |
| *Setter* | capture\_set\_device(value) |
| *Getter* | capture\_get\_device() |
Name of the current device for audio input (see [capture\_get\_device\_list](#class-audioserver-method-capture-get-device-list)). On systems with multiple audio inputs (such as analog, USB and HDMI audio), this can be used to select the audio input device. The value `"Default"` will record audio on the system-wide default audio input. If an invalid device name is set, the value will be reverted back to `"Default"`.
**Note:** [ProjectSettings.audio/enable\_audio\_input](class_projectsettings#class-projectsettings-property-audio-enable-audio-input) must be `true` for audio input to work. See also that setting's description for caveats related to permissions and operating system privacy settings.
### [String](class_string#class-string) device
| | |
| --- | --- |
| *Default* | `"Default"` |
| *Setter* | set\_device(value) |
| *Getter* | get\_device() |
Name of the current device for audio output (see [get\_device\_list](#class-audioserver-method-get-device-list)). On systems with multiple audio outputs (such as analog, USB and HDMI audio), this can be used to select the audio output device. The value `"Default"` will play audio on the system-wide default audio output. If an invalid device name is set, the value will be reverted back to `"Default"`.
### [float](class_float#class-float) global\_rate\_scale
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_global\_rate\_scale(value) |
| *Getter* | get\_global\_rate\_scale() |
Scales the rate at which audio is played (i.e. setting it to `0.5` will make the audio be played twice as fast).
Method Descriptions
-------------------
### void add\_bus ( [int](class_int#class-int) at\_position=-1 )
Adds a bus at `at_position`.
### void add\_bus\_effect ( [int](class_int#class-int) bus\_idx, [AudioEffect](class_audioeffect#class-audioeffect) effect, [int](class_int#class-int) at\_position=-1 )
Adds an [AudioEffect](class_audioeffect#class-audioeffect) effect to the bus `bus_idx` at `at_position`.
### [Array](class_array#class-array) capture\_get\_device\_list ( )
Returns the names of all audio input devices detected on the system.
**Note:** [ProjectSettings.audio/enable\_audio\_input](class_projectsettings#class-projectsettings-property-audio-enable-audio-input) must be `true` for audio input to work. See also that setting's description for caveats related to permissions and operating system privacy settings.
### [AudioBusLayout](class_audiobuslayout#class-audiobuslayout) generate\_bus\_layout ( ) const
Generates an [AudioBusLayout](class_audiobuslayout#class-audiobuslayout) using the available buses and effects.
### [int](class_int#class-int) get\_bus\_channels ( [int](class_int#class-int) bus\_idx ) const
Returns the amount of channels of the bus at index `bus_idx`.
### [AudioEffect](class_audioeffect#class-audioeffect) get\_bus\_effect ( [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx )
Returns the [AudioEffect](class_audioeffect#class-audioeffect) at position `effect_idx` in bus `bus_idx`.
### [int](class_int#class-int) get\_bus\_effect\_count ( [int](class_int#class-int) bus\_idx )
Returns the number of effects on the bus at `bus_idx`.
### [AudioEffectInstance](class_audioeffectinstance#class-audioeffectinstance) get\_bus\_effect\_instance ( [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx, [int](class_int#class-int) channel=0 )
Returns the [AudioEffectInstance](class_audioeffectinstance#class-audioeffectinstance) assigned to the given bus and effect indices (and optionally channel).
### [int](class_int#class-int) get\_bus\_index ( [String](class_string#class-string) bus\_name ) const
Returns the index of the bus with the name `bus_name`.
### [String](class_string#class-string) get\_bus\_name ( [int](class_int#class-int) bus\_idx ) const
Returns the name of the bus with the index `bus_idx`.
### [float](class_float#class-float) get\_bus\_peak\_volume\_left\_db ( [int](class_int#class-int) bus\_idx, [int](class_int#class-int) channel ) const
Returns the peak volume of the left speaker at bus index `bus_idx` and channel index `channel`.
### [float](class_float#class-float) get\_bus\_peak\_volume\_right\_db ( [int](class_int#class-int) bus\_idx, [int](class_int#class-int) channel ) const
Returns the peak volume of the right speaker at bus index `bus_idx` and channel index `channel`.
### [String](class_string#class-string) get\_bus\_send ( [int](class_int#class-int) bus\_idx ) const
Returns the name of the bus that the bus at index `bus_idx` sends to.
### [float](class_float#class-float) get\_bus\_volume\_db ( [int](class_int#class-int) bus\_idx ) const
Returns the volume of the bus at index `bus_idx` in dB.
### [Array](class_array#class-array) get\_device\_list ( )
Returns the names of all audio devices detected on the system.
### [float](class_float#class-float) get\_mix\_rate ( ) const
Returns the sample rate at the output of the `AudioServer`.
### [float](class_float#class-float) get\_output\_latency ( ) const
Returns the audio driver's output latency.
### [SpeakerMode](#enum-audioserver-speakermode) get\_speaker\_mode ( ) const
Returns the speaker configuration.
### [float](class_float#class-float) get\_time\_since\_last\_mix ( ) const
Returns the relative time since the last mix occurred.
### [float](class_float#class-float) get\_time\_to\_next\_mix ( ) const
Returns the relative time until the next mix occurs.
### [bool](class_bool#class-bool) is\_bus\_bypassing\_effects ( [int](class_int#class-int) bus\_idx ) const
If `true`, the bus at index `bus_idx` is bypassing effects.
### [bool](class_bool#class-bool) is\_bus\_effect\_enabled ( [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx ) const
If `true`, the effect at index `effect_idx` on the bus at index `bus_idx` is enabled.
### [bool](class_bool#class-bool) is\_bus\_mute ( [int](class_int#class-int) bus\_idx ) const
If `true`, the bus at index `bus_idx` is muted.
### [bool](class_bool#class-bool) is\_bus\_solo ( [int](class_int#class-int) bus\_idx ) const
If `true`, the bus at index `bus_idx` is in solo mode.
### void lock ( )
Locks the audio driver's main loop.
**Note:** Remember to unlock it afterwards.
### void move\_bus ( [int](class_int#class-int) index, [int](class_int#class-int) to\_index )
Moves the bus from index `index` to index `to_index`.
### void remove\_bus ( [int](class_int#class-int) index )
Removes the bus at index `index`.
### void remove\_bus\_effect ( [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx )
Removes the effect at index `effect_idx` from the bus at index `bus_idx`.
### void set\_bus\_bypass\_effects ( [int](class_int#class-int) bus\_idx, [bool](class_bool#class-bool) enable )
If `true`, the bus at index `bus_idx` is bypassing effects.
### void set\_bus\_effect\_enabled ( [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx, [bool](class_bool#class-bool) enabled )
If `true`, the effect at index `effect_idx` on the bus at index `bus_idx` is enabled.
### void set\_bus\_layout ( [AudioBusLayout](class_audiobuslayout#class-audiobuslayout) bus\_layout )
Overwrites the currently used [AudioBusLayout](class_audiobuslayout#class-audiobuslayout).
### void set\_bus\_mute ( [int](class_int#class-int) bus\_idx, [bool](class_bool#class-bool) enable )
If `true`, the bus at index `bus_idx` is muted.
### void set\_bus\_name ( [int](class_int#class-int) bus\_idx, [String](class_string#class-string) name )
Sets the name of the bus at index `bus_idx` to `name`.
### void set\_bus\_send ( [int](class_int#class-int) bus\_idx, [String](class_string#class-string) send )
Connects the output of the bus at `bus_idx` to the bus named `send`.
### void set\_bus\_solo ( [int](class_int#class-int) bus\_idx, [bool](class_bool#class-bool) enable )
If `true`, the bus at index `bus_idx` is in solo mode.
### void set\_bus\_volume\_db ( [int](class_int#class-int) bus\_idx, [float](class_float#class-float) volume\_db )
Sets the volume of the bus at index `bus_idx` to `volume_db`.
### void swap\_bus\_effects ( [int](class_int#class-int) bus\_idx, [int](class_int#class-int) effect\_idx, [int](class_int#class-int) by\_effect\_idx )
Swaps the position of two effects in bus `bus_idx`.
### void unlock ( )
Unlocks the audio driver's main loop. (After locking it, you should always unlock it.)
godot Translation Translation
===========
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [PHashTranslation](class_phashtranslation#class-phashtranslation)
Language Translation.
Description
-----------
Translations are resources that can be loaded and unloaded on demand. They map a string to another string.
Tutorials
---------
* [Internationalizing games](https://docs.godotengine.org/en/3.5/tutorials/i18n/internationalizing_games.html)
* [Locales](https://docs.godotengine.org/en/3.5/tutorials/i18n/locales.html)
Properties
----------
| | | |
| --- | --- | --- |
| [String](class_string#class-string) | [locale](#class-translation-property-locale) | `"en"` |
Methods
-------
| | |
| --- | --- |
| [String](class_string#class-string) | [\_get\_message](#class-translation-method-get-message) **(** [String](class_string#class-string) src\_message **)** virtual |
| void | [add\_message](#class-translation-method-add-message) **(** [String](class_string#class-string) src\_message, [String](class_string#class-string) xlated\_message **)** |
| void | [erase\_message](#class-translation-method-erase-message) **(** [String](class_string#class-string) src\_message **)** |
| [String](class_string#class-string) | [get\_message](#id1) **(** [String](class_string#class-string) src\_message **)** const |
| [int](class_int#class-int) | [get\_message\_count](#class-translation-method-get-message-count) **(** **)** const |
| [PoolStringArray](class_poolstringarray#class-poolstringarray) | [get\_message\_list](#class-translation-method-get-message-list) **(** **)** const |
Property Descriptions
---------------------
### [String](class_string#class-string) locale
| | |
| --- | --- |
| *Default* | `"en"` |
| *Setter* | set\_locale(value) |
| *Getter* | get\_locale() |
The locale of the translation.
Method Descriptions
-------------------
### [String](class_string#class-string) \_get\_message ( [String](class_string#class-string) src\_message ) virtual
Virtual method to override [get\_message](#id1).
### void add\_message ( [String](class_string#class-string) src\_message, [String](class_string#class-string) xlated\_message )
Adds a message if nonexistent, followed by its translation.
### void erase\_message ( [String](class_string#class-string) src\_message )
Erases a message.
### [String](class_string#class-string) get\_message ( [String](class_string#class-string) src\_message ) const
Returns a message's translation.
### [int](class_int#class-int) get\_message\_count ( ) const
Returns the number of existing messages.
### [PoolStringArray](class_poolstringarray#class-poolstringarray) get\_message\_list ( ) const
Returns all the messages (keys).
| programming_docs |
godot ProxyTexture ProxyTexture
============
**Inherits:** [Texture](class_texture#class-texture) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Properties
----------
| | | |
| --- | --- | --- |
| [Texture](class_texture#class-texture) | [base](#class-proxytexture-property-base) | |
| [int](class_int#class-int) | flags | `0` (overrides [Texture](class_texture#class-texture-property-flags)) |
Property Descriptions
---------------------
### [Texture](class_texture#class-texture) base
| | |
| --- | --- |
| *Setter* | set\_base(value) |
| *Getter* | get\_base() |
godot AudioEffectCapture AudioEffectCapture
==================
**Inherits:** [AudioEffect](class_audioeffect#class-audioeffect) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Captures audio from an audio bus in real-time.
Description
-----------
AudioEffectCapture is an AudioEffect which copies all audio frames from the attached audio effect bus into its internal ring buffer.
Application code should consume these audio frames from this ring buffer using [get\_buffer](#class-audioeffectcapture-method-get-buffer) and process it as needed, for example to capture data from an [AudioStreamMicrophone](class_audiostreammicrophone#class-audiostreammicrophone), implement application-defined effects, or to transmit audio over the network. When capturing audio data from a microphone, the format of the samples will be stereo 32-bit floating point PCM.
**Note:** [ProjectSettings.audio/enable\_audio\_input](class_projectsettings#class-projectsettings-property-audio-enable-audio-input) must be `true` for audio input to work. See also that setting's description for caveats related to permissions and operating system privacy settings.
Tutorials
---------
* [Audio buses](https://docs.godotengine.org/en/3.5/tutorials/audio/audio_buses.html)
* [Audio Mic Record Demo](https://github.com/godotengine/godot-demo-projects/tree/master/audio/mic_record)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [buffer\_length](#class-audioeffectcapture-property-buffer-length) | `0.1` |
Methods
-------
| | |
| --- | --- |
| [bool](class_bool#class-bool) | [can\_get\_buffer](#class-audioeffectcapture-method-can-get-buffer) **(** [int](class_int#class-int) frames **)** const |
| void | [clear\_buffer](#class-audioeffectcapture-method-clear-buffer) **(** **)** |
| [PoolVector2Array](class_poolvector2array#class-poolvector2array) | [get\_buffer](#class-audioeffectcapture-method-get-buffer) **(** [int](class_int#class-int) frames **)** |
| [int](class_int#class-int) | [get\_buffer\_length\_frames](#class-audioeffectcapture-method-get-buffer-length-frames) **(** **)** const |
| [int](class_int#class-int) | [get\_discarded\_frames](#class-audioeffectcapture-method-get-discarded-frames) **(** **)** const |
| [int](class_int#class-int) | [get\_frames\_available](#class-audioeffectcapture-method-get-frames-available) **(** **)** const |
| [int](class_int#class-int) | [get\_pushed\_frames](#class-audioeffectcapture-method-get-pushed-frames) **(** **)** const |
Property Descriptions
---------------------
### [float](class_float#class-float) buffer\_length
| | |
| --- | --- |
| *Default* | `0.1` |
| *Setter* | set\_buffer\_length(value) |
| *Getter* | get\_buffer\_length() |
Length of the internal ring buffer, in seconds. Setting the buffer length will have no effect if already initialized.
Method Descriptions
-------------------
### [bool](class_bool#class-bool) can\_get\_buffer ( [int](class_int#class-int) frames ) const
Returns `true` if at least `frames` audio frames are available to read in the internal ring buffer.
### void clear\_buffer ( )
Clears the internal ring buffer.
### [PoolVector2Array](class_poolvector2array#class-poolvector2array) get\_buffer ( [int](class_int#class-int) frames )
Gets the next `frames` audio samples from the internal ring buffer.
Returns a [PoolVector2Array](class_poolvector2array#class-poolvector2array) containing exactly `frames` audio samples if available, or an empty [PoolVector2Array](class_poolvector2array#class-poolvector2array) if insufficient data was available.
### [int](class_int#class-int) get\_buffer\_length\_frames ( ) const
Returns the total size of the internal ring buffer in frames.
### [int](class_int#class-int) get\_discarded\_frames ( ) const
Returns the number of audio frames discarded from the audio bus due to full buffer.
### [int](class_int#class-int) get\_frames\_available ( ) const
Returns the number of frames available to read using [get\_buffer](#class-audioeffectcapture-method-get-buffer).
### [int](class_int#class-int) get\_pushed\_frames ( ) const
Returns the number of audio frames inserted from the audio bus.
godot World World
=====
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Class that has everything pertaining to a world.
Description
-----------
Class that has everything pertaining to a world. A physics space, a visual scenario, a navigation map and a sound space. Spatial nodes register their resources into the current world.
Tutorials
---------
* [Ray-casting](https://docs.godotengine.org/en/3.5/tutorials/physics/ray-casting.html)
Properties
----------
| | |
| --- | --- |
| [PhysicsDirectSpaceState](class_physicsdirectspacestate#class-physicsdirectspacestate) | [direct\_space\_state](#class-world-property-direct-space-state) |
| [Environment](class_environment#class-environment) | [environment](#class-world-property-environment) |
| [Environment](class_environment#class-environment) | [fallback\_environment](#class-world-property-fallback-environment) |
| [RID](class_rid#class-rid) | [navigation\_map](#class-world-property-navigation-map) |
| [RID](class_rid#class-rid) | [scenario](#class-world-property-scenario) |
| [RID](class_rid#class-rid) | [space](#class-world-property-space) |
Property Descriptions
---------------------
### [PhysicsDirectSpaceState](class_physicsdirectspacestate#class-physicsdirectspacestate) direct\_space\_state
| | |
| --- | --- |
| *Getter* | get\_direct\_space\_state() |
Direct access to the world's physics 3D space state. Used for querying current and potential collisions.
### [Environment](class_environment#class-environment) environment
| | |
| --- | --- |
| *Setter* | set\_environment(value) |
| *Getter* | get\_environment() |
The World's [Environment](class_environment#class-environment).
### [Environment](class_environment#class-environment) fallback\_environment
| | |
| --- | --- |
| *Setter* | set\_fallback\_environment(value) |
| *Getter* | get\_fallback\_environment() |
The World's fallback environment will be used if [environment](#class-world-property-environment) fails or is missing.
### [RID](class_rid#class-rid) navigation\_map
| | |
| --- | --- |
| *Getter* | get\_navigation\_map() |
The [RID](class_rid#class-rid) of this world's navigation map. Used by the [NavigationServer](class_navigationserver#class-navigationserver).
### [RID](class_rid#class-rid) scenario
| | |
| --- | --- |
| *Getter* | get\_scenario() |
The World's visual scenario.
### [RID](class_rid#class-rid) space
| | |
| --- | --- |
| *Getter* | get\_space() |
The World's physics space.
godot PacketPeerGDNative PacketPeerGDNative
==================
**Inherits:** [PacketPeer](class_packetpeer#class-packetpeer) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
godot GLTFAnimation GLTFAnimation
=============
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Description
-----------
**Note:** This class is only compiled in editor builds. Run-time glTF loading and saving is *not* available in exported projects. References to `GLTFAnimation` within a script will cause an error in an exported project.
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [loop](#class-gltfanimation-property-loop) | `false` |
Property Descriptions
---------------------
### [bool](class_bool#class-bool) loop
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_loop(value) |
| *Getter* | get\_loop() |
godot EditorSceneImporter EditorSceneImporter
===================
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [EditorSceneImporterFBX](class_editorsceneimporterfbx#class-editorsceneimporterfbx), [EditorSceneImporterGLTF](class_editorsceneimportergltf#class-editorsceneimportergltf)
Imports scenes from third-parties' 3D files.
Description
-----------
`EditorSceneImporter` allows to define an importer script for a third-party 3D format.
To use `EditorSceneImporter`, register it using the [EditorPlugin.add\_scene\_import\_plugin](class_editorplugin#class-editorplugin-method-add-scene-import-plugin) method first.
Methods
-------
| | |
| --- | --- |
| [Array](class_array#class-array) | [\_get\_extensions](#class-editorsceneimporter-method-get-extensions) **(** **)** virtual |
| [int](class_int#class-int) | [\_get\_import\_flags](#class-editorsceneimporter-method-get-import-flags) **(** **)** virtual |
| [Animation](class_animation#class-animation) | [\_import\_animation](#class-editorsceneimporter-method-import-animation) **(** [String](class_string#class-string) path, [int](class_int#class-int) flags, [int](class_int#class-int) bake\_fps **)** virtual |
| [Node](class_node#class-node) | [\_import\_scene](#class-editorsceneimporter-method-import-scene) **(** [String](class_string#class-string) path, [int](class_int#class-int) flags, [int](class_int#class-int) bake\_fps **)** virtual |
| [Animation](class_animation#class-animation) | [import\_animation\_from\_other\_importer](#class-editorsceneimporter-method-import-animation-from-other-importer) **(** [String](class_string#class-string) path, [int](class_int#class-int) flags, [int](class_int#class-int) bake\_fps **)** |
| [Node](class_node#class-node) | [import\_scene\_from\_other\_importer](#class-editorsceneimporter-method-import-scene-from-other-importer) **(** [String](class_string#class-string) path, [int](class_int#class-int) flags, [int](class_int#class-int) bake\_fps, [int](class_int#class-int) compress\_flags **)** |
Constants
---------
* **IMPORT\_SCENE** = **1**
* **IMPORT\_ANIMATION** = **2**
* **IMPORT\_ANIMATION\_DETECT\_LOOP** = **4**
* **IMPORT\_ANIMATION\_OPTIMIZE** = **8**
* **IMPORT\_ANIMATION\_FORCE\_ALL\_TRACKS\_IN\_ALL\_CLIPS** = **16**
* **IMPORT\_ANIMATION\_KEEP\_VALUE\_TRACKS** = **32**
* **IMPORT\_GENERATE\_TANGENT\_ARRAYS** = **256**
* **IMPORT\_FAIL\_ON\_MISSING\_DEPENDENCIES** = **512**
* **IMPORT\_MATERIALS\_IN\_INSTANCES** = **1024**
Method Descriptions
-------------------
### [Array](class_array#class-array) \_get\_extensions ( ) virtual
### [int](class_int#class-int) \_get\_import\_flags ( ) virtual
### [Animation](class_animation#class-animation) \_import\_animation ( [String](class_string#class-string) path, [int](class_int#class-int) flags, [int](class_int#class-int) bake\_fps ) virtual
### [Node](class_node#class-node) \_import\_scene ( [String](class_string#class-string) path, [int](class_int#class-int) flags, [int](class_int#class-int) bake\_fps ) virtual
### [Animation](class_animation#class-animation) import\_animation\_from\_other\_importer ( [String](class_string#class-string) path, [int](class_int#class-int) flags, [int](class_int#class-int) bake\_fps )
### [Node](class_node#class-node) import\_scene\_from\_other\_importer ( [String](class_string#class-string) path, [int](class_int#class-int) flags, [int](class_int#class-int) bake\_fps, [int](class_int#class-int) compress\_flags )
godot GLTFTexture GLTFTexture
===========
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Description
-----------
**Note:** This class is only compiled in editor builds. Run-time glTF loading and saving is *not* available in exported projects. References to `GLTFTexture` within a script will cause an error in an exported project.
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [src\_image](#class-gltftexture-property-src-image) | `0` |
Property Descriptions
---------------------
### [int](class_int#class-int) src\_image
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_src\_image(value) |
| *Getter* | get\_src\_image() |
godot InputEventMouse InputEventMouse
===============
**Inherits:** [InputEventWithModifiers](class_inputeventwithmodifiers#class-inputeventwithmodifiers) **<** [InputEvent](class_inputevent#class-inputevent) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [InputEventMouseButton](class_inputeventmousebutton#class-inputeventmousebutton), [InputEventMouseMotion](class_inputeventmousemotion#class-inputeventmousemotion)
Base input event type for mouse events.
Description
-----------
Stores general mouse events information.
Tutorials
---------
* [Using InputEvent](https://docs.godotengine.org/en/3.5/tutorials/inputs/inputevent.html)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [button\_mask](#class-inputeventmouse-property-button-mask) | `0` |
| [Vector2](class_vector2#class-vector2) | [global\_position](#class-inputeventmouse-property-global-position) | `Vector2( 0, 0 )` |
| [Vector2](class_vector2#class-vector2) | [position](#class-inputeventmouse-property-position) | `Vector2( 0, 0 )` |
Property Descriptions
---------------------
### [int](class_int#class-int) button\_mask
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_button\_mask(value) |
| *Getter* | get\_button\_mask() |
The mouse button mask identifier, one of or a bitwise combination of the [ButtonList](class_%40globalscope#enum-globalscope-buttonlist) button masks.
### [Vector2](class_vector2#class-vector2) global\_position
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_global\_position(value) |
| *Getter* | get\_global\_position() |
When received in [Node.\_input](class_node#class-node-method-input) or [Node.\_unhandled\_input](class_node#class-node-method-unhandled-input), returns the mouse's position in the root [Viewport](class_viewport#class-viewport) using the coordinate system of the root [Viewport](class_viewport#class-viewport).
When received in [Control.\_gui\_input](class_control#class-control-method-gui-input), returns the mouse's position in the [CanvasLayer](class_canvaslayer#class-canvaslayer) that the [Control](class_control#class-control) is in using the coordinate system of the [CanvasLayer](class_canvaslayer#class-canvaslayer).
### [Vector2](class_vector2#class-vector2) position
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_position(value) |
| *Getter* | get\_position() |
When received in [Node.\_input](class_node#class-node-method-input) or [Node.\_unhandled\_input](class_node#class-node-method-unhandled-input), returns the mouse's position in the [Viewport](class_viewport#class-viewport) this [Node](class_node#class-node) is in using the coordinate system of this [Viewport](class_viewport#class-viewport).
When received in [Control.\_gui\_input](class_control#class-control-method-gui-input), returns the mouse's position in the [Control](class_control#class-control) using the local coordinate system of the [Control](class_control#class-control).
godot StyleBoxLine StyleBoxLine
============
**Inherits:** [StyleBox](class_stylebox#class-stylebox) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
[StyleBox](class_stylebox#class-stylebox) that displays a single line.
Description
-----------
[StyleBox](class_stylebox#class-stylebox) that displays a single line of a given color and thickness. It can be used to draw things like separators.
Properties
----------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [color](#class-styleboxline-property-color) | `Color( 0, 0, 0, 1 )` |
| [float](class_float#class-float) | [grow\_begin](#class-styleboxline-property-grow-begin) | `1.0` |
| [float](class_float#class-float) | [grow\_end](#class-styleboxline-property-grow-end) | `1.0` |
| [int](class_int#class-int) | [thickness](#class-styleboxline-property-thickness) | `1` |
| [bool](class_bool#class-bool) | [vertical](#class-styleboxline-property-vertical) | `false` |
Property Descriptions
---------------------
### [Color](class_color#class-color) color
| | |
| --- | --- |
| *Default* | `Color( 0, 0, 0, 1 )` |
| *Setter* | set\_color(value) |
| *Getter* | get\_color() |
The line's color.
### [float](class_float#class-float) grow\_begin
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_grow\_begin(value) |
| *Getter* | get\_grow\_begin() |
The number of pixels the line will extend before the `StyleBoxLine`'s bounds. If set to a negative value, the line will begin inside the `StyleBoxLine`'s bounds.
### [float](class_float#class-float) grow\_end
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_grow\_end(value) |
| *Getter* | get\_grow\_end() |
The number of pixels the line will extend past the `StyleBoxLine`'s bounds. If set to a negative value, the line will end inside the `StyleBoxLine`'s bounds.
### [int](class_int#class-int) thickness
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_thickness(value) |
| *Getter* | get\_thickness() |
The line's thickness in pixels.
### [bool](class_bool#class-bool) vertical
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_vertical(value) |
| *Getter* | is\_vertical() |
If `true`, the line will be vertical. If `false`, the line will be horizontal.
godot InputEventWithModifiers InputEventWithModifiers
=======================
**Inherits:** [InputEvent](class_inputevent#class-inputevent) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [InputEventGesture](class_inputeventgesture#class-inputeventgesture), [InputEventKey](class_inputeventkey#class-inputeventkey), [InputEventMouse](class_inputeventmouse#class-inputeventmouse)
Base class for keys events with modifiers.
Description
-----------
Contains keys events information with modifiers support like `Shift` or `Alt`. See [Node.\_input](class_node#class-node-method-input).
Tutorials
---------
* [Using InputEvent](https://docs.godotengine.org/en/3.5/tutorials/inputs/inputevent.html)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [alt](#class-inputeventwithmodifiers-property-alt) | `false` |
| [bool](class_bool#class-bool) | [command](#class-inputeventwithmodifiers-property-command) | `false` |
| [bool](class_bool#class-bool) | [control](#class-inputeventwithmodifiers-property-control) | `false` |
| [bool](class_bool#class-bool) | [meta](#class-inputeventwithmodifiers-property-meta) | `false` |
| [bool](class_bool#class-bool) | [shift](#class-inputeventwithmodifiers-property-shift) | `false` |
Property Descriptions
---------------------
### [bool](class_bool#class-bool) alt
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_alt(value) |
| *Getter* | get\_alt() |
State of the `Alt` modifier.
### [bool](class_bool#class-bool) command
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_command(value) |
| *Getter* | get\_command() |
State of the `Command` modifier.
### [bool](class_bool#class-bool) control
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_control(value) |
| *Getter* | get\_control() |
State of the `Ctrl` modifier.
### [bool](class_bool#class-bool) meta
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_metakey(value) |
| *Getter* | get\_metakey() |
State of the `Meta` modifier.
### [bool](class_bool#class-bool) shift
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_shift(value) |
| *Getter* | get\_shift() |
State of the `Shift` modifier.
| programming_docs |
godot InputEventJoypadButton InputEventJoypadButton
======================
**Inherits:** [InputEvent](class_inputevent#class-inputevent) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Input event for gamepad buttons.
Description
-----------
Input event type for gamepad buttons. For gamepad analog sticks and joysticks, see [InputEventJoypadMotion](class_inputeventjoypadmotion#class-inputeventjoypadmotion).
Tutorials
---------
* [Using InputEvent](https://docs.godotengine.org/en/3.5/tutorials/inputs/inputevent.html)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [button\_index](#class-inputeventjoypadbutton-property-button-index) | `0` |
| [bool](class_bool#class-bool) | [pressed](#class-inputeventjoypadbutton-property-pressed) | `false` |
| [float](class_float#class-float) | [pressure](#class-inputeventjoypadbutton-property-pressure) | `0.0` |
Property Descriptions
---------------------
### [int](class_int#class-int) button\_index
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_button\_index(value) |
| *Getter* | get\_button\_index() |
Button identifier. One of the [JoystickList](class_%40globalscope#enum-globalscope-joysticklist) button constants.
### [bool](class_bool#class-bool) pressed
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_pressed(value) |
| *Getter* | is\_pressed() |
If `true`, the button's state is pressed. If `false`, the button's state is released.
### [float](class_float#class-float) pressure
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_pressure(value) |
| *Getter* | get\_pressure() |
Represents the pressure the user puts on the button with their finger, if the controller supports it. Ranges from `0` to `1`.
godot ParallaxBackground ParallaxBackground
==================
**Inherits:** [CanvasLayer](class_canvaslayer#class-canvaslayer) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
A node used to create a parallax scrolling background.
Description
-----------
A ParallaxBackground uses one or more [ParallaxLayer](class_parallaxlayer#class-parallaxlayer) child nodes to create a parallax effect. Each [ParallaxLayer](class_parallaxlayer#class-parallaxlayer) can move at a different speed using [ParallaxLayer.motion\_offset](class_parallaxlayer#class-parallaxlayer-property-motion-offset). This creates an illusion of depth in a 2D game. If not used with a [Camera2D](class_camera2d#class-camera2d), you must manually calculate the [scroll\_offset](#class-parallaxbackground-property-scroll-offset).
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | layer | `-100` (overrides [CanvasLayer](class_canvaslayer#class-canvaslayer-property-layer)) |
| [Vector2](class_vector2#class-vector2) | [scroll\_base\_offset](#class-parallaxbackground-property-scroll-base-offset) | `Vector2( 0, 0 )` |
| [Vector2](class_vector2#class-vector2) | [scroll\_base\_scale](#class-parallaxbackground-property-scroll-base-scale) | `Vector2( 1, 1 )` |
| [bool](class_bool#class-bool) | [scroll\_ignore\_camera\_zoom](#class-parallaxbackground-property-scroll-ignore-camera-zoom) | `false` |
| [Vector2](class_vector2#class-vector2) | [scroll\_limit\_begin](#class-parallaxbackground-property-scroll-limit-begin) | `Vector2( 0, 0 )` |
| [Vector2](class_vector2#class-vector2) | [scroll\_limit\_end](#class-parallaxbackground-property-scroll-limit-end) | `Vector2( 0, 0 )` |
| [Vector2](class_vector2#class-vector2) | [scroll\_offset](#class-parallaxbackground-property-scroll-offset) | `Vector2( 0, 0 )` |
Property Descriptions
---------------------
### [Vector2](class_vector2#class-vector2) scroll\_base\_offset
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_scroll\_base\_offset(value) |
| *Getter* | get\_scroll\_base\_offset() |
The base position offset for all [ParallaxLayer](class_parallaxlayer#class-parallaxlayer) children.
### [Vector2](class_vector2#class-vector2) scroll\_base\_scale
| | |
| --- | --- |
| *Default* | `Vector2( 1, 1 )` |
| *Setter* | set\_scroll\_base\_scale(value) |
| *Getter* | get\_scroll\_base\_scale() |
The base motion scale for all [ParallaxLayer](class_parallaxlayer#class-parallaxlayer) children.
### [bool](class_bool#class-bool) scroll\_ignore\_camera\_zoom
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_ignore\_camera\_zoom(value) |
| *Getter* | is\_ignore\_camera\_zoom() |
If `true`, elements in [ParallaxLayer](class_parallaxlayer#class-parallaxlayer) child aren't affected by the zoom level of the camera.
### [Vector2](class_vector2#class-vector2) scroll\_limit\_begin
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_limit\_begin(value) |
| *Getter* | get\_limit\_begin() |
Top-left limits for scrolling to begin. If the camera is outside of this limit, the background will stop scrolling. Must be lower than [scroll\_limit\_end](#class-parallaxbackground-property-scroll-limit-end) to work.
### [Vector2](class_vector2#class-vector2) scroll\_limit\_end
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_limit\_end(value) |
| *Getter* | get\_limit\_end() |
Bottom-right limits for scrolling to end. If the camera is outside of this limit, the background will stop scrolling. Must be higher than [scroll\_limit\_begin](#class-parallaxbackground-property-scroll-limit-begin) to work.
### [Vector2](class_vector2#class-vector2) scroll\_offset
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_scroll\_offset(value) |
| *Getter* | get\_scroll\_offset() |
The ParallaxBackground's scroll value. Calculated automatically when using a [Camera2D](class_camera2d#class-camera2d), but can be used to manually manage scrolling when no camera is present.
godot OccluderShapeSphere OccluderShapeSphere
===================
**Inherits:** [OccluderShape](class_occludershape#class-occludershape) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Spherical occlusion primitive for use with the [Occluder](class_occluder#class-occluder) node.
Description
-----------
[OccluderShape](class_occludershape#class-occludershape)s are resources used by [Occluder](class_occluder#class-occluder) nodes, allowing geometric occlusion culling.
This shape can include multiple spheres. These can be created and deleted either in the Editor inspector or by calling `set_spheres`. The sphere positions can be set by dragging the handle in the Editor viewport. The radius can be set with the smaller handle.
Properties
----------
| | | |
| --- | --- | --- |
| [Array](class_array#class-array) | [spheres](#class-occludershapesphere-property-spheres) | `[ Plane( 0, 0, 0, 1 ) ]` |
Methods
-------
| | |
| --- | --- |
| void | [set\_sphere\_position](#class-occludershapesphere-method-set-sphere-position) **(** [int](class_int#class-int) index, [Vector3](class_vector3#class-vector3) position **)** |
| void | [set\_sphere\_radius](#class-occludershapesphere-method-set-sphere-radius) **(** [int](class_int#class-int) index, [float](class_float#class-float) radius **)** |
Property Descriptions
---------------------
### [Array](class_array#class-array) spheres
| | |
| --- | --- |
| *Default* | `[ Plane( 0, 0, 0, 1 ) ]` |
| *Setter* | set\_spheres(value) |
| *Getter* | get\_spheres() |
The sphere data can be accessed as an array of [Plane](class_plane#class-plane)s. The position of each sphere is stored in the `normal`, and the radius is stored in the `d` value of the plane.
Method Descriptions
-------------------
### void set\_sphere\_position ( [int](class_int#class-int) index, [Vector3](class_vector3#class-vector3) position )
Sets an individual sphere's position.
### void set\_sphere\_radius ( [int](class_int#class-int) index, [float](class_float#class-float) radius )
Sets an individual sphere's radius.
godot AudioEffectDistortion AudioEffectDistortion
=====================
**Inherits:** [AudioEffect](class_audioeffect#class-audioeffect) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Adds a distortion audio effect to an Audio bus.
Modify the sound to make it distorted.
Description
-----------
Different types are available: clip, tan, lo-fi (bit crushing), overdrive, or waveshape.
By distorting the waveform the frequency content change, which will often make the sound "crunchy" or "abrasive". For games, it can simulate sound coming from some saturated device or speaker very efficiently.
Tutorials
---------
* [Audio buses](https://docs.godotengine.org/en/3.5/tutorials/audio/audio_buses.html)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [drive](#class-audioeffectdistortion-property-drive) | `0.0` |
| [float](class_float#class-float) | [keep\_hf\_hz](#class-audioeffectdistortion-property-keep-hf-hz) | `16000.0` |
| [Mode](#enum-audioeffectdistortion-mode) | [mode](#class-audioeffectdistortion-property-mode) | `0` |
| [float](class_float#class-float) | [post\_gain](#class-audioeffectdistortion-property-post-gain) | `0.0` |
| [float](class_float#class-float) | [pre\_gain](#class-audioeffectdistortion-property-pre-gain) | `0.0` |
Enumerations
------------
enum **Mode**:
* **MODE\_CLIP** = **0** --- Digital distortion effect which cuts off peaks at the top and bottom of the waveform.
* **MODE\_ATAN** = **1**
* **MODE\_LOFI** = **2** --- Low-resolution digital distortion effect. You can use it to emulate the sound of early digital audio devices.
* **MODE\_OVERDRIVE** = **3** --- Emulates the warm distortion produced by a field effect transistor, which is commonly used in solid-state musical instrument amplifiers.
* **MODE\_WAVESHAPE** = **4** --- Waveshaper distortions are used mainly by electronic musicians to achieve an extra-abrasive sound.
Property Descriptions
---------------------
### [float](class_float#class-float) drive
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_drive(value) |
| *Getter* | get\_drive() |
Distortion power. Value can range from 0 to 1.
### [float](class_float#class-float) keep\_hf\_hz
| | |
| --- | --- |
| *Default* | `16000.0` |
| *Setter* | set\_keep\_hf\_hz(value) |
| *Getter* | get\_keep\_hf\_hz() |
High-pass filter, in Hz. Frequencies higher than this value will not be affected by the distortion. Value can range from 1 to 20000.
### [Mode](#enum-audioeffectdistortion-mode) mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_mode(value) |
| *Getter* | get\_mode() |
Distortion type.
### [float](class_float#class-float) post\_gain
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_post\_gain(value) |
| *Getter* | get\_post\_gain() |
Increases or decreases the volume after the effect. Value can range from -80 to 24.
### [float](class_float#class-float) pre\_gain
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_pre\_gain(value) |
| *Getter* | get\_pre\_gain() |
Increases or decreases the volume before the effect. Value can range from -60 to 60.
godot Sprite Sprite
======
**Inherits:** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
General-purpose sprite node.
Description
-----------
A node that displays a 2D texture. The texture displayed can be a region from a larger atlas texture, or a frame from a sprite sheet animation.
Tutorials
---------
* [Instancing Demo](https://godotengine.org/asset-library/asset/148)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [centered](#class-sprite-property-centered) | `true` |
| [bool](class_bool#class-bool) | [flip\_h](#class-sprite-property-flip-h) | `false` |
| [bool](class_bool#class-bool) | [flip\_v](#class-sprite-property-flip-v) | `false` |
| [int](class_int#class-int) | [frame](#class-sprite-property-frame) | `0` |
| [Vector2](class_vector2#class-vector2) | [frame\_coords](#class-sprite-property-frame-coords) | `Vector2( 0, 0 )` |
| [int](class_int#class-int) | [hframes](#class-sprite-property-hframes) | `1` |
| [Texture](class_texture#class-texture) | [normal\_map](#class-sprite-property-normal-map) | |
| [Vector2](class_vector2#class-vector2) | [offset](#class-sprite-property-offset) | `Vector2( 0, 0 )` |
| [bool](class_bool#class-bool) | [region\_enabled](#class-sprite-property-region-enabled) | `false` |
| [bool](class_bool#class-bool) | [region\_filter\_clip](#class-sprite-property-region-filter-clip) | `false` |
| [Rect2](class_rect2#class-rect2) | [region\_rect](#class-sprite-property-region-rect) | `Rect2( 0, 0, 0, 0 )` |
| [Texture](class_texture#class-texture) | [texture](#class-sprite-property-texture) | |
| [int](class_int#class-int) | [vframes](#class-sprite-property-vframes) | `1` |
Methods
-------
| | |
| --- | --- |
| [Rect2](class_rect2#class-rect2) | [get\_rect](#class-sprite-method-get-rect) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_pixel\_opaque](#class-sprite-method-is-pixel-opaque) **(** [Vector2](class_vector2#class-vector2) pos **)** const |
Signals
-------
### frame\_changed ( )
Emitted when the [frame](#class-sprite-property-frame) changes.
### texture\_changed ( )
Emitted when the [texture](#class-sprite-property-texture) changes.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) centered
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_centered(value) |
| *Getter* | is\_centered() |
If `true`, texture is centered.
### [bool](class_bool#class-bool) flip\_h
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flip\_h(value) |
| *Getter* | is\_flipped\_h() |
If `true`, texture is flipped horizontally.
### [bool](class_bool#class-bool) flip\_v
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flip\_v(value) |
| *Getter* | is\_flipped\_v() |
If `true`, texture is flipped vertically.
### [int](class_int#class-int) frame
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_frame(value) |
| *Getter* | get\_frame() |
Current frame to display from sprite sheet. [hframes](#class-sprite-property-hframes) or [vframes](#class-sprite-property-vframes) must be greater than 1.
### [Vector2](class_vector2#class-vector2) frame\_coords
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_frame\_coords(value) |
| *Getter* | get\_frame\_coords() |
Coordinates of the frame to display from sprite sheet. This is as an alias for the [frame](#class-sprite-property-frame) property. [hframes](#class-sprite-property-hframes) or [vframes](#class-sprite-property-vframes) must be greater than 1.
### [int](class_int#class-int) hframes
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_hframes(value) |
| *Getter* | get\_hframes() |
The number of columns in the sprite sheet.
### [Texture](class_texture#class-texture) normal\_map
| | |
| --- | --- |
| *Setter* | set\_normal\_map(value) |
| *Getter* | get\_normal\_map() |
The normal map gives depth to the Sprite.
**Note:** Godot expects the normal map to use X+, Y-, and Z+ coordinates. See [this page](http://wiki.polycount.com/wiki/Normal_Map_Technical_Details#Common_Swizzle_Coordinates) for a comparison of normal map coordinates expected by popular engines.
### [Vector2](class_vector2#class-vector2) offset
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_offset(value) |
| *Getter* | get\_offset() |
The texture's drawing offset.
### [bool](class_bool#class-bool) region\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_region(value) |
| *Getter* | is\_region() |
If `true`, texture is cut from a larger atlas texture. See [region\_rect](#class-sprite-property-region-rect).
### [bool](class_bool#class-bool) region\_filter\_clip
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_region\_filter\_clip(value) |
| *Getter* | is\_region\_filter\_clip\_enabled() |
If `true`, the outermost pixels get blurred out.
### [Rect2](class_rect2#class-rect2) region\_rect
| | |
| --- | --- |
| *Default* | `Rect2( 0, 0, 0, 0 )` |
| *Setter* | set\_region\_rect(value) |
| *Getter* | get\_region\_rect() |
The region of the atlas texture to display. [region\_enabled](#class-sprite-property-region-enabled) must be `true`.
### [Texture](class_texture#class-texture) texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
[Texture](class_texture#class-texture) object to draw.
### [int](class_int#class-int) vframes
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_vframes(value) |
| *Getter* | get\_vframes() |
The number of rows in the sprite sheet.
Method Descriptions
-------------------
### [Rect2](class_rect2#class-rect2) get\_rect ( ) const
Returns a [Rect2](class_rect2#class-rect2) representing the Sprite's boundary in local coordinates. Can be used to detect if the Sprite was clicked. Example:
```
func _input(event):
if event is InputEventMouseButton and event.pressed and event.button_index == BUTTON_LEFT:
if get_rect().has_point(to_local(event.position)):
print("A click!")
```
### [bool](class_bool#class-bool) is\_pixel\_opaque ( [Vector2](class_vector2#class-vector2) pos ) const
Returns `true`, if the pixel at the given position is opaque and `false` in other case.
**Note:** It also returns `false`, if the sprite's texture is `null` or if the given position is invalid.
godot JNISingleton JNISingleton
============
**Inherits:** [Object](class_object#class-object)
Singleton that connects the engine with Android plugins to interface with native Android code.
Description
-----------
The JNISingleton is implemented only in the Android export. It's used to call methods and connect signals from an Android plugin written in Java or Kotlin. Methods and signals can be called and connected to the JNISingleton as if it is a Node. See [Java Native Interface - Wikipedia](https://en.wikipedia.org/wiki/Java_Native_Interface) for more information.
Tutorials
---------
* [Creating Android plugins](https://docs.godotengine.org/en/3.5/tutorials/platform/android/android_plugin.html)
godot TextureArray TextureArray
============
**Inherits:** [TextureLayered](class_texturelayered#class-texturelayered) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Array of textures stored in a single primitive.
Description
-----------
`TextureArray`s store an array of [Image](class_image#class-image)s in a single [Texture](class_texture#class-texture) primitive. Each layer of the texture array has its own mipmap chain. This makes it is a good alternative to texture atlases. See also [Texture3D](class_texture3d#class-texture3d).
`TextureArray`s must be displayed using shaders. After importing your file as a `TextureArray` and setting the appropriate Horizontal and Vertical Slices, display it by setting it as a uniform to a shader, for example (2D):
```
shader_type canvas_item;
uniform sampler2DArray tex;
uniform int index;
void fragment() {
COLOR = texture(tex, vec3(UV.x, UV.y, float(index)));
}
```
Set the integer uniform "index" to show a particular part of the texture as defined by the Horizontal and Vertical Slices in the importer.
**Note:** When sampling an albedo texture from a texture array in 3D, the sRGB -> linear conversion hint (`hint_albedo`) should be used to prevent colors from looking washed out:
```
shader_type spatial;
uniform sampler2DArray tex : hint_albedo;
uniform int index;
void fragment() {
ALBEDO = texture(tex, vec3(UV.x, UV.y, float(index)));
}
```
**Note:** `TextureArray`s can only be sampled in shaders in the GLES3 backend. In GLES2, their data can be accessed via scripting, but there is no way to render them in a hardware-accelerated manner.
Methods
-------
| | |
| --- | --- |
| void | [create](#class-texturearray-method-create) **(** [int](class_int#class-int) width, [int](class_int#class-int) height, [int](class_int#class-int) depth, [Format](class_image#enum-image-format) format, [int](class_int#class-int) flags=7 **)** |
Method Descriptions
-------------------
### void create ( [int](class_int#class-int) width, [int](class_int#class-int) height, [int](class_int#class-int) depth, [Format](class_image#enum-image-format) format, [int](class_int#class-int) flags=7 )
Creates the TextureArray with specified `width`, `height`, and `depth`. See [Format](class_image#enum-image-format) for `format` options. See [Flags](class_texturelayered#enum-texturelayered-flags) enumerator for `flags` options.
| programming_docs |
godot AspectRatioContainer AspectRatioContainer
====================
**Inherits:** [Container](class_container#class-container) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Container that preserves its child controls' aspect ratio.
Description
-----------
Arranges child controls in a way to preserve their aspect ratio automatically whenever the container is resized. Solves the problem where the container size is dynamic and the contents' size needs to adjust accordingly without losing proportions.
Tutorials
---------
* [GUI containers](https://docs.godotengine.org/en/3.5/tutorials/ui/gui_containers.html)
Properties
----------
| | | |
| --- | --- | --- |
| [AlignMode](#enum-aspectratiocontainer-alignmode) | [alignment\_horizontal](#class-aspectratiocontainer-property-alignment-horizontal) | `1` |
| [AlignMode](#enum-aspectratiocontainer-alignmode) | [alignment\_vertical](#class-aspectratiocontainer-property-alignment-vertical) | `1` |
| [float](class_float#class-float) | [ratio](#class-aspectratiocontainer-property-ratio) | `1.0` |
| [StretchMode](#enum-aspectratiocontainer-stretchmode) | [stretch\_mode](#class-aspectratiocontainer-property-stretch-mode) | `2` |
Enumerations
------------
enum **StretchMode**:
* **STRETCH\_WIDTH\_CONTROLS\_HEIGHT** = **0** --- The height of child controls is automatically adjusted based on the width of the container.
* **STRETCH\_HEIGHT\_CONTROLS\_WIDTH** = **1** --- The width of child controls is automatically adjusted based on the height of the container.
* **STRETCH\_FIT** = **2** --- The bounding rectangle of child controls is automatically adjusted to fit inside the container while keeping the aspect ratio.
* **STRETCH\_COVER** = **3** --- The width and height of child controls is automatically adjusted to make their bounding rectangle cover the entire area of the container while keeping the aspect ratio.
When the bounding rectangle of child controls exceed the container's size and [Control.rect\_clip\_content](class_control#class-control-property-rect-clip-content) is enabled, this allows to show only the container's area restricted by its own bounding rectangle.
enum **AlignMode**:
* **ALIGN\_BEGIN** = **0** --- Aligns child controls with the beginning (left or top) of the container.
* **ALIGN\_CENTER** = **1** --- Aligns child controls with the center of the container.
* **ALIGN\_END** = **2** --- Aligns child controls with the end (right or bottom) of the container.
Property Descriptions
---------------------
### [AlignMode](#enum-aspectratiocontainer-alignmode) alignment\_horizontal
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_alignment\_horizontal(value) |
| *Getter* | get\_alignment\_horizontal() |
Specifies the horizontal relative position of child controls.
### [AlignMode](#enum-aspectratiocontainer-alignmode) alignment\_vertical
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_alignment\_vertical(value) |
| *Getter* | get\_alignment\_vertical() |
Specifies the vertical relative position of child controls.
### [float](class_float#class-float) ratio
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_ratio(value) |
| *Getter* | get\_ratio() |
The aspect ratio to enforce on child controls. This is the width divided by the height. The ratio depends on the [stretch\_mode](#class-aspectratiocontainer-property-stretch-mode).
### [StretchMode](#enum-aspectratiocontainer-stretchmode) stretch\_mode
| | |
| --- | --- |
| *Default* | `2` |
| *Setter* | set\_stretch\_mode(value) |
| *Getter* | get\_stretch\_mode() |
The stretch mode used to align child controls.
godot AudioStreamRandomPitch AudioStreamRandomPitch
======================
**Inherits:** [AudioStream](class_audiostream#class-audiostream) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Plays audio with random pitch shifting.
Description
-----------
Randomly varies pitch on each start.
Properties
----------
| | | |
| --- | --- | --- |
| [AudioStream](class_audiostream#class-audiostream) | [audio\_stream](#class-audiostreamrandompitch-property-audio-stream) | |
| [float](class_float#class-float) | [random\_pitch](#class-audiostreamrandompitch-property-random-pitch) | `1.1` |
Property Descriptions
---------------------
### [AudioStream](class_audiostream#class-audiostream) audio\_stream
| | |
| --- | --- |
| *Setter* | set\_audio\_stream(value) |
| *Getter* | get\_audio\_stream() |
The current [AudioStream](class_audiostream#class-audiostream).
### [float](class_float#class-float) random\_pitch
| | |
| --- | --- |
| *Default* | `1.1` |
| *Setter* | set\_random\_pitch(value) |
| *Getter* | get\_random\_pitch() |
The intensity of random pitch variation.
godot Occluder Occluder
========
**Inherits:** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Allows [OccluderShape](class_occludershape#class-occludershape)s to be used for occlusion culling.
Description
-----------
`Occluder`s that are placed within your scene will automatically cull objects that are hidden from view by the occluder. This can increase performance by decreasing the amount of objects drawn.
`Occluder`s are totally dynamic, you can move them as you wish. This means you can for example, place occluders on a moving spaceship, and have it occlude objects as it flies past.
You can place a large number of `Occluder`s within a scene. As it would be counterproductive to cull against hundreds of occluders, the system will automatically choose a selection of these for active use during any given frame, based a screen space metric. Larger occluders are favored, as well as those close to the camera. Note that a small occluder close to the camera may be a better occluder in terms of screen space than a large occluder far in the distance.
The type of occlusion primitive is determined by the [OccluderShape](class_occludershape#class-occludershape) that you add to the `Occluder`. Some [OccluderShape](class_occludershape#class-occludershape)s may allow more than one primitive in a single, node, for greater efficiency.
Although `Occluder`s work in general use, they also become even more powerful when used in conjunction with the portal system. Occluders are placed in rooms (based on their origin), and can block portals (and thus entire rooms) as well as objects from rendering.
Properties
----------
| | |
| --- | --- |
| [OccluderShape](class_occludershape#class-occludershape) | [shape](#class-occluder-property-shape) |
Methods
-------
| | |
| --- | --- |
| void | [resource\_changed](#class-occluder-method-resource-changed) **(** [Resource](class_resource#class-resource) resource **)** |
Property Descriptions
---------------------
### [OccluderShape](class_occludershape#class-occludershape) shape
| | |
| --- | --- |
| *Setter* | set\_shape(value) |
| *Getter* | get\_shape() |
Method Descriptions
-------------------
### void resource\_changed ( [Resource](class_resource#class-resource) resource )
godot OccluderPolygon2D OccluderPolygon2D
=================
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Defines a 2D polygon for LightOccluder2D.
Description
-----------
Editor facility that helps you draw a 2D polygon used as resource for [LightOccluder2D](class_lightoccluder2d#class-lightoccluder2d).
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [closed](#class-occluderpolygon2d-property-closed) | `true` |
| [CullMode](#enum-occluderpolygon2d-cullmode) | [cull\_mode](#class-occluderpolygon2d-property-cull-mode) | `0` |
| [PoolVector2Array](class_poolvector2array#class-poolvector2array) | [polygon](#class-occluderpolygon2d-property-polygon) | `PoolVector2Array( )` |
Enumerations
------------
enum **CullMode**:
* **CULL\_DISABLED** = **0** --- Culling is disabled. See [cull\_mode](#class-occluderpolygon2d-property-cull-mode).
* **CULL\_CLOCKWISE** = **1** --- Culling is performed in the clockwise direction. See [cull\_mode](#class-occluderpolygon2d-property-cull-mode).
* **CULL\_COUNTER\_CLOCKWISE** = **2** --- Culling is performed in the counterclockwise direction. See [cull\_mode](#class-occluderpolygon2d-property-cull-mode).
Property Descriptions
---------------------
### [bool](class_bool#class-bool) closed
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_closed(value) |
| *Getter* | is\_closed() |
If `true`, closes the polygon. A closed OccluderPolygon2D occludes the light coming from any direction. An opened OccluderPolygon2D occludes the light only at its outline's direction.
### [CullMode](#enum-occluderpolygon2d-cullmode) cull\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_cull\_mode(value) |
| *Getter* | get\_cull\_mode() |
The culling mode to use.
### [PoolVector2Array](class_poolvector2array#class-poolvector2array) polygon
| | |
| --- | --- |
| *Default* | `PoolVector2Array( )` |
| *Setter* | set\_polygon(value) |
| *Getter* | get\_polygon() |
A [Vector2](class_vector2#class-vector2) array with the index for polygon's vertices positions.
**Note:** The returned value is a copy of the underlying array, rather than a reference.
godot AudioEffectPanner AudioEffectPanner
=================
**Inherits:** [AudioEffect](class_audioeffect#class-audioeffect) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Adds a panner audio effect to an Audio bus. Pans sound left or right.
Description
-----------
Determines how much of an audio signal is sent to the left and right buses.
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [pan](#class-audioeffectpanner-property-pan) | `0.0` |
Property Descriptions
---------------------
### [float](class_float#class-float) pan
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_pan(value) |
| *Getter* | get\_pan() |
Pan position. Value can range from -1 (fully left) to 1 (fully right).
godot VisualShaderNodeVec3Uniform VisualShaderNodeVec3Uniform
===========================
**Inherits:** [VisualShaderNodeUniform](class_visualshadernodeuniform#class-visualshadernodeuniform) **<** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A [Vector3](class_vector3#class-vector3) uniform to be used within the visual shader graph.
Description
-----------
Translated to `uniform vec3` in the shader language.
Properties
----------
| | | |
| --- | --- | --- |
| [Vector3](class_vector3#class-vector3) | [default\_value](#class-visualshadernodevec3uniform-property-default-value) | `Vector3( 0, 0, 0 )` |
| [bool](class_bool#class-bool) | [default\_value\_enabled](#class-visualshadernodevec3uniform-property-default-value-enabled) | `false` |
Property Descriptions
---------------------
### [Vector3](class_vector3#class-vector3) default\_value
| | |
| --- | --- |
| *Default* | `Vector3( 0, 0, 0 )` |
| *Setter* | set\_default\_value(value) |
| *Getter* | get\_default\_value() |
A default value to be assigned within the shader.
### [bool](class_bool#class-bool) default\_value\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_default\_value\_enabled(value) |
| *Getter* | is\_default\_value\_enabled() |
Enables usage of the [default\_value](#class-visualshadernodevec3uniform-property-default-value).
godot AudioStreamOGGVorbis AudioStreamOGGVorbis
====================
**Inherits:** [AudioStream](class_audiostream#class-audiostream) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
OGG Vorbis audio stream driver.
Description
-----------
OGG Vorbis audio stream driver.
Properties
----------
| | | |
| --- | --- | --- |
| [PoolByteArray](class_poolbytearray#class-poolbytearray) | [data](#class-audiostreamoggvorbis-property-data) | `PoolByteArray( )` |
| [bool](class_bool#class-bool) | [loop](#class-audiostreamoggvorbis-property-loop) | `false` |
| [float](class_float#class-float) | [loop\_offset](#class-audiostreamoggvorbis-property-loop-offset) | `0.0` |
Property Descriptions
---------------------
### [PoolByteArray](class_poolbytearray#class-poolbytearray) data
| | |
| --- | --- |
| *Default* | `PoolByteArray( )` |
| *Setter* | set\_data(value) |
| *Getter* | get\_data() |
Contains the audio data in bytes.
### [bool](class_bool#class-bool) loop
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_loop(value) |
| *Getter* | has\_loop() |
If `true`, the stream will automatically loop when it reaches the end.
### [float](class_float#class-float) loop\_offset
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_loop\_offset(value) |
| *Getter* | get\_loop\_offset() |
Time in seconds at which the stream starts after being looped.
godot Listener Listener
========
**Inherits:** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Overrides the location sounds are heard from.
Description
-----------
Once added to the scene tree and enabled using [make\_current](#class-listener-method-make-current), this node will override the location sounds are heard from. This can be used to listen from a location different from the [Camera](class_camera#class-camera).
Methods
-------
| | |
| --- | --- |
| void | [clear\_current](#class-listener-method-clear-current) **(** **)** |
| [Transform](class_transform#class-transform) | [get\_listener\_transform](#class-listener-method-get-listener-transform) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_current](#class-listener-method-is-current) **(** **)** const |
| void | [make\_current](#class-listener-method-make-current) **(** **)** |
Method Descriptions
-------------------
### void clear\_current ( )
Disables the listener to use the current camera's listener instead.
### [Transform](class_transform#class-transform) get\_listener\_transform ( ) const
Returns the listener's global orthonormalized [Transform](class_transform#class-transform).
### [bool](class_bool#class-bool) is\_current ( ) const
Returns `true` if the listener was made current using [make\_current](#class-listener-method-make-current), `false` otherwise.
**Note:** There may be more than one Listener marked as "current" in the scene tree, but only the one that was made current last will be used.
### void make\_current ( )
Enables the listener. This will override the current camera's listener.
godot EditorFileDialog EditorFileDialog
================
**Inherits:** [ConfirmationDialog](class_confirmationdialog#class-confirmationdialog) **<** [AcceptDialog](class_acceptdialog#class-acceptdialog) **<** [WindowDialog](class_windowdialog#class-windowdialog) **<** [Popup](class_popup#class-popup) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
A modified version of [FileDialog](class_filedialog#class-filedialog) used by the editor.
Properties
----------
| | | |
| --- | --- | --- |
| [Access](#enum-editorfiledialog-access) | [access](#class-editorfiledialog-property-access) | `0` |
| [String](class_string#class-string) | [current\_dir](#class-editorfiledialog-property-current-dir) | |
| [String](class_string#class-string) | [current\_file](#class-editorfiledialog-property-current-file) | |
| [String](class_string#class-string) | [current\_path](#class-editorfiledialog-property-current-path) | |
| [bool](class_bool#class-bool) | dialog\_hide\_on\_ok | `false` (overrides [AcceptDialog](class_acceptdialog#class-acceptdialog-property-dialog-hide-on-ok)) |
| [bool](class_bool#class-bool) | [disable\_overwrite\_warning](#class-editorfiledialog-property-disable-overwrite-warning) | `false` |
| [DisplayMode](#enum-editorfiledialog-displaymode) | [display\_mode](#class-editorfiledialog-property-display-mode) | `0` |
| [Mode](#enum-editorfiledialog-mode) | [mode](#class-editorfiledialog-property-mode) | `4` |
| [bool](class_bool#class-bool) | resizable | `true` (overrides [WindowDialog](class_windowdialog#class-windowdialog-property-resizable)) |
| [bool](class_bool#class-bool) | [show\_hidden\_files](#class-editorfiledialog-property-show-hidden-files) | `false` |
| [String](class_string#class-string) | window\_title | `"Save a File"` (overrides [WindowDialog](class_windowdialog#class-windowdialog-property-window-title)) |
Methods
-------
| | |
| --- | --- |
| void | [add\_filter](#class-editorfiledialog-method-add-filter) **(** [String](class_string#class-string) filter **)** |
| void | [clear\_filters](#class-editorfiledialog-method-clear-filters) **(** **)** |
| [VBoxContainer](class_vboxcontainer#class-vboxcontainer) | [get\_vbox](#class-editorfiledialog-method-get-vbox) **(** **)** |
| void | [invalidate](#class-editorfiledialog-method-invalidate) **(** **)** |
Signals
-------
### dir\_selected ( [String](class_string#class-string) dir )
Emitted when a directory is selected.
### file\_selected ( [String](class_string#class-string) path )
Emitted when a file is selected.
### files\_selected ( [PoolStringArray](class_poolstringarray#class-poolstringarray) paths )
Emitted when multiple files are selected.
Enumerations
------------
enum **Mode**:
* **MODE\_OPEN\_FILE** = **0** --- The `EditorFileDialog` can select only one file. Accepting the window will open the file.
* **MODE\_OPEN\_FILES** = **1** --- The `EditorFileDialog` can select multiple files. Accepting the window will open all files.
* **MODE\_OPEN\_DIR** = **2** --- The `EditorFileDialog` can select only one directory. Accepting the window will open the directory.
* **MODE\_OPEN\_ANY** = **3** --- The `EditorFileDialog` can select a file or directory. Accepting the window will open it.
* **MODE\_SAVE\_FILE** = **4** --- The `EditorFileDialog` can select only one file. Accepting the window will save the file.
enum **Access**:
* **ACCESS\_RESOURCES** = **0** --- The `EditorFileDialog` can only view `res://` directory contents.
* **ACCESS\_USERDATA** = **1** --- The `EditorFileDialog` can only view `user://` directory contents.
* **ACCESS\_FILESYSTEM** = **2** --- The `EditorFileDialog` can view the entire local file system.
enum **DisplayMode**:
* **DISPLAY\_THUMBNAILS** = **0** --- The `EditorFileDialog` displays resources as thumbnails.
* **DISPLAY\_LIST** = **1** --- The `EditorFileDialog` displays resources as a list of filenames.
Property Descriptions
---------------------
### [Access](#enum-editorfiledialog-access) access
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_access(value) |
| *Getter* | get\_access() |
The location from which the user may select a file, including `res://`, `user://`, and the local file system.
### [String](class_string#class-string) current\_dir
| | |
| --- | --- |
| *Setter* | set\_current\_dir(value) |
| *Getter* | get\_current\_dir() |
The currently occupied directory.
### [String](class_string#class-string) current\_file
| | |
| --- | --- |
| *Setter* | set\_current\_file(value) |
| *Getter* | get\_current\_file() |
The currently selected file.
### [String](class_string#class-string) current\_path
| | |
| --- | --- |
| *Setter* | set\_current\_path(value) |
| *Getter* | get\_current\_path() |
The file system path in the address bar.
### [bool](class_bool#class-bool) disable\_overwrite\_warning
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_disable\_overwrite\_warning(value) |
| *Getter* | is\_overwrite\_warning\_disabled() |
If `true`, the `EditorFileDialog` will not warn the user before overwriting files.
### [DisplayMode](#enum-editorfiledialog-displaymode) display\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_display\_mode(value) |
| *Getter* | get\_display\_mode() |
The view format in which the `EditorFileDialog` displays resources to the user.
### [Mode](#enum-editorfiledialog-mode) mode
| | |
| --- | --- |
| *Default* | `4` |
| *Setter* | set\_mode(value) |
| *Getter* | get\_mode() |
The purpose of the `EditorFileDialog`, which defines the allowed behaviors.
### [bool](class_bool#class-bool) show\_hidden\_files
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_show\_hidden\_files(value) |
| *Getter* | is\_showing\_hidden\_files() |
If `true`, hidden files and directories will be visible in the `EditorFileDialog`.
Method Descriptions
-------------------
### void add\_filter ( [String](class_string#class-string) filter )
Adds a comma-delimited file extension filter option to the `EditorFileDialog` with an optional semi-colon-delimited label.
For example, `"*.tscn, *.scn; Scenes"` results in filter text "Scenes (\*.tscn, \*.scn)".
### void clear\_filters ( )
Removes all filters except for "All Files (\*)".
### [VBoxContainer](class_vboxcontainer#class-vboxcontainer) get\_vbox ( )
Returns the `VBoxContainer` used to display the file system.
**Warning:** This is a required internal node, removing and freeing it may cause a crash. If you wish to hide it or any of its children, use their [CanvasItem.visible](class_canvasitem#class-canvasitem-property-visible) property.
### void invalidate ( )
Notify the `EditorFileDialog` that its view of the data is no longer accurate. Updates the view contents on next view update.
| programming_docs |
godot GIProbe GIProbe
=======
**Inherits:** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Real-time global illumination (GI) probe.
Description
-----------
`GIProbe`s are used to provide high-quality real-time indirect light to scenes. They precompute the effect of objects that emit light and the effect of static geometry to simulate the behavior of complex light in real-time. `GIProbe`s need to be baked before using, however, once baked, dynamic objects will receive light from them. Further, lights can be fully dynamic or baked.
Having `GIProbe`s in a scene can be expensive, the quality of the probe can be turned down in exchange for better performance in the [ProjectSettings](class_projectsettings#class-projectsettings) using [ProjectSettings.rendering/quality/voxel\_cone\_tracing/high\_quality](class_projectsettings#class-projectsettings-property-rendering-quality-voxel-cone-tracing-high-quality).
**Procedural generation:** `GIProbe` can be baked in an exported project, which makes it suitable for procedurally generated or user-built levels as long as all the geometry is generated in advance.
**Performance:** `GIProbe` is relatively demanding on the GPU and is not suited to low-end hardware such as integrated graphics (consider [BakedLightmap](class_bakedlightmap#class-bakedlightmap) instead). To provide a fallback for low-end hardware, consider adding an option to disable `GIProbe` in your project's options menus. A `GIProbe` node can be disabled by hiding it.
**Note:** Meshes should have sufficiently thick walls to avoid light leaks (avoid one-sided walls). For interior levels, enclose your level geometry in a sufficiently large box and bridge the loops to close the mesh. To further prevent light leaks, you can also strategically place temporary [MeshInstance](class_meshinstance#class-meshinstance) nodes with [GeometryInstance.use\_in\_baked\_light](class_geometryinstance#class-geometryinstance-property-use-in-baked-light) enabled. These temporary nodes can then be hidden after baking the `GIProbe` node.
**Note:** Due to a renderer limitation, emissive [ShaderMaterial](class_shadermaterial#class-shadermaterial)s cannot emit light when used in a `GIProbe`. Only emissive [SpatialMaterial](class_spatialmaterial#class-spatialmaterial)s can emit light in a `GIProbe`.
Tutorials
---------
* [GI probes](https://docs.godotengine.org/en/3.5/tutorials/3d/gi_probes.html)
* [Third Person Shooter Demo](https://godotengine.org/asset-library/asset/678)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [bias](#class-giprobe-property-bias) | `1.5` |
| [bool](class_bool#class-bool) | [compress](#class-giprobe-property-compress) | `false` |
| [GIProbeData](class_giprobedata#class-giprobedata) | [data](#class-giprobe-property-data) | |
| [int](class_int#class-int) | [dynamic\_range](#class-giprobe-property-dynamic-range) | `4` |
| [float](class_float#class-float) | [energy](#class-giprobe-property-energy) | `1.0` |
| [Vector3](class_vector3#class-vector3) | [extents](#class-giprobe-property-extents) | `Vector3( 10, 10, 10 )` |
| [bool](class_bool#class-bool) | [interior](#class-giprobe-property-interior) | `false` |
| [float](class_float#class-float) | [normal\_bias](#class-giprobe-property-normal-bias) | `0.0` |
| [float](class_float#class-float) | [propagation](#class-giprobe-property-propagation) | `0.7` |
| [Subdiv](#enum-giprobe-subdiv) | [subdiv](#class-giprobe-property-subdiv) | `1` |
Methods
-------
| | |
| --- | --- |
| void | [bake](#class-giprobe-method-bake) **(** [Node](class_node#class-node) from\_node=null, [bool](class_bool#class-bool) create\_visual\_debug=false **)** |
| void | [debug\_bake](#class-giprobe-method-debug-bake) **(** **)** |
Enumerations
------------
enum **Subdiv**:
* **SUBDIV\_64** = **0** --- Use 64 subdivisions. This is the lowest quality setting, but the fastest. Use it if you can, but especially use it on lower-end hardware.
* **SUBDIV\_128** = **1** --- Use 128 subdivisions. This is the default quality setting.
* **SUBDIV\_256** = **2** --- Use 256 subdivisions.
* **SUBDIV\_512** = **3** --- Use 512 subdivisions. This is the highest quality setting, but the slowest. On lower-end hardware, this could cause the GPU to stall.
* **SUBDIV\_MAX** = **4** --- Represents the size of the [Subdiv](#enum-giprobe-subdiv) enum.
Property Descriptions
---------------------
### [float](class_float#class-float) bias
| | |
| --- | --- |
| *Default* | `1.5` |
| *Setter* | set\_bias(value) |
| *Getter* | get\_bias() |
Offsets the lookup of the light contribution from the `GIProbe`. This can be used to avoid self-shadowing, but may introduce light leaking at higher values. This and [normal\_bias](#class-giprobe-property-normal-bias) should be played around with to minimize self-shadowing and light leaking.
**Note:** `bias` should usually be above 1.0 as that is the size of the voxels.
### [bool](class_bool#class-bool) compress
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_compress(value) |
| *Getter* | is\_compressed() |
*Deprecated.* This property has been deprecated due to known bugs and no longer has any effect when enabled.
### [GIProbeData](class_giprobedata#class-giprobedata) data
| | |
| --- | --- |
| *Setter* | set\_probe\_data(value) |
| *Getter* | get\_probe\_data() |
The [GIProbeData](class_giprobedata#class-giprobedata) resource that holds the data for this `GIProbe`.
### [int](class_int#class-int) dynamic\_range
| | |
| --- | --- |
| *Default* | `4` |
| *Setter* | set\_dynamic\_range(value) |
| *Getter* | get\_dynamic\_range() |
The maximum brightness that the `GIProbe` will recognize. Brightness will be scaled within this range.
### [float](class_float#class-float) energy
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_energy(value) |
| *Getter* | get\_energy() |
Energy multiplier. Makes the lighting contribution from the `GIProbe` brighter.
### [Vector3](class_vector3#class-vector3) extents
| | |
| --- | --- |
| *Default* | `Vector3( 10, 10, 10 )` |
| *Setter* | set\_extents(value) |
| *Getter* | get\_extents() |
The size of the area covered by the `GIProbe`. If you make the extents larger without increasing the subdivisions with [subdiv](#class-giprobe-property-subdiv), the size of each cell will increase and result in lower detailed lighting.
### [bool](class_bool#class-bool) interior
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_interior(value) |
| *Getter* | is\_interior() |
If `true`, ignores the sky contribution when calculating lighting.
### [float](class_float#class-float) normal\_bias
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_normal\_bias(value) |
| *Getter* | get\_normal\_bias() |
Offsets the lookup into the `GIProbe` based on the object's normal direction. Can be used to reduce some self-shadowing artifacts.
### [float](class_float#class-float) propagation
| | |
| --- | --- |
| *Default* | `0.7` |
| *Setter* | set\_propagation(value) |
| *Getter* | get\_propagation() |
How much light propagates through the probe internally. A higher value allows light to spread further.
### [Subdiv](#enum-giprobe-subdiv) subdiv
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_subdiv(value) |
| *Getter* | get\_subdiv() |
Number of times to subdivide the grid that the `GIProbe` operates on. A higher number results in finer detail and thus higher visual quality, while lower numbers result in better performance.
Method Descriptions
-------------------
### void bake ( [Node](class_node#class-node) from\_node=null, [bool](class_bool#class-bool) create\_visual\_debug=false )
Bakes the effect from all [GeometryInstance](class_geometryinstance#class-geometryinstance)s marked with [GeometryInstance.use\_in\_baked\_light](class_geometryinstance#class-geometryinstance-property-use-in-baked-light) and [Light](class_light#class-light)s marked with either [Light.BAKE\_INDIRECT](class_light#class-light-constant-bake-indirect) or [Light.BAKE\_ALL](class_light#class-light-constant-bake-all). If `create_visual_debug` is `true`, after baking the light, this will generate a [MultiMesh](class_multimesh#class-multimesh) that has a cube representing each solid cell with each cube colored to the cell's albedo color. This can be used to visualize the `GIProbe`'s data and debug any issues that may be occurring.
**Note:** [bake](#class-giprobe-method-bake) works from the editor and in exported projects. This makes it suitable for procedurally generated or user-built levels. Baking a `GIProbe` generally takes from 5 to 20 seconds in most scenes. Reducing [subdiv](#class-giprobe-property-subdiv) can speed up baking.
**Note:** [GeometryInstance](class_geometryinstance#class-geometryinstance)s and [Light](class_light#class-light)s must be fully ready before [bake](#class-giprobe-method-bake) is called. If you are procedurally creating those and some meshes or lights are missing from your baked `GIProbe`, use `call_deferred("bake")` instead of calling [bake](#class-giprobe-method-bake) directly.
### void debug\_bake ( )
Calls [bake](#class-giprobe-method-bake) with `create_visual_debug` enabled.
godot AudioStreamMP3 AudioStreamMP3
==============
**Inherits:** [AudioStream](class_audiostream#class-audiostream) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
MP3 audio stream driver.
Description
-----------
MP3 audio stream driver.
Properties
----------
| | | |
| --- | --- | --- |
| [PoolByteArray](class_poolbytearray#class-poolbytearray) | [data](#class-audiostreammp3-property-data) | `PoolByteArray( )` |
| [bool](class_bool#class-bool) | [loop](#class-audiostreammp3-property-loop) | `false` |
| [float](class_float#class-float) | [loop\_offset](#class-audiostreammp3-property-loop-offset) | `0.0` |
Property Descriptions
---------------------
### [PoolByteArray](class_poolbytearray#class-poolbytearray) data
| | |
| --- | --- |
| *Default* | `PoolByteArray( )` |
| *Setter* | set\_data(value) |
| *Getter* | get\_data() |
Contains the audio data in bytes.
### [bool](class_bool#class-bool) loop
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_loop(value) |
| *Getter* | has\_loop() |
If `true`, the stream will automatically loop when it reaches the end.
### [float](class_float#class-float) loop\_offset
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_loop\_offset(value) |
| *Getter* | get\_loop\_offset() |
Time in seconds at which the stream starts after being looped.
godot TriangleMesh TriangleMesh
============
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Internal mesh type.
Description
-----------
Mesh type used internally for collision calculations.
godot VisualScriptTypeCast VisualScriptTypeCast
====================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A Visual Script node that casts the given value to another type.
Description
-----------
`VisualScriptTypeCast` will perform a type conversion to an [Object](class_object#class-object)-derived type.
Properties
----------
| | | |
| --- | --- | --- |
| [String](class_string#class-string) | [base\_script](#class-visualscripttypecast-property-base-script) | `""` |
| [String](class_string#class-string) | [base\_type](#class-visualscripttypecast-property-base-type) | `"Object"` |
Property Descriptions
---------------------
### [String](class_string#class-string) base\_script
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_base\_script(value) |
| *Getter* | get\_base\_script() |
The target script class to be converted to. If none, only the [base\_type](#class-visualscripttypecast-property-base-type) will be used.
### [String](class_string#class-string) base\_type
| | |
| --- | --- |
| *Default* | `"Object"` |
| *Setter* | set\_base\_type(value) |
| *Getter* | get\_base\_type() |
The target type to be converted to.
godot GodotSharp GodotSharp
==========
**Inherits:** [Object](class_object#class-object)
Bridge between Godot and the Mono runtime (Mono-enabled builds only).
Description
-----------
This class is a bridge between Godot and the Mono runtime. It exposes several low-level operations and is only available in Mono-enabled Godot builds.
See also [CSharpScript](class_csharpscript#class-csharpscript).
Methods
-------
| | |
| --- | --- |
| void | [attach\_thread](#class-godotsharp-method-attach-thread) **(** **)** |
| void | [detach\_thread](#class-godotsharp-method-detach-thread) **(** **)** |
| [int](class_int#class-int) | [get\_domain\_id](#class-godotsharp-method-get-domain-id) **(** **)** |
| [int](class_int#class-int) | [get\_scripts\_domain\_id](#class-godotsharp-method-get-scripts-domain-id) **(** **)** |
| [bool](class_bool#class-bool) | [is\_domain\_finalizing\_for\_unload](#class-godotsharp-method-is-domain-finalizing-for-unload) **(** [int](class_int#class-int) domain\_id **)** |
| [bool](class_bool#class-bool) | [is\_runtime\_initialized](#class-godotsharp-method-is-runtime-initialized) **(** **)** |
| [bool](class_bool#class-bool) | [is\_runtime\_shutting\_down](#class-godotsharp-method-is-runtime-shutting-down) **(** **)** |
| [bool](class_bool#class-bool) | [is\_scripts\_domain\_loaded](#class-godotsharp-method-is-scripts-domain-loaded) **(** **)** |
Method Descriptions
-------------------
### void attach\_thread ( )
Attaches the current thread to the Mono runtime.
### void detach\_thread ( )
Detaches the current thread from the Mono runtime.
### [int](class_int#class-int) get\_domain\_id ( )
Returns the current MonoDomain ID.
**Note:** The Mono runtime must be initialized for this method to work (use [is\_runtime\_initialized](#class-godotsharp-method-is-runtime-initialized) to check). If the Mono runtime isn't initialized at the time this method is called, the engine will crash.
### [int](class_int#class-int) get\_scripts\_domain\_id ( )
Returns the scripts MonoDomain's ID. This will be the same MonoDomain ID as [get\_domain\_id](#class-godotsharp-method-get-domain-id), unless the scripts domain isn't loaded.
**Note:** The Mono runtime must be initialized for this method to work (use [is\_runtime\_initialized](#class-godotsharp-method-is-runtime-initialized) to check). If the Mono runtime isn't initialized at the time this method is called, the engine will crash.
### [bool](class_bool#class-bool) is\_domain\_finalizing\_for\_unload ( [int](class_int#class-int) domain\_id )
Returns `true` if the domain is being finalized, `false` otherwise.
### [bool](class_bool#class-bool) is\_runtime\_initialized ( )
Returns `true` if the Mono runtime is initialized, `false` otherwise.
### [bool](class_bool#class-bool) is\_runtime\_shutting\_down ( )
Returns `true` if the Mono runtime is shutting down, `false` otherwise.
### [bool](class_bool#class-bool) is\_scripts\_domain\_loaded ( )
Returns `true` if the scripts domain is loaded, `false` otherwise.
godot Rect2 Rect2
=====
2D axis-aligned bounding box.
Description
-----------
`Rect2` consists of a position, a size, and several utility functions. It is typically used for fast overlap tests.
It uses floating-point coordinates.
The 3D counterpart to `Rect2` is [AABB](class_aabb#class-aabb).
Tutorials
---------
* [Math tutorial index](https://docs.godotengine.org/en/3.5/tutorials/math/index.html)
* [Vector math](https://docs.godotengine.org/en/3.5/tutorials/math/vector_math.html)
* [Advanced vector math](https://docs.godotengine.org/en/3.5/tutorials/math/vectors_advanced.html)
Properties
----------
| | | |
| --- | --- | --- |
| [Vector2](class_vector2#class-vector2) | [end](#class-rect2-property-end) | `Vector2( 0, 0 )` |
| [Vector2](class_vector2#class-vector2) | [position](#class-rect2-property-position) | `Vector2( 0, 0 )` |
| [Vector2](class_vector2#class-vector2) | [size](#class-rect2-property-size) | `Vector2( 0, 0 )` |
Methods
-------
| | |
| --- | --- |
| [Rect2](#class-rect2) | [Rect2](#class-rect2-method-rect2) **(** [Vector2](class_vector2#class-vector2) position, [Vector2](class_vector2#class-vector2) size **)** |
| [Rect2](#class-rect2) | [Rect2](#class-rect2-method-rect2) **(** [float](class_float#class-float) x, [float](class_float#class-float) y, [float](class_float#class-float) width, [float](class_float#class-float) height **)** |
| [Rect2](#class-rect2) | [abs](#class-rect2-method-abs) **(** **)** |
| [Rect2](#class-rect2) | [clip](#class-rect2-method-clip) **(** [Rect2](#class-rect2) b **)** |
| [bool](class_bool#class-bool) | [encloses](#class-rect2-method-encloses) **(** [Rect2](#class-rect2) b **)** |
| [Rect2](#class-rect2) | [expand](#class-rect2-method-expand) **(** [Vector2](class_vector2#class-vector2) to **)** |
| [float](class_float#class-float) | [get\_area](#class-rect2-method-get-area) **(** **)** |
| [Vector2](class_vector2#class-vector2) | [get\_center](#class-rect2-method-get-center) **(** **)** |
| [Rect2](#class-rect2) | [grow](#class-rect2-method-grow) **(** [float](class_float#class-float) by **)** |
| [Rect2](#class-rect2) | [grow\_individual](#class-rect2-method-grow-individual) **(** [float](class_float#class-float) left, [float](class_float#class-float) top, [float](class_float#class-float) right, [float](class_float#class-float) bottom **)** |
| [Rect2](#class-rect2) | [grow\_margin](#class-rect2-method-grow-margin) **(** [int](class_int#class-int) margin, [float](class_float#class-float) by **)** |
| [bool](class_bool#class-bool) | [has\_no\_area](#class-rect2-method-has-no-area) **(** **)** |
| [bool](class_bool#class-bool) | [has\_point](#class-rect2-method-has-point) **(** [Vector2](class_vector2#class-vector2) point **)** |
| [bool](class_bool#class-bool) | [intersects](#class-rect2-method-intersects) **(** [Rect2](#class-rect2) b, [bool](class_bool#class-bool) include\_borders=false **)** |
| [bool](class_bool#class-bool) | [is\_equal\_approx](#class-rect2-method-is-equal-approx) **(** [Rect2](#class-rect2) rect **)** |
| [Rect2](#class-rect2) | [merge](#class-rect2-method-merge) **(** [Rect2](#class-rect2) b **)** |
Property Descriptions
---------------------
### [Vector2](class_vector2#class-vector2) end
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
Ending corner. This is calculated as `position + size`. Setting this value will change the size.
### [Vector2](class_vector2#class-vector2) position
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
Beginning corner. Typically has values lower than [end](#class-rect2-property-end).
### [Vector2](class_vector2#class-vector2) size
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
Size from [position](#class-rect2-property-position) to [end](#class-rect2-property-end). Typically, all components are positive.
If the size is negative, you can use [abs](#class-rect2-method-abs) to fix it.
Method Descriptions
-------------------
### [Rect2](#class-rect2) Rect2 ( [Vector2](class_vector2#class-vector2) position, [Vector2](class_vector2#class-vector2) size )
Constructs a `Rect2` by position and size.
* [Rect2](#class-rect2) **Rect2** **(** [float](class_float#class-float) x, [float](class_float#class-float) y, [float](class_float#class-float) width, [float](class_float#class-float) height **)**
Constructs a `Rect2` by x, y, width, and height.
### [Rect2](#class-rect2) abs ( )
Returns a `Rect2` with equivalent position and area, modified so that the top-left corner is the origin and `width` and `height` are positive.
### [Rect2](#class-rect2) clip ( [Rect2](#class-rect2) b )
Returns the intersection of this `Rect2` and b.
### [bool](class_bool#class-bool) encloses ( [Rect2](#class-rect2) b )
Returns `true` if this `Rect2` completely encloses another one.
### [Rect2](#class-rect2) expand ( [Vector2](class_vector2#class-vector2) to )
Returns a copy of this `Rect2` expanded to include a given point.
**Example:**
```
# position (-3, 2), size (1, 1)
var rect = Rect2(Vector2(-3, 2), Vector2(1, 1))
# position (-3, -1), size (3, 4), so we fit both rect and Vector2(0, -1)
var rect2 = rect.expand(Vector2(0, -1))
```
### [float](class_float#class-float) get\_area ( )
Returns the area of the `Rect2`. See also [has\_no\_area](#class-rect2-method-has-no-area).
### [Vector2](class_vector2#class-vector2) get\_center ( )
Returns the center of the `Rect2`, which is equal to [position](#class-rect2-property-position) + ([size](#class-rect2-property-size) / 2).
### [Rect2](#class-rect2) grow ( [float](class_float#class-float) by )
Returns a copy of the `Rect2` grown a given amount of units towards all the sides.
### [Rect2](#class-rect2) grow\_individual ( [float](class_float#class-float) left, [float](class_float#class-float) top, [float](class_float#class-float) right, [float](class_float#class-float) bottom )
Returns a copy of the `Rect2` grown a given amount of units towards each direction individually.
### [Rect2](#class-rect2) grow\_margin ( [int](class_int#class-int) margin, [float](class_float#class-float) by )
Returns a copy of the `Rect2` grown a given amount of units towards the [Margin](class_%40globalscope#enum-globalscope-margin) direction.
### [bool](class_bool#class-bool) has\_no\_area ( )
Returns `true` if the `Rect2` is flat or empty, `false` otherwise. See also [get\_area](#class-rect2-method-get-area).
**Note:** If the `Rect2` has a negative size and is not flat or empty, [has\_no\_area](#class-rect2-method-has-no-area) will return `true`.
### [bool](class_bool#class-bool) has\_point ( [Vector2](class_vector2#class-vector2) point )
Returns `true` if the `Rect2` contains a point. By convention, the right and bottom edges of the `Rect2` are considered exclusive, so points on these edges are **not** included.
**Note:** This method is not reliable for `Rect2` with a *negative size*. Use [abs](#class-rect2-method-abs) to get a positive sized equivalent rectangle to check for contained points.
### [bool](class_bool#class-bool) intersects ( [Rect2](#class-rect2) b, [bool](class_bool#class-bool) include\_borders=false )
Returns `true` if the `Rect2` overlaps with `b` (i.e. they have at least one point in common).
If `include_borders` is `true`, they will also be considered overlapping if their borders touch, even without intersection.
### [bool](class_bool#class-bool) is\_equal\_approx ( [Rect2](#class-rect2) rect )
Returns `true` if this `Rect2` and `rect` are approximately equal, by calling `is_equal_approx` on each component.
### [Rect2](#class-rect2) merge ( [Rect2](#class-rect2) b )
Returns a larger `Rect2` that contains this `Rect2` and `b`.
| programming_docs |
godot PhysicsBody PhysicsBody
===========
**Inherits:** [CollisionObject](class_collisionobject#class-collisionobject) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
**Inherited By:** [KinematicBody](class_kinematicbody#class-kinematicbody), [PhysicalBone](class_physicalbone#class-physicalbone), [RigidBody](class_rigidbody#class-rigidbody), [StaticBody](class_staticbody#class-staticbody)
Base class for all objects affected by physics in 3D space.
Description
-----------
PhysicsBody is an abstract base class for implementing a physics body. All \*Body types inherit from it.
Tutorials
---------
* [Physics introduction](https://docs.godotengine.org/en/3.5/tutorials/physics/physics_introduction.html)
Methods
-------
| | |
| --- | --- |
| void | [add\_collision\_exception\_with](#class-physicsbody-method-add-collision-exception-with) **(** [Node](class_node#class-node) body **)** |
| [Array](class_array#class-array) | [get\_collision\_exceptions](#class-physicsbody-method-get-collision-exceptions) **(** **)** |
| void | [remove\_collision\_exception\_with](#class-physicsbody-method-remove-collision-exception-with) **(** [Node](class_node#class-node) body **)** |
Method Descriptions
-------------------
### void add\_collision\_exception\_with ( [Node](class_node#class-node) body )
Adds a body to the list of bodies that this body can't collide with.
### [Array](class_array#class-array) get\_collision\_exceptions ( )
Returns an array of nodes that were added as collision exceptions for this body.
### void remove\_collision\_exception\_with ( [Node](class_node#class-node) body )
Removes a body from the list of bodies that this body can't collide with.
godot VisualShaderNodeScalarSwitch VisualShaderNodeScalarSwitch
============================
**Inherits:** [VisualShaderNodeSwitch](class_visualshadernodeswitch#class-visualshadernodeswitch) **<** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A boolean/scalar function for use within the visual shader graph.
Description
-----------
Returns an associated scalar if the provided boolean value is `true` or `false`.
godot VisualScriptSwitch VisualScriptSwitch
==================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Branches program flow based on a given input's value.
Description
-----------
Branches the flow based on an input's value. Use **Case Count** in the Inspector to set the number of branches and each comparison's optional type.
**Input Ports:**
* Sequence: `'input' is`
* Data (variant): `=`
* Data (variant): `=` (optional)
* Data (variant): `input`
**Output Ports:**
* Sequence
* Sequence (optional)
* Sequence: `done`
godot NavigationAgent2D NavigationAgent2D
=================
**Inherits:** [Node](class_node#class-node) **<** [Object](class_object#class-object)
2D agent used in navigation for collision avoidance.
Description
-----------
2D agent that is used in navigation to reach a location while avoiding static and dynamic obstacles. The dynamic obstacles are avoided using RVO (Reciprocal Velocity Obstacles) collision avoidance. The agent needs navigation data to work correctly. By default this node will register to the default [World2D](class_world2d#class-world2d) navigation map. If this node is a child of a [Navigation2D](class_navigation2d#class-navigation2d) node it will register to the navigation map of the navigation node or the function [set\_navigation](#class-navigationagent2d-method-set-navigation) can be used to set the navigation node directly. `NavigationAgent2D` is physics safe.
**Note:** After [set\_target\_location](#class-navigationagent2d-method-set-target-location) is used it is required to use the [get\_next\_location](#class-navigationagent2d-method-get-next-location) function once every physics frame to update the internal path logic of the NavigationAgent. The returned vector position from this function should be used as the next movement position for the agent's parent Node.
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [avoidance\_enabled](#class-navigationagent2d-property-avoidance-enabled) | `false` |
| [int](class_int#class-int) | [max\_neighbors](#class-navigationagent2d-property-max-neighbors) | `10` |
| [float](class_float#class-float) | [max\_speed](#class-navigationagent2d-property-max-speed) | `200.0` |
| [int](class_int#class-int) | [navigation\_layers](#class-navigationagent2d-property-navigation-layers) | `1` |
| [float](class_float#class-float) | [neighbor\_dist](#class-navigationagent2d-property-neighbor-dist) | `500.0` |
| [float](class_float#class-float) | [path\_desired\_distance](#class-navigationagent2d-property-path-desired-distance) | `1.0` |
| [float](class_float#class-float) | [path\_max\_distance](#class-navigationagent2d-property-path-max-distance) | `3.0` |
| [float](class_float#class-float) | [radius](#class-navigationagent2d-property-radius) | `10.0` |
| [float](class_float#class-float) | [target\_desired\_distance](#class-navigationagent2d-property-target-desired-distance) | `1.0` |
| [float](class_float#class-float) | [time\_horizon](#class-navigationagent2d-property-time-horizon) | `20.0` |
Methods
-------
| | |
| --- | --- |
| [float](class_float#class-float) | [distance\_to\_target](#class-navigationagent2d-method-distance-to-target) **(** **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_final\_location](#class-navigationagent2d-method-get-final-location) **(** **)** |
| [PoolVector2Array](class_poolvector2array#class-poolvector2array) | [get\_nav\_path](#class-navigationagent2d-method-get-nav-path) **(** **)** const |
| [int](class_int#class-int) | [get\_nav\_path\_index](#class-navigationagent2d-method-get-nav-path-index) **(** **)** const |
| [Node](class_node#class-node) | [get\_navigation](#class-navigationagent2d-method-get-navigation) **(** **)** const |
| [RID](class_rid#class-rid) | [get\_navigation\_map](#class-navigationagent2d-method-get-navigation-map) **(** **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_next\_location](#class-navigationagent2d-method-get-next-location) **(** **)** |
| [RID](class_rid#class-rid) | [get\_rid](#class-navigationagent2d-method-get-rid) **(** **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_target\_location](#class-navigationagent2d-method-get-target-location) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_navigation\_finished](#class-navigationagent2d-method-is-navigation-finished) **(** **)** |
| [bool](class_bool#class-bool) | [is\_target\_reachable](#class-navigationagent2d-method-is-target-reachable) **(** **)** |
| [bool](class_bool#class-bool) | [is\_target\_reached](#class-navigationagent2d-method-is-target-reached) **(** **)** const |
| void | [set\_navigation](#class-navigationagent2d-method-set-navigation) **(** [Node](class_node#class-node) navigation **)** |
| void | [set\_navigation\_map](#class-navigationagent2d-method-set-navigation-map) **(** [RID](class_rid#class-rid) navigation\_map **)** |
| void | [set\_target\_location](#class-navigationagent2d-method-set-target-location) **(** [Vector2](class_vector2#class-vector2) location **)** |
| void | [set\_velocity](#class-navigationagent2d-method-set-velocity) **(** [Vector2](class_vector2#class-vector2) velocity **)** |
Signals
-------
### navigation\_finished ( )
Notifies when the final location is reached.
### path\_changed ( )
Notifies when the navigation path changes. This can be triggered by the navigation system or by the user changing the path.
### target\_reached ( )
Notifies when the player-defined target, set with [set\_target\_location](#class-navigationagent2d-method-set-target-location), is reached.
### velocity\_computed ( [Vector2](class_vector2#class-vector2) safe\_velocity )
Notifies when the collision avoidance velocity is calculated after a call to [set\_velocity](#class-navigationagent2d-method-set-velocity). Only emitted when [avoidance\_enabled](#class-navigationagent2d-property-avoidance-enabled) is true.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) avoidance\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_avoidance\_enabled(value) |
| *Getter* | get\_avoidance\_enabled() |
If `true` the agent is registered for an RVO avoidance callback on the [Navigation2DServer](class_navigation2dserver#class-navigation2dserver). When [set\_velocity](#class-navigationagent2d-method-set-velocity) is used and the processing is completed a `safe_velocity` Vector2 is received with a signal connection to [velocity\_computed](#class-navigationagent2d-signal-velocity-computed). Avoidance processing with many registered agents has a significant performance cost and should only be enabled on agents that currently require it.
### [int](class_int#class-int) max\_neighbors
| | |
| --- | --- |
| *Default* | `10` |
| *Setter* | set\_max\_neighbors(value) |
| *Getter* | get\_max\_neighbors() |
The maximum number of neighbors for the agent to consider.
### [float](class_float#class-float) max\_speed
| | |
| --- | --- |
| *Default* | `200.0` |
| *Setter* | set\_max\_speed(value) |
| *Getter* | get\_max\_speed() |
The maximum speed that an agent can move.
### [int](class_int#class-int) navigation\_layers
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_navigation\_layers(value) |
| *Getter* | get\_navigation\_layers() |
A bitfield determining all navigation map layers the `NavigationAgent2D` belongs to. On path requests the agent will ignore navmeshes without at least one matching layer.
### [float](class_float#class-float) neighbor\_dist
| | |
| --- | --- |
| *Default* | `500.0` |
| *Setter* | set\_neighbor\_dist(value) |
| *Getter* | get\_neighbor\_dist() |
The distance to search for other agents.
### [float](class_float#class-float) path\_desired\_distance
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_path\_desired\_distance(value) |
| *Getter* | get\_path\_desired\_distance() |
The distance threshold before a path point is considered to be reached. This will allow an agent to not have to hit a path point on the path exactly, but in the area. If this value is set to high the NavigationAgent will skip points on the path which can lead to leaving the navigation mesh. If this value is set to low the NavigationAgent will be stuck in a repath loop cause it will constantly overshoot or undershoot the distance to the next point on each physics frame update.
### [float](class_float#class-float) path\_max\_distance
| | |
| --- | --- |
| *Default* | `3.0` |
| *Setter* | set\_path\_max\_distance(value) |
| *Getter* | get\_path\_max\_distance() |
The maximum distance the agent is allowed away from the ideal path to the final location. This can happen due to trying to avoid collisions. When the maximum distance is exceeded, it recalculates the ideal path.
### [float](class_float#class-float) radius
| | |
| --- | --- |
| *Default* | `10.0` |
| *Setter* | set\_radius(value) |
| *Getter* | get\_radius() |
The radius of the avoidance agent. This is the "body" of the avoidance agent and not the avoidance maneuver starting radius (which is controlled by [neighbor\_dist](#class-navigationagent2d-property-neighbor-dist)).
Does not affect normal pathfinding.
### [float](class_float#class-float) target\_desired\_distance
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_target\_desired\_distance(value) |
| *Getter* | get\_target\_desired\_distance() |
The distance threshold before the final target point is considered to be reached. This will allow an agent to not have to hit the point of the final target exactly, but only the area. If this value is set to low the NavigationAgent will be stuck in a repath loop cause it will constantly overshoot or undershoot the distance to the final target point on each physics frame update.
### [float](class_float#class-float) time\_horizon
| | |
| --- | --- |
| *Default* | `20.0` |
| *Setter* | set\_time\_horizon(value) |
| *Getter* | get\_time\_horizon() |
The minimal amount of time for which this agent's velocities, that are computed with the collision avoidance algorithm, are safe with respect to other agents. The larger the number, the sooner the agent will respond to other agents, but the less freedom in choosing its velocities. Must be positive.
Method Descriptions
-------------------
### [float](class_float#class-float) distance\_to\_target ( ) const
Returns the distance to the target location, using the agent's global position. The user must set the target location with [set\_target\_location](#class-navigationagent2d-method-set-target-location) in order for this to be accurate.
### [Vector2](class_vector2#class-vector2) get\_final\_location ( )
Returns the reachable final location in global coordinates. This can change if the navigation path is altered in any way. Because of this, it would be best to check this each frame.
### [PoolVector2Array](class_poolvector2array#class-poolvector2array) get\_nav\_path ( ) const
Returns this agent's current path from start to finish in global coordinates. The path only updates when the target location is changed or the agent requires a repath. The path array is not intended to be used in direct path movement as the agent has its own internal path logic that would get corrupted by changing the path array manually. Use the intended [get\_next\_location](#class-navigationagent2d-method-get-next-location) once every physics frame to receive the next path point for the agents movement as this function also updates the internal path logic.
### [int](class_int#class-int) get\_nav\_path\_index ( ) const
Returns which index the agent is currently on in the navigation path's [PoolVector2Array](class_poolvector2array#class-poolvector2array).
### [Node](class_node#class-node) get\_navigation ( ) const
Returns the [Navigation2D](class_navigation2d#class-navigation2d) node that the agent is using for its navigation system.
### [RID](class_rid#class-rid) get\_navigation\_map ( ) const
Returns the [RID](class_rid#class-rid) of the navigation map for this NavigationAgent node. This function returns always the map set on the NavigationAgent node and not the map of the abstract agent on the NavigationServer. If the agent map is changed directly with the NavigationServer API the NavigationAgent node will not be aware of the map change. Use [set\_navigation\_map](#class-navigationagent2d-method-set-navigation-map) to change the navigation map for the NavigationAgent and also update the agent on the NavigationServer.
### [Vector2](class_vector2#class-vector2) get\_next\_location ( )
Returns the next location in global coordinates that can be moved to, making sure that there are no static objects in the way. If the agent does not have a navigation path, it will return the position of the agent's parent. The use of this function once every physics frame is required to update the internal path logic of the NavigationAgent.
### [RID](class_rid#class-rid) get\_rid ( ) const
Returns the [RID](class_rid#class-rid) of this agent on the [Navigation2DServer](class_navigation2dserver#class-navigation2dserver).
### [Vector2](class_vector2#class-vector2) get\_target\_location ( ) const
Returns the user-defined target location (set with [set\_target\_location](#class-navigationagent2d-method-set-target-location)).
### [bool](class_bool#class-bool) is\_navigation\_finished ( )
Returns `true` if the navigation path's final location has been reached.
### [bool](class_bool#class-bool) is\_target\_reachable ( )
Returns `true` if the target location is reachable. The target location is set using [set\_target\_location](#class-navigationagent2d-method-set-target-location).
### [bool](class_bool#class-bool) is\_target\_reached ( ) const
Returns `true` if the target location is reached. The target location is set using [set\_target\_location](#class-navigationagent2d-method-set-target-location). It may not always be possible to reach the target location. It should always be possible to reach the final location though. See [get\_final\_location](#class-navigationagent2d-method-get-final-location).
### void set\_navigation ( [Node](class_node#class-node) navigation )
Sets the [Navigation2D](class_navigation2d#class-navigation2d) node used by the agent. Useful when you don't want to make the agent a child of a [Navigation2D](class_navigation2d#class-navigation2d) node.
### void set\_navigation\_map ( [RID](class_rid#class-rid) navigation\_map )
Sets the [RID](class_rid#class-rid) of the navigation map this NavigationAgent node should use and also updates the `agent` on the NavigationServer.
### void set\_target\_location ( [Vector2](class_vector2#class-vector2) location )
Sets the user desired final location. This will clear the current navigation path.
### void set\_velocity ( [Vector2](class_vector2#class-vector2) velocity )
Sends the passed in velocity to the collision avoidance algorithm. It will adjust the velocity to avoid collisions. Once the adjustment to the velocity is complete, it will emit the [velocity\_computed](#class-navigationagent2d-signal-velocity-computed) signal.
godot EditorFileSystemDirectory EditorFileSystemDirectory
=========================
**Inherits:** [Object](class_object#class-object)
A directory for the resource filesystem.
Description
-----------
A more generalized, low-level variation of the directory concept.
Methods
-------
| | |
| --- | --- |
| [int](class_int#class-int) | [find\_dir\_index](#class-editorfilesystemdirectory-method-find-dir-index) **(** [String](class_string#class-string) name **)** const |
| [int](class_int#class-int) | [find\_file\_index](#class-editorfilesystemdirectory-method-find-file-index) **(** [String](class_string#class-string) name **)** const |
| [String](class_string#class-string) | [get\_file](#class-editorfilesystemdirectory-method-get-file) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_file\_count](#class-editorfilesystemdirectory-method-get-file-count) **(** **)** const |
| [bool](class_bool#class-bool) | [get\_file\_import\_is\_valid](#class-editorfilesystemdirectory-method-get-file-import-is-valid) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_file\_path](#class-editorfilesystemdirectory-method-get-file-path) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_file\_script\_class\_extends](#class-editorfilesystemdirectory-method-get-file-script-class-extends) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_file\_script\_class\_name](#class-editorfilesystemdirectory-method-get-file-script-class-name) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_file\_type](#class-editorfilesystemdirectory-method-get-file-type) **(** [int](class_int#class-int) idx **)** const |
| [String](class_string#class-string) | [get\_name](#class-editorfilesystemdirectory-method-get-name) **(** **)** |
| [EditorFileSystemDirectory](#class-editorfilesystemdirectory) | [get\_parent](#class-editorfilesystemdirectory-method-get-parent) **(** **)** |
| [String](class_string#class-string) | [get\_path](#class-editorfilesystemdirectory-method-get-path) **(** **)** const |
| [EditorFileSystemDirectory](#class-editorfilesystemdirectory) | [get\_subdir](#class-editorfilesystemdirectory-method-get-subdir) **(** [int](class_int#class-int) idx **)** |
| [int](class_int#class-int) | [get\_subdir\_count](#class-editorfilesystemdirectory-method-get-subdir-count) **(** **)** const |
Method Descriptions
-------------------
### [int](class_int#class-int) find\_dir\_index ( [String](class_string#class-string) name ) const
Returns the index of the directory with name `name` or `-1` if not found.
### [int](class_int#class-int) find\_file\_index ( [String](class_string#class-string) name ) const
Returns the index of the file with name `name` or `-1` if not found.
### [String](class_string#class-string) get\_file ( [int](class_int#class-int) idx ) const
Returns the name of the file at index `idx`.
### [int](class_int#class-int) get\_file\_count ( ) const
Returns the number of files in this directory.
### [bool](class_bool#class-bool) get\_file\_import\_is\_valid ( [int](class_int#class-int) idx ) const
Returns `true` if the file at index `idx` imported properly.
### [String](class_string#class-string) get\_file\_path ( [int](class_int#class-int) idx ) const
Returns the path to the file at index `idx`.
### [String](class_string#class-string) get\_file\_script\_class\_extends ( [int](class_int#class-int) idx ) const
Returns the base class of the script class defined in the file at index `idx`. If the file doesn't define a script class using the `class_name` syntax, this will return an empty string.
### [String](class_string#class-string) get\_file\_script\_class\_name ( [int](class_int#class-int) idx ) const
Returns the name of the script class defined in the file at index `idx`. If the file doesn't define a script class using the `class_name` syntax, this will return an empty string.
### [String](class_string#class-string) get\_file\_type ( [int](class_int#class-int) idx ) const
Returns the resource type of the file at index `idx`. This returns a string such as `"Resource"` or `"GDScript"`, *not* a file extension such as `".gd"`.
### [String](class_string#class-string) get\_name ( )
Returns the name of this directory.
### [EditorFileSystemDirectory](#class-editorfilesystemdirectory) get\_parent ( )
Returns the parent directory for this directory or `null` if called on a directory at `res://` or `user://`.
### [String](class_string#class-string) get\_path ( ) const
Returns the path to this directory.
### [EditorFileSystemDirectory](#class-editorfilesystemdirectory) get\_subdir ( [int](class_int#class-int) idx )
Returns the subdirectory at index `idx`.
### [int](class_int#class-int) get\_subdir\_count ( ) const
Returns the number of subdirectories in this directory.
| programming_docs |
godot AudioEffectRecord AudioEffectRecord
=================
**Inherits:** [AudioEffect](class_audioeffect#class-audioeffect) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Audio effect used for recording the sound from an audio bus.
Description
-----------
Allows the user to record the sound from an audio bus. This can include all audio output by Godot when used on the "Master" audio bus.
Can be used (with an [AudioStreamMicrophone](class_audiostreammicrophone#class-audiostreammicrophone)) to record from a microphone.
It sets and gets the format in which the audio file will be recorded (8-bit, 16-bit, or compressed). It checks whether or not the recording is active, and if it is, records the sound. It then returns the recorded sample.
Tutorials
---------
* [Recording with microphone](https://docs.godotengine.org/en/3.5/tutorials/audio/recording_with_microphone.html)
* [Audio Mic Record Demo](https://godotengine.org/asset-library/asset/527)
Properties
----------
| | | |
| --- | --- | --- |
| [Format](class_audiostreamsample#enum-audiostreamsample-format) | [format](#class-audioeffectrecord-property-format) | `1` |
Methods
-------
| | |
| --- | --- |
| [AudioStreamSample](class_audiostreamsample#class-audiostreamsample) | [get\_recording](#class-audioeffectrecord-method-get-recording) **(** **)** const |
| [bool](class_bool#class-bool) | [is\_recording\_active](#class-audioeffectrecord-method-is-recording-active) **(** **)** const |
| void | [set\_recording\_active](#class-audioeffectrecord-method-set-recording-active) **(** [bool](class_bool#class-bool) record **)** |
Property Descriptions
---------------------
### [Format](class_audiostreamsample#enum-audiostreamsample-format) format
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_format(value) |
| *Getter* | get\_format() |
Specifies the format in which the sample will be recorded. See [Format](class_audiostreamsample#enum-audiostreamsample-format) for available formats.
Method Descriptions
-------------------
### [AudioStreamSample](class_audiostreamsample#class-audiostreamsample) get\_recording ( ) const
Returns the recorded sample.
### [bool](class_bool#class-bool) is\_recording\_active ( ) const
Returns whether the recording is active or not.
### void set\_recording\_active ( [bool](class_bool#class-bool) record )
If `true`, the sound will be recorded. Note that restarting the recording will remove the previously recorded sample.
godot VisualScriptCondition VisualScriptCondition
=====================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A Visual Script node which branches the flow.
Description
-----------
A Visual Script node that checks a [bool](class_bool#class-bool) input port. If `true`, it will exit via the "true" sequence port. If `false`, it will exit via the "false" sequence port. After exiting either, it exits via the "done" port. Sequence ports may be left disconnected.
**Input Ports:**
* Sequence: `if (cond) is`
* Data (boolean): `cond`
**Output Ports:**
* Sequence: `true`
* Sequence: `false`
* Sequence: `done`
godot ARVRInterface ARVRInterface
=============
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [ARVRInterfaceGDNative](class_arvrinterfacegdnative#class-arvrinterfacegdnative), [MobileVRInterface](class_mobilevrinterface#class-mobilevrinterface), [WebXRInterface](class_webxrinterface#class-webxrinterface)
Base class for an AR/VR interface implementation.
Description
-----------
This class needs to be implemented to make an AR or VR platform available to Godot and these should be implemented as C++ modules or GDNative modules (note that for GDNative the subclass ARVRScriptInterface should be used). Part of the interface is exposed to GDScript so you can detect, enable and configure an AR or VR platform.
Interfaces should be written in such a way that simply enabling them will give us a working setup. You can query the available interfaces through [ARVRServer](class_arvrserver#class-arvrserver).
Tutorials
---------
* [XR (AR/VR)](https://docs.godotengine.org/en/3.5/tutorials/vr/index.html)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [ar\_is\_anchor\_detection\_enabled](#class-arvrinterface-property-ar-is-anchor-detection-enabled) | `false` |
| [bool](class_bool#class-bool) | [interface\_is\_initialized](#class-arvrinterface-property-interface-is-initialized) | `false` |
| [bool](class_bool#class-bool) | [interface\_is\_primary](#class-arvrinterface-property-interface-is-primary) | `false` |
Methods
-------
| | |
| --- | --- |
| [int](class_int#class-int) | [get\_camera\_feed\_id](#class-arvrinterface-method-get-camera-feed-id) **(** **)** |
| [int](class_int#class-int) | [get\_capabilities](#class-arvrinterface-method-get-capabilities) **(** **)** const |
| [String](class_string#class-string) | [get\_name](#class-arvrinterface-method-get-name) **(** **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_render\_targetsize](#class-arvrinterface-method-get-render-targetsize) **(** **)** |
| [Tracking\_status](#enum-arvrinterface-tracking-status) | [get\_tracking\_status](#class-arvrinterface-method-get-tracking-status) **(** **)** const |
| [bool](class_bool#class-bool) | [initialize](#class-arvrinterface-method-initialize) **(** **)** |
| [bool](class_bool#class-bool) | [is\_stereo](#class-arvrinterface-method-is-stereo) **(** **)** |
| void | [uninitialize](#class-arvrinterface-method-uninitialize) **(** **)** |
Enumerations
------------
enum **Capabilities**:
* **ARVR\_NONE** = **0** --- No ARVR capabilities.
* **ARVR\_MONO** = **1** --- This interface can work with normal rendering output (non-HMD based AR).
* **ARVR\_STEREO** = **2** --- This interface supports stereoscopic rendering.
* **ARVR\_AR** = **4** --- This interface supports AR (video background and real world tracking).
* **ARVR\_EXTERNAL** = **8** --- This interface outputs to an external device. If the main viewport is used, the on screen output is an unmodified buffer of either the left or right eye (stretched if the viewport size is not changed to the same aspect ratio of [get\_render\_targetsize](#class-arvrinterface-method-get-render-targetsize)). Using a separate viewport node frees up the main viewport for other purposes.
enum **Eyes**:
* **EYE\_MONO** = **0** --- Mono output, this is mostly used internally when retrieving positioning information for our camera node or when stereo scopic rendering is not supported.
* **EYE\_LEFT** = **1** --- Left eye output, this is mostly used internally when rendering the image for the left eye and obtaining positioning and projection information.
* **EYE\_RIGHT** = **2** --- Right eye output, this is mostly used internally when rendering the image for the right eye and obtaining positioning and projection information.
enum **Tracking\_status**:
* **ARVR\_NORMAL\_TRACKING** = **0** --- Tracking is behaving as expected.
* **ARVR\_EXCESSIVE\_MOTION** = **1** --- Tracking is hindered by excessive motion (the player is moving faster than tracking can keep up).
* **ARVR\_INSUFFICIENT\_FEATURES** = **2** --- Tracking is hindered by insufficient features, it's too dark (for camera-based tracking), player is blocked, etc.
* **ARVR\_UNKNOWN\_TRACKING** = **3** --- We don't know the status of the tracking or this interface does not provide feedback.
* **ARVR\_NOT\_TRACKING** = **4** --- Tracking is not functional (camera not plugged in or obscured, lighthouses turned off, etc.).
Property Descriptions
---------------------
### [bool](class_bool#class-bool) ar\_is\_anchor\_detection\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_anchor\_detection\_is\_enabled(value) |
| *Getter* | get\_anchor\_detection\_is\_enabled() |
On an AR interface, `true` if anchor detection is enabled.
### [bool](class_bool#class-bool) interface\_is\_initialized
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_is\_initialized(value) |
| *Getter* | is\_initialized() |
`true` if this interface been initialized.
### [bool](class_bool#class-bool) interface\_is\_primary
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_is\_primary(value) |
| *Getter* | is\_primary() |
`true` if this is the primary interface.
Method Descriptions
-------------------
### [int](class_int#class-int) get\_camera\_feed\_id ( )
If this is an AR interface that requires displaying a camera feed as the background, this method returns the feed ID in the [CameraServer](class_cameraserver#class-cameraserver) for this interface.
### [int](class_int#class-int) get\_capabilities ( ) const
Returns a combination of [Capabilities](#enum-arvrinterface-capabilities) flags providing information about the capabilities of this interface.
### [String](class_string#class-string) get\_name ( ) const
Returns the name of this interface (OpenVR, OpenHMD, ARKit, etc).
### [Vector2](class_vector2#class-vector2) get\_render\_targetsize ( )
Returns the resolution at which we should render our intermediate results before things like lens distortion are applied by the VR platform.
### [Tracking\_status](#enum-arvrinterface-tracking-status) get\_tracking\_status ( ) const
If supported, returns the status of our tracking. This will allow you to provide feedback to the user whether there are issues with positional tracking.
### [bool](class_bool#class-bool) initialize ( )
Call this to initialize this interface. The first interface that is initialized is identified as the primary interface and it will be used for rendering output.
After initializing the interface you want to use you then need to enable the AR/VR mode of a viewport and rendering should commence.
**Note:** You must enable the AR/VR mode on the main viewport for any device that uses the main output of Godot, such as for mobile VR.
If you do this for a platform that handles its own output (such as OpenVR) Godot will show just one eye without distortion on screen. Alternatively, you can add a separate viewport node to your scene and enable AR/VR on that viewport. It will be used to output to the HMD, leaving you free to do anything you like in the main window, such as using a separate camera as a spectator camera or rendering something completely different.
While currently not used, you can activate additional interfaces. You may wish to do this if you want to track controllers from other platforms. However, at this point in time only one interface can render to an HMD.
### [bool](class_bool#class-bool) is\_stereo ( )
Returns `true` if the current output of this interface is in stereo.
### void uninitialize ( )
Turns the interface off.
godot InputEventMIDI InputEventMIDI
==============
**Inherits:** [InputEvent](class_inputevent#class-inputevent) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Input event for MIDI inputs.
Description
-----------
InputEventMIDI allows receiving input events from MIDI devices such as a piano. MIDI stands for Musical Instrument Digital Interface.
MIDI signals can be sent over a 5-pin MIDI connector or over USB, if your device supports both be sure to check the settings in the device to see which output it's using.
To receive input events from MIDI devices, you need to call [OS.open\_midi\_inputs](class_os#class-os-method-open-midi-inputs). You can check which devices are detected using [OS.get\_connected\_midi\_inputs](class_os#class-os-method-get-connected-midi-inputs).
Note that Godot does not currently support MIDI output, so there is no way to emit MIDI signals from Godot. Only MIDI input works.
Tutorials
---------
* [MIDI Message Status Byte List](https://www.midi.org/specifications-old/item/table-2-expanded-messages-list-status-bytes)
* [Wikipedia General MIDI Instrument List](https://en.wikipedia.org/wiki/General_MIDI#Program_change_events)
* [Wikipedia Piano Key Frequencies List](https://en.wikipedia.org/wiki/Piano_key_frequencies#List)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [channel](#class-inputeventmidi-property-channel) | `0` |
| [int](class_int#class-int) | [controller\_number](#class-inputeventmidi-property-controller-number) | `0` |
| [int](class_int#class-int) | [controller\_value](#class-inputeventmidi-property-controller-value) | `0` |
| [int](class_int#class-int) | [instrument](#class-inputeventmidi-property-instrument) | `0` |
| [int](class_int#class-int) | [message](#class-inputeventmidi-property-message) | `0` |
| [int](class_int#class-int) | [pitch](#class-inputeventmidi-property-pitch) | `0` |
| [int](class_int#class-int) | [pressure](#class-inputeventmidi-property-pressure) | `0` |
| [int](class_int#class-int) | [velocity](#class-inputeventmidi-property-velocity) | `0` |
Property Descriptions
---------------------
### [int](class_int#class-int) channel
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_channel(value) |
| *Getter* | get\_channel() |
The MIDI channel of this input event. There are 16 channels, so this value ranges from 0 to 15. MIDI channel 9 is reserved for the use with percussion instruments, the rest of the channels are for non-percussion instruments.
### [int](class_int#class-int) controller\_number
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_controller\_number(value) |
| *Getter* | get\_controller\_number() |
If the message is `MIDI_MESSAGE_CONTROL_CHANGE`, this indicates the controller number, otherwise this is zero. Controllers include devices such as pedals and levers.
### [int](class_int#class-int) controller\_value
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_controller\_value(value) |
| *Getter* | get\_controller\_value() |
If the message is `MIDI_MESSAGE_CONTROL_CHANGE`, this indicates the controller value, otherwise this is zero. Controllers include devices such as pedals and levers.
### [int](class_int#class-int) instrument
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_instrument(value) |
| *Getter* | get\_instrument() |
The instrument of this input event. This value ranges from 0 to 127. Refer to the instrument list on the General MIDI wikipedia article to see a list of instruments, except that this value is 0-index, so subtract one from every number on that chart. A standard piano will have an instrument number of 0.
### [int](class_int#class-int) message
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_message(value) |
| *Getter* | get\_message() |
Returns a value indicating the type of message for this MIDI signal. This is a member of the [MidiMessageList](class_%40globalscope#enum-globalscope-midimessagelist) enum.
For MIDI messages between 0x80 and 0xEF, only the left half of the bits are returned as this value, as the other part is the channel (ex: 0x94 becomes 0x9). For MIDI messages from 0xF0 to 0xFF, the value is returned as-is.
Notes will return `MIDI_MESSAGE_NOTE_ON` when activated, but they might not always return `MIDI_MESSAGE_NOTE_OFF` when deactivated, therefore your code should treat the input as stopped if some period of time has passed.
For more information, see the MIDI message status byte list chart linked above.
### [int](class_int#class-int) pitch
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_pitch(value) |
| *Getter* | get\_pitch() |
The pitch index number of this MIDI signal. This value ranges from 0 to 127. On a piano, middle C is 60, and A440 is 69, see the "MIDI note" column of the piano key frequency chart on Wikipedia for more information.
### [int](class_int#class-int) pressure
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_pressure(value) |
| *Getter* | get\_pressure() |
The pressure of the MIDI signal. This value ranges from 0 to 127. For many devices, this value is always zero.
### [int](class_int#class-int) velocity
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_velocity(value) |
| *Getter* | get\_velocity() |
The velocity of the MIDI signal. This value ranges from 0 to 127. For a piano, this corresponds to how quickly the key was pressed, and is rarely above about 110 in practice.
godot SpatialGizmo SpatialGizmo
============
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [EditorSpatialGizmo](class_editorspatialgizmo#class-editorspatialgizmo)
godot ExternalTexture ExternalTexture
===============
**Inherits:** [Texture](class_texture#class-texture) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Enable OpenGL ES external texture extension.
Description
-----------
Enable support for the OpenGL ES external texture extension as defined by [OES\_EGL\_image\_external](https://www.khronos.org/registry/OpenGL/extensions/OES/OES_EGL_image_external.txt).
**Note:** This is only supported for Android platforms.
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | flags | `2048` (overrides [Texture](class_texture#class-texture-property-flags)) |
| [Vector2](class_vector2#class-vector2) | [size](#class-externaltexture-property-size) | `Vector2( 1, 1 )` |
Methods
-------
| | |
| --- | --- |
| [int](class_int#class-int) | [get\_external\_texture\_id](#class-externaltexture-method-get-external-texture-id) **(** **)** |
Property Descriptions
---------------------
### [Vector2](class_vector2#class-vector2) size
| | |
| --- | --- |
| *Default* | `Vector2( 1, 1 )` |
| *Setter* | set\_size(value) |
| *Getter* | get\_size() |
External texture size.
Method Descriptions
-------------------
### [int](class_int#class-int) get\_external\_texture\_id ( )
Returns the external texture name.
godot VisualScriptDeconstruct VisualScriptDeconstruct
=======================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A Visual Script node which deconstructs a base type instance into its parts.
Description
-----------
A Visual Script node which deconstructs a base type instance into its parts.
Properties
----------
| | | |
| --- | --- | --- |
| [Variant.Type](class_%40globalscope#enum-globalscope-variant-type) | [type](#class-visualscriptdeconstruct-property-type) | `0` |
Property Descriptions
---------------------
### [Variant.Type](class_%40globalscope#enum-globalscope-variant-type) type
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_deconstruct\_type(value) |
| *Getter* | get\_deconstruct\_type() |
The type to deconstruct.
godot Listener2D Listener2D
==========
**Inherits:** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Overrides the location sounds are heard from.
Description
-----------
Once added to the scene tree and enabled using [make\_current](#class-listener2d-method-make-current), this node will override the location sounds are heard from. Only one `Listener2D` can be current. Using [make\_current](#class-listener2d-method-make-current) will disable the previous `Listener2D`.
If there is no active `Listener2D` in the current [Viewport](class_viewport#class-viewport), center of the screen will be used as a hearing point for the audio. `Listener2D` needs to be inside [SceneTree](class_scenetree#class-scenetree) to function.
Methods
-------
| | |
| --- | --- |
| void | [clear\_current](#class-listener2d-method-clear-current) **(** **)** |
| [bool](class_bool#class-bool) | [is\_current](#class-listener2d-method-is-current) **(** **)** const |
| void | [make\_current](#class-listener2d-method-make-current) **(** **)** |
Method Descriptions
-------------------
### void clear\_current ( )
Disables the `Listener2D`. If it's not set as current, this method will have no effect.
### [bool](class_bool#class-bool) is\_current ( ) const
Returns `true` if this `Listener2D` is currently active.
### void make\_current ( )
Makes the `Listener2D` active, setting it as the hearing point for the sounds. If there is already another active `Listener2D`, it will be disabled.
This method will have no effect if the `Listener2D` is not added to [SceneTree](class_scenetree#class-scenetree).
| programming_docs |
godot CSGTorus CSGTorus
========
**Inherits:** [CSGPrimitive](class_csgprimitive#class-csgprimitive) **<** [CSGShape](class_csgshape#class-csgshape) **<** [GeometryInstance](class_geometryinstance#class-geometryinstance) **<** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
A CSG Torus shape.
Description
-----------
This node allows you to create a torus for use with the CSG system.
**Note:** CSG nodes are intended to be used for level prototyping. Creating CSG nodes has a significant CPU cost compared to creating a [MeshInstance](class_meshinstance#class-meshinstance) with a [PrimitiveMesh](class_primitivemesh#class-primitivemesh). Moving a CSG node within another CSG node also has a significant CPU cost, so it should be avoided during gameplay.
Tutorials
---------
* [Prototyping levels with CSG](https://docs.godotengine.org/en/3.5/tutorials/3d/csg_tools.html)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [inner\_radius](#class-csgtorus-property-inner-radius) | `2.0` |
| [Material](class_material#class-material) | [material](#class-csgtorus-property-material) | |
| [float](class_float#class-float) | [outer\_radius](#class-csgtorus-property-outer-radius) | `3.0` |
| [int](class_int#class-int) | [ring\_sides](#class-csgtorus-property-ring-sides) | `6` |
| [int](class_int#class-int) | [sides](#class-csgtorus-property-sides) | `8` |
| [bool](class_bool#class-bool) | [smooth\_faces](#class-csgtorus-property-smooth-faces) | `true` |
Property Descriptions
---------------------
### [float](class_float#class-float) inner\_radius
| | |
| --- | --- |
| *Default* | `2.0` |
| *Setter* | set\_inner\_radius(value) |
| *Getter* | get\_inner\_radius() |
The inner radius of the torus.
### [Material](class_material#class-material) material
| | |
| --- | --- |
| *Setter* | set\_material(value) |
| *Getter* | get\_material() |
The material used to render the torus.
### [float](class_float#class-float) outer\_radius
| | |
| --- | --- |
| *Default* | `3.0` |
| *Setter* | set\_outer\_radius(value) |
| *Getter* | get\_outer\_radius() |
The outer radius of the torus.
### [int](class_int#class-int) ring\_sides
| | |
| --- | --- |
| *Default* | `6` |
| *Setter* | set\_ring\_sides(value) |
| *Getter* | get\_ring\_sides() |
The number of edges each ring of the torus is constructed of.
### [int](class_int#class-int) sides
| | |
| --- | --- |
| *Default* | `8` |
| *Setter* | set\_sides(value) |
| *Getter* | get\_sides() |
The number of slices the torus is constructed of.
### [bool](class_bool#class-bool) smooth\_faces
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_smooth\_faces(value) |
| *Getter* | get\_smooth\_faces() |
If `true` the normals of the torus are set to give a smooth effect making the torus seem rounded. If `false` the torus will have a flat shaded look.
godot VisualShaderNodeColorFunc VisualShaderNodeColorFunc
=========================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A [Color](class_color#class-color) function to be used within the visual shader graph.
Description
-----------
Accept a [Color](class_color#class-color) to the input port and transform it according to [function](#class-visualshadernodecolorfunc-property-function).
Properties
----------
| | | |
| --- | --- | --- |
| [Function](#enum-visualshadernodecolorfunc-function) | [function](#class-visualshadernodecolorfunc-property-function) | `0` |
Enumerations
------------
enum **Function**:
* **FUNC\_GRAYSCALE** = **0** --- Converts the color to grayscale using the following formula:
```
vec3 c = input;
float max1 = max(c.r, c.g);
float max2 = max(max1, c.b);
float max3 = max(max1, max2);
return vec3(max3, max3, max3);
```
* **FUNC\_SEPIA** = **1** --- Applies sepia tone effect using the following formula:
```
vec3 c = input;
float r = (c.r * 0.393) + (c.g * 0.769) + (c.b * 0.189);
float g = (c.r * 0.349) + (c.g * 0.686) + (c.b * 0.168);
float b = (c.r * 0.272) + (c.g * 0.534) + (c.b * 0.131);
return vec3(r, g, b);
```
Property Descriptions
---------------------
### [Function](#enum-visualshadernodecolorfunc-function) function
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_function(value) |
| *Getter* | get\_function() |
A function to be applied to the input color. See [Function](#enum-visualshadernodecolorfunc-function) for options.
godot JavaClassWrapper JavaClassWrapper
================
**Inherits:** [Object](class_object#class-object)
Methods
-------
| | |
| --- | --- |
| [JavaClass](class_javaclass#class-javaclass) | [wrap](#class-javaclasswrapper-method-wrap) **(** [String](class_string#class-string) name **)** |
Method Descriptions
-------------------
### [JavaClass](class_javaclass#class-javaclass) wrap ( [String](class_string#class-string) name )
godot GDNative GDNative
========
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Properties
----------
| | |
| --- | --- |
| [GDNativeLibrary](class_gdnativelibrary#class-gdnativelibrary) | [library](#class-gdnative-property-library) |
Methods
-------
| | |
| --- | --- |
| [Variant](class_variant#class-variant) | [call\_native](#class-gdnative-method-call-native) **(** [String](class_string#class-string) calling\_type, [String](class_string#class-string) procedure\_name, [Array](class_array#class-array) arguments **)** |
| [bool](class_bool#class-bool) | [initialize](#class-gdnative-method-initialize) **(** **)** |
| [bool](class_bool#class-bool) | [terminate](#class-gdnative-method-terminate) **(** **)** |
Property Descriptions
---------------------
### [GDNativeLibrary](class_gdnativelibrary#class-gdnativelibrary) library
| | |
| --- | --- |
| *Setter* | set\_library(value) |
| *Getter* | get\_library() |
Method Descriptions
-------------------
### [Variant](class_variant#class-variant) call\_native ( [String](class_string#class-string) calling\_type, [String](class_string#class-string) procedure\_name, [Array](class_array#class-array) arguments )
### [bool](class_bool#class-bool) initialize ( )
### [bool](class_bool#class-bool) terminate ( )
godot VisualShaderNodeVectorLen VisualShaderNodeVectorLen
=========================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Returns the length of a [Vector3](class_vector3#class-vector3) within the visual shader graph.
Description
-----------
Translated to `length(p0)` in the shader language.
godot VisualShaderNodeExpression VisualShaderNodeExpression
==========================
**Inherits:** [VisualShaderNodeGroupBase](class_visualshadernodegroupbase#class-visualshadernodegroupbase) **<** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
**Inherited By:** [VisualShaderNodeGlobalExpression](class_visualshadernodeglobalexpression#class-visualshadernodeglobalexpression)
A custom visual shader graph expression written in Godot Shading Language.
Description
-----------
Custom Godot Shading Language expression, with a custom amount of input and output ports.
The provided code is directly injected into the graph's matching shader function (`vertex`, `fragment`, or `light`), so it cannot be used to declare functions, varyings, uniforms, or global constants. See [VisualShaderNodeGlobalExpression](class_visualshadernodeglobalexpression#class-visualshadernodeglobalexpression) for such global definitions.
Properties
----------
| | | |
| --- | --- | --- |
| [String](class_string#class-string) | [expression](#class-visualshadernodeexpression-property-expression) | `""` |
Property Descriptions
---------------------
### [String](class_string#class-string) expression
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_expression(value) |
| *Getter* | get\_expression() |
An expression in Godot Shading Language, which will be injected at the start of the graph's matching shader function (`vertex`, `fragment`, or `light`), and thus cannot be used to declare functions, varyings, uniforms, or global constants.
godot SpatialMaterial SpatialMaterial
===============
**Inherits:** [Material](class_material#class-material) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Default 3D rendering material.
Description
-----------
This provides a default material with a wide variety of rendering features and properties without the need to write shader code. See the tutorial below for details.
Tutorials
---------
* [Spatial Material](https://docs.godotengine.org/en/3.5/tutorials/3d/spatial_material.html)
Properties
----------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [albedo\_color](#class-spatialmaterial-property-albedo-color) | `Color( 1, 1, 1, 1 )` |
| [Texture](class_texture#class-texture) | [albedo\_texture](#class-spatialmaterial-property-albedo-texture) | |
| [float](class_float#class-float) | [anisotropy](#class-spatialmaterial-property-anisotropy) | |
| [bool](class_bool#class-bool) | [anisotropy\_enabled](#class-spatialmaterial-property-anisotropy-enabled) | `false` |
| [Texture](class_texture#class-texture) | [anisotropy\_flowmap](#class-spatialmaterial-property-anisotropy-flowmap) | |
| [bool](class_bool#class-bool) | [ao\_enabled](#class-spatialmaterial-property-ao-enabled) | `false` |
| [float](class_float#class-float) | [ao\_light\_affect](#class-spatialmaterial-property-ao-light-affect) | |
| [bool](class_bool#class-bool) | [ao\_on\_uv2](#class-spatialmaterial-property-ao-on-uv2) | |
| [Texture](class_texture#class-texture) | [ao\_texture](#class-spatialmaterial-property-ao-texture) | |
| [TextureChannel](#enum-spatialmaterial-texturechannel) | [ao\_texture\_channel](#class-spatialmaterial-property-ao-texture-channel) | |
| [AsyncMode](#enum-spatialmaterial-asyncmode) | [async\_mode](#class-spatialmaterial-property-async-mode) | `0` |
| [float](class_float#class-float) | [clearcoat](#class-spatialmaterial-property-clearcoat) | |
| [bool](class_bool#class-bool) | [clearcoat\_enabled](#class-spatialmaterial-property-clearcoat-enabled) | `false` |
| [float](class_float#class-float) | [clearcoat\_gloss](#class-spatialmaterial-property-clearcoat-gloss) | |
| [Texture](class_texture#class-texture) | [clearcoat\_texture](#class-spatialmaterial-property-clearcoat-texture) | |
| [bool](class_bool#class-bool) | [depth\_deep\_parallax](#class-spatialmaterial-property-depth-deep-parallax) | |
| [bool](class_bool#class-bool) | [depth\_enabled](#class-spatialmaterial-property-depth-enabled) | `false` |
| [bool](class_bool#class-bool) | [depth\_flip\_binormal](#class-spatialmaterial-property-depth-flip-binormal) | |
| [bool](class_bool#class-bool) | [depth\_flip\_tangent](#class-spatialmaterial-property-depth-flip-tangent) | |
| [int](class_int#class-int) | [depth\_max\_layers](#class-spatialmaterial-property-depth-max-layers) | |
| [int](class_int#class-int) | [depth\_min\_layers](#class-spatialmaterial-property-depth-min-layers) | |
| [float](class_float#class-float) | [depth\_scale](#class-spatialmaterial-property-depth-scale) | |
| [Texture](class_texture#class-texture) | [depth\_texture](#class-spatialmaterial-property-depth-texture) | |
| [Texture](class_texture#class-texture) | [detail\_albedo](#class-spatialmaterial-property-detail-albedo) | |
| [BlendMode](#enum-spatialmaterial-blendmode) | [detail\_blend\_mode](#class-spatialmaterial-property-detail-blend-mode) | |
| [bool](class_bool#class-bool) | [detail\_enabled](#class-spatialmaterial-property-detail-enabled) | `false` |
| [Texture](class_texture#class-texture) | [detail\_mask](#class-spatialmaterial-property-detail-mask) | |
| [Texture](class_texture#class-texture) | [detail\_normal](#class-spatialmaterial-property-detail-normal) | |
| [DetailUV](#enum-spatialmaterial-detailuv) | [detail\_uv\_layer](#class-spatialmaterial-property-detail-uv-layer) | |
| [float](class_float#class-float) | [distance\_fade\_max\_distance](#class-spatialmaterial-property-distance-fade-max-distance) | |
| [float](class_float#class-float) | [distance\_fade\_min\_distance](#class-spatialmaterial-property-distance-fade-min-distance) | |
| [DistanceFadeMode](#enum-spatialmaterial-distancefademode) | [distance\_fade\_mode](#class-spatialmaterial-property-distance-fade-mode) | `0` |
| [Color](class_color#class-color) | [emission](#class-spatialmaterial-property-emission) | |
| [bool](class_bool#class-bool) | [emission\_enabled](#class-spatialmaterial-property-emission-enabled) | `false` |
| [float](class_float#class-float) | [emission\_energy](#class-spatialmaterial-property-emission-energy) | |
| [bool](class_bool#class-bool) | [emission\_on\_uv2](#class-spatialmaterial-property-emission-on-uv2) | |
| [EmissionOperator](#enum-spatialmaterial-emissionoperator) | [emission\_operator](#class-spatialmaterial-property-emission-operator) | |
| [Texture](class_texture#class-texture) | [emission\_texture](#class-spatialmaterial-property-emission-texture) | |
| [bool](class_bool#class-bool) | [flags\_albedo\_tex\_force\_srgb](#class-spatialmaterial-property-flags-albedo-tex-force-srgb) | `false` |
| [bool](class_bool#class-bool) | [flags\_albedo\_tex\_msdf](#class-spatialmaterial-property-flags-albedo-tex-msdf) | `false` |
| [bool](class_bool#class-bool) | [flags\_disable\_ambient\_light](#class-spatialmaterial-property-flags-disable-ambient-light) | `false` |
| [bool](class_bool#class-bool) | [flags\_do\_not\_receive\_shadows](#class-spatialmaterial-property-flags-do-not-receive-shadows) | `false` |
| [bool](class_bool#class-bool) | [flags\_ensure\_correct\_normals](#class-spatialmaterial-property-flags-ensure-correct-normals) | `false` |
| [bool](class_bool#class-bool) | [flags\_fixed\_size](#class-spatialmaterial-property-flags-fixed-size) | `false` |
| [bool](class_bool#class-bool) | [flags\_no\_depth\_test](#class-spatialmaterial-property-flags-no-depth-test) | `false` |
| [bool](class_bool#class-bool) | [flags\_transparent](#class-spatialmaterial-property-flags-transparent) | `false` |
| [bool](class_bool#class-bool) | [flags\_unshaded](#class-spatialmaterial-property-flags-unshaded) | `false` |
| [bool](class_bool#class-bool) | [flags\_use\_point\_size](#class-spatialmaterial-property-flags-use-point-size) | `false` |
| [bool](class_bool#class-bool) | [flags\_use\_shadow\_to\_opacity](#class-spatialmaterial-property-flags-use-shadow-to-opacity) | `false` |
| [bool](class_bool#class-bool) | [flags\_vertex\_lighting](#class-spatialmaterial-property-flags-vertex-lighting) | `false` |
| [bool](class_bool#class-bool) | [flags\_world\_triplanar](#class-spatialmaterial-property-flags-world-triplanar) | `false` |
| [float](class_float#class-float) | [metallic](#class-spatialmaterial-property-metallic) | `0.0` |
| [float](class_float#class-float) | [metallic\_specular](#class-spatialmaterial-property-metallic-specular) | `0.5` |
| [Texture](class_texture#class-texture) | [metallic\_texture](#class-spatialmaterial-property-metallic-texture) | |
| [TextureChannel](#enum-spatialmaterial-texturechannel) | [metallic\_texture\_channel](#class-spatialmaterial-property-metallic-texture-channel) | `0` |
| [bool](class_bool#class-bool) | [normal\_enabled](#class-spatialmaterial-property-normal-enabled) | `false` |
| [float](class_float#class-float) | [normal\_scale](#class-spatialmaterial-property-normal-scale) | |
| [Texture](class_texture#class-texture) | [normal\_texture](#class-spatialmaterial-property-normal-texture) | |
| [float](class_float#class-float) | [params\_alpha\_scissor\_threshold](#class-spatialmaterial-property-params-alpha-scissor-threshold) | |
| [bool](class_bool#class-bool) | [params\_billboard\_keep\_scale](#class-spatialmaterial-property-params-billboard-keep-scale) | `false` |
| [BillboardMode](#enum-spatialmaterial-billboardmode) | [params\_billboard\_mode](#class-spatialmaterial-property-params-billboard-mode) | `0` |
| [BlendMode](#enum-spatialmaterial-blendmode) | [params\_blend\_mode](#class-spatialmaterial-property-params-blend-mode) | `0` |
| [CullMode](#enum-spatialmaterial-cullmode) | [params\_cull\_mode](#class-spatialmaterial-property-params-cull-mode) | `0` |
| [DepthDrawMode](#enum-spatialmaterial-depthdrawmode) | [params\_depth\_draw\_mode](#class-spatialmaterial-property-params-depth-draw-mode) | `0` |
| [DiffuseMode](#enum-spatialmaterial-diffusemode) | [params\_diffuse\_mode](#class-spatialmaterial-property-params-diffuse-mode) | `0` |
| [bool](class_bool#class-bool) | [params\_grow](#class-spatialmaterial-property-params-grow) | `false` |
| [float](class_float#class-float) | [params\_grow\_amount](#class-spatialmaterial-property-params-grow-amount) | |
| [float](class_float#class-float) | [params\_line\_width](#class-spatialmaterial-property-params-line-width) | `1.0` |
| [float](class_float#class-float) | [params\_point\_size](#class-spatialmaterial-property-params-point-size) | `1.0` |
| [SpecularMode](#enum-spatialmaterial-specularmode) | [params\_specular\_mode](#class-spatialmaterial-property-params-specular-mode) | `0` |
| [bool](class_bool#class-bool) | [params\_use\_alpha\_scissor](#class-spatialmaterial-property-params-use-alpha-scissor) | `false` |
| [int](class_int#class-int) | [particles\_anim\_h\_frames](#class-spatialmaterial-property-particles-anim-h-frames) | |
| [bool](class_bool#class-bool) | [particles\_anim\_loop](#class-spatialmaterial-property-particles-anim-loop) | |
| [int](class_int#class-int) | [particles\_anim\_v\_frames](#class-spatialmaterial-property-particles-anim-v-frames) | |
| [float](class_float#class-float) | [proximity\_fade\_distance](#class-spatialmaterial-property-proximity-fade-distance) | |
| [bool](class_bool#class-bool) | [proximity\_fade\_enable](#class-spatialmaterial-property-proximity-fade-enable) | `false` |
| [bool](class_bool#class-bool) | [refraction\_enabled](#class-spatialmaterial-property-refraction-enabled) | `false` |
| [float](class_float#class-float) | [refraction\_scale](#class-spatialmaterial-property-refraction-scale) | |
| [Texture](class_texture#class-texture) | [refraction\_texture](#class-spatialmaterial-property-refraction-texture) | |
| [TextureChannel](#enum-spatialmaterial-texturechannel) | [refraction\_texture\_channel](#class-spatialmaterial-property-refraction-texture-channel) | |
| [float](class_float#class-float) | [rim](#class-spatialmaterial-property-rim) | |
| [bool](class_bool#class-bool) | [rim\_enabled](#class-spatialmaterial-property-rim-enabled) | `false` |
| [Texture](class_texture#class-texture) | [rim\_texture](#class-spatialmaterial-property-rim-texture) | |
| [float](class_float#class-float) | [rim\_tint](#class-spatialmaterial-property-rim-tint) | |
| [float](class_float#class-float) | [roughness](#class-spatialmaterial-property-roughness) | `1.0` |
| [Texture](class_texture#class-texture) | [roughness\_texture](#class-spatialmaterial-property-roughness-texture) | |
| [TextureChannel](#enum-spatialmaterial-texturechannel) | [roughness\_texture\_channel](#class-spatialmaterial-property-roughness-texture-channel) | `0` |
| [bool](class_bool#class-bool) | [subsurf\_scatter\_enabled](#class-spatialmaterial-property-subsurf-scatter-enabled) | `false` |
| [float](class_float#class-float) | [subsurf\_scatter\_strength](#class-spatialmaterial-property-subsurf-scatter-strength) | |
| [Texture](class_texture#class-texture) | [subsurf\_scatter\_texture](#class-spatialmaterial-property-subsurf-scatter-texture) | |
| [Color](class_color#class-color) | [transmission](#class-spatialmaterial-property-transmission) | |
| [bool](class_bool#class-bool) | [transmission\_enabled](#class-spatialmaterial-property-transmission-enabled) | `false` |
| [Texture](class_texture#class-texture) | [transmission\_texture](#class-spatialmaterial-property-transmission-texture) | |
| [Vector3](class_vector3#class-vector3) | [uv1\_offset](#class-spatialmaterial-property-uv1-offset) | `Vector3( 0, 0, 0 )` |
| [Vector3](class_vector3#class-vector3) | [uv1\_scale](#class-spatialmaterial-property-uv1-scale) | `Vector3( 1, 1, 1 )` |
| [bool](class_bool#class-bool) | [uv1\_triplanar](#class-spatialmaterial-property-uv1-triplanar) | `false` |
| [float](class_float#class-float) | [uv1\_triplanar\_sharpness](#class-spatialmaterial-property-uv1-triplanar-sharpness) | `1.0` |
| [Vector3](class_vector3#class-vector3) | [uv2\_offset](#class-spatialmaterial-property-uv2-offset) | `Vector3( 0, 0, 0 )` |
| [Vector3](class_vector3#class-vector3) | [uv2\_scale](#class-spatialmaterial-property-uv2-scale) | `Vector3( 1, 1, 1 )` |
| [bool](class_bool#class-bool) | [uv2\_triplanar](#class-spatialmaterial-property-uv2-triplanar) | `false` |
| [float](class_float#class-float) | [uv2\_triplanar\_sharpness](#class-spatialmaterial-property-uv2-triplanar-sharpness) | `1.0` |
| [bool](class_bool#class-bool) | [vertex\_color\_is\_srgb](#class-spatialmaterial-property-vertex-color-is-srgb) | `false` |
| [bool](class_bool#class-bool) | [vertex\_color\_use\_as\_albedo](#class-spatialmaterial-property-vertex-color-use-as-albedo) | `false` |
Methods
-------
| | |
| --- | --- |
| [bool](class_bool#class-bool) | [get\_feature](#class-spatialmaterial-method-get-feature) **(** [Feature](#enum-spatialmaterial-feature) feature **)** const |
| [bool](class_bool#class-bool) | [get\_flag](#class-spatialmaterial-method-get-flag) **(** [Flags](#enum-spatialmaterial-flags) flag **)** const |
| [Texture](class_texture#class-texture) | [get\_texture](#class-spatialmaterial-method-get-texture) **(** [TextureParam](#enum-spatialmaterial-textureparam) param **)** const |
| void | [set\_feature](#class-spatialmaterial-method-set-feature) **(** [Feature](#enum-spatialmaterial-feature) feature, [bool](class_bool#class-bool) enable **)** |
| void | [set\_flag](#class-spatialmaterial-method-set-flag) **(** [Flags](#enum-spatialmaterial-flags) flag, [bool](class_bool#class-bool) enable **)** |
| void | [set\_texture](#class-spatialmaterial-method-set-texture) **(** [TextureParam](#enum-spatialmaterial-textureparam) param, [Texture](class_texture#class-texture) texture **)** |
Enumerations
------------
enum **TextureParam**:
* **TEXTURE\_ALBEDO** = **0** --- Texture specifying per-pixel color.
* **TEXTURE\_METALLIC** = **1** --- Texture specifying per-pixel metallic value.
* **TEXTURE\_ROUGHNESS** = **2** --- Texture specifying per-pixel roughness value.
* **TEXTURE\_EMISSION** = **3** --- Texture specifying per-pixel emission color.
* **TEXTURE\_NORMAL** = **4** --- Texture specifying per-pixel normal vector.
* **TEXTURE\_RIM** = **5** --- Texture specifying per-pixel rim value.
* **TEXTURE\_CLEARCOAT** = **6** --- Texture specifying per-pixel clearcoat value.
* **TEXTURE\_FLOWMAP** = **7** --- Texture specifying per-pixel flowmap direction for use with [anisotropy](#class-spatialmaterial-property-anisotropy).
* **TEXTURE\_AMBIENT\_OCCLUSION** = **8** --- Texture specifying per-pixel ambient occlusion value.
* **TEXTURE\_DEPTH** = **9** --- Texture specifying per-pixel depth.
* **TEXTURE\_SUBSURFACE\_SCATTERING** = **10** --- Texture specifying per-pixel subsurface scattering.
* **TEXTURE\_TRANSMISSION** = **11** --- Texture specifying per-pixel transmission color.
* **TEXTURE\_REFRACTION** = **12** --- Texture specifying per-pixel refraction strength.
* **TEXTURE\_DETAIL\_MASK** = **13** --- Texture specifying per-pixel detail mask blending value.
* **TEXTURE\_DETAIL\_ALBEDO** = **14** --- Texture specifying per-pixel detail color.
* **TEXTURE\_DETAIL\_NORMAL** = **15** --- Texture specifying per-pixel detail normal.
* **TEXTURE\_MAX** = **16** --- Represents the size of the [TextureParam](#enum-spatialmaterial-textureparam) enum.
enum **DetailUV**:
* **DETAIL\_UV\_1** = **0** --- Use `UV` with the detail texture.
* **DETAIL\_UV\_2** = **1** --- Use `UV2` with the detail texture.
enum **Feature**:
* **FEATURE\_TRANSPARENT** = **0** --- Constant for setting [flags\_transparent](#class-spatialmaterial-property-flags-transparent).
* **FEATURE\_EMISSION** = **1** --- Constant for setting [emission\_enabled](#class-spatialmaterial-property-emission-enabled).
* **FEATURE\_NORMAL\_MAPPING** = **2** --- Constant for setting [normal\_enabled](#class-spatialmaterial-property-normal-enabled).
* **FEATURE\_RIM** = **3** --- Constant for setting [rim\_enabled](#class-spatialmaterial-property-rim-enabled).
* **FEATURE\_CLEARCOAT** = **4** --- Constant for setting [clearcoat\_enabled](#class-spatialmaterial-property-clearcoat-enabled).
* **FEATURE\_ANISOTROPY** = **5** --- Constant for setting [anisotropy\_enabled](#class-spatialmaterial-property-anisotropy-enabled).
* **FEATURE\_AMBIENT\_OCCLUSION** = **6** --- Constant for setting [ao\_enabled](#class-spatialmaterial-property-ao-enabled).
* **FEATURE\_DEPTH\_MAPPING** = **7** --- Constant for setting [depth\_enabled](#class-spatialmaterial-property-depth-enabled).
* **FEATURE\_SUBSURACE\_SCATTERING** = **8** --- Constant for setting [subsurf\_scatter\_enabled](#class-spatialmaterial-property-subsurf-scatter-enabled).
* **FEATURE\_TRANSMISSION** = **9** --- Constant for setting [transmission\_enabled](#class-spatialmaterial-property-transmission-enabled).
* **FEATURE\_REFRACTION** = **10** --- Constant for setting [refraction\_enabled](#class-spatialmaterial-property-refraction-enabled).
* **FEATURE\_DETAIL** = **11** --- Constant for setting [detail\_enabled](#class-spatialmaterial-property-detail-enabled).
* **FEATURE\_MAX** = **12** --- Represents the size of the [Feature](#enum-spatialmaterial-feature) enum.
enum **BlendMode**:
* **BLEND\_MODE\_MIX** = **0** --- Default blend mode. The color of the object is blended over the background based on the object's alpha value.
* **BLEND\_MODE\_ADD** = **1** --- The color of the object is added to the background.
* **BLEND\_MODE\_SUB** = **2** --- The color of the object is subtracted from the background.
* **BLEND\_MODE\_MUL** = **3** --- The color of the object is multiplied by the background.
enum **DepthDrawMode**:
* **DEPTH\_DRAW\_OPAQUE\_ONLY** = **0** --- Default depth draw mode. Depth is drawn only for opaque objects.
* **DEPTH\_DRAW\_ALWAYS** = **1** --- Depth draw is calculated for both opaque and transparent objects.
* **DEPTH\_DRAW\_DISABLED** = **2** --- No depth draw.
* **DEPTH\_DRAW\_ALPHA\_OPAQUE\_PREPASS** = **3** --- For transparent objects, an opaque pass is made first with the opaque parts, then transparency is drawn.
enum **CullMode**:
* **CULL\_BACK** = **0** --- Default cull mode. The back of the object is culled when not visible.
* **CULL\_FRONT** = **1** --- The front of the object is culled when not visible.
* **CULL\_DISABLED** = **2** --- No culling is performed.
enum **Flags**:
* **FLAG\_UNSHADED** = **0** --- No lighting is used on the object. Color comes directly from `ALBEDO`.
* **FLAG\_USE\_VERTEX\_LIGHTING** = **1** --- Lighting is calculated per-vertex rather than per-pixel. This can be used to increase the speed of the shader at the cost of quality.
* **FLAG\_DISABLE\_DEPTH\_TEST** = **2** --- Disables the depth test, so this object is drawn on top of all others. However, objects drawn after it in the draw order may cover it.
* **FLAG\_ALBEDO\_FROM\_VERTEX\_COLOR** = **3** --- Set `ALBEDO` to the per-vertex color specified in the mesh.
* **FLAG\_SRGB\_VERTEX\_COLOR** = **4** --- Vertex color is in sRGB space and needs to be converted to linear. Only applies in the GLES3 renderer.
* **FLAG\_USE\_POINT\_SIZE** = **5** --- Uses point size to alter the size of primitive points. Also changes the albedo texture lookup to use `POINT_COORD` instead of `UV`.
* **FLAG\_FIXED\_SIZE** = **6** --- Object is scaled by depth so that it always appears the same size on screen.
* **FLAG\_BILLBOARD\_KEEP\_SCALE** = **7** --- Shader will keep the scale set for the mesh. Otherwise the scale is lost when billboarding. Only applies when [params\_billboard\_mode](#class-spatialmaterial-property-params-billboard-mode) is [BILLBOARD\_ENABLED](#class-spatialmaterial-constant-billboard-enabled).
* **FLAG\_UV1\_USE\_TRIPLANAR** = **8** --- Use triplanar texture lookup for all texture lookups that would normally use `UV`.
* **FLAG\_UV2\_USE\_TRIPLANAR** = **9** --- Use triplanar texture lookup for all texture lookups that would normally use `UV2`.
* **FLAG\_AO\_ON\_UV2** = **11** --- Use `UV2` coordinates to look up from the [ao\_texture](#class-spatialmaterial-property-ao-texture).
* **FLAG\_EMISSION\_ON\_UV2** = **12** --- Use `UV2` coordinates to look up from the [emission\_texture](#class-spatialmaterial-property-emission-texture).
* **FLAG\_USE\_ALPHA\_SCISSOR** = **13** --- Use alpha scissor. Set by [params\_use\_alpha\_scissor](#class-spatialmaterial-property-params-use-alpha-scissor).
* **FLAG\_TRIPLANAR\_USE\_WORLD** = **10** --- Use world coordinates in the triplanar texture lookup instead of local coordinates.
* **FLAG\_ALBEDO\_TEXTURE\_FORCE\_SRGB** = **14** --- Forces the shader to convert albedo from sRGB space to linear space.
* **FLAG\_DONT\_RECEIVE\_SHADOWS** = **15** --- Disables receiving shadows from other objects.
* **FLAG\_DISABLE\_AMBIENT\_LIGHT** = **17** --- Disables receiving ambient light.
* **FLAG\_ENSURE\_CORRECT\_NORMALS** = **16** --- Ensures that normals appear correct, even with non-uniform scaling.
* **FLAG\_USE\_SHADOW\_TO\_OPACITY** = **18** --- Enables the shadow to opacity feature.
* **FLAG\_ALBEDO\_TEXTURE\_SDF** = **19** --- Enables signed distance field rendering shader.
* **FLAG\_MAX** = **20** --- Represents the size of the [Flags](#enum-spatialmaterial-flags) enum.
enum **DiffuseMode**:
* **DIFFUSE\_BURLEY** = **0** --- Default diffuse scattering algorithm.
* **DIFFUSE\_LAMBERT** = **1** --- Diffuse scattering ignores roughness.
* **DIFFUSE\_LAMBERT\_WRAP** = **2** --- Extends Lambert to cover more than 90 degrees when roughness increases.
* **DIFFUSE\_OREN\_NAYAR** = **3** --- Attempts to use roughness to emulate microsurfacing.
* **DIFFUSE\_TOON** = **4** --- Uses a hard cut for lighting, with smoothing affected by roughness.
enum **SpecularMode**:
* **SPECULAR\_SCHLICK\_GGX** = **0** --- Default specular blob.
* **SPECULAR\_BLINN** = **1** --- Older specular algorithm, included for compatibility.
* **SPECULAR\_PHONG** = **2** --- Older specular algorithm, included for compatibility.
* **SPECULAR\_TOON** = **3** --- Toon blob which changes size based on roughness.
* **SPECULAR\_DISABLED** = **4** --- No specular blob.
enum **BillboardMode**:
* **BILLBOARD\_DISABLED** = **0** --- Billboard mode is disabled.
* **BILLBOARD\_ENABLED** = **1** --- The object's Z axis will always face the camera.
* **BILLBOARD\_FIXED\_Y** = **2** --- The object's X axis will always face the camera.
* **BILLBOARD\_PARTICLES** = **3** --- Used for particle systems when assigned to [Particles](class_particles#class-particles) and [CPUParticles](class_cpuparticles#class-cpuparticles) nodes. Enables `particles_anim_*` properties.
The [ParticlesMaterial.anim\_speed](class_particlesmaterial#class-particlesmaterial-property-anim-speed) or [CPUParticles.anim\_speed](class_cpuparticles#class-cpuparticles-property-anim-speed) should also be set to a positive value for the animation to play.
enum **TextureChannel**:
* **TEXTURE\_CHANNEL\_RED** = **0** --- Used to read from the red channel of a texture.
* **TEXTURE\_CHANNEL\_GREEN** = **1** --- Used to read from the green channel of a texture.
* **TEXTURE\_CHANNEL\_BLUE** = **2** --- Used to read from the blue channel of a texture.
* **TEXTURE\_CHANNEL\_ALPHA** = **3** --- Used to read from the alpha channel of a texture.
* **TEXTURE\_CHANNEL\_GRAYSCALE** = **4** --- Currently unused.
enum **EmissionOperator**:
* **EMISSION\_OP\_ADD** = **0** --- Adds the emission color to the color from the emission texture.
* **EMISSION\_OP\_MULTIPLY** = **1** --- Multiplies the emission color by the color from the emission texture.
enum **DistanceFadeMode**:
* **DISTANCE\_FADE\_DISABLED** = **0** --- Do not use distance fade.
* **DISTANCE\_FADE\_PIXEL\_ALPHA** = **1** --- Smoothly fades the object out based on each pixel's distance from the camera using the alpha channel.
* **DISTANCE\_FADE\_PIXEL\_DITHER** = **2** --- Smoothly fades the object out based on each pixel's distance from the camera using a dither approach. Dithering discards pixels based on a set pattern to smoothly fade without enabling transparency. On certain hardware this can be faster than [DISTANCE\_FADE\_PIXEL\_ALPHA](#class-spatialmaterial-constant-distance-fade-pixel-alpha).
* **DISTANCE\_FADE\_OBJECT\_DITHER** = **3** --- Smoothly fades the object out based on the object's distance from the camera using a dither approach. Dithering discards pixels based on a set pattern to smoothly fade without enabling transparency. On certain hardware this can be faster than [DISTANCE\_FADE\_PIXEL\_ALPHA](#class-spatialmaterial-constant-distance-fade-pixel-alpha).
enum **AsyncMode**:
* **ASYNC\_MODE\_VISIBLE** = **0** --- The real conditioned shader needed on each situation will be sent for background compilation. In the meantime, a very complex shader that adapts to every situation will be used ("ubershader"). This ubershader is much slower to render, but will keep the game running without stalling to compile. Once shader compilation is done, the ubershader is replaced by the traditional optimized shader.
* **ASYNC\_MODE\_HIDDEN** = **1** --- Anything with this material applied won't be rendered while this material's shader is being compiled.
This is useful for optimization, in cases where the visuals won't suffer from having certain non-essential elements missing during the short time their shaders are being compiled.
Property Descriptions
---------------------
### [Color](class_color#class-color) albedo\_color
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
| *Setter* | set\_albedo(value) |
| *Getter* | get\_albedo() |
The material's base color.
### [Texture](class_texture#class-texture) albedo\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture to multiply by [albedo\_color](#class-spatialmaterial-property-albedo-color). Used for basic texturing of objects.
### [float](class_float#class-float) anisotropy
| | |
| --- | --- |
| *Setter* | set\_anisotropy(value) |
| *Getter* | get\_anisotropy() |
The strength of the anisotropy effect. This is multiplied by [anisotropy\_flowmap](#class-spatialmaterial-property-anisotropy-flowmap)'s alpha channel if a texture is defined there and the texture contains an alpha channel.
### [bool](class_bool#class-bool) anisotropy\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, anisotropy is enabled. Anisotropy changes the shape of the specular blob and aligns it to tangent space. This is useful for brushed aluminium and hair reflections.
**Note:** Mesh tangents are needed for anisotropy to work. If the mesh does not contain tangents, the anisotropy effect will appear broken.
**Note:** Material anisotropy should not to be confused with anisotropic texture filtering. Anisotropic texture filtering can be enabled by selecting a texture in the FileSystem dock, going to the Import dock, checking the **Anisotropic** checkbox then clicking **Reimport**. The anisotropic filtering level can be changed by adjusting [ProjectSettings.rendering/quality/filters/anisotropic\_filter\_level](class_projectsettings#class-projectsettings-property-rendering-quality-filters-anisotropic-filter-level).
### [Texture](class_texture#class-texture) anisotropy\_flowmap
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture that offsets the tangent map for anisotropy calculations and optionally controls the anisotropy effect (if an alpha channel is present). The flowmap texture is expected to be a derivative map, with the red channel representing distortion on the X axis and green channel representing distortion on the Y axis. Values below 0.5 will result in negative distortion, whereas values above 0.5 will result in positive distortion.
If present, the texture's alpha channel will be used to multiply the strength of the [anisotropy](#class-spatialmaterial-property-anisotropy) effect. Fully opaque pixels will keep the anisotropy effect's original strength while fully transparent pixels will disable the anisotropy effect entirely. The flowmap texture's blue channel is ignored.
### [bool](class_bool#class-bool) ao\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, ambient occlusion is enabled. Ambient occlusion darkens areas based on the [ao\_texture](#class-spatialmaterial-property-ao-texture).
### [float](class_float#class-float) ao\_light\_affect
| | |
| --- | --- |
| *Setter* | set\_ao\_light\_affect(value) |
| *Getter* | get\_ao\_light\_affect() |
Amount that ambient occlusion affects lighting from lights. If `0`, ambient occlusion only affects ambient light. If `1`, ambient occlusion affects lights just as much as it affects ambient light. This can be used to impact the strength of the ambient occlusion effect, but typically looks unrealistic.
### [bool](class_bool#class-bool) ao\_on\_uv2
| | |
| --- | --- |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, use `UV2` coordinates to look up from the [ao\_texture](#class-spatialmaterial-property-ao-texture).
### [Texture](class_texture#class-texture) ao\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture that defines the amount of ambient occlusion for a given point on the object.
### [TextureChannel](#enum-spatialmaterial-texturechannel) ao\_texture\_channel
| | |
| --- | --- |
| *Setter* | set\_ao\_texture\_channel(value) |
| *Getter* | get\_ao\_texture\_channel() |
Specifies the channel of the [ao\_texture](#class-spatialmaterial-property-ao-texture) in which the ambient occlusion information is stored. This is useful when you store the information for multiple effects in a single texture. For example if you stored metallic in the red channel, roughness in the blue, and ambient occlusion in the green you could reduce the number of textures you use.
### [AsyncMode](#enum-spatialmaterial-asyncmode) async\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_async\_mode(value) |
| *Getter* | get\_async\_mode() |
If [ProjectSettings.rendering/gles3/shaders/shader\_compilation\_mode](class_projectsettings#class-projectsettings-property-rendering-gles3-shaders-shader-compilation-mode) is `Synchronous` (with or without cache), this determines how this material must behave in regards to asynchronous shader compilation.
[ASYNC\_MODE\_VISIBLE](#class-spatialmaterial-constant-async-mode-visible) is the default and the best for most cases.
### [float](class_float#class-float) clearcoat
| | |
| --- | --- |
| *Setter* | set\_clearcoat(value) |
| *Getter* | get\_clearcoat() |
Sets the strength of the clearcoat effect. Setting to `0` looks the same as disabling the clearcoat effect.
### [bool](class_bool#class-bool) clearcoat\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, clearcoat rendering is enabled. Adds a secondary transparent pass to the lighting calculation resulting in an added specular blob. This makes materials appear as if they have a clear layer on them that can be either glossy or rough.
**Note:** Clearcoat rendering is not visible if the material has [flags\_unshaded](#class-spatialmaterial-property-flags-unshaded) set to `true`.
### [float](class_float#class-float) clearcoat\_gloss
| | |
| --- | --- |
| *Setter* | set\_clearcoat\_gloss(value) |
| *Getter* | get\_clearcoat\_gloss() |
Sets the roughness of the clearcoat pass. A higher value results in a smoother clearcoat while a lower value results in a rougher clearcoat.
### [Texture](class_texture#class-texture) clearcoat\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture that defines the strength of the clearcoat effect and the glossiness of the clearcoat. Strength is specified in the red channel while glossiness is specified in the green channel.
### [bool](class_bool#class-bool) depth\_deep\_parallax
| | |
| --- | --- |
| *Setter* | set\_depth\_deep\_parallax(value) |
| *Getter* | is\_depth\_deep\_parallax\_enabled() |
If `true`, the shader will read depth texture at multiple points along the view ray to determine occlusion and parrallax. This can be very performance demanding, but results in more realistic looking depth mapping.
### [bool](class_bool#class-bool) depth\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, depth mapping is enabled (also called "parallax mapping" or "height mapping"). See also [normal\_enabled](#class-spatialmaterial-property-normal-enabled).
**Note:** Depth mapping is not supported if triplanar mapping is used on the same material. The value of [depth\_enabled](#class-spatialmaterial-property-depth-enabled) will be ignored if [uv1\_triplanar](#class-spatialmaterial-property-uv1-triplanar) is enabled.
### [bool](class_bool#class-bool) depth\_flip\_binormal
| | |
| --- | --- |
| *Setter* | set\_depth\_deep\_parallax\_flip\_binormal(value) |
| *Getter* | get\_depth\_deep\_parallax\_flip\_binormal() |
If `true`, direction of the binormal is flipped before using in the depth effect. This may be necessary if you have encoded your binormals in a way that is conflicting with the depth effect.
### [bool](class_bool#class-bool) depth\_flip\_tangent
| | |
| --- | --- |
| *Setter* | set\_depth\_deep\_parallax\_flip\_tangent(value) |
| *Getter* | get\_depth\_deep\_parallax\_flip\_tangent() |
If `true`, direction of the tangent is flipped before using in the depth effect. This may be necessary if you have encoded your tangents in a way that is conflicting with the depth effect.
### [int](class_int#class-int) depth\_max\_layers
| | |
| --- | --- |
| *Setter* | set\_depth\_deep\_parallax\_max\_layers(value) |
| *Getter* | get\_depth\_deep\_parallax\_max\_layers() |
Number of layers to use when using [depth\_deep\_parallax](#class-spatialmaterial-property-depth-deep-parallax) and the view direction is perpendicular to the surface of the object. A higher number will be more performance demanding while a lower number may not look as crisp.
### [int](class_int#class-int) depth\_min\_layers
| | |
| --- | --- |
| *Setter* | set\_depth\_deep\_parallax\_min\_layers(value) |
| *Getter* | get\_depth\_deep\_parallax\_min\_layers() |
Number of layers to use when using [depth\_deep\_parallax](#class-spatialmaterial-property-depth-deep-parallax) and the view direction is parallel to the surface of the object. A higher number will be more performance demanding while a lower number may not look as crisp.
### [float](class_float#class-float) depth\_scale
| | |
| --- | --- |
| *Setter* | set\_depth\_scale(value) |
| *Getter* | get\_depth\_scale() |
Scales the depth offset effect. A higher number will create a larger depth.
### [Texture](class_texture#class-texture) depth\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture used to determine depth at a given pixel. Depth is always stored in the red channel.
### [Texture](class_texture#class-texture) detail\_albedo
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture that specifies the color of the detail overlay.
### [BlendMode](#enum-spatialmaterial-blendmode) detail\_blend\_mode
| | |
| --- | --- |
| *Setter* | set\_detail\_blend\_mode(value) |
| *Getter* | get\_detail\_blend\_mode() |
Specifies how the [detail\_albedo](#class-spatialmaterial-property-detail-albedo) should blend with the current `ALBEDO`. See [BlendMode](#enum-spatialmaterial-blendmode) for options.
### [bool](class_bool#class-bool) detail\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, enables the detail overlay. Detail is a second texture that gets mixed over the surface of the object based on [detail\_mask](#class-spatialmaterial-property-detail-mask). This can be used to add variation to objects, or to blend between two different albedo/normal textures.
### [Texture](class_texture#class-texture) detail\_mask
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture used to specify how the detail textures get blended with the base textures.
### [Texture](class_texture#class-texture) detail\_normal
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture that specifies the per-pixel normal of the detail overlay.
**Note:** Godot expects the normal map to use X+, Y+, and Z+ coordinates. See [this page](http://wiki.polycount.com/wiki/Normal_Map_Technical_Details#Common_Swizzle_Coordinates) for a comparison of normal map coordinates expected by popular engines.
### [DetailUV](#enum-spatialmaterial-detailuv) detail\_uv\_layer
| | |
| --- | --- |
| *Setter* | set\_detail\_uv(value) |
| *Getter* | get\_detail\_uv() |
Specifies whether to use `UV` or `UV2` for the detail layer. See [DetailUV](#enum-spatialmaterial-detailuv) for options.
### [float](class_float#class-float) distance\_fade\_max\_distance
| | |
| --- | --- |
| *Setter* | set\_distance\_fade\_max\_distance(value) |
| *Getter* | get\_distance\_fade\_max\_distance() |
Distance at which the object appears fully opaque.
**Note:** If `distance_fade_max_distance` is less than `distance_fade_min_distance`, the behavior will be reversed. The object will start to fade away at `distance_fade_max_distance` and will fully disappear once it reaches `distance_fade_min_distance`.
### [float](class_float#class-float) distance\_fade\_min\_distance
| | |
| --- | --- |
| *Setter* | set\_distance\_fade\_min\_distance(value) |
| *Getter* | get\_distance\_fade\_min\_distance() |
Distance at which the object starts to become visible. If the object is less than this distance away, it will be invisible.
**Note:** If `distance_fade_min_distance` is greater than `distance_fade_max_distance`, the behavior will be reversed. The object will start to fade away at `distance_fade_max_distance` and will fully disappear once it reaches `distance_fade_min_distance`.
### [DistanceFadeMode](#enum-spatialmaterial-distancefademode) distance\_fade\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_distance\_fade(value) |
| *Getter* | get\_distance\_fade() |
Specifies which type of fade to use. Can be any of the [DistanceFadeMode](#enum-spatialmaterial-distancefademode)s.
### [Color](class_color#class-color) emission
| | |
| --- | --- |
| *Setter* | set\_emission(value) |
| *Getter* | get\_emission() |
The emitted light's color. See [emission\_enabled](#class-spatialmaterial-property-emission-enabled).
### [bool](class_bool#class-bool) emission\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, the body emits light. Emitting light makes the object appear brighter. The object can also cast light on other objects if a [GIProbe](class_giprobe#class-giprobe) or [BakedLightmap](class_bakedlightmap#class-bakedlightmap) is used and this object is used in baked lighting.
### [float](class_float#class-float) emission\_energy
| | |
| --- | --- |
| *Setter* | set\_emission\_energy(value) |
| *Getter* | get\_emission\_energy() |
The emitted light's strength. See [emission\_enabled](#class-spatialmaterial-property-emission-enabled).
### [bool](class_bool#class-bool) emission\_on\_uv2
| | |
| --- | --- |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
Use `UV2` to read from the [emission\_texture](#class-spatialmaterial-property-emission-texture).
### [EmissionOperator](#enum-spatialmaterial-emissionoperator) emission\_operator
| | |
| --- | --- |
| *Setter* | set\_emission\_operator(value) |
| *Getter* | get\_emission\_operator() |
Sets how [emission](#class-spatialmaterial-property-emission) interacts with [emission\_texture](#class-spatialmaterial-property-emission-texture). Can either add or multiply. See [EmissionOperator](#enum-spatialmaterial-emissionoperator) for options.
### [Texture](class_texture#class-texture) emission\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture that specifies how much surface emits light at a given point.
### [bool](class_bool#class-bool) flags\_albedo\_tex\_force\_srgb
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
Forces a conversion of the [albedo\_texture](#class-spatialmaterial-property-albedo-texture) from sRGB space to linear space.
### [bool](class_bool#class-bool) flags\_albedo\_tex\_msdf
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
Enables signed distance field rendering shader.
### [bool](class_bool#class-bool) flags\_disable\_ambient\_light
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the object receives no ambient light.
### [bool](class_bool#class-bool) flags\_do\_not\_receive\_shadows
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the object receives no shadow that would otherwise be cast onto it.
### [bool](class_bool#class-bool) flags\_ensure\_correct\_normals
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the shader will compute extra operations to make sure the normal stays correct when using a non-uniform scale. Only enable if using non-uniform scaling.
### [bool](class_bool#class-bool) flags\_fixed\_size
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the object is rendered at the same size regardless of distance.
### [bool](class_bool#class-bool) flags\_no\_depth\_test
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, depth testing is disabled and the object will be drawn in render order.
### [bool](class_bool#class-bool) flags\_transparent
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, transparency is enabled on the body. See also [params\_blend\_mode](#class-spatialmaterial-property-params-blend-mode).
### [bool](class_bool#class-bool) flags\_unshaded
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the object is unaffected by lighting.
### [bool](class_bool#class-bool) flags\_use\_point\_size
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, render point size can be changed.
**Note:** This is only effective for objects whose geometry is point-based rather than triangle-based. See also [params\_point\_size](#class-spatialmaterial-property-params-point-size).
### [bool](class_bool#class-bool) flags\_use\_shadow\_to\_opacity
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, enables the "shadow to opacity" render mode where lighting modifies the alpha so shadowed areas are opaque and non-shadowed areas are transparent. Useful for overlaying shadows onto a camera feed in AR.
### [bool](class_bool#class-bool) flags\_vertex\_lighting
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, lighting is calculated per vertex rather than per pixel. This may increase performance on low-end devices, especially for meshes with a lower polygon count. The downside is that shading becomes much less accurate, with visible linear interpolation between vertices that are joined together. This can be compensated by ensuring meshes have a sufficient level of subdivision (but not too much, to avoid reducing performance). Some material features are also not supported when vertex shading is enabled.
See also [ProjectSettings.rendering/quality/shading/force\_vertex\_shading](class_projectsettings#class-projectsettings-property-rendering-quality-shading-force-vertex-shading) which can globally enable vertex shading on all materials.
**Note:** By default, vertex shading is enforced on mobile platforms by [ProjectSettings.rendering/quality/shading/force\_vertex\_shading](class_projectsettings#class-projectsettings-property-rendering-quality-shading-force-vertex-shading)'s `mobile` override.
**Note:** [flags\_vertex\_lighting](#class-spatialmaterial-property-flags-vertex-lighting) has no effect if [flags\_unshaded](#class-spatialmaterial-property-flags-unshaded) is `true`.
### [bool](class_bool#class-bool) flags\_world\_triplanar
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, triplanar mapping is calculated in world space rather than object local space. See also [uv1\_triplanar](#class-spatialmaterial-property-uv1-triplanar).
### [float](class_float#class-float) metallic
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_metallic(value) |
| *Getter* | get\_metallic() |
A high value makes the material appear more like a metal. Non-metals use their albedo as the diffuse color and add diffuse to the specular reflection. With non-metals, the reflection appears on top of the albedo color. Metals use their albedo as a multiplier to the specular reflection and set the diffuse color to black resulting in a tinted reflection. Materials work better when fully metal or fully non-metal, values between `0` and `1` should only be used for blending between metal and non-metal sections. To alter the amount of reflection use [roughness](#class-spatialmaterial-property-roughness).
### [float](class_float#class-float) metallic\_specular
| | |
| --- | --- |
| *Default* | `0.5` |
| *Setter* | set\_specular(value) |
| *Getter* | get\_specular() |
Sets the size of the specular lobe. The specular lobe is the bright spot that is reflected from light sources.
**Note:** Unlike [metallic](#class-spatialmaterial-property-metallic), this is not energy-conserving, so it should be left at `0.5` in most cases. See also [roughness](#class-spatialmaterial-property-roughness).
### [Texture](class_texture#class-texture) metallic\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture used to specify metallic for an object. This is multiplied by [metallic](#class-spatialmaterial-property-metallic).
### [TextureChannel](#enum-spatialmaterial-texturechannel) metallic\_texture\_channel
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_metallic\_texture\_channel(value) |
| *Getter* | get\_metallic\_texture\_channel() |
Specifies the channel of the [metallic\_texture](#class-spatialmaterial-property-metallic-texture) in which the metallic information is stored. This is useful when you store the information for multiple effects in a single texture. For example if you stored metallic in the red channel, roughness in the blue, and ambient occlusion in the green you could reduce the number of textures you use.
### [bool](class_bool#class-bool) normal\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, normal mapping is enabled.
### [float](class_float#class-float) normal\_scale
| | |
| --- | --- |
| *Setter* | set\_normal\_scale(value) |
| *Getter* | get\_normal\_scale() |
The strength of the normal map's effect.
### [Texture](class_texture#class-texture) normal\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture used to specify the normal at a given pixel. The `normal_texture` only uses the red and green channels; the blue and alpha channels are ignored. The normal read from `normal_texture` is oriented around the surface normal provided by the [Mesh](class_mesh#class-mesh).
**Note:** The mesh must have both normals and tangents defined in its vertex data. Otherwise, the normal map won't render correctly and will only appear to darken the whole surface. If creating geometry with [SurfaceTool](class_surfacetool#class-surfacetool), you can use [SurfaceTool.generate\_normals](class_surfacetool#class-surfacetool-method-generate-normals) and [SurfaceTool.generate\_tangents](class_surfacetool#class-surfacetool-method-generate-tangents) to automatically generate normals and tangents respectively.
**Note:** Godot expects the normal map to use X+, Y+, and Z+ coordinates. See [this page](http://wiki.polycount.com/wiki/Normal_Map_Technical_Details#Common_Swizzle_Coordinates) for a comparison of normal map coordinates expected by popular engines.
### [float](class_float#class-float) params\_alpha\_scissor\_threshold
| | |
| --- | --- |
| *Setter* | set\_alpha\_scissor\_threshold(value) |
| *Getter* | get\_alpha\_scissor\_threshold() |
Threshold at which the alpha scissor will discard values.
### [bool](class_bool#class-bool) params\_billboard\_keep\_scale
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the shader will keep the scale set for the mesh. Otherwise the scale is lost when billboarding. Only applies when [params\_billboard\_mode](#class-spatialmaterial-property-params-billboard-mode) is [BILLBOARD\_ENABLED](#class-spatialmaterial-constant-billboard-enabled).
### [BillboardMode](#enum-spatialmaterial-billboardmode) params\_billboard\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_billboard\_mode(value) |
| *Getter* | get\_billboard\_mode() |
Controls how the object faces the camera. See [BillboardMode](#enum-spatialmaterial-billboardmode).
**Note:** Billboard mode is not suitable for VR because the left-right vector of the camera is not horizontal when the screen is attached to your head instead of on the table. See [GitHub issue #41567](https://github.com/godotengine/godot/issues/41567) for details.
### [BlendMode](#enum-spatialmaterial-blendmode) params\_blend\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_blend\_mode(value) |
| *Getter* | get\_blend\_mode() |
The material's blend mode.
**Note:** Values other than `Mix` force the object into the transparent pipeline. See [BlendMode](#enum-spatialmaterial-blendmode).
### [CullMode](#enum-spatialmaterial-cullmode) params\_cull\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_cull\_mode(value) |
| *Getter* | get\_cull\_mode() |
Which side of the object is not drawn when backfaces are rendered. See [CullMode](#enum-spatialmaterial-cullmode).
### [DepthDrawMode](#enum-spatialmaterial-depthdrawmode) params\_depth\_draw\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_depth\_draw\_mode(value) |
| *Getter* | get\_depth\_draw\_mode() |
Determines when depth rendering takes place. See [DepthDrawMode](#enum-spatialmaterial-depthdrawmode). See also [flags\_transparent](#class-spatialmaterial-property-flags-transparent).
### [DiffuseMode](#enum-spatialmaterial-diffusemode) params\_diffuse\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_diffuse\_mode(value) |
| *Getter* | get\_diffuse\_mode() |
The algorithm used for diffuse light scattering. See [DiffuseMode](#enum-spatialmaterial-diffusemode).
### [bool](class_bool#class-bool) params\_grow
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_grow\_enabled(value) |
| *Getter* | is\_grow\_enabled() |
If `true`, enables the vertex grow setting. See [params\_grow\_amount](#class-spatialmaterial-property-params-grow-amount).
### [float](class_float#class-float) params\_grow\_amount
| | |
| --- | --- |
| *Setter* | set\_grow(value) |
| *Getter* | get\_grow() |
Grows object vertices in the direction of their normals.
### [float](class_float#class-float) params\_line\_width
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_line\_width(value) |
| *Getter* | get\_line\_width() |
Currently unimplemented in Godot.
### [float](class_float#class-float) params\_point\_size
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_point\_size(value) |
| *Getter* | get\_point\_size() |
The point size in pixels. See [flags\_use\_point\_size](#class-spatialmaterial-property-flags-use-point-size).
### [SpecularMode](#enum-spatialmaterial-specularmode) params\_specular\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_specular\_mode(value) |
| *Getter* | get\_specular\_mode() |
The method for rendering the specular blob. See [SpecularMode](#enum-spatialmaterial-specularmode).
### [bool](class_bool#class-bool) params\_use\_alpha\_scissor
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the shader will discard all pixels that have an alpha value less than [params\_alpha\_scissor\_threshold](#class-spatialmaterial-property-params-alpha-scissor-threshold).
### [int](class_int#class-int) particles\_anim\_h\_frames
| | |
| --- | --- |
| *Setter* | set\_particles\_anim\_h\_frames(value) |
| *Getter* | get\_particles\_anim\_h\_frames() |
The number of horizontal frames in the particle sprite sheet. Only enabled when using [BILLBOARD\_PARTICLES](#class-spatialmaterial-constant-billboard-particles). See [params\_billboard\_mode](#class-spatialmaterial-property-params-billboard-mode).
### [bool](class_bool#class-bool) particles\_anim\_loop
| | |
| --- | --- |
| *Setter* | set\_particles\_anim\_loop(value) |
| *Getter* | get\_particles\_anim\_loop() |
If `true`, particle animations are looped. Only enabled when using [BILLBOARD\_PARTICLES](#class-spatialmaterial-constant-billboard-particles). See [params\_billboard\_mode](#class-spatialmaterial-property-params-billboard-mode).
### [int](class_int#class-int) particles\_anim\_v\_frames
| | |
| --- | --- |
| *Setter* | set\_particles\_anim\_v\_frames(value) |
| *Getter* | get\_particles\_anim\_v\_frames() |
The number of vertical frames in the particle sprite sheet. Only enabled when using [BILLBOARD\_PARTICLES](#class-spatialmaterial-constant-billboard-particles). See [params\_billboard\_mode](#class-spatialmaterial-property-params-billboard-mode).
### [float](class_float#class-float) proximity\_fade\_distance
| | |
| --- | --- |
| *Setter* | set\_proximity\_fade\_distance(value) |
| *Getter* | get\_proximity\_fade\_distance() |
Distance over which the fade effect takes place. The larger the distance the longer it takes for an object to fade.
### [bool](class_bool#class-bool) proximity\_fade\_enable
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_proximity\_fade(value) |
| *Getter* | is\_proximity\_fade\_enabled() |
If `true`, the proximity fade effect is enabled. The proximity fade effect fades out each pixel based on its distance to another object.
### [bool](class_bool#class-bool) refraction\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, the refraction effect is enabled. Refraction distorts transparency based on light from behind the object. When using the GLES3 backend, the material's roughness value will affect the blurriness of the refraction. Higher roughness values will make the refraction look blurrier.
### [float](class_float#class-float) refraction\_scale
| | |
| --- | --- |
| *Setter* | set\_refraction(value) |
| *Getter* | get\_refraction() |
The strength of the refraction effect. Higher values result in a more distorted appearance for the refraction.
### [Texture](class_texture#class-texture) refraction\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture that controls the strength of the refraction per-pixel. Multiplied by [refraction\_scale](#class-spatialmaterial-property-refraction-scale).
### [TextureChannel](#enum-spatialmaterial-texturechannel) refraction\_texture\_channel
| | |
| --- | --- |
| *Setter* | set\_refraction\_texture\_channel(value) |
| *Getter* | get\_refraction\_texture\_channel() |
Specifies the channel of the [refraction\_texture](#class-spatialmaterial-property-refraction-texture) in which the refraction information is stored. This is useful when you store the information for multiple effects in a single texture. For example if you stored metallic in the red channel, roughness in the blue, and ambient occlusion in the green you could reduce the number of textures you use.
### [float](class_float#class-float) rim
| | |
| --- | --- |
| *Setter* | set\_rim(value) |
| *Getter* | get\_rim() |
Sets the strength of the rim lighting effect.
### [bool](class_bool#class-bool) rim\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, rim effect is enabled. Rim lighting increases the brightness at glancing angles on an object.
**Note:** Rim lighting is not visible if the material has [flags\_unshaded](#class-spatialmaterial-property-flags-unshaded) set to `true`.
### [Texture](class_texture#class-texture) rim\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture used to set the strength of the rim lighting effect per-pixel. Multiplied by [rim](#class-spatialmaterial-property-rim).
### [float](class_float#class-float) rim\_tint
| | |
| --- | --- |
| *Setter* | set\_rim\_tint(value) |
| *Getter* | get\_rim\_tint() |
The amount of to blend light and albedo color when rendering rim effect. If `0` the light color is used, while `1` means albedo color is used. An intermediate value generally works best.
### [float](class_float#class-float) roughness
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_roughness(value) |
| *Getter* | get\_roughness() |
Surface reflection. A value of `0` represents a perfect mirror while a value of `1` completely blurs the reflection. See also [metallic](#class-spatialmaterial-property-metallic).
### [Texture](class_texture#class-texture) roughness\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture used to control the roughness per-pixel. Multiplied by [roughness](#class-spatialmaterial-property-roughness).
### [TextureChannel](#enum-spatialmaterial-texturechannel) roughness\_texture\_channel
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_roughness\_texture\_channel(value) |
| *Getter* | get\_roughness\_texture\_channel() |
Specifies the channel of the [ao\_texture](#class-spatialmaterial-property-ao-texture) in which the ambient occlusion information is stored. This is useful when you store the information for multiple effects in a single texture. For example if you stored metallic in the red channel, roughness in the blue, and ambient occlusion in the green you could reduce the number of textures you use.
### [bool](class_bool#class-bool) subsurf\_scatter\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, subsurface scattering is enabled. Emulates light that penetrates an object's surface, is scattered, and then emerges.
### [float](class_float#class-float) subsurf\_scatter\_strength
| | |
| --- | --- |
| *Setter* | set\_subsurface\_scattering\_strength(value) |
| *Getter* | get\_subsurface\_scattering\_strength() |
The strength of the subsurface scattering effect.
### [Texture](class_texture#class-texture) subsurf\_scatter\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture used to control the subsurface scattering strength. Stored in the red texture channel. Multiplied by [subsurf\_scatter\_strength](#class-spatialmaterial-property-subsurf-scatter-strength).
### [Color](class_color#class-color) transmission
| | |
| --- | --- |
| *Setter* | set\_transmission(value) |
| *Getter* | get\_transmission() |
The color used by the transmission effect. Represents the light passing through an object.
### [bool](class_bool#class-bool) transmission\_enabled
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_feature(value) |
| *Getter* | get\_feature() |
If `true`, the transmission effect is enabled.
### [Texture](class_texture#class-texture) transmission\_texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
Texture used to control the transmission effect per-pixel. Added to [transmission](#class-spatialmaterial-property-transmission).
### [Vector3](class_vector3#class-vector3) uv1\_offset
| | |
| --- | --- |
| *Default* | `Vector3( 0, 0, 0 )` |
| *Setter* | set\_uv1\_offset(value) |
| *Getter* | get\_uv1\_offset() |
How much to offset the `UV` coordinates. This amount will be added to `UV` in the vertex function. This can be used to offset a texture.
### [Vector3](class_vector3#class-vector3) uv1\_scale
| | |
| --- | --- |
| *Default* | `Vector3( 1, 1, 1 )` |
| *Setter* | set\_uv1\_scale(value) |
| *Getter* | get\_uv1\_scale() |
How much to scale the `UV` coordinates. This is multiplied by `UV` in the vertex function.
### [bool](class_bool#class-bool) uv1\_triplanar
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, instead of using `UV` textures will use a triplanar texture lookup to determine how to apply textures. Triplanar uses the orientation of the object's surface to blend between texture coordinates. It reads from the source texture 3 times, once for each axis and then blends between the results based on how closely the pixel aligns with each axis. This is often used for natural features to get a realistic blend of materials. Because triplanar texturing requires many more texture reads per-pixel it is much slower than normal UV texturing. Additionally, because it is blending the texture between the three axes, it is unsuitable when you are trying to achieve crisp texturing.
### [float](class_float#class-float) uv1\_triplanar\_sharpness
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_uv1\_triplanar\_blend\_sharpness(value) |
| *Getter* | get\_uv1\_triplanar\_blend\_sharpness() |
A lower number blends the texture more softly while a higher number blends the texture more sharply.
### [Vector3](class_vector3#class-vector3) uv2\_offset
| | |
| --- | --- |
| *Default* | `Vector3( 0, 0, 0 )` |
| *Setter* | set\_uv2\_offset(value) |
| *Getter* | get\_uv2\_offset() |
How much to offset the `UV2` coordinates. This amount will be added to `UV2` in the vertex function. This can be used to offset a texture.
### [Vector3](class_vector3#class-vector3) uv2\_scale
| | |
| --- | --- |
| *Default* | `Vector3( 1, 1, 1 )` |
| *Setter* | set\_uv2\_scale(value) |
| *Getter* | get\_uv2\_scale() |
How much to scale the `UV2` coordinates. This is multiplied by `UV2` in the vertex function.
### [bool](class_bool#class-bool) uv2\_triplanar
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, instead of using `UV2` textures will use a triplanar texture lookup to determine how to apply textures. Triplanar uses the orientation of the object's surface to blend between texture coordinates. It reads from the source texture 3 times, once for each axis and then blends between the results based on how closely the pixel aligns with each axis. This is often used for natural features to get a realistic blend of materials. Because triplanar texturing requires many more texture reads per-pixel it is much slower than normal UV texturing. Additionally, because it is blending the texture between the three axes, it is unsuitable when you are trying to achieve crisp texturing.
### [float](class_float#class-float) uv2\_triplanar\_sharpness
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_uv2\_triplanar\_blend\_sharpness(value) |
| *Getter* | get\_uv2\_triplanar\_blend\_sharpness() |
A lower number blends the texture more softly while a higher number blends the texture more sharply.
### [bool](class_bool#class-bool) vertex\_color\_is\_srgb
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the model's vertex colors are processed as sRGB mode.
### [bool](class_bool#class-bool) vertex\_color\_use\_as\_albedo
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the vertex color is used as albedo color.
Method Descriptions
-------------------
### [bool](class_bool#class-bool) get\_feature ( [Feature](#enum-spatialmaterial-feature) feature ) const
Returns `true`, if the specified [Feature](#enum-spatialmaterial-feature) is enabled.
### [bool](class_bool#class-bool) get\_flag ( [Flags](#enum-spatialmaterial-flags) flag ) const
Returns `true`, if the specified flag is enabled. See [Flags](#enum-spatialmaterial-flags) enumerator for options.
### [Texture](class_texture#class-texture) get\_texture ( [TextureParam](#enum-spatialmaterial-textureparam) param ) const
Returns the [Texture](class_texture#class-texture) associated with the specified [TextureParam](#enum-spatialmaterial-textureparam).
### void set\_feature ( [Feature](#enum-spatialmaterial-feature) feature, [bool](class_bool#class-bool) enable )
If `true`, enables the specified [Feature](#enum-spatialmaterial-feature). Many features that are available in `SpatialMaterial`s need to be enabled before use. This way the cost for using the feature is only incurred when specified. Features can also be enabled by setting the corresponding member to `true`.
### void set\_flag ( [Flags](#enum-spatialmaterial-flags) flag, [bool](class_bool#class-bool) enable )
If `true`, enables the specified flag. Flags are optional behavior that can be turned on and off. Only one flag can be enabled at a time with this function, the flag enumerators cannot be bit-masked together to enable or disable multiple flags at once. Flags can also be enabled by setting the corresponding member to `true`. See [Flags](#enum-spatialmaterial-flags) enumerator for options.
### void set\_texture ( [TextureParam](#enum-spatialmaterial-textureparam) param, [Texture](class_texture#class-texture) texture )
Sets the [Texture](class_texture#class-texture) to be used by the specified [TextureParam](#enum-spatialmaterial-textureparam). This function is called when setting members ending in `*_texture`.
| programming_docs |
godot VisualShaderNodeVectorInterp VisualShaderNodeVectorInterp
============================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Linearly interpolates between two vectors within the visual shader graph.
Description
-----------
Translates to `mix(a, b, weight)` in the shader language, where `weight` is a [Vector3](class_vector3#class-vector3) with weights for each component.
godot PathFollow2D PathFollow2D
============
**Inherits:** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Point sampler for a [Path2D](class_path2d#class-path2d).
Description
-----------
This node takes its parent [Path2D](class_path2d#class-path2d), and returns the coordinates of a point within it, given a distance from the first vertex.
It is useful for making other nodes follow a path, without coding the movement pattern. For that, the nodes must be children of this node. The descendant nodes will then move accordingly when setting an offset in this node.
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [cubic\_interp](#class-pathfollow2d-property-cubic-interp) | `true` |
| [float](class_float#class-float) | [h\_offset](#class-pathfollow2d-property-h-offset) | `0.0` |
| [float](class_float#class-float) | [lookahead](#class-pathfollow2d-property-lookahead) | `4.0` |
| [bool](class_bool#class-bool) | [loop](#class-pathfollow2d-property-loop) | `true` |
| [float](class_float#class-float) | [offset](#class-pathfollow2d-property-offset) | `0.0` |
| [bool](class_bool#class-bool) | [rotate](#class-pathfollow2d-property-rotate) | `true` |
| [float](class_float#class-float) | [unit\_offset](#class-pathfollow2d-property-unit-offset) | `0.0` |
| [float](class_float#class-float) | [v\_offset](#class-pathfollow2d-property-v-offset) | `0.0` |
Property Descriptions
---------------------
### [bool](class_bool#class-bool) cubic\_interp
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_cubic\_interpolation(value) |
| *Getter* | get\_cubic\_interpolation() |
If `true`, the position between two cached points is interpolated cubically, and linearly otherwise.
The points along the [Curve2D](class_curve2d#class-curve2d) of the [Path2D](class_path2d#class-path2d) are precomputed before use, for faster calculations. The point at the requested offset is then calculated interpolating between two adjacent cached points. This may present a problem if the curve makes sharp turns, as the cached points may not follow the curve closely enough.
There are two answers to this problem: either increase the number of cached points and increase memory consumption, or make a cubic interpolation between two points at the cost of (slightly) slower calculations.
### [float](class_float#class-float) h\_offset
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_h\_offset(value) |
| *Getter* | get\_h\_offset() |
The node's offset along the curve.
### [float](class_float#class-float) lookahead
| | |
| --- | --- |
| *Default* | `4.0` |
| *Setter* | set\_lookahead(value) |
| *Getter* | get\_lookahead() |
How far to look ahead of the curve to calculate the tangent if the node is rotating. E.g. shorter lookaheads will lead to faster rotations.
### [bool](class_bool#class-bool) loop
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_loop(value) |
| *Getter* | has\_loop() |
If `true`, any offset outside the path's length will wrap around, instead of stopping at the ends. Use it for cyclic paths.
### [float](class_float#class-float) offset
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_offset(value) |
| *Getter* | get\_offset() |
The distance along the path in pixels.
### [bool](class_bool#class-bool) rotate
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_rotate(value) |
| *Getter* | is\_rotating() |
If `true`, this node rotates to follow the path, making its descendants rotate.
### [float](class_float#class-float) unit\_offset
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_unit\_offset(value) |
| *Getter* | get\_unit\_offset() |
The distance along the path as a number in the range 0.0 (for the first vertex) to 1.0 (for the last). This is just another way of expressing the offset within the path, as the offset supplied is multiplied internally by the path's length.
### [float](class_float#class-float) v\_offset
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_v\_offset(value) |
| *Getter* | get\_v\_offset() |
The node's offset perpendicular to the curve.
godot VisualShaderNodeVectorDistance VisualShaderNodeVectorDistance
==============================
**Inherits:** [VisualShaderNode](class_visualshadernode#class-visualshadernode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Returns the distance between two points. To be used within the visual shader graph.
Description
-----------
Calculates distance from point represented by vector `p0` to vector `p1`.
Translated to `distance(p0, p1)` in the shader language.
godot CSGBox CSGBox
======
**Inherits:** [CSGPrimitive](class_csgprimitive#class-csgprimitive) **<** [CSGShape](class_csgshape#class-csgshape) **<** [GeometryInstance](class_geometryinstance#class-geometryinstance) **<** [VisualInstance](class_visualinstance#class-visualinstance) **<** [CullInstance](class_cullinstance#class-cullinstance) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
A CSG Box shape.
Description
-----------
This node allows you to create a box for use with the CSG system.
**Note:** CSG nodes are intended to be used for level prototyping. Creating CSG nodes has a significant CPU cost compared to creating a [MeshInstance](class_meshinstance#class-meshinstance) with a [PrimitiveMesh](class_primitivemesh#class-primitivemesh). Moving a CSG node within another CSG node also has a significant CPU cost, so it should be avoided during gameplay.
Tutorials
---------
* [Prototyping levels with CSG](https://docs.godotengine.org/en/3.5/tutorials/3d/csg_tools.html)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [depth](#class-csgbox-property-depth) | `2.0` |
| [float](class_float#class-float) | [height](#class-csgbox-property-height) | `2.0` |
| [Material](class_material#class-material) | [material](#class-csgbox-property-material) | |
| [float](class_float#class-float) | [width](#class-csgbox-property-width) | `2.0` |
Property Descriptions
---------------------
### [float](class_float#class-float) depth
| | |
| --- | --- |
| *Default* | `2.0` |
| *Setter* | set\_depth(value) |
| *Getter* | get\_depth() |
Depth of the box measured from the center of the box.
### [float](class_float#class-float) height
| | |
| --- | --- |
| *Default* | `2.0` |
| *Setter* | set\_height(value) |
| *Getter* | get\_height() |
Height of the box measured from the center of the box.
### [Material](class_material#class-material) material
| | |
| --- | --- |
| *Setter* | set\_material(value) |
| *Getter* | get\_material() |
The material used to render the box.
### [float](class_float#class-float) width
| | |
| --- | --- |
| *Default* | `2.0` |
| *Setter* | set\_width(value) |
| *Getter* | get\_width() |
Width of the box measured from the center of the box.
godot Line2D Line2D
======
**Inherits:** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
A 2D line.
Description
-----------
A line through several points in 2D space. Supports varying width and color over the line's length, texturing, and several cap/joint types.
**Note:** By default, Godot can only draw up to 4,096 polygon points at a time. To increase this limit, open the Project Settings and increase [ProjectSettings.rendering/limits/buffers/canvas\_polygon\_buffer\_size\_kb](class_projectsettings#class-projectsettings-property-rendering-limits-buffers-canvas-polygon-buffer-size-kb) and [ProjectSettings.rendering/limits/buffers/canvas\_polygon\_index\_buffer\_size\_kb](class_projectsettings#class-projectsettings-property-rendering-limits-buffers-canvas-polygon-index-buffer-size-kb).
Tutorials
---------
* [Matrix Transform Demo](https://godotengine.org/asset-library/asset/584)
* [2.5D Demo](https://godotengine.org/asset-library/asset/583)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [antialiased](#class-line2d-property-antialiased) | `false` |
| [LineCapMode](#enum-line2d-linecapmode) | [begin\_cap\_mode](#class-line2d-property-begin-cap-mode) | `0` |
| [Color](class_color#class-color) | [default\_color](#class-line2d-property-default-color) | `Color( 0.4, 0.5, 1, 1 )` |
| [LineCapMode](#enum-line2d-linecapmode) | [end\_cap\_mode](#class-line2d-property-end-cap-mode) | `0` |
| [Gradient](class_gradient#class-gradient) | [gradient](#class-line2d-property-gradient) | |
| [LineJointMode](#enum-line2d-linejointmode) | [joint\_mode](#class-line2d-property-joint-mode) | `0` |
| [PoolVector2Array](class_poolvector2array#class-poolvector2array) | [points](#class-line2d-property-points) | `PoolVector2Array( )` |
| [int](class_int#class-int) | [round\_precision](#class-line2d-property-round-precision) | `8` |
| [float](class_float#class-float) | [sharp\_limit](#class-line2d-property-sharp-limit) | `2.0` |
| [Texture](class_texture#class-texture) | [texture](#class-line2d-property-texture) | |
| [LineTextureMode](#enum-line2d-linetexturemode) | [texture\_mode](#class-line2d-property-texture-mode) | `0` |
| [float](class_float#class-float) | [width](#class-line2d-property-width) | `10.0` |
| [Curve](class_curve#class-curve) | [width\_curve](#class-line2d-property-width-curve) | |
Methods
-------
| | |
| --- | --- |
| void | [add\_point](#class-line2d-method-add-point) **(** [Vector2](class_vector2#class-vector2) position, [int](class_int#class-int) index=-1 **)** |
| void | [clear\_points](#class-line2d-method-clear-points) **(** **)** |
| [int](class_int#class-int) | [get\_point\_count](#class-line2d-method-get-point-count) **(** **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_point\_position](#class-line2d-method-get-point-position) **(** [int](class_int#class-int) index **)** const |
| void | [remove\_point](#class-line2d-method-remove-point) **(** [int](class_int#class-int) index **)** |
| void | [set\_point\_position](#class-line2d-method-set-point-position) **(** [int](class_int#class-int) index, [Vector2](class_vector2#class-vector2) position **)** |
Enumerations
------------
enum **LineJointMode**:
* **LINE\_JOINT\_SHARP** = **0** --- The line's joints will be pointy. If `sharp_limit` is greater than the rotation of a joint, it becomes a bevel joint instead.
* **LINE\_JOINT\_BEVEL** = **1** --- The line's joints will be bevelled/chamfered.
* **LINE\_JOINT\_ROUND** = **2** --- The line's joints will be rounded.
enum **LineCapMode**:
* **LINE\_CAP\_NONE** = **0** --- Don't draw a line cap.
* **LINE\_CAP\_BOX** = **1** --- Draws the line cap as a box.
* **LINE\_CAP\_ROUND** = **2** --- Draws the line cap as a circle.
enum **LineTextureMode**:
* **LINE\_TEXTURE\_NONE** = **0** --- Takes the left pixels of the texture and renders it over the whole line.
* **LINE\_TEXTURE\_TILE** = **1** --- Tiles the texture over the line. The texture must be imported with **Repeat** enabled for it to work properly.
* **LINE\_TEXTURE\_STRETCH** = **2** --- Stretches the texture across the line. Import the texture with **Repeat** disabled for best results.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) antialiased
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_antialiased(value) |
| *Getter* | get\_antialiased() |
If `true`, the line's border will attempt to perform antialiasing by drawing thin OpenGL smooth lines on the line's edges.
**Note:** Line2D is not accelerated by batching if [antialiased](#class-line2d-property-antialiased) is `true`.
**Note:** Due to how it works, built-in antialiasing will not look correct for translucent lines and may not work on certain platforms. As a workaround, install the [Antialiased Line2D](https://github.com/godot-extended-libraries/godot-antialiased-line2d) add-on then create an AntialiasedLine2D node. That node relies on a texture with custom mipmaps to perform antialiasing. 2D batching is also still supported with those antialiased lines.
### [LineCapMode](#enum-line2d-linecapmode) begin\_cap\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_begin\_cap\_mode(value) |
| *Getter* | get\_begin\_cap\_mode() |
Controls the style of the line's first point. Use [LineCapMode](#enum-line2d-linecapmode) constants.
### [Color](class_color#class-color) default\_color
| | |
| --- | --- |
| *Default* | `Color( 0.4, 0.5, 1, 1 )` |
| *Setter* | set\_default\_color(value) |
| *Getter* | get\_default\_color() |
The line's color. Will not be used if a gradient is set.
### [LineCapMode](#enum-line2d-linecapmode) end\_cap\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_end\_cap\_mode(value) |
| *Getter* | get\_end\_cap\_mode() |
Controls the style of the line's last point. Use [LineCapMode](#enum-line2d-linecapmode) constants.
### [Gradient](class_gradient#class-gradient) gradient
| | |
| --- | --- |
| *Setter* | set\_gradient(value) |
| *Getter* | get\_gradient() |
The gradient is drawn through the whole line from start to finish. The default color will not be used if a gradient is set.
### [LineJointMode](#enum-line2d-linejointmode) joint\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_joint\_mode(value) |
| *Getter* | get\_joint\_mode() |
The style for the points between the start and the end.
### [PoolVector2Array](class_poolvector2array#class-poolvector2array) points
| | |
| --- | --- |
| *Default* | `PoolVector2Array( )` |
| *Setter* | set\_points(value) |
| *Getter* | get\_points() |
The points that form the lines. The line is drawn between every point set in this array. Points are interpreted as local vectors.
### [int](class_int#class-int) round\_precision
| | |
| --- | --- |
| *Default* | `8` |
| *Setter* | set\_round\_precision(value) |
| *Getter* | get\_round\_precision() |
The smoothness of the rounded joints and caps. Higher values result in smoother corners, but are more demanding to render and update. This is only used if a cap or joint is set as round.
**Note:** The default value is tuned for lines with the default [width](#class-line2d-property-width). For thin lines, this value should be reduced to a number between `2` and `4` to improve performance.
### [float](class_float#class-float) sharp\_limit
| | |
| --- | --- |
| *Default* | `2.0` |
| *Setter* | set\_sharp\_limit(value) |
| *Getter* | get\_sharp\_limit() |
The direction difference in radians between vector points. This value is only used if [joint\_mode](#class-line2d-property-joint-mode) is set to [LINE\_JOINT\_SHARP](#class-line2d-constant-line-joint-sharp).
### [Texture](class_texture#class-texture) texture
| | |
| --- | --- |
| *Setter* | set\_texture(value) |
| *Getter* | get\_texture() |
The texture used for the line's texture. Uses `texture_mode` for drawing style.
### [LineTextureMode](#enum-line2d-linetexturemode) texture\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_texture\_mode(value) |
| *Getter* | get\_texture\_mode() |
The style to render the `texture` on the line. Use [LineTextureMode](#enum-line2d-linetexturemode) constants.
### [float](class_float#class-float) width
| | |
| --- | --- |
| *Default* | `10.0` |
| *Setter* | set\_width(value) |
| *Getter* | get\_width() |
The line's width.
### [Curve](class_curve#class-curve) width\_curve
| | |
| --- | --- |
| *Setter* | set\_curve(value) |
| *Getter* | get\_curve() |
The line's width varies with the curve. The original width is simply multiply by the value of the Curve.
Method Descriptions
-------------------
### void add\_point ( [Vector2](class_vector2#class-vector2) position, [int](class_int#class-int) index=-1 )
Adds a point with the specified `position` relative to the line's own position. Appends the new point at the end of the point list.
If `index` is given, the new point is inserted before the existing point identified by index `index`. Every existing point starting from `index` is shifted further down the list of points. The index must be greater than or equal to `0` and must not exceed the number of existing points in the line. See [get\_point\_count](#class-line2d-method-get-point-count).
### void clear\_points ( )
Removes all points from the line.
### [int](class_int#class-int) get\_point\_count ( ) const
Returns the amount of points in the line.
### [Vector2](class_vector2#class-vector2) get\_point\_position ( [int](class_int#class-int) index ) const
Returns the position of the point at index `index`.
### void remove\_point ( [int](class_int#class-int) index )
Removes the point at index `index` from the line.
### void set\_point\_position ( [int](class_int#class-int) index, [Vector2](class_vector2#class-vector2) position )
Overwrites the position of the point at index `index` with the supplied `position`.
godot TextureButton TextureButton
=============
**Inherits:** [BaseButton](class_basebutton#class-basebutton) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Texture-based button. Supports Pressed, Hover, Disabled and Focused states.
Description
-----------
`TextureButton` has the same functionality as [Button](class_button#class-button), except it uses sprites instead of Godot's [Theme](class_theme#class-theme) resource. It is faster to create, but it doesn't support localization like more complex [Control](class_control#class-control)s.
The "normal" state must contain a texture ([texture\_normal](#class-texturebutton-property-texture-normal)); other textures are optional.
See also [BaseButton](class_basebutton#class-basebutton) which contains common properties and methods associated with this node.
Tutorials
---------
* [3D Voxel Demo](https://godotengine.org/asset-library/asset/676)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [expand](#class-texturebutton-property-expand) | `false` |
| [bool](class_bool#class-bool) | [flip\_h](#class-texturebutton-property-flip-h) | `false` |
| [bool](class_bool#class-bool) | [flip\_v](#class-texturebutton-property-flip-v) | `false` |
| [StretchMode](#enum-texturebutton-stretchmode) | [stretch\_mode](#class-texturebutton-property-stretch-mode) | `0` |
| [BitMap](class_bitmap#class-bitmap) | [texture\_click\_mask](#class-texturebutton-property-texture-click-mask) | |
| [Texture](class_texture#class-texture) | [texture\_disabled](#class-texturebutton-property-texture-disabled) | |
| [Texture](class_texture#class-texture) | [texture\_focused](#class-texturebutton-property-texture-focused) | |
| [Texture](class_texture#class-texture) | [texture\_hover](#class-texturebutton-property-texture-hover) | |
| [Texture](class_texture#class-texture) | [texture\_normal](#class-texturebutton-property-texture-normal) | |
| [Texture](class_texture#class-texture) | [texture\_pressed](#class-texturebutton-property-texture-pressed) | |
Enumerations
------------
enum **StretchMode**:
* **STRETCH\_SCALE** = **0** --- Scale to fit the node's bounding rectangle.
* **STRETCH\_TILE** = **1** --- Tile inside the node's bounding rectangle.
* **STRETCH\_KEEP** = **2** --- The texture keeps its original size and stays in the bounding rectangle's top-left corner.
* **STRETCH\_KEEP\_CENTERED** = **3** --- The texture keeps its original size and stays centered in the node's bounding rectangle.
* **STRETCH\_KEEP\_ASPECT** = **4** --- Scale the texture to fit the node's bounding rectangle, but maintain the texture's aspect ratio.
* **STRETCH\_KEEP\_ASPECT\_CENTERED** = **5** --- Scale the texture to fit the node's bounding rectangle, center it, and maintain its aspect ratio.
* **STRETCH\_KEEP\_ASPECT\_COVERED** = **6** --- Scale the texture so that the shorter side fits the bounding rectangle. The other side clips to the node's limits.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) expand
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_expand(value) |
| *Getter* | get\_expand() |
If `true`, the texture stretches to the edges of the node's bounding rectangle using the [stretch\_mode](#class-texturebutton-property-stretch-mode). If `false`, the texture will not scale with the node.
### [bool](class_bool#class-bool) flip\_h
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flip\_h(value) |
| *Getter* | is\_flipped\_h() |
If `true`, texture is flipped horizontally.
### [bool](class_bool#class-bool) flip\_v
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flip\_v(value) |
| *Getter* | is\_flipped\_v() |
If `true`, texture is flipped vertically.
### [StretchMode](#enum-texturebutton-stretchmode) stretch\_mode
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_stretch\_mode(value) |
| *Getter* | get\_stretch\_mode() |
Controls the texture's behavior when you resize the node's bounding rectangle, **only if** [expand](#class-texturebutton-property-expand) is `true`. Set it to one of the [StretchMode](#enum-texturebutton-stretchmode) constants. See the constants to learn more.
### [BitMap](class_bitmap#class-bitmap) texture\_click\_mask
| | |
| --- | --- |
| *Setter* | set\_click\_mask(value) |
| *Getter* | get\_click\_mask() |
Pure black and white [BitMap](class_bitmap#class-bitmap) image to use for click detection. On the mask, white pixels represent the button's clickable area. Use it to create buttons with curved shapes.
### [Texture](class_texture#class-texture) texture\_disabled
| | |
| --- | --- |
| *Setter* | set\_disabled\_texture(value) |
| *Getter* | get\_disabled\_texture() |
Texture to display when the node is disabled. See [BaseButton.disabled](class_basebutton#class-basebutton-property-disabled).
### [Texture](class_texture#class-texture) texture\_focused
| | |
| --- | --- |
| *Setter* | set\_focused\_texture(value) |
| *Getter* | get\_focused\_texture() |
Texture to display when the node has mouse or keyboard focus.
### [Texture](class_texture#class-texture) texture\_hover
| | |
| --- | --- |
| *Setter* | set\_hover\_texture(value) |
| *Getter* | get\_hover\_texture() |
Texture to display when the mouse hovers the node.
### [Texture](class_texture#class-texture) texture\_normal
| | |
| --- | --- |
| *Setter* | set\_normal\_texture(value) |
| *Getter* | get\_normal\_texture() |
Texture to display by default, when the node is **not** in the disabled, focused, hover or pressed state.
### [Texture](class_texture#class-texture) texture\_pressed
| | |
| --- | --- |
| *Setter* | set\_pressed\_texture(value) |
| *Getter* | get\_pressed\_texture() |
Texture to display on mouse down over the node, if the node has keyboard focus and the player presses the Enter key or if the player presses the [BaseButton.shortcut](class_basebutton#class-basebutton-property-shortcut) key.
| programming_docs |
godot DynamicFontData DynamicFontData
===============
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Used with [DynamicFont](class_dynamicfont#class-dynamicfont) to describe the location of a font file.
Description
-----------
Used with [DynamicFont](class_dynamicfont#class-dynamicfont) to describe the location of a vector font file for dynamic rendering at runtime.
Tutorials
---------
* [3D Voxel Demo](https://godotengine.org/asset-library/asset/676)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [antialiased](#class-dynamicfontdata-property-antialiased) | `true` |
| [String](class_string#class-string) | [font\_path](#class-dynamicfontdata-property-font-path) | `""` |
| [Hinting](#enum-dynamicfontdata-hinting) | [hinting](#class-dynamicfontdata-property-hinting) | `2` |
| [float](class_float#class-float) | [override\_oversampling](#class-dynamicfontdata-property-override-oversampling) | `0.0` |
Enumerations
------------
enum **Hinting**:
* **HINTING\_NONE** = **0** --- Disables font hinting (smoother but less crisp).
* **HINTING\_LIGHT** = **1** --- Use the light font hinting mode.
* **HINTING\_NORMAL** = **2** --- Use the default font hinting mode (crisper but less smooth).
Property Descriptions
---------------------
### [bool](class_bool#class-bool) antialiased
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_antialiased(value) |
| *Getter* | is\_antialiased() |
If `true`, the font is rendered with anti-aliasing. This property applies both to the main font and its outline (if it has one).
### [String](class_string#class-string) font\_path
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_font\_path(value) |
| *Getter* | get\_font\_path() |
The path to the vector font file.
### [Hinting](#enum-dynamicfontdata-hinting) hinting
| | |
| --- | --- |
| *Default* | `2` |
| *Setter* | set\_hinting(value) |
| *Getter* | get\_hinting() |
The font hinting mode used by FreeType. See [Hinting](#enum-dynamicfontdata-hinting) for options.
### [float](class_float#class-float) override\_oversampling
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_override\_oversampling(value) |
| *Getter* | get\_override\_oversampling() |
If set to a value greater than `0.0`, it will override default font oversampling, ignoring [SceneTree.use\_font\_oversampling](class_scenetree#class-scenetree-property-use-font-oversampling) value and viewport stretch mode.
godot Tween Tween
=====
**Inherits:** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Smoothly animates a node's properties over time.
Description
-----------
Tweens are useful for animations requiring a numerical property to be interpolated over a range of values. The name *tween* comes from *in-betweening*, an animation technique where you specify *keyframes* and the computer interpolates the frames that appear between them.
`Tween` is more suited than [AnimationPlayer](class_animationplayer#class-animationplayer) for animations where you don't know the final values in advance. For example, interpolating a dynamically-chosen camera zoom value is best done with a `Tween` node; it would be difficult to do the same thing with an [AnimationPlayer](class_animationplayer#class-animationplayer) node.
Here is a brief usage example that makes a 2D node move smoothly between two positions:
```
var tween = get_node("Tween")
tween.interpolate_property($Node2D, "position",
Vector2(0, 0), Vector2(100, 100), 1,
Tween.TRANS_LINEAR, Tween.EASE_IN_OUT)
tween.start()
```
Many methods require a property name, such as `"position"` above. You can find the correct property name by hovering over the property in the Inspector. You can also provide the components of a property directly by using `"property:component"` (e.g. `position:x`), where it would only apply to that particular component.
Many of the methods accept `trans_type` and `ease_type`. The first accepts an [TransitionType](#enum-tween-transitiontype) constant, and refers to the way the timing of the animation is handled (see [easings.net](https://easings.net/) for some examples). The second accepts an [EaseType](#enum-tween-easetype) constant, and controls where the `trans_type` is applied to the interpolation (in the beginning, the end, or both). If you don't know which transition and easing to pick, you can try different [TransitionType](#enum-tween-transitiontype) constants with [EASE\_IN\_OUT](#class-tween-constant-ease-in-out), and use the one that looks best.
[Tween easing and transition types cheatsheet](https://raw.githubusercontent.com/godotengine/godot-docs/master/img/tween_cheatsheet.png)
**Note:** Tween methods will return `false` if the requested operation cannot be completed.
**Note:** For an alternative method of tweening, that doesn't require using nodes, see [SceneTreeTween](class_scenetreetween#class-scenetreetween).
Properties
----------
| | | |
| --- | --- | --- |
| [TweenProcessMode](#enum-tween-tweenprocessmode) | [playback\_process\_mode](#class-tween-property-playback-process-mode) | `1` |
| [float](class_float#class-float) | [playback\_speed](#class-tween-property-playback-speed) | `1.0` |
| [bool](class_bool#class-bool) | [repeat](#class-tween-property-repeat) | `false` |
Methods
-------
| | |
| --- | --- |
| [bool](class_bool#class-bool) | [follow\_method](#class-tween-method-follow-method) **(** [Object](class_object#class-object) object, [String](class_string#class-string) method, [Variant](class_variant#class-variant) initial\_val, [Object](class_object#class-object) target, [String](class_string#class-string) target\_method, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 **)** |
| [bool](class_bool#class-bool) | [follow\_property](#class-tween-method-follow-property) **(** [Object](class_object#class-object) object, [NodePath](class_nodepath#class-nodepath) property, [Variant](class_variant#class-variant) initial\_val, [Object](class_object#class-object) target, [NodePath](class_nodepath#class-nodepath) target\_property, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 **)** |
| [float](class_float#class-float) | [get\_runtime](#class-tween-method-get-runtime) **(** **)** const |
| [bool](class_bool#class-bool) | [interpolate\_callback](#class-tween-method-interpolate-callback) **(** [Object](class_object#class-object) object, [float](class_float#class-float) duration, [String](class_string#class-string) callback, [Variant](class_variant#class-variant) arg1=null, [Variant](class_variant#class-variant) arg2=null, [Variant](class_variant#class-variant) arg3=null, [Variant](class_variant#class-variant) arg4=null, [Variant](class_variant#class-variant) arg5=null, [Variant](class_variant#class-variant) arg6=null, [Variant](class_variant#class-variant) arg7=null, [Variant](class_variant#class-variant) arg8=null **)** |
| [bool](class_bool#class-bool) | [interpolate\_deferred\_callback](#class-tween-method-interpolate-deferred-callback) **(** [Object](class_object#class-object) object, [float](class_float#class-float) duration, [String](class_string#class-string) callback, [Variant](class_variant#class-variant) arg1=null, [Variant](class_variant#class-variant) arg2=null, [Variant](class_variant#class-variant) arg3=null, [Variant](class_variant#class-variant) arg4=null, [Variant](class_variant#class-variant) arg5=null, [Variant](class_variant#class-variant) arg6=null, [Variant](class_variant#class-variant) arg7=null, [Variant](class_variant#class-variant) arg8=null **)** |
| [bool](class_bool#class-bool) | [interpolate\_method](#class-tween-method-interpolate-method) **(** [Object](class_object#class-object) object, [String](class_string#class-string) method, [Variant](class_variant#class-variant) initial\_val, [Variant](class_variant#class-variant) final\_val, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 **)** |
| [bool](class_bool#class-bool) | [interpolate\_property](#class-tween-method-interpolate-property) **(** [Object](class_object#class-object) object, [NodePath](class_nodepath#class-nodepath) property, [Variant](class_variant#class-variant) initial\_val, [Variant](class_variant#class-variant) final\_val, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 **)** |
| [bool](class_bool#class-bool) | [is\_active](#class-tween-method-is-active) **(** **)** const |
| [bool](class_bool#class-bool) | [remove](#class-tween-method-remove) **(** [Object](class_object#class-object) object, [String](class_string#class-string) key="" **)** |
| [bool](class_bool#class-bool) | [remove\_all](#class-tween-method-remove-all) **(** **)** |
| [bool](class_bool#class-bool) | [reset](#class-tween-method-reset) **(** [Object](class_object#class-object) object, [String](class_string#class-string) key="" **)** |
| [bool](class_bool#class-bool) | [reset\_all](#class-tween-method-reset-all) **(** **)** |
| [bool](class_bool#class-bool) | [resume](#class-tween-method-resume) **(** [Object](class_object#class-object) object, [String](class_string#class-string) key="" **)** |
| [bool](class_bool#class-bool) | [resume\_all](#class-tween-method-resume-all) **(** **)** |
| [bool](class_bool#class-bool) | [seek](#class-tween-method-seek) **(** [float](class_float#class-float) time **)** |
| void | [set\_active](#class-tween-method-set-active) **(** [bool](class_bool#class-bool) active **)** |
| [bool](class_bool#class-bool) | [start](#class-tween-method-start) **(** **)** |
| [bool](class_bool#class-bool) | [stop](#class-tween-method-stop) **(** [Object](class_object#class-object) object, [String](class_string#class-string) key="" **)** |
| [bool](class_bool#class-bool) | [stop\_all](#class-tween-method-stop-all) **(** **)** |
| [bool](class_bool#class-bool) | [targeting\_method](#class-tween-method-targeting-method) **(** [Object](class_object#class-object) object, [String](class_string#class-string) method, [Object](class_object#class-object) initial, [String](class_string#class-string) initial\_method, [Variant](class_variant#class-variant) final\_val, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 **)** |
| [bool](class_bool#class-bool) | [targeting\_property](#class-tween-method-targeting-property) **(** [Object](class_object#class-object) object, [NodePath](class_nodepath#class-nodepath) property, [Object](class_object#class-object) initial, [NodePath](class_nodepath#class-nodepath) initial\_val, [Variant](class_variant#class-variant) final\_val, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 **)** |
| [float](class_float#class-float) | [tell](#class-tween-method-tell) **(** **)** const |
Signals
-------
### tween\_all\_completed ( )
Emitted when all processes in a tween end.
### tween\_completed ( [Object](class_object#class-object) object, [NodePath](class_nodepath#class-nodepath) key )
Emitted when a tween ends.
### tween\_started ( [Object](class_object#class-object) object, [NodePath](class_nodepath#class-nodepath) key )
Emitted when a tween starts.
### tween\_step ( [Object](class_object#class-object) object, [NodePath](class_nodepath#class-nodepath) key, [float](class_float#class-float) elapsed, [Object](class_object#class-object) value )
Emitted at each step of the animation.
Enumerations
------------
enum **TweenProcessMode**:
* **TWEEN\_PROCESS\_PHYSICS** = **0** --- The tween updates with the `_physics_process` callback.
* **TWEEN\_PROCESS\_IDLE** = **1** --- The tween updates with the `_process` callback.
enum **TransitionType**:
* **TRANS\_LINEAR** = **0** --- The animation is interpolated linearly.
* **TRANS\_SINE** = **1** --- The animation is interpolated using a sine function.
* **TRANS\_QUINT** = **2** --- The animation is interpolated with a quintic (to the power of 5) function.
* **TRANS\_QUART** = **3** --- The animation is interpolated with a quartic (to the power of 4) function.
* **TRANS\_QUAD** = **4** --- The animation is interpolated with a quadratic (to the power of 2) function.
* **TRANS\_EXPO** = **5** --- The animation is interpolated with an exponential (to the power of x) function.
* **TRANS\_ELASTIC** = **6** --- The animation is interpolated with elasticity, wiggling around the edges.
* **TRANS\_CUBIC** = **7** --- The animation is interpolated with a cubic (to the power of 3) function.
* **TRANS\_CIRC** = **8** --- The animation is interpolated with a function using square roots.
* **TRANS\_BOUNCE** = **9** --- The animation is interpolated by bouncing at the end.
* **TRANS\_BACK** = **10** --- The animation is interpolated backing out at ends.
enum **EaseType**:
* **EASE\_IN** = **0** --- The interpolation starts slowly and speeds up towards the end.
* **EASE\_OUT** = **1** --- The interpolation starts quickly and slows down towards the end.
* **EASE\_IN\_OUT** = **2** --- A combination of [EASE\_IN](#class-tween-constant-ease-in) and [EASE\_OUT](#class-tween-constant-ease-out). The interpolation is slowest at both ends.
* **EASE\_OUT\_IN** = **3** --- A combination of [EASE\_IN](#class-tween-constant-ease-in) and [EASE\_OUT](#class-tween-constant-ease-out). The interpolation is fastest at both ends.
Property Descriptions
---------------------
### [TweenProcessMode](#enum-tween-tweenprocessmode) playback\_process\_mode
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_tween\_process\_mode(value) |
| *Getter* | get\_tween\_process\_mode() |
The tween's animation process thread. See [TweenProcessMode](#enum-tween-tweenprocessmode).
### [float](class_float#class-float) playback\_speed
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_speed\_scale(value) |
| *Getter* | get\_speed\_scale() |
The tween's speed multiplier. For example, set it to `1.0` for normal speed, `2.0` for two times normal speed, or `0.5` for half of the normal speed. A value of `0` pauses the animation, but see also [set\_active](#class-tween-method-set-active) or [stop\_all](#class-tween-method-stop-all) for this.
### [bool](class_bool#class-bool) repeat
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_repeat(value) |
| *Getter* | is\_repeat() |
If `true`, the tween loops.
Method Descriptions
-------------------
### [bool](class_bool#class-bool) follow\_method ( [Object](class_object#class-object) object, [String](class_string#class-string) method, [Variant](class_variant#class-variant) initial\_val, [Object](class_object#class-object) target, [String](class_string#class-string) target\_method, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 )
Follows `method` of `object` and applies the returned value on `target_method` of `target`, beginning from `initial_val` for `duration` seconds, `delay` later. Methods are called with consecutive values.
Use [TransitionType](#enum-tween-transitiontype) for `trans_type` and [EaseType](#enum-tween-easetype) for `ease_type` parameters. These values control the timing and direction of the interpolation. See the class description for more information.
### [bool](class_bool#class-bool) follow\_property ( [Object](class_object#class-object) object, [NodePath](class_nodepath#class-nodepath) property, [Variant](class_variant#class-variant) initial\_val, [Object](class_object#class-object) target, [NodePath](class_nodepath#class-nodepath) target\_property, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 )
Follows `property` of `object` and applies it on `target_property` of `target`, beginning from `initial_val` for `duration` seconds, `delay` seconds later.
Use [TransitionType](#enum-tween-transitiontype) for `trans_type` and [EaseType](#enum-tween-easetype) for `ease_type` parameters. These values control the timing and direction of the interpolation. See the class description for more information.
### [float](class_float#class-float) get\_runtime ( ) const
Returns the total time needed for all tweens to end. If you have two tweens, one lasting 10 seconds and the other 20 seconds, it would return 20 seconds, as by that time all tweens would have finished.
### [bool](class_bool#class-bool) interpolate\_callback ( [Object](class_object#class-object) object, [float](class_float#class-float) duration, [String](class_string#class-string) callback, [Variant](class_variant#class-variant) arg1=null, [Variant](class_variant#class-variant) arg2=null, [Variant](class_variant#class-variant) arg3=null, [Variant](class_variant#class-variant) arg4=null, [Variant](class_variant#class-variant) arg5=null, [Variant](class_variant#class-variant) arg6=null, [Variant](class_variant#class-variant) arg7=null, [Variant](class_variant#class-variant) arg8=null )
Calls `callback` of `object` after `duration`. `arg1`-`arg5` are arguments to be passed to the callback.
### [bool](class_bool#class-bool) interpolate\_deferred\_callback ( [Object](class_object#class-object) object, [float](class_float#class-float) duration, [String](class_string#class-string) callback, [Variant](class_variant#class-variant) arg1=null, [Variant](class_variant#class-variant) arg2=null, [Variant](class_variant#class-variant) arg3=null, [Variant](class_variant#class-variant) arg4=null, [Variant](class_variant#class-variant) arg5=null, [Variant](class_variant#class-variant) arg6=null, [Variant](class_variant#class-variant) arg7=null, [Variant](class_variant#class-variant) arg8=null )
Calls `callback` of `object` after `duration` on the main thread (similar to [Object.call\_deferred](class_object#class-object-method-call-deferred)). `arg1`-`arg5` are arguments to be passed to the callback.
### [bool](class_bool#class-bool) interpolate\_method ( [Object](class_object#class-object) object, [String](class_string#class-string) method, [Variant](class_variant#class-variant) initial\_val, [Variant](class_variant#class-variant) final\_val, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 )
Animates `method` of `object` from `initial_val` to `final_val` for `duration` seconds, `delay` seconds later. Methods are called with consecutive values.
Use [TransitionType](#enum-tween-transitiontype) for `trans_type` and [EaseType](#enum-tween-easetype) for `ease_type` parameters. These values control the timing and direction of the interpolation. See the class description for more information.
### [bool](class_bool#class-bool) interpolate\_property ( [Object](class_object#class-object) object, [NodePath](class_nodepath#class-nodepath) property, [Variant](class_variant#class-variant) initial\_val, [Variant](class_variant#class-variant) final\_val, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 )
Animates `property` of `object` from `initial_val` to `final_val` for `duration` seconds, `delay` seconds later. Setting the initial value to `null` uses the current value of the property.
Use [TransitionType](#enum-tween-transitiontype) for `trans_type` and [EaseType](#enum-tween-easetype) for `ease_type` parameters. These values control the timing and direction of the interpolation. See the class description for more information.
### [bool](class_bool#class-bool) is\_active ( ) const
Returns `true` if any tweens are currently running.
**Note:** This method doesn't consider tweens that have ended.
### [bool](class_bool#class-bool) remove ( [Object](class_object#class-object) object, [String](class_string#class-string) key="" )
Stops animation and removes a tween, given its object and property/method pair. By default, all tweens are removed, unless `key` is specified.
### [bool](class_bool#class-bool) remove\_all ( )
Stops animation and removes all tweens.
### [bool](class_bool#class-bool) reset ( [Object](class_object#class-object) object, [String](class_string#class-string) key="" )
Resets a tween to its initial value (the one given, not the one before the tween), given its object and property/method pair. By default, all tweens are reset, unless `key` is specified.
### [bool](class_bool#class-bool) reset\_all ( )
Resets all tweens to their initial values (the ones given, not those before the tween).
### [bool](class_bool#class-bool) resume ( [Object](class_object#class-object) object, [String](class_string#class-string) key="" )
Continues animating a stopped tween, given its object and property/method pair. By default, all tweens are resumed, unless `key` is specified.
### [bool](class_bool#class-bool) resume\_all ( )
Continues animating all stopped tweens.
### [bool](class_bool#class-bool) seek ( [float](class_float#class-float) time )
Sets the interpolation to the given `time` in seconds.
### void set\_active ( [bool](class_bool#class-bool) active )
Activates/deactivates the tween. See also [stop\_all](#class-tween-method-stop-all) and [resume\_all](#class-tween-method-resume-all).
### [bool](class_bool#class-bool) start ( )
Starts the tween. You can define animations both before and after this.
### [bool](class_bool#class-bool) stop ( [Object](class_object#class-object) object, [String](class_string#class-string) key="" )
Stops a tween, given its object and property/method pair. By default, all tweens are stopped, unless `key` is specified.
### [bool](class_bool#class-bool) stop\_all ( )
Stops animating all tweens.
### [bool](class_bool#class-bool) targeting\_method ( [Object](class_object#class-object) object, [String](class_string#class-string) method, [Object](class_object#class-object) initial, [String](class_string#class-string) initial\_method, [Variant](class_variant#class-variant) final\_val, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 )
Animates `method` of `object` from the value returned by `initial_method` to `final_val` for `duration` seconds, `delay` seconds later. Methods are animated by calling them with consecutive values.
Use [TransitionType](#enum-tween-transitiontype) for `trans_type` and [EaseType](#enum-tween-easetype) for `ease_type` parameters. These values control the timing and direction of the interpolation. See the class description for more information.
### [bool](class_bool#class-bool) targeting\_property ( [Object](class_object#class-object) object, [NodePath](class_nodepath#class-nodepath) property, [Object](class_object#class-object) initial, [NodePath](class_nodepath#class-nodepath) initial\_val, [Variant](class_variant#class-variant) final\_val, [float](class_float#class-float) duration, [TransitionType](#enum-tween-transitiontype) trans\_type=0, [EaseType](#enum-tween-easetype) ease\_type=2, [float](class_float#class-float) delay=0 )
Animates `property` of `object` from the current value of the `initial_val` property of `initial` to `final_val` for `duration` seconds, `delay` seconds later.
Use [TransitionType](#enum-tween-transitiontype) for `trans_type` and [EaseType](#enum-tween-easetype) for `ease_type` parameters. These values control the timing and direction of the interpolation. See the class description for more information.
### [float](class_float#class-float) tell ( ) const
Returns the current time of the tween.
| programming_docs |
godot EditorSpinSlider EditorSpinSlider
================
**Inherits:** [Range](class_range#class-range) **<** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Godot editor's control for editing numeric values.
Description
-----------
This [Control](class_control#class-control) node is used in the editor's Inspector dock to allow editing of numeric values. Can be used with [EditorInspectorPlugin](class_editorinspectorplugin#class-editorinspectorplugin) to recreate the same behavior.
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [flat](#class-editorspinslider-property-flat) | `false` |
| [FocusMode](class_control#enum-control-focusmode) | focus\_mode | `2` (overrides [Control](class_control#class-control-property-focus-mode)) |
| [bool](class_bool#class-bool) | [hide\_slider](#class-editorspinslider-property-hide-slider) | `false` |
| [String](class_string#class-string) | [label](#class-editorspinslider-property-label) | `""` |
| [bool](class_bool#class-bool) | [read\_only](#class-editorspinslider-property-read-only) | `false` |
Property Descriptions
---------------------
### [bool](class_bool#class-bool) flat
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flat(value) |
| *Getter* | is\_flat() |
### [bool](class_bool#class-bool) hide\_slider
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_hide\_slider(value) |
| *Getter* | is\_hiding\_slider() |
If `true`, the slider is hidden.
### [String](class_string#class-string) label
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_label(value) |
| *Getter* | get\_label() |
### [bool](class_bool#class-bool) read\_only
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_read\_only(value) |
| *Getter* | is\_read\_only() |
godot AudioEffectReverb AudioEffectReverb
=================
**Inherits:** [AudioEffect](class_audioeffect#class-audioeffect) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Adds a reverberation audio effect to an Audio bus.
Simulates the sound of acoustic environments such as rooms, concert halls, caverns, or an open spaces.
Description
-----------
Simulates rooms of different sizes. Its parameters can be adjusted to simulate the sound of a specific room.
Tutorials
---------
* [Third Person Shooter Demo](https://godotengine.org/asset-library/asset/678)
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [damping](#class-audioeffectreverb-property-damping) | `0.5` |
| [float](class_float#class-float) | [dry](#class-audioeffectreverb-property-dry) | `1.0` |
| [float](class_float#class-float) | [hipass](#class-audioeffectreverb-property-hipass) | `0.0` |
| [float](class_float#class-float) | [predelay\_feedback](#class-audioeffectreverb-property-predelay-feedback) | `0.4` |
| [float](class_float#class-float) | [predelay\_msec](#class-audioeffectreverb-property-predelay-msec) | `150.0` |
| [float](class_float#class-float) | [room\_size](#class-audioeffectreverb-property-room-size) | `0.8` |
| [float](class_float#class-float) | [spread](#class-audioeffectreverb-property-spread) | `1.0` |
| [float](class_float#class-float) | [wet](#class-audioeffectreverb-property-wet) | `0.5` |
Property Descriptions
---------------------
### [float](class_float#class-float) damping
| | |
| --- | --- |
| *Default* | `0.5` |
| *Setter* | set\_damping(value) |
| *Getter* | get\_damping() |
Defines how reflective the imaginary room's walls are. Value can range from 0 to 1.
### [float](class_float#class-float) dry
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_dry(value) |
| *Getter* | get\_dry() |
Output percent of original sound. At 0, only modified sound is outputted. Value can range from 0 to 1.
### [float](class_float#class-float) hipass
| | |
| --- | --- |
| *Default* | `0.0` |
| *Setter* | set\_hpf(value) |
| *Getter* | get\_hpf() |
High-pass filter passes signals with a frequency higher than a certain cutoff frequency and attenuates signals with frequencies lower than the cutoff frequency. Value can range from 0 to 1.
### [float](class_float#class-float) predelay\_feedback
| | |
| --- | --- |
| *Default* | `0.4` |
| *Setter* | set\_predelay\_feedback(value) |
| *Getter* | get\_predelay\_feedback() |
Output percent of predelay. Value can range from 0 to 1.
### [float](class_float#class-float) predelay\_msec
| | |
| --- | --- |
| *Default* | `150.0` |
| *Setter* | set\_predelay\_msec(value) |
| *Getter* | get\_predelay\_msec() |
Time between the original signal and the early reflections of the reverb signal, in milliseconds.
### [float](class_float#class-float) room\_size
| | |
| --- | --- |
| *Default* | `0.8` |
| *Setter* | set\_room\_size(value) |
| *Getter* | get\_room\_size() |
Dimensions of simulated room. Bigger means more echoes. Value can range from 0 to 1.
### [float](class_float#class-float) spread
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_spread(value) |
| *Getter* | get\_spread() |
Widens or narrows the stereo image of the reverb tail. 1 means fully widens. Value can range from 0 to 1.
### [float](class_float#class-float) wet
| | |
| --- | --- |
| *Default* | `0.5` |
| *Setter* | set\_wet(value) |
| *Getter* | get\_wet() |
Output percent of modified sound. At 0, only original sound is outputted. Value can range from 0 to 1.
godot CallbackTweener CallbackTweener
===============
**Inherits:** [Tweener](class_tweener#class-tweener) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Calls the specified method after optional delay.
Description
-----------
`CallbackTweener` is used to call a method in a tweening sequence. See [SceneTreeTween.tween\_callback](class_scenetreetween#class-scenetreetween-method-tween-callback) for more usage information.
**Note:** [SceneTreeTween.tween\_callback](class_scenetreetween#class-scenetreetween-method-tween-callback) is the only correct way to create `CallbackTweener`. Any `CallbackTweener` created manually will not function correctly.
Methods
-------
| | |
| --- | --- |
| [CallbackTweener](#class-callbacktweener) | [set\_delay](#class-callbacktweener-method-set-delay) **(** [float](class_float#class-float) delay **)** |
Method Descriptions
-------------------
### [CallbackTweener](#class-callbacktweener) set\_delay ( [float](class_float#class-float) delay )
Makes the callback call delayed by given time in seconds. Example:
```
var tween = get_tree().create_tween()
tween.tween_callback(queue_free).set_delay(2) #this will call queue_free() after 2 seconds
```
godot HashingContext HashingContext
==============
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Context to compute cryptographic hashes over multiple iterations.
Description
-----------
The HashingContext class provides an interface for computing cryptographic hashes over multiple iterations. This is useful for example when computing hashes of big files (so you don't have to load them all in memory), network streams, and data streams in general (so you don't have to hold buffers).
The [HashType](#enum-hashingcontext-hashtype) enum shows the supported hashing algorithms.
```
const CHUNK_SIZE = 1024
func hash_file(path):
var ctx = HashingContext.new()
var file = File.new()
# Start a SHA-256 context.
ctx.start(HashingContext.HASH_SHA256)
# Check that file exists.
if not file.file_exists(path):
return
# Open the file to hash.
file.open(path, File.READ)
# Update the context after reading each chunk.
while not file.eof_reached():
ctx.update(file.get_buffer(CHUNK_SIZE))
# Get the computed hash.
var res = ctx.finish()
# Print the result as hex string and array.
printt(res.hex_encode(), Array(res))
```
Methods
-------
| | |
| --- | --- |
| [PoolByteArray](class_poolbytearray#class-poolbytearray) | [finish](#class-hashingcontext-method-finish) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [start](#class-hashingcontext-method-start) **(** [HashType](#enum-hashingcontext-hashtype) type **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [update](#class-hashingcontext-method-update) **(** [PoolByteArray](class_poolbytearray#class-poolbytearray) chunk **)** |
Enumerations
------------
enum **HashType**:
* **HASH\_MD5** = **0** --- Hashing algorithm: MD5.
* **HASH\_SHA1** = **1** --- Hashing algorithm: SHA-1.
* **HASH\_SHA256** = **2** --- Hashing algorithm: SHA-256.
Method Descriptions
-------------------
### [PoolByteArray](class_poolbytearray#class-poolbytearray) finish ( )
Closes the current context, and return the computed hash.
### [Error](class_%40globalscope#enum-globalscope-error) start ( [HashType](#enum-hashingcontext-hashtype) type )
Starts a new hash computation of the given `type` (e.g. [HASH\_SHA256](#class-hashingcontext-constant-hash-sha256) to start computation of a SHA-256).
### [Error](class_%40globalscope#enum-globalscope-error) update ( [PoolByteArray](class_poolbytearray#class-poolbytearray) chunk )
Updates the computation with the given `chunk` of data.
godot ResourceSaver ResourceSaver
=============
**Inherits:** [Object](class_object#class-object)
Singleton for saving Godot-specific resource types.
Description
-----------
Singleton for saving Godot-specific resource types to the filesystem.
It uses the many [ResourceFormatSaver](class_resourceformatsaver#class-resourceformatsaver) classes registered in the engine (either built-in or from a plugin) to save engine-specific resource data to text-based (e.g. `.tres` or `.tscn`) or binary files (e.g. `.res` or `.scn`).
Methods
-------
| | |
| --- | --- |
| [PoolStringArray](class_poolstringarray#class-poolstringarray) | [get\_recognized\_extensions](#class-resourcesaver-method-get-recognized-extensions) **(** [Resource](class_resource#class-resource) type **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [save](#class-resourcesaver-method-save) **(** [String](class_string#class-string) path, [Resource](class_resource#class-resource) resource, [SaverFlags](#enum-resourcesaver-saverflags) flags=0 **)** |
Enumerations
------------
enum **SaverFlags**:
* **FLAG\_RELATIVE\_PATHS** = **1** --- Save the resource with a path relative to the scene which uses it.
* **FLAG\_BUNDLE\_RESOURCES** = **2** --- Bundles external resources.
* **FLAG\_CHANGE\_PATH** = **4** --- Changes the [Resource.resource\_path](class_resource#class-resource-property-resource-path) of the saved resource to match its new location.
* **FLAG\_OMIT\_EDITOR\_PROPERTIES** = **8** --- Do not save editor-specific metadata (identified by their `__editor` prefix).
* **FLAG\_SAVE\_BIG\_ENDIAN** = **16** --- Save as big endian (see [File.endian\_swap](class_file#class-file-property-endian-swap)).
* **FLAG\_COMPRESS** = **32** --- Compress the resource on save using [File.COMPRESSION\_ZSTD](class_file#class-file-constant-compression-zstd). Only available for binary resource types.
* **FLAG\_REPLACE\_SUBRESOURCE\_PATHS** = **64** --- Take over the paths of the saved subresources (see [Resource.take\_over\_path](class_resource#class-resource-method-take-over-path)).
Method Descriptions
-------------------
### [PoolStringArray](class_poolstringarray#class-poolstringarray) get\_recognized\_extensions ( [Resource](class_resource#class-resource) type )
Returns the list of extensions available for saving a resource of a given type.
### [Error](class_%40globalscope#enum-globalscope-error) save ( [String](class_string#class-string) path, [Resource](class_resource#class-resource) resource, [SaverFlags](#enum-resourcesaver-saverflags) flags=0 )
Saves a resource to disk to the given path, using a [ResourceFormatSaver](class_resourceformatsaver#class-resourceformatsaver) that recognizes the resource object.
The `flags` bitmask can be specified to customize the save behavior.
Returns [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok) on success.
godot Directory Directory
=========
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Type used to handle the filesystem.
Description
-----------
Directory type. It is used to manage directories and their content (not restricted to the project folder).
When creating a new `Directory`, its default opened directory will be `res://`. This may change in the future, so it is advised to always use [open](#class-directory-method-open) to initialize your `Directory` where you want to operate, with explicit error checking.
**Note:** Many resources types are imported (e.g. textures or sound files), and their source asset will not be included in the exported game, as only the imported version is used. Use [ResourceLoader](class_resourceloader#class-resourceloader) to access imported resources.
Here is an example on how to iterate through the files of a directory:
```
func dir_contents(path):
var dir = Directory.new()
if dir.open(path) == OK:
dir.list_dir_begin()
var file_name = dir.get_next()
while file_name != "":
if dir.current_is_dir():
print("Found directory: " + file_name)
else:
print("Found file: " + file_name)
file_name = dir.get_next()
else:
print("An error occurred when trying to access the path.")
```
Tutorials
---------
* [File system](https://docs.godotengine.org/en/3.5/tutorials/scripting/filesystem.html)
Methods
-------
| | |
| --- | --- |
| [Error](class_%40globalscope#enum-globalscope-error) | [change\_dir](#class-directory-method-change-dir) **(** [String](class_string#class-string) todir **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [copy](#class-directory-method-copy) **(** [String](class_string#class-string) from, [String](class_string#class-string) to **)** |
| [bool](class_bool#class-bool) | [current\_is\_dir](#class-directory-method-current-is-dir) **(** **)** const |
| [bool](class_bool#class-bool) | [dir\_exists](#class-directory-method-dir-exists) **(** [String](class_string#class-string) path **)** |
| [bool](class_bool#class-bool) | [file\_exists](#class-directory-method-file-exists) **(** [String](class_string#class-string) path **)** |
| [String](class_string#class-string) | [get\_current\_dir](#class-directory-method-get-current-dir) **(** **)** |
| [int](class_int#class-int) | [get\_current\_drive](#class-directory-method-get-current-drive) **(** **)** |
| [String](class_string#class-string) | [get\_drive](#class-directory-method-get-drive) **(** [int](class_int#class-int) idx **)** |
| [int](class_int#class-int) | [get\_drive\_count](#class-directory-method-get-drive-count) **(** **)** |
| [String](class_string#class-string) | [get\_next](#class-directory-method-get-next) **(** **)** |
| [int](class_int#class-int) | [get\_space\_left](#class-directory-method-get-space-left) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [list\_dir\_begin](#class-directory-method-list-dir-begin) **(** [bool](class_bool#class-bool) skip\_navigational=false, [bool](class_bool#class-bool) skip\_hidden=false **)** |
| void | [list\_dir\_end](#class-directory-method-list-dir-end) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [make\_dir](#class-directory-method-make-dir) **(** [String](class_string#class-string) path **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [make\_dir\_recursive](#class-directory-method-make-dir-recursive) **(** [String](class_string#class-string) path **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [open](#class-directory-method-open) **(** [String](class_string#class-string) path **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [remove](#class-directory-method-remove) **(** [String](class_string#class-string) path **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [rename](#class-directory-method-rename) **(** [String](class_string#class-string) from, [String](class_string#class-string) to **)** |
Method Descriptions
-------------------
### [Error](class_%40globalscope#enum-globalscope-error) change\_dir ( [String](class_string#class-string) todir )
Changes the currently opened directory to the one passed as an argument. The argument can be relative to the current directory (e.g. `newdir` or `../newdir`), or an absolute path (e.g. `/tmp/newdir` or `res://somedir/newdir`).
Returns one of the [Error](class_%40globalscope#enum-globalscope-error) code constants (`OK` on success).
### [Error](class_%40globalscope#enum-globalscope-error) copy ( [String](class_string#class-string) from, [String](class_string#class-string) to )
Copies the `from` file to the `to` destination. Both arguments should be paths to files, either relative or absolute. If the destination file exists and is not access-protected, it will be overwritten.
Returns one of the [Error](class_%40globalscope#enum-globalscope-error) code constants (`OK` on success).
### [bool](class_bool#class-bool) current\_is\_dir ( ) const
Returns whether the current item processed with the last [get\_next](#class-directory-method-get-next) call is a directory (`.` and `..` are considered directories).
### [bool](class_bool#class-bool) dir\_exists ( [String](class_string#class-string) path )
Returns whether the target directory exists. The argument can be relative to the current directory, or an absolute path.
### [bool](class_bool#class-bool) file\_exists ( [String](class_string#class-string) path )
Returns whether the target file exists. The argument can be relative to the current directory, or an absolute path.
### [String](class_string#class-string) get\_current\_dir ( )
Returns the absolute path to the currently opened directory (e.g. `res://folder` or `C:\tmp\folder`).
### [int](class_int#class-int) get\_current\_drive ( )
Returns the currently opened directory's drive index. See [get\_drive](#class-directory-method-get-drive) to convert returned index to the name of the drive.
### [String](class_string#class-string) get\_drive ( [int](class_int#class-int) idx )
On Windows, returns the name of the drive (partition) passed as an argument (e.g. `C:`).
On macOS, returns the path to the mounted volume passed as an argument.
On Linux, returns the path to the mounted volume or GTK 3 bookmark passed as an argument.
On other platforms, or if the requested drive does not exist, the method returns an empty String.
### [int](class_int#class-int) get\_drive\_count ( )
On Windows, returns the number of drives (partitions) mounted on the current filesystem.
On macOS, returns the number of mounted volumes.
On Linux, returns the number of mounted volumes and GTK 3 bookmarks.
On other platforms, the method returns 0.
### [String](class_string#class-string) get\_next ( )
Returns the next element (file or directory) in the current directory (including `.` and `..`, unless `skip_navigational` was given to [list\_dir\_begin](#class-directory-method-list-dir-begin)).
The name of the file or directory is returned (and not its full path). Once the stream has been fully processed, the method returns an empty String and closes the stream automatically (i.e. [list\_dir\_end](#class-directory-method-list-dir-end) would not be mandatory in such a case).
### [int](class_int#class-int) get\_space\_left ( )
On UNIX desktop systems, returns the available space on the current directory's disk. On other platforms, this information is not available and the method returns 0 or -1.
### [Error](class_%40globalscope#enum-globalscope-error) list\_dir\_begin ( [bool](class_bool#class-bool) skip\_navigational=false, [bool](class_bool#class-bool) skip\_hidden=false )
Initializes the stream used to list all files and directories using the [get\_next](#class-directory-method-get-next) function, closing the currently opened stream if needed. Once the stream has been processed, it should typically be closed with [list\_dir\_end](#class-directory-method-list-dir-end).
If `skip_navigational` is `true`, `.` and `..` are filtered out.
If `skip_hidden` is `true`, hidden files are filtered out.
### void list\_dir\_end ( )
Closes the current stream opened with [list\_dir\_begin](#class-directory-method-list-dir-begin) (whether it has been fully processed with [get\_next](#class-directory-method-get-next) does not matter).
### [Error](class_%40globalscope#enum-globalscope-error) make\_dir ( [String](class_string#class-string) path )
Creates a directory. The argument can be relative to the current directory, or an absolute path. The target directory should be placed in an already existing directory (to create the full path recursively, see [make\_dir\_recursive](#class-directory-method-make-dir-recursive)).
Returns one of the [Error](class_%40globalscope#enum-globalscope-error) code constants (`OK` on success).
### [Error](class_%40globalscope#enum-globalscope-error) make\_dir\_recursive ( [String](class_string#class-string) path )
Creates a target directory and all necessary intermediate directories in its path, by calling [make\_dir](#class-directory-method-make-dir) recursively. The argument can be relative to the current directory, or an absolute path.
Returns one of the [Error](class_%40globalscope#enum-globalscope-error) code constants (`OK` on success).
### [Error](class_%40globalscope#enum-globalscope-error) open ( [String](class_string#class-string) path )
Opens an existing directory of the filesystem. The `path` argument can be within the project tree (`res://folder`), the user directory (`user://folder`) or an absolute path of the user filesystem (e.g. `/tmp/folder` or `C:\tmp\folder`).
Returns one of the [Error](class_%40globalscope#enum-globalscope-error) code constants (`OK` on success).
### [Error](class_%40globalscope#enum-globalscope-error) remove ( [String](class_string#class-string) path )
Permanently deletes the target file or an empty directory. The argument can be relative to the current directory, or an absolute path. If the target directory is not empty, the operation will fail.
If you don't want to delete the file/directory permanently, use [OS.move\_to\_trash](class_os#class-os-method-move-to-trash) instead.
Returns one of the [Error](class_%40globalscope#enum-globalscope-error) code constants (`OK` on success).
### [Error](class_%40globalscope#enum-globalscope-error) rename ( [String](class_string#class-string) from, [String](class_string#class-string) to )
Renames (move) the `from` file or directory to the `to` destination. Both arguments should be paths to files or directories, either relative or absolute. If the destination file or directory exists and is not access-protected, it will be overwritten.
Returns one of the [Error](class_%40globalscope#enum-globalscope-error) code constants (`OK` on success).
| programming_docs |
godot VisualScriptSequence VisualScriptSequence
====================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Executes a series of Sequence ports.
Description
-----------
Steps through a series of one or more output Sequence ports. The `current` data port outputs the currently executing item.
**Input Ports:**
* Sequence: `in order`
**Output Ports:**
* Sequence: `1`
* Sequence: `2 - n` (optional)
* Data (int): `current`
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | [steps](#class-visualscriptsequence-property-steps) | `1` |
Property Descriptions
---------------------
### [int](class_int#class-int) steps
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_steps(value) |
| *Getter* | get\_steps() |
The number of steps in the sequence.
godot AnimatedSprite AnimatedSprite
==============
**Inherits:** [Node2D](class_node2d#class-node2d) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Sprite node that contains multiple textures as frames to play for animation.
Description
-----------
`AnimatedSprite` is similar to the [Sprite](class_sprite#class-sprite) node, except it carries multiple textures as animation frames. Animations are created using a [SpriteFrames](class_spriteframes#class-spriteframes) resource, which allows you to import image files (or a folder containing said files) to provide the animation frames for the sprite. The [SpriteFrames](class_spriteframes#class-spriteframes) resource can be configured in the editor via the SpriteFrames bottom panel.
**Note:** You can associate a set of normal or specular maps by creating additional [SpriteFrames](class_spriteframes#class-spriteframes) resources with a `_normal` or `_specular` suffix. For example, having 3 [SpriteFrames](class_spriteframes#class-spriteframes) resources `run`, `run_normal`, and `run_specular` will make it so the `run` animation uses normal and specular maps.
Tutorials
---------
* [2D Sprite animation](https://docs.godotengine.org/en/3.5/tutorials/2d/2d_sprite_animation.html)
* [2D Dodge The Creeps Demo](https://godotengine.org/asset-library/asset/515)
Properties
----------
| | | |
| --- | --- | --- |
| [String](class_string#class-string) | [animation](#class-animatedsprite-property-animation) | `"default"` |
| [bool](class_bool#class-bool) | [centered](#class-animatedsprite-property-centered) | `true` |
| [bool](class_bool#class-bool) | [flip\_h](#class-animatedsprite-property-flip-h) | `false` |
| [bool](class_bool#class-bool) | [flip\_v](#class-animatedsprite-property-flip-v) | `false` |
| [int](class_int#class-int) | [frame](#class-animatedsprite-property-frame) | `0` |
| [SpriteFrames](class_spriteframes#class-spriteframes) | [frames](#class-animatedsprite-property-frames) | |
| [Vector2](class_vector2#class-vector2) | [offset](#class-animatedsprite-property-offset) | `Vector2( 0, 0 )` |
| [bool](class_bool#class-bool) | [playing](#class-animatedsprite-property-playing) | `false` |
| [float](class_float#class-float) | [speed\_scale](#class-animatedsprite-property-speed-scale) | `1.0` |
Methods
-------
| | |
| --- | --- |
| void | [play](#class-animatedsprite-method-play) **(** [String](class_string#class-string) anim="", [bool](class_bool#class-bool) backwards=false **)** |
| void | [stop](#class-animatedsprite-method-stop) **(** **)** |
Signals
-------
### animation\_finished ( )
Emitted when the animation is finished (when it plays the last frame). If the animation is looping, this signal is emitted every time the last frame is drawn.
### frame\_changed ( )
Emitted when [frame](#class-animatedsprite-property-frame) changed.
Property Descriptions
---------------------
### [String](class_string#class-string) animation
| | |
| --- | --- |
| *Default* | `"default"` |
| *Setter* | set\_animation(value) |
| *Getter* | get\_animation() |
The current animation from the [frames](#class-animatedsprite-property-frames) resource. If this value changes, the `frame` counter is reset.
### [bool](class_bool#class-bool) centered
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_centered(value) |
| *Getter* | is\_centered() |
If `true`, texture will be centered.
### [bool](class_bool#class-bool) flip\_h
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flip\_h(value) |
| *Getter* | is\_flipped\_h() |
If `true`, texture is flipped horizontally.
### [bool](class_bool#class-bool) flip\_v
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flip\_v(value) |
| *Getter* | is\_flipped\_v() |
If `true`, texture is flipped vertically.
### [int](class_int#class-int) frame
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_frame(value) |
| *Getter* | get\_frame() |
The displayed animation frame's index.
### [SpriteFrames](class_spriteframes#class-spriteframes) frames
| | |
| --- | --- |
| *Setter* | set\_sprite\_frames(value) |
| *Getter* | get\_sprite\_frames() |
The [SpriteFrames](class_spriteframes#class-spriteframes) resource containing the animation(s). Allows you the option to load, edit, clear, make unique and save the states of the [SpriteFrames](class_spriteframes#class-spriteframes) resource.
### [Vector2](class_vector2#class-vector2) offset
| | |
| --- | --- |
| *Default* | `Vector2( 0, 0 )` |
| *Setter* | set\_offset(value) |
| *Getter* | get\_offset() |
The texture's drawing offset.
### [bool](class_bool#class-bool) playing
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_playing(value) |
| *Getter* | is\_playing() |
If `true`, the [animation](#class-animatedsprite-property-animation) is currently playing.
### [float](class_float#class-float) speed\_scale
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_speed\_scale(value) |
| *Getter* | get\_speed\_scale() |
The animation speed is multiplied by this value.
Method Descriptions
-------------------
### void play ( [String](class_string#class-string) anim="", [bool](class_bool#class-bool) backwards=false )
Plays the animation named `anim`. If no `anim` is provided, the current animation is played. If `backwards` is `true`, the animation will be played in reverse.
### void stop ( )
Stops the current animation (does not reset the frame counter).
godot ImageTexture ImageTexture
============
**Inherits:** [Texture](class_texture#class-texture) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A [Texture](class_texture#class-texture) based on an [Image](class_image#class-image).
Description
-----------
A [Texture](class_texture#class-texture) based on an [Image](class_image#class-image). For an image to be displayed, an `ImageTexture` has to be created from it using the [create\_from\_image](#class-imagetexture-method-create-from-image) method:
```
var texture = ImageTexture.new()
var image = Image.new()
image.load("res://icon.png")
texture.create_from_image(image)
$Sprite.texture = texture
```
This way, textures can be created at run-time by loading images both from within the editor and externally.
**Warning:** Prefer to load imported textures with [@GDScript.load](class_%40gdscript#class-gdscript-method-load) over loading them from within the filesystem dynamically with [Image.load](class_image#class-image-method-load), as it may not work in exported projects:
```
var texture = load("res://icon.png")
$Sprite.texture = texture
```
This is because images have to be imported as [StreamTexture](class_streamtexture#class-streamtexture) first to be loaded with [@GDScript.load](class_%40gdscript#class-gdscript-method-load). If you'd still like to load an image file just like any other [Resource](class_resource#class-resource), import it as an [Image](class_image#class-image) resource instead, and then load it normally using the [@GDScript.load](class_%40gdscript#class-gdscript-method-load) method.
But do note that the image data can still be retrieved from an imported texture as well using the [Texture.get\_data](class_texture#class-texture-method-get-data) method, which returns a copy of the data:
```
var texture = load("res://icon.png")
var image : Image = texture.get_data()
```
An `ImageTexture` is not meant to be operated from within the editor interface directly, and is mostly useful for rendering images on screen dynamically via code. If you need to generate images procedurally from within the editor, consider saving and importing images as custom texture resources implementing a new [EditorImportPlugin](class_editorimportplugin#class-editorimportplugin).
**Note:** The maximum texture size is 16384×16384 pixels due to graphics hardware limitations.
Tutorials
---------
* [Importing images](https://docs.godotengine.org/en/3.5/tutorials/assets_pipeline/importing_images.html)
Properties
----------
| | | |
| --- | --- | --- |
| [int](class_int#class-int) | flags | `7` (overrides [Texture](class_texture#class-texture-property-flags)) |
| [float](class_float#class-float) | [lossy\_quality](#class-imagetexture-property-lossy-quality) | `0.7` |
| [Storage](#enum-imagetexture-storage) | [storage](#class-imagetexture-property-storage) | `0` |
Methods
-------
| | |
| --- | --- |
| void | [create](#class-imagetexture-method-create) **(** [int](class_int#class-int) width, [int](class_int#class-int) height, [Format](class_image#enum-image-format) format, [int](class_int#class-int) flags=7 **)** |
| void | [create\_from\_image](#class-imagetexture-method-create-from-image) **(** [Image](class_image#class-image) image, [int](class_int#class-int) flags=7 **)** |
| [Format](class_image#enum-image-format) | [get\_format](#class-imagetexture-method-get-format) **(** **)** const |
| [Error](class_%40globalscope#enum-globalscope-error) | [load](#class-imagetexture-method-load) **(** [String](class_string#class-string) path **)** |
| void | [set\_data](#class-imagetexture-method-set-data) **(** [Image](class_image#class-image) image **)** |
| void | [set\_size\_override](#class-imagetexture-method-set-size-override) **(** [Vector2](class_vector2#class-vector2) size **)** |
Enumerations
------------
enum **Storage**:
* **STORAGE\_RAW** = **0** --- [Image](class_image#class-image) data is stored raw and unaltered.
* **STORAGE\_COMPRESS\_LOSSY** = **1** --- [Image](class_image#class-image) data is compressed with a lossy algorithm. You can set the storage quality with [lossy\_quality](#class-imagetexture-property-lossy-quality).
* **STORAGE\_COMPRESS\_LOSSLESS** = **2** --- [Image](class_image#class-image) data is compressed with a lossless algorithm.
Property Descriptions
---------------------
### [float](class_float#class-float) lossy\_quality
| | |
| --- | --- |
| *Default* | `0.7` |
| *Setter* | set\_lossy\_storage\_quality(value) |
| *Getter* | get\_lossy\_storage\_quality() |
The storage quality for [STORAGE\_COMPRESS\_LOSSY](#class-imagetexture-constant-storage-compress-lossy).
### [Storage](#enum-imagetexture-storage) storage
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_storage(value) |
| *Getter* | get\_storage() |
The storage type (raw, lossy, or compressed).
Method Descriptions
-------------------
### void create ( [int](class_int#class-int) width, [int](class_int#class-int) height, [Format](class_image#enum-image-format) format, [int](class_int#class-int) flags=7 )
Create a new `ImageTexture` with `width` and `height`.
`format` is a value from [Format](class_image#enum-image-format), `flags` is any combination of [Flags](class_texture#enum-texture-flags).
### void create\_from\_image ( [Image](class_image#class-image) image, [int](class_int#class-int) flags=7 )
Initializes the texture by allocating and setting the data from an [Image](class_image#class-image) with `flags` from [Flags](class_texture#enum-texture-flags). An sRGB to linear color space conversion can take place, according to [Format](class_image#enum-image-format).
### [Format](class_image#enum-image-format) get\_format ( ) const
Returns the format of the texture, one of [Format](class_image#enum-image-format).
### [Error](class_%40globalscope#enum-globalscope-error) load ( [String](class_string#class-string) path )
Loads an image from a file path and creates a texture from it.
**Note:** This method is deprecated and will be removed in Godot 4.0, use [Image.load](class_image#class-image-method-load) and [create\_from\_image](#class-imagetexture-method-create-from-image) instead.
### void set\_data ( [Image](class_image#class-image) image )
Replaces the texture's data with a new [Image](class_image#class-image).
**Note:** The texture has to be initialized first with the [create\_from\_image](#class-imagetexture-method-create-from-image) method before it can be updated. The new image dimensions, format, and mipmaps configuration should match the existing texture's image configuration, otherwise it has to be re-created with the [create\_from\_image](#class-imagetexture-method-create-from-image) method.
Use this method over [create\_from\_image](#class-imagetexture-method-create-from-image) if you need to update the texture frequently, which is faster than allocating additional memory for a new texture each time.
### void set\_size\_override ( [Vector2](class_vector2#class-vector2) size )
Resizes the texture to the specified dimensions.
godot MultiMesh MultiMesh
=========
**Inherits:** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Provides high-performance mesh instancing.
Description
-----------
MultiMesh provides low-level mesh instancing. Drawing thousands of [MeshInstance](class_meshinstance#class-meshinstance) nodes can be slow, since each object is submitted to the GPU then drawn individually.
MultiMesh is much faster as it can draw thousands of instances with a single draw call, resulting in less API overhead.
As a drawback, if the instances are too far away from each other, performance may be reduced as every single instance will always render (they are spatially indexed as one, for the whole object).
Since instances may have any behavior, the AABB used for visibility must be provided by the user.
Tutorials
---------
* [Animating thousands of fish with MultiMeshInstance](https://docs.godotengine.org/en/3.5/tutorials/performance/vertex_animation/animating_thousands_of_fish.html)
* [Optimization using MultiMeshes](https://docs.godotengine.org/en/3.5/tutorials/performance/using_multimesh.html)
Properties
----------
| | | |
| --- | --- | --- |
| [ColorFormat](#enum-multimesh-colorformat) | [color\_format](#class-multimesh-property-color-format) | `0` |
| [CustomDataFormat](#enum-multimesh-customdataformat) | [custom\_data\_format](#class-multimesh-property-custom-data-format) | `0` |
| [int](class_int#class-int) | [instance\_count](#class-multimesh-property-instance-count) | `0` |
| [Mesh](class_mesh#class-mesh) | [mesh](#class-multimesh-property-mesh) | |
| [PhysicsInterpolationQuality](#enum-multimesh-physicsinterpolationquality) | [physics\_interpolation\_quality](#class-multimesh-property-physics-interpolation-quality) | `0` |
| [TransformFormat](#enum-multimesh-transformformat) | [transform\_format](#class-multimesh-property-transform-format) | `0` |
| [int](class_int#class-int) | [visible\_instance\_count](#class-multimesh-property-visible-instance-count) | `-1` |
Methods
-------
| | |
| --- | --- |
| [AABB](class_aabb#class-aabb) | [get\_aabb](#class-multimesh-method-get-aabb) **(** **)** const |
| [Color](class_color#class-color) | [get\_instance\_color](#class-multimesh-method-get-instance-color) **(** [int](class_int#class-int) instance **)** const |
| [Color](class_color#class-color) | [get\_instance\_custom\_data](#class-multimesh-method-get-instance-custom-data) **(** [int](class_int#class-int) instance **)** const |
| [Transform](class_transform#class-transform) | [get\_instance\_transform](#class-multimesh-method-get-instance-transform) **(** [int](class_int#class-int) instance **)** const |
| [Transform2D](class_transform2d#class-transform2d) | [get\_instance\_transform\_2d](#class-multimesh-method-get-instance-transform-2d) **(** [int](class_int#class-int) instance **)** const |
| void | [reset\_instance\_physics\_interpolation](#class-multimesh-method-reset-instance-physics-interpolation) **(** [int](class_int#class-int) instance **)** |
| void | [set\_as\_bulk\_array](#class-multimesh-method-set-as-bulk-array) **(** [PoolRealArray](class_poolrealarray#class-poolrealarray) array **)** |
| void | [set\_as\_bulk\_array\_interpolated](#class-multimesh-method-set-as-bulk-array-interpolated) **(** [PoolRealArray](class_poolrealarray#class-poolrealarray) array\_current, [PoolRealArray](class_poolrealarray#class-poolrealarray) array\_previous **)** |
| void | [set\_instance\_color](#class-multimesh-method-set-instance-color) **(** [int](class_int#class-int) instance, [Color](class_color#class-color) color **)** |
| void | [set\_instance\_custom\_data](#class-multimesh-method-set-instance-custom-data) **(** [int](class_int#class-int) instance, [Color](class_color#class-color) custom\_data **)** |
| void | [set\_instance\_transform](#class-multimesh-method-set-instance-transform) **(** [int](class_int#class-int) instance, [Transform](class_transform#class-transform) transform **)** |
| void | [set\_instance\_transform\_2d](#class-multimesh-method-set-instance-transform-2d) **(** [int](class_int#class-int) instance, [Transform2D](class_transform2d#class-transform2d) transform **)** |
Enumerations
------------
enum **TransformFormat**:
* **TRANSFORM\_2D** = **0** --- Use this when using 2D transforms.
* **TRANSFORM\_3D** = **1** --- Use this when using 3D transforms.
enum **ColorFormat**:
* **COLOR\_NONE** = **0** --- Use when you are not using per-instance [Color](class_color#class-color)s.
* **COLOR\_8BIT** = **1** --- Compress [Color](class_color#class-color) data into 8 bits when passing to shader. This uses less memory and can be faster, but the [Color](class_color#class-color) loses precision.
* **COLOR\_FLOAT** = **2** --- The [Color](class_color#class-color) passed into [set\_instance\_color](#class-multimesh-method-set-instance-color) will use 4 floats. Use this for highest precision [Color](class_color#class-color).
enum **CustomDataFormat**:
* **CUSTOM\_DATA\_NONE** = **0** --- Use when you are not using per-instance custom data.
* **CUSTOM\_DATA\_8BIT** = **1** --- Compress custom\_data into 8 bits when passing to shader. This uses less memory and can be faster, but loses precision and range. Floats packed into 8 bits can only represent values between 0 and 1, numbers outside that range will be clamped.
* **CUSTOM\_DATA\_FLOAT** = **2** --- The [Color](class_color#class-color) passed into [set\_instance\_custom\_data](#class-multimesh-method-set-instance-custom-data) will use 4 floats. Use this for highest precision.
enum **PhysicsInterpolationQuality**:
* **INTERP\_QUALITY\_FAST** = **0** --- Always interpolate using Basis lerping, which can produce warping artifacts in some situations.
* **INTERP\_QUALITY\_HIGH** = **1** --- Attempt to interpolate using Basis slerping (spherical linear interpolation) where possible, otherwise fall back to lerping.
Property Descriptions
---------------------
### [ColorFormat](#enum-multimesh-colorformat) color\_format
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_color\_format(value) |
| *Getter* | get\_color\_format() |
Format of colors in color array that gets passed to shader.
### [CustomDataFormat](#enum-multimesh-customdataformat) custom\_data\_format
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_custom\_data\_format(value) |
| *Getter* | get\_custom\_data\_format() |
Format of custom data in custom data array that gets passed to shader.
### [int](class_int#class-int) instance\_count
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_instance\_count(value) |
| *Getter* | get\_instance\_count() |
Number of instances that will get drawn. This clears and (re)sizes the buffers. By default, all instances are drawn but you can limit this with [visible\_instance\_count](#class-multimesh-property-visible-instance-count).
### [Mesh](class_mesh#class-mesh) mesh
| | |
| --- | --- |
| *Setter* | set\_mesh(value) |
| *Getter* | get\_mesh() |
Mesh to be drawn.
### [PhysicsInterpolationQuality](#enum-multimesh-physicsinterpolationquality) physics\_interpolation\_quality
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_physics\_interpolation\_quality(value) |
| *Getter* | get\_physics\_interpolation\_quality() |
Choose whether to use an interpolation method that favors speed or quality.
When using low physics tick rates (typically below 20) or high rates of object rotation, you may get better results from the high quality setting.
**Note:** Fast quality does not equate to low quality. Except in the special cases mentioned above, the quality should be comparable to high quality.
### [TransformFormat](#enum-multimesh-transformformat) transform\_format
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_transform\_format(value) |
| *Getter* | get\_transform\_format() |
Format of transform used to transform mesh, either 2D or 3D.
### [int](class_int#class-int) visible\_instance\_count
| | |
| --- | --- |
| *Default* | `-1` |
| *Setter* | set\_visible\_instance\_count(value) |
| *Getter* | get\_visible\_instance\_count() |
Limits the number of instances drawn, -1 draws all instances. Changing this does not change the sizes of the buffers.
Method Descriptions
-------------------
### [AABB](class_aabb#class-aabb) get\_aabb ( ) const
Returns the visibility axis-aligned bounding box in local space. See also [VisualInstance.get\_transformed\_aabb](class_visualinstance#class-visualinstance-method-get-transformed-aabb).
### [Color](class_color#class-color) get\_instance\_color ( [int](class_int#class-int) instance ) const
Gets a specific instance's color.
### [Color](class_color#class-color) get\_instance\_custom\_data ( [int](class_int#class-int) instance ) const
Returns the custom data that has been set for a specific instance.
### [Transform](class_transform#class-transform) get\_instance\_transform ( [int](class_int#class-int) instance ) const
Returns the [Transform](class_transform#class-transform) of a specific instance.
### [Transform2D](class_transform2d#class-transform2d) get\_instance\_transform\_2d ( [int](class_int#class-int) instance ) const
Returns the [Transform2D](class_transform2d#class-transform2d) of a specific instance.
### void reset\_instance\_physics\_interpolation ( [int](class_int#class-int) instance )
When using *physics interpolation*, this function allows you to prevent interpolation on an instance in the current physics tick.
This allows you to move instances instantaneously, and should usually be used when initially placing an instance such as a bullet to prevent graphical glitches.
### void set\_as\_bulk\_array ( [PoolRealArray](class_poolrealarray#class-poolrealarray) array )
Sets all data related to the instances in one go. This is especially useful when loading the data from disk or preparing the data from GDNative.
All data is packed in one large float array. An array may look like this: Transform for instance 1, color data for instance 1, custom data for instance 1, transform for instance 2, color data for instance 2, etc...
[Transform](class_transform#class-transform) is stored as 12 floats, [Transform2D](class_transform2d#class-transform2d) is stored as 8 floats, `COLOR_8BIT` / `CUSTOM_DATA_8BIT` is stored as 1 float (4 bytes as is) and `COLOR_FLOAT` / `CUSTOM_DATA_FLOAT` is stored as 4 floats.
### void set\_as\_bulk\_array\_interpolated ( [PoolRealArray](class_poolrealarray#class-poolrealarray) array\_current, [PoolRealArray](class_poolrealarray#class-poolrealarray) array\_previous )
An alternative version of [set\_as\_bulk\_array](#class-multimesh-method-set-as-bulk-array) which can be used with *physics interpolation*. This method takes two arrays, and can set the data for the current and previous tick in one go. The renderer will automatically interpolate the data at each frame.
This is useful for situations where the order of instances may change from physics tick to tick, such as particle systems.
When the order of instances is coherent, the simpler [set\_as\_bulk\_array](#class-multimesh-method-set-as-bulk-array) can still be used with interpolation.
### void set\_instance\_color ( [int](class_int#class-int) instance, [Color](class_color#class-color) color )
Sets the color of a specific instance by *multiplying* the mesh's existing vertex colors.
For the color to take effect, ensure that [color\_format](#class-multimesh-property-color-format) is non-`null` on the `MultiMesh` and [SpatialMaterial.vertex\_color\_use\_as\_albedo](class_spatialmaterial#class-spatialmaterial-property-vertex-color-use-as-albedo) is `true` on the material. If the color doesn't look as expected, make sure the material's albedo color is set to pure white (`Color(1, 1, 1)`).
### void set\_instance\_custom\_data ( [int](class_int#class-int) instance, [Color](class_color#class-color) custom\_data )
Sets custom data for a specific instance. Although [Color](class_color#class-color) is used, it is just a container for 4 floating point numbers. The format of the number can change depending on the [CustomDataFormat](#enum-multimesh-customdataformat) used.
### void set\_instance\_transform ( [int](class_int#class-int) instance, [Transform](class_transform#class-transform) transform )
Sets the [Transform](class_transform#class-transform) for a specific instance.
### void set\_instance\_transform\_2d ( [int](class_int#class-int) instance, [Transform2D](class_transform2d#class-transform2d) transform )
Sets the [Transform2D](class_transform2d#class-transform2d) for a specific instance.
| programming_docs |
godot MeshDataTool MeshDataTool
============
**Inherits:** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
Helper tool to access and edit [Mesh](class_mesh#class-mesh) data.
Description
-----------
MeshDataTool provides access to individual vertices in a [Mesh](class_mesh#class-mesh). It allows users to read and edit vertex data of meshes. It also creates an array of faces and edges.
To use MeshDataTool, load a mesh with [create\_from\_surface](#class-meshdatatool-method-create-from-surface). When you are finished editing the data commit the data to a mesh with [commit\_to\_surface](#class-meshdatatool-method-commit-to-surface).
Below is an example of how MeshDataTool may be used.
```
var mesh = ArrayMesh.new()
mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, CubeMesh.new().get_mesh_arrays())
var mdt = MeshDataTool.new()
mdt.create_from_surface(mesh, 0)
for i in range(mdt.get_vertex_count()):
var vertex = mdt.get_vertex(i)
# In this example we extend the mesh by one unit, which results in separated faces as it is flat shaded.
vertex += mdt.get_vertex_normal(i)
# Save your change.
mdt.set_vertex(i, vertex)
mesh.surface_remove(0)
mdt.commit_to_surface(mesh)
var mi = MeshInstance.new()
mi.mesh = mesh
add_child(mi)
```
See also [ArrayMesh](class_arraymesh#class-arraymesh), [ImmediateGeometry](class_immediategeometry#class-immediategeometry) and [SurfaceTool](class_surfacetool#class-surfacetool) for procedural geometry generation.
**Note:** Godot uses clockwise [winding order](https://learnopengl.com/Advanced-OpenGL/Face-culling) for front faces of triangle primitive modes.
Methods
-------
| | |
| --- | --- |
| void | [clear](#class-meshdatatool-method-clear) **(** **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [commit\_to\_surface](#class-meshdatatool-method-commit-to-surface) **(** [ArrayMesh](class_arraymesh#class-arraymesh) mesh **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [create\_from\_surface](#class-meshdatatool-method-create-from-surface) **(** [ArrayMesh](class_arraymesh#class-arraymesh) mesh, [int](class_int#class-int) surface **)** |
| [int](class_int#class-int) | [get\_edge\_count](#class-meshdatatool-method-get-edge-count) **(** **)** const |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [get\_edge\_faces](#class-meshdatatool-method-get-edge-faces) **(** [int](class_int#class-int) idx **)** const |
| [Variant](class_variant#class-variant) | [get\_edge\_meta](#class-meshdatatool-method-get-edge-meta) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_edge\_vertex](#class-meshdatatool-method-get-edge-vertex) **(** [int](class_int#class-int) idx, [int](class_int#class-int) vertex **)** const |
| [int](class_int#class-int) | [get\_face\_count](#class-meshdatatool-method-get-face-count) **(** **)** const |
| [int](class_int#class-int) | [get\_face\_edge](#class-meshdatatool-method-get-face-edge) **(** [int](class_int#class-int) idx, [int](class_int#class-int) edge **)** const |
| [Variant](class_variant#class-variant) | [get\_face\_meta](#class-meshdatatool-method-get-face-meta) **(** [int](class_int#class-int) idx **)** const |
| [Vector3](class_vector3#class-vector3) | [get\_face\_normal](#class-meshdatatool-method-get-face-normal) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_face\_vertex](#class-meshdatatool-method-get-face-vertex) **(** [int](class_int#class-int) idx, [int](class_int#class-int) vertex **)** const |
| [int](class_int#class-int) | [get\_format](#class-meshdatatool-method-get-format) **(** **)** const |
| [Material](class_material#class-material) | [get\_material](#class-meshdatatool-method-get-material) **(** **)** const |
| [Vector3](class_vector3#class-vector3) | [get\_vertex](#class-meshdatatool-method-get-vertex) **(** [int](class_int#class-int) idx **)** const |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [get\_vertex\_bones](#class-meshdatatool-method-get-vertex-bones) **(** [int](class_int#class-int) idx **)** const |
| [Color](class_color#class-color) | [get\_vertex\_color](#class-meshdatatool-method-get-vertex-color) **(** [int](class_int#class-int) idx **)** const |
| [int](class_int#class-int) | [get\_vertex\_count](#class-meshdatatool-method-get-vertex-count) **(** **)** const |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [get\_vertex\_edges](#class-meshdatatool-method-get-vertex-edges) **(** [int](class_int#class-int) idx **)** const |
| [PoolIntArray](class_poolintarray#class-poolintarray) | [get\_vertex\_faces](#class-meshdatatool-method-get-vertex-faces) **(** [int](class_int#class-int) idx **)** const |
| [Variant](class_variant#class-variant) | [get\_vertex\_meta](#class-meshdatatool-method-get-vertex-meta) **(** [int](class_int#class-int) idx **)** const |
| [Vector3](class_vector3#class-vector3) | [get\_vertex\_normal](#class-meshdatatool-method-get-vertex-normal) **(** [int](class_int#class-int) idx **)** const |
| [Plane](class_plane#class-plane) | [get\_vertex\_tangent](#class-meshdatatool-method-get-vertex-tangent) **(** [int](class_int#class-int) idx **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_vertex\_uv](#class-meshdatatool-method-get-vertex-uv) **(** [int](class_int#class-int) idx **)** const |
| [Vector2](class_vector2#class-vector2) | [get\_vertex\_uv2](#class-meshdatatool-method-get-vertex-uv2) **(** [int](class_int#class-int) idx **)** const |
| [PoolRealArray](class_poolrealarray#class-poolrealarray) | [get\_vertex\_weights](#class-meshdatatool-method-get-vertex-weights) **(** [int](class_int#class-int) idx **)** const |
| void | [set\_edge\_meta](#class-meshdatatool-method-set-edge-meta) **(** [int](class_int#class-int) idx, [Variant](class_variant#class-variant) meta **)** |
| void | [set\_face\_meta](#class-meshdatatool-method-set-face-meta) **(** [int](class_int#class-int) idx, [Variant](class_variant#class-variant) meta **)** |
| void | [set\_material](#class-meshdatatool-method-set-material) **(** [Material](class_material#class-material) material **)** |
| void | [set\_vertex](#class-meshdatatool-method-set-vertex) **(** [int](class_int#class-int) idx, [Vector3](class_vector3#class-vector3) vertex **)** |
| void | [set\_vertex\_bones](#class-meshdatatool-method-set-vertex-bones) **(** [int](class_int#class-int) idx, [PoolIntArray](class_poolintarray#class-poolintarray) bones **)** |
| void | [set\_vertex\_color](#class-meshdatatool-method-set-vertex-color) **(** [int](class_int#class-int) idx, [Color](class_color#class-color) color **)** |
| void | [set\_vertex\_meta](#class-meshdatatool-method-set-vertex-meta) **(** [int](class_int#class-int) idx, [Variant](class_variant#class-variant) meta **)** |
| void | [set\_vertex\_normal](#class-meshdatatool-method-set-vertex-normal) **(** [int](class_int#class-int) idx, [Vector3](class_vector3#class-vector3) normal **)** |
| void | [set\_vertex\_tangent](#class-meshdatatool-method-set-vertex-tangent) **(** [int](class_int#class-int) idx, [Plane](class_plane#class-plane) tangent **)** |
| void | [set\_vertex\_uv](#class-meshdatatool-method-set-vertex-uv) **(** [int](class_int#class-int) idx, [Vector2](class_vector2#class-vector2) uv **)** |
| void | [set\_vertex\_uv2](#class-meshdatatool-method-set-vertex-uv2) **(** [int](class_int#class-int) idx, [Vector2](class_vector2#class-vector2) uv2 **)** |
| void | [set\_vertex\_weights](#class-meshdatatool-method-set-vertex-weights) **(** [int](class_int#class-int) idx, [PoolRealArray](class_poolrealarray#class-poolrealarray) weights **)** |
Method Descriptions
-------------------
### void clear ( )
Clears all data currently in MeshDataTool.
### [Error](class_%40globalscope#enum-globalscope-error) commit\_to\_surface ( [ArrayMesh](class_arraymesh#class-arraymesh) mesh )
Adds a new surface to specified [Mesh](class_mesh#class-mesh) with edited data.
### [Error](class_%40globalscope#enum-globalscope-error) create\_from\_surface ( [ArrayMesh](class_arraymesh#class-arraymesh) mesh, [int](class_int#class-int) surface )
Uses specified surface of given [Mesh](class_mesh#class-mesh) to populate data for MeshDataTool.
Requires [Mesh](class_mesh#class-mesh) with primitive type [Mesh.PRIMITIVE\_TRIANGLES](class_mesh#class-mesh-constant-primitive-triangles).
### [int](class_int#class-int) get\_edge\_count ( ) const
Returns the number of edges in this [Mesh](class_mesh#class-mesh).
### [PoolIntArray](class_poolintarray#class-poolintarray) get\_edge\_faces ( [int](class_int#class-int) idx ) const
Returns array of faces that touch given edge.
### [Variant](class_variant#class-variant) get\_edge\_meta ( [int](class_int#class-int) idx ) const
Returns meta information assigned to given edge.
### [int](class_int#class-int) get\_edge\_vertex ( [int](class_int#class-int) idx, [int](class_int#class-int) vertex ) const
Returns index of specified vertex connected to given edge.
Vertex argument can only be 0 or 1 because edges are comprised of two vertices.
### [int](class_int#class-int) get\_face\_count ( ) const
Returns the number of faces in this [Mesh](class_mesh#class-mesh).
### [int](class_int#class-int) get\_face\_edge ( [int](class_int#class-int) idx, [int](class_int#class-int) edge ) const
Returns specified edge associated with given face.
Edge argument must be either 0, 1, or 2 because a face only has three edges.
### [Variant](class_variant#class-variant) get\_face\_meta ( [int](class_int#class-int) idx ) const
Returns the metadata associated with the given face.
### [Vector3](class_vector3#class-vector3) get\_face\_normal ( [int](class_int#class-int) idx ) const
Calculates and returns the face normal of the given face.
### [int](class_int#class-int) get\_face\_vertex ( [int](class_int#class-int) idx, [int](class_int#class-int) vertex ) const
Returns the specified vertex of the given face.
Vertex argument must be either 0, 1, or 2 because faces contain three vertices.
### [int](class_int#class-int) get\_format ( ) const
Returns the [Mesh](class_mesh#class-mesh)'s format. Format is an integer made up of [Mesh](class_mesh#class-mesh) format flags combined together. For example, a mesh containing both vertices and normals would return a format of `3` because [ArrayMesh.ARRAY\_FORMAT\_VERTEX](class_arraymesh#class-arraymesh-constant-array-format-vertex) is `1` and [ArrayMesh.ARRAY\_FORMAT\_NORMAL](class_arraymesh#class-arraymesh-constant-array-format-normal) is `2`.
See [ArrayFormat](class_arraymesh#enum-arraymesh-arrayformat) for a list of format flags.
### [Material](class_material#class-material) get\_material ( ) const
Returns the material assigned to the [Mesh](class_mesh#class-mesh).
### [Vector3](class_vector3#class-vector3) get\_vertex ( [int](class_int#class-int) idx ) const
Returns the vertex at given index.
### [PoolIntArray](class_poolintarray#class-poolintarray) get\_vertex\_bones ( [int](class_int#class-int) idx ) const
Returns the bones of the given vertex.
### [Color](class_color#class-color) get\_vertex\_color ( [int](class_int#class-int) idx ) const
Returns the color of the given vertex.
### [int](class_int#class-int) get\_vertex\_count ( ) const
Returns the total number of vertices in [Mesh](class_mesh#class-mesh).
### [PoolIntArray](class_poolintarray#class-poolintarray) get\_vertex\_edges ( [int](class_int#class-int) idx ) const
Returns an array of edges that share the given vertex.
### [PoolIntArray](class_poolintarray#class-poolintarray) get\_vertex\_faces ( [int](class_int#class-int) idx ) const
Returns an array of faces that share the given vertex.
### [Variant](class_variant#class-variant) get\_vertex\_meta ( [int](class_int#class-int) idx ) const
Returns the metadata associated with the given vertex.
### [Vector3](class_vector3#class-vector3) get\_vertex\_normal ( [int](class_int#class-int) idx ) const
Returns the normal of the given vertex.
### [Plane](class_plane#class-plane) get\_vertex\_tangent ( [int](class_int#class-int) idx ) const
Returns the tangent of the given vertex.
### [Vector2](class_vector2#class-vector2) get\_vertex\_uv ( [int](class_int#class-int) idx ) const
Returns the UV of the given vertex.
### [Vector2](class_vector2#class-vector2) get\_vertex\_uv2 ( [int](class_int#class-int) idx ) const
Returns the UV2 of the given vertex.
### [PoolRealArray](class_poolrealarray#class-poolrealarray) get\_vertex\_weights ( [int](class_int#class-int) idx ) const
Returns bone weights of the given vertex.
### void set\_edge\_meta ( [int](class_int#class-int) idx, [Variant](class_variant#class-variant) meta )
Sets the metadata of the given edge.
### void set\_face\_meta ( [int](class_int#class-int) idx, [Variant](class_variant#class-variant) meta )
Sets the metadata of the given face.
### void set\_material ( [Material](class_material#class-material) material )
Sets the material to be used by newly-constructed [Mesh](class_mesh#class-mesh).
### void set\_vertex ( [int](class_int#class-int) idx, [Vector3](class_vector3#class-vector3) vertex )
Sets the position of the given vertex.
### void set\_vertex\_bones ( [int](class_int#class-int) idx, [PoolIntArray](class_poolintarray#class-poolintarray) bones )
Sets the bones of the given vertex.
### void set\_vertex\_color ( [int](class_int#class-int) idx, [Color](class_color#class-color) color )
Sets the color of the given vertex.
### void set\_vertex\_meta ( [int](class_int#class-int) idx, [Variant](class_variant#class-variant) meta )
Sets the metadata associated with the given vertex.
### void set\_vertex\_normal ( [int](class_int#class-int) idx, [Vector3](class_vector3#class-vector3) normal )
Sets the normal of the given vertex.
### void set\_vertex\_tangent ( [int](class_int#class-int) idx, [Plane](class_plane#class-plane) tangent )
Sets the tangent of the given vertex.
### void set\_vertex\_uv ( [int](class_int#class-int) idx, [Vector2](class_vector2#class-vector2) uv )
Sets the UV of the given vertex.
### void set\_vertex\_uv2 ( [int](class_int#class-int) idx, [Vector2](class_vector2#class-vector2) uv2 )
Sets the UV2 of the given vertex.
### void set\_vertex\_weights ( [int](class_int#class-int) idx, [PoolRealArray](class_poolrealarray#class-poolrealarray) weights )
Sets the bone weights of the given vertex.
godot NetworkedMultiplayerENet NetworkedMultiplayerENet
========================
**Inherits:** [NetworkedMultiplayerPeer](class_networkedmultiplayerpeer#class-networkedmultiplayerpeer) **<** [PacketPeer](class_packetpeer#class-packetpeer) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
PacketPeer implementation using the [ENet](http://enet.bespin.org/index.html) library.
Description
-----------
A PacketPeer implementation that should be passed to [SceneTree.network\_peer](class_scenetree#class-scenetree-property-network-peer) after being initialized as either a client or server. Events can then be handled by connecting to [SceneTree](class_scenetree#class-scenetree) signals.
ENet's purpose is to provide a relatively thin, simple and robust network communication layer on top of UDP (User Datagram Protocol).
**Note:** ENet only uses UDP, not TCP. When forwarding the server port to make your server accessible on the public Internet, you only need to forward the server port in UDP. You can use the [UPNP](class_upnp#class-upnp) class to try to forward the server port automatically when starting the server.
Tutorials
---------
* [High-level multiplayer](https://docs.godotengine.org/en/3.5/tutorials/networking/high_level_multiplayer.html)
* <http://enet.bespin.org/usergroup0.html>
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [always\_ordered](#class-networkedmultiplayerenet-property-always-ordered) | `false` |
| [int](class_int#class-int) | [channel\_count](#class-networkedmultiplayerenet-property-channel-count) | `3` |
| [CompressionMode](#enum-networkedmultiplayerenet-compressionmode) | [compression\_mode](#class-networkedmultiplayerenet-property-compression-mode) | `1` |
| [String](class_string#class-string) | [dtls\_hostname](#class-networkedmultiplayerenet-property-dtls-hostname) | `""` |
| [bool](class_bool#class-bool) | [dtls\_verify](#class-networkedmultiplayerenet-property-dtls-verify) | `true` |
| [bool](class_bool#class-bool) | [server\_relay](#class-networkedmultiplayerenet-property-server-relay) | `true` |
| [int](class_int#class-int) | [transfer\_channel](#class-networkedmultiplayerenet-property-transfer-channel) | `-1` |
| [bool](class_bool#class-bool) | [use\_dtls](#class-networkedmultiplayerenet-property-use-dtls) | `false` |
Methods
-------
| | |
| --- | --- |
| void | [close\_connection](#class-networkedmultiplayerenet-method-close-connection) **(** [int](class_int#class-int) wait\_usec=100 **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [create\_client](#class-networkedmultiplayerenet-method-create-client) **(** [String](class_string#class-string) address, [int](class_int#class-int) port, [int](class_int#class-int) in\_bandwidth=0, [int](class_int#class-int) out\_bandwidth=0, [int](class_int#class-int) client\_port=0 **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [create\_server](#class-networkedmultiplayerenet-method-create-server) **(** [int](class_int#class-int) port, [int](class_int#class-int) max\_clients=32, [int](class_int#class-int) in\_bandwidth=0, [int](class_int#class-int) out\_bandwidth=0 **)** |
| void | [disconnect\_peer](#class-networkedmultiplayerenet-method-disconnect-peer) **(** [int](class_int#class-int) id, [bool](class_bool#class-bool) now=false **)** |
| [int](class_int#class-int) | [get\_last\_packet\_channel](#class-networkedmultiplayerenet-method-get-last-packet-channel) **(** **)** const |
| [int](class_int#class-int) | [get\_packet\_channel](#class-networkedmultiplayerenet-method-get-packet-channel) **(** **)** const |
| [String](class_string#class-string) | [get\_peer\_address](#class-networkedmultiplayerenet-method-get-peer-address) **(** [int](class_int#class-int) id **)** const |
| [int](class_int#class-int) | [get\_peer\_port](#class-networkedmultiplayerenet-method-get-peer-port) **(** [int](class_int#class-int) id **)** const |
| void | [set\_bind\_ip](#class-networkedmultiplayerenet-method-set-bind-ip) **(** [String](class_string#class-string) ip **)** |
| void | [set\_dtls\_certificate](#class-networkedmultiplayerenet-method-set-dtls-certificate) **(** [X509Certificate](class_x509certificate#class-x509certificate) certificate **)** |
| void | [set\_dtls\_key](#class-networkedmultiplayerenet-method-set-dtls-key) **(** [CryptoKey](class_cryptokey#class-cryptokey) key **)** |
| void | [set\_peer\_timeout](#class-networkedmultiplayerenet-method-set-peer-timeout) **(** [int](class_int#class-int) id, [int](class_int#class-int) timeout\_limit, [int](class_int#class-int) timeout\_min, [int](class_int#class-int) timeout\_max **)** |
Enumerations
------------
enum **CompressionMode**:
* **COMPRESS\_NONE** = **0** --- No compression. This uses the most bandwidth, but has the upside of requiring the fewest CPU resources. This option may also be used to make network debugging using tools like Wireshark easier.
* **COMPRESS\_RANGE\_CODER** = **1** --- ENet's built-in range encoding. Works well on small packets, but is not the most efficient algorithm on packets larger than 4 KB.
* **COMPRESS\_FASTLZ** = **2** --- [FastLZ](http://fastlz.org/) compression. This option uses less CPU resources compared to [COMPRESS\_ZLIB](#class-networkedmultiplayerenet-constant-compress-zlib), at the expense of using more bandwidth.
* **COMPRESS\_ZLIB** = **3** --- [Zlib](https://www.zlib.net/) compression. This option uses less bandwidth compared to [COMPRESS\_FASTLZ](#class-networkedmultiplayerenet-constant-compress-fastlz), at the expense of using more CPU resources. Note that this algorithm is not very efficient on packets smaller than 4 KB. Therefore, it's recommended to use other compression algorithms in most cases.
* **COMPRESS\_ZSTD** = **4** --- [Zstandard](https://facebook.github.io/zstd/) compression.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) always\_ordered
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_always\_ordered(value) |
| *Getter* | is\_always\_ordered() |
Enforce ordered packets when using [NetworkedMultiplayerPeer.TRANSFER\_MODE\_UNRELIABLE](class_networkedmultiplayerpeer#class-networkedmultiplayerpeer-constant-transfer-mode-unreliable) (thus behaving similarly to [NetworkedMultiplayerPeer.TRANSFER\_MODE\_UNRELIABLE\_ORDERED](class_networkedmultiplayerpeer#class-networkedmultiplayerpeer-constant-transfer-mode-unreliable-ordered)). This is the only way to use ordering with the RPC system.
### [int](class_int#class-int) channel\_count
| | |
| --- | --- |
| *Default* | `3` |
| *Setter* | set\_channel\_count(value) |
| *Getter* | get\_channel\_count() |
The number of channels to be used by ENet. Channels are used to separate different kinds of data. In reliable or ordered mode, for example, the packet delivery order is ensured on a per-channel basis. This is done to combat latency and reduces ordering restrictions on packets. The delivery status of a packet in one channel won't stall the delivery of other packets in another channel.
### [CompressionMode](#enum-networkedmultiplayerenet-compressionmode) compression\_mode
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_compression\_mode(value) |
| *Getter* | get\_compression\_mode() |
The compression method used for network packets. These have different tradeoffs of compression speed versus bandwidth, you may need to test which one works best for your use case if you use compression at all.
**Note:** Most games' network design involve sending many small packets frequently (smaller than 4 KB each). If in doubt, it is recommended to keep the default compression algorithm as it works best on these small packets.
**Note:** [compression\_mode](#class-networkedmultiplayerenet-property-compression-mode) must be set to the same value on both the server and all its clients. Clients will fail to connect if the [compression\_mode](#class-networkedmultiplayerenet-property-compression-mode) set on the client differs from the one set on the server. Prior to Godot 3.4, the default [compression\_mode](#class-networkedmultiplayerenet-property-compression-mode) was [COMPRESS\_NONE](#class-networkedmultiplayerenet-constant-compress-none). Nonetheless, mixing engine versions between clients and server is not recommended and not officially supported.
### [String](class_string#class-string) dtls\_hostname
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_dtls\_hostname(value) |
| *Getter* | get\_dtls\_hostname() |
The hostname used for DTLS verification, to be compared against the "CN" value in the certificate provided by the server.
When set to an empty string, the `address` parameter passed to [create\_client](#class-networkedmultiplayerenet-method-create-client) is used instead.
### [bool](class_bool#class-bool) dtls\_verify
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_dtls\_verify\_enabled(value) |
| *Getter* | is\_dtls\_verify\_enabled() |
Enable or disable certificate verification when [use\_dtls](#class-networkedmultiplayerenet-property-use-dtls) is `true`.
### [bool](class_bool#class-bool) server\_relay
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_server\_relay\_enabled(value) |
| *Getter* | is\_server\_relay\_enabled() |
Enable or disable the server feature that notifies clients of other peers' connection/disconnection, and relays messages between them. When this option is `false`, clients won't be automatically notified of other peers and won't be able to send them packets through the server.
### [int](class_int#class-int) transfer\_channel
| | |
| --- | --- |
| *Default* | `-1` |
| *Setter* | set\_transfer\_channel(value) |
| *Getter* | get\_transfer\_channel() |
Set the default channel to be used to transfer data. By default, this value is `-1` which means that ENet will only use 2 channels: one for reliable packets, and one for unreliable packets. The channel `0` is reserved and cannot be used. Setting this member to any value between `0` and [channel\_count](#class-networkedmultiplayerenet-property-channel-count) (excluded) will force ENet to use that channel for sending data. See [channel\_count](#class-networkedmultiplayerenet-property-channel-count) for more information about ENet channels.
### [bool](class_bool#class-bool) use\_dtls
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_dtls\_enabled(value) |
| *Getter* | is\_dtls\_enabled() |
When enabled, the client or server created by this peer, will use [PacketPeerDTLS](class_packetpeerdtls#class-packetpeerdtls) instead of raw UDP sockets for communicating with the remote peer. This will make the communication encrypted with DTLS at the cost of higher resource usage and potentially larger packet size.
**Note:** When creating a DTLS server, make sure you setup the key/certificate pair via [set\_dtls\_key](#class-networkedmultiplayerenet-method-set-dtls-key) and [set\_dtls\_certificate](#class-networkedmultiplayerenet-method-set-dtls-certificate). For DTLS clients, have a look at the [dtls\_verify](#class-networkedmultiplayerenet-property-dtls-verify) option, and configure the certificate accordingly via [set\_dtls\_certificate](#class-networkedmultiplayerenet-method-set-dtls-certificate).
Method Descriptions
-------------------
### void close\_connection ( [int](class_int#class-int) wait\_usec=100 )
Closes the connection. Ignored if no connection is currently established. If this is a server it tries to notify all clients before forcibly disconnecting them. If this is a client it simply closes the connection to the server.
### [Error](class_%40globalscope#enum-globalscope-error) create\_client ( [String](class_string#class-string) address, [int](class_int#class-int) port, [int](class_int#class-int) in\_bandwidth=0, [int](class_int#class-int) out\_bandwidth=0, [int](class_int#class-int) client\_port=0 )
Create client that connects to a server at `address` using specified `port`. The given address needs to be either a fully qualified domain name (e.g. `"www.example.com"`) or an IP address in IPv4 or IPv6 format (e.g. `"192.168.1.1"`). The `port` is the port the server is listening on. The `in_bandwidth` and `out_bandwidth` parameters can be used to limit the incoming and outgoing bandwidth to the given number of bytes per second. The default of 0 means unlimited bandwidth. Note that ENet will strategically drop packets on specific sides of a connection between peers to ensure the peer's bandwidth is not overwhelmed. The bandwidth parameters also determine the window size of a connection which limits the amount of reliable packets that may be in transit at any given time. Returns [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok) if a client was created, [@GlobalScope.ERR\_ALREADY\_IN\_USE](class_%40globalscope#class-globalscope-constant-err-already-in-use) if this NetworkedMultiplayerENet instance already has an open connection (in which case you need to call [close\_connection](#class-networkedmultiplayerenet-method-close-connection) first) or [@GlobalScope.ERR\_CANT\_CREATE](class_%40globalscope#class-globalscope-constant-err-cant-create) if the client could not be created. If `client_port` is specified, the client will also listen to the given port; this is useful for some NAT traversal techniques.
### [Error](class_%40globalscope#enum-globalscope-error) create\_server ( [int](class_int#class-int) port, [int](class_int#class-int) max\_clients=32, [int](class_int#class-int) in\_bandwidth=0, [int](class_int#class-int) out\_bandwidth=0 )
Create server that listens to connections via `port`. The port needs to be an available, unused port between 0 and 65535. Note that ports below 1024 are privileged and may require elevated permissions depending on the platform. To change the interface the server listens on, use [set\_bind\_ip](#class-networkedmultiplayerenet-method-set-bind-ip). The default IP is the wildcard `"*"`, which listens on all available interfaces. `max_clients` is the maximum number of clients that are allowed at once, any number up to 4095 may be used, although the achievable number of simultaneous clients may be far lower and depends on the application. For additional details on the bandwidth parameters, see [create\_client](#class-networkedmultiplayerenet-method-create-client). Returns [@GlobalScope.OK](class_%40globalscope#class-globalscope-constant-ok) if a server was created, [@GlobalScope.ERR\_ALREADY\_IN\_USE](class_%40globalscope#class-globalscope-constant-err-already-in-use) if this NetworkedMultiplayerENet instance already has an open connection (in which case you need to call [close\_connection](#class-networkedmultiplayerenet-method-close-connection) first) or [@GlobalScope.ERR\_CANT\_CREATE](class_%40globalscope#class-globalscope-constant-err-cant-create) if the server could not be created.
### void disconnect\_peer ( [int](class_int#class-int) id, [bool](class_bool#class-bool) now=false )
Disconnect the given peer. If "now" is set to `true`, the connection will be closed immediately without flushing queued messages.
### [int](class_int#class-int) get\_last\_packet\_channel ( ) const
Returns the channel of the last packet fetched via [PacketPeer.get\_packet](class_packetpeer#class-packetpeer-method-get-packet).
### [int](class_int#class-int) get\_packet\_channel ( ) const
Returns the channel of the next packet that will be retrieved via [PacketPeer.get\_packet](class_packetpeer#class-packetpeer-method-get-packet).
### [String](class_string#class-string) get\_peer\_address ( [int](class_int#class-int) id ) const
Returns the IP address of the given peer.
### [int](class_int#class-int) get\_peer\_port ( [int](class_int#class-int) id ) const
Returns the remote port of the given peer.
### void set\_bind\_ip ( [String](class_string#class-string) ip )
The IP used when creating a server. This is set to the wildcard `"*"` by default, which binds to all available interfaces. The given IP needs to be in IPv4 or IPv6 address format, for example: `"192.168.1.1"`.
### void set\_dtls\_certificate ( [X509Certificate](class_x509certificate#class-x509certificate) certificate )
Configure the [X509Certificate](class_x509certificate#class-x509certificate) to use when [use\_dtls](#class-networkedmultiplayerenet-property-use-dtls) is `true`. For servers, you must also setup the [CryptoKey](class_cryptokey#class-cryptokey) via [set\_dtls\_key](#class-networkedmultiplayerenet-method-set-dtls-key).
### void set\_dtls\_key ( [CryptoKey](class_cryptokey#class-cryptokey) key )
Configure the [CryptoKey](class_cryptokey#class-cryptokey) to use when [use\_dtls](#class-networkedmultiplayerenet-property-use-dtls) is `true`. Remember to also call [set\_dtls\_certificate](#class-networkedmultiplayerenet-method-set-dtls-certificate) to setup your [X509Certificate](class_x509certificate#class-x509certificate).
### void set\_peer\_timeout ( [int](class_int#class-int) id, [int](class_int#class-int) timeout\_limit, [int](class_int#class-int) timeout\_min, [int](class_int#class-int) timeout\_max )
Sets the timeout parameters for a peer. The timeout parameters control how and when a peer will timeout from a failure to acknowledge reliable traffic. Timeout values are expressed in milliseconds.
The `timeout_limit` is a factor that, multiplied by a value based on the average round trip time, will determine the timeout limit for a reliable packet. When that limit is reached, the timeout will be doubled, and the peer will be disconnected if that limit has reached `timeout_min`. The `timeout_max` parameter, on the other hand, defines a fixed timeout for which any packet must be acknowledged or the peer will be dropped.
| programming_docs |
godot HingeJoint HingeJoint
==========
**Inherits:** [Joint](class_joint#class-joint) **<** [Spatial](class_spatial#class-spatial) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
A hinge between two 3D PhysicsBodies.
Description
-----------
A HingeJoint normally uses the Z axis of body A as the hinge axis, another axis can be specified when adding it manually though. See also [Generic6DOFJoint](class_generic6dofjoint#class-generic6dofjoint).
Properties
----------
| | | |
| --- | --- | --- |
| [float](class_float#class-float) | [angular\_limit/bias](#class-hingejoint-property-angular-limit-bias) | `0.3` |
| [bool](class_bool#class-bool) | [angular\_limit/enable](#class-hingejoint-property-angular-limit-enable) | `false` |
| [float](class_float#class-float) | [angular\_limit/lower](#class-hingejoint-property-angular-limit-lower) | `-90.0` |
| [float](class_float#class-float) | [angular\_limit/relaxation](#class-hingejoint-property-angular-limit-relaxation) | `1.0` |
| [float](class_float#class-float) | [angular\_limit/softness](#class-hingejoint-property-angular-limit-softness) | `0.9` |
| [float](class_float#class-float) | [angular\_limit/upper](#class-hingejoint-property-angular-limit-upper) | `90.0` |
| [bool](class_bool#class-bool) | [motor/enable](#class-hingejoint-property-motor-enable) | `false` |
| [float](class_float#class-float) | [motor/max\_impulse](#class-hingejoint-property-motor-max-impulse) | `1.0` |
| [float](class_float#class-float) | [motor/target\_velocity](#class-hingejoint-property-motor-target-velocity) | `1.0` |
| [float](class_float#class-float) | [params/bias](#class-hingejoint-property-params-bias) | `0.3` |
Methods
-------
| | |
| --- | --- |
| [bool](class_bool#class-bool) | [get\_flag](#class-hingejoint-method-get-flag) **(** [Flag](#enum-hingejoint-flag) flag **)** const |
| [float](class_float#class-float) | [get\_param](#class-hingejoint-method-get-param) **(** [Param](#enum-hingejoint-param) param **)** const |
| void | [set\_flag](#class-hingejoint-method-set-flag) **(** [Flag](#enum-hingejoint-flag) flag, [bool](class_bool#class-bool) enabled **)** |
| void | [set\_param](#class-hingejoint-method-set-param) **(** [Param](#enum-hingejoint-param) param, [float](class_float#class-float) value **)** |
Enumerations
------------
enum **Param**:
* **PARAM\_BIAS** = **0** --- The speed with which the two bodies get pulled together when they move in different directions.
* **PARAM\_LIMIT\_UPPER** = **1** --- The maximum rotation. Only active if [angular\_limit/enable](#class-hingejoint-property-angular-limit-enable) is `true`.
* **PARAM\_LIMIT\_LOWER** = **2** --- The minimum rotation. Only active if [angular\_limit/enable](#class-hingejoint-property-angular-limit-enable) is `true`.
* **PARAM\_LIMIT\_BIAS** = **3** --- The speed with which the rotation across the axis perpendicular to the hinge gets corrected.
* **PARAM\_LIMIT\_SOFTNESS** = **4**
* **PARAM\_LIMIT\_RELAXATION** = **5** --- The lower this value, the more the rotation gets slowed down.
* **PARAM\_MOTOR\_TARGET\_VELOCITY** = **6** --- Target speed for the motor.
* **PARAM\_MOTOR\_MAX\_IMPULSE** = **7** --- Maximum acceleration for the motor.
* **PARAM\_MAX** = **8** --- Represents the size of the [Param](#enum-hingejoint-param) enum.
enum **Flag**:
* **FLAG\_USE\_LIMIT** = **0** --- If `true`, the hinges maximum and minimum rotation, defined by [angular\_limit/lower](#class-hingejoint-property-angular-limit-lower) and [angular\_limit/upper](#class-hingejoint-property-angular-limit-upper) has effects.
* **FLAG\_ENABLE\_MOTOR** = **1** --- When activated, a motor turns the hinge.
* **FLAG\_MAX** = **2** --- Represents the size of the [Flag](#enum-hingejoint-flag) enum.
Property Descriptions
---------------------
### [float](class_float#class-float) angular\_limit/bias
| | |
| --- | --- |
| *Default* | `0.3` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
The speed with which the rotation across the axis perpendicular to the hinge gets corrected.
### [bool](class_bool#class-bool) angular\_limit/enable
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
If `true`, the hinges maximum and minimum rotation, defined by [angular\_limit/lower](#class-hingejoint-property-angular-limit-lower) and [angular\_limit/upper](#class-hingejoint-property-angular-limit-upper) has effects.
### [float](class_float#class-float) angular\_limit/lower
| | |
| --- | --- |
| *Default* | `-90.0` |
The minimum rotation. Only active if [angular\_limit/enable](#class-hingejoint-property-angular-limit-enable) is `true`.
### [float](class_float#class-float) angular\_limit/relaxation
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
The lower this value, the more the rotation gets slowed down.
### [float](class_float#class-float) angular\_limit/softness
| | |
| --- | --- |
| *Default* | `0.9` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
### [float](class_float#class-float) angular\_limit/upper
| | |
| --- | --- |
| *Default* | `90.0` |
The maximum rotation. Only active if [angular\_limit/enable](#class-hingejoint-property-angular-limit-enable) is `true`.
### [bool](class_bool#class-bool) motor/enable
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_flag(value) |
| *Getter* | get\_flag() |
When activated, a motor turns the hinge.
### [float](class_float#class-float) motor/max\_impulse
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
Maximum acceleration for the motor.
### [float](class_float#class-float) motor/target\_velocity
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
Target speed for the motor.
### [float](class_float#class-float) params/bias
| | |
| --- | --- |
| *Default* | `0.3` |
| *Setter* | set\_param(value) |
| *Getter* | get\_param() |
The speed with which the two bodies get pulled together when they move in different directions.
Method Descriptions
-------------------
### [bool](class_bool#class-bool) get\_flag ( [Flag](#enum-hingejoint-flag) flag ) const
Returns the value of the specified flag.
### [float](class_float#class-float) get\_param ( [Param](#enum-hingejoint-param) param ) const
Returns the value of the specified parameter.
### void set\_flag ( [Flag](#enum-hingejoint-flag) flag, [bool](class_bool#class-bool) enabled )
If `true`, enables the specified flag.
### void set\_param ( [Param](#enum-hingejoint-param) param, [float](class_float#class-float) value )
Sets the value of the specified parameter.
godot InputMap InputMap
========
**Inherits:** [Object](class_object#class-object)
Singleton that manages [InputEventAction](class_inputeventaction#class-inputeventaction).
Description
-----------
Manages all [InputEventAction](class_inputeventaction#class-inputeventaction) which can be created/modified from the project settings menu **Project > Project Settings > Input Map** or in code with [add\_action](#class-inputmap-method-add-action) and [action\_add\_event](#class-inputmap-method-action-add-event). See [Node.\_input](class_node#class-node-method-input).
Tutorials
---------
* [#inputmap](https://docs.godotengine.org/en/3.5/tutorials/inputs/inputevent.html#inputmap) in [Using InputEvent](https://docs.godotengine.org/en/3.5/tutorials/inputs/inputevent.html)
Methods
-------
| | |
| --- | --- |
| void | [action\_add\_event](#class-inputmap-method-action-add-event) **(** [String](class_string#class-string) action, [InputEvent](class_inputevent#class-inputevent) event **)** |
| void | [action\_erase\_event](#class-inputmap-method-action-erase-event) **(** [String](class_string#class-string) action, [InputEvent](class_inputevent#class-inputevent) event **)** |
| void | [action\_erase\_events](#class-inputmap-method-action-erase-events) **(** [String](class_string#class-string) action **)** |
| [float](class_float#class-float) | [action\_get\_deadzone](#class-inputmap-method-action-get-deadzone) **(** [String](class_string#class-string) action **)** |
| [bool](class_bool#class-bool) | [action\_has\_event](#class-inputmap-method-action-has-event) **(** [String](class_string#class-string) action, [InputEvent](class_inputevent#class-inputevent) event **)** |
| void | [action\_set\_deadzone](#class-inputmap-method-action-set-deadzone) **(** [String](class_string#class-string) action, [float](class_float#class-float) deadzone **)** |
| void | [add\_action](#class-inputmap-method-add-action) **(** [String](class_string#class-string) action, [float](class_float#class-float) deadzone=0.5 **)** |
| void | [erase\_action](#class-inputmap-method-erase-action) **(** [String](class_string#class-string) action **)** |
| [bool](class_bool#class-bool) | [event\_is\_action](#class-inputmap-method-event-is-action) **(** [InputEvent](class_inputevent#class-inputevent) event, [String](class_string#class-string) action, [bool](class_bool#class-bool) exact\_match=false **)** const |
| [Array](class_array#class-array) | [get\_action\_list](#class-inputmap-method-get-action-list) **(** [String](class_string#class-string) action **)** |
| [Array](class_array#class-array) | [get\_actions](#class-inputmap-method-get-actions) **(** **)** |
| [bool](class_bool#class-bool) | [has\_action](#class-inputmap-method-has-action) **(** [String](class_string#class-string) action **)** const |
| void | [load\_from\_globals](#class-inputmap-method-load-from-globals) **(** **)** |
Method Descriptions
-------------------
### void action\_add\_event ( [String](class_string#class-string) action, [InputEvent](class_inputevent#class-inputevent) event )
Adds an [InputEvent](class_inputevent#class-inputevent) to an action. This [InputEvent](class_inputevent#class-inputevent) will trigger the action.
### void action\_erase\_event ( [String](class_string#class-string) action, [InputEvent](class_inputevent#class-inputevent) event )
Removes an [InputEvent](class_inputevent#class-inputevent) from an action.
### void action\_erase\_events ( [String](class_string#class-string) action )
Removes all events from an action.
### [float](class_float#class-float) action\_get\_deadzone ( [String](class_string#class-string) action )
Returns a deadzone value for the action.
### [bool](class_bool#class-bool) action\_has\_event ( [String](class_string#class-string) action, [InputEvent](class_inputevent#class-inputevent) event )
Returns `true` if the action has the given [InputEvent](class_inputevent#class-inputevent) associated with it.
### void action\_set\_deadzone ( [String](class_string#class-string) action, [float](class_float#class-float) deadzone )
Sets a deadzone value for the action.
### void add\_action ( [String](class_string#class-string) action, [float](class_float#class-float) deadzone=0.5 )
Adds an empty action to the `InputMap` with a configurable `deadzone`.
An [InputEvent](class_inputevent#class-inputevent) can then be added to this action with [action\_add\_event](#class-inputmap-method-action-add-event).
### void erase\_action ( [String](class_string#class-string) action )
Removes an action from the `InputMap`.
### [bool](class_bool#class-bool) event\_is\_action ( [InputEvent](class_inputevent#class-inputevent) event, [String](class_string#class-string) action, [bool](class_bool#class-bool) exact\_match=false ) const
Returns `true` if the given event is part of an existing action. This method ignores keyboard modifiers if the given [InputEvent](class_inputevent#class-inputevent) is not pressed (for proper release detection). See [action\_has\_event](#class-inputmap-method-action-has-event) if you don't want this behavior.
If `exact_match` is `false`, it ignores additional input modifiers for [InputEventKey](class_inputeventkey#class-inputeventkey) and [InputEventMouseButton](class_inputeventmousebutton#class-inputeventmousebutton) events, and the direction for [InputEventJoypadMotion](class_inputeventjoypadmotion#class-inputeventjoypadmotion) events.
### [Array](class_array#class-array) get\_action\_list ( [String](class_string#class-string) action )
Returns an array of [InputEvent](class_inputevent#class-inputevent)s associated with a given action.
**Note:** When used in the editor (e.g. a tool script or [EditorPlugin](class_editorplugin#class-editorplugin)), this method will return events for the editor action. If you want to access your project's input binds from the editor, read the `input/*` settings from [ProjectSettings](class_projectsettings#class-projectsettings).
### [Array](class_array#class-array) get\_actions ( )
Returns an array of all actions in the `InputMap`.
### [bool](class_bool#class-bool) has\_action ( [String](class_string#class-string) action ) const
Returns `true` if the `InputMap` has a registered action with the given name.
### void load\_from\_globals ( )
Clears all [InputEventAction](class_inputeventaction#class-inputeventaction) in the `InputMap` and load it anew from [ProjectSettings](class_projectsettings#class-projectsettings).
godot VisualScriptBasicTypeConstant VisualScriptBasicTypeConstant
=============================
**Inherits:** [VisualScriptNode](class_visualscriptnode#class-visualscriptnode) **<** [Resource](class_resource#class-resource) **<** [Reference](class_reference#class-reference) **<** [Object](class_object#class-object)
A Visual Script node representing a constant from the base types.
Description
-----------
A Visual Script node representing a constant from base types, such as [Vector3.AXIS\_X](class_vector3#class-vector3-constant-axis-x).
Properties
----------
| | | |
| --- | --- | --- |
| [Variant.Type](class_%40globalscope#enum-globalscope-variant-type) | [basic\_type](#class-visualscriptbasictypeconstant-property-basic-type) | `0` |
| [String](class_string#class-string) | [constant](#class-visualscriptbasictypeconstant-property-constant) | |
Property Descriptions
---------------------
### [Variant.Type](class_%40globalscope#enum-globalscope-variant-type) basic\_type
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_basic\_type(value) |
| *Getter* | get\_basic\_type() |
The type to get the constant from.
### [String](class_string#class-string) constant
| | |
| --- | --- |
| *Setter* | set\_basic\_type\_constant(value) |
| *Getter* | get\_basic\_type\_constant() |
The name of the constant to return.
godot Label Label
=====
**Inherits:** [Control](class_control#class-control) **<** [CanvasItem](class_canvasitem#class-canvasitem) **<** [Node](class_node#class-node) **<** [Object](class_object#class-object)
Displays plain text in a line or wrapped inside a rectangle. For formatted text, use [RichTextLabel](class_richtextlabel#class-richtextlabel).
Description
-----------
Label displays plain text on the screen. It gives you control over the horizontal and vertical alignment and can wrap the text inside the node's bounding rectangle. It doesn't support bold, italics, or other formatting. For that, use [RichTextLabel](class_richtextlabel#class-richtextlabel) instead.
**Note:** Contrarily to most other [Control](class_control#class-control)s, Label's [Control.mouse\_filter](class_control#class-control-property-mouse-filter) defaults to [Control.MOUSE\_FILTER\_IGNORE](class_control#class-control-constant-mouse-filter-ignore) (i.e. it doesn't react to mouse input events). This implies that a label won't display any configured [Control.hint\_tooltip](class_control#class-control-property-hint-tooltip), unless you change its mouse filter.
**Note:** Unicode characters after `0xffff` (such as most emoji) are *not* supported on Windows. They will display as unknown characters instead. This will be resolved in Godot 4.0.
Tutorials
---------
* [2D Dodge The Creeps Demo](https://godotengine.org/asset-library/asset/515)
Properties
----------
| | | |
| --- | --- | --- |
| [Align](#enum-label-align) | [align](#class-label-property-align) | `0` |
| [bool](class_bool#class-bool) | [autowrap](#class-label-property-autowrap) | `false` |
| [bool](class_bool#class-bool) | [clip\_text](#class-label-property-clip-text) | `false` |
| [int](class_int#class-int) | [lines\_skipped](#class-label-property-lines-skipped) | `0` |
| [int](class_int#class-int) | [max\_lines\_visible](#class-label-property-max-lines-visible) | `-1` |
| [MouseFilter](class_control#enum-control-mousefilter) | mouse\_filter | `2` (overrides [Control](class_control#class-control-property-mouse-filter)) |
| [float](class_float#class-float) | [percent\_visible](#class-label-property-percent-visible) | `1.0` |
| [int](class_int#class-int) | size\_flags\_vertical | `4` (overrides [Control](class_control#class-control-property-size-flags-vertical)) |
| [String](class_string#class-string) | [text](#class-label-property-text) | `""` |
| [bool](class_bool#class-bool) | [uppercase](#class-label-property-uppercase) | `false` |
| [VAlign](#enum-label-valign) | [valign](#class-label-property-valign) | `0` |
| [int](class_int#class-int) | [visible\_characters](#class-label-property-visible-characters) | `-1` |
Methods
-------
| | |
| --- | --- |
| [int](class_int#class-int) | [get\_line\_count](#class-label-method-get-line-count) **(** **)** const |
| [int](class_int#class-int) | [get\_line\_height](#class-label-method-get-line-height) **(** **)** const |
| [int](class_int#class-int) | [get\_total\_character\_count](#class-label-method-get-total-character-count) **(** **)** const |
| [int](class_int#class-int) | [get\_visible\_line\_count](#class-label-method-get-visible-line-count) **(** **)** const |
Theme Properties
----------------
| | | |
| --- | --- | --- |
| [Color](class_color#class-color) | [font\_color](#class-label-theme-color-font-color) | `Color( 1, 1, 1, 1 )` |
| [Color](class_color#class-color) | [font\_color\_shadow](#class-label-theme-color-font-color-shadow) | `Color( 0, 0, 0, 0 )` |
| [Color](class_color#class-color) | [font\_outline\_modulate](#class-label-theme-color-font-outline-modulate) | `Color( 1, 1, 1, 1 )` |
| [int](class_int#class-int) | [line\_spacing](#class-label-theme-constant-line-spacing) | `3` |
| [int](class_int#class-int) | [shadow\_as\_outline](#class-label-theme-constant-shadow-as-outline) | `0` |
| [int](class_int#class-int) | [shadow\_offset\_x](#class-label-theme-constant-shadow-offset-x) | `1` |
| [int](class_int#class-int) | [shadow\_offset\_y](#class-label-theme-constant-shadow-offset-y) | `1` |
| [Font](class_font#class-font) | [font](#class-label-theme-font-font) | |
| [StyleBox](class_stylebox#class-stylebox) | [normal](#class-label-theme-style-normal) | |
Enumerations
------------
enum **Align**:
* **ALIGN\_LEFT** = **0** --- Align rows to the left (default).
* **ALIGN\_CENTER** = **1** --- Align rows centered.
* **ALIGN\_RIGHT** = **2** --- Align rows to the right.
* **ALIGN\_FILL** = **3** --- Expand row whitespaces to fit the width.
enum **VAlign**:
* **VALIGN\_TOP** = **0** --- Align the whole text to the top.
* **VALIGN\_CENTER** = **1** --- Align the whole text to the center.
* **VALIGN\_BOTTOM** = **2** --- Align the whole text to the bottom.
* **VALIGN\_FILL** = **3** --- Align the whole text by spreading the rows.
Property Descriptions
---------------------
### [Align](#enum-label-align) align
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_align(value) |
| *Getter* | get\_align() |
Controls the text's horizontal align. Supports left, center, right, and fill, or justify. Set it to one of the [Align](#enum-label-align) constants.
### [bool](class_bool#class-bool) autowrap
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_autowrap(value) |
| *Getter* | has\_autowrap() |
If `true`, wraps the text inside the node's bounding rectangle. If you resize the node, it will change its height automatically to show all the text.
### [bool](class_bool#class-bool) clip\_text
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_clip\_text(value) |
| *Getter* | is\_clipping\_text() |
If `true`, the Label only shows the text that fits inside its bounding rectangle and will clip text horizontally.
### [int](class_int#class-int) lines\_skipped
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_lines\_skipped(value) |
| *Getter* | get\_lines\_skipped() |
The node ignores the first `lines_skipped` lines before it starts to display text.
### [int](class_int#class-int) max\_lines\_visible
| | |
| --- | --- |
| *Default* | `-1` |
| *Setter* | set\_max\_lines\_visible(value) |
| *Getter* | get\_max\_lines\_visible() |
Limits the lines of text the node shows on screen.
### [float](class_float#class-float) percent\_visible
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_percent\_visible(value) |
| *Getter* | get\_percent\_visible() |
Limits the amount of visible characters. If you set `percent_visible` to 0.5, only up to half of the text's characters will display on screen. Useful to animate the text in a dialog box.
### [String](class_string#class-string) text
| | |
| --- | --- |
| *Default* | `""` |
| *Setter* | set\_text(value) |
| *Getter* | get\_text() |
The text to display on screen.
### [bool](class_bool#class-bool) uppercase
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_uppercase(value) |
| *Getter* | is\_uppercase() |
If `true`, all the text displays as UPPERCASE.
### [VAlign](#enum-label-valign) valign
| | |
| --- | --- |
| *Default* | `0` |
| *Setter* | set\_valign(value) |
| *Getter* | get\_valign() |
Controls the text's vertical align. Supports top, center, bottom, and fill. Set it to one of the [VAlign](#enum-label-valign) constants.
### [int](class_int#class-int) visible\_characters
| | |
| --- | --- |
| *Default* | `-1` |
| *Setter* | set\_visible\_characters(value) |
| *Getter* | get\_visible\_characters() |
Restricts the number of characters to display. Set to -1 to disable.
Method Descriptions
-------------------
### [int](class_int#class-int) get\_line\_count ( ) const
Returns the amount of lines of text the Label has.
### [int](class_int#class-int) get\_line\_height ( ) const
Returns the font size in pixels.
### [int](class_int#class-int) get\_total\_character\_count ( ) const
Returns the total number of printable characters in the text (excluding spaces and newlines).
### [int](class_int#class-int) get\_visible\_line\_count ( ) const
Returns the number of lines shown. Useful if the `Label`'s height cannot currently display all lines.
Theme Property Descriptions
---------------------------
### [Color](class_color#class-color) font\_color
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
Default text [Color](class_color#class-color) of the `Label`.
### [Color](class_color#class-color) font\_color\_shadow
| | |
| --- | --- |
| *Default* | `Color( 0, 0, 0, 0 )` |
[Color](class_color#class-color) of the text's shadow effect.
### [Color](class_color#class-color) font\_outline\_modulate
| | |
| --- | --- |
| *Default* | `Color( 1, 1, 1, 1 )` |
The tint of [Font](class_font#class-font)'s outline. See [DynamicFont.outline\_color](class_dynamicfont#class-dynamicfont-property-outline-color).
### [int](class_int#class-int) line\_spacing
| | |
| --- | --- |
| *Default* | `3` |
Vertical space between lines in multiline `Label`.
### [int](class_int#class-int) shadow\_as\_outline
| | |
| --- | --- |
| *Default* | `0` |
Boolean value. If set to 1 (`true`), the shadow will be displayed around the whole text as an outline.
### [int](class_int#class-int) shadow\_offset\_x
| | |
| --- | --- |
| *Default* | `1` |
The horizontal offset of the text's shadow.
### [int](class_int#class-int) shadow\_offset\_y
| | |
| --- | --- |
| *Default* | `1` |
The vertical offset of the text's shadow.
### [Font](class_font#class-font) font
[Font](class_font#class-font) used for the `Label`'s text.
### [StyleBox](class_stylebox#class-stylebox) normal
Background [StyleBox](class_stylebox#class-stylebox) for the `Label`.
| programming_docs |
godot NavigationObstacle2D NavigationObstacle2D
====================
**Inherits:** [Node](class_node#class-node) **<** [Object](class_object#class-object)
2D obstacle used in navigation for collision avoidance.
Description
-----------
2D obstacle used in navigation for collision avoidance. The obstacle needs navigation data to work correctly. This can be done by having the obstacle as a child of a [Navigation2D](class_navigation2d#class-navigation2d) node, or using [set\_navigation](#class-navigationobstacle2d-method-set-navigation). `NavigationObstacle2D` is physics safe.
**Note:** Obstacles are intended as a last resort option for constantly moving objects that cannot be (re)baked to a navigation mesh efficiently.
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [estimate\_radius](#class-navigationobstacle2d-property-estimate-radius) | `true` |
| [float](class_float#class-float) | [radius](#class-navigationobstacle2d-property-radius) | `1.0` |
Methods
-------
| | |
| --- | --- |
| [Node](class_node#class-node) | [get\_navigation](#class-navigationobstacle2d-method-get-navigation) **(** **)** const |
| [RID](class_rid#class-rid) | [get\_rid](#class-navigationobstacle2d-method-get-rid) **(** **)** const |
| void | [set\_navigation](#class-navigationobstacle2d-method-set-navigation) **(** [Node](class_node#class-node) navigation **)** |
Property Descriptions
---------------------
### [bool](class_bool#class-bool) estimate\_radius
| | |
| --- | --- |
| *Default* | `true` |
| *Setter* | set\_estimate\_radius(value) |
| *Getter* | is\_radius\_estimated() |
Enables radius estimation algorithm which uses parent's collision shapes to determine the obstacle radius.
### [float](class_float#class-float) radius
| | |
| --- | --- |
| *Default* | `1.0` |
| *Setter* | set\_radius(value) |
| *Getter* | get\_radius() |
The radius of the agent. Used only if [estimate\_radius](#class-navigationobstacle2d-property-estimate-radius) is set to `false`.
Method Descriptions
-------------------
### [Node](class_node#class-node) get\_navigation ( ) const
Returns the [Navigation2D](class_navigation2d#class-navigation2d) node that the obstacle is using for its navigation system.
### [RID](class_rid#class-rid) get\_rid ( ) const
Returns the [RID](class_rid#class-rid) of this obstacle on the [Navigation2DServer](class_navigation2dserver#class-navigation2dserver).
### void set\_navigation ( [Node](class_node#class-node) navigation )
Sets the [Navigation2D](class_navigation2d#class-navigation2d) node used by the obstacle. Useful when you don't want to make the obstacle a child of a [Navigation2D](class_navigation2d#class-navigation2d) node.
godot AnimationTreePlayer AnimationTreePlayer
===================
**Inherits:** [Node](class_node#class-node) **<** [Object](class_object#class-object)
*Deprecated.* Animation player that uses a node graph for blending animations. Superseded by [AnimationTree](class_animationtree#class-animationtree).
Description
-----------
*Deprecated.* A node graph tool for blending multiple animations bound to an [AnimationPlayer](class_animationplayer#class-animationplayer). Especially useful for animating characters or other skeleton-based rigs. It can combine several animations to form a desired pose.
It takes [Animation](class_animation#class-animation)s from an [AnimationPlayer](class_animationplayer#class-animationplayer) node and mixes them depending on the graph.
See [AnimationTree](class_animationtree#class-animationtree) for a more full-featured replacement of this node.
Tutorials
---------
* [Using AnimationTree](https://docs.godotengine.org/en/3.5/tutorials/animation/animation_tree.html)
Properties
----------
| | | |
| --- | --- | --- |
| [bool](class_bool#class-bool) | [active](#class-animationtreeplayer-property-active) | `false` |
| [NodePath](class_nodepath#class-nodepath) | [base\_path](#class-animationtreeplayer-property-base-path) | `NodePath("..")` |
| [NodePath](class_nodepath#class-nodepath) | [master\_player](#class-animationtreeplayer-property-master-player) | `NodePath("")` |
| [AnimationProcessMode](#enum-animationtreeplayer-animationprocessmode) | [playback\_process\_mode](#class-animationtreeplayer-property-playback-process-mode) | `1` |
Methods
-------
| | |
| --- | --- |
| void | [add\_node](#class-animationtreeplayer-method-add-node) **(** [NodeType](#enum-animationtreeplayer-nodetype) type, [String](class_string#class-string) id **)** |
| void | [advance](#class-animationtreeplayer-method-advance) **(** [float](class_float#class-float) delta **)** |
| [Animation](class_animation#class-animation) | [animation\_node\_get\_animation](#class-animationtreeplayer-method-animation-node-get-animation) **(** [String](class_string#class-string) id **)** const |
| [String](class_string#class-string) | [animation\_node\_get\_master\_animation](#class-animationtreeplayer-method-animation-node-get-master-animation) **(** [String](class_string#class-string) id **)** const |
| [float](class_float#class-float) | [animation\_node\_get\_position](#class-animationtreeplayer-method-animation-node-get-position) **(** [String](class_string#class-string) id **)** const |
| void | [animation\_node\_set\_animation](#class-animationtreeplayer-method-animation-node-set-animation) **(** [String](class_string#class-string) id, [Animation](class_animation#class-animation) animation **)** |
| void | [animation\_node\_set\_filter\_path](#class-animationtreeplayer-method-animation-node-set-filter-path) **(** [String](class_string#class-string) id, [NodePath](class_nodepath#class-nodepath) path, [bool](class_bool#class-bool) enable **)** |
| void | [animation\_node\_set\_master\_animation](#class-animationtreeplayer-method-animation-node-set-master-animation) **(** [String](class_string#class-string) id, [String](class_string#class-string) source **)** |
| [bool](class_bool#class-bool) | [are\_nodes\_connected](#class-animationtreeplayer-method-are-nodes-connected) **(** [String](class_string#class-string) id, [String](class_string#class-string) dst\_id, [int](class_int#class-int) dst\_input\_idx **)** const |
| [float](class_float#class-float) | [blend2\_node\_get\_amount](#class-animationtreeplayer-method-blend2-node-get-amount) **(** [String](class_string#class-string) id **)** const |
| void | [blend2\_node\_set\_amount](#class-animationtreeplayer-method-blend2-node-set-amount) **(** [String](class_string#class-string) id, [float](class_float#class-float) blend **)** |
| void | [blend2\_node\_set\_filter\_path](#class-animationtreeplayer-method-blend2-node-set-filter-path) **(** [String](class_string#class-string) id, [NodePath](class_nodepath#class-nodepath) path, [bool](class_bool#class-bool) enable **)** |
| [float](class_float#class-float) | [blend3\_node\_get\_amount](#class-animationtreeplayer-method-blend3-node-get-amount) **(** [String](class_string#class-string) id **)** const |
| void | [blend3\_node\_set\_amount](#class-animationtreeplayer-method-blend3-node-set-amount) **(** [String](class_string#class-string) id, [float](class_float#class-float) blend **)** |
| [Vector2](class_vector2#class-vector2) | [blend4\_node\_get\_amount](#class-animationtreeplayer-method-blend4-node-get-amount) **(** [String](class_string#class-string) id **)** const |
| void | [blend4\_node\_set\_amount](#class-animationtreeplayer-method-blend4-node-set-amount) **(** [String](class_string#class-string) id, [Vector2](class_vector2#class-vector2) blend **)** |
| [Error](class_%40globalscope#enum-globalscope-error) | [connect\_nodes](#class-animationtreeplayer-method-connect-nodes) **(** [String](class_string#class-string) id, [String](class_string#class-string) dst\_id, [int](class_int#class-int) dst\_input\_idx **)** |
| void | [disconnect\_nodes](#class-animationtreeplayer-method-disconnect-nodes) **(** [String](class_string#class-string) id, [int](class_int#class-int) dst\_input\_idx **)** |
| [PoolStringArray](class_poolstringarray#class-poolstringarray) | [get\_node\_list](#class-animationtreeplayer-method-get-node-list) **(** **)** |
| [float](class_float#class-float) | [mix\_node\_get\_amount](#class-animationtreeplayer-method-mix-node-get-amount) **(** [String](class_string#class-string) id **)** const |
| void | [mix\_node\_set\_amount](#class-animationtreeplayer-method-mix-node-set-amount) **(** [String](class_string#class-string) id, [float](class_float#class-float) ratio **)** |
| [bool](class_bool#class-bool) | [node\_exists](#class-animationtreeplayer-method-node-exists) **(** [String](class_string#class-string) node **)** const |
| [int](class_int#class-int) | [node\_get\_input\_count](#class-animationtreeplayer-method-node-get-input-count) **(** [String](class_string#class-string) id **)** const |
| [String](class_string#class-string) | [node\_get\_input\_source](#class-animationtreeplayer-method-node-get-input-source) **(** [String](class_string#class-string) id, [int](class_int#class-int) idx **)** const |
| [Vector2](class_vector2#class-vector2) | [node\_get\_position](#class-animationtreeplayer-method-node-get-position) **(** [String](class_string#class-string) id **)** const |
| [NodeType](#enum-animationtreeplayer-nodetype) | [node\_get\_type](#class-animationtreeplayer-method-node-get-type) **(** [String](class_string#class-string) id **)** const |
| [Error](class_%40globalscope#enum-globalscope-error) | [node\_rename](#class-animationtreeplayer-method-node-rename) **(** [String](class_string#class-string) node, [String](class_string#class-string) new\_name **)** |
| void | [node\_set\_position](#class-animationtreeplayer-method-node-set-position) **(** [String](class_string#class-string) id, [Vector2](class_vector2#class-vector2) screen\_position **)** |
| [float](class_float#class-float) | [oneshot\_node\_get\_autorestart\_delay](#class-animationtreeplayer-method-oneshot-node-get-autorestart-delay) **(** [String](class_string#class-string) id **)** const |
| [float](class_float#class-float) | [oneshot\_node\_get\_autorestart\_random\_delay](#class-animationtreeplayer-method-oneshot-node-get-autorestart-random-delay) **(** [String](class_string#class-string) id **)** const |
| [float](class_float#class-float) | [oneshot\_node\_get\_fadein\_time](#class-animationtreeplayer-method-oneshot-node-get-fadein-time) **(** [String](class_string#class-string) id **)** const |
| [float](class_float#class-float) | [oneshot\_node\_get\_fadeout\_time](#class-animationtreeplayer-method-oneshot-node-get-fadeout-time) **(** [String](class_string#class-string) id **)** const |
| [bool](class_bool#class-bool) | [oneshot\_node\_has\_autorestart](#class-animationtreeplayer-method-oneshot-node-has-autorestart) **(** [String](class_string#class-string) id **)** const |
| [bool](class_bool#class-bool) | [oneshot\_node\_is\_active](#class-animationtreeplayer-method-oneshot-node-is-active) **(** [String](class_string#class-string) id **)** const |
| void | [oneshot\_node\_set\_autorestart](#class-animationtreeplayer-method-oneshot-node-set-autorestart) **(** [String](class_string#class-string) id, [bool](class_bool#class-bool) enable **)** |
| void | [oneshot\_node\_set\_autorestart\_delay](#class-animationtreeplayer-method-oneshot-node-set-autorestart-delay) **(** [String](class_string#class-string) id, [float](class_float#class-float) delay\_sec **)** |
| void | [oneshot\_node\_set\_autorestart\_random\_delay](#class-animationtreeplayer-method-oneshot-node-set-autorestart-random-delay) **(** [String](class_string#class-string) id, [float](class_float#class-float) rand\_sec **)** |
| void | [oneshot\_node\_set\_fadein\_time](#class-animationtreeplayer-method-oneshot-node-set-fadein-time) **(** [String](class_string#class-string) id, [float](class_float#class-float) time\_sec **)** |
| void | [oneshot\_node\_set\_fadeout\_time](#class-animationtreeplayer-method-oneshot-node-set-fadeout-time) **(** [String](class_string#class-string) id, [float](class_float#class-float) time\_sec **)** |
| void | [oneshot\_node\_set\_filter\_path](#class-animationtreeplayer-method-oneshot-node-set-filter-path) **(** [String](class_string#class-string) id, [NodePath](class_nodepath#class-nodepath) path, [bool](class_bool#class-bool) enable **)** |
| void | [oneshot\_node\_start](#class-animationtreeplayer-method-oneshot-node-start) **(** [String](class_string#class-string) id **)** |
| void | [oneshot\_node\_stop](#class-animationtreeplayer-method-oneshot-node-stop) **(** [String](class_string#class-string) id **)** |
| void | [recompute\_caches](#class-animationtreeplayer-method-recompute-caches) **(** **)** |
| void | [remove\_node](#class-animationtreeplayer-method-remove-node) **(** [String](class_string#class-string) id **)** |
| void | [reset](#class-animationtreeplayer-method-reset) **(** **)** |
| [float](class_float#class-float) | [timescale\_node\_get\_scale](#class-animationtreeplayer-method-timescale-node-get-scale) **(** [String](class_string#class-string) id **)** const |
| void | [timescale\_node\_set\_scale](#class-animationtreeplayer-method-timescale-node-set-scale) **(** [String](class_string#class-string) id, [float](class_float#class-float) scale **)** |
| void | [timeseek\_node\_seek](#class-animationtreeplayer-method-timeseek-node-seek) **(** [String](class_string#class-string) id, [float](class_float#class-float) seconds **)** |
| void | [transition\_node\_delete\_input](#class-animationtreeplayer-method-transition-node-delete-input) **(** [String](class_string#class-string) id, [int](class_int#class-int) input\_idx **)** |
| [int](class_int#class-int) | [transition\_node\_get\_current](#class-animationtreeplayer-method-transition-node-get-current) **(** [String](class_string#class-string) id **)** const |
| [int](class_int#class-int) | [transition\_node\_get\_input\_count](#class-animationtreeplayer-method-transition-node-get-input-count) **(** [String](class_string#class-string) id **)** const |
| [float](class_float#class-float) | [transition\_node\_get\_xfade\_time](#class-animationtreeplayer-method-transition-node-get-xfade-time) **(** [String](class_string#class-string) id **)** const |
| [bool](class_bool#class-bool) | [transition\_node\_has\_input\_auto\_advance](#class-animationtreeplayer-method-transition-node-has-input-auto-advance) **(** [String](class_string#class-string) id, [int](class_int#class-int) input\_idx **)** const |
| void | [transition\_node\_set\_current](#class-animationtreeplayer-method-transition-node-set-current) **(** [String](class_string#class-string) id, [int](class_int#class-int) input\_idx **)** |
| void | [transition\_node\_set\_input\_auto\_advance](#class-animationtreeplayer-method-transition-node-set-input-auto-advance) **(** [String](class_string#class-string) id, [int](class_int#class-int) input\_idx, [bool](class_bool#class-bool) enable **)** |
| void | [transition\_node\_set\_input\_count](#class-animationtreeplayer-method-transition-node-set-input-count) **(** [String](class_string#class-string) id, [int](class_int#class-int) count **)** |
| void | [transition\_node\_set\_xfade\_time](#class-animationtreeplayer-method-transition-node-set-xfade-time) **(** [String](class_string#class-string) id, [float](class_float#class-float) time\_sec **)** |
Enumerations
------------
enum **NodeType**:
* **NODE\_OUTPUT** = **0** --- Output node.
* **NODE\_ANIMATION** = **1** --- Animation node.
* **NODE\_ONESHOT** = **2** --- OneShot node.
* **NODE\_MIX** = **3** --- Mix node.
* **NODE\_BLEND2** = **4** --- Blend2 node.
* **NODE\_BLEND3** = **5** --- Blend3 node.
* **NODE\_BLEND4** = **6** --- Blend4 node.
* **NODE\_TIMESCALE** = **7** --- TimeScale node.
* **NODE\_TIMESEEK** = **8** --- TimeSeek node.
* **NODE\_TRANSITION** = **9** --- Transition node.
enum **AnimationProcessMode**:
* **ANIMATION\_PROCESS\_PHYSICS** = **0** --- Process animation during the physics process. This is especially useful when animating physics bodies.
* **ANIMATION\_PROCESS\_IDLE** = **1** --- Process animation during the idle process.
Property Descriptions
---------------------
### [bool](class_bool#class-bool) active
| | |
| --- | --- |
| *Default* | `false` |
| *Setter* | set\_active(value) |
| *Getter* | is\_active() |
If `true`, the `AnimationTreePlayer` is able to play animations.
### [NodePath](class_nodepath#class-nodepath) base\_path
| | |
| --- | --- |
| *Default* | `NodePath("..")` |
| *Setter* | set\_base\_path(value) |
| *Getter* | get\_base\_path() |
The node from which to relatively access other nodes.
It accesses the bones, so it should point to the same node the [AnimationPlayer](class_animationplayer#class-animationplayer) would point its Root Node at.
### [NodePath](class_nodepath#class-nodepath) master\_player
| | |
| --- | --- |
| *Default* | `NodePath("")` |
| *Setter* | set\_master\_player(value) |
| *Getter* | get\_master\_player() |
The path to the [AnimationPlayer](class_animationplayer#class-animationplayer) from which this `AnimationTreePlayer` binds animations to animation nodes.
Once set, [Animation](class_animation#class-animation) nodes can be added to the `AnimationTreePlayer`.
### [AnimationProcessMode](#enum-animationtreeplayer-animationprocessmode) playback\_process\_mode
| | |
| --- | --- |
| *Default* | `1` |
| *Setter* | set\_animation\_process\_mode(value) |
| *Getter* | get\_animation\_process\_mode() |
The thread in which to update animations.
Method Descriptions
-------------------
### void add\_node ( [NodeType](#enum-animationtreeplayer-nodetype) type, [String](class_string#class-string) id )
Adds a `type` node to the graph with name `id`.
### void advance ( [float](class_float#class-float) delta )
Shifts position in the animation timeline. `delta` is the time in seconds to shift. Events between the current frame and `delta` are handled.
### [Animation](class_animation#class-animation) animation\_node\_get\_animation ( [String](class_string#class-string) id ) const
Returns the [AnimationPlayer](class_animationplayer#class-animationplayer)'s [Animation](class_animation#class-animation) bound to the `AnimationTreePlayer`'s animation node with name `id`.
### [String](class_string#class-string) animation\_node\_get\_master\_animation ( [String](class_string#class-string) id ) const
Returns the name of the [master\_player](#class-animationtreeplayer-property-master-player)'s [Animation](class_animation#class-animation) bound to this animation node.
### [float](class_float#class-float) animation\_node\_get\_position ( [String](class_string#class-string) id ) const
Returns the absolute playback timestamp of the animation node with name `id`.
### void animation\_node\_set\_animation ( [String](class_string#class-string) id, [Animation](class_animation#class-animation) animation )
Binds a new [Animation](class_animation#class-animation) from the [master\_player](#class-animationtreeplayer-property-master-player) to the `AnimationTreePlayer`'s animation node with name `id`.
### void animation\_node\_set\_filter\_path ( [String](class_string#class-string) id, [NodePath](class_nodepath#class-nodepath) path, [bool](class_bool#class-bool) enable )
If `enable` is `true`, the animation node with ID `id` turns off the track modifying the property at `path`. The modified node's children continue to animate.
### void animation\_node\_set\_master\_animation ( [String](class_string#class-string) id, [String](class_string#class-string) source )
Binds the [Animation](class_animation#class-animation) named `source` from [master\_player](#class-animationtreeplayer-property-master-player) to the animation node `id`. Recalculates caches.
### [bool](class_bool#class-bool) are\_nodes\_connected ( [String](class_string#class-string) id, [String](class_string#class-string) dst\_id, [int](class_int#class-int) dst\_input\_idx ) const
Returns whether node `id` and `dst_id` are connected at the specified slot.
### [float](class_float#class-float) blend2\_node\_get\_amount ( [String](class_string#class-string) id ) const
Returns the blend amount of a Blend2 node given its name.
### void blend2\_node\_set\_amount ( [String](class_string#class-string) id, [float](class_float#class-float) blend )
Sets the blend amount of a Blend2 node given its name and value.
A Blend2 node blends two animations (A and B) with the amount between 0 and 1.
At 0, output is input A. Towards 1, the influence of A gets lessened, the influence of B gets raised. At 1, output is input B.
### void blend2\_node\_set\_filter\_path ( [String](class_string#class-string) id, [NodePath](class_nodepath#class-nodepath) path, [bool](class_bool#class-bool) enable )
If `enable` is `true`, the Blend2 node with name `id` turns off the track modifying the property at `path`. The modified node's children continue to animate.
### [float](class_float#class-float) blend3\_node\_get\_amount ( [String](class_string#class-string) id ) const
Returns the blend amount of a Blend3 node given its name.
### void blend3\_node\_set\_amount ( [String](class_string#class-string) id, [float](class_float#class-float) blend )
Sets the blend amount of a Blend3 node given its name and value.
A Blend3 Node blends three animations (A, B-, B+) with the amount between -1 and 1.
At -1, output is input B-. From -1 to 0, the influence of B- gets lessened, the influence of A gets raised and the influence of B+ is 0. At 0, output is input A. From 0 to 1, the influence of A gets lessened, the influence of B+ gets raised and the influence of B+ is 0. At 1, output is input B+.
### [Vector2](class_vector2#class-vector2) blend4\_node\_get\_amount ( [String](class_string#class-string) id ) const
Returns the blend amount of a Blend4 node given its name.
### void blend4\_node\_set\_amount ( [String](class_string#class-string) id, [Vector2](class_vector2#class-vector2) blend )
Sets the blend amount of a Blend4 node given its name and value.
A Blend4 Node blends two pairs of animations.
The two pairs are blended like Blend2 and then added together.
### [Error](class_%40globalscope#enum-globalscope-error) connect\_nodes ( [String](class_string#class-string) id, [String](class_string#class-string) dst\_id, [int](class_int#class-int) dst\_input\_idx )
Connects node `id` to `dst_id` at the specified input slot.
### void disconnect\_nodes ( [String](class_string#class-string) id, [int](class_int#class-int) dst\_input\_idx )
Disconnects nodes connected to `id` at the specified input slot.
### [PoolStringArray](class_poolstringarray#class-poolstringarray) get\_node\_list ( )
Returns a [PoolStringArray](class_poolstringarray#class-poolstringarray) containing the name of all nodes.
### [float](class_float#class-float) mix\_node\_get\_amount ( [String](class_string#class-string) id ) const
Returns the mix amount of a Mix node given its name.
### void mix\_node\_set\_amount ( [String](class_string#class-string) id, [float](class_float#class-float) ratio )
Sets the mix amount of a Mix node given its name and value.
A Mix node adds input b to input a by the amount given by ratio.
### [bool](class_bool#class-bool) node\_exists ( [String](class_string#class-string) node ) const
Check if a node exists (by name).
### [int](class_int#class-int) node\_get\_input\_count ( [String](class_string#class-string) id ) const
Returns the input count for a given node. Different types of nodes have different amount of inputs.
### [String](class_string#class-string) node\_get\_input\_source ( [String](class_string#class-string) id, [int](class_int#class-int) idx ) const
Returns the input source for a given node input.
### [Vector2](class_vector2#class-vector2) node\_get\_position ( [String](class_string#class-string) id ) const
Returns position of a node in the graph given its name.
### [NodeType](#enum-animationtreeplayer-nodetype) node\_get\_type ( [String](class_string#class-string) id ) const
Gets the node type, will return from [NodeType](#enum-animationtreeplayer-nodetype) enum.
### [Error](class_%40globalscope#enum-globalscope-error) node\_rename ( [String](class_string#class-string) node, [String](class_string#class-string) new\_name )
Renames a node in the graph.
### void node\_set\_position ( [String](class_string#class-string) id, [Vector2](class_vector2#class-vector2) screen\_position )
Sets the position of a node in the graph given its name and position.
### [float](class_float#class-float) oneshot\_node\_get\_autorestart\_delay ( [String](class_string#class-string) id ) const
Returns the autostart delay of a OneShot node given its name.
### [float](class_float#class-float) oneshot\_node\_get\_autorestart\_random\_delay ( [String](class_string#class-string) id ) const
Returns the autostart random delay of a OneShot node given its name.
### [float](class_float#class-float) oneshot\_node\_get\_fadein\_time ( [String](class_string#class-string) id ) const
Returns the fade in time of a OneShot node given its name.
### [float](class_float#class-float) oneshot\_node\_get\_fadeout\_time ( [String](class_string#class-string) id ) const
Returns the fade out time of a OneShot node given its name.
### [bool](class_bool#class-bool) oneshot\_node\_has\_autorestart ( [String](class_string#class-string) id ) const
Returns whether a OneShot node will auto restart given its name.
### [bool](class_bool#class-bool) oneshot\_node\_is\_active ( [String](class_string#class-string) id ) const
Returns whether a OneShot node is active given its name.
### void oneshot\_node\_set\_autorestart ( [String](class_string#class-string) id, [bool](class_bool#class-bool) enable )
Sets the autorestart property of a OneShot node given its name and value.
### void oneshot\_node\_set\_autorestart\_delay ( [String](class_string#class-string) id, [float](class_float#class-float) delay\_sec )
Sets the autorestart delay of a OneShot node given its name and value in seconds.
### void oneshot\_node\_set\_autorestart\_random\_delay ( [String](class_string#class-string) id, [float](class_float#class-float) rand\_sec )
Sets the autorestart random delay of a OneShot node given its name and value in seconds.
### void oneshot\_node\_set\_fadein\_time ( [String](class_string#class-string) id, [float](class_float#class-float) time\_sec )
Sets the fade in time of a OneShot node given its name and value in seconds.
### void oneshot\_node\_set\_fadeout\_time ( [String](class_string#class-string) id, [float](class_float#class-float) time\_sec )
Sets the fade out time of a OneShot node given its name and value in seconds.
### void oneshot\_node\_set\_filter\_path ( [String](class_string#class-string) id, [NodePath](class_nodepath#class-nodepath) path, [bool](class_bool#class-bool) enable )
If `enable` is `true`, the OneShot node with ID `id` turns off the track modifying the property at `path`. The modified node's children continue to animate.
### void oneshot\_node\_start ( [String](class_string#class-string) id )
Starts a OneShot node given its name.
### void oneshot\_node\_stop ( [String](class_string#class-string) id )
Stops the OneShot node with name `id`.
### void recompute\_caches ( )
Manually recalculates the cache of track information generated from animation nodes. Needed when external sources modify the animation nodes' state.
### void remove\_node ( [String](class_string#class-string) id )
Removes the animation node with name `id`.
### void reset ( )
Resets this `AnimationTreePlayer`.
### [float](class_float#class-float) timescale\_node\_get\_scale ( [String](class_string#class-string) id ) const
Returns the time scale value of the TimeScale node with name `id`.
### void timescale\_node\_set\_scale ( [String](class_string#class-string) id, [float](class_float#class-float) scale )
Sets the time scale of the TimeScale node with name `id` to `scale`.
The TimeScale node is used to speed [Animation](class_animation#class-animation)s up if the scale is above 1 or slow them down if it is below 1.
If applied after a blend or mix, affects all input animations to that blend or mix.
### void timeseek\_node\_seek ( [String](class_string#class-string) id, [float](class_float#class-float) seconds )
Sets the time seek value of the TimeSeek node with name `id` to `seconds`.
This functions as a seek in the [Animation](class_animation#class-animation) or the blend or mix of [Animation](class_animation#class-animation)s input in it.
### void transition\_node\_delete\_input ( [String](class_string#class-string) id, [int](class_int#class-int) input\_idx )
Deletes the input at `input_idx` for the transition node with name `id`.
### [int](class_int#class-int) transition\_node\_get\_current ( [String](class_string#class-string) id ) const
Returns the index of the currently evaluated input for the transition node with name `id`.
### [int](class_int#class-int) transition\_node\_get\_input\_count ( [String](class_string#class-string) id ) const
Returns the number of inputs for the transition node with name `id`. You can add inputs by right-clicking on the transition node.
### [float](class_float#class-float) transition\_node\_get\_xfade\_time ( [String](class_string#class-string) id ) const
Returns the cross fade time for the transition node with name `id`.
### [bool](class_bool#class-bool) transition\_node\_has\_input\_auto\_advance ( [String](class_string#class-string) id, [int](class_int#class-int) input\_idx ) const
Returns `true` if the input at `input_idx` on the transition node with name `id` is set to automatically advance to the next input upon completion.
### void transition\_node\_set\_current ( [String](class_string#class-string) id, [int](class_int#class-int) input\_idx )
The transition node with name `id` sets its current input at `input_idx`.
### void transition\_node\_set\_input\_auto\_advance ( [String](class_string#class-string) id, [int](class_int#class-int) input\_idx, [bool](class_bool#class-bool) enable )
The transition node with name `id` advances to its next input automatically when the input at `input_idx` completes.
### void transition\_node\_set\_input\_count ( [String](class_string#class-string) id, [int](class_int#class-int) count )
Resizes the number of inputs available for the transition node with name `id`.
### void transition\_node\_set\_xfade\_time ( [String](class_string#class-string) id, [float](class_float#class-float) time\_sec )
The transition node with name `id` sets its cross fade time to `time_sec`.
| programming_docs |
godot Godot's design philosophy Godot's design philosophy
=========================
Now that you've gotten your feet wet, let's talk about Godot's design.
**Every game engine is different and fits different needs.** Not only do they offer a range of features, but the design of each engine is unique. This leads to different workflows and different ways to form your games' structures. This all stems from their respective design philosophies.
This page is here to help you understand how Godot works, starting with some of its core pillars. It is not a list of available features, nor is it an engine comparison. To know if any engine can be a good fit for your project, you need to try it out for yourself and understand its design and limitations.
Please watch [Godot explained in 5 minutes](https://www.youtube.com/watch?v=KjX5llYZ5eQ) if you're looking for an overview of the engine's features.
Object-oriented design and composition
--------------------------------------
Godot embraces object-oriented design at its core with its flexible scene system and Node hierarchy. It tries to stay away from strict programming patterns to offer an intuitive way to structure your game.
For one, Godot lets you **compose or aggregate** scenes. It's like nested prefabs: you can create a BlinkingLight scene and a BrokenLantern scene that uses the BlinkingLight. Then, create a city filled with BrokenLanterns. Change the BlinkingLight's color, save, and all the BrokenLanterns in the city will update instantly.
On top of that, you can **inherit** from any scene.
A Godot scene could be a Weapon, a Character, an Item, a Door, a Level, part of a level… anything you'd like. It works like a class in pure code, except you're free to design it by using the editor, using only the code, or mixing and matching the two.
It's different from prefabs you find in several 3D engines, as you can then inherit from and extend those scenes. You may create a Magician that extends your Character. Modify the Character in the editor and the Magician will update as well. It helps you build your projects so that their structure matches the game's design.
Also note that Godot offers many different types of objects called nodes, each with a specific purpose. Nodes are part of a tree and always inherit from their parents up to the Node class. Although the engine does feature some nodes like collision shapes that a parent physics body will use, most nodes work independently from one another.
In other words, Godot's nodes do not work like components in some other game engines.
Sprite is a Node2D, a CanvasItem and a Node. It has all the properties and features of its three parent classes, like transforms or the ability to draw custom shapes and render with a custom shader.
All-inclusive package
---------------------
Godot tries to provide its own tools to answer most common needs. It has a dedicated scripting workspace, an animation editor, a tilemap editor, a shader editor, a debugger, a profiler, the ability to hot-reload locally and on remote devices, etc.
The goal is to offer a full package to create games and a continuous user experience. You can still work with external programs as long as there is an import plugin for it. Or you can create one, like the [Tiled Map Importer](https://github.com/vnen/godot-tiled-importer).
That is also partly why Godot offers its own programming languages GDScript and VisualScript, along with C#. They're designed for the needs of game developers and game designers, and they're tightly integrated in the engine and the editor.
GDScript lets you write code using an indentation-based syntax, yet it detects types and offers a static language's quality of auto-completion. It is also optimized for gameplay code with built-in types like Vectors and Colors.
Note that with GDNative, you can write high-performance code using compiled languages like C, C++, Rust, or Python (using the Cython compiler) without recompiling the engine.
*VisualScript is a node-based programming language that integrates well in the editor. You can drag and drop nodes or resources into the graph to create new code blocks.*
Note that the 3D workspace doesn't feature as many tools as the 2D workspace. You'll need external programs or add-ons to edit terrains, animate complex characters, and so on. Godot provides a complete API to extend the editor's functionality using game code. See [The Godot editor is a Godot game](#the-godot-editor-is-a-godot-game) below.
*A State Machine editor plugin in Godot 2 by kubecz3k. It lets you manage states and transitions visually.*
Warning
[Godot 4.0 will remove VisualScript from core entirely.](https://godotengine.org/article/godot-4-will-discontinue-visual-scripting) As a result, creating new projects using visual scripting in Godot is not recommended. Future Godot 4.x releases may have VisualScript reimplemented as an extension.
While Godot 3.x will keep VisualScript supported, we recommend [trying out GDScript](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/index.html#toc-learn-scripting-gdscript) instead, especially if you intend to migrate your project to Godot 4.
Open source
-----------
Godot offers a fully open source codebase under the **MIT license**. This means all the technologies that ship with it have to be Free (as in freedom) as well. For the most part, they're developed from the ground up by contributors.
Anyone can plug in proprietary tools for the needs of their projects — they just won't ship with the engine. This may include Google AdMob, or FMOD. Any of these can come as third-party plugins instead.
On the other hand, an open codebase means you can **learn from and extend the engine** to your heart's content. You can also debug games easily, as Godot will print errors with a stack trace, even if they come from the engine itself.
Note
This **does not affect the work you do with Godot** in any way: there's no strings attached to the engine or anything you make with it.
Community-driven
----------------
**Godot is made by its community, for the community, and for all game creators out there.** It's the needs of the users and open discussions that drive the core updates. New features from the core developers often focus on what will benefit the most users first.
That said, although a handful of core developers work on it full-time, the project has over 600 contributors at the time of writing. Benevolent programmers work on features they may need themselves, so you'll see improvements in all corners of the engine at the same time in every major release.
The Godot editor is a Godot game
--------------------------------
The Godot editor runs on the game engine. It uses the engine's own UI system, it can hot-reload code and scenes when you test your projects, or run game code in the editor. This means you can **use the same code** and scenes for your games, or **build plugins and extend the editor.**
This leads to a reliable and flexible UI system, as it powers the editor itself. With the `tool` keyword, you can run any game code in the editor.
*RPG in a Box is a voxel RPG editor made with Godot 2. It uses Godot's UI tools for its node-based programming system and for the rest of the interface.*
Put the `tool` keyword at the top of any GDScript file and it will run in the editor. This lets you import and export plugins, create plugins like custom level editors, or create scripts with the same nodes and API you use in your projects.
Note
The editor is fully written in C++ and is statically compiled into the binary. This means you can't import it as a typical project that would have a `project.godot` file.
Separate 2D and 3D engines
--------------------------
Godot offers dedicated 2D and 3D rendering engines. As a result, **the base unit for 2D scenes is pixels.** Even though the engines are separate, you can render 2D in 3D, 3D in 2D, and overlay 2D sprites and interfaces over your 3D world.
godot First look at Godot's editor First look at Godot's editor
============================
This page will give you a brief overview of Godot's interface. We're going to look at the different main screens and docks to help you situate yourself.
See also
For a comprehensive breakdown of the editor's interface and how to use it, see the [Editor manual](https://docs.godotengine.org/en/3.5/tutorials/editor/index.html#toc-learn-editor).
The Project manager
-------------------
When you launch Godot, the first window you see is the Project Manager. In the default tab, "Projects," you can manage existing projects, import or create new ones, and more.
 At the top of the window, there is another tab named "Asset Library Projects". In the open-source asset library you can search for demo projects, templates, and completed projects, including many that are developed by the community.
 You can also change the editor's language using the drop-down menu to the right of the engine's version in the window's top-right corner. By default, it is in English (EN).
 First look at Godot's editor
----------------------------
When you open a new or an existing project, the editor's interface appears. Let's look at its main areas.
 By default, it features **menus**, **main screens**, and playtest buttons along the window's top edge.
 In the center is the **viewport** with its **toolbar** at the top, where you'll find tools to move, scale, or lock the scene's nodes.
 On either side of the viewport sit the **docks**. And at the bottom of the window lies the **bottom panel**.
The toolbar changes based on the context and selected node. Here is the 2D toolbar.
 Below is the 3D one.
 Let's look at the docks. The **FileSystem** dock lists your project files, be it scripts, images, audio samples, and more.
 The **Scene** dock lists the active scene's nodes.
 The **Inspector** allows you to edit the properties of a selected node.
 The **bottom panel**, situated below the viewport, is the host for the debug console, the animation editor, the audio mixer, and more. They can take precious space, that's why they're folded by default.
 When you click on one, it expands vertically. Below, you can see the animation editor opened.
 The four main screens
---------------------
There are four main screen buttons centered at the top of the editor: 2D, 3D, Script, and AssetLib.
You'll use the **2D screen** for all types of games. In addition to 2D games, the 2D screen is where you'll build your interfaces.
 In the **3D screen**, you can work with meshes, lights, and design levels for 3D games.
 Notice the perspective button under the toolbar. Clicking on it opens a list of options related to the 3D view.
 Note
Read [Introduction to 3D](https://docs.godotengine.org/en/3.5/tutorials/3d/introduction_to_3d.html#doc-introduction-to-3d) for more detail about the **3D main screen**.
The **Script screen** is a complete code editor with a debugger, rich auto-completion, and built-in code reference.
 Finally, the **AssetLib** is a library of free and open-source add-ons, scripts, and assets to use in your projects.
 See also
You can learn more about the asset library in [About the Asset Library](https://docs.godotengine.org/en/3.5/community/asset_library/what_is_assetlib.html#doc-what-is-assetlib).
Integrated class reference
--------------------------
Godot comes with a built-in class reference.
You can search for information about a class, method, property, constant, or signal by any one of the following methods:
* Pressing `F1` (or ``Alt` + `Space`` on macOS) anywhere in the editor.
* Clicking the "Search Help" button in the top-right of the Script main screen.
* Clicking on the Help menu and Search Help.
* Clicking while pressing the `Ctrl` key on a class name, function name, or built-in variable in the script editor.
 When you do any of these, a window pops up. Type to search for any item. You can also use it to browse available objects and methods.
 Double-click on an item to open the corresponding page in the script main screen.
godot Learn to code with GDScript Learn to code with GDScript
===========================
In Godot, you can write code using the GDScript and C# programming languages.
If you are new to programming, we recommend starting with GDScript because we designed it to be simpler than all-purpose languages like C#. It will be both faster and easier to learn.
While GDScript is a language specific to Godot, the techniques you will learn with it will apply to other programming languages.
Note that it is completely normal for a programmer to learn and use multiple languages. Programming languages have more similarities than differences, so once you know one, you can learn another much faster.
Learn in your browser with the GDScript app
-------------------------------------------
To learn GDScript, you can use the app Learn GDScript From Zero. It is a complete beginner course with interactive practices you can do right in your browser.
 Click here to access the app: [Learn GDScript From Zero app](https://gdquest.github.io/learn-gdscript/?ref=godot-docs)
This app is an open-source project. To report bugs or contribute, head to the app's source code repository: [GitHub repository](https://github.com/GDQuest/learn-gdscript).
In the next part, you will get an overview of the engine's essential concepts.
godot Overview of Godot's key concepts Overview of Godot's key concepts
================================
Every game engine revolves around abstractions you use to build your applications. In Godot, a game is a **tree** of **nodes** that you group together into **scenes**. You can then wire these nodes so they can communicate using **signals**.
These are the four concepts you will learn here. We're going to look at them briefly to give you a sense of how the engine works. In the getting started series, you will get to use them in practice.
Scenes
------
In Godot, you break down your game in reusable scenes. A scene can be a character, a weapon, a menu in the user interface, a single house, an entire level, or anything you can think of. Godot's scenes are flexible; they fill the role of both prefabs and scenes in some other game engines.
 You can also nest scenes. For example, you can put your character in a level, and drag and drop a scene as a child of it.
 Nodes
-----
A scene is composed of one or more **nodes**. Nodes are your game's smallest building blocks that you arrange into trees. Here's an example of a character's nodes.
 It is made of a `KinematicBody2D` node named "Character", a `Sprite`, a `Camera2D`, and a `CollisionShape2D`.
Note
The node names end with "2D" because this is a 2D scene. Their 3D counterpart have names that end with "3D".
Notice how nodes and scenes look the same in the editor. When you save a tree of nodes as a scene, it then shows as a single node, with its internal structure hidden in the editor.
Godot provides an extensive library of base node types you can combine and extend to build more powerful ones. 2D, 3D, or user interface, you will do most things with these nodes.
 The scene tree
--------------
All your game's scenes come together in the **scene tree**, literally a tree of scenes. And as scenes are trees of nodes, the scene tree also is a tree of nodes. But it's easier to think of your game in terms of scenes as they can represent characters, weapons, doors, or your user interface.
 Signals
-------
Nodes emit signals when some event occurs. This feature allows you to make nodes communicate without hard-wiring them in code. It gives you a lot of flexibility in how you structure your scenes.
 Note
Signals are Godot's version of the *observer* pattern. You can read more about it here: <https://gameprogrammingpatterns.com/observer.html>
For example, buttons emit a signal when pressed. You can connect to this signal to run code in reaction to this event, like starting the game or opening a menu.
Other built-in signals can tell you when two objects collided, when a character or monster entered a given area, and much more. You can also define new signals tailored to your game.
Summary
-------
Nodes, scenes, the scene tree, and signals are four core concepts in Godot that you will manipulate all the time.
Nodes are your game's smallest building blocks. You combine them to create scenes that you then combine and nest into the scene tree. You can then use signals to make nodes react to events in other nodes or different scene tree branches.
After this short breakdown, you probably have many questions. Bear with us as you will get many answers throughout the getting started series.
| programming_docs |
godot Introduction to Godot Introduction to Godot
=====================
This article is here to help you figure out whether Godot might be a good fit for you. We will introduce some broad features of the engine to give you a feel for what you can achieve with it and answer questions such as "what do I need to know to get started?".
This is by no means an exhaustive overview. We will introduce many more features in this getting started series.
What is Godot?
--------------
Godot is a general-purpose 2D and 3D game engine designed to support all sorts of projects. You can use it to create games or applications you can then release on desktop or mobile, as well as on the web.
You can also create console games with it, although you either need strong programming skills or a developer to port the game for you.
Note
The Godot team can't provide an open-source console export due to the licensing terms imposed by console manufacturers. Regardless of the engine you use, though, releasing games on consoles is always a lot of work. You can read more on that here: [Console support in Godot](https://docs.godotengine.org/en/3.5/tutorials/platform/consoles.html#doc-consoles).
What can the engine do?
-----------------------
Godot was initially developed in-house by an Argentinan game studio. Its development started in 2001, and the engine was rewritten and improved tremendously since its open-source release in 2014.
Some examples of games created with Godot include Ex-Zodiac and Helms of Fury.
  As for applications, the open-source pixel art drawing program Pixelorama is powered by Godot, and so is the voxel RPG creator RPG in a box.
 You can find many more examples in the [official showcase videos](https://www.youtube.com/playlist?list=PLeG_dAglpVo6EpaO9A1nkwJZOwrfiLdQ8).
How does it work and look?
--------------------------
Godot comes with a fully-fledged game editor with integrated tools to answer the most common needs. It includes a code editor, an animation editor, a tilemap editor, a shader editor, a debugger, a profiler, and more.
 The team strives to offer a feature-rich game editor with a consistent user experience. While there is always room for improvement, the user interface keeps getting refined.
Of course, if you prefer, you can work with external programs. We officially support importing 3D scenes designed in [Blender](https://www.blender.org/) and maintain plugins to code in [VSCode](https://github.com/godotengine/godot-vscode-plugin) and [Emacs](https://github.com/godotengine/emacs-gdscript-mode) for GDScript and C#. We also support Visual Studio for C# on Windows.
 Programming languages
---------------------
Let's talk about the available programming languages.
You can code your games using [GDScript](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/index.html#toc-learn-scripting-gdscript), a Godot-specific and tightly integrated language with a lightweight syntax, or [C#](https://docs.godotengine.org/en/3.5/tutorials/scripting/c_sharp/index.html#toc-learn-scripting-c), which is popular in the games industry. These are the two main scripting languages we support.
Godot also supports a node-based visual programming language named [VisualScript](https://docs.godotengine.org/en/3.5/tutorials/scripting/visual_script/index.html#toc-learn-scripting-visual-script).
With the [GDNative](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdnative/index.html#toc-tutorials-gdnative) technology, you can also write gameplay or high-performance algorithms in C or C++ without recompiling the engine. You can use this technology to integrate third-party libraries and other Software Development Kits (SDK) in the engine.
Of course, you can also directly add modules and features to the engine, as it's completely free and open-source.
See also
These are the five officially supported programming languages. The community maintains support for many more. For more information, see [GDNative third-party bindings](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdnative/what_is_gdnative.html#doc-what-is-gdnative-third-party-bindings).
What do I need to know to use Godot?
------------------------------------
Godot is a feature-packed game engine. With its thousands of features, there is a lot to learn. To make the most of it, you need good programming foundations. While we try to make the engine accessible, you will benefit a lot from knowing how to think like a programmer first.
In the next part, we'll show you a free and open-source app you can use to learn the basics of programming with Godot's GDScript programming language.
godot Learning new features Learning new features
=====================
Godot is a feature-rich game engine. There is a lot to learn about it. This page explains how you can use the online manual, built-in code reference, and join online communities to learn new features and techniques.
Making the most of this manual
------------------------------
What you are reading now is the user manual. It documents each of the engine's concepts and available features. When learning a new topic, you can start by browsing the corresponding section of this website. The left menu allows you to explore broad topics while the search bar will help you find more specific pages. If a page exists for a given theme, it will often link to more related content.
 The manual has a companion class reference that explains each Godot class's available functions and properties when programming. While the manual covers general features, concepts, and how to use the editor, the reference is all about using Godot's scripting API (Application Programming Interface). You can access it both online and offline. We recommend browsing the reference offline, from within the Godot editor. To do so, go to Help -> Search or press `F1`.
 To browse it online, head to the manual's [Class Reference](../../classes/index#toc-class-ref) section.
A class reference's page tells you:
1. Where the class exists in the inheritance hierarchy. You can click the top links to jump to parent classes and see the properties and methods a type inherits.
2. A summary of the class's role and use cases.
3. An explanation of the class's properties, methods, signals, enums, and constants.
4. Links to manual pages further detailing the class.
Note
If the manual or class reference is missing or has insufficient information, please open an Issue in the official [godot-docs](https://github.com/godotengine/godot-docs/issues) GitHub repository to report it.
You can Ctrl-click any underlined text like the name of a class, property, method, signal, or constant to jump to it.
Learning with the community
---------------------------
Godot has a growing community of users. If you're stuck on a problem or need help to better understand how to achieve something, you can ask other users for help on one of the many [active communities](https://godotengine.org/community).
The best place to ask for questions and find already answered ones is the official [Questions & Answers](https://godotengine.org/qa/) site. These responses show up in search engine results and get saved, allowing other users to benefit from discussions on the platform. Once you asked a question there, you can share its link on other social platforms. Before asking a question, be sure to look for existing answers that might solve your problem on this website or using your preferred search engine.
Asking questions well and providing details will help others answer you faster and better. When asking questions, we recommend including the following information:
1. **Describe your goal**. You want to explain what you are trying to achieve design-wise. If you are having trouble figuring out how to make a solution work, there may be a different, easier solution that accomplishes the same goal.
2. If there is an error involved, **share the exact error message**. You can copy the exact error message in the editor's Debugger bottom panel by clicking the Copy Error icon. Knowing what it says can help community members better identify how you triggered the error.
3. If there is code involved, **share a code sample**. Other users won't be able to help you fix a problem without seeing your code. Share the code as text directly. To do so, you can copy and paste a short code snippet in a chat box, or use a website like [Pastebin](https://pastebin.com/) to share long files.
4. **Share a screenshot** of your *Scene* dock along with your written code. Most of the code you write affects nodes in your scenes. As a result, you should think of those scenes as part of your source code.
 Also, please don't take a picture with your phone, the low quality and screen reflections can make it hard to understand the image. Your operating system should have a built-in tool to take screenshots with the `PrtSc` (Print Screen) key.
Alternatively, you can use a program like [ShareX](https://getsharex.com/) on Windows or [FlameShot](https://flameshot.org/) on Linux.
5. Sharing a video of your running game can also be really **useful to troubleshoot your game**. You can use programs like [OBS Studio](https://obsproject.com/) and [Screen to GIF](https://www.screentogif.com/) to capture your screen.
You can then use a service like [streamable](https://streamable.com/) or a cloud provider to upload and share your videos for free.
6. If you're not using the stable version of Godot, please mention the version you're using. The answer can be different as available features and the interface evolve rapidly.
Following these guidelines will maximize your chances of getting the answer you're looking for. They will save time both to you and the persons helping you.
Community tutorials
-------------------
This manual aims to provide a comprehensive reference of Godot's features. Aside from the 2D and 3D getting started series, it does not contain tutorials to implement specific game genres. If you're looking for a tutorial about creating a role-playing game, a platformer, or other, please see [Tutorials and resources](https://docs.godotengine.org/en/3.5/community/tutorials.html#doc-community-tutorials), which lists content made by the Godot community.
godot Coding the player Coding the player
=================
In this lesson, we'll add player movement, animation, and set it up to detect collisions.
To do so, we need to add some functionality that we can't get from a built-in node, so we'll add a script. Click the `Player` node and click the "Attach Script" button:
 In the script settings window, you can leave the default settings alone. Just click "Create":
Note
If you're creating a C# script or other languages, select the language from the `language` drop down menu before hitting create.
 Note
If this is your first time encountering GDScript, please read [Scripting languages](../step_by_step/scripting_languages#doc-scripting) before continuing.
Start by declaring the member variables this object will need:
```
extends Area2D
export var speed = 400 # How fast the player will move (pixels/sec).
var screen_size # Size of the game window.
```
```
using Godot;
using System;
public class Player : Area2D
{
[Export]
public int Speed = 400; // How fast the player will move (pixels/sec).
public Vector2 ScreenSize; // Size of the game window.
}
```
```
// A `player.gdns` file has already been created for you. Attach it to the Player node.
// Create two files `player.cpp` and `player.hpp` next to `entry.cpp` in `src`.
// This code goes in `player.hpp`. We also define the methods we'll be using here.
#ifndef PLAYER_H
#define PLAYER_H
#include <AnimatedSprite.hpp>
#include <Area2D.hpp>
#include <CollisionShape2D.hpp>
#include <Godot.hpp>
#include <Input.hpp>
class Player : public godot::Area2D {
GODOT_CLASS(Player, godot::Area2D)
godot::AnimatedSprite *_animated_sprite;
godot::CollisionShape2D *_collision_shape;
godot::Input *_input;
godot::Vector2 _screen_size; // Size of the game window.
public:
real_t speed = 400; // How fast the player will move (pixels/sec).
void _init() {}
void _ready();
void _process(const double p_delta);
void start(const godot::Vector2 p_position);
void _on_Player_body_entered(godot::Node2D *_body);
static void _register_methods();
};
#endif // PLAYER_H
```
Using the `export` keyword on the first variable `speed` allows us to set its value in the Inspector. This can be handy for values that you want to be able to adjust just like a node's built-in properties. Click on the `Player` node and you'll see the property now appears in the "Script Variables" section of the Inspector. Remember, if you change the value here, it will override the value written in the script.
Warning
If you're using C#, you need to (re)build the project assemblies whenever you want to see new export variables or signals. This build can be manually triggered by clicking the word "Mono" at the bottom of the editor window to reveal the Mono Panel, then clicking the "Build Project" button.
 The `_ready()` function is called when a node enters the scene tree, which is a good time to find the size of the game window:
```
func _ready():
screen_size = get_viewport_rect().size
```
```
public override void _Ready()
{
ScreenSize = GetViewportRect().Size;
}
```
```
// This code goes in `player.cpp`.
#include "player.hpp"
void Player::_ready() {
_animated_sprite = get_node<godot::AnimatedSprite>("AnimatedSprite");
_collision_shape = get_node<godot::CollisionShape2D>("CollisionShape2D");
_input = godot::Input::get_singleton();
_screen_size = get_viewport_rect().size;
}
```
Now we can use the `_process()` function to define what the player will do. `_process()` is called every frame, so we'll use it to update elements of our game, which we expect will change often. For the player, we need to do the following:
* Check for input.
* Move in the given direction.
* Play the appropriate animation.
First, we need to check for input - is the player pressing a key? For this game, we have 4 direction inputs to check. Input actions are defined in the Project Settings under "Input Map". Here, you can define custom events and assign different keys, mouse events, or other inputs to them. For this game, we will map the arrow keys to the four directions.
Click on *Project -> Project Settings* to open the project settings window and click on the *Input Map* tab at the top. Type "move\_right" in the top bar and click the "Add" button to add the `move_right` action.
 We need to assign a key to this action. Click the "+" icon on the right, then click the "Key" option in the drop-down menu. A dialog asks you to type in the desired key. Press the right arrow on your keyboard and click "Ok".
 Repeat these steps to add three more mappings:
1. `move_left` mapped to the left arrow key.
2. `move_up` mapped to the up arrow key.
3. And `move_down` mapped to the down arrow key.
Your input map tab should look like this:
 Click the "Close" button to close the project settings.
Note
We only mapped one key to each input action, but you can map multiple keys, joystick buttons, or mouse buttons to the same input action.
You can detect whether a key is pressed using `Input.is_action_pressed()`, which returns `true` if it's pressed or `false` if it isn't.
```
func _process(delta):
var velocity = Vector2.ZERO # The player's movement vector.
if Input.is_action_pressed("move_right"):
velocity.x += 1
if Input.is_action_pressed("move_left"):
velocity.x -= 1
if Input.is_action_pressed("move_down"):
velocity.y += 1
if Input.is_action_pressed("move_up"):
velocity.y -= 1
if velocity.length() > 0:
velocity = velocity.normalized() * speed
$AnimatedSprite.play()
else:
$AnimatedSprite.stop()
```
```
public override void _Process(float delta)
{
var velocity = Vector2.Zero; // The player's movement vector.
if (Input.IsActionPressed("move_right"))
{
velocity.x += 1;
}
if (Input.IsActionPressed("move_left"))
{
velocity.x -= 1;
}
if (Input.IsActionPressed("move_down"))
{
velocity.y += 1;
}
if (Input.IsActionPressed("move_up"))
{
velocity.y -= 1;
}
var animatedSprite = GetNode<AnimatedSprite>("AnimatedSprite");
if (velocity.Length() > 0)
{
velocity = velocity.Normalized() * Speed;
animatedSprite.Play();
}
else
{
animatedSprite.Stop();
}
}
```
```
// This code goes in `player.cpp`.
void Player::_process(const double p_delta) {
godot::Vector2 velocity(0, 0);
velocity.x = _input->get_action_strength("move_right") - _input->get_action_strength("move_left");
velocity.y = _input->get_action_strength("move_down") - _input->get_action_strength("move_up");
if (velocity.length() > 0) {
velocity = velocity.normalized() * speed;
_animated_sprite->play();
} else {
_animated_sprite->stop();
}
}
```
We start by setting the `velocity` to `(0, 0)` - by default, the player should not be moving. Then we check each input and add/subtract from the `velocity` to obtain a total direction. For example, if you hold `right` and `down` at the same time, the resulting `velocity` vector will be `(1, 1)`. In this case, since we're adding a horizontal and a vertical movement, the player would move *faster* diagonally than if it just moved horizontally.
We can prevent that if we *normalize* the velocity, which means we set its *length* to `1`, then multiply by the desired speed. This means no more fast diagonal movement.
Tip
If you've never used vector math before, or need a refresher, you can see an explanation of vector usage in Godot at [Vector math](https://docs.godotengine.org/en/3.5/tutorials/math/vector_math.html#doc-vector-math). It's good to know but won't be necessary for the rest of this tutorial.
We also check whether the player is moving so we can call `play()` or `stop()` on the AnimatedSprite.
Tip
`$` is shorthand for `get_node()`. So in the code above, `$AnimatedSprite.play()` is the same as `get_node("AnimatedSprite").play()`.
In GDScript, `$` returns the node at the relative path from the current node, or returns `null` if the node is not found. Since AnimatedSprite is a child of the current node, we can use `$AnimatedSprite`.
Now that we have a movement direction, we can update the player's position. We can also use `clamp()` to prevent it from leaving the screen. *Clamping* a value means restricting it to a given range. Add the following to the bottom of the `_process` function (make sure it's not indented under the `else`):
```
position += velocity * delta
position.x = clamp(position.x, 0, screen_size.x)
position.y = clamp(position.y, 0, screen_size.y)
```
```
Position += velocity * delta;
Position = new Vector2(
x: Mathf.Clamp(Position.x, 0, ScreenSize.x),
y: Mathf.Clamp(Position.y, 0, ScreenSize.y)
);
```
```
godot::Vector2 position = get_position();
position += velocity * (real_t)p_delta;
position.x = godot::Math::clamp(position.x, (real_t)0.0, _screen_size.x);
position.y = godot::Math::clamp(position.y, (real_t)0.0, _screen_size.y);
set_position(position);
```
Tip
The `delta` parameter in the `_process()` function refers to the *frame length* - the amount of time that the previous frame took to complete. Using this value ensures that your movement will remain consistent even if the frame rate changes.
Click "Play Scene" (`F6`, ``Cmd` + `R`` on macOS) and confirm you can move the player around the screen in all directions.
Warning
If you get an error in the "Debugger" panel that says
`Attempt to call function 'play' in base 'null instance' on a null
instance`
this likely means you spelled the name of the AnimatedSprite node wrong. Node names are case-sensitive and `$NodeName` must match the name you see in the scene tree.
Choosing animations
-------------------
Now that the player can move, we need to change which animation the AnimatedSprite is playing based on its direction. We have the "walk" animation, which shows the player walking to the right. This animation should be flipped horizontally using the `flip_h` property for left movement. We also have the "up" animation, which should be flipped vertically with `flip_v` for downward movement. Let's place this code at the end of the `_process()` function:
```
if velocity.x != 0:
$AnimatedSprite.animation = "walk"
$AnimatedSprite.flip_v = false
# See the note below about boolean assignment.
$AnimatedSprite.flip_h = velocity.x < 0
elif velocity.y != 0:
$AnimatedSprite.animation = "up"
$AnimatedSprite.flip_v = velocity.y > 0
```
```
if (velocity.x != 0)
{
animatedSprite.Animation = "walk";
animatedSprite.FlipV = false;
// See the note below about boolean assignment.
animatedSprite.FlipH = velocity.x < 0;
}
else if (velocity.y != 0)
{
animatedSprite.Animation = "up";
animatedSprite.FlipV = velocity.y > 0;
}
```
```
if (velocity.x != 0) {
_animated_sprite->set_animation("walk");
_animated_sprite->set_flip_v(false);
// See the note below about boolean assignment.
_animated_sprite->set_flip_h(velocity.x < 0);
} else if (velocity.y != 0) {
_animated_sprite->set_animation("up");
_animated_sprite->set_flip_v(velocity.y > 0);
}
```
Note
The boolean assignments in the code above are a common shorthand for programmers. Since we're doing a comparison test (boolean) and also *assigning* a boolean value, we can do both at the same time. Consider this code versus the one-line boolean assignment above:
```
if velocity.x < 0:
$AnimatedSprite.flip_h = true
else:
$AnimatedSprite.flip_h = false
```
```
if (velocity.x < 0)
{
animatedSprite.FlipH = true;
}
else
{
animatedSprite.FlipH = false;
}
```
Play the scene again and check that the animations are correct in each of the directions.
Tip
A common mistake here is to type the names of the animations wrong. The animation names in the SpriteFrames panel must match what you type in the code. If you named the animation `"Walk"`, you must also use a capital "W" in the code.
When you're sure the movement is working correctly, add this line to `_ready()`, so the player will be hidden when the game starts:
```
hide()
```
```
Hide();
```
```
hide();
```
Preparing for collisions
------------------------
We want `Player` to detect when it's hit by an enemy, but we haven't made any enemies yet! That's OK, because we're going to use Godot's *signal* functionality to make it work.
Add the following at the top of the script, after `extends Area2D`:
```
signal hit
```
```
// Don't forget to rebuild the project so the editor knows about the new signal.
[Signal]
public delegate void Hit();
```
```
// This code goes in `player.cpp`.
// We need to register the signal here, and while we're here, we can also
// register the other methods and register the speed property.
void Player::_register_methods() {
godot::register_method("_ready", &Player::_ready);
godot::register_method("_process", &Player::_process);
godot::register_method("start", &Player::start);
godot::register_method("_on_Player_body_entered", &Player::_on_Player_body_entered);
godot::register_property("speed", &Player::speed, (real_t)400.0);
// This below line is the signal.
godot::register_signal<Player>("hit", godot::Dictionary());
}
```
This defines a custom signal called "hit" that we will have our player emit (send out) when it collides with an enemy. We will use `Area2D` to detect the collision. Select the `Player` node and click the "Node" tab next to the Inspector tab to see the list of signals the player can emit:
 Notice our custom "hit" signal is there as well! Since our enemies are going to be `RigidBody2D` nodes, we want the `body_entered(body: Node)` signal. This signal will be emitted when a body contacts the player. Click "Connect.." and the "Connect a Signal" window appears. We don't need to change any of these settings so click "Connect" again. Godot will automatically create a function in your player's script.
 Note the green icon indicating that a signal is connected to this function. Add this code to the function:
```
func _on_Player_body_entered(body):
hide() # Player disappears after being hit.
emit_signal("hit")
# Must be deferred as we can't change physics properties on a physics callback.
$CollisionShape2D.set_deferred("disabled", true)
```
```
public void OnPlayerBodyEntered(PhysicsBody2D body)
{
Hide(); // Player disappears after being hit.
EmitSignal(nameof(Hit));
// Must be deferred as we can't change physics properties on a physics callback.
GetNode<CollisionShape2D>("CollisionShape2D").SetDeferred("disabled", true);
}
```
```
// This code goes in `player.cpp`.
void Player::_on_Player_body_entered(godot::Node2D *_body) {
hide(); // Player disappears after being hit.
emit_signal("hit");
// Must be deferred as we can't change physics properties on a physics callback.
_collision_shape->set_deferred("disabled", true);
}
```
Each time an enemy hits the player, the signal is going to be emitted. We need to disable the player's collision so that we don't trigger the `hit` signal more than once.
Note
Disabling the area's collision shape can cause an error if it happens in the middle of the engine's collision processing. Using `set_deferred()` tells Godot to wait to disable the shape until it's safe to do so.
The last piece is to add a function we can call to reset the player when starting a new game.
```
func start(pos):
position = pos
show()
$CollisionShape2D.disabled = false
```
```
public void Start(Vector2 pos)
{
Position = pos;
Show();
GetNode<CollisionShape2D>("CollisionShape2D").Disabled = false;
}
```
```
// This code goes in `player.cpp`.
void Player::start(const godot::Vector2 p_position) {
set_position(p_position);
show();
_collision_shape->set_disabled(false);
}
```
With the player working, we'll work on the enemy in the next lesson.
| programming_docs |
godot Setting up the project Setting up the project
======================
In this short first part, we'll set up and organize the project.
Launch Godot and create a new project.
Download [`dodge_assets.zip`](https://docs.godotengine.org/en/3.5/_downloads/923b18d4e18125cf494ee5f7efba7e03/dodge_assets.zip). The archive contains the images and sounds you'll be using to make the game. Extract the archive and move the `art/` and `fonts/` directories to your project's directory.
Download [`dodge_assets.zip`](https://docs.godotengine.org/en/3.5/_downloads/923b18d4e18125cf494ee5f7efba7e03/dodge_assets.zip). The archive contains the images and sounds you'll be using to make the game. Extract the archive and move the `art/` and `fonts/` directories to your project's directory.
Ensure that you have the required dependencies to use C# in Godot. You need the .NET Core 3.1 SDK, and an editor such as VS Code. See [Setting up C# for Godot](https://docs.godotengine.org/en/3.5/tutorials/scripting/c_sharp/c_sharp_basics.html#doc-c-sharp-setup).
Download [`dodge_assets_with_gdnative.zip`](https://docs.godotengine.org/en/3.5/_downloads/bc92b79e2c329bcf6d38cc24d9cd7f1b/dodge_assets_with_gdnative.zip). The archive contains the images and sounds you'll be using to make the game. It also contains a starter GDNative project including a `SConstruct` file, a `dodge_the_creeps.gdnlib` file, a `player.gdns` file, and an `entry.cpp` file.
Ensure that you have the required dependencies to use GDNative C++. You need a C++ compiler such as GCC or Clang or MSVC that supports C++14. On Windows you can download Visual Studio 2019 and select the C++ workload. You also need SCons to use the build system (the SConstruct file). Then you need to [download the Godot C++ bindings](https://github.com/godotengine/godot-cpp) and place them in your project.
Your project folder should look like this.
 This game is designed for portrait mode, so we need to adjust the size of the game window. Click on *Project -> Project Settings* to open the project settings window and in the left column, open the *Display -> Window* tab. There, set "Width" to `480` and "Height" to `720`.
 Also, scroll down to the bottom of the section and, under the "Stretch" options, set `Mode` to "2d" and `Aspect` to "keep". This ensures that the game scales consistently on different sized screens.
 Organizing the project
----------------------
In this project, we will make 3 independent scenes: `Player`, `Mob`, and `HUD`, which we will combine into the game's `Main` scene.
In a larger project, it might be useful to create folders to hold the various scenes and their scripts, but for this relatively small game, you can save your scenes and scripts in the project's root folder, identified by `res://`. You can see your project folders in the FileSystem dock in the lower left corner:
 With the project in place, we're ready to design the player scene in the next lesson.
godot Finishing up Finishing up
============
We have now completed all the functionality for our game. Below are some remaining steps to add a bit more "juice" to improve the game experience.
Feel free to expand the gameplay with your own ideas.
Background
----------
The default gray background is not very appealing, so let's change its color. One way to do this is to use a [ColorRect](../../classes/class_colorrect#class-colorrect) node. Make it the first node under `Main` so that it will be drawn behind the other nodes. `ColorRect` only has one property: `Color`. Choose a color you like and select "Layout" -> "Full Rect" so that it covers the screen.
You could also add a background image, if you have one, by using a `TextureRect` node instead.
Sound effects
-------------
Sound and music can be the single most effective way to add appeal to the game experience. In your game assets folder, you have two sound files: "House In a Forest Loop.ogg" for background music, and "gameover.wav" for when the player loses.
Add two [AudioStreamPlayer](../../classes/class_audiostreamplayer#class-audiostreamplayer) nodes as children of `Main`. Name one of them `Music` and the other `DeathSound`. On each one, click on the `Stream` property, select "Load", and choose the corresponding audio file.
To play the music, add `$Music.play()` in the `new_game()` function and `$Music.stop()` in the `game_over()` function.
Finally, add `$DeathSound.play()` in the `game_over()` function.
Keyboard shortcut
-----------------
Since the game is played with keyboard controls, it would be convenient if we could also start the game by pressing a key on the keyboard. We can do this with the "Shortcut" property of the `Button` node.
In a previous lesson, we created four input actions to move the character. We will create a similar input action to map to the start button.
Select "Project" -> "Project Settings" and then click on the "Input Map" tab. In the same way you created the movement input actions, create a new input action called `start_game` and add a key mapping for the `Enter` key.
In the `HUD` scene, select the `StartButton` and find its *Shortcut* property in the Inspector. Select "New Shortcut" and click on the "Shortcut" item. A second *Shortcut* property will appear. Select "New InputEventAction" and click the new "InputEventAction". Finally, in the *Action* property, type the name `start_game`.
 Now when the start button appears, you can either click it or press `Enter` to start the game.
And with that, you completed your first 2D game in Godot.
 You got to make a player-controlled character, enemies that spawn randomly around the game board, count the score, implement a game over and replay, user interface, sounds, and more. Congratulations!
There's still much to learn, but you can take a moment to appreciate what you achieved.
And when you're ready, you can move on to [Your first 3D game](../first_3d_game/index#doc-your-first-3d-game) to learn to create a complete 3D game from scratch, in Godot.
godot Creating the player scene Creating the player scene
=========================
With the project settings in place, we can start working on the player-controlled character.
The first scene will define the `Player` object. One of the benefits of creating a separate Player scene is that we can test it separately, even before we've created other parts of the game.
Node structure
--------------
To begin, we need to choose a root node for the player object. As a general rule, a scene's root node should reflect the object's desired functionality - what the object *is*. Click the "Other Node" button and add an [Area2D](../../classes/class_area2d#class-area2d) node to the scene.
 Godot will display a warning icon next to the node in the scene tree. You can ignore it for now. We will address it later.
With `Area2D` we can detect objects that overlap or run into the player. Change the node's name to `Player` by double-clicking on it. Now that we've set the scene's root node, we can add additional nodes to give it more functionality.
Before we add any children to the `Player` node, we want to make sure we don't accidentally move or resize them by clicking on them. Select the node and click the icon to the right of the lock; its tooltip says "Makes sure the object's children are not selectable."
 Save the scene. Click Scene -> Save, or press ``Ctrl` + `S`` on Windows/Linux or ``Cmd` + `S`` on macOS.
Note
For this project, we will be following the Godot naming conventions.
* **GDScript**: Classes (nodes) use PascalCase, variables and functions use snake\_case, and constants use ALL\_CAPS (See [GDScript style guide](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/gdscript_styleguide.html#doc-gdscript-styleguide)).
* **C#**: Classes, export variables and methods use PascalCase, private fields use \_camelCase, local variables and parameters use camelCase (See [C# style guide](https://docs.godotengine.org/en/3.5/tutorials/scripting/c_sharp/c_sharp_style_guide.html#doc-c-sharp-styleguide)). Be careful to type the method names precisely when connecting signals.
Sprite animation
----------------
Click on the `Player` node and add an [AnimatedSprite](../../classes/class_animatedsprite#class-animatedsprite) node as a child. The `AnimatedSprite` will handle the appearance and animations for our player. Notice that there is a warning symbol next to the node. An `AnimatedSprite` requires a [SpriteFrames](../../classes/class_spriteframes#class-spriteframes) resource, which is a list of the animations it can display. To create one, find the `Frames` property in the Inspector and click "[empty]" -> "New SpriteFrames". Click again to open the "SpriteFrames" panel:
 On the left is a list of animations. Click the "default" one and rename it to "walk". Then click the "New Animation" button to create a second animation named "up". Find the player images in the "FileSystem" tab - they're in the `art` folder you unzipped earlier. Drag the two images for each animation, named `playerGrey_up[1/2]` and `playerGrey_walk[1/2]`, into the "Animation Frames" side of the panel for the corresponding animation:
 The player images are a bit too large for the game window, so we need to scale them down. Click on the `AnimatedSprite` node and set the `Scale` property to `(0.5, 0.5)`. You can find it in the Inspector under the `Node2D` heading.
 Finally, add a [CollisionShape2D](../../classes/class_collisionshape2d#class-collisionshape2d) as a child of `Player`. This will determine the player's "hitbox", or the bounds of its collision area. For this character, a `CapsuleShape2D` node gives the best fit, so next to "Shape" in the Inspector, click "[empty]"" -> "New CapsuleShape2D". Using the two size handles, resize the shape to cover the sprite:
 When you're finished, your `Player` scene should look like this:
 Make sure to save the scene again after these changes.
In the next part, we'll add a script to the player node to move and animate it. Then, we'll set up collision detection to know when the player got hit by something.
godot Heads up display Heads up display
================
The final piece our game needs is a User Interface (UI) to display things like score, a "game over" message, and a restart button.
Create a new scene, and add a [CanvasLayer](../../classes/class_canvaslayer#class-canvaslayer) node named `HUD`. "HUD" stands for "heads-up display", an informational display that appears as an overlay on top of the game view.
The [CanvasLayer](../../classes/class_canvaslayer#class-canvaslayer) node lets us draw our UI elements on a layer above the rest of the game, so that the information it displays isn't covered up by any game elements like the player or mobs.
The HUD needs to display the following information:
* Score, changed by `ScoreTimer`.
* A message, such as "Game Over" or "Get Ready!"
* A "Start" button to begin the game.
The basic node for UI elements is [Control](../../classes/class_control#class-control). To create our UI, we'll use two types of [Control](../../classes/class_control#class-control) nodes: [Label](../../classes/class_label#class-label) and [Button](../../classes/class_button#class-button).
Create the following as children of the `HUD` node:
* [Label](../../classes/class_label#class-label) named `ScoreLabel`.
* [Label](../../classes/class_label#class-label) named `Message`.
* [Button](../../classes/class_button#class-button) named `StartButton`.
* [Timer](../../classes/class_timer#class-timer) named `MessageTimer`.
Click on the `ScoreLabel` and type a number into the `Text` field in the Inspector. The default font for `Control` nodes is small and doesn't scale well. There is a font file included in the game assets called "Xolonium-Regular.ttf". To use this font, do the following:
1. Under **Theme overrides > Fonts** click on the empty box and select "New DynamicFont"
 2. Click on the "DynamicFont" you added, and under **Font > FontData**, choose "Load" and select the "Xolonium-Regular.ttf" file.
 Set the "Size" property under `Settings`, `64` works well.
 Once you've done this on the `ScoreLabel`, you can click the down arrow next to the Font property and choose "Copy", then "Paste" it in the same place on the other two Control nodes.
Note
**Anchors and Margins:** `Control` nodes have a position and size, but they also have anchors and margins. Anchors define the origin - the reference point for the edges of the node. Margins update automatically when you move or resize a control node. They represent the distance from the control node's edges to its anchor.
Arrange the nodes as shown below. Click the "Layout" button to set a Control node's layout:
 You can drag the nodes to place them manually, or for more precise placement, use the following settings:
ScoreLabel
----------
* *Layout* : "Top Wide"
* *Text* : `0`
* *Align* : "Center"
Message
-------
* *Layout* : "HCenter Wide"
* *Text* : `Dodge the Creeps!`
* *Align* : "Center"
* *Autowrap* : "On"
StartButton
-----------
* *Text* : `Start`
* *Layout* : "Center Bottom"
* *Margin* :
+ Top: `-200`
+ Bottom: `-100`
On the `MessageTimer`, set the `Wait Time` to `2` and set the `One Shot` property to "On".
Now add this script to `HUD`:
```
extends CanvasLayer
signal start_game
```
```
public class HUD : CanvasLayer
{
// Don't forget to rebuild the project so the editor knows about the new signal.
[Signal]
public delegate void StartGame();
}
```
```
// Copy `player.gdns` to `hud.gdns` and replace `Player` with `HUD`.
// Attach the `hud.gdns` file to the HUD node.
// Create two files `hud.cpp` and `hud.hpp` next to `entry.cpp` in `src`.
// This code goes in `hud.hpp`. We also define the methods we'll be using here.
#ifndef HUD_H
#define HUD_H
#include <Button.hpp>
#include <CanvasLayer.hpp>
#include <Godot.hpp>
#include <Label.hpp>
#include <Timer.hpp>
class HUD : public godot::CanvasLayer {
GODOT_CLASS(HUD, godot::CanvasLayer)
godot::Label *_score_label;
godot::Label *_message_label;
godot::Timer *_start_message_timer;
godot::Timer *_get_ready_message_timer;
godot::Button *_start_button;
godot::Timer *_start_button_timer;
public:
void _init() {}
void _ready();
void show_get_ready();
void show_game_over();
void update_score(const int score);
void _on_StartButton_pressed();
void _on_StartMessageTimer_timeout();
void _on_GetReadyMessageTimer_timeout();
static void _register_methods();
};
#endif // HUD_H
```
The `start_game` signal tells the `Main` node that the button has been pressed.
```
func show_message(text):
$Message.text = text
$Message.show()
$MessageTimer.start()
```
```
public void ShowMessage(string text)
{
var message = GetNode<Label>("Message");
message.Text = text;
message.Show();
GetNode<Timer>("MessageTimer").Start();
}
```
```
// This code goes in `hud.cpp`.
#include "hud.hpp"
void HUD::_ready() {
_score_label = get_node<godot::Label>("ScoreLabel");
_message_label = get_node<godot::Label>("MessageLabel");
_start_message_timer = get_node<godot::Timer>("StartMessageTimer");
_get_ready_message_timer = get_node<godot::Timer>("GetReadyMessageTimer");
_start_button = get_node<godot::Button>("StartButton");
_start_button_timer = get_node<godot::Timer>("StartButtonTimer");
}
void HUD::_register_methods() {
godot::register_method("_ready", &HUD::_ready);
godot::register_method("show_get_ready", &HUD::show_get_ready);
godot::register_method("show_game_over", &HUD::show_game_over);
godot::register_method("update_score", &HUD::update_score);
godot::register_method("_on_StartButton_pressed", &HUD::_on_StartButton_pressed);
godot::register_method("_on_StartMessageTimer_timeout", &HUD::_on_StartMessageTimer_timeout);
godot::register_method("_on_GetReadyMessageTimer_timeout", &HUD::_on_GetReadyMessageTimer_timeout);
godot::register_signal<HUD>("start_game", godot::Dictionary());
}
```
This function is called when we want to display a message temporarily, such as "Get Ready".
```
func show_game_over():
show_message("Game Over")
# Wait until the MessageTimer has counted down.
yield($MessageTimer, "timeout")
$Message.text = "Dodge the\nCreeps!"
$Message.show()
# Make a one-shot timer and wait for it to finish.
yield(get_tree().create_timer(1), "timeout")
$StartButton.show()
```
```
async public void ShowGameOver()
{
ShowMessage("Game Over");
var messageTimer = GetNode<Timer>("MessageTimer");
await ToSignal(messageTimer, "timeout");
var message = GetNode<Label>("Message");
message.Text = "Dodge the\nCreeps!";
message.Show();
await ToSignal(GetTree().CreateTimer(1), "timeout");
GetNode<Button>("StartButton").Show();
}
```
```
// This code goes in `hud.cpp`.
// There is no `yield` in GDNative, so we need to have every
// step be its own method that is called on timer timeout.
void HUD::show_get_ready() {
_message_label->set_text("Get Ready");
_message_label->show();
_get_ready_message_timer->start();
}
void HUD::show_game_over() {
_message_label->set_text("Game Over");
_message_label->show();
_start_message_timer->start();
}
```
This function is called when the player loses. It will show "Game Over" for 2 seconds, then return to the title screen and, after a brief pause, show the "Start" button.
Note
When you need to pause for a brief time, an alternative to using a Timer node is to use the SceneTree's `create_timer()` function. This can be very useful to add delays such as in the above code, where we want to wait some time before showing the "Start" button.
```
func update_score(score):
$ScoreLabel.text = str(score)
```
```
public void UpdateScore(int score)
{
GetNode<Label>("ScoreLabel").Text = score.ToString();
}
```
```
// This code goes in `hud.cpp`.
void HUD::update_score(const int p_score) {
_score_label->set_text(godot::Variant(p_score));
}
```
This function is called by `Main` whenever the score changes.
Connect the `timeout()` signal of `MessageTimer` and the `pressed()` signal of `StartButton` and add the following code to the new functions:
```
func _on_StartButton_pressed():
$StartButton.hide()
emit_signal("start_game")
func _on_MessageTimer_timeout():
$Message.hide()
```
```
public void OnStartButtonPressed()
{
GetNode<Button>("StartButton").Hide();
EmitSignal("StartGame");
}
public void OnMessageTimerTimeout()
{
GetNode<Label>("Message").Hide();
}
```
```
// This code goes in `hud.cpp`.
void HUD::_on_StartButton_pressed() {
_start_button_timer->stop();
_start_button->hide();
emit_signal("start_game");
}
void HUD::_on_StartMessageTimer_timeout() {
_message_label->set_text("Dodge the\nCreeps");
_message_label->show();
_start_button_timer->start();
}
void HUD::_on_GetReadyMessageTimer_timeout() {
_message_label->hide();
}
```
Connecting HUD to Main
----------------------
Now that we're done creating the `HUD` scene, go back to `Main`. Instance the `HUD` scene in `Main` like you did the `Player` scene. The scene tree should look like this, so make sure you didn't miss anything:
 Now we need to connect the `HUD` functionality to our `Main` script. This requires a few additions to the `Main` scene:
In the Node tab, connect the HUD's `start_game` signal to the `new_game()` function of the Main node by typing "new\_game" in the "Receiver Method" in the "Connect a Signal" window. Verify that the green connection icon now appears next to `func new_game()` in the script.
In `new_game()`, update the score display and show the "Get Ready" message:
```
$HUD.update_score(score)
$HUD.show_message("Get Ready")
```
```
var hud = GetNode<HUD>("HUD");
hud.UpdateScore(Score);
hud.ShowMessage("Get Ready!");
```
```
_hud->update_score(score);
_hud->show_get_ready();
```
In `game_over()` we need to call the corresponding `HUD` function:
```
$HUD.show_game_over()
```
```
GetNode<HUD>("HUD").ShowGameOver();
```
```
_hud->show_game_over();
```
Finally, add this to `_on_ScoreTimer_timeout()` to keep the display in sync with the changing score:
```
$HUD.update_score(score)
```
```
GetNode<HUD>("HUD").UpdateScore(Score);
```
```
_hud->update_score(score);
```
Now you're ready to play! Click the "Play the Project" button. You will be asked to select a main scene, so choose `Main.tscn`.
Removing old creeps
-------------------
If you play until "Game Over" and then start a new game right away, the creeps from the previous game may still be on the screen. It would be better if they all disappeared at the start of a new game. We just need a way to tell *all* the mobs to remove themselves. We can do this with the "group" feature.
In the `Mob` scene, select the root node and click the "Node" tab next to the Inspector (the same place where you find the node's signals). Next to "Signals", click "Groups" and you can type a new group name and click "Add".
 Now all mobs will be in the "mobs" group. We can then add the following line to the `new_game()` function in `Main`:
```
get_tree().call_group("mobs", "queue_free")
```
```
// Note that for calling Godot-provided methods with strings,
// we have to use the original Godot snake_case name.
GetTree().CallGroup("mobs", "queue_free");
```
```
get_tree()->call_group("mobs", "queue_free");
```
The `call_group()` function calls the named function on every node in a group - in this case we are telling every mob to delete itself.
The game's mostly done at this point. In the next and last part, we'll polish it a bit by adding a background, looping music, and some keyboard shortcuts.
| programming_docs |
godot Creating the enemy Creating the enemy
==================
Now it's time to make the enemies our player will have to dodge. Their behavior will not be very complex: mobs will spawn randomly at the edges of the screen, choose a random direction, and move in a straight line.
We'll create a `Mob` scene, which we can then *instance* to create any number of independent mobs in the game.
Node setup
----------
Click Scene -> New Scene and add the following nodes:
* [RigidBody2D](../../classes/class_rigidbody2d#class-rigidbody2d) (named `Mob`)
+ [AnimatedSprite](../../classes/class_animatedsprite#class-animatedsprite)
+ [CollisionShape2D](../../classes/class_collisionshape2d#class-collisionshape2d)
+ [VisibilityNotifier2D](../../classes/class_visibilitynotifier2d#class-visibilitynotifier2d)
Don't forget to set the children so they can't be selected, like you did with the Player scene.
In the [RigidBody2D](../../classes/class_rigidbody2d#class-rigidbody2d) properties, set `Gravity Scale` to `0`, so the mob will not fall downward. In addition, under the [CollisionObject2D](../../classes/class_collisionobject2d#class-collisionobject2d) section, click the `Mask` property and uncheck the first box. This will ensure the mobs do not collide with each other.
 Set up the [AnimatedSprite](../../classes/class_animatedsprite#class-animatedsprite) like you did for the player. This time, we have 3 animations: `fly`, `swim`, and `walk`. There are two images for each animation in the art folder.
Adjust the "Speed (FPS)" to `3` for all animations.
 Set the `Playing` property in the Inspector to "On".
We'll select one of these animations randomly so that the mobs will have some variety.
Like the player images, these mob images need to be scaled down. Set the `AnimatedSprite`'s `Scale` property to `(0.75, 0.75)`.
As in the `Player` scene, add a `CapsuleShape2D` for the collision. To align the shape with the image, you'll need to set the `Rotation Degrees` property to `90` (under "Transform" in the Inspector).
Save the scene.
Enemy script
------------
Add a script to the `Mob` like this:
```
extends RigidBody2D
```
```
public class Mob : RigidBody2D
{
// Don't forget to rebuild the project.
}
```
```
// Copy `player.gdns` to `mob.gdns` and replace `Player` with `Mob`.
// Attach the `mob.gdns` file to the Mob node.
// Create two files `mob.cpp` and `mob.hpp` next to `entry.cpp` in `src`.
// This code goes in `mob.hpp`. We also define the methods we'll be using here.
#ifndef MOB_H
#define MOB_H
#include <AnimatedSprite.hpp>
#include <Godot.hpp>
#include <RigidBody2D.hpp>
class Mob : public godot::RigidBody2D {
GODOT_CLASS(Mob, godot::RigidBody2D)
godot::AnimatedSprite *_animated_sprite;
public:
void _init() {}
void _ready();
void _on_VisibilityNotifier2D_screen_exited();
static void _register_methods();
};
#endif // MOB_H
```
Now let's look at the rest of the script. In `_ready()` we play the animation and randomly choose one of the three animation types:
```
func _ready():
$AnimatedSprite.playing = true
var mob_types = $AnimatedSprite.frames.get_animation_names()
$AnimatedSprite.animation = mob_types[randi() % mob_types.size()]
```
```
public override void _Ready()
{
var animSprite = GetNode<AnimatedSprite>("AnimatedSprite");
animSprite.Playing = true;
string[] mobTypes = animSprite.Frames.GetAnimationNames();
animSprite.Animation = mobTypes[GD.Randi() % mobTypes.Length];
}
```
```
// This code goes in `mob.cpp`.
#include "mob.hpp"
#include <RandomNumberGenerator.hpp>
#include <SpriteFrames.hpp>
void Mob::_ready() {
godot::Ref<godot::RandomNumberGenerator> random = godot::RandomNumberGenerator::_new();
random->randomize();
_animated_sprite = get_node<godot::AnimatedSprite>("AnimatedSprite");
_animated_sprite->_set_playing(true);
godot::PoolStringArray mob_types = _animated_sprite->get_sprite_frames()->get_animation_names();
_animated_sprite->set_animation(mob_types[random->randi() % mob_types.size()]);
}
```
First, we get the list of animation names from the AnimatedSprite's `frames` property. This returns an Array containing all three animation names: `["walk",
"swim", "fly"]`.
We then need to pick a random number between `0` and `2` to select one of these names from the list (array indices start at `0`). `randi() % n` selects a random integer between `0` and `n-1`.
Note
You must use `randomize()` if you want your sequence of "random" numbers to be different every time you run the scene. We're going to use `randomize()` in our `Main` scene, so we won't need it here.
The last piece is to make the mobs delete themselves when they leave the screen. Connect the `screen_exited()` signal of the `VisibilityNotifier2D` node and add this code:
```
func _on_VisibilityNotifier2D_screen_exited():
queue_free()
```
```
public void OnVisibilityNotifier2DScreenExited()
{
QueueFree();
}
```
```
// This code goes in `mob.cpp`.
void Mob::_on_VisibilityNotifier2D_screen_exited() {
queue_free();
}
```
This completes the `Mob` scene.
With the player and enemies ready, in the next part, we'll bring them together in a new scene. We'll make enemies spawn randomly around the game board and move forward, turning our project into a playable game.
godot The main game scene The main game scene
===================
Now it's time to bring everything we did together into a playable game scene.
Create a new scene and add a [Node](../../classes/class_node#class-node) named `Main`. (The reason we are using Node instead of Node2D is because this node will be a container for handling game logic. It does not require 2D functionality itself.)
Click the **Instance** button (represented by a chain link icon) and select your saved `Player.tscn`.
 Now, add the following nodes as children of `Main`, and name them as shown (values are in seconds):
* [Timer](../../classes/class_timer#class-timer) (named `MobTimer`) - to control how often mobs spawn
* [Timer](../../classes/class_timer#class-timer) (named `ScoreTimer`) - to increment the score every second
* [Timer](../../classes/class_timer#class-timer) (named `StartTimer`) - to give a delay before starting
* [Position2D](../../classes/class_position2d#class-position2d) (named `StartPosition`) - to indicate the player's start position
Set the `Wait Time` property of each of the `Timer` nodes as follows:
* `MobTimer`: `0.5`
* `ScoreTimer`: `1`
* `StartTimer`: `2`
In addition, set the `One Shot` property of `StartTimer` to "On" and set `Position` of the `StartPosition` node to `(240, 450)`.
Spawning mobs
-------------
The Main node will be spawning new mobs, and we want them to appear at a random location on the edge of the screen. Add a [Path2D](../../classes/class_path2d#class-path2d) node named `MobPath` as a child of `Main`. When you select `Path2D`, you will see some new buttons at the top of the editor:
 Select the middle one ("Add Point") and draw the path by clicking to add the points at the corners shown. To have the points snap to the grid, make sure "Use Grid Snap" and "Use Snap" are both selected. These options can be found to the left of the "Lock" button, appearing as a magnet next to some dots and intersecting lines, respectively.
 Important
Draw the path in *clockwise* order, or your mobs will spawn pointing *outwards* instead of *inwards*!
 After placing point `4` in the image, click the "Close Curve" button and your curve will be complete.
Now that the path is defined, add a [PathFollow2D](../../classes/class_pathfollow2d#class-pathfollow2d) node as a child of `MobPath` and name it `MobSpawnLocation`. This node will automatically rotate and follow the path as it moves, so we can use it to select a random position and direction along the path.
Your scene should look like this:
 Main script
-----------
Add a script to `Main`. At the top of the script, we use `export
(PackedScene)` to allow us to choose the Mob scene we want to instance.
```
extends Node
export(PackedScene) var mob_scene
var score
```
```
public class Main : Node
{
// Don't forget to rebuild the project so the editor knows about the new export variable.
#pragma warning disable 649
// We assign this in the editor, so we don't need the warning about not being assigned.
[Export]
public PackedScene MobScene;
#pragma warning restore 649
public int Score;
}
```
```
// Copy `player.gdns` to `main.gdns` and replace `Player` with `Main`.
// Attach the `main.gdns` file to the Main node.
// Create two files `main.cpp` and `main.hpp` next to `entry.cpp` in `src`.
// This code goes in `main.hpp`. We also define the methods we'll be using here.
#ifndef MAIN_H
#define MAIN_H
#include <AudioStreamPlayer.hpp>
#include <CanvasLayer.hpp>
#include <Godot.hpp>
#include <Node.hpp>
#include <PackedScene.hpp>
#include <PathFollow2D.hpp>
#include <RandomNumberGenerator.hpp>
#include <Timer.hpp>
#include "hud.hpp"
#include "player.hpp"
class Main : public godot::Node {
GODOT_CLASS(Main, godot::Node)
int score;
HUD *_hud;
Player *_player;
godot::Node2D *_start_position;
godot::PathFollow2D *_mob_spawn_location;
godot::Timer *_mob_timer;
godot::Timer *_score_timer;
godot::Timer *_start_timer;
godot::AudioStreamPlayer *_music;
godot::AudioStreamPlayer *_death_sound;
godot::Ref<godot::RandomNumberGenerator> _random;
public:
godot::Ref<godot::PackedScene> mob_scene;
void _init() {}
void _ready();
void game_over();
void new_game();
void _on_MobTimer_timeout();
void _on_ScoreTimer_timeout();
void _on_StartTimer_timeout();
static void _register_methods();
};
#endif // MAIN_H
```
We also add a call to `randomize()` here so that the random number generator generates different random numbers each time the game is run:
```
func _ready():
randomize()
```
```
public override void _Ready()
{
GD.Randomize();
}
```
```
// This code goes in `main.cpp`.
#include "main.hpp"
#include <SceneTree.hpp>
#include "mob.hpp"
void Main::_ready() {
_hud = get_node<HUD>("HUD");
_player = get_node<Player>("Player");
_start_position = get_node<godot::Node2D>("StartPosition");
_mob_spawn_location = get_node<godot::PathFollow2D>("MobPath/MobSpawnLocation");
_mob_timer = get_node<godot::Timer>("MobTimer");
_score_timer = get_node<godot::Timer>("ScoreTimer");
_start_timer = get_node<godot::Timer>("StartTimer");
// Uncomment these after adding the nodes in the "Sound effects" section of "Finishing up".
//_music = get_node<godot::AudioStreamPlayer>("Music");
//_death_sound = get_node<godot::AudioStreamPlayer>("DeathSound");
_random = (godot::Ref<godot::RandomNumberGenerator>)godot::RandomNumberGenerator::_new();
_random->randomize();
}
```
Click the `Main` node and you will see the `Mob Scene` property in the Inspector under "Script Variables".
You can assign this property's value in two ways:
* Drag `Mob.tscn` from the "FileSystem" dock and drop it in the **Mob Scene** property.
* Click the down arrow next to "[empty]" and choose "Load". Select `Mob.tscn`.
Next, select the `Player` node in the Scene dock, and access the Node dock on the sidebar. Make sure to have the Signals tab selected in the Node dock.
You should see a list of the signals for the `Player` node. Find and double-click the `hit` signal in the list (or right-click it and select "Connect..."). This will open the signal connection dialog. We want to make a new function named `game_over`, which will handle what needs to happen when a game ends. Type "game\_over" in the "Receiver Method" box at the bottom of the signal connection dialog and click "Connect". Add the following code to the new function, as well as a `new_game` function that will set everything up for a new game:
```
func game_over():
$ScoreTimer.stop()
$MobTimer.stop()
func new_game():
score = 0
$Player.start($StartPosition.position)
$StartTimer.start()
```
```
public void GameOver()
{
GetNode<Timer>("MobTimer").Stop();
GetNode<Timer>("ScoreTimer").Stop();
}
public void NewGame()
{
Score = 0;
var player = GetNode<Player>("Player");
var startPosition = GetNode<Position2D>("StartPosition");
player.Start(startPosition.Position);
GetNode<Timer>("StartTimer").Start();
}
```
```
// This code goes in `main.cpp`.
void Main::game_over() {
_score_timer->stop();
_mob_timer->stop();
}
void Main::new_game() {
score = 0;
_player->start(_start_position->get_position());
_start_timer->start();
}
```
Now connect the `timeout()` signal of each of the Timer nodes (`StartTimer`, `ScoreTimer` , and `MobTimer`) to the main script. `StartTimer` will start the other two timers. `ScoreTimer` will increment the score by 1.
```
func _on_ScoreTimer_timeout():
score += 1
func _on_StartTimer_timeout():
$MobTimer.start()
$ScoreTimer.start()
```
```
public void OnScoreTimerTimeout()
{
Score++;
}
public void OnStartTimerTimeout()
{
GetNode<Timer>("MobTimer").Start();
GetNode<Timer>("ScoreTimer").Start();
}
```
```
// This code goes in `main.cpp`.
void Main::_on_ScoreTimer_timeout() {
score += 1;
}
void Main::_on_StartTimer_timeout() {
_mob_timer->start();
_score_timer->start();
}
// Also add this to register all methods and the mob scene property.
void Main::_register_methods() {
godot::register_method("_ready", &Main::_ready);
godot::register_method("game_over", &Main::game_over);
godot::register_method("new_game", &Main::new_game);
godot::register_method("_on_MobTimer_timeout", &Main::_on_MobTimer_timeout);
godot::register_method("_on_ScoreTimer_timeout", &Main::_on_ScoreTimer_timeout);
godot::register_method("_on_StartTimer_timeout", &Main::_on_StartTimer_timeout);
godot::register_property("mob_scene", &Main::mob_scene, (godot::Ref<godot::PackedScene>)nullptr);
}
```
In `_on_MobTimer_timeout()`, we will create a mob instance, pick a random starting location along the `Path2D`, and set the mob in motion. The `PathFollow2D` node will automatically rotate as it follows the path, so we will use that to select the mob's direction as well as its position. When we spawn a mob, we'll pick a random value between `150.0` and `250.0` for how fast each mob will move (it would be boring if they were all moving at the same speed).
Note that a new instance must be added to the scene using `add_child()`.
```
func _on_MobTimer_timeout():
# Create a new instance of the Mob scene.
var mob = mob_scene.instance()
# Choose a random location on Path2D.
var mob_spawn_location = get_node("MobPath/MobSpawnLocation")
mob_spawn_location.offset = randi()
# Set the mob's direction perpendicular to the path direction.
var direction = mob_spawn_location.rotation + PI / 2
# Set the mob's position to a random location.
mob.position = mob_spawn_location.position
# Add some randomness to the direction.
direction += rand_range(-PI / 4, PI / 4)
mob.rotation = direction
# Choose the velocity for the mob.
var velocity = Vector2(rand_range(150.0, 250.0), 0.0)
mob.linear_velocity = velocity.rotated(direction)
# Spawn the mob by adding it to the Main scene.
add_child(mob)
```
```
public void OnMobTimerTimeout()
{
// Note: Normally it is best to use explicit types rather than the `var`
// keyword. However, var is acceptable to use here because the types are
// obviously Mob and PathFollow2D, since they appear later on the line.
// Create a new instance of the Mob scene.
var mob = (Mob)MobScene.Instance();
// Choose a random location on Path2D.
var mobSpawnLocation = GetNode<PathFollow2D>("MobPath/MobSpawnLocation");
mobSpawnLocation.Offset = GD.Randi();
// Set the mob's direction perpendicular to the path direction.
float direction = mobSpawnLocation.Rotation + Mathf.Pi / 2;
// Set the mob's position to a random location.
mob.Position = mobSpawnLocation.Position;
// Add some randomness to the direction.
direction += (float)GD.RandRange(-Mathf.Pi / 4, Mathf.Pi / 4);
mob.Rotation = direction;
// Choose the velocity.
var velocity = new Vector2((float)GD.RandRange(150.0, 250.0), 0);
mob.LinearVelocity = velocity.Rotated(direction);
// Spawn the mob by adding it to the Main scene.
AddChild(mob);
}
```
```
// This code goes in `main.cpp`.
void Main::_on_MobTimer_timeout() {
// Create a new instance of the Mob scene.
godot::Node *mob = mob_scene->instance();
// Choose a random location on Path2D.
_mob_spawn_location->set_offset((real_t)_random->randi());
// Set the mob's direction perpendicular to the path direction.
real_t direction = _mob_spawn_location->get_rotation() + (real_t)Math_PI / 2;
// Set the mob's position to a random location.
mob->set("position", _mob_spawn_location->get_position());
// Add some randomness to the direction.
direction += _random->randf_range((real_t)-Math_PI / 4, (real_t)Math_PI / 4);
mob->set("rotation", direction);
// Choose the velocity for the mob.
godot::Vector2 velocity = godot::Vector2(_random->randf_range(150.0, 250.0), 0.0);
mob->set("linear_velocity", velocity.rotated(direction));
// Spawn the mob by adding it to the Main scene.
add_child(mob);
}
```
Important
Why `PI`? In functions requiring angles, Godot uses *radians*, not degrees. Pi represents a half turn in radians, about `3.1415` (there is also `TAU` which is equal to `2 * PI`). If you're more comfortable working with degrees, you'll need to use the `deg2rad()` and `rad2deg()` functions to convert between the two.
Testing the scene
-----------------
Let's test the scene to make sure everything is working. Add this `new_game` call to `_ready()`:
```
func _ready():
randomize()
new_game()
```
```
public override void _Ready()
{
NewGame();
}
```
```
// This code goes in `main.cpp`.
void Main::_ready() {
new_game();
}
```
Let's also assign `Main` as our "Main Scene" - the one that runs automatically when the game launches. Press the "Play" button and select `Main.tscn` when prompted.
Tip
If you had already set another scene as the "Main Scene", you can right click `Main.tscn` in the FileSystem dock and select "Set As Main Scene".
You should be able to move the player around, see mobs spawning, and see the player disappear when hit by a mob.
When you're sure everything is working, remove the call to `new_game()` from `_ready()`.
What's our game lacking? Some user interface. In the next lesson, we'll add a title screen and display the player's score.
godot Killing the player Killing the player
==================
We can kill enemies by jumping on them, but the player still can't die. Let's fix this.
We want to detect being hit by an enemy differently from squashing them. We want the player to die when they're moving on the floor, but not if they're in the air. We could use vector math to distinguish the two kinds of collisions. Instead, though, we will use an *Area* node, which works well for hitboxes.
Hitbox with the Area node
-------------------------
Head back to the *Player* scene and add a new *Area* node. Name it *MobDetector*. Add a *CollisionShape* node as a child of it.
In the *Inspector*, assign a cylinder shape to it.
Here is a trick you can use to make the collisions only happen when the player is on the ground or close to it. You can reduce the cylinder's height and move it up to the top of the character. This way, when the player jumps, the shape will be too high up for the enemies to collide with it.
You also want the cylinder to be wider than the sphere. This way, the player gets hit before colliding and being pushed on top of the monster's collision box.
The wider the cylinder, the more easily the player will get killed.
Next, select the *MobDetector* node again, and in the *Inspector*, turn off its *Monitorable* property. This makes it so other physics nodes cannot detect the area. The complementary *Monitoring* property allows it to detect collisions. Then, remove the *Collision -> Layer* and set the mask to the "enemies" layer.
When areas detect a collision, they emit signals. We're going to connect one to the *Player* node. In the *Node* tab, double-click the `body_entered` signal and connect it to the *Player*.
The *MobDetector* will emit `body_entered` when a *KinematicBody* or a *RigidBody* node enters it. As it only masks the "enemies" physics layers, it will only detect the *Mob* nodes.
Code-wise, we're going to do two things: emit a signal we'll later use to end the game and destroy the player. We can wrap these operations in a `die()` function that helps us put a descriptive label on the code.
```
# Emitted when the player was hit by a mob.
# Put this at the top of the script.
signal hit
# And this function at the bottom.
func die():
emit_signal("hit")
queue_free()
func _on_MobDetector_body_entered(_body):
die()
```
```
// Don't forget to rebuild the project so the editor knows about the new signal.
// Emitted when the player was hit by a mob.
[Signal]
public delegate void Hit();
// ...
private void Die()
{
EmitSignal(nameof(Hit));
QueueFree();
}
// We also specified this function name in PascalCase in the editor's connection window
public void OnMobDetectorBodyEntered(Node body)
{
Die();
}
```
Try the game again by pressing `F5`. If everything is set up correctly, the character should die when an enemy runs into it.
However, note that this depends entirely on the size and position of the *Player* and the *Mob*'s collision shapes. You may need to move them and resize them to achieve a tight game feel.
Ending the game
---------------
We can use the *Player*'s `hit` signal to end the game. All we need to do is connect it to the *Main* node and stop the *MobTimer* in reaction.
Open `Main.tscn`, select the *Player* node, and in the *Node* dock, connect its `hit` signal to the *Main* node.
Get and stop the timer in the `_on_Player_hit()` function.
```
func _on_Player_hit():
$MobTimer.stop()
```
```
// We also specified this function name in PascalCase in the editor's connection window
public void OnPlayerHit()
{
GetNode<Timer>("MobTimer").Stop();
}
```
If you try the game now, the monsters will stop spawning when you die, and the remaining ones will leave the screen.
You can pat yourself in the back: you prototyped a complete 3D game, even if it's still a bit rough.
From there, we'll add a score, the option to retry the game, and you'll see how you can make the game feel much more alive with minimalistic animations.
Code checkpoint
---------------
Here are the complete scripts for the *Main*, *Mob*, and *Player* nodes, for reference. You can use them to compare and check your code.
Starting with `Main.gd`.
```
extends Node
export(PackedScene) var mob_scene
func _ready():
randomize()
func _on_MobTimer_timeout():
# Create a new instance of the Mob scene.
var mob = mob_scene.instance()
# Choose a random location on the SpawnPath.
var mob_spawn_location = get_node("SpawnPath/SpawnLocation")
# And give it a random offset.
mob_spawn_location.unit_offset = randf()
# Communicate the spawn location and the player's location to the mob.
var player_position = $Player.transform.origin
mob.initialize(mob_spawn_location.translation, player_position)
# Spawn the mob by adding it to the Main scene.
add_child(mob)
func _on_Player_hit():
$MobTimer.stop()
```
```
public class Main : Node
{
#pragma warning disable 649
[Export]
public PackedScene MobScene;
#pragma warning restore 649
public override void _Ready()
{
GD.Randomize();
}
public void OnMobTimerTimeout()
{
// Create a new instance of the Mob scene.
var mob = (Mob)MobScene.Instance();
// Choose a random location on the SpawnPath.
// We store the reference to the SpawnLocation node.
var mobSpawnLocation = GetNode<PathFollow>("SpawnPath/SpawnLocation");
// And give it a random offset.
mobSpawnLocation.UnitOffset = GD.Randf();
// Communicate the spawn location and the player's location to the mob.
Vector3 playerPosition = GetNode<Player>("Player").Transform.origin;
mob.Initialize(mobSpawnLocation.Translation, playerPosition);
// Spawn the mob by adding it to the Main scene.
AddChild(mob);
}
public void OnPlayerHit()
{
GetNode<Timer>("MobTimer").Stop();
}
}
```
Next is `Mob.gd`.
```
extends KinematicBody
# Emitted when the player jumped on the mob.
signal squashed
# Minimum speed of the mob in meters per second.
export var min_speed = 10
# Maximum speed of the mob in meters per second.
export var max_speed = 18
var velocity = Vector3.ZERO
func _physics_process(_delta):
move_and_slide(velocity)
func initialize(start_position, player_position):
look_at_from_position(start_position, player_position, Vector3.UP)
rotate_y(rand_range(-PI / 4, PI / 4))
var random_speed = rand_range(min_speed, max_speed)
velocity = Vector3.FORWARD * random_speed
velocity = velocity.rotated(Vector3.UP, rotation.y)
func squash():
emit_signal("squashed")
queue_free()
func _on_VisibilityNotifier_screen_exited():
queue_free()
```
```
public class Mob : KinematicBody
{
// Emitted when the played jumped on the mob.
[Signal]
public delegate void Squashed();
// Minimum speed of the mob in meters per second
[Export]
public int MinSpeed = 10;
// Maximum speed of the mob in meters per second
[Export]
public int MaxSpeed = 18;
private Vector3 _velocity = Vector3.Zero;
public override void _PhysicsProcess(float delta)
{
MoveAndSlide(_velocity);
}
public void Initialize(Vector3 startPosition, Vector3 playerPosition)
{
LookAtFromPosition(startPosition, playerPosition, Vector3.Up);
RotateY((float)GD.RandRange(-Mathf.Pi / 4.0, Mathf.Pi / 4.0));
float randomSpeed = (float)GD.RandRange(MinSpeed, MaxSpeed);
_velocity = Vector3.Forward * randomSpeed;
_velocity = _velocity.Rotated(Vector3.Up, Rotation.y);
}
public void Squash()
{
EmitSignal(nameof(Squashed));
QueueFree();
}
public void OnVisibilityNotifierScreenExited()
{
QueueFree();
}
}
```
Finally, the longest script, `Player.gd`.
```
extends KinematicBody
# Emitted when a mob hit the player.
signal hit
# How fast the player moves in meters per second.
export var speed = 14
# The downward acceleration when in the air, in meters per second squared.
export var fall_acceleration = 75
# Vertical impulse applied to the character upon jumping in meters per second.
export var jump_impulse = 20
# Vertical impulse applied to the character upon bouncing over a mob in meters per second.
export var bounce_impulse = 16
var velocity = Vector3.ZERO
func _physics_process(delta):
var direction = Vector3.ZERO
if Input.is_action_pressed("move_right"):
direction.x += 1
if Input.is_action_pressed("move_left"):
direction.x -= 1
if Input.is_action_pressed("move_back"):
direction.z += 1
if Input.is_action_pressed("move_forward"):
direction.z -= 1
if direction != Vector3.ZERO:
direction = direction.normalized()
$Pivot.look_at(translation + direction, Vector3.UP)
velocity.x = direction.x * speed
velocity.z = direction.z * speed
# Jumping.
if is_on_floor() and Input.is_action_just_pressed("jump"):
velocity.y += jump_impulse
velocity.y -= fall_acceleration * delta
velocity = move_and_slide(velocity, Vector3.UP)
for index in range(get_slide_count()):
var collision = get_slide_collision(index)
if collision.collider.is_in_group("mob"):
var mob = collision.collider
if Vector3.UP.dot(collision.normal) > 0.1:
mob.squash()
velocity.y = bounce_impulse
func die():
emit_signal("hit")
queue_free()
func _on_MobDetector_body_entered(_body):
die()
```
```
public class Player : KinematicBody
{
// Emitted when the player was hit by a mob.
[Signal]
public delegate void Hit();
// How fast the player moves in meters per second.
[Export]
public int Speed = 14;
// The downward acceleration when in the air, in meters per second squared.
[Export]
public int FallAcceleration = 75;
// Vertical impulse applied to the character upon jumping in meters per second.
[Export]
public int JumpImpulse = 20;
// Vertical impulse applied to the character upon bouncing over a mob in meters per second.
[Export]
public int BounceImpulse = 16;
private Vector3 _velocity = Vector3.Zero;
public override void _PhysicsProcess(float delta)
{
var direction = Vector3.Zero;
if (Input.IsActionPressed("move_right"))
{
direction.x += 1f;
}
if (Input.IsActionPressed("move_left"))
{
direction.x -= 1f;
}
if (Input.IsActionPressed("move_back"))
{
direction.z += 1f;
}
if (Input.IsActionPressed("move_forward"))
{
direction.z -= 1f;
}
if (direction != Vector3.Zero)
{
direction = direction.Normalized();
GetNode<Spatial>("Pivot").LookAt(Translation + direction, Vector3.Up);
}
_velocity.x = direction.x * Speed;
_velocity.z = direction.z * Speed;
// Jumping.
if (IsOnFloor() && Input.IsActionJustPressed("jump"))
{
_velocity.y += JumpImpulse;
}
_velocity.y -= FallAcceleration * delta;
_velocity = MoveAndSlide(_velocity, Vector3.Up);
for (int index = 0; index < GetSlideCount(); index++)
{
KinematicCollision collision = GetSlideCollision(index);
if (collision.Collider is Mob mob && mob.IsInGroup("mob"))
{
if (Vector3.Up.Dot(collision.Normal) > 0.1f)
{
mob.Squash();
_velocity.y = BounceImpulse;
}
}
}
}
private void Die()
{
EmitSignal(nameof(Hit));
QueueFree();
}
public void OnMobDetectorBodyEntered(Node body)
{
Die();
}
}
```
See you in the next lesson to add the score and the retry option.
| programming_docs |
godot Character animation Character animation
===================
In this final lesson, we'll use Godot's built-in animation tools to make our characters float and flap. You'll learn to design animations in the editor and use code to make your game feel alive.
We'll start with an introduction to using the animation editor.
Using the animation editor
--------------------------
The engine comes with tools to author animations in the editor. You can then use the code to play and control them at runtime.
Open the player scene, select the player node, and add an *AnimationPlayer* node.
The *Animation* dock appears in the bottom panel.
It features a toolbar and the animation drop-down menu at the top, a track editor in the middle that's currently empty, and filter, snap, and zoom options at the bottom.
Let's create an animation. Click on *Animation -> New*.
Name the animation "float".
Once you created the animation, the timeline appears with numbers representing time in seconds.
We want the animation to start playback automatically at the start of the game. Also, it should loop.
To do so, you can click the button with an "A+" icon in the animation toolbar and the looping arrows, respectively.
You can also pin the animation editor by clicking the pin icon in the top-right. This prevents it from folding when you click on the viewport and deselect the nodes.
Set the animation duration to `1.2` seconds in the top-right of the dock.
You should see the gray ribbon widen a bit. It shows you the start and end of your animation and the vertical blue line is your time cursor.
You can click and drag the slider in the bottom-right to zoom in and out of the timeline.
The float animation
-------------------
With the animation player node, you can animate most properties on as many nodes as you need. Notice the key icon next to properties in the *Inspector*. You can click any of them to create a keyframe, a time and value pair for the corresponding property. The keyframe gets inserted where your time cursor is in the timeline.
Let's insert our first keys. Here, we will animate both the translation and the rotation of the *Character* node.
Select the *Character* and click the key icon next to *Translation* in the *Inspector*. Do the same for *Rotation Degrees*.
Two tracks appear in the editor with a diamond icon representing each keyframe.
You can click and drag on the diamonds to move them in time. Move the translation key to `0.2` seconds and the rotation key to `0.1` seconds.
Move the time cursor to `0.5` seconds by clicking and dragging on the gray timeline. In the *Inspector*, set the *Translation*'s *Y* axis to about `0.65` meters and the *Rotation Degrees*' *X* axis to `8`.
Create a keyframe for both properties and shift the translation key to `0.7` seconds by dragging it on the timeline.
Note
A lecture on the principles of animation is beyond the scope of this tutorial. Just note that you don't want to time and space everything evenly. Instead, animators play with timing and spacing, two core animation principles. You want to offset and contrast in your character's motion to make them feel alive.
Move the time cursor to the end of the animation, at `1.2` seconds. Set the Y translation to about `0.35` and the X rotation to `-9` degrees. Once again, create a key for both properties.
You can preview the result by clicking the play button or pressing ``Shift` + `D``. Click the stop button or press `S` to stop playback.
You can see that the engine interpolates between your keyframes to produce a continuous animation. At the moment, though, the motion feels very robotic. This is because the default interpolation is linear, causing constant transitions, unlike how living things move in the real world.
We can control the transition between keyframes using easing curves.
Click and drag around the first two keys in the timeline to box select them.
You can edit the properties of both keys simultaneously in the *Inspector*, where you can see an *Easing* property.
Click and drag on the curve, pulling it towards the left. This will make it ease-out, that is to say, transition fast initially and slow down as the time cursor reaches the next keyframe.
Play the animation again to see the difference. The first half should already feel a bit bouncier.
Apply an ease-out to the second keyframe in the rotation track.
Do the opposite for the second translation keyframe, dragging it to the right.
Your animation should look something like this.
Note
Animations update the properties of the animated nodes every frame, overriding initial values. If we directly animated the *Player* node, it would prevent us from moving it in code. This is where the *Pivot* node comes in handy: even though we animated the *Character*, we can still move and rotate the *Pivot* and layer changes on top of the animation in a script.
If you play the game, the player's creature will now float!
If the creature is a little too close to the floor, you can move the *Pivot* up to offset it.
### Controlling the animation in code
We can use code to control the animation playback based on the player's input. Let's change the animation speed when the character is moving.
Open the *Player*'s script by clicking the script icon next to it.
In `_physics_process()`, after the line where we check the `direction` vector, add the following code.
```
func _physics_process(delta):
#...
#if direction != Vector3.ZERO:
#...
$AnimationPlayer.playback_speed = 4
else:
$AnimationPlayer.playback_speed = 1
```
```
public override void _PhysicsProcess(float delta)
{
// ...
if (direction != Vector3.Zero)
{
// ...
GetNode<AnimationPlayer>("AnimationPlayer").PlaybackSpeed = 4;
}
else
{
GetNode<AnimationPlayer>("AnimationPlayer").PlaybackSpeed = 1;
}
}
```
This code makes it so when the player moves, we multiply the playback speed by `4`. When they stop, we reset it to normal.
We mentioned that the pivot could layer transforms on top of the animation. We can make the character arc when jumping using the following line of code. Add it at the end of `_physics_process()`.
```
func _physics_process(delta):
#...
$Pivot.rotation.x = PI / 6 * velocity.y / jump_impulse
```
```
public override void _PhysicsProcess(float delta)
{
// ...
var pivot = GetNode<Spatial>("Pivot");
pivot.Rotation = new Vector3(Mathf.Pi / 6f * _velocity.y / JumpImpulse, pivot.Rotation.y, pivot.Rotation.z);
}
```
Animating the mobs
------------------
Here's another nice trick with animations in Godot: as long as you use a similar node structure, you can copy them to different scenes.
For example, both the *Mob* and the *Player* scenes have a *Pivot* and a *Character* node, so we can reuse animations between them.
Open the *Player* scene, select the animation player node and open the "float" animation. Next, click on **Animation > Copy**. Then open `Mob.tscn` and open its animation player. Click **Animation > Paste**. That's it; all monsters will now play the float animation.
We can change the playback speed based on the creature's `random_speed`. Open the *Mob*'s script and at the end of the `initialize()` function, add the following line.
```
func initialize(start_position, player_position):
#...
$AnimationPlayer.playback_speed = random_speed / min_speed
```
```
public void Initialize(Vector3 startPosition, Vector3 playerPosition)
{
// ...
GetNode<AnimationPlayer>("AnimationPlayer").PlaybackSpeed = randomSpeed / MinSpeed;
}
```
And with that, you finished coding your first complete 3D game.
**Congratulations**!
In the next part, we'll quickly recap what you learned and give you some links to keep learning more. But for now, here are the complete `Player.gd` and `Mob.gd` so you can check your code against them.
Here's the *Player* script.
```
extends KinematicBody
# Emitted when the player was hit by a mob.
signal hit
# How fast the player moves in meters per second.
export var speed = 14
# The downward acceleration when in the air, in meters per second per second.
export var fall_acceleration = 75
# Vertical impulse applied to the character upon jumping in meters per second.
export var jump_impulse = 20
# Vertical impulse applied to the character upon bouncing over a mob in meters per second.
export var bounce_impulse = 16
var velocity = Vector3.ZERO
func _physics_process(delta):
var direction = Vector3.ZERO
if Input.is_action_pressed("move_right"):
direction.x += 1
if Input.is_action_pressed("move_left"):
direction.x -= 1
if Input.is_action_pressed("move_back"):
direction.z += 1
if Input.is_action_pressed("move_forward"):
direction.z -= 1
if direction != Vector3.ZERO:
direction = direction.normalized()
$Pivot.look_at(translation + direction, Vector3.UP)
$AnimationPlayer.playback_speed = 4
else:
$AnimationPlayer.playback_speed = 1
velocity.x = direction.x * speed
velocity.z = direction.z * speed
# Jumping
if is_on_floor() and Input.is_action_just_pressed("jump"):
velocity.y += jump_impulse
velocity.y -= fall_acceleration * delta
velocity = move_and_slide(velocity, Vector3.UP)
for index in range(get_slide_count()):
var collision = get_slide_collision(index)
if collision.collider.is_in_group("mob"):
var mob = collision.collider
if Vector3.UP.dot(collision.normal) > 0.1:
mob.squash()
velocity.y = bounce_impulse
$Pivot.rotation.x = PI / 6 * velocity.y / jump_impulse
func die():
emit_signal("hit")
queue_free()
func _on_MobDetector_body_entered(_body):
die()
```
```
public class Player : KinematicBody
{
// Emitted when the player was hit by a mob.
[Signal]
public delegate void Hit();
// How fast the player moves in meters per second.
[Export]
public int Speed = 14;
// The downward acceleration when in the air, in meters per second squared.
[Export]
public int FallAcceleration = 75;
// Vertical impulse applied to the character upon jumping in meters per second.
[Export]
public int JumpImpulse = 20;
// Vertical impulse applied to the character upon bouncing over a mob in meters per second.
[Export]
public int BounceImpulse = 16;
private Vector3 _velocity = Vector3.Zero;
public override void _PhysicsProcess(float delta)
{
var direction = Vector3.Zero;
if (Input.IsActionPressed("move_right"))
{
direction.x += 1f;
}
if (Input.IsActionPressed("move_left"))
{
direction.x -= 1f;
}
if (Input.IsActionPressed("move_back"))
{
direction.z += 1f;
}
if (Input.IsActionPressed("move_forward"))
{
direction.z -= 1f;
}
if (direction != Vector3.Zero)
{
direction = direction.Normalized();
GetNode<Spatial>("Pivot").LookAt(Translation + direction, Vector3.Up);
GetNode<AnimationPlayer>("AnimationPlayer").PlaybackSpeed = 4;
}
else
{
GetNode<AnimationPlayer>("AnimationPlayer").PlaybackSpeed = 1;
}
_velocity.x = direction.x * Speed;
_velocity.z = direction.z * Speed;
// Jumping.
if (IsOnFloor() && Input.IsActionJustPressed("jump"))
{
_velocity.y += JumpImpulse;
}
_velocity.y -= FallAcceleration * delta;
_velocity = MoveAndSlide(_velocity, Vector3.Up);
for (int index = 0; index < GetSlideCount(); index++)
{
KinematicCollision collision = GetSlideCollision(index);
if (collision.Collider is Mob mob && mob.IsInGroup("mob"))
{
if (Vector3.Up.Dot(collision.Normal) > 0.1f)
{
mob.Squash();
_velocity.y = BounceImpulse;
}
}
}
var pivot = GetNode<Spatial>("Pivot");
pivot.Rotation = new Vector3(Mathf.Pi / 6f * _velocity.y / JumpImpulse, pivot.Rotation.y, pivot.Rotation.z);
}
private void Die()
{
EmitSignal(nameof(Hit));
QueueFree();
}
public void OnMobDetectorBodyEntered(Node body)
{
Die();
}
}
```
And the *Mob*'s script.
```
extends KinematicBody
# Emitted when the player jumped on the mob.
signal squashed
# Minimum speed of the mob in meters per second.
export var min_speed = 10
# Maximum speed of the mob in meters per second.
export var max_speed = 18
var velocity = Vector3.ZERO
func _physics_process(_delta):
move_and_slide(velocity)
func initialize(start_position, player_position):
look_at_from_position(start_position, player_position, Vector3.UP)
rotate_y(rand_range(-PI / 4, PI / 4))
var random_speed = rand_range(min_speed, max_speed)
velocity = Vector3.FORWARD * random_speed
velocity = velocity.rotated(Vector3.UP, rotation.y)
$AnimationPlayer.playback_speed = random_speed / min_speed
func squash():
emit_signal("squashed")
queue_free()
func _on_VisibilityNotifier_screen_exited():
queue_free()
```
```
public class Mob : KinematicBody
{
// Emitted when the played jumped on the mob.
[Signal]
public delegate void Squashed();
// Minimum speed of the mob in meters per second
[Export]
public int MinSpeed = 10;
// Maximum speed of the mob in meters per second
[Export]
public int MaxSpeed = 18;
private Vector3 _velocity = Vector3.Zero;
public override void _PhysicsProcess(float delta)
{
MoveAndSlide(_velocity);
}
public void Initialize(Vector3 startPosition, Vector3 playerPosition)
{
LookAtFromPosition(startPosition, playerPosition, Vector3.Up);
RotateY((float)GD.RandRange(-Mathf.Pi / 4.0, Mathf.Pi / 4.0));
float randomSpeed = (float)GD.RandRange(MinSpeed, MaxSpeed);
_velocity = Vector3.Forward * randomSpeed;
_velocity = _velocity.Rotated(Vector3.Up, Rotation.y);
GetNode<AnimationPlayer>("AnimationPlayer").PlaybackSpeed = randomSpeed / MinSpeed;
}
public void Squash()
{
EmitSignal(nameof(Squashed));
QueueFree();
}
public void OnVisibilityNotifierScreenExited()
{
QueueFree();
}
}
```
godot Player scene and input actions Player scene and input actions
==============================
In the next two lessons, we will design the player scene, register custom input actions, and code player movement. By the end, you'll have a playable character that moves in eight directions.
Create a new scene by going to the Scene menu in the top-left and clicking *New Scene*. Create a *KinematicBody* node as the root and name it *Player*.
Kinematic bodies are complementary to the area and rigid bodies used in the 2D game tutorial. Like rigid bodies, they can move and collide with the environment, but instead of being controlled by the physics engine, you dictate their movement. You will see how we use the node's unique features when we code the jump and squash mechanics.
See also
To learn more about the different physics node types, see the [Physics introduction](https://docs.godotengine.org/en/3.5/tutorials/physics/physics_introduction.html#doc-physics-introduction).
For now, we're going to create a basic rig for our character's 3D model. This will allow us to rotate the model later via code while it plays an animation.
Add a *Spatial* node as a child of *Player* and name it *Pivot*. Then, in the FileSystem dock, expand the `art/` folder by double-clicking it and drag and drop `player.glb` onto the *Pivot* node.
This should instantiate the model as a child of *Pivot*. You can rename it to *Character*.
Note
The `.glb` files contain 3D scene data based on the open-source GLTF 2.0 specification. They're a modern and powerful alternative to a proprietary format like FBX, which Godot also supports. To produce these files, we designed the model in [Blender 3D](https://www.blender.org/) and exported it to GLTF.
As with all kinds of physics nodes, we need a collision shape for our character to collide with the environment. Select the *Player* node again and add a *CollisionShape*. In the *Inspector*, assign a *SphereShape* to the *Shape* property. The sphere's wireframe appears below the character.
It will be the shape the physics engine uses to collide with the environment, so we want it to better fit the 3D model. Shrink it a bit by dragging the orange dot in the viewport. My sphere has a radius of about `0.8` meters.
Then, move the shape up so its bottom roughly aligns with the grid's plane.
You can toggle the model's visibility by clicking the eye icon next to the *Character* or the *Pivot* nodes.
Save the scene as `Player.tscn`.
With the nodes ready, we can almost get coding. But first, we need to define some input actions.
Creating input actions
----------------------
To move the character, we will listen to the player's input, like pressing the arrow keys. In Godot, while we could write all the key bindings in code, there's a powerful system that allows you to assign a label to a set of keys and buttons. This simplifies our scripts and makes them more readable.
This system is the Input Map. To access its editor, head to the *Project* menu and select *Project Settings…*.
At the top, there are multiple tabs. Click on *Input Map*. This window allows you to add new actions at the top; they are your labels. In the bottom part, you can bind keys to these actions.
Godot projects come with some predefined actions designed for user interface design, which we could use here. But we're defining our own to support gamepads.
We're going to name our actions `move_left`, `move_right`, `move_forward`, `move_back`, and `jump`.
To add an action, write its name in the bar at the top and press Enter.
Create the five actions. Your window should have them all listed at the bottom.
To bind a key or button to an action, click the "+" button to its right. Do this for `move_left` and in the drop-down menu, click *Key*.
This option allows you to add a keyboard input. A popup appears and waits for you to press a key. Press the left arrow key and click *OK*.
Do the same for the A key.
Let's now add support for a gamepad's left joystick. Click the "+" button again but this time, select *Joy Axis*.
The popup gives you two drop-down menus. On the left, you can select a gamepad by index. *Device 0* corresponds to the first plugged gamepad, *Device 1* corresponds to the second, and so on. You can select the joystick and direction you want to bind to the input action on the right. Leave the default values and press the *Add* button.
Do the same for the other input actions. For example, bind the right arrow, D, and the left joystick's right axis to `move_right`. After binding all keys, your interface should look like this.
We have the `jump` action left to set up. Bind the Space key and the gamepad's A button. To bind a gamepad's button, select the *Joy Button* option in the menu.
Leave the default values and click the *Add* button.
Your jump input action should look like this.
That's all the actions we need for this game. You can use this menu to label any groups of keys and buttons in your projects.
In the next part, we'll code and test the player's movement.
| programming_docs |
godot Moving the player with code Moving the player with code
===========================
It's time to code! We're going to use the input actions we created in the last part to move the character.
Right-click the *Player* node and select *Attach Script* to add a new script to it. In the popup, set the *Template* to *Empty* before pressing the *Create* button.
Let's start with the class's properties. We're going to define a movement speed, a fall acceleration representing gravity, and a velocity we'll use to move the character.
```
extends KinematicBody
# How fast the player moves in meters per second.
export var speed = 14
# The downward acceleration when in the air, in meters per second squared.
export var fall_acceleration = 75
var velocity = Vector3.ZERO
```
```
public class Player : KinematicBody
{
// Don't forget to rebuild the project so the editor knows about the new export variable.
// How fast the player moves in meters per second.
[Export]
public int Speed = 14;
// The downward acceleration when in the air, in meters per second squared.
[Export]
public int FallAcceleration = 75;
private Vector3 _velocity = Vector3.Zero;
}
```
These are common properties for a moving body. The `velocity` is a 3D vector combining a speed with a direction. Here, we define it as a property because we want to update and reuse its value across frames.
Note
The values are quite different from 2D code because distances are in meters. While in 2D, a thousand units (pixels) may only correspond to half of your screen's width, in 3D, it's a kilometer.
Let's code the movement now. We start by calculating the input direction vector using the global `Input` object, in `_physics_process()`.
```
func _physics_process(delta):
# We create a local variable to store the input direction.
var direction = Vector3.ZERO
# We check for each move input and update the direction accordingly.
if Input.is_action_pressed("move_right"):
direction.x += 1
if Input.is_action_pressed("move_left"):
direction.x -= 1
if Input.is_action_pressed("move_back"):
# Notice how we are working with the vector's x and z axes.
# In 3D, the XZ plane is the ground plane.
direction.z += 1
if Input.is_action_pressed("move_forward"):
direction.z -= 1
```
```
public override void _PhysicsProcess(float delta)
{
// We create a local variable to store the input direction.
var direction = Vector3.Zero;
// We check for each move input and update the direction accordingly
if (Input.IsActionPressed("move_right"))
{
direction.x += 1f;
}
if (Input.IsActionPressed("move_left"))
{
direction.x -= 1f;
}
if (Input.IsActionPressed("move_back"))
{
// Notice how we are working with the vector's x and z axes.
// In 3D, the XZ plane is the ground plane.
direction.z += 1f;
}
if (Input.IsActionPressed("move_forward"))
{
direction.z -= 1f;
}
}
```
Here, we're going to make all calculations using the `_physics_process()` virtual function. Like `_process()`, it allows you to update the node every frame, but it's designed specifically for physics-related code like moving a kinematic or rigid body.
See also
To learn more about the difference between `_process()` and `_physics_process()`, see [Idle and Physics Processing](https://docs.godotengine.org/en/3.5/tutorials/scripting/idle_and_physics_processing.html#doc-idle-and-physics-processing).
We start by initializing a `direction` variable to `Vector3.ZERO`. Then, we check if the player is pressing one or more of the `move_*` inputs and update the vector's `x` and `z` components accordingly. These correspond to the ground plane's axes.
These four conditions give us eight possibilities and eight possible directions.
In case the player presses, say, both W and D simultaneously, the vector will have a length of about `1.4`. But if they press a single key, it will have a length of `1`. We want the vector's length to be consistent. To do so, we can call its `normalize()` method.
```
#func _physics_process(delta):
#...
if direction != Vector3.ZERO:
direction = direction.normalized()
$Pivot.look_at(translation + direction, Vector3.UP)
```
```
public override void _PhysicsProcess(float delta)
{
// ...
if (direction != Vector3.Zero)
{
direction = direction.Normalized();
GetNode<Spatial>("Pivot").LookAt(Translation + direction, Vector3.Up);
}
}
```
Here, we only normalize the vector if the direction has a length greater than zero, which means the player is pressing a direction key.
In this case, we also get the *Pivot* node and call its `look_at()` method. This method takes a position in space to look at in global coordinates and the up direction. In this case, we can use the `Vector3.UP` constant.
Note
A node's local coordinates, like `translation`, are relative to their parent. Global coordinates are relative to the world's main axes you can see in the viewport instead.
In 3D, the property that contains a node's position is `translation`. By adding the `direction` to it, we get a position to look at that's one meter away from the *Player*.
Then, we update the velocity. We have to calculate the ground velocity and the fall speed separately. Be sure to go back one tab so the lines are inside the `_physics_process()` function but outside the condition we just wrote.
```
func _physics_process(delta):
#...
if direction != Vector3.ZERO:
#...
# Ground velocity
velocity.x = direction.x * speed
velocity.z = direction.z * speed
# Vertical velocity
velocity.y -= fall_acceleration * delta
# Moving the character
velocity = move_and_slide(velocity, Vector3.UP)
```
```
public override void _PhysicsProcess(float delta)
{
// ...
// Ground velocity
_velocity.x = direction.x * Speed;
_velocity.z = direction.z * Speed;
// Vertical velocity
_velocity.y -= FallAcceleration * delta;
// Moving the character
_velocity = MoveAndSlide(_velocity, Vector3.Up);
}
```
For the vertical velocity, we subtract the fall acceleration multiplied by the delta time every frame. Notice the use of the `-=` operator, which is a shorthand for `variable = variable - ...`.
This line of code will cause our character to fall in every frame. This may seem strange if it's already on the floor. But we have to do this for the character to collide with the ground every frame.
The physics engine can only detect interactions with walls, the floor, or other bodies during a given frame if movement and collisions happen. We will use this property later to code the jump.
On the last line, we call `KinematicBody.move_and_slide()`. It's a powerful method of the `KinematicBody` class that allows you to move a character smoothly. If it hits a wall midway through a motion, the engine will try to smooth it out for you.
The function takes two parameters: our velocity and the up direction. It moves the character and returns a leftover velocity after applying collisions. When hitting the floor or a wall, the function will reduce or reset the speed in that direction from you. In our case, storing the function's returned value prevents the character from accumulating vertical momentum, which could otherwise get so big the character would move through the ground slab after a while.
And that's all the code you need to move the character on the floor.
Here is the complete `Player.gd` code for reference.
```
extends KinematicBody
# How fast the player moves in meters per second.
export var speed = 14
# The downward acceleration when in the air, in meters per second squared.
export var fall_acceleration = 75
var velocity = Vector3.ZERO
func _physics_process(delta):
var direction = Vector3.ZERO
if Input.is_action_pressed("move_right"):
direction.x += 1
if Input.is_action_pressed("move_left"):
direction.x -= 1
if Input.is_action_pressed("move_back"):
direction.z += 1
if Input.is_action_pressed("move_forward"):
direction.z -= 1
if direction != Vector3.ZERO:
direction = direction.normalized()
$Pivot.look_at(translation + direction, Vector3.UP)
velocity.x = direction.x * speed
velocity.z = direction.z * speed
velocity.y -= fall_acceleration * delta
velocity = move_and_slide(velocity, Vector3.UP)
```
```
public class Player : KinematicBody
{
// How fast the player moves in meters per second.
[Export]
public int Speed = 14;
// The downward acceleration when in the air, in meters per second squared.
[Export]
public int FallAcceleration = 75;
private Vector3 _velocity = Vector3.Zero;
public override void _PhysicsProcess(float delta)
{
// We create a local variable to store the input direction.
var direction = Vector3.Zero;
// We check for each move input and update the direction accordingly
if (Input.IsActionPressed("move_right"))
{
direction.x += 1f;
}
if (Input.IsActionPressed("move_left"))
{
direction.x -= 1f;
}
if (Input.IsActionPressed("move_back"))
{
// Notice how we are working with the vector's x and z axes.
// In 3D, the XZ plane is the ground plane.
direction.z += 1f;
}
if (Input.IsActionPressed("move_forward"))
{
direction.z -= 1f;
}
if (direction != Vector3.Zero)
{
direction = direction.Normalized();
GetNode<Spatial>("Pivot").LookAt(Translation + direction, Vector3.Up);
}
// Ground velocity
_velocity.x = direction.x * Speed;
_velocity.z = direction.z * Speed;
// Vertical velocity
_velocity.y -= FallAcceleration * delta;
// Moving the character
_velocity = MoveAndSlide(_velocity, Vector3.Up);
}
}
```
Testing our player's movement
-----------------------------
We're going to put our player in the *Main* scene to test it. To do so, we need to instantiate the player and then add a camera. Unlike in 2D, in 3D, you won't see anything if your viewport doesn't have a camera pointing at something.
Save your *Player* scene and open the *Main* scene. You can click on the *Main* tab at the top of the editor to do so.
If you closed the scene before, head to the *FileSystem* dock and double-click `Main.tscn` to re-open it.
To instantiate the *Player*, right-click on the *Main* node and select *Instance Child Scene*.
In the popup, double-click *Player.tscn*. The character should appear in the center of the viewport.
### Adding a camera
Let's add the camera next. Like we did with our *Player*'s *Pivot*, we're going to create a basic rig. Right-click on the *Main* node again and select *Add Child Node* this time. Create a new *Position3D*, name it *CameraPivot*, and add a *Camera* node as a child of it. Your scene tree should look like this.
Notice the *Preview* checkbox that appears in the top-left when you have the *Camera* selected. You can click it to preview the in-game camera projection.
We're going to use the *Pivot* to rotate the camera as if it was on a crane. Let's first split the 3D view to be able to freely navigate the scene and see what the camera sees.
In the toolbar right above the viewport, click on *View*, then *2 Viewports*. You can also press ``Ctrl` + `2`` (``Cmd` + `2`` on macOS).
On the bottom view, select the *Camera* and turn on camera preview by clicking the checkbox.
In the top view, move the camera about `19` units on the Z axis (the blue one).
Here's where the magic happens. Select the *CameraPivot* and rotate it `45` degrees around the X axis (using the red circle). You'll see the camera move as if it was attached to a crane.
You can run the scene by pressing `F6` and press the arrow keys to move the character.
We can see some empty space around the character due to the perspective projection. In this game, we're going to use an orthographic projection instead to better frame the gameplay area and make it easier for the player to read distances.
Select the *Camera* again and in the *Inspector*, set the *Projection* to *Orthogonal* and the *Size* to `19`. The character should now look flatter and the ground should fill the background.
With that, we have both player movement and the view in place. Next, we will work on the monsters.
godot Score and replay Score and replay
================
In this part, we'll add the score, music playback, and the ability to restart the game.
We have to keep track of the current score in a variable and display it on screen using a minimal interface. We will use a text label to do that.
In the main scene, add a new *Control* node as a child of *Main* and name it *UserInterface*. You will automatically be taken to the 2D screen, where you can edit your User Interface (UI).
Add a *Label* node and rename it to *ScoreLabel*.
In the *Inspector*, set the *Label*'s *Text* to a placeholder like "Score: 0".
Also, the text is white by default, like our game's background. We need to change its color to see it at runtime.
Scroll down to *Theme Overrides*, and expand *Colors* and click the black box next to *Font Color* to tint the text.
Pick a dark tone so it contrasts well with the 3D scene.
Finally, click and drag on the text in the viewport to move it away from the top-left corner.
The *UserInterface* node allows us to group our UI in a branch of the scene tree and use a theme resource that will propagate to all its children. We'll use it to set our game's font.
Creating a UI theme
-------------------
Once again, select the *UserInterface* node. In the *Inspector*, create a new theme resource in *Theme -> Theme*.
Click on it to open the theme editor In the bottom panel. It gives you a preview of how all the built-in UI widgets will look with your theme resource.
By default, a theme only has one property, the *Default Font*.
See also
You can add more properties to the theme resource to design complex user interfaces, but that is beyond the scope of this series. To learn more about creating and editing themes, see [Introduction to GUI skinning](https://docs.godotengine.org/en/3.5/tutorials/ui/gui_skinning.html#doc-gui-skinning).
Click the *Default Font* property and create a new *DynamicFont*.
Expand the *DynamicFont* by clicking on it and expand its *Font* section. There, you will see an empty *Font Data* field.
This one expects a font file like the ones you have on your computer. DynamicFont supports the following formats:
* TrueType (`.ttf`)
* OpenType (`.otf`)
* Web Open Font Format 1 (`.woff`)
* Web Open Font Format 2 (`.woff2`, since Godot 3.5)
In the *FileSystem* dock, expand the `fonts` directory and click and drag the `Montserrat-Medium.ttf` file we included in the project onto the *Font Data*. The text will reappear in the theme preview.
The text is a bit small. Set the *Settings -> Size* to `22` pixels to increase the text's size.
Keeping track of the score
--------------------------
Let's work on the score next. Attach a new script to the *ScoreLabel* and define the `score` variable.
```
extends Label
var score = 0
```
```
public class ScoreLabel : Label
{
private int _score = 0;
}
```
The score should increase by `1` every time we squash a monster. We can use their `squashed` signal to know when that happens. However, as we instantiate monsters from the code, we cannot do the connection in the editor.
Instead, we have to make the connection from the code every time we spawn a monster.
Open the script `Main.gd`. If it's still open, you can click on its name in the script editor's left column.
Alternatively, you can double-click the `Main.gd` file in the *FileSystem* dock.
At the bottom of the `_on_MobTimer_timeout()` function, add the following line.
```
func _on_MobTimer_timeout():
#...
# We connect the mob to the score label to update the score upon squashing one.
mob.connect("squashed", $UserInterface/ScoreLabel, "_on_Mob_squashed")
```
```
public void OnMobTimerTimeout()
{
// ...
// We connect the mob to the score label to update the score upon squashing one.
mob.Connect(nameof(Mob.Squashed), GetNode<ScoreLabel>("UserInterface/ScoreLabel"), nameof(ScoreLabel.OnMobSquashed));
}
```
This line means that when the mob emits the `squashed` signal, the *ScoreLabel* node will receive it and call the function `_on_Mob_squashed()`.
Head back to the `ScoreLabel.gd` script to define the `_on_Mob_squashed()` callback function.
There, we increment the score and update the displayed text.
```
func _on_Mob_squashed():
score += 1
text = "Score: %s" % score
```
```
public void OnMobSquashed()
{
_score += 1;
Text = string.Format("Score: {0}", _score);
}
```
The second line uses the value of the `score` variable to replace the placeholder `%s`. When using this feature, Godot automatically converts values to text, which is convenient to output text in labels or using the `print()` function.
See also
You can learn more about string formatting here: [GDScript format strings](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/gdscript_format_string.html#doc-gdscript-printf).
You can now play the game and squash a few enemies to see the score increase.
Note
In a complex game, you may want to completely separate your user interface from the game world. In that case, you would not keep track of the score on the label. Instead, you may want to store it in a separate, dedicated object. But when prototyping or when your project is simple, it is fine to keep your code simple. Programming is always a balancing act.
Retrying the game
-----------------
We'll now add the ability to play again after dying. When the player dies, we'll display a message on the screen and wait for input.
Head back to the *Main* scene, select the *UserInterface* node, add a *ColorRect* node as a child of it and name it *Retry*. This node fills a rectangle with a uniform color and will serve as an overlay to darken the screen.
To make it span over the whole viewport, you can use the *Layout* menu in the toolbar.
Open it and apply the *Full Rect* command.
Nothing happens. Well, almost nothing: only the four green pins move to the corners of the selection box.
This is because UI nodes (all the ones with a green icon) work with anchors and margins relative to their parent's bounding box. Here, the *UserInterface* node has a small size and the *Retry* one is limited by it.
Select the *UserInterface* and apply *Layout -> Full Rect* to it as well. The *Retry* node should now span the whole viewport.
Let's change its color so it darkens the game area. Select *Retry* and in the *Inspector*, set its *Color* to something both dark and transparent. To do so, in the color picker, drag the *A* slider to the left. It controls the color's alpha channel, that is to say, its opacity.
Next, add a *Label* as a child of *Retry* and give it the *Text* "Press Enter to retry."
To move it and anchor it in the center of the screen, apply *Layout -> Center* to it.
### Coding the retry option
We can now head to the code to show and hide the *Retry* node when the player dies and plays again.
Open the script `Main.gd`. First, we want to hide the overlay at the start of the game. Add this line to the `_ready()` function.
```
func _ready():
#...
$UserInterface/Retry.hide()
```
```
public override void _Ready()
{
// ...
GetNode<Control>("UserInterface/Retry").Hide();
}
```
Then, when the player gets hit, we show the overlay.
```
func _on_Player_hit():
#...
$UserInterface/Retry.show()
```
```
public void OnPlayerHit()
{
//...
GetNode<Control>("UserInterface/Retry").Show();
}
```
Finally, when the *Retry* node is visible, we need to listen to the player's input and restart the game if they press enter. To do this, we use the built-in `_unhandled_input()` callback.
If the player pressed the predefined `ui_accept` input action and *Retry* is visible, we reload the current scene.
```
func _unhandled_input(event):
if event.is_action_pressed("ui_accept") and $UserInterface/Retry.visible:
# This restarts the current scene.
get_tree().reload_current_scene()
```
```
public override void _UnhandledInput(InputEvent @event)
{
if (@event.IsActionPressed("ui_accept") && GetNode<Control>("UserInterface/Retry").Visible)
{
// This restarts the current scene.
GetTree().ReloadCurrentScene();
}
}
```
The function `get_tree()` gives us access to the global [SceneTree](../../classes/class_scenetree#class-scenetree) object, which allows us to reload and restart the current scene.
Adding music
------------
To add music that plays continuously in the background, we're going to use another feature in Godot: [autoloads](https://docs.godotengine.org/en/3.5/tutorials/scripting/singletons_autoload.html#doc-singletons-autoload).
To play audio, all you need to do is add an *AudioStreamPlayer* node to your scene and attach an audio file to it. When you start the scene, it can play automatically. However, when you reload the scene, like we do to play again, the audio nodes are also reset, and the music starts back from the beginning.
You can use the autoload feature to have Godot load a node or a scene automatically at the start of the game, outside the current scene. You can also use it to create globally accessible objects.
Create a new scene by going to the *Scene* menu and clicking *New Scene*.
Click the *Other Node* button to create an *AudioStreamPlayer* and rename it to *MusicPlayer*.
We included a music soundtrack in the `art/` directory, `House In a Forest
Loop.ogg`. Click and drag it onto the *Stream* property in the *Inspector*. Also, turn on *Autoplay* so the music plays automatically at the start of the game.
Save the scene as `MusicPlayer.tscn`.
We have to register it as an autoload. Head to the *Project -> Project Settings…* menu and click on the *Autoload* tab.
In the *Path* field, you want to enter the path to your scene. Click the folder icon to open the file browser and double-click on `MusicPlayer.tscn`. Then, click the *Add* button on the right to register the node.
If you run the game now, the music will play automatically. And even when you lose and retry, it keeps going.
Before we wrap up this lesson, here's a quick look at how it works under the hood. When you run the game, your *Scene* dock changes to give you two tabs: *Remote* and *Local*.
The *Remote* tab allows you to visualize the node tree of your running game. There, you will see the *Main* node and everything the scene contains and the instantiated mobs at the bottom.
At the top are the autoloaded *MusicPlayer* and a *root* node, which is your game's viewport.
And that does it for this lesson. In the next part, we'll add an animation to make the game both look and feel much nicer.
Here is the complete `Main.gd` script for reference.
```
extends Node
export (PackedScene) var mob_scene
func _ready():
randomize()
$UserInterface/Retry.hide()
func _unhandled_input(event):
if event.is_action_pressed("ui_accept") and $UserInterface/Retry.visible:
get_tree().reload_current_scene()
func _on_MobTimer_timeout():
var mob = mob_scene.instance()
var mob_spawn_location = get_node("SpawnPath/SpawnLocation")
mob_spawn_location.unit_offset = randf()
var player_position = $Player.transform.origin
mob.initialize(mob_spawn_location.translation, player_position)
add_child(mob)
mob.connect("squashed", $UserInterface/ScoreLabel, "_on_Mob_squashed")
func _on_Player_hit():
$MobTimer.stop()
$UserInterface/Retry.show()
```
```
public class Main : Node
{
#pragma warning disable 649
[Export]
public PackedScene MobScene;
#pragma warning restore 649
public override void _Ready()
{
GD.Randomize();
GetNode<Control>("UserInterface/Retry").Hide();
}
public override void _UnhandledInput(InputEvent @event)
{
if (@event.IsActionPressed("ui_accept") && GetNode<Control>("UserInterface/Retry").Visible)
{
GetTree().ReloadCurrentScene();
}
}
public void OnMobTimerTimeout()
{
Mob mob = (Mob)MobScene.Instance();
var mobSpawnLocation = GetNode<PathFollow>("SpawnPath/SpawnLocation");
mobSpawnLocation.UnitOffset = GD.Randf();
Vector3 playerPosition = GetNode<Player>("Player").Transform.origin;
mob.Initialize(mobSpawnLocation.Translation, playerPosition);
AddChild(mob);
mob.Connect(nameof(Mob.Squashed), GetNode<ScoreLabel>("UserInterface/ScoreLabel"), nameof(ScoreLabel.OnMobSquashed));
}
public void OnPlayerHit()
{
GetNode<Timer>("MobTimer").Stop();
GetNode<Control>("UserInterface/Retry").Show();
}
}
```
| programming_docs |
godot Designing the mob scene Designing the mob scene
=======================
In this part, you're going to code the monsters, which we'll call mobs. In the next lesson, we'll spawn them randomly around the playable area.
Let's design the monsters themselves in a new scene. The node structure is going to be similar to the *Player* scene.
Create a scene with, once again, a *KinematicBody* node as its root. Name it *Mob*. Add a *Spatial* node as a child of it, name it *Pivot*. And drag and drop the file `mob.glb` from the *FileSystem* dock onto the *Pivot* to add the monster's 3D model to the scene. You can rename the newly created *mob* node into *Character*.
We need a collision shape for our body to work. Right-click on the *Mob* node, the scene's root, and click *Add Child Node*.
Add a *CollisionShape*.
In the *Inspector*, assign a *BoxShape* to the *Shape* property.
We should change its size to fit the 3D model better. You can do so interactively by clicking and dragging on the orange dots.
The box should touch the floor and be a little thinner than the model. Physics engines work in such a way that if the player's sphere touches even the box's corner, a collision will occur. If the box is a little too big compared to the 3D model, you may die at a distance from the monster, and the game will feel unfair to the players.
Notice that my box is taller than the monster. It is okay in this game because we're looking at the scene from above and using a fixed perspective. Collision shapes don't have to match the model exactly. It's the way the game feels when you test it that should dictate their form and size.
Removing monsters off-screen
----------------------------
We're going to spawn monsters at regular time intervals in the game level. If we're not careful, their count could increase to infinity, and we don't want that. Each mob instance has both a memory and a processing cost, and we don't want to pay for it when the mob's outside the screen.
Once a monster leaves the screen, we don't need it anymore, so we can delete it. Godot has a node that detects when objects leave the screen, *VisibilityNotifier*, and we're going to use it to destroy our mobs.
Note
When you keep instancing an object in games, there's a technique you can use to avoid the cost of creating and destroying instances all the time called pooling. It consists of pre-creating an array of objects and reusing them over and over.
When working with GDScript, you don't need to worry about this. The main reason to use pools is to avoid freezes with garbage-collected languages like C# or Lua. GDScript uses a different technique to manage memory, reference counting, which doesn't have that caveat. You can learn more about that here [Memory management](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/gdscript_basics.html#doc-gdscript-basics-memory-management).
Select the *Mob* node and add a *VisibilityNotifier* as a child of it. Another box, pink this time, appears. When this box completely leaves the screen, the node will emit a signal.
Resize it using the orange dots until it covers the entire 3D model.
### Coding the mob's movement
Let's implement the monster's motion. We're going to do this in two steps. First, we'll write a script on the *Mob* that defines a function to initialize the monster. We'll then code the randomized spawn mechanism in the *Main* scene and call the function from there.
Attach a script to the *Mob*.
Here's the movement code to start with. We define two properties, `min_speed` and `max_speed`, to define a random speed range. We then define and initialize the `velocity`.
```
extends KinematicBody
# Minimum speed of the mob in meters per second.
export var min_speed = 10
# Maximum speed of the mob in meters per second.
export var max_speed = 18
var velocity = Vector3.ZERO
func _physics_process(_delta):
move_and_slide(velocity)
```
```
public class Mob : KinematicBody
{
// Don't forget to rebuild the project so the editor knows about the new export variable.
// Minimum speed of the mob in meters per second
[Export]
public int MinSpeed = 10;
// Maximum speed of the mob in meters per second
[Export]
public int MaxSpeed = 18;
private Vector3 _velocity = Vector3.Zero;
public override void _PhysicsProcess(float delta)
{
MoveAndSlide(_velocity);
}
}
```
Similarly to the player, we move the mob every frame by calling `KinematicBody`'s `move_and_slide()` method. This time, we don't update the `velocity` every frame: we want the monster to move at a constant speed and leave the screen, even if it were to hit an obstacle.
You may see a warning in GDScript that the return value from `move_and_slide()` is unused. This is expected. You can simply ignore the warning or, if you want to hide it entirely, add the comment `# warning-ignore:return_value_discarded` just above the `move_and_slide(velocity)` line. To read more about the GDScript warning system, see [GDScript warning system](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/warning_system.html#doc-gdscript-warning-system).
We need to define another function to calculate the start velocity. This function will turn the monster towards the player and randomize both its angle of motion and its velocity.
The function will take a `start_position`, the mob's spawn position, and the `player_position` as its arguments.
We position the mob at `start_position` and turn it towards the player using the `look_at_from_position()` method, and randomize the angle by rotating a random amount around the Y axis. Below, `rand_range()` outputs a random value between `-PI / 4` radians and `PI / 4` radians.
```
# We will call this function from the Main scene.
func initialize(start_position, player_position):
# We position the mob and turn it so that it looks at the player.
look_at_from_position(start_position, player_position, Vector3.UP)
# And rotate it randomly so it doesn't move exactly toward the player.
rotate_y(rand_range(-PI / 4, PI / 4))
```
```
// We will call this function from the Main scene
public void Initialize(Vector3 startPosition, Vector3 playerPosition)
{
// We position the mob and turn it so that it looks at the player.
LookAtFromPosition(startPosition, playerPosition, Vector3.Up);
// And rotate it randomly so it doesn't move exactly toward the player.
RotateY((float)GD.RandRange(-Mathf.Pi / 4.0, Mathf.Pi / 4.0));
}
```
We then calculate a random speed using `rand_range()` once again and we use it to calculate the velocity.
We start by creating a 3D vector pointing forward, multiply it by our `random_speed`, and finally rotate it using the `Vector3` class's `rotated()` method.
```
func initialize(start_position, player_position):
# ...
# We calculate a random speed.
var random_speed = rand_range(min_speed, max_speed)
# We calculate a forward velocity that represents the speed.
velocity = Vector3.FORWARD * random_speed
# We then rotate the vector based on the mob's Y rotation to move in the direction it's looking.
velocity = velocity.rotated(Vector3.UP, rotation.y)
```
```
public void Initialize(Vector3 startPosition, Vector3 playerPosition)
{
// ...
// We calculate a random speed.
float randomSpeed = (float)GD.RandRange(MinSpeed, MaxSpeed);
// We calculate a forward velocity that represents the speed.
_velocity = Vector3.Forward * randomSpeed;
// We then rotate the vector based on the mob's Y rotation to move in the direction it's looking
_velocity = _velocity.Rotated(Vector3.Up, Rotation.y);
}
```
### Leaving the screen
We still have to destroy the mobs when they leave the screen. To do so, we'll connect our *VisibilityNotifier* node's `screen_exited` signal to the *Mob*.
Head back to the 3D viewport by clicking on the *3D* label at the top of the editor. You can also press ``Ctrl` + `F2`` (``Alt` + `2`` on macOS).
Select the *VisibilityNotifier* node and on the right side of the interface, navigate to the *Node* dock. Double-click the *screen\_exited()* signal.
Connect the signal to the *Mob*.
This will take you back to the script editor and add a new function for you, `_on_VisibilityNotifier_screen_exited()`. From it, call the `queue_free()` method. This will destroy the mob instance when the *VisibilityNotifier* 's box leaves the screen.
```
func _on_VisibilityNotifier_screen_exited():
queue_free()
```
```
// We also specified this function name in PascalCase in the editor's connection window
public void OnVisibilityNotifierScreenExited()
{
QueueFree();
}
```
Our monster is ready to enter the game! In the next part, you will spawn monsters in the game level.
Here is the complete `Mob.gd` script for reference.
```
extends KinematicBody
# Minimum speed of the mob in meters per second.
export var min_speed = 10
# Maximum speed of the mob in meters per second.
export var max_speed = 18
var velocity = Vector3.ZERO
func _physics_process(_delta):
move_and_slide(velocity)
func initialize(start_position, player_position):
look_at_from_position(start_position, player_position, Vector3.UP)
rotate_y(rand_range(-PI / 4, PI / 4))
var random_speed = rand_range(min_speed, max_speed)
velocity = Vector3.FORWARD * random_speed
velocity = velocity.rotated(Vector3.UP, rotation.y)
func _on_VisibilityNotifier_screen_exited():
queue_free()
```
```
public class Mob : KinematicBody
{
// Minimum speed of the mob in meters per second
[Export]
public int MinSpeed = 10;
// Maximum speed of the mob in meters per second
[Export]
public int MaxSpeed = 18;
private Vector3 _velocity = Vector3.Zero;
public override void _PhysicsProcess(float delta)
{
MoveAndSlide(_velocity);
}
// We will call this function from the Main scene
public void Initialize(Vector3 startPosition, Vector3 playerPosition)
{
LookAtFromPosition(startPosition, playerPosition, Vector3.Up);
RotateY((float)GD.RandRange(-Mathf.Pi / 4.0, Mathf.Pi / 4.0));
var randomSpeed = (float)GD.RandRange(MinSpeed, MaxSpeed);
_velocity = Vector3.Forward * randomSpeed;
_velocity = _velocity.Rotated(Vector3.Up, Rotation.y);
}
// We also specified this function name in PascalCase in the editor's connection window
public void OnVisibilityNotifierScreenExited()
{
QueueFree();
}
}
```
godot Jumping and squashing monsters Jumping and squashing monsters
==============================
In this part, we'll add the ability to jump, to squash the monsters. In the next lesson, we'll make the player die when a monster hits them on the ground.
First, we have to change a few settings related to physics interactions. Enter the world of [physics layers](https://docs.godotengine.org/en/3.5/tutorials/physics/physics_introduction.html#doc-physics-introduction-collision-layers-and-masks).
Controlling physics interactions
--------------------------------
Physics bodies have access to two complementary properties: layers and masks. Layers define on which physics layer(s) an object is.
Masks control the layers that a body will listen to and detect. This affects collision detection. When you want two bodies to interact, you need at least one to have a mask corresponding to the other.
If that's confusing, don't worry, we'll see three examples in a second.
The important point is that you can use layers and masks to filter physics interactions, control performance, and remove the need for extra conditions in your code.
By default, all physics bodies and areas are set to both layer and mask `0`. This means they all collide with each other.
Physics layers are represented by numbers, but we can give them names to keep track of what's what.
### Setting layer names
Let's give our physics layers a name. Go to *Project -> Project Settings*.
In the left menu, navigate down to *Layer Names -> 3D Physics*. You can see a list of layers with a field next to each of them on the right. You can set their names there. Name the first three layers *player*, *enemies*, and *world*, respectively.
Now, we can assign them to our physics nodes.
### Assigning layers and masks
In the *Main* scene, select the *Ground* node. In the *Inspector*, expand the *Collision* section. There, you can see the node's layers and masks as a grid of buttons.
The ground is part of the world, so we want it to be part of the third layer. Click the lit button to toggle off the first *Layer* and toggle on the third one. Then, toggle off the *Mask* by clicking on it.
As I mentioned above, the *Mask* property allows a node to listen to interaction with other physics objects, but we don't need it to have collisions. The *Ground* doesn't need to listen to anything; it's just there to prevent creatures from falling.
Note that you can click the "..." button on the right side of the properties to see a list of named checkboxes.
Next up are the *Player* and the *Mob*. Open `Player.tscn` by double-clicking the file in the *FileSystem* dock.
Select the *Player* node and set its *Collision -> Mask* to both "enemies" and "world". You can leave the default *Layer* property as the first layer is the "player" one.
Then, open the *Mob* scene by double-clicking on `Mob.tscn` and select the *Mob* node.
Set its *Collision -> Layer* to "enemies" and unset its *Collision -> Mask*, leaving the mask empty.
These settings mean the monsters will move through one another. If you want the monsters to collide with and slide against each other, turn on the "enemies" mask.
Note
The mobs don't need to mask the "world" layer because they only move on the XZ plane. We don't apply any gravity to them by design.
Jumping
-------
The jumping mechanic itself requires only two lines of code. Open the *Player* script. We need a value to control the jump's strength and update `_physics_process()` to code the jump.
After the line that defines `fall_acceleration`, at the top of the script, add the `jump_impulse`.
```
#...
# Vertical impulse applied to the character upon jumping in meters per second.
export var jump_impulse = 20
```
```
// Don't forget to rebuild the project so the editor knows about the new export variable.
// ...
// Vertical impulse applied to the character upon jumping in meters per second.
[Export]
public int JumpImpulse = 20;
```
Inside `_physics_process()`, add the following code before the line where we called `move_and_slide()`.
```
func _physics_process(delta):
#...
# Jumping.
if is_on_floor() and Input.is_action_just_pressed("jump"):
velocity.y += jump_impulse
#...
```
```
public override void _PhysicsProcess(float delta)
{
// ...
// Jumping.
if (IsOnFloor() && Input.IsActionJustPressed("jump"))
{
_velocity.y += JumpImpulse;
}
// ...
}
```
That's all you need to jump!
The `is_on_floor()` method is a tool from the `KinematicBody` class. It returns `true` if the body collided with the floor in this frame. That's why we apply gravity to the *Player*: so we collide with the floor instead of floating over it like the monsters.
If the character is on the floor and the player presses "jump", we instantly give them a lot of vertical speed. In games, you really want controls to be responsive and giving instant speed boosts like these, while unrealistic, feel great.
Notice that the Y axis is positive upwards. That's unlike 2D, where the Y axis is positive downward.
Squashing monsters
------------------
Let's add the squash mechanic next. We're going to make the character bounce over monsters and kill them at the same time.
We need to detect collisions with a monster and to differentiate them from collisions with the floor. To do so, we can use Godot's [group](https://docs.godotengine.org/en/3.5/tutorials/scripting/groups.html#doc-groups) tagging feature.
Open the scene `Mob.tscn` again and select the *Mob* node. Go to the *Node* dock on the right to see a list of signals. The *Node* dock has two tabs: *Signals*, which you've already used, and *Groups*, which allows you to assign tags to nodes.
Click on it to reveal a field where you can write a tag name. Enter "mob" in the field and click the *Add* button.
An icon appears in the *Scene* dock to indicate the node is part of at least one group.
We can now use the group from the code to distinguish collisions with monsters from collisions with the floor.
### Coding the squash mechanic
Head back to the *Player* script to code the squash and bounce.
At the top of the script, we need another property, `bounce_impulse`. When squashing an enemy, we don't necessarily want the character to go as high up as when jumping.
```
# Vertical impulse applied to the character upon bouncing over a mob in
# meters per second.
export var bounce_impulse = 16
```
```
// Don't forget to rebuild the project so the editor knows about the new export variable.
// Vertical impulse applied to the character upon bouncing over a mob in meters per second.
[Export]
public int BounceImpulse = 16;
```
Then, at the bottom of `_physics_process()`, add the following loop. With `move_and_slide()`, Godot makes the body move sometimes multiple times in a row to smooth out the character's motion. So we have to loop over all collisions that may have happened.
In every iteration of the loop, we check if we landed on a mob. If so, we kill it and bounce.
With this code, if no collisions occurred on a given frame, the loop won't run.
```
func _physics_process(delta):
#...
for index in range(get_slide_count()):
# We check every collision that occurred this frame.
var collision = get_slide_collision(index)
# If we collide with a monster...
if collision.collider.is_in_group("mob"):
var mob = collision.collider
# ...we check that we are hitting it from above.
if Vector3.UP.dot(collision.normal) > 0.1:
# If so, we squash it and bounce.
mob.squash()
velocity.y = bounce_impulse
```
```
public override void _PhysicsProcess(float delta)
{
// ...
for (int index = 0; index < GetSlideCount(); index++)
{
// We check every collision that occurred this frame.
KinematicCollision collision = GetSlideCollision(index);
// If we collide with a monster...
if (collision.Collider is Mob mob && mob.IsInGroup("mob"))
{
// ...we check that we are hitting it from above.
if (Vector3.Up.Dot(collision.Normal) > 0.1f)
{
// If so, we squash it and bounce.
mob.Squash();
_velocity.y = BounceImpulse;
}
}
}
}
```
That's a lot of new functions. Here's some more information about them.
The functions `get_slide_count()` and `get_slide_collision()` both come from the [KinematicBody](../../classes/class_kinematicbody#class-kinematicbody) class and are related to `move_and_slide()`.
`get_slide_collision()` returns a [KinematicCollision](../../classes/class_kinematiccollision#class-kinematiccollision) object that holds information about where and how the collision occurred. For example, we use its `collider` property to check if we collided with a "mob" by calling `is_in_group()` on it: `collision.collider.is_in_group("mob")`.
Note
The method `is_in_group()` is available on every [Node](../../classes/class_node#class-node).
To check that we are landing on the monster, we use the vector dot product: `Vector3.UP.dot(collision.normal) > 0.1`. The collision normal is a 3D vector that is perpendicular to the plane where the collision occurred. The dot product allows us to compare it to the up direction.
With dot products, when the result is greater than `0`, the two vectors are at an angle of fewer than 90 degrees. A value higher than `0.1` tells us that we are roughly above the monster.
We are calling one undefined function, `mob.squash()`. We have to add it to the Mob class.
Open the script `Mob.gd` by double-clicking on it in the *FileSystem* dock. At the top of the script, we want to define a new signal named `squashed`. And at the bottom, you can add the squash function, where we emit the signal and destroy the mob.
```
# Emitted when the player jumped on the mob.
signal squashed
# ...
func squash():
emit_signal("squashed")
queue_free()
```
```
// Don't forget to rebuild the project so the editor knows about the new signal.
// Emitted when the played jumped on the mob.
[Signal]
public delegate void Squashed();
// ...
public void Squash()
{
EmitSignal(nameof(Squashed));
QueueFree();
}
```
We will use the signal to add points to the score in the next lesson.
With that, you should be able to kill monsters by jumping on them. You can press `F5` to try the game and set `Main.tscn` as your project's main scene.
However, the player won't die yet. We'll work on that in the next part.
| programming_docs |
godot Spawning monsters Spawning monsters
=================
In this part, we're going to spawn monsters along a path randomly. By the end, you will have monsters roaming the game board.
Double-click on `Main.tscn` in the *FileSystem* dock to open the *Main* scene.
Before drawing the path, we're going to change the game resolution. Our game has a default window size of `1024x600`. We're going to set it to `720x540`, a nice little box.
Go to *Project -> Project Settings*.
In the left menu, navigate down to *Display -> Window*. On the right, set the *Width* to `720` and the *Height* to `540`.
Creating the spawn path
-----------------------
Like you did in the 2D game tutorial, you're going to design a path and use a *PathFollow* node to sample random locations on it.
In 3D though, it's a bit more complicated to draw the path. We want it to be around the game view so monsters appear right outside the screen. But if we draw a path, we won't see it from the camera preview.
To find the view's limits, we can use some placeholder meshes. Your viewport should still be split into two parts, with the camera preview at the bottom. If that isn't the case, press ``Ctrl` + `2`` (``Cmd` + `2`` on macOS) to split the view into two. Select the *Camera* node and click the *Preview* checkbox in the bottom viewport.
### Adding placeholder cylinders
Let's add the placeholder meshes. Add a new *Spatial* node as a child of the *Main* node and name it *Cylinders*. We'll use it to group the cylinders. As a child of it, add a *MeshInstance* node.
In the *Inspector*, assign a *CylinderMesh* to the *Mesh* property.
Set the top viewport to the top orthogonal view using the menu in the viewport's top-left corner. Alternatively, you can press the keypad's 7 key.
The grid is a bit distracting for me. You can toggle it by going to the *View* menu in the toolbar and clicking *View Grid*.
You now want to move the cylinder along the ground plane, looking at the camera preview in the bottom viewport. I recommend using grid snap to do so. You can toggle it by clicking the magnet icon in the toolbar or pressing Y.
Place the cylinder so it's right outside the camera's view in the top-left corner.
We're going to create copies of the mesh and place them around the game area. Press ``Ctrl` + `D`` (``Cmd` + `D`` on macOS) to duplicate the node. You can also right-click the node in the *Scene* dock and select *Duplicate*. Move the copy down along the blue Z axis until it's right outside the camera's preview.
Select both cylinders by pressing the `Shift` key and clicking on the unselected one and duplicate them.
Move them to the right by dragging the red X axis.
They're a bit hard to see in white, aren't they? Let's make them stand out by giving them a new material.
In 3D, materials define a surface's visual properties like its color, how it reflects light, and more. We can use them to change the color of a mesh.
We can update all four cylinders at once. Select all the mesh instances in the *Scene* dock. To do so, you can click on the first one and Shift click on the last one.
In the *Inspector*, expand the *Material* section and assign a *SpatialMaterial* to slot *0*.
Click the sphere icon to open the material resource. You get a preview of the material and a long list of sections filled with properties. You can use these to create all sorts of surfaces, from metal to rock or water.
Expand the *Albedo* section and set the color to something that contrasts with the background, like a bright orange.
We can now use the cylinders as guides. Fold them in the *Scene* dock by clicking the grey arrow next to them. Moving forward, you can also toggle their visibility by clicking the eye icon next to *Cylinders*.
Add a *Path* node as a child of *Main*. In the toolbar, four icons appear. Click the *Add Point* tool, the icon with the green "+" sign.
Note
You can hover any icon to see a tooltip describing the tool.
Click in the center of each cylinder to create a point. Then, click the *Close Curve* icon in the toolbar to close the path. If any point is a bit off, you can click and drag on it to reposition it.
Your path should look like this.
To sample random positions on it, we need a *PathFollow* node. Add a *PathFollow* as a child of the *Path*. Rename the two nodes to *SpawnPath* and *SpawnLocation*, respectively. It's more descriptive of what we'll use them for.
With that, we're ready to code the spawn mechanism.
Spawning monsters randomly
--------------------------
Right-click on the *Main* node and attach a new script to it.
We first export a variable to the *Inspector* so that we can assign `Mob.tscn` or any other monster to it.
Then, as we're going to spawn the monsters procedurally, we want to randomize numbers every time we play the game. If we don't do that, the monsters will always spawn following the same sequence.
```
extends Node
export (PackedScene) var mob_scene
func _ready():
randomize()
```
```
public class Main : Node
{
// Don't forget to rebuild the project so the editor knows about the new export variable.
#pragma warning disable 649
// We assign this in the editor, so we don't need the warning about not being assigned.
[Export]
public PackedScene MobScene;
#pragma warning restore 649
public override void _Ready()
{
GD.Randomize();
}
}
```
We want to spawn mobs at regular time intervals. To do this, we need to go back to the scene and add a timer. Before that, though, we need to assign the `Mob.tscn` file to the `mob_scene` property.
Head back to the 3D screen and select the *Main* node. Drag `Mob.tscn` from the *FileSystem* dock to the *Mob Scene* slot in the *Inspector*.
Add a new *Timer* node as a child of *Main*. Name it *MobTimer*.
In the *Inspector*, set its *Wait Time* to `0.5` seconds and turn on *Autostart* so it automatically starts when we run the game.
Timers emit a `timeout` signal every time they reach the end of their *Wait Time*. By default, they restart automatically, emitting the signal in a cycle. We can connect to this signal from the *Main* node to spawn monsters every `0.5` seconds.
With the *MobTimer* still selected, head to the *Node* dock on the right and double-click the `timeout` signal.
Connect it to the *Main* node.
This will take you back to the script, with a new empty `_on_MobTimer_timeout()` function.
Let's code the mob spawning logic. We're going to:
1. Instantiate the mob scene.
2. Sample a random position on the spawn path.
3. Get the player's position.
4. Call the mob's `initialize()` method, passing it the random position and the player's position.
5. Add the mob as a child of the *Main* node.
```
func _on_MobTimer_timeout():
# Create a new instance of the Mob scene.
var mob = mob_scene.instance()
# Choose a random location on the SpawnPath.
# We store the reference to the SpawnLocation node.
var mob_spawn_location = get_node("SpawnPath/SpawnLocation")
# And give it a random offset.
mob_spawn_location.unit_offset = randf()
var player_position = $Player.transform.origin
mob.initialize(mob_spawn_location.translation, player_position)
add_child(mob)
```
```
// We also specified this function name in PascalCase in the editor's connection window
public void OnMobTimerTimeout()
{
// Create a new instance of the Mob scene.
Mob mob = (Mob)MobScene.Instance();
// Choose a random location on the SpawnPath.
// We store the reference to the SpawnLocation node.
var mobSpawnLocation = GetNode<PathFollow>("SpawnPath/SpawnLocation");
// And give it a random offset.
mobSpawnLocation.UnitOffset = GD.Randf();
Vector3 playerPosition = GetNode<Player>("Player").Transform.origin;
mob.Initialize(mobSpawnLocation.Translation, playerPosition);
AddChild(mob);
}
```
Above, `randf()` produces a random value between `0` and `1`, which is what the *PathFollow* node's `unit_offset` expects.
Here is the complete `Main.gd` script so far, for reference.
```
extends Node
export (PackedScene) var mob_scene
func _ready():
randomize()
func _on_MobTimer_timeout():
var mob = mob_scene.instance()
var mob_spawn_location = get_node("SpawnPath/SpawnLocation")
mob_spawn_location.unit_offset = randf()
var player_position = $Player.transform.origin
mob.initialize(mob_spawn_location.translation, player_position)
add_child(mob)
```
```
public class Main : Node
{
#pragma warning disable 649
[Export]
public PackedScene MobScene;
#pragma warning restore 649
public override void _Ready()
{
GD.Randomize();
}
public void OnMobTimerTimeout()
{
Mob mob = (Mob)MobScene.Instance();
var mobSpawnLocation = GetNode<PathFollow>("SpawnPath/SpawnLocation");
mobSpawnLocation.UnitOffset = GD.Randf();
Vector3 playerPosition = GetNode<Player>("Player").Transform.origin;
mob.Initialize(mobSpawnLocation.Translation, playerPosition);
AddChild(mob);
}
}
```
You can test the scene by pressing `F6`. You should see the monsters spawn and move in a straight line.
For now, they bump and slide against one another when their paths cross. We'll address this in the next part.
godot Setting up the game area Setting up the game area
========================
In this first part, we're going to set up the game area. Let's get started by importing the start assets and setting up the game scene.
We've prepared a Godot project with the 3D models and sounds we'll use for this tutorial, linked in the index page. If you haven't done so yet, you can download the archive here: [Squash the Creeps assets](https://github.com/GDQuest/godot-3d-dodge-the-creeps/releases/tag/1.0.0).
Once you downloaded it, extract the .zip archive on your computer. Open the Godot project manager and click the *Import* button.
In the import popup, enter the full path to the freshly created directory `squash_the_creeps_start/`. You can click the *Browse* button on the right to open a file browser and navigate to the `project.godot` file the folder contains.
Click *Import & Edit* to open the project in the editor.
The start project contains an icon and two folders: `art/` and `fonts/`. There, you will find the art assets and music we'll use in the game.
There are two 3D models, `player.glb` and `mob.glb`, some materials that belong to these models, and a music track.
Setting up the playable area
----------------------------
We're going to create our main scene with a plain *Node* as its root. In the *Scene* dock, click the *Add Node* button represented by a "+" icon in the top-left and double-click on *Node*. Name the node "Main". Alternatively, to add a node to the scene, you can press ``Ctrl` + `a`` (or ``Cmd` + `a`` on macOS).
Save the scene as `Main.tscn` by pressing ``Ctrl` + `s`` (``Cmd` + `s`` on macOS).
We'll start by adding a floor that'll prevent the characters from falling. To create static colliders like the floor, walls, or ceilings, you can use *StaticBody* nodes. They require *CollisionShape* child nodes to define the collision area. With the *Main* node selected, add a *StaticBody* node, then a *CollisionShape*. Rename the *StaticBody* as *Ground*.
A warning sign next to the *CollisionShape* appears because we haven't defined its shape. If you click the icon, a popup appears to give you more information.
To create a shape, with the *CollisionShape* selected, head to the *Inspector* and click the *[empty]* field next to the *Shape* property. Create a new *Box Shape*.
The box shape is perfect for flat ground and walls. Its thickness makes it reliable to block even fast-moving objects.
A box's wireframe appears in the viewport with three orange dots. You can click and drag these to edit the shape's extents interactively. We can also precisely set the size in the inspector. Click on the *BoxShape* to expand the resource. Set its *Extents* to `30` on the X axis, `1` for the Y axis, and `30` for the Z axis.
Note
In 3D, translation and size units are in meters. The box's total size is twice its extents: `60` by `60` meters on the ground plane and `2` units tall. The ground plane is defined by the X and Z axes, while the Y axis represents the height.
Collision shapes are invisible. We need to add a visual floor that goes along with it. Select the *Ground* node and add a *MeshInstance* as its child.
In the *Inspector*, click on the field next to *Mesh* and create a *CubeMesh* resource to create a visible cube.
Once again, it's too small by default. Click the cube icon to expand the resource and set its *Size* to `60`, `2`, and `60`. As the cube resource works with a size rather than extents, we need to use these values so it matches our collision shape.
You should see a wide grey slab that covers the grid and blue and red axes in the viewport.
We're going to move the ground down so we can see the floor grid. Select the *Ground* node, hold the `Ctrl` key down to turn on grid snapping (`Cmd` on macOS), and click and drag down on the Y axis. It's the green arrow in the move gizmo.
Note
If you can't see the 3D object manipulator like on the image above, ensure the *Select Mode* is active in the toolbar above the view.
Move the ground down `1` meter. A label in the bottom-left corner of the viewport tells you how much you're translating the node.
Note
Moving the *Ground* node down moves both children along with it. Ensure you move the *Ground* node, **not** the *MeshInstance* or the *CollisionShape*.
Let's add a directional light so our scene isn't all grey. Select the *Main* node and add a *DirectionalLight* as a child of it. We need to move it and rotate it. Move it up by clicking and dragging on the manipulator's green arrow and click and drag on the red arc to rotate it around the X axis, until the ground is lit.
In the *Inspector*, turn on *Shadow -> Enabled* by clicking the checkbox.
At this point, your project should look like this.
That's our starting point. In the next part, we will work on the player scene and base movement.
godot Going further Going further
=============
You can pat yourself on the back for having completed your first 3D game with Godot.
In this series, we went over a wide range of techniques and editor features. Hopefully, you’ve witnessed how intuitive Godot’s scene system can be and learned a few tricks you can apply in your projects.
But we just scratched the surface: Godot has a lot more in store for you to save time creating games. And you can learn all that by browsing the documentation.
Where should you begin? Below, you’ll find a few pages to start exploring and build upon what you’ve learned so far.
But before that, here’s a link to download a completed version of the project: <https://github.com/GDQuest/godot-3d-dodge-the-creeps>.
Exploring the manual
--------------------
The manual is your ally whenever you have a doubt or you’re curious about a feature. It does not contain tutorials about specific game genres or mechanics. Instead, it explains how Godot works in general. In it, you will find information about 2D, 3D, physics, rendering and performance, and much more.
Here are the sections we recommend you to explore next:
1. Read the [Scripting section](https://docs.godotengine.org/en/3.5/tutorials/scripting/index.html#toc-scripting-core-features) to learn essential programming features you’ll use in every project.
2. The [3D](https://docs.godotengine.org/en/3.5/tutorials/3d/index.html#toc-learn-features-3d) and [Physics](https://docs.godotengine.org/en/3.5/tutorials/physics/index.html#toc-learn-features-physics) sections will teach you more about 3D game creation in the engine.
3. [Inputs](https://docs.godotengine.org/en/3.5/tutorials/inputs/index.html#toc-learn-features-inputs) is another important one for any game project.
You can start with these or, if you prefer, look at the sidebar menu on the left and pick your options.
We hope you enjoyed this tutorial series, and we’re looking forward to seeing what you achieve using Godot.
godot Creating your first script Creating your first script
==========================
In this lesson, you will code your first script to make the Godot icon turn in circles using GDScript. As we mentioned [in the introduction](../introduction/index#toc-learn-introduction), we assume you have programming foundations. The equivalent C# code has been included in another tab for convenience.
 See also
To learn more about GDScript, its keywords, and its syntax, head to the [GDScript reference](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/gdscript_basics.html#doc-gdscript).
See also
To learn more about C#, head to the [C# basics](https://docs.godotengine.org/en/3.5/tutorials/scripting/c_sharp/c_sharp_basics.html#doc-c-sharp) page.
Project setup
-------------
Please create a new project to start with a clean slate. Your project should contain one picture: the Godot icon, which we often use for prototyping in the community.
We need to create a Sprite node to display it in the game. In the Scene dock, click the Other Node button.
 Type "Sprite" in the search bar to filter nodes and double-click on Sprite to create the node.
 Your Scene tab should now only have a Sprite node.
 A Sprite node needs a texture to display. In the Inspector on the right, you can see that the Texture property says "[empty]". To display the Godot icon, click and drag the file `icon.png` from the FileSystem dock onto the Texture slot.
 Note
You can create Sprite nodes automatically by dragging and dropping images on the viewport.
 Then, click and drag the icon in the viewport to center it in the game view.
 Creating a new script
---------------------
To create and attach a new script to our node, right-click on Sprite in the scene dock and select "Attach Script".
 The Attach Node Script window appears. It allows you to select the script's language and file path, among other options.
Change the Template from Default to Empty to start with a clean file. Leave the other options by default and click the Create button to create the script.
 The Script workspace should appear with your new `Sprite.gd` file open and the following line of code:
```
extends Sprite
```
```
public class Sprite : Godot.Sprite
// Declare member variables here. Examples:
// private int a = 2;
// private string b = "text";
// Called when the node enters the scene tree for the first time.
public override void _Ready()
{
}
// // Called every frame. 'delta' is the elapsed time since the previous frame.
// public override void _Process(float delta)
// {
//
// }
```
Every GDScript file is implicitly a class. The `extends` keyword defines the class this script inherits or extends. In this case, it's `Sprite`, meaning our script will get access to all the properties and functions of the Sprite node, including classes it extends, like `Node2D`, `CanvasItem`, and `Node`.
Note
In GDScript, if you omit the line with the `extends` keyword, your class will implicitly extend [Reference](../../classes/class_reference#class-reference), which Godot uses to manage your application's memory.
Inherited properties include the ones you can see in the Inspector dock, like our node's `texture`.
Note
By default, the Inspector displays a node's properties in "Title Case", with capitalized words separated by a space. In GDScript code, these properties are in "snake\_case", which is lowercase with words separated by an underscore.
You can hover any property's name in the Inspector to see a description and its identifier in code.
Hello, world!
-------------
Our script currently doesn't do anything. Let's make it print the text "Hello, world!" to the Output bottom panel to get started.
Add the following code to your script:
```
func _init():
print("Hello, world!")
```
```
public Sprite()
{
GD.Print("Hello, world!");
}
```
Let's break it down. The `func` keyword defines a new function named `_init`. This is a special name for our class's constructor. The engine calls `_init()` on every object or node upon creating it in memory, if you define this function.
Note
GDScript is an indent-based language. The tab at the start of the line that says `print()` is necessary for the code to work. If you omit it or don't indent a line correctly, the editor will highlight it in red and display the following error message: "Indented block expected".
Save the scene if you haven't already, then press `F6` (``Cmd` + `R`` on macOS) to run it. Look at the **Output** bottom panel that expands. It should display "Hello, world!".
 Delete the `_init()` function, so you're only left with the line `extends
Sprite`.
Turning around
--------------
It's time to make our node move and rotate. To do so, we're going to add two member variables to our script: the movement speed in pixels per second and the angular speed in radians per second.
```
var speed = 400
var angular_speed = PI
```
```
private int Speed = 400;
private float AngularSpeed = Mathf.Pi;
```
Member variables sit near the top of the script, after any "extends" lines, but before functions. Every node instance with this script attached to it will have its own copy of the `speed` and `angular_speed` properties.
Note
Angles in Godot work in radians by default, but you have built-in functions and properties available if you prefer to calculate angles in degrees instead.
To move our icon, we need to update its position and rotation every frame in the game loop. We can use the `_process()` virtual function of the `Node` class. If you define it in any class that extends the Node class, like Sprite, Godot will call the function every frame and pass it an argument named `delta`, the time elapsed since the last frame.
Note
Games work by rendering many images per second, each called a frame, and they do so in a loop. We measure the rate at which a game produces images in Frames Per Second (FPS). Most games aim for 60 FPS, although you might find figures like 30 FPS on slower mobile devices or 90 to 240 for virtual reality games.
The engine and game developers do their best to update the game world and render images at a constant time interval, but there are always small variations in frame render times. That's why the engine provides us with this delta time value, making our motion independent of our framerate.
At the bottom of the script, define the function:
```
func _process(delta):
rotation += angular_speed * delta
```
```
public override void _Process(float delta)
{
Rotation += AngularSpeed * delta;
}
```
The `func` keyword defines a new function. After it, we have to write the function's name and arguments it takes in parentheses. A colon ends the definition, and the indented blocks that follow are the function's content or instructions.
Note
Notice how `_process()`, like `_init()`, starts with a leading underscore. By convention, Godot's virtual functions, that is to say, built-in functions you can override to communicate with the engine, start with an underscore.
The line inside the function, `rotation += angular_speed * delta`, increments our sprite's rotation every frame. Here, `rotation` is a property inherited from the class `Node2D`, which `Sprite` extends. It controls the rotation of our node and works with radians.
Tip
In the code editor, you can ctrl-click on any built-in property or function like `position`, `rotation`, or `_process` to open the corresponding documentation in a new tab.
Run the scene to see the Godot icon turn in-place.
 ### Moving forward
Let's now make the node move. Add the following two lines to the `_process()` function, ensuring the new lines are indented the same way as the one before them.
```
var velocity = Vector2.UP.rotated(rotation) * speed
position += velocity * delta
```
```
var velocity = Vector2.Up.Rotated(Rotation) * Speed;
Position += velocity * delta;
```
As we already saw, the `var` keyword defines a new variable. If you put it at the top of the script, it defines a property of the class. Inside a function, it defines a local variable: it only exists within the function's scope.
We define a local variable named `velocity`, a 2D vector representing both a direction and a speed. To make the node move forward, we start from the Vector2 class's constant Vector2.UP, a vector pointing up, and rotate it by calling the `Vector2.rotated()` method. This expression, `Vector2.UP.rotated(rotation)`, is a vector pointing forward relative to our icon. Multiplied by our `speed` property, it gives us a velocity we can use to move the node forward.
We add `velocity * delta` to the node's `position` to move it. The position itself is of type [Vector2](../../classes/class_vector2#class-vector2), a built-in type in Godot representing a 2D vector.
Run the scene to see the Godot head run in circles.
 Note
Moving a node like that does not take into account colliding with walls or the floor. In [Your first 2D game](../first_2d_game/index#doc-your-first-2d-game), you will learn another approach to moving objects while detecting collisions.
Our node currently moves by itself. In the next part [Listening to player input](scripting_player_input#doc-scripting-player-input), we'll use player input to control it.
Complete script
---------------
Here is the complete `Sprite.gd` file for reference.
```
extends Sprite
var speed = 400
var angular_speed = PI
func _process(delta):
rotation += angular_speed * delta
var velocity = Vector2.UP.rotated(rotation) * speed
position += velocity * delta
```
```
using Godot;
public class Sprite : Godot.Sprite
{
private int Speed = 400;
private float AngularSpeed = Mathf.Pi;
public override void _Process(float delta)
{
Rotation += AngularSpeed * delta;
var velocity = Vector2.Up.Rotated(Rotation) * Speed;
Position += velocity * delta;
}
}
```
| programming_docs |
godot Using signals Using signals
=============
In this lesson, we will look at signals. They are messages that nodes emit when something specific happens to them, like a button being pressed. Other nodes can connect to that signal and call a function when the event occurs.
Signals are a delegation mechanism built into Godot that allows one game object to react to a change in another without them referencing one another. Using signals limits [coupling](https://en.wikipedia.org/wiki/Coupling_(computer_programming)) and keeps your code flexible.
For example, you might have a life bar on the screen that represents the player’s health. When the player takes damage or uses a healing potion, you want the bar to reflect the change. To do so, in Godot, you would use signals.
Note
As mentioned in the introduction, signals are Godot's version of the observer pattern. You can learn more about it here: <https://gameprogrammingpatterns.com/observer.html>
We will now use a signal to make our Godot icon from the previous lesson ([Listening to player input](scripting_player_input#doc-scripting-player-input)) move and stop by pressing a button.
Scene setup
-----------
To add a button to our game, we will create a new "main" scene which will include both a button and the `Sprite.tscn` scene that we scripted in previous lessons.
Create a new scene by going to the menu Scene -> New Scene.
 In the Scene dock, click the 2D Scene button. This will add a Node2D as our root.
 In the FileSystem dock, click and drag the `Sprite.tscn` file you saved previously onto the Node2D to instantiate it.
 We want to add another node as a sibling of the Sprite. To do so, right-click on Node2D and select Add Child Node.
 Search for the Button node type and add it.
 The node is small by default. Click and drag on the bottom-right handle of the Button in the viewport to resize it.
 If you don't see the handles, ensure the select tool is active in the toolbar.
 Click and drag on the button itself to move it closer to the sprite.
You can also write a label on the Button by editing its Text property in the Inspector. Enter "Toggle motion".
 Your scene tree and viewport should look like this.
 Save your newly created scene. You can then run it with `F6`. At the moment, the button will be visible, but nothing will happen if you press it.
Connecting a signal in the editor
---------------------------------
Here, we want to connect the Button's "pressed" signal to our Sprite, and we want to call a new function that will toggle its motion on and off. We need to have a script attached to the Sprite node, which we do from the previous lesson.
You can connect signals in the Node dock. Select the Button node and, on the right side of the editor, click on the tab named "Node" next to the Inspector.
 The dock displays a list of signals available on the selected node.
 Double-click the "pressed" signal to open the node connection window.
 There, you can connect the signal to the Sprite node. The node needs a receiver method, a function that Godot will call when the Button emits the signal. The editor generates one for you. By convention, we name these callback methods "\_on\_NodeName\_signal\_name". Here, it'll be "\_on\_Button\_pressed".
Note
When connecting signals via the editor's Node dock, you can use two modes. The simple one only allows you to connect to nodes that have a script attached to them and creates a new callback function on them.
 The advanced view lets you connect to any node and any built-in function, add arguments to the callback, and set options. You can toggle the mode in the window's bottom-right by clicking the Advanced button.
Click the Connect button to complete the signal connection and jump to the Script workspace. You should see the new method with a connection icon in the left margin.
 If you click the icon, a window pops up and displays information about the connection. This feature is only available when connecting nodes in the editor.
 Let's replace the line with the `pass` keyword with code that'll toggle the node's motion.
Our Sprite moves thanks to code in the `_process()` function. Godot provides a method to toggle processing on and off: [Node.set\_process()](../../classes/class_node#class-node-method-set-process). Another method of the Node class, `is_processing()`, returns `true` if idle processing is active. We can use the `not` keyword to invert the value.
```
func _on_Button_pressed():
set_process(not is_processing())
```
This function will toggle processing and, in turn, the icon's motion on and off upon pressing the button.
Before trying the game, we need to simplify our `_process()` function to move the node automatically and not wait for user input. Replace it with the following code, which we saw two lessons ago:
```
func _process(delta):
rotation += angular_speed * delta
var velocity = Vector2.UP.rotated(rotation) * speed
position += velocity * delta
```
Your complete `Sprite.gd` code should look like the following.
```
extends Sprite
var speed = 400
var angular_speed = PI
func _process(delta):
rotation += angular_speed * delta
var velocity = Vector2.UP.rotated(rotation) * speed
position += velocity * delta
func _on_Button_pressed():
set_process(not is_processing())
```
Run the scene now and click the button to see the sprite start and stop.
Connecting a signal via code
----------------------------
You can connect signals via code instead of using the editor. This is necessary when you create nodes or instantiate scenes inside of a script.
Let's use a different node here. Godot has a [Timer](../../classes/class_timer#class-timer) node that's useful to implement skill cooldown times, weapon reloading, and more.
Head back to the 2D workspace. You can either click the "2D" text at the top of the window or press ``Ctrl` + `F1`` (``Alt` + `1`` on macOS).
In the Scene dock, right-click on the Sprite node and add a new child node. Search for Timer and add the corresponding node. Your scene should now look like this.
 With the Timer node selected, go to the Inspector and check the **Autostart** property.
 Click the script icon next to Sprite to jump back to the scripting workspace.
 We need to do two operations to connect the nodes via code:
1. Get a reference to the Timer from the Sprite.
2. Call the Timer's `connect()` method.
Note
To connect to a signal via code, you need to call the `connect()` method of the node you want to listen to. In this case, we want to listen to the Timer's "timeout" signal.
We want to connect the signal when the scene is instantiated, and we can do that using the [Node.\_ready()](../../classes/class_node#class-node-method-ready) built-in function, which is called automatically by the engine when a node is fully instantiated.
To get a reference to a node relative to the current one, we use the method [Node.get\_node()](../../classes/class_node#class-node-method-get-node). We can store the reference in a variable.
```
func _ready():
var timer = get_node("Timer")
```
The function `get_node()` looks at the Sprite's children and gets nodes by their name. For example, if you renamed the Timer node to "BlinkingTimer" in the editor, you would have to change the call to `get_node("BlinkingTimer")`.
We can now connect the Timer to the Sprite in the `_ready()` function.
```
func _ready():
var timer = get_node("Timer")
timer.connect("timeout", self, "_on_Timer_timeout")
```
The line reads like so: we connect the Timer's "timeout" signal to the node to which the script is attached (`self`). When the Timer emits "timeout", we want to call the function "\_on\_Timer\_timeout", that we need to define. Let's add it at the bottom of our script and use it to toggle our sprite's visibility.
```
func _on_Timer_timeout():
visible = not visible
```
The `visible` property is a boolean that controls the visibility of our node. The line `visible = not visible` toggles the value. If `visible` is `true`, it becomes `false`, and vice-versa.
If you run the scene now, you will see that the sprite blinks on and off, at one second intervals.
Complete script
---------------
That's it for our little moving and blinking Godot icon demo! Here is the complete `Sprite.gd` file for reference.
```
extends Sprite
var speed = 400
var angular_speed = PI
func _ready():
var timer = get_node("Timer")
timer.connect("timeout", self, "_on_Timer_timeout")
func _process(delta):
rotation += angular_speed * delta
var velocity = Vector2.UP.rotated(rotation) * speed
position += velocity * delta
func _on_Button_pressed():
set_process(not is_processing())
func _on_Timer_timeout():
visible = not visible
```
Custom signals
--------------
Note
This section is a reference on how to define and use your own signals, and does not build upon the project created in previous lessons.
You can define custom signals in a script. Say, for example, that you want to show a game over screen when the player's health reaches zero. To do so, you could define a signal named "died" or "health\_depleted" when their health reaches 0.
```
extends Node2D
signal health_depleted
var health = 10
```
Note
As signals represent events that just occurred, we generally use an action verb in the past tense in their names.
Your signals work the same way as built-in ones: they appear in the Node tab and you can connect to them like any other.
 To emit a signal in your scripts, call `emit_signal()`.
```
func take_damage(amount):
health -= amount
if health <= 0:
emit_signal("health_depleted")
```
A signal can optionally declare one or more arguments. Specify the argument names between parentheses:
```
extends Node
signal health_changed(old_value, new_value)
```
Note
The signal arguments show up in the editor's node dock, and Godot can use them to generate callback functions for you. However, you can still emit any number of arguments when you emit signals. So it's up to you to emit the correct values.
To emit values along with the signal, add them as extra arguments to the `emit_signal()` function:
```
func take_damage(amount):
var old_health = health
health -= amount
emit_signal("health_changed", old_health, health)
```
Summary
-------
Any node in Godot emits signals when something specific happens to them, like a button being pressed. Other nodes can connect to individual signals and react to selected events.
Signals have many uses. With them, you can react to a node entering or exiting the game world, to a collision, to a character entering or leaving an area, to an element of the interface changing size, and much more.
For example, an [Area2D](../../classes/class_area2d#class-area2d) representing a coin emits a `body_entered` signal whenever the player's physics body enters its collision shape, allowing you to know when the player collected it.
In the next section, [Your first 2D game](../first_2d_game/index#doc-your-first-2d-game), you'll create a complete 2D game and put everything you learned so far into practice.
godot Scripting languages Scripting languages
===================
This lesson will give you an overview of the available scripting languages in Godot. You will learn the pros and cons of each option. In the next part, you will write your first script using GDScript.
**Scripts attach to a node and extend its behavior**. This means that scripts inherit all functions and properties of the node they attach to.
For example, take a game where a Camera2D node follows a ship. The Camera2D node follows its parent by default. Imagine you want the camera to shake when the player takes damage. As this feature is not built into Godot, you would attach a script to the Camera2D node and code the shake.
 Available scripting languages
-----------------------------
Godot offers **five gameplay programming languages**: GDScript, C#, VisualScript, and, via its GDNative technology, C and C++. There are more [community-supported languages](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdnative/what_is_gdnative.html#doc-what-is-gdnative-third-party-bindings), but these are the official ones.
You can use multiple languages in a single project. For instance, in a team, you could code gameplay logic in GDScript as it's fast to write, let level designers script quests in the graphical language VisualScript, and use C# or C++ to implement complex algorithms and maximize their performance. Or you can write everything in GDScript or C#. It's your call.
We provide this flexibility to answer the needs of different game projects and developers.
Warning
[Godot 4.0 will remove VisualScript from core entirely.](https://godotengine.org/article/godot-4-will-discontinue-visual-scripting) As a result, creating new projects using visual scripting in Godot is not recommended. Future Godot 4.x releases may have VisualScript reimplemented as an extension.
While Godot 3.x will keep VisualScript supported, we recommend [trying out GDScript](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/index.html#toc-learn-scripting-gdscript) instead, especially if you intend to migrate your project to Godot 4.
Which language should I use?
----------------------------
If you're a beginner, we recommend to **start with GDScript**. We made this language specifically for Godot and the needs of game developers. It has a lightweight and straightforward syntax and provides the tightest integration with Godot.
 For C#, you will need an external code editor like [VSCode](https://code.visualstudio.com/) or Visual Studio. While C# support is now mature, you will find fewer learning resources for it compared to GDScript. That's why we recommend C# mainly to users who already have experience with the language.
Let's look at each language's features, as well as its pros and cons.
### GDScript
[GDScript](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/gdscript_basics.html#doc-gdscript) is an [object-oriented](https://en.wikipedia.org/wiki/Object-oriented_programming) and [imperative](https://en.wikipedia.org/wiki/Imperative_programming) programming language built for Godot. It's made by and for game developers to save you time coding games. Its features include:
* A simple syntax that leads to short files.
* Blazing fast compilation and loading times.
* Tight editor integration, with code completion for nodes, signals, and more information from the scene it's attached to.
* Built-in vector and transform types, making it efficient for heavy use of linear algebra, a must for games.
* Supports multiple threads as efficiently as statically typed languages.
* No [garbage collection](https://en.wikipedia.org/wiki/Garbage_collection_(computer_science)), as this feature eventually gets in the way when creating games. The engine counts references and manages the memory for you in most cases by default, but you can also control memory if you need to.
* [Gradual typing](https://en.wikipedia.org/wiki/Gradual_typing). Variables have dynamic types by default, but you also can use type hints for strong type checks.
GDScript looks like Python as you structure your code blocks using indentations, but it doesn't work the same way in practice. It's inspired by multiple languages, including Squirrel, Lua, and Python.
Note
Why don't we use Python or Lua directly?
Years ago, Godot used Python, then Lua. Both languages' integration took a lot of work and had severe limitations. For example, threading support was a big challenge with Python.
Developing a dedicated language doesn't take us more work and we can tailor it to game developers' needs. We're now working on performance optimizations and features that would've been difficult to offer with third-party languages.
### .NET / C#
As Microsoft's [C#](https://en.wikipedia.org/wiki/C_Sharp_(programming_language)) is a favorite amongst game developers, we officially support it. C# is a mature and flexible language with tons of libraries written for it. We could add support for it thanks to a generous donation from Microsoft.
 C# offers a good tradeoff between performance and ease of use, although you should be aware of its garbage collector.
Note
You must use the Mono edition of the Godot editor to script in C#. You can download it on the Godot website's [download](https://godotengine.org/download/) page.
Since Godot uses the [Mono](https://mono-project.com) .NET runtime, in theory, you can use any third-party .NET library or framework in Godot, as well as any Common Language Infrastructure-compliant programming language, such as F#, Boo, or ClojureCLR. However, C# is the only officially supported .NET option.
Note
GDScript code itself doesn't execute as fast as compiled C# or C++. However, most script code calls functions written with fast algorithms in C++ code inside the engine. In many cases, writing gameplay logic in GDScript, C#, or C++ won't have a significant impact on performance.
### VisualScript
Warning
[Godot 4.0 will remove VisualScript from core entirely.](https://godotengine.org/article/godot-4-will-discontinue-visual-scripting) As a result, creating new projects using visual scripting in Godot is not recommended. Future Godot 4.x releases may have VisualScript reimplemented as an extension.
While Godot 3.x will keep VisualScript supported, we recommend [trying out GDScript](https://docs.godotengine.org/en/3.5/tutorials/scripting/gdscript/index.html#toc-learn-scripting-gdscript) instead, especially if you intend to migrate your project to Godot 4.
[Visual Scripting](https://docs.godotengine.org/en/3.5/tutorials/scripting/visual_script/what_is_visual_scripting.html#doc-what-is-visual-script) is a graph-based visual programming language where you connect blocks. It can be a great tool for non-programmers like game designers and artists.
 You can use other languages to create custom blocks that are specific to your game, for example, to script AIs, quests, or dialogues. That's where the strength of VisualScript lies.
While it provides all the basic building blocks you need to code complete games, we do not recommend to use VisualScript this way. Programming everything with it is slow compared to using other programming languages.
See also
For more information, see [Getting started with VisualScript](https://docs.godotengine.org/en/3.5/tutorials/scripting/visual_script/getting_started.html#doc-getting-started-visual-script).
### C and C++ via GDNative
GDNative allows you to write game code in C or C++ without needing to recompile or even restart Godot.
 You can use any version of the language or mix compiler brands and versions for the generated shared libraries, thanks to our use of an internal C API Bridge.
GDNative is the best choice for performance. You don't need to use it throughout an entire game, as you can write other parts in GDScript, C#, or VisualScript.
When working with GDNative, the available types, functions, and properties closely resemble Godot's actual C++ API.
Summary
-------
Scripts are files containing code that you attach to a node to extend its functionality.
Godot supports five official scripting languages, offering you flexibility between performance and ease of use.
You can mix languages, for instance, to implement demanding algorithms with C or C++ and write most of the game logic with GDScript or C#.
| programming_docs |
godot Nodes and Scenes Nodes and Scenes
================
In [Overview of Godot's key concepts](../introduction/key_concepts_overview#doc-key-concepts-overview), we saw that a Godot game is a tree of scenes and that each scene is a tree of nodes. In this lesson, we explain a bit more about them. You will also create your first scene.
Nodes
-----
**Nodes are the fundamental building blocks of your game**. They are like the ingredients in a recipe. There are dozens of kinds that can display an image, play a sound, represent a camera, and much more.
 All nodes have the following attributes:
* A name.
* Editable properties.
* They receive callbacks to update every frame.
* You can extend them with new properties and functions.
* You can add them to another node as a child.
The last attribute is key. **Together, nodes form a tree**, which is a powerful feature to organize projects. Since different nodes have different functions, combining them produces more complex behavior. As we saw before, you can build a playable character the camera follows using a kinematic body node named "Character", a sprite node, a camera node, and a collision shape node.
 Scenes
------
When you organize nodes in a tree, like our character, we call this construct a scene. Once saved, scenes work like new node types in the editor, where you can add them as a child of an existing node. In that case, the instance of the scene appears as a single node with its internals hidden.
Scenes allow you to structure your game's code however you want. You can **compose nodes** to create custom and complex node types, like a game character that runs and jumps, a life bar, a chest with which you can interact, and more.
 The Godot editor essentially is a **scene editor**. It has plenty of tools for editing 2D and 3D scenes, as well as user interfaces. A Godot project can contain as many of these scenes as you need. The engine only requires one as your application's **main scene**. This is the scene Godot will first load when you or a player runs the game.
On top of acting like nodes, scenes have the following attributes:
1. They always have one root node, like the "Character" in our example.
2. You can save them to your hard drive and load them later.
3. You can create as many instances of a scene as you'd like. You could have five or ten characters in your game, created from your Character scene.
Creating your first scene
-------------------------
Let's create our first scene with a single node. To do so, you will need to create a new project first. After opening the project, you should see an empty editor.
 In an empty scene, the Scene dock on the left shows several options to add a root node quickly. "2D Scene" adds a Node2D node, "3D Scene" adds a Spatial node, and "User Interface" adds a Control node. These presets are here for convenience; they are not mandatory. "Other Node" lets you select any node to be the root node. In an empty scene, "Other Node" is equivalent to pressing the "Add Child Node" button at the top-left of the Scene dock, which usually adds a new node as a child of the currently selected node.
We're going to add a single Label node to our scene. Its function is to draw text on the screen.
Press the "Add Child Node" button or "Other Node" to create a root node.
 The Create Node dialog opens, showing the long list of available nodes.
 Select the Label node. You can type its name to filter down the list.
 Click on the Label node to select it and click the Create button at the bottom of the window.
 A lot happens when you add a scene's first node. The scene changes to the 2D workspace because Label is a 2D node type. The Label appears, selected, in the top-left corner of the viewport. The node appears in the Scene dock on the left, and the node's properties appear in the Inspector dock on the right.
Changing a node's properties
----------------------------
The next step is to change the Label's "Text" property. Let's change it to "Hello World".
Head to the Inspector dock on the right of the viewport. Click inside the field below the Text property and type "Hello World".
 You will see the text draw in the viewport as you type.
You can move your Label node in the viewport by selecting the move tool in the toolbar.
 With the Label selected, click and drag anywhere in the viewport to move it to the center of the view delimited by the rectangle.
 Running the scene
-----------------
Everything's ready to run the scene! Press the Play Scene button in the top-right of the screen or press `F6` (``Cmd` + `R`` on macOS).
 A popup invites you to save the scene, which is required to run it.
 Click the Yes button, and in the file browser that appears, press the Save button to save it as "Label.tscn".
 Note
The Save Scene As dialog, like other file dialogs in the editor, only allows you to save files inside the project. The `res://` path at the top of the window represents the project's root directory and stands for "resource path". For more information about file paths in Godot, see [File system](https://docs.godotengine.org/en/3.5/tutorials/scripting/filesystem.html#doc-filesystem).
The application should open in a new window and display the text "Hello World".
 Close the window or press `F8` to quit the running scene.
Note
If this doesn't immediately work and you have a hiDPI display on at least one of your monitors, go to Project -> Project Settings -> Display -> Window then enable Allow Hidpi under Dpi.
Setting the main scene
----------------------
To run our test scene, we used the Play Scene button. Another button next to it allows you to set and run the project's main scene. You can press `F5` (``Cmd` + `B`` on macOS) to do so.
 A popup window appears and invites you to select the main scene.
 Click the Select button, and in the file dialog that appears, double click on Label.tscn.
 The demo should run again. Moving forward, every time you run the project, Godot will use this scene as a starting point.
Note
The editor saves the main scene's path in a project.godot file in your project's directory. While you can edit this text file directly to change project settings, you can also use the "Project -> Project Settings" window to do so.
In the next part, we will discuss another key concept in games and in Godot: creating instances of a scene.
godot Listening to player input Listening to player input
=========================
Building upon the previous lesson [Creating your first script](scripting_first_script#doc-scripting-first-script), let's look at another important feature of any game: giving control to the player. To add this, we need to modify our `Sprite.gd` code.
 You have two main tools to process the player's input in Godot:
1. The built-in input callbacks, mainly `_unhandled_input()`. Like `_process()`, it's a built-in virtual function that Godot calls every time the player presses a key. It's the tool you want to use to react to events that don't happen every frame, like pressing `Space` to jump. To learn more about input callbacks, see [Using InputEvent](https://docs.godotengine.org/en/3.5/tutorials/inputs/inputevent.html#doc-inputevent).
2. The `Input` singleton. A singleton is a globally accessible object. Godot provides access to several in scripts. It's the right tool to check for input every frame.
We're going to use the `Input` singleton here as we need to know if the player wants to turn or move every frame.
For turning, we should use a new variable: `direction`. In our `_process()` function, replace the `rotation += angular_speed * delta` line with the code below.
```
var direction = 0
if Input.is_action_pressed("ui_left"):
direction = -1
if Input.is_action_pressed("ui_right"):
direction = 1
rotation += angular_speed * direction * delta
```
```
var direction = 0;
if (Input.IsActionPressed("ui_left"))
{
direction = -1;
}
if (Input.IsActionPressed("ui_right"))
{
direction = 1;
}
Rotation += AngularSpeed * direction * delta;
```
Our `direction` local variable is a multiplier representing the direction in which the player wants to turn. A value of `0` means the player isn't pressing the left or the right arrow key. A value of `1` means the player wants to turn right, and `-1` means they want to turn left.
To produce these values, we introduce conditions and the use of `Input`. A condition starts with the `if` keyword in GDScript and ends with a colon. The condition is the expression between the keyword and the end of the line.
To check if a key was pressed this frame, we call `Input.is_action_pressed()`. The method takes a text string representing an input action and returns `true` if the action is pressed, `false` otherwise.
The two actions we use above, "ui\_left" and "ui\_right", are predefined in every Godot project. They respectively trigger when the player presses the left and right arrows on the keyboard or left and right on a gamepad's D-pad.
Note
You can see and edit input actions in your project by going to Project -> Project Settings and clicking on the Input Map tab.
Finally, we use the `direction` as a multiplier when we update the node's `rotation`: `rotation += angular_speed * direction * delta`.
If you run the scene with this code, the icon should rotate when you press `Left` and `Right`.
Moving when pressing "up"
-------------------------
To only move when pressing a key, we need to modify the code that calculates the velocity. Replace the line starting with `var velocity` with the code below.
```
var velocity = Vector2.ZERO
if Input.is_action_pressed("ui_up"):
velocity = Vector2.UP.rotated(rotation) * speed
```
```
var velocity = Vector2.Zero;
if (Input.IsActionPressed("ui_up"))
{
velocity = Vector2.Up.Rotated(Rotation) * Speed;
}
```
We initialize the `velocity` with a value of `Vector2.ZERO`, another constant of the built-in `Vector` type representing a 2D vector of length 0.
If the player presses the "ui\_up" action, we then update the velocity's value, causing the sprite to move forward.
Complete script
---------------
Here is the complete `Sprite.gd` file for reference.
```
extends Sprite
var speed = 400
var angular_speed = PI
func _process(delta):
var direction = 0
if Input.is_action_pressed("ui_left"):
direction = -1
if Input.is_action_pressed("ui_right"):
direction = 1
rotation += angular_speed * direction * delta
var velocity = Vector2.ZERO
if Input.is_action_pressed("ui_up"):
velocity = Vector2.UP.rotated(rotation) * speed
position += velocity * delta
```
```
using Godot;
public class Sprite : Godot.Sprite
{
private float Speed = 400;
private float AngularSpeed = Mathf.Pi;
public override void _Process(float delta)
{
var direction = 0;
if (Input.IsActionPressed("ui_left"))
{
direction = -1;
}
if (Input.IsActionPressed("ui_right"))
{
direction = 1;
}
Rotation += AngularSpeed * direction * delta;
var velocity = Vector2.Zero;
if (Input.IsActionPressed("ui_up"))
{
velocity = Vector2.Up.Rotated(Rotation) * Speed;
}
Position += velocity * delta;
}
}
```
If you run the scene, you should now be able to rotate with the left and right arrow keys and move forward by pressing `Up`.
 Summary
-------
In summary, every script in Godot represents a class and extends one of the engine's built-in classes. The node types your classes inherit from give you access to properties like `rotation` and `position` in our sprite's case. You also inherit many functions, which we didn't get to use in this example.
In GDScript, the variables you put at the top of the file are your class's properties, also called member variables. Besides variables, you can define functions, which, for the most part, will be your classes' methods.
Godot provides several virtual functions you can define to connect your class with the engine. These include `_process()`, to apply changes to the node every frame, and `_unhandled_input()`, to receive input events like key and button presses from the users. There are quite a few more.
The `Input` singleton allows you to react to the players' input anywhere in your code. In particular, you'll get to use it in the `_process()` loop.
In the next lesson [Using signals](signals#doc-signals), we'll build upon the relationship between scripts and nodes by having our nodes trigger code in scripts.
godot Creating instances Creating instances
==================
In the previous part, we saw that a scene is a collection of nodes organized in a tree structure, with a single node as its root. You can split your project into any number of scenes. This feature helps you break down and organize your game's different components.
You can create as many scenes as you'd like and save them as files with the `.tscn` extension, which stands for "text scene". The `Label.tscn` file from the previous lesson was an example. We call those files "Packed Scenes" as they pack information about your scene's content.
Here's an example of a ball. It's composed of a [RigidBody2D](../../classes/class_rigidbody2d#class-rigidbody2d) node as its root named Ball, which allows the ball to fall and bounce on walls, a [Sprite](../../classes/class_sprite#class-sprite) node, and a [CollisionShape2D](../../classes/class_collisionshape2d#class-collisionshape2d).
 Once you saved a scene, it works as a blueprint: you can reproduce it in other scenes as many times as you'd like. Replicating an object from a template like this is called **instancing**.
 As we mentioned in the previous part, instanced scenes behave like a node: the editor hides their content by default. When you instance the Ball, you only see the Ball node. Notice also how each duplicate has a unique name.
Every instance of the Ball scene starts with the same structure and properties as `Ball.tscn`. However, you can modify each independently, such as changing how they bounce, how heavy they are, or any property exposed by the source scene.
In practice
-----------
Let's use instancing in practice to see how it works in Godot. We invite you to download the ball's sample project we prepared for you: [`instancing.zip`](https://docs.godotengine.org/en/3.5/_downloads/0f77439a03c9c1eb57dab630d028b82d/instancing.zip).
Extract the archive on your computer. Then, open Godot, and in the project manager, click the Import button to import the project.
 In the pop-up that appears, click the browse button and navigate to the folder you extracted.
 Double-click the `project.godot` file to open it.
 Finally, click the Import & Edit button.
 The project contains two packed scenes: `Main.tscn`, containing walls against which the ball collides, and `Ball.tscn`. The Main scene should open automatically.
 Let's add a ball as a child of the Main node. In the Scene dock, select the Main node. Then, click the link icon at the top of the scene dock. This button allows you to add an instance of a scene as a child of the currently selected node.
 Double-click the ball scene to instance it.
 The ball appears in the top-left corner of the viewport.
 Click on it and drag it towards the center of the view.
 Play the game by pressing F5. You should see it fall.
Now, we want to create more instances of the Ball node. With the ball still selected, press ``Ctrl`-`D`` (``Cmd`-`D`` on macOS) to call the duplicate command. Click and drag to move the new ball to a different location.
 You can repeat this process until you have several in the scene.
 Play the game again. You should now see every ball fall independently from one another. This is what instances do. Each is an independent reproduction of a template scene.
Editing scenes and instances
----------------------------
There is more to instances. With this feature, you can:
1. Change the properties of one ball without affecting the others using the Inspector.
2. Change the default properties of every Ball by opening the `Ball.tscn` scene and making a change to the Ball node there. Upon saving, all instances of the Ball in the project will see their values update.
Note
Changing a property on an instance always overrides values from the corresponding packed scene.
Let's try this. Open `Ball.tscn` and select the Ball node. In the Inspector on the right, click on the PhysicsMaterial property to expand it.
 Set its Bounce property to `2` by clicking on the number field, typing `2`, and pressing `Enter`.
 Play the game by pressing `F5` and notice how all balls now bounce a lot more. As the Ball scene is a template for all instances, modifying it and saving causes all instances to update accordingly.
Let's now adjust an individual instance. Head back to the Main scene by clicking on the corresponding tab above the viewport.
 Select one of the instanced Ball nodes and, in the Inspector, set its Gravity Scale value to `10`.
 A grey "revert" button appears next to the adjusted property.
 This icon indicates you are overriding a value from the source packed scene. Even if you modify the property in the original scene, the value override will be preserved in the instance. Clicking the revert icon will restore the property to the value in the saved scene.
Rerun the game and notice how this ball now falls much faster than the others.
Note
If you change a value on the `PhysicsMaterial` of one instance, it will affect all the others. This is because `PhysicsMaterial` is a resource, and resources are shared between instances. To make a resource unique for one instance, right-click on it in the Inspector and click Make Unique in the contextual menu.
Resources are another essential building block of Godot games we will cover in a later lesson.
Scene instances as a design language
------------------------------------
Instances and scenes in Godot offer an excellent design language, setting the engine apart from others out there. We designed Godot around this concept from the ground up.
We recommend dismissing architectural code patterns when making games with Godot, such as Model-View-Controller (MVC) or Entity-Relationship diagrams. Instead, you can start by imagining the elements players will see in your game and structure your code around them.
For example, you could break down a shooter game like so:
 You can come up with a diagram like this for almost any type of game. Each rectangle represents an entity that's visible in the game from the player's perspective. The arrows tell you which scene owns which.
Once you have a diagram, we recommended creating a scene for each element listed in it to develop your game. You'll use instancing, either by code or directly in the editor, to build your tree of scenes.
Programmers tend to spend a lot of time designing abstract architectures and trying to fit components into it. Designing based on scenes makes development faster and more straightforward, allowing you to focus on the game logic itself. Because most game components map directly to a scene, using a design based on scene instantiation means you need little other architectural code.
Here's the example of a scene diagram for an open-world game with tons of assets and nested elements:
 Imagine we started by creating the room. We could make a couple of different room scenes, with unique arrangements of furniture in them. Later, we could make a house scene that uses multiple room instances for the interior. We would create a citadel out of many instanced houses and a large terrain on which we would place the citadel. Each of these would be a scene instancing one or more sub-scenes.
Later, we could create scenes representing guards and add them to the citadel. They would be indirectly added to the overall game world.
With Godot, it's easy to iterate on your game like this, as all you need to do is create and instantiate more scenes. We designed the editor to be accessible to programmers, designers, and artists alike. A typical team development process can involve 2D or 3D artists, level designers, game designers, and animators, all working with the Godot editor.
Summary
-------
Instancing, the process of producing an object from a blueprint has many handy uses. With scenes, it gives you:
* The ability to divide your game into reusable components.
* A tool to structure and encapsulate complex systems.
* A language to think about your game project's structure in a natural way.
| programming_docs |
node None Deprecated APIs
---------------
Node.js APIs might be deprecated for any of the following reasons:
* Use of the API is unsafe.
* An improved alternative API is available.
* Breaking changes to the API are expected in a future major release.
Node.js uses three kinds of Deprecations:
* Documentation-only
* Runtime
* End-of-Life
A Documentation-only deprecation is one that is expressed only within the Node.js API docs. These generate no side-effects while running Node.js. Some Documentation-only deprecations trigger a runtime warning when launched with [`--pending-deprecation`](cli#--pending-deprecation) flag (or its alternative, `NODE_PENDING_DEPRECATION=1` environment variable), similarly to Runtime deprecations below. Documentation-only deprecations that support that flag are explicitly labeled as such in the [list of Deprecated APIs](#list-of-deprecated-apis).
A Runtime deprecation will, by default, generate a process warning that will be printed to `stderr` the first time the deprecated API is used. When the [`--throw-deprecation`](cli#--throw-deprecation) command-line flag is used, a Runtime deprecation will cause an error to be thrown.
An End-of-Life deprecation is used when functionality is or will soon be removed from Node.js.
### Revoking deprecations
Occasionally, the deprecation of an API might be reversed. In such situations, this document will be updated with information relevant to the decision. However, the deprecation identifier will not be modified.
### List of deprecated APIs
#### DEP0001: `http.OutgoingMessage.prototype.flush`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v1.6.0 | Runtime deprecation. |
Type: End-of-Life
`OutgoingMessage.prototype.flush()` has been removed. Use `OutgoingMessage.prototype.flushHeaders()` instead.
#### DEP0002: `require('_linklist')`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | End-of-Life. |
| v6.12.0 | A deprecation code has been assigned. |
| v5.0.0 | Runtime deprecation. |
Type: End-of-Life
The `_linklist` module is deprecated. Please use a userland alternative.
#### DEP0003: `_writableState.buffer`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.15 | Runtime deprecation. |
Type: End-of-Life
The `_writableState.buffer` has been removed. Use `_writableState.getBuffer()` instead.
#### DEP0004: `CryptoStream.prototype.readyState`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.4.0 | Documentation-only deprecation. |
Type: End-of-Life
The `CryptoStream.prototype.readyState` property was removed.
#### DEP0005: `Buffer()` constructor
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Runtime deprecation. |
| v6.12.0 | A deprecation code has been assigned. |
| v6.0.0 | Documentation-only deprecation. |
Type: Runtime (supports [`--pending-deprecation`](cli#--pending-deprecation))
The `Buffer()` function and `new Buffer()` constructor are deprecated due to API usability issues that can lead to accidental security issues.
As an alternative, use one of the following methods of constructing `Buffer` objects:
* [`Buffer.alloc(size[, fill[, encoding]])`](buffer#static-method-bufferallocsize-fill-encoding): Create a `Buffer` with *initialized* memory.
* [`Buffer.allocUnsafe(size)`](buffer#static-method-bufferallocunsafesize): Create a `Buffer` with *uninitialized* memory.
* [`Buffer.allocUnsafeSlow(size)`](buffer#static-method-bufferallocunsafeslowsize): Create a `Buffer` with *uninitialized* memory.
* [`Buffer.from(array)`](buffer#static-method-bufferfromarray): Create a `Buffer` with a copy of `array`
* [`Buffer.from(arrayBuffer[, byteOffset[, length]])`](buffer#static-method-bufferfromarraybuffer-byteoffset-length) - Create a `Buffer` that wraps the given `arrayBuffer`.
* [`Buffer.from(buffer)`](buffer#static-method-bufferfrombuffer): Create a `Buffer` that copies `buffer`.
* [`Buffer.from(string[, encoding])`](buffer#static-method-bufferfromstring-encoding): Create a `Buffer` that copies `string`.
Without `--pending-deprecation`, runtime warnings occur only for code not in `node_modules`. This means there will not be deprecation warnings for `Buffer()` usage in dependencies. With `--pending-deprecation`, a runtime warning results no matter where the `Buffer()` usage occurs.
#### DEP0006: `child_process` `options.customFds`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.14 | Runtime deprecation. |
| v0.5.10 | Documentation-only deprecation. |
Type: End-of-Life
Within the [`child_process`](child_process) module's `spawn()`, `fork()`, and `exec()` methods, the `options.customFds` option is deprecated. The `options.stdio` option should be used instead.
#### DEP0007: Replace `cluster` `worker.suicide` with `worker.exitedAfterDisconnect`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | End-of-Life. |
| v7.0.0 | Runtime deprecation. |
| v6.12.0 | A deprecation code has been assigned. |
| v6.0.0 | Documentation-only deprecation. |
Type: End-of-Life
In an earlier version of the Node.js `cluster`, a boolean property with the name `suicide` was added to the `Worker` object. The intent of this property was to provide an indication of how and why the `Worker` instance exited. In Node.js 6.0.0, the old property was deprecated and replaced with a new [`worker.exitedAfterDisconnect`](cluster#workerexitedafterdisconnect) property. The old property name did not precisely describe the actual semantics and was unnecessarily emotion-laden.
#### DEP0008: `require('node:constants')`
History
| Version | Changes |
| --- | --- |
| v6.12.0 | A deprecation code has been assigned. |
| v6.3.0 | Documentation-only deprecation. |
Type: Documentation-only
The `node:constants` module is deprecated. When requiring access to constants relevant to specific Node.js builtin modules, developers should instead refer to the `constants` property exposed by the relevant module. For instance, `require('node:fs').constants` and `require('node:os').constants`.
#### DEP0009: `crypto.pbkdf2` without digest
History
| Version | Changes |
| --- | --- |
| v14.0.0 | End-of-Life (for `digest === null`). |
| v11.0.0 | Runtime deprecation (for `digest === null`). |
| v8.0.0 | End-of-Life (for `digest === undefined`). |
| v6.12.0 | A deprecation code has been assigned. |
| v6.0.0 | Runtime deprecation (for `digest === undefined`). |
Type: End-of-Life
Use of the [`crypto.pbkdf2()`](crypto#cryptopbkdf2password-salt-iterations-keylen-digest-callback) API without specifying a digest was deprecated in Node.js 6.0 because the method defaulted to using the non-recommended `'SHA1'` digest. Previously, a deprecation warning was printed. Starting in Node.js 8.0.0, calling `crypto.pbkdf2()` or `crypto.pbkdf2Sync()` with `digest` set to `undefined` will throw a `TypeError`.
Beginning in Node.js v11.0.0, calling these functions with `digest` set to `null` would print a deprecation warning to align with the behavior when `digest` is `undefined`.
Now, however, passing either `undefined` or `null` will throw a `TypeError`.
#### DEP0010: `crypto.createCredentials`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.13 | Runtime deprecation. |
Type: End-of-Life
The `crypto.createCredentials()` API was removed. Please use [`tls.createSecureContext()`](tls#tlscreatesecurecontextoptions) instead.
#### DEP0011: `crypto.Credentials`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.13 | Runtime deprecation. |
Type: End-of-Life
The `crypto.Credentials` class was removed. Please use [`tls.SecureContext`](tls#tlscreatesecurecontextoptions) instead.
#### DEP0012: `Domain.dispose`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.7 | Runtime deprecation. |
Type: End-of-Life
`Domain.dispose()` has been removed. Recover from failed I/O actions explicitly via error event handlers set on the domain instead.
#### DEP0013: `fs` asynchronous function without callback
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v7.0.0 | Runtime deprecation. |
Type: End-of-Life
Calling an asynchronous function without a callback throws a `TypeError` in Node.js 10.0.0 onwards. See <https://github.com/nodejs/node/pull/12562>.
#### DEP0014: `fs.read` legacy String interface
History
| Version | Changes |
| --- | --- |
| v8.0.0 | End-of-Life. |
| v6.0.0 | Runtime deprecation. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.1.96 | Documentation-only deprecation. |
Type: End-of-Life
The [`fs.read()`](fs#fsreadfd-buffer-offset-length-position-callback) legacy `String` interface is deprecated. Use the `Buffer` API as mentioned in the documentation instead.
#### DEP0015: `fs.readSync` legacy String interface
History
| Version | Changes |
| --- | --- |
| v8.0.0 | End-of-Life. |
| v6.0.0 | Runtime deprecation. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.1.96 | Documentation-only deprecation. |
Type: End-of-Life
The [`fs.readSync()`](fs#fsreadsyncfd-buffer-offset-length-position) legacy `String` interface is deprecated. Use the `Buffer` API as mentioned in the documentation instead.
#### DEP0016: `GLOBAL`/`root`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | End-of-Life. |
| v6.12.0 | A deprecation code has been assigned. |
| v6.0.0 | Runtime deprecation. |
Type: End-of-Life
The `GLOBAL` and `root` aliases for the `global` property were deprecated in Node.js 6.0.0 and have since been removed.
#### DEP0017: `Intl.v8BreakIterator`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | End-of-Life. |
| v7.0.0 | Runtime deprecation. |
Type: End-of-Life
`Intl.v8BreakIterator` was a non-standard extension and has been removed. See [`Intl.Segmenter`](https://github.com/tc39/proposal-intl-segmenter).
#### DEP0018: Unhandled promise rejections
History
| Version | Changes |
| --- | --- |
| v15.0.0 | End-of-Life. |
| v7.0.0 | Runtime deprecation. |
Type: End-of-Life
Unhandled promise rejections are deprecated. By default, promise rejections that are not handled terminate the Node.js process with a non-zero exit code. To change the way Node.js treats unhandled rejections, use the [`--unhandled-rejections`](cli#--unhandled-rejectionsmode) command-line option.
#### DEP0019: `require('.')` resolved outside directory
History
| Version | Changes |
| --- | --- |
| v12.0.0 | Removed functionality. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v1.8.1 | Runtime deprecation. |
Type: End-of-Life
In certain cases, `require('.')` could resolve outside the package directory. This behavior has been removed.
#### DEP0020: `Server.connections`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Server.connections has been removed. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.9.7 | Runtime deprecation. |
Type: End-of-Life
The `Server.connections` property was deprecated in Node.js v0.9.7 and has been removed. Please use the [`Server.getConnections()`](net#servergetconnectionscallback) method instead.
#### DEP0021: `Server.listenFD`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.7.12 | Runtime deprecation. |
Type: End-of-Life
The `Server.listenFD()` method was deprecated and removed. Please use [`Server.listen({fd: <number>})`](net#serverlistenhandle-backlog-callback) instead.
#### DEP0022: `os.tmpDir()`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | End-of-Life. |
| v7.0.0 | Runtime deprecation. |
Type: End-of-Life
The `os.tmpDir()` API was deprecated in Node.js 7.0.0 and has since been removed. Please use [`os.tmpdir()`](os#ostmpdir) instead.
#### DEP0023: `os.getNetworkInterfaces()`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.6.0 | Runtime deprecation. |
Type: End-of-Life
The `os.getNetworkInterfaces()` method is deprecated. Please use the [`os.networkInterfaces()`](os#osnetworkinterfaces) method instead.
#### DEP0024: `REPLServer.prototype.convertToContext()`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | End-of-Life. |
| v7.0.0 | Runtime deprecation. |
Type: End-of-Life
The `REPLServer.prototype.convertToContext()` API has been removed.
#### DEP0025: `require('node:sys')`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v1.0.0 | Runtime deprecation. |
Type: Runtime
The `node:sys` module is deprecated. Please use the [`util`](util) module instead.
#### DEP0026: `util.print()`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.3 | Runtime deprecation. |
Type: End-of-Life
`util.print()` has been removed. Please use [`console.log()`](console#consolelogdata-args) instead.
#### DEP0027: `util.puts()`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.3 | Runtime deprecation. |
Type: End-of-Life
`util.puts()` has been removed. Please use [`console.log()`](console#consolelogdata-args) instead.
#### DEP0028: `util.debug()`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.3 | Runtime deprecation. |
Type: End-of-Life
`util.debug()` has been removed. Please use [`console.error()`](console#consoleerrordata-args) instead.
#### DEP0029: `util.error()`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.3 | Runtime deprecation. |
Type: End-of-Life
`util.error()` has been removed. Please use [`console.error()`](console#consoleerrordata-args) instead.
#### DEP0030: `SlowBuffer`
History
| Version | Changes |
| --- | --- |
| v6.12.0 | A deprecation code has been assigned. |
| v6.0.0 | Documentation-only deprecation. |
Type: Documentation-only
The [`SlowBuffer`](buffer#class-slowbuffer) class is deprecated. Please use [`Buffer.allocUnsafeSlow(size)`](buffer#static-method-bufferallocunsafeslowsize) instead.
#### DEP0031: `ecdh.setPublicKey()`
History
| Version | Changes |
| --- | --- |
| v6.12.0 | A deprecation code has been assigned. |
| v5.2.0 | Documentation-only deprecation. |
Type: Documentation-only
The [`ecdh.setPublicKey()`](crypto#ecdhsetpublickeypublickey-encoding) method is now deprecated as its inclusion in the API is not useful.
#### DEP0032: `node:domain` module
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v1.4.2 | Documentation-only deprecation. |
Type: Documentation-only
The [`domain`](domain) module is deprecated and should not be used.
#### DEP0033: `EventEmitter.listenerCount()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v3.2.0 | Documentation-only deprecation. |
Type: Documentation-only
The [`events.listenerCount(emitter, eventName)`](events#eventslistenercountemitter-eventname) API is deprecated. Please use [`emitter.listenerCount(eventName)`](events#emitterlistenercounteventname) instead.
#### DEP0034: `fs.exists(path, callback)`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v1.0.0 | Documentation-only deprecation. |
Type: Documentation-only
The [`fs.exists(path, callback)`](fs#fsexistspath-callback) API is deprecated. Please use [`fs.stat()`](fs#fsstatpath-options-callback) or [`fs.access()`](fs#fsaccesspath-mode-callback) instead.
#### DEP0035: `fs.lchmod(path, mode, callback)`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.4.7 | Documentation-only deprecation. |
Type: Documentation-only
The [`fs.lchmod(path, mode, callback)`](fs#fslchmodpath-mode-callback) API is deprecated.
#### DEP0036: `fs.lchmodSync(path, mode)`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.4.7 | Documentation-only deprecation. |
Type: Documentation-only
The [`fs.lchmodSync(path, mode)`](fs#fslchmodsyncpath-mode) API is deprecated.
#### DEP0037: `fs.lchown(path, uid, gid, callback)`
History
| Version | Changes |
| --- | --- |
| v10.6.0 | Deprecation revoked. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.4.7 | Documentation-only deprecation. |
Type: Deprecation revoked
The [`fs.lchown(path, uid, gid, callback)`](fs#fslchownpath-uid-gid-callback) API was deprecated. The deprecation was revoked because the requisite supporting APIs were added in libuv.
#### DEP0038: `fs.lchownSync(path, uid, gid)`
History
| Version | Changes |
| --- | --- |
| v10.6.0 | Deprecation revoked. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.4.7 | Documentation-only deprecation. |
Type: Deprecation revoked
The [`fs.lchownSync(path, uid, gid)`](fs#fslchownsyncpath-uid-gid) API was deprecated. The deprecation was revoked because the requisite supporting APIs were added in libuv.
#### DEP0039: `require.extensions`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.10.6 | Documentation-only deprecation. |
Type: Documentation-only
The [`require.extensions`](modules#requireextensions) property is deprecated.
#### DEP0040: `node:punycode` module
History
| Version | Changes |
| --- | --- |
| v16.6.0 | Added support for `--pending-deprecation`. |
| v7.0.0 | Documentation-only deprecation. |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
The [`punycode`](punycode) module is deprecated. Please use a userland alternative instead.
#### DEP0041: `NODE_REPL_HISTORY_FILE` environment variable
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v3.0.0 | Documentation-only deprecation. |
Type: End-of-Life
The `NODE_REPL_HISTORY_FILE` environment variable was removed. Please use `NODE_REPL_HISTORY` instead.
#### DEP0042: `tls.CryptoStream`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v0.11.3 | Documentation-only deprecation. |
Type: End-of-Life
The [`tls.CryptoStream`](tls#class-tlscryptostream) class was removed. Please use [`tls.TLSSocket`](tls#class-tlstlssocket) instead.
#### DEP0043: `tls.SecurePair`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | Runtime deprecation. |
| v6.12.0 | A deprecation code has been assigned. |
| v6.0.0 | Documentation-only deprecation. |
| v0.11.15 | Deprecation revoked. |
| v0.11.3 | Runtime deprecation. |
Type: Documentation-only
The [`tls.SecurePair`](tls#class-tlssecurepair) class is deprecated. Please use [`tls.TLSSocket`](tls#class-tlstlssocket) instead.
#### DEP0044: `util.isArray()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isArray()`](util#utilisarrayobject) API is deprecated. Please use `Array.isArray()` instead.
#### DEP0045: `util.isBoolean()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isBoolean()`](util#utilisbooleanobject) API is deprecated.
#### DEP0046: `util.isBuffer()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isBuffer()`](util#utilisbufferobject) API is deprecated. Please use [`Buffer.isBuffer()`](buffer#static-method-bufferisbufferobj) instead.
#### DEP0047: `util.isDate()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isDate()`](util#utilisdateobject) API is deprecated.
#### DEP0048: `util.isError()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isError()`](util#utiliserrorobject) API is deprecated.
#### DEP0049: `util.isFunction()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isFunction()`](util#utilisfunctionobject) API is deprecated.
#### DEP0050: `util.isNull()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isNull()`](util#utilisnullobject) API is deprecated.
#### DEP0051: `util.isNullOrUndefined()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isNullOrUndefined()`](util#utilisnullorundefinedobject) API is deprecated.
#### DEP0052: `util.isNumber()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isNumber()`](util#utilisnumberobject) API is deprecated.
#### DEP0053: `util.isObject()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isObject()`](util#utilisobjectobject) API is deprecated.
#### DEP0054: `util.isPrimitive()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isPrimitive()`](util#utilisprimitiveobject) API is deprecated.
#### DEP0055: `util.isRegExp()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isRegExp()`](util#utilisregexpobject) API is deprecated.
#### DEP0056: `util.isString()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isString()`](util#utilisstringobject) API is deprecated.
#### DEP0057: `util.isSymbol()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isSymbol()`](util#utilissymbolobject) API is deprecated.
#### DEP0058: `util.isUndefined()`
History
| Version | Changes |
| --- | --- |
| v6.12.0, v4.8.6 | A deprecation code has been assigned. |
| v4.0.0, v3.3.1 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.isUndefined()`](util#utilisundefinedobject) API is deprecated.
#### DEP0059: `util.log()`
History
| Version | Changes |
| --- | --- |
| v6.12.0 | A deprecation code has been assigned. |
| v6.0.0 | Documentation-only deprecation. |
Type: Documentation-only
The [`util.log()`](util#utillogstring) API is deprecated.
#### DEP0060: `util._extend()`
History
| Version | Changes |
| --- | --- |
| v6.12.0 | A deprecation code has been assigned. |
| v6.0.0 | Documentation-only deprecation. |
Type: Documentation-only
The [`util._extend()`](util#util_extendtarget-source) API is deprecated.
#### DEP0061: `fs.SyncWriteStream`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | End-of-Life. |
| v8.0.0 | Runtime deprecation. |
| v7.0.0 | Documentation-only deprecation. |
Type: End-of-Life
The `fs.SyncWriteStream` class was never intended to be a publicly accessible API and has been removed. No alternative API is available. Please use a userland alternative.
#### DEP0062: `node --debug`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v8.0.0 | Runtime deprecation. |
Type: End-of-Life
`--debug` activates the legacy V8 debugger interface, which was removed as of V8 5.8. It is replaced by Inspector which is activated with `--inspect` instead.
#### DEP0063: `ServerResponse.prototype.writeHeader()`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | Documentation-only deprecation. |
Type: Documentation-only
The `node:http` module `ServerResponse.prototype.writeHeader()` API is deprecated. Please use `ServerResponse.prototype.writeHead()` instead.
The `ServerResponse.prototype.writeHeader()` method was never documented as an officially supported API.
#### DEP0064: `tls.createSecurePair()`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | Runtime deprecation. |
| v6.12.0 | A deprecation code has been assigned. |
| v6.0.0 | Documentation-only deprecation. |
| v0.11.15 | Deprecation revoked. |
| v0.11.3 | Runtime deprecation. |
Type: Runtime
The `tls.createSecurePair()` API was deprecated in documentation in Node.js 0.11.3. Users should use `tls.Socket` instead.
#### DEP0065: `repl.REPL_MODE_MAGIC` and `NODE_REPL_MODE=magic`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v8.0.0 | Documentation-only deprecation. |
Type: End-of-Life
The `node:repl` module's `REPL_MODE_MAGIC` constant, used for `replMode` option, has been removed. Its behavior has been functionally identical to that of `REPL_MODE_SLOPPY` since Node.js 6.0.0, when V8 5.0 was imported. Please use `REPL_MODE_SLOPPY` instead.
The `NODE_REPL_MODE` environment variable is used to set the underlying `replMode` of an interactive `node` session. Its value, `magic`, is also removed. Please use `sloppy` instead.
#### DEP0066: `OutgoingMessage.prototype._headers, OutgoingMessage.prototype._headerNames`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | Runtime deprecation. |
| v8.0.0 | Documentation-only deprecation. |
Type: Runtime
The `node:http` module `OutgoingMessage.prototype._headers` and `OutgoingMessage.prototype._headerNames` properties are deprecated. Use one of the public methods (e.g. `OutgoingMessage.prototype.getHeader()`, `OutgoingMessage.prototype.getHeaders()`, `OutgoingMessage.prototype.getHeaderNames()`, `OutgoingMessage.prototype.getRawHeaderNames()`, `OutgoingMessage.prototype.hasHeader()`, `OutgoingMessage.prototype.removeHeader()`, `OutgoingMessage.prototype.setHeader()`) for working with outgoing headers.
The `OutgoingMessage.prototype._headers` and `OutgoingMessage.prototype._headerNames` properties were never documented as officially supported properties.
#### DEP0067: `OutgoingMessage.prototype._renderHeaders`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | Documentation-only deprecation. |
Type: Documentation-only
The `node:http` module `OutgoingMessage.prototype._renderHeaders()` API is deprecated.
The `OutgoingMessage.prototype._renderHeaders` property was never documented as an officially supported API.
#### DEP0068: `node debug`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The legacy `node debug` command was removed. |
| v8.0.0 | Runtime deprecation. |
Type: End-of-Life
`node debug` corresponds to the legacy CLI debugger which has been replaced with a V8-inspector based CLI debugger available through `node inspect`.
#### DEP0069: `vm.runInDebugContext(string)`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v9.0.0 | Runtime deprecation. |
| v8.0.0 | Documentation-only deprecation. |
Type: End-of-Life
DebugContext has been removed in V8 and is not available in Node.js 10+.
DebugContext was an experimental API.
#### DEP0070: `async_hooks.currentId()`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | End-of-Life. |
| v8.2.0 | Runtime deprecation. |
Type: End-of-Life
`async_hooks.currentId()` was renamed to `async_hooks.executionAsyncId()` for clarity.
This change was made while `async_hooks` was an experimental API.
#### DEP0071: `async_hooks.triggerId()`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | End-of-Life. |
| v8.2.0 | Runtime deprecation. |
Type: End-of-Life
`async_hooks.triggerId()` was renamed to `async_hooks.triggerAsyncId()` for clarity.
This change was made while `async_hooks` was an experimental API.
#### DEP0072: `async_hooks.AsyncResource.triggerId()`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | End-of-Life. |
| v8.2.0 | Runtime deprecation. |
Type: End-of-Life
`async_hooks.AsyncResource.triggerId()` was renamed to `async_hooks.AsyncResource.triggerAsyncId()` for clarity.
This change was made while `async_hooks` was an experimental API.
#### DEP0073: Several internal properties of `net.Server`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v9.0.0 | Runtime deprecation. |
Type: End-of-Life
Accessing several internal, undocumented properties of `net.Server` instances with inappropriate names is deprecated.
As the original API was undocumented and not generally useful for non-internal code, no replacement API is provided.
#### DEP0074: `REPLServer.bufferedCommand`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | End-of-Life. |
| v9.0.0 | Runtime deprecation. |
Type: End-of-Life
The `REPLServer.bufferedCommand` property was deprecated in favor of [`REPLServer.clearBufferedCommand()`](repl#replserverclearbufferedcommand).
#### DEP0075: `REPLServer.parseREPLKeyword()`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | End-of-Life. |
| v9.0.0 | Runtime deprecation. |
Type: End-of-Life
`REPLServer.parseREPLKeyword()` was removed from userland visibility.
#### DEP0076: `tls.parseCertString()`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | End-of-Life. |
| v9.0.0 | Runtime deprecation. |
| v8.6.0 | Documentation-only deprecation. |
Type: End-of-Life
`tls.parseCertString()` was a trivial parsing helper that was made public by mistake. While it was supposed to parse certificate subject and issuer strings, it never handled multi-value Relative Distinguished Names correctly.
Earlier versions of this document suggested using `querystring.parse()` as an alternative to `tls.parseCertString()`. However, `querystring.parse()` also does not handle all certificate subjects correctly and should not be used.
#### DEP0077: `Module._debug()`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | Runtime deprecation. |
Type: Runtime
`Module._debug()` is deprecated.
The `Module._debug()` function was never documented as an officially supported API.
#### DEP0078: `REPLServer.turnOffEditorMode()`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | End-of-Life. |
| v9.0.0 | Runtime deprecation. |
Type: End-of-Life
`REPLServer.turnOffEditorMode()` was removed from userland visibility.
#### DEP0079: Custom inspection function on objects via `.inspect()`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | End-of-Life. |
| v10.0.0 | Runtime deprecation. |
| v8.7.0 | Documentation-only deprecation. |
Type: End-of-Life
Using a property named `inspect` on an object to specify a custom inspection function for [`util.inspect()`](util#utilinspectobject-options) is deprecated. Use [`util.inspect.custom`](util#utilinspectcustom) instead. For backward compatibility with Node.js prior to version 6.4.0, both can be specified.
#### DEP0080: `path._makeLong()`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | Documentation-only deprecation. |
Type: Documentation-only
The internal `path._makeLong()` was not intended for public use. However, userland modules have found it useful. The internal API is deprecated and replaced with an identical, public `path.toNamespacedPath()` method.
#### DEP0081: `fs.truncate()` using a file descriptor
History
| Version | Changes |
| --- | --- |
| v9.0.0 | Runtime deprecation. |
Type: Runtime
`fs.truncate()` `fs.truncateSync()` usage with a file descriptor is deprecated. Please use `fs.ftruncate()` or `fs.ftruncateSync()` to work with file descriptors.
#### DEP0082: `REPLServer.prototype.memory()`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | End-of-Life. |
| v9.0.0 | Runtime deprecation. |
Type: End-of-Life
`REPLServer.prototype.memory()` is only necessary for the internal mechanics of the `REPLServer` itself. Do not use this function.
#### DEP0083: Disabling ECDH by setting `ecdhCurve` to `false`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v9.2.0 | Runtime deprecation. |
Type: End-of-Life.
The `ecdhCurve` option to `tls.createSecureContext()` and `tls.TLSSocket` could be set to `false` to disable ECDH entirely on the server only. This mode was deprecated in preparation for migrating to OpenSSL 1.1.0 and consistency with the client and is now unsupported. Use the `ciphers` parameter instead.
#### DEP0084: requiring bundled internal dependencies
History
| Version | Changes |
| --- | --- |
| v12.0.0 | This functionality has been removed. |
| v10.0.0 | Runtime deprecation. |
Type: End-of-Life
Since Node.js versions 4.4.0 and 5.2.0, several modules only intended for internal usage were mistakenly exposed to user code through `require()`. These modules were:
* `v8/tools/codemap`
* `v8/tools/consarray`
* `v8/tools/csvparser`
* `v8/tools/logreader`
* `v8/tools/profile_view`
* `v8/tools/profile`
* `v8/tools/SourceMap`
* `v8/tools/splaytree`
* `v8/tools/tickprocessor-driver`
* `v8/tools/tickprocessor`
* `node-inspect/lib/_inspect` (from 7.6.0)
* `node-inspect/lib/internal/inspect_client` (from 7.6.0)
* `node-inspect/lib/internal/inspect_repl` (from 7.6.0)
The `v8/*` modules do not have any exports, and if not imported in a specific order would in fact throw errors. As such there are virtually no legitimate use cases for importing them through `require()`.
On the other hand, `node-inspect` can be installed locally through a package manager, as it is published on the npm registry under the same name. No source code modification is necessary if that is done.
#### DEP0085: AsyncHooks sensitive API
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v9.4.0, v8.10.0 | Runtime deprecation. |
Type: End-of-Life
The AsyncHooks sensitive API was never documented and had various minor issues. Use the `AsyncResource` API instead. See <https://github.com/nodejs/node/issues/15572>.
#### DEP0086: Remove `runInAsyncIdScope`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
| v9.4.0, v8.10.0 | Runtime deprecation. |
Type: End-of-Life
`runInAsyncIdScope` doesn't emit the `'before'` or `'after'` event and can thus cause a lot of issues. See <https://github.com/nodejs/node/issues/14328>.
#### DEP0089: `require('node:assert')`
History
| Version | Changes |
| --- | --- |
| v12.8.0 | Deprecation revoked. |
| v9.9.0, v8.13.0 | Documentation-only deprecation. |
Type: Deprecation revoked
Importing assert directly was not recommended as the exposed functions use loose equality checks. The deprecation was revoked because use of the `node:assert` module is not discouraged, and the deprecation caused developer confusion.
#### DEP0090: Invalid GCM authentication tag lengths
History
| Version | Changes |
| --- | --- |
| v11.0.0 | End-of-Life. |
| v10.0.0 | Runtime deprecation. |
Type: End-of-Life
Node.js used to support all GCM authentication tag lengths which are accepted by OpenSSL when calling [`decipher.setAuthTag()`](crypto#deciphersetauthtagbuffer-encoding). Beginning with Node.js v11.0.0, only authentication tag lengths of 128, 120, 112, 104, 96, 64, and 32 bits are allowed. Authentication tags of other lengths are invalid per [NIST SP 800-38D](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf).
#### DEP0091: `crypto.DEFAULT_ENCODING`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Runtime deprecation. |
Type: Runtime
The [`crypto.DEFAULT_ENCODING`](crypto#cryptodefault_encoding) property is deprecated.
#### DEP0092: Top-level `this` bound to `module.exports`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Documentation-only deprecation. |
Type: Documentation-only
Assigning properties to the top-level `this` as an alternative to `module.exports` is deprecated. Developers should use `exports` or `module.exports` instead.
#### DEP0093: `crypto.fips` is deprecated and replaced
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Documentation-only deprecation. |
Type: Documentation-only
The [`crypto.fips`](crypto#cryptofips) property is deprecated. Please use `crypto.setFips()` and `crypto.getFips()` instead.
#### DEP0094: Using `assert.fail()` with more than one argument
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Runtime deprecation. |
Type: Runtime
Using `assert.fail()` with more than one argument is deprecated. Use `assert.fail()` with only one argument or use a different `node:assert` module method.
#### DEP0095: `timers.enroll()`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Runtime deprecation. |
Type: Runtime
`timers.enroll()` is deprecated. Please use the publicly documented [`setTimeout()`](timers#settimeoutcallback-delay-args) or [`setInterval()`](timers#setintervalcallback-delay-args) instead.
#### DEP0096: `timers.unenroll()`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Runtime deprecation. |
Type: Runtime
`timers.unenroll()` is deprecated. Please use the publicly documented [`clearTimeout()`](timers#cleartimeouttimeout) or [`clearInterval()`](timers#clearintervaltimeout) instead.
#### DEP0097: `MakeCallback` with `domain` property
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Runtime deprecation. |
Type: Runtime
Users of `MakeCallback` that add the `domain` property to carry context, should start using the `async_context` variant of `MakeCallback` or `CallbackScope`, or the high-level `AsyncResource` class.
#### DEP0098: AsyncHooks embedder `AsyncResource.emitBefore` and `AsyncResource.emitAfter` APIs
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v10.0.0, v9.6.0, v8.12.0 | Runtime deprecation. |
Type: End-of-Life
The embedded API provided by AsyncHooks exposes `.emitBefore()` and `.emitAfter()` methods which are very easy to use incorrectly which can lead to unrecoverable errors.
Use [`asyncResource.runInAsyncScope()`](async_context#asyncresourceruninasyncscopefn-thisarg-args) API instead which provides a much safer, and more convenient, alternative. See <https://github.com/nodejs/node/pull/18513>.
#### DEP0099: Async context-unaware `node::MakeCallback` C++ APIs
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Compile-time deprecation. |
Type: Compile-time
Certain versions of `node::MakeCallback` APIs available to native addons are deprecated. Please use the versions of the API that accept an `async_context` parameter.
#### DEP0100: `process.assert()`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Runtime deprecation. |
| v0.3.7 | Documentation-only deprecation. |
Type: Runtime
`process.assert()` is deprecated. Please use the [`assert`](assert) module instead.
This was never a documented feature.
#### DEP0101: `--with-lttng`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
Type: End-of-Life
The `--with-lttng` compile-time option has been removed.
#### DEP0102: Using `noAssert` in `Buffer#(read|write)` operations
History
| Version | Changes |
| --- | --- |
| v10.0.0 | End-of-Life. |
Type: End-of-Life
Using the `noAssert` argument has no functionality anymore. All input is verified regardless of the value of `noAssert`. Skipping the verification could lead to hard-to-find errors and crashes.
#### DEP0103: `process.binding('util').is[...]` typechecks
History
| Version | Changes |
| --- | --- |
| v10.9.0 | Superseded by [DEP0111](#DEP0111). |
| v10.0.0 | Documentation-only deprecation. |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
Using `process.binding()` in general should be avoided. The type checking methods in particular can be replaced by using [`util.types`](util#utiltypes).
This deprecation has been superseded by the deprecation of the `process.binding()` API ([DEP0111](#DEP0111)).
#### DEP0104: `process.env` string coercion
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Documentation-only deprecation. |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
When assigning a non-string property to [`process.env`](process#processenv), the assigned value is implicitly converted to a string. This behavior is deprecated if the assigned value is not a string, boolean, or number. In the future, such assignment might result in a thrown error. Please convert the property to a string before assigning it to `process.env`.
#### DEP0105: `decipher.finaltol`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | End-of-Life. |
| v10.0.0 | Runtime deprecation. |
Type: End-of-Life
`decipher.finaltol()` has never been documented and was an alias for [`decipher.final()`](crypto#decipherfinaloutputencoding). This API has been removed, and it is recommended to use [`decipher.final()`](crypto#decipherfinaloutputencoding) instead.
#### DEP0106: `crypto.createCipher` and `crypto.createDecipher`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | Runtime deprecation. |
| v10.0.0 | Documentation-only deprecation. |
Type: Runtime
Using [`crypto.createCipher()`](crypto#cryptocreatecipheralgorithm-password-options) and [`crypto.createDecipher()`](crypto#cryptocreatedecipheralgorithm-password-options) must be avoided as they use a weak key derivation function (MD5 with no salt) and static initialization vectors. It is recommended to derive a key using [`crypto.pbkdf2()`](crypto#cryptopbkdf2password-salt-iterations-keylen-digest-callback) or [`crypto.scrypt()`](crypto#cryptoscryptpassword-salt-keylen-options-callback) with random salts and to use [`crypto.createCipheriv()`](crypto#cryptocreatecipherivalgorithm-key-iv-options) and [`crypto.createDecipheriv()`](crypto#cryptocreatedecipherivalgorithm-key-iv-options) to obtain the [`Cipher`](crypto#class-cipher) and [`Decipher`](crypto#class-decipher) objects respectively.
#### DEP0107: `tls.convertNPNProtocols()`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | End-of-Life. |
| v10.0.0 | Runtime deprecation. |
Type: End-of-Life
This was an undocumented helper function not intended for use outside Node.js core and obsoleted by the removal of NPN (Next Protocol Negotiation) support.
#### DEP0108: `zlib.bytesRead`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | Runtime deprecation. |
| v10.0.0 | Documentation-only deprecation. |
Type: Runtime
Deprecated alias for [`zlib.bytesWritten`](zlib#zlibbyteswritten). This original name was chosen because it also made sense to interpret the value as the number of bytes read by the engine, but is inconsistent with other streams in Node.js that expose values under these names.
#### DEP0109: `http`, `https`, and `tls` support for invalid URLs
History
| Version | Changes |
| --- | --- |
| v16.0.0 | End-of-Life. |
| v11.0.0 | Runtime deprecation. |
Type: End-of-Life
Some previously supported (but strictly invalid) URLs were accepted through the [`http.request()`](http#httprequestoptions-callback), [`http.get()`](http#httpgetoptions-callback), [`https.request()`](https#httpsrequestoptions-callback), [`https.get()`](https#httpsgetoptions-callback), and [`tls.checkServerIdentity()`](tls#tlscheckserveridentityhostname-cert) APIs because those were accepted by the legacy `url.parse()` API. The mentioned APIs now use the WHATWG URL parser that requires strictly valid URLs. Passing an invalid URL is deprecated and support will be removed in the future.
#### DEP0110: `vm.Script` cached data
History
| Version | Changes |
| --- | --- |
| v10.6.0 | Documentation-only deprecation. |
Type: Documentation-only
The `produceCachedData` option is deprecated. Use [`script.createCachedData()`](vm#scriptcreatecacheddata) instead.
#### DEP0111: `process.binding()`
History
| Version | Changes |
| --- | --- |
| v11.12.0 | Added support for `--pending-deprecation`. |
| v10.9.0 | Documentation-only deprecation. |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
`process.binding()` is for use by Node.js internal code only.
#### DEP0112: `dgram` private APIs
History
| Version | Changes |
| --- | --- |
| v11.0.0 | Runtime deprecation. |
Type: Runtime
The `node:dgram` module previously contained several APIs that were never meant to accessed outside of Node.js core: `Socket.prototype._handle`, `Socket.prototype._receiving`, `Socket.prototype._bindState`, `Socket.prototype._queue`, `Socket.prototype._reuseAddr`, `Socket.prototype._healthCheck()`, `Socket.prototype._stopReceiving()`, and `dgram._createSocketHandle()`.
#### DEP0113: `Cipher.setAuthTag()`, `Decipher.getAuthTag()`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v11.0.0 | Runtime deprecation. |
Type: End-of-Life
`Cipher.setAuthTag()` and `Decipher.getAuthTag()` are no longer available. They were never documented and would throw when called.
#### DEP0114: `crypto._toBuf()`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v11.0.0 | Runtime deprecation. |
Type: End-of-Life
The `crypto._toBuf()` function was not designed to be used by modules outside of Node.js core and was removed.
#### DEP0115: `crypto.prng()`, `crypto.pseudoRandomBytes()`, `crypto.rng()`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | Added documentation-only deprecation with `--pending-deprecation` support. |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
In recent versions of Node.js, there is no difference between [`crypto.randomBytes()`](crypto#cryptorandombytessize-callback) and `crypto.pseudoRandomBytes()`. The latter is deprecated along with the undocumented aliases `crypto.prng()` and `crypto.rng()` in favor of [`crypto.randomBytes()`](crypto#cryptorandombytessize-callback) and might be removed in a future release.
#### DEP0116: Legacy URL API
History
| Version | Changes |
| --- | --- |
| v19.0.0 | `url.parse()` is deprecated again in DEP0169. |
| v15.13.0, v14.17.0 | Deprecation revoked. Status changed to "Legacy". |
| v11.0.0 | Documentation-only deprecation. |
Type: Deprecation revoked
The [legacy URL API](url#legacy-url-api) is deprecated. This includes [`url.format()`](url#urlformaturlobject), [`url.parse()`](url#urlparseurlstring-parsequerystring-slashesdenotehost), [`url.resolve()`](url#urlresolvefrom-to), and the [legacy `urlObject`](url#legacy-urlobject). Please use the [WHATWG URL API](url#the-whatwg-url-api) instead.
#### DEP0117: Native crypto handles
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v11.0.0 | Runtime deprecation. |
Type: End-of-Life
Previous versions of Node.js exposed handles to internal native objects through the `_handle` property of the `Cipher`, `Decipher`, `DiffieHellman`, `DiffieHellmanGroup`, `ECDH`, `Hash`, `Hmac`, `Sign`, and `Verify` classes. The `_handle` property has been removed because improper use of the native object can lead to crashing the application.
#### DEP0118: `dns.lookup()` support for a falsy host name
History
| Version | Changes |
| --- | --- |
| v11.0.0 | Runtime deprecation. |
Type: Runtime
Previous versions of Node.js supported `dns.lookup()` with a falsy host name like `dns.lookup(false)` due to backward compatibility. This behavior is undocumented and is thought to be unused in real world apps. It will become an error in future versions of Node.js.
#### DEP0119: `process.binding('uv').errname()` private API
History
| Version | Changes |
| --- | --- |
| v11.0.0 | Documentation-only deprecation. |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
`process.binding('uv').errname()` is deprecated. Please use [`util.getSystemErrorName()`](util#utilgetsystemerrornameerr) instead.
#### DEP0120: Windows Performance Counter support
History
| Version | Changes |
| --- | --- |
| v12.0.0 | End-of-Life. |
| v11.0.0 | Runtime deprecation. |
Type: End-of-Life
Windows Performance Counter support has been removed from Node.js. The undocumented `COUNTER_NET_SERVER_CONNECTION()`, `COUNTER_NET_SERVER_CONNECTION_CLOSE()`, `COUNTER_HTTP_SERVER_REQUEST()`, `COUNTER_HTTP_SERVER_RESPONSE()`, `COUNTER_HTTP_CLIENT_REQUEST()`, and `COUNTER_HTTP_CLIENT_RESPONSE()` functions have been deprecated.
#### DEP0121: `net._setSimultaneousAccepts()`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | Runtime deprecation. |
Type: Runtime
The undocumented `net._setSimultaneousAccepts()` function was originally intended for debugging and performance tuning when using the `node:child_process` and `node:cluster` modules on Windows. The function is not generally useful and is being removed. See discussion here: <https://github.com/nodejs/node/issues/18391>
#### DEP0122: `tls` `Server.prototype.setOptions()`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | Runtime deprecation. |
Type: Runtime
Please use `Server.prototype.setSecureContext()` instead.
#### DEP0123: setting the TLS ServerName to an IP address
History
| Version | Changes |
| --- | --- |
| v12.0.0 | Runtime deprecation. |
Type: Runtime
Setting the TLS ServerName to an IP address is not permitted by [RFC 6066](https://tools.ietf.org/html/rfc6066#section-3). This will be ignored in a future version.
#### DEP0124: using `REPLServer.rli`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | End-of-Life. |
| v12.0.0 | Runtime deprecation. |
Type: End-of-Life
This property is a reference to the instance itself.
#### DEP0125: `require('node:_stream_wrap')`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | Runtime deprecation. |
Type: Runtime
The `node:_stream_wrap` module is deprecated.
#### DEP0126: `timers.active()`
History
| Version | Changes |
| --- | --- |
| v11.14.0 | Runtime deprecation. |
Type: Runtime
The previously undocumented `timers.active()` is deprecated. Please use the publicly documented [`timeout.refresh()`](timers#timeoutrefresh) instead. If re-referencing the timeout is necessary, [`timeout.ref()`](timers#timeoutref) can be used with no performance impact since Node.js 10.
#### DEP0127: `timers._unrefActive()`
History
| Version | Changes |
| --- | --- |
| v11.14.0 | Runtime deprecation. |
Type: Runtime
The previously undocumented and "private" `timers._unrefActive()` is deprecated. Please use the publicly documented [`timeout.refresh()`](timers#timeoutrefresh) instead. If unreferencing the timeout is necessary, [`timeout.unref()`](timers#timeoutunref) can be used with no performance impact since Node.js 10.
#### DEP0128: modules with an invalid `main` entry and an `index.js` file
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Runtime deprecation. |
| v12.0.0 | Documentation-only. |
Type: Runtime
Modules that have an invalid `main` entry (e.g., `./does-not-exist.js`) and also have an `index.js` file in the top level directory will resolve the `index.js` file. That is deprecated and is going to throw an error in future Node.js versions.
#### DEP0129: `ChildProcess._channel`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | Runtime deprecation. |
| v11.14.0 | Documentation-only. |
Type: Runtime
The `_channel` property of child process objects returned by `spawn()` and similar functions is not intended for public use. Use `ChildProcess.channel` instead.
#### DEP0130: `Module.createRequireFromPath()`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | End-of-life. |
| v13.0.0 | Runtime deprecation. |
| v12.2.0 | Documentation-only. |
Type: End-of-Life
Use [`module.createRequire()`](module#modulecreaterequirefilename) instead.
#### DEP0131: Legacy HTTP parser
History
| Version | Changes |
| --- | --- |
| v13.0.0 | This feature has been removed. |
| v12.22.0 | Runtime deprecation. |
| v12.3.0 | Documentation-only. |
Type: End-of-Life
The legacy HTTP parser, used by default in versions of Node.js prior to 12.0.0, is deprecated and has been removed in v13.0.0. Prior to v13.0.0, the `--http-parser=legacy` command-line flag could be used to revert to using the legacy parser.
#### DEP0132: `worker.terminate()` with callback
History
| Version | Changes |
| --- | --- |
| v12.5.0 | Runtime deprecation. |
Type: Runtime
Passing a callback to [`worker.terminate()`](worker_threads#workerterminate) is deprecated. Use the returned `Promise` instead, or a listener to the worker's `'exit'` event.
#### DEP0133: `http` `connection`
History
| Version | Changes |
| --- | --- |
| v12.12.0 | Documentation-only deprecation. |
Type: Documentation-only
Prefer [`response.socket`](http#responsesocket) over [`response.connection`](http#responseconnection) and [`request.socket`](http#requestsocket) over [`request.connection`](http#requestconnection).
#### DEP0134: `process._tickCallback`
History
| Version | Changes |
| --- | --- |
| v12.12.0 | Documentation-only deprecation. |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
The `process._tickCallback` property was never documented as an officially supported API.
#### DEP0135: `WriteStream.open()` and `ReadStream.open()` are internal
History
| Version | Changes |
| --- | --- |
| v13.0.0 | Runtime deprecation. |
Type: Runtime
[`WriteStream.open()`](fs#class-fswritestream) and [`ReadStream.open()`](fs#class-fsreadstream) are undocumented internal APIs that do not make sense to use in userland. File streams should always be opened through their corresponding factory methods [`fs.createWriteStream()`](fs#fscreatewritestreampath-options) and [`fs.createReadStream()`](fs#fscreatereadstreampath-options)) or by passing a file descriptor in options.
#### DEP0136: `http` `finished`
History
| Version | Changes |
| --- | --- |
| v13.4.0, v12.16.0 | Documentation-only deprecation. |
Type: Documentation-only
[`response.finished`](http#responsefinished) indicates whether [`response.end()`](http#responseenddata-encoding-callback) has been called, not whether `'finish'` has been emitted and the underlying data is flushed.
Use [`response.writableFinished`](http#responsewritablefinished) or [`response.writableEnded`](http#responsewritableended) accordingly instead to avoid the ambiguity.
To maintain existing behavior `response.finished` should be replaced with `response.writableEnded`.
#### DEP0137: Closing fs.FileHandle on garbage collection
History
| Version | Changes |
| --- | --- |
| v14.0.0 | Runtime deprecation. |
Type: Runtime
Allowing a [`fs.FileHandle`](fs#class-filehandle) object to be closed on garbage collection is deprecated. In the future, doing so might result in a thrown error that will terminate the process.
Please ensure that all `fs.FileHandle` objects are explicitly closed using `FileHandle.prototype.close()` when the `fs.FileHandle` is no longer needed:
```
const fsPromises = require('node:fs').promises;
async function openAndClose() {
let filehandle;
try {
filehandle = await fsPromises.open('thefile.txt', 'r');
} finally {
if (filehandle !== undefined)
await filehandle.close();
}
}
```
#### DEP0138: `process.mainModule`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | Documentation-only deprecation. |
Type: Documentation-only
[`process.mainModule`](process#processmainmodule) is a CommonJS-only feature while `process` global object is shared with non-CommonJS environment. Its use within ECMAScript modules is unsupported.
It is deprecated in favor of [`require.main`](modules#accessing-the-main-module), because it serves the same purpose and is only available on CommonJS environment.
#### DEP0139: `process.umask()` with no arguments
History
| Version | Changes |
| --- | --- |
| v14.0.0, v12.19.0 | Documentation-only deprecation. |
Type: Documentation-only
Calling `process.umask()` with no argument causes the process-wide umask to be written twice. This introduces a race condition between threads, and is a potential security vulnerability. There is no safe, cross-platform alternative API.
#### DEP0140: Use `request.destroy()` instead of `request.abort()`
History
| Version | Changes |
| --- | --- |
| v14.1.0, v13.14.0 | Documentation-only deprecation. |
Type: Documentation-only
Use [`request.destroy()`](http#requestdestroyerror) instead of [`request.abort()`](http#requestabort).
#### DEP0141: `repl.inputStream` and `repl.outputStream`
History
| Version | Changes |
| --- | --- |
| v14.3.0 | Documentation-only (supports [`--pending-deprecation`][]). |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
The `node:repl` module exported the input and output stream twice. Use `.input` instead of `.inputStream` and `.output` instead of `.outputStream`.
#### DEP0142: `repl._builtinLibs`
History
| Version | Changes |
| --- | --- |
| v14.3.0 | Documentation-only (supports [`--pending-deprecation`][]). |
Type: Documentation-only
The `node:repl` module exports a `_builtinLibs` property that contains an array of built-in modules. It was incomplete so far and instead it's better to rely upon `require('node:module').builtinModules`.
#### DEP0143: `Transform._transformState`
History
| Version | Changes |
| --- | --- |
| v14.5.0 | Runtime deprecation. |
Type: Runtime `Transform._transformState` will be removed in future versions where it is no longer required due to simplification of the implementation.
#### DEP0144: `module.parent`
History
| Version | Changes |
| --- | --- |
| v14.6.0, v12.19.0 | Documentation-only deprecation. |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
A CommonJS module can access the first module that required it using `module.parent`. This feature is deprecated because it does not work consistently in the presence of ECMAScript modules and because it gives an inaccurate representation of the CommonJS module graph.
Some modules use it to check if they are the entry point of the current process. Instead, it is recommended to compare `require.main` and `module`:
```
if (require.main === module) {
// Code section that will run only if current file is the entry point.
}
```
When looking for the CommonJS modules that have required the current one, `require.cache` and `module.children` can be used:
```
const moduleParents = Object.values(require.cache)
.filter((m) => m.children.includes(module));
```
#### DEP0145: `socket.bufferSize`
History
| Version | Changes |
| --- | --- |
| v14.6.0 | Documentation-only deprecation. |
Type: Documentation-only
[`socket.bufferSize`](net#socketbuffersize) is just an alias for [`writable.writableLength`](stream#writablewritablelength).
#### DEP0146: `new crypto.Certificate()`
History
| Version | Changes |
| --- | --- |
| v14.9.0 | Documentation-only deprecation. |
Type: Documentation-only
The [`crypto.Certificate()` constructor](crypto#legacy-api) is deprecated. Use [static methods of `crypto.Certificate()`](crypto#class-certificate) instead.
#### DEP0147: `fs.rmdir(path, { recursive: true })`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Runtime deprecation. |
| v15.0.0 | Runtime deprecation for permissive behavior. |
| v14.14.0 | Documentation-only deprecation. |
Type: Runtime
In future versions of Node.js, `recursive` option will be ignored for `fs.rmdir`, `fs.rmdirSync`, and `fs.promises.rmdir`.
Use `fs.rm(path, { recursive: true, force: true })`, `fs.rmSync(path, { recursive: true, force: true })` or `fs.promises.rm(path, { recursive: true, force: true })` instead.
#### DEP0148: Folder mappings in `"exports"` (trailing `"/"`)
History
| Version | Changes |
| --- | --- |
| v17.0.0 | End-of-Life. |
| v16.0.0 | Runtime deprecation. |
| v15.1.0 | Runtime deprecation for self-referencing imports. |
| v14.13.0 | Documentation-only deprecation. |
Type: Runtime
Using a trailing `"/"` to define subpath folder mappings in the [subpath exports](packages#subpath-exports) or [subpath imports](packages#subpath-imports) fields is deprecated. Use [subpath patterns](packages#subpath-patterns) instead.
#### DEP0149: `http.IncomingMessage#connection`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Documentation-only deprecation. |
Type: Documentation-only.
Prefer [`message.socket`](http#messagesocket) over [`message.connection`](http#messageconnection).
#### DEP0150: Changing the value of `process.config`
History
| Version | Changes |
| --- | --- |
| v18.10.0 | End-of-Life. |
| v16.0.0 | Runtime deprecation. |
Type: End-of-Life
The `process.config` property provides access to Node.js compile-time settings. However, the property is mutable and therefore subject to tampering. The ability to change the value will be removed in a future version of Node.js.
#### DEP0151: Main index lookup and extension searching
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Runtime deprecation. |
| v15.8.0, v14.18.0 | Documentation-only deprecation with `--pending-deprecation` support. |
Type: Runtime
Previously, `index.js` and extension searching lookups would apply to `import 'pkg'` main entry point resolution, even when resolving ES modules.
With this deprecation, all ES module main entry point resolutions require an explicit [`"exports"` or `"main"` entry](packages#main-entry-point-export) with the exact file extension.
#### DEP0152: Extension PerformanceEntry properties
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Runtime deprecation. |
Type: Runtime
The `'gc'`, `'http2'`, and `'http'` [<PerformanceEntry>](perf_hooks#class-performanceentry) object types have additional properties assigned to them that provide additional information. These properties are now available within the standard `detail` property of the `PerformanceEntry` object. The existing accessors have been deprecated and should no longer be used.
#### DEP0153: `dns.lookup` and `dnsPromises.lookup` options type coercion
History
| Version | Changes |
| --- | --- |
| v18.0.0 | End-of-Life. |
| v17.0.0 | Runtime deprecation. |
| v16.8.0 | Documentation-only deprecation. |
Type: End-of-Life
Using a non-nullish non-integer value for `family` option, a non-nullish non-number value for `hints` option, a non-nullish non-boolean value for `all` option, or a non-nullish non-boolean value for `verbatim` option in [`dns.lookup()`](dns#dnslookuphostname-options-callback) and [`dnsPromises.lookup()`](dns#dnspromiseslookuphostname-options) throws an `ERR_INVALID_ARG_TYPE` error.
#### DEP0154: RSA-PSS generate key pair options
History
| Version | Changes |
| --- | --- |
| v16.10.0 | Documentation-only deprecation. |
Type: Documentation-only (supports [`--pending-deprecation`](cli#--pending-deprecation))
The `'hash'` and `'mgf1Hash'` options are replaced with `'hashAlgorithm'` and `'mgf1HashAlgorithm'`.
#### DEP0155: Trailing slashes in pattern specifier resolutions
History
| Version | Changes |
| --- | --- |
| v17.0.0 | Runtime deprecation. |
| v16.10.0 | Documentation-only deprecation with `--pending-deprecation` support. |
Type: Runtime
The remapping of specifiers ending in `"/"` like `import 'pkg/x/'` is deprecated for package `"exports"` and `"imports"` pattern resolutions.
#### DEP0156: `.aborted` property and `'abort'`, `'aborted'` event in `http`
History
| Version | Changes |
| --- | --- |
| v17.0.0, v16.12.0 | Documentation-only deprecation. |
Type: Documentation-only
Move to [<Stream>](stream#stream) API instead, as the [`http.ClientRequest`](http#class-httpclientrequest), [`http.ServerResponse`](http#class-httpserverresponse), and [`http.IncomingMessage`](http#class-httpincomingmessage) are all stream-based. Check `stream.destroyed` instead of the `.aborted` property, and listen for `'close'` instead of `'abort'`, `'aborted'` event.
The `.aborted` property and `'abort'` event are only useful for detecting `.abort()` calls. For closing a request early, use the Stream `.destroy([error])` then check the `.destroyed` property and `'close'` event should have the same effect. The receiving end should also check the [`readable.readableEnded`](stream#readablereadableended) value on [`http.IncomingMessage`](http#class-httpincomingmessage) to get whether it was an aborted or graceful destroy.
#### DEP0157: Thenable support in streams
History
| Version | Changes |
| --- | --- |
| v18.0.0 | End-of-life. |
| v17.2.0, v16.14.0 | Documentation-only deprecation. |
Type: End-of-Life
An undocumented feature of Node.js streams was to support thenables in implementation methods. This is now deprecated, use callbacks instead and avoid use of async function for streams implementation methods.
This feature caused users to encounter unexpected problems where the user implements the function in callback style but uses e.g. an async method which would cause an error since mixing promise and callback semantics is not valid.
```
const w = new Writable({
async final(callback) {
await someOp();
callback();
}
});
```
#### DEP0158: `buffer.slice(start, end)`
History
| Version | Changes |
| --- | --- |
| v17.5.0, v16.15.0 | Documentation-only deprecation. |
Type: Documentation-only
This method was deprecated because it is not compatible with `Uint8Array.prototype.slice()`, which is a superclass of `Buffer`.
Use [`buffer.subarray`](buffer#bufsubarraystart-end) which does the same thing instead.
#### DEP0159: `ERR_INVALID_CALLBACK`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | End-of-Life. |
Type: End-of-Life
This error code was removed due to adding more confusion to the errors used for value type validation.
#### DEP0160: `process.on('multipleResolves', handler)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Runtime deprecation. |
| v17.6.0, v16.15.0 | Documentation-only deprecation. |
Type: Runtime.
This event was deprecated because it did not work with V8 promise combinators which diminished its usefulness.
#### DEP0161: `process._getActiveRequests()` and `process._getActiveHandles()`
History
| Version | Changes |
| --- | --- |
| v17.6.0, v16.15.0 | Documentation-only deprecation. |
Type: Documentation-only
The `process._getActiveHandles()` and `process._getActiveRequests()` functions are not intended for public use and can be removed in future releases.
Use [`process.getActiveResourcesInfo()`](process#processgetactiveresourcesinfo) to get a list of types of active resources and not the actual references.
#### DEP0162: `fs.write()`, `fs.writeFileSync()` coercion to string
History
| Version | Changes |
| --- | --- |
| v18.10.0 | End-of-Life. |
| v18.0.0 | Runtime deprecation. |
| v17.8.0, v16.15.0 | Documentation-only deprecation. |
Type: End-of-Life
Implicit coercion of objects with own `toString` property, passed as second parameter in [`fs.write()`](fs#fswritefd-buffer-offset-length-position-callback), [`fs.writeFile()`](fs#fswritefilefile-data-options-callback), [`fs.appendFile()`](fs#fsappendfilepath-data-options-callback), [`fs.writeFileSync()`](fs#fswritefilesyncfile-data-options), and [`fs.appendFileSync()`](fs#fsappendfilesyncpath-data-options) is deprecated. Convert them to primitive strings.
#### DEP0163: `channel.subscribe(onMessage)`, `channel.unsubscribe(onMessage)`
History
| Version | Changes |
| --- | --- |
| v18.7.0, v16.17.0 | Documentation-only deprecation. |
Type: Documentation-only
These methods were deprecated because they can be used in a way which does not hold the channel reference alive long enough to receive the events.
Use [`diagnostics_channel.subscribe(name, onMessage)`](diagnostics_channel#diagnostics_channelsubscribename-onmessage) or [`diagnostics_channel.unsubscribe(name, onMessage)`](diagnostics_channel#diagnostics_channelunsubscribename-onmessage) which does the same thing instead.
#### DEP0164: `process.exit(code)`, `process.exitCode` coercion to integer
History
| Version | Changes |
| --- | --- |
| v19.0.0 | Runtime deprecation. |
| v18.10.0, v16.18.0 | Documentation-only deprecation of `process.exitCode` integer coercion. |
| v18.7.0, v16.17.0 | Documentation-only deprecation of `process.exit(code)` integer coercion. |
Type: Runtime
Values other than `undefined`, `null`, integer numbers, and integer strings (e.g., `'1'`) are deprecated as value for the `code` parameter in [`process.exit()`](process#processexitcode) and as value to assign to [`process.exitCode`](process#processexitcode_1).
#### DEP0165: `--trace-atomics-wait`
History
| Version | Changes |
| --- | --- |
| v18.8.0, v16.18.0 | Documentation-only deprecation. |
Type: Documentation-only
The [`--trace-atomics-wait`](cli#--trace-atomics-wait) flag is deprecated.
#### DEP0166: Double slashes in imports and exports targets
History
| Version | Changes |
| --- | --- |
| v18.10.0 | Runtime deprecation. |
| v18.10.0 | Documentation-only deprecation with `--pending-deprecation` support. |
Type: Runtime
Package imports and exports targets mapping into paths including a double slash (of *"/"* or *"\"*) are deprecated and will fail with a resolution validation error in a future release. This same deprecation also applies to pattern matches starting or ending in a slash.
#### DEP0167: Weak `DiffieHellmanGroup` instances (`modp1`, `modp2`, `modp5`)
History
| Version | Changes |
| --- | --- |
| v18.10.0, v16.18.0 | Documentation-only deprecation. |
Type: Documentation-only
The well-known MODP groups `modp1`, `modp2`, and `modp5` are deprecated because they are not secure against practical attacks. See [RFC 8247 Section 2.4](https://www.rfc-editor.org/rfc/rfc8247#section-2.4) for details.
These groups might be removed in future versions of Node.js. Applications that rely on these groups should evaluate using stronger MODP groups instead.
#### DEP0168: Unhandled exception in Node-API callbacks
History
| Version | Changes |
| --- | --- |
| v18.3.0, v16.17.0 | Runtime deprecation. |
Type: Runtime
The implicit suppression of uncaught exceptions in Node-API callbacks is now deprecated.
Set the flag [`--force-node-api-uncaught-exceptions-policy`](cli#--force-node-api-uncaught-exceptions-policy) to force Node.js to emit an [`'uncaughtException'`](process#event-uncaughtexception) event if the exception is not handled in Node-API callbacks.
#### DEP0169: Insecure url.parse()
History
| Version | Changes |
| --- | --- |
| v19.0.0 | Documentation-only deprecation. |
Type: Documentation-only
[`url.parse()`](url#urlparseurlstring-parsequerystring-slashesdenotehost) behavior is not standardized and prone to errors that have security implications. Use the [WHATWG URL API](url#the-whatwg-url-api) instead. CVEs are not issued for `url.parse()` vulnerabilities.
| programming_docs |
node None Net
---
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/net.js](https://github.com/nodejs/node/blob/v19.0.1/lib/net.js)
The `node:net` module provides an asynchronous network API for creating stream-based TCP or [IPC](#ipc-support) servers ([`net.createServer()`](#netcreateserveroptions-connectionlistener)) and clients ([`net.createConnection()`](#netcreateconnection)).
It can be accessed using:
```
const net = require('node:net');
```
### IPC support
The `node:net` module supports IPC with named pipes on Windows, and Unix domain sockets on other operating systems.
#### Identifying paths for IPC connections
[`net.connect()`](#netconnect), [`net.createConnection()`](#netcreateconnection), [`server.listen()`](#serverlisten), and [`socket.connect()`](#socketconnect) take a `path` parameter to identify IPC endpoints.
On Unix, the local domain is also known as the Unix domain. The path is a filesystem pathname. It gets truncated to an OS-dependent length of `sizeof(sockaddr_un.sun_path) - 1`. Typical values are 107 bytes on Linux and 103 bytes on macOS. If a Node.js API abstraction creates the Unix domain socket, it will unlink the Unix domain socket as well. For example, [`net.createServer()`](#netcreateserveroptions-connectionlistener) may create a Unix domain socket and [`server.close()`](#serverclosecallback) will unlink it. But if a user creates the Unix domain socket outside of these abstractions, the user will need to remove it. The same applies when a Node.js API creates a Unix domain socket but the program then crashes. In short, a Unix domain socket will be visible in the filesystem and will persist until unlinked.
On Windows, the local domain is implemented using a named pipe. The path *must* refer to an entry in `\\?\pipe\` or `\\.\pipe\`. Any characters are permitted, but the latter may do some processing of pipe names, such as resolving `..` sequences. Despite how it might look, the pipe namespace is flat. Pipes will *not persist*. They are removed when the last reference to them is closed. Unlike Unix domain sockets, Windows will close and remove the pipe when the owning process exits.
JavaScript string escaping requires paths to be specified with extra backslash escaping such as:
```
net.createServer().listen(
path.join('\\\\?\\pipe', process.cwd(), 'myctl'));
```
### Class: `net.BlockList`
Added in: v15.0.0, v14.18.0 The `BlockList` object can be used with some network APIs to specify rules for disabling inbound or outbound access to specific IP addresses, IP ranges, or IP subnets.
####
`blockList.addAddress(address[, type])`
Added in: v15.0.0, v14.18.0 * `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<net.SocketAddress>](net#class-netsocketaddress) An IPv4 or IPv6 address.
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'ipv4'` or `'ipv6'`. **Default:** `'ipv4'`.
Adds a rule to block the given IP address.
####
`blockList.addRange(start, end[, type])`
Added in: v15.0.0, v14.18.0 * `start` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<net.SocketAddress>](net#class-netsocketaddress) The starting IPv4 or IPv6 address in the range.
* `end` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<net.SocketAddress>](net#class-netsocketaddress) The ending IPv4 or IPv6 address in the range.
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'ipv4'` or `'ipv6'`. **Default:** `'ipv4'`.
Adds a rule to block a range of IP addresses from `start` (inclusive) to `end` (inclusive).
####
`blockList.addSubnet(net, prefix[, type])`
Added in: v15.0.0, v14.18.0 * `net` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<net.SocketAddress>](net#class-netsocketaddress) The network IPv4 or IPv6 address.
* `prefix` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of CIDR prefix bits. For IPv4, this must be a value between `0` and `32`. For IPv6, this must be between `0` and `128`.
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'ipv4'` or `'ipv6'`. **Default:** `'ipv4'`.
Adds a rule to block a range of IP addresses specified as a subnet mask.
####
`blockList.check(address[, type])`
Added in: v15.0.0, v14.18.0 * `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<net.SocketAddress>](net#class-netsocketaddress) The IP address to check
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'ipv4'` or `'ipv6'`. **Default:** `'ipv4'`.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given IP address matches any of the rules added to the `BlockList`.
```
const blockList = new net.BlockList();
blockList.addAddress('123.123.123.123');
blockList.addRange('10.0.0.1', '10.0.0.10');
blockList.addSubnet('8592:757c:efae:4e45::', 64, 'ipv6');
console.log(blockList.check('123.123.123.123')); // Prints: true
console.log(blockList.check('10.0.0.3')); // Prints: true
console.log(blockList.check('222.111.111.222')); // Prints: false
// IPv6 notation for IPv4 addresses works:
console.log(blockList.check('::ffff:7b7b:7b7b', 'ipv6')); // Prints: true
console.log(blockList.check('::ffff:123.123.123.123', 'ipv6')); // Prints: true
```
####
`blockList.rules`
Added in: v15.0.0, v14.18.0 * Type: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The list of rules added to the blocklist.
### Class: `net.SocketAddress`
Added in: v15.14.0, v14.18.0 ####
`new net.SocketAddress([options])`
Added in: v15.14.0, v14.18.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The network address as either an IPv4 or IPv6 string. **Default**: `'127.0.0.1'` if `family` is `'ipv4'`; `'::'` if `family` is `'ipv6'`.
+ `family` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) One of either `'ipv4'` or `'ipv6'`. **Default**: `'ipv4'`.
+ `flowlabel` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) An IPv6 flow-label used only if `family` is `'ipv6'`.
+ `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) An IP port.
####
`socketaddress.address`
Added in: v15.14.0, v14.18.0 * Type [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
####
`socketaddress.family`
Added in: v15.14.0, v14.18.0 * Type [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'ipv4'` or `'ipv6'`.
####
`socketaddress.flowlabel`
Added in: v15.14.0, v14.18.0 * Type [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
####
`socketaddress.port`
Added in: v15.14.0, v14.18.0 * Type [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
### Class: `net.Server`
Added in: v0.1.90 * Extends: [<EventEmitter>](events#class-eventemitter)
This class is used to create a TCP or [IPC](#ipc-support) server.
####
`new net.Server([options][, connectionListener])`
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) See [`net.createServer([options][, connectionListener])`](#netcreateserveroptions-connectionlistener).
* `connectionListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Automatically set as a listener for the [`'connection'`](#event-connection) event.
* Returns: [<net.Server>](net#class-netserver)
`net.Server` is an [`EventEmitter`](events#class-eventemitter) with the following events:
#### Event: `'close'`
Added in: v0.5.0 Emitted when the server closes. If connections exist, this event is not emitted until all connections are ended.
#### Event: `'connection'`
Added in: v0.1.90 * [<net.Socket>](net#class-netsocket) The connection object
Emitted when a new connection is made. `socket` is an instance of `net.Socket`.
#### Event: `'error'`
Added in: v0.1.90 * [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Emitted when an error occurs. Unlike [`net.Socket`](#class-netsocket), the [`'close'`](#event-close) event will **not** be emitted directly following this event unless [`server.close()`](#serverclosecallback) is manually called. See the example in discussion of [`server.listen()`](#serverlisten).
#### Event: `'listening'`
Added in: v0.1.90 Emitted when the server has been bound after calling [`server.listen()`](#serverlisten).
#### Event: `'drop'`
Added in: v18.6.0, v16.17.0 When the number of connections reaches the threshold of `server.maxConnections`, the server will drop new connections and emit `'drop'` event instead. If it is a TCP server, the argument is as follows, otherwise the argument is `undefined`.
* `data` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The argument passed to event listener.
+ `localAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Local address.
+ `localPort` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Local port.
+ `localFamily` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Local family.
+ `remoteAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Remote address.
+ `remotePort` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Remote port.
+ `remoteFamily` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Remote IP family. `'IPv4'` or `'IPv6'`.
####
`server.address()`
History
| Version | Changes |
| --- | --- |
| v18.4.0 | The `family` property now returns a string instead of a number. |
| v18.0.0 | The `family` property now returns a number instead of a string. |
| v0.1.90 | Added in: v0.1.90 |
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
Returns the bound `address`, the address `family` name, and `port` of the server as reported by the operating system if listening on an IP socket (useful to find which port was assigned when getting an OS-assigned address): `{ port: 12346, family: 'IPv4', address: '127.0.0.1' }`.
For a server listening on a pipe or Unix domain socket, the name is returned as a string.
```
const server = net.createServer((socket) => {
socket.end('goodbye\n');
}).on('error', (err) => {
// Handle errors here.
throw err;
});
// Grab an arbitrary unused port.
server.listen(() => {
console.log('opened server on', server.address());
});
```
`server.address()` returns `null` before the `'listening'` event has been emitted or after calling `server.close()`.
####
`server.close([callback])`
Added in: v0.1.90 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called when the server is closed.
* Returns: [<net.Server>](net#class-netserver)
Stops the server from accepting new connections and keeps existing connections. This function is asynchronous, the server is finally closed when all connections are ended and the server emits a [`'close'`](#event-close) event. The optional `callback` will be called once the `'close'` event occurs. Unlike that event, it will be called with an `Error` as its only argument if the server was not open when it was closed.
####
`server.getConnections(callback)`
Added in: v0.9.7 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<net.Server>](net#class-netserver)
Asynchronously get the number of concurrent connections on the server. Works when sockets were sent to forks.
Callback should take two arguments `err` and `count`.
####
`server.listen()`
Start a server listening for connections. A `net.Server` can be a TCP or an [IPC](#ipc-support) server depending on what it listens to.
Possible signatures:
* [`server.listen(handle[, backlog][, callback])`](#serverlistenhandle-backlog-callback)
* [`server.listen(options[, callback])`](#serverlistenoptions-callback)
* [`server.listen(path[, backlog][, callback])`](#serverlistenpath-backlog-callback) for [IPC](#ipc-support) servers
* [`server.listen([port[, host[, backlog]]][, callback])`](#serverlistenport-host-backlog-callback) for TCP servers
This function is asynchronous. When the server starts listening, the [`'listening'`](#event-listening) event will be emitted. The last parameter `callback` will be added as a listener for the [`'listening'`](#event-listening) event.
All `listen()` methods can take a `backlog` parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as `tcp_max_syn_backlog` and `somaxconn` on Linux. The default value of this parameter is 511 (not 512).
All [`net.Socket`](#class-netsocket) are set to `SO_REUSEADDR` (see [`socket(7)`](https://man7.org/linux/man-pages/man7/socket.7.html) for details).
The `server.listen()` method can be called again if and only if there was an error during the first `server.listen()` call or `server.close()` has been called. Otherwise, an `ERR_SERVER_ALREADY_LISTEN` error will be thrown.
One of the most common errors raised when listening is `EADDRINUSE`. This happens when another server is already listening on the requested `port`/`path`/`handle`. One way to handle this would be to retry after a certain amount of time:
```
server.on('error', (e) => {
if (e.code === 'EADDRINUSE') {
console.log('Address in use, retrying...');
setTimeout(() => {
server.close();
server.listen(PORT, HOST);
}, 1000);
}
});
```
#####
`server.listen(handle[, backlog][, callback])`
Added in: v0.5.10 * `handle` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `backlog` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Common parameter of [`server.listen()`](#serverlisten) functions
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<net.Server>](net#class-netserver)
Start a server listening for connections on a given `handle` that has already been bound to a port, a Unix domain socket, or a Windows named pipe.
The `handle` object can be either a server, a socket (anything with an underlying `_handle` member), or an object with an `fd` member that is a valid file descriptor.
Listening on a file descriptor is not supported on Windows.
#####
`server.listen(options[, callback])`
History
| Version | Changes |
| --- | --- |
| v15.6.0 | AbortSignal support was added. |
| v11.4.0 | The `ipv6Only` option is supported. |
| v0.11.14 | Added in: v0.11.14 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Required. Supports the following properties:
+ `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Will be ignored if `port` is specified. See [Identifying paths for IPC connections](#identifying-paths-for-ipc-connections).
+ `backlog` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Common parameter of [`server.listen()`](#serverlisten) functions.
+ `exclusive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
+ `readableAll` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) For IPC servers makes the pipe readable for all users. **Default:** `false`.
+ `writableAll` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) For IPC servers makes the pipe writable for all users. **Default:** `false`.
+ `ipv6Only` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) For TCP servers, setting `ipv6Only` to `true` will disable dual-stack support, i.e., binding to host `::` won't make `0.0.0.0` be bound. **Default:** `false`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) An AbortSignal that may be used to close a listening server.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) functions.
* Returns: [<net.Server>](net#class-netserver)
If `port` is specified, it behaves the same as [`server.listen([port[, host[, backlog]]][, callback])`](#serverlistenport-host-backlog-callback). Otherwise, if `path` is specified, it behaves the same as [`server.listen(path[, backlog][, callback])`](#serverlistenpath-backlog-callback). If none of them is specified, an error will be thrown.
If `exclusive` is `false` (default), then cluster workers will use the same underlying handle, allowing connection handling duties to be shared. When `exclusive` is `true`, the handle is not shared, and attempted port sharing results in an error. An example which listens on an exclusive port is shown below.
```
server.listen({
host: 'localhost',
port: 80,
exclusive: true
});
```
When `exclusive` is `true` and the underlying handle is shared, it is possible that several workers query a handle with different backlogs. In this case, the first `backlog` passed to the master process will be used.
Starting an IPC server as root may cause the server path to be inaccessible for unprivileged users. Using `readableAll` and `writableAll` will make the server accessible for all users.
If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.close()` on the server:
```
const controller = new AbortController();
server.listen({
host: 'localhost',
port: 80,
signal: controller.signal
});
// Later, when you want to close the server.
controller.abort();
```
#####
`server.listen(path[, backlog][, callback])`
Added in: v0.1.90 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Path the server should listen to. See [Identifying paths for IPC connections](#identifying-paths-for-ipc-connections).
* `backlog` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Common parameter of [`server.listen()`](#serverlisten) functions.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function).
* Returns: [<net.Server>](net#class-netserver)
Start an [IPC](#ipc-support) server listening for connections on the given `path`.
#####
`server.listen([port[, host[, backlog]]][, callback])`
Added in: v0.1.90 * `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `backlog` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Common parameter of [`server.listen()`](#serverlisten) functions.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function).
* Returns: [<net.Server>](net#class-netserver)
Start a TCP server listening for connections on the given `port` and `host`.
If `port` is omitted or is 0, the operating system will assign an arbitrary unused port, which can be retrieved by using `server.address().port` after the [`'listening'`](#event-listening) event has been emitted.
If `host` is omitted, the server will accept connections on the [unspecified IPv6 address](https://en.wikipedia.org/wiki/IPv6_address#Unspecified_address) (`::`) when IPv6 is available, or the [unspecified IPv4 address](https://en.wikipedia.org/wiki/0.0.0.0) (`0.0.0.0`) otherwise.
In most operating systems, listening to the [unspecified IPv6 address](https://en.wikipedia.org/wiki/IPv6_address#Unspecified_address) (`::`) may cause the `net.Server` to also listen on the [unspecified IPv4 address](https://en.wikipedia.org/wiki/0.0.0.0) (`0.0.0.0`).
####
`server.listening`
Added in: v5.7.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Indicates whether or not the server is listening for connections.
####
`server.maxConnections`
Added in: v0.2.0 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Set this property to reject connections when the server's connection count gets high.
It is not recommended to use this option once a socket has been sent to a child with [`child_process.fork()`](child_process#child_processforkmodulepath-args-options).
####
`server.ref()`
Added in: v0.9.1 * Returns: [<net.Server>](net#class-netserver)
Opposite of `unref()`, calling `ref()` on a previously `unref`ed server will *not* let the program exit if it's the only server left (the default behavior). If the server is `ref`ed calling `ref()` again will have no effect.
####
`server.unref()`
Added in: v0.9.1 * Returns: [<net.Server>](net#class-netserver)
Calling `unref()` on a server will allow the program to exit if this is the only active server in the event system. If the server is already `unref`ed calling `unref()` again will have no effect.
### Class: `net.Socket`
Added in: v0.3.4 * Extends: [<stream.Duplex>](stream#class-streamduplex)
This class is an abstraction of a TCP socket or a streaming [IPC](#ipc-support) endpoint (uses named pipes on Windows, and Unix domain sockets otherwise). It is also an [`EventEmitter`](events#class-eventemitter).
A `net.Socket` can be created by the user and used directly to interact with a server. For example, it is returned by [`net.createConnection()`](#netcreateconnection), so the user can use it to talk to the server.
It can also be created by Node.js and passed to the user when a connection is received. For example, it is passed to the listeners of a [`'connection'`](#event-connection) event emitted on a [`net.Server`](#class-netserver), so the user can use it to interact with the client.
####
`new net.Socket([options])`
History
| Version | Changes |
| --- | --- |
| v15.14.0 | AbortSignal support was added. |
| v0.3.4 | Added in: v0.3.4 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Available options are:
+ `fd` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If specified, wrap around an existing socket with the given file descriptor, otherwise a new socket will be created.
+ `allowHalfOpen` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `false`, then the socket will automatically end the writable side when the readable side ends. See [`net.createServer()`](#netcreateserveroptions-connectionlistener) and the [`'end'`](#event-end) event for details. **Default:** `false`.
+ `readable` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Allow reads on the socket when an `fd` is passed, otherwise ignored. **Default:** `false`.
+ `writable` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Allow writes on the socket when an `fd` is passed, otherwise ignored. **Default:** `false`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) An Abort signal that may be used to destroy the socket.
* Returns: [<net.Socket>](net#class-netsocket)
Creates a new socket object.
The newly created socket can be either a TCP socket or a streaming [IPC](#ipc-support) endpoint, depending on what it [`connect()`](#socketconnect) to.
#### Event: `'close'`
Added in: v0.1.90 * `hadError` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the socket had a transmission error.
Emitted once the socket is fully closed. The argument `hadError` is a boolean which says if the socket was closed due to a transmission error.
#### Event: `'connect'`
Added in: v0.1.90 Emitted when a socket connection is successfully established. See [`net.createConnection()`](#netcreateconnection).
#### Event: `'data'`
Added in: v0.1.90 * [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Emitted when data is received. The argument `data` will be a `Buffer` or `String`. Encoding of data is set by [`socket.setEncoding()`](#socketsetencodingencoding).
The data will be lost if there is no listener when a `Socket` emits a `'data'` event.
#### Event: `'drain'`
Added in: v0.1.90 Emitted when the write buffer becomes empty. Can be used to throttle uploads.
See also: the return values of `socket.write()`.
#### Event: `'end'`
Added in: v0.1.90 Emitted when the other end of the socket signals the end of transmission, thus ending the readable side of the socket.
By default (`allowHalfOpen` is `false`) the socket will send an end of transmission packet back and destroy its file descriptor once it has written out its pending write queue. However, if `allowHalfOpen` is set to `true`, the socket will not automatically [`end()`](#socketenddata-encoding-callback) its writable side, allowing the user to write arbitrary amounts of data. The user must call [`end()`](#socketenddata-encoding-callback) explicitly to close the connection (i.e. sending a FIN packet back).
#### Event: `'error'`
Added in: v0.1.90 * [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Emitted when an error occurs. The `'close'` event will be called directly following this event.
#### Event: `'lookup'`
History
| Version | Changes |
| --- | --- |
| v5.10.0 | The `host` parameter is supported now. |
| v0.11.3 | Added in: v0.11.3 |
Emitted after resolving the host name but before connecting. Not applicable to Unix sockets.
* `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The error object. See [`dns.lookup()`](dns#dnslookuphostname-options-callback).
* `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The IP address.
* `family` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The address type. See [`dns.lookup()`](dns#dnslookuphostname-options-callback).
* `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The host name.
#### Event: `'ready'`
Added in: v9.11.0 Emitted when a socket is ready to be used.
Triggered immediately after `'connect'`.
#### Event: `'timeout'`
Added in: v0.1.90 Emitted if the socket times out from inactivity. This is only to notify that the socket has been idle. The user must manually close the connection.
See also: [`socket.setTimeout()`](#socketsettimeouttimeout-callback).
####
`socket.address()`
History
| Version | Changes |
| --- | --- |
| v18.4.0 | The `family` property now returns a string instead of a number. |
| v18.0.0 | The `family` property now returns a number instead of a string. |
| v0.1.90 | Added in: v0.1.90 |
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns the bound `address`, the address `family` name and `port` of the socket as reported by the operating system: `{ port: 12346, family: 'IPv4', address: '127.0.0.1' }`
####
`socket.bufferSize`
Added in: v0.3.8Deprecated since: v14.6.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`writable.writableLength`](stream#writablewritablelength) instead.
* [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
This property shows the number of characters buffered for writing. The buffer may contain strings whose length after encoding is not yet known. So this number is only an approximation of the number of bytes in the buffer.
`net.Socket` has the property that `socket.write()` always works. This is to help users get up and running quickly. The computer cannot always keep up with the amount of data that is written to a socket. The network connection simply might be too slow. Node.js will internally queue up the data written to a socket and send it out over the wire when it is possible.
The consequence of this internal buffering is that memory may grow. Users who experience large or growing `bufferSize` should attempt to "throttle" the data flows in their program with [`socket.pause()`](#socketpause) and [`socket.resume()`](#socketresume).
####
`socket.bytesRead`
Added in: v0.5.3 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The amount of received bytes.
####
`socket.bytesWritten`
Added in: v0.5.3 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The amount of bytes sent.
####
`socket.connect()`
Initiate a connection on a given socket.
Possible signatures:
* [`socket.connect(options[, connectListener])`](#socketconnectoptions-connectlistener)
* [`socket.connect(path[, connectListener])`](#socketconnectpath-connectlistener) for [IPC](#ipc-support) connections.
* [`socket.connect(port[, host][, connectListener])`](#socketconnectport-host-connectlistener) for TCP connections.
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
This function is asynchronous. When the connection is established, the [`'connect'`](#event-connect) event will be emitted. If there is a problem connecting, instead of a [`'connect'`](#event-connect) event, an [`'error'`](#event-error_1) event will be emitted with the error passed to the [`'error'`](#event-error_1) listener. The last parameter `connectListener`, if supplied, will be added as a listener for the [`'connect'`](#event-connect) event **once**.
This function should only be used for reconnecting a socket after `'close'` has been emitted or otherwise it may lead to undefined behavior.
#####
`socket.connect(options[, connectListener])`
History
| Version | Changes |
| --- | --- |
| v17.7.0, v16.15.0 | The `noDelay`, `keepAlive`, and `keepAliveInitialDelay` options are supported now. |
| v12.10.0 | Added `onread` option. |
| v6.0.0 | The `hints` option defaults to `0` in all cases now. Previously, in the absence of the `family` option it would default to `dns.ADDRCONFIG | dns.V4MAPPED`. |
| v5.11.0 | The `hints` option is supported now. |
| v0.1.90 | Added in: v0.1.90 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `connectListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Common parameter of [`socket.connect()`](#socketconnect) methods. Will be added as a listener for the [`'connect'`](#event-connect) event once.
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Initiate a connection on a given socket. Normally this method is not needed, the socket should be created and opened with [`net.createConnection()`](#netcreateconnection). Use this only when implementing a custom Socket.
For TCP connections, available `options` are:
* `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Required. Port the socket should connect to.
* `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host the socket should connect to. **Default:** `'localhost'`.
* `localAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Local address the socket should connect from.
* `localPort` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Local port the socket should connect from.
* `family` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type): Version of IP stack. Must be `4`, `6`, or `0`. The value `0` indicates that both IPv4 and IPv6 addresses are allowed. **Default:** `0`.
* `hints` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optional [`dns.lookup()` hints](dns#supported-getaddrinfo-flags).
* `lookup` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Custom lookup function. **Default:** [`dns.lookup()`](dns#dnslookuphostname-options-callback).
* `noDelay` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `true`, it disables the use of Nagle's algorithm immediately after the socket is established. **Default:** `false`.
* `keepAlive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `true`, it enables keep-alive functionality on the socket immediately after the connection is established, similarly on what is done in [`socket.setKeepAlive([enable][, initialDelay])`](#socketsetkeepaliveenable-initialdelay). **Default:** `false`.
* `keepAliveInitialDelay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If set to a positive number, it sets the initial delay before the first keepalive probe is sent on an idle socket.**Default:** `0`.
For [IPC](#ipc-support) connections, available `options` are:
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Required. Path the client should connect to. See [Identifying paths for IPC connections](#identifying-paths-for-ipc-connections). If provided, the TCP-specific options above are ignored.
For both types, available `options` include:
* `onread` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) If specified, incoming data is stored in a single `buffer` and passed to the supplied `callback` when data arrives on the socket. This will cause the streaming functionality to not provide any data. The socket will emit events like `'error'`, `'end'`, and `'close'` as usual. Methods like `pause()` and `resume()` will also behave as expected.
+ `buffer` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Either a reusable chunk of memory to use for storing incoming data or a function that returns such.
+ `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) This function is called for every chunk of incoming data. Two arguments are passed to it: the number of bytes written to `buffer` and a reference to `buffer`. Return `false` from this function to implicitly `pause()` the socket. This function will be executed in the global context.
Following is an example of a client using the `onread` option:
```
const net = require('node:net');
net.connect({
port: 80,
onread: {
// Reuses a 4KiB Buffer for every read from the socket.
buffer: Buffer.alloc(4 * 1024),
callback: function(nread, buf) {
// Received data is available in `buf` from 0 to `nread`.
console.log(buf.toString('utf8', 0, nread));
}
}
});
```
#####
`socket.connect(path[, connectListener])`
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Path the client should connect to. See [Identifying paths for IPC connections](#identifying-paths-for-ipc-connections).
* `connectListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Common parameter of [`socket.connect()`](#socketconnect) methods. Will be added as a listener for the [`'connect'`](#event-connect) event once.
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Initiate an [IPC](#ipc-support) connection on the given socket.
Alias to [`socket.connect(options[, connectListener])`](#socketconnectoptions-connectlistener) called with `{ path: path }` as `options`.
#####
`socket.connect(port[, host][, connectListener])`
Added in: v0.1.90 * `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Port the client should connect to.
* `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host the client should connect to.
* `connectListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Common parameter of [`socket.connect()`](#socketconnect) methods. Will be added as a listener for the [`'connect'`](#event-connect) event once.
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Initiate a TCP connection on the given socket.
Alias to [`socket.connect(options[, connectListener])`](#socketconnectoptions-connectlistener) called with `{port: port, host: host}` as `options`.
####
`socket.connecting`
Added in: v6.1.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If `true`, [`socket.connect(options[, connectListener])`](#socketconnectoptions-connectlistener) was called and has not yet finished. It will stay `true` until the socket becomes connected, then it is set to `false` and the `'connect'` event is emitted. Note that the [`socket.connect(options[, connectListener])`](#socketconnectoptions-connectlistener) callback is a listener for the `'connect'` event.
####
`socket.destroy([error])`
Added in: v0.1.90 * `error` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<net.Socket>](net#class-netsocket)
Ensures that no more I/O activity happens on this socket. Destroys the stream and closes the connection.
See [`writable.destroy()`](stream#writabledestroyerror) for further details.
####
`socket.destroyed`
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Indicates if the connection is destroyed or not. Once a connection is destroyed no further data can be transferred using it.
See [`writable.destroyed`](stream#writabledestroyed) for further details.
####
`socket.end([data[, encoding]][, callback])`
Added in: v0.1.90 * `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Only used when data is `string`. **Default:** `'utf8'`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Optional callback for when the socket is finished.
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data.
See [`writable.end()`](stream#writableendchunk-encoding-callback) for further details.
####
`socket.localAddress`
Added in: v0.9.6 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The string representation of the local IP address the remote client is connecting on. For example, in a server listening on `'0.0.0.0'`, if a client connects on `'192.168.1.1'`, the value of `socket.localAddress` would be `'192.168.1.1'`.
####
`socket.localPort`
Added in: v0.9.6 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The numeric representation of the local port. For example, `80` or `21`.
####
`socket.localFamily`
Added in: v18.8.0, v16.18.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The string representation of the local IP family. `'IPv4'` or `'IPv6'`.
####
`socket.pause()`
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Pauses the reading of data. That is, [`'data'`](#event-data) events will not be emitted. Useful to throttle back an upload.
####
`socket.pending`
Added in: v11.2.0, v10.16.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
This is `true` if the socket is not connected yet, either because `.connect()` has not yet been called or because it is still in the process of connecting (see [`socket.connecting`](#socketconnecting)).
####
`socket.ref()`
Added in: v0.9.1 * Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Opposite of `unref()`, calling `ref()` on a previously `unref`ed socket will *not* let the program exit if it's the only socket left (the default behavior). If the socket is `ref`ed calling `ref` again will have no effect.
####
`socket.remoteAddress`
Added in: v0.5.10 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The string representation of the remote IP address. For example, `'74.125.127.100'` or `'2001:4860:a005::68'`. Value may be `undefined` if the socket is destroyed (for example, if the client disconnected).
####
`socket.remoteFamily`
Added in: v0.11.14 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The string representation of the remote IP family. `'IPv4'` or `'IPv6'`.
####
`socket.remotePort`
Added in: v0.5.10 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The numeric representation of the remote port. For example, `80` or `21`.
####
`socket.resetAndDestroy()`
Added in: v18.3.0, v16.17.0 * Returns: [<net.Socket>](net#class-netsocket)
Close the TCP connection by sending an RST packet and destroy the stream. If this TCP socket is in connecting status, it will send an RST packet and destroy this TCP socket once it is connected. Otherwise, it will call `socket.destroy` with an `ERR_SOCKET_CLOSED` Error. If this is not a TCP socket (for example, a pipe), calling this method will immediately throw an `ERR_INVALID_HANDLE_TYPE` Error.
####
`socket.resume()`
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Resumes reading after a call to [`socket.pause()`](#socketpause).
####
`socket.setEncoding([encoding])`
Added in: v0.1.90 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Set the encoding for the socket as a [Readable Stream](stream#class-streamreadable). See [`readable.setEncoding()`](stream#readablesetencodingencoding) for more information.
####
`socket.setKeepAlive([enable][, initialDelay])`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | New defaults for `TCP_KEEPCNT` and `TCP_KEEPINTVL` socket options were added. |
| v0.1.92 | Added in: v0.1.92 |
* `enable` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
* `initialDelay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Enable/disable keep-alive functionality, and optionally set the initial delay before the first keepalive probe is sent on an idle socket.
Set `initialDelay` (in milliseconds) to set the delay between the last data packet received and the first keepalive probe. Setting `0` for `initialDelay` will leave the value unchanged from the default (or previous) setting.
Enabling the keep-alive functionality will set the following socket options:
* `SO_KEEPALIVE=1`
* `TCP_KEEPIDLE=initialDelay`
* `TCP_KEEPCNT=10`
* `TCP_KEEPINTVL=1`
####
`socket.setNoDelay([noDelay])`
Added in: v0.1.90 * `noDelay` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Enable/disable the use of Nagle's algorithm.
When a TCP connection is created, it will have Nagle's algorithm enabled.
Nagle's algorithm delays data before it is sent via the network. It attempts to optimize throughput at the expense of latency.
Passing `true` for `noDelay` or not passing an argument will disable Nagle's algorithm for the socket. Passing `false` for `noDelay` will enable Nagle's algorithm.
####
`socket.setTimeout(timeout[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.1.90 | Added in: v0.1.90 |
* `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Sets the socket to timeout after `timeout` milliseconds of inactivity on the socket. By default `net.Socket` do not have a timeout.
When an idle timeout is triggered the socket will receive a [`'timeout'`](#event-timeout) event but the connection will not be severed. The user must manually call [`socket.end()`](#socketenddata-encoding-callback) or [`socket.destroy()`](#socketdestroyerror) to end the connection.
```
socket.setTimeout(3000);
socket.on('timeout', () => {
console.log('socket timeout');
socket.end();
});
```
If `timeout` is 0, then the existing idle timeout is disabled.
The optional `callback` parameter will be added as a one-time listener for the [`'timeout'`](#event-timeout) event.
####
`socket.timeout`
Added in: v10.7.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
The socket timeout in milliseconds as set by [`socket.setTimeout()`](#socketsettimeouttimeout-callback). It is `undefined` if a timeout has not been set.
####
`socket.unref()`
Added in: v0.9.1 * Returns: [<net.Socket>](net#class-netsocket) The socket itself.
Calling `unref()` on a socket will allow the program to exit if this is the only active socket in the event system. If the socket is already `unref`ed calling `unref()` again will have no effect.
####
`socket.write(data[, encoding][, callback])`
Added in: v0.1.90 * `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Only used when data is `string`. **Default:** `utf8`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Sends data on the socket. The second parameter specifies the encoding in the case of a string. It defaults to UTF8 encoding.
Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in user memory. [`'drain'`](#event-drain) will be emitted when the buffer is again free.
The optional `callback` parameter will be executed when the data is finally written out, which may not be immediately.
See `Writable` stream [`write()`](stream#writablewritechunk-encoding-callback) method for more information.
####
`socket.readyState`
Added in: v0.5.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
This property represents the state of the connection as a string.
* If the stream is connecting `socket.readyState` is `opening`.
* If the stream is readable and writable, it is `open`.
* If the stream is readable and not writable, it is `readOnly`.
* If the stream is not readable and writable, it is `writeOnly`.
###
`net.connect()`
Aliases to [`net.createConnection()`](#netcreateconnection).
Possible signatures:
* [`net.connect(options[, connectListener])`](#netconnectoptions-connectlistener)
* [`net.connect(path[, connectListener])`](#netconnectpath-connectlistener) for [IPC](#ipc-support) connections.
* [`net.connect(port[, host][, connectListener])`](#netconnectport-host-connectlistener) for TCP connections.
####
`net.connect(options[, connectListener])`
Added in: v0.7.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `connectListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<net.Socket>](net#class-netsocket)
Alias to [`net.createConnection(options[, connectListener])`](#netcreateconnectionoptions-connectlistener).
####
`net.connect(path[, connectListener])`
Added in: v0.1.90 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `connectListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<net.Socket>](net#class-netsocket)
Alias to [`net.createConnection(path[, connectListener])`](#netcreateconnectionpath-connectlistener).
####
`net.connect(port[, host][, connectListener])`
Added in: v0.1.90 * `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `connectListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<net.Socket>](net#class-netsocket)
Alias to [`net.createConnection(port[, host][, connectListener])`](#netcreateconnectionport-host-connectlistener).
###
`net.createConnection()`
A factory function, which creates a new [`net.Socket`](#class-netsocket), immediately initiates connection with [`socket.connect()`](#socketconnect), then returns the `net.Socket` that starts the connection.
When the connection is established, a [`'connect'`](#event-connect) event will be emitted on the returned socket. The last parameter `connectListener`, if supplied, will be added as a listener for the [`'connect'`](#event-connect) event **once**.
Possible signatures:
* [`net.createConnection(options[, connectListener])`](#netcreateconnectionoptions-connectlistener)
* [`net.createConnection(path[, connectListener])`](#netcreateconnectionpath-connectlistener) for [IPC](#ipc-support) connections.
* [`net.createConnection(port[, host][, connectListener])`](#netcreateconnectionport-host-connectlistener) for TCP connections.
The [`net.connect()`](#netconnect) function is an alias to this function.
####
`net.createConnection(options[, connectListener])`
Added in: v0.1.90 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Required. Will be passed to both the [`new net.Socket([options])`](#new-netsocketoptions) call and the [`socket.connect(options[, connectListener])`](#socketconnectoptions-connectlistener) method.
* `connectListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Common parameter of the [`net.createConnection()`](#netcreateconnection) functions. If supplied, will be added as a listener for the [`'connect'`](#event-connect) event on the returned socket once.
* Returns: [<net.Socket>](net#class-netsocket) The newly created socket used to start the connection.
For available options, see [`new net.Socket([options])`](#new-netsocketoptions) and [`socket.connect(options[, connectListener])`](#socketconnectoptions-connectlistener).
Additional options:
* `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If set, will be used to call [`socket.setTimeout(timeout)`](#socketsettimeouttimeout-callback) after the socket is created, but before it starts the connection.
Following is an example of a client of the echo server described in the [`net.createServer()`](#netcreateserveroptions-connectionlistener) section:
```
const net = require('node:net');
const client = net.createConnection({ port: 8124 }, () => {
// 'connect' listener.
console.log('connected to server!');
client.write('world!\r\n');
});
client.on('data', (data) => {
console.log(data.toString());
client.end();
});
client.on('end', () => {
console.log('disconnected from server');
});
```
To connect on the socket `/tmp/echo.sock`:
```
const client = net.createConnection({ path: '/tmp/echo.sock' });
```
####
`net.createConnection(path[, connectListener])`
Added in: v0.1.90 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Path the socket should connect to. Will be passed to [`socket.connect(path[, connectListener])`](#socketconnectpath-connectlistener). See [Identifying paths for IPC connections](#identifying-paths-for-ipc-connections).
* `connectListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Common parameter of the [`net.createConnection()`](#netcreateconnection) functions, an "once" listener for the `'connect'` event on the initiating socket. Will be passed to [`socket.connect(path[, connectListener])`](#socketconnectpath-connectlistener).
* Returns: [<net.Socket>](net#class-netsocket) The newly created socket used to start the connection.
Initiates an [IPC](#ipc-support) connection.
This function creates a new [`net.Socket`](#class-netsocket) with all options set to default, immediately initiates connection with [`socket.connect(path[, connectListener])`](#socketconnectpath-connectlistener), then returns the `net.Socket` that starts the connection.
####
`net.createConnection(port[, host][, connectListener])`
Added in: v0.1.90 * `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Port the socket should connect to. Will be passed to [`socket.connect(port[, host][, connectListener])`](#socketconnectport-host-connectlistener).
* `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host the socket should connect to. Will be passed to [`socket.connect(port[, host][, connectListener])`](#socketconnectport-host-connectlistener). **Default:** `'localhost'`.
* `connectListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Common parameter of the [`net.createConnection()`](#netcreateconnection) functions, an "once" listener for the `'connect'` event on the initiating socket. Will be passed to [`socket.connect(port[, host][, connectListener])`](#socketconnectport-host-connectlistener).
* Returns: [<net.Socket>](net#class-netsocket) The newly created socket used to start the connection.
Initiates a TCP connection.
This function creates a new [`net.Socket`](#class-netsocket) with all options set to default, immediately initiates connection with [`socket.connect(port[, host][, connectListener])`](#socketconnectport-host-connectlistener), then returns the `net.Socket` that starts the connection.
###
`net.createServer([options][, connectionListener])`
History
| Version | Changes |
| --- | --- |
| v17.7.0, v16.15.0 | The `noDelay`, `keepAlive`, and `keepAliveInitialDelay` options are supported now. |
| v0.5.0 | Added in: v0.5.0 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `allowHalfOpen` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `false`, then the socket will automatically end the writable side when the readable side ends. **Default:** `false`.
+ `pauseOnConnect` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Indicates whether the socket should be paused on incoming connections. **Default:** `false`.
+ `noDelay` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `true`, it disables the use of Nagle's algorithm immediately after a new incoming connection is received. **Default:** `false`.
+ `keepAlive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `true`, it enables keep-alive functionality on the socket immediately after a new incoming connection is received, similarly on what is done in [`socket.setKeepAlive([enable][, initialDelay])`](#socketsetkeepaliveenable-initialdelay). **Default:** `false`.
+ `keepAliveInitialDelay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If set to a positive number, it sets the initial delay before the first keepalive probe is sent on an idle socket.**Default:** `0`.
* `connectionListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Automatically set as a listener for the [`'connection'`](#event-connection) event.
* Returns: [<net.Server>](net#class-netserver)
Creates a new TCP or [IPC](#ipc-support) server.
If `allowHalfOpen` is set to `true`, when the other end of the socket signals the end of transmission, the server will only send back the end of transmission when [`socket.end()`](#socketenddata-encoding-callback) is explicitly called. For example, in the context of TCP, when a FIN packed is received, a FIN packed is sent back only when [`socket.end()`](#socketenddata-encoding-callback) is explicitly called. Until then the connection is half-closed (non-readable but still writable). See [`'end'`](#event-end) event and [RFC 1122](https://tools.ietf.org/html/rfc1122) (section 4.2.2.13) for more information.
If `pauseOnConnect` is set to `true`, then the socket associated with each incoming connection will be paused, and no data will be read from its handle. This allows connections to be passed between processes without any data being read by the original process. To begin reading data from a paused socket, call [`socket.resume()`](#socketresume).
The server can be a TCP server or an [IPC](#ipc-support) server, depending on what it [`listen()`](#serverlisten) to.
Here is an example of a TCP echo server which listens for connections on port 8124:
```
const net = require('node:net');
const server = net.createServer((c) => {
// 'connection' listener.
console.log('client connected');
c.on('end', () => {
console.log('client disconnected');
});
c.write('hello\r\n');
c.pipe(c);
});
server.on('error', (err) => {
throw err;
});
server.listen(8124, () => {
console.log('server bound');
});
```
Test this by using `telnet`:
```
$ telnet localhost 8124
```
To listen on the socket `/tmp/echo.sock`:
```
server.listen('/tmp/echo.sock', () => {
console.log('server bound');
});
```
Use `nc` to connect to a Unix domain socket server:
```
$ nc -U /tmp/echo.sock
```
###
`net.isIP(input)`
Added in: v0.3.0 * `input` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns `6` if `input` is an IPv6 address. Returns `4` if `input` is an IPv4 address in [dot-decimal notation](https://en.wikipedia.org/wiki/Dot-decimal_notation) with no leading zeroes. Otherwise, returns `0`.
```
net.isIP('::1'); // returns 6
net.isIP('127.0.0.1'); // returns 4
net.isIP('127.000.000.001'); // returns 0
net.isIP('127.0.0.1/24'); // returns 0
net.isIP('fhqwhgads'); // returns 0
```
###
`net.isIPv4(input)`
Added in: v0.3.0 * `input` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if `input` is an IPv4 address in [dot-decimal notation](https://en.wikipedia.org/wiki/Dot-decimal_notation) with no leading zeroes. Otherwise, returns `false`.
```
net.isIPv4('127.0.0.1'); // returns true
net.isIPv4('127.000.000.001'); // returns false
net.isIPv4('127.0.0.1/24'); // returns false
net.isIPv4('fhqwhgads'); // returns false
```
###
`net.isIPv6(input)`
Added in: v0.3.0 * `input` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if `input` is an IPv6 address. Otherwise, returns `false`.
```
net.isIPv6('::1'); // returns true
net.isIPv6('fhqwhgads'); // returns false
```
| programming_docs |
node None Internationalization support
----------------------------
Node.js has many features that make it easier to write internationalized programs. Some of them are:
* Locale-sensitive or Unicode-aware functions in the [ECMAScript Language Specification](https://tc39.github.io/ecma262/):
+ [`String.prototype.normalize()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize)
+ [`String.prototype.toLowerCase()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toLowerCase)
+ [`String.prototype.toUpperCase()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toUpperCase)
* All functionality described in the [ECMAScript Internationalization API Specification](https://tc39.github.io/ecma402/) (aka ECMA-402):
+ [`Intl`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl) object
+ Locale-sensitive methods like [`String.prototype.localeCompare()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare) and [`Date.prototype.toLocaleString()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toLocaleString)
* The [WHATWG URL parser](url#the-whatwg-url-api)'s [internationalized domain names](https://en.wikipedia.org/wiki/Internationalized_domain_name) (IDNs) support
* [`require('node:buffer').transcode()`](buffer#buffertranscodesource-fromenc-toenc)
* More accurate [REPL](repl#repl) line editing
* [`require('node:util').TextDecoder`](util#class-utiltextdecoder)
* [`RegExp` Unicode Property Escapes](https://github.com/tc39/proposal-regexp-unicode-property-escapes)
Node.js and the underlying V8 engine use [International Components for Unicode (ICU)](http://site.icu-project.org/) to implement these features in native C/C++ code. The full ICU data set is provided by Node.js by default. However, due to the size of the ICU data file, several options are provided for customizing the ICU data set either when building or running Node.js.
### Options for building Node.js
To control how ICU is used in Node.js, four `configure` options are available during compilation. Additional details on how to compile Node.js are documented in [BUILDING.md](https://github.com/nodejs/node/blob/HEAD/BUILDING.md).
* `--with-intl=none`/`--without-intl`
* `--with-intl=system-icu`
* `--with-intl=small-icu`
* `--with-intl=full-icu` (default)
An overview of available Node.js and JavaScript features for each `configure` option:
| Feature | `none` | `system-icu` | `small-icu` | `full-icu` |
| --- | --- | --- | --- | --- |
| [`String.prototype.normalize()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize) | none (function is no-op) | full | full | full |
| `String.prototype.to*Case()` | full | full | full | full |
| [`Intl`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl) | none (object does not exist) | partial/full (depends on OS) | partial (English-only) | full |
| [`String.prototype.localeCompare()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare) | partial (not locale-aware) | full | full | full |
| `String.prototype.toLocale*Case()` | partial (not locale-aware) | full | full | full |
| [`Number.prototype.toLocaleString()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toLocaleString) | partial (not locale-aware) | partial/full (depends on OS) | partial (English-only) | full |
| `Date.prototype.toLocale*String()` | partial (not locale-aware) | partial/full (depends on OS) | partial (English-only) | full |
| [Legacy URL Parser](url#legacy-url-api) | partial (no IDN support) | full | full | full |
| [WHATWG URL Parser](url#the-whatwg-url-api) | partial (no IDN support) | full | full | full |
| [`require('node:buffer').transcode()`](buffer#buffertranscodesource-fromenc-toenc) | none (function does not exist) | full | full | full |
| [REPL](repl#repl) | partial (inaccurate line editing) | full | full | full |
| [`require('node:util').TextDecoder`](util#class-utiltextdecoder) | partial (basic encodings support) | partial/full (depends on OS) | partial (Unicode-only) | full |
| [`RegExp` Unicode Property Escapes](https://github.com/tc39/proposal-regexp-unicode-property-escapes) | none (invalid `RegExp` error) | full | full | full |
The "(not locale-aware)" designation denotes that the function carries out its operation just like the non-`Locale` version of the function, if one exists. For example, under `none` mode, `Date.prototype.toLocaleString()`'s operation is identical to that of `Date.prototype.toString()`.
#### Disable all internationalization features (`none`)
If this option is chosen, ICU is disabled and most internationalization features mentioned above will be **unavailable** in the resulting `node` binary.
#### Build with a pre-installed ICU (`system-icu`)
Node.js can link against an ICU build already installed on the system. In fact, most Linux distributions already come with ICU installed, and this option would make it possible to reuse the same set of data used by other components in the OS.
Functionalities that only require the ICU library itself, such as [`String.prototype.normalize()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize) and the [WHATWG URL parser](url#the-whatwg-url-api), are fully supported under `system-icu`. Features that require ICU locale data in addition, such as [`Intl.DateTimeFormat`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DateTimeFormat) *may* be fully or partially supported, depending on the completeness of the ICU data installed on the system.
#### Embed a limited set of ICU data (`small-icu`)
This option makes the resulting binary link against the ICU library statically, and includes a subset of ICU data (typically only the English locale) within the `node` executable.
Functionalities that only require the ICU library itself, such as [`String.prototype.normalize()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize) and the [WHATWG URL parser](url#the-whatwg-url-api), are fully supported under `small-icu`. Features that require ICU locale data in addition, such as [`Intl.DateTimeFormat`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DateTimeFormat), generally only work with the English locale:
```
const january = new Date(9e8);
const english = new Intl.DateTimeFormat('en', { month: 'long' });
const spanish = new Intl.DateTimeFormat('es', { month: 'long' });
console.log(english.format(january));
// Prints "January"
console.log(spanish.format(january));
// Prints either "M01" or "January" on small-icu, depending on the user’s default locale
// Should print "enero"
```
This mode provides a balance between features and binary size.
##### Providing ICU data at runtime
If the `small-icu` option is used, one can still provide additional locale data at runtime so that the JS methods would work for all ICU locales. Assuming the data file is stored at `/some/directory`, it can be made available to ICU through either:
* The [`NODE_ICU_DATA`](cli#node_icu_datafile) environment variable:
```
env NODE_ICU_DATA=/some/directory node
```
* The [`--icu-data-dir`](cli#--icu-data-dirfile) CLI parameter:
```
node --icu-data-dir=/some/directory
```
(If both are specified, the `--icu-data-dir` CLI parameter takes precedence.)
ICU is able to automatically find and load a variety of data formats, but the data must be appropriate for the ICU version, and the file correctly named. The most common name for the data file is `icudt6X[bl].dat`, where `6X` denotes the intended ICU version, and `b` or `l` indicates the system's endianness. Check ["ICU Data"](http://userguide.icu-project.org/icudata) article in the ICU User Guide for other supported formats and more details on ICU data in general.
The [full-icu](https://www.npmjs.com/package/full-icu) npm module can greatly simplify ICU data installation by detecting the ICU version of the running `node` executable and downloading the appropriate data file. After installing the module through `npm i full-icu`, the data file will be available at `./node_modules/full-icu`. This path can be then passed either to `NODE_ICU_DATA` or `--icu-data-dir` as shown above to enable full `Intl` support.
#### Embed the entire ICU (`full-icu`)
This option makes the resulting binary link against ICU statically and include a full set of ICU data. A binary created this way has no further external dependencies and supports all locales, but might be rather large. This is the default behavior if no `--with-intl` flag is passed. The official binaries are also built in this mode.
### Detecting internationalization support
To verify that ICU is enabled at all (`system-icu`, `small-icu`, or `full-icu`), simply checking the existence of `Intl` should suffice:
```
const hasICU = typeof Intl === 'object';
```
Alternatively, checking for `process.versions.icu`, a property defined only when ICU is enabled, works too:
```
const hasICU = typeof process.versions.icu === 'string';
```
To check for support for a non-English locale (i.e. `full-icu` or `system-icu`), [`Intl.DateTimeFormat`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DateTimeFormat) can be a good distinguishing factor:
```
const hasFullICU = (() => {
try {
const january = new Date(9e8);
const spanish = new Intl.DateTimeFormat('es', { month: 'long' });
return spanish.format(january) === 'enero';
} catch (err) {
return false;
}
})();
```
For more verbose tests for `Intl` support, the following resources may be found to be helpful:
* [btest402](https://github.com/srl295/btest402): Generally used to check whether Node.js with `Intl` support is built correctly.
* [Test262](https://github.com/tc39/test262/tree/HEAD/test/intl402): ECMAScript's official conformance test suite includes a section dedicated to ECMA-402.
node Node.js Node.js
=======
* [About this documentation](https://nodejs.org/api/documentation.html)
* [Usage and example](https://nodejs.org/api/synopsis.html)
* [Assertion testing](assert)
* [Asynchronous context tracking](async_context)
* [Async hooks](async_hooks)
* [Buffer](buffer)
* [C++ addons](addons)
* [C/C++ addons with Node-API](n-api)
* [C++ embedder API](embedding)
* [Child processes](child_process)
* [Cluster](cluster)
* [Command-line options](cli)
* [Console](console)
* [Corepack](corepack)
* [Crypto](crypto)
* [Debugger](debugger)
* [Deprecated APIs](deprecations)
* [Diagnostics Channel](diagnostics_channel)
* [DNS](dns)
* [Domain](domain)
* [Errors](errors)
* [Events](events)
* [File system](fs)
* [Globals](globals)
* [HTTP](http)
* [HTTP/2](http2)
* [HTTPS](https)
* [Inspector](inspector)
* [Internationalization](intl)
* [Modules: CommonJS modules](modules)
* [Modules: ECMAScript modules](esm)
* [Modules: `node:module` API](module)
* [Modules: Packages](packages)
* [Net](net)
* [OS](os)
* [Path](path)
* [Performance hooks](perf_hooks)
* [Permissions](permissions)
* [Process](process)
* [Punycode](punycode)
* [Query strings](querystring)
* [Readline](readline)
* [REPL](repl)
* [Report](report)
* [Stream](stream)
* [String decoder](string_decoder)
* [Test runner](test)
* [Timers](timers)
* [TLS/SSL](tls)
* [Trace events](tracing)
* [TTY](tty)
* [UDP/datagram](dgram)
* [URL](url)
* [Utilities](util)
* [V8](v8)
* [VM](vm)
* [WASI](wasi)
* [Web Crypto API](webcrypto)
* [Web Streams API](webstreams)
* [Worker threads](worker_threads)
* [Zlib](zlib)
* [Code repository and issue tracker](https://github.com/nodejs/node)
node None Util
----
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/util.js](https://github.com/nodejs/node/blob/v19.0.1/lib/util.js)
The `node:util` module supports the needs of Node.js internal APIs. Many of the utilities are useful for application and module developers as well. To access it:
```
const util = require('node:util');
```
###
`util.callbackify(original)`
Added in: v8.2.0 * `original` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) An `async` function
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) a callback style function
Takes an `async` function (or a function that returns a `Promise`) and returns a function following the error-first callback style, i.e. taking an `(err, value) => ...` callback as the last argument. In the callback, the first argument will be the rejection reason (or `null` if the `Promise` resolved), and the second argument will be the resolved value.
```
const util = require('node:util');
async function fn() {
return 'hello world';
}
const callbackFunction = util.callbackify(fn);
callbackFunction((err, ret) => {
if (err) throw err;
console.log(ret);
});
```
Will print:
```
hello world
```
The callback is executed asynchronously, and will have a limited stack trace. If the callback throws, the process will emit an [`'uncaughtException'`](process#event-uncaughtexception) event, and if not handled will exit.
Since `null` has a special meaning as the first argument to a callback, if a wrapped function rejects a `Promise` with a falsy value as a reason, the value is wrapped in an `Error` with the original value stored in a field named `reason`.
```
function fn() {
return Promise.reject(null);
}
const callbackFunction = util.callbackify(fn);
callbackFunction((err, ret) => {
// When the Promise was rejected with `null` it is wrapped with an Error and
// the original value is stored in `reason`.
err && Object.hasOwn(err, 'reason') && err.reason === null; // true
});
```
###
`util.debuglog(section[, callback])`
Added in: v0.11.3 * `section` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A string identifying the portion of the application for which the `debuglog` function is being created.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback invoked the first time the logging function is called with a function argument that is a more optimized logging function.
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The logging function
The `util.debuglog()` method is used to create a function that conditionally writes debug messages to `stderr` based on the existence of the `NODE_DEBUG` environment variable. If the `section` name appears within the value of that environment variable, then the returned function operates similar to [`console.error()`](console#consoleerrordata-args). If not, then the returned function is a no-op.
```
const util = require('node:util');
const debuglog = util.debuglog('foo');
debuglog('hello from foo [%d]', 123);
```
If this program is run with `NODE_DEBUG=foo` in the environment, then it will output something like:
```
FOO 3245: hello from foo [123]
```
where `3245` is the process id. If it is not run with that environment variable set, then it will not print anything.
The `section` supports wildcard also:
```
const util = require('node:util');
const debuglog = util.debuglog('foo-bar');
debuglog('hi there, it\'s foo-bar [%d]', 2333);
```
if it is run with `NODE_DEBUG=foo*` in the environment, then it will output something like:
```
FOO-BAR 3257: hi there, it's foo-bar [2333]
```
Multiple comma-separated `section` names may be specified in the `NODE_DEBUG` environment variable: `NODE_DEBUG=fs,net,tls`.
The optional `callback` argument can be used to replace the logging function with a different function that doesn't have any initialization or unnecessary wrapping.
```
const util = require('node:util');
let debuglog = util.debuglog('internals', (debug) => {
// Replace with a logging function that optimizes out
// testing if the section is enabled
debuglog = debug;
});
```
####
`debuglog().enabled`
Added in: v14.9.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `util.debuglog().enabled` getter is used to create a test that can be used in conditionals based on the existence of the `NODE_DEBUG` environment variable. If the `section` name appears within the value of that environment variable, then the returned value will be `true`. If not, then the returned value will be `false`.
```
const util = require('node:util');
const enabled = util.debuglog('foo').enabled;
if (enabled) {
console.log('hello from foo [%d]', 123);
}
```
If this program is run with `NODE_DEBUG=foo` in the environment, then it will output something like:
```
hello from foo [123]
```
###
`util.debug(section)`
Added in: v14.9.0 Alias for `util.debuglog`. Usage allows for readability of that doesn't imply logging when only using `util.debuglog().enabled`.
###
`util.deprecate(fn, msg[, code])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Deprecation warnings are only emitted once for each code. |
| v0.8.0 | Added in: v0.8.0 |
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function that is being deprecated.
* `msg` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A warning message to display when the deprecated function is invoked.
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A deprecation code. See the [list of deprecated APIs](deprecations#list-of-deprecated-apis) for a list of codes.
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The deprecated function wrapped to emit a warning.
The `util.deprecate()` method wraps `fn` (which may be a function or class) in such a way that it is marked as deprecated.
```
const util = require('node:util');
exports.obsoleteFunction = util.deprecate(() => {
// Do something here.
}, 'obsoleteFunction() is deprecated. Use newShinyFunction() instead.');
```
When called, `util.deprecate()` will return a function that will emit a `DeprecationWarning` using the [`'warning'`](process#event-warning) event. The warning will be emitted and printed to `stderr` the first time the returned function is called. After the warning is emitted, the wrapped function is called without emitting a warning.
If the same optional `code` is supplied in multiple calls to `util.deprecate()`, the warning will be emitted only once for that `code`.
```
const util = require('node:util');
const fn1 = util.deprecate(someFunction, someMessage, 'DEP0001');
const fn2 = util.deprecate(someOtherFunction, someOtherMessage, 'DEP0001');
fn1(); // Emits a deprecation warning with code DEP0001
fn2(); // Does not emit a deprecation warning because it has the same code
```
If either the `--no-deprecation` or `--no-warnings` command-line flags are used, or if the `process.noDeprecation` property is set to `true` *prior* to the first deprecation warning, the `util.deprecate()` method does nothing.
If the `--trace-deprecation` or `--trace-warnings` command-line flags are set, or the `process.traceDeprecation` property is set to `true`, a warning and a stack trace are printed to `stderr` the first time the deprecated function is called.
If the `--throw-deprecation` command-line flag is set, or the `process.throwDeprecation` property is set to `true`, then an exception will be thrown when the deprecated function is called.
The `--throw-deprecation` command-line flag and `process.throwDeprecation` property take precedence over `--trace-deprecation` and `process.traceDeprecation`.
###
`util.format(format[, ...args])`
History
| Version | Changes |
| --- | --- |
| v12.11.0 | The `%c` specifier is ignored now. |
| v12.0.0 | The `format` argument is now only taken as such if it actually contains format specifiers. |
| v12.0.0 | If the `format` argument is not a format string, the output string's formatting is no longer dependent on the type of the first argument. This change removes previously present quotes from strings that were being output when the first argument was not a string. |
| v11.4.0 | The `%d`, `%f`, and `%i` specifiers now support Symbols properly. |
| v11.4.0 | The `%o` specifier's `depth` has default depth of 4 again. |
| v11.0.0 | The `%o` specifier's `depth` option will now fall back to the default depth. |
| v10.12.0 | The `%d` and `%i` specifiers now support BigInt. |
| v8.4.0 | The `%o` and `%O` specifiers are supported now. |
| v0.5.3 | Added in: v0.5.3 |
* `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A `printf`-like format string.
The `util.format()` method returns a formatted string using the first argument as a `printf`-like format string which can contain zero or more format specifiers. Each specifier is replaced with the converted value from the corresponding argument. Supported specifiers are:
* `%s`: `String` will be used to convert all values except `BigInt`, `Object` and `-0`. `BigInt` values will be represented with an `n` and Objects that have no user defined `toString` function are inspected using `util.inspect()` with options `{ depth: 0, colors: false, compact: 3 }`.
* `%d`: `Number` will be used to convert all values except `BigInt` and `Symbol`.
* `%i`: `parseInt(value, 10)` is used for all values except `BigInt` and `Symbol`.
* `%f`: `parseFloat(value)` is used for all values expect `Symbol`.
* `%j`: JSON. Replaced with the string `'[Circular]'` if the argument contains circular references.
* `%o`: `Object`. A string representation of an object with generic JavaScript object formatting. Similar to `util.inspect()` with options `{ showHidden: true, showProxy: true }`. This will show the full object including non-enumerable properties and proxies.
* `%O`: `Object`. A string representation of an object with generic JavaScript object formatting. Similar to `util.inspect()` without options. This will show the full object not including non-enumerable properties and proxies.
* `%c`: `CSS`. This specifier is ignored and will skip any CSS passed in.
* `%%`: single percent sign (`'%'`). This does not consume an argument.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The formatted string
If a specifier does not have a corresponding argument, it is not replaced:
```
util.format('%s:%s', 'foo');
// Returns: 'foo:%s'
```
Values that are not part of the format string are formatted using `util.inspect()` if their type is not `string`.
If there are more arguments passed to the `util.format()` method than the number of specifiers, the extra arguments are concatenated to the returned string, separated by spaces:
```
util.format('%s:%s', 'foo', 'bar', 'baz');
// Returns: 'foo:bar baz'
```
If the first argument does not contain a valid format specifier, `util.format()` returns a string that is the concatenation of all arguments separated by spaces:
```
util.format(1, 2, 3);
// Returns: '1 2 3'
```
If only one argument is passed to `util.format()`, it is returned as it is without any formatting:
```
util.format('%% %s');
// Returns: '%% %s'
```
`util.format()` is a synchronous method that is intended as a debugging tool. Some input values can have a significant performance overhead that can block the event loop. Use this function with care and never in a hot code path.
###
`util.formatWithOptions(inspectOptions, format[, ...args])`
Added in: v10.0.0 * `inspectOptions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
This function is identical to [`util.format()`](#utilformatformat-args), except in that it takes an `inspectOptions` argument which specifies options that are passed along to [`util.inspect()`](#utilinspectobject-options).
```
util.formatWithOptions({ colors: true }, 'See object %O', { foo: 42 });
// Returns 'See object { foo: 42 }', where `42` is colored as a number
// when printed to a terminal.
```
###
`util.getSystemErrorName(err)`
Added in: v9.7.0 * `err` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the string name for a numeric error code that comes from a Node.js API. The mapping between error codes and error names is platform-dependent. See [Common System Errors](errors#common-system-errors) for the names of common errors.
```
fs.access('file/that/does/not/exist', (err) => {
const name = util.getSystemErrorName(err.errno);
console.error(name); // ENOENT
});
```
###
`util.getSystemErrorMap()`
Added in: v16.0.0, v14.17.0 * Returns: [<Map>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
Returns a Map of all system error codes available from the Node.js API. The mapping between error codes and error names is platform-dependent. See [Common System Errors](errors#common-system-errors) for the names of common errors.
```
fs.access('file/that/does/not/exist', (err) => {
const errorMap = util.getSystemErrorMap();
const name = errorMap.get(err.errno);
console.error(name); // ENOENT
});
```
###
`util.inherits(constructor, superConstructor)`
History
| Version | Changes |
| --- | --- |
| v5.0.0 | The `constructor` parameter can refer to an ES6 class now. |
| v0.3.0 | Added in: v0.3.0 |
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use ES2015 class syntax and `extends` keyword instead.
* `constructor` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `superConstructor` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Usage of `util.inherits()` is discouraged. Please use the ES6 `class` and `extends` keywords to get language level inheritance support. Also note that the two styles are [semantically incompatible](https://github.com/nodejs/node/issues/4179).
Inherit the prototype methods from one [constructor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/constructor) into another. The prototype of `constructor` will be set to a new object created from `superConstructor`.
This mainly adds some input validation on top of `Object.setPrototypeOf(constructor.prototype, superConstructor.prototype)`. As an additional convenience, `superConstructor` will be accessible through the `constructor.super_` property.
```
const util = require('node:util');
const EventEmitter = require('node:events');
function MyStream() {
EventEmitter.call(this);
}
util.inherits(MyStream, EventEmitter);
MyStream.prototype.write = function(data) {
this.emit('data', data);
};
const stream = new MyStream();
console.log(stream instanceof EventEmitter); // true
console.log(MyStream.super_ === EventEmitter); // true
stream.on('data', (data) => {
console.log(`Received data: "${data}"`);
});
stream.write('It works!'); // Received data: "It works!"
```
ES6 example using `class` and `extends`:
```
const EventEmitter = require('node:events');
class MyStream extends EventEmitter {
write(data) {
this.emit('data', data);
}
}
const stream = new MyStream();
stream.on('data', (data) => {
console.log(`Received data: "${data}"`);
});
stream.write('With ES6');
```
###
`util.inspect(object[, options])`
###
`util.inspect(object[, showHidden[, depth[, colors]]])`
History
| Version | Changes |
| --- | --- |
| v16.18.0 | add support for `maxArrayLength` when inspecting `Set` and `Map`. |
| v17.3.0, v16.14.0 | The `numericSeparator` option is supported now. |
| v13.0.0 | Circular references now include a marker to the reference. |
| v14.6.0, v12.19.0 | If `object` is from a different `vm.Context` now, a custom inspection function on it will not receive context-specific arguments anymore. |
| v13.13.0, v12.17.0 | The `maxStringLength` option is supported now. |
| v13.5.0, v12.16.0 | User defined prototype properties are inspected in case `showHidden` is `true`. |
| v12.0.0 | The `compact` options default is changed to `3` and the `breakLength` options default is changed to `80`. |
| v12.0.0 | Internal properties no longer appear in the context argument of a custom inspection function. |
| v11.11.0 | The `compact` option accepts numbers for a new output mode. |
| v11.7.0 | ArrayBuffers now also show their binary contents. |
| v11.5.0 | The `getters` option is supported now. |
| v11.4.0 | The `depth` default changed back to `2`. |
| v11.0.0 | The `depth` default changed to `20`. |
| v11.0.0 | The inspection output is now limited to about 128 MiB. Data above that size will not be fully inspected. |
| v10.12.0 | The `sorted` option is supported now. |
| v10.6.0 | Inspecting linked lists and similar objects is now possible up to the maximum call stack size. |
| v10.0.0 | The `WeakMap` and `WeakSet` entries can now be inspected as well. |
| v9.9.0 | The `compact` option is supported now. |
| v6.6.0 | Custom inspection functions can now return `this`. |
| v6.3.0 | The `breakLength` option is supported now. |
| v6.1.0 | The `maxArrayLength` option is supported now; in particular, long arrays are truncated by default. |
| v6.1.0 | The `showProxy` option is supported now. |
| v0.3.0 | Added in: v0.3.0 |
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Any JavaScript primitive or `Object`.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `showHidden` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, `object`'s non-enumerable symbols and properties are included in the formatted result. [`WeakMap`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap) and [`WeakSet`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet) entries are also included as well as user defined prototype properties (excluding method properties). **Default:** `false`.
+ `depth` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the number of times to recurse while formatting `object`. This is useful for inspecting large objects. To recurse up to the maximum call stack size pass `Infinity` or `null`. **Default:** `2`.
+ `colors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, the output is styled with ANSI color codes. Colors are customizable. See [Customizing `util.inspect` colors](#customizing-utilinspect-colors). **Default:** `false`.
+ `customInspect` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `false`, `[util.inspect.custom](depth, opts, inspect)` functions are not invoked. **Default:** `true`.
+ `showProxy` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, `Proxy` inspection includes the [`target` and `handler`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy#Terminology) objects. **Default:** `false`.
+ `maxArrayLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the maximum number of `Array`, [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map), [`Set`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set), [`WeakMap`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap), and [`WeakSet`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet) elements to include when formatting. Set to `null` or `Infinity` to show all elements. Set to `0` or negative to show no elements. **Default:** `100`.
+ `maxStringLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the maximum number of characters to include when formatting. Set to `null` or `Infinity` to show all elements. Set to `0` or negative to show no characters. **Default:** `10000`.
+ `breakLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The length at which input values are split across multiple lines. Set to `Infinity` to format the input as a single line (in combination with `compact` set to `true` or any number >= `1`). **Default:** `80`.
+ `compact` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Setting this to `false` causes each object key to be displayed on a new line. It will break on new lines in text that is longer than `breakLength`. If set to a number, the most `n` inner elements are united on a single line as long as all properties fit into `breakLength`. Short array elements are also grouped together. For more information, see the example below. **Default:** `3`.
+ `sorted` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) If set to `true` or a function, all properties of an object, and `Set` and `Map` entries are sorted in the resulting string. If set to `true` the [default sort](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort) is used. If set to a function, it is used as a [compare function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Parameters).
+ `getters` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If set to `true`, getters are inspected. If set to `'get'`, only getters without a corresponding setter are inspected. If set to `'set'`, only getters with a corresponding setter are inspected. This might cause side effects depending on the getter function. **Default:** `false`.
+ `numericSeparator` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `true`, an underscore is used to separate every three digits in all bigints and numbers. **Default:** `false`.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The representation of `object`.
The `util.inspect()` method returns a string representation of `object` that is intended for debugging. The output of `util.inspect` may change at any time and should not be depended upon programmatically. Additional `options` may be passed that alter the result. `util.inspect()` will use the constructor's name and/or `@@toStringTag` to make an identifiable tag for an inspected value.
```
class Foo {
get [Symbol.toStringTag]() {
return 'bar';
}
}
class Bar {}
const baz = Object.create(null, { [Symbol.toStringTag]: { value: 'foo' } });
util.inspect(new Foo()); // 'Foo [bar] {}'
util.inspect(new Bar()); // 'Bar {}'
util.inspect(baz); // '[foo] {}'
```
Circular references point to their anchor by using a reference index:
```
const { inspect } = require('node:util');
const obj = {};
obj.a = [obj];
obj.b = {};
obj.b.inner = obj.b;
obj.b.obj = obj;
console.log(inspect(obj));
// <ref *1> {
// a: [ [Circular *1] ],
// b: <ref *2> { inner: [Circular *2], obj: [Circular *1] }
// }
```
The following example inspects all properties of the `util` object:
```
const util = require('node:util');
console.log(util.inspect(util, { showHidden: true, depth: null }));
```
The following example highlights the effect of the `compact` option:
```
const util = require('node:util');
const o = {
a: [1, 2, [[
'Lorem ipsum dolor sit amet,\nconsectetur adipiscing elit, sed do ' +
'eiusmod \ntempor incididunt ut labore et dolore magna aliqua.',
'test',
'foo']], 4],
b: new Map([['za', 1], ['zb', 'test']])
};
console.log(util.inspect(o, { compact: true, depth: 5, breakLength: 80 }));
// { a:
// [ 1,
// 2,
// [ [ 'Lorem ipsum dolor sit amet,\nconsectetur [...]', // A long line
// 'test',
// 'foo' ] ],
// 4 ],
// b: Map(2) { 'za' => 1, 'zb' => 'test' } }
// Setting `compact` to false or an integer creates more reader friendly output.
console.log(util.inspect(o, { compact: false, depth: 5, breakLength: 80 }));
// {
// a: [
// 1,
// 2,
// [
// [
// 'Lorem ipsum dolor sit amet,\n' +
// 'consectetur adipiscing elit, sed do eiusmod \n' +
// 'tempor incididunt ut labore et dolore magna aliqua.',
// 'test',
// 'foo'
// ]
// ],
// 4
// ],
// b: Map(2) {
// 'za' => 1,
// 'zb' => 'test'
// }
// }
// Setting `breakLength` to e.g. 150 will print the "Lorem ipsum" text in a
// single line.
```
The `showHidden` option allows [`WeakMap`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap) and [`WeakSet`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet) entries to be inspected. If there are more entries than `maxArrayLength`, there is no guarantee which entries are displayed. That means retrieving the same [`WeakSet`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet) entries twice may result in different output. Furthermore, entries with no remaining strong references may be garbage collected at any time.
```
const { inspect } = require('node:util');
const obj = { a: 1 };
const obj2 = { b: 2 };
const weakSet = new WeakSet([obj, obj2]);
console.log(inspect(weakSet, { showHidden: true }));
// WeakSet { { a: 1 }, { b: 2 } }
```
The `sorted` option ensures that an object's property insertion order does not impact the result of `util.inspect()`.
```
const { inspect } = require('node:util');
const assert = require('node:assert');
const o1 = {
b: [2, 3, 1],
a: '`a` comes before `b`',
c: new Set([2, 3, 1])
};
console.log(inspect(o1, { sorted: true }));
// { a: '`a` comes before `b`', b: [ 2, 3, 1 ], c: Set(3) { 1, 2, 3 } }
console.log(inspect(o1, { sorted: (a, b) => b.localeCompare(a) }));
// { c: Set(3) { 3, 2, 1 }, b: [ 2, 3, 1 ], a: '`a` comes before `b`' }
const o2 = {
c: new Set([2, 1, 3]),
a: '`a` comes before `b`',
b: [2, 3, 1]
};
assert.strict.equal(
inspect(o1, { sorted: true }),
inspect(o2, { sorted: true })
);
```
The `numericSeparator` option adds an underscore every three digits to all numbers.
```
const { inspect } = require('node:util');
const thousand = 1_000;
const million = 1_000_000;
const bigNumber = 123_456_789n;
const bigDecimal = 1_234.123_45;
console.log(thousand, million, bigNumber, bigDecimal);
// 1_000 1_000_000 123_456_789n 1_234.123_45
```
`util.inspect()` is a synchronous method intended for debugging. Its maximum output length is approximately 128 MiB. Inputs that result in longer output will be truncated.
#### Customizing `util.inspect` colors
Color output (if enabled) of `util.inspect` is customizable globally via the `util.inspect.styles` and `util.inspect.colors` properties.
`util.inspect.styles` is a map associating a style name to a color from `util.inspect.colors`.
The default styles and associated colors are:
* `bigint`: `yellow`
* `boolean`: `yellow`
* `date`: `magenta`
* `module`: `underline`
* `name`: (no styling)
* `null`: `bold`
* `number`: `yellow`
* `regexp`: `red`
* `special`: `cyan` (e.g., `Proxies`)
* `string`: `green`
* `symbol`: `green`
* `undefined`: `grey`
Color styling uses ANSI control codes that may not be supported on all terminals. To verify color support use [`tty.hasColors()`](tty#writestreamhascolorscount-env).
Predefined control codes are listed below (grouped as "Modifiers", "Foreground colors", and "Background colors").
##### Modifiers
Modifier support varies throughout different terminals. They will mostly be ignored, if not supported.
* `reset` - Resets all (color) modifiers to their defaults
* **bold** - Make text bold
* *italic* - Make text italic
* underline - Make text underlined
* ~~strikethrough~~ - Puts a horizontal line through the center of the text (Alias: `strikeThrough`, `crossedout`, `crossedOut`)
* `hidden` - Prints the text, but makes it invisible (Alias: conceal)
* dim - Decreased color intensity (Alias: `faint`)
* overlined - Make text overlined
* blink - Hides and shows the text in an interval
* inverse - Swap foreground and background colors (Alias: `swapcolors`, `swapColors`)
* doubleunderline - Make text double underlined (Alias: `doubleUnderline`)
* framed - Draw a frame around the text
##### Foreground colors
* `black`
* `red`
* `green`
* `yellow`
* `blue`
* `magenta`
* `cyan`
* `white`
* `gray` (alias: `grey`, `blackBright`)
* `redBright`
* `greenBright`
* `yellowBright`
* `blueBright`
* `magentaBright`
* `cyanBright`
* `whiteBright`
##### Background colors
* `bgBlack`
* `bgRed`
* `bgGreen`
* `bgYellow`
* `bgBlue`
* `bgMagenta`
* `bgCyan`
* `bgWhite`
* `bgGray` (alias: `bgGrey`, `bgBlackBright`)
* `bgRedBright`
* `bgGreenBright`
* `bgYellowBright`
* `bgBlueBright`
* `bgMagentaBright`
* `bgCyanBright`
* `bgWhiteBright`
#### Custom inspection functions on objects
History
| Version | Changes |
| --- | --- |
| v17.3.0, v16.14.0 | The inspect argument is added for more interoperability. |
| v0.1.97 | Added in: v0.1.97 |
Objects may also define their own [`[util.inspect.custom](depth, opts, inspect)`](#utilinspectcustom) function, which `util.inspect()` will invoke and use the result of when inspecting the object.
```
const util = require('node:util');
class Box {
constructor(value) {
this.value = value;
}
[util.inspect.custom](depth, options, inspect) {
if (depth < 0) {
return options.stylize('[Box]', 'special');
}
const newOptions = Object.assign({}, options, {
depth: options.depth === null ? null : options.depth - 1
});
// Five space padding because that's the size of "Box< ".
const padding = ' '.repeat(5);
const inner = inspect(this.value, newOptions)
.replace(/\n/g, `\n${padding}`);
return `${options.stylize('Box', 'special')}< ${inner} >`;
}
}
const box = new Box(true);
util.inspect(box);
// Returns: "Box< true >"
```
Custom `[util.inspect.custom](depth, opts, inspect)` functions typically return a string but may return a value of any type that will be formatted accordingly by `util.inspect()`.
```
const util = require('node:util');
const obj = { foo: 'this will not show up in the inspect() output' };
obj[util.inspect.custom] = (depth) => {
return { bar: 'baz' };
};
util.inspect(obj);
// Returns: "{ bar: 'baz' }"
```
####
`util.inspect.custom`
History
| Version | Changes |
| --- | --- |
| v10.12.0 | This is now defined as a shared symbol. |
| v6.6.0 | Added in: v6.6.0 |
* [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) that can be used to declare custom inspect functions.
In addition to being accessible through `util.inspect.custom`, this symbol is [registered globally](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for) and can be accessed in any environment as `Symbol.for('nodejs.util.inspect.custom')`.
Using this allows code to be written in a portable fashion, so that the custom inspect function is used in an Node.js environment and ignored in the browser. The `util.inspect()` function itself is passed as third argument to the custom inspect function to allow further portability.
```
const customInspectSymbol = Symbol.for('nodejs.util.inspect.custom');
class Password {
constructor(value) {
this.value = value;
}
toString() {
return 'xxxxxxxx';
}
[customInspectSymbol](depth, inspectOptions, inspect) {
return `Password <${this.toString()}>`;
}
}
const password = new Password('r0sebud');
console.log(password);
// Prints Password <xxxxxxxx>
```
See [Custom inspection functions on Objects](#custom-inspection-functions-on-objects) for more details.
####
`util.inspect.defaultOptions`
Added in: v6.4.0 The `defaultOptions` value allows customization of the default options used by `util.inspect`. This is useful for functions like `console.log` or `util.format` which implicitly call into `util.inspect`. It shall be set to an object containing one or more valid [`util.inspect()`](#utilinspectobject-options) options. Setting option properties directly is also supported.
```
const util = require('node:util');
const arr = Array(101).fill(0);
console.log(arr); // Logs the truncated array
util.inspect.defaultOptions.maxArrayLength = null;
console.log(arr); // logs the full array
```
###
`util.isDeepStrictEqual(val1, val2)`
Added in: v9.0.0 * `val1` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `val2` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if there is deep strict equality between `val1` and `val2`. Otherwise, returns `false`.
See [`assert.deepStrictEqual()`](assert#assertdeepstrictequalactual-expected-message) for more information about deep strict equality.
###
`util.parseArgs([config])`
History
| Version | Changes |
| --- | --- |
| v18.11.0 | Add support for default values in input `config`. |
| v18.3.0, v16.17.0 | Added in: v18.3.0, v16.17.0 |
| v18.7.0, v16.17.0 | add support for returning detailed parse information using `tokens` in input `config` and returned properties. |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `config` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Used to provide arguments for parsing and to configure the parser. `config` supports the following properties:
+ `args` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) array of argument strings. **Default:** `process.argv` with `execPath` and `filename` removed.
+ `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Used to describe arguments known to the parser. Keys of `options` are the long names of options and values are an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) accepting the following properties:
- `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Type of argument, which must be either `boolean` or `string`.
- `multiple` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether this option can be provided multiple times. If `true`, all values will be collected in an array. If `false`, values for the option are last-wins. **Default:** `false`.
- `short` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A single character alias for the option.
- `default` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<boolean[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) The default option value when it is not set by args. It must be of the same type as the the `type` property. When `multiple` is `true`, it must be an array.
+ `strict` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Should an error be thrown when unknown arguments are encountered, or when arguments are passed that do not match the `type` configured in `options`. **Default:** `true`.
+ `allowPositionals` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether this command accepts positional arguments. **Default:** `false` if `strict` is `true`, otherwise `true`.
+ `tokens` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Return the parsed tokens. This is useful for extending the built-in behavior, from adding additional checks through to reprocessing the tokens in different ways. **Default:** `false`.
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The parsed command line arguments:
+ `values` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A mapping of parsed option names with their [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) or [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) values.
+ `positionals` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Positional arguments.
+ `tokens` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) See [parseArgs tokens](#parseargs-tokens) section. Only returned if `config` includes `tokens: true`.
Provides a higher level API for command-line argument parsing than interacting with `process.argv` directly. Takes a specification for the expected arguments and returns a structured object with the parsed options and positionals.
MJS modules
```
import { parseArgs } from 'node:util';
const args = ['-f', '--bar', 'b'];
const options = {
foo: {
type: 'boolean',
short: 'f'
},
bar: {
type: 'string'
}
};
const {
values,
positionals
} = parseArgs({ args, options });
console.log(values, positionals);
// Prints: [Object: null prototype] { foo: true, bar: 'b' } []
```
CJS modules
```
const { parseArgs } = require('node:util');
const args = ['-f', '--bar', 'b'];
const options = {
foo: {
type: 'boolean',
short: 'f'
},
bar: {
type: 'string'
}
};
const {
values,
positionals
} = parseArgs({ args, options });
console.log(values, positionals);
// Prints: [Object: null prototype] { foo: true, bar: 'b' } []
```
`util.parseArgs` is experimental and behavior may change. Join the conversation in [pkgjs/parseargs](https://github.com/pkgjs/parseargs) to contribute to the design.
####
`parseArgs` `tokens`
Detailed parse information is available for adding custom behaviours by specifying `tokens: true` in the configuration. The returned tokens have properties describing:
* all tokens
+ `kind` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) One of 'option', 'positional', or 'option-terminator'.
+ `index` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Index of element in `args` containing token. So the source argument for a token is `args[token.index]`.
* option tokens
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Long name of option.
+ `rawName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) How option used in args, like `-f` of `--foo`.
+ `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Option value specified in args. Undefined for boolean options.
+ `inlineValue` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Whether option value specified inline, like `--foo=bar`.
* positional tokens
+ `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The value of the positional argument in args (i.e. `args[index]`).
* option-terminator token
The returned tokens are in the order encountered in the input args. Options that appear more than once in args produce a token for each use. Short option groups like `-xy` expand to a token for each option. So `-xxx` produces three tokens.
For example to use the returned tokens to add support for a negated option like `--no-color`, the tokens can be reprocessed to change the value stored for the negated option.
MJS modules
```
import { parseArgs } from 'node:util';
const options = {
'color': { type: 'boolean' },
'no-color': { type: 'boolean' },
'logfile': { type: 'string' },
'no-logfile': { type: 'boolean' },
};
const { values, tokens } = parseArgs({ options, tokens: true });
// Reprocess the option tokens and overwrite the returned values.
tokens
.filter((token) => token.kind === 'option')
.forEach((token) => {
if (token.name.startsWith('no-')) {
// Store foo:false for --no-foo
const positiveName = token.name.slice(3);
values[positiveName] = false;
delete values[token.name];
} else {
// Resave value so last one wins if both --foo and --no-foo.
values[token.name] = token.value ?? true;
}
});
const color = values.color;
const logfile = values.logfile ?? 'default.log';
console.log({ logfile, color });
```
CJS modules
```
const { parseArgs } = require('node:util');
const options = {
'color': { type: 'boolean' },
'no-color': { type: 'boolean' },
'logfile': { type: 'string' },
'no-logfile': { type: 'boolean' },
};
const { values, tokens } = parseArgs({ options, tokens: true });
// Reprocess the option tokens and overwrite the returned values.
tokens
.filter((token) => token.kind === 'option')
.forEach((token) => {
if (token.name.startsWith('no-')) {
// Store foo:false for --no-foo
const positiveName = token.name.slice(3);
values[positiveName] = false;
delete values[token.name];
} else {
// Resave value so last one wins if both --foo and --no-foo.
values[token.name] = token.value ?? true;
}
});
const color = values.color;
const logfile = values.logfile ?? 'default.log';
console.log({ logfile, color });
```
Example usage showing negated options, and when an option is used multiple ways then last one wins.
```
$ node negate.js
{ logfile: 'default.log', color: undefined }
$ node negate.js --no-logfile --no-color
{ logfile: false, color: false }
$ node negate.js --logfile=test.log --color
{ logfile: 'test.log', color: true }
$ node negate.js --no-logfile --logfile=test.log --color --no-color
{ logfile: 'test.log', color: false }
```
###
`util.promisify(original)`
Added in: v8.0.0 * `original` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Takes a function following the common error-first callback style, i.e. taking an `(err, value) => ...` callback as the last argument, and returns a version that returns promises.
```
const util = require('node:util');
const fs = require('node:fs');
const stat = util.promisify(fs.stat);
stat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});
```
Or, equivalently using `async function`s:
```
const util = require('node:util');
const fs = require('node:fs');
const stat = util.promisify(fs.stat);
async function callStat() {
const stats = await stat('.');
console.log(`This directory is owned by ${stats.uid}`);
}
```
If there is an `original[util.promisify.custom]` property present, `promisify` will return its value, see [Custom promisified functions](#custom-promisified-functions).
`promisify()` assumes that `original` is a function taking a callback as its final argument in all cases. If `original` is not a function, `promisify()` will throw an error. If `original` is a function but its last argument is not an error-first callback, it will still be passed an error-first callback as its last argument.
Using `promisify()` on class methods or other methods that use `this` may not work as expected unless handled specially:
```
const util = require('node:util');
class Foo {
constructor() {
this.a = 42;
}
bar(callback) {
callback(null, this.a);
}
}
const foo = new Foo();
const naiveBar = util.promisify(foo.bar);
// TypeError: Cannot read property 'a' of undefined
// naiveBar().then(a => console.log(a));
naiveBar.call(foo).then((a) => console.log(a)); // '42'
const bindBar = naiveBar.bind(foo);
bindBar().then((a) => console.log(a)); // '42'
```
#### Custom promisified functions
Using the `util.promisify.custom` symbol one can override the return value of [`util.promisify()`](#utilpromisifyoriginal):
```
const util = require('node:util');
function doSomething(foo, callback) {
// ...
}
doSomething[util.promisify.custom] = (foo) => {
return getPromiseSomehow();
};
const promisified = util.promisify(doSomething);
console.log(promisified === doSomething[util.promisify.custom]);
// prints 'true'
```
This can be useful for cases where the original function does not follow the standard format of taking an error-first callback as the last argument.
For example, with a function that takes in `(foo, onSuccessCallback, onErrorCallback)`:
```
doSomething[util.promisify.custom] = (foo) => {
return new Promise((resolve, reject) => {
doSomething(foo, resolve, reject);
});
};
```
If `promisify.custom` is defined but is not a function, `promisify()` will throw an error.
####
`util.promisify.custom`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.16.2 | This is now defined as a shared symbol. |
| v8.0.0 | Added in: v8.0.0 |
* [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) that can be used to declare custom promisified variants of functions, see [Custom promisified functions](#custom-promisified-functions).
In addition to being accessible through `util.promisify.custom`, this symbol is [registered globally](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for) and can be accessed in any environment as `Symbol.for('nodejs.util.promisify.custom')`.
For example, with a function that takes in `(foo, onSuccessCallback, onErrorCallback)`:
```
const kCustomPromisifiedSymbol = Symbol.for('nodejs.util.promisify.custom');
doSomething[kCustomPromisifiedSymbol] = (foo) => {
return new Promise((resolve, reject) => {
doSomething(foo, resolve, reject);
});
};
```
###
`util.stripVTControlCharacters(str)`
Added in: v16.11.0 * `str` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns `str` with any ANSI escape codes removed.
```
console.log(util.stripVTControlCharacters('\u001B[4mvalue\u001B[0m'));
// Prints "value"
```
### Class: `util.TextDecoder`
Added in: v8.3.0 An implementation of the [WHATWG Encoding Standard](https://encoding.spec.whatwg.org/) `TextDecoder` API.
```
const decoder = new TextDecoder();
const u8arr = new Uint8Array([72, 101, 108, 108, 111]);
console.log(decoder.decode(u8arr)); // Hello
```
#### WHATWG supported encodings
Per the [WHATWG Encoding Standard](https://encoding.spec.whatwg.org/), the encodings supported by the `TextDecoder` API are outlined in the tables below. For each encoding, one or more aliases may be used.
Different Node.js build configurations support different sets of encodings. (see [Internationalization](intl))
##### Encodings supported by default (with full ICU data)
| Encoding | Aliases |
| --- | --- |
| `'ibm866'` | `'866'`, `'cp866'`, `'csibm866'` |
| `'iso-8859-2'` | `'csisolatin2'`, `'iso-ir-101'`, `'iso8859-2'`, `'iso88592'`, `'iso_8859-2'`, `'iso_8859-2:1987'`, `'l2'`, `'latin2'` |
| `'iso-8859-3'` | `'csisolatin3'`, `'iso-ir-109'`, `'iso8859-3'`, `'iso88593'`, `'iso_8859-3'`, `'iso_8859-3:1988'`, `'l3'`, `'latin3'` |
| `'iso-8859-4'` | `'csisolatin4'`, `'iso-ir-110'`, `'iso8859-4'`, `'iso88594'`, `'iso_8859-4'`, `'iso_8859-4:1988'`, `'l4'`, `'latin4'` |
| `'iso-8859-5'` | `'csisolatincyrillic'`, `'cyrillic'`, `'iso-ir-144'`, `'iso8859-5'`, `'iso88595'`, `'iso_8859-5'`, `'iso_8859-5:1988'` |
| `'iso-8859-6'` | `'arabic'`, `'asmo-708'`, `'csiso88596e'`, `'csiso88596i'`, `'csisolatinarabic'`, `'ecma-114'`, `'iso-8859-6-e'`, `'iso-8859-6-i'`, `'iso-ir-127'`, `'iso8859-6'`, `'iso88596'`, `'iso_8859-6'`, `'iso_8859-6:1987'` |
| `'iso-8859-7'` | `'csisolatingreek'`, `'ecma-118'`, `'elot_928'`, `'greek'`, `'greek8'`, `'iso-ir-126'`, `'iso8859-7'`, `'iso88597'`, `'iso_8859-7'`, `'iso_8859-7:1987'`, `'sun_eu_greek'` |
| `'iso-8859-8'` | `'csiso88598e'`, `'csisolatinhebrew'`, `'hebrew'`, `'iso-8859-8-e'`, `'iso-ir-138'`, `'iso8859-8'`, `'iso88598'`, `'iso_8859-8'`, `'iso_8859-8:1988'`, `'visual'` |
| `'iso-8859-8-i'` | `'csiso88598i'`, `'logical'` |
| `'iso-8859-10'` | `'csisolatin6'`, `'iso-ir-157'`, `'iso8859-10'`, `'iso885910'`, `'l6'`, `'latin6'` |
| `'iso-8859-13'` | `'iso8859-13'`, `'iso885913'` |
| `'iso-8859-14'` | `'iso8859-14'`, `'iso885914'` |
| `'iso-8859-15'` | `'csisolatin9'`, `'iso8859-15'`, `'iso885915'`, `'iso_8859-15'`, `'l9'` |
| `'koi8-r'` | `'cskoi8r'`, `'koi'`, `'koi8'`, `'koi8_r'` |
| `'koi8-u'` | `'koi8-ru'` |
| `'macintosh'` | `'csmacintosh'`, `'mac'`, `'x-mac-roman'` |
| `'windows-874'` | `'dos-874'`, `'iso-8859-11'`, `'iso8859-11'`, `'iso885911'`, `'tis-620'` |
| `'windows-1250'` | `'cp1250'`, `'x-cp1250'` |
| `'windows-1251'` | `'cp1251'`, `'x-cp1251'` |
| `'windows-1252'` | `'ansi_x3.4-1968'`, `'ascii'`, `'cp1252'`, `'cp819'`, `'csisolatin1'`, `'ibm819'`, `'iso-8859-1'`, `'iso-ir-100'`, `'iso8859-1'`, `'iso88591'`, `'iso_8859-1'`, `'iso_8859-1:1987'`, `'l1'`, `'latin1'`, `'us-ascii'`, `'x-cp1252'` |
| `'windows-1253'` | `'cp1253'`, `'x-cp1253'` |
| `'windows-1254'` | `'cp1254'`, `'csisolatin5'`, `'iso-8859-9'`, `'iso-ir-148'`, `'iso8859-9'`, `'iso88599'`, `'iso_8859-9'`, `'iso_8859-9:1989'`, `'l5'`, `'latin5'`, `'x-cp1254'` |
| `'windows-1255'` | `'cp1255'`, `'x-cp1255'` |
| `'windows-1256'` | `'cp1256'`, `'x-cp1256'` |
| `'windows-1257'` | `'cp1257'`, `'x-cp1257'` |
| `'windows-1258'` | `'cp1258'`, `'x-cp1258'` |
| `'x-mac-cyrillic'` | `'x-mac-ukrainian'` |
| `'gbk'` | `'chinese'`, `'csgb2312'`, `'csiso58gb231280'`, `'gb2312'`, `'gb_2312'`, `'gb_2312-80'`, `'iso-ir-58'`, `'x-gbk'` |
| `'gb18030'` | |
| `'big5'` | `'big5-hkscs'`, `'cn-big5'`, `'csbig5'`, `'x-x-big5'` |
| `'euc-jp'` | `'cseucpkdfmtjapanese'`, `'x-euc-jp'` |
| `'iso-2022-jp'` | `'csiso2022jp'` |
| `'shift_jis'` | `'csshiftjis'`, `'ms932'`, `'ms_kanji'`, `'shift-jis'`, `'sjis'`, `'windows-31j'`, `'x-sjis'` |
| `'euc-kr'` | `'cseuckr'`, `'csksc56011987'`, `'iso-ir-149'`, `'korean'`, `'ks_c_5601-1987'`, `'ks_c_5601-1989'`, `'ksc5601'`, `'ksc_5601'`, `'windows-949'` |
##### Encodings supported when Node.js is built with the `small-icu` option
| Encoding | Aliases |
| --- | --- |
| `'utf-8'` | `'unicode-1-1-utf-8'`, `'utf8'` |
| `'utf-16le'` | `'utf-16'` |
| `'utf-16be'` | |
##### Encodings supported when ICU is disabled
| Encoding | Aliases |
| --- | --- |
| `'utf-8'` | `'unicode-1-1-utf-8'`, `'utf8'` |
| `'utf-16le'` | `'utf-16'` |
The `'iso-8859-16'` encoding listed in the [WHATWG Encoding Standard](https://encoding.spec.whatwg.org/) is not supported.
####
`new TextDecoder([encoding[, options]])`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | The class is now available on the global object. |
| v8.3.0 | Added in: v8.3.0 |
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Identifies the `encoding` that this `TextDecoder` instance supports. **Default:** `'utf-8'`.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `fatal` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if decoding failures are fatal. This option is not supported when ICU is disabled (see [Internationalization](intl)). **Default:** `false`.
+ `ignoreBOM` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the `TextDecoder` will include the byte order mark in the decoded result. When `false`, the byte order mark will be removed from the output. This option is only used when `encoding` is `'utf-8'`, `'utf-16be'`, or `'utf-16le'`. **Default:** `false`.
Creates a new `TextDecoder` instance. The `encoding` may specify one of the supported encodings or an alias.
The `TextDecoder` class is also available on the global object.
####
`textDecoder.decode([input[, options]])`
* `input` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) An `ArrayBuffer`, `DataView`, or `TypedArray` instance containing the encoded data.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `stream` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if additional chunks of data are expected. **Default:** `false`.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Decodes the `input` and returns a string. If `options.stream` is `true`, any incomplete byte sequences occurring at the end of the `input` are buffered internally and emitted after the next call to `textDecoder.decode()`.
If `textDecoder.fatal` is `true`, decoding errors that occur will result in a `TypeError` being thrown.
####
`textDecoder.encoding`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The encoding supported by the `TextDecoder` instance.
####
`textDecoder.fatal`
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The value will be `true` if decoding errors result in a `TypeError` being thrown.
####
`textDecoder.ignoreBOM`
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The value will be `true` if the decoding result will include the byte order mark.
### Class: `util.TextEncoder`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | The class is now available on the global object. |
| v8.3.0 | Added in: v8.3.0 |
An implementation of the [WHATWG Encoding Standard](https://encoding.spec.whatwg.org/) `TextEncoder` API. All instances of `TextEncoder` only support UTF-8 encoding.
```
const encoder = new TextEncoder();
const uint8array = encoder.encode('this is some data');
```
The `TextEncoder` class is also available on the global object.
####
`textEncoder.encode([input])`
* `input` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The text to encode. **Default:** an empty string.
* Returns: [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
UTF-8 encodes the `input` string and returns a `Uint8Array` containing the encoded bytes.
####
`textEncoder.encodeInto(src, dest)`
* `src` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The text to encode.
* `dest` [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) The array to hold the encode result.
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `read` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The read Unicode code units of src.
+ `written` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The written UTF-8 bytes of dest.
UTF-8 encodes the `src` string to the `dest` Uint8Array and returns an object containing the read Unicode code units and written UTF-8 bytes.
```
const encoder = new TextEncoder();
const src = 'this is some data';
const dest = new Uint8Array(10);
const { read, written } = encoder.encodeInto(src, dest);
```
####
`textEncoder.encoding`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The encoding supported by the `TextEncoder` instance. Always set to `'utf-8'`.
###
`util.toUSVString(string)`
Added in: v16.8.0, v14.18.0 * `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the `string` after replacing any surrogate code points (or equivalently, any unpaired surrogate code units) with the Unicode "replacement character" U+FFFD.
###
`util.transferableAbortController()`
Added in: v18.11.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Creates and returns an [<AbortController>](globals#class-abortcontroller) instance whose [<AbortSignal>](globals#class-abortsignal) is marked as transferable and can be used with `structuredClone()` or `postMessage()`.
###
`util.transferableAbortSignal(signal)`
Added in: v18.11.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `signal` [<AbortSignal>](globals#class-abortsignal)
* Returns: [<AbortSignal>](globals#class-abortsignal)
Marks the given [<AbortSignal>](globals#class-abortsignal) as transferable so that it can be used with `structuredClone()` and `postMessage()`.
```
const signal = transferableAbortSignal(AbortSignal.timeout(100));
const channel = new MessageChannel();
channel.port2.postMessage(signal, [signal]);
```
###
`util.types`
History
| Version | Changes |
| --- | --- |
| v15.3.0 | Exposed as `require('util/types')`. |
| v10.0.0 | Added in: v10.0.0 |
`util.types` provides type checks for different kinds of built-in objects. Unlike `instanceof` or `Object.prototype.toString.call(value)`, these checks do not inspect properties of the object that are accessible from JavaScript (like their prototype), and usually have the overhead of calling into C++.
The result generally does not make any guarantees about what kinds of properties or behavior a value exposes in JavaScript. They are primarily useful for addon developers who prefer to do type checking in JavaScript.
The API is accessible via `require('node:util').types` or `require('node:util/types')`.
####
`util.types.isAnyArrayBuffer(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) or [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) instance.
See also [`util.types.isArrayBuffer()`](#utiltypesisarraybuffervalue) and [`util.types.isSharedArrayBuffer()`](#utiltypesissharedarraybuffervalue).
```
util.types.isAnyArrayBuffer(new ArrayBuffer()); // Returns true
util.types.isAnyArrayBuffer(new SharedArrayBuffer()); // Returns true
```
####
`util.types.isArrayBufferView(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is an instance of one of the [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) views, such as typed array objects or [`DataView`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView). Equivalent to [`ArrayBuffer.isView()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView).
```
util.types.isArrayBufferView(new Int8Array()); // true
util.types.isArrayBufferView(Buffer.from('hello world')); // true
util.types.isArrayBufferView(new DataView(new ArrayBuffer(16))); // true
util.types.isArrayBufferView(new ArrayBuffer()); // false
```
####
`util.types.isArgumentsObject(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is an `arguments` object.
```
function foo() {
util.types.isArgumentsObject(arguments); // Returns true
}
```
####
`util.types.isArrayBuffer(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) instance. This does *not* include [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) instances. Usually, it is desirable to test for both; See [`util.types.isAnyArrayBuffer()`](#utiltypesisanyarraybuffervalue) for that.
```
util.types.isArrayBuffer(new ArrayBuffer()); // Returns true
util.types.isArrayBuffer(new SharedArrayBuffer()); // Returns false
```
####
`util.types.isAsyncFunction(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is an [async function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function). This only reports back what the JavaScript engine is seeing; in particular, the return value may not match the original source code if a transpilation tool was used.
```
util.types.isAsyncFunction(function foo() {}); // Returns false
util.types.isAsyncFunction(async function foo() {}); // Returns true
```
####
`util.types.isBigInt64Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a `BigInt64Array` instance.
```
util.types.isBigInt64Array(new BigInt64Array()); // Returns true
util.types.isBigInt64Array(new BigUint64Array()); // Returns false
```
####
`util.types.isBigUint64Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a `BigUint64Array` instance.
```
util.types.isBigUint64Array(new BigInt64Array()); // Returns false
util.types.isBigUint64Array(new BigUint64Array()); // Returns true
```
####
`util.types.isBooleanObject(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a boolean object, e.g. created by `new Boolean()`.
```
util.types.isBooleanObject(false); // Returns false
util.types.isBooleanObject(true); // Returns false
util.types.isBooleanObject(new Boolean(false)); // Returns true
util.types.isBooleanObject(new Boolean(true)); // Returns true
util.types.isBooleanObject(Boolean(false)); // Returns false
util.types.isBooleanObject(Boolean(true)); // Returns false
```
####
`util.types.isBoxedPrimitive(value)`
Added in: v10.11.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is any boxed primitive object, e.g. created by `new Boolean()`, `new String()` or `Object(Symbol())`.
For example:
```
util.types.isBoxedPrimitive(false); // Returns false
util.types.isBoxedPrimitive(new Boolean(false)); // Returns true
util.types.isBoxedPrimitive(Symbol('foo')); // Returns false
util.types.isBoxedPrimitive(Object(Symbol('foo'))); // Returns true
util.types.isBoxedPrimitive(Object(BigInt(5))); // Returns true
```
####
`util.types.isCryptoKey(value)`
Added in: v16.2.0 * `value` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if `value` is a [<CryptoKey>](webcrypto#class-cryptokey), `false` otherwise.
####
`util.types.isDataView(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`DataView`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) instance.
```
const ab = new ArrayBuffer(20);
util.types.isDataView(new DataView(ab)); // Returns true
util.types.isDataView(new Float64Array()); // Returns false
```
See also [`ArrayBuffer.isView()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView).
####
`util.types.isDate(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Date`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date) instance.
```
util.types.isDate(new Date()); // Returns true
```
####
`util.types.isExternal(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a native `External` value.
A native `External` value is a special type of object that contains a raw C++ pointer (`void*`) for access from native code, and has no other properties. Such objects are created either by Node.js internals or native addons. In JavaScript, they are [frozen](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze) objects with a `null` prototype.
```
#include <js_native_api.h>
#include <stdlib.h>
napi_value result;
static napi_value MyNapi(napi_env env, napi_callback_info info) {
int* raw = (int*) malloc(1024);
napi_status status = napi_create_external(env, (void*) raw, NULL, NULL, &result);
if (status != napi_ok) {
napi_throw_error(env, NULL, "napi_create_external failed");
return NULL;
}
return result;
}
...
DECLARE_NAPI_PROPERTY("myNapi", MyNapi)
...
```
```
const native = require('napi_addon.node');
const data = native.myNapi();
util.types.isExternal(data); // returns true
util.types.isExternal(0); // returns false
util.types.isExternal(new String('foo')); // returns false
```
For further information on `napi_create_external`, refer to [`napi_create_external()`](n-api#napi_create_external).
####
`util.types.isFloat32Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Float32Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array) instance.
```
util.types.isFloat32Array(new ArrayBuffer()); // Returns false
util.types.isFloat32Array(new Float32Array()); // Returns true
util.types.isFloat32Array(new Float64Array()); // Returns false
```
####
`util.types.isFloat64Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Float64Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float64Array) instance.
```
util.types.isFloat64Array(new ArrayBuffer()); // Returns false
util.types.isFloat64Array(new Uint8Array()); // Returns false
util.types.isFloat64Array(new Float64Array()); // Returns true
```
####
`util.types.isGeneratorFunction(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a generator function. This only reports back what the JavaScript engine is seeing; in particular, the return value may not match the original source code if a transpilation tool was used.
```
util.types.isGeneratorFunction(function foo() {}); // Returns false
util.types.isGeneratorFunction(function* foo() {}); // Returns true
```
####
`util.types.isGeneratorObject(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a generator object as returned from a built-in generator function. This only reports back what the JavaScript engine is seeing; in particular, the return value may not match the original source code if a transpilation tool was used.
```
function* foo() {}
const generator = foo();
util.types.isGeneratorObject(generator); // Returns true
```
####
`util.types.isInt8Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Int8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int8Array) instance.
```
util.types.isInt8Array(new ArrayBuffer()); // Returns false
util.types.isInt8Array(new Int8Array()); // Returns true
util.types.isInt8Array(new Float64Array()); // Returns false
```
####
`util.types.isInt16Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Int16Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int16Array) instance.
```
util.types.isInt16Array(new ArrayBuffer()); // Returns false
util.types.isInt16Array(new Int16Array()); // Returns true
util.types.isInt16Array(new Float64Array()); // Returns false
```
####
`util.types.isInt32Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Int32Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int32Array) instance.
```
util.types.isInt32Array(new ArrayBuffer()); // Returns false
util.types.isInt32Array(new Int32Array()); // Returns true
util.types.isInt32Array(new Float64Array()); // Returns false
```
####
`util.types.isKeyObject(value)`
Added in: v16.2.0 * `value` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if `value` is a [<KeyObject>](crypto#class-keyobject), `false` otherwise.
####
`util.types.isMap(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) instance.
```
util.types.isMap(new Map()); // Returns true
```
####
`util.types.isMapIterator(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is an iterator returned for a built-in [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) instance.
```
const map = new Map();
util.types.isMapIterator(map.keys()); // Returns true
util.types.isMapIterator(map.values()); // Returns true
util.types.isMapIterator(map.entries()); // Returns true
util.types.isMapIterator(map[Symbol.iterator]()); // Returns true
```
####
`util.types.isModuleNamespaceObject(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is an instance of a [Module Namespace Object](https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects).
```
import * as ns from './a.js';
util.types.isModuleNamespaceObject(ns); // Returns true
```
####
`util.types.isNativeError(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is an instance of a built-in [`Error`](errors#class-error) type.
```
util.types.isNativeError(new Error()); // Returns true
util.types.isNativeError(new TypeError()); // Returns true
util.types.isNativeError(new RangeError()); // Returns true
```
####
`util.types.isNumberObject(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a number object, e.g. created by `new Number()`.
```
util.types.isNumberObject(0); // Returns false
util.types.isNumberObject(new Number(0)); // Returns true
```
####
`util.types.isPromise(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise).
```
util.types.isPromise(Promise.resolve(42)); // Returns true
```
####
`util.types.isProxy(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a [`Proxy`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy) instance.
```
const target = {};
const proxy = new Proxy(target, {});
util.types.isProxy(target); // Returns false
util.types.isProxy(proxy); // Returns true
```
####
`util.types.isRegExp(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a regular expression object.
```
util.types.isRegExp(/abc/); // Returns true
util.types.isRegExp(new RegExp('abc')); // Returns true
```
####
`util.types.isSet(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Set`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set) instance.
```
util.types.isSet(new Set()); // Returns true
```
####
`util.types.isSetIterator(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is an iterator returned for a built-in [`Set`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set) instance.
```
const set = new Set();
util.types.isSetIterator(set.keys()); // Returns true
util.types.isSetIterator(set.values()); // Returns true
util.types.isSetIterator(set.entries()); // Returns true
util.types.isSetIterator(set[Symbol.iterator]()); // Returns true
```
####
`util.types.isSharedArrayBuffer(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) instance. This does *not* include [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) instances. Usually, it is desirable to test for both; See [`util.types.isAnyArrayBuffer()`](#utiltypesisanyarraybuffervalue) for that.
```
util.types.isSharedArrayBuffer(new ArrayBuffer()); // Returns false
util.types.isSharedArrayBuffer(new SharedArrayBuffer()); // Returns true
```
####
`util.types.isStringObject(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a string object, e.g. created by `new String()`.
```
util.types.isStringObject('foo'); // Returns false
util.types.isStringObject(new String('foo')); // Returns true
```
####
`util.types.isSymbolObject(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a symbol object, created by calling `Object()` on a `Symbol` primitive.
```
const symbol = Symbol('foo');
util.types.isSymbolObject(symbol); // Returns false
util.types.isSymbolObject(Object(symbol)); // Returns true
```
####
`util.types.isTypedArray(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) instance.
```
util.types.isTypedArray(new ArrayBuffer()); // Returns false
util.types.isTypedArray(new Uint8Array()); // Returns true
util.types.isTypedArray(new Float64Array()); // Returns true
```
See also [`ArrayBuffer.isView()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView).
####
`util.types.isUint8Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) instance.
```
util.types.isUint8Array(new ArrayBuffer()); // Returns false
util.types.isUint8Array(new Uint8Array()); // Returns true
util.types.isUint8Array(new Float64Array()); // Returns false
```
####
`util.types.isUint8ClampedArray(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Uint8ClampedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8ClampedArray) instance.
```
util.types.isUint8ClampedArray(new ArrayBuffer()); // Returns false
util.types.isUint8ClampedArray(new Uint8ClampedArray()); // Returns true
util.types.isUint8ClampedArray(new Float64Array()); // Returns false
```
####
`util.types.isUint16Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Uint16Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint16Array) instance.
```
util.types.isUint16Array(new ArrayBuffer()); // Returns false
util.types.isUint16Array(new Uint16Array()); // Returns true
util.types.isUint16Array(new Float64Array()); // Returns false
```
####
`util.types.isUint32Array(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`Uint32Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array) instance.
```
util.types.isUint32Array(new ArrayBuffer()); // Returns false
util.types.isUint32Array(new Uint32Array()); // Returns true
util.types.isUint32Array(new Float64Array()); // Returns false
```
####
`util.types.isWeakMap(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`WeakMap`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap) instance.
```
util.types.isWeakMap(new WeakMap()); // Returns true
```
####
`util.types.isWeakSet(value)`
Added in: v10.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`WeakSet`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet) instance.
```
util.types.isWeakSet(new WeakSet()); // Returns true
```
####
`util.types.isWebAssemblyCompiledModule(value)`
Added in: v10.0.0Deprecated since: v14.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `value instanceof WebAssembly.Module` instead.
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the value is a built-in [`WebAssembly.Module`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Module) instance.
```
const module = new WebAssembly.Module(wasmBuffer);
util.types.isWebAssemblyCompiledModule(module); // Returns true
```
### Deprecated APIs
The following APIs are deprecated and should no longer be used. Existing applications and modules should be updated to find alternative approaches.
####
`util._extend(target, source)`
Added in: v0.7.5Deprecated since: v6.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Object.assign()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign) instead.
* `target` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `source` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `util._extend()` method was never intended to be used outside of internal Node.js modules. The community found and used it anyway.
It is deprecated and should not be used in new code. JavaScript comes with very similar built-in functionality through [`Object.assign()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign).
####
`util.isArray(object)`
Added in: v0.6.0Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Array.isArray()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray) instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Alias for [`Array.isArray()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray).
Returns `true` if the given `object` is an `Array`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isArray([]);
// Returns: true
util.isArray(new Array());
// Returns: true
util.isArray({});
// Returns: false
```
####
`util.isBoolean(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `typeof value === 'boolean'` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is a `Boolean`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isBoolean(1);
// Returns: false
util.isBoolean(0);
// Returns: false
util.isBoolean(false);
// Returns: true
```
####
`util.isBuffer(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Buffer.isBuffer()`](buffer#static-method-bufferisbufferobj) instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is a `Buffer`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isBuffer({ length: 0 });
// Returns: false
util.isBuffer([]);
// Returns: false
util.isBuffer(Buffer.from('hello world'));
// Returns: true
```
####
`util.isDate(object)`
Added in: v0.6.0Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`util.types.isDate()`](#utiltypesisdatevalue) instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is a `Date`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isDate(new Date());
// Returns: true
util.isDate(Date());
// false (without 'new' returns a String)
util.isDate({});
// Returns: false
```
####
`util.isError(object)`
Added in: v0.6.0Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`util.types.isNativeError()`](#utiltypesisnativeerrorvalue) instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is an [`Error`](errors#class-error). Otherwise, returns `false`.
```
const util = require('node:util');
util.isError(new Error());
// Returns: true
util.isError(new TypeError());
// Returns: true
util.isError({ name: 'Error', message: 'an error occurred' });
// Returns: false
```
This method relies on `Object.prototype.toString()` behavior. It is possible to obtain an incorrect result when the `object` argument manipulates `@@toStringTag`.
```
const util = require('node:util');
const obj = { name: 'Error', message: 'an error occurred' };
util.isError(obj);
// Returns: false
obj[Symbol.toStringTag] = 'Error';
util.isError(obj);
// Returns: true
```
####
`util.isFunction(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `typeof value === 'function'` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is a `Function`. Otherwise, returns `false`.
```
const util = require('node:util');
function Foo() {}
const Bar = () => {};
util.isFunction({});
// Returns: false
util.isFunction(Foo);
// Returns: true
util.isFunction(Bar);
// Returns: true
```
####
`util.isNull(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `value === null` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is strictly `null`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isNull(0);
// Returns: false
util.isNull(undefined);
// Returns: false
util.isNull(null);
// Returns: true
```
####
`util.isNullOrUndefined(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `value === undefined || value === null` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is `null` or `undefined`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isNullOrUndefined(0);
// Returns: false
util.isNullOrUndefined(undefined);
// Returns: true
util.isNullOrUndefined(null);
// Returns: true
```
####
`util.isNumber(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `typeof value === 'number'` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is a `Number`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isNumber(false);
// Returns: false
util.isNumber(Infinity);
// Returns: true
util.isNumber(0);
// Returns: true
util.isNumber(NaN);
// Returns: true
```
####
`util.isObject(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `value !== null && typeof value === 'object'` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is strictly an `Object` **and** not a `Function` (even though functions are objects in JavaScript). Otherwise, returns `false`.
```
const util = require('node:util');
util.isObject(5);
// Returns: false
util.isObject(null);
// Returns: false
util.isObject({});
// Returns: true
util.isObject(() => {});
// Returns: false
```
####
`util.isPrimitive(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `(typeof value !== 'object' && typeof value !== 'function') || value === null` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is a primitive type. Otherwise, returns `false`.
```
const util = require('node:util');
util.isPrimitive(5);
// Returns: true
util.isPrimitive('foo');
// Returns: true
util.isPrimitive(false);
// Returns: true
util.isPrimitive(null);
// Returns: true
util.isPrimitive(undefined);
// Returns: true
util.isPrimitive({});
// Returns: false
util.isPrimitive(() => {});
// Returns: false
util.isPrimitive(/^$/);
// Returns: false
util.isPrimitive(new Date());
// Returns: false
```
####
`util.isRegExp(object)`
Added in: v0.6.0Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is a `RegExp`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isRegExp(/some regexp/);
// Returns: true
util.isRegExp(new RegExp('another regexp'));
// Returns: true
util.isRegExp({});
// Returns: false
```
####
`util.isString(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `typeof value === 'string'` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is a `string`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isString('');
// Returns: true
util.isString('foo');
// Returns: true
util.isString(String('foo'));
// Returns: true
util.isString(5);
// Returns: false
```
####
`util.isSymbol(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `typeof value === 'symbol'` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is a `Symbol`. Otherwise, returns `false`.
```
const util = require('node:util');
util.isSymbol(5);
// Returns: false
util.isSymbol('foo');
// Returns: false
util.isSymbol(Symbol('foo'));
// Returns: true
```
####
`util.isUndefined(object)`
Added in: v0.11.5Deprecated since: v4.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `value === undefined` instead.
* `object` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` is `undefined`. Otherwise, returns `false`.
```
const util = require('node:util');
const foo = undefined;
util.isUndefined(5);
// Returns: false
util.isUndefined(foo);
// Returns: true
util.isUndefined(null);
// Returns: false
```
####
`util.log(string)`
Added in: v0.3.0Deprecated since: v6.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use a third party module instead.
* `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `util.log()` method prints the given `string` to `stdout` with an included timestamp.
```
const util = require('node:util');
util.log('Timestamped message.');
```
| programming_docs |
node None WebAssembly System Interface (WASI)
-----------------------------------
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
**Source Code:** [lib/wasi.js](https://github.com/nodejs/node/blob/v19.0.1/lib/wasi.js)
The WASI API provides an implementation of the [WebAssembly System Interface](https://wasi.dev/) specification. WASI gives sandboxed WebAssembly applications access to the underlying operating system via a collection of POSIX-like functions.
MJS modules
```
import { readFile } from 'node:fs/promises';
import { WASI } from 'wasi';
import { argv, env } from 'node:process';
const wasi = new WASI({
args: argv,
env,
preopens: {
'/sandbox': '/some/real/path/that/wasm/can/access'
}
});
// Some WASI binaries require:
// const importObject = { wasi_unstable: wasi.wasiImport };
const importObject = { wasi_snapshot_preview1: wasi.wasiImport };
const wasm = await WebAssembly.compile(
await readFile(new URL('./demo.wasm', import.meta.url))
);
const instance = await WebAssembly.instantiate(wasm, importObject);
wasi.start(instance);
```
CJS modules
```
'use strict';
const { readFile } = require('node:fs/promises');
const { WASI } = require('wasi');
const { argv, env } = require('node:process');
const { join } = require('node:path');
const wasi = new WASI({
args: argv,
env,
preopens: {
'/sandbox': '/some/real/path/that/wasm/can/access'
}
});
// Some WASI binaries require:
// const importObject = { wasi_unstable: wasi.wasiImport };
const importObject = { wasi_snapshot_preview1: wasi.wasiImport };
(async () => {
const wasm = await WebAssembly.compile(
await readFile(join(__dirname, 'demo.wasm'))
);
const instance = await WebAssembly.instantiate(wasm, importObject);
wasi.start(instance);
})();
```
To run the above example, create a new WebAssembly text format file named `demo.wat`:
```
(module
;; Import the required fd_write WASI function which will write the given io vectors to stdout
;; The function signature for fd_write is:
;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written
(import "wasi_snapshot_preview1" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32)))
(memory 1)
(export "memory" (memory 0))
;; Write 'hello world\n' to memory at an offset of 8 bytes
;; Note the trailing newline which is required for the text to appear
(data (i32.const 8) "hello world\n")
(func $main (export "_start")
;; Creating a new io vector within linear memory
(i32.store (i32.const 0) (i32.const 8)) ;; iov.iov_base - This is a pointer to the start of the 'hello world\n' string
(i32.store (i32.const 4) (i32.const 12)) ;; iov.iov_len - The length of the 'hello world\n' string
(call $fd_write
(i32.const 1) ;; file_descriptor - 1 for stdout
(i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0
(i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one.
(i32.const 20) ;; nwritten - A place in memory to store the number of bytes written
)
drop ;; Discard the number of bytes written from the top of the stack
)
)
```
Use [wabt](https://github.com/WebAssembly/wabt) to compile `.wat` to `.wasm`
```
$ wat2wasm demo.wat
```
The `--experimental-wasi-unstable-preview1` CLI argument is needed for this example to run.
### Class: `WASI`
Added in: v13.3.0, v12.16.0 The `WASI` class provides the WASI system call API and additional convenience methods for working with WASI-based applications. Each `WASI` instance represents a distinct sandbox environment. For security purposes, each `WASI` instance must have its command-line arguments, environment variables, and sandbox directory structure configured explicitly.
####
`new WASI([options])`
Added in: v13.3.0, v12.16.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `args` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) An array of strings that the WebAssembly application will see as command-line arguments. The first argument is the virtual path to the WASI command itself. **Default:** `[]`.
+ `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object similar to `process.env` that the WebAssembly application will see as its environment. **Default:** `{}`.
+ `preopens` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) This object represents the WebAssembly application's sandbox directory structure. The string keys of `preopens` are treated as directories within the sandbox. The corresponding values in `preopens` are the real paths to those directories on the host machine.
+ `returnOnExit` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) By default, WASI applications terminate the Node.js process via the `__wasi_proc_exit()` function. Setting this option to `true` causes `wasi.start()` to return the exit code rather than terminate the process. **Default:** `false`.
+ `stdin` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The file descriptor used as standard input in the WebAssembly application. **Default:** `0`.
+ `stdout` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The file descriptor used as standard output in the WebAssembly application. **Default:** `1`.
+ `stderr` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The file descriptor used as standard error in the WebAssembly application. **Default:** `2`.
####
`wasi.start(instance)`
Added in: v13.3.0, v12.16.0 * `instance` [<WebAssembly.Instance>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance)
Attempt to begin execution of `instance` as a WASI command by invoking its `_start()` export. If `instance` does not contain a `_start()` export, or if `instance` contains an `_initialize()` export, then an exception is thrown.
`start()` requires that `instance` exports a [`WebAssembly.Memory`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory) named `memory`. If `instance` does not have a `memory` export an exception is thrown.
If `start()` is called more than once, an exception is thrown.
####
`wasi.initialize(instance)`
Added in: v14.6.0, v12.19.0 * `instance` [<WebAssembly.Instance>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance)
Attempt to initialize `instance` as a WASI reactor by invoking its `_initialize()` export, if it is present. If `instance` contains a `_start()` export, then an exception is thrown.
`initialize()` requires that `instance` exports a [`WebAssembly.Memory`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory) named `memory`. If `instance` does not have a `memory` export an exception is thrown.
If `initialize()` is called more than once, an exception is thrown.
####
`wasi.wasiImport`
Added in: v13.3.0, v12.16.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
`wasiImport` is an object that implements the WASI system call API. This object should be passed as the `wasi_snapshot_preview1` import during the instantiation of a [`WebAssembly.Instance`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance).
node None Modules: CommonJS modules
-------------------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
CommonJS modules are the original way to package JavaScript code for Node.js. Node.js also supports the [ECMAScript modules](esm) standard used by browsers and other JavaScript runtimes.
In Node.js, each file is treated as a separate module. For example, consider a file named `foo.js`:
```
const circle = require('./circle.js');
console.log(`The area of a circle of radius 4 is ${circle.area(4)}`);
```
On the first line, `foo.js` loads the module `circle.js` that is in the same directory as `foo.js`.
Here are the contents of `circle.js`:
```
const { PI } = Math;
exports.area = (r) => PI * r ** 2;
exports.circumference = (r) => 2 * PI * r;
```
The module `circle.js` has exported the functions `area()` and `circumference()`. Functions and objects are added to the root of a module by specifying additional properties on the special `exports` object.
Variables local to the module will be private, because the module is wrapped in a function by Node.js (see [module wrapper](#the-module-wrapper)). In this example, the variable `PI` is private to `circle.js`.
The `module.exports` property can be assigned a new value (such as a function or object).
Below, `bar.js` makes use of the `square` module, which exports a Square class:
```
const Square = require('./square.js');
const mySquare = new Square(2);
console.log(`The area of mySquare is ${mySquare.area()}`);
```
The `square` module is defined in `square.js`:
```
// Assigning to exports will not modify module, must use module.exports
module.exports = class Square {
constructor(width) {
this.width = width;
}
area() {
return this.width ** 2;
}
};
```
The CommonJS module system is implemented in the [`module` core module](module).
### Enabling
Node.js has two module systems: CommonJS modules and [ECMAScript modules](esm).
By default, Node.js will treat the following as CommonJS modules:
* Files with a `.cjs` extension;
* Files with a `.js` extension when the nearest parent `package.json` file contains a top-level field [`"type"`](packages#type) with a value of `"commonjs"`.
* Files with a `.js` extension when the nearest parent `package.json` file doesn't contain a top-level field [`"type"`](packages#type). Package authors should include the [`"type"`](packages#type) field, even in packages where all sources are CommonJS. Being explicit about the `type` of the package will make things easier for build tools and loaders to determine how the files in the package should be interpreted.
* Files with an extension that is not `.mjs`, `.cjs`, `.json`, `.node`, or `.js` (when the nearest parent `package.json` file contains a top-level field [`"type"`](packages#type) with a value of `"module"`, those files will be recognized as CommonJS modules only if they are being `require`d, not when used as the command-line entry point of the program).
See [Determining module system](packages#determining-module-system) for more details.
Calling `require()` always use the CommonJS module loader. Calling `import()` always use the ECMAScript module loader.
### Accessing the main module
When a file is run directly from Node.js, `require.main` is set to its `module`. That means that it is possible to determine whether a file has been run directly by testing `require.main === module`.
For a file `foo.js`, this will be `true` if run via `node foo.js`, but `false` if run by `require('./foo')`.
When the entry point is not a CommonJS module, `require.main` is `undefined`, and the main module is out of reach.
### Package manager tips
The semantics of the Node.js `require()` function were designed to be general enough to support reasonable directory structures. Package manager programs such as `dpkg`, `rpm`, and `npm` will hopefully find it possible to build native packages from Node.js modules without modification.
Below we give a suggested directory structure that could work:
Let's say that we wanted to have the folder at `/usr/lib/node/<some-package>/<some-version>` hold the contents of a specific version of a package.
Packages can depend on one another. In order to install package `foo`, it may be necessary to install a specific version of package `bar`. The `bar` package may itself have dependencies, and in some cases, these may even collide or form cyclic dependencies.
Because Node.js looks up the `realpath` of any modules it loads (that is, it resolves symlinks) and then [looks for their dependencies in `node_modules` folders](#loading-from-node_modules-folders), this situation can be resolved with the following architecture:
* `/usr/lib/node/foo/1.2.3/`: Contents of the `foo` package, version 1.2.3.
* `/usr/lib/node/bar/4.3.2/`: Contents of the `bar` package that `foo` depends on.
* `/usr/lib/node/foo/1.2.3/node_modules/bar`: Symbolic link to `/usr/lib/node/bar/4.3.2/`.
* `/usr/lib/node/bar/4.3.2/node_modules/*`: Symbolic links to the packages that `bar` depends on.
Thus, even if a cycle is encountered, or if there are dependency conflicts, every module will be able to get a version of its dependency that it can use.
When the code in the `foo` package does `require('bar')`, it will get the version that is symlinked into `/usr/lib/node/foo/1.2.3/node_modules/bar`. Then, when the code in the `bar` package calls `require('quux')`, it'll get the version that is symlinked into `/usr/lib/node/bar/4.3.2/node_modules/quux`.
Furthermore, to make the module lookup process even more optimal, rather than putting packages directly in `/usr/lib/node`, we could put them in `/usr/lib/node_modules/<name>/<version>`. Then Node.js will not bother looking for missing dependencies in `/usr/node_modules` or `/node_modules`.
In order to make modules available to the Node.js REPL, it might be useful to also add the `/usr/lib/node_modules` folder to the `$NODE_PATH` environment variable. Since the module lookups using `node_modules` folders are all relative, and based on the real path of the files making the calls to `require()`, the packages themselves can be anywhere.
### The `.mjs` extension
Due to the synchronous nature of `require()`, it is not possible to use it to load ECMAScript module files. Attempting to do so will throw a [`ERR_REQUIRE_ESM`](errors#err_require_esm) error. Use [`import()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import) instead.
The `.mjs` extension is reserved for [ECMAScript Modules](esm) which cannot be loaded via `require()`. See [Determining module system](packages#determining-module-system) section for more info regarding which files are parsed as ECMAScript modules.
### All together
To get the exact filename that will be loaded when `require()` is called, use the `require.resolve()` function.
Putting together all of the above, here is the high-level algorithm in pseudocode of what `require()` does:
```
require(X) from module at path Y
1. If X is a core module,
a. return the core module
b. STOP
2. If X begins with '/'
a. set Y to be the filesystem root
3. If X begins with './' or '/' or '../'
a. LOAD_AS_FILE(Y + X)
b. LOAD_AS_DIRECTORY(Y + X)
c. THROW "not found"
4. If X begins with '#'
a. LOAD_PACKAGE_IMPORTS(X, dirname(Y))
5. LOAD_PACKAGE_SELF(X, dirname(Y))
6. LOAD_NODE_MODULES(X, dirname(Y))
7. THROW "not found"
LOAD_AS_FILE(X)
1. If X is a file, load X as its file extension format. STOP
2. If X.js is a file, load X.js as JavaScript text. STOP
3. If X.json is a file, parse X.json to a JavaScript Object. STOP
4. If X.node is a file, load X.node as binary addon. STOP
LOAD_INDEX(X)
1. If X/index.js is a file, load X/index.js as JavaScript text. STOP
2. If X/index.json is a file, parse X/index.json to a JavaScript object. STOP
3. If X/index.node is a file, load X/index.node as binary addon. STOP
LOAD_AS_DIRECTORY(X)
1. If X/package.json is a file,
a. Parse X/package.json, and look for "main" field.
b. If "main" is a falsy value, GOTO 2.
c. let M = X + (json main field)
d. LOAD_AS_FILE(M)
e. LOAD_INDEX(M)
f. LOAD_INDEX(X) DEPRECATED
g. THROW "not found"
2. LOAD_INDEX(X)
LOAD_NODE_MODULES(X, START)
1. let DIRS = NODE_MODULES_PATHS(START)
2. for each DIR in DIRS:
a. LOAD_PACKAGE_EXPORTS(X, DIR)
b. LOAD_AS_FILE(DIR/X)
c. LOAD_AS_DIRECTORY(DIR/X)
NODE_MODULES_PATHS(START)
1. let PARTS = path split(START)
2. let I = count of PARTS - 1
3. let DIRS = []
4. while I >= 0,
a. if PARTS[I] = "node_modules" CONTINUE
b. DIR = path join(PARTS[0 .. I] + "node_modules")
c. DIRS = DIR + DIRS
d. let I = I - 1
5. return DIRS + GLOBAL_FOLDERS
LOAD_PACKAGE_IMPORTS(X, DIR)
1. Find the closest package scope SCOPE to DIR.
2. If no scope was found, return.
3. If the SCOPE/package.json "imports" is null or undefined, return.
4. let MATCH = PACKAGE_IMPORTS_RESOLVE(X, pathToFileURL(SCOPE),
["node", "require"]) [defined in the ESM resolver](esm.md#resolver-algorithm-specification).
5. RESOLVE_ESM_MATCH(MATCH).
LOAD_PACKAGE_EXPORTS(X, DIR)
1. Try to interpret X as a combination of NAME and SUBPATH where the name
may have a @scope/ prefix and the subpath begins with a slash (`/`).
2. If X does not match this pattern or DIR/NAME/package.json is not a file,
return.
3. Parse DIR/NAME/package.json, and look for "exports" field.
4. If "exports" is null or undefined, return.
5. let MATCH = PACKAGE_EXPORTS_RESOLVE(pathToFileURL(DIR/NAME), "." + SUBPATH,
`package.json` "exports", ["node", "require"]) [defined in the ESM resolver](esm.md#resolver-algorithm-specification).
6. RESOLVE_ESM_MATCH(MATCH)
LOAD_PACKAGE_SELF(X, DIR)
1. Find the closest package scope SCOPE to DIR.
2. If no scope was found, return.
3. If the SCOPE/package.json "exports" is null or undefined, return.
4. If the SCOPE/package.json "name" is not the first segment of X, return.
5. let MATCH = PACKAGE_EXPORTS_RESOLVE(pathToFileURL(SCOPE),
"." + X.slice("name".length), `package.json` "exports", ["node", "require"])
[defined in the ESM resolver](esm.md#resolver-algorithm-specification).
6. RESOLVE_ESM_MATCH(MATCH)
RESOLVE_ESM_MATCH(MATCH)
1. let { RESOLVED, EXACT } = MATCH
2. let RESOLVED_PATH = fileURLToPath(RESOLVED)
3. If EXACT is true,
a. If the file at RESOLVED_PATH exists, load RESOLVED_PATH as its extension
format. STOP
4. Otherwise, if EXACT is false,
a. LOAD_AS_FILE(RESOLVED_PATH)
b. LOAD_AS_DIRECTORY(RESOLVED_PATH)
5. THROW "not found"
```
### Caching
Modules are cached after the first time they are loaded. This means (among other things) that every call to `require('foo')` will get exactly the same object returned, if it would resolve to the same file.
Provided `require.cache` is not modified, multiple calls to `require('foo')` will not cause the module code to be executed multiple times. This is an important feature. With it, "partially done" objects can be returned, thus allowing transitive dependencies to be loaded even when they would cause cycles.
To have a module execute code multiple times, export a function, and call that function.
#### Module caching caveats
Modules are cached based on their resolved filename. Since modules may resolve to a different filename based on the location of the calling module (loading from `node_modules` folders), it is not a *guarantee* that `require('foo')` will always return the exact same object, if it would resolve to different files.
Additionally, on case-insensitive file systems or operating systems, different resolved filenames can point to the same file, but the cache will still treat them as different modules and will reload the file multiple times. For example, `require('./foo')` and `require('./FOO')` return two different objects, irrespective of whether or not `./foo` and `./FOO` are the same file.
### Core modules
History
| Version | Changes |
| --- | --- |
| v16.0.0, v14.18.0 | Added `node:` import support to `require(...)`. |
Node.js has several modules compiled into the binary. These modules are described in greater detail elsewhere in this documentation.
The core modules are defined within the Node.js source and are located in the `lib/` folder.
Core modules can be identified using the `node:` prefix, in which case it bypasses the `require` cache. For instance, `require('node:http')` will always return the built in HTTP module, even if there is `require.cache` entry by that name.
Some core modules are always preferentially loaded if their identifier is passed to `require()`. For instance, `require('http')` will always return the built-in HTTP module, even if there is a file by that name. The list of core modules that can be loaded without using the `node:` prefix is exposed as [`module.builtinModules`](module#modulebuiltinmodules).
### Cycles
When there are circular `require()` calls, a module might not have finished executing when it is returned.
Consider this situation:
`a.js`:
```
console.log('a starting');
exports.done = false;
const b = require('./b.js');
console.log('in a, b.done = %j', b.done);
exports.done = true;
console.log('a done');
```
`b.js`:
```
console.log('b starting');
exports.done = false;
const a = require('./a.js');
console.log('in b, a.done = %j', a.done);
exports.done = true;
console.log('b done');
```
`main.js`:
```
console.log('main starting');
const a = require('./a.js');
const b = require('./b.js');
console.log('in main, a.done = %j, b.done = %j', a.done, b.done);
```
When `main.js` loads `a.js`, then `a.js` in turn loads `b.js`. At that point, `b.js` tries to load `a.js`. In order to prevent an infinite loop, an **unfinished copy** of the `a.js` exports object is returned to the `b.js` module. `b.js` then finishes loading, and its `exports` object is provided to the `a.js` module.
By the time `main.js` has loaded both modules, they're both finished. The output of this program would thus be:
```
$ node main.js
main starting
a starting
b starting
in b, a.done = false
b done
in a, b.done = true
a done
in main, a.done = true, b.done = true
```
Careful planning is required to allow cyclic module dependencies to work correctly within an application.
### File modules
If the exact filename is not found, then Node.js will attempt to load the required filename with the added extensions: `.js`, `.json`, and finally `.node`. When loading a file that has a different extension (e.g. `.cjs`), its full name must be passed to `require()`, including its file extension (e.g. `require('./file.cjs')`).
`.json` files are parsed as JSON text files, `.node` files are interpreted as compiled addon modules loaded with `process.dlopen()`. Files using any other extension (or no extension at all) are parsed as JavaScript text files. Refer to the [Determining module system](packages#determining-module-system) section to understand what parse goal will be used.
A required module prefixed with `'/'` is an absolute path to the file. For example, `require('/home/marco/foo.js')` will load the file at `/home/marco/foo.js`.
A required module prefixed with `'./'` is relative to the file calling `require()`. That is, `circle.js` must be in the same directory as `foo.js` for `require('./circle')` to find it.
Without a leading `'/'`, `'./'`, or `'../'` to indicate a file, the module must either be a core module or is loaded from a `node_modules` folder.
If the given path does not exist, `require()` will throw a [`MODULE_NOT_FOUND`](errors#module_not_found) error.
### Folders as modules
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use [subpath exports](packages#subpath-exports) or [subpath imports](packages#subpath-imports) instead.
There are three ways in which a folder may be passed to `require()` as an argument.
The first is to create a [`package.json`](packages#nodejs-packagejson-field-definitions) file in the root of the folder, which specifies a `main` module. An example [`package.json`](packages#nodejs-packagejson-field-definitions) file might look like this:
```
{ "name" : "some-library",
"main" : "./lib/some-library.js" }
```
If this was in a folder at `./some-library`, then `require('./some-library')` would attempt to load `./some-library/lib/some-library.js`.
If there is no [`package.json`](packages#nodejs-packagejson-field-definitions) file present in the directory, or if the [`"main"`](packages#main) entry is missing or cannot be resolved, then Node.js will attempt to load an `index.js` or `index.node` file out of that directory. For example, if there was no [`package.json`](packages#nodejs-packagejson-field-definitions) file in the previous example, then `require('./some-library')` would attempt to load:
* `./some-library/index.js`
* `./some-library/index.node`
If these attempts fail, then Node.js will report the entire module as missing with the default error:
```
Error: Cannot find module 'some-library'
```
In all three above cases, an `import('./some-library')` call would result in a [`ERR_UNSUPPORTED_DIR_IMPORT`](errors#err_unsupported_dir_import) error. Using package [subpath exports](packages#subpath-exports) or [subpath imports](packages#subpath-imports) can provide the same containment organization benefits as folders as modules, and work for both `require` and `import`.
### Loading from `node_modules` folders
If the module identifier passed to `require()` is not a [core](#core-modules) module, and does not begin with `'/'`, `'../'`, or `'./'`, then Node.js starts at the directory of the current module, and adds `/node_modules`, and attempts to load the module from that location. Node.js will not append `node_modules` to a path already ending in `node_modules`.
If it is not found there, then it moves to the parent directory, and so on, until the root of the file system is reached.
For example, if the file at `'/home/ry/projects/foo.js'` called `require('bar.js')`, then Node.js would look in the following locations, in this order:
* `/home/ry/projects/node_modules/bar.js`
* `/home/ry/node_modules/bar.js`
* `/home/node_modules/bar.js`
* `/node_modules/bar.js`
This allows programs to localize their dependencies, so that they do not clash.
It is possible to require specific files or sub modules distributed with a module by including a path suffix after the module name. For instance `require('example-module/path/to/file')` would resolve `path/to/file` relative to where `example-module` is located. The suffixed path follows the same module resolution semantics.
### Loading from the global folders
If the `NODE_PATH` environment variable is set to a colon-delimited list of absolute paths, then Node.js will search those paths for modules if they are not found elsewhere.
On Windows, `NODE_PATH` is delimited by semicolons (`;`) instead of colons.
`NODE_PATH` was originally created to support loading modules from varying paths before the current [module resolution](#all-together) algorithm was defined.
`NODE_PATH` is still supported, but is less necessary now that the Node.js ecosystem has settled on a convention for locating dependent modules. Sometimes deployments that rely on `NODE_PATH` show surprising behavior when people are unaware that `NODE_PATH` must be set. Sometimes a module's dependencies change, causing a different version (or even a different module) to be loaded as the `NODE_PATH` is searched.
Additionally, Node.js will search in the following list of GLOBAL\_FOLDERS:
* 1: `$HOME/.node_modules`
* 2: `$HOME/.node_libraries`
* 3: `$PREFIX/lib/node`
Where `$HOME` is the user's home directory, and `$PREFIX` is the Node.js configured `node_prefix`.
These are mostly for historic reasons.
It is strongly encouraged to place dependencies in the local `node_modules` folder. These will be loaded faster, and more reliably.
### The module wrapper
Before a module's code is executed, Node.js will wrap it with a function wrapper that looks like the following:
```
(function(exports, require, module, __filename, __dirname) {
// Module code actually lives in here
});
```
By doing this, Node.js achieves a few things:
* It keeps top-level variables (defined with `var`, `const`, or `let`) scoped to the module rather than the global object.
* It helps to provide some global-looking variables that are actually specific to the module, such as:
+ The `module` and `exports` objects that the implementor can use to export values from the module.
+ The convenience variables `__filename` and `__dirname`, containing the module's absolute filename and directory path.
### The module scope
####
`__dirname`
Added in: v0.1.27 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The directory name of the current module. This is the same as the [`path.dirname()`](path#pathdirnamepath) of the [`__filename`](#__filename).
Example: running `node example.js` from `/Users/mjr`
```
console.log(__dirname);
// Prints: /Users/mjr
console.log(path.dirname(__filename));
// Prints: /Users/mjr
```
####
`__filename`
Added in: v0.0.1 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The file name of the current module. This is the current module file's absolute path with symlinks resolved.
For a main program this is not necessarily the same as the file name used in the command line.
See [`__dirname`](#__dirname) for the directory name of the current module.
Examples:
Running `node example.js` from `/Users/mjr`
```
console.log(__filename);
// Prints: /Users/mjr/example.js
console.log(__dirname);
// Prints: /Users/mjr
```
Given two modules: `a` and `b`, where `b` is a dependency of `a` and there is a directory structure of:
* `/Users/mjr/app/a.js`
* `/Users/mjr/app/node_modules/b/b.js`
References to `__filename` within `b.js` will return `/Users/mjr/app/node_modules/b/b.js` while references to `__filename` within `a.js` will return `/Users/mjr/app/a.js`.
####
`exports`
Added in: v0.1.12 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
A reference to the `module.exports` that is shorter to type. See the section about the [exports shortcut](#exports-shortcut) for details on when to use `exports` and when to use `module.exports`.
####
`module`
Added in: v0.1.16 * [<module>](modules#the-module-object)
A reference to the current module, see the section about the [`module` object](#the-module-object). In particular, `module.exports` is used for defining what a module exports and makes available through `require()`.
####
`require(id)`
Added in: v0.1.13 * `id` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) module name or path
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) exported module content
Used to import modules, `JSON`, and local files. Modules can be imported from `node_modules`. Local modules and JSON files can be imported using a relative path (e.g. `./`, `./foo`, `./bar/baz`, `../foo`) that will be resolved against the directory named by [`__dirname`](#__dirname) (if defined) or the current working directory. The relative paths of POSIX style are resolved in an OS independent fashion, meaning that the examples above will work on Windows in the same way they would on Unix systems.
```
// Importing a local module with a path relative to the `__dirname` or current
// working directory. (On Windows, this would resolve to .\path\myLocalModule.)
const myLocalModule = require('./path/myLocalModule');
// Importing a JSON file:
const jsonData = require('./path/filename.json');
// Importing a module from node_modules or Node.js built-in module:
const crypto = require('node:crypto');
```
#####
`require.cache`
Added in: v0.3.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Modules are cached in this object when they are required. By deleting a key value from this object, the next `require` will reload the module. This does not apply to [native addons](addons), for which reloading will result in an error.
Adding or replacing entries is also possible. This cache is checked before built-in modules and if a name matching a built-in module is added to the cache, only `node:`-prefixed require calls are going to receive the built-in module. Use with care!
```
const assert = require('node:assert');
const realFs = require('node:fs');
const fakeFs = {};
require.cache.fs = { exports: fakeFs };
assert.strictEqual(require('fs'), fakeFs);
assert.strictEqual(require('node:fs'), realFs);
```
#####
`require.extensions`
Added in: v0.3.0Deprecated since: v0.10.6
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Instruct `require` on how to handle certain file extensions.
Process files with the extension `.sjs` as `.js`:
```
require.extensions['.sjs'] = require.extensions['.js'];
```
**Deprecated.** In the past, this list has been used to load non-JavaScript modules into Node.js by compiling them on-demand. However, in practice, there are much better ways to do this, such as loading modules via some other Node.js program, or compiling them to JavaScript ahead of time.
Avoid using `require.extensions`. Use could cause subtle bugs and resolving the extensions gets slower with each registered extension.
#####
`require.main`
Added in: v0.1.17 * [<module>](modules#the-module-object) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
The `Module` object representing the entry script loaded when the Node.js process launched, or `undefined` if the entry point of the program is not a CommonJS module. See ["Accessing the main module"](#accessing-the-main-module).
In `entry.js` script:
```
console.log(require.main);
```
```
node entry.js
```
```
Module {
id: '.',
path: '/absolute/path/to',
exports: {},
filename: '/absolute/path/to/entry.js',
loaded: false,
children: [],
paths:
[ '/absolute/path/to/node_modules',
'/absolute/path/node_modules',
'/absolute/node_modules',
'/node_modules' ] }
```
#####
`require.resolve(request[, options])`
History
| Version | Changes |
| --- | --- |
| v8.9.0 | The `paths` option is now supported. |
| v0.3.0 | Added in: v0.3.0 |
* `request` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The module path to resolve.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `paths` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Paths to resolve module location from. If present, these paths are used instead of the default resolution paths, with the exception of [GLOBAL\_FOLDERS](#loading-from-the-global-folders) like `$HOME/.node_modules`, which are always included. Each of these paths is used as a starting point for the module resolution algorithm, meaning that the `node_modules` hierarchy is checked from this location.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Use the internal `require()` machinery to look up the location of a module, but rather than loading the module, just return the resolved filename.
If the module can not be found, a `MODULE_NOT_FOUND` error is thrown.
######
`require.resolve.paths(request)`
Added in: v8.9.0 * `request` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The module path whose lookup paths are being retrieved.
* Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
Returns an array containing the paths searched during resolution of `request` or `null` if the `request` string references a core module, for example `http` or `fs`.
### The `module` object
Added in: v0.1.16 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
In each module, the `module` free variable is a reference to the object representing the current module. For convenience, `module.exports` is also accessible via the `exports` module-global. `module` is not actually a global but rather local to each module.
####
`module.children`
Added in: v0.1.16 * [<module[]>](modules#the-module-object)
The module objects required for the first time by this one.
####
`module.exports`
Added in: v0.1.16 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `module.exports` object is created by the `Module` system. Sometimes this is not acceptable; many want their module to be an instance of some class. To do this, assign the desired export object to `module.exports`. Assigning the desired object to `exports` will simply rebind the local `exports` variable, which is probably not what is desired.
For example, suppose we were making a module called `a.js`:
```
const EventEmitter = require('node:events');
module.exports = new EventEmitter();
// Do some work, and after some time emit
// the 'ready' event from the module itself.
setTimeout(() => {
module.exports.emit('ready');
}, 1000);
```
Then in another file we could do:
```
const a = require('./a');
a.on('ready', () => {
console.log('module "a" is ready');
});
```
Assignment to `module.exports` must be done immediately. It cannot be done in any callbacks. This does not work:
`x.js`:
```
setTimeout(() => {
module.exports = { a: 'hello' };
}, 0);
```
`y.js`:
```
const x = require('./x');
console.log(x.a);
```
#####
`exports` shortcut
Added in: v0.1.16 The `exports` variable is available within a module's file-level scope, and is assigned the value of `module.exports` before the module is evaluated.
It allows a shortcut, so that `module.exports.f = ...` can be written more succinctly as `exports.f = ...`. However, be aware that like any variable, if a new value is assigned to `exports`, it is no longer bound to `module.exports`:
```
module.exports.hello = true; // Exported from require of module
exports = { hello: false }; // Not exported, only available in the module
```
When the `module.exports` property is being completely replaced by a new object, it is common to also reassign `exports`:
```
module.exports = exports = function Constructor() {
// ... etc.
};
```
To illustrate the behavior, imagine this hypothetical implementation of `require()`, which is quite similar to what is actually done by `require()`:
```
function require(/* ... */) {
const module = { exports: {} };
((module, exports) => {
// Module code here. In this example, define a function.
function someFunc() {}
exports = someFunc;
// At this point, exports is no longer a shortcut to module.exports, and
// this module will still export an empty default object.
module.exports = someFunc;
// At this point, the module will now export someFunc, instead of the
// default object.
})(module, module.exports);
return module.exports;
}
```
####
`module.filename`
Added in: v0.1.16 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The fully resolved filename of the module.
####
`module.id`
Added in: v0.1.16 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The identifier for the module. Typically this is the fully resolved filename.
####
`module.isPreloading`
Added in: v15.4.0, v14.17.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the module is running during the Node.js preload phase.
####
`module.loaded`
Added in: v0.1.16 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Whether or not the module is done loading, or is in the process of loading.
####
`module.parent`
Added in: v0.1.16Deprecated since: v14.6.0, v12.19.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Please use [`require.main`](#requiremain) and [`module.children`](#modulechildren) instead.
* [<module>](modules#the-module-object) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
The module that first required this one, or `null` if the current module is the entry point of the current process, or `undefined` if the module was loaded by something that is not a CommonJS module (E.G.: REPL or `import`).
####
`module.path`
Added in: v11.14.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The directory name of the module. This is usually the same as the [`path.dirname()`](path#pathdirnamepath) of the [`module.id`](#moduleid).
####
`module.paths`
Added in: v0.4.0 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The search paths for the module.
####
`module.require(id)`
Added in: v0.5.1 * `id` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) exported module content
The `module.require()` method provides a way to load a module as if `require()` was called from the original module.
In order to do this, it is necessary to get a reference to the `module` object. Since `require()` returns the `module.exports`, and the `module` is typically *only* available within a specific module's code, it must be explicitly exported in order to be used.
### The `Module` object
This section was moved to [Modules: `module` core module](module#the-module-object).
* [`module.builtinModules`](module#modulebuiltinmodules)
* [`module.createRequire(filename)`](module#modulecreaterequirefilename)
* [`module.syncBuiltinESMExports()`](module#modulesyncbuiltinesmexports)
### Source map v3 support
This section was moved to [Modules: `module` core module](module#source-map-v3-support).
* [`module.findSourceMap(path)`](module#modulefindsourcemappath)
* [Class: `module.SourceMap`](module#class-modulesourcemap)
+ [`new SourceMap(payload)`](module#new-sourcemappayload)
+ [`sourceMap.payload`](module#sourcemappayload)
+ [`sourceMap.findEntry(lineNumber, columnNumber)`](module#sourcemapfindentrylinenumber-columnnumber)
| programming_docs |
node None Process
-------
**Source Code:** [lib/process.js](https://github.com/nodejs/node/blob/v19.0.1/lib/process.js)
The `process` object provides information about, and control over, the current Node.js process.
MJS modules
```
import process from 'node:process';
```
CJS modules
```
const process = require('node:process');
```
### Process events
The `process` object is an instance of [`EventEmitter`](events#class-eventemitter).
#### Event: `'beforeExit'`
Added in: v0.11.12 The `'beforeExit'` event is emitted when Node.js empties its event loop and has no additional work to schedule. Normally, the Node.js process will exit when there is no work scheduled, but a listener registered on the `'beforeExit'` event can make asynchronous calls, and thereby cause the Node.js process to continue.
The listener callback function is invoked with the value of [`process.exitCode`](#processexitcode_1) passed as the only argument.
The `'beforeExit'` event is *not* emitted for conditions causing explicit termination, such as calling [`process.exit()`](#processexitcode) or uncaught exceptions.
The `'beforeExit'` should *not* be used as an alternative to the `'exit'` event unless the intention is to schedule additional work.
MJS modules
```
import process from 'node:process';
process.on('beforeExit', (code) => {
console.log('Process beforeExit event with code: ', code);
});
process.on('exit', (code) => {
console.log('Process exit event with code: ', code);
});
console.log('This message is displayed first.');
// Prints:
// This message is displayed first.
// Process beforeExit event with code: 0
// Process exit event with code: 0
```
CJS modules
```
const process = require('node:process');
process.on('beforeExit', (code) => {
console.log('Process beforeExit event with code: ', code);
});
process.on('exit', (code) => {
console.log('Process exit event with code: ', code);
});
console.log('This message is displayed first.');
// Prints:
// This message is displayed first.
// Process beforeExit event with code: 0
// Process exit event with code: 0
```
#### Event: `'disconnect'`
Added in: v0.7.7 If the Node.js process is spawned with an IPC channel (see the [Child Process](child_process) and [Cluster](cluster) documentation), the `'disconnect'` event will be emitted when the IPC channel is closed.
#### Event: `'exit'`
Added in: v0.1.7 * `code` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `'exit'` event is emitted when the Node.js process is about to exit as a result of either:
* The `process.exit()` method being called explicitly;
* The Node.js event loop no longer having any additional work to perform.
There is no way to prevent the exiting of the event loop at this point, and once all `'exit'` listeners have finished running the Node.js process will terminate.
The listener callback function is invoked with the exit code specified either by the [`process.exitCode`](#processexitcode_1) property, or the `exitCode` argument passed to the [`process.exit()`](#processexitcode) method.
MJS modules
```
import process from 'node:process';
process.on('exit', (code) => {
console.log(`About to exit with code: ${code}`);
});
```
CJS modules
```
const process = require('node:process');
process.on('exit', (code) => {
console.log(`About to exit with code: ${code}`);
});
```
Listener functions **must** only perform **synchronous** operations. The Node.js process will exit immediately after calling the `'exit'` event listeners causing any additional work still queued in the event loop to be abandoned. In the following example, for instance, the timeout will never occur:
MJS modules
```
import process from 'node:process';
process.on('exit', (code) => {
setTimeout(() => {
console.log('This will not run');
}, 0);
});
```
CJS modules
```
const process = require('node:process');
process.on('exit', (code) => {
setTimeout(() => {
console.log('This will not run');
}, 0);
});
```
#### Event: `'message'`
Added in: v0.5.10 * `message` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) a parsed JSON object or a serializable primitive value.
* `sendHandle` [<net.Server>](net#class-netserver) | [<net.Socket>](net#class-netsocket) a [`net.Server`](net#class-netserver) or [`net.Socket`](net#class-netsocket) object, or undefined.
If the Node.js process is spawned with an IPC channel (see the [Child Process](child_process) and [Cluster](cluster) documentation), the `'message'` event is emitted whenever a message sent by a parent process using [`childprocess.send()`](child_process#subprocesssendmessage-sendhandle-options-callback) is received by the child process.
The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent.
If the `serialization` option was set to `advanced` used when spawning the process, the `message` argument can contain data that JSON is not able to represent. See [Advanced serialization for `child_process`](child_process#advanced-serialization) for more details.
#### Event: `'multipleResolves'`
Added in: v10.12.0Deprecated since: v17.6.0, v16.15.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The resolution type. One of `'resolve'` or `'reject'`.
* `promise` [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) The promise that resolved or rejected more than once.
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The value with which the promise was either resolved or rejected after the original resolve.
The `'multipleResolves'` event is emitted whenever a `Promise` has been either:
* Resolved more than once.
* Rejected more than once.
* Rejected after resolve.
* Resolved after reject.
This is useful for tracking potential errors in an application while using the `Promise` constructor, as multiple resolutions are silently swallowed. However, the occurrence of this event does not necessarily indicate an error. For example, [`Promise.race()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/race) can trigger a `'multipleResolves'` event.
Because of the unreliability of the event in cases like the [`Promise.race()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/race) example above it has been deprecated.
MJS modules
```
import process from 'node:process';
process.on('multipleResolves', (type, promise, reason) => {
console.error(type, promise, reason);
setImmediate(() => process.exit(1));
});
async function main() {
try {
return await new Promise((resolve, reject) => {
resolve('First call');
resolve('Swallowed resolve');
reject(new Error('Swallowed reject'));
});
} catch {
throw new Error('Failed');
}
}
main().then(console.log);
// resolve: Promise { 'First call' } 'Swallowed resolve'
// reject: Promise { 'First call' } Error: Swallowed reject
// at Promise (*)
// at new Promise (<anonymous>)
// at main (*)
// First call
```
CJS modules
```
const process = require('node:process');
process.on('multipleResolves', (type, promise, reason) => {
console.error(type, promise, reason);
setImmediate(() => process.exit(1));
});
async function main() {
try {
return await new Promise((resolve, reject) => {
resolve('First call');
resolve('Swallowed resolve');
reject(new Error('Swallowed reject'));
});
} catch {
throw new Error('Failed');
}
}
main().then(console.log);
// resolve: Promise { 'First call' } 'Swallowed resolve'
// reject: Promise { 'First call' } Error: Swallowed reject
// at Promise (*)
// at new Promise (<anonymous>)
// at main (*)
// First call
```
#### Event: `'rejectionHandled'`
Added in: v1.4.1 * `promise` [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) The late handled promise.
The `'rejectionHandled'` event is emitted whenever a `Promise` has been rejected and an error handler was attached to it (using [`promise.catch()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/catch), for example) later than one turn of the Node.js event loop.
The `Promise` object would have previously been emitted in an `'unhandledRejection'` event, but during the course of processing gained a rejection handler.
There is no notion of a top level for a `Promise` chain at which rejections can always be handled. Being inherently asynchronous in nature, a `Promise` rejection can be handled at a future point in time, possibly much later than the event loop turn it takes for the `'unhandledRejection'` event to be emitted.
Another way of stating this is that, unlike in synchronous code where there is an ever-growing list of unhandled exceptions, with Promises there can be a growing-and-shrinking list of unhandled rejections.
In synchronous code, the `'uncaughtException'` event is emitted when the list of unhandled exceptions grows.
In asynchronous code, the `'unhandledRejection'` event is emitted when the list of unhandled rejections grows, and the `'rejectionHandled'` event is emitted when the list of unhandled rejections shrinks.
MJS modules
```
import process from 'node:process';
const unhandledRejections = new Map();
process.on('unhandledRejection', (reason, promise) => {
unhandledRejections.set(promise, reason);
});
process.on('rejectionHandled', (promise) => {
unhandledRejections.delete(promise);
});
```
CJS modules
```
const process = require('node:process');
const unhandledRejections = new Map();
process.on('unhandledRejection', (reason, promise) => {
unhandledRejections.set(promise, reason);
});
process.on('rejectionHandled', (promise) => {
unhandledRejections.delete(promise);
});
```
In this example, the `unhandledRejections` `Map` will grow and shrink over time, reflecting rejections that start unhandled and then become handled. It is possible to record such errors in an error log, either periodically (which is likely best for long-running application) or upon process exit (which is likely most convenient for scripts).
#### Event: `'uncaughtException'`
History
| Version | Changes |
| --- | --- |
| v12.0.0, v10.17.0 | Added the `origin` argument. |
| v0.1.18 | Added in: v0.1.18 |
* `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) The uncaught exception.
* `origin` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Indicates if the exception originates from an unhandled rejection or from a synchronous error. Can either be `'uncaughtException'` or `'unhandledRejection'`. The latter is used when an exception happens in a `Promise` based async context (or if a `Promise` is rejected) and [`--unhandled-rejections`](cli#--unhandled-rejectionsmode) flag set to `strict` or `throw` (which is the default) and the rejection is not handled, or when a rejection happens during the command line entry point's ES module static loading phase.
The `'uncaughtException'` event is emitted when an uncaught JavaScript exception bubbles all the way back to the event loop. By default, Node.js handles such exceptions by printing the stack trace to `stderr` and exiting with code 1, overriding any previously set [`process.exitCode`](#processexitcode_1). Adding a handler for the `'uncaughtException'` event overrides this default behavior. Alternatively, change the [`process.exitCode`](#processexitcode_1) in the `'uncaughtException'` handler which will result in the process exiting with the provided exit code. Otherwise, in the presence of such handler the process will exit with 0.
MJS modules
```
import process from 'node:process';
process.on('uncaughtException', (err, origin) => {
fs.writeSync(
process.stderr.fd,
`Caught exception: ${err}\n` +
`Exception origin: ${origin}`
);
});
setTimeout(() => {
console.log('This will still run.');
}, 500);
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');
```
CJS modules
```
const process = require('node:process');
process.on('uncaughtException', (err, origin) => {
fs.writeSync(
process.stderr.fd,
`Caught exception: ${err}\n` +
`Exception origin: ${origin}`
);
});
setTimeout(() => {
console.log('This will still run.');
}, 500);
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');
```
It is possible to monitor `'uncaughtException'` events without overriding the default behavior to exit the process by installing a `'uncaughtExceptionMonitor'` listener.
##### Warning: Using `'uncaughtException'` correctly
`'uncaughtException'` is a crude mechanism for exception handling intended to be used only as a last resort. The event *should not* be used as an equivalent to `On Error Resume Next`. Unhandled exceptions inherently mean that an application is in an undefined state. Attempting to resume application code without properly recovering from the exception can cause additional unforeseen and unpredictable issues.
Exceptions thrown from within the event handler will not be caught. Instead the process will exit with a non-zero exit code and the stack trace will be printed. This is to avoid infinite recursion.
Attempting to resume normally after an uncaught exception can be similar to pulling out the power cord when upgrading a computer. Nine out of ten times, nothing happens. But the tenth time, the system becomes corrupted.
The correct use of `'uncaughtException'` is to perform synchronous cleanup of allocated resources (e.g. file descriptors, handles, etc) before shutting down the process. **It is not safe to resume normal operation after `'uncaughtException'`.**
To restart a crashed application in a more reliable way, whether `'uncaughtException'` is emitted or not, an external monitor should be employed in a separate process to detect application failures and recover or restart as needed.
#### Event: `'uncaughtExceptionMonitor'`
Added in: v13.7.0, v12.17.0 * `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) The uncaught exception.
* `origin` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Indicates if the exception originates from an unhandled rejection or from synchronous errors. Can either be `'uncaughtException'` or `'unhandledRejection'`. The latter is used when an exception happens in a `Promise` based async context (or if a `Promise` is rejected) and [`--unhandled-rejections`](cli#--unhandled-rejectionsmode) flag set to `strict` or `throw` (which is the default) and the rejection is not handled, or when a rejection happens during the command line entry point's ES module static loading phase.
The `'uncaughtExceptionMonitor'` event is emitted before an `'uncaughtException'` event is emitted or a hook installed via [`process.setUncaughtExceptionCaptureCallback()`](#processsetuncaughtexceptioncapturecallbackfn) is called.
Installing an `'uncaughtExceptionMonitor'` listener does not change the behavior once an `'uncaughtException'` event is emitted. The process will still crash if no `'uncaughtException'` listener is installed.
MJS modules
```
import process from 'node:process';
process.on('uncaughtExceptionMonitor', (err, origin) => {
MyMonitoringTool.logSync(err, origin);
});
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
// Still crashes Node.js
```
CJS modules
```
const process = require('node:process');
process.on('uncaughtExceptionMonitor', (err, origin) => {
MyMonitoringTool.logSync(err, origin);
});
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
// Still crashes Node.js
```
#### Event: `'unhandledRejection'`
History
| Version | Changes |
| --- | --- |
| v7.0.0 | Not handling `Promise` rejections is deprecated. |
| v6.6.0 | Unhandled `Promise` rejections will now emit a process warning. |
| v1.4.1 | Added in: v1.4.1 |
* `reason` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) | [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The object with which the promise was rejected (typically an [`Error`](errors#class-error) object).
* `promise` [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) The rejected promise.
The `'unhandledRejection'` event is emitted whenever a `Promise` is rejected and no error handler is attached to the promise within a turn of the event loop. When programming with Promises, exceptions are encapsulated as "rejected promises". Rejections can be caught and handled using [`promise.catch()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/catch) and are propagated through a `Promise` chain. The `'unhandledRejection'` event is useful for detecting and keeping track of promises that were rejected whose rejections have not yet been handled.
MJS modules
```
import process from 'node:process';
process.on('unhandledRejection', (reason, promise) => {
console.log('Unhandled Rejection at:', promise, 'reason:', reason);
// Application specific logging, throwing an error, or other logic here
});
somePromise.then((res) => {
return reportToUser(JSON.pasre(res)); // Note the typo (`pasre`)
}); // No `.catch()` or `.then()`
```
CJS modules
```
const process = require('node:process');
process.on('unhandledRejection', (reason, promise) => {
console.log('Unhandled Rejection at:', promise, 'reason:', reason);
// Application specific logging, throwing an error, or other logic here
});
somePromise.then((res) => {
return reportToUser(JSON.pasre(res)); // Note the typo (`pasre`)
}); // No `.catch()` or `.then()`
```
The following will also trigger the `'unhandledRejection'` event to be emitted:
MJS modules
```
import process from 'node:process';
function SomeResource() {
// Initially set the loaded status to a rejected promise
this.loaded = Promise.reject(new Error('Resource not yet loaded!'));
}
const resource = new SomeResource();
// no .catch or .then on resource.loaded for at least a turn
```
CJS modules
```
const process = require('node:process');
function SomeResource() {
// Initially set the loaded status to a rejected promise
this.loaded = Promise.reject(new Error('Resource not yet loaded!'));
}
const resource = new SomeResource();
// no .catch or .then on resource.loaded for at least a turn
```
In this example case, it is possible to track the rejection as a developer error as would typically be the case for other `'unhandledRejection'` events. To address such failures, a non-operational [`.catch(() => { })`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/catch) handler may be attached to `resource.loaded`, which would prevent the `'unhandledRejection'` event from being emitted.
#### Event: `'warning'`
Added in: v6.0.0 * `warning` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) Key properties of the warning are:
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the warning. **Default:** `'Warning'`.
+ `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A system-provided description of the warning.
+ `stack` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A stack trace to the location in the code where the warning was issued.
The `'warning'` event is emitted whenever Node.js emits a process warning.
A process warning is similar to an error in that it describes exceptional conditions that are being brought to the user's attention. However, warnings are not part of the normal Node.js and JavaScript error handling flow. Node.js can emit warnings whenever it detects bad coding practices that could lead to sub-optimal application performance, bugs, or security vulnerabilities.
MJS modules
```
import process from 'node:process';
process.on('warning', (warning) => {
console.warn(warning.name); // Print the warning name
console.warn(warning.message); // Print the warning message
console.warn(warning.stack); // Print the stack trace
});
```
CJS modules
```
const process = require('node:process');
process.on('warning', (warning) => {
console.warn(warning.name); // Print the warning name
console.warn(warning.message); // Print the warning message
console.warn(warning.stack); // Print the stack trace
});
```
By default, Node.js will print process warnings to `stderr`. The `--no-warnings` command-line option can be used to suppress the default console output but the `'warning'` event will still be emitted by the `process` object.
The following example illustrates the warning that is printed to `stderr` when too many listeners have been added to an event:
```
$ node
> events.defaultMaxListeners = 1;
> process.on('foo', () => {});
> process.on('foo', () => {});
> (node:38638) MaxListenersExceededWarning: Possible EventEmitter memory leak
detected. 2 foo listeners added. Use emitter.setMaxListeners() to increase limit
```
In contrast, the following example turns off the default warning output and adds a custom handler to the `'warning'` event:
```
$ node --no-warnings
> const p = process.on('warning', (warning) => console.warn('Do not do that!'));
> events.defaultMaxListeners = 1;
> process.on('foo', () => {});
> process.on('foo', () => {});
> Do not do that!
```
The `--trace-warnings` command-line option can be used to have the default console output for warnings include the full stack trace of the warning.
Launching Node.js using the `--throw-deprecation` command-line flag will cause custom deprecation warnings to be thrown as exceptions.
Using the `--trace-deprecation` command-line flag will cause the custom deprecation to be printed to `stderr` along with the stack trace.
Using the `--no-deprecation` command-line flag will suppress all reporting of the custom deprecation.
The `*-deprecation` command-line flags only affect warnings that use the name `'DeprecationWarning'`.
#### Event: `'worker'`
Added in: v16.2.0, v14.18.0 * `worker` [<Worker>](worker_threads#class-worker) The [<Worker>](worker_threads#class-worker) that was created.
The `'worker'` event is emitted after a new [<Worker>](worker_threads#class-worker) thread has been created.
##### Emitting custom warnings
See the [`process.emitWarning()`](#processemitwarningwarning-type-code-ctor) method for issuing custom or application-specific warnings.
##### Node.js warning names
There are no strict guidelines for warning types (as identified by the `name` property) emitted by Node.js. New types of warnings can be added at any time. A few of the warning types that are most common include:
* `'DeprecationWarning'` - Indicates use of a deprecated Node.js API or feature. Such warnings must include a `'code'` property identifying the [deprecation code](deprecations).
* `'ExperimentalWarning'` - Indicates use of an experimental Node.js API or feature. Such features must be used with caution as they may change at any time and are not subject to the same strict semantic-versioning and long-term support policies as supported features.
* `'MaxListenersExceededWarning'` - Indicates that too many listeners for a given event have been registered on either an `EventEmitter` or `EventTarget`. This is often an indication of a memory leak.
* `'TimeoutOverflowWarning'` - Indicates that a numeric value that cannot fit within a 32-bit signed integer has been provided to either the `setTimeout()` or `setInterval()` functions.
* `'UnsupportedWarning'` - Indicates use of an unsupported option or feature that will be ignored rather than treated as an error. One example is use of the HTTP response status message when using the HTTP/2 compatibility API.
#### Signal events
Signal events will be emitted when the Node.js process receives a signal. Please refer to [`signal(7)`](http://man7.org/linux/man-pages/man7/signal.7.html) for a listing of standard POSIX signal names such as `'SIGINT'`, `'SIGHUP'`, etc.
Signals are not available on [`Worker`](worker_threads#class-worker) threads.
The signal handler will receive the signal's name (`'SIGINT'`, `'SIGTERM'`, etc.) as the first argument.
The name of each event will be the uppercase common name for the signal (e.g. `'SIGINT'` for `SIGINT` signals).
MJS modules
```
import process from 'node:process';
// Begin reading from stdin so the process does not exit.
process.stdin.resume();
process.on('SIGINT', () => {
console.log('Received SIGINT. Press Control-D to exit.');
});
// Using a single function to handle multiple signals
function handle(signal) {
console.log(`Received ${signal}`);
}
process.on('SIGINT', handle);
process.on('SIGTERM', handle);
```
CJS modules
```
const process = require('node:process');
// Begin reading from stdin so the process does not exit.
process.stdin.resume();
process.on('SIGINT', () => {
console.log('Received SIGINT. Press Control-D to exit.');
});
// Using a single function to handle multiple signals
function handle(signal) {
console.log(`Received ${signal}`);
}
process.on('SIGINT', handle);
process.on('SIGTERM', handle);
```
* `'SIGUSR1'` is reserved by Node.js to start the <debugger>. It's possible to install a listener but doing so might interfere with the debugger.
* `'SIGTERM'` and `'SIGINT'` have default handlers on non-Windows platforms that reset the terminal mode before exiting with code `128 + signal number`. If one of these signals has a listener installed, its default behavior will be removed (Node.js will no longer exit).
* `'SIGPIPE'` is ignored by default. It can have a listener installed.
* `'SIGHUP'` is generated on Windows when the console window is closed, and on other platforms under various similar conditions. See [`signal(7)`](http://man7.org/linux/man-pages/man7/signal.7.html). It can have a listener installed, however Node.js will be unconditionally terminated by Windows about 10 seconds later. On non-Windows platforms, the default behavior of `SIGHUP` is to terminate Node.js, but once a listener has been installed its default behavior will be removed.
* `'SIGTERM'` is not supported on Windows, it can be listened on.
* `'SIGINT'` from the terminal is supported on all platforms, and can usually be generated with `Ctrl`+`C` (though this may be configurable). It is not generated when [terminal raw mode](tty#readstreamsetrawmodemode) is enabled and `Ctrl`+`C` is used.
* `'SIGBREAK'` is delivered on Windows when `Ctrl`+`Break` is pressed. On non-Windows platforms, it can be listened on, but there is no way to send or generate it.
* `'SIGWINCH'` is delivered when the console has been resized. On Windows, this will only happen on write to the console when the cursor is being moved, or when a readable tty is used in raw mode.
* `'SIGKILL'` cannot have a listener installed, it will unconditionally terminate Node.js on all platforms.
* `'SIGSTOP'` cannot have a listener installed.
* `'SIGBUS'`, `'SIGFPE'`, `'SIGSEGV'`, and `'SIGILL'`, when not raised artificially using [`kill(2)`](http://man7.org/linux/man-pages/man2/kill.2.html), inherently leave the process in a state from which it is not safe to call JS listeners. Doing so might cause the process to stop responding.
* `0` can be sent to test for the existence of a process, it has no effect if the process exists, but will throw an error if the process does not exist.
Windows does not support signals so has no equivalent to termination by signal, but Node.js offers some emulation with [`process.kill()`](#processkillpid-signal), and [`subprocess.kill()`](child_process#subprocesskillsignal):
* Sending `SIGINT`, `SIGTERM`, and `SIGKILL` will cause the unconditional termination of the target process, and afterwards, subprocess will report that the process was terminated by signal.
* Sending signal `0` can be used as a platform independent way to test for the existence of a process.
###
`process.abort()`
Added in: v0.7.0 The `process.abort()` method causes the Node.js process to exit immediately and generate a core file.
This feature is not available in [`Worker`](worker_threads#class-worker) threads.
###
`process.allowedNodeEnvironmentFlags`
Added in: v10.10.0 * [<Set>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set)
The `process.allowedNodeEnvironmentFlags` property is a special, read-only `Set` of flags allowable within the [`NODE_OPTIONS`](cli#node_optionsoptions) environment variable.
`process.allowedNodeEnvironmentFlags` extends `Set`, but overrides `Set.prototype.has` to recognize several different possible flag representations. `process.allowedNodeEnvironmentFlags.has()` will return `true` in the following cases:
* Flags may omit leading single (`-`) or double (`--`) dashes; e.g., `inspect-brk` for `--inspect-brk`, or `r` for `-r`.
* Flags passed through to V8 (as listed in `--v8-options`) may replace one or more *non-leading* dashes for an underscore, or vice-versa; e.g., `--perf_basic_prof`, `--perf-basic-prof`, `--perf_basic-prof`, etc.
* Flags may contain one or more equals (`=`) characters; all characters after and including the first equals will be ignored; e.g., `--stack-trace-limit=100`.
* Flags *must* be allowable within [`NODE_OPTIONS`](cli#node_optionsoptions).
When iterating over `process.allowedNodeEnvironmentFlags`, flags will appear only *once*; each will begin with one or more dashes. Flags passed through to V8 will contain underscores instead of non-leading dashes:
MJS modules
```
import { allowedNodeEnvironmentFlags } from 'node:process';
allowedNodeEnvironmentFlags.forEach((flag) => {
// -r
// --inspect-brk
// --abort_on_uncaught_exception
// ...
});
```
CJS modules
```
const { allowedNodeEnvironmentFlags } = require('node:process');
allowedNodeEnvironmentFlags.forEach((flag) => {
// -r
// --inspect-brk
// --abort_on_uncaught_exception
// ...
});
```
The methods `add()`, `clear()`, and `delete()` of `process.allowedNodeEnvironmentFlags` do nothing, and will fail silently.
If Node.js was compiled *without* [`NODE_OPTIONS`](cli#node_optionsoptions) support (shown in [`process.config`](#processconfig)), `process.allowedNodeEnvironmentFlags` will contain what *would have* been allowable.
###
`process.arch`
Added in: v0.5.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The operating system CPU architecture for which the Node.js binary was compiled. Possible values are: `'arm'`, `'arm64'`, `'ia32'`, `'mips'`,`'mipsel'`, `'ppc'`, `'ppc64'`, `'s390'`, `'s390x'`, and `'x64'`.
MJS modules
```
import { arch } from 'node:process';
console.log(`This processor architecture is ${arch}`);
```
CJS modules
```
const { arch } = require('node:process');
console.log(`This processor architecture is ${arch}`);
```
###
`process.argv`
Added in: v0.1.27 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.argv` property returns an array containing the command-line arguments passed when the Node.js process was launched. The first element will be [`process.execPath`](#processexecpath). See `process.argv0` if access to the original value of `argv[0]` is needed. The second element will be the path to the JavaScript file being executed. The remaining elements will be any additional command-line arguments.
For example, assuming the following script for `process-args.js`:
MJS modules
```
import { argv } from 'node:process';
// print process.argv
argv.forEach((val, index) => {
console.log(`${index}: ${val}`);
});
```
CJS modules
```
const { argv } = require('node:process');
// print process.argv
argv.forEach((val, index) => {
console.log(`${index}: ${val}`);
});
```
Launching the Node.js process as:
```
$ node process-args.js one two=three four
```
Would generate the output:
```
0: /usr/local/bin/node
1: /Users/mjr/work/node/process-args.js
2: one
3: two=three
4: four
```
###
`process.argv0`
Added in: v6.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.argv0` property stores a read-only copy of the original value of `argv[0]` passed when Node.js starts.
```
$ bash -c 'exec -a customArgv0 ./node'
> process.argv[0]
'/Volumes/code/external/node/out/Release/node'
> process.argv0
'customArgv0'
```
###
`process.channel`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | The object no longer accidentally exposes native C++ bindings. |
| v7.1.0 | Added in: v7.1.0 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
If the Node.js process was spawned with an IPC channel (see the [Child Process](child_process) documentation), the `process.channel` property is a reference to the IPC channel. If no IPC channel exists, this property is `undefined`.
####
`process.channel.ref()`
Added in: v7.1.0 This method makes the IPC channel keep the event loop of the process running if `.unref()` has been called before.
Typically, this is managed through the number of `'disconnect'` and `'message'` listeners on the `process` object. However, this method can be used to explicitly request a specific behavior.
####
`process.channel.unref()`
Added in: v7.1.0 This method makes the IPC channel not keep the event loop of the process running, and lets it finish even while the channel is open.
Typically, this is managed through the number of `'disconnect'` and `'message'` listeners on the `process` object. However, this method can be used to explicitly request a specific behavior.
###
`process.chdir(directory)`
Added in: v0.1.17 * `directory` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.chdir()` method changes the current working directory of the Node.js process or throws an exception if doing so fails (for instance, if the specified `directory` does not exist).
MJS modules
```
import { chdir, cwd } from 'node:process';
console.log(`Starting directory: ${cwd()}`);
try {
chdir('/tmp');
console.log(`New directory: ${cwd()}`);
} catch (err) {
console.error(`chdir: ${err}`);
}
```
CJS modules
```
const { chdir, cwd } = require('node:process');
console.log(`Starting directory: ${cwd()}`);
try {
chdir('/tmp');
console.log(`New directory: ${cwd()}`);
} catch (err) {
console.error(`chdir: ${err}`);
}
```
This feature is not available in [`Worker`](worker_threads#class-worker) threads.
###
`process.config`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | The `process.config` object is now frozen. |
| v16.0.0 | Modifying process.config has been deprecated. |
| v0.7.7 | Added in: v0.7.7 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `process.config` property returns a frozen `Object` containing the JavaScript representation of the configure options used to compile the current Node.js executable. This is the same as the `config.gypi` file that was produced when running the `./configure` script.
An example of the possible output looks like:
```
{
target_defaults:
{ cflags: [],
default_configuration: 'Release',
defines: [],
include_dirs: [],
libraries: [] },
variables:
{
host_arch: 'x64',
napi_build_version: 5,
node_install_npm: 'true',
node_prefix: '',
node_shared_cares: 'false',
node_shared_http_parser: 'false',
node_shared_libuv: 'false',
node_shared_zlib: 'false',
node_use_openssl: 'true',
node_shared_openssl: 'false',
strict_aliasing: 'true',
target_arch: 'x64',
v8_use_snapshot: 1
}
}
```
###
`process.connected`
Added in: v0.7.2 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If the Node.js process is spawned with an IPC channel (see the [Child Process](child_process) and [Cluster](cluster) documentation), the `process.connected` property will return `true` so long as the IPC channel is connected and will return `false` after `process.disconnect()` is called.
Once `process.connected` is `false`, it is no longer possible to send messages over the IPC channel using `process.send()`.
###
`process.cpuUsage([previousValue])`
Added in: v6.1.0 * `previousValue` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A previous return value from calling `process.cpuUsage()`
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `user` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `system` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `process.cpuUsage()` method returns the user and system CPU time usage of the current process, in an object with properties `user` and `system`, whose values are microsecond values (millionth of a second). These values measure time spent in user and system code respectively, and may end up being greater than actual elapsed time if multiple CPU cores are performing work for this process.
The result of a previous call to `process.cpuUsage()` can be passed as the argument to the function, to get a diff reading.
MJS modules
```
import { cpuUsage } from 'node:process';
const startUsage = cpuUsage();
// { user: 38579, system: 6986 }
// spin the CPU for 500 milliseconds
const now = Date.now();
while (Date.now() - now < 500);
console.log(cpuUsage(startUsage));
// { user: 514883, system: 11226 }
```
CJS modules
```
const { cpuUsage } = require('node:process');
const startUsage = cpuUsage();
// { user: 38579, system: 6986 }
// spin the CPU for 500 milliseconds
const now = Date.now();
while (Date.now() - now < 500);
console.log(cpuUsage(startUsage));
// { user: 514883, system: 11226 }
```
###
`process.cwd()`
Added in: v0.1.8 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.cwd()` method returns the current working directory of the Node.js process.
MJS modules
```
import { cwd } from 'node:process';
console.log(`Current directory: ${cwd()}`);
```
CJS modules
```
const { cwd } = require('node:process');
console.log(`Current directory: ${cwd()}`);
```
###
`process.debugPort`
Added in: v0.7.2 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The port used by the Node.js debugger when enabled.
MJS modules
```
import process from 'node:process';
process.debugPort = 5858;
```
CJS modules
```
const process = require('node:process');
process.debugPort = 5858;
```
###
`process.disconnect()`
Added in: v0.7.2 If the Node.js process is spawned with an IPC channel (see the [Child Process](child_process) and [Cluster](cluster) documentation), the `process.disconnect()` method will close the IPC channel to the parent process, allowing the child process to exit gracefully once there are no other connections keeping it alive.
The effect of calling `process.disconnect()` is the same as calling [`ChildProcess.disconnect()`](child_process#subprocessdisconnect) from the parent process.
If the Node.js process was not spawned with an IPC channel, `process.disconnect()` will be `undefined`.
###
`process.dlopen(module, filename[, flags])`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | Added support for the `flags` argument. |
| v0.1.16 | Added in: v0.1.16 |
* `module` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `flags` [<os.constants.dlopen>](os#dlopen-constants) **Default:** `os.constants.dlopen.RTLD_LAZY`
The `process.dlopen()` method allows dynamically loading shared objects. It is primarily used by `require()` to load C++ Addons, and should not be used directly, except in special cases. In other words, [`require()`](globals#require) should be preferred over `process.dlopen()` unless there are specific reasons such as custom dlopen flags or loading from ES modules.
The `flags` argument is an integer that allows to specify dlopen behavior. See the [`os.constants.dlopen`](os#dlopen-constants) documentation for details.
An important requirement when calling `process.dlopen()` is that the `module` instance must be passed. Functions exported by the C++ Addon are then accessible via `module.exports`.
The example below shows how to load a C++ Addon, named `local.node`, that exports a `foo` function. All the symbols are loaded before the call returns, by passing the `RTLD_NOW` constant. In this example the constant is assumed to be available.
MJS modules
```
import { dlopen } from 'node:process';
import { constants } from 'node:os';
import { fileURLToPath } from 'node:url';
const module = { exports: {} };
dlopen(module, fileURLToPath(new URL('local.node', import.meta.url)),
constants.dlopen.RTLD_NOW);
module.exports.foo();
```
CJS modules
```
const { dlopen } = require('node:process');
const { constants } = require('node:os');
const { join } = require('node:path');
const module = { exports: {} };
dlopen(module, join(__dirname, 'local.node'), constants.dlopen.RTLD_NOW);
module.exports.foo();
```
###
`process.emitWarning(warning[, options])`
Added in: v8.0.0 * `warning` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) The warning to emit.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) When `warning` is a `String`, `type` is the name to use for the *type* of warning being emitted. **Default:** `'Warning'`.
+ `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A unique identifier for the warning instance being emitted.
+ `ctor` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) When `warning` is a `String`, `ctor` is an optional function used to limit the generated stack trace. **Default:** `process.emitWarning`.
+ `detail` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Additional text to include with the error.
The `process.emitWarning()` method can be used to emit custom or application specific process warnings. These can be listened for by adding a handler to the [`'warning'`](#event-warning) event.
MJS modules
```
import { emitWarning } from 'node:process';
// Emit a warning with a code and additional detail.
emitWarning('Something happened!', {
code: 'MY_WARNING',
detail: 'This is some additional information'
});
// Emits:
// (node:56338) [MY_WARNING] Warning: Something happened!
// This is some additional information
```
CJS modules
```
const { emitWarning } = require('node:process');
// Emit a warning with a code and additional detail.
emitWarning('Something happened!', {
code: 'MY_WARNING',
detail: 'This is some additional information'
});
// Emits:
// (node:56338) [MY_WARNING] Warning: Something happened!
// This is some additional information
```
In this example, an `Error` object is generated internally by `process.emitWarning()` and passed through to the [`'warning'`](#event-warning) handler.
MJS modules
```
import process from 'node:process';
process.on('warning', (warning) => {
console.warn(warning.name); // 'Warning'
console.warn(warning.message); // 'Something happened!'
console.warn(warning.code); // 'MY_WARNING'
console.warn(warning.stack); // Stack trace
console.warn(warning.detail); // 'This is some additional information'
});
```
CJS modules
```
const process = require('node:process');
process.on('warning', (warning) => {
console.warn(warning.name); // 'Warning'
console.warn(warning.message); // 'Something happened!'
console.warn(warning.code); // 'MY_WARNING'
console.warn(warning.stack); // Stack trace
console.warn(warning.detail); // 'This is some additional information'
});
```
If `warning` is passed as an `Error` object, the `options` argument is ignored.
###
`process.emitWarning(warning[, type[, code]][, ctor])`
Added in: v6.0.0 * `warning` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) The warning to emit.
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) When `warning` is a `String`, `type` is the name to use for the *type* of warning being emitted. **Default:** `'Warning'`.
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A unique identifier for the warning instance being emitted.
* `ctor` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) When `warning` is a `String`, `ctor` is an optional function used to limit the generated stack trace. **Default:** `process.emitWarning`.
The `process.emitWarning()` method can be used to emit custom or application specific process warnings. These can be listened for by adding a handler to the [`'warning'`](#event-warning) event.
MJS modules
```
import { emitWarning } from 'node:process';
// Emit a warning using a string.
emitWarning('Something happened!');
// Emits: (node: 56338) Warning: Something happened!
```
CJS modules
```
const { emitWarning } = require('node:process');
// Emit a warning using a string.
emitWarning('Something happened!');
// Emits: (node: 56338) Warning: Something happened!
```
MJS modules
```
import { emitWarning } from 'node:process';
// Emit a warning using a string and a type.
emitWarning('Something Happened!', 'CustomWarning');
// Emits: (node:56338) CustomWarning: Something Happened!
```
CJS modules
```
const { emitWarning } = require('node:process');
// Emit a warning using a string and a type.
emitWarning('Something Happened!', 'CustomWarning');
// Emits: (node:56338) CustomWarning: Something Happened!
```
MJS modules
```
import { emitWarning } from 'node:process';
emitWarning('Something happened!', 'CustomWarning', 'WARN001');
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!
```
CJS modules
```
const { emitWarning } = require('node:process');
process.emitWarning('Something happened!', 'CustomWarning', 'WARN001');
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!
```
In each of the previous examples, an `Error` object is generated internally by `process.emitWarning()` and passed through to the [`'warning'`](#event-warning) handler.
MJS modules
```
import process from 'node:process';
process.on('warning', (warning) => {
console.warn(warning.name);
console.warn(warning.message);
console.warn(warning.code);
console.warn(warning.stack);
});
```
CJS modules
```
const process = require('node:process');
process.on('warning', (warning) => {
console.warn(warning.name);
console.warn(warning.message);
console.warn(warning.code);
console.warn(warning.stack);
});
```
If `warning` is passed as an `Error` object, it will be passed through to the `'warning'` event handler unmodified (and the optional `type`, `code` and `ctor` arguments will be ignored):
MJS modules
```
import { emitWarning } from 'node:process';
// Emit a warning using an Error object.
const myWarning = new Error('Something happened!');
// Use the Error name property to specify the type name
myWarning.name = 'CustomWarning';
myWarning.code = 'WARN001';
emitWarning(myWarning);
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!
```
CJS modules
```
const { emitWarning } = require('node:process');
// Emit a warning using an Error object.
const myWarning = new Error('Something happened!');
// Use the Error name property to specify the type name
myWarning.name = 'CustomWarning';
myWarning.code = 'WARN001';
emitWarning(myWarning);
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!
```
A `TypeError` is thrown if `warning` is anything other than a string or `Error` object.
While process warnings use `Error` objects, the process warning mechanism is **not** a replacement for normal error handling mechanisms.
The following additional handling is implemented if the warning `type` is `'DeprecationWarning'`:
* If the `--throw-deprecation` command-line flag is used, the deprecation warning is thrown as an exception rather than being emitted as an event.
* If the `--no-deprecation` command-line flag is used, the deprecation warning is suppressed.
* If the `--trace-deprecation` command-line flag is used, the deprecation warning is printed to `stderr` along with the full stack trace.
#### Avoiding duplicate warnings
As a best practice, warnings should be emitted only once per process. To do so, place the `emitWarning()` behind a boolean.
MJS modules
```
import { emitWarning } from 'node:process';
function emitMyWarning() {
if (!emitMyWarning.warned) {
emitMyWarning.warned = true;
emitWarning('Only warn once!');
}
}
emitMyWarning();
// Emits: (node: 56339) Warning: Only warn once!
emitMyWarning();
// Emits nothing
```
CJS modules
```
const { emitWarning } = require('node:process');
function emitMyWarning() {
if (!emitMyWarning.warned) {
emitMyWarning.warned = true;
emitWarning('Only warn once!');
}
}
emitMyWarning();
// Emits: (node: 56339) Warning: Only warn once!
emitMyWarning();
// Emits nothing
```
###
`process.env`
History
| Version | Changes |
| --- | --- |
| v11.14.0 | Worker threads will now use a copy of the parent thread's `process.env` by default, configurable through the `env` option of the `Worker` constructor. |
| v10.0.0 | Implicit conversion of variable value to string is deprecated. |
| v0.1.27 | Added in: v0.1.27 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `process.env` property returns an object containing the user environment. See [`environ(7)`](http://man7.org/linux/man-pages/man7/environ.7.html).
An example of this object looks like:
```
{
TERM: 'xterm-256color',
SHELL: '/usr/local/bin/bash',
USER: 'maciej',
PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
PWD: '/Users/maciej',
EDITOR: 'vim',
SHLVL: '1',
HOME: '/Users/maciej',
LOGNAME: 'maciej',
_: '/usr/local/bin/node'
}
```
It is possible to modify this object, but such modifications will not be reflected outside the Node.js process, or (unless explicitly requested) to other [`Worker`](worker_threads#class-worker) threads. In other words, the following example would not work:
```
$ node -e 'process.env.foo = "bar"' && echo $foo
```
While the following will:
MJS modules
```
import { env } from 'node:process';
env.foo = 'bar';
console.log(env.foo);
```
CJS modules
```
const { env } = require('node:process');
env.foo = 'bar';
console.log(env.foo);
```
Assigning a property on `process.env` will implicitly convert the value to a string. **This behavior is deprecated.** Future versions of Node.js may throw an error when the value is not a string, number, or boolean.
MJS modules
```
import { env } from 'node:process';
env.test = null;
console.log(env.test);
// => 'null'
env.test = undefined;
console.log(env.test);
// => 'undefined'
```
CJS modules
```
const { env } = require('node:process');
env.test = null;
console.log(env.test);
// => 'null'
env.test = undefined;
console.log(env.test);
// => 'undefined'
```
Use `delete` to delete a property from `process.env`.
MJS modules
```
import { env } from 'node:process';
env.TEST = 1;
delete env.TEST;
console.log(env.TEST);
// => undefined
```
CJS modules
```
const { env } = require('node:process');
env.TEST = 1;
delete env.TEST;
console.log(env.TEST);
// => undefined
```
On Windows operating systems, environment variables are case-insensitive.
MJS modules
```
import { env } from 'node:process';
env.TEST = 1;
console.log(env.test);
// => 1
```
CJS modules
```
const { env } = require('node:process');
env.TEST = 1;
console.log(env.test);
// => 1
```
Unless explicitly specified when creating a [`Worker`](worker_threads#class-worker) instance, each [`Worker`](worker_threads#class-worker) thread has its own copy of `process.env`, based on its parent thread's `process.env`, or whatever was specified as the `env` option to the [`Worker`](worker_threads#class-worker) constructor. Changes to `process.env` will not be visible across [`Worker`](worker_threads#class-worker) threads, and only the main thread can make changes that are visible to the operating system or to native add-ons.
###
`process.execArgv`
Added in: v0.7.7 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.execArgv` property returns the set of Node.js-specific command-line options passed when the Node.js process was launched. These options do not appear in the array returned by the [`process.argv`](#processargv) property, and do not include the Node.js executable, the name of the script, or any options following the script name. These options are useful in order to spawn child processes with the same execution environment as the parent.
```
$ node --harmony script.js --version
```
Results in `process.execArgv`:
```
['--harmony']
```
And `process.argv`:
```
['/usr/local/bin/node', 'script.js', '--version']
```
Refer to [`Worker` constructor](worker_threads#new-workerfilename-options) for the detailed behavior of worker threads with this property.
###
`process.execPath`
Added in: v0.1.100 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.execPath` property returns the absolute pathname of the executable that started the Node.js process. Symbolic links, if any, are resolved.
```
'/usr/local/bin/node'
```
###
`process.exit([code])`
Added in: v0.1.13 * `code` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The exit code. **Default:** `0`.
The `process.exit()` method instructs Node.js to terminate the process synchronously with an exit status of `code`. If `code` is omitted, exit uses either the 'success' code `0` or the value of `process.exitCode` if it has been set. Node.js will not terminate until all the [`'exit'`](#event-exit) event listeners are called.
To exit with a 'failure' code:
MJS modules
```
import { exit } from 'node:process';
exit(1);
```
CJS modules
```
const { exit } = require('node:process');
exit(1);
```
The shell that executed Node.js should see the exit code as `1`.
Calling `process.exit()` will force the process to exit as quickly as possible even if there are still asynchronous operations pending that have not yet completed fully, including I/O operations to `process.stdout` and `process.stderr`.
In most situations, it is not actually necessary to call `process.exit()` explicitly. The Node.js process will exit on its own *if there is no additional work pending* in the event loop. The `process.exitCode` property can be set to tell the process which exit code to use when the process exits gracefully.
For instance, the following example illustrates a *misuse* of the `process.exit()` method that could lead to data printed to stdout being truncated and lost:
MJS modules
```
import { exit } from 'node:process';
// This is an example of what *not* to do:
if (someConditionNotMet()) {
printUsageToStdout();
exit(1);
}
```
CJS modules
```
const { exit } = require('node:process');
// This is an example of what *not* to do:
if (someConditionNotMet()) {
printUsageToStdout();
exit(1);
}
```
The reason this is problematic is because writes to `process.stdout` in Node.js are sometimes *asynchronous* and may occur over multiple ticks of the Node.js event loop. Calling `process.exit()`, however, forces the process to exit *before* those additional writes to `stdout` can be performed.
Rather than calling `process.exit()` directly, the code *should* set the `process.exitCode` and allow the process to exit naturally by avoiding scheduling any additional work for the event loop:
MJS modules
```
import process from 'node:process';
// How to properly set the exit code while letting
// the process exit gracefully.
if (someConditionNotMet()) {
printUsageToStdout();
process.exitCode = 1;
}
```
CJS modules
```
const process = require('node:process');
// How to properly set the exit code while letting
// the process exit gracefully.
if (someConditionNotMet()) {
printUsageToStdout();
process.exitCode = 1;
}
```
If it is necessary to terminate the Node.js process due to an error condition, throwing an *uncaught* error and allowing the process to terminate accordingly is safer than calling `process.exit()`.
In [`Worker`](worker_threads#class-worker) threads, this function stops the current thread rather than the current process.
###
`process.exitCode`
Added in: v0.11.8 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
A number which will be the process exit code, when the process either exits gracefully, or is exited via [`process.exit()`](#processexitcode) without specifying a code.
Specifying a code to [`process.exit(code)`](#processexitcode) will override any previous setting of `process.exitCode`.
###
`process.getActiveResourcesInfo()`
Added in: v17.3.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.getActiveResourcesInfo()` method returns an array of strings containing the types of the active resources that are currently keeping the event loop alive.
MJS modules
```
import { getActiveResourcesInfo } from 'node:process';
import { setTimeout } from 'node:timers';
console.log('Before:', getActiveResourcesInfo());
setTimeout(() => {}, 1000);
console.log('After:', getActiveResourcesInfo());
// Prints:
// Before: [ 'CloseReq', 'TTYWrap', 'TTYWrap', 'TTYWrap' ]
// After: [ 'CloseReq', 'TTYWrap', 'TTYWrap', 'TTYWrap', 'Timeout' ]
```
CJS modules
```
const { getActiveResourcesInfo } = require('node:process');
const { setTimeout } = require('node:timers');
console.log('Before:', getActiveResourcesInfo());
setTimeout(() => {}, 1000);
console.log('After:', getActiveResourcesInfo());
// Prints:
// Before: [ 'TTYWrap', 'TTYWrap', 'TTYWrap' ]
// After: [ 'TTYWrap', 'TTYWrap', 'TTYWrap', 'Timeout' ]
```
###
`process.getegid()`
Added in: v2.0.0 The `process.getegid()` method returns the numerical effective group identity of the Node.js process. (See [`getegid(2)`](http://man7.org/linux/man-pages/man2/getegid.2.html).)
MJS modules
```
import process from 'node:process';
if (process.getegid) {
console.log(`Current gid: ${process.getegid()}`);
}
```
CJS modules
```
const process = require('node:process');
if (process.getegid) {
console.log(`Current gid: ${process.getegid()}`);
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android).
###
`process.geteuid()`
Added in: v2.0.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `process.geteuid()` method returns the numerical effective user identity of the process. (See [`geteuid(2)`](http://man7.org/linux/man-pages/man2/geteuid.2.html).)
MJS modules
```
import process from 'node:process';
if (process.geteuid) {
console.log(`Current uid: ${process.geteuid()}`);
}
```
CJS modules
```
const process = require('node:process');
if (process.geteuid) {
console.log(`Current uid: ${process.geteuid()}`);
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android).
###
`process.getgid()`
Added in: v0.1.31 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `process.getgid()` method returns the numerical group identity of the process. (See [`getgid(2)`](http://man7.org/linux/man-pages/man2/getgid.2.html).)
MJS modules
```
import process from 'node:process';
if (process.getgid) {
console.log(`Current gid: ${process.getgid()}`);
}
```
CJS modules
```
const process = require('node:process');
if (process.getgid) {
console.log(`Current gid: ${process.getgid()}`);
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android).
###
`process.getgroups()`
Added in: v0.9.4 * Returns: [<integer[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `process.getgroups()` method returns an array with the supplementary group IDs. POSIX leaves it unspecified if the effective group ID is included but Node.js ensures it always is.
MJS modules
```
import process from 'node:process';
if (process.getgroups) {
console.log(process.getgroups()); // [ 16, 21, 297 ]
}
```
CJS modules
```
const process = require('node:process');
if (process.getgroups) {
console.log(process.getgroups()); // [ 16, 21, 297 ]
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android).
###
`process.getuid()`
Added in: v0.1.28 * Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `process.getuid()` method returns the numeric user identity of the process. (See [`getuid(2)`](http://man7.org/linux/man-pages/man2/getuid.2.html).)
MJS modules
```
import process from 'node:process';
if (process.getuid) {
console.log(`Current uid: ${process.getuid()}`);
}
```
CJS modules
```
const process = require('node:process');
if (process.getuid) {
console.log(`Current uid: ${process.getuid()}`);
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android).
###
`process.hasUncaughtExceptionCaptureCallback()`
Added in: v9.3.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Indicates whether a callback has been set using [`process.setUncaughtExceptionCaptureCallback()`](#processsetuncaughtexceptioncapturecallbackfn).
###
`process.hrtime([time])`
Added in: v0.7.6
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy. Use [`process.hrtime.bigint()`](#processhrtimebigint) instead.
* `time` [<integer[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The result of a previous call to `process.hrtime()`
* Returns: [<integer[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
This is the legacy version of [`process.hrtime.bigint()`](#processhrtimebigint) before `bigint` was introduced in JavaScript.
The `process.hrtime()` method returns the current high-resolution real time in a `[seconds, nanoseconds]` tuple `Array`, where `nanoseconds` is the remaining part of the real time that can't be represented in second precision.
`time` is an optional parameter that must be the result of a previous `process.hrtime()` call to diff with the current time. If the parameter passed in is not a tuple `Array`, a `TypeError` will be thrown. Passing in a user-defined array instead of the result of a previous call to `process.hrtime()` will lead to undefined behavior.
These times are relative to an arbitrary time in the past, and not related to the time of day and therefore not subject to clock drift. The primary use is for measuring performance between intervals:
MJS modules
```
import { hrtime } from 'node:process';
const NS_PER_SEC = 1e9;
const time = hrtime();
// [ 1800216, 25 ]
setTimeout(() => {
const diff = hrtime(time);
// [ 1, 552 ]
console.log(`Benchmark took ${diff[0] * NS_PER_SEC + diff[1]} nanoseconds`);
// Benchmark took 1000000552 nanoseconds
}, 1000);
```
CJS modules
```
const { hrtime } = require('node:process');
const NS_PER_SEC = 1e9;
const time = hrtime();
// [ 1800216, 25 ]
setTimeout(() => {
const diff = hrtime(time);
// [ 1, 552 ]
console.log(`Benchmark took ${diff[0] * NS_PER_SEC + diff[1]} nanoseconds`);
// Benchmark took 1000000552 nanoseconds
}, 1000);
```
###
`process.hrtime.bigint()`
Added in: v10.7.0 * Returns: [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The `bigint` version of the [`process.hrtime()`](#processhrtimetime) method returning the current high-resolution real time in nanoseconds as a `bigint`.
Unlike [`process.hrtime()`](#processhrtimetime), it does not support an additional `time` argument since the difference can just be computed directly by subtraction of the two `bigint`s.
MJS modules
```
import { hrtime } from 'node:process';
const start = hrtime.bigint();
// 191051479007711n
setTimeout(() => {
const end = hrtime.bigint();
// 191052633396993n
console.log(`Benchmark took ${end - start} nanoseconds`);
// Benchmark took 1154389282 nanoseconds
}, 1000);
```
CJS modules
```
const { hrtime } = require('node:process');
const start = hrtime.bigint();
// 191051479007711n
setTimeout(() => {
const end = hrtime.bigint();
// 191052633396993n
console.log(`Benchmark took ${end - start} nanoseconds`);
// Benchmark took 1154389282 nanoseconds
}, 1000);
```
###
`process.initgroups(user, extraGroup)`
Added in: v0.9.4 * `user` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The user name or numeric identifier.
* `extraGroup` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A group name or numeric identifier.
The `process.initgroups()` method reads the `/etc/group` file and initializes the group access list, using all groups of which the user is a member. This is a privileged operation that requires that the Node.js process either have `root` access or the `CAP_SETGID` capability.
Use care when dropping privileges:
MJS modules
```
import { getgroups, initgroups, setgid } from 'node:process';
console.log(getgroups()); // [ 0 ]
initgroups('nodeuser', 1000); // switch user
console.log(getgroups()); // [ 27, 30, 46, 1000, 0 ]
setgid(1000); // drop root gid
console.log(getgroups()); // [ 27, 30, 46, 1000 ]
```
CJS modules
```
const { getgroups, initgroups, setgid } = require('node:process');
console.log(getgroups()); // [ 0 ]
initgroups('nodeuser', 1000); // switch user
console.log(getgroups()); // [ 27, 30, 46, 1000, 0 ]
setgid(1000); // drop root gid
console.log(getgroups()); // [ 27, 30, 46, 1000 ]
```
This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in [`Worker`](worker_threads#class-worker) threads.
###
`process.kill(pid[, signal])`
Added in: v0.0.6 * `pid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A process ID
* `signal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The signal to send, either as a string or number. **Default:** `'SIGTERM'`.
The `process.kill()` method sends the `signal` to the process identified by `pid`.
Signal names are strings such as `'SIGINT'` or `'SIGHUP'`. See [Signal Events](#signal-events) and [`kill(2)`](http://man7.org/linux/man-pages/man2/kill.2.html) for more information.
This method will throw an error if the target `pid` does not exist. As a special case, a signal of `0` can be used to test for the existence of a process. Windows platforms will throw an error if the `pid` is used to kill a process group.
Even though the name of this function is `process.kill()`, it is really just a signal sender, like the `kill` system call. The signal sent may do something other than kill the target process.
MJS modules
```
import process, { kill } from 'node:process';
process.on('SIGHUP', () => {
console.log('Got SIGHUP signal.');
});
setTimeout(() => {
console.log('Exiting.');
process.exit(0);
}, 100);
kill(process.pid, 'SIGHUP');
```
CJS modules
```
const process = require('node:process');
process.on('SIGHUP', () => {
console.log('Got SIGHUP signal.');
});
setTimeout(() => {
console.log('Exiting.');
process.exit(0);
}, 100);
process.kill(process.pid, 'SIGHUP');
```
When `SIGUSR1` is received by a Node.js process, Node.js will start the debugger. See [Signal Events](#signal-events).
###
`process.mainModule`
Added in: v0.1.17Deprecated since: v14.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`require.main`](modules#accessing-the-main-module) instead.
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `process.mainModule` property provides an alternative way of retrieving [`require.main`](modules#accessing-the-main-module). The difference is that if the main module changes at runtime, [`require.main`](modules#accessing-the-main-module) may still refer to the original main module in modules that were required before the change occurred. Generally, it's safe to assume that the two refer to the same module.
As with [`require.main`](modules#accessing-the-main-module), `process.mainModule` will be `undefined` if there is no entry script.
###
`process.memoryUsage()`
History
| Version | Changes |
| --- | --- |
| v13.9.0, v12.17.0 | Added `arrayBuffers` to the returned object. |
| v7.2.0 | Added `external` to the returned object. |
| v0.1.16 | Added in: v0.1.16 |
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `rss` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `heapTotal` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `heapUsed` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `external` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `arrayBuffers` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns an object describing the memory usage of the Node.js process measured in bytes.
MJS modules
```
import { memoryUsage } from 'node:process';
console.log(memoryUsage());
// Prints:
// {
// rss: 4935680,
// heapTotal: 1826816,
// heapUsed: 650472,
// external: 49879,
// arrayBuffers: 9386
// }
```
CJS modules
```
const { memoryUsage } = require('node:process');
console.log(memoryUsage());
// Prints:
// {
// rss: 4935680,
// heapTotal: 1826816,
// heapUsed: 650472,
// external: 49879,
// arrayBuffers: 9386
// }
```
* `heapTotal` and `heapUsed` refer to V8's memory usage.
* `external` refers to the memory usage of C++ objects bound to JavaScript objects managed by V8.
* `rss`, Resident Set Size, is the amount of space occupied in the main memory device (that is a subset of the total allocated memory) for the process, including all C++ and JavaScript objects and code.
* `arrayBuffers` refers to memory allocated for `ArrayBuffer`s and `SharedArrayBuffer`s, including all Node.js [`Buffer`](buffer)s. This is also included in the `external` value. When Node.js is used as an embedded library, this value may be `0` because allocations for `ArrayBuffer`s may not be tracked in that case.
When using [`Worker`](worker_threads#class-worker) threads, `rss` will be a value that is valid for the entire process, while the other fields will only refer to the current thread.
The `process.memoryUsage()` method iterates over each page to gather information about memory usage which might be slow depending on the program memory allocations.
###
`process.memoryUsage.rss()`
Added in: v15.6.0, v14.18.0 * Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `process.memoryUsage.rss()` method returns an integer representing the Resident Set Size (RSS) in bytes.
The Resident Set Size, is the amount of space occupied in the main memory device (that is a subset of the total allocated memory) for the process, including all C++ and JavaScript objects and code.
This is the same value as the `rss` property provided by `process.memoryUsage()` but `process.memoryUsage.rss()` is faster.
MJS modules
```
import { memoryUsage } from 'node:process';
console.log(memoryUsage.rss());
// 35655680
```
CJS modules
```
const { rss } = require('node:process');
console.log(memoryUsage.rss());
// 35655680
```
###
`process.nextTick(callback[, ...args])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v1.8.1 | Additional arguments after `callback` are now supported. |
| v0.1.26 | Added in: v0.1.26 |
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Additional arguments to pass when invoking the `callback`
`process.nextTick()` adds `callback` to the "next tick queue". This queue is fully drained after the current operation on the JavaScript stack runs to completion and before the event loop is allowed to continue. It's possible to create an infinite loop if one were to recursively call `process.nextTick()`. See the [Event Loop](https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/#process-nexttick) guide for more background.
MJS modules
```
import { nextTick } from 'node:process';
console.log('start');
nextTick(() => {
console.log('nextTick callback');
});
console.log('scheduled');
// Output:
// start
// scheduled
// nextTick callback
```
CJS modules
```
const { nextTick } = require('node:process');
console.log('start');
nextTick(() => {
console.log('nextTick callback');
});
console.log('scheduled');
// Output:
// start
// scheduled
// nextTick callback
```
This is important when developing APIs in order to give users the opportunity to assign event handlers *after* an object has been constructed but before any I/O has occurred:
MJS modules
```
import { nextTick } from 'node:process';
function MyThing(options) {
this.setupOptions(options);
nextTick(() => {
this.startDoingStuff();
});
}
const thing = new MyThing();
thing.getReadyForStuff();
// thing.startDoingStuff() gets called now, not before.
```
CJS modules
```
const { nextTick } = require('node:process');
function MyThing(options) {
this.setupOptions(options);
nextTick(() => {
this.startDoingStuff();
});
}
const thing = new MyThing();
thing.getReadyForStuff();
// thing.startDoingStuff() gets called now, not before.
```
It is very important for APIs to be either 100% synchronous or 100% asynchronous. Consider this example:
```
// WARNING! DO NOT USE! BAD UNSAFE HAZARD!
function maybeSync(arg, cb) {
if (arg) {
cb();
return;
}
fs.stat('file', cb);
}
```
This API is hazardous because in the following case:
```
const maybeTrue = Math.random() > 0.5;
maybeSync(maybeTrue, () => {
foo();
});
bar();
```
It is not clear whether `foo()` or `bar()` will be called first.
The following approach is much better:
MJS modules
```
import { nextTick } from 'node:process';
function definitelyAsync(arg, cb) {
if (arg) {
nextTick(cb);
return;
}
fs.stat('file', cb);
}
```
CJS modules
```
const { nextTick } = require('node:process');
function definitelyAsync(arg, cb) {
if (arg) {
nextTick(cb);
return;
}
fs.stat('file', cb);
}
```
#### When to use `queueMicrotask()` vs. `process.nextTick()`
The [`queueMicrotask()`](globals#queuemicrotaskcallback) API is an alternative to `process.nextTick()` that also defers execution of a function using the same microtask queue used to execute the then, catch, and finally handlers of resolved promises. Within Node.js, every time the "next tick queue" is drained, the microtask queue is drained immediately after.
MJS modules
```
import { nextTick } from 'node:process';
Promise.resolve().then(() => console.log(2));
queueMicrotask(() => console.log(3));
nextTick(() => console.log(1));
// Output:
// 1
// 2
// 3
```
CJS modules
```
const { nextTick } = require('node:process');
Promise.resolve().then(() => console.log(2));
queueMicrotask(() => console.log(3));
nextTick(() => console.log(1));
// Output:
// 1
// 2
// 3
```
For *most* userland use cases, the `queueMicrotask()` API provides a portable and reliable mechanism for deferring execution that works across multiple JavaScript platform environments and should be favored over `process.nextTick()`. In simple scenarios, `queueMicrotask()` can be a drop-in replacement for `process.nextTick()`.
```
console.log('start');
queueMicrotask(() => {
console.log('microtask callback');
});
console.log('scheduled');
// Output:
// start
// scheduled
// microtask callback
```
One note-worthy difference between the two APIs is that `process.nextTick()` allows specifying additional values that will be passed as arguments to the deferred function when it is called. Achieving the same result with `queueMicrotask()` requires using either a closure or a bound function:
```
function deferred(a, b) {
console.log('microtask', a + b);
}
console.log('start');
queueMicrotask(deferred.bind(undefined, 1, 2));
console.log('scheduled');
// Output:
// start
// scheduled
// microtask 3
```
There are minor differences in the way errors raised from within the next tick queue and microtask queue are handled. Errors thrown within a queued microtask callback should be handled within the queued callback when possible. If they are not, the `process.on('uncaughtException')` event handler can be used to capture and handle the errors.
When in doubt, unless the specific capabilities of `process.nextTick()` are needed, use `queueMicrotask()`.
###
`process.noDeprecation`
Added in: v0.8.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `process.noDeprecation` property indicates whether the `--no-deprecation` flag is set on the current Node.js process. See the documentation for the [`'warning'` event](#event-warning) and the [`emitWarning()` method](#processemitwarningwarning-type-code-ctor) for more information about this flag's behavior.
###
`process.pid`
Added in: v0.1.15 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `process.pid` property returns the PID of the process.
MJS modules
```
import { pid } from 'node:process';
console.log(`This process is pid ${pid}`);
```
CJS modules
```
const { pid } = require('node:process');
console.log(`This process is pid ${pid}`);
```
###
`process.platform`
Added in: v0.1.16 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.platform` property returns a string identifying the operating system platform for which the Node.js binary was compiled.
Currently possible values are:
* `'aix'`
* `'darwin'`
* `'freebsd'`
* `'linux'`
* `'openbsd'`
* `'sunos'`
* `'win32'`
MJS modules
```
import { platform } from 'node:process';
console.log(`This platform is ${platform}`);
```
CJS modules
```
const { platform } = require('node:process');
console.log(`This platform is ${platform}`);
```
The value `'android'` may also be returned if the Node.js is built on the Android operating system. However, Android support in Node.js [is experimental](https://github.com/nodejs/node/blob/HEAD/BUILDING.md#androidandroid-based-devices-eg-firefox-os).
###
`process.ppid`
Added in: v9.2.0, v8.10.0, v6.13.0 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `process.ppid` property returns the PID of the parent of the current process.
MJS modules
```
import { ppid } from 'node:process';
console.log(`The parent process is pid ${ppid}`);
```
CJS modules
```
const { ppid } = require('node:process');
console.log(`The parent process is pid ${ppid}`);
```
###
`process.release`
History
| Version | Changes |
| --- | --- |
| v4.2.0 | The `lts` property is now supported. |
| v3.0.0 | Added in: v3.0.0 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `process.release` property returns an `Object` containing metadata related to the current release, including URLs for the source tarball and headers-only tarball.
`process.release` contains the following properties:
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A value that will always be `'node'`.
* `sourceUrl` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) an absolute URL pointing to a *`.tar.gz`* file containing the source code of the current release.
* `headersUrl`[<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) an absolute URL pointing to a *`.tar.gz`* file containing only the source header files for the current release. This file is significantly smaller than the full source file and can be used for compiling Node.js native add-ons.
* `libUrl` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) an absolute URL pointing to a *`node.lib`* file matching the architecture and version of the current release. This file is used for compiling Node.js native add-ons. *This property is only present on Windows builds of Node.js and will be missing on all other platforms.*
* `lts` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) a string label identifying the [LTS](https://github.com/nodejs/Release) label for this release. This property only exists for LTS releases and is `undefined` for all other release types, including *Current* releases. Valid values include the LTS Release code names (including those that are no longer supported).
+ `'Dubnium'` for the 10.x LTS line beginning with 10.13.0.
+ `'Erbium'` for the 12.x LTS line beginning with 12.13.0. For other LTS Release code names, see [Node.js Changelog Archive](https://github.com/nodejs/node/blob/HEAD/doc/changelogs/CHANGELOG_ARCHIVE.md)
```
{
name: 'node',
lts: 'Erbium',
sourceUrl: 'https://nodejs.org/download/release/v12.18.1/node-v12.18.1.tar.gz',
headersUrl: 'https://nodejs.org/download/release/v12.18.1/node-v12.18.1-headers.tar.gz',
libUrl: 'https://nodejs.org/download/release/v12.18.1/win-x64/node.lib'
}
```
In custom builds from non-release versions of the source tree, only the `name` property may be present. The additional properties should not be relied upon to exist.
###
`process.report`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This API is no longer experimental. |
| v11.8.0 | Added in: v11.8.0 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
`process.report` is an object whose methods are used to generate diagnostic reports for the current process. Additional documentation is available in the [report documentation](report).
####
`process.report.compact`
Added in: v13.12.0, v12.17.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Write reports in a compact format, single-line JSON, more easily consumable by log processing systems than the default multi-line format designed for human consumption.
MJS modules
```
import { report } from 'node:process';
console.log(`Reports are compact? ${report.compact}`);
```
CJS modules
```
const { report } = require('node:process');
console.log(`Reports are compact? ${report.compact}`);
```
####
`process.report.directory`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This API is no longer experimental. |
| v11.12.0 | Added in: v11.12.0 |
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Directory where the report is written. The default value is the empty string, indicating that reports are written to the current working directory of the Node.js process.
MJS modules
```
import { report } from 'node:process';
console.log(`Report directory is ${report.directory}`);
```
CJS modules
```
const { report } = require('node:process');
console.log(`Report directory is ${report.directory}`);
```
####
`process.report.filename`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This API is no longer experimental. |
| v11.12.0 | Added in: v11.12.0 |
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Filename where the report is written. If set to the empty string, the output filename will be comprised of a timestamp, PID, and sequence number. The default value is the empty string.
If the value of `process.report.filename` is set to `'stdout'` or `'stderr'`, the report is written to the stdout or stderr of the process respectively.
MJS modules
```
import { report } from 'node:process';
console.log(`Report filename is ${report.filename}`);
```
CJS modules
```
const { report } = require('node:process');
console.log(`Report filename is ${report.filename}`);
```
####
`process.report.getReport([err])`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This API is no longer experimental. |
| v11.8.0 | Added in: v11.8.0 |
* `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) A custom error used for reporting the JavaScript stack.
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns a JavaScript Object representation of a diagnostic report for the running process. The report's JavaScript stack trace is taken from `err`, if present.
MJS modules
```
import { report } from 'node:process';
const data = report.getReport();
console.log(data.header.nodejsVersion);
// Similar to process.report.writeReport()
import fs from 'node:fs';
fs.writeFileSync('my-report.log', util.inspect(data), 'utf8');
```
CJS modules
```
const { report } = require('node:process');
const data = report.getReport();
console.log(data.header.nodejsVersion);
// Similar to process.report.writeReport()
const fs = require('node:fs');
fs.writeFileSync('my-report.log', util.inspect(data), 'utf8');
```
Additional documentation is available in the [report documentation](report).
####
`process.report.reportOnFatalError`
History
| Version | Changes |
| --- | --- |
| v15.0.0, v14.17.0 | This API is no longer experimental. |
| v11.12.0 | Added in: v11.12.0 |
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If `true`, a diagnostic report is generated on fatal errors, such as out of memory errors or failed C++ assertions.
MJS modules
```
import { report } from 'node:process';
console.log(`Report on fatal error: ${report.reportOnFatalError}`);
```
CJS modules
```
const { report } = require('node:process');
console.log(`Report on fatal error: ${report.reportOnFatalError}`);
```
####
`process.report.reportOnSignal`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This API is no longer experimental. |
| v11.12.0 | Added in: v11.12.0 |
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If `true`, a diagnostic report is generated when the process receives the signal specified by `process.report.signal`.
MJS modules
```
import { report } from 'node:process';
console.log(`Report on signal: ${report.reportOnSignal}`);
```
CJS modules
```
const { report } = require('node:process');
console.log(`Report on signal: ${report.reportOnSignal}`);
```
####
`process.report.reportOnUncaughtException`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This API is no longer experimental. |
| v11.12.0 | Added in: v11.12.0 |
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If `true`, a diagnostic report is generated on uncaught exception.
MJS modules
```
import { report } from 'node:process';
console.log(`Report on exception: ${report.reportOnUncaughtException}`);
```
CJS modules
```
const { report } = require('node:process');
console.log(`Report on exception: ${report.reportOnUncaughtException}`);
```
####
`process.report.signal`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This API is no longer experimental. |
| v11.12.0 | Added in: v11.12.0 |
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The signal used to trigger the creation of a diagnostic report. Defaults to `'SIGUSR2'`.
MJS modules
```
import { report } from 'node:process';
console.log(`Report signal: ${report.signal}`);
```
CJS modules
```
const { report } = require('node:process');
console.log(`Report signal: ${report.signal}`);
```
####
`process.report.writeReport([filename][, err])`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This API is no longer experimental. |
| v11.8.0 | Added in: v11.8.0 |
* `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the file where the report is written. This should be a relative path, that will be appended to the directory specified in `process.report.directory`, or the current working directory of the Node.js process, if unspecified.
* `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) A custom error used for reporting the JavaScript stack.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Returns the filename of the generated report.
Writes a diagnostic report to a file. If `filename` is not provided, the default filename includes the date, time, PID, and a sequence number. The report's JavaScript stack trace is taken from `err`, if present.
If the value of `filename` is set to `'stdout'` or `'stderr'`, the report is written to the stdout or stderr of the process respectively.
MJS modules
```
import { report } from 'node:process';
report.writeReport();
```
CJS modules
```
const { report } = require('node:process');
report.writeReport();
```
Additional documentation is available in the [report documentation](report).
###
`process.resourceUsage()`
Added in: v12.6.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) the resource usage for the current process. All of these values come from the `uv_getrusage` call which returns a [`uv_rusage_t` struct](https://docs.libuv.org/en/v1.x/misc.html#c.uv_rusage_t).
+ `userCPUTime` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_utime` computed in microseconds. It is the same value as [`process.cpuUsage().user`](#processcpuusagepreviousvalue).
+ `systemCPUTime` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_stime` computed in microseconds. It is the same value as [`process.cpuUsage().system`](#processcpuusagepreviousvalue).
+ `maxRSS` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_maxrss` which is the maximum resident set size used in kilobytes.
+ `sharedMemorySize` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_ixrss` but is not supported by any platform.
+ `unsharedDataSize` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_idrss` but is not supported by any platform.
+ `unsharedStackSize` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_isrss` but is not supported by any platform.
+ `minorPageFault` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_minflt` which is the number of minor page faults for the process, see [this article for more details](https://en.wikipedia.org/wiki/Page_fault#Minor).
+ `majorPageFault` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_majflt` which is the number of major page faults for the process, see [this article for more details](https://en.wikipedia.org/wiki/Page_fault#Major). This field is not supported on Windows.
+ `swappedOut` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_nswap` but is not supported by any platform.
+ `fsRead` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_inblock` which is the number of times the file system had to perform input.
+ `fsWrite` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_oublock` which is the number of times the file system had to perform output.
+ `ipcSent` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_msgsnd` but is not supported by any platform.
+ `ipcReceived` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_msgrcv` but is not supported by any platform.
+ `signalsCount` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_nsignals` but is not supported by any platform.
+ `voluntaryContextSwitches` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_nvcsw` which is the number of times a CPU context switch resulted due to a process voluntarily giving up the processor before its time slice was completed (usually to await availability of a resource). This field is not supported on Windows.
+ `involuntaryContextSwitches` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to `ru_nivcsw` which is the number of times a CPU context switch resulted due to a higher priority process becoming runnable or because the current process exceeded its time slice. This field is not supported on Windows.
MJS modules
```
import { resourceUsage } from 'node:process';
console.log(resourceUsage());
/*
Will output:
{
userCPUTime: 82872,
systemCPUTime: 4143,
maxRSS: 33164,
sharedMemorySize: 0,
unsharedDataSize: 0,
unsharedStackSize: 0,
minorPageFault: 2469,
majorPageFault: 0,
swappedOut: 0,
fsRead: 0,
fsWrite: 8,
ipcSent: 0,
ipcReceived: 0,
signalsCount: 0,
voluntaryContextSwitches: 79,
involuntaryContextSwitches: 1
}
*/
```
CJS modules
```
const { resourceUsage } = require('node:process');
console.log(resourceUsage());
/*
Will output:
{
userCPUTime: 82872,
systemCPUTime: 4143,
maxRSS: 33164,
sharedMemorySize: 0,
unsharedDataSize: 0,
unsharedStackSize: 0,
minorPageFault: 2469,
majorPageFault: 0,
swappedOut: 0,
fsRead: 0,
fsWrite: 8,
ipcSent: 0,
ipcReceived: 0,
signalsCount: 0,
voluntaryContextSwitches: 79,
involuntaryContextSwitches: 1
}
*/
```
###
`process.send(message[, sendHandle[, options]][, callback])`
Added in: v0.5.9 * `message` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `sendHandle` [<net.Server>](net#class-netserver) | [<net.Socket>](net#class-netsocket)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) used to parameterize the sending of certain types of handles.`options` supports the following properties:
+ `keepOpen` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) A value that can be used when passing instances of `net.Socket`. When `true`, the socket is kept open in the sending process. **Default:** `false`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If Node.js is spawned with an IPC channel, the `process.send()` method can be used to send messages to the parent process. Messages will be received as a [`'message'`](child_process#event-message) event on the parent's [`ChildProcess`](child_process#class-childprocess) object.
If Node.js was not spawned with an IPC channel, `process.send` will be `undefined`.
The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent.
###
`process.setegid(id)`
Added in: v2.0.0 * `id` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A group name or ID
The `process.setegid()` method sets the effective group identity of the process. (See [`setegid(2)`](http://man7.org/linux/man-pages/man2/setegid.2.html).) The `id` can be passed as either a numeric ID or a group name string. If a group name is specified, this method blocks while resolving the associated a numeric ID.
MJS modules
```
import process from 'node:process';
if (process.getegid && process.setegid) {
console.log(`Current gid: ${process.getegid()}`);
try {
process.setegid(501);
console.log(`New gid: ${process.getegid()}`);
} catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}
```
CJS modules
```
const process = require('node:process');
if (process.getegid && process.setegid) {
console.log(`Current gid: ${process.getegid()}`);
try {
process.setegid(501);
console.log(`New gid: ${process.getegid()}`);
} catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in [`Worker`](worker_threads#class-worker) threads.
###
`process.seteuid(id)`
Added in: v2.0.0 * `id` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A user name or ID
The `process.seteuid()` method sets the effective user identity of the process. (See [`seteuid(2)`](http://man7.org/linux/man-pages/man2/seteuid.2.html).) The `id` can be passed as either a numeric ID or a username string. If a username is specified, the method blocks while resolving the associated numeric ID.
MJS modules
```
import process from 'node:process';
if (process.geteuid && process.seteuid) {
console.log(`Current uid: ${process.geteuid()}`);
try {
process.seteuid(501);
console.log(`New uid: ${process.geteuid()}`);
} catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}
```
CJS modules
```
const process = require('node:process');
if (process.geteuid && process.seteuid) {
console.log(`Current uid: ${process.geteuid()}`);
try {
process.seteuid(501);
console.log(`New uid: ${process.geteuid()}`);
} catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in [`Worker`](worker_threads#class-worker) threads.
###
`process.setgid(id)`
Added in: v0.1.31 * `id` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The group name or ID
The `process.setgid()` method sets the group identity of the process. (See [`setgid(2)`](http://man7.org/linux/man-pages/man2/setgid.2.html).) The `id` can be passed as either a numeric ID or a group name string. If a group name is specified, this method blocks while resolving the associated numeric ID.
MJS modules
```
import process from 'node:process';
if (process.getgid && process.setgid) {
console.log(`Current gid: ${process.getgid()}`);
try {
process.setgid(501);
console.log(`New gid: ${process.getgid()}`);
} catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}
```
CJS modules
```
const process = require('node:process');
if (process.getgid && process.setgid) {
console.log(`Current gid: ${process.getgid()}`);
try {
process.setgid(501);
console.log(`New gid: ${process.getgid()}`);
} catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in [`Worker`](worker_threads#class-worker) threads.
###
`process.setgroups(groups)`
Added in: v0.9.4 * `groups` [<integer[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `process.setgroups()` method sets the supplementary group IDs for the Node.js process. This is a privileged operation that requires the Node.js process to have `root` or the `CAP_SETGID` capability.
The `groups` array can contain numeric group IDs, group names, or both.
MJS modules
```
import process from 'node:process';
if (process.getgroups && process.setgroups) {
try {
process.setgroups([501]);
console.log(process.getgroups()); // new groups
} catch (err) {
console.log(`Failed to set groups: ${err}`);
}
}
```
CJS modules
```
const process = require('node:process');
if (process.getgroups && process.setgroups) {
try {
process.setgroups([501]);
console.log(process.getgroups()); // new groups
} catch (err) {
console.log(`Failed to set groups: ${err}`);
}
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in [`Worker`](worker_threads#class-worker) threads.
###
`process.setuid(id)`
Added in: v0.1.28 * `id` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.setuid(id)` method sets the user identity of the process. (See [`setuid(2)`](http://man7.org/linux/man-pages/man2/setuid.2.html).) The `id` can be passed as either a numeric ID or a username string. If a username is specified, the method blocks while resolving the associated numeric ID.
MJS modules
```
import process from 'node:process';
if (process.getuid && process.setuid) {
console.log(`Current uid: ${process.getuid()}`);
try {
process.setuid(501);
console.log(`New uid: ${process.getuid()}`);
} catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}
```
CJS modules
```
const process = require('node:process');
if (process.getuid && process.setuid) {
console.log(`Current uid: ${process.getuid()}`);
try {
process.setuid(501);
console.log(`New uid: ${process.getuid()}`);
} catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}
```
This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in [`Worker`](worker_threads#class-worker) threads.
###
`process.setSourceMapsEnabled(val)`
Added in: v16.6.0, v14.18.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `val` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
This function enables or disables the [Source Map v3](https://sourcemaps.info/spec.html) support for stack traces.
It provides same features as launching Node.js process with commandline options `--enable-source-maps`.
Only source maps in JavaScript files that are loaded after source maps has been enabled will be parsed and loaded.
###
`process.setUncaughtExceptionCaptureCallback(fn)`
Added in: v9.3.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
The `process.setUncaughtExceptionCaptureCallback()` function sets a function that will be invoked when an uncaught exception occurs, which will receive the exception value itself as its first argument.
If such a function is set, the [`'uncaughtException'`](#event-uncaughtexception) event will not be emitted. If `--abort-on-uncaught-exception` was passed from the command line or set through [`v8.setFlagsFromString()`](v8#v8setflagsfromstringflags), the process will not abort. Actions configured to take place on exceptions such as report generations will be affected too
To unset the capture function, `process.setUncaughtExceptionCaptureCallback(null)` may be used. Calling this method with a non-`null` argument while another capture function is set will throw an error.
Using this function is mutually exclusive with using the deprecated [`domain`](domain) built-in module.
###
`process.stderr`
* [<Stream>](stream#stream)
The `process.stderr` property returns a stream connected to `stderr` (fd `2`). It is a [`net.Socket`](net#class-netsocket) (which is a [Duplex](stream#duplex-and-transform-streams) stream) unless fd `2` refers to a file, in which case it is a [Writable](stream#writable-streams) stream.
`process.stderr` differs from other Node.js streams in important ways. See [note on process I/O](#a-note-on-process-io) for more information.
####
`process.stderr.fd`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
This property refers to the value of underlying file descriptor of `process.stderr`. The value is fixed at `2`. In [`Worker`](worker_threads#class-worker) threads, this field does not exist.
###
`process.stdin`
* [<Stream>](stream#stream)
The `process.stdin` property returns a stream connected to `stdin` (fd `0`). It is a [`net.Socket`](net#class-netsocket) (which is a [Duplex](stream#duplex-and-transform-streams) stream) unless fd `0` refers to a file, in which case it is a [Readable](stream#readable-streams) stream.
For details of how to read from `stdin` see [`readable.read()`](stream#readablereadsize).
As a [Duplex](stream#duplex-and-transform-streams) stream, `process.stdin` can also be used in "old" mode that is compatible with scripts written for Node.js prior to v0.10. For more information see [Stream compatibility](stream#compatibility-with-older-nodejs-versions).
In "old" streams mode the `stdin` stream is paused by default, so one must call `process.stdin.resume()` to read from it. Note also that calling `process.stdin.resume()` itself would switch stream to "old" mode.
####
`process.stdin.fd`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
This property refers to the value of underlying file descriptor of `process.stdin`. The value is fixed at `0`. In [`Worker`](worker_threads#class-worker) threads, this field does not exist.
###
`process.stdout`
* [<Stream>](stream#stream)
The `process.stdout` property returns a stream connected to `stdout` (fd `1`). It is a [`net.Socket`](net#class-netsocket) (which is a [Duplex](stream#duplex-and-transform-streams) stream) unless fd `1` refers to a file, in which case it is a [Writable](stream#writable-streams) stream.
For example, to copy `process.stdin` to `process.stdout`:
MJS modules
```
import { stdin, stdout } from 'node:process';
stdin.pipe(stdout);
```
CJS modules
```
const { stdin, stdout } = require('node:process');
stdin.pipe(stdout);
```
`process.stdout` differs from other Node.js streams in important ways. See [note on process I/O](#a-note-on-process-io) for more information.
####
`process.stdout.fd`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
This property refers to the value of underlying file descriptor of `process.stdout`. The value is fixed at `1`. In [`Worker`](worker_threads#class-worker) threads, this field does not exist.
#### A note on process I/O
`process.stdout` and `process.stderr` differ from other Node.js streams in important ways:
1. They are used internally by [`console.log()`](console#consolelogdata-args) and [`console.error()`](console#consoleerrordata-args), respectively.
2. Writes may be synchronous depending on what the stream is connected to and whether the system is Windows or POSIX:
* Files: *synchronous* on Windows and POSIX
* TTYs (Terminals): *asynchronous* on Windows, *synchronous* on POSIX
* Pipes (and sockets): *synchronous* on Windows, *asynchronous* on POSIX
These behaviors are partly for historical reasons, as changing them would create backward incompatibility, but they are also expected by some users.
Synchronous writes avoid problems such as output written with `console.log()` or `console.error()` being unexpectedly interleaved, or not written at all if `process.exit()` is called before an asynchronous write completes. See [`process.exit()`](#processexitcode) for more information.
***Warning***: Synchronous writes block the event loop until the write has completed. This can be near instantaneous in the case of output to a file, but under high system load, pipes that are not being read at the receiving end, or with slow terminals or file systems, it's possible for the event loop to be blocked often enough and long enough to have severe negative performance impacts. This may not be a problem when writing to an interactive terminal session, but consider this particularly careful when doing production logging to the process output streams.
To check if a stream is connected to a [TTY](tty#tty) context, check the `isTTY` property.
For instance:
```
$ node -p "Boolean(process.stdin.isTTY)"
true
$ echo "foo" | node -p "Boolean(process.stdin.isTTY)"
false
$ node -p "Boolean(process.stdout.isTTY)"
true
$ node -p "Boolean(process.stdout.isTTY)" | cat
false
```
See the [TTY](tty#tty) documentation for more information.
###
`process.throwDeprecation`
Added in: v0.9.12 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The initial value of `process.throwDeprecation` indicates whether the `--throw-deprecation` flag is set on the current Node.js process. `process.throwDeprecation` is mutable, so whether or not deprecation warnings result in errors may be altered at runtime. See the documentation for the [`'warning'` event](#event-warning) and the [`emitWarning()` method](#processemitwarningwarning-type-code-ctor) for more information.
```
$ node --throw-deprecation -p "process.throwDeprecation"
true
$ node -p "process.throwDeprecation"
undefined
$ node
> process.emitWarning('test', 'DeprecationWarning');
undefined
> (node:26598) DeprecationWarning: test
> process.throwDeprecation = true;
true
> process.emitWarning('test', 'DeprecationWarning');
Thrown:
[DeprecationWarning: test] { name: 'DeprecationWarning' }
```
###
`process.title`
Added in: v0.1.104 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.title` property returns the current process title (i.e. returns the current value of `ps`). Assigning a new value to `process.title` modifies the current value of `ps`.
When a new value is assigned, different platforms will impose different maximum length restrictions on the title. Usually such restrictions are quite limited. For instance, on Linux and macOS, `process.title` is limited to the size of the binary name plus the length of the command-line arguments because setting the `process.title` overwrites the `argv` memory of the process. Node.js v0.8 allowed for longer process title strings by also overwriting the `environ` memory but that was potentially insecure and confusing in some (rather obscure) cases.
Assigning a value to `process.title` might not result in an accurate label within process manager applications such as macOS Activity Monitor or Windows Services Manager.
###
`process.traceDeprecation`
Added in: v0.8.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `process.traceDeprecation` property indicates whether the `--trace-deprecation` flag is set on the current Node.js process. See the documentation for the [`'warning'` event](#event-warning) and the [`emitWarning()` method](#processemitwarningwarning-type-code-ctor) for more information about this flag's behavior.
###
`process.umask()`
History
| Version | Changes |
| --- | --- |
| v14.0.0, v12.19.0 | Calling `process.umask()` with no arguments is deprecated. |
| v0.1.19 | Added in: v0.1.19 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Calling `process.umask()` with no argument causes the process-wide umask to be written twice. This introduces a race condition between threads, and is a potential security vulnerability. There is no safe, cross-platform alternative API.
`process.umask()` returns the Node.js process's file mode creation mask. Child processes inherit the mask from the parent process.
###
`process.umask(mask)`
Added in: v0.1.19 * `mask` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
`process.umask(mask)` sets the Node.js process's file mode creation mask. Child processes inherit the mask from the parent process. Returns the previous mask.
MJS modules
```
import { umask } from 'node:process';
const newmask = 0o022;
const oldmask = umask(newmask);
console.log(
`Changed umask from ${oldmask.toString(8)} to ${newmask.toString(8)}`
);
```
CJS modules
```
const { umask } = require('node:process');
const newmask = 0o022;
const oldmask = umask(newmask);
console.log(
`Changed umask from ${oldmask.toString(8)} to ${newmask.toString(8)}`
);
```
In [`Worker`](worker_threads#class-worker) threads, `process.umask(mask)` will throw an exception.
###
`process.uptime()`
Added in: v0.5.0 * Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `process.uptime()` method returns the number of seconds the current Node.js process has been running.
The return value includes fractions of a second. Use `Math.floor()` to get whole seconds.
###
`process.version`
Added in: v0.1.3 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `process.version` property contains the Node.js version string.
MJS modules
```
import { version } from 'node:process';
console.log(`Version: ${version}`);
// Version: v14.8.0
```
CJS modules
```
const { version } = require('node:process');
console.log(`Version: ${version}`);
// Version: v14.8.0
```
To get the version string without the prepended *v*, use `process.versions.node`.
###
`process.versions`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | The `v8` property now includes a Node.js specific suffix. |
| v4.2.0 | The `icu` property is now supported. |
| v0.2.0 | Added in: v0.2.0 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `process.versions` property returns an object listing the version strings of Node.js and its dependencies. `process.versions.modules` indicates the current ABI version, which is increased whenever a C++ API changes. Node.js will refuse to load modules that were compiled against a different module ABI version.
MJS modules
```
import { versions } from 'node:process';
console.log(versions);
```
CJS modules
```
const { versions } = require('node:process');
console.log(versions);
```
Will generate an object similar to:
```
{ node: '11.13.0',
v8: '7.0.276.38-node.18',
uv: '1.27.0',
zlib: '1.2.11',
brotli: '1.0.7',
ares: '1.15.0',
modules: '67',
nghttp2: '1.34.0',
napi: '4',
llhttp: '1.1.1',
openssl: '1.1.1b',
cldr: '34.0',
icu: '63.1',
tz: '2018e',
unicode: '11.0' }
```
### Exit codes
Node.js will normally exit with a `0` status code when no more async operations are pending. The following status codes are used in other cases:
* `1` **Uncaught Fatal Exception**: There was an uncaught exception, and it was not handled by a domain or an [`'uncaughtException'`](#event-uncaughtexception) event handler.
* `2`: Unused (reserved by Bash for builtin misuse)
* `3` **Internal JavaScript Parse Error**: The JavaScript source code internal in the Node.js bootstrapping process caused a parse error. This is extremely rare, and generally can only happen during development of Node.js itself.
* `4` **Internal JavaScript Evaluation Failure**: The JavaScript source code internal in the Node.js bootstrapping process failed to return a function value when evaluated. This is extremely rare, and generally can only happen during development of Node.js itself.
* `5` **Fatal Error**: There was a fatal unrecoverable error in V8. Typically a message will be printed to stderr with the prefix `FATAL ERROR`.
* `6` **Non-function Internal Exception Handler**: There was an uncaught exception, but the internal fatal exception handler function was somehow set to a non-function, and could not be called.
* `7` **Internal Exception Handler Run-Time Failure**: There was an uncaught exception, and the internal fatal exception handler function itself threw an error while attempting to handle it. This can happen, for example, if an [`'uncaughtException'`](#event-uncaughtexception) or `domain.on('error')` handler throws an error.
* `8`: Unused. In previous versions of Node.js, exit code 8 sometimes indicated an uncaught exception.
* `9` **Invalid Argument**: Either an unknown option was specified, or an option requiring a value was provided without a value.
* `10` **Internal JavaScript Run-Time Failure**: The JavaScript source code internal in the Node.js bootstrapping process threw an error when the bootstrapping function was called. This is extremely rare, and generally can only happen during development of Node.js itself.
* `12` **Invalid Debug Argument**: The `--inspect` and/or `--inspect-brk` options were set, but the port number chosen was invalid or unavailable.
* `13` **Unfinished Top-Level Await**: `await` was used outside of a function in the top-level code, but the passed `Promise` never resolved.
* `14` **Snapshot Failure**: Node.js was started to build a V8 startup snapshot and it failed because certain requirements of the state of the application were not met.
* `>128` **Signal Exits**: If Node.js receives a fatal signal such as `SIGKILL` or `SIGHUP`, then its exit code will be `128` plus the value of the signal code. This is a standard POSIX practice, since exit codes are defined to be 7-bit integers, and signal exits set the high-order bit, and then contain the value of the signal code. For example, signal `SIGABRT` has value `6`, so the expected exit code will be `128` + `6`, or `134`.
| programming_docs |
node None Zlib
----
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/zlib.js](https://github.com/nodejs/node/blob/v19.0.1/lib/zlib.js)
The `node:zlib` module provides compression functionality implemented using Gzip, Deflate/Inflate, and Brotli.
To access it:
```
const zlib = require('node:zlib');
```
Compression and decompression are built around the Node.js [Streams API](stream).
Compressing or decompressing a stream (such as a file) can be accomplished by piping the source stream through a `zlib` `Transform` stream into a destination stream:
```
const { createGzip } = require('node:zlib');
const { pipeline } = require('node:stream');
const {
createReadStream,
createWriteStream
} = require('node:fs');
const gzip = createGzip();
const source = createReadStream('input.txt');
const destination = createWriteStream('input.txt.gz');
pipeline(source, gzip, destination, (err) => {
if (err) {
console.error('An error occurred:', err);
process.exitCode = 1;
}
});
// Or, Promisified
const { promisify } = require('node:util');
const pipe = promisify(pipeline);
async function do_gzip(input, output) {
const gzip = createGzip();
const source = createReadStream(input);
const destination = createWriteStream(output);
await pipe(source, gzip, destination);
}
do_gzip('input.txt', 'input.txt.gz')
.catch((err) => {
console.error('An error occurred:', err);
process.exitCode = 1;
});
```
It is also possible to compress or decompress data in a single step:
```
const { deflate, unzip } = require('node:zlib');
const input = '.................................';
deflate(input, (err, buffer) => {
if (err) {
console.error('An error occurred:', err);
process.exitCode = 1;
}
console.log(buffer.toString('base64'));
});
const buffer = Buffer.from('eJzT0yMAAGTvBe8=', 'base64');
unzip(buffer, (err, buffer) => {
if (err) {
console.error('An error occurred:', err);
process.exitCode = 1;
}
console.log(buffer.toString());
});
// Or, Promisified
const { promisify } = require('node:util');
const do_unzip = promisify(unzip);
do_unzip(buffer)
.then((buf) => console.log(buf.toString()))
.catch((err) => {
console.error('An error occurred:', err);
process.exitCode = 1;
});
```
### Threadpool usage and performance considerations
All `zlib` APIs, except those that are explicitly synchronous, use the Node.js internal threadpool. This can lead to surprising effects and performance limitations in some applications.
Creating and using a large number of zlib objects simultaneously can cause significant memory fragmentation.
```
const zlib = require('node:zlib');
const payload = Buffer.from('This is some data');
// WARNING: DO NOT DO THIS!
for (let i = 0; i < 30000; ++i) {
zlib.deflate(payload, (err, buffer) => {});
}
```
In the preceding example, 30,000 deflate instances are created concurrently. Because of how some operating systems handle memory allocation and deallocation, this may lead to significant memory fragmentation.
It is strongly recommended that the results of compression operations be cached to avoid duplication of effort.
### Compressing HTTP requests and responses
The `node:zlib` module can be used to implement support for the `gzip`, `deflate` and `br` content-encoding mechanisms defined by [HTTP](https://tools.ietf.org/html/rfc7230#section-4.2).
The HTTP [`Accept-Encoding`](https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3) header is used within an HTTP request to identify the compression encodings accepted by the client. The [`Content-Encoding`](https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.11) header is used to identify the compression encodings actually applied to a message.
The examples given below are drastically simplified to show the basic concept. Using `zlib` encoding can be expensive, and the results ought to be cached. See [Memory usage tuning](#memory-usage-tuning) for more information on the speed/memory/compression tradeoffs involved in `zlib` usage.
```
// Client request example
const zlib = require('node:zlib');
const http = require('node:http');
const fs = require('node:fs');
const { pipeline } = require('node:stream');
const request = http.get({ host: 'example.com',
path: '/',
port: 80,
headers: { 'Accept-Encoding': 'br,gzip,deflate' } });
request.on('response', (response) => {
const output = fs.createWriteStream('example.com_index.html');
const onError = (err) => {
if (err) {
console.error('An error occurred:', err);
process.exitCode = 1;
}
};
switch (response.headers['content-encoding']) {
case 'br':
pipeline(response, zlib.createBrotliDecompress(), output, onError);
break;
// Or, just use zlib.createUnzip() to handle both of the following cases:
case 'gzip':
pipeline(response, zlib.createGunzip(), output, onError);
break;
case 'deflate':
pipeline(response, zlib.createInflate(), output, onError);
break;
default:
pipeline(response, output, onError);
break;
}
});
```
```
// server example
// Running a gzip operation on every request is quite expensive.
// It would be much more efficient to cache the compressed buffer.
const zlib = require('node:zlib');
const http = require('node:http');
const fs = require('node:fs');
const { pipeline } = require('node:stream');
http.createServer((request, response) => {
const raw = fs.createReadStream('index.html');
// Store both a compressed and an uncompressed version of the resource.
response.setHeader('Vary', 'Accept-Encoding');
let acceptEncoding = request.headers['accept-encoding'];
if (!acceptEncoding) {
acceptEncoding = '';
}
const onError = (err) => {
if (err) {
// If an error occurs, there's not much we can do because
// the server has already sent the 200 response code and
// some amount of data has already been sent to the client.
// The best we can do is terminate the response immediately
// and log the error.
response.end();
console.error('An error occurred:', err);
}
};
// Note: This is not a conformant accept-encoding parser.
// See https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
if (/\bdeflate\b/.test(acceptEncoding)) {
response.writeHead(200, { 'Content-Encoding': 'deflate' });
pipeline(raw, zlib.createDeflate(), response, onError);
} else if (/\bgzip\b/.test(acceptEncoding)) {
response.writeHead(200, { 'Content-Encoding': 'gzip' });
pipeline(raw, zlib.createGzip(), response, onError);
} else if (/\bbr\b/.test(acceptEncoding)) {
response.writeHead(200, { 'Content-Encoding': 'br' });
pipeline(raw, zlib.createBrotliCompress(), response, onError);
} else {
response.writeHead(200, {});
pipeline(raw, response, onError);
}
}).listen(1337);
```
By default, the `zlib` methods will throw an error when decompressing truncated data. However, if it is known that the data is incomplete, or the desire is to inspect only the beginning of a compressed file, it is possible to suppress the default error handling by changing the flushing method that is used to decompress the last chunk of input data:
```
// This is a truncated version of the buffer from the above examples
const buffer = Buffer.from('eJzT0yMA', 'base64');
zlib.unzip(
buffer,
// For Brotli, the equivalent is zlib.constants.BROTLI_OPERATION_FLUSH.
{ finishFlush: zlib.constants.Z_SYNC_FLUSH },
(err, buffer) => {
if (err) {
console.error('An error occurred:', err);
process.exitCode = 1;
}
console.log(buffer.toString());
});
```
This will not change the behavior in other error-throwing situations, e.g. when the input data has an invalid format. Using this method, it will not be possible to determine whether the input ended prematurely or lacks the integrity checks, making it necessary to manually check that the decompressed result is valid.
### Memory usage tuning
#### For zlib-based streams
From `zlib/zconf.h`, modified for Node.js usage:
The memory requirements for deflate are (in bytes):
```
(1 << (windowBits + 2)) + (1 << (memLevel + 9))
```
That is: 128K for `windowBits` = 15 + 128K for `memLevel` = 8 (default values) plus a few kilobytes for small objects.
For example, to reduce the default memory requirements from 256K to 128K, the options should be set to:
```
const options = { windowBits: 14, memLevel: 7 };
```
This will, however, generally degrade compression.
The memory requirements for inflate are (in bytes) `1 << windowBits`. That is, 32K for `windowBits` = 15 (default value) plus a few kilobytes for small objects.
This is in addition to a single internal output slab buffer of size `chunkSize`, which defaults to 16K.
The speed of `zlib` compression is affected most dramatically by the `level` setting. A higher level will result in better compression, but will take longer to complete. A lower level will result in less compression, but will be much faster.
In general, greater memory usage options will mean that Node.js has to make fewer calls to `zlib` because it will be able to process more data on each `write` operation. So, this is another factor that affects the speed, at the cost of memory usage.
#### For Brotli-based streams
There are equivalents to the zlib options for Brotli-based streams, although these options have different ranges than the zlib ones:
* zlib's `level` option matches Brotli's `BROTLI_PARAM_QUALITY` option.
* zlib's `windowBits` option matches Brotli's `BROTLI_PARAM_LGWIN` option.
See [below](#brotli-constants) for more details on Brotli-specific options.
### Flushing
Calling [`.flush()`](#zlibflushkind-callback) on a compression stream will make `zlib` return as much output as currently possible. This may come at the cost of degraded compression quality, but can be useful when data needs to be available as soon as possible.
In the following example, `flush()` is used to write a compressed partial HTTP response to the client:
```
const zlib = require('node:zlib');
const http = require('node:http');
const { pipeline } = require('node:stream');
http.createServer((request, response) => {
// For the sake of simplicity, the Accept-Encoding checks are omitted.
response.writeHead(200, { 'content-encoding': 'gzip' });
const output = zlib.createGzip();
let i;
pipeline(output, response, (err) => {
if (err) {
// If an error occurs, there's not much we can do because
// the server has already sent the 200 response code and
// some amount of data has already been sent to the client.
// The best we can do is terminate the response immediately
// and log the error.
clearInterval(i);
response.end();
console.error('An error occurred:', err);
}
});
i = setInterval(() => {
output.write(`The current time is ${Date()}\n`, () => {
// The data has been passed to zlib, but the compression algorithm may
// have decided to buffer the data for more efficient compression.
// Calling .flush() will make the data available as soon as the client
// is ready to receive it.
output.flush();
});
}, 1000);
}).listen(1337);
```
### Constants
Added in: v0.5.8 #### zlib constants
All of the constants defined in `zlib.h` are also defined on `require('node:zlib').constants`. In the normal course of operations, it will not be necessary to use these constants. They are documented so that their presence is not surprising. This section is taken almost directly from the [zlib documentation](https://zlib.net/manual.html#Constants).
Previously, the constants were available directly from `require('node:zlib')`, for instance `zlib.Z_NO_FLUSH`. Accessing the constants directly from the module is currently still possible but is deprecated.
Allowed flush values.
* `zlib.constants.Z_NO_FLUSH`
* `zlib.constants.Z_PARTIAL_FLUSH`
* `zlib.constants.Z_SYNC_FLUSH`
* `zlib.constants.Z_FULL_FLUSH`
* `zlib.constants.Z_FINISH`
* `zlib.constants.Z_BLOCK`
* `zlib.constants.Z_TREES`
Return codes for the compression/decompression functions. Negative values are errors, positive values are used for special but normal events.
* `zlib.constants.Z_OK`
* `zlib.constants.Z_STREAM_END`
* `zlib.constants.Z_NEED_DICT`
* `zlib.constants.Z_ERRNO`
* `zlib.constants.Z_STREAM_ERROR`
* `zlib.constants.Z_DATA_ERROR`
* `zlib.constants.Z_MEM_ERROR`
* `zlib.constants.Z_BUF_ERROR`
* `zlib.constants.Z_VERSION_ERROR`
Compression levels.
* `zlib.constants.Z_NO_COMPRESSION`
* `zlib.constants.Z_BEST_SPEED`
* `zlib.constants.Z_BEST_COMPRESSION`
* `zlib.constants.Z_DEFAULT_COMPRESSION`
Compression strategy.
* `zlib.constants.Z_FILTERED`
* `zlib.constants.Z_HUFFMAN_ONLY`
* `zlib.constants.Z_RLE`
* `zlib.constants.Z_FIXED`
* `zlib.constants.Z_DEFAULT_STRATEGY`
#### Brotli constants
Added in: v11.7.0, v10.16.0 There are several options and other constants available for Brotli-based streams:
##### Flush operations
The following values are valid flush operations for Brotli-based streams:
* `zlib.constants.BROTLI_OPERATION_PROCESS` (default for all operations)
* `zlib.constants.BROTLI_OPERATION_FLUSH` (default when calling `.flush()`)
* `zlib.constants.BROTLI_OPERATION_FINISH` (default for the last chunk)
* `zlib.constants.BROTLI_OPERATION_EMIT_METADATA`
+ This particular operation may be hard to use in a Node.js context, as the streaming layer makes it hard to know which data will end up in this frame. Also, there is currently no way to consume this data through the Node.js API.
##### Compressor options
There are several options that can be set on Brotli encoders, affecting compression efficiency and speed. Both the keys and the values can be accessed as properties of the `zlib.constants` object.
The most important options are:
* `BROTLI_PARAM_MODE`
+ `BROTLI_MODE_GENERIC` (default)
+ `BROTLI_MODE_TEXT`, adjusted for UTF-8 text
+ `BROTLI_MODE_FONT`, adjusted for WOFF 2.0 fonts
* `BROTLI_PARAM_QUALITY`
+ Ranges from `BROTLI_MIN_QUALITY` to `BROTLI_MAX_QUALITY`, with a default of `BROTLI_DEFAULT_QUALITY`.
* `BROTLI_PARAM_SIZE_HINT`
+ Integer value representing the expected input size; defaults to `0` for an unknown input size.
The following flags can be set for advanced control over the compression algorithm and memory usage tuning:
* `BROTLI_PARAM_LGWIN`
+ Ranges from `BROTLI_MIN_WINDOW_BITS` to `BROTLI_MAX_WINDOW_BITS`, with a default of `BROTLI_DEFAULT_WINDOW`, or up to `BROTLI_LARGE_MAX_WINDOW_BITS` if the `BROTLI_PARAM_LARGE_WINDOW` flag is set.
* `BROTLI_PARAM_LGBLOCK`
+ Ranges from `BROTLI_MIN_INPUT_BLOCK_BITS` to `BROTLI_MAX_INPUT_BLOCK_BITS`.
* `BROTLI_PARAM_DISABLE_LITERAL_CONTEXT_MODELING`
+ Boolean flag that decreases compression ratio in favour of decompression speed.
* `BROTLI_PARAM_LARGE_WINDOW`
+ Boolean flag enabling “Large Window Brotli” mode (not compatible with the Brotli format as standardized in [RFC 7932](https://www.rfc-editor.org/rfc/rfc7932.txt)).
* `BROTLI_PARAM_NPOSTFIX`
+ Ranges from `0` to `BROTLI_MAX_NPOSTFIX`.
* `BROTLI_PARAM_NDIRECT`
+ Ranges from `0` to `15 << NPOSTFIX` in steps of `1 << NPOSTFIX`.
##### Decompressor options
These advanced options are available for controlling decompression:
* `BROTLI_DECODER_PARAM_DISABLE_RING_BUFFER_REALLOCATION`
+ Boolean flag that affects internal memory allocation patterns.
* `BROTLI_DECODER_PARAM_LARGE_WINDOW`
+ Boolean flag enabling “Large Window Brotli” mode (not compatible with the Brotli format as standardized in [RFC 7932](https://www.rfc-editor.org/rfc/rfc7932.txt)).
### Class: `Options`
History
| Version | Changes |
| --- | --- |
| v14.5.0, v12.19.0 | The `maxOutputLength` option is supported now. |
| v9.4.0 | The `dictionary` option can be an `ArrayBuffer`. |
| v8.0.0 | The `dictionary` option can be an `Uint8Array` now. |
| v5.11.0 | The `finishFlush` option is supported now. |
| v0.11.1 | Added in: v0.11.1 |
Each zlib-based class takes an `options` object. No options are required.
Some options are only relevant when compressing and are ignored by the decompression classes.
* `flush` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `zlib.constants.Z_NO_FLUSH`
* `finishFlush` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `zlib.constants.Z_FINISH`
* `chunkSize` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `16 * 1024`
* `windowBits` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `level` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) (compression only)
* `memLevel` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) (compression only)
* `strategy` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) (compression only)
* `dictionary` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) (deflate/inflate only, empty dictionary by default)
* `info` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) (If `true`, returns an object with `buffer` and `engine`.)
* `maxOutputLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Limits output size when using [convenience methods](#convenience-methods). **Default:** [`buffer.kMaxLength`](buffer#bufferkmaxlength)
See the [`deflateInit2` and `inflateInit2`](https://zlib.net/manual.html#Advanced) documentation for more information.
### Class: `BrotliOptions`
History
| Version | Changes |
| --- | --- |
| v14.5.0, v12.19.0 | The `maxOutputLength` option is supported now. |
| v11.7.0 | Added in: v11.7.0 |
Each Brotli-based class takes an `options` object. All options are optional.
* `flush` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `zlib.constants.BROTLI_OPERATION_PROCESS`
* `finishFlush` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `zlib.constants.BROTLI_OPERATION_FINISH`
* `chunkSize` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `16 * 1024`
* `params` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Key-value object containing indexed [Brotli parameters](#brotli-constants).
* `maxOutputLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Limits output size when using [convenience methods](#convenience-methods). **Default:** [`buffer.kMaxLength`](buffer#bufferkmaxlength)
For example:
```
const stream = zlib.createBrotliCompress({
chunkSize: 32 * 1024,
params: {
[zlib.constants.BROTLI_PARAM_MODE]: zlib.constants.BROTLI_MODE_TEXT,
[zlib.constants.BROTLI_PARAM_QUALITY]: 4,
[zlib.constants.BROTLI_PARAM_SIZE_HINT]: fs.statSync(inputFile).size
}
});
```
### Class: `zlib.BrotliCompress`
Added in: v11.7.0, v10.16.0 Compress data using the Brotli algorithm.
### Class: `zlib.BrotliDecompress`
Added in: v11.7.0, v10.16.0 Decompress data using the Brotli algorithm.
### Class: `zlib.Deflate`
Added in: v0.5.8 Compress data using deflate.
### Class: `zlib.DeflateRaw`
Added in: v0.5.8 Compress data using deflate, and do not append a `zlib` header.
### Class: `zlib.Gunzip`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | Trailing garbage at the end of the input stream will now result in an `'error'` event. |
| v5.9.0 | Multiple concatenated gzip file members are supported now. |
| v5.0.0 | A truncated input stream will now result in an `'error'` event. |
| v0.5.8 | Added in: v0.5.8 |
Decompress a gzip stream.
### Class: `zlib.Gzip`
Added in: v0.5.8 Compress data using gzip.
### Class: `zlib.Inflate`
History
| Version | Changes |
| --- | --- |
| v5.0.0 | A truncated input stream will now result in an `'error'` event. |
| v0.5.8 | Added in: v0.5.8 |
Decompress a deflate stream.
### Class: `zlib.InflateRaw`
History
| Version | Changes |
| --- | --- |
| v6.8.0 | Custom dictionaries are now supported by `InflateRaw`. |
| v5.0.0 | A truncated input stream will now result in an `'error'` event. |
| v0.5.8 | Added in: v0.5.8 |
Decompress a raw deflate stream.
### Class: `zlib.Unzip`
Added in: v0.5.8 Decompress either a Gzip- or Deflate-compressed stream by auto-detecting the header.
### Class: `zlib.ZlibBase`
History
| Version | Changes |
| --- | --- |
| v11.7.0, v10.16.0 | This class was renamed from `Zlib` to `ZlibBase`. |
| v0.5.8 | Added in: v0.5.8 |
Not exported by the `node:zlib` module. It is documented here because it is the base class of the compressor/decompressor classes.
This class inherits from [`stream.Transform`](stream#class-streamtransform), allowing `node:zlib` objects to be used in pipes and similar stream operations.
####
`zlib.bytesRead`
Added in: v8.1.0Deprecated since: v10.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`zlib.bytesWritten`](#zlibbyteswritten) instead.
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Deprecated alias for [`zlib.bytesWritten`](#zlibbyteswritten). This original name was chosen because it also made sense to interpret the value as the number of bytes read by the engine, but is inconsistent with other streams in Node.js that expose values under these names.
####
`zlib.bytesWritten`
Added in: v10.0.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `zlib.bytesWritten` property specifies the number of bytes written to the engine, before the bytes are processed (compressed or decompressed, as appropriate for the derived class).
####
`zlib.close([callback])`
Added in: v0.9.4 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Close the underlying handle.
####
`zlib.flush([kind, ]callback)`
Added in: v0.5.8 * `kind` **Default:** `zlib.constants.Z_FULL_FLUSH` for zlib-based streams, `zlib.constants.BROTLI_OPERATION_FLUSH` for Brotli-based streams.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Flush pending data. Don't call this frivolously, premature flushes negatively impact the effectiveness of the compression algorithm.
Calling this only flushes data from the internal `zlib` state, and does not perform flushing of any kind on the streams level. Rather, it behaves like a normal call to `.write()`, i.e. it will be queued up behind other pending writes and will only produce output when data is being read from the stream.
####
`zlib.params(level, strategy, callback)`
Added in: v0.11.4 * `level` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `strategy` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
This function is only available for zlib-based streams, i.e. not Brotli.
Dynamically update the compression level and compression strategy. Only applicable to deflate algorithm.
####
`zlib.reset()`
Added in: v0.7.0 Reset the compressor/decompressor to factory defaults. Only applicable to the inflate and deflate algorithms.
###
`zlib.constants`
Added in: v7.0.0 Provides an object enumerating Zlib-related constants.
###
`zlib.createBrotliCompress([options])`
Added in: v11.7.0, v10.16.0 * `options` [<brotli options>](zlib#class-brotlioptions)
Creates and returns a new [`BrotliCompress`](#class-zlibbrotlicompress) object.
###
`zlib.createBrotliDecompress([options])`
Added in: v11.7.0, v10.16.0 * `options` [<brotli options>](zlib#class-brotlioptions)
Creates and returns a new [`BrotliDecompress`](#class-zlibbrotlidecompress) object.
###
`zlib.createDeflate([options])`
Added in: v0.5.8 * `options` [<zlib options>](zlib#class-options)
Creates and returns a new [`Deflate`](#class-zlibdeflate) object.
###
`zlib.createDeflateRaw([options])`
Added in: v0.5.8 * `options` [<zlib options>](zlib#class-options)
Creates and returns a new [`DeflateRaw`](#class-zlibdeflateraw) object.
An upgrade of zlib from 1.2.8 to 1.2.11 changed behavior when `windowBits` is set to 8 for raw deflate streams. zlib would automatically set `windowBits` to 9 if was initially set to 8. Newer versions of zlib will throw an exception, so Node.js restored the original behavior of upgrading a value of 8 to 9, since passing `windowBits = 9` to zlib actually results in a compressed stream that effectively uses an 8-bit window only.
###
`zlib.createGunzip([options])`
Added in: v0.5.8 * `options` [<zlib options>](zlib#class-options)
Creates and returns a new [`Gunzip`](#class-zlibgunzip) object.
###
`zlib.createGzip([options])`
Added in: v0.5.8 * `options` [<zlib options>](zlib#class-options)
Creates and returns a new [`Gzip`](#class-zlibgzip) object. See [example](#zlib).
###
`zlib.createInflate([options])`
Added in: v0.5.8 * `options` [<zlib options>](zlib#class-options)
Creates and returns a new [`Inflate`](#class-zlibinflate) object.
###
`zlib.createInflateRaw([options])`
Added in: v0.5.8 * `options` [<zlib options>](zlib#class-options)
Creates and returns a new [`InflateRaw`](#class-zlibinflateraw) object.
###
`zlib.createUnzip([options])`
Added in: v0.5.8 * `options` [<zlib options>](zlib#class-options)
Creates and returns a new [`Unzip`](#class-zlibunzip) object.
### Convenience methods
All of these take a [`Buffer`](buffer#class-buffer), [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), [`DataView`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView), [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) or string as the first argument, an optional second argument to supply options to the `zlib` classes and will call the supplied callback with `callback(error, result)`.
Every method has a `*Sync` counterpart, which accept the same arguments, but without a callback.
####
`zlib.brotliCompress(buffer[, options], callback)`
Added in: v11.7.0, v10.16.0 * `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<brotli options>](zlib#class-brotlioptions)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
####
`zlib.brotliCompressSync(buffer[, options])`
Added in: v11.7.0, v10.16.0 * `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<brotli options>](zlib#class-brotlioptions)
Compress a chunk of data with [`BrotliCompress`](#class-zlibbrotlicompress).
####
`zlib.brotliDecompress(buffer[, options], callback)`
Added in: v11.7.0, v10.16.0 * `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<brotli options>](zlib#class-brotlioptions)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
####
`zlib.brotliDecompressSync(buffer[, options])`
Added in: v11.7.0, v10.16.0 * `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<brotli options>](zlib#class-brotlioptions)
Decompress a chunk of data with [`BrotliDecompress`](#class-zlibbrotlidecompress).
####
`zlib.deflate(buffer[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.6.0 | Added in: v0.6.0 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
####
`zlib.deflateSync(buffer[, options])`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.11.12 | Added in: v0.11.12 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
Compress a chunk of data with [`Deflate`](#class-zlibdeflate).
####
`zlib.deflateRaw(buffer[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.6.0 | Added in: v0.6.0 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
####
`zlib.deflateRawSync(buffer[, options])`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.11.12 | Added in: v0.11.12 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
Compress a chunk of data with [`DeflateRaw`](#class-zlibdeflateraw).
####
`zlib.gunzip(buffer[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.6.0 | Added in: v0.6.0 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
####
`zlib.gunzipSync(buffer[, options])`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.11.12 | Added in: v0.11.12 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
Decompress a chunk of data with [`Gunzip`](#class-zlibgunzip).
####
`zlib.gzip(buffer[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.6.0 | Added in: v0.6.0 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
####
`zlib.gzipSync(buffer[, options])`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.11.12 | Added in: v0.11.12 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
Compress a chunk of data with [`Gzip`](#class-zlibgzip).
####
`zlib.inflate(buffer[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.6.0 | Added in: v0.6.0 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
####
`zlib.inflateSync(buffer[, options])`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.11.12 | Added in: v0.11.12 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
Decompress a chunk of data with [`Inflate`](#class-zlibinflate).
####
`zlib.inflateRaw(buffer[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.6.0 | Added in: v0.6.0 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
####
`zlib.inflateRawSync(buffer[, options])`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.11.12 | Added in: v0.11.12 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
Decompress a chunk of data with [`InflateRaw`](#class-zlibinflateraw).
####
`zlib.unzip(buffer[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.6.0 | Added in: v0.6.0 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
####
`zlib.unzipSync(buffer[, options])`
History
| Version | Changes |
| --- | --- |
| v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`. |
| v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`. |
| v8.0.0 | The `buffer` parameter can be an `Uint8Array` now. |
| v0.11.12 | Added in: v0.11.12 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<zlib options>](zlib#class-options)
Decompress a chunk of data with [`Unzip`](#class-zlibunzip).
| programming_docs |
node None Modules: `node:module` API
--------------------------
Added in: v0.3.7 ### The `Module` object
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Provides general utility methods when interacting with instances of `Module`, the [`module`](modules#the-module-object) variable often seen in [CommonJS](modules) modules. Accessed via `import 'node:module'` or `require('node:module')`.
####
`module.builtinModules`
Added in: v9.3.0, v8.10.0, v6.13.0 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
A list of the names of all modules provided by Node.js. Can be used to verify if a module is maintained by a third party or not.
`module` in this context isn't the same object that's provided by the [module wrapper](modules#the-module-wrapper). To access it, require the `Module` module:
MJS modules
```
// module.mjs
// In an ECMAScript module
import { builtinModules as builtin } from 'node:module';
```
CJS modules
```
// module.cjs
// In a CommonJS module
const builtin = require('node:module').builtinModules;
```
####
`module.createRequire(filename)`
Added in: v12.2.0 * `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Filename to be used to construct the require function. Must be a file URL object, file URL string, or absolute path string.
* Returns: [<require>](modules#requireid) Require function
```
import { createRequire } from 'node:module';
const require = createRequire(import.meta.url);
// sibling-module.js is a CommonJS module.
const siblingModule = require('./sibling-module');
```
####
`module.isBuiltin(moduleName)`
Added in: v18.6.0, v16.17.0 * `moduleName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) name of the module
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) returns true if the module is builtin else returns false
```
import { isBuiltin } from 'node:module';
isBuiltin('node:fs'); // true
isBuiltin('fs'); // true
isBuiltin('wss'); // false
```
####
`module.syncBuiltinESMExports()`
Added in: v12.12.0 The `module.syncBuiltinESMExports()` method updates all the live bindings for builtin [ES Modules](esm) to match the properties of the [CommonJS](modules) exports. It does not add or remove exported names from the [ES Modules](esm).
```
const fs = require('node:fs');
const assert = require('node:assert');
const { syncBuiltinESMExports } = require('node:module');
fs.readFile = newAPI;
delete fs.readFileSync;
function newAPI() {
// ...
}
fs.newAPI = newAPI;
syncBuiltinESMExports();
import('node:fs').then((esmFS) => {
// It syncs the existing readFile property with the new value
assert.strictEqual(esmFS.readFile, newAPI);
// readFileSync has been deleted from the required fs
assert.strictEqual('readFileSync' in fs, false);
// syncBuiltinESMExports() does not remove readFileSync from esmFS
assert.strictEqual('readFileSync' in esmFS, true);
// syncBuiltinESMExports() does not add names
assert.strictEqual(esmFS.newAPI, undefined);
});
```
### Source map v3 support
Added in: v13.7.0, v12.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Helpers for interacting with the source map cache. This cache is populated when source map parsing is enabled and [source map include directives](https://sourcemaps.info/spec.html#h.lmz475t4mvbx) are found in a modules' footer.
To enable source map parsing, Node.js must be run with the flag [`--enable-source-maps`](cli#--enable-source-maps), or with code coverage enabled by setting [`NODE_V8_COVERAGE=dir`](cli#node_v8_coveragedir).
MJS modules
```
// module.mjs
// In an ECMAScript module
import { findSourceMap, SourceMap } from 'node:module';
```
CJS modules
```
// module.cjs
// In a CommonJS module
const { findSourceMap, SourceMap } = require('node:module');
```
####
`module.findSourceMap(path)`
Added in: v13.7.0, v12.17.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<module.SourceMap>](module#class-modulesourcemap) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Returns `module.SourceMap` if a source map is found, `undefined` otherwise.
`path` is the resolved path for the file for which a corresponding source map should be fetched.
#### Class: `module.SourceMap`
Added in: v13.7.0, v12.17.0 #####
`new SourceMap(payload)`
* `payload` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Creates a new `sourceMap` instance.
`payload` is an object with keys matching the [Source map v3 format](https://sourcemaps.info/spec.html#h.mofvlxcwqzej):
* `file`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `version`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `sources`: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `sourcesContent`: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `names`: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `mappings`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `sourceRoot`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
#####
`sourceMap.payload`
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Getter for the payload used to construct the [`SourceMap`](#class-modulesourcemap) instance.
#####
`sourceMap.findEntry(lineNumber, columnNumber)`
* `lineNumber` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `columnNumber` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Given a line number and column number in the generated source file, returns an object representing the position in the original file. The object returned consists of the following keys:
* generatedLine: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* generatedColumn: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* originalSource: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* originalLine: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* originalColumn: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* name: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
node None Modules: Packages
-----------------
History
| Version | Changes |
| --- | --- |
| v14.13.0, v12.20.0 | Add support for `"exports"` patterns. |
| v14.6.0, v12.19.0 | Add package `"imports"` field. |
| v13.7.0, v12.17.0 | Unflag conditional exports. |
| v13.7.0, v12.16.0 | Remove the `--experimental-conditional-exports` option. In 12.16.0, conditional exports are still behind `--experimental-modules`. |
| v13.6.0, v12.16.0 | Unflag self-referencing a package using its name. |
| v12.7.0 | Introduce `"exports"` `package.json` field as a more powerful alternative to the classic `"main"` field. |
| v12.0.0 | Add support for ES modules using `.js` file extension via `package.json` `"type"` field. |
### Introduction
A package is a folder tree described by a `package.json` file. The package consists of the folder containing the `package.json` file and all subfolders until the next folder containing another `package.json` file, or a folder named `node_modules`.
This page provides guidance for package authors writing `package.json` files along with a reference for the [`package.json`](#nodejs-packagejson-field-definitions) fields defined by Node.js.
### Determining module system
Node.js will treat the following as [ES modules](esm) when passed to `node` as the initial input, or when referenced by `import` statements or `import()` expressions:
* Files with an `.mjs` extension.
* Files with a `.js` extension when the nearest parent `package.json` file contains a top-level [`"type"`](#type) field with a value of `"module"`.
* Strings passed in as an argument to `--eval`, or piped to `node` via `STDIN`, with the flag `--input-type=module`.
Node.js will treat as [CommonJS](modules) all other forms of input, such as `.js` files where the nearest parent `package.json` file contains no top-level `"type"` field, or string input without the flag `--input-type`. This behavior is to preserve backward compatibility. However, now that Node.js supports both CommonJS and ES modules, it is best to be explicit whenever possible. Node.js will treat the following as CommonJS when passed to `node` as the initial input, or when referenced by `import` statements, `import()` expressions, or `require()` expressions:
* Files with a `.cjs` extension.
* Files with a `.js` extension when the nearest parent `package.json` file contains a top-level field [`"type"`](#type) with a value of `"commonjs"`.
* Strings passed in as an argument to `--eval` or `--print`, or piped to `node` via `STDIN`, with the flag `--input-type=commonjs`.
Package authors should include the [`"type"`](#type) field, even in packages where all sources are CommonJS. Being explicit about the `type` of the package will future-proof the package in case the default type of Node.js ever changes, and it will also make things easier for build tools and loaders to determine how the files in the package should be interpreted.
#### Modules loaders
Node.js has two systems for resolving a specifier and loading modules.
There is the CommonJS module loader:
* It is fully synchronous.
* It is responsible for handling `require()` calls.
* It is monkey patchable.
* It supports [folders as modules](modules#folders-as-modules).
* When resolving a specifier, if no exact match is found, it will try to add extensions (`.js`, `.json`, and finally `.node`) and then attempt to resolve [folders as modules](modules#folders-as-modules).
* It treats `.json` as JSON text files.
* `.node` files are interpreted as compiled addon modules loaded with `process.dlopen()`.
* It treats all files that lack `.json` or `.node` extensions as JavaScript text files.
* It cannot be used to load ECMAScript modules (although it is possible to [load ECMASCript modules from CommonJS modules](modules#the-mjs-extension)). When used to load a JavaScript text file that is not an ECMAScript module, it loads it as a CommonJS module.
There is the ECMAScript module loader:
* It is asynchronous.
* It is responsible for handling `import` statements and `import()` expressions.
* It is not monkey patchable, can be customized using [loader hooks](esm#loaders).
* It does not support folders as modules, directory indexes (e.g. `'./startup/index.js'`) must be fully specified.
* It does no extension searching. A file extension must be provided when the specifier is a relative or absolute file URL.
* It can load JSON modules, but an import assertion is required.
* It accepts only `.js`, `.mjs`, and `.cjs` extensions for JavaScript text files.
* It can be used to load JavaScript CommonJS modules. Such modules are passed through the `cjs-module-lexer` to try to identify named exports, which are available if they can be determined through static analysis. Imported CommonJS modules have their URLs converted to absolute paths and are then loaded via the CommonJS module loader.
####
`package.json` and file extensions
Within a package, the [`package.json`](#nodejs-packagejson-field-definitions) [`"type"`](#type) field defines how Node.js should interpret `.js` files. If a `package.json` file does not have a `"type"` field, `.js` files are treated as [CommonJS](modules).
A `package.json` `"type"` value of `"module"` tells Node.js to interpret `.js` files within that package as using [ES module](esm) syntax.
The `"type"` field applies not only to initial entry points (`node my-app.js`) but also to files referenced by `import` statements and `import()` expressions.
```
// my-app.js, treated as an ES module because there is a package.json
// file in the same folder with "type": "module".
import './startup/init.js';
// Loaded as ES module since ./startup contains no package.json file,
// and therefore inherits the "type" value from one level up.
import 'commonjs-package';
// Loaded as CommonJS since ./node_modules/commonjs-package/package.json
// lacks a "type" field or contains "type": "commonjs".
import './node_modules/commonjs-package/index.js';
// Loaded as CommonJS since ./node_modules/commonjs-package/package.json
// lacks a "type" field or contains "type": "commonjs".
```
Files ending with `.mjs` are always loaded as [ES modules](esm) regardless of the nearest parent `package.json`.
Files ending with `.cjs` are always loaded as [CommonJS](modules) regardless of the nearest parent `package.json`.
```
import './legacy-file.cjs';
// Loaded as CommonJS since .cjs is always loaded as CommonJS.
import 'commonjs-package/src/index.mjs';
// Loaded as ES module since .mjs is always loaded as ES module.
```
The `.mjs` and `.cjs` extensions can be used to mix types within the same package:
* Within a `"type": "module"` package, Node.js can be instructed to interpret a particular file as [CommonJS](modules) by naming it with a `.cjs` extension (since both `.js` and `.mjs` files are treated as ES modules within a `"module"` package).
* Within a `"type": "commonjs"` package, Node.js can be instructed to interpret a particular file as an [ES module](esm) by naming it with an `.mjs` extension (since both `.js` and `.cjs` files are treated as CommonJS within a `"commonjs"` package).
####
`--input-type` flag
Added in: v12.0.0 Strings passed in as an argument to `--eval` (or `-e`), or piped to `node` via `STDIN`, are treated as [ES modules](esm) when the `--input-type=module` flag is set.
```
node --input-type=module --eval "import { sep } from 'node:path'; console.log(sep);"
echo "import { sep } from 'node:path'; console.log(sep);" | node --input-type=module
```
For completeness there is also `--input-type=commonjs`, for explicitly running string input as CommonJS. This is the default behavior if `--input-type` is unspecified.
### Determining package manager
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
While all Node.js projects are expected to be installable by all package managers once published, their development teams are often required to use one specific package manager. To make this process easier, Node.js ships with a tool called [Corepack](corepack) that aims to make all package managers transparently available in your environment - provided you have Node.js installed.
By default Corepack won't enforce any specific package manager and will use the generic "Last Known Good" versions associated with each Node.js release, but you can improve this experience by setting the [`"packageManager"`](#packagemanager) field in your project's `package.json`.
### Package entry points
In a package's `package.json` file, two fields can define entry points for a package: [`"main"`](#main) and [`"exports"`](#exports). Both fields apply to both ES module and CommonJS module entry points.
The [`"main"`](#main) field is supported in all versions of Node.js, but its capabilities are limited: it only defines the main entry point of the package.
The [`"exports"`](#exports) provides a modern alternative to [`"main"`](#main) allowing multiple entry points to be defined, conditional entry resolution support between environments, and **preventing any other entry points besides those defined in [`"exports"`](#exports)**. This encapsulation allows module authors to clearly define the public interface for their package.
For new packages targeting the currently supported versions of Node.js, the [`"exports"`](#exports) field is recommended. For packages supporting Node.js 10 and below, the [`"main"`](#main) field is required. If both [`"exports"`](#exports) and [`"main"`](#main) are defined, the [`"exports"`](#exports) field takes precedence over [`"main"`](#main) in supported versions of Node.js.
[Conditional exports](#conditional-exports) can be used within [`"exports"`](#exports) to define different package entry points per environment, including whether the package is referenced via `require` or via `import`. For more information about supporting both CommonJS and ES modules in a single package please consult [the dual CommonJS/ES module packages section](#dual-commonjses-module-packages).
Existing packages introducing the [`"exports"`](#exports) field will prevent consumers of the package from using any entry points that are not defined, including the [`package.json`](#nodejs-packagejson-field-definitions) (e.g. `require('your-package/package.json')`. **This will likely be a breaking change.**
To make the introduction of [`"exports"`](#exports) non-breaking, ensure that every previously supported entry point is exported. It is best to explicitly specify entry points so that the package's public API is well-defined. For example, a project that previously exported `main`, `lib`, `feature`, and the `package.json` could use the following `package.exports`:
```
{
"name": "my-package",
"exports": {
".": "./lib/index.js",
"./lib": "./lib/index.js",
"./lib/index": "./lib/index.js",
"./lib/index.js": "./lib/index.js",
"./feature": "./feature/index.js",
"./feature/index": "./feature/index.js",
"./feature/index.js": "./feature/index.js",
"./package.json": "./package.json"
}
}
```
Alternatively a project could choose to export entire folders both with and without extensioned subpaths using export patterns:
```
{
"name": "my-package",
"exports": {
".": "./lib/index.js",
"./lib": "./lib/index.js",
"./lib/*": "./lib/*.js",
"./lib/*.js": "./lib/*.js",
"./feature": "./feature/index.js",
"./feature/*": "./feature/*.js",
"./feature/*.js": "./feature/*.js",
"./package.json": "./package.json"
}
}
```
With the above providing backwards-compatibility for any minor package versions, a future major change for the package can then properly restrict the exports to only the specific feature exports exposed:
```
{
"name": "my-package",
"exports": {
".": "./lib/index.js",
"./feature/*.js": "./feature/*.js",
"./feature/internal/*": null
}
}
```
#### Main entry point export
When writing a new package, it is recommended to use the [`"exports"`](#exports) field:
```
{
"exports": "./index.js"
}
```
When the [`"exports"`](#exports) field is defined, all subpaths of the package are encapsulated and no longer available to importers. For example, `require('pkg/subpath.js')` throws an [`ERR_PACKAGE_PATH_NOT_EXPORTED`](errors#err_package_path_not_exported) error.
This encapsulation of exports provides more reliable guarantees about package interfaces for tools and when handling semver upgrades for a package. It is not a strong encapsulation since a direct require of any absolute subpath of the package such as `require('/path/to/node_modules/pkg/subpath.js')` will still load `subpath.js`.
All currently supported versions of Node.js and modern build tools support the `"exports"` field. For projects using an older version of Node.js or a related build tool, compatibility can be achieved by including the `"main"` field alongside `"exports"` pointing to the same module:
```
{
"main": "./index.js",
"exports": "./index.js"
}
```
#### Subpath exports
Added in: v12.7.0 When using the [`"exports"`](#exports) field, custom subpaths can be defined along with the main entry point by treating the main entry point as the `"."` subpath:
```
{
"exports": {
".": "./index.js",
"./submodule.js": "./src/submodule.js"
}
}
```
Now only the defined subpath in [`"exports"`](#exports) can be imported by a consumer:
```
import submodule from 'es-module-package/submodule.js';
// Loads ./node_modules/es-module-package/src/submodule.js
```
While other subpaths will error:
```
import submodule from 'es-module-package/private-module.js';
// Throws ERR_PACKAGE_PATH_NOT_EXPORTED
```
##### Extensions in subpaths
Package authors should provide either extensioned (`import 'pkg/subpath.js'`) or extensionless (`import 'pkg/subpath'`) subpaths in their exports. This ensures that there is only one subpath for each exported module so that all dependents import the same consistent specifier, keeping the package contract clear for consumers and simplifying package subpath completions.
Traditionally, packages tended to use the extensionless style, which has the benefits of readability and of masking the true path of the file within the package.
With [import maps](https://github.com/WICG/import-maps) now providing a standard for package resolution in browsers and other JavaScript runtimes, using the extensionless style can result in bloated import map definitions. Explicit file extensions can avoid this issue by enabling the import map to utilize a [packages folder mapping](https://github.com/WICG/import-maps#packages-via-trailing-slashes) to map multiple subpaths where possible instead of a separate map entry per package subpath export. This also mirrors the requirement of using [the full specifier path](esm#mandatory-file-extensions) in relative and absolute import specifiers.
#### Exports sugar
Added in: v12.11.0 If the `"."` export is the only export, the [`"exports"`](#exports) field provides sugar for this case being the direct [`"exports"`](#exports) field value.
```
{
"exports": {
".": "./index.js"
}
}
```
can be written:
```
{
"exports": "./index.js"
}
```
#### Subpath imports
Added in: v14.6.0, v12.19.0 In addition to the [`"exports"`](#exports) field, there is a package `"imports"` field to create private mappings that only apply to import specifiers from within the package itself.
Entries in the `"imports"` field must always start with `#` to ensure they are disambiguated from external package specifiers.
For example, the imports field can be used to gain the benefits of conditional exports for internal modules:
```
// package.json
{
"imports": {
"#dep": {
"node": "dep-node-native",
"default": "./dep-polyfill.js"
}
},
"dependencies": {
"dep-node-native": "^1.0.0"
}
}
```
where `import '#dep'` does not get the resolution of the external package `dep-node-native` (including its exports in turn), and instead gets the local file `./dep-polyfill.js` relative to the package in other environments.
Unlike the `"exports"` field, the `"imports"` field permits mapping to external packages.
The resolution rules for the imports field are otherwise analogous to the exports field.
#### Subpath patterns
History
| Version | Changes |
| --- | --- |
| v16.10.0, v14.19.0 | Support pattern trailers in "imports" field. |
| v16.9.0, v14.19.0 | Support pattern trailers. |
| v14.13.0, v12.20.0 | Added in: v14.13.0, v12.20.0 |
For packages with a small number of exports or imports, we recommend explicitly listing each exports subpath entry. But for packages that have large numbers of subpaths, this might cause `package.json` bloat and maintenance issues.
For these use cases, subpath export patterns can be used instead:
```
// ./node_modules/es-module-package/package.json
{
"exports": {
"./features/*.js": "./src/features/*.js"
},
"imports": {
"#internal/*.js": "./src/internal/*.js"
}
}
```
**`*` maps expose nested subpaths as it is a string replacement syntax only.**
All instances of `*` on the right hand side will then be replaced with this value, including if it contains any `/` separators.
```
import featureX from 'es-module-package/features/x.js';
// Loads ./node_modules/es-module-package/src/features/x.js
import featureY from 'es-module-package/features/y/y.js';
// Loads ./node_modules/es-module-package/src/features/y/y.js
import internalZ from '#internal/z.js';
// Loads ./node_modules/es-module-package/src/internal/z.js
```
This is a direct static matching and replacement without any special handling for file extensions. Including the `"*.js"` on both sides of the mapping restricts the exposed package exports to only JS files.
The property of exports being statically enumerable is maintained with exports patterns since the individual exports for a package can be determined by treating the right hand side target pattern as a `**` glob against the list of files within the package. Because `node_modules` paths are forbidden in exports targets, this expansion is dependent on only the files of the package itself.
To exclude private subfolders from patterns, `null` targets can be used:
```
// ./node_modules/es-module-package/package.json
{
"exports": {
"./features/*.js": "./src/features/*.js",
"./features/private-internal/*": null
}
}
```
```
import featureInternal from 'es-module-package/features/private-internal/m.js';
// Throws: ERR_PACKAGE_PATH_NOT_EXPORTED
import featureX from 'es-module-package/features/x.js';
// Loads ./node_modules/es-module-package/src/features/x.js
```
#### Conditional exports
History
| Version | Changes |
| --- | --- |
| v13.2.0, v12.16.0 | Added in: v13.2.0, v12.16.0 |
| v13.7.0, v12.16.0 | Unflag conditional exports. |
Conditional exports provide a way to map to different paths depending on certain conditions. They are supported for both CommonJS and ES module imports.
For example, a package that wants to provide different ES module exports for `require()` and `import` can be written:
```
// package.json
{
"exports": {
"import": "./index-module.js",
"require": "./index-require.cjs"
},
"type": "module"
}
```
Node.js implements the following conditions, listed in order from most specific to least specific as conditions should be defined:
* `"node-addons"` - similar to `"node"` and matches for any Node.js environment. This condition can be used to provide an entry point which uses native C++ addons as opposed to an entry point which is more universal and doesn't rely on native addons. This condition can be disabled via the [`--no-addons` flag](cli#--no-addons).
* `"node"` - matches for any Node.js environment. Can be a CommonJS or ES module file. *In most cases explicitly calling out the Node.js platform is not necessary.*
* `"import"` - matches when the package is loaded via `import` or `import()`, or via any top-level import or resolve operation by the ECMAScript module loader. Applies regardless of the module format of the target file. *Always mutually exclusive with `"require"`.*
* `"require"` - matches when the package is loaded via `require()`. The referenced file should be loadable with `require()` although the condition matches regardless of the module format of the target file. Expected formats include CommonJS, JSON, and native addons but not ES modules as `require()` doesn't support them. *Always mutually exclusive with `"import"`.*
* `"default"` - the generic fallback that always matches. Can be a CommonJS or ES module file. *This condition should always come last.*
Within the [`"exports"`](#exports) object, key order is significant. During condition matching, earlier entries have higher priority and take precedence over later entries. *The general rule is that conditions should be from most specific to least specific in object order*.
Using the `"import"` and `"require"` conditions can lead to some hazards, which are further explained in [the dual CommonJS/ES module packages section](#dual-commonjses-module-packages).
The `"node-addons"` condition can be used to provide an entry point which uses native C++ addons. However, this condition can be disabled via the [`--no-addons` flag](cli#--no-addons). When using `"node-addons"`, it's recommended to treat `"default"` as an enhancement that provides a more universal entry point, e.g. using WebAssembly instead of a native addon.
Conditional exports can also be extended to exports subpaths, for example:
```
{
"exports": {
".": "./index.js",
"./feature.js": {
"node": "./feature-node.js",
"default": "./feature.js"
}
}
}
```
Defines a package where `require('pkg/feature.js')` and `import 'pkg/feature.js'` could provide different implementations between Node.js and other JS environments.
When using environment branches, always include a `"default"` condition where possible. Providing a `"default"` condition ensures that any unknown JS environments are able to use this universal implementation, which helps avoid these JS environments from having to pretend to be existing environments in order to support packages with conditional exports. For this reason, using `"node"` and `"default"` condition branches is usually preferable to using `"node"` and `"browser"` condition branches.
#### Nested conditions
In addition to direct mappings, Node.js also supports nested condition objects.
For example, to define a package that only has dual mode entry points for use in Node.js but not the browser:
```
{
"exports": {
"node": {
"import": "./feature-node.mjs",
"require": "./feature-node.cjs"
},
"default": "./feature.mjs"
}
}
```
Conditions continue to be matched in order as with flat conditions. If a nested condition does not have any mapping it will continue checking the remaining conditions of the parent condition. In this way nested conditions behave analogously to nested JavaScript `if` statements.
#### Resolving user conditions
Added in: v14.9.0, v12.19.0 When running Node.js, custom user conditions can be added with the `--conditions` flag:
```
node --conditions=development index.js
```
which would then resolve the `"development"` condition in package imports and exports, while resolving the existing `"node"`, `"node-addons"`, `"default"`, `"import"`, and `"require"` conditions as appropriate.
Any number of custom conditions can be set with repeat flags.
#### Community Conditions Definitions
Condition strings other than the `"import"`, `"require"`, `"node"`, `"node-addons"` and `"default"` conditions [implemented in Node.js core](#conditional-exports) are ignored by default.
Other platforms may implement other conditions and user conditions can be enabled in Node.js via the [`--conditions` / `-C` flag](#resolving-user-conditions).
Since custom package conditions require clear definitions to ensure correct usage, a list of common known package conditions and their strict definitions is provided below to assist with ecosystem coordination.
* `"types"` - can be used by typing systems to resolve the typing file for the given export. *This condition should always be included first.*
* `"deno"` - indicates a variation for the Deno platform.
* `"browser"` - any web browser environment.
* `"development"` - can be used to define a development-only environment entry point, for example to provide additional debugging context such as better error messages when running in a development mode. *Must always be mutually exclusive with `"production"`.*
* `"production"` - can be used to define a production environment entry point. *Must always be mutually exclusive with `"development"`.*
New conditions definitions may be added to this list by creating a pull request to the [Node.js documentation for this section](https://github.com/nodejs/node/blob/HEAD/doc/api/packages.md#conditions-definitions). The requirements for listing a new condition definition here are that:
* The definition should be clear and unambiguous for all implementers.
* The use case for why the condition is needed should be clearly justified.
* There should exist sufficient existing implementation usage.
* The condition name should not conflict with another condition definition or condition in wide usage.
* The listing of the condition definition should provide a coordination benefit to the ecosystem that wouldn't otherwise be possible. For example, this would not necessarily be the case for company-specific or application-specific conditions.
The above definitions may be moved to a dedicated conditions registry in due course.
#### Self-referencing a package using its name
History
| Version | Changes |
| --- | --- |
| v13.1.0, v12.16.0 | Added in: v13.1.0, v12.16.0 |
| v13.6.0, v12.16.0 | Unflag self-referencing a package using its name. |
Within a package, the values defined in the package's `package.json` [`"exports"`](#exports) field can be referenced via the package's name. For example, assuming the `package.json` is:
```
// package.json
{
"name": "a-package",
"exports": {
".": "./index.mjs",
"./foo.js": "./foo.js"
}
}
```
Then any module *in that package* can reference an export in the package itself:
```
// ./a-module.mjs
import { something } from 'a-package'; // Imports "something" from ./index.mjs.
```
Self-referencing is available only if `package.json` has [`"exports"`](#exports), and will allow importing only what that [`"exports"`](#exports) (in the `package.json`) allows. So the code below, given the previous package, will generate a runtime error:
```
// ./another-module.mjs
// Imports "another" from ./m.mjs. Fails because
// the "package.json" "exports" field
// does not provide an export named "./m.mjs".
import { another } from 'a-package/m.mjs';
```
Self-referencing is also available when using `require`, both in an ES module, and in a CommonJS one. For example, this code will also work:
```
// ./a-module.js
const { something } = require('a-package/foo.js'); // Loads from ./foo.js.
```
Finally, self-referencing also works with scoped packages. For example, this code will also work:
```
// package.json
{
"name": "@my/package",
"exports": "./index.js"
}
```
```
// ./index.js
module.exports = 42;
```
```
// ./other.js
console.log(require('@my/package'));
```
```
$ node other.js
42
```
### Dual CommonJS/ES module packages
Prior to the introduction of support for ES modules in Node.js, it was a common pattern for package authors to include both CommonJS and ES module JavaScript sources in their package, with `package.json` [`"main"`](#main) specifying the CommonJS entry point and `package.json` `"module"` specifying the ES module entry point. This enabled Node.js to run the CommonJS entry point while build tools such as bundlers used the ES module entry point, since Node.js ignored (and still ignores) the top-level `"module"` field.
Node.js can now run ES module entry points, and a package can contain both CommonJS and ES module entry points (either via separate specifiers such as `'pkg'` and `'pkg/es-module'`, or both at the same specifier via [Conditional exports](#conditional-exports)). Unlike in the scenario where `"module"` is only used by bundlers, or ES module files are transpiled into CommonJS on the fly before evaluation by Node.js, the files referenced by the ES module entry point are evaluated as ES modules.
#### Dual package hazard
When an application is using a package that provides both CommonJS and ES module sources, there is a risk of certain bugs if both versions of the package get loaded. This potential comes from the fact that the `pkgInstance` created by `const pkgInstance = require('pkg')` is not the same as the `pkgInstance` created by `import pkgInstance from 'pkg'` (or an alternative main path like `'pkg/module'`). This is the “dual package hazard,” where two versions of the same package can be loaded within the same runtime environment. While it is unlikely that an application or package would intentionally load both versions directly, it is common for an application to load one version while a dependency of the application loads the other version. This hazard can happen because Node.js supports intermixing CommonJS and ES modules, and can lead to unexpected behavior.
If the package main export is a constructor, an `instanceof` comparison of instances created by the two versions returns `false`, and if the export is an object, properties added to one (like `pkgInstance.foo = 3`) are not present on the other. This differs from how `import` and `require` statements work in all-CommonJS or all-ES module environments, respectively, and therefore is surprising to users. It also differs from the behavior users are familiar with when using transpilation via tools like [Babel](https://babeljs.io/) or [`esm`](https://github.com/standard-things/esm#readme).
#### Writing dual packages while avoiding or minimizing hazards
First, the hazard described in the previous section occurs when a package contains both CommonJS and ES module sources and both sources are provided for use in Node.js, either via separate main entry points or exported paths. A package might instead be written where any version of Node.js receives only CommonJS sources, and any separate ES module sources the package might contain are intended only for other environments such as browsers. Such a package would be usable by any version of Node.js, since `import` can refer to CommonJS files; but it would not provide any of the advantages of using ES module syntax.
A package might also switch from CommonJS to ES module syntax in a [breaking change](https://semver.org/) version bump. This has the disadvantage that the newest version of the package would only be usable in ES module-supporting versions of Node.js.
Every pattern has tradeoffs, but there are two broad approaches that satisfy the following conditions:
1. The package is usable via both `require` and `import`.
2. The package is usable in both current Node.js and older versions of Node.js that lack support for ES modules.
3. The package main entry point, e.g. `'pkg'` can be used by both `require` to resolve to a CommonJS file and by `import` to resolve to an ES module file. (And likewise for exported paths, e.g. `'pkg/feature'`.)
4. The package provides named exports, e.g. `import { name } from 'pkg'` rather than `import pkg from 'pkg'; pkg.name`.
5. The package is potentially usable in other ES module environments such as browsers.
6. The hazards described in the previous section are avoided or minimized.
##### Approach #1: Use an ES module wrapper
Write the package in CommonJS or transpile ES module sources into CommonJS, and create an ES module wrapper file that defines the named exports. Using [Conditional exports](#conditional-exports), the ES module wrapper is used for `import` and the CommonJS entry point for `require`.
```
// ./node_modules/pkg/package.json
{
"type": "module",
"exports": {
"import": "./wrapper.mjs",
"require": "./index.cjs"
}
}
```
The preceding example uses explicit extensions `.mjs` and `.cjs`. If your files use the `.js` extension, `"type": "module"` will cause such files to be treated as ES modules, just as `"type": "commonjs"` would cause them to be treated as CommonJS. See [Enabling](esm#enabling).
```
// ./node_modules/pkg/index.cjs
exports.name = 'value';
```
```
// ./node_modules/pkg/wrapper.mjs
import cjsModule from './index.cjs';
export const name = cjsModule.name;
```
In this example, the `name` from `import { name } from 'pkg'` is the same singleton as the `name` from `const { name } = require('pkg')`. Therefore `===` returns `true` when comparing the two `name`s and the divergent specifier hazard is avoided.
If the module is not simply a list of named exports, but rather contains a unique function or object export like `module.exports = function () { ... }`, or if support in the wrapper for the `import pkg from 'pkg'` pattern is desired, then the wrapper would instead be written to export the default optionally along with any named exports as well:
```
import cjsModule from './index.cjs';
export const name = cjsModule.name;
export default cjsModule;
```
This approach is appropriate for any of the following use cases:
* The package is currently written in CommonJS and the author would prefer not to refactor it into ES module syntax, but wishes to provide named exports for ES module consumers.
* The package has other packages that depend on it, and the end user might install both this package and those other packages. For example a `utilities` package is used directly in an application, and a `utilities-plus` package adds a few more functions to `utilities`. Because the wrapper exports underlying CommonJS files, it doesn't matter if `utilities-plus` is written in CommonJS or ES module syntax; it will work either way.
* The package stores internal state, and the package author would prefer not to refactor the package to isolate its state management. See the next section.
A variant of this approach not requiring conditional exports for consumers could be to add an export, e.g. `"./module"`, to point to an all-ES module-syntax version of the package. This could be used via `import 'pkg/module'` by users who are certain that the CommonJS version will not be loaded anywhere in the application, such as by dependencies; or if the CommonJS version can be loaded but doesn't affect the ES module version (for example, because the package is stateless):
```
// ./node_modules/pkg/package.json
{
"type": "module",
"exports": {
".": "./index.cjs",
"./module": "./wrapper.mjs"
}
}
```
##### Approach #2: Isolate state
A [`package.json`](#nodejs-packagejson-field-definitions) file can define the separate CommonJS and ES module entry points directly:
```
// ./node_modules/pkg/package.json
{
"type": "module",
"exports": {
"import": "./index.mjs",
"require": "./index.cjs"
}
}
```
This can be done if both the CommonJS and ES module versions of the package are equivalent, for example because one is the transpiled output of the other; and the package's management of state is carefully isolated (or the package is stateless).
The reason that state is an issue is because both the CommonJS and ES module versions of the package might get used within an application; for example, the user's application code could `import` the ES module version while a dependency `require`s the CommonJS version. If that were to occur, two copies of the package would be loaded in memory and therefore two separate states would be present. This would likely cause hard-to-troubleshoot bugs.
Aside from writing a stateless package (if JavaScript's `Math` were a package, for example, it would be stateless as all of its methods are static), there are some ways to isolate state so that it's shared between the potentially loaded CommonJS and ES module instances of the package:
1. If possible, contain all state within an instantiated object. JavaScript's `Date`, for example, needs to be instantiated to contain state; if it were a package, it would be used like this:
```
import Date from 'date';
const someDate = new Date();
// someDate contains state; Date does not
```
The `new` keyword isn't required; a package's function can return a new object, or modify a passed-in object, to keep the state external to the package.
2. Isolate the state in one or more CommonJS files that are shared between the CommonJS and ES module versions of the package. For example, if the CommonJS and ES module entry points are `index.cjs` and `index.mjs`, respectively:
```
// ./node_modules/pkg/index.cjs
const state = require('./state.cjs');
module.exports.state = state;
```
```
// ./node_modules/pkg/index.mjs
import state from './state.cjs';
export {
state
};
```
Even if `pkg` is used via both `require` and `import` in an application (for example, via `import` in application code and via `require` by a dependency) each reference of `pkg` will contain the same state; and modifying that state from either module system will apply to both.
Any plugins that attach to the package's singleton would need to separately attach to both the CommonJS and ES module singletons.
This approach is appropriate for any of the following use cases:
* The package is currently written in ES module syntax and the package author wants that version to be used wherever such syntax is supported.
* The package is stateless or its state can be isolated without too much difficulty.
* The package is unlikely to have other public packages that depend on it, or if it does, the package is stateless or has state that need not be shared between dependencies or with the overall application.
Even with isolated state, there is still the cost of possible extra code execution between the CommonJS and ES module versions of a package.
As with the previous approach, a variant of this approach not requiring conditional exports for consumers could be to add an export, e.g. `"./module"`, to point to an all-ES module-syntax version of the package:
```
// ./node_modules/pkg/package.json
{
"type": "module",
"exports": {
".": "./index.cjs",
"./module": "./index.mjs"
}
}
```
### Node.js `package.json` field definitions
This section describes the fields used by the Node.js runtime. Other tools (such as [npm](https://docs.npmjs.com/cli/v8/configuring-npm/package-json)) use additional fields which are ignored by Node.js and not documented here.
The following fields in `package.json` files are used in Node.js:
* [`"name"`](#name) - Relevant when using named imports within a package. Also used by package managers as the name of the package.
* [`"main"`](#main) - The default module when loading the package, if exports is not specified, and in versions of Node.js prior to the introduction of exports.
* [`"packageManager"`](#packagemanager) - The package manager recommended when contributing to the package. Leveraged by the [Corepack](corepack) shims.
* [`"type"`](#type) - The package type determining whether to load `.js` files as CommonJS or ES modules.
* [`"exports"`](#exports) - Package exports and conditional exports. When present, limits which submodules can be loaded from within the package.
* [`"imports"`](#imports) - Package imports, for use by modules within the package itself.
####
`"name"`
History
| Version | Changes |
| --- | --- |
| v13.1.0, v12.16.0 | Added in: v13.1.0, v12.16.0 |
| v13.6.0, v12.16.0 | Remove the `--experimental-resolve-self` option. |
* Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
```
{
"name": "package-name"
}
```
The `"name"` field defines your package's name. Publishing to the *npm* registry requires a name that satisfies [certain requirements](https://docs.npmjs.com/files/package.json#name).
The `"name"` field can be used in addition to the [`"exports"`](#exports) field to [self-reference](#self-referencing-a-package-using-its-name) a package using its name.
####
`"main"`
Added in: v0.4.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
```
{
"main": "./index.js"
}
```
The `"main"` field defines the entry point of a package when imported by name via a `node_modules` lookup. Its value is a path.
When a package has an [`"exports"`](#exports) field, this will take precedence over the `"main"` field when importing the package by name.
It also defines the script that is used when the [package directory is loaded via `require()`](modules#folders-as-modules).
```
// This resolves to ./path/to/directory/index.js.
require('./path/to/directory');
```
####
`"packageManager"`
Added in: v16.9.0, v14.19.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
```
{
"packageManager": "<package manager name>@<version>"
}
```
The `"packageManager"` field defines which package manager is expected to be used when working on the current project. It can set to any of the [supported package managers](corepack#supported-package-managers), and will ensure that your teams use the exact same package manager versions without having to install anything else than Node.js.
This field is currently experimental and needs to be opted-in; check the [Corepack](corepack) page for details about the procedure.
####
`"type"`
History
| Version | Changes |
| --- | --- |
| v13.2.0, v12.17.0 | Unflag `--experimental-modules`. |
| v12.0.0 | Added in: v12.0.0 |
* Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `"type"` field defines the module format that Node.js uses for all `.js` files that have that `package.json` file as their nearest parent.
Files ending with `.js` are loaded as ES modules when the nearest parent `package.json` file contains a top-level field `"type"` with a value of `"module"`.
The nearest parent `package.json` is defined as the first `package.json` found when searching in the current folder, that folder's parent, and so on up until a node\_modules folder or the volume root is reached.
```
// package.json
{
"type": "module"
}
```
```
# In same folder as preceding package.json
node my-app.js # Runs as ES module
```
If the nearest parent `package.json` lacks a `"type"` field, or contains `"type": "commonjs"`, `.js` files are treated as [CommonJS](modules). If the volume root is reached and no `package.json` is found, `.js` files are treated as [CommonJS](modules).
`import` statements of `.js` files are treated as ES modules if the nearest parent `package.json` contains `"type": "module"`.
```
// my-app.js, part of the same example as above
import './startup.js'; // Loaded as ES module because of package.json
```
Regardless of the value of the `"type"` field, `.mjs` files are always treated as ES modules and `.cjs` files are always treated as CommonJS.
####
`"exports"`
History
| Version | Changes |
| --- | --- |
| v14.13.0, v12.20.0 | Add support for `"exports"` patterns. |
| v13.7.0, v12.17.0 | Unflag conditional exports. |
| v13.7.0, v12.16.0 | Implement logical conditional exports ordering. |
| v13.7.0, v12.16.0 | Remove the `--experimental-conditional-exports` option. In 12.16.0, conditional exports are still behind `--experimental-modules`. |
| v13.2.0, v12.16.0 | Implement conditional exports. |
| v12.7.0 | Added in: v12.7.0 |
* Type: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
```
{
"exports": "./index.js"
}
```
The `"exports"` field allows defining the [entry points](#package-entry-points) of a package when imported by name loaded either via a `node_modules` lookup or a [self-reference](#self-referencing-a-package-using-its-name) to its own name. It is supported in Node.js 12+ as an alternative to the [`"main"`](#main) that can support defining [subpath exports](#subpath-exports) and [conditional exports](#conditional-exports) while encapsulating internal unexported modules.
[Conditional Exports](#conditional-exports) can also be used within `"exports"` to define different package entry points per environment, including whether the package is referenced via `require` or via `import`.
All paths defined in the `"exports"` must be relative file URLs starting with `./`.
####
`"imports"`
Added in: v14.6.0, v12.19.0 * Type: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
```
// package.json
{
"imports": {
"#dep": {
"node": "dep-node-native",
"default": "./dep-polyfill.js"
}
},
"dependencies": {
"dep-node-native": "^1.0.0"
}
}
```
Entries in the imports field must be strings starting with `#`.
Package imports permit mapping to external packages.
This field defines [subpath imports](#subpath-imports) for the current package.
| programming_docs |
node None Child process
-------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/child\_process.js](https://github.com/nodejs/node/blob/v19.0.1/lib/child_process.js)
The `node:child_process` module provides the ability to spawn subprocesses in a manner that is similar, but not identical, to [`popen(3)`](http://man7.org/linux/man-pages/man3/popen.3.html). This capability is primarily provided by the [`child_process.spawn()`](#child_processspawncommand-args-options) function:
```
const { spawn } = require('node:child_process');
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.error(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
```
By default, pipes for `stdin`, `stdout`, and `stderr` are established between the parent Node.js process and the spawned subprocess. These pipes have limited (and platform-specific) capacity. If the subprocess writes to stdout in excess of that limit without the output being captured, the subprocess blocks waiting for the pipe buffer to accept more data. This is identical to the behavior of pipes in the shell. Use the `{ stdio: 'ignore' }` option if the output will not be consumed.
The command lookup is performed using the `options.env.PATH` environment variable if `env` is in the `options` object. Otherwise, `process.env.PATH` is used. If `options.env` is set without `PATH`, lookup on Unix is performed on a default search path search of `/usr/bin:/bin` (see your operating system's manual for execvpe/execvp), on Windows the current processes environment variable `PATH` is used.
On Windows, environment variables are case-insensitive. Node.js lexicographically sorts the `env` keys and uses the first one that case-insensitively matches. Only first (in lexicographic order) entry will be passed to the subprocess. This might lead to issues on Windows when passing objects to the `env` option that have multiple variants of the same key, such as `PATH` and `Path`.
The [`child_process.spawn()`](#child_processspawncommand-args-options) method spawns the child process asynchronously, without blocking the Node.js event loop. The [`child_process.spawnSync()`](#child_processspawnsynccommand-args-options) function provides equivalent functionality in a synchronous manner that blocks the event loop until the spawned process either exits or is terminated.
For convenience, the `node:child_process` module provides a handful of synchronous and asynchronous alternatives to [`child_process.spawn()`](#child_processspawncommand-args-options) and [`child_process.spawnSync()`](#child_processspawnsynccommand-args-options). Each of these alternatives are implemented on top of [`child_process.spawn()`](#child_processspawncommand-args-options) or [`child_process.spawnSync()`](#child_processspawnsynccommand-args-options).
* [`child_process.exec()`](#child_processexeccommand-options-callback): spawns a shell and runs a command within that shell, passing the `stdout` and `stderr` to a callback function when complete.
* [`child_process.execFile()`](#child_processexecfilefile-args-options-callback): similar to [`child_process.exec()`](#child_processexeccommand-options-callback) except that it spawns the command directly without first spawning a shell by default.
* [`child_process.fork()`](#child_processforkmodulepath-args-options): spawns a new Node.js process and invokes a specified module with an IPC communication channel established that allows sending messages between parent and child.
* [`child_process.execSync()`](#child_processexecsynccommand-options): a synchronous version of [`child_process.exec()`](#child_processexeccommand-options-callback) that will block the Node.js event loop.
* [`child_process.execFileSync()`](#child_processexecfilesyncfile-args-options): a synchronous version of [`child_process.execFile()`](#child_processexecfilefile-args-options-callback) that will block the Node.js event loop.
For certain use cases, such as automating shell scripts, the [synchronous counterparts](#synchronous-process-creation) may be more convenient. In many cases, however, the synchronous methods can have significant impact on performance due to stalling the event loop while spawned processes complete.
### Asynchronous process creation
The [`child_process.spawn()`](#child_processspawncommand-args-options), [`child_process.fork()`](#child_processforkmodulepath-args-options), [`child_process.exec()`](#child_processexeccommand-options-callback), and [`child_process.execFile()`](#child_processexecfilefile-args-options-callback) methods all follow the idiomatic asynchronous programming pattern typical of other Node.js APIs.
Each of the methods returns a [`ChildProcess`](#class-childprocess) instance. These objects implement the Node.js [`EventEmitter`](events#class-eventemitter) API, allowing the parent process to register listener functions that are called when certain events occur during the life cycle of the child process.
The [`child_process.exec()`](#child_processexeccommand-options-callback) and [`child_process.execFile()`](#child_processexecfilefile-args-options-callback) methods additionally allow for an optional `callback` function to be specified that is invoked when the child process terminates.
#### Spawning `.bat` and `.cmd` files on Windows
The importance of the distinction between [`child_process.exec()`](#child_processexeccommand-options-callback) and [`child_process.execFile()`](#child_processexecfilefile-args-options-callback) can vary based on platform. On Unix-type operating systems (Unix, Linux, macOS) [`child_process.execFile()`](#child_processexecfilefile-args-options-callback) can be more efficient because it does not spawn a shell by default. On Windows, however, `.bat` and `.cmd` files are not executable on their own without a terminal, and therefore cannot be launched using [`child_process.execFile()`](#child_processexecfilefile-args-options-callback). When running on Windows, `.bat` and `.cmd` files can be invoked using [`child_process.spawn()`](#child_processspawncommand-args-options) with the `shell` option set, with [`child_process.exec()`](#child_processexeccommand-options-callback), or by spawning `cmd.exe` and passing the `.bat` or `.cmd` file as an argument (which is what the `shell` option and [`child_process.exec()`](#child_processexeccommand-options-callback) do). In any case, if the script filename contains spaces it needs to be quoted.
```
// On Windows Only...
const { spawn } = require('node:child_process');
const bat = spawn('cmd.exe', ['/c', 'my.bat']);
bat.stdout.on('data', (data) => {
console.log(data.toString());
});
bat.stderr.on('data', (data) => {
console.error(data.toString());
});
bat.on('exit', (code) => {
console.log(`Child exited with code ${code}`);
});
```
```
// OR...
const { exec, spawn } = require('node:child_process');
exec('my.bat', (err, stdout, stderr) => {
if (err) {
console.error(err);
return;
}
console.log(stdout);
});
// Script with spaces in the filename:
const bat = spawn('"my script.cmd"', ['a', 'b'], { shell: true });
// or:
exec('"my script.cmd" a b', (err, stdout, stderr) => {
// ...
});
```
####
`child_process.exec(command[, options][, callback])`
History
| Version | Changes |
| --- | --- |
| v15.4.0 | AbortSignal support was added. |
| v16.4.0, v14.18.0 | The `cwd` option can be a WHATWG `URL` object using `file:` protocol. |
| v8.8.0 | The `windowsHide` option is supported now. |
| v0.1.90 | Added in: v0.1.90 |
* `command` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The command to run, with space-separated arguments.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cwd` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Current working directory of the child process. **Default:** `process.cwd()`.
+ `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Environment key-value pairs. **Default:** `process.env`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
+ `shell` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Shell to execute the command with. See [Shell requirements](#shell-requirements) and [Default Windows shell](#default-windows-shell). **Default:** `'/bin/sh'` on Unix, `process.env.ComSpec` on Windows.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows aborting the child process using an AbortSignal.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
+ `maxBuffer` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated and any output is truncated. See caveat at [`maxBuffer` and Unicode](#maxbuffer-and-unicode). **Default:** `1024 * 1024`.
+ `killSignal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `'SIGTERM'`
+ `uid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the user identity of the process (see [`setuid(2)`](http://man7.org/linux/man-pages/man2/setuid.2.html)).
+ `gid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the group identity of the process (see [`setgid(2)`](http://man7.org/linux/man-pages/man2/setgid.2.html)).
+ `windowsHide` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) called with the output when process terminates.
+ `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `stdout` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
+ `stderr` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* Returns: [<ChildProcess>](child_process#class-childprocess)
Spawns a shell then executes the `command` within that shell, buffering any generated output. The `command` string passed to the exec function is processed directly by the shell and special characters (vary based on [shell](https://en.wikipedia.org/wiki/List_of_command-line_interpreters)) need to be dealt with accordingly:
```
const { exec } = require('node:child_process');
exec('"/path/to/test file/test.sh" arg1 arg2');
// Double quotes are used so that the space in the path is not interpreted as
// a delimiter of multiple arguments.
exec('echo "The \\$HOME variable is $HOME"');
// The $HOME variable is escaped in the first instance, but not in the second.
```
**Never pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.**
If a `callback` function is provided, it is called with the arguments `(error, stdout, stderr)`. On success, `error` will be `null`. On error, `error` will be an instance of [`Error`](errors#class-error). The `error.code` property will be the exit code of the process. By convention, any exit code other than `0` indicates an error. `error.signal` will be the signal that terminated the process.
The `stdout` and `stderr` arguments passed to the callback will contain the stdout and stderr output of the child process. By default, Node.js will decode the output as UTF-8 and pass strings to the callback. The `encoding` option can be used to specify the character encoding used to decode the stdout and stderr output. If `encoding` is `'buffer'`, or an unrecognized character encoding, `Buffer` objects will be passed to the callback instead.
```
const { exec } = require('node:child_process');
exec('cat *.js missing_file | wc -l', (error, stdout, stderr) => {
if (error) {
console.error(`exec error: ${error}`);
return;
}
console.log(`stdout: ${stdout}`);
console.error(`stderr: ${stderr}`);
});
```
If `timeout` is greater than `0`, the parent will send the signal identified by the `killSignal` property (the default is `'SIGTERM'`) if the child runs longer than `timeout` milliseconds.
Unlike the [`exec(3)`](http://man7.org/linux/man-pages/man3/exec.3.html) POSIX system call, `child_process.exec()` does not replace the existing process and uses a shell to execute the command.
If this method is invoked as its [`util.promisify()`](util#utilpromisifyoriginal)ed version, it returns a `Promise` for an `Object` with `stdout` and `stderr` properties. The returned `ChildProcess` instance is attached to the `Promise` as a `child` property. In case of an error (including any error resulting in an exit code other than 0), a rejected promise is returned, with the same `error` object given in the callback, but with two additional properties `stdout` and `stderr`.
```
const util = require('node:util');
const exec = util.promisify(require('node:child_process').exec);
async function lsExample() {
const { stdout, stderr } = await exec('ls');
console.log('stdout:', stdout);
console.error('stderr:', stderr);
}
lsExample();
```
If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.kill()` on the child process except the error passed to the callback will be an `AbortError`:
```
const { exec } = require('node:child_process');
const controller = new AbortController();
const { signal } = controller;
const child = exec('grep ssh', { signal }, (error) => {
console.log(error); // an AbortError
});
controller.abort();
```
####
`child_process.execFile(file[, args][, options][, callback])`
History
| Version | Changes |
| --- | --- |
| v16.4.0, v14.18.0 | The `cwd` option can be a WHATWG `URL` object using `file:` protocol. |
| v15.4.0, v14.17.0 | AbortSignal support was added. |
| v8.8.0 | The `windowsHide` option is supported now. |
| v0.1.91 | Added in: v0.1.91 |
* `file` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name or path of the executable file to run.
* `args` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) List of string arguments.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cwd` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Current working directory of the child process.
+ `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Environment key-value pairs. **Default:** `process.env`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
+ `maxBuffer` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated and any output is truncated. See caveat at [`maxBuffer` and Unicode](#maxbuffer-and-unicode). **Default:** `1024 * 1024`.
+ `killSignal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `'SIGTERM'`
+ `uid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the user identity of the process (see [`setuid(2)`](http://man7.org/linux/man-pages/man2/setuid.2.html)).
+ `gid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the group identity of the process (see [`setgid(2)`](http://man7.org/linux/man-pages/man2/setgid.2.html)).
+ `windowsHide` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`.
+ `windowsVerbatimArguments` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) No quoting or escaping of arguments is done on Windows. Ignored on Unix. **Default:** `false`.
+ `shell` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See [Shell requirements](#shell-requirements) and [Default Windows shell](#default-windows-shell). **Default:** `false` (no shell).
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows aborting the child process using an AbortSignal.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called with the output when process terminates.
+ `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `stdout` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
+ `stderr` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* Returns: [<ChildProcess>](child_process#class-childprocess)
The `child_process.execFile()` function is similar to [`child_process.exec()`](#child_processexeccommand-options-callback) except that it does not spawn a shell by default. Rather, the specified executable `file` is spawned directly as a new process making it slightly more efficient than [`child_process.exec()`](#child_processexeccommand-options-callback).
The same options as [`child_process.exec()`](#child_processexeccommand-options-callback) are supported. Since a shell is not spawned, behaviors such as I/O redirection and file globbing are not supported.
```
const { execFile } = require('node:child_process');
const child = execFile('node', ['--version'], (error, stdout, stderr) => {
if (error) {
throw error;
}
console.log(stdout);
});
```
The `stdout` and `stderr` arguments passed to the callback will contain the stdout and stderr output of the child process. By default, Node.js will decode the output as UTF-8 and pass strings to the callback. The `encoding` option can be used to specify the character encoding used to decode the stdout and stderr output. If `encoding` is `'buffer'`, or an unrecognized character encoding, `Buffer` objects will be passed to the callback instead.
If this method is invoked as its [`util.promisify()`](util#utilpromisifyoriginal)ed version, it returns a `Promise` for an `Object` with `stdout` and `stderr` properties. The returned `ChildProcess` instance is attached to the `Promise` as a `child` property. In case of an error (including any error resulting in an exit code other than 0), a rejected promise is returned, with the same `error` object given in the callback, but with two additional properties `stdout` and `stderr`.
```
const util = require('node:util');
const execFile = util.promisify(require('node:child_process').execFile);
async function getVersion() {
const { stdout } = await execFile('node', ['--version']);
console.log(stdout);
}
getVersion();
```
**If the `shell` option is enabled, do not pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.**
If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.kill()` on the child process except the error passed to the callback will be an `AbortError`:
```
const { execFile } = require('node:child_process');
const controller = new AbortController();
const { signal } = controller;
const child = execFile('node', ['--version'], { signal }, (error) => {
console.log(error); // an AbortError
});
controller.abort();
```
####
`child_process.fork(modulePath[, args][, options])`
History
| Version | Changes |
| --- | --- |
| v17.4.0, v16.14.0 | The `modulePath` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v16.4.0, v14.18.0 | The `cwd` option can be a WHATWG `URL` object using `file:` protocol. |
| v15.13.0, v14.18.0 | timeout was added. |
| v15.11.0, v14.18.0 | killSignal for AbortSignal was added. |
| v15.6.0, v14.17.0 | AbortSignal support was added. |
| v13.2.0, v12.16.0 | The `serialization` option is supported now. |
| v8.0.0 | The `stdio` option can now be a string. |
| v6.4.0 | The `stdio` option is supported now. |
| v0.5.0 | Added in: v0.5.0 |
* `modulePath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) The module to run in the child.
* `args` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) List of string arguments.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cwd` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Current working directory of the child process.
+ `detached` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Prepare child to run independently of its parent process. Specific behavior depends on the platform, see [`options.detached`](#optionsdetached)).
+ `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Environment key-value pairs. **Default:** `process.env`.
+ `execPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Executable used to create the child process.
+ `execArgv` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) List of string arguments passed to the executable. **Default:** `process.execArgv`.
+ `gid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the group identity of the process (see [`setgid(2)`](http://man7.org/linux/man-pages/man2/setgid.2.html)).
+ `serialization` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specify the kind of serialization used for sending messages between processes. Possible values are `'json'` and `'advanced'`. See [Advanced serialization](#advanced-serialization) for more details. **Default:** `'json'`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows closing the child process using an AbortSignal.
+ `killSignal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The signal value to be used when the spawned process will be killed by timeout or abort signal. **Default:** `'SIGTERM'`.
+ `silent` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, stdin, stdout, and stderr of the child will be piped to the parent, otherwise they will be inherited from the parent, see the `'pipe'` and `'inherit'` options for [`child_process.spawn()`](#child_processspawncommand-args-options)'s [`stdio`](#optionsstdio) for more details. **Default:** `false`.
+ `stdio` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [`child_process.spawn()`](#child_processspawncommand-args-options)'s [`stdio`](#optionsstdio). When this option is provided, it overrides `silent`. If the array variant is used, it must contain exactly one item with value `'ipc'` or an error will be thrown. For instance `[0, 1, 2, 'ipc']`.
+ `uid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the user identity of the process (see [`setuid(2)`](http://man7.org/linux/man-pages/man2/setuid.2.html)).
+ `windowsVerbatimArguments` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) No quoting or escaping of arguments is done on Windows. Ignored on Unix. **Default:** `false`.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) In milliseconds the maximum amount of time the process is allowed to run. **Default:** `undefined`.
* Returns: [<ChildProcess>](child_process#class-childprocess)
The `child_process.fork()` method is a special case of [`child_process.spawn()`](#child_processspawncommand-args-options) used specifically to spawn new Node.js processes. Like [`child_process.spawn()`](#child_processspawncommand-args-options), a [`ChildProcess`](#class-childprocess) object is returned. The returned [`ChildProcess`](#class-childprocess) will have an additional communication channel built-in that allows messages to be passed back and forth between the parent and child. See [`subprocess.send()`](#subprocesssendmessage-sendhandle-options-callback) for details.
Keep in mind that spawned Node.js child processes are independent of the parent with exception of the IPC communication channel that is established between the two. Each process has its own memory, with their own V8 instances. Because of the additional resource allocations required, spawning a large number of child Node.js processes is not recommended.
By default, `child_process.fork()` will spawn new Node.js instances using the [`process.execPath`](process#processexecpath) of the parent process. The `execPath` property in the `options` object allows for an alternative execution path to be used.
Node.js processes launched with a custom `execPath` will communicate with the parent process using the file descriptor (fd) identified using the environment variable `NODE_CHANNEL_FD` on the child process.
Unlike the [`fork(2)`](http://man7.org/linux/man-pages/man2/fork.2.html) POSIX system call, `child_process.fork()` does not clone the current process.
The `shell` option available in [`child_process.spawn()`](#child_processspawncommand-args-options) is not supported by `child_process.fork()` and will be ignored if set.
If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.kill()` on the child process except the error passed to the callback will be an `AbortError`:
```
if (process.argv[2] === 'child') {
setTimeout(() => {
console.log(`Hello from ${process.argv[2]}!`);
}, 1_000);
} else {
const { fork } = require('node:child_process');
const controller = new AbortController();
const { signal } = controller;
const child = fork(__filename, ['child'], { signal });
child.on('error', (err) => {
// This will be called with err being an AbortError if the controller aborts
});
controller.abort(); // Stops the child process
}
```
####
`child_process.spawn(command[, args][, options])`
History
| Version | Changes |
| --- | --- |
| v16.4.0, v14.18.0 | The `cwd` option can be a WHATWG `URL` object using `file:` protocol. |
| v15.13.0, v14.18.0 | timeout was added. |
| v15.11.0, v14.18.0 | killSignal for AbortSignal was added. |
| v15.5.0, v14.17.0 | AbortSignal support was added. |
| v13.2.0, v12.16.0 | The `serialization` option is supported now. |
| v8.8.0 | The `windowsHide` option is supported now. |
| v6.4.0 | The `argv0` option is supported now. |
| v5.7.0 | The `shell` option is supported now. |
| v0.1.90 | Added in: v0.1.90 |
* `command` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The command to run.
* `args` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) List of string arguments.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cwd` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Current working directory of the child process.
+ `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Environment key-value pairs. **Default:** `process.env`.
+ `argv0` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Explicitly set the value of `argv[0]` sent to the child process. This will be set to `command` if not specified.
+ `stdio` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Child's stdio configuration (see [`options.stdio`](#optionsstdio)).
+ `detached` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Prepare child to run independently of its parent process. Specific behavior depends on the platform, see [`options.detached`](#optionsdetached)).
+ `uid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the user identity of the process (see [`setuid(2)`](http://man7.org/linux/man-pages/man2/setuid.2.html)).
+ `gid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the group identity of the process (see [`setgid(2)`](http://man7.org/linux/man-pages/man2/setgid.2.html)).
+ `serialization` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specify the kind of serialization used for sending messages between processes. Possible values are `'json'` and `'advanced'`. See [Advanced serialization](#advanced-serialization) for more details. **Default:** `'json'`.
+ `shell` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See [Shell requirements](#shell-requirements) and [Default Windows shell](#default-windows-shell). **Default:** `false` (no shell).
+ `windowsVerbatimArguments` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) No quoting or escaping of arguments is done on Windows. Ignored on Unix. This is set to `true` automatically when `shell` is specified and is CMD. **Default:** `false`.
+ `windowsHide` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows aborting the child process using an AbortSignal.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) In milliseconds the maximum amount of time the process is allowed to run. **Default:** `undefined`.
+ `killSignal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The signal value to be used when the spawned process will be killed by timeout or abort signal. **Default:** `'SIGTERM'`.
* Returns: [<ChildProcess>](child_process#class-childprocess)
The `child_process.spawn()` method spawns a new process using the given `command`, with command-line arguments in `args`. If omitted, `args` defaults to an empty array.
**If the `shell` option is enabled, do not pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.**
A third argument may be used to specify additional options, with these defaults:
```
const defaults = {
cwd: undefined,
env: process.env
};
```
Use `cwd` to specify the working directory from which the process is spawned. If not given, the default is to inherit the current working directory. If given, but the path does not exist, the child process emits an `ENOENT` error and exits immediately. `ENOENT` is also emitted when the command does not exist.
Use `env` to specify environment variables that will be visible to the new process, the default is [`process.env`](process#processenv).
`undefined` values in `env` will be ignored.
Example of running `ls -lh /usr`, capturing `stdout`, `stderr`, and the exit code:
```
const { spawn } = require('node:child_process');
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.error(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
```
Example: A very elaborate way to run `ps ax | grep ssh`
```
const { spawn } = require('node:child_process');
const ps = spawn('ps', ['ax']);
const grep = spawn('grep', ['ssh']);
ps.stdout.on('data', (data) => {
grep.stdin.write(data);
});
ps.stderr.on('data', (data) => {
console.error(`ps stderr: ${data}`);
});
ps.on('close', (code) => {
if (code !== 0) {
console.log(`ps process exited with code ${code}`);
}
grep.stdin.end();
});
grep.stdout.on('data', (data) => {
console.log(data.toString());
});
grep.stderr.on('data', (data) => {
console.error(`grep stderr: ${data}`);
});
grep.on('close', (code) => {
if (code !== 0) {
console.log(`grep process exited with code ${code}`);
}
});
```
Example of checking for failed `spawn`:
```
const { spawn } = require('node:child_process');
const subprocess = spawn('bad_command');
subprocess.on('error', (err) => {
console.error('Failed to start subprocess.');
});
```
Certain platforms (macOS, Linux) will use the value of `argv[0]` for the process title while others (Windows, SunOS) will use `command`.
Node.js overwrites `argv[0]` with `process.execPath` on startup, so `process.argv[0]` in a Node.js child process will not match the `argv0` parameter passed to `spawn` from the parent. Retrieve it with the `process.argv0` property instead.
If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.kill()` on the child process except the error passed to the callback will be an `AbortError`:
```
const { spawn } = require('node:child_process');
const controller = new AbortController();
const { signal } = controller;
const grep = spawn('grep', ['ssh'], { signal });
grep.on('error', (err) => {
// This will be called with err being an AbortError if the controller aborts
});
controller.abort(); // Stops the child process
```
#####
`options.detached`
Added in: v0.7.10 On Windows, setting `options.detached` to `true` makes it possible for the child process to continue running after the parent exits. The child will have its own console window. Once enabled for a child process, it cannot be disabled.
On non-Windows platforms, if `options.detached` is set to `true`, the child process will be made the leader of a new process group and session. Child processes may continue running after the parent exits regardless of whether they are detached or not. See [`setsid(2)`](http://man7.org/linux/man-pages/man2/setsid.2.html) for more information.
By default, the parent will wait for the detached child to exit. To prevent the parent from waiting for a given `subprocess` to exit, use the `subprocess.unref()` method. Doing so will cause the parent's event loop to not include the child in its reference count, allowing the parent to exit independently of the child, unless there is an established IPC channel between the child and the parent.
When using the `detached` option to start a long-running process, the process will not stay running in the background after the parent exits unless it is provided with a `stdio` configuration that is not connected to the parent. If the parent's `stdio` is inherited, the child will remain attached to the controlling terminal.
Example of a long-running process, by detaching and also ignoring its parent `stdio` file descriptors, in order to ignore the parent's termination:
```
const { spawn } = require('node:child_process');
const subprocess = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: 'ignore'
});
subprocess.unref();
```
Alternatively one can redirect the child process' output into files:
```
const fs = require('node:fs');
const { spawn } = require('node:child_process');
const out = fs.openSync('./out.log', 'a');
const err = fs.openSync('./out.log', 'a');
const subprocess = spawn('prg', [], {
detached: true,
stdio: [ 'ignore', out, err ]
});
subprocess.unref();
```
#####
`options.stdio`
History
| Version | Changes |
| --- | --- |
| v15.6.0, v14.18.0 | Added the `overlapped` stdio flag. |
| v3.3.1 | The value `0` is now accepted as a file descriptor. |
| v0.7.10 | Added in: v0.7.10 |
The `options.stdio` option is used to configure the pipes that are established between the parent and child process. By default, the child's stdin, stdout, and stderr are redirected to corresponding [`subprocess.stdin`](#subprocessstdin), [`subprocess.stdout`](#subprocessstdout), and [`subprocess.stderr`](#subprocessstderr) streams on the [`ChildProcess`](#class-childprocess) object. This is equivalent to setting the `options.stdio` equal to `['pipe', 'pipe', 'pipe']`.
For convenience, `options.stdio` may be one of the following strings:
* `'pipe'`: equivalent to `['pipe', 'pipe', 'pipe']` (the default)
* `'overlapped'`: equivalent to `['overlapped', 'overlapped', 'overlapped']`
* `'ignore'`: equivalent to `['ignore', 'ignore', 'ignore']`
* `'inherit'`: equivalent to `['inherit', 'inherit', 'inherit']` or `[0, 1, 2]`
Otherwise, the value of `options.stdio` is an array where each index corresponds to an fd in the child. The fds 0, 1, and 2 correspond to stdin, stdout, and stderr, respectively. Additional fds can be specified to create additional pipes between the parent and child. The value is one of the following:
1. `'pipe'`: Create a pipe between the child process and the parent process. The parent end of the pipe is exposed to the parent as a property on the `child_process` object as [`subprocess.stdio[fd]`](#subprocessstdio). Pipes created for fds 0, 1, and 2 are also available as [`subprocess.stdin`](#subprocessstdin), [`subprocess.stdout`](#subprocessstdout) and [`subprocess.stderr`](#subprocessstderr), respectively. These are not actual Unix pipes and therefore the child process can not use them by their descriptor files, e.g. `/dev/fd/2` or `/dev/stdout`.
2. `'overlapped'`: Same as `'pipe'` except that the `FILE_FLAG_OVERLAPPED` flag is set on the handle. This is necessary for overlapped I/O on the child process's stdio handles. See the [docs](https://docs.microsoft.com/en-us/windows/win32/fileio/synchronous-and-asynchronous-i-o) for more details. This is exactly the same as `'pipe'` on non-Windows systems.
3. `'ipc'`: Create an IPC channel for passing messages/file descriptors between parent and child. A [`ChildProcess`](#class-childprocess) may have at most one IPC stdio file descriptor. Setting this option enables the [`subprocess.send()`](#subprocesssendmessage-sendhandle-options-callback) method. If the child is a Node.js process, the presence of an IPC channel will enable [`process.send()`](process#processsendmessage-sendhandle-options-callback) and [`process.disconnect()`](process#processdisconnect) methods, as well as [`'disconnect'`](process#event-disconnect) and [`'message'`](process#event-message) events within the child.
Accessing the IPC channel fd in any way other than [`process.send()`](process#processsendmessage-sendhandle-options-callback) or using the IPC channel with a child process that is not a Node.js instance is not supported.
4. `'ignore'`: Instructs Node.js to ignore the fd in the child. While Node.js will always open fds 0, 1, and 2 for the processes it spawns, setting the fd to `'ignore'` will cause Node.js to open `/dev/null` and attach it to the child's fd.
5. `'inherit'`: Pass through the corresponding stdio stream to/from the parent process. In the first three positions, this is equivalent to `process.stdin`, `process.stdout`, and `process.stderr`, respectively. In any other position, equivalent to `'ignore'`.
6. [<Stream>](stream#stream) object: Share a readable or writable stream that refers to a tty, file, socket, or a pipe with the child process. The stream's underlying file descriptor is duplicated in the child process to the fd that corresponds to the index in the `stdio` array. The stream must have an underlying descriptor (file streams do not until the `'open'` event has occurred).
7. Positive integer: The integer value is interpreted as a file descriptor that is open in the parent process. It is shared with the child process, similar to how [<Stream>](stream#stream) objects can be shared. Passing sockets is not supported on Windows.
8. `null`, `undefined`: Use default value. For stdio fds 0, 1, and 2 (in other words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the default is `'ignore'`.
```
const { spawn } = require('node:child_process');
// Child will use parent's stdios.
spawn('prg', [], { stdio: 'inherit' });
// Spawn child sharing only stderr.
spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] });
// Open an extra fd=4, to interact with programs presenting a
// startd-style interface.
spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });
```
*It is worth noting that when an IPC channel is established between the parent and child processes, and the child is a Node.js process, the child is launched with the IPC channel unreferenced (using `unref()`) until the child registers an event handler for the [`'disconnect'`](process#event-disconnect) event or the [`'message'`](process#event-message) event. This allows the child to exit normally without the process being held open by the open IPC channel.*
On Unix-like operating systems, the [`child_process.spawn()`](#child_processspawncommand-args-options) method performs memory operations synchronously before decoupling the event loop from the child. Applications with a large memory footprint may find frequent [`child_process.spawn()`](#child_processspawncommand-args-options) calls to be a bottleneck. For more information, see [V8 issue 7381](https://bugs.chromium.org/p/v8/issues/detail?id=7381).
See also: [`child_process.exec()`](#child_processexeccommand-options-callback) and [`child_process.fork()`](#child_processforkmodulepath-args-options).
### Synchronous process creation
The [`child_process.spawnSync()`](#child_processspawnsynccommand-args-options), [`child_process.execSync()`](#child_processexecsynccommand-options), and [`child_process.execFileSync()`](#child_processexecfilesyncfile-args-options) methods are synchronous and will block the Node.js event loop, pausing execution of any additional code until the spawned process exits.
Blocking calls like these are mostly useful for simplifying general-purpose scripting tasks and for simplifying the loading/processing of application configuration at startup.
####
`child_process.execFileSync(file[, args][, options])`
History
| Version | Changes |
| --- | --- |
| v16.4.0, v14.18.0 | The `cwd` option can be a WHATWG `URL` object using `file:` protocol. |
| v10.10.0 | The `input` option can now be any `TypedArray` or a `DataView`. |
| v8.8.0 | The `windowsHide` option is supported now. |
| v8.0.0 | The `input` option can now be a `Uint8Array`. |
| v6.2.1, v4.5.0 | The `encoding` option can now explicitly be set to `buffer`. |
| v0.11.12 | Added in: v0.11.12 |
* `file` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name or path of the executable file to run.
* `args` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) List of string arguments.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cwd` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Current working directory of the child process.
+ `input` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The value which will be passed as stdin to the spawned process. Supplying this value will override `stdio[0]`.
+ `stdio` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) Child's stdio configuration. `stderr` by default will be output to the parent process' stderr unless `stdio` is specified. **Default:** `'pipe'`.
+ `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Environment key-value pairs. **Default:** `process.env`.
+ `uid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the user identity of the process (see [`setuid(2)`](http://man7.org/linux/man-pages/man2/setuid.2.html)).
+ `gid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the group identity of the process (see [`setgid(2)`](http://man7.org/linux/man-pages/man2/setgid.2.html)).
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) In milliseconds the maximum amount of time the process is allowed to run. **Default:** `undefined`.
+ `killSignal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The signal value to be used when the spawned process will be killed. **Default:** `'SIGTERM'`.
+ `maxBuffer` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated. See caveat at [`maxBuffer` and Unicode](#maxbuffer-and-unicode). **Default:** `1024 * 1024`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The encoding used for all stdio inputs and outputs. **Default:** `'buffer'`.
+ `windowsHide` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`.
+ `shell` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See [Shell requirements](#shell-requirements) and [Default Windows shell](#default-windows-shell). **Default:** `false` (no shell).
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The stdout from the command.
The `child_process.execFileSync()` method is generally identical to [`child_process.execFile()`](#child_processexecfilefile-args-options-callback) with the exception that the method will not return until the child process has fully closed. When a timeout has been encountered and `killSignal` is sent, the method won't return until the process has completely exited.
If the child process intercepts and handles the `SIGTERM` signal and does not exit, the parent process will still wait until the child process has exited.
If the process times out or has a non-zero exit code, this method will throw an [`Error`](errors#class-error) that will include the full result of the underlying [`child_process.spawnSync()`](#child_processspawnsynccommand-args-options).
**If the `shell` option is enabled, do not pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.**
####
`child_process.execSync(command[, options])`
History
| Version | Changes |
| --- | --- |
| v16.4.0, v14.18.0 | The `cwd` option can be a WHATWG `URL` object using `file:` protocol. |
| v10.10.0 | The `input` option can now be any `TypedArray` or a `DataView`. |
| v8.8.0 | The `windowsHide` option is supported now. |
| v8.0.0 | The `input` option can now be a `Uint8Array`. |
| v0.11.12 | Added in: v0.11.12 |
* `command` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The command to run.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cwd` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Current working directory of the child process.
+ `input` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The value which will be passed as stdin to the spawned process. Supplying this value will override `stdio[0]`.
+ `stdio` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) Child's stdio configuration. `stderr` by default will be output to the parent process' stderr unless `stdio` is specified. **Default:** `'pipe'`.
+ `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Environment key-value pairs. **Default:** `process.env`.
+ `shell` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Shell to execute the command with. See [Shell requirements](#shell-requirements) and [Default Windows shell](#default-windows-shell). **Default:** `'/bin/sh'` on Unix, `process.env.ComSpec` on Windows.
+ `uid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the user identity of the process. (See [`setuid(2)`](http://man7.org/linux/man-pages/man2/setuid.2.html)).
+ `gid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the group identity of the process. (See [`setgid(2)`](http://man7.org/linux/man-pages/man2/setgid.2.html)).
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) In milliseconds the maximum amount of time the process is allowed to run. **Default:** `undefined`.
+ `killSignal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The signal value to be used when the spawned process will be killed. **Default:** `'SIGTERM'`.
+ `maxBuffer` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated and any output is truncated. See caveat at [`maxBuffer` and Unicode](#maxbuffer-and-unicode). **Default:** `1024 * 1024`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The encoding used for all stdio inputs and outputs. **Default:** `'buffer'`.
+ `windowsHide` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The stdout from the command.
The `child_process.execSync()` method is generally identical to [`child_process.exec()`](#child_processexeccommand-options-callback) with the exception that the method will not return until the child process has fully closed. When a timeout has been encountered and `killSignal` is sent, the method won't return until the process has completely exited. If the child process intercepts and handles the `SIGTERM` signal and doesn't exit, the parent process will wait until the child process has exited.
If the process times out or has a non-zero exit code, this method will throw. The [`Error`](errors#class-error) object will contain the entire result from [`child_process.spawnSync()`](#child_processspawnsynccommand-args-options).
**Never pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.**
####
`child_process.spawnSync(command[, args][, options])`
History
| Version | Changes |
| --- | --- |
| v16.4.0, v14.18.0 | The `cwd` option can be a WHATWG `URL` object using `file:` protocol. |
| v10.10.0 | The `input` option can now be any `TypedArray` or a `DataView`. |
| v8.8.0 | The `windowsHide` option is supported now. |
| v8.0.0 | The `input` option can now be a `Uint8Array`. |
| v5.7.0 | The `shell` option is supported now. |
| v6.2.1, v4.5.0 | The `encoding` option can now explicitly be set to `buffer`. |
| v0.11.12 | Added in: v0.11.12 |
* `command` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The command to run.
* `args` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) List of string arguments.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cwd` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Current working directory of the child process.
+ `input` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The value which will be passed as stdin to the spawned process. Supplying this value will override `stdio[0]`.
+ `argv0` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Explicitly set the value of `argv[0]` sent to the child process. This will be set to `command` if not specified.
+ `stdio` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) Child's stdio configuration.
+ `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Environment key-value pairs. **Default:** `process.env`.
+ `uid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the user identity of the process (see [`setuid(2)`](http://man7.org/linux/man-pages/man2/setuid.2.html)).
+ `gid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the group identity of the process (see [`setgid(2)`](http://man7.org/linux/man-pages/man2/setgid.2.html)).
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) In milliseconds the maximum amount of time the process is allowed to run. **Default:** `undefined`.
+ `killSignal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The signal value to be used when the spawned process will be killed. **Default:** `'SIGTERM'`.
+ `maxBuffer` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated and any output is truncated. See caveat at [`maxBuffer` and Unicode](#maxbuffer-and-unicode). **Default:** `1024 * 1024`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The encoding used for all stdio inputs and outputs. **Default:** `'buffer'`.
+ `shell` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See [Shell requirements](#shell-requirements) and [Default Windows shell](#default-windows-shell). **Default:** `false` (no shell).
+ `windowsVerbatimArguments` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) No quoting or escaping of arguments is done on Windows. Ignored on Unix. This is set to `true` automatically when `shell` is specified and is CMD. **Default:** `false`.
+ `windowsHide` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`.
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `pid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Pid of the child process.
+ `output` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) Array of results from stdio output.
+ `stdout` [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The contents of `output[1]`.
+ `stderr` [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The contents of `output[2]`.
+ `status` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The exit code of the subprocess, or `null` if the subprocess terminated due to a signal.
+ `signal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The signal used to kill the subprocess, or `null` if the subprocess did not terminate due to a signal.
+ `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) The error object if the child process failed or timed out.
The `child_process.spawnSync()` method is generally identical to [`child_process.spawn()`](#child_processspawncommand-args-options) with the exception that the function will not return until the child process has fully closed. When a timeout has been encountered and `killSignal` is sent, the method won't return until the process has completely exited. If the process intercepts and handles the `SIGTERM` signal and doesn't exit, the parent process will wait until the child process has exited.
**If the `shell` option is enabled, do not pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.**
### Class: `ChildProcess`
Added in: v2.2.0 * Extends: [<EventEmitter>](events#class-eventemitter)
Instances of the `ChildProcess` represent spawned child processes.
Instances of `ChildProcess` are not intended to be created directly. Rather, use the [`child_process.spawn()`](#child_processspawncommand-args-options), [`child_process.exec()`](#child_processexeccommand-options-callback), [`child_process.execFile()`](#child_processexecfilefile-args-options-callback), or [`child_process.fork()`](#child_processforkmodulepath-args-options) methods to create instances of `ChildProcess`.
#### Event: `'close'`
Added in: v0.7.7 * `code` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The exit code if the child exited on its own.
* `signal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The signal by which the child process was terminated.
The `'close'` event is emitted after a process has ended *and* the stdio streams of a child process have been closed. This is distinct from the [`'exit'`](#event-exit) event, since multiple processes might share the same stdio streams. The `'close'` event will always emit after [`'exit'`](#event-exit) was already emitted, or [`'error'`](#event-error) if the child failed to spawn.
```
const { spawn } = require('node:child_process');
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process close all stdio with code ${code}`);
});
ls.on('exit', (code) => {
console.log(`child process exited with code ${code}`);
});
```
#### Event: `'disconnect'`
Added in: v0.7.2 The `'disconnect'` event is emitted after calling the [`subprocess.disconnect()`](#subprocessdisconnect) method in parent process or [`process.disconnect()`](process#processdisconnect) in child process. After disconnecting it is no longer possible to send or receive messages, and the [`subprocess.connected`](#subprocessconnected) property is `false`.
#### Event: `'error'`
* `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) The error.
The `'error'` event is emitted whenever:
1. The process could not be spawned, or
2. The process could not be killed, or
3. Sending a message to the child process failed.
The `'exit'` event may or may not fire after an error has occurred. When listening to both the `'exit'` and `'error'` events, guard against accidentally invoking handler functions multiple times.
See also [`subprocess.kill()`](#subprocesskillsignal) and [`subprocess.send()`](#subprocesssendmessage-sendhandle-options-callback).
#### Event: `'exit'`
Added in: v0.1.90 * `code` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The exit code if the child exited on its own.
* `signal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The signal by which the child process was terminated.
The `'exit'` event is emitted after the child process ends. If the process exited, `code` is the final exit code of the process, otherwise `null`. If the process terminated due to receipt of a signal, `signal` is the string name of the signal, otherwise `null`. One of the two will always be non-`null`.
When the `'exit'` event is triggered, child process stdio streams might still be open.
Node.js establishes signal handlers for `SIGINT` and `SIGTERM` and Node.js processes will not terminate immediately due to receipt of those signals. Rather, Node.js will perform a sequence of cleanup actions and then will re-raise the handled signal.
See [`waitpid(2)`](http://man7.org/linux/man-pages/man2/waitpid.2.html).
#### Event: `'message'`
Added in: v0.5.9 * `message` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A parsed JSON object or primitive value.
* `sendHandle` [<Handle>](net#serverlistenhandle-backlog-callback) A [`net.Socket`](net#class-netsocket) or [`net.Server`](net#class-netserver) object, or undefined.
The `'message'` event is triggered when a child process uses [`process.send()`](process#processsendmessage-sendhandle-options-callback) to send messages.
The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent.
If the `serialization` option was set to `'advanced'` used when spawning the child process, the `message` argument can contain data that JSON is not able to represent. See [Advanced serialization](#advanced-serialization) for more details.
#### Event: `'spawn'`
Added in: v15.1.0, v14.17.0 The `'spawn'` event is emitted once the child process has spawned successfully. If the child process does not spawn successfully, the `'spawn'` event is not emitted and the `'error'` event is emitted instead.
If emitted, the `'spawn'` event comes before all other events and before any data is received via `stdout` or `stderr`.
The `'spawn'` event will fire regardless of whether an error occurs **within** the spawned process. For example, if `bash some-command` spawns successfully, the `'spawn'` event will fire, though `bash` may fail to spawn `some-command`. This caveat also applies when using `{ shell: true }`.
####
`subprocess.channel`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | The object no longer accidentally exposes native C++ bindings. |
| v7.1.0 | Added in: v7.1.0 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A pipe representing the IPC channel to the child process.
The `subprocess.channel` property is a reference to the child's IPC channel. If no IPC channel exists, this property is `undefined`.
#####
`subprocess.channel.ref()`
Added in: v7.1.0 This method makes the IPC channel keep the event loop of the parent process running if `.unref()` has been called before.
#####
`subprocess.channel.unref()`
Added in: v7.1.0 This method makes the IPC channel not keep the event loop of the parent process running, and lets it finish even while the channel is open.
####
`subprocess.connected`
Added in: v0.7.2 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Set to `false` after `subprocess.disconnect()` is called.
The `subprocess.connected` property indicates whether it is still possible to send and receive messages from a child process. When `subprocess.connected` is `false`, it is no longer possible to send or receive messages.
####
`subprocess.disconnect()`
Added in: v0.7.2 Closes the IPC channel between parent and child, allowing the child to exit gracefully once there are no other connections keeping it alive. After calling this method the `subprocess.connected` and `process.connected` properties in both the parent and child (respectively) will be set to `false`, and it will be no longer possible to pass messages between the processes.
The `'disconnect'` event will be emitted when there are no messages in the process of being received. This will most often be triggered immediately after calling `subprocess.disconnect()`.
When the child process is a Node.js instance (e.g. spawned using [`child_process.fork()`](#child_processforkmodulepath-args-options)), the `process.disconnect()` method can be invoked within the child process to close the IPC channel as well.
####
`subprocess.exitCode`
* [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `subprocess.exitCode` property indicates the exit code of the child process. If the child process is still running, the field will be `null`.
####
`subprocess.kill([signal])`
Added in: v0.1.90 * `signal` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `subprocess.kill()` method sends a signal to the child process. If no argument is given, the process will be sent the `'SIGTERM'` signal. See [`signal(7)`](http://man7.org/linux/man-pages/man7/signal.7.html) for a list of available signals. This function returns `true` if [`kill(2)`](http://man7.org/linux/man-pages/man2/kill.2.html) succeeds, and `false` otherwise.
```
const { spawn } = require('node:child_process');
const grep = spawn('grep', ['ssh']);
grep.on('close', (code, signal) => {
console.log(
`child process terminated due to receipt of signal ${signal}`);
});
// Send SIGHUP to process.
grep.kill('SIGHUP');
```
The [`ChildProcess`](#class-childprocess) object may emit an [`'error'`](#event-error) event if the signal cannot be delivered. Sending a signal to a child process that has already exited is not an error but may have unforeseen consequences. Specifically, if the process identifier (PID) has been reassigned to another process, the signal will be delivered to that process instead which can have unexpected results.
While the function is called `kill`, the signal delivered to the child process may not actually terminate the process.
See [`kill(2)`](http://man7.org/linux/man-pages/man2/kill.2.html) for reference.
On Windows, where POSIX signals do not exist, the `signal` argument will be ignored, and the process will be killed forcefully and abruptly (similar to `'SIGKILL'`). See [Signal Events](process#signal-events) for more details.
On Linux, child processes of child processes will not be terminated when attempting to kill their parent. This is likely to happen when running a new process in a shell or with the use of the `shell` option of `ChildProcess`:
```
'use strict';
const { spawn } = require('node:child_process');
const subprocess = spawn(
'sh',
[
'-c',
`node -e "setInterval(() => {
console.log(process.pid, 'is alive')
}, 500);"`,
], {
stdio: ['inherit', 'inherit', 'inherit']
}
);
setTimeout(() => {
subprocess.kill(); // Does not terminate the Node.js process in the shell.
}, 2000);
```
####
`subprocess.killed`
Added in: v0.5.10 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Set to `true` after `subprocess.kill()` is used to successfully send a signal to the child process.
The `subprocess.killed` property indicates whether the child process successfully received a signal from `subprocess.kill()`. The `killed` property does not indicate that the child process has been terminated.
####
`subprocess.pid`
Added in: v0.1.90 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
Returns the process identifier (PID) of the child process. If the child process fails to spawn due to errors, then the value is `undefined` and `error` is emitted.
```
const { spawn } = require('node:child_process');
const grep = spawn('grep', ['ssh']);
console.log(`Spawned child pid: ${grep.pid}`);
grep.stdin.end();
```
####
`subprocess.ref()`
Added in: v0.7.10 Calling `subprocess.ref()` after making a call to `subprocess.unref()` will restore the removed reference count for the child process, forcing the parent to wait for the child to exit before exiting itself.
```
const { spawn } = require('node:child_process');
const subprocess = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: 'ignore'
});
subprocess.unref();
subprocess.ref();
```
####
`subprocess.send(message[, sendHandle[, options]][, callback])`
History
| Version | Changes |
| --- | --- |
| v5.8.0 | The `options` parameter, and the `keepOpen` option in particular, is supported now. |
| v5.0.0 | This method returns a boolean for flow control now. |
| v4.0.0 | The `callback` parameter is supported now. |
| v0.5.9 | Added in: v0.5.9 |
* `message` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `sendHandle` [<Handle>](net#serverlistenhandle-backlog-callback)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The `options` argument, if present, is an object used to parameterize the sending of certain types of handles. `options` supports the following properties:
+ `keepOpen` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) A value that can be used when passing instances of `net.Socket`. When `true`, the socket is kept open in the sending process. **Default:** `false`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
When an IPC channel has been established between the parent and child ( i.e. when using [`child_process.fork()`](#child_processforkmodulepath-args-options)), the `subprocess.send()` method can be used to send messages to the child process. When the child process is a Node.js instance, these messages can be received via the [`'message'`](process#event-message) event.
The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent.
For example, in the parent script:
```
const cp = require('node:child_process');
const n = cp.fork(`${__dirname}/sub.js`);
n.on('message', (m) => {
console.log('PARENT got message:', m);
});
// Causes the child to print: CHILD got message: { hello: 'world' }
n.send({ hello: 'world' });
```
And then the child script, `'sub.js'` might look like this:
```
process.on('message', (m) => {
console.log('CHILD got message:', m);
});
// Causes the parent to print: PARENT got message: { foo: 'bar', baz: null }
process.send({ foo: 'bar', baz: NaN });
```
Child Node.js processes will have a [`process.send()`](process#processsendmessage-sendhandle-options-callback) method of their own that allows the child to send messages back to the parent.
There is a special case when sending a `{cmd: 'NODE_foo'}` message. Messages containing a `NODE_` prefix in the `cmd` property are reserved for use within Node.js core and will not be emitted in the child's [`'message'`](process#event-message) event. Rather, such messages are emitted using the `'internalMessage'` event and are consumed internally by Node.js. Applications should avoid using such messages or listening for `'internalMessage'` events as it is subject to change without notice.
The optional `sendHandle` argument that may be passed to `subprocess.send()` is for passing a TCP server or socket object to the child process. The child will receive the object as the second argument passed to the callback function registered on the [`'message'`](process#event-message) event. Any data that is received and buffered in the socket will not be sent to the child.
The optional `callback` is a function that is invoked after the message is sent but before the child may have received it. The function is called with a single argument: `null` on success, or an [`Error`](errors#class-error) object on failure.
If no `callback` function is provided and the message cannot be sent, an `'error'` event will be emitted by the [`ChildProcess`](#class-childprocess) object. This can happen, for instance, when the child process has already exited.
`subprocess.send()` will return `false` if the channel has closed or when the backlog of unsent messages exceeds a threshold that makes it unwise to send more. Otherwise, the method returns `true`. The `callback` function can be used to implement flow control.
##### Example: sending a server object
The `sendHandle` argument can be used, for instance, to pass the handle of a TCP server object to the child process as illustrated in the example below:
```
const subprocess = require('node:child_process').fork('subprocess.js');
// Open up the server object and send the handle.
const server = require('node:net').createServer();
server.on('connection', (socket) => {
socket.end('handled by parent');
});
server.listen(1337, () => {
subprocess.send('server', server);
});
```
The child would then receive the server object as:
```
process.on('message', (m, server) => {
if (m === 'server') {
server.on('connection', (socket) => {
socket.end('handled by child');
});
}
});
```
Once the server is now shared between the parent and child, some connections can be handled by the parent and some by the child.
While the example above uses a server created using the `node:net` module, `node:dgram` module servers use exactly the same workflow with the exceptions of listening on a `'message'` event instead of `'connection'` and using `server.bind()` instead of `server.listen()`. This is, however, only supported on Unix platforms.
##### Example: sending a socket object
Similarly, the `sendHandler` argument can be used to pass the handle of a socket to the child process. The example below spawns two children that each handle connections with "normal" or "special" priority:
```
const { fork } = require('node:child_process');
const normal = fork('subprocess.js', ['normal']);
const special = fork('subprocess.js', ['special']);
// Open up the server and send sockets to child. Use pauseOnConnect to prevent
// the sockets from being read before they are sent to the child process.
const server = require('node:net').createServer({ pauseOnConnect: true });
server.on('connection', (socket) => {
// If this is special priority...
if (socket.remoteAddress === '74.125.127.100') {
special.send('socket', socket);
return;
}
// This is normal priority.
normal.send('socket', socket);
});
server.listen(1337);
```
The `subprocess.js` would receive the socket handle as the second argument passed to the event callback function:
```
process.on('message', (m, socket) => {
if (m === 'socket') {
if (socket) {
// Check that the client socket exists.
// It is possible for the socket to be closed between the time it is
// sent and the time it is received in the child process.
socket.end(`Request handled with ${process.argv[2]} priority`);
}
}
});
```
Do not use `.maxConnections` on a socket that has been passed to a subprocess. The parent cannot track when the socket is destroyed.
Any `'message'` handlers in the subprocess should verify that `socket` exists, as the connection may have been closed during the time it takes to send the connection to the child.
####
`subprocess.signalCode`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
The `subprocess.signalCode` property indicates the signal received by the child process if any, else `null`.
####
`subprocess.spawnargs`
* [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)
The `subprocess.spawnargs` property represents the full list of command-line arguments the child process was launched with.
####
`subprocess.spawnfile`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `subprocess.spawnfile` property indicates the executable file name of the child process that is launched.
For [`child_process.fork()`](#child_processforkmodulepath-args-options), its value will be equal to [`process.execPath`](process#processexecpath). For [`child_process.spawn()`](#child_processspawncommand-args-options), its value will be the name of the executable file. For [`child_process.exec()`](#child_processexeccommand-options-callback), its value will be the name of the shell in which the child process is launched.
####
`subprocess.stderr`
Added in: v0.1.90 * [<stream.Readable>](stream#class-streamreadable) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
A `Readable Stream` that represents the child process's `stderr`.
If the child was spawned with `stdio[2]` set to anything other than `'pipe'`, then this will be `null`.
`subprocess.stderr` is an alias for `subprocess.stdio[2]`. Both properties will refer to the same value.
The `subprocess.stderr` property can be `null` or `undefined` if the child process could not be successfully spawned.
####
`subprocess.stdin`
Added in: v0.1.90 * [<stream.Writable>](stream#class-streamwritable) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
A `Writable Stream` that represents the child process's `stdin`.
If a child process waits to read all of its input, the child will not continue until this stream has been closed via `end()`.
If the child was spawned with `stdio[0]` set to anything other than `'pipe'`, then this will be `null`.
`subprocess.stdin` is an alias for `subprocess.stdio[0]`. Both properties will refer to the same value.
The `subprocess.stdin` property can be `null` or `undefined` if the child process could not be successfully spawned.
####
`subprocess.stdio`
Added in: v0.7.10 * [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)
A sparse array of pipes to the child process, corresponding with positions in the [`stdio`](#optionsstdio) option passed to [`child_process.spawn()`](#child_processspawncommand-args-options) that have been set to the value `'pipe'`. `subprocess.stdio[0]`, `subprocess.stdio[1]`, and `subprocess.stdio[2]` are also available as `subprocess.stdin`, `subprocess.stdout`, and `subprocess.stderr`, respectively.
In the following example, only the child's fd `1` (stdout) is configured as a pipe, so only the parent's `subprocess.stdio[1]` is a stream, all other values in the array are `null`.
```
const assert = require('node:assert');
const fs = require('node:fs');
const child_process = require('node:child_process');
const subprocess = child_process.spawn('ls', {
stdio: [
0, // Use parent's stdin for child.
'pipe', // Pipe child's stdout to parent.
fs.openSync('err.out', 'w'), // Direct child's stderr to a file.
]
});
assert.strictEqual(subprocess.stdio[0], null);
assert.strictEqual(subprocess.stdio[0], subprocess.stdin);
assert(subprocess.stdout);
assert.strictEqual(subprocess.stdio[1], subprocess.stdout);
assert.strictEqual(subprocess.stdio[2], null);
assert.strictEqual(subprocess.stdio[2], subprocess.stderr);
```
The `subprocess.stdio` property can be `undefined` if the child process could not be successfully spawned.
####
`subprocess.stdout`
Added in: v0.1.90 * [<stream.Readable>](stream#class-streamreadable) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
A `Readable Stream` that represents the child process's `stdout`.
If the child was spawned with `stdio[1]` set to anything other than `'pipe'`, then this will be `null`.
`subprocess.stdout` is an alias for `subprocess.stdio[1]`. Both properties will refer to the same value.
```
const { spawn } = require('node:child_process');
const subprocess = spawn('ls');
subprocess.stdout.on('data', (data) => {
console.log(`Received chunk ${data}`);
});
```
The `subprocess.stdout` property can be `null` or `undefined` if the child process could not be successfully spawned.
####
`subprocess.unref()`
Added in: v0.7.10 By default, the parent will wait for the detached child to exit. To prevent the parent from waiting for a given `subprocess` to exit, use the `subprocess.unref()` method. Doing so will cause the parent's event loop to not include the child in its reference count, allowing the parent to exit independently of the child, unless there is an established IPC channel between the child and the parent.
```
const { spawn } = require('node:child_process');
const subprocess = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: 'ignore'
});
subprocess.unref();
```
###
`maxBuffer` and Unicode
The `maxBuffer` option specifies the largest number of bytes allowed on `stdout` or `stderr`. If this value is exceeded, then the child process is terminated. This impacts output that includes multibyte character encodings such as UTF-8 or UTF-16. For instance, `console.log('中文测试')` will send 13 UTF-8 encoded bytes to `stdout` although there are only 4 characters.
### Shell requirements
The shell should understand the `-c` switch. If the shell is `'cmd.exe'`, it should understand the `/d /s /c` switches and command-line parsing should be compatible.
### Default Windows shell
Although Microsoft specifies `%COMSPEC%` must contain the path to `'cmd.exe'` in the root environment, child processes are not always subject to the same requirement. Thus, in `child_process` functions where a shell can be spawned, `'cmd.exe'` is used as a fallback if `process.env.ComSpec` is unavailable.
### Advanced serialization
Added in: v13.2.0, v12.16.0 Child processes support a serialization mechanism for IPC that is based on the [serialization API of the `node:v8` module](v8#serialization-api), based on the [HTML structured clone algorithm](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm). This is generally more powerful and supports more built-in JavaScript object types, such as `BigInt`, `Map` and `Set`, `ArrayBuffer` and `TypedArray`, `Buffer`, `Error`, `RegExp` etc.
However, this format is not a full superset of JSON, and e.g. properties set on objects of such built-in types will not be passed on through the serialization step. Additionally, performance may not be equivalent to that of JSON, depending on the structure of the passed data. Therefore, this feature requires opting in by setting the `serialization` option to `'advanced'` when calling [`child_process.spawn()`](#child_processspawncommand-args-options) or [`child_process.fork()`](#child_processforkmodulepath-args-options).
| programming_docs |
node None UDP/datagram sockets
--------------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/dgram.js](https://github.com/nodejs/node/blob/v19.0.1/lib/dgram.js)
The `node:dgram` module provides an implementation of UDP datagram sockets.
MJS modules
```
import dgram from 'node:dgram';
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// Prints: server listening 0.0.0.0:41234
```
CJS modules
```
const dgram = require('node:dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// Prints: server listening 0.0.0.0:41234
```
### Class: `dgram.Socket`
Added in: v0.1.99 * Extends: [<EventEmitter>](events#class-eventemitter)
Encapsulates the datagram functionality.
New instances of `dgram.Socket` are created using [`dgram.createSocket()`](#dgramcreatesocketoptions-callback). The `new` keyword is not to be used to create `dgram.Socket` instances.
#### Event: `'close'`
Added in: v0.1.99 The `'close'` event is emitted after a socket is closed with [`close()`](#socketclosecallback). Once triggered, no new `'message'` events will be emitted on this socket.
#### Event: `'connect'`
Added in: v12.0.0 The `'connect'` event is emitted after a socket is associated to a remote address as a result of a successful [`connect()`](#socketconnectport-address-callback) call.
#### Event: `'error'`
Added in: v0.1.99 * `exception` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
The `'error'` event is emitted whenever any error occurs. The event handler function is passed a single `Error` object.
#### Event: `'listening'`
Added in: v0.1.99 The `'listening'` event is emitted once the `dgram.Socket` is addressable and can receive data. This happens either explicitly with `socket.bind()` or implicitly the first time data is sent using `socket.send()`. Until the `dgram.Socket` is listening, the underlying system resources do not exist and calls such as `socket.address()` and `socket.setTTL()` will fail.
#### Event: `'message'`
History
| Version | Changes |
| --- | --- |
| v18.4.0 | The `family` property now returns a string instead of a number. |
| v18.0.0 | The `family` property now returns a number instead of a string. |
| v0.1.99 | Added in: v0.1.99 |
The `'message'` event is emitted when a new datagram is available on a socket. The event handler function is passed two arguments: `msg` and `rinfo`.
* `msg` [<Buffer>](buffer#class-buffer) The message.
* `rinfo` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Remote address information.
+ `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The sender address.
+ `family` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The address family (`'IPv4'` or `'IPv6'`).
+ `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The sender port.
+ `size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The message size.
If the source address of the incoming packet is an IPv6 link-local address, the interface name is added to the `address`. For example, a packet received on the `en0` interface might have the address field set to `'fe80::2618:1234:ab11:3b9c%en0'`, where `'%en0'` is the interface name as a zone ID suffix.
####
`socket.addMembership(multicastAddress[, multicastInterface])`
Added in: v0.6.9 * `multicastAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `multicastInterface` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Tells the kernel to join a multicast group at the given `multicastAddress` and `multicastInterface` using the `IP_ADD_MEMBERSHIP` socket option. If the `multicastInterface` argument is not specified, the operating system will choose one interface and will add membership to it. To add membership to every available interface, call `addMembership` multiple times, once per interface.
When called on an unbound socket, this method will implicitly bind to a random port, listening on all interfaces.
When sharing a UDP socket across multiple `cluster` workers, the `socket.addMembership()` function must be called only once or an `EADDRINUSE` error will occur:
MJS modules
```
import cluster from 'node:cluster';
import dgram from 'node:dgram';
if (cluster.isPrimary) {
cluster.fork(); // Works ok.
cluster.fork(); // Fails with EADDRINUSE.
} else {
const s = dgram.createSocket('udp4');
s.bind(1234, () => {
s.addMembership('224.0.0.114');
});
}
```
CJS modules
```
const cluster = require('node:cluster');
const dgram = require('node:dgram');
if (cluster.isPrimary) {
cluster.fork(); // Works ok.
cluster.fork(); // Fails with EADDRINUSE.
} else {
const s = dgram.createSocket('udp4');
s.bind(1234, () => {
s.addMembership('224.0.0.114');
});
}
```
####
`socket.addSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])`
Added in: v13.1.0, v12.16.0 * `sourceAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `groupAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `multicastInterface` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Tells the kernel to join a source-specific multicast channel at the given `sourceAddress` and `groupAddress`, using the `multicastInterface` with the `IP_ADD_SOURCE_MEMBERSHIP` socket option. If the `multicastInterface` argument is not specified, the operating system will choose one interface and will add membership to it. To add membership to every available interface, call `socket.addSourceSpecificMembership()` multiple times, once per interface.
When called on an unbound socket, this method will implicitly bind to a random port, listening on all interfaces.
####
`socket.address()`
Added in: v0.1.99 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns an object containing the address information for a socket. For UDP sockets, this object will contain `address`, `family`, and `port` properties.
This method throws `EBADF` if called on an unbound socket.
####
`socket.bind([port][, address][, callback])`
History
| Version | Changes |
| --- | --- |
| v0.9.1 | The method was changed to an asynchronous execution model. Legacy code would need to be changed to pass a callback function to the method call. |
| v0.1.99 | Added in: v0.1.99 |
* `port` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) with no parameters. Called when binding is complete.
For UDP sockets, causes the `dgram.Socket` to listen for datagram messages on a named `port` and optional `address`. If `port` is not specified or is `0`, the operating system will attempt to bind to a random port. If `address` is not specified, the operating system will attempt to listen on all addresses. Once binding is complete, a `'listening'` event is emitted and the optional `callback` function is called.
Specifying both a `'listening'` event listener and passing a `callback` to the `socket.bind()` method is not harmful but not very useful.
A bound datagram socket keeps the Node.js process running to receive datagram messages.
If binding fails, an `'error'` event is generated. In rare case (e.g. attempting to bind with a closed socket), an [`Error`](errors#class-error) may be thrown.
Example of a UDP server listening on port 41234:
MJS modules
```
import dgram from 'node:dgram';
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// Prints: server listening 0.0.0.0:41234
```
CJS modules
```
const dgram = require('node:dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// Prints: server listening 0.0.0.0:41234
```
####
`socket.bind(options[, callback])`
Added in: v0.11.14 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Required. Supports the following properties:
+ `port` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `exclusive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
+ `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
For UDP sockets, causes the `dgram.Socket` to listen for datagram messages on a named `port` and optional `address` that are passed as properties of an `options` object passed as the first argument. If `port` is not specified or is `0`, the operating system will attempt to bind to a random port. If `address` is not specified, the operating system will attempt to listen on all addresses. Once binding is complete, a `'listening'` event is emitted and the optional `callback` function is called.
The `options` object may contain a `fd` property. When a `fd` greater than `0` is set, it will wrap around an existing socket with the given file descriptor. In this case, the properties of `port` and `address` will be ignored.
Specifying both a `'listening'` event listener and passing a `callback` to the `socket.bind()` method is not harmful but not very useful.
The `options` object may contain an additional `exclusive` property that is used when using `dgram.Socket` objects with the [`cluster`](cluster) module. When `exclusive` is set to `false` (the default), cluster workers will use the same underlying socket handle allowing connection handling duties to be shared. When `exclusive` is `true`, however, the handle is not shared and attempted port sharing results in an error.
A bound datagram socket keeps the Node.js process running to receive datagram messages.
If binding fails, an `'error'` event is generated. In rare case (e.g. attempting to bind with a closed socket), an [`Error`](errors#class-error) may be thrown.
An example socket listening on an exclusive port is shown below.
```
socket.bind({
address: 'localhost',
port: 8000,
exclusive: true
});
```
####
`socket.close([callback])`
Added in: v0.1.99 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called when the socket has been closed.
Close the underlying socket and stop listening for data on it. If a callback is provided, it is added as a listener for the [`'close'`](#event-close) event.
####
`socket.connect(port[, address][, callback])`
Added in: v12.0.0 * `port` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called when the connection is completed or on error.
Associates the `dgram.Socket` to a remote address and port. Every message sent by this handle is automatically sent to that destination. Also, the socket will only receive messages from that remote peer. Trying to call `connect()` on an already connected socket will result in an [`ERR_SOCKET_DGRAM_IS_CONNECTED`](errors#err_socket_dgram_is_connected) exception. If `address` is not provided, `'127.0.0.1'` (for `udp4` sockets) or `'::1'` (for `udp6` sockets) will be used by default. Once the connection is complete, a `'connect'` event is emitted and the optional `callback` function is called. In case of failure, the `callback` is called or, failing this, an `'error'` event is emitted.
####
`socket.disconnect()`
Added in: v12.0.0 A synchronous function that disassociates a connected `dgram.Socket` from its remote address. Trying to call `disconnect()` on an unbound or already disconnected socket will result in an [`ERR_SOCKET_DGRAM_NOT_CONNECTED`](errors#err_socket_dgram_not_connected) exception.
####
`socket.dropMembership(multicastAddress[, multicastInterface])`
Added in: v0.6.9 * `multicastAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `multicastInterface` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Instructs the kernel to leave a multicast group at `multicastAddress` using the `IP_DROP_MEMBERSHIP` socket option. This method is automatically called by the kernel when the socket is closed or the process terminates, so most apps will never have reason to call this.
If `multicastInterface` is not specified, the operating system will attempt to drop membership on all valid interfaces.
####
`socket.dropSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])`
Added in: v13.1.0, v12.16.0 * `sourceAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `groupAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `multicastInterface` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Instructs the kernel to leave a source-specific multicast channel at the given `sourceAddress` and `groupAddress` using the `IP_DROP_SOURCE_MEMBERSHIP` socket option. This method is automatically called by the kernel when the socket is closed or the process terminates, so most apps will never have reason to call this.
If `multicastInterface` is not specified, the operating system will attempt to drop membership on all valid interfaces.
####
`socket.getRecvBufferSize()`
Added in: v8.7.0 * Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the `SO_RCVBUF` socket receive buffer size in bytes.
This method throws [`ERR_SOCKET_BUFFER_SIZE`](errors#err_socket_buffer_size) if called on an unbound socket.
####
`socket.getSendBufferSize()`
Added in: v8.7.0 * Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the `SO_SNDBUF` socket send buffer size in bytes.
This method throws [`ERR_SOCKET_BUFFER_SIZE`](errors#err_socket_buffer_size) if called on an unbound socket.
####
`socket.getSendQueueSize()`
Added in: v18.8.0 * Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes queued for sending.
####
`socket.getSendQueueCount()`
Added in: v18.8.0 * Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of send requests currently in the queue awaiting to be processed.
####
`socket.ref()`
Added in: v0.9.1 * Returns: [<dgram.Socket>](dgram#class-dgramsocket)
By default, binding a socket will cause it to block the Node.js process from exiting as long as the socket is open. The `socket.unref()` method can be used to exclude the socket from the reference counting that keeps the Node.js process active. The `socket.ref()` method adds the socket back to the reference counting and restores the default behavior.
Calling `socket.ref()` multiples times will have no additional effect.
The `socket.ref()` method returns a reference to the socket so calls can be chained.
####
`socket.remoteAddress()`
Added in: v12.0.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns an object containing the `address`, `family`, and `port` of the remote endpoint. This method throws an [`ERR_SOCKET_DGRAM_NOT_CONNECTED`](errors#err_socket_dgram_not_connected) exception if the socket is not connected.
####
`socket.send(msg[, offset, length][, port][, address][, callback])`
History
| Version | Changes |
| --- | --- |
| v17.0.0 | The `address` parameter now only accepts a `string`, `null` or `undefined`. |
| v14.5.0, v12.19.0 | The `msg` parameter can now be any `TypedArray` or `DataView`. |
| v12.0.0 | Added support for sending data on connected sockets. |
| v8.0.0 | The `msg` parameter can be an `Uint8Array` now. |
| v8.0.0 | The `address` parameter is always optional now. |
| v6.0.0 | On success, `callback` will now be called with an `error` argument of `null` rather than `0`. |
| v5.7.0 | The `msg` parameter can be an array now. Also, the `offset` and `length` parameters are optional now. |
| v0.1.99 | Added in: v0.1.99 |
* `msg` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) Message to be sent.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Offset in the buffer where the message starts.
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes in the message.
* `port` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Destination port.
* `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Destination host name or IP address.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called when the message has been sent.
Broadcasts a datagram on the socket. For connectionless sockets, the destination `port` and `address` must be specified. Connected sockets, on the other hand, will use their associated remote endpoint, so the `port` and `address` arguments must not be set.
The `msg` argument contains the message to be sent. Depending on its type, different behavior can apply. If `msg` is a `Buffer`, any `TypedArray` or a `DataView`, the `offset` and `length` specify the offset within the `Buffer` where the message begins and the number of bytes in the message, respectively. If `msg` is a `String`, then it is automatically converted to a `Buffer` with `'utf8'` encoding. With messages that contain multi-byte characters, `offset` and `length` will be calculated with respect to [byte length](buffer#static-method-bufferbytelengthstring-encoding) and not the character position. If `msg` is an array, `offset` and `length` must not be specified.
The `address` argument is a string. If the value of `address` is a host name, DNS will be used to resolve the address of the host. If `address` is not provided or otherwise nullish, `'127.0.0.1'` (for `udp4` sockets) or `'::1'` (for `udp6` sockets) will be used by default.
If the socket has not been previously bound with a call to `bind`, the socket is assigned a random port number and is bound to the "all interfaces" address (`'0.0.0.0'` for `udp4` sockets, `'::0'` for `udp6` sockets.)
An optional `callback` function may be specified to as a way of reporting DNS errors or for determining when it is safe to reuse the `buf` object. DNS lookups delay the time to send for at least one tick of the Node.js event loop.
The only way to know for sure that the datagram has been sent is by using a `callback`. If an error occurs and a `callback` is given, the error will be passed as the first argument to the `callback`. If a `callback` is not given, the error is emitted as an `'error'` event on the `socket` object.
Offset and length are optional but both *must* be set if either are used. They are supported only when the first argument is a `Buffer`, a `TypedArray`, or a `DataView`.
This method throws [`ERR_SOCKET_BAD_PORT`](errors#err_socket_bad_port) if called on an unbound socket.
Example of sending a UDP packet to a port on `localhost`;
MJS modules
```
import dgram from 'node:dgram';
import { Buffer } from 'node:buffer';
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');
client.send(message, 41234, 'localhost', (err) => {
client.close();
});
```
CJS modules
```
const dgram = require('node:dgram');
const { Buffer } = require('node:buffer');
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');
client.send(message, 41234, 'localhost', (err) => {
client.close();
});
```
Example of sending a UDP packet composed of multiple buffers to a port on `127.0.0.1`;
MJS modules
```
import dgram from 'node:dgram';
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('Some ');
const buf2 = Buffer.from('bytes');
const client = dgram.createSocket('udp4');
client.send([buf1, buf2], 41234, (err) => {
client.close();
});
```
CJS modules
```
const dgram = require('node:dgram');
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('Some ');
const buf2 = Buffer.from('bytes');
const client = dgram.createSocket('udp4');
client.send([buf1, buf2], 41234, (err) => {
client.close();
});
```
Sending multiple buffers might be faster or slower depending on the application and operating system. Run benchmarks to determine the optimal strategy on a case-by-case basis. Generally speaking, however, sending multiple buffers is faster.
Example of sending a UDP packet using a socket connected to a port on `localhost`:
MJS modules
```
import dgram from 'node:dgram';
import { Buffer } from 'node:buffer';
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');
client.connect(41234, 'localhost', (err) => {
client.send(message, (err) => {
client.close();
});
});
```
CJS modules
```
const dgram = require('node:dgram');
const { Buffer } = require('node:buffer');
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');
client.connect(41234, 'localhost', (err) => {
client.send(message, (err) => {
client.close();
});
});
```
##### Note about UDP datagram size
The maximum size of an IPv4/v6 datagram depends on the `MTU` (Maximum Transmission Unit) and on the `Payload Length` field size.
* The `Payload Length` field is 16 bits wide, which means that a normal payload cannot exceed 64K octets including the internet header and data (65,507 bytes = 65,535 − 8 bytes UDP header − 20 bytes IP header); this is generally true for loopback interfaces, but such long datagram messages are impractical for most hosts and networks.
* The `MTU` is the largest size a given link layer technology can support for datagram messages. For any link, IPv4 mandates a minimum `MTU` of 68 octets, while the recommended `MTU` for IPv4 is 576 (typically recommended as the `MTU` for dial-up type applications), whether they arrive whole or in fragments.
For IPv6, the minimum `MTU` is 1280 octets. However, the mandatory minimum fragment reassembly buffer size is 1500 octets. The value of 68 octets is very small, since most current link layer technologies, like Ethernet, have a minimum `MTU` of 1500.
It is impossible to know in advance the MTU of each link through which a packet might travel. Sending a datagram greater than the receiver `MTU` will not work because the packet will get silently dropped without informing the source that the data did not reach its intended recipient.
####
`socket.setBroadcast(flag)`
Added in: v0.6.9 * `flag` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Sets or clears the `SO_BROADCAST` socket option. When set to `true`, UDP packets may be sent to a local interface's broadcast address.
This method throws `EBADF` if called on an unbound socket.
####
`socket.setMulticastInterface(multicastInterface)`
Added in: v8.6.0 * `multicastInterface` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
*All references to scope in this section are referring to [IPv6 Zone Indices](https://en.wikipedia.org/wiki/IPv6_address#Scoped_literal_IPv6_addresses), which are defined by [RFC 4007](https://tools.ietf.org/html/rfc4007). In string form, an IP with a scope index is written as `'IP%scope'` where scope is an interface name or interface number.*
Sets the default outgoing multicast interface of the socket to a chosen interface or back to system interface selection. The `multicastInterface` must be a valid string representation of an IP from the socket's family.
For IPv4 sockets, this should be the IP configured for the desired physical interface. All packets sent to multicast on the socket will be sent on the interface determined by the most recent successful use of this call.
For IPv6 sockets, `multicastInterface` should include a scope to indicate the interface as in the examples that follow. In IPv6, individual `send` calls can also use explicit scope in addresses, so only packets sent to a multicast address without specifying an explicit scope are affected by the most recent successful use of this call.
This method throws `EBADF` if called on an unbound socket.
##### Example: IPv6 outgoing multicast interface
On most systems, where scope format uses the interface name:
```
const socket = dgram.createSocket('udp6');
socket.bind(1234, () => {
socket.setMulticastInterface('::%eth1');
});
```
On Windows, where scope format uses an interface number:
```
const socket = dgram.createSocket('udp6');
socket.bind(1234, () => {
socket.setMulticastInterface('::%2');
});
```
##### Example: IPv4 outgoing multicast interface
All systems use an IP of the host on the desired physical interface:
```
const socket = dgram.createSocket('udp4');
socket.bind(1234, () => {
socket.setMulticastInterface('10.0.0.2');
});
```
##### Call results
A call on a socket that is not ready to send or no longer open may throw a *Not running* [`Error`](errors#class-error).
If `multicastInterface` can not be parsed into an IP then an *EINVAL* [`System Error`](errors#class-systemerror) is thrown.
On IPv4, if `multicastInterface` is a valid address but does not match any interface, or if the address does not match the family then a [`System Error`](errors#class-systemerror) such as `EADDRNOTAVAIL` or `EPROTONOSUP` is thrown.
On IPv6, most errors with specifying or omitting scope will result in the socket continuing to use (or returning to) the system's default interface selection.
A socket's address family's ANY address (IPv4 `'0.0.0.0'` or IPv6 `'::'`) can be used to return control of the sockets default outgoing interface to the system for future multicast packets.
####
`socket.setMulticastLoopback(flag)`
Added in: v0.3.8 * `flag` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Sets or clears the `IP_MULTICAST_LOOP` socket option. When set to `true`, multicast packets will also be received on the local interface.
This method throws `EBADF` if called on an unbound socket.
####
`socket.setMulticastTTL(ttl)`
Added in: v0.3.8 * `ttl` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Sets the `IP_MULTICAST_TTL` socket option. While TTL generally stands for "Time to Live", in this context it specifies the number of IP hops that a packet is allowed to travel through, specifically for multicast traffic. Each router or gateway that forwards a packet decrements the TTL. If the TTL is decremented to 0 by a router, it will not be forwarded.
The `ttl` argument may be between 0 and 255. The default on most systems is `1`.
This method throws `EBADF` if called on an unbound socket.
####
`socket.setRecvBufferSize(size)`
Added in: v8.7.0 * `size` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Sets the `SO_RCVBUF` socket option. Sets the maximum socket receive buffer in bytes.
This method throws [`ERR_SOCKET_BUFFER_SIZE`](errors#err_socket_buffer_size) if called on an unbound socket.
####
`socket.setSendBufferSize(size)`
Added in: v8.7.0 * `size` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Sets the `SO_SNDBUF` socket option. Sets the maximum socket send buffer in bytes.
This method throws [`ERR_SOCKET_BUFFER_SIZE`](errors#err_socket_buffer_size) if called on an unbound socket.
####
`socket.setTTL(ttl)`
Added in: v0.1.101 * `ttl` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Sets the `IP_TTL` socket option. While TTL generally stands for "Time to Live", in this context it specifies the number of IP hops that a packet is allowed to travel through. Each router or gateway that forwards a packet decrements the TTL. If the TTL is decremented to 0 by a router, it will not be forwarded. Changing TTL values is typically done for network probes or when multicasting.
The `ttl` argument may be between 1 and 255. The default on most systems is 64.
This method throws `EBADF` if called on an unbound socket.
####
`socket.unref()`
Added in: v0.9.1 * Returns: [<dgram.Socket>](dgram#class-dgramsocket)
By default, binding a socket will cause it to block the Node.js process from exiting as long as the socket is open. The `socket.unref()` method can be used to exclude the socket from the reference counting that keeps the Node.js process active, allowing the process to exit even if the socket is still listening.
Calling `socket.unref()` multiple times will have no addition effect.
The `socket.unref()` method returns a reference to the socket so calls can be chained.
###
`node:dgram` module functions
####
`dgram.createSocket(options[, callback])`
History
| Version | Changes |
| --- | --- |
| v15.8.0 | AbortSignal support was added. |
| v11.4.0 | The `ipv6Only` option is supported. |
| v8.7.0 | The `recvBufferSize` and `sendBufferSize` options are supported now. |
| v8.6.0 | The `lookup` option is supported. |
| v0.11.13 | Added in: v0.11.13 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Available options are:
+ `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The family of socket. Must be either `'udp4'` or `'udp6'`. Required.
+ `reuseAddr` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true` [`socket.bind()`](#socketbindport-address-callback) will reuse the address, even if another process has already bound a socket on it. **Default:** `false`.
+ `ipv6Only` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Setting `ipv6Only` to `true` will disable dual-stack support, i.e., binding to address `::` won't make `0.0.0.0` be bound. **Default:** `false`.
+ `recvBufferSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the `SO_RCVBUF` socket value.
+ `sendBufferSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the `SO_SNDBUF` socket value.
+ `lookup` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Custom lookup function. **Default:** [`dns.lookup()`](dns#dnslookuphostname-options-callback).
+ `signal` [<AbortSignal>](globals#class-abortsignal) An AbortSignal that may be used to close a socket.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Attached as a listener for `'message'` events. Optional.
* Returns: [<dgram.Socket>](dgram#class-dgramsocket)
Creates a `dgram.Socket` object. Once the socket is created, calling [`socket.bind()`](#socketbindport-address-callback) will instruct the socket to begin listening for datagram messages. When `address` and `port` are not passed to [`socket.bind()`](#socketbindport-address-callback) the method will bind the socket to the "all interfaces" address on a random port (it does the right thing for both `udp4` and `udp6` sockets). The bound address and port can be retrieved using [`socket.address().address`](#socketaddress) and [`socket.address().port`](#socketaddress).
If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.close()` on the socket:
```
const controller = new AbortController();
const { signal } = controller;
const server = dgram.createSocket({ type: 'udp4', signal });
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
// Later, when you want to close the server.
controller.abort();
```
####
`dgram.createSocket(type[, callback])`
Added in: v0.1.99 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'udp4'` or `'udp6'`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Attached as a listener to `'message'` events.
* Returns: [<dgram.Socket>](dgram#class-dgramsocket)
Creates a `dgram.Socket` object of the specified `type`.
Once the socket is created, calling [`socket.bind()`](#socketbindport-address-callback) will instruct the socket to begin listening for datagram messages. When `address` and `port` are not passed to [`socket.bind()`](#socketbindport-address-callback) the method will bind the socket to the "all interfaces" address on a random port (it does the right thing for both `udp4` and `udp6` sockets). The bound address and port can be retrieved using [`socket.address().address`](#socketaddress) and [`socket.address().port`](#socketaddress).
| programming_docs |
node None REPL
----
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/repl.js](https://github.com/nodejs/node/blob/v19.0.1/lib/repl.js)
The `node:repl` module provides a Read-Eval-Print-Loop (REPL) implementation that is available both as a standalone program or includible in other applications. It can be accessed using:
```
const repl = require('node:repl');
```
### Design and features
The `node:repl` module exports the [`repl.REPLServer`](#class-replserver) class. While running, instances of [`repl.REPLServer`](#class-replserver) will accept individual lines of user input, evaluate those according to a user-defined evaluation function, then output the result. Input and output may be from `stdin` and `stdout`, respectively, or may be connected to any Node.js <stream>.
Instances of [`repl.REPLServer`](#class-replserver) support automatic completion of inputs, completion preview, simplistic Emacs-style line editing, multi-line inputs, [ZSH](https://en.wikipedia.org/wiki/Z_shell)-like reverse-i-search, [ZSH](https://en.wikipedia.org/wiki/Z_shell)-like substring-based history search, ANSI-styled output, saving and restoring current REPL session state, error recovery, and customizable evaluation functions. Terminals that do not support ANSI styles and Emacs-style line editing automatically fall back to a limited feature set.
#### Commands and special keys
The following special commands are supported by all REPL instances:
* `.break`: When in the process of inputting a multi-line expression, enter the `.break` command (or press `Ctrl`+`C`) to abort further input or processing of that expression.
* `.clear`: Resets the REPL `context` to an empty object and clears any multi-line expression being input.
* `.exit`: Close the I/O stream, causing the REPL to exit.
* `.help`: Show this list of special commands.
* `.save`: Save the current REPL session to a file: `> .save ./file/to/save.js`
* `.load`: Load a file into the current REPL session. `> .load ./file/to/load.js`
* `.editor`: Enter editor mode (`Ctrl`+`D` to finish, `Ctrl`+`C` to cancel).
```
> .editor
// Entering editor mode (^D to finish, ^C to cancel)
function welcome(name) {
return `Hello ${name}!`;
}
welcome('Node.js User');
// ^D
'Hello Node.js User!'
>
```
The following key combinations in the REPL have these special effects:
* `Ctrl`+`C`: When pressed once, has the same effect as the `.break` command. When pressed twice on a blank line, has the same effect as the `.exit` command.
* `Ctrl`+`D`: Has the same effect as the `.exit` command.
* `Tab`: When pressed on a blank line, displays global and local (scope) variables. When pressed while entering other input, displays relevant autocompletion options.
For key bindings related to the reverse-i-search, see [`reverse-i-search`](#reverse-i-search). For all other key bindings, see [TTY keybindings](readline#tty-keybindings).
#### Default evaluation
By default, all instances of [`repl.REPLServer`](#class-replserver) use an evaluation function that evaluates JavaScript expressions and provides access to Node.js built-in modules. This default behavior can be overridden by passing in an alternative evaluation function when the [`repl.REPLServer`](#class-replserver) instance is created.
##### JavaScript expressions
The default evaluator supports direct evaluation of JavaScript expressions:
```
> 1 + 1
2
> const m = 2
undefined
> m + 1
3
```
Unless otherwise scoped within blocks or functions, variables declared either implicitly or using the `const`, `let`, or `var` keywords are declared at the global scope.
##### Global and local scope
The default evaluator provides access to any variables that exist in the global scope. It is possible to expose a variable to the REPL explicitly by assigning it to the `context` object associated with each `REPLServer`:
```
const repl = require('node:repl');
const msg = 'message';
repl.start('> ').context.m = msg;
```
Properties in the `context` object appear as local within the REPL:
```
$ node repl_test.js
> m
'message'
```
Context properties are not read-only by default. To specify read-only globals, context properties must be defined using `Object.defineProperty()`:
```
const repl = require('node:repl');
const msg = 'message';
const r = repl.start('> ');
Object.defineProperty(r.context, 'm', {
configurable: false,
enumerable: true,
value: msg
});
```
##### Accessing core Node.js modules
The default evaluator will automatically load Node.js core modules into the REPL environment when used. For instance, unless otherwise declared as a global or scoped variable, the input `fs` will be evaluated on-demand as `global.fs = require('node:fs')`.
```
> fs.createReadStream('./some/file');
```
##### Global uncaught exceptions
History
| Version | Changes |
| --- | --- |
| v12.3.0 | The `'uncaughtException'` event is from now on triggered if the repl is used as standalone program. |
The REPL uses the [`domain`](domain) module to catch all uncaught exceptions for that REPL session.
This use of the [`domain`](domain) module in the REPL has these side effects:
* Uncaught exceptions only emit the [`'uncaughtException'`](process#event-uncaughtexception) event in the standalone REPL. Adding a listener for this event in a REPL within another Node.js program results in [`ERR_INVALID_REPL_INPUT`](errors#err_invalid_repl_input).
```
const r = repl.start();
r.write('process.on("uncaughtException", () => console.log("Foobar"));\n');
// Output stream includes:
// TypeError [ERR_INVALID_REPL_INPUT]: Listeners for `uncaughtException`
// cannot be used in the REPL
r.close();
```
* Trying to use [`process.setUncaughtExceptionCaptureCallback()`](process#processsetuncaughtexceptioncapturecallbackfn) throws an [`ERR_DOMAIN_CANNOT_SET_UNCAUGHT_EXCEPTION_CAPTURE`](errors#err_domain_cannot_set_uncaught_exception_capture) error.
##### Assignment of the `_` (underscore) variable
History
| Version | Changes |
| --- | --- |
| v9.8.0 | Added `_error` support. |
The default evaluator will, by default, assign the result of the most recently evaluated expression to the special variable `_` (underscore). Explicitly setting `_` to a value will disable this behavior.
```
> [ 'a', 'b', 'c' ]
[ 'a', 'b', 'c' ]
> _.length
3
> _ += 1
Expression assignment to _ now disabled.
4
> 1 + 1
2
> _
4
```
Similarly, `_error` will refer to the last seen error, if there was any. Explicitly setting `_error` to a value will disable this behavior.
```
> throw new Error('foo');
Error: foo
> _error.message
'foo'
```
#####
`await` keyword
Support for the `await` keyword is enabled at the top level.
```
> await Promise.resolve(123)
123
> await Promise.reject(new Error('REPL await'))
Error: REPL await
at repl:1:45
> const timeout = util.promisify(setTimeout);
undefined
> const old = Date.now(); await timeout(1000); console.log(Date.now() - old);
1002
undefined
```
One known limitation of using the `await` keyword in the REPL is that it will invalidate the lexical scoping of the `const` and `let` keywords.
For example:
```
> const m = await Promise.resolve(123)
undefined
> m
123
> const m = await Promise.resolve(234)
undefined
> m
234
```
[`--no-experimental-repl-await`](cli#--no-experimental-repl-await) shall disable top-level await in REPL.
#### Reverse-i-search
Added in: v13.6.0, v12.17.0 The REPL supports bi-directional reverse-i-search similar to [ZSH](https://en.wikipedia.org/wiki/Z_shell). It is triggered with `Ctrl`+`R` to search backward and `Ctrl`+`S` to search forwards.
Duplicated history entries will be skipped.
Entries are accepted as soon as any key is pressed that doesn't correspond with the reverse search. Cancelling is possible by pressing `Esc` or `Ctrl`+`C`.
Changing the direction immediately searches for the next entry in the expected direction from the current position on.
#### Custom evaluation functions
When a new [`repl.REPLServer`](#class-replserver) is created, a custom evaluation function may be provided. This can be used, for instance, to implement fully customized REPL applications.
The following illustrates a hypothetical example of a REPL that performs translation of text from one language to another:
```
const repl = require('node:repl');
const { Translator } = require('translator');
const myTranslator = new Translator('en', 'fr');
function myEval(cmd, context, filename, callback) {
callback(null, myTranslator.translate(cmd));
}
repl.start({ prompt: '> ', eval: myEval });
```
##### Recoverable errors
At the REPL prompt, pressing `Enter` sends the current line of input to the `eval` function. In order to support multi-line input, the `eval` function can return an instance of `repl.Recoverable` to the provided callback function:
```
function myEval(cmd, context, filename, callback) {
let result;
try {
result = vm.runInThisContext(cmd);
} catch (e) {
if (isRecoverableError(e)) {
return callback(new repl.Recoverable(e));
}
}
callback(null, result);
}
function isRecoverableError(error) {
if (error.name === 'SyntaxError') {
return /^(Unexpected end of input|Unexpected token)/.test(error.message);
}
return false;
}
```
#### Customizing REPL output
By default, [`repl.REPLServer`](#class-replserver) instances format output using the [`util.inspect()`](util#utilinspectobject-options) method before writing the output to the provided `Writable` stream (`process.stdout` by default). The `showProxy` inspection option is set to true by default and the `colors` option is set to true depending on the REPL's `useColors` option.
The `useColors` boolean option can be specified at construction to instruct the default writer to use ANSI style codes to colorize the output from the `util.inspect()` method.
If the REPL is run as standalone program, it is also possible to change the REPL's [inspection defaults](util#utilinspectobject-options) from inside the REPL by using the `inspect.replDefaults` property which mirrors the `defaultOptions` from [`util.inspect()`](util#utilinspectobject-options).
```
> util.inspect.replDefaults.compact = false;
false
> [1]
[
1
]
>
```
To fully customize the output of a [`repl.REPLServer`](#class-replserver) instance pass in a new function for the `writer` option on construction. The following example, for instance, simply converts any input text to upper case:
```
const repl = require('node:repl');
const r = repl.start({ prompt: '> ', eval: myEval, writer: myWriter });
function myEval(cmd, context, filename, callback) {
callback(null, cmd);
}
function myWriter(output) {
return output.toUpperCase();
}
```
### Class: `REPLServer`
Added in: v0.1.91 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [`repl.start()`](#replstartoptions)
* Extends: [<readline.Interface>](readline#class-readlineinterface)
Instances of `repl.REPLServer` are created using the [`repl.start()`](#replstartoptions) method or directly using the JavaScript `new` keyword.
```
const repl = require('node:repl');
const options = { useColors: true };
const firstInstance = repl.start(options);
const secondInstance = new repl.REPLServer(options);
```
#### Event: `'exit'`
Added in: v0.7.7 The `'exit'` event is emitted when the REPL is exited either by receiving the `.exit` command as input, the user pressing `Ctrl`+`C` twice to signal `SIGINT`, or by pressing `Ctrl`+`D` to signal `'end'` on the input stream. The listener callback is invoked without any arguments.
```
replServer.on('exit', () => {
console.log('Received "exit" event from repl!');
process.exit();
});
```
#### Event: `'reset'`
Added in: v0.11.0 The `'reset'` event is emitted when the REPL's context is reset. This occurs whenever the `.clear` command is received as input *unless* the REPL is using the default evaluator and the `repl.REPLServer` instance was created with the `useGlobal` option set to `true`. The listener callback will be called with a reference to the `context` object as the only argument.
This can be used primarily to re-initialize REPL context to some pre-defined state:
```
const repl = require('node:repl');
function initializeContext(context) {
context.m = 'test';
}
const r = repl.start({ prompt: '> ' });
initializeContext(r.context);
r.on('reset', initializeContext);
```
When this code is executed, the global `'m'` variable can be modified but then reset to its initial value using the `.clear` command:
```
$ ./node example.js
> m
'test'
> m = 1
1
> m
1
> .clear
Clearing context...
> m
'test'
>
```
####
`replServer.defineCommand(keyword, cmd)`
Added in: v0.3.0 * `keyword` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The command keyword (*without* a leading `.` character).
* `cmd` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to invoke when the command is processed.
The `replServer.defineCommand()` method is used to add new `.`-prefixed commands to the REPL instance. Such commands are invoked by typing a `.` followed by the `keyword`. The `cmd` is either a `Function` or an `Object` with the following properties:
* `help` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Help text to be displayed when `.help` is entered (Optional).
* `action` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to execute, optionally accepting a single string argument.
The following example shows two new commands added to the REPL instance:
```
const repl = require('node:repl');
const replServer = repl.start({ prompt: '> ' });
replServer.defineCommand('sayhello', {
help: 'Say hello',
action(name) {
this.clearBufferedCommand();
console.log(`Hello, ${name}!`);
this.displayPrompt();
}
});
replServer.defineCommand('saybye', function saybye() {
console.log('Goodbye!');
this.close();
});
```
The new commands can then be used from within the REPL instance:
```
> .sayhello Node.js User
Hello, Node.js User!
> .saybye
Goodbye!
```
####
`replServer.displayPrompt([preserveCursor])`
Added in: v0.1.91 * `preserveCursor` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `replServer.displayPrompt()` method readies the REPL instance for input from the user, printing the configured `prompt` to a new line in the `output` and resuming the `input` to accept new input.
When multi-line input is being entered, an ellipsis is printed rather than the 'prompt'.
When `preserveCursor` is `true`, the cursor placement will not be reset to `0`.
The `replServer.displayPrompt` method is primarily intended to be called from within the action function for commands registered using the `replServer.defineCommand()` method.
####
`replServer.clearBufferedCommand()`
Added in: v9.0.0 The `replServer.clearBufferedCommand()` method clears any command that has been buffered but not yet executed. This method is primarily intended to be called from within the action function for commands registered using the `replServer.defineCommand()` method.
####
`replServer.parseREPLKeyword(keyword[, rest])`
Added in: v0.8.9Deprecated since: v9.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated.
* `keyword` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) the potential keyword to parse and execute
* `rest` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) any parameters to the keyword command
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
An internal method used to parse and execute `REPLServer` keywords. Returns `true` if `keyword` is a valid keyword, otherwise `false`.
####
`replServer.setupHistory(historyPath, callback)`
Added in: v11.10.0 * `historyPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) the path to the history file
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) called when history writes are ready or upon error
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `repl` [<repl.REPLServer>](repl#class-replserver)
Initializes a history log file for the REPL instance. When executing the Node.js binary and using the command-line REPL, a history file is initialized by default. However, this is not the case when creating a REPL programmatically. Use this method to initialize a history log file when working with REPL instances programmatically.
###
`repl.builtinModules`
Added in: v14.5.0 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
A list of the names of all Node.js modules, e.g., `'http'`.
###
`repl.start([options])`
History
| Version | Changes |
| --- | --- |
| v13.4.0, v12.17.0 | The `preview` option is now available. |
| v12.0.0 | The `terminal` option now follows the default description in all cases and `useColors` checks `hasColors()` if available. |
| v10.0.0 | The `REPL_MAGIC_MODE` `replMode` was removed. |
| v6.3.0 | The `breakEvalOnSigint` option is supported now. |
| v5.8.0 | The `options` parameter is optional now. |
| v0.1.91 | Added in: v0.1.91 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `prompt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The input prompt to display. **Default:** `'> '` (with a trailing space).
+ `input` [<stream.Readable>](stream#class-streamreadable) The `Readable` stream from which REPL input will be read. **Default:** `process.stdin`.
+ `output` [<stream.Writable>](stream#class-streamwritable) The `Writable` stream to which REPL output will be written. **Default:** `process.stdout`.
+ `terminal` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, specifies that the `output` should be treated as a TTY terminal. **Default:** checking the value of the `isTTY` property on the `output` stream upon instantiation.
+ `eval` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to be used when evaluating each given line of input. **Default:** an async wrapper for the JavaScript `eval()` function. An `eval` function can error with `repl.Recoverable` to indicate the input was incomplete and prompt for additional lines.
+ `useColors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, specifies that the default `writer` function should include ANSI color styling to REPL output. If a custom `writer` function is provided then this has no effect. **Default:** checking color support on the `output` stream if the REPL instance's `terminal` value is `true`.
+ `useGlobal` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, specifies that the default evaluation function will use the JavaScript `global` as the context as opposed to creating a new separate context for the REPL instance. The node CLI REPL sets this value to `true`. **Default:** `false`.
+ `ignoreUndefined` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, specifies that the default writer will not output the return value of a command if it evaluates to `undefined`. **Default:** `false`.
+ `writer` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to invoke to format the output of each command before writing to `output`. **Default:** [`util.inspect()`](util#utilinspectobject-options).
+ `completer` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) An optional function used for custom Tab auto completion. See [`readline.InterfaceCompleter`](readline#use-of-the-completer-function) for an example.
+ `replMode` [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) A flag that specifies whether the default evaluator executes all JavaScript commands in strict mode or default (sloppy) mode. Acceptable values are:
- `repl.REPL_MODE_SLOPPY` to evaluate expressions in sloppy mode.
- `repl.REPL_MODE_STRICT` to evaluate expressions in strict mode. This is equivalent to prefacing every repl statement with `'use strict'`.
+ `breakEvalOnSigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Stop evaluating the current piece of code when `SIGINT` is received, such as when `Ctrl`+`C` is pressed. This cannot be used together with a custom `eval` function. **Default:** `false`.
+ `preview` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Defines if the repl prints autocomplete and output previews or not. **Default:** `true` with the default eval function and `false` in case a custom eval function is used. If `terminal` is falsy, then there are no previews and the value of `preview` has no effect.
* Returns: [<repl.REPLServer>](repl#class-replserver)
The `repl.start()` method creates and starts a [`repl.REPLServer`](#class-replserver) instance.
If `options` is a string, then it specifies the input prompt:
```
const repl = require('node:repl');
// a Unix style prompt
repl.start('$ ');
```
### The Node.js REPL
Node.js itself uses the `node:repl` module to provide its own interactive interface for executing JavaScript. This can be used by executing the Node.js binary without passing any arguments (or by passing the `-i` argument):
```
$ node
> const a = [1, 2, 3];
undefined
> a
[ 1, 2, 3 ]
> a.forEach((v) => {
... console.log(v);
... });
1
2
3
```
#### Environment variable options
Various behaviors of the Node.js REPL can be customized using the following environment variables:
* `NODE_REPL_HISTORY`: When a valid path is given, persistent REPL history will be saved to the specified file rather than `.node_repl_history` in the user's home directory. Setting this value to `''` (an empty string) will disable persistent REPL history. Whitespace will be trimmed from the value. On Windows platforms environment variables with empty values are invalid so set this variable to one or more spaces to disable persistent REPL history.
* `NODE_REPL_HISTORY_SIZE`: Controls how many lines of history will be persisted if history is available. Must be a positive number. **Default:** `1000`.
* `NODE_REPL_MODE`: May be either `'sloppy'` or `'strict'`. **Default:** `'sloppy'`, which will allow non-strict mode code to be run.
#### Persistent history
By default, the Node.js REPL will persist history between `node` REPL sessions by saving inputs to a `.node_repl_history` file located in the user's home directory. This can be disabled by setting the environment variable `NODE_REPL_HISTORY=''`.
#### Using the Node.js REPL with advanced line-editors
For advanced line-editors, start Node.js with the environment variable `NODE_NO_READLINE=1`. This will start the main and debugger REPL in canonical terminal settings, which will allow use with `rlwrap`.
For example, the following can be added to a `.bashrc` file:
```
alias node="env NODE_NO_READLINE=1 rlwrap node"
```
#### Starting multiple REPL instances against a single running instance
It is possible to create and run multiple REPL instances against a single running instance of Node.js that share a single `global` object but have separate I/O interfaces.
The following example, for instance, provides separate REPLs on `stdin`, a Unix socket, and a TCP socket:
```
const net = require('node:net');
const repl = require('node:repl');
let connections = 0;
repl.start({
prompt: 'Node.js via stdin> ',
input: process.stdin,
output: process.stdout
});
net.createServer((socket) => {
connections += 1;
repl.start({
prompt: 'Node.js via Unix socket> ',
input: socket,
output: socket
}).on('exit', () => {
socket.end();
});
}).listen('/tmp/node-repl-sock');
net.createServer((socket) => {
connections += 1;
repl.start({
prompt: 'Node.js via TCP socket> ',
input: socket,
output: socket
}).on('exit', () => {
socket.end();
});
}).listen(5001);
```
Running this application from the command line will start a REPL on stdin. Other REPL clients may connect through the Unix socket or TCP socket. `telnet`, for instance, is useful for connecting to TCP sockets, while `socat` can be used to connect to both Unix and TCP sockets.
By starting a REPL from a Unix socket-based server instead of stdin, it is possible to connect to a long-running Node.js process without restarting it.
For an example of running a "full-featured" (`terminal`) REPL over a `net.Server` and `net.Socket` instance, see: <https://gist.github.com/TooTallNate/2209310>.
For an example of running a REPL instance over [`curl(1)`](https://curl.haxx.se/docs/manpage.html), see: <https://gist.github.com/TooTallNate/2053342>.
| programming_docs |
node None File system
-----------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/fs.js](https://github.com/nodejs/node/blob/v19.0.1/lib/fs.js)
The `node:fs` module enables interacting with the file system in a way modeled on standard POSIX functions.
To use the promise-based APIs:
MJS modules
```
import * as fs from 'node:fs/promises';
```
CJS modules
```
const fs = require('node:fs/promises');
```
To use the callback and sync APIs:
MJS modules
```
import * as fs from 'node:fs';
```
CJS modules
```
const fs = require('node:fs');
```
All file system operations have synchronous, callback, and promise-based forms, and are accessible using both CommonJS syntax and ES6 Modules (ESM).
### Promise example
Promise-based operations return a promise that is fulfilled when the asynchronous operation is complete.
MJS modules
```
import { unlink } from 'node:fs/promises';
try {
await unlink('/tmp/hello');
console.log('successfully deleted /tmp/hello');
} catch (error) {
console.error('there was an error:', error.message);
}
```
CJS modules
```
const { unlink } = require('node:fs/promises');
(async function(path) {
try {
await unlink(path);
console.log(`successfully deleted ${path}`);
} catch (error) {
console.error('there was an error:', error.message);
}
})('/tmp/hello');
```
### Callback example
The callback form takes a completion callback function as its last argument and invokes the operation asynchronously. The arguments passed to the completion callback depend on the method, but the first argument is always reserved for an exception. If the operation is completed successfully, then the first argument is `null` or `undefined`.
MJS modules
```
import { unlink } from 'node:fs';
unlink('/tmp/hello', (err) => {
if (err) throw err;
console.log('successfully deleted /tmp/hello');
});
```
CJS modules
```
const { unlink } = require('node:fs');
unlink('/tmp/hello', (err) => {
if (err) throw err;
console.log('successfully deleted /tmp/hello');
});
```
The callback-based versions of the `node:fs` module APIs are preferable over the use of the promise APIs when maximal performance (both in terms of execution time and memory allocation) is required.
### Synchronous example
The synchronous APIs block the Node.js event loop and further JavaScript execution until the operation is complete. Exceptions are thrown immediately and can be handled using `try…catch`, or can be allowed to bubble up.
MJS modules
```
import { unlinkSync } from 'node:fs';
try {
unlinkSync('/tmp/hello');
console.log('successfully deleted /tmp/hello');
} catch (err) {
// handle the error
}
```
CJS modules
```
const { unlinkSync } = require('node:fs');
try {
unlinkSync('/tmp/hello');
console.log('successfully deleted /tmp/hello');
} catch (err) {
// handle the error
}
```
### Promises API
History
| Version | Changes |
| --- | --- |
| v14.0.0 | Exposed as `require('fs/promises')`. |
| v11.14.0, v10.17.0 | This API is no longer experimental. |
| v10.1.0 | The API is accessible via `require('fs').promises` only. |
| v10.0.0 | Added in: v10.0.0 |
The `fs/promises` API provides asynchronous file system methods that return promises.
The promise APIs use the underlying Node.js threadpool to perform file system operations off the event loop thread. These operations are not synchronized or threadsafe. Care must be taken when performing multiple concurrent modifications on the same file or data corruption may occur.
#### Class: `FileHandle`
Added in: v10.0.0 A [<FileHandle>](fs#class-filehandle) object is an object wrapper for a numeric file descriptor.
Instances of the [<FileHandle>](fs#class-filehandle) object are created by the `fsPromises.open()` method.
All [<FileHandle>](fs#class-filehandle) objects are [<EventEmitter>](events#class-eventemitter)s.
If a [<FileHandle>](fs#class-filehandle) is not closed using the `filehandle.close()` method, it will try to automatically close the file descriptor and emit a process warning, helping to prevent memory leaks. Please do not rely on this behavior because it can be unreliable and the file may not be closed. Instead, always explicitly close [<FileHandle>](fs#class-filehandle)s. Node.js may change this behavior in the future.
##### Event: `'close'`
Added in: v15.4.0 The `'close'` event is emitted when the [<FileHandle>](fs#class-filehandle) has been closed and can no longer be used.
#####
`filehandle.appendFile(data[, options])`
History
| Version | Changes |
| --- | --- |
| v15.14.0, v14.18.0 | The `data` argument supports `AsyncIterable`, `Iterable`, and `Stream`. |
| v14.0.0 | The `data` parameter won't coerce unsupported input to strings anymore. |
| v10.0.0 | Added in: v10.0.0 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface) | [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) | [<Stream>](stream#stream)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Alias of [`filehandle.writeFile()`](#filehandlewritefiledata-options).
When operating on file handles, the mode cannot be changed from what it was set to with [`fsPromises.open()`](#fspromisesopenpath-flags-mode). Therefore, this is equivalent to [`filehandle.writeFile()`](#filehandlewritefiledata-options).
#####
`filehandle.chmod(mode)`
Added in: v10.0.0 * `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the file mode bit mask.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Modifies the permissions on the file. See [`chmod(2)`](http://man7.org/linux/man-pages/man2/chmod.2.html).
#####
`filehandle.chown(uid, gid)`
Added in: v10.0.0 * `uid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The file's new owner's user id.
* `gid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The file's new group's group id.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Changes the ownership of the file. A wrapper for [`chown(2)`](http://man7.org/linux/man-pages/man2/chown.2.html).
#####
`filehandle.close()`
Added in: v10.0.0 * Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Closes the file handle after waiting for any pending operation on the handle to complete.
```
import { open } from 'node:fs/promises';
let filehandle;
try {
filehandle = await open('thefile.txt', 'r');
} finally {
await filehandle?.close();
}
```
#####
`filehandle.createReadStream([options])`
Added in: v16.11.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `null`
+ `autoClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `emitClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `start` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `end` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `Infinity`
+ `highWaterMark` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `64 * 1024`
* Returns: [<fs.ReadStream>](fs#class-fsreadstream)
Unlike the 16 KiB default `highWaterMark` for a [<stream.Readable>](stream#class-streamreadable), the stream returned by this method has a default `highWaterMark` of 64 KiB.
`options` can include `start` and `end` values to read a range of bytes from the file instead of the entire file. Both `start` and `end` are inclusive and start counting at 0, allowed values are in the [0, [`Number.MAX_SAFE_INTEGER`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER)] range. If `start` is omitted or `undefined`, `filehandle.createReadStream()` reads sequentially from the current file position. The `encoding` can be any one of those accepted by [<Buffer>](buffer#class-buffer).
If the `FileHandle` points to a character device that only supports blocking reads (such as keyboard or sound card), read operations do not finish until data is available. This can prevent the process from exiting and the stream from closing naturally.
By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior.
```
import { open } from 'node:fs/promises';
const fd = await open('/dev/input/event0');
// Create a stream from some character device.
const stream = fd.createReadStream();
setTimeout(() => {
stream.close(); // This may not close the stream.
// Artificially marking end-of-stream, as if the underlying resource had
// indicated end-of-file by itself, allows the stream to close.
// This does not cancel pending read operations, and if there is such an
// operation, the process may still not be able to exit successfully
// until it finishes.
stream.push(null);
stream.read(0);
}, 100);
```
If `autoClose` is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak. If `autoClose` is set to true (default behavior), on `'error'` or `'end'` the file descriptor will be closed automatically.
An example to read the last 10 bytes of a file which is 100 bytes long:
```
import { open } from 'node:fs/promises';
const fd = await open('sample.txt');
fd.createReadStream({ start: 90, end: 99 });
```
#####
`filehandle.createWriteStream([options])`
Added in: v16.11.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
+ `autoClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `emitClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `start` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: [<fs.WriteStream>](fs#class-fswritestream)
`options` may also include a `start` option to allow writing data at some position past the beginning of the file, allowed values are in the [0, [`Number.MAX_SAFE_INTEGER`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER)] range. Modifying a file rather than replacing it may require the `flags` `open` option to be set to `r+` rather than the default `r`. The `encoding` can be any one of those accepted by [<Buffer>](buffer#class-buffer).
If `autoClose` is set to true (default behavior) on `'error'` or `'finish'` the file descriptor will be closed automatically. If `autoClose` is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak.
By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior.
#####
`filehandle.datasync()`
Added in: v10.0.0 * Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX [`fdatasync(2)`](http://man7.org/linux/man-pages/man2/fdatasync.2.html) documentation for details.
Unlike `filehandle.sync` this method does not flush modified metadata.
#####
`filehandle.fd`
Added in: v10.0.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The numeric file descriptor managed by the [<FileHandle>](fs#class-filehandle) object.
#####
`filehandle.read(buffer, offset, length, position)`
Added in: v10.0.0 * `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A buffer that will be filled with the file data read.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The location in the buffer at which to start filling.
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes to read.
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The location where to begin reading data from the file. If `null`, data will be read from the current file position, and the position will be updated. If `position` is an integer, the current file position will remain unchanged.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills upon success with an object with two properties:
+ `bytesRead` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes read
+ `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A reference to the passed in `buffer` argument.
Reads data from the file and stores that in the given buffer.
If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero.
#####
`filehandle.read([options])`
Added in: v13.11.0, v12.17.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A buffer that will be filled with the file data read. **Default:** `Buffer.alloc(16384)`
+ `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The location in the buffer at which to start filling. **Default:** `0`
+ `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes to read. **Default:** `buffer.byteLength - offset`
+ `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The location where to begin reading data from the file. If `null`, data will be read from the current file position, and the position will be updated. If `position` is an integer, the current file position will remain unchanged. **Default:**: `null`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills upon success with an object with two properties:
+ `bytesRead` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes read
+ `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A reference to the passed in `buffer` argument.
Reads data from the file and stores that in the given buffer.
If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero.
#####
`filehandle.read(buffer[, options])`
Added in: v18.2.0, v16.17.0 * `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A buffer that will be filled with the file data read.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The location in the buffer at which to start filling. **Default:** `0`
+ `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes to read. **Default:** `buffer.byteLength - offset`
+ `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The location where to begin reading data from the file. If `null`, data will be read from the current file position, and the position will be updated. If `position` is an integer, the current file position will remain unchanged. **Default:**: `null`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills upon success with an object with two properties:
+ `bytesRead` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes read
+ `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A reference to the passed in `buffer` argument.
Reads data from the file and stores that in the given buffer.
If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero.
#####
`filehandle.readableWebStream()`
Added in: v17.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* Returns: [<ReadableStream>](webstreams#class-readablestream)
Returns a `ReadableStream` that may be used to read the files data.
An error will be thrown if this method is called more than once or is called after the `FileHandle` is closed or closing.
MJS modules
```
import {
open,
} from 'node:fs/promises';
const file = await open('./some/file/to/read');
for await (const chunk of file.readableWebStream())
console.log(chunk);
await file.close();
```
CJS modules
```
const {
open,
} = require('node:fs/promises');
(async () => {
const file = await open('./some/file/to/read');
for await (const chunk of file.readableWebStream())
console.log(chunk);
await file.close();
})();
```
While the `ReadableStream` will read the file to completion, it will not close the `FileHandle` automatically. User code must still call the `fileHandle.close()` method.
#####
`filehandle.readFile(options)`
Added in: v10.0.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows aborting an in-progress readFile
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills upon a successful read with the contents of the file. If no encoding is specified (using `options.encoding`), the data is returned as a [<Buffer>](buffer#class-buffer) object. Otherwise, the data will be a string.
Asynchronously reads the entire contents of a file.
If `options` is a string, then it specifies the `encoding`.
The [<FileHandle>](fs#class-filehandle) has to support reading.
If one or more `filehandle.read()` calls are made on a file handle and then a `filehandle.readFile()` call is made, the data will be read from the current position till the end of the file. It doesn't always read from the beginning of the file.
#####
`filehandle.readLines([options])`
Added in: v18.11.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `null`
+ `autoClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `emitClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `start` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `end` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `Infinity`
+ `highWaterMark` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `64 * 1024`
* Returns: [<readline.InterfaceConstructor>](readline#class-interfaceconstructor)
Convenience method to create a `readline` interface and stream over the file. See [`filehandle.createReadStream()`](#filehandlecreatereadstreamoptions) for the options.
MJS modules
```
import { open } from 'node:fs/promises';
const file = await open('./some/file/to/read');
for await (const line of file.readLines()) {
console.log(line);
}
```
CJS modules
```
const { open } = require('node:fs/promises');
(async () => {
const file = await open('./some/file/to/read');
for await (const line of file.readLines()) {
console.log(line);
}
})();
```
#####
`filehandle.readv(buffers[, position])`
Added in: v13.13.0, v12.17.0 * `buffers` [<Buffer[]>](buffer#class-buffer) | [<TypedArray[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The offset from the beginning of the file where the data should be read from. If `position` is not a `number`, the data will be read from the current position. **Default:** `null`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills upon success an object containing two properties:
+ `bytesRead` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the number of bytes read
+ `buffers` [<Buffer[]>](buffer#class-buffer) | [<TypedArray[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) property containing a reference to the `buffers` input.
Read from a file and write to an array of [<ArrayBufferView>](https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView)s
#####
`filehandle.stat([options])`
History
| Version | Changes |
| --- | --- |
| v10.5.0 | Accepts an additional `options` object to specify whether the numeric values returned should be bigint. |
| v10.0.0 | Added in: v10.0.0 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the numeric values in the returned [<fs.Stats>](fs#class-fsstats) object should be `bigint`. **Default:** `false`.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with an [<fs.Stats>](fs#class-fsstats) for the file.
#####
`filehandle.sync()`
Added in: v10.0.0 * Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX [`fsync(2)`](http://man7.org/linux/man-pages/man2/fsync.2.html) documentation for more detail.
#####
`filehandle.truncate(len)`
Added in: v10.0.0 * `len` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Truncates the file.
If the file was larger than `len` bytes, only the first `len` bytes will be retained in the file.
The following example retains only the first four bytes of the file:
```
import { open } from 'node:fs/promises';
let filehandle = null;
try {
filehandle = await open('temp.txt', 'r+');
await filehandle.truncate(4);
} finally {
await filehandle?.close();
}
```
If the file previously was shorter than `len` bytes, it is extended, and the extended part is filled with null bytes (`'\0'`):
If `len` is negative then `0` will be used.
#####
`filehandle.utimes(atime, mtime)`
Added in: v10.0.0 * `atime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `mtime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Change the file system timestamps of the object referenced by the [<FileHandle>](fs#class-filehandle) then resolves the promise with no arguments upon success.
#####
`filehandle.write(buffer, offset[, length[, position]])`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | The `buffer` parameter won't coerce unsupported input to buffers anymore. |
| v10.0.0 | Added in: v10.0.0 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The start position from within `buffer` where the data to write begins.
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes from `buffer` to write. **Default:** `buffer.byteLength - offset`
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The offset from the beginning of the file where the data from `buffer` should be written. If `position` is not a `number`, the data will be written at the current position. See the POSIX [`pwrite(2)`](http://man7.org/linux/man-pages/man2/pwrite.2.html) documentation for more detail. **Default:** `null`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Write `buffer` to the file.
The promise is resolved with an object containing two properties:
* `bytesWritten` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the number of bytes written
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) a reference to the `buffer` written.
It is unsafe to use `filehandle.write()` multiple times on the same file without waiting for the promise to be resolved (or rejected). For this scenario, use [`filehandle.createWriteStream()`](#filehandlecreatewritestreamoptions).
On Linux, positional writes do not work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
#####
`filehandle.write(buffer[, options])`
Added in: v18.3.0, v16.17.0 * `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
+ `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.byteLength - offset`
+ `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `null`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Write `buffer` to the file.
Similar to the above `filehandle.write` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values.
#####
`filehandle.write(string[, position[, encoding]])`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | The `string` parameter won't coerce unsupported input to strings anymore. |
| v10.0.0 | Added in: v10.0.0 |
* `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The offset from the beginning of the file where the data from `string` should be written. If `position` is not a `number` the data will be written at the current position. See the POSIX [`pwrite(2)`](http://man7.org/linux/man-pages/man2/pwrite.2.html) documentation for more detail. **Default:** `null`
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The expected string encoding. **Default:** `'utf8'`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Write `string` to the file. If `string` is not a string, the promise is rejected with an error.
The promise is resolved with an object containing two properties:
* `bytesWritten` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the number of bytes written
* `buffer` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) a reference to the `string` written.
It is unsafe to use `filehandle.write()` multiple times on the same file without waiting for the promise to be resolved (or rejected). For this scenario, use [`filehandle.createWriteStream()`](#filehandlecreatewritestreamoptions).
On Linux, positional writes do not work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
#####
`filehandle.writeFile(data, options)`
History
| Version | Changes |
| --- | --- |
| v15.14.0, v14.18.0 | The `data` argument supports `AsyncIterable`, `Iterable`, and `Stream`. |
| v14.0.0 | The `data` parameter won't coerce unsupported input to strings anymore. |
| v10.0.0 | Added in: v10.0.0 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface) | [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) | [<Stream>](stream#stream)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The expected character encoding when `data` is a string. **Default:** `'utf8'`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Asynchronously writes data to a file, replacing the file if it already exists. `data` can be a string, a buffer, an [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface), or an [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) object. The promise is resolved with no arguments upon success.
If `options` is a string, then it specifies the `encoding`.
The [<FileHandle>](fs#class-filehandle) has to support writing.
It is unsafe to use `filehandle.writeFile()` multiple times on the same file without waiting for the promise to be resolved (or rejected).
If one or more `filehandle.write()` calls are made on a file handle and then a `filehandle.writeFile()` call is made, the data will be written from the current position till the end of the file. It doesn't always write from the beginning of the file.
#####
`filehandle.writev(buffers[, position])`
Added in: v12.9.0 * `buffers` [<Buffer[]>](buffer#class-buffer) | [<TypedArray[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The offset from the beginning of the file where the data from `buffers` should be written. If `position` is not a `number`, the data will be written at the current position. **Default:** `null`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Write an array of [<ArrayBufferView>](https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView)s to the file.
The promise is resolved with an object containing a two properties:
* `bytesWritten` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the number of bytes written
* `buffers` [<Buffer[]>](buffer#class-buffer) | [<TypedArray[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) a reference to the `buffers` input.
It is unsafe to call `writev()` multiple times on the same file without waiting for the promise to be resolved (or rejected).
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
####
`fsPromises.access(path[, mode])`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `fs.constants.F_OK`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Tests a user's permissions for the file or directory specified by `path`. The `mode` argument is an optional integer that specifies the accessibility checks to be performed. `mode` should be either the value `fs.constants.F_OK` or a mask consisting of the bitwise OR of any of `fs.constants.R_OK`, `fs.constants.W_OK`, and `fs.constants.X_OK` (e.g. `fs.constants.W_OK | fs.constants.R_OK`). Check [File access constants](#file-access-constants) for possible values of `mode`.
If the accessibility check is successful, the promise is resolved with no value. If any of the accessibility checks fail, the promise is rejected with an [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) object. The following example checks if the file `/etc/passwd` can be read and written by the current process.
```
import { access, constants } from 'node:fs/promises';
try {
await access('/etc/passwd', constants.R_OK | constants.W_OK);
console.log('can access');
} catch {
console.error('cannot access');
}
```
Using `fsPromises.access()` to check for the accessibility of a file before calling `fsPromises.open()` is not recommended. Doing so introduces a race condition, since other processes may change the file's state between the two calls. Instead, user code should open/read/write the file directly and handle the error raised if the file is not accessible.
####
`fsPromises.appendFile(path, data[, options])`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) | [<FileHandle>](fs#class-filehandle) filename or [<FileHandle>](fs#class-filehandle)
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
+ `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666`
+ `flag` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'a'`.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Asynchronously append data to a file, creating the file if it does not yet exist. `data` can be a string or a [<Buffer>](buffer#class-buffer).
If `options` is a string, then it specifies the `encoding`.
The `mode` option only affects the newly created file. See [`fs.open()`](#fsopenpath-flags-mode-callback) for more details.
The `path` may be specified as a [<FileHandle>](fs#class-filehandle) that has been opened for appending (using `fsPromises.open()`).
####
`fsPromises.chmod(path, mode)`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Changes the permissions of a file.
####
`fsPromises.chown(path, uid, gid)`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `uid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `gid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Changes the ownership of a file.
####
`fsPromises.copyFile(src, dest[, mode])`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | Changed `flags` argument to `mode` and imposed stricter type validation. |
| v10.0.0 | Added in: v10.0.0 |
* `src` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) source filename to copy
* `dest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) destination filename of the copy operation
* `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optional modifiers that specify the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. `fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE`) **Default:** `0`.
+ `fs.constants.COPYFILE_EXCL`: The copy operation will fail if `dest` already exists.
+ `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used.
+ `fs.constants.COPYFILE_FICLONE_FORCE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Asynchronously copies `src` to `dest`. By default, `dest` is overwritten if it already exists.
No guarantees are made about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, an attempt will be made to remove the destination.
```
import { copyFile, constants } from 'node:fs/promises';
try {
await copyFile('source.txt', 'destination.txt');
console.log('source.txt was copied to destination.txt');
} catch {
console.log('The file could not be copied');
}
// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.
try {
await copyFile('source.txt', 'destination.txt', constants.COPYFILE_EXCL);
console.log('source.txt was copied to destination.txt');
} catch {
console.log('The file could not be copied');
}
```
####
`fsPromises.cp(src, dest[, options])`
History
| Version | Changes |
| --- | --- |
| v17.6.0, v16.15.0 | Accepts an additional `verbatimSymlinks` option to specify whether to perform path resolution for symlinks. |
| v16.7.0 | Added in: v16.7.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `src` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) source path to copy.
* `dest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) destination path to copy to.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `dereference` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) dereference symlinks. **Default:** `false`.
+ `errorOnExist` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) when `force` is `false`, and the destination exists, throw an error. **Default:** `false`.
+ `filter` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Function to filter copied files/directories. Return `true` to copy the item, `false` to ignore it. Can also return a `Promise` that resolves to `true` or `false` **Default:** `undefined`.
+ `force` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) overwrite existing file or directory. The copy operation will ignore errors if you set this to false and the destination exists. Use the `errorOnExist` option to change this behavior. **Default:** `true`.
+ `preserveTimestamps` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true` timestamps from `src` will be preserved. **Default:** `false`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) copy directories recursively **Default:** `false`
+ `verbatimSymlinks` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, path resolution for symlinks will be skipped. **Default:** `false`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Asynchronously copies the entire directory structure from `src` to `dest`, including subdirectories and files.
When copying a directory to another directory, globs are not supported and behavior is similar to `cp dir1/ dir2/`.
####
`fsPromises.lchmod(path, mode)`
Deprecated since: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Changes the permissions on a symbolic link.
This method is only implemented on macOS.
####
`fsPromises.lchown(path, uid, gid)`
History
| Version | Changes |
| --- | --- |
| v10.6.0 | This API is no longer deprecated. |
| v10.0.0 | Added in: v10.0.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `uid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `gid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Changes the ownership on a symbolic link.
####
`fsPromises.lutimes(path, atime, mtime)`
Added in: v14.5.0, v12.19.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `atime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `mtime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Changes the access and modification times of a file in the same way as [`fsPromises.utimes()`](#fspromisesutimespath-atime-mtime), with the difference that if the path refers to a symbolic link, then the link is not dereferenced: instead, the timestamps of the symbolic link itself are changed.
####
`fsPromises.link(existingPath, newPath)`
Added in: v10.0.0 * `existingPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `newPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Creates a new link from the `existingPath` to the `newPath`. See the POSIX [`link(2)`](http://man7.org/linux/man-pages/man2/link.2.html) documentation for more detail.
####
`fsPromises.lstat(path[, options])`
History
| Version | Changes |
| --- | --- |
| v10.5.0 | Accepts an additional `options` object to specify whether the numeric values returned should be bigint. |
| v10.0.0 | Added in: v10.0.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the numeric values in the returned [<fs.Stats>](fs#class-fsstats) object should be `bigint`. **Default:** `false`.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with the [<fs.Stats>](fs#class-fsstats) object for the given symbolic link `path`.
Equivalent to [`fsPromises.stat()`](#fspromisesstatpath-options) unless `path` refers to a symbolic link, in which case the link itself is stat-ed, not the file that it refers to. Refer to the POSIX [`lstat(2)`](http://man7.org/linux/man-pages/man2/lstat.2.html) document for more detail.
####
`fsPromises.mkdir(path[, options])`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
+ `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Not supported on Windows. **Default:** `0o777`.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Upon success, fulfills with `undefined` if `recursive` is `false`, or the first directory path created if `recursive` is `true`.
Asynchronously creates a directory.
The optional `options` argument can be an integer specifying `mode` (permission and sticky bits), or an object with a `mode` property and a `recursive` property indicating whether parent directories should be created. Calling `fsPromises.mkdir()` when `path` is a directory that exists results in a rejection only when `recursive` is false.
MJS modules
```
import { mkdir } from 'node:fs/promises';
try {
const projectFolder = new URL('./test/project/', import.meta.url);
const createDir = await mkdir(projectFolder, { recursive: true });
console.log(`created ${createDir}`);
} catch (err) {
console.error(err.message);
}
```
CJS modules
```
const { mkdir } = require('node:fs/promises');
const { resolve, join } = require('node:path');
async function makeDirectory() {
const projectFolder = join(__dirname, 'test', 'project');
const dirCreation = await mkdir(projectFolder, { recursive: true });
console.log(dirCreation);
return dirCreation;
}
makeDirectory().catch(console.error);
```
####
`fsPromises.mkdtemp(prefix[, options])`
History
| Version | Changes |
| --- | --- |
| v16.5.0, v14.18.0 | The `prefix` parameter now accepts an empty string. |
| v10.0.0 | Added in: v10.0.0 |
* `prefix` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with a string containing the filesystem path of the newly created temporary directory.
Creates a unique temporary directory. A unique directory name is generated by appending six random characters to the end of the provided `prefix`. Due to platform inconsistencies, avoid trailing `X` characters in `prefix`. Some platforms, notably the BSDs, can return more than six random characters, and replace trailing `X` characters in `prefix` with random characters.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use.
```
import { mkdtemp } from 'node:fs/promises';
try {
await mkdtemp(path.join(os.tmpdir(), 'foo-'));
} catch (err) {
console.error(err);
}
```
The `fsPromises.mkdtemp()` method will append the six randomly selected characters directly to the `prefix` string. For instance, given a directory `/tmp`, if the intention is to create a temporary directory *within* `/tmp`, the `prefix` must end with a trailing platform-specific path separator (`require('node:path').sep`).
####
`fsPromises.open(path, flags[, mode])`
History
| Version | Changes |
| --- | --- |
| v11.1.0 | The `flags` argument is now optional and defaults to `'r'`. |
| v10.0.0 | Added in: v10.0.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `flags` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) See [support of file system `flags`](#file-system-flags). **Default:** `'r'`.
* `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the file mode (permission and sticky bits) if the file is created. **Default:** `0o666` (readable and writable)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with a [<FileHandle>](fs#class-filehandle) object.
Opens a [<FileHandle>](fs#class-filehandle).
Refer to the POSIX [`open(2)`](http://man7.org/linux/man-pages/man2/open.2.html) documentation for more detail.
Some characters (`< > : " / \ | ? *`) are reserved under Windows as documented by [Naming Files, Paths, and Namespaces](https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file). Under NTFS, if the filename contains a colon, Node.js will open a file system stream, as described by [this MSDN page](https://docs.microsoft.com/en-us/windows/desktop/FileIO/using-streams).
####
`fsPromises.opendir(path[, options])`
History
| Version | Changes |
| --- | --- |
| v13.1.0, v12.16.0 | The `bufferSize` option was introduced. |
| v12.12.0 | Added in: v12.12.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
+ `bufferSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of directory entries that are buffered internally when reading from the directory. Higher values lead to better performance but higher memory usage. **Default:** `32`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with an [<fs.Dir>](fs#class-fsdir).
Asynchronously open a directory for iterative scanning. See the POSIX [`opendir(3)`](http://man7.org/linux/man-pages/man3/opendir.3.html) documentation for more detail.
Creates an [<fs.Dir>](fs#class-fsdir), which contains all further functions for reading from and cleaning up the directory.
The `encoding` option sets the encoding for the `path` while opening the directory and subsequent read operations.
Example using async iteration:
```
import { opendir } from 'node:fs/promises';
try {
const dir = await opendir('./');
for await (const dirent of dir)
console.log(dirent.name);
} catch (err) {
console.error(err);
}
```
When using the async iterator, the [<fs.Dir>](fs#class-fsdir) object will be automatically closed after the iterator exits.
####
`fsPromises.readdir(path[, options])`
History
| Version | Changes |
| --- | --- |
| v10.11.0 | New option `withFileTypes` was added. |
| v10.0.0 | Added in: v10.0.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
+ `withFileTypes` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with an array of the names of the files in the directory excluding `'.'` and `'..'`.
Reads the contents of a directory.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the filenames. If the `encoding` is set to `'buffer'`, the filenames returned will be passed as [<Buffer>](buffer#class-buffer) objects.
If `options.withFileTypes` is set to `true`, the resolved array will contain [<fs.Dirent>](fs#class-fsdirent) objects.
```
import { readdir } from 'node:fs/promises';
try {
const files = await readdir(path);
for (const file of files)
console.log(file);
} catch (err) {
console.error(err);
}
```
####
`fsPromises.readFile(path[, options])`
History
| Version | Changes |
| --- | --- |
| v15.2.0, v14.17.0 | The options argument may include an AbortSignal to abort an ongoing readFile request. |
| v10.0.0 | Added in: v10.0.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) | [<FileHandle>](fs#class-filehandle) filename or `FileHandle`
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
+ `flag` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'r'`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows aborting an in-progress readFile
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with the contents of the file.
Asynchronously reads the entire contents of a file.
If no encoding is specified (using `options.encoding`), the data is returned as a [<Buffer>](buffer#class-buffer) object. Otherwise, the data will be a string.
If `options` is a string, then it specifies the encoding.
When the `path` is a directory, the behavior of `fsPromises.readFile()` is platform-specific. On macOS, Linux, and Windows, the promise will be rejected with an error. On FreeBSD, a representation of the directory's contents will be returned.
An example of reading a `package.json` file located in the same directory of the running code:
MJS modules
```
import { readFile } from 'node:fs/promises';
try {
const filePath = new URL('./package.json', import.meta.url);
const contents = await readFile(filePath, { encoding: 'utf8' });
console.log(contents);
} catch (err) {
console.error(err.message);
}
```
CJS modules
```
const { readFile } = require('node:fs/promises');
const { resolve } = require('node:path');
async function logFile() {
try {
const filePath = resolve('./package.json');
const contents = await readFile(filePath, { encoding: 'utf8' });
console.log(contents);
} catch (err) {
console.error(err.message);
}
}
logFile();
```
It is possible to abort an ongoing `readFile` using an [<AbortSignal>](globals#class-abortsignal). If a request is aborted the promise returned is rejected with an `AbortError`:
```
import { readFile } from 'node:fs/promises';
try {
const controller = new AbortController();
const { signal } = controller;
const promise = readFile(fileName, { signal });
// Abort the request before the promise settles.
controller.abort();
await promise;
} catch (err) {
// When a request is aborted - err is an AbortError
console.error(err);
}
```
Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.readFile` performs.
Any specified [<FileHandle>](fs#class-filehandle) has to support reading.
####
`fsPromises.readlink(path[, options])`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with the `linkString` upon success.
Reads the contents of the symbolic link referred to by `path`. See the POSIX [`readlink(2)`](http://man7.org/linux/man-pages/man2/readlink.2.html) documentation for more detail. The promise is resolved with the `linkString` upon success.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the link path returned. If the `encoding` is set to `'buffer'`, the link path returned will be passed as a [<Buffer>](buffer#class-buffer) object.
####
`fsPromises.realpath(path[, options])`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with the resolved path upon success.
Determines the actual location of `path` using the same semantics as the `fs.realpath.native()` function.
Only paths that can be converted to UTF8 strings are supported.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the path. If the `encoding` is set to `'buffer'`, the path returned will be passed as a [<Buffer>](buffer#class-buffer) object.
On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on `/proc` in order for this function to work. Glibc does not have this restriction.
####
`fsPromises.rename(oldPath, newPath)`
Added in: v10.0.0 * `oldPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `newPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Renames `oldPath` to `newPath`.
####
`fsPromises.rmdir(path[, options])`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Using `fsPromises.rmdir(path, { recursive: true })` on a `path` that is a file is no longer permitted and results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. |
| v16.0.0 | Using `fsPromises.rmdir(path, { recursive: true })` on a `path` that does not exist is no longer permitted and results in a `ENOENT` error. |
| v16.0.0 | The `recursive` option is deprecated, using it triggers a deprecation warning. |
| v14.14.0 | The `recursive` option is deprecated, use `fsPromises.rm` instead. |
| v13.3.0, v12.16.0 | The `maxBusyTries` option is renamed to `maxRetries`, and its default is 0. The `emfileWait` option has been removed, and `EMFILE` errors use the same retry logic as other errors. The `retryDelay` option is now supported. `ENFILE` errors are now retried. |
| v12.10.0 | The `recursive`, `maxBusyTries`, and `emfileWait` options are now supported. |
| v10.0.0 | Added in: v10.0.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `maxRetries` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js retries the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, perform a recursive directory removal. In recursive mode, operations are retried on failure. **Default:** `false`. **Deprecated.**
+ `retryDelay` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Removes the directory identified by `path`.
Using `fsPromises.rmdir()` on a file (not a directory) results in the promise being rejected with an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX.
To get a behavior similar to the `rm -rf` Unix command, use [`fsPromises.rm()`](#fspromisesrmpath-options) with options `{ recursive: true, force: true }`.
####
`fsPromises.rm(path[, options])`
Added in: v14.14.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `force` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, exceptions will be ignored if `path` does not exist. **Default:** `false`.
+ `maxRetries` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js will retry the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, perform a recursive directory removal. In recursive mode operations are retried on failure. **Default:** `false`.
+ `retryDelay` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Removes files and directories (modeled on the standard POSIX `rm` utility).
####
`fsPromises.stat(path[, options])`
History
| Version | Changes |
| --- | --- |
| v10.5.0 | Accepts an additional `options` object to specify whether the numeric values returned should be bigint. |
| v10.0.0 | Added in: v10.0.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the numeric values in the returned [<fs.Stats>](fs#class-fsstats) object should be `bigint`. **Default:** `false`.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with the [<fs.Stats>](fs#class-fsstats) object for the given `path`.
####
`fsPromises.symlink(target, path[, type])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | If the `type` argument is `null` or omitted, Node.js will autodetect `target` type and automatically select `dir` or `file`. |
| v10.0.0 | Added in: v10.0.0 |
* `target` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Creates a symbolic link.
The `type` argument is only used on Windows platforms and can be one of `'dir'`, `'file'`, or `'junction'`. If the `type` argument is not a string, Node.js will autodetect `target` type and use `'file'` or `'dir'`. If the `target` does not exist, `'file'` will be used. Windows junction points require the destination path to be absolute. When using `'junction'`, the `target` argument will automatically be normalized to absolute path.
####
`fsPromises.truncate(path[, len])`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `len` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Truncates (shortens or extends the length) of the content at `path` to `len` bytes.
####
`fsPromises.unlink(path)`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
If `path` refers to a symbolic link, then the link is removed without affecting the file or directory to which that link refers. If the `path` refers to a file path that is not a symbolic link, the file is deleted. See the POSIX [`unlink(2)`](http://man7.org/linux/man-pages/man2/unlink.2.html) documentation for more detail.
####
`fsPromises.utimes(path, atime, mtime)`
Added in: v10.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `atime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `mtime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Change the file system timestamps of the object referenced by `path`.
The `atime` and `mtime` arguments follow these rules:
* Values can be either numbers representing Unix epoch time, `Date`s, or a numeric string like `'123456789.0'`.
* If the value can not be converted to a number, or is `NaN`, `Infinity`, or `-Infinity`, an `Error` will be thrown.
####
`fsPromises.watch(filename[, options])`
Added in: v15.9.0, v14.18.0 * `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `persistent` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Indicates whether the process should continue to run as long as files are being watched. **Default:** `true`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Indicates whether all subdirectories should be watched, or only the current directory. This applies when a directory is specified, and only on supported platforms (See [caveats](#caveats)). **Default:** `false`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specifies the character encoding to be used for the filename passed to the listener. **Default:** `'utf8'`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) An [<AbortSignal>](globals#class-abortsignal) used to signal when the watcher should stop.
* Returns: [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface) of objects with the properties:
+ `eventType` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The type of change
+ `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) The name of the file changed.
Returns an async iterator that watches for changes on `filename`, where `filename` is either a file or a directory.
```
const { watch } = require('node:fs/promises');
const ac = new AbortController();
const { signal } = ac;
setTimeout(() => ac.abort(), 10000);
(async () => {
try {
const watcher = watch(__filename, { signal });
for await (const event of watcher)
console.log(event);
} catch (err) {
if (err.name === 'AbortError')
return;
throw err;
}
})();
```
On most platforms, `'rename'` is emitted whenever a filename appears or disappears in the directory.
All the [caveats](#caveats) for `fs.watch()` also apply to `fsPromises.watch()`.
####
`fsPromises.writeFile(file, data[, options])`
History
| Version | Changes |
| --- | --- |
| v15.14.0, v14.18.0 | The `data` argument supports `AsyncIterable`, `Iterable`, and `Stream`. |
| v15.2.0, v14.17.0 | The options argument may include an AbortSignal to abort an ongoing writeFile request. |
| v14.0.0 | The `data` parameter won't coerce unsupported input to strings anymore. |
| v10.0.0 | Added in: v10.0.0 |
* `file` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) | [<FileHandle>](fs#class-filehandle) filename or `FileHandle`
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface) | [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) | [<Stream>](stream#stream)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
+ `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666`
+ `flag` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'w'`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows aborting an in-progress writeFile
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Asynchronously writes data to a file, replacing the file if it already exists. `data` can be a string, a buffer, an [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface), or an [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) object.
The `encoding` option is ignored if `data` is a buffer.
If `options` is a string, then it specifies the encoding.
The `mode` option only affects the newly created file. See [`fs.open()`](#fsopenpath-flags-mode-callback) for more details.
Any specified [<FileHandle>](fs#class-filehandle) has to support writing.
It is unsafe to use `fsPromises.writeFile()` multiple times on the same file without waiting for the promise to be settled.
Similarly to `fsPromises.readFile` - `fsPromises.writeFile` is a convenience method that performs multiple `write` calls internally to write the buffer passed to it. For performance sensitive code consider using [`fs.createWriteStream()`](#fscreatewritestreampath-options) or [`filehandle.createWriteStream()`](#filehandlecreatewritestreamoptions).
It is possible to use an [<AbortSignal>](globals#class-abortsignal) to cancel an `fsPromises.writeFile()`. Cancelation is "best effort", and some amount of data is likely still to be written.
```
import { writeFile } from 'node:fs/promises';
import { Buffer } from 'node:buffer';
try {
const controller = new AbortController();
const { signal } = controller;
const data = new Uint8Array(Buffer.from('Hello Node.js'));
const promise = writeFile('message.txt', data, { signal });
// Abort the request before the promise settles.
controller.abort();
await promise;
} catch (err) {
// When a request is aborted - err is an AbortError
console.error(err);
}
```
Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.writeFile` performs.
####
`fsPromises.constants`
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns an object containing commonly used constants for file system operations. The object is the same as `fs.constants`. See [FS constants](#fs-constants) for more details.
### Callback API
The callback APIs perform all operations asynchronously, without blocking the event loop, then invoke a callback function upon completion or error.
The callback APIs use the underlying Node.js threadpool to perform file system operations off the event loop thread. These operations are not synchronized or threadsafe. Care must be taken when performing multiple concurrent modifications on the same file or data corruption may occur.
####
`fs.access(path[, mode], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v6.3.0 | The constants like `fs.R_OK`, etc which were present directly on `fs` were moved into `fs.constants` as a soft deprecation. Thus for Node.js `< v6.3.0` use `fs` to access those constants, or do something like `(fs.constants || fs).R_OK` to work with all versions. |
| v0.11.15 | Added in: v0.11.15 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `fs.constants.F_OK`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Tests a user's permissions for the file or directory specified by `path`. The `mode` argument is an optional integer that specifies the accessibility checks to be performed. `mode` should be either the value `fs.constants.F_OK` or a mask consisting of the bitwise OR of any of `fs.constants.R_OK`, `fs.constants.W_OK`, and `fs.constants.X_OK` (e.g. `fs.constants.W_OK | fs.constants.R_OK`). Check [File access constants](#file-access-constants) for possible values of `mode`.
The final argument, `callback`, is a callback function that is invoked with a possible error argument. If any of the accessibility checks fail, the error argument will be an `Error` object. The following examples check if `package.json` exists, and if it is readable or writable.
```
import { access, constants } from 'node:fs';
const file = 'package.json';
// Check if the file exists in the current directory.
access(file, constants.F_OK, (err) => {
console.log(`${file} ${err ? 'does not exist' : 'exists'}`);
});
// Check if the file is readable.
access(file, constants.R_OK, (err) => {
console.log(`${file} ${err ? 'is not readable' : 'is readable'}`);
});
// Check if the file is writable.
access(file, constants.W_OK, (err) => {
console.log(`${file} ${err ? 'is not writable' : 'is writable'}`);
});
// Check if the file is readable and writable.
access(file, constants.R_OK | constants.W_OK, (err) => {
console.log(`${file} ${err ? 'is not' : 'is'} readable and writable`);
});
```
Do not use `fs.access()` to check for the accessibility of a file before calling `fs.open()`, `fs.readFile()`, or `fs.writeFile()`. Doing so introduces a race condition, since other processes may change the file's state between the two calls. Instead, user code should open/read/write the file directly and handle the error raised if the file is not accessible.
**write (NOT RECOMMENDED)**
```
import { access, open, close } from 'node:fs';
access('myfile', (err) => {
if (!err) {
console.error('myfile already exists');
return;
}
open('myfile', 'wx', (err, fd) => {
if (err) throw err;
try {
writeMyData(fd);
} finally {
close(fd, (err) => {
if (err) throw err;
});
}
});
});
```
**write (RECOMMENDED)**
```
import { open, close } from 'node:fs';
open('myfile', 'wx', (err, fd) => {
if (err) {
if (err.code === 'EEXIST') {
console.error('myfile already exists');
return;
}
throw err;
}
try {
writeMyData(fd);
} finally {
close(fd, (err) => {
if (err) throw err;
});
}
});
```
**read (NOT RECOMMENDED)**
```
import { access, open, close } from 'node:fs';
access('myfile', (err) => {
if (err) {
if (err.code === 'ENOENT') {
console.error('myfile does not exist');
return;
}
throw err;
}
open('myfile', 'r', (err, fd) => {
if (err) throw err;
try {
readMyData(fd);
} finally {
close(fd, (err) => {
if (err) throw err;
});
}
});
});
```
**read (RECOMMENDED)**
```
import { open, close } from 'node:fs';
open('myfile', 'r', (err, fd) => {
if (err) {
if (err.code === 'ENOENT') {
console.error('myfile does not exist');
return;
}
throw err;
}
try {
readMyData(fd);
} finally {
close(fd, (err) => {
if (err) throw err;
});
}
});
```
The "not recommended" examples above check for accessibility and then use the file; the "recommended" examples are better because they use the file directly and handle the error, if any.
In general, check for the accessibility of a file only if the file will not be used directly, for example when its accessibility is a signal from another process.
On Windows, access-control policies (ACLs) on a directory may limit access to a file or directory. The `fs.access()` function, however, does not check the ACL and therefore may report that a path is accessible even if the ACL restricts the user from reading or writing to it.
####
`fs.appendFile(path, data[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v7.0.0 | The passed `options` object will never be modified. |
| v5.0.0 | The `file` parameter can be a file descriptor now. |
| v0.6.7 | Added in: v0.6.7 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) filename or file descriptor
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
+ `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666`
+ `flag` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'a'`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Asynchronously append data to a file, creating the file if it does not yet exist. `data` can be a string or a [<Buffer>](buffer#class-buffer).
The `mode` option only affects the newly created file. See [`fs.open()`](#fsopenpath-flags-mode-callback) for more details.
```
import { appendFile } from 'node:fs';
appendFile('message.txt', 'data to append', (err) => {
if (err) throw err;
console.log('The "data to append" was appended to file!');
});
```
If `options` is a string, then it specifies the encoding:
```
import { appendFile } from 'node:fs';
appendFile('message.txt', 'data to append', 'utf8', callback);
```
The `path` may be specified as a numeric file descriptor that has been opened for appending (using `fs.open()` or `fs.openSync()`). The file descriptor will not be closed automatically.
```
import { open, close, appendFile } from 'node:fs';
function closeFd(fd) {
close(fd, (err) => {
if (err) throw err;
});
}
open('message.txt', 'a', (err, fd) => {
if (err) throw err;
try {
appendFile(fd, 'data to append', 'utf8', (err) => {
closeFd(fd);
if (err) throw err;
});
} catch (err) {
closeFd(fd);
throw err;
}
});
```
####
`fs.chmod(path, mode, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.1.30 | Added in: v0.1.30 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Asynchronously changes the permissions of a file. No arguments other than a possible exception are given to the completion callback.
See the POSIX [`chmod(2)`](http://man7.org/linux/man-pages/man2/chmod.2.html) documentation for more detail.
```
import { chmod } from 'node:fs';
chmod('my_file.txt', 0o775, (err) => {
if (err) throw err;
console.log('The permissions for file "my_file.txt" have been changed!');
});
```
##### File modes
The `mode` argument used in both the `fs.chmod()` and `fs.chmodSync()` methods is a numeric bitmask created using a logical OR of the following constants:
| Constant | Octal | Description |
| --- | --- | --- |
| `fs.constants.S_IRUSR` | `0o400` | read by owner |
| `fs.constants.S_IWUSR` | `0o200` | write by owner |
| `fs.constants.S_IXUSR` | `0o100` | execute/search by owner |
| `fs.constants.S_IRGRP` | `0o40` | read by group |
| `fs.constants.S_IWGRP` | `0o20` | write by group |
| `fs.constants.S_IXGRP` | `0o10` | execute/search by group |
| `fs.constants.S_IROTH` | `0o4` | read by others |
| `fs.constants.S_IWOTH` | `0o2` | write by others |
| `fs.constants.S_IXOTH` | `0o1` | execute/search by others |
An easier method of constructing the `mode` is to use a sequence of three octal digits (e.g. `765`). The left-most digit (`7` in the example), specifies the permissions for the file owner. The middle digit (`6` in the example), specifies permissions for the group. The right-most digit (`5` in the example), specifies the permissions for others.
| Number | Description |
| --- | --- |
| `7` | read, write, and execute |
| `6` | read and write |
| `5` | read and execute |
| `4` | read only |
| `3` | write and execute |
| `2` | write only |
| `1` | execute only |
| `0` | no permission |
For example, the octal value `0o765` means:
* The owner may read, write, and execute the file.
* The group may read and write the file.
* Others may read and execute the file.
When using raw numbers where file modes are expected, any value larger than `0o777` may result in platform-specific behaviors that are not supported to work consistently. Therefore constants like `S_ISVTX`, `S_ISGID`, or `S_ISUID` are not exposed in `fs.constants`.
Caveats: on Windows only the write permission can be changed, and the distinction among the permissions of group, owner, or others is not implemented.
####
`fs.chown(path, uid, gid, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.1.97 | Added in: v0.1.97 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `uid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `gid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Asynchronously changes owner and group of a file. No arguments other than a possible exception are given to the completion callback.
See the POSIX [`chown(2)`](http://man7.org/linux/man-pages/man2/chown.2.html) documentation for more detail.
####
`fs.close(fd[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v15.9.0, v14.17.0 | A default callback is now used if one is not provided. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.0.2 | Added in: v0.0.2 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Closes the file descriptor. No arguments other than a possible exception are given to the completion callback.
Calling `fs.close()` on any file descriptor (`fd`) that is currently in use through any other `fs` operation may lead to undefined behavior.
See the POSIX [`close(2)`](http://man7.org/linux/man-pages/man2/close.2.html) documentation for more detail.
####
`fs.copyFile(src, dest[, mode], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v14.0.0 | Changed `flags` argument to `mode` and imposed stricter type validation. |
| v8.5.0 | Added in: v8.5.0 |
* `src` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) source filename to copy
* `dest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) destination filename of the copy operation
* `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) modifiers for copy operation. **Default:** `0`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Asynchronously copies `src` to `dest`. By default, `dest` is overwritten if it already exists. No arguments other than a possible exception are given to the callback function. Node.js makes no guarantees about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, Node.js will attempt to remove the destination.
`mode` is an optional integer that specifies the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. `fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE`).
* `fs.constants.COPYFILE_EXCL`: The copy operation will fail if `dest` already exists.
* `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used.
* `fs.constants.COPYFILE_FICLONE_FORCE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail.
```
import { copyFile, constants } from 'node:fs';
function callback(err) {
if (err) throw err;
console.log('source.txt was copied to destination.txt');
}
// destination.txt will be created or overwritten by default.
copyFile('source.txt', 'destination.txt', callback);
// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.
copyFile('source.txt', 'destination.txt', constants.COPYFILE_EXCL, callback);
```
####
`fs.cp(src, dest[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v17.6.0, v16.15.0 | Accepts an additional `verbatimSymlinks` option to specify whether to perform path resolution for symlinks. |
| v16.7.0 | Added in: v16.7.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `src` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) source path to copy.
* `dest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) destination path to copy to.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `dereference` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) dereference symlinks. **Default:** `false`.
+ `errorOnExist` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) when `force` is `false`, and the destination exists, throw an error. **Default:** `false`.
+ `filter` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Function to filter copied files/directories. Return `true` to copy the item, `false` to ignore it. Can also return a `Promise` that resolves to `true` or `false` **Default:** `undefined`.
+ `force` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) overwrite existing file or directory. The copy operation will ignore errors if you set this to false and the destination exists. Use the `errorOnExist` option to change this behavior. **Default:** `true`.
+ `preserveTimestamps` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true` timestamps from `src` will be preserved. **Default:** `false`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) copy directories recursively **Default:** `false`
+ `verbatimSymlinks` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, path resolution for symlinks will be skipped. **Default:** `false`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Asynchronously copies the entire directory structure from `src` to `dest`, including subdirectories and files.
When copying a directory to another directory, globs are not supported and behavior is similar to `cp dir1/ dir2/`.
####
`fs.createReadStream(path[, options])`
History
| Version | Changes |
| --- | --- |
| v16.10.0 | The `fs` option does not need `open` method if an `fd` was provided. |
| v16.10.0 | The `fs` option does not need `close` method if `autoClose` is `false`. |
| v15.4.0 | The `fd` option accepts FileHandle arguments. |
| v14.0.0 | Change `emitClose` default to `true`. |
| v13.6.0, v12.17.0 | The `fs` options allow overriding the used `fs` implementation. |
| v12.10.0 | Enable `emitClose` option. |
| v11.0.0 | Impose new restrictions on `start` and `end`, throwing more appropriate errors in cases when we cannot reasonably handle the input values. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The passed `options` object will never be modified. |
| v2.3.0 | The passed `options` object can be a string now. |
| v0.1.31 | Added in: v0.1.31 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `flags` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'r'`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `null`
+ `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<FileHandle>](fs#class-filehandle) **Default:** `null`
+ `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666`
+ `autoClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `emitClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `start` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `end` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `Infinity`
+ `highWaterMark` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `64 * 1024`
+ `fs` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* Returns: [<fs.ReadStream>](fs#class-fsreadstream)
Unlike the 16 KiB default `highWaterMark` for a [<stream.Readable>](stream#class-streamreadable), the stream returned by this method has a default `highWaterMark` of 64 KiB.
`options` can include `start` and `end` values to read a range of bytes from the file instead of the entire file. Both `start` and `end` are inclusive and start counting at 0, allowed values are in the [0, [`Number.MAX_SAFE_INTEGER`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER)] range. If `fd` is specified and `start` is omitted or `undefined`, `fs.createReadStream()` reads sequentially from the current file position. The `encoding` can be any one of those accepted by [<Buffer>](buffer#class-buffer).
If `fd` is specified, `ReadStream` will ignore the `path` argument and will use the specified file descriptor. This means that no `'open'` event will be emitted. `fd` should be blocking; non-blocking `fd`s should be passed to [<net.Socket>](net#class-netsocket).
If `fd` points to a character device that only supports blocking reads (such as keyboard or sound card), read operations do not finish until data is available. This can prevent the process from exiting and the stream from closing naturally.
By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior.
By providing the `fs` option, it is possible to override the corresponding `fs` implementations for `open`, `read`, and `close`. When providing the `fs` option, an override for `read` is required. If no `fd` is provided, an override for `open` is also required. If `autoClose` is `true`, an override for `close` is also required.
```
import { createReadStream } from 'node:fs';
// Create a stream from some character device.
const stream = createReadStream('/dev/input/event0');
setTimeout(() => {
stream.close(); // This may not close the stream.
// Artificially marking end-of-stream, as if the underlying resource had
// indicated end-of-file by itself, allows the stream to close.
// This does not cancel pending read operations, and if there is such an
// operation, the process may still not be able to exit successfully
// until it finishes.
stream.push(null);
stream.read(0);
}, 100);
```
If `autoClose` is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak. If `autoClose` is set to true (default behavior), on `'error'` or `'end'` the file descriptor will be closed automatically.
`mode` sets the file mode (permission and sticky bits), but only if the file was created.
An example to read the last 10 bytes of a file which is 100 bytes long:
```
import { createReadStream } from 'node:fs';
createReadStream('sample.txt', { start: 90, end: 99 });
```
If `options` is a string, then it specifies the encoding.
####
`fs.createWriteStream(path[, options])`
History
| Version | Changes |
| --- | --- |
| v16.10.0 | The `fs` option does not need `open` method if an `fd` was provided. |
| v16.10.0 | The `fs` option does not need `close` method if `autoClose` is `false`. |
| v15.4.0 | The `fd` option accepts FileHandle arguments. |
| v14.0.0 | Change `emitClose` default to `true`. |
| v13.6.0, v12.17.0 | The `fs` options allow overriding the used `fs` implementation. |
| v12.10.0 | Enable `emitClose` option. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The passed `options` object will never be modified. |
| v5.5.0 | The `autoClose` option is supported now. |
| v2.3.0 | The passed `options` object can be a string now. |
| v0.1.31 | Added in: v0.1.31 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `flags` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'w'`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
+ `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<FileHandle>](fs#class-filehandle) **Default:** `null`
+ `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666`
+ `autoClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `emitClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `start` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `fs` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* Returns: [<fs.WriteStream>](fs#class-fswritestream)
`options` may also include a `start` option to allow writing data at some position past the beginning of the file, allowed values are in the [0, [`Number.MAX_SAFE_INTEGER`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER)] range. Modifying a file rather than replacing it may require the `flags` option to be set to `r+` rather than the default `w`. The `encoding` can be any one of those accepted by [<Buffer>](buffer#class-buffer).
If `autoClose` is set to true (default behavior) on `'error'` or `'finish'` the file descriptor will be closed automatically. If `autoClose` is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak.
By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior.
By providing the `fs` option it is possible to override the corresponding `fs` implementations for `open`, `write`, `writev`, and `close`. Overriding `write()` without `writev()` can reduce performance as some optimizations (`_writev()`) will be disabled. When providing the `fs` option, overrides for at least one of `write` and `writev` are required. If no `fd` option is supplied, an override for `open` is also required. If `autoClose` is `true`, an override for `close` is also required.
Like [<fs.ReadStream>](fs#class-fsreadstream), if `fd` is specified, [<fs.WriteStream>](fs#class-fswritestream) will ignore the `path` argument and will use the specified file descriptor. This means that no `'open'` event will be emitted. `fd` should be blocking; non-blocking `fd`s should be passed to [<net.Socket>](net#class-netsocket).
If `options` is a string, then it specifies the encoding.
####
`fs.exists(path, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v1.0.0 | Deprecated since: v1.0.0 |
| v0.0.2 | Added in: v0.0.2 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`fs.stat()`](#fsstatpath-options-callback) or [`fs.access()`](#fsaccesspath-mode-callback) instead.
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `exists` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Test whether or not the given path exists by checking with the file system. Then call the `callback` argument with either true or false:
```
import { exists } from 'node:fs';
exists('/etc/passwd', (e) => {
console.log(e ? 'it exists' : 'no passwd!');
});
```
**The parameters for this callback are not consistent with other Node.js callbacks.** Normally, the first parameter to a Node.js callback is an `err` parameter, optionally followed by other parameters. The `fs.exists()` callback has only one boolean parameter. This is one reason `fs.access()` is recommended instead of `fs.exists()`.
Using `fs.exists()` to check for the existence of a file before calling `fs.open()`, `fs.readFile()`, or `fs.writeFile()` is not recommended. Doing so introduces a race condition, since other processes may change the file's state between the two calls. Instead, user code should open/read/write the file directly and handle the error raised if the file does not exist.
**write (NOT RECOMMENDED)**
```
import { exists, open, close } from 'node:fs';
exists('myfile', (e) => {
if (e) {
console.error('myfile already exists');
} else {
open('myfile', 'wx', (err, fd) => {
if (err) throw err;
try {
writeMyData(fd);
} finally {
close(fd, (err) => {
if (err) throw err;
});
}
});
}
});
```
**write (RECOMMENDED)**
```
import { open, close } from 'node:fs';
open('myfile', 'wx', (err, fd) => {
if (err) {
if (err.code === 'EEXIST') {
console.error('myfile already exists');
return;
}
throw err;
}
try {
writeMyData(fd);
} finally {
close(fd, (err) => {
if (err) throw err;
});
}
});
```
**read (NOT RECOMMENDED)**
```
import { open, close, exists } from 'node:fs';
exists('myfile', (e) => {
if (e) {
open('myfile', 'r', (err, fd) => {
if (err) throw err;
try {
readMyData(fd);
} finally {
close(fd, (err) => {
if (err) throw err;
});
}
});
} else {
console.error('myfile does not exist');
}
});
```
**read (RECOMMENDED)**
```
import { open, close } from 'node:fs';
open('myfile', 'r', (err, fd) => {
if (err) {
if (err.code === 'ENOENT') {
console.error('myfile does not exist');
return;
}
throw err;
}
try {
readMyData(fd);
} finally {
close(fd, (err) => {
if (err) throw err;
});
}
});
```
The "not recommended" examples above check for existence and then use the file; the "recommended" examples are better because they use the file directly and handle the error, if any.
In general, check for the existence of a file only if the file won't be used directly, for example when its existence is a signal from another process.
####
`fs.fchmod(fd, mode, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.4.7 | Added in: v0.4.7 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Sets the permissions on the file. No arguments other than a possible exception are given to the completion callback.
See the POSIX [`fchmod(2)`](http://man7.org/linux/man-pages/man2/fchmod.2.html) documentation for more detail.
####
`fs.fchown(fd, uid, gid, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.4.7 | Added in: v0.4.7 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `uid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `gid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Sets the owner of the file. No arguments other than a possible exception are given to the completion callback.
See the POSIX [`fchown(2)`](http://man7.org/linux/man-pages/man2/fchown.2.html) documentation for more detail.
####
`fs.fdatasync(fd, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.1.96 | Added in: v0.1.96 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX [`fdatasync(2)`](http://man7.org/linux/man-pages/man2/fdatasync.2.html) documentation for details. No arguments other than a possible exception are given to the completion callback.
####
`fs.fstat(fd[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.5.0 | Accepts an additional `options` object to specify whether the numeric values returned should be bigint. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.1.95 | Added in: v0.1.95 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the numeric values in the returned [<fs.Stats>](fs#class-fsstats) object should be `bigint`. **Default:** `false`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `stats` [<fs.Stats>](fs#class-fsstats)
Invokes the callback with the [<fs.Stats>](fs#class-fsstats) for the file descriptor.
See the POSIX [`fstat(2)`](http://man7.org/linux/man-pages/man2/fstat.2.html) documentation for more detail.
####
`fs.fsync(fd, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.1.96 | Added in: v0.1.96 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX [`fsync(2)`](http://man7.org/linux/man-pages/man2/fsync.2.html) documentation for more detail. No arguments other than a possible exception are given to the completion callback.
####
`fs.ftruncate(fd[, len], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.8.6 | Added in: v0.8.6 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `len` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Truncates the file descriptor. No arguments other than a possible exception are given to the completion callback.
See the POSIX [`ftruncate(2)`](http://man7.org/linux/man-pages/man2/ftruncate.2.html) documentation for more detail.
If the file referred to by the file descriptor was larger than `len` bytes, only the first `len` bytes will be retained in the file.
For example, the following program retains only the first four bytes of the file:
```
import { open, close, ftruncate } from 'node:fs';
function closeFd(fd) {
close(fd, (err) => {
if (err) throw err;
});
}
open('temp.txt', 'r+', (err, fd) => {
if (err) throw err;
try {
ftruncate(fd, 4, (err) => {
closeFd(fd);
if (err) throw err;
});
} catch (err) {
closeFd(fd);
if (err) throw err;
}
});
```
If the file previously was shorter than `len` bytes, it is extended, and the extended part is filled with null bytes (`'\0'`):
If `len` is negative then `0` will be used.
####
`fs.futimes(fd, atime, mtime, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v4.1.0 | Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. |
| v0.4.2 | Added in: v0.4.2 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `atime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `mtime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Change the file system timestamps of the object referenced by the supplied file descriptor. See [`fs.utimes()`](#fsutimespath-atime-mtime-callback).
####
`fs.lchmod(path, mode, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v16.0.0 | The error returned may be an `AggregateError` if more than one error is returned. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.4.7 | Deprecated since: v0.4.7 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) | [<AggregateError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError)
Changes the permissions on a symbolic link. No arguments other than a possible exception are given to the completion callback.
This method is only implemented on macOS.
See the POSIX [`lchmod(2)`](https://www.freebsd.org/cgi/man.cgi?query=lchmod&sektion=2) documentation for more detail.
####
`fs.lchown(path, uid, gid, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.6.0 | This API is no longer deprecated. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.4.7 | Documentation-only deprecation. |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `uid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `gid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Set the owner of the symbolic link. No arguments other than a possible exception are given to the completion callback.
See the POSIX [`lchown(2)`](http://man7.org/linux/man-pages/man2/lchown.2.html) documentation for more detail.
####
`fs.lutimes(path, atime, mtime, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v14.5.0, v12.19.0 | Added in: v14.5.0, v12.19.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `atime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `mtime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Changes the access and modification times of a file in the same way as [`fs.utimes()`](#fsutimespath-atime-mtime-callback), with the difference that if the path refers to a symbolic link, then the link is not dereferenced: instead, the timestamps of the symbolic link itself are changed.
No arguments other than a possible exception are given to the completion callback.
####
`fs.link(existingPath, newPath, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `existingPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.1.31 | Added in: v0.1.31 |
* `existingPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `newPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Creates a new link from the `existingPath` to the `newPath`. See the POSIX [`link(2)`](http://man7.org/linux/man-pages/man2/link.2.html) documentation for more detail. No arguments other than a possible exception are given to the completion callback.
####
`fs.lstat(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.5.0 | Accepts an additional `options` object to specify whether the numeric values returned should be bigint. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.1.30 | Added in: v0.1.30 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the numeric values in the returned [<fs.Stats>](fs#class-fsstats) object should be `bigint`. **Default:** `false`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `stats` [<fs.Stats>](fs#class-fsstats)
Retrieves the [<fs.Stats>](fs#class-fsstats) for the symbolic link referred to by the path. The callback gets two arguments `(err, stats)` where `stats` is a [<fs.Stats>](fs#class-fsstats) object. `lstat()` is identical to `stat()`, except that if `path` is a symbolic link, then the link itself is stat-ed, not the file that it refers to.
See the POSIX [`lstat(2)`](http://man7.org/linux/man-pages/man2/lstat.2.html) documentation for more details.
####
`fs.mkdir(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v13.11.0, v12.17.0 | In `recursive` mode, the callback now receives the first created path as an argument. |
| v10.12.0 | The second argument can now be an `options` object with `recursive` and `mode` properties. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.1.8 | Added in: v0.1.8 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
+ `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Not supported on Windows. **Default:** `0o777`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Present only if a directory is created with `recursive` set to `true`.
Asynchronously creates a directory.
The callback is given a possible exception and, if `recursive` is `true`, the first directory path created, `(err[, path])`. `path` can still be `undefined` when `recursive` is `true`, if no directory was created.
The optional `options` argument can be an integer specifying `mode` (permission and sticky bits), or an object with a `mode` property and a `recursive` property indicating whether parent directories should be created. Calling `fs.mkdir()` when `path` is a directory that exists results in an error only when `recursive` is false.
```
import { mkdir } from 'node:fs';
// Creates /tmp/a/apple, regardless of whether `/tmp` and /tmp/a exist.
mkdir('/tmp/a/apple', { recursive: true }, (err) => {
if (err) throw err;
});
```
On Windows, using `fs.mkdir()` on the root directory even with recursion will result in an error:
```
import { mkdir } from 'node:fs';
mkdir('/', { recursive: true }, (err) => {
// => [Error: EPERM: operation not permitted, mkdir 'C:\']
});
```
See the POSIX [`mkdir(2)`](http://man7.org/linux/man-pages/man2/mkdir.2.html) documentation for more details.
####
`fs.mkdtemp(prefix[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v16.5.0, v14.18.0 | The `prefix` parameter now accepts an empty string. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v6.2.1 | The `callback` parameter is optional now. |
| v5.10.0 | Added in: v5.10.0 |
* `prefix` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `directory` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Creates a unique temporary directory.
Generates six random characters to be appended behind a required `prefix` to create a unique temporary directory. Due to platform inconsistencies, avoid trailing `X` characters in `prefix`. Some platforms, notably the BSDs, can return more than six random characters, and replace trailing `X` characters in `prefix` with random characters.
The created directory path is passed as a string to the callback's second parameter.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use.
```
import { mkdtemp } from 'node:fs';
mkdtemp(path.join(os.tmpdir(), 'foo-'), (err, directory) => {
if (err) throw err;
console.log(directory);
// Prints: /tmp/foo-itXde2 or C:\Users\...\AppData\Local\Temp\foo-itXde2
});
```
The `fs.mkdtemp()` method will append the six randomly selected characters directly to the `prefix` string. For instance, given a directory `/tmp`, if the intention is to create a temporary directory *within* `/tmp`, the `prefix` must end with a trailing platform-specific path separator (`require('node:path').sep`).
```
import { tmpdir } from 'node:os';
import { mkdtemp } from 'node:fs';
// The parent directory for the new temporary directory
const tmpDir = tmpdir();
// This method is *INCORRECT*:
mkdtemp(tmpDir, (err, directory) => {
if (err) throw err;
console.log(directory);
// Will print something similar to `/tmpabc123`.
// A new temporary directory is created at the file system root
// rather than *within* the /tmp directory.
});
// This method is *CORRECT*:
import { sep } from 'node:path';
mkdtemp(`${tmpDir}${sep}`, (err, directory) => {
if (err) throw err;
console.log(directory);
// Will print something similar to `/tmp/abc123`.
// A new temporary directory is created within
// the /tmp directory.
});
```
####
`fs.open(path[, flags[, mode]], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v11.1.0 | The `flags` argument is now optional and defaults to `'r'`. |
| v9.9.0 | The `as` and `as+` flags are supported now. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.0.2 | Added in: v0.0.2 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `flags` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) See [support of file system `flags`](#file-system-flags). **Default:** `'r'`.
* `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666` (readable and writable)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Asynchronous file open. See the POSIX [`open(2)`](http://man7.org/linux/man-pages/man2/open.2.html) documentation for more details.
`mode` sets the file mode (permission and sticky bits), but only if the file was created. On Windows, only the write permission can be manipulated; see [`fs.chmod()`](#fschmodpath-mode-callback).
The callback gets two arguments `(err, fd)`.
Some characters (`< > : " / \ | ? *`) are reserved under Windows as documented by [Naming Files, Paths, and Namespaces](https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file). Under NTFS, if the filename contains a colon, Node.js will open a file system stream, as described by [this MSDN page](https://docs.microsoft.com/en-us/windows/desktop/FileIO/using-streams).
Functions based on `fs.open()` exhibit this behavior as well: `fs.writeFile()`, `fs.readFile()`, etc.
####
`fs.opendir(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v13.1.0, v12.16.0 | The `bufferSize` option was introduced. |
| v12.12.0 | Added in: v12.12.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
+ `bufferSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of directory entries that are buffered internally when reading from the directory. Higher values lead to better performance but higher memory usage. **Default:** `32`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `dir` [<fs.Dir>](fs#class-fsdir)
Asynchronously open a directory. See the POSIX [`opendir(3)`](http://man7.org/linux/man-pages/man3/opendir.3.html) documentation for more details.
Creates an [<fs.Dir>](fs#class-fsdir), which contains all further functions for reading from and cleaning up the directory.
The `encoding` option sets the encoding for the `path` while opening the directory and subsequent read operations.
####
`fs.read(fd, buffer, offset, length, position, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.10.0 | The `buffer` parameter can now be any `TypedArray`, or a `DataView`. |
| v7.4.0 | The `buffer` parameter can now be a `Uint8Array`. |
| v6.0.0 | The `length` parameter can now be `0`. |
| v0.0.2 | Added in: v0.0.2 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The buffer that the data will be written to.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The position in `buffer` to write the data to.
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes to read.
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) Specifies where to begin reading from in the file. If `position` is `null` or `-1` , data will be read from the current file position, and the file position will be updated. If `position` is an integer, the file position will be unchanged.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `bytesRead` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `buffer` [<Buffer>](buffer#class-buffer)
Read data from the file specified by `fd`.
The callback is given the three arguments, `(err, bytesRead, buffer)`.
If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero.
If this method is invoked as its [`util.promisify()`](util#utilpromisifyoriginal)ed version, it returns a promise for an `Object` with `bytesRead` and `buffer` properties.
####
`fs.read(fd[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v13.11.0, v12.17.0 | Added in: v13.11.0, v12.17.0 |
| v13.11.0, v12.17.0 | Options object can be passed in to make buffer, offset, length, and position optional. |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) **Default:** `Buffer.alloc(16384)`
+ `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
+ `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.byteLength - offset`
+ `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `bytesRead` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `buffer` [<Buffer>](buffer#class-buffer)
Similar to the [`fs.read()`](#fsreadfd-buffer-offset-length-position-callback) function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values.
####
`fs.read(fd, buffer[, options], callback)`
Added in: v18.2.0, v16.17.0 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The buffer that the data will be written to.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
+ `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.byteLength - offset`
+ `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) **Default:** `null`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `bytesRead` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `buffer` [<Buffer>](buffer#class-buffer)
Similar to the [`fs.read()`](#fsreadfd-buffer-offset-length-position-callback) function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values.
####
`fs.readdir(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.10.0 | New option `withFileTypes` was added. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v6.0.0 | The `options` parameter was added. |
| v0.1.8 | Added in: v0.1.8 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
+ `withFileTypes` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `files` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer[]>](buffer#class-buffer) | [<fs.Dirent[]>](fs#class-fsdirent)
Reads the contents of a directory. The callback gets two arguments `(err, files)` where `files` is an array of the names of the files in the directory excluding `'.'` and `'..'`.
See the POSIX [`readdir(3)`](http://man7.org/linux/man-pages/man3/readdir.3.html) documentation for more details.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the filenames passed to the callback. If the `encoding` is set to `'buffer'`, the filenames returned will be passed as [<Buffer>](buffer#class-buffer) objects.
If `options.withFileTypes` is set to `true`, the `files` array will contain [<fs.Dirent>](fs#class-fsdirent) objects.
####
`fs.readFile(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v16.0.0 | The error returned may be an `AggregateError` if more than one error is returned. |
| v15.2.0, v14.17.0 | The options argument may include an AbortSignal to abort an ongoing readFile request. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v5.1.0 | The `callback` will always be called with `null` as the `error` parameter in case of success. |
| v5.0.0 | The `path` parameter can be a file descriptor now. |
| v0.1.29 | Added in: v0.1.29 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) filename or file descriptor
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
+ `flag` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'r'`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows aborting an in-progress readFile
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) | [<AggregateError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError)
+ `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
Asynchronously reads the entire contents of a file.
```
import { readFile } from 'node:fs';
readFile('/etc/passwd', (err, data) => {
if (err) throw err;
console.log(data);
});
```
The callback is passed two arguments `(err, data)`, where `data` is the contents of the file.
If no encoding is specified, then the raw buffer is returned.
If `options` is a string, then it specifies the encoding:
```
import { readFile } from 'node:fs';
readFile('/etc/passwd', 'utf8', callback);
```
When the path is a directory, the behavior of `fs.readFile()` and [`fs.readFileSync()`](#fsreadfilesyncpath-options) is platform-specific. On macOS, Linux, and Windows, an error will be returned. On FreeBSD, a representation of the directory's contents will be returned.
```
import { readFile } from 'node:fs';
// macOS, Linux, and Windows
readFile('<directory>', (err, data) => {
// => [Error: EISDIR: illegal operation on a directory, read <directory>]
});
// FreeBSD
readFile('<directory>', (err, data) => {
// => null, <data>
});
```
It is possible to abort an ongoing request using an `AbortSignal`. If a request is aborted the callback is called with an `AbortError`:
```
import { readFile } from 'node:fs';
const controller = new AbortController();
const signal = controller.signal;
readFile(fileInfo[0].name, { signal }, (err, buf) => {
// ...
});
// When you want to abort the request
controller.abort();
```
The `fs.readFile()` function buffers the entire file. To minimize memory costs, when possible prefer streaming via `fs.createReadStream()`.
Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.readFile` performs.
##### File descriptors
1. Any specified file descriptor has to support reading.
2. If a file descriptor is specified as the `path`, it will not be closed automatically.
3. The reading will begin at the current position. For example, if the file already had `'Hello World`' and six bytes are read with the file descriptor, the call to `fs.readFile()` with the same file descriptor, would give `'World'`, rather than `'Hello World'`.
##### Performance Considerations
The `fs.readFile()` method asynchronously reads the contents of a file into memory one chunk at a time, allowing the event loop to turn between each chunk. This allows the read operation to have less impact on other activity that may be using the underlying libuv thread pool but means that it will take longer to read a complete file into memory.
The additional read overhead can vary broadly on different systems and depends on the type of file being read. If the file type is not a regular file (a pipe for instance) and Node.js is unable to determine an actual file size, each read operation will load on 64 KiB of data. For regular files, each read will process 512 KiB of data.
For applications that require as-fast-as-possible reading of file contents, it is better to use `fs.read()` directly and for application code to manage reading the full contents of the file itself.
The Node.js GitHub issue [#25741](https://github.com/nodejs/node/issues/25741) provides more information and a detailed analysis on the performance of `fs.readFile()` for multiple file sizes in different Node.js versions.
####
`fs.readlink(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.1.31 | Added in: v0.1.31 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `linkString` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
Reads the contents of the symbolic link referred to by `path`. The callback gets two arguments `(err, linkString)`.
See the POSIX [`readlink(2)`](http://man7.org/linux/man-pages/man2/readlink.2.html) documentation for more details.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the link path passed to the callback. If the `encoding` is set to `'buffer'`, the link path returned will be passed as a [<Buffer>](buffer#class-buffer) object.
####
`fs.readv(fd, buffers[, position], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v13.13.0, v12.17.0 | Added in: v13.13.0, v12.17.0 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffers` [<ArrayBufferView[]>](https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `bytesRead` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `buffers` [<ArrayBufferView[]>](https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView)
Read from a file specified by `fd` and write to an array of `ArrayBufferView`s using `readv()`.
`position` is the offset from the beginning of the file from where data should be read. If `typeof position !== 'number'`, the data will be read from the current position.
The callback will be given three arguments: `err`, `bytesRead`, and `buffers`. `bytesRead` is how many bytes were read from the file.
If this method is invoked as its [`util.promisify()`](util#utilpromisifyoriginal)ed version, it returns a promise for an `Object` with `bytesRead` and `buffers` properties.
####
`fs.realpath(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v8.0.0 | Pipe/Socket resolve support was added. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v6.4.0 | Calling `realpath` now works again for various edge cases on Windows. |
| v6.0.0 | The `cache` parameter was removed. |
| v0.1.31 | Added in: v0.1.31 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `resolvedPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
Asynchronously computes the canonical pathname by resolving `.`, `..`, and symbolic links.
A canonical pathname is not necessarily unique. Hard links and bind mounts can expose a file system entity through many pathnames.
This function behaves like [`realpath(3)`](http://man7.org/linux/man-pages/man3/realpath.3.html), with some exceptions:
1. No case conversion is performed on case-insensitive file systems.
2. The maximum number of symbolic links is platform-independent and generally (much) higher than what the native [`realpath(3)`](http://man7.org/linux/man-pages/man3/realpath.3.html) implementation supports.
The `callback` gets two arguments `(err, resolvedPath)`. May use `process.cwd` to resolve relative paths.
Only paths that can be converted to UTF8 strings are supported.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the path passed to the callback. If the `encoding` is set to `'buffer'`, the path returned will be passed as a [<Buffer>](buffer#class-buffer) object.
If `path` resolves to a socket or a pipe, the function will return a system dependent name for that object.
####
`fs.realpath.native(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v9.2.0 | Added in: v9.2.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `resolvedPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
Asynchronous [`realpath(3)`](http://man7.org/linux/man-pages/man3/realpath.3.html).
The `callback` gets two arguments `(err, resolvedPath)`.
Only paths that can be converted to UTF8 strings are supported.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the path passed to the callback. If the `encoding` is set to `'buffer'`, the path returned will be passed as a [<Buffer>](buffer#class-buffer) object.
On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on `/proc` in order for this function to work. Glibc does not have this restriction.
####
`fs.rename(oldPath, newPath, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `oldPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.0.2 | Added in: v0.0.2 |
* `oldPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `newPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Asynchronously rename file at `oldPath` to the pathname provided as `newPath`. In the case that `newPath` already exists, it will be overwritten. If there is a directory at `newPath`, an error will be raised instead. No arguments other than a possible exception are given to the completion callback.
See also: [`rename(2)`](http://man7.org/linux/man-pages/man2/rename.2.html).
```
import { rename } from 'node:fs';
rename('oldFile.txt', 'newFile.txt', (err) => {
if (err) throw err;
console.log('Rename complete!');
});
```
####
`fs.rmdir(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v16.0.0 | Using `fs.rmdir(path, { recursive: true })` on a `path` that is a file is no longer permitted and results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. |
| v16.0.0 | Using `fs.rmdir(path, { recursive: true })` on a `path` that does not exist is no longer permitted and results in a `ENOENT` error. |
| v16.0.0 | The `recursive` option is deprecated, using it triggers a deprecation warning. |
| v14.14.0 | The `recursive` option is deprecated, use `fs.rm` instead. |
| v13.3.0, v12.16.0 | The `maxBusyTries` option is renamed to `maxRetries`, and its default is 0. The `emfileWait` option has been removed, and `EMFILE` errors use the same retry logic as other errors. The `retryDelay` option is now supported. `ENFILE` errors are now retried. |
| v12.10.0 | The `recursive`, `maxBusyTries`, and `emfileWait` options are now supported. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameters can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.0.2 | Added in: v0.0.2 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `maxRetries` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js retries the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, perform a recursive directory removal. In recursive mode, operations are retried on failure. **Default:** `false`. **Deprecated.**
+ `retryDelay` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Asynchronous [`rmdir(2)`](http://man7.org/linux/man-pages/man2/rmdir.2.html). No arguments other than a possible exception are given to the completion callback.
Using `fs.rmdir()` on a file (not a directory) results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX.
To get a behavior similar to the `rm -rf` Unix command, use [`fs.rm()`](#fsrmpath-options-callback) with options `{ recursive: true, force: true }`.
####
`fs.rm(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v17.3.0, v16.14.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v14.14.0 | Added in: v14.14.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `force` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, exceptions will be ignored if `path` does not exist. **Default:** `false`.
+ `maxRetries` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js will retry the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, perform a recursive removal. In recursive mode operations are retried on failure. **Default:** `false`.
+ `retryDelay` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Asynchronously removes files and directories (modeled on the standard POSIX `rm` utility). No arguments other than a possible exception are given to the completion callback.
####
`fs.stat(path[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.5.0 | Accepts an additional `options` object to specify whether the numeric values returned should be bigint. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.0.2 | Added in: v0.0.2 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the numeric values in the returned [<fs.Stats>](fs#class-fsstats) object should be `bigint`. **Default:** `false`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `stats` [<fs.Stats>](fs#class-fsstats)
Asynchronous [`stat(2)`](http://man7.org/linux/man-pages/man2/stat.2.html). The callback gets two arguments `(err, stats)` where `stats` is an [<fs.Stats>](fs#class-fsstats) object.
In case of an error, the `err.code` will be one of [Common System Errors](errors#common-system-errors).
Using `fs.stat()` to check for the existence of a file before calling `fs.open()`, `fs.readFile()`, or `fs.writeFile()` is not recommended. Instead, user code should open/read/write the file directly and handle the error raised if the file is not available.
To check if a file exists without manipulating it afterwards, [`fs.access()`](#fsaccesspath-mode-callback) is recommended.
For example, given the following directory structure:
```
- txtDir
-- file.txt
- app.js
```
The next program will check for the stats of the given paths:
```
import { stat } from 'node:fs';
const pathsToCheck = ['./txtDir', './txtDir/file.txt'];
for (let i = 0; i < pathsToCheck.length; i++) {
stat(pathsToCheck[i], (err, stats) => {
console.log(stats.isDirectory());
console.log(stats);
});
}
```
The resulting output will resemble:
```
true
Stats {
dev: 16777220,
mode: 16877,
nlink: 3,
uid: 501,
gid: 20,
rdev: 0,
blksize: 4096,
ino: 14214262,
size: 96,
blocks: 0,
atimeMs: 1561174653071.963,
mtimeMs: 1561174614583.3518,
ctimeMs: 1561174626623.5366,
birthtimeMs: 1561174126937.2893,
atime: 2019-06-22T03:37:33.072Z,
mtime: 2019-06-22T03:36:54.583Z,
ctime: 2019-06-22T03:37:06.624Z,
birthtime: 2019-06-22T03:28:46.937Z
}
false
Stats {
dev: 16777220,
mode: 33188,
nlink: 1,
uid: 501,
gid: 20,
rdev: 0,
blksize: 4096,
ino: 14214074,
size: 8,
blocks: 8,
atimeMs: 1561174616618.8555,
mtimeMs: 1561174614584,
ctimeMs: 1561174614583.8145,
birthtimeMs: 1561174007710.7478,
atime: 2019-06-22T03:36:56.619Z,
mtime: 2019-06-22T03:36:54.584Z,
ctime: 2019-06-22T03:36:54.584Z,
birthtime: 2019-06-22T03:26:47.711Z
}
```
####
`fs.symlink(target, path[, type], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v12.0.0 | If the `type` argument is left undefined, Node will autodetect `target` type and automatically select `dir` or `file`. |
| v7.6.0 | The `target` and `path` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. |
| v0.1.31 | Added in: v0.1.31 |
* `target` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Creates the link called `path` pointing to `target`. No arguments other than a possible exception are given to the completion callback.
See the POSIX [`symlink(2)`](http://man7.org/linux/man-pages/man2/symlink.2.html) documentation for more details.
The `type` argument is only available on Windows and ignored on other platforms. It can be set to `'dir'`, `'file'`, or `'junction'`. If the `type` argument is not a string, Node.js will autodetect `target` type and use `'file'` or `'dir'`. If the `target` does not exist, `'file'` will be used. Windows junction points require the destination path to be absolute. When using `'junction'`, the `target` argument will automatically be normalized to absolute path.
Relative targets are relative to the link's parent directory.
```
import { symlink } from 'node:fs';
symlink('./mew', './mewtwo', callback);
```
The above example creates a symbolic link `mewtwo` which points to `mew` in the same directory:
```
$ tree .
.
├── mew
└── mewtwo -> ./mew
```
####
`fs.truncate(path[, len], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v16.0.0 | The error returned may be an `AggregateError` if more than one error is returned. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.8.6 | Added in: v0.8.6 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `len` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) | [<AggregateError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError)
Truncates the file. No arguments other than a possible exception are given to the completion callback. A file descriptor can also be passed as the first argument. In this case, `fs.ftruncate()` is called.
MJS modules
```
import { truncate } from 'node:fs';
// Assuming that 'path/file.txt' is a regular file.
truncate('path/file.txt', (err) => {
if (err) throw err;
console.log('path/file.txt was truncated');
});
```
CJS modules
```
const { truncate } = require('node:fs');
// Assuming that 'path/file.txt' is a regular file.
truncate('path/file.txt', (err) => {
if (err) throw err;
console.log('path/file.txt was truncated');
});
```
Passing a file descriptor is deprecated and may result in an error being thrown in the future.
See the POSIX [`truncate(2)`](http://man7.org/linux/man-pages/man2/truncate.2.html) documentation for more details.
####
`fs.unlink(path, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.0.2 | Added in: v0.0.2 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Asynchronously removes a file or symbolic link. No arguments other than a possible exception are given to the completion callback.
```
import { unlink } from 'node:fs';
// Assuming that 'path/file.txt' is a regular file.
unlink('path/file.txt', (err) => {
if (err) throw err;
console.log('path/file.txt was deleted');
});
```
`fs.unlink()` will not work on a directory, empty or otherwise. To remove a directory, use [`fs.rmdir()`](#fsrmdirpath-options-callback).
See the POSIX [`unlink(2)`](http://man7.org/linux/man-pages/man2/unlink.2.html) documentation for more details.
####
`fs.unwatchFile(filename[, listener])`
Added in: v0.1.31 * `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Optional, a listener previously attached using `fs.watchFile()`
Stop watching for changes on `filename`. If `listener` is specified, only that particular listener is removed. Otherwise, *all* listeners are removed, effectively stopping watching of `filename`.
Calling `fs.unwatchFile()` with a filename that is not being watched is a no-op, not an error.
Using [`fs.watch()`](#fswatchfilename-options-listener) is more efficient than `fs.watchFile()` and `fs.unwatchFile()`. `fs.watch()` should be used instead of `fs.watchFile()` and `fs.unwatchFile()` when possible.
####
`fs.utimes(path, atime, mtime, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v8.0.0 | `NaN`, `Infinity`, and `-Infinity` are no longer valid time specifiers. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v4.1.0 | Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. |
| v0.4.2 | Added in: v0.4.2 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `atime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `mtime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Change the file system timestamps of the object referenced by `path`.
The `atime` and `mtime` arguments follow these rules:
* Values can be either numbers representing Unix epoch time in seconds, `Date`s, or a numeric string like `'123456789.0'`.
* If the value can not be converted to a number, or is `NaN`, `Infinity`, or `-Infinity`, an `Error` will be thrown.
####
`fs.watch(filename[, options][, listener])`
History
| Version | Changes |
| --- | --- |
| v15.9.0, v14.17.0 | Added support for closing the watcher with an AbortSignal. |
| v7.6.0 | The `filename` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v7.0.0 | The passed `options` object will never be modified. |
| v0.5.10 | Added in: v0.5.10 |
* `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `persistent` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Indicates whether the process should continue to run as long as files are being watched. **Default:** `true`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Indicates whether all subdirectories should be watched, or only the current directory. This applies when a directory is specified, and only on supported platforms (See [caveats](#caveats)). **Default:** `false`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specifies the character encoding to be used for the filename passed to the listener. **Default:** `'utf8'`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows closing the watcher with an AbortSignal.
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) **Default:** `undefined`
+ `eventType` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* Returns: [<fs.FSWatcher>](fs#class-fsfswatcher)
Watch for changes on `filename`, where `filename` is either a file or a directory.
The second argument is optional. If `options` is provided as a string, it specifies the `encoding`. Otherwise `options` should be passed as an object.
The listener callback gets two arguments `(eventType, filename)`. `eventType` is either `'rename'` or `'change'`, and `filename` is the name of the file which triggered the event.
On most platforms, `'rename'` is emitted whenever a filename appears or disappears in the directory.
The listener callback is attached to the `'change'` event fired by [<fs.FSWatcher>](fs#class-fsfswatcher), but it is not the same thing as the `'change'` value of `eventType`.
If a `signal` is passed, aborting the corresponding AbortController will close the returned [<fs.FSWatcher>](fs#class-fsfswatcher).
##### Caveats
The `fs.watch` API is not 100% consistent across platforms, and is unavailable in some situations.
The recursive option is only supported on macOS and Windows. An `ERR_FEATURE_UNAVAILABLE_ON_PLATFORM` exception will be thrown when the option is used on a platform that does not support it.
On Windows, no events will be emitted if the watched directory is moved or renamed. An `EPERM` error is reported when the watched directory is deleted.
###### Availability
This feature depends on the underlying operating system providing a way to be notified of filesystem changes.
* On Linux systems, this uses [`inotify(7)`](https://man7.org/linux/man-pages/man7/inotify.7.html).
* On BSD systems, this uses [`kqueue(2)`](https://www.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2).
* On macOS, this uses [`kqueue(2)`](https://www.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2) for files and [`FSEvents`](https://developer.apple.com/documentation/coreservices/file_system_events) for directories.
* On SunOS systems (including Solaris and SmartOS), this uses [`event ports`](https://illumos.org/man/port_create).
* On Windows systems, this feature depends on [`ReadDirectoryChangesW`](https://docs.microsoft.com/en-us/windows/desktop/api/winbase/nf-winbase-readdirectorychangesw).
* On AIX systems, this feature depends on [`AHAFS`](https://developer.ibm.com/articles/au-aix_event_infrastructure/), which must be enabled.
* On IBM i systems, this feature is not supported.
If the underlying functionality is not available for some reason, then `fs.watch()` will not be able to function and may throw an exception. For example, watching files or directories can be unreliable, and in some cases impossible, on network file systems (NFS, SMB, etc) or host file systems when using virtualization software such as Vagrant or Docker.
It is still possible to use `fs.watchFile()`, which uses stat polling, but this method is slower and less reliable.
###### Inodes
On Linux and macOS systems, `fs.watch()` resolves the path to an [inode](https://en.wikipedia.org/wiki/Inode) and watches the inode. If the watched path is deleted and recreated, it is assigned a new inode. The watch will emit an event for the delete but will continue watching the *original* inode. Events for the new inode will not be emitted. This is expected behavior.
AIX files retain the same inode for the lifetime of a file. Saving and closing a watched file on AIX will result in two notifications (one for adding new content, and one for truncation).
###### Filename argument
Providing `filename` argument in the callback is only supported on Linux, macOS, Windows, and AIX. Even on supported platforms, `filename` is not always guaranteed to be provided. Therefore, don't assume that `filename` argument is always provided in the callback, and have some fallback logic if it is `null`.
```
import { watch } from 'node:fs';
watch('somedir', (eventType, filename) => {
console.log(`event type is: ${eventType}`);
if (filename) {
console.log(`filename provided: ${filename}`);
} else {
console.log('filename not provided');
}
});
```
####
`fs.watchFile(filename[, options], listener)`
History
| Version | Changes |
| --- | --- |
| v10.5.0 | The `bigint` option is now supported. |
| v7.6.0 | The `filename` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.31 | Added in: v0.1.31 |
* `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
+ `persistent` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
+ `interval` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `5007`
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `current` [<fs.Stats>](fs#class-fsstats)
+ `previous` [<fs.Stats>](fs#class-fsstats)
* Returns: [<fs.StatWatcher>](fs#class-fsstatwatcher)
Watch for changes on `filename`. The callback `listener` will be called each time the file is accessed.
The `options` argument may be omitted. If provided, it should be an object. The `options` object may contain a boolean named `persistent` that indicates whether the process should continue to run as long as files are being watched. The `options` object may specify an `interval` property indicating how often the target should be polled in milliseconds.
The `listener` gets two arguments the current stat object and the previous stat object:
```
import { watchFile } from 'node:fs';
watchFile('message.text', (curr, prev) => {
console.log(`the current mtime is: ${curr.mtime}`);
console.log(`the previous mtime was: ${prev.mtime}`);
});
```
These stat objects are instances of `fs.Stat`. If the `bigint` option is `true`, the numeric values in these objects are specified as `BigInt`s.
To be notified when the file was modified, not just accessed, it is necessary to compare `curr.mtimeMs` and `prev.mtimeMs`.
When an `fs.watchFile` operation results in an `ENOENT` error, it will invoke the listener once, with all the fields zeroed (or, for dates, the Unix Epoch). If the file is created later on, the listener will be called again, with the latest stat objects. This is a change in functionality since v0.10.
Using [`fs.watch()`](#fswatchfilename-options-listener) is more efficient than `fs.watchFile` and `fs.unwatchFile`. `fs.watch` should be used instead of `fs.watchFile` and `fs.unwatchFile` when possible.
When a file being watched by `fs.watchFile()` disappears and reappears, then the contents of `previous` in the second callback event (the file's reappearance) will be the same as the contents of `previous` in the first callback event (its disappearance).
This happens when:
* the file is deleted, followed by a restore
* the file is renamed and then renamed a second time back to its original name
####
`fs.write(fd, buffer, offset[, length[, position]], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v14.0.0 | The `buffer` parameter won't coerce unsupported input to strings anymore. |
| v10.10.0 | The `buffer` parameter can now be any `TypedArray` or a `DataView`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.4.0 | The `buffer` parameter can now be a `Uint8Array`. |
| v7.2.0 | The `offset` and `length` parameters are optional now. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.0.2 | Added in: v0.0.2 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.byteLength - offset`
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `bytesWritten` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
Write `buffer` to the file specified by `fd`.
`offset` determines the part of the buffer to be written, and `length` is an integer specifying the number of bytes to write.
`position` refers to the offset from the beginning of the file where this data should be written. If `typeof position !== 'number'`, the data will be written at the current position. See [`pwrite(2)`](http://man7.org/linux/man-pages/man2/pwrite.2.html).
The callback will be given three arguments `(err, bytesWritten, buffer)` where `bytesWritten` specifies how many *bytes* were written from `buffer`.
If this method is invoked as its [`util.promisify()`](util#utilpromisifyoriginal)ed version, it returns a promise for an `Object` with `bytesWritten` and `buffer` properties.
It is unsafe to use `fs.write()` multiple times on the same file without waiting for the callback. For this scenario, [`fs.createWriteStream()`](#fscreatewritestreampath-options) is recommended.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
####
`fs.write(fd, buffer[, options], callback)`
Added in: v18.3.0, v16.17.0 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
+ `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.byteLength - offset`
+ `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `null`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `bytesWritten` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
Write `buffer` to the file specified by `fd`.
Similar to the above `fs.write` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values.
####
`fs.write(fd, string[, position[, encoding]], callback)`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | Passing to the `string` parameter an object with an own `toString` function is no longer supported. |
| v17.8.0 | Passing to the `string` parameter an object with an own `toString` function is deprecated. |
| v14.12.0 | The `string` parameter will stringify an object with an explicit `toString` function. |
| v14.0.0 | The `string` parameter won't coerce unsupported input to strings anymore. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.2.0 | The `position` parameter is optional now. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v0.11.5 | Added in: v0.11.5 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `written` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Write `string` to the file specified by `fd`. If `string` is not a string, an exception is thrown.
`position` refers to the offset from the beginning of the file where this data should be written. If `typeof position !== 'number'` the data will be written at the current position. See [`pwrite(2)`](http://man7.org/linux/man-pages/man2/pwrite.2.html).
`encoding` is the expected string encoding.
The callback will receive the arguments `(err, written, string)` where `written` specifies how many *bytes* the passed string required to be written. Bytes written is not necessarily the same as string characters written. See [`Buffer.byteLength`](buffer#static-method-bufferbytelengthstring-encoding).
It is unsafe to use `fs.write()` multiple times on the same file without waiting for the callback. For this scenario, [`fs.createWriteStream()`](#fscreatewritestreampath-options) is recommended.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
On Windows, if the file descriptor is connected to the console (e.g. `fd == 1` or `stdout`) a string containing non-ASCII characters will not be rendered properly by default, regardless of the encoding used. It is possible to configure the console to render UTF-8 properly by changing the active codepage with the `chcp 65001` command. See the [chcp](https://ss64.com/nt/chcp.html) docs for more details.
####
`fs.writeFile(file, data[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | Passing to the `string` parameter an object with an own `toString` function is no longer supported. |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v17.8.0 | Passing to the `string` parameter an object with an own `toString` function is deprecated. |
| v16.0.0 | The error returned may be an `AggregateError` if more than one error is returned. |
| v15.2.0, v14.17.0 | The options argument may include an AbortSignal to abort an ongoing writeFile request. |
| v14.12.0 | The `data` parameter will stringify an object with an explicit `toString` function. |
| v14.0.0 | The `data` parameter won't coerce unsupported input to strings anymore. |
| v10.10.0 | The `data` parameter can now be any `TypedArray` or a `DataView`. |
| v10.0.0 | The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. |
| v7.4.0 | The `data` parameter can now be a `Uint8Array`. |
| v7.0.0 | The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. |
| v5.0.0 | The `file` parameter can be a file descriptor now. |
| v0.1.29 | Added in: v0.1.29 |
* `file` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) filename or file descriptor
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
+ `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666`
+ `flag` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'w'`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows aborting an in-progress writeFile
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) | [<AggregateError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError)
When `file` is a filename, asynchronously writes data to the file, replacing the file if it already exists. `data` can be a string or a buffer.
When `file` is a file descriptor, the behavior is similar to calling `fs.write()` directly (which is recommended). See the notes below on using a file descriptor.
The `encoding` option is ignored if `data` is a buffer.
The `mode` option only affects the newly created file. See [`fs.open()`](#fsopenpath-flags-mode-callback) for more details.
```
import { writeFile } from 'node:fs';
import { Buffer } from 'node:buffer';
const data = new Uint8Array(Buffer.from('Hello Node.js'));
writeFile('message.txt', data, (err) => {
if (err) throw err;
console.log('The file has been saved!');
});
```
If `options` is a string, then it specifies the encoding:
```
import { writeFile } from 'node:fs';
writeFile('message.txt', 'Hello Node.js', 'utf8', callback);
```
It is unsafe to use `fs.writeFile()` multiple times on the same file without waiting for the callback. For this scenario, [`fs.createWriteStream()`](#fscreatewritestreampath-options) is recommended.
Similarly to `fs.readFile` - `fs.writeFile` is a convenience method that performs multiple `write` calls internally to write the buffer passed to it. For performance sensitive code consider using [`fs.createWriteStream()`](#fscreatewritestreampath-options).
It is possible to use an [<AbortSignal>](globals#class-abortsignal) to cancel an `fs.writeFile()`. Cancelation is "best effort", and some amount of data is likely still to be written.
```
import { writeFile } from 'node:fs';
import { Buffer } from 'node:buffer';
const controller = new AbortController();
const { signal } = controller;
const data = new Uint8Array(Buffer.from('Hello Node.js'));
writeFile('message.txt', data, { signal }, (err) => {
// When a request is aborted - the callback is called with an AbortError
});
// When the request should be aborted
controller.abort();
```
Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.writeFile` performs.
##### Using `fs.writeFile()` with file descriptors
When `file` is a file descriptor, the behavior is almost identical to directly calling `fs.write()` like:
```
import { write } from 'node:fs';
import { Buffer } from 'node:buffer';
write(fd, Buffer.from(data, options.encoding), callback);
```
The difference from directly calling `fs.write()` is that under some unusual conditions, `fs.write()` might write only part of the buffer and need to be retried to write the remaining data, whereas `fs.writeFile()` retries until the data is entirely written (or an error occurs).
The implications of this are a common source of confusion. In the file descriptor case, the file is not replaced! The data is not necessarily written to the beginning of the file, and the file's original data may remain before and/or after the newly written data.
For example, if `fs.writeFile()` is called twice in a row, first to write the string `'Hello'`, then to write the string `', World'`, the file would contain `'Hello, World'`, and might contain some of the file's original data (depending on the size of the original file, and the position of the file descriptor). If a file name had been used instead of a descriptor, the file would be guaranteed to contain only `', World'`.
####
`fs.writev(fd, buffers[, position], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v12.9.0 | Added in: v12.9.0 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffers` [<ArrayBufferView[]>](https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `bytesWritten` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `buffers` [<ArrayBufferView[]>](https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView)
Write an array of `ArrayBufferView`s to the file specified by `fd` using `writev()`.
`position` is the offset from the beginning of the file where this data should be written. If `typeof position !== 'number'`, the data will be written at the current position.
The callback will be given three arguments: `err`, `bytesWritten`, and `buffers`. `bytesWritten` is how many bytes were written from `buffers`.
If this method is [`util.promisify()`](util#utilpromisifyoriginal)ed, it returns a promise for an `Object` with `bytesWritten` and `buffers` properties.
It is unsafe to use `fs.writev()` multiple times on the same file without waiting for the callback. For this scenario, use [`fs.createWriteStream()`](#fscreatewritestreampath-options).
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
### Synchronous API
The synchronous APIs perform all operations synchronously, blocking the event loop until the operation completes or fails.
####
`fs.accessSync(path[, mode])`
History
| Version | Changes |
| --- | --- |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.11.15 | Added in: v0.11.15 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `fs.constants.F_OK`
Synchronously tests a user's permissions for the file or directory specified by `path`. The `mode` argument is an optional integer that specifies the accessibility checks to be performed. `mode` should be either the value `fs.constants.F_OK` or a mask consisting of the bitwise OR of any of `fs.constants.R_OK`, `fs.constants.W_OK`, and `fs.constants.X_OK` (e.g. `fs.constants.W_OK | fs.constants.R_OK`). Check [File access constants](#file-access-constants) for possible values of `mode`.
If any of the accessibility checks fail, an `Error` will be thrown. Otherwise, the method will return `undefined`.
```
import { accessSync, constants } from 'node:fs';
try {
accessSync('etc/passwd', constants.R_OK | constants.W_OK);
console.log('can read/write');
} catch (err) {
console.error('no access!');
}
```
####
`fs.appendFileSync(path, data[, options])`
History
| Version | Changes |
| --- | --- |
| v7.0.0 | The passed `options` object will never be modified. |
| v5.0.0 | The `file` parameter can be a file descriptor now. |
| v0.6.7 | Added in: v0.6.7 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) filename or file descriptor
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
+ `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666`
+ `flag` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'a'`.
Synchronously append data to a file, creating the file if it does not yet exist. `data` can be a string or a [<Buffer>](buffer#class-buffer).
The `mode` option only affects the newly created file. See [`fs.open()`](#fsopenpath-flags-mode-callback) for more details.
```
import { appendFileSync } from 'node:fs';
try {
appendFileSync('message.txt', 'data to append');
console.log('The "data to append" was appended to file!');
} catch (err) {
/* Handle the error */
}
```
If `options` is a string, then it specifies the encoding:
```
import { appendFileSync } from 'node:fs';
appendFileSync('message.txt', 'data to append', 'utf8');
```
The `path` may be specified as a numeric file descriptor that has been opened for appending (using `fs.open()` or `fs.openSync()`). The file descriptor will not be closed automatically.
```
import { openSync, closeSync, appendFileSync } from 'node:fs';
let fd;
try {
fd = openSync('message.txt', 'a');
appendFileSync(fd, 'data to append', 'utf8');
} catch (err) {
/* Handle the error */
} finally {
if (fd !== undefined)
closeSync(fd);
}
```
####
`fs.chmodSync(path, mode)`
History
| Version | Changes |
| --- | --- |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.6.7 | Added in: v0.6.7 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
For detailed information, see the documentation of the asynchronous version of this API: [`fs.chmod()`](#fschmodpath-mode-callback).
See the POSIX [`chmod(2)`](http://man7.org/linux/man-pages/man2/chmod.2.html) documentation for more detail.
####
`fs.chownSync(path, uid, gid)`
History
| Version | Changes |
| --- | --- |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.97 | Added in: v0.1.97 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `uid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `gid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Synchronously changes owner and group of a file. Returns `undefined`. This is the synchronous version of [`fs.chown()`](#fschownpath-uid-gid-callback).
See the POSIX [`chown(2)`](http://man7.org/linux/man-pages/man2/chown.2.html) documentation for more detail.
####
`fs.closeSync(fd)`
Added in: v0.1.21 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Closes the file descriptor. Returns `undefined`.
Calling `fs.closeSync()` on any file descriptor (`fd`) that is currently in use through any other `fs` operation may lead to undefined behavior.
See the POSIX [`close(2)`](http://man7.org/linux/man-pages/man2/close.2.html) documentation for more detail.
####
`fs.copyFileSync(src, dest[, mode])`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | Changed `flags` argument to `mode` and imposed stricter type validation. |
| v8.5.0 | Added in: v8.5.0 |
* `src` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) source filename to copy
* `dest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) destination filename of the copy operation
* `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) modifiers for copy operation. **Default:** `0`.
Synchronously copies `src` to `dest`. By default, `dest` is overwritten if it already exists. Returns `undefined`. Node.js makes no guarantees about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, Node.js will attempt to remove the destination.
`mode` is an optional integer that specifies the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. `fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE`).
* `fs.constants.COPYFILE_EXCL`: The copy operation will fail if `dest` already exists.
* `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used.
* `fs.constants.COPYFILE_FICLONE_FORCE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail.
```
import { copyFileSync, constants } from 'node:fs';
// destination.txt will be created or overwritten by default.
copyFileSync('source.txt', 'destination.txt');
console.log('source.txt was copied to destination.txt');
// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.
copyFileSync('source.txt', 'destination.txt', constants.COPYFILE_EXCL);
```
####
`fs.cpSync(src, dest[, options])`
History
| Version | Changes |
| --- | --- |
| v17.6.0, v16.15.0 | Accepts an additional `verbatimSymlinks` option to specify whether to perform path resolution for symlinks. |
| v16.7.0 | Added in: v16.7.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `src` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) source path to copy.
* `dest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) destination path to copy to.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `dereference` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) dereference symlinks. **Default:** `false`.
+ `errorOnExist` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) when `force` is `false`, and the destination exists, throw an error. **Default:** `false`.
+ `filter` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Function to filter copied files/directories. Return `true` to copy the item, `false` to ignore it. **Default:** `undefined`
+ `force` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) overwrite existing file or directory. The copy operation will ignore errors if you set this to false and the destination exists. Use the `errorOnExist` option to change this behavior. **Default:** `true`.
+ `preserveTimestamps` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true` timestamps from `src` will be preserved. **Default:** `false`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) copy directories recursively **Default:** `false`
+ `verbatimSymlinks` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, path resolution for symlinks will be skipped. **Default:** `false`
Synchronously copies the entire directory structure from `src` to `dest`, including subdirectories and files.
When copying a directory to another directory, globs are not supported and behavior is similar to `cp dir1/ dir2/`.
####
`fs.existsSync(path)`
History
| Version | Changes |
| --- | --- |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.21 | Added in: v0.1.21 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the path exists, `false` otherwise.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.exists()`](#fsexistspath-callback).
`fs.exists()` is deprecated, but `fs.existsSync()` is not. The `callback` parameter to `fs.exists()` accepts parameters that are inconsistent with other Node.js callbacks. `fs.existsSync()` does not use a callback.
```
import { existsSync } from 'node:fs';
if (existsSync('/etc/passwd'))
console.log('The path exists.');
```
####
`fs.fchmodSync(fd, mode)`
Added in: v0.4.7 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Sets the permissions on the file. Returns `undefined`.
See the POSIX [`fchmod(2)`](http://man7.org/linux/man-pages/man2/fchmod.2.html) documentation for more detail.
####
`fs.fchownSync(fd, uid, gid)`
Added in: v0.4.7 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `uid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The file's new owner's user id.
* `gid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The file's new group's group id.
Sets the owner of the file. Returns `undefined`.
See the POSIX [`fchown(2)`](http://man7.org/linux/man-pages/man2/fchown.2.html) documentation for more detail.
####
`fs.fdatasyncSync(fd)`
Added in: v0.1.96 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX [`fdatasync(2)`](http://man7.org/linux/man-pages/man2/fdatasync.2.html) documentation for details. Returns `undefined`.
####
`fs.fstatSync(fd[, options])`
History
| Version | Changes |
| --- | --- |
| v10.5.0 | Accepts an additional `options` object to specify whether the numeric values returned should be bigint. |
| v0.1.95 | Added in: v0.1.95 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the numeric values in the returned [<fs.Stats>](fs#class-fsstats) object should be `bigint`. **Default:** `false`.
* Returns: [<fs.Stats>](fs#class-fsstats)
Retrieves the [<fs.Stats>](fs#class-fsstats) for the file descriptor.
See the POSIX [`fstat(2)`](http://man7.org/linux/man-pages/man2/fstat.2.html) documentation for more detail.
####
`fs.fsyncSync(fd)`
Added in: v0.1.96 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX [`fsync(2)`](http://man7.org/linux/man-pages/man2/fsync.2.html) documentation for more detail. Returns `undefined`.
####
`fs.ftruncateSync(fd[, len])`
Added in: v0.8.6 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `len` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
Truncates the file descriptor. Returns `undefined`.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.ftruncate()`](#fsftruncatefd-len-callback).
####
`fs.futimesSync(fd, atime, mtime)`
History
| Version | Changes |
| --- | --- |
| v4.1.0 | Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. |
| v0.4.2 | Added in: v0.4.2 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `atime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `mtime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
Synchronous version of [`fs.futimes()`](#fsfutimesfd-atime-mtime-callback). Returns `undefined`.
####
`fs.lchmodSync(path, mode)`
Deprecated since: v0.4.7 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Changes the permissions on a symbolic link. Returns `undefined`.
This method is only implemented on macOS.
See the POSIX [`lchmod(2)`](https://www.freebsd.org/cgi/man.cgi?query=lchmod&sektion=2) documentation for more detail.
####
`fs.lchownSync(path, uid, gid)`
History
| Version | Changes |
| --- | --- |
| v10.6.0 | This API is no longer deprecated. |
| v0.4.7 | Documentation-only deprecation. |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `uid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The file's new owner's user id.
* `gid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The file's new group's group id.
Set the owner for the path. Returns `undefined`.
See the POSIX [`lchown(2)`](http://man7.org/linux/man-pages/man2/lchown.2.html) documentation for more details.
####
`fs.lutimesSync(path, atime, mtime)`
Added in: v14.5.0, v12.19.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `atime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `mtime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
Change the file system timestamps of the symbolic link referenced by `path`. Returns `undefined`, or throws an exception when parameters are incorrect or the operation fails. This is the synchronous version of [`fs.lutimes()`](#fslutimespath-atime-mtime-callback).
####
`fs.linkSync(existingPath, newPath)`
History
| Version | Changes |
| --- | --- |
| v7.6.0 | The `existingPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. |
| v0.1.31 | Added in: v0.1.31 |
* `existingPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `newPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
Creates a new link from the `existingPath` to the `newPath`. See the POSIX [`link(2)`](http://man7.org/linux/man-pages/man2/link.2.html) documentation for more detail. Returns `undefined`.
####
`fs.lstatSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v15.3.0, v14.17.0 | Accepts a `throwIfNoEntry` option to specify whether an exception should be thrown if the entry does not exist. |
| v10.5.0 | Accepts an additional `options` object to specify whether the numeric values returned should be bigint. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.30 | Added in: v0.1.30 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the numeric values in the returned [<fs.Stats>](fs#class-fsstats) object should be `bigint`. **Default:** `false`.
+ `throwIfNoEntry` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether an exception will be thrown if no file system entry exists, rather than returning `undefined`. **Default:** `true`.
* Returns: [<fs.Stats>](fs#class-fsstats)
Retrieves the [<fs.Stats>](fs#class-fsstats) for the symbolic link referred to by `path`.
See the POSIX [`lstat(2)`](http://man7.org/linux/man-pages/man2/lstat.2.html) documentation for more details.
####
`fs.mkdirSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v13.11.0, v12.17.0 | In `recursive` mode, the first created path is returned now. |
| v10.12.0 | The second argument can now be an `options` object with `recursive` and `mode` properties. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.21 | Added in: v0.1.21 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
+ `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Not supported on Windows. **Default:** `0o777`.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
Synchronously creates a directory. Returns `undefined`, or if `recursive` is `true`, the first directory path created. This is the synchronous version of [`fs.mkdir()`](#fsmkdirpath-options-callback).
See the POSIX [`mkdir(2)`](http://man7.org/linux/man-pages/man2/mkdir.2.html) documentation for more details.
####
`fs.mkdtempSync(prefix[, options])`
History
| Version | Changes |
| --- | --- |
| v16.5.0, v14.18.0 | The `prefix` parameter now accepts an empty string. |
| v5.10.0 | Added in: v5.10.0 |
* `prefix` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the created directory path.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.mkdtemp()`](#fsmkdtempprefix-options-callback).
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use.
####
`fs.opendirSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v13.1.0, v12.16.0 | The `bufferSize` option was introduced. |
| v12.12.0 | Added in: v12.12.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
+ `bufferSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of directory entries that are buffered internally when reading from the directory. Higher values lead to better performance but higher memory usage. **Default:** `32`
* Returns: [<fs.Dir>](fs#class-fsdir)
Synchronously open a directory. See [`opendir(3)`](http://man7.org/linux/man-pages/man3/opendir.3.html).
Creates an [<fs.Dir>](fs#class-fsdir), which contains all further functions for reading from and cleaning up the directory.
The `encoding` option sets the encoding for the `path` while opening the directory and subsequent read operations.
####
`fs.openSync(path[, flags[, mode]])`
History
| Version | Changes |
| --- | --- |
| v11.1.0 | The `flags` argument is now optional and defaults to `'r'`. |
| v9.9.0 | The `as` and `as+` flags are supported now. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.21 | Added in: v0.1.21 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `flags` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `'r'`. See [support of file system `flags`](#file-system-flags).
* `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns an integer representing the file descriptor.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.open()`](#fsopenpath-flags-mode-callback).
####
`fs.readdirSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v10.10.0 | New option `withFileTypes` was added. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.21 | Added in: v0.1.21 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
+ `withFileTypes` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
* Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer[]>](buffer#class-buffer) | [<fs.Dirent[]>](fs#class-fsdirent)
Reads the contents of the directory.
See the POSIX [`readdir(3)`](http://man7.org/linux/man-pages/man3/readdir.3.html) documentation for more details.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the filenames returned. If the `encoding` is set to `'buffer'`, the filenames returned will be passed as [<Buffer>](buffer#class-buffer) objects.
If `options.withFileTypes` is set to `true`, the result will contain [<fs.Dirent>](fs#class-fsdirent) objects.
####
`fs.readFileSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v5.0.0 | The `path` parameter can be a file descriptor now. |
| v0.1.8 | Added in: v0.1.8 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) filename or file descriptor
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
+ `flag` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'r'`.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
Returns the contents of the `path`.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.readFile()`](#fsreadfilepath-options-callback).
If the `encoding` option is specified then this function returns a string. Otherwise it returns a buffer.
Similar to [`fs.readFile()`](#fsreadfilepath-options-callback), when the path is a directory, the behavior of `fs.readFileSync()` is platform-specific.
```
import { readFileSync } from 'node:fs';
// macOS, Linux, and Windows
readFileSync('<directory>');
// => [Error: EISDIR: illegal operation on a directory, read <directory>]
// FreeBSD
readFileSync('<directory>'); // => <data>
```
####
`fs.readlinkSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.31 | Added in: v0.1.31 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
Returns the symbolic link's string value.
See the POSIX [`readlink(2)`](http://man7.org/linux/man-pages/man2/readlink.2.html) documentation for more details.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the link path returned. If the `encoding` is set to `'buffer'`, the link path returned will be passed as a [<Buffer>](buffer#class-buffer) object.
####
`fs.readSync(fd, buffer, offset, length[, position])`
History
| Version | Changes |
| --- | --- |
| v10.10.0 | The `buffer` parameter can now be any `TypedArray` or a `DataView`. |
| v6.0.0 | The `length` parameter can now be `0`. |
| v0.1.21 | Added in: v0.1.21 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the number of `bytesRead`.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.read()`](#fsreadfd-buffer-offset-length-position-callback).
####
`fs.readSync(fd, buffer[, options])`
History
| Version | Changes |
| --- | --- |
| v13.13.0, v12.17.0 | Added in: v13.13.0, v12.17.0 |
| v13.13.0, v12.17.0 | Options object can be passed in to make offset, length, and position optional. |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
+ `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.byteLength - offset`
+ `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the number of `bytesRead`.
Similar to the above `fs.readSync` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.read()`](#fsreadfd-buffer-offset-length-position-callback).
####
`fs.readvSync(fd, buffers[, position])`
Added in: v13.13.0, v12.17.0 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffers` [<ArrayBufferView[]>](https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes read.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.readv()`](#fsreadvfd-buffers-position-callback).
####
`fs.realpathSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | Pipe/Socket resolve support was added. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v6.4.0 | Calling `realpathSync` now works again for various edge cases on Windows. |
| v6.0.0 | The `cache` parameter was removed. |
| v0.1.31 | Added in: v0.1.31 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
Returns the resolved pathname.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.realpath()`](#fsrealpathpath-options-callback).
####
`fs.realpathSync.native(path[, options])`
Added in: v9.2.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
Synchronous [`realpath(3)`](http://man7.org/linux/man-pages/man3/realpath.3.html).
Only paths that can be converted to UTF8 strings are supported.
The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the path returned. If the `encoding` is set to `'buffer'`, the path returned will be passed as a [<Buffer>](buffer#class-buffer) object.
On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on `/proc` in order for this function to work. Glibc does not have this restriction.
####
`fs.renameSync(oldPath, newPath)`
History
| Version | Changes |
| --- | --- |
| v7.6.0 | The `oldPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. |
| v0.1.21 | Added in: v0.1.21 |
* `oldPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `newPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
Renames the file from `oldPath` to `newPath`. Returns `undefined`.
See the POSIX [`rename(2)`](http://man7.org/linux/man-pages/man2/rename.2.html) documentation for more details.
####
`fs.rmdirSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Using `fs.rmdirSync(path, { recursive: true })` on a `path` that is a file is no longer permitted and results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. |
| v16.0.0 | Using `fs.rmdirSync(path, { recursive: true })` on a `path` that does not exist is no longer permitted and results in a `ENOENT` error. |
| v16.0.0 | The `recursive` option is deprecated, using it triggers a deprecation warning. |
| v14.14.0 | The `recursive` option is deprecated, use `fs.rmSync` instead. |
| v13.3.0, v12.16.0 | The `maxBusyTries` option is renamed to `maxRetries`, and its default is 0. The `emfileWait` option has been removed, and `EMFILE` errors use the same retry logic as other errors. The `retryDelay` option is now supported. `ENFILE` errors are now retried. |
| v12.10.0 | The `recursive`, `maxBusyTries`, and `emfileWait` options are now supported. |
| v7.6.0 | The `path` parameters can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.21 | Added in: v0.1.21 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `maxRetries` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js retries the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, perform a recursive directory removal. In recursive mode, operations are retried on failure. **Default:** `false`. **Deprecated.**
+ `retryDelay` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`.
Synchronous [`rmdir(2)`](http://man7.org/linux/man-pages/man2/rmdir.2.html). Returns `undefined`.
Using `fs.rmdirSync()` on a file (not a directory) results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX.
To get a behavior similar to the `rm -rf` Unix command, use [`fs.rmSync()`](#fsrmsyncpath-options) with options `{ recursive: true, force: true }`.
####
`fs.rmSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v17.3.0, v16.14.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v14.14.0 | Added in: v14.14.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `force` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, exceptions will be ignored if `path` does not exist. **Default:** `false`.
+ `maxRetries` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js will retry the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`.
+ `recursive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, perform a recursive directory removal. In recursive mode operations are retried on failure. **Default:** `false`.
+ `retryDelay` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`.
Synchronously removes files and directories (modeled on the standard POSIX `rm` utility). Returns `undefined`.
####
`fs.statSync(path[, options])`
History
| Version | Changes |
| --- | --- |
| v15.3.0, v14.17.0 | Accepts a `throwIfNoEntry` option to specify whether an exception should be thrown if the entry does not exist. |
| v10.5.0 | Accepts an additional `options` object to specify whether the numeric values returned should be bigint. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.21 | Added in: v0.1.21 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the numeric values in the returned [<fs.Stats>](fs#class-fsstats) object should be `bigint`. **Default:** `false`.
+ `throwIfNoEntry` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether an exception will be thrown if no file system entry exists, rather than returning `undefined`. **Default:** `true`.
* Returns: [<fs.Stats>](fs#class-fsstats)
Retrieves the [<fs.Stats>](fs#class-fsstats) for the path.
####
`fs.symlinkSync(target, path[, type])`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | If the `type` argument is left undefined, Node will autodetect `target` type and automatically select `dir` or `file`. |
| v7.6.0 | The `target` and `path` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. |
| v0.1.31 | Added in: v0.1.31 |
* `target` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
Returns `undefined`.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.symlink()`](#fssymlinktarget-path-type-callback).
####
`fs.truncateSync(path[, len])`
Added in: v0.8.6 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `len` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
Truncates the file. Returns `undefined`. A file descriptor can also be passed as the first argument. In this case, `fs.ftruncateSync()` is called.
Passing a file descriptor is deprecated and may result in an error being thrown in the future.
####
`fs.unlinkSync(path)`
History
| Version | Changes |
| --- | --- |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v0.1.21 | Added in: v0.1.21 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
Synchronous [`unlink(2)`](http://man7.org/linux/man-pages/man2/unlink.2.html). Returns `undefined`.
####
`fs.utimesSync(path, atime, mtime)`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | `NaN`, `Infinity`, and `-Infinity` are no longer valid time specifiers. |
| v7.6.0 | The `path` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v4.1.0 | Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. |
| v0.4.2 | Added in: v0.4.2 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `atime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
* `mtime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
Returns `undefined`.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.utimes()`](#fsutimespath-atime-mtime-callback).
####
`fs.writeFileSync(file, data[, options])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | Passing to the `data` parameter an object with an own `toString` function is no longer supported. |
| v17.8.0 | Passing to the `data` parameter an object with an own `toString` function is deprecated. |
| v14.12.0 | The `data` parameter will stringify an object with an explicit `toString` function. |
| v14.0.0 | The `data` parameter won't coerce unsupported input to strings anymore. |
| v10.10.0 | The `data` parameter can now be any `TypedArray` or a `DataView`. |
| v7.4.0 | The `data` parameter can now be a `Uint8Array`. |
| v5.0.0 | The `file` parameter can be a file descriptor now. |
| v0.1.29 | Added in: v0.1.29 |
* `file` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) filename or file descriptor
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `'utf8'`
+ `mode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0o666`
+ `flag` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [support of file system `flags`](#file-system-flags). **Default:** `'w'`.
Returns `undefined`.
The `mode` option only affects the newly created file. See [`fs.open()`](#fsopenpath-flags-mode-callback) for more details.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.writeFile()`](#fswritefilefile-data-options-callback).
####
`fs.writeSync(fd, buffer, offset[, length[, position]])`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | The `buffer` parameter won't coerce unsupported input to strings anymore. |
| v10.10.0 | The `buffer` parameter can now be any `TypedArray` or a `DataView`. |
| v7.4.0 | The `buffer` parameter can now be a `Uint8Array`. |
| v7.2.0 | The `offset` and `length` parameters are optional now. |
| v0.1.21 | Added in: v0.1.21 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.byteLength - offset`
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes written.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.write(fd, buffer...)`](#fswritefd-buffer-offset-length-position-callback).
####
`fs.writeSync(fd, buffer[, options])`
Added in: v18.3.0, v16.17.0 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
+ `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.byteLength - offset`
+ `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `null`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes written.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.write(fd, buffer...)`](#fswritefd-buffer-offset-length-position-callback).
####
`fs.writeSync(fd, string[, position[, encoding]])`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | The `string` parameter won't coerce unsupported input to strings anymore. |
| v7.2.0 | The `position` parameter is optional now. |
| v0.11.5 | Added in: v0.11.5 |
* `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes written.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.write(fd, string...)`](#fswritefd-string-position-encoding-callback).
####
`fs.writevSync(fd, buffers[, position])`
Added in: v12.9.0 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `buffers` [<ArrayBufferView[]>](https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView)
* `position` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) **Default:** `null`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes written.
For detailed information, see the documentation of the asynchronous version of this API: [`fs.writev()`](#fswritevfd-buffers-position-callback).
### Common Objects
The common objects are shared by all of the file system API variants (promise, callback, and synchronous).
#### Class: `fs.Dir`
Added in: v12.12.0 A class representing a directory stream.
Created by [`fs.opendir()`](#fsopendirpath-options-callback), [`fs.opendirSync()`](#fsopendirsyncpath-options), or [`fsPromises.opendir()`](#fspromisesopendirpath-options).
```
import { opendir } from 'node:fs/promises';
try {
const dir = await opendir('./');
for await (const dirent of dir)
console.log(dirent.name);
} catch (err) {
console.error(err);
}
```
When using the async iterator, the [<fs.Dir>](fs#class-fsdir) object will be automatically closed after the iterator exits.
#####
`dir.close()`
Added in: v12.12.0 * Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Asynchronously close the directory's underlying resource handle. Subsequent reads will result in errors.
A promise is returned that will be resolved after the resource has been closed.
#####
`dir.close(callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v12.12.0 | Added in: v12.12.0 |
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Asynchronously close the directory's underlying resource handle. Subsequent reads will result in errors.
The `callback` will be called after the resource handle has been closed.
#####
`dir.closeSync()`
Added in: v12.12.0 Synchronously close the directory's underlying resource handle. Subsequent reads will result in errors.
#####
`dir.path`
Added in: v12.12.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The read-only path of this directory as was provided to [`fs.opendir()`](#fsopendirpath-options-callback), [`fs.opendirSync()`](#fsopendirsyncpath-options), or [`fsPromises.opendir()`](#fspromisesopendirpath-options).
#####
`dir.read()`
Added in: v12.12.0 * Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<fs.Dirent>](fs#class-fsdirent) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
Asynchronously read the next directory entry via [`readdir(3)`](http://man7.org/linux/man-pages/man3/readdir.3.html) as an [<fs.Dirent>](fs#class-fsdirent).
A promise is returned that will be resolved with an [<fs.Dirent>](fs#class-fsdirent), or `null` if there are no more directory entries to read.
Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results.
#####
`dir.read(callback)`
Added in: v12.12.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `dirent` [<fs.Dirent>](fs#class-fsdirent) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
Asynchronously read the next directory entry via [`readdir(3)`](http://man7.org/linux/man-pages/man3/readdir.3.html) as an [<fs.Dirent>](fs#class-fsdirent).
After the read is completed, the `callback` will be called with an [<fs.Dirent>](fs#class-fsdirent), or `null` if there are no more directory entries to read.
Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results.
#####
`dir.readSync()`
Added in: v12.12.0 * Returns: [<fs.Dirent>](fs#class-fsdirent) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
Synchronously read the next directory entry as an [<fs.Dirent>](fs#class-fsdirent). See the POSIX [`readdir(3)`](http://man7.org/linux/man-pages/man3/readdir.3.html) documentation for more detail.
If there are no more directory entries to read, `null` will be returned.
Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results.
#####
`dir[Symbol.asyncIterator]()`
Added in: v12.12.0 * Returns: [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface) of [<fs.Dirent>](fs#class-fsdirent)
Asynchronously iterates over the directory until all entries have been read. Refer to the POSIX [`readdir(3)`](http://man7.org/linux/man-pages/man3/readdir.3.html) documentation for more detail.
Entries returned by the async iterator are always an [<fs.Dirent>](fs#class-fsdirent). The `null` case from `dir.read()` is handled internally.
See [<fs.Dir>](fs#class-fsdir) for an example.
Directory entries returned by this iterator are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results.
#### Class: `fs.Dirent`
Added in: v10.10.0 A representation of a directory entry, which can be a file or a subdirectory within the directory, as returned by reading from an [<fs.Dir>](fs#class-fsdir). The directory entry is a combination of the file name and file type pairs.
Additionally, when [`fs.readdir()`](#fsreaddirpath-options-callback) or [`fs.readdirSync()`](#fsreaddirsyncpath-options) is called with the `withFileTypes` option set to `true`, the resulting array is filled with [<fs.Dirent>](fs#class-fsdirent) objects, rather than strings or [<Buffer>](buffer#class-buffer)s.
#####
`dirent.isBlockDevice()`
Added in: v10.10.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Dirent>](fs#class-fsdirent) object describes a block device.
#####
`dirent.isCharacterDevice()`
Added in: v10.10.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Dirent>](fs#class-fsdirent) object describes a character device.
#####
`dirent.isDirectory()`
Added in: v10.10.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Dirent>](fs#class-fsdirent) object describes a file system directory.
#####
`dirent.isFIFO()`
Added in: v10.10.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Dirent>](fs#class-fsdirent) object describes a first-in-first-out (FIFO) pipe.
#####
`dirent.isFile()`
Added in: v10.10.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Dirent>](fs#class-fsdirent) object describes a regular file.
#####
`dirent.isSocket()`
Added in: v10.10.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Dirent>](fs#class-fsdirent) object describes a socket.
#####
`dirent.isSymbolicLink()`
Added in: v10.10.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Dirent>](fs#class-fsdirent) object describes a symbolic link.
#####
`dirent.name`
Added in: v10.10.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
The file name that this [<fs.Dirent>](fs#class-fsdirent) object refers to. The type of this value is determined by the `options.encoding` passed to [`fs.readdir()`](#fsreaddirpath-options-callback) or [`fs.readdirSync()`](#fsreaddirsyncpath-options).
#### Class: `fs.FSWatcher`
Added in: v0.5.8 * Extends [<EventEmitter>](events#class-eventemitter)
A successful call to [`fs.watch()`](#fswatchfilename-options-listener) method will return a new [<fs.FSWatcher>](fs#class-fsfswatcher) object.
All [<fs.FSWatcher>](fs#class-fsfswatcher) objects emit a `'change'` event whenever a specific watched file is modified.
##### Event: `'change'`
Added in: v0.5.8 * `eventType` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The type of change event that has occurred
* `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) The filename that changed (if relevant/available)
Emitted when something changes in a watched directory or file. See more details in [`fs.watch()`](#fswatchfilename-options-listener).
The `filename` argument may not be provided depending on operating system support. If `filename` is provided, it will be provided as a [<Buffer>](buffer#class-buffer) if `fs.watch()` is called with its `encoding` option set to `'buffer'`, otherwise `filename` will be a UTF-8 string.
```
import { watch } from 'node:fs';
// Example when handled through fs.watch() listener
watch('./tmp', { encoding: 'buffer' }, (eventType, filename) => {
if (filename) {
console.log(filename);
// Prints: <Buffer ...>
}
});
```
##### Event: `'close'`
Added in: v10.0.0 Emitted when the watcher stops watching for changes. The closed [<fs.FSWatcher>](fs#class-fsfswatcher) object is no longer usable in the event handler.
##### Event: `'error'`
Added in: v0.5.8 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Emitted when an error occurs while watching the file. The errored [<fs.FSWatcher>](fs#class-fsfswatcher) object is no longer usable in the event handler.
#####
`watcher.close()`
Added in: v0.5.8 Stop watching for changes on the given [<fs.FSWatcher>](fs#class-fsfswatcher). Once stopped, the [<fs.FSWatcher>](fs#class-fsfswatcher) object is no longer usable.
#####
`watcher.ref()`
Added in: v14.3.0, v12.20.0 * Returns: [<fs.FSWatcher>](fs#class-fsfswatcher)
When called, requests that the Node.js event loop *not* exit so long as the [<fs.FSWatcher>](fs#class-fsfswatcher) is active. Calling `watcher.ref()` multiple times will have no effect.
By default, all [<fs.FSWatcher>](fs#class-fsfswatcher) objects are "ref'ed", making it normally unnecessary to call `watcher.ref()` unless `watcher.unref()` had been called previously.
#####
`watcher.unref()`
Added in: v14.3.0, v12.20.0 * Returns: [<fs.FSWatcher>](fs#class-fsfswatcher)
When called, the active [<fs.FSWatcher>](fs#class-fsfswatcher) object will not require the Node.js event loop to remain active. If there is no other activity keeping the event loop running, the process may exit before the [<fs.FSWatcher>](fs#class-fsfswatcher) object's callback is invoked. Calling `watcher.unref()` multiple times will have no effect.
#### Class: `fs.StatWatcher`
Added in: v14.3.0, v12.20.0 * Extends [<EventEmitter>](events#class-eventemitter)
A successful call to `fs.watchFile()` method will return a new [<fs.StatWatcher>](fs#class-fsstatwatcher) object.
#####
`watcher.ref()`
Added in: v14.3.0, v12.20.0 * Returns: [<fs.StatWatcher>](fs#class-fsstatwatcher)
When called, requests that the Node.js event loop *not* exit so long as the [<fs.StatWatcher>](fs#class-fsstatwatcher) is active. Calling `watcher.ref()` multiple times will have no effect.
By default, all [<fs.StatWatcher>](fs#class-fsstatwatcher) objects are "ref'ed", making it normally unnecessary to call `watcher.ref()` unless `watcher.unref()` had been called previously.
#####
`watcher.unref()`
Added in: v14.3.0, v12.20.0 * Returns: [<fs.StatWatcher>](fs#class-fsstatwatcher)
When called, the active [<fs.StatWatcher>](fs#class-fsstatwatcher) object will not require the Node.js event loop to remain active. If there is no other activity keeping the event loop running, the process may exit before the [<fs.StatWatcher>](fs#class-fsstatwatcher) object's callback is invoked. Calling `watcher.unref()` multiple times will have no effect.
#### Class: `fs.ReadStream`
Added in: v0.1.93 * Extends: [<stream.Readable>](stream#class-streamreadable)
Instances of [<fs.ReadStream>](fs#class-fsreadstream) are created and returned using the [`fs.createReadStream()`](#fscreatereadstreampath-options) function.
##### Event: `'close'`
Added in: v0.1.93 Emitted when the [<fs.ReadStream>](fs#class-fsreadstream)'s underlying file descriptor has been closed.
##### Event: `'open'`
Added in: v0.1.93 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Integer file descriptor used by the [<fs.ReadStream>](fs#class-fsreadstream).
Emitted when the [<fs.ReadStream>](fs#class-fsreadstream)'s file descriptor has been opened.
##### Event: `'ready'`
Added in: v9.11.0 Emitted when the [<fs.ReadStream>](fs#class-fsreadstream) is ready to be used.
Fires immediately after `'open'`.
#####
`readStream.bytesRead`
Added in: v6.4.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The number of bytes that have been read so far.
#####
`readStream.path`
Added in: v0.1.93 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
The path to the file the stream is reading from as specified in the first argument to `fs.createReadStream()`. If `path` is passed as a string, then `readStream.path` will be a string. If `path` is passed as a [<Buffer>](buffer#class-buffer), then `readStream.path` will be a [<Buffer>](buffer#class-buffer). If `fd` is specified, then `readStream.path` will be `undefined`.
#####
`readStream.pending`
Added in: v11.2.0, v10.16.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
This property is `true` if the underlying file has not been opened yet, i.e. before the `'ready'` event is emitted.
#### Class: `fs.Stats`
History
| Version | Changes |
| --- | --- |
| v8.1.0 | Added times as numbers. |
| v0.1.21 | Added in: v0.1.21 |
A [<fs.Stats>](fs#class-fsstats) object provides information about a file.
Objects returned from [`fs.stat()`](#fsstatpath-options-callback), [`fs.lstat()`](#fslstatpath-options-callback), [`fs.fstat()`](#fsfstatfd-options-callback), and their synchronous counterparts are of this type. If `bigint` in the `options` passed to those methods is true, the numeric values will be `bigint` instead of `number`, and the object will contain additional nanosecond-precision properties suffixed with `Ns`.
```
Stats {
dev: 2114,
ino: 48064969,
mode: 33188,
nlink: 1,
uid: 85,
gid: 100,
rdev: 0,
size: 527,
blksize: 4096,
blocks: 8,
atimeMs: 1318289051000.1,
mtimeMs: 1318289051000.1,
ctimeMs: 1318289051000.1,
birthtimeMs: 1318289051000.1,
atime: Mon, 10 Oct 2011 23:24:11 GMT,
mtime: Mon, 10 Oct 2011 23:24:11 GMT,
ctime: Mon, 10 Oct 2011 23:24:11 GMT,
birthtime: Mon, 10 Oct 2011 23:24:11 GMT }
```
`bigint` version:
```
BigIntStats {
dev: 2114n,
ino: 48064969n,
mode: 33188n,
nlink: 1n,
uid: 85n,
gid: 100n,
rdev: 0n,
size: 527n,
blksize: 4096n,
blocks: 8n,
atimeMs: 1318289051000n,
mtimeMs: 1318289051000n,
ctimeMs: 1318289051000n,
birthtimeMs: 1318289051000n,
atimeNs: 1318289051000000000n,
mtimeNs: 1318289051000000000n,
ctimeNs: 1318289051000000000n,
birthtimeNs: 1318289051000000000n,
atime: Mon, 10 Oct 2011 23:24:11 GMT,
mtime: Mon, 10 Oct 2011 23:24:11 GMT,
ctime: Mon, 10 Oct 2011 23:24:11 GMT,
birthtime: Mon, 10 Oct 2011 23:24:11 GMT }
```
#####
`stats.isBlockDevice()`
Added in: v0.1.10 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Stats>](fs#class-fsstats) object describes a block device.
#####
`stats.isCharacterDevice()`
Added in: v0.1.10 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Stats>](fs#class-fsstats) object describes a character device.
#####
`stats.isDirectory()`
Added in: v0.1.10 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Stats>](fs#class-fsstats) object describes a file system directory.
If the [<fs.Stats>](fs#class-fsstats) object was obtained from [`fs.lstat()`](#fslstatpath-options-callback), this method will always return `false`. This is because [`fs.lstat()`](#fslstatpath-options-callback) returns information about a symbolic link itself and not the path it resolves to.
#####
`stats.isFIFO()`
Added in: v0.1.10 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Stats>](fs#class-fsstats) object describes a first-in-first-out (FIFO) pipe.
#####
`stats.isFile()`
Added in: v0.1.10 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Stats>](fs#class-fsstats) object describes a regular file.
#####
`stats.isSocket()`
Added in: v0.1.10 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Stats>](fs#class-fsstats) object describes a socket.
#####
`stats.isSymbolicLink()`
Added in: v0.1.10 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the [<fs.Stats>](fs#class-fsstats) object describes a symbolic link.
This method is only valid when using [`fs.lstat()`](#fslstatpath-options-callback).
#####
`stats.dev`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The numeric identifier of the device containing the file.
#####
`stats.ino`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The file system specific "Inode" number for the file.
#####
`stats.mode`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
A bit-field describing the file type and mode.
#####
`stats.nlink`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The number of hard-links that exist for the file.
#####
`stats.uid`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The numeric user identifier of the user that owns the file (POSIX).
#####
`stats.gid`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The numeric group identifier of the group that owns the file (POSIX).
#####
`stats.rdev`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
A numeric device identifier if the file represents a device.
#####
`stats.size`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The size of the file in bytes.
If the underlying file system does not support getting the size of the file, this will be `0`.
#####
`stats.blksize`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The file system block size for i/o operations.
#####
`stats.blocks`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The number of blocks allocated for this file.
#####
`stats.atimeMs`
Added in: v8.1.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The timestamp indicating the last time this file was accessed expressed in milliseconds since the POSIX Epoch.
#####
`stats.mtimeMs`
Added in: v8.1.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The timestamp indicating the last time this file was modified expressed in milliseconds since the POSIX Epoch.
#####
`stats.ctimeMs`
Added in: v8.1.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The timestamp indicating the last time the file status was changed expressed in milliseconds since the POSIX Epoch.
#####
`stats.birthtimeMs`
Added in: v8.1.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The timestamp indicating the creation time of this file expressed in milliseconds since the POSIX Epoch.
#####
`stats.atimeNs`
Added in: v12.10.0 * [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the last time this file was accessed expressed in nanoseconds since the POSIX Epoch.
#####
`stats.mtimeNs`
Added in: v12.10.0 * [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the last time this file was modified expressed in nanoseconds since the POSIX Epoch.
#####
`stats.ctimeNs`
Added in: v12.10.0 * [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the last time the file status was changed expressed in nanoseconds since the POSIX Epoch.
#####
`stats.birthtimeNs`
Added in: v12.10.0 * [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the creation time of this file expressed in nanoseconds since the POSIX Epoch.
#####
`stats.atime`
Added in: v0.11.13 * [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
The timestamp indicating the last time this file was accessed.
#####
`stats.mtime`
Added in: v0.11.13 * [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
The timestamp indicating the last time this file was modified.
#####
`stats.ctime`
Added in: v0.11.13 * [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
The timestamp indicating the last time the file status was changed.
#####
`stats.birthtime`
Added in: v0.11.13 * [<Date>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
The timestamp indicating the creation time of this file.
##### Stat time values
The `atimeMs`, `mtimeMs`, `ctimeMs`, `birthtimeMs` properties are numeric values that hold the corresponding times in milliseconds. Their precision is platform specific. When `bigint: true` is passed into the method that generates the object, the properties will be [bigints](https://tc39.github.io/proposal-bigint), otherwise they will be [numbers](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type).
The `atimeNs`, `mtimeNs`, `ctimeNs`, `birthtimeNs` properties are [bigints](https://tc39.github.io/proposal-bigint) that hold the corresponding times in nanoseconds. They are only present when `bigint: true` is passed into the method that generates the object. Their precision is platform specific.
`atime`, `mtime`, `ctime`, and `birthtime` are [`Date`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date) object alternate representations of the various times. The `Date` and number values are not connected. Assigning a new number value, or mutating the `Date` value, will not be reflected in the corresponding alternate representation.
The times in the stat object have the following semantics:
* `atime` "Access Time": Time when file data last accessed. Changed by the [`mknod(2)`](http://man7.org/linux/man-pages/man2/mknod.2.html), [`utimes(2)`](http://man7.org/linux/man-pages/man2/utimes.2.html), and [`read(2)`](http://man7.org/linux/man-pages/man2/read.2.html) system calls.
* `mtime` "Modified Time": Time when file data last modified. Changed by the [`mknod(2)`](http://man7.org/linux/man-pages/man2/mknod.2.html), [`utimes(2)`](http://man7.org/linux/man-pages/man2/utimes.2.html), and [`write(2)`](http://man7.org/linux/man-pages/man2/write.2.html) system calls.
* `ctime` "Change Time": Time when file status was last changed (inode data modification). Changed by the [`chmod(2)`](http://man7.org/linux/man-pages/man2/chmod.2.html), [`chown(2)`](http://man7.org/linux/man-pages/man2/chown.2.html), [`link(2)`](http://man7.org/linux/man-pages/man2/link.2.html), [`mknod(2)`](http://man7.org/linux/man-pages/man2/mknod.2.html), [`rename(2)`](http://man7.org/linux/man-pages/man2/rename.2.html), [`unlink(2)`](http://man7.org/linux/man-pages/man2/unlink.2.html), [`utimes(2)`](http://man7.org/linux/man-pages/man2/utimes.2.html), [`read(2)`](http://man7.org/linux/man-pages/man2/read.2.html), and [`write(2)`](http://man7.org/linux/man-pages/man2/write.2.html) system calls.
* `birthtime` "Birth Time": Time of file creation. Set once when the file is created. On filesystems where birthtime is not available, this field may instead hold either the `ctime` or `1970-01-01T00:00Z` (ie, Unix epoch timestamp `0`). This value may be greater than `atime` or `mtime` in this case. On Darwin and other FreeBSD variants, also set if the `atime` is explicitly set to an earlier value than the current `birthtime` using the [`utimes(2)`](http://man7.org/linux/man-pages/man2/utimes.2.html) system call.
Prior to Node.js 0.12, the `ctime` held the `birthtime` on Windows systems. As of 0.12, `ctime` is not "creation time", and on Unix systems, it never was.
#### Class: `fs.WriteStream`
Added in: v0.1.93 * Extends [<stream.Writable>](stream#class-streamwritable)
Instances of [<fs.WriteStream>](fs#class-fswritestream) are created and returned using the [`fs.createWriteStream()`](#fscreatewritestreampath-options) function.
##### Event: `'close'`
Added in: v0.1.93 Emitted when the [<fs.WriteStream>](fs#class-fswritestream)'s underlying file descriptor has been closed.
##### Event: `'open'`
Added in: v0.1.93 * `fd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Integer file descriptor used by the [<fs.WriteStream>](fs#class-fswritestream).
Emitted when the [<fs.WriteStream>](fs#class-fswritestream)'s file is opened.
##### Event: `'ready'`
Added in: v9.11.0 Emitted when the [<fs.WriteStream>](fs#class-fswritestream) is ready to be used.
Fires immediately after `'open'`.
#####
`writeStream.bytesWritten`
Added in: v0.4.7 The number of bytes written so far. Does not include data that is still queued for writing.
#####
`writeStream.close([callback])`
Added in: v0.9.4 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Closes `writeStream`. Optionally accepts a callback that will be executed once the `writeStream` is closed.
#####
`writeStream.path`
Added in: v0.1.93 The path to the file the stream is writing to as specified in the first argument to [`fs.createWriteStream()`](#fscreatewritestreampath-options). If `path` is passed as a string, then `writeStream.path` will be a string. If `path` is passed as a [<Buffer>](buffer#class-buffer), then `writeStream.path` will be a [<Buffer>](buffer#class-buffer).
#####
`writeStream.pending`
Added in: v11.2.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
This property is `true` if the underlying file has not been opened yet, i.e. before the `'ready'` event is emitted.
####
`fs.constants`
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns an object containing commonly used constants for file system operations.
##### FS constants
The following constants are exported by `fs.constants` and `fsPromises.constants`.
Not every constant will be available on every operating system; this is especially important for Windows, where many of the POSIX specific definitions are not available. For portable applications it is recommended to check for their presence before use.
To use more than one constant, use the bitwise OR `|` operator.
Example:
```
import { open, constants } from 'node:fs';
const {
O_RDWR,
O_CREAT,
O_EXCL
} = constants;
open('/path/to/my/file', O_RDWR | O_CREAT | O_EXCL, (err, fd) => {
// ...
});
```
###### File access constants
The following constants are meant for use as the `mode` parameter passed to [`fsPromises.access()`](#fspromisesaccesspath-mode), [`fs.access()`](#fsaccesspath-mode-callback), and [`fs.accessSync()`](#fsaccesssyncpath-mode).
| Constant | Description |
| --- | --- |
| `F_OK` | Flag indicating that the file is visible to the calling process. This is useful for determining if a file exists, but says nothing about `rwx` permissions. Default if no mode is specified. |
| `R_OK` | Flag indicating that the file can be read by the calling process. |
| `W_OK` | Flag indicating that the file can be written by the calling process. |
| `X_OK` | Flag indicating that the file can be executed by the calling process. This has no effect on Windows (will behave like `fs.constants.F_OK`). |
The definitions are also available on Windows.
###### File copy constants
The following constants are meant for use with [`fs.copyFile()`](#fscopyfilesrc-dest-mode-callback).
| Constant | Description |
| --- | --- |
| `COPYFILE_EXCL` | If present, the copy operation will fail with an error if the destination path already exists. |
| `COPYFILE_FICLONE` | If present, the copy operation will attempt to create a copy-on-write reflink. If the underlying platform does not support copy-on-write, then a fallback copy mechanism is used. |
| `COPYFILE_FICLONE_FORCE` | If present, the copy operation will attempt to create a copy-on-write reflink. If the underlying platform does not support copy-on-write, then the operation will fail with an error. |
The definitions are also available on Windows.
###### File open constants
The following constants are meant for use with `fs.open()`.
| Constant | Description |
| --- | --- |
| `O_RDONLY` | Flag indicating to open a file for read-only access. |
| `O_WRONLY` | Flag indicating to open a file for write-only access. |
| `O_RDWR` | Flag indicating to open a file for read-write access. |
| `O_CREAT` | Flag indicating to create the file if it does not already exist. |
| `O_EXCL` | Flag indicating that opening a file should fail if the `O_CREAT` flag is set and the file already exists. |
| `O_NOCTTY` | Flag indicating that if path identifies a terminal device, opening the path shall not cause that terminal to become the controlling terminal for the process (if the process does not already have one). |
| `O_TRUNC` | Flag indicating that if the file exists and is a regular file, and the file is opened successfully for write access, its length shall be truncated to zero. |
| `O_APPEND` | Flag indicating that data will be appended to the end of the file. |
| `O_DIRECTORY` | Flag indicating that the open should fail if the path is not a directory. |
| `O_NOATIME` | Flag indicating reading accesses to the file system will no longer result in an update to the `atime` information associated with the file. This flag is available on Linux operating systems only. |
| `O_NOFOLLOW` | Flag indicating that the open should fail if the path is a symbolic link. |
| `O_SYNC` | Flag indicating that the file is opened for synchronized I/O with write operations waiting for file integrity. |
| `O_DSYNC` | Flag indicating that the file is opened for synchronized I/O with write operations waiting for data integrity. |
| `O_SYMLINK` | Flag indicating to open the symbolic link itself rather than the resource it is pointing to. |
| `O_DIRECT` | When set, an attempt will be made to minimize caching effects of file I/O. |
| `O_NONBLOCK` | Flag indicating to open the file in nonblocking mode when possible. |
| `UV_FS_O_FILEMAP` | When set, a memory file mapping is used to access the file. This flag is available on Windows operating systems only. On other operating systems, this flag is ignored. |
On Windows, only `O_APPEND`, `O_CREAT`, `O_EXCL`, `O_RDONLY`, `O_RDWR`, `O_TRUNC`, `O_WRONLY`, and `UV_FS_O_FILEMAP` are available.
###### File type constants
The following constants are meant for use with the [<fs.Stats>](fs#class-fsstats) object's `mode` property for determining a file's type.
| Constant | Description |
| --- | --- |
| `S_IFMT` | Bit mask used to extract the file type code. |
| `S_IFREG` | File type constant for a regular file. |
| `S_IFDIR` | File type constant for a directory. |
| `S_IFCHR` | File type constant for a character-oriented device file. |
| `S_IFBLK` | File type constant for a block-oriented device file. |
| `S_IFIFO` | File type constant for a FIFO/pipe. |
| `S_IFLNK` | File type constant for a symbolic link. |
| `S_IFSOCK` | File type constant for a socket. |
On Windows, only `S_IFCHR`, `S_IFDIR`, `S_IFLNK`, `S_IFMT`, and `S_IFREG`, are available.
###### File mode constants
The following constants are meant for use with the [<fs.Stats>](fs#class-fsstats) object's `mode` property for determining the access permissions for a file.
| Constant | Description |
| --- | --- |
| `S_IRWXU` | File mode indicating readable, writable, and executable by owner. |
| `S_IRUSR` | File mode indicating readable by owner. |
| `S_IWUSR` | File mode indicating writable by owner. |
| `S_IXUSR` | File mode indicating executable by owner. |
| `S_IRWXG` | File mode indicating readable, writable, and executable by group. |
| `S_IRGRP` | File mode indicating readable by group. |
| `S_IWGRP` | File mode indicating writable by group. |
| `S_IXGRP` | File mode indicating executable by group. |
| `S_IRWXO` | File mode indicating readable, writable, and executable by others. |
| `S_IROTH` | File mode indicating readable by others. |
| `S_IWOTH` | File mode indicating writable by others. |
| `S_IXOTH` | File mode indicating executable by others. |
On Windows, only `S_IRUSR` and `S_IWUSR` are available.
### Notes
#### Ordering of callback and promise-based operations
Because they are executed asynchronously by the underlying thread pool, there is no guaranteed ordering when using either the callback or promise-based methods.
For example, the following is prone to error because the `fs.stat()` operation might complete before the `fs.rename()` operation:
```
fs.rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
console.log('renamed complete');
});
fs.stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
```
It is important to correctly order the operations by awaiting the results of one before invoking the other:
MJS modules
```
import { rename, stat } from 'node:fs/promises';
const from = '/tmp/hello';
const to = '/tmp/world';
try {
await rename(from, to);
const stats = await stat(to);
console.log(`stats: ${JSON.stringify(stats)}`);
} catch (error) {
console.error('there was an error:', error.message);
}
```
CJS modules
```
const { rename, stat } = require('node:fs/promises');
(async function(from, to) {
try {
await rename(from, to);
const stats = await stat(to);
console.log(`stats: ${JSON.stringify(stats)}`);
} catch (error) {
console.error('there was an error:', error.message);
}
})('/tmp/hello', '/tmp/world');
```
Or, when using the callback APIs, move the `fs.stat()` call into the callback of the `fs.rename()` operation:
MJS modules
```
import { rename, stat } from 'node:fs';
rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
});
```
CJS modules
```
const { rename, stat } = require('node:fs/promises');
rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
});
```
#### File paths
Most `fs` operations accept file paths that may be specified in the form of a string, a [<Buffer>](buffer#class-buffer), or a [<URL>](url#the-whatwg-url-api) object using the `file:` protocol.
##### String paths
String paths are interpreted as UTF-8 character sequences identifying the absolute or relative filename. Relative paths will be resolved relative to the current working directory as determined by calling `process.cwd()`.
Example using an absolute path on POSIX:
```
import { open } from 'node:fs/promises';
let fd;
try {
fd = await open('/open/some/file.txt', 'r');
// Do something with the file
} finally {
await fd.close();
}
```
Example using a relative path on POSIX (relative to `process.cwd()`):
```
import { open } from 'node:fs/promises';
let fd;
try {
fd = await open('file.txt', 'r');
// Do something with the file
} finally {
await fd.close();
}
```
##### File URL paths
Added in: v7.6.0 For most `node:fs` module functions, the `path` or `filename` argument may be passed as a [<URL>](url#the-whatwg-url-api) object using the `file:` protocol.
```
import { readFileSync } from 'node:fs';
readFileSync(new URL('file:///tmp/hello'));
```
`file:` URLs are always absolute paths.
###### Platform-specific considerations
On Windows, `file:` [<URL>](url#the-whatwg-url-api)s with a host name convert to UNC paths, while `file:` [<URL>](url#the-whatwg-url-api)s with drive letters convert to local absolute paths. `file:` [<URL>](url#the-whatwg-url-api)s with no host name and no drive letter will result in an error:
```
import { readFileSync } from 'node:fs';
// On Windows :
// - WHATWG file URLs with hostname convert to UNC path
// file://hostname/p/a/t/h/file => \\hostname\p\a\t\h\file
readFileSync(new URL('file://hostname/p/a/t/h/file'));
// - WHATWG file URLs with drive letters convert to absolute path
// file:///C:/tmp/hello => C:\tmp\hello
readFileSync(new URL('file:///C:/tmp/hello'));
// - WHATWG file URLs without hostname must have a drive letters
readFileSync(new URL('file:///notdriveletter/p/a/t/h/file'));
readFileSync(new URL('file:///c/p/a/t/h/file'));
// TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must be absolute
```
`file:` [<URL>](url#the-whatwg-url-api)s with drive letters must use `:` as a separator just after the drive letter. Using another separator will result in an error.
On all other platforms, `file:` [<URL>](url#the-whatwg-url-api)s with a host name are unsupported and will result in an error:
```
import { readFileSync } from 'node:fs';
// On other platforms:
// - WHATWG file URLs with hostname are unsupported
// file://hostname/p/a/t/h/file => throw!
readFileSync(new URL('file://hostname/p/a/t/h/file'));
// TypeError [ERR_INVALID_FILE_URL_PATH]: must be absolute
// - WHATWG file URLs convert to absolute path
// file:///tmp/hello => /tmp/hello
readFileSync(new URL('file:///tmp/hello'));
```
A `file:` [<URL>](url#the-whatwg-url-api) having encoded slash characters will result in an error on all platforms:
```
import { readFileSync } from 'node:fs';
// On Windows
readFileSync(new URL('file:///C:/p/a/t/h/%2F'));
readFileSync(new URL('file:///C:/p/a/t/h/%2f'));
/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded
\ or / characters */
// On POSIX
readFileSync(new URL('file:///p/a/t/h/%2F'));
readFileSync(new URL('file:///p/a/t/h/%2f'));
/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded
/ characters */
```
On Windows, `file:` [<URL>](url#the-whatwg-url-api)s having encoded backslash will result in an error:
```
import { readFileSync } from 'node:fs';
// On Windows
readFileSync(new URL('file:///C:/path/%5C'));
readFileSync(new URL('file:///C:/path/%5c'));
/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded
\ or / characters */
```
##### Buffer paths
Paths specified using a [<Buffer>](buffer#class-buffer) are useful primarily on certain POSIX operating systems that treat file paths as opaque byte sequences. On such systems, it is possible for a single file path to contain sub-sequences that use multiple character encodings. As with string paths, [<Buffer>](buffer#class-buffer) paths may be relative or absolute:
Example using an absolute path on POSIX:
```
import { open } from 'node:fs/promises';
import { Buffer } from 'node:buffer';
let fd;
try {
fd = await open(Buffer.from('/open/some/file.txt'), 'r');
// Do something with the file
} finally {
await fd.close();
}
```
##### Per-drive working directories on Windows
On Windows, Node.js follows the concept of per-drive working directory. This behavior can be observed when using a drive path without a backslash. For example `fs.readdirSync('C:\\')` can potentially return a different result than `fs.readdirSync('C:')`. For more information, see [this MSDN page](https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file#fully-qualified-vs-relative-paths).
#### File descriptors
On POSIX systems, for every process, the kernel maintains a table of currently open files and resources. Each open file is assigned a simple numeric identifier called a *file descriptor*. At the system-level, all file system operations use these file descriptors to identify and track each specific file. Windows systems use a different but conceptually similar mechanism for tracking resources. To simplify things for users, Node.js abstracts away the differences between operating systems and assigns all open files a numeric file descriptor.
The callback-based `fs.open()`, and synchronous `fs.openSync()` methods open a file and allocate a new file descriptor. Once allocated, the file descriptor may be used to read data from, write data to, or request information about the file.
Operating systems limit the number of file descriptors that may be open at any given time so it is critical to close the descriptor when operations are completed. Failure to do so will result in a memory leak that will eventually cause an application to crash.
```
import { open, close, fstat } from 'node:fs';
function closeFd(fd) {
close(fd, (err) => {
if (err) throw err;
});
}
open('/open/some/file.txt', 'r', (err, fd) => {
if (err) throw err;
try {
fstat(fd, (err, stat) => {
if (err) {
closeFd(fd);
throw err;
}
// use stat
closeFd(fd);
});
} catch (err) {
closeFd(fd);
throw err;
}
});
```
The promise-based APIs use a [<FileHandle>](fs#class-filehandle) object in place of the numeric file descriptor. These objects are better managed by the system to ensure that resources are not leaked. However, it is still required that they are closed when operations are completed:
```
import { open } from 'node:fs/promises';
let file;
try {
file = await open('/open/some/file.txt', 'r');
const stat = await file.stat();
// use stat
} finally {
await file.close();
}
```
#### Threadpool usage
All callback and promise-based file system APIs (with the exception of `fs.FSWatcher()`) use libuv's threadpool. This can have surprising and negative performance implications for some applications. See the [`UV_THREADPOOL_SIZE`](cli#uv_threadpool_sizesize) documentation for more information.
#### File system flags
The following flags are available wherever the `flag` option takes a string.
* `'a'`: Open file for appending. The file is created if it does not exist.
* `'ax'`: Like `'a'` but fails if the path exists.
* `'a+'`: Open file for reading and appending. The file is created if it does not exist.
* `'ax+'`: Like `'a+'` but fails if the path exists.
* `'as'`: Open file for appending in synchronous mode. The file is created if it does not exist.
* `'as+'`: Open file for reading and appending in synchronous mode. The file is created if it does not exist.
* `'r'`: Open file for reading. An exception occurs if the file does not exist.
* `'r+'`: Open file for reading and writing. An exception occurs if the file does not exist.
* `'rs+'`: Open file for reading and writing in synchronous mode. Instructs the operating system to bypass the local file system cache.
This is primarily useful for opening files on NFS mounts as it allows skipping the potentially stale local cache. It has a very real impact on I/O performance so using this flag is not recommended unless it is needed.
This doesn't turn `fs.open()` or `fsPromises.open()` into a synchronous blocking call. If synchronous operation is desired, something like `fs.openSync()` should be used.
* `'w'`: Open file for writing. The file is created (if it does not exist) or truncated (if it exists).
* `'wx'`: Like `'w'` but fails if the path exists.
* `'w+'`: Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists).
* `'wx+'`: Like `'w+'` but fails if the path exists.
`flag` can also be a number as documented by [`open(2)`](http://man7.org/linux/man-pages/man2/open.2.html); commonly used constants are available from `fs.constants`. On Windows, flags are translated to their equivalent ones where applicable, e.g. `O_WRONLY` to `FILE_GENERIC_WRITE`, or `O_EXCL|O_CREAT` to `CREATE_NEW`, as accepted by `CreateFileW`.
The exclusive flag `'x'` (`O_EXCL` flag in [`open(2)`](http://man7.org/linux/man-pages/man2/open.2.html)) causes the operation to return an error if the path already exists. On POSIX, if the path is a symbolic link, using `O_EXCL` returns an error even if the link is to a path that does not exist. The exclusive flag might not work with network file systems.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
Modifying a file rather than replacing it may require the `flag` option to be set to `'r+'` rather than the default `'w'`.
The behavior of some flags are platform-specific. As such, opening a directory on macOS and Linux with the `'a+'` flag, as in the example below, will return an error. In contrast, on Windows and FreeBSD, a file descriptor or a `FileHandle` will be returned.
```
// macOS and Linux
fs.open('<directory>', 'a+', (err, fd) => {
// => [Error: EISDIR: illegal operation on a directory, open <directory>]
});
// Windows and FreeBSD
fs.open('<directory>', 'a+', (err, fd) => {
// => null, <fd>
});
```
On Windows, opening an existing hidden file using the `'w'` flag (either through `fs.open()`, `fs.writeFile()`, or `fsPromises.open()`) will fail with `EPERM`. Existing hidden files can be opened for writing with the `'r+'` flag.
A call to `fs.ftruncate()` or `filehandle.truncate()` can be used to reset the file contents.
| programming_docs |
node None HTTPS
-----
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/https.js](https://github.com/nodejs/node/blob/v19.0.1/lib/https.js)
HTTPS is the HTTP protocol over TLS/SSL. In Node.js this is implemented as a separate module.
### Determining if crypto support is unavailable
It is possible for Node.js to be built without including support for the `node:crypto` module. In such cases, attempting to `import` from `https` or calling `require('node:https')` will result in an error being thrown.
When using CommonJS, the error thrown can be caught using try/catch:
```
let https;
try {
https = require('node:https');
} catch (err) {
console.log('https support is disabled!');
}
```
When using the lexical ESM `import` keyword, the error can only be caught if a handler for `process.on('uncaughtException')` is registered *before* any attempt to load the module is made (using, for instance, a preload module).
When using ESM, if there is a chance that the code may be run on a build of Node.js where crypto support is not enabled, consider using the [`import()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import) function instead of the lexical `import` keyword:
```
let https;
try {
https = await import('node:https');
} catch (err) {
console.log('https support is disabled!');
}
```
### Class: `https.Agent`
History
| Version | Changes |
| --- | --- |
| v5.3.0 | support `0` `maxCachedSessions` to disable TLS session caching. |
| v2.5.0 | parameter `maxCachedSessions` added to `options` for TLS sessions reuse. |
| v0.4.5 | Added in: v0.4.5 |
An [`Agent`](#class-httpsagent) object for HTTPS similar to [`http.Agent`](http#class-httpagent). See [`https.request()`](#httpsrequestoptions-callback) for more information.
####
`new Agent([options])`
History
| Version | Changes |
| --- | --- |
| v12.5.0 | do not automatically set servername if the target host was specified using an IP address. |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Set of configurable options to set on the agent. Can have the same fields as for [`http.Agent(options)`](http#new-agentoptions), and
+ `maxCachedSessions` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maximum number of TLS cached sessions. Use `0` to disable TLS session caching. **Default:** `100`.
+ `servername` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) the value of [Server Name Indication extension](https://en.wikipedia.org/wiki/Server_Name_Indication) to be sent to the server. Use empty string `''` to disable sending the extension. **Default:** host name of the target server, unless the target server is specified using an IP address, in which case the default is `''` (no extension).
See [`Session Resumption`](tls#session-resumption) for information about TLS session reuse.
##### Event: `'keylog'`
Added in: v13.2.0, v12.16.0 * `line` [<Buffer>](buffer#class-buffer) Line of ASCII text, in NSS `SSLKEYLOGFILE` format.
* `tlsSocket` [<tls.TLSSocket>](tls#class-tlstlssocket) The `tls.TLSSocket` instance on which it was generated.
The `keylog` event is emitted when key material is generated or received by a connection managed by this agent (typically before handshake has completed, but not necessarily). This keying material can be stored for debugging, as it allows captured TLS traffic to be decrypted. It may be emitted multiple times for each socket.
A typical use case is to append received lines to a common text file, which is later used by software (such as Wireshark) to decrypt the traffic:
```
// ...
https.globalAgent.on('keylog', (line, tlsSocket) => {
fs.appendFileSync('/tmp/ssl-keys.log', line, { mode: 0o600 });
});
```
### Class: `https.Server`
Added in: v0.3.4 * Extends: [<tls.Server>](tls#class-tlsserver)
See [`http.Server`](http#class-httpserver) for more information.
####
`server.close([callback])`
Added in: v0.1.90 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<https.Server>](https#class-httpsserver)
See [`server.close()`](http#serverclosecallback) in the `node:http` module.
####
`server.closeAllConnections()`
Added in: v18.2.0 See [`server.closeAllConnections()`](http#servercloseallconnections) in the `node:http` module.
####
`server.closeIdleConnections()`
Added in: v18.2.0 See [`server.closeIdleConnections()`](http#servercloseidleconnections) in the `node:http` module.
####
`server.headersTimeout`
Added in: v11.3.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `60000`
See [`server.headersTimeout`](http#serverheaderstimeout) in the `node:http` module.
####
`server.listen()`
Starts the HTTPS server listening for encrypted connections. This method is identical to [`server.listen()`](net#serverlisten) from [`net.Server`](net#class-netserver).
####
`server.maxHeadersCount`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `2000`
See [`server.maxHeadersCount`](http#servermaxheaderscount) in the `node:http` module.
####
`server.requestTimeout`
Added in: v14.11.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
See [`server.requestTimeout`](http#serverrequesttimeout) in the `node:http` module.
####
`server.setTimeout([msecs][, callback])`
Added in: v0.11.2 * `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `120000` (2 minutes)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<https.Server>](https#class-httpsserver)
See [`server.setTimeout()`](http#serversettimeoutmsecs-callback) in the `node:http` module.
####
`server.timeout`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The default timeout changed from 120s to 0 (no timeout). |
| v0.11.2 | Added in: v0.11.2 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** 0 (no timeout)
See [`server.timeout`](http#servertimeout) in the `node:http` module.
####
`server.keepAliveTimeout`
Added in: v8.0.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `5000` (5 seconds)
See [`server.keepAliveTimeout`](http#serverkeepalivetimeout) in the `node:http` module.
###
`https.createServer([options][, requestListener])`
Added in: v0.3.4 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Accepts `options` from [`tls.createServer()`](tls#tlscreateserveroptions-secureconnectionlistener), [`tls.createSecureContext()`](tls#tlscreatesecurecontextoptions) and [`http.createServer()`](http#httpcreateserveroptions-requestlistener).
* `requestListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A listener to be added to the `'request'` event.
* Returns: [<https.Server>](https#class-httpsserver)
```
// curl -k https://localhost:8000/
const https = require('node:https');
const fs = require('node:fs');
const options = {
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
https.createServer(options, (req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
```
Or
```
const https = require('node:https');
const fs = require('node:fs');
const options = {
pfx: fs.readFileSync('test/fixtures/test_cert.pfx'),
passphrase: 'sample'
};
https.createServer(options, (req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
```
###
`https.get(options[, callback])`
###
`https.get(url[, options][, callback])`
History
| Version | Changes |
| --- | --- |
| v10.9.0 | The `url` parameter can now be passed along with a separate `options` object. |
| v7.5.0 | The `options` parameter can be a WHATWG `URL` object. |
| v0.3.6 | Added in: v0.3.6 |
* `url` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Accepts the same `options` as [`https.request()`](#httpsrequestoptions-callback), with the `method` always set to `GET`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Like [`http.get()`](http#httpgetoptions-callback) but for HTTPS.
`options` can be an object, a string, or a [`URL`](url#the-whatwg-url-api) object. If `options` is a string, it is automatically parsed with [`new URL()`](url#new-urlinput-base). If it is a [`URL`](url#the-whatwg-url-api) object, it will be automatically converted to an ordinary `options` object.
```
const https = require('node:https');
https.get('https://encrypted.google.com/', (res) => {
console.log('statusCode:', res.statusCode);
console.log('headers:', res.headers);
res.on('data', (d) => {
process.stdout.write(d);
});
}).on('error', (e) => {
console.error(e);
});
```
###
`https.globalAgent`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | The agent now uses HTTP Keep-Alive by default. |
| v0.5.9 | Added in: v0.5.9 |
Global instance of [`https.Agent`](#class-httpsagent) for all HTTPS client requests.
###
`https.request(options[, callback])`
###
`https.request(url[, options][, callback])`
History
| Version | Changes |
| --- | --- |
| v16.7.0, v14.18.0 | When using a `URL` object parsed username and password will now be properly URI decoded. |
| v14.1.0, v13.14.0 | The `highWaterMark` option is accepted now. |
| v10.9.0 | The `url` parameter can now be passed along with a separate `options` object. |
| v9.3.0 | The `options` parameter can now include `clientCertEngine`. |
| v7.5.0 | The `options` parameter can be a WHATWG `URL` object. |
| v0.3.6 | Added in: v0.3.6 |
* `url` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) Accepts all `options` from [`http.request()`](http#httprequestoptions-callback), with some differences in default values:
+ `protocol` **Default:** `'https:'`
+ `port` **Default:** `443`
+ `agent` **Default:** `https.globalAgent`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<http.ClientRequest>](http#class-httpclientrequest)
Makes a request to a secure web server.
The following additional `options` from [`tls.connect()`](tls#tlsconnectoptions-callback) are also accepted: `ca`, `cert`, `ciphers`, `clientCertEngine`, `crl`, `dhparam`, `ecdhCurve`, `honorCipherOrder`, `key`, `passphrase`, `pfx`, `rejectUnauthorized`, `secureOptions`, `secureProtocol`, `servername`, `sessionIdContext`, `highWaterMark`.
`options` can be an object, a string, or a [`URL`](url#the-whatwg-url-api) object. If `options` is a string, it is automatically parsed with [`new URL()`](url#new-urlinput-base). If it is a [`URL`](url#the-whatwg-url-api) object, it will be automatically converted to an ordinary `options` object.
`https.request()` returns an instance of the [`http.ClientRequest`](http#class-httpclientrequest) class. The `ClientRequest` instance is a writable stream. If one needs to upload a file with a POST request, then write to the `ClientRequest` object.
```
const https = require('node:https');
const options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET'
};
const req = https.request(options, (res) => {
console.log('statusCode:', res.statusCode);
console.log('headers:', res.headers);
res.on('data', (d) => {
process.stdout.write(d);
});
});
req.on('error', (e) => {
console.error(e);
});
req.end();
```
Example using options from [`tls.connect()`](tls#tlsconnectoptions-callback):
```
const options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET',
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
options.agent = new https.Agent(options);
const req = https.request(options, (res) => {
// ...
});
```
Alternatively, opt out of connection pooling by not using an [`Agent`](#class-httpsagent).
```
const options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET',
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem'),
agent: false
};
const req = https.request(options, (res) => {
// ...
});
```
Example using a [`URL`](url#the-whatwg-url-api) as `options`:
```
const options = new URL('https://abc:[email protected]');
const req = https.request(options, (res) => {
// ...
});
```
Example pinning on certificate fingerprint, or the public key (similar to `pin-sha256`):
```
const tls = require('node:tls');
const https = require('node:https');
const crypto = require('node:crypto');
function sha256(s) {
return crypto.createHash('sha256').update(s).digest('base64');
}
const options = {
hostname: 'github.com',
port: 443,
path: '/',
method: 'GET',
checkServerIdentity: function(host, cert) {
// Make sure the certificate is issued to the host we are connected to
const err = tls.checkServerIdentity(host, cert);
if (err) {
return err;
}
// Pin the public key, similar to HPKP pin-sha256 pinning
const pubkey256 = 'pL1+qb9HTMRZJmuC/bB/ZI9d302BYrrqiVuRyW+DGrU=';
if (sha256(cert.pubkey) !== pubkey256) {
const msg = 'Certificate verification error: ' +
`The public key of '${cert.subject.CN}' ` +
'does not match our pinned fingerprint';
return new Error(msg);
}
// Pin the exact certificate, rather than the pub key
const cert256 = '25:FE:39:32:D9:63:8C:8A:FC:A1:9A:29:87:' +
'D8:3E:4C:1D:98:DB:71:E4:1A:48:03:98:EA:22:6A:BD:8B:93:16';
if (cert.fingerprint256 !== cert256) {
const msg = 'Certificate verification error: ' +
`The certificate of '${cert.subject.CN}' ` +
'does not match our pinned fingerprint';
return new Error(msg);
}
// This loop is informational only.
// Print the certificate and public key fingerprints of all certs in the
// chain. Its common to pin the public key of the issuer on the public
// internet, while pinning the public key of the service in sensitive
// environments.
do {
console.log('Subject Common Name:', cert.subject.CN);
console.log(' Certificate SHA256 fingerprint:', cert.fingerprint256);
hash = crypto.createHash('sha256');
console.log(' Public key ping-sha256:', sha256(cert.pubkey));
lastprint256 = cert.fingerprint256;
cert = cert.issuerCertificate;
} while (cert.fingerprint256 !== lastprint256);
},
};
options.agent = new https.Agent(options);
const req = https.request(options, (res) => {
console.log('All OK. Server matched our pinned cert or public key');
console.log('statusCode:', res.statusCode);
// Print the HPKP values
console.log('headers:', res.headers['public-key-pins']);
res.on('data', (d) => {});
});
req.on('error', (e) => {
console.error(e.message);
});
req.end();
```
Outputs for example:
```
Subject Common Name: github.com
Certificate SHA256 fingerprint: 25:FE:39:32:D9:63:8C:8A:FC:A1:9A:29:87:D8:3E:4C:1D:98:DB:71:E4:1A:48:03:98:EA:22:6A:BD:8B:93:16
Public key ping-sha256: pL1+qb9HTMRZJmuC/bB/ZI9d302BYrrqiVuRyW+DGrU=
Subject Common Name: DigiCert SHA2 Extended Validation Server CA
Certificate SHA256 fingerprint: 40:3E:06:2A:26:53:05:91:13:28:5B:AF:80:A0:D4:AE:42:2C:84:8C:9F:78:FA:D0:1F:C9:4B:C5:B8:7F:EF:1A
Public key ping-sha256: RRM1dGqnDFsCJXBTHky16vi1obOlCgFFn/yOhI/y+ho=
Subject Common Name: DigiCert High Assurance EV Root CA
Certificate SHA256 fingerprint: 74:31:E5:F4:C3:C1:CE:46:90:77:4F:0B:61:E0:54:40:88:3B:A9:A0:1E:D0:0B:A6:AB:D7:80:6E:D3:B1:18:CF
Public key ping-sha256: WoiWRyIOVNa9ihaBciRSC7XHjliYS9VwUGOIud4PB18=
All OK. Server matched our pinned cert or public key
statusCode: 200
headers: max-age=0; pin-sha256="WoiWRyIOVNa9ihaBciRSC7XHjliYS9VwUGOIud4PB18="; pin-sha256="RRM1dGqnDFsCJXBTHky16vi1obOlCgFFn/yOhI/y+ho="; pin-sha256="k2v657xBsOVe1PQRwOsHsw3bsGT2VzIqz5K+59sNQws="; pin-sha256="K87oWBWM9UZfyddvDfoxL+8lpNyoUB2ptGtn0fv6G2Q="; pin-sha256="IQBnNBEiFuhj+8x6X8XLgh01V9Ic5/V3IRQLNFFc7v4="; pin-sha256="iie1VXtL7HzAMF+/PVPR9xzT80kQxdZeJ+zduCB3uj0="; pin-sha256="LvRiGEjRqfzurezaWuj8Wie2gyHMrW5Q06LspMnox7A="; includeSubDomains
```
node None Corepack
--------
Added in: v16.9.0, v14.19.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
*[Corepack](https://github.com/nodejs/corepack)* is an experimental tool to help with managing versions of your package managers. It exposes binary proxies for each [supported package manager](#supported-package-managers) that, when called, will identify whatever package manager is configured for the current project, transparently install it if needed, and finally run it without requiring explicit user interactions.
This feature simplifies two core workflows:
* It eases new contributor onboarding, since they won't have to follow system-specific installation processes anymore just to have the package manager you want them to.
* It allows you to ensure that everyone in your team will use exactly the package manager version you intend them to, without them having to manually synchronize it each time you need to make an update.
### Workflows
#### Enabling the feature
Due to its experimental status, Corepack currently needs to be explicitly enabled to have any effect. To do that, run [`corepack enable`](https://github.com/nodejs/corepack#corepack-enable--name), which will set up the symlinks in your environment next to the `node` binary (and overwrite the existing symlinks if necessary).
From this point forward, any call to the [supported binaries](#supported-package-managers) will work without further setup. Should you experience a problem, run [`corepack disable`](https://github.com/nodejs/corepack#corepack-disable--name) to remove the proxies from your system (and consider opening an issue on the [Corepack repository](https://github.com/nodejs/corepack) to let us know).
#### Configuring a package
The Corepack proxies will find the closest [`package.json`](packages#nodejs-packagejson-field-definitions) file in your current directory hierarchy to extract its [`"packageManager"`](packages#packagemanager) property.
If the value corresponds to a [supported package manager](#supported-package-managers), Corepack will make sure that all calls to the relevant binaries are run against the requested version, downloading it on demand if needed, and aborting if it cannot be successfully retrieved.
#### Upgrading the global versions
When running outside of an existing project (for example when running `yarn init`), Corepack will by default use predefined versions roughly corresponding to the latest stable releases from each tool. Those versions can be overridden by running the [`corepack prepare`](https://github.com/nodejs/corepack#corepack-prepare--nameversion) command along with the package manager version you wish to set:
```
corepack prepare [email protected] --activate
```
Alternately, a tag or range may be used:
```
corepack prepare pnpm@latest --activate
corepack prepare yarn@stable --activate
```
#### Offline workflow
Many production environments don't have network access. Since Corepack usually downloads the package manager releases straight from their registries, it can conflict with such environments. To avoid that happening, call the [`corepack prepare`](https://github.com/nodejs/corepack#corepack-prepare--nameversion) command while you still have network access (typically at the same time you're preparing your deploy image). This will ensure that the required package managers are available even without network access.
The `prepare` command has [various flags](https://github.com/nodejs/corepack#utility-commands). Consult the detailed [Corepack documentation](https://github.com/nodejs/corepack#readme) for more information.
### Supported package managers
The following binaries are provided through Corepack:
| Package manager | Binary names |
| --- | --- |
| [Yarn](https://yarnpkg.com) | `yarn`, `yarnpkg` |
| [pnpm](https://pnpm.js.org) | `pnpm`, `pnpx` |
### Common questions
#### How does Corepack interact with npm?
While Corepack could support npm like any other package manager, its shims aren't enabled by default. This has a few consequences:
* It's always possible to run a `npm` command within a project configured to be used with another package manager, since Corepack cannot intercept it.
* While `npm` is a valid option in the [`"packageManager"`](packages#packagemanager) property, the lack of shim will cause the global npm to be used.
#### Running `npm install -g yarn` doesn't work
npm prevents accidentally overriding the Corepack binaries when doing a global install. To avoid this problem, consider one of the following options:
* Don't run this command; Corepack will provide the package manager binaries anyway and will ensure that the requested versions are always available, so installing the package managers explicitly isn't needed.
* Add the `--force` flag to `npm install`; this will tell npm that it's fine to override binaries, but you'll erase the Corepack ones in the process. (Run [`corepack enable`](https://github.com/nodejs/corepack#corepack-enable--name) to add them back.)
| programming_docs |
node None Assert
------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/assert.js](https://github.com/nodejs/node/blob/v19.0.1/lib/assert.js)
The `node:assert` module provides a set of assertion functions for verifying invariants.
### Strict assertion mode
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Exposed as `require('node:assert/strict')`. |
| v13.9.0, v12.16.2 | Changed "strict mode" to "strict assertion mode" and "legacy mode" to "legacy assertion mode" to avoid confusion with the more usual meaning of "strict mode". |
| v9.9.0 | Added error diffs to the strict assertion mode. |
| v9.9.0 | Added strict assertion mode to the assert module. |
| v9.9.0 | Added in: v9.9.0 |
In strict assertion mode, non-strict methods behave like their corresponding strict methods. For example, [`assert.deepEqual()`](#assertdeepequalactual-expected-message) will behave like [`assert.deepStrictEqual()`](#assertdeepstrictequalactual-expected-message).
In strict assertion mode, error messages for objects display a diff. In legacy assertion mode, error messages for objects display the objects, often truncated.
To use strict assertion mode:
MJS modules
```
import { strict as assert } from 'node:assert';
```
CJS modules
```
const assert = require('node:assert').strict;
```
MJS modules
```
import assert from 'node:assert/strict';
```
CJS modules
```
const assert = require('node:assert/strict');
```
Example error diff:
MJS modules
```
import { strict as assert } from 'node:assert';
assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected ... Lines skipped
//
// [
// [
// ...
// 2,
// + 3
// - '3'
// ],
// ...
// 5
// ]
```
CJS modules
```
const assert = require('node:assert/strict');
assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected ... Lines skipped
//
// [
// [
// ...
// 2,
// + 3
// - '3'
// ],
// ...
// 5
// ]
```
To deactivate the colors, use the `NO_COLOR` or `NODE_DISABLE_COLORS` environment variables. This will also deactivate the colors in the REPL. For more on color support in terminal environments, read the tty [`getColorDepth()`](tty#writestreamgetcolordepthenv) documentation.
### Legacy assertion mode
Legacy assertion mode uses the [`==` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality) in:
* [`assert.deepEqual()`](#assertdeepequalactual-expected-message)
* [`assert.equal()`](#assertequalactual-expected-message)
* [`assert.notDeepEqual()`](#assertnotdeepequalactual-expected-message)
* [`assert.notEqual()`](#assertnotequalactual-expected-message)
To use legacy assertion mode:
MJS modules
```
import assert from 'node:assert';
```
CJS modules
```
const assert = require('node:assert');
```
Legacy assertion mode may have surprising results, especially when using [`assert.deepEqual()`](#assertdeepequalactual-expected-message):
```
// WARNING: This does not throw an AssertionError in legacy assertion mode!
assert.deepEqual(/a/gi, new Date());
```
### Class: assert.AssertionError[[src]](https://github.com/nodejs/node/blob/6ac3a22f89ae43402d41166baf44266e60595fcb/lib/assert.js#L177)
* Extends: [<errors.Error>](errors#class-error)
Indicates the failure of an assertion. All errors thrown by the `node:assert` module will be instances of the `AssertionError` class.
####
`new assert.AssertionError(options)`
Added in: v0.1.21 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If provided, the error message is set to this value.
+ `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The `actual` property on the error instance.
+ `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The `expected` property on the error instance.
+ `operator` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The `operator` property on the error instance.
+ `stackStartFn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) If provided, the generated stack trace omits frames before this function.
A subclass of `Error` that indicates the failure of an assertion.
All instances contain the built-in `Error` properties (`message` and `name`) and:
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Set to the `actual` argument for methods such as [`assert.strictEqual()`](#assertstrictequalactual-expected-message).
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Set to the `expected` value for methods such as [`assert.strictEqual()`](#assertstrictequalactual-expected-message).
* `generatedMessage` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Indicates if the message was auto-generated (`true`) or not.
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Value is always `ERR_ASSERTION` to show that the error is an assertion error.
* `operator` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Set to the passed in operator value.
MJS modules
```
import assert from 'node:assert';
// Generate an AssertionError to compare the error message later:
const { message } = new assert.AssertionError({
actual: 1,
expected: 2,
operator: 'strictEqual'
});
// Verify error output:
try {
assert.strictEqual(1, 2);
} catch (err) {
assert(err instanceof assert.AssertionError);
assert.strictEqual(err.message, message);
assert.strictEqual(err.name, 'AssertionError');
assert.strictEqual(err.actual, 1);
assert.strictEqual(err.expected, 2);
assert.strictEqual(err.code, 'ERR_ASSERTION');
assert.strictEqual(err.operator, 'strictEqual');
assert.strictEqual(err.generatedMessage, true);
}
```
CJS modules
```
const assert = require('node:assert');
// Generate an AssertionError to compare the error message later:
const { message } = new assert.AssertionError({
actual: 1,
expected: 2,
operator: 'strictEqual'
});
// Verify error output:
try {
assert.strictEqual(1, 2);
} catch (err) {
assert(err instanceof assert.AssertionError);
assert.strictEqual(err.message, message);
assert.strictEqual(err.name, 'AssertionError');
assert.strictEqual(err.actual, 1);
assert.strictEqual(err.expected, 2);
assert.strictEqual(err.code, 'ERR_ASSERTION');
assert.strictEqual(err.operator, 'strictEqual');
assert.strictEqual(err.generatedMessage, true);
}
```
### Class: `assert.CallTracker`
Added in: v14.2.0, v12.19.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
This feature is currently experimental and behavior might still change.
####
`new assert.CallTracker()`
Added in: v14.2.0, v12.19.0 Creates a new [`CallTracker`](#class-assertcalltracker) object which can be used to track if functions were called a specific number of times. The `tracker.verify()` must be called for the verification to take place. The usual pattern would be to call it in a [`process.on('exit')`](process#event-exit) handler.
MJS modules
```
import assert from 'node:assert';
import process from 'node:process';
const tracker = new assert.CallTracker();
function func() {}
// callsfunc() must be called exactly 1 time before tracker.verify().
const callsfunc = tracker.calls(func, 1);
callsfunc();
// Calls tracker.verify() and verifies if all tracker.calls() functions have
// been called exact times.
process.on('exit', () => {
tracker.verify();
});
```
CJS modules
```
const assert = require('node:assert');
const tracker = new assert.CallTracker();
function func() {}
// callsfunc() must be called exactly 1 time before tracker.verify().
const callsfunc = tracker.calls(func, 1);
callsfunc();
// Calls tracker.verify() and verifies if all tracker.calls() functions have
// been called exact times.
process.on('exit', () => {
tracker.verify();
});
```
####
`tracker.calls([fn][, exact])`
Added in: v14.2.0, v12.19.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) **Default:** A no-op function.
* `exact` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `1`.
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) that wraps `fn`.
The wrapper function is expected to be called exactly `exact` times. If the function has not been called exactly `exact` times when [`tracker.verify()`](#trackerverify) is called, then [`tracker.verify()`](#trackerverify) will throw an error.
MJS modules
```
import assert from 'node:assert';
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func);
```
CJS modules
```
const assert = require('node:assert');
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func);
```
####
`tracker.getCalls(fn)`
Added in: v18.8.0, v16.18.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function).
* Returns: [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) with all the calls to a tracked function.
* Object [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `thisArg` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `arguments` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) the arguments passed to the tracked function
MJS modules
```
import assert from 'node:assert';
const tracker = new assert.CallTracker();
function func() {}
const callsfunc = tracker.calls(func);
callsfunc(1, 2, 3);
assert.deepStrictEqual(tracker.getCalls(callsfunc),
[{ thisArg: this, arguments: [1, 2, 3 ] }]);
```
CJS modules
```
const assert = require('node:assert');
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
const callsfunc = tracker.calls(func);
callsfunc(1, 2, 3);
assert.deepStrictEqual(tracker.getCalls(callsfunc),
[{ thisArg: this, arguments: [1, 2, 3 ] }]);
```
####
`tracker.report()`
Added in: v14.2.0, v12.19.0 * Returns: [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) of objects containing information about the wrapper functions returned by [`tracker.calls()`](#trackercallsfn-exact).
* Object [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `actual` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The actual number of times the function was called.
+ `expected` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of times the function was expected to be called.
+ `operator` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the function that is wrapped.
+ `stack` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A stack trace of the function.
The arrays contains information about the expected and actual number of calls of the functions that have not been called the expected number of times.
MJS modules
```
import assert from 'node:assert';
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func, 2);
// Returns an array containing information on callsfunc()
tracker.report();
// [
// {
// message: 'Expected the func function to be executed 2 time(s) but was
// executed 0 time(s).',
// actual: 0,
// expected: 2,
// operator: 'func',
// stack: stack trace
// }
// ]
```
CJS modules
```
const assert = require('node:assert');
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func, 2);
// Returns an array containing information on callsfunc()
tracker.report();
// [
// {
// message: 'Expected the func function to be executed 2 time(s) but was
// executed 0 time(s).',
// actual: 0,
// expected: 2,
// operator: 'func',
// stack: stack trace
// }
// ]
```
####
`tracker.reset([fn])`
Added in: v18.8.0, v16.18.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) a tracked function to reset.
reset calls of the call tracker. if a tracked function is passed as an argument, the calls will be reset for it. if no arguments are passed, all tracked functions will be reset
MJS modules
```
import assert from 'node:assert';
const tracker = new assert.CallTracker();
function func() {}
const callsfunc = tracker.calls(func);
callsfunc();
// Tracker was called once
tracker.getCalls(callsfunc).length === 1;
tracker.reset(callsfunc);
tracker.getCalls(callsfunc).length === 0;
```
CJS modules
```
const assert = require('node:assert');
function func() {}
const callsfunc = tracker.calls(func);
callsfunc();
// Tracker was called once
tracker.getCalls(callsfunc).length === 1;
tracker.reset(callsfunc);
tracker.getCalls(callsfunc).length === 0;
```
####
`tracker.verify()`
Added in: v14.2.0, v12.19.0 Iterates through the list of functions passed to [`tracker.calls()`](#trackercallsfn-exact) and will throw an error for functions that have not been called the expected number of times.
MJS modules
```
import assert from 'node:assert';
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func, 2);
callsfunc();
// Will throw an error since callsfunc() was only called once.
tracker.verify();
```
CJS modules
```
const assert = require('node:assert');
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func, 2);
callsfunc();
// Will throw an error since callsfunc() was only called once.
tracker.verify();
```
###
`assert(value[, message])`
Added in: v0.5.9 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The input that is checked for being truthy.
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
An alias of [`assert.ok()`](#assertokvalue-message).
###
`assert.deepEqual(actual, expected[, message])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Regular expressions lastIndex property is now compared as well. |
| v16.0.0, v14.18.0 | In Legacy assertion mode, changed status from Deprecated to Legacy. |
| v14.0.0 | NaN is now treated as being identical if both sides are NaN. |
| v12.0.0 | The type tags are now properly compared and there are a couple minor comparison adjustments to make the check less surprising. |
| v9.0.0 | The `Error` names and messages are now properly compared. |
| v8.0.0 | The `Set` and `Map` content is also compared. |
| v6.4.0, v4.7.1 | Typed array slices are handled correctly now. |
| v6.1.0, v4.5.0 | Objects with circular references can be used as inputs now. |
| v5.10.1, v4.4.3 | Handle non-`Uint8Array` typed arrays correctly. |
| v0.1.21 | Added in: v0.1.21 |
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
**Strict assertion mode**
An alias of [`assert.deepStrictEqual()`](#assertdeepstrictequalactual-expected-message).
**Legacy assertion mode**
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use [`assert.deepStrictEqual()`](#assertdeepstrictequalactual-expected-message) instead.
Tests for deep equality between the `actual` and `expected` parameters. Consider using [`assert.deepStrictEqual()`](#assertdeepstrictequalactual-expected-message) instead. [`assert.deepEqual()`](#assertdeepequalactual-expected-message) can have surprising results.
*Deep equality* means that the enumerable "own" properties of child objects are also recursively evaluated by the following rules.
#### Comparison details
* Primitive values are compared with the [`==` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality), with the exception of `NaN`. It is treated as being identical in case both sides are `NaN`.
* [Type tags](https://tc39.github.io/ecma262/#sec-object.prototype.tostring) of objects should be the same.
* Only [enumerable "own" properties](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties) are considered.
* [`Error`](errors#class-error) names and messages are always compared, even if these are not enumerable properties.
* [Object wrappers](https://developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript) are compared both as objects and unwrapped values.
* `Object` properties are compared unordered.
* [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) keys and [`Set`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set) items are compared unordered.
* Recursion stops when both sides differ or both sides encounter a circular reference.
* Implementation does not test the [`[[Prototype]]`](https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots) of objects.
* [`Symbol`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol) properties are not compared.
* [`WeakMap`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap) and [`WeakSet`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet) comparison does not rely on their values.
* [`RegExp`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions) lastIndex, flags, and source are always compared, even if these are not enumerable properties.
The following example does not throw an [`AssertionError`](#class-assertassertionerror) because the primitives are compared using the [`==` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality).
MJS modules
```
import assert from 'node:assert';
// WARNING: This does not throw an AssertionError!
assert.deepEqual('+00000000', false);
```
CJS modules
```
const assert = require('node:assert');
// WARNING: This does not throw an AssertionError!
assert.deepEqual('+00000000', false);
```
"Deep" equality means that the enumerable "own" properties of child objects are evaluated also:
MJS modules
```
import assert from 'node:assert';
const obj1 = {
a: {
b: 1
}
};
const obj2 = {
a: {
b: 2
}
};
const obj3 = {
a: {
b: 1
}
};
const obj4 = Object.create(obj1);
assert.deepEqual(obj1, obj1);
// OK
// Values of b are different:
assert.deepEqual(obj1, obj2);
// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }
assert.deepEqual(obj1, obj3);
// OK
// Prototypes are ignored:
assert.deepEqual(obj1, obj4);
// AssertionError: { a: { b: 1 } } deepEqual {}
```
CJS modules
```
const assert = require('node:assert');
const obj1 = {
a: {
b: 1
}
};
const obj2 = {
a: {
b: 2
}
};
const obj3 = {
a: {
b: 1
}
};
const obj4 = Object.create(obj1);
assert.deepEqual(obj1, obj1);
// OK
// Values of b are different:
assert.deepEqual(obj1, obj2);
// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }
assert.deepEqual(obj1, obj3);
// OK
// Prototypes are ignored:
assert.deepEqual(obj1, obj4);
// AssertionError: { a: { b: 1 } } deepEqual {}
```
If the values are not equal, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the [`AssertionError`](#class-assertassertionerror).
###
`assert.deepStrictEqual(actual, expected[, message])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Regular expressions lastIndex property is now compared as well. |
| v9.0.0 | Enumerable symbol properties are now compared. |
| v9.0.0 | The `NaN` is now compared using the [SameValueZero](https://tc39.github.io/ecma262/#sec-samevaluezero) comparison. |
| v8.5.0 | The `Error` names and messages are now properly compared. |
| v8.0.0 | The `Set` and `Map` content is also compared. |
| v6.1.0 | Objects with circular references can be used as inputs now. |
| v6.4.0, v4.7.1 | Typed array slices are handled correctly now. |
| v5.10.1, v4.4.3 | Handle non-`Uint8Array` typed arrays correctly. |
| v1.2.0 | Added in: v1.2.0 |
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Tests for deep equality between the `actual` and `expected` parameters. "Deep" equality means that the enumerable "own" properties of child objects are recursively evaluated also by the following rules.
#### Comparison details
* Primitive values are compared using [`Object.is()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is).
* [Type tags](https://tc39.github.io/ecma262/#sec-object.prototype.tostring) of objects should be the same.
* [`[[Prototype]]`](https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots) of objects are compared using the [`===` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Strict_equality).
* Only [enumerable "own" properties](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties) are considered.
* [`Error`](errors#class-error) names and messages are always compared, even if these are not enumerable properties.
* Enumerable own [`Symbol`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol) properties are compared as well.
* [Object wrappers](https://developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript) are compared both as objects and unwrapped values.
* `Object` properties are compared unordered.
* [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) keys and [`Set`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set) items are compared unordered.
* Recursion stops when both sides differ or both sides encounter a circular reference.
* [`WeakMap`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap) and [`WeakSet`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet) comparison does not rely on their values. See below for further details.
* [`RegExp`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions) lastIndex, flags, and source are always compared, even if these are not enumerable properties.
MJS modules
```
import assert from 'node:assert/strict';
// This fails because 1 !== '1'.
assert.deepStrictEqual({ a: 1 }, { a: '1' });
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// {
// + a: 1
// - a: '1'
// }
// The following objects don't have own properties
const date = new Date();
const object = {};
const fakeDate = {};
Object.setPrototypeOf(fakeDate, Date.prototype);
// Different [[Prototype]]:
assert.deepStrictEqual(object, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + {}
// - Date {}
// Different type tags:
assert.deepStrictEqual(date, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 2018-04-26T00:49:08.604Z
// - Date {}
assert.deepStrictEqual(NaN, NaN);
// OK because Object.is(NaN, NaN) is true.
// Different unwrapped numbers:
assert.deepStrictEqual(new Number(1), new Number(2));
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + [Number: 1]
// - [Number: 2]
assert.deepStrictEqual(new String('foo'), Object('foo'));
// OK because the object and the string are identical when unwrapped.
assert.deepStrictEqual(-0, -0);
// OK
// Different zeros:
assert.deepStrictEqual(0, -0);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 0
// - -0
const symbol1 = Symbol();
const symbol2 = Symbol();
assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 });
// OK, because it is the same symbol on both objects.
assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });
// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:
//
// {
// [Symbol()]: 1
// }
const weakMap1 = new WeakMap();
const weakMap2 = new WeakMap([[{}, {}]]);
const weakMap3 = new WeakMap();
weakMap3.unequal = true;
assert.deepStrictEqual(weakMap1, weakMap2);
// OK, because it is impossible to compare the entries
// Fails because weakMap3 has a property that weakMap1 does not contain:
assert.deepStrictEqual(weakMap1, weakMap3);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// WeakMap {
// + [items unknown]
// - [items unknown],
// - unequal: true
// }
```
CJS modules
```
const assert = require('node:assert/strict');
// This fails because 1 !== '1'.
assert.deepStrictEqual({ a: 1 }, { a: '1' });
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// {
// + a: 1
// - a: '1'
// }
// The following objects don't have own properties
const date = new Date();
const object = {};
const fakeDate = {};
Object.setPrototypeOf(fakeDate, Date.prototype);
// Different [[Prototype]]:
assert.deepStrictEqual(object, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + {}
// - Date {}
// Different type tags:
assert.deepStrictEqual(date, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 2018-04-26T00:49:08.604Z
// - Date {}
assert.deepStrictEqual(NaN, NaN);
// OK because Object.is(NaN, NaN) is true.
// Different unwrapped numbers:
assert.deepStrictEqual(new Number(1), new Number(2));
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + [Number: 1]
// - [Number: 2]
assert.deepStrictEqual(new String('foo'), Object('foo'));
// OK because the object and the string are identical when unwrapped.
assert.deepStrictEqual(-0, -0);
// OK
// Different zeros:
assert.deepStrictEqual(0, -0);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 0
// - -0
const symbol1 = Symbol();
const symbol2 = Symbol();
assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 });
// OK, because it is the same symbol on both objects.
assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });
// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:
//
// {
// [Symbol()]: 1
// }
const weakMap1 = new WeakMap();
const weakMap2 = new WeakMap([[{}, {}]]);
const weakMap3 = new WeakMap();
weakMap3.unequal = true;
assert.deepStrictEqual(weakMap1, weakMap2);
// OK, because it is impossible to compare the entries
// Fails because weakMap3 has a property that weakMap1 does not contain:
assert.deepStrictEqual(weakMap1, weakMap3);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// WeakMap {
// + [items unknown]
// - [items unknown],
// - unequal: true
// }
```
If the values are not equal, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the `AssertionError`.
###
`assert.doesNotMatch(string, regexp[, message])`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | This API is no longer experimental. |
| v13.6.0, v12.16.0 | Added in: v13.6.0, v12.16.0 |
* `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `regexp` [<RegExp>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Expects the `string` input not to match the regular expression.
MJS modules
```
import assert from 'node:assert/strict';
assert.doesNotMatch('I will fail', /fail/);
// AssertionError [ERR_ASSERTION]: The input was expected to not match the ...
assert.doesNotMatch(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.
assert.doesNotMatch('I will pass', /different/);
// OK
```
CJS modules
```
const assert = require('node:assert/strict');
assert.doesNotMatch('I will fail', /fail/);
// AssertionError [ERR_ASSERTION]: The input was expected to not match the ...
assert.doesNotMatch(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.
assert.doesNotMatch('I will pass', /different/);
// OK
```
If the values do match, or if the `string` argument is of another type than `string`, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the [`AssertionError`](#class-assertassertionerror).
###
`assert.doesNotReject(asyncFn[, error][, message])`
Added in: v10.0.0 * `asyncFn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
* `error` [<RegExp>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Awaits the `asyncFn` promise or, if `asyncFn` is a function, immediately calls the function and awaits the returned promise to complete. It will then check that the promise is not rejected.
If `asyncFn` is a function and it throws an error synchronously, `assert.doesNotReject()` will return a rejected `Promise` with that error. If the function does not return a promise, `assert.doesNotReject()` will return a rejected `Promise` with an [`ERR_INVALID_RETURN_VALUE`](errors#err_invalid_return_value) error. In both cases the error handler is skipped.
Using `assert.doesNotReject()` is actually not useful because there is little benefit in catching a rejection and then rejecting it again. Instead, consider adding a comment next to the specific code path that should not reject and keep error messages as expressive as possible.
If specified, `error` can be a [`Class`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes), [`RegExp`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions), or a validation function. See [`assert.throws()`](#assertthrowsfn-error-message) for more details.
Besides the async nature to await the completion behaves identically to [`assert.doesNotThrow()`](#assertdoesnotthrowfn-error-message).
MJS modules
```
import assert from 'node:assert/strict';
await assert.doesNotReject(
async () => {
throw new TypeError('Wrong value');
},
SyntaxError
);
```
CJS modules
```
const assert = require('node:assert/strict');
(async () => {
await assert.doesNotReject(
async () => {
throw new TypeError('Wrong value');
},
SyntaxError
);
})();
```
MJS modules
```
import assert from 'node:assert/strict';
assert.doesNotReject(Promise.reject(new TypeError('Wrong value')))
.then(() => {
// ...
});
```
CJS modules
```
const assert = require('node:assert/strict');
assert.doesNotReject(Promise.reject(new TypeError('Wrong value')))
.then(() => {
// ...
});
```
###
`assert.doesNotThrow(fn[, error][, message])`
History
| Version | Changes |
| --- | --- |
| v5.11.0, v4.4.5 | The `message` parameter is respected now. |
| v4.2.0 | The `error` parameter can now be an arrow function. |
| v0.1.21 | Added in: v0.1.21 |
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `error` [<RegExp>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Asserts that the function `fn` does not throw an error.
Using `assert.doesNotThrow()` is actually not useful because there is no benefit in catching an error and then rethrowing it. Instead, consider adding a comment next to the specific code path that should not throw and keep error messages as expressive as possible.
When `assert.doesNotThrow()` is called, it will immediately call the `fn` function.
If an error is thrown and it is the same type as that specified by the `error` parameter, then an [`AssertionError`](#class-assertassertionerror) is thrown. If the error is of a different type, or if the `error` parameter is undefined, the error is propagated back to the caller.
If specified, `error` can be a [`Class`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes), [`RegExp`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions), or a validation function. See [`assert.throws()`](#assertthrowsfn-error-message) for more details.
The following, for instance, will throw the [`TypeError`](errors#class-typeerror) because there is no matching error type in the assertion:
MJS modules
```
import assert from 'node:assert/strict';
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
SyntaxError
);
```
CJS modules
```
const assert = require('node:assert/strict');
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
SyntaxError
);
```
However, the following will result in an [`AssertionError`](#class-assertassertionerror) with the message 'Got unwanted exception...':
MJS modules
```
import assert from 'node:assert/strict';
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError
);
```
CJS modules
```
const assert = require('node:assert/strict');
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError
);
```
If an [`AssertionError`](#class-assertassertionerror) is thrown and a value is provided for the `message` parameter, the value of `message` will be appended to the [`AssertionError`](#class-assertassertionerror) message:
MJS modules
```
import assert from 'node:assert/strict';
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
/Wrong value/,
'Whoops'
);
// Throws: AssertionError: Got unwanted exception: Whoops
```
CJS modules
```
const assert = require('node:assert/strict');
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
/Wrong value/,
'Whoops'
);
// Throws: AssertionError: Got unwanted exception: Whoops
```
###
`assert.equal(actual, expected[, message])`
History
| Version | Changes |
| --- | --- |
| v16.0.0, v14.18.0 | In Legacy assertion mode, changed status from Deprecated to Legacy. |
| v14.0.0 | NaN is now treated as being identical if both sides are NaN. |
| v0.1.21 | Added in: v0.1.21 |
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
**Strict assertion mode**
An alias of [`assert.strictEqual()`](#assertstrictequalactual-expected-message).
**Legacy assertion mode**
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use [`assert.strictEqual()`](#assertstrictequalactual-expected-message) instead.
Tests shallow, coercive equality between the `actual` and `expected` parameters using the [`==` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality). `NaN` is specially handled and treated as being identical if both sides are `NaN`.
MJS modules
```
import assert from 'node:assert';
assert.equal(1, 1);
// OK, 1 == 1
assert.equal(1, '1');
// OK, 1 == '1'
assert.equal(NaN, NaN);
// OK
assert.equal(1, 2);
// AssertionError: 1 == 2
assert.equal({ a: { b: 1 } }, { a: { b: 1 } });
// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }
```
CJS modules
```
const assert = require('node:assert');
assert.equal(1, 1);
// OK, 1 == 1
assert.equal(1, '1');
// OK, 1 == '1'
assert.equal(NaN, NaN);
// OK
assert.equal(1, 2);
// AssertionError: 1 == 2
assert.equal({ a: { b: 1 } }, { a: { b: 1 } });
// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }
```
If the values are not equal, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the `AssertionError`.
###
`assert.fail([message])`
Added in: v0.1.21 * `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) **Default:** `'Failed'`
Throws an [`AssertionError`](#class-assertassertionerror) with the provided error message or a default error message. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the [`AssertionError`](#class-assertassertionerror).
MJS modules
```
import assert from 'node:assert/strict';
assert.fail();
// AssertionError [ERR_ASSERTION]: Failed
assert.fail('boom');
// AssertionError [ERR_ASSERTION]: boom
assert.fail(new TypeError('need array'));
// TypeError: need array
```
CJS modules
```
const assert = require('node:assert/strict');
assert.fail();
// AssertionError [ERR_ASSERTION]: Failed
assert.fail('boom');
// AssertionError [ERR_ASSERTION]: boom
assert.fail(new TypeError('need array'));
// TypeError: need array
```
Using `assert.fail()` with more than two arguments is possible but deprecated. See below for further details.
###
`assert.fail(actual, expected[, message[, operator[, stackStartFn]]])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Calling `assert.fail()` with more than one argument is deprecated and emits a warning. |
| v0.1.21 | Added in: v0.1.21 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `assert.fail([message])` or other assert functions instead.
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
* `operator` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'!='`
* `stackStartFn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) **Default:** `assert.fail`
If `message` is falsy, the error message is set as the values of `actual` and `expected` separated by the provided `operator`. If just the two `actual` and `expected` arguments are provided, `operator` will default to `'!='`. If `message` is provided as third argument it will be used as the error message and the other arguments will be stored as properties on the thrown object. If `stackStartFn` is provided, all stack frames above that function will be removed from stacktrace (see [`Error.captureStackTrace`](errors#errorcapturestacktracetargetobject-constructoropt)). If no arguments are given, the default message `Failed` will be used.
MJS modules
```
import assert from 'node:assert/strict';
assert.fail('a', 'b');
// AssertionError [ERR_ASSERTION]: 'a' != 'b'
assert.fail(1, 2, undefined, '>');
// AssertionError [ERR_ASSERTION]: 1 > 2
assert.fail(1, 2, 'fail');
// AssertionError [ERR_ASSERTION]: fail
assert.fail(1, 2, 'whoops', '>');
// AssertionError [ERR_ASSERTION]: whoops
assert.fail(1, 2, new TypeError('need array'));
// TypeError: need array
```
CJS modules
```
const assert = require('node:assert/strict');
assert.fail('a', 'b');
// AssertionError [ERR_ASSERTION]: 'a' != 'b'
assert.fail(1, 2, undefined, '>');
// AssertionError [ERR_ASSERTION]: 1 > 2
assert.fail(1, 2, 'fail');
// AssertionError [ERR_ASSERTION]: fail
assert.fail(1, 2, 'whoops', '>');
// AssertionError [ERR_ASSERTION]: whoops
assert.fail(1, 2, new TypeError('need array'));
// TypeError: need array
```
In the last three cases `actual`, `expected`, and `operator` have no influence on the error message.
Example use of `stackStartFn` for truncating the exception's stacktrace:
MJS modules
```
import assert from 'node:assert/strict';
function suppressFrame() {
assert.fail('a', 'b', undefined, '!==', suppressFrame);
}
suppressFrame();
// AssertionError [ERR_ASSERTION]: 'a' !== 'b'
// at repl:1:1
// at ContextifyScript.Script.runInThisContext (vm.js:44:33)
// ...
```
CJS modules
```
const assert = require('node:assert/strict');
function suppressFrame() {
assert.fail('a', 'b', undefined, '!==', suppressFrame);
}
suppressFrame();
// AssertionError [ERR_ASSERTION]: 'a' !== 'b'
// at repl:1:1
// at ContextifyScript.Script.runInThisContext (vm.js:44:33)
// ...
```
###
`assert.ifError(value)`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Instead of throwing the original error it is now wrapped into an [`AssertionError`][] that contains the full stack trace. |
| v10.0.0 | Value may now only be `undefined` or `null`. Before all falsy values were handled the same as `null` and did not throw. |
| v0.1.97 | Added in: v0.1.97 |
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Throws `value` if `value` is not `undefined` or `null`. This is useful when testing the `error` argument in callbacks. The stack trace contains all frames from the error passed to `ifError()` including the potential new frames for `ifError()` itself.
MJS modules
```
import assert from 'node:assert/strict';
assert.ifError(null);
// OK
assert.ifError(0);
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0
assert.ifError('error');
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'
assert.ifError(new Error());
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error
// Create some random error frames.
let err;
(function errorFrame() {
err = new Error('test error');
})();
(function ifErrorFrame() {
assert.ifError(err);
})();
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error
// at ifErrorFrame
// at errorFrame
```
CJS modules
```
const assert = require('node:assert/strict');
assert.ifError(null);
// OK
assert.ifError(0);
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0
assert.ifError('error');
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'
assert.ifError(new Error());
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error
// Create some random error frames.
let err;
(function errorFrame() {
err = new Error('test error');
})();
(function ifErrorFrame() {
assert.ifError(err);
})();
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error
// at ifErrorFrame
// at errorFrame
```
###
`assert.match(string, regexp[, message])`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | This API is no longer experimental. |
| v13.6.0, v12.16.0 | Added in: v13.6.0, v12.16.0 |
* `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `regexp` [<RegExp>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Expects the `string` input to match the regular expression.
MJS modules
```
import assert from 'node:assert/strict';
assert.match('I will fail', /pass/);
// AssertionError [ERR_ASSERTION]: The input did not match the regular ...
assert.match(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.
assert.match('I will pass', /pass/);
// OK
```
CJS modules
```
const assert = require('node:assert/strict');
assert.match('I will fail', /pass/);
// AssertionError [ERR_ASSERTION]: The input did not match the regular ...
assert.match(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.
assert.match('I will pass', /pass/);
// OK
```
If the values do not match, or if the `string` argument is of another type than `string`, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the [`AssertionError`](#class-assertassertionerror).
###
`assert.notDeepEqual(actual, expected[, message])`
History
| Version | Changes |
| --- | --- |
| v16.0.0, v14.18.0 | In Legacy assertion mode, changed status from Deprecated to Legacy. |
| v14.0.0 | NaN is now treated as being identical if both sides are NaN. |
| v9.0.0 | The `Error` names and messages are now properly compared. |
| v8.0.0 | The `Set` and `Map` content is also compared. |
| v6.4.0, v4.7.1 | Typed array slices are handled correctly now. |
| v6.1.0, v4.5.0 | Objects with circular references can be used as inputs now. |
| v5.10.1, v4.4.3 | Handle non-`Uint8Array` typed arrays correctly. |
| v0.1.21 | Added in: v0.1.21 |
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
**Strict assertion mode**
An alias of [`assert.notDeepStrictEqual()`](#assertnotdeepstrictequalactual-expected-message).
**Legacy assertion mode**
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use [`assert.notDeepStrictEqual()`](#assertnotdeepstrictequalactual-expected-message) instead.
Tests for any deep inequality. Opposite of [`assert.deepEqual()`](#assertdeepequalactual-expected-message).
MJS modules
```
import assert from 'node:assert';
const obj1 = {
a: {
b: 1
}
};
const obj2 = {
a: {
b: 2
}
};
const obj3 = {
a: {
b: 1
}
};
const obj4 = Object.create(obj1);
assert.notDeepEqual(obj1, obj1);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj2);
// OK
assert.notDeepEqual(obj1, obj3);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj4);
// OK
```
CJS modules
```
const assert = require('node:assert');
const obj1 = {
a: {
b: 1
}
};
const obj2 = {
a: {
b: 2
}
};
const obj3 = {
a: {
b: 1
}
};
const obj4 = Object.create(obj1);
assert.notDeepEqual(obj1, obj1);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj2);
// OK
assert.notDeepEqual(obj1, obj3);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj4);
// OK
```
If the values are deeply equal, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the `AssertionError`.
###
`assert.notDeepStrictEqual(actual, expected[, message])`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | The `-0` and `+0` are not considered equal anymore. |
| v9.0.0 | The `NaN` is now compared using the [SameValueZero](https://tc39.github.io/ecma262/#sec-samevaluezero) comparison. |
| v9.0.0 | The `Error` names and messages are now properly compared. |
| v8.0.0 | The `Set` and `Map` content is also compared. |
| v6.1.0 | Objects with circular references can be used as inputs now. |
| v6.4.0, v4.7.1 | Typed array slices are handled correctly now. |
| v5.10.1, v4.4.3 | Handle non-`Uint8Array` typed arrays correctly. |
| v1.2.0 | Added in: v1.2.0 |
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Tests for deep strict inequality. Opposite of [`assert.deepStrictEqual()`](#assertdeepstrictequalactual-expected-message).
MJS modules
```
import assert from 'node:assert/strict';
assert.notDeepStrictEqual({ a: 1 }, { a: '1' });
// OK
```
CJS modules
```
const assert = require('node:assert/strict');
assert.notDeepStrictEqual({ a: 1 }, { a: '1' });
// OK
```
If the values are deeply and strictly equal, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the [`AssertionError`](#class-assertassertionerror).
###
`assert.notEqual(actual, expected[, message])`
History
| Version | Changes |
| --- | --- |
| v16.0.0, v14.18.0 | In Legacy assertion mode, changed status from Deprecated to Legacy. |
| v14.0.0 | NaN is now treated as being identical if both sides are NaN. |
| v0.1.21 | Added in: v0.1.21 |
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
**Strict assertion mode**
An alias of [`assert.notStrictEqual()`](#assertnotstrictequalactual-expected-message).
**Legacy assertion mode**
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use [`assert.notStrictEqual()`](#assertnotstrictequalactual-expected-message) instead.
Tests shallow, coercive inequality with the [`!=` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Inequality). `NaN` is specially handled and treated as being identical if both sides are `NaN`.
MJS modules
```
import assert from 'node:assert';
assert.notEqual(1, 2);
// OK
assert.notEqual(1, 1);
// AssertionError: 1 != 1
assert.notEqual(1, '1');
// AssertionError: 1 != '1'
```
CJS modules
```
const assert = require('node:assert');
assert.notEqual(1, 2);
// OK
assert.notEqual(1, 1);
// AssertionError: 1 != 1
assert.notEqual(1, '1');
// AssertionError: 1 != '1'
```
If the values are equal, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the `AssertionError`.
###
`assert.notStrictEqual(actual, expected[, message])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Used comparison changed from Strict Equality to `Object.is()`. |
| v0.1.21 | Added in: v0.1.21 |
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Tests strict inequality between the `actual` and `expected` parameters as determined by [`Object.is()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is).
MJS modules
```
import assert from 'node:assert/strict';
assert.notStrictEqual(1, 2);
// OK
assert.notStrictEqual(1, 1);
// AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to:
//
// 1
assert.notStrictEqual(1, '1');
// OK
```
CJS modules
```
const assert = require('node:assert/strict');
assert.notStrictEqual(1, 2);
// OK
assert.notStrictEqual(1, 1);
// AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to:
//
// 1
assert.notStrictEqual(1, '1');
// OK
```
If the values are strictly equal, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the `AssertionError`.
###
`assert.ok(value[, message])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | The `assert.ok()` (no arguments) will now use a predefined error message. |
| v0.1.21 | Added in: v0.1.21 |
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Tests if `value` is truthy. It is equivalent to `assert.equal(!!value, true, message)`.
If `value` is not truthy, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is `undefined`, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the `AssertionError`. If no arguments are passed in at all `message` will be set to the string: `'No value argument passed to `assert.ok()`'`.
Be aware that in the `repl` the error message will be different to the one thrown in a file! See below for further details.
MJS modules
```
import assert from 'node:assert/strict';
assert.ok(true);
// OK
assert.ok(1);
// OK
assert.ok();
// AssertionError: No value argument passed to `assert.ok()`
assert.ok(false, 'it\'s false');
// AssertionError: it's false
// In the repl:
assert.ok(typeof 123 === 'string');
// AssertionError: false == true
// In a file (e.g. test.js):
assert.ok(typeof 123 === 'string');
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(typeof 123 === 'string')
assert.ok(false);
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(false)
assert.ok(0);
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(0)
```
CJS modules
```
const assert = require('node:assert/strict');
assert.ok(true);
// OK
assert.ok(1);
// OK
assert.ok();
// AssertionError: No value argument passed to `assert.ok()`
assert.ok(false, 'it\'s false');
// AssertionError: it's false
// In the repl:
assert.ok(typeof 123 === 'string');
// AssertionError: false == true
// In a file (e.g. test.js):
assert.ok(typeof 123 === 'string');
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(typeof 123 === 'string')
assert.ok(false);
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(false)
assert.ok(0);
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(0)
```
MJS modules
```
import assert from 'node:assert/strict';
// Using `assert()` works the same:
assert(0);
// AssertionError: The expression evaluated to a falsy value:
//
// assert(0)
```
CJS modules
```
const assert = require('node:assert');
// Using `assert()` works the same:
assert(0);
// AssertionError: The expression evaluated to a falsy value:
//
// assert(0)
```
###
`assert.rejects(asyncFn[, error][, message])`
Added in: v10.0.0 * `asyncFn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
* `error` [<RegExp>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Awaits the `asyncFn` promise or, if `asyncFn` is a function, immediately calls the function and awaits the returned promise to complete. It will then check that the promise is rejected.
If `asyncFn` is a function and it throws an error synchronously, `assert.rejects()` will return a rejected `Promise` with that error. If the function does not return a promise, `assert.rejects()` will return a rejected `Promise` with an [`ERR_INVALID_RETURN_VALUE`](errors#err_invalid_return_value) error. In both cases the error handler is skipped.
Besides the async nature to await the completion behaves identically to [`assert.throws()`](#assertthrowsfn-error-message).
If specified, `error` can be a [`Class`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes), [`RegExp`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions), a validation function, an object where each property will be tested for, or an instance of error where each property will be tested for including the non-enumerable `message` and `name` properties.
If specified, `message` will be the message provided by the [`AssertionError`](#class-assertassertionerror) if the `asyncFn` fails to reject.
MJS modules
```
import assert from 'node:assert/strict';
await assert.rejects(
async () => {
throw new TypeError('Wrong value');
},
{
name: 'TypeError',
message: 'Wrong value'
}
);
```
CJS modules
```
const assert = require('node:assert/strict');
(async () => {
await assert.rejects(
async () => {
throw new TypeError('Wrong value');
},
{
name: 'TypeError',
message: 'Wrong value'
}
);
})();
```
MJS modules
```
import assert from 'node:assert/strict';
await assert.rejects(
async () => {
throw new TypeError('Wrong value');
},
(err) => {
assert.strictEqual(err.name, 'TypeError');
assert.strictEqual(err.message, 'Wrong value');
return true;
}
);
```
CJS modules
```
const assert = require('node:assert/strict');
(async () => {
await assert.rejects(
async () => {
throw new TypeError('Wrong value');
},
(err) => {
assert.strictEqual(err.name, 'TypeError');
assert.strictEqual(err.message, 'Wrong value');
return true;
}
);
})();
```
MJS modules
```
import assert from 'node:assert/strict';
assert.rejects(
Promise.reject(new Error('Wrong value')),
Error
).then(() => {
// ...
});
```
CJS modules
```
const assert = require('node:assert/strict');
assert.rejects(
Promise.reject(new Error('Wrong value')),
Error
).then(() => {
// ...
});
```
`error` cannot be a string. If a string is provided as the second argument, then `error` is assumed to be omitted and the string will be used for `message` instead. This can lead to easy-to-miss mistakes. Please read the example in [`assert.throws()`](#assertthrowsfn-error-message) carefully if using a string as the second argument gets considered.
###
`assert.snapshot(value, name)`
Added in: v18.8.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the value to snapshot.
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) the name of the snapshot.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Reads the `name` snapshot from a file and compares `value` to the snapshot. `value` is serialized with [`util.inspect()`](util#utilinspectobject-options). If the value is not strictly equal to the snapshot, `assert.snapshot()` returns a rejected `Promise` with an [`AssertionError`](#class-assertassertionerror).
The snapshot filename uses the same basename as the application's main entrypoint with a `.snapshot` extension. If the snapshot file does not exist, it is created. The [`--update-assert-snapshot`](cli#--update-assert-snapshot) command line flag can be used to force the update of an existing snapshot.
MJS modules
```
import assert from 'node:assert/strict';
// Assuming that the application's main entrypoint is app.mjs, this reads the
// 'snapshotName' snapshot from app.snapshot and strictly compares its value
// to `util.inspect('value')`.
await assert.snapshot('value', 'snapshotName');
```
CJS modules
```
const assert = require('node:assert/strict');
(async () => {
// Assuming that the application's main entrypoint is app.js, this reads the
// 'snapshotName' snapshot from app.snapshot and strictly compares its value
// to `util.inspect('value')`.
await assert.snapshot('value', 'snapshotName');
})();
```
###
`assert.strictEqual(actual, expected[, message])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Used comparison changed from Strict Equality to `Object.is()`. |
| v0.1.21 | Added in: v0.1.21 |
* `actual` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `expected` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Tests strict equality between the `actual` and `expected` parameters as determined by [`Object.is()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is).
MJS modules
```
import assert from 'node:assert/strict';
assert.strictEqual(1, 2);
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
//
// 1 !== 2
assert.strictEqual(1, 1);
// OK
assert.strictEqual('Hello foobar', 'Hello World!');
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
// + actual - expected
//
// + 'Hello foobar'
// - 'Hello World!'
// ^
const apples = 1;
const oranges = 2;
assert.strictEqual(apples, oranges, `apples ${apples} !== oranges ${oranges}`);
// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2
assert.strictEqual(1, '1', new TypeError('Inputs are not identical'));
// TypeError: Inputs are not identical
```
CJS modules
```
const assert = require('node:assert/strict');
assert.strictEqual(1, 2);
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
//
// 1 !== 2
assert.strictEqual(1, 1);
// OK
assert.strictEqual('Hello foobar', 'Hello World!');
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
// + actual - expected
//
// + 'Hello foobar'
// - 'Hello World!'
// ^
const apples = 1;
const oranges = 2;
assert.strictEqual(apples, oranges, `apples ${apples} !== oranges ${oranges}`);
// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2
assert.strictEqual(1, '1', new TypeError('Inputs are not identical'));
// TypeError: Inputs are not identical
```
If the values are not strictly equal, an [`AssertionError`](#class-assertassertionerror) is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of an [`Error`](errors#class-error) then it will be thrown instead of the [`AssertionError`](#class-assertassertionerror).
###
`assert.throws(fn[, error][, message])`
History
| Version | Changes |
| --- | --- |
| v10.2.0 | The `error` parameter can be an object containing regular expressions now. |
| v9.9.0 | The `error` parameter can now be an object as well. |
| v4.2.0 | The `error` parameter can now be an arrow function. |
| v0.1.21 | Added in: v0.1.21 |
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `error` [<RegExp>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Expects the function `fn` to throw an error.
If specified, `error` can be a [`Class`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes), [`RegExp`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions), a validation function, a validation object where each property will be tested for strict deep equality, or an instance of error where each property will be tested for strict deep equality including the non-enumerable `message` and `name` properties. When using an object, it is also possible to use a regular expression, when validating against a string property. See below for examples.
If specified, `message` will be appended to the message provided by the `AssertionError` if the `fn` call fails to throw or in case the error validation fails.
Custom validation object/error instance:
MJS modules
```
import assert from 'node:assert/strict';
const err = new TypeError('Wrong value');
err.code = 404;
err.foo = 'bar';
err.info = {
nested: true,
baz: 'text'
};
err.reg = /abc/i;
assert.throws(
() => {
throw err;
},
{
name: 'TypeError',
message: 'Wrong value',
info: {
nested: true,
baz: 'text'
}
// Only properties on the validation object will be tested for.
// Using nested objects requires all properties to be present. Otherwise
// the validation is going to fail.
}
);
// Using regular expressions to validate error properties:
assert.throws(
() => {
throw err;
},
{
// The `name` and `message` properties are strings and using regular
// expressions on those will match against the string. If they fail, an
// error is thrown.
name: /^TypeError$/,
message: /Wrong/,
foo: 'bar',
info: {
nested: true,
// It is not possible to use regular expressions for nested properties!
baz: 'text'
},
// The `reg` property contains a regular expression and only if the
// validation object contains an identical regular expression, it is going
// to pass.
reg: /abc/i
}
);
// Fails due to the different `message` and `name` properties:
assert.throws(
() => {
const otherErr = new Error('Not found');
// Copy all enumerable properties from `err` to `otherErr`.
for (const [key, value] of Object.entries(err)) {
otherErr[key] = value;
}
throw otherErr;
},
// The error's `message` and `name` properties will also be checked when using
// an error as validation object.
err
);
```
CJS modules
```
const assert = require('node:assert/strict');
const err = new TypeError('Wrong value');
err.code = 404;
err.foo = 'bar';
err.info = {
nested: true,
baz: 'text'
};
err.reg = /abc/i;
assert.throws(
() => {
throw err;
},
{
name: 'TypeError',
message: 'Wrong value',
info: {
nested: true,
baz: 'text'
}
// Only properties on the validation object will be tested for.
// Using nested objects requires all properties to be present. Otherwise
// the validation is going to fail.
}
);
// Using regular expressions to validate error properties:
assert.throws(
() => {
throw err;
},
{
// The `name` and `message` properties are strings and using regular
// expressions on those will match against the string. If they fail, an
// error is thrown.
name: /^TypeError$/,
message: /Wrong/,
foo: 'bar',
info: {
nested: true,
// It is not possible to use regular expressions for nested properties!
baz: 'text'
},
// The `reg` property contains a regular expression and only if the
// validation object contains an identical regular expression, it is going
// to pass.
reg: /abc/i
}
);
// Fails due to the different `message` and `name` properties:
assert.throws(
() => {
const otherErr = new Error('Not found');
// Copy all enumerable properties from `err` to `otherErr`.
for (const [key, value] of Object.entries(err)) {
otherErr[key] = value;
}
throw otherErr;
},
// The error's `message` and `name` properties will also be checked when using
// an error as validation object.
err
);
```
Validate instanceof using constructor:
MJS modules
```
import assert from 'node:assert/strict';
assert.throws(
() => {
throw new Error('Wrong value');
},
Error
);
```
CJS modules
```
const assert = require('node:assert/strict');
assert.throws(
() => {
throw new Error('Wrong value');
},
Error
);
```
Validate error message using [`RegExp`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions):
Using a regular expression runs `.toString` on the error object, and will therefore also include the error name.
MJS modules
```
import assert from 'node:assert/strict';
assert.throws(
() => {
throw new Error('Wrong value');
},
/^Error: Wrong value$/
);
```
CJS modules
```
const assert = require('node:assert/strict');
assert.throws(
() => {
throw new Error('Wrong value');
},
/^Error: Wrong value$/
);
```
Custom error validation:
The function must return `true` to indicate all internal validations passed. It will otherwise fail with an [`AssertionError`](#class-assertassertionerror).
MJS modules
```
import assert from 'node:assert/strict';
assert.throws(
() => {
throw new Error('Wrong value');
},
(err) => {
assert(err instanceof Error);
assert(/value/.test(err));
// Avoid returning anything from validation functions besides `true`.
// Otherwise, it's not clear what part of the validation failed. Instead,
// throw an error about the specific validation that failed (as done in this
// example) and add as much helpful debugging information to that error as
// possible.
return true;
},
'unexpected error'
);
```
CJS modules
```
const assert = require('node:assert/strict');
assert.throws(
() => {
throw new Error('Wrong value');
},
(err) => {
assert(err instanceof Error);
assert(/value/.test(err));
// Avoid returning anything from validation functions besides `true`.
// Otherwise, it's not clear what part of the validation failed. Instead,
// throw an error about the specific validation that failed (as done in this
// example) and add as much helpful debugging information to that error as
// possible.
return true;
},
'unexpected error'
);
```
`error` cannot be a string. If a string is provided as the second argument, then `error` is assumed to be omitted and the string will be used for `message` instead. This can lead to easy-to-miss mistakes. Using the same message as the thrown error message is going to result in an `ERR_AMBIGUOUS_ARGUMENT` error. Please read the example below carefully if using a string as the second argument gets considered:
MJS modules
```
import assert from 'node:assert/strict';
function throwingFirst() {
throw new Error('First');
}
function throwingSecond() {
throw new Error('Second');
}
function notThrowing() {}
// The second argument is a string and the input function threw an Error.
// The first case will not throw as it does not match for the error message
// thrown by the input function!
assert.throws(throwingFirst, 'Second');
// In the next example the message has no benefit over the message from the
// error and since it is not clear if the user intended to actually match
// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.
assert.throws(throwingSecond, 'Second');
// TypeError [ERR_AMBIGUOUS_ARGUMENT]
// The string is only used (as message) in case the function does not throw:
assert.throws(notThrowing, 'Second');
// AssertionError [ERR_ASSERTION]: Missing expected exception: Second
// If it was intended to match for the error message do this instead:
// It does not throw because the error messages match.
assert.throws(throwingSecond, /Second$/);
// If the error message does not match, an AssertionError is thrown.
assert.throws(throwingFirst, /Second$/);
// AssertionError [ERR_ASSERTION]
```
CJS modules
```
const assert = require('node:assert/strict');
function throwingFirst() {
throw new Error('First');
}
function throwingSecond() {
throw new Error('Second');
}
function notThrowing() {}
// The second argument is a string and the input function threw an Error.
// The first case will not throw as it does not match for the error message
// thrown by the input function!
assert.throws(throwingFirst, 'Second');
// In the next example the message has no benefit over the message from the
// error and since it is not clear if the user intended to actually match
// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.
assert.throws(throwingSecond, 'Second');
// TypeError [ERR_AMBIGUOUS_ARGUMENT]
// The string is only used (as message) in case the function does not throw:
assert.throws(notThrowing, 'Second');
// AssertionError [ERR_ASSERTION]: Missing expected exception: Second
// If it was intended to match for the error message do this instead:
// It does not throw because the error messages match.
assert.throws(throwingSecond, /Second$/);
// If the error message does not match, an AssertionError is thrown.
assert.throws(throwingFirst, /Second$/);
// AssertionError [ERR_ASSERTION]
```
Due to the confusing error-prone notation, avoid a string as the second argument.
| programming_docs |
node None Node-API
--------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
Node-API (formerly N-API) is an API for building native Addons. It is independent from the underlying JavaScript runtime (for example, V8) and is maintained as part of Node.js itself. This API will be Application Binary Interface (ABI) stable across versions of Node.js. It is intended to insulate addons from changes in the underlying JavaScript engine and allow modules compiled for one major version to run on later major versions of Node.js without recompilation. The [ABI Stability](https://nodejs.org/en/docs/guides/abi-stability/) guide provides a more in-depth explanation.
Addons are built/packaged with the same approach/tools outlined in the section titled [C++ Addons](addons). The only difference is the set of APIs that are used by the native code. Instead of using the V8 or [Native Abstractions for Node.js](https://github.com/nodejs/nan) APIs, the functions available in Node-API are used.
APIs exposed by Node-API are generally used to create and manipulate JavaScript values. Concepts and operations generally map to ideas specified in the ECMA-262 Language Specification. The APIs have the following properties:
* All Node-API calls return a status code of type `napi_status`. This status indicates whether the API call succeeded or failed.
* The API's return value is passed via an out parameter.
* All JavaScript values are abstracted behind an opaque type named `napi_value`.
* In case of an error status code, additional information can be obtained using `napi_get_last_error_info`. More information can be found in the error handling section [Error handling](#error-handling).
Node-API is a C API that ensures ABI stability across Node.js versions and different compiler levels. A C++ API can be easier to use. To support using C++, the project maintains a C++ wrapper module called [`node-addon-api`](https://github.com/nodejs/node-addon-api). This wrapper provides an inlineable C++ API. Binaries built with `node-addon-api` will depend on the symbols for the Node-API C-based functions exported by Node.js. `node-addon-api` is a more efficient way to write code that calls Node-API. Take, for example, the following `node-addon-api` code. The first section shows the `node-addon-api` code and the second section shows what actually gets used in the addon.
```
Object obj = Object::New(env);
obj["foo"] = String::New(env, "bar");
```
```
napi_status status;
napi_value object, string;
status = napi_create_object(env, &object);
if (status != napi_ok) {
napi_throw_error(env, ...);
return;
}
status = napi_create_string_utf8(env, "bar", NAPI_AUTO_LENGTH, &string);
if (status != napi_ok) {
napi_throw_error(env, ...);
return;
}
status = napi_set_named_property(env, object, "foo", string);
if (status != napi_ok) {
napi_throw_error(env, ...);
return;
}
```
The end result is that the addon only uses the exported C APIs. As a result, it still gets the benefits of the ABI stability provided by the C API.
When using `node-addon-api` instead of the C APIs, start with the API [docs](https://github.com/nodejs/node-addon-api#api-documentation) for `node-addon-api`.
The [Node-API Resource](https://nodejs.github.io/node-addon-examples/) offers an excellent orientation and tips for developers just getting started with Node-API and `node-addon-api`.
### Implications of ABI stability
Although Node-API provides an ABI stability guarantee, other parts of Node.js do not, and any external libraries used from the addon may not. In particular, none of the following APIs provide an ABI stability guarantee across major versions:
* the Node.js C++ APIs available via any of
```
#include <node.h>
#include <node_buffer.h>
#include <node_version.h>
#include <node_object_wrap.h>
```
* the libuv APIs which are also included with Node.js and available via
```
#include <uv.h>
```
* the V8 API available via
```
#include <v8.h>
```
Thus, for an addon to remain ABI-compatible across Node.js major versions, it must use Node-API exclusively by restricting itself to using
```
#include <node_api.h>
```
and by checking, for all external libraries that it uses, that the external library makes ABI stability guarantees similar to Node-API.
### Building
Unlike modules written in JavaScript, developing and deploying Node.js native addons using Node-API requires an additional set of tools. Besides the basic tools required to develop for Node.js, the native addon developer requires a toolchain that can compile C and C++ code into a binary. In addition, depending upon how the native addon is deployed, the *user* of the native addon will also need to have a C/C++ toolchain installed.
For Linux developers, the necessary C/C++ toolchain packages are readily available. [GCC](https://gcc.gnu.org) is widely used in the Node.js community to build and test across a variety of platforms. For many developers, the [LLVM](https://llvm.org) compiler infrastructure is also a good choice.
For Mac developers, [Xcode](https://developer.apple.com/xcode/) offers all the required compiler tools. However, it is not necessary to install the entire Xcode IDE. The following command installs the necessary toolchain:
```
xcode-select --install
```
For Windows developers, [Visual Studio](https://visualstudio.microsoft.com) offers all the required compiler tools. However, it is not necessary to install the entire Visual Studio IDE. The following command installs the necessary toolchain:
```
npm install --global windows-build-tools
```
The sections below describe the additional tools available for developing and deploying Node.js native addons.
#### Build tools
Both the tools listed here require that *users* of the native addon have a C/C++ toolchain installed in order to successfully install the native addon.
##### node-gyp
[node-gyp](https://github.com/nodejs/node-gyp) is a build system based on the [gyp-next](https://github.com/nodejs/gyp-next) fork of Google's [GYP](https://gyp.gsrc.io) tool and comes bundled with npm. GYP, and therefore node-gyp, requires that Python be installed.
Historically, node-gyp has been the tool of choice for building native addons. It has widespread adoption and documentation. However, some developers have run into limitations in node-gyp.
##### CMake.js
[CMake.js](https://github.com/cmake-js/cmake-js) is an alternative build system based on [CMake](https://cmake.org).
CMake.js is a good choice for projects that already use CMake or for developers affected by limitations in node-gyp.
#### Uploading precompiled binaries
The three tools listed here permit native addon developers and maintainers to create and upload binaries to public or private servers. These tools are typically integrated with CI/CD build systems like [Travis CI](https://travis-ci.org) and [AppVeyor](https://www.appveyor.com) to build and upload binaries for a variety of platforms and architectures. These binaries are then available for download by users who do not need to have a C/C++ toolchain installed.
##### node-pre-gyp
[node-pre-gyp](https://github.com/mapbox/node-pre-gyp) is a tool based on node-gyp that adds the ability to upload binaries to a server of the developer's choice. node-pre-gyp has particularly good support for uploading binaries to Amazon S3.
##### prebuild
[prebuild](https://github.com/prebuild/prebuild) is a tool that supports builds using either node-gyp or CMake.js. Unlike node-pre-gyp which supports a variety of servers, prebuild uploads binaries only to [GitHub releases](https://help.github.com/en/github/administering-a-repository/about-releases). prebuild is a good choice for GitHub projects using CMake.js.
##### prebuildify
[prebuildify](https://github.com/prebuild/prebuildify) is a tool based on node-gyp. The advantage of prebuildify is that the built binaries are bundled with the native addon when it's uploaded to npm. The binaries are downloaded from npm and are immediately available to the module user when the native addon is installed.
### Usage
In order to use the Node-API functions, include the file [`node_api.h`](https://github.com/nodejs/node/blob/HEAD/src/node_api.h) which is located in the src directory in the node development tree:
```
#include <node_api.h>
```
This will opt into the default `NAPI_VERSION` for the given release of Node.js. In order to ensure compatibility with specific versions of Node-API, the version can be specified explicitly when including the header:
```
#define NAPI_VERSION 3
#include <node_api.h>
```
This restricts the Node-API surface to just the functionality that was available in the specified (and earlier) versions.
Some of the Node-API surface is experimental and requires explicit opt-in:
```
#define NAPI_EXPERIMENTAL
#include <node_api.h>
```
In this case the entire API surface, including any experimental APIs, will be available to the module code.
### Node-API version matrix
Node-API versions are additive and versioned independently from Node.js. Version 4 is an extension to version 3 in that it has all of the APIs from version 3 with some additions. This means that it is not necessary to recompile for new versions of Node.js which are listed as supporting a later version.
| | | | |
| --- | --- | --- | --- |
| | 1 | 2 | 3 |
| v6.x | | | v6.14.2\* |
| v8.x | v8.6.0\*\* | v8.10.0\* | v8.11.2 |
| v9.x | v9.0.0\* | v9.3.0\* | v9.11.0\* |
| ≥ v10.x | all releases | all releases | all releases |
| | | | | | |
| --- | --- | --- | --- | --- | --- |
| | 4 | 5 | 6 | 7 | 8 |
| v10.x | v10.16.0 | v10.17.0 | v10.20.0 | v10.23.0 | |
| v11.x | v11.8.0 | | | | |
| v12.x | v12.0.0 | v12.11.0 | v12.17.0 | v12.19.0 | v12.22.0 |
| v13.x | v13.0.0 | v13.0.0 | | | |
| v14.x | v14.0.0 | v14.0.0 | v14.0.0 | v14.12.0 | v14.17.0 |
| v15.x | v15.0.0 | v15.0.0 | v15.0.0 | v15.0.0 | v15.12.0 |
| v16.x | v16.0.0 | v16.0.0 | v16.0.0 | v16.0.0 | v16.0.0 |
\* Node-API was experimental.
\*\* Node.js 8.0.0 included Node-API as experimental. It was released as Node-API version 1 but continued to evolve until Node.js 8.6.0. The API is different in versions prior to Node.js 8.6.0. We recommend Node-API version 3 or later.
Each API documented for Node-API will have a header named `added in:`, and APIs which are stable will have the additional header `Node-API version:`. APIs are directly usable when using a Node.js version which supports the Node-API version shown in `Node-API version:` or higher. When using a Node.js version that does not support the `Node-API version:` listed or if there is no `Node-API version:` listed, then the API will only be available if `#define NAPI_EXPERIMENTAL` precedes the inclusion of `node_api.h` or `js_native_api.h`. If an API appears not to be available on a version of Node.js which is later than the one shown in `added in:` then this is most likely the reason for the apparent absence.
The Node-APIs associated strictly with accessing ECMAScript features from native code can be found separately in `js_native_api.h` and `js_native_api_types.h`. The APIs defined in these headers are included in `node_api.h` and `node_api_types.h`. The headers are structured in this way in order to allow implementations of Node-API outside of Node.js. For those implementations the Node.js specific APIs may not be applicable.
The Node.js-specific parts of an addon can be separated from the code that exposes the actual functionality to the JavaScript environment so that the latter may be used with multiple implementations of Node-API. In the example below, `addon.c` and `addon.h` refer only to `js_native_api.h`. This ensures that `addon.c` can be reused to compile against either the Node.js implementation of Node-API or any implementation of Node-API outside of Node.js.
`addon_node.c` is a separate file that contains the Node.js specific entry point to the addon and which instantiates the addon by calling into `addon.c` when the addon is loaded into a Node.js environment.
```
// addon.h
#ifndef _ADDON_H_
#define _ADDON_H_
#include <js_native_api.h>
napi_value create_addon(napi_env env);
#endif // _ADDON_H_
```
```
// addon.c
#include "addon.h"
#define NAPI_CALL(env, call) \
do { \
napi_status status = (call); \
if (status != napi_ok) { \
const napi_extended_error_info* error_info = NULL; \
napi_get_last_error_info((env), &error_info); \
const char* err_message = error_info->error_message; \
bool is_pending; \
napi_is_exception_pending((env), &is_pending); \
if (!is_pending) { \
const char* message = (err_message == NULL) \
? "empty error message" \
: err_message; \
napi_throw_error((env), NULL, message); \
return NULL; \
} \
} \
} while(0)
static napi_value
DoSomethingUseful(napi_env env, napi_callback_info info) {
// Do something useful.
return NULL;
}
napi_value create_addon(napi_env env) {
napi_value result;
NAPI_CALL(env, napi_create_object(env, &result));
napi_value exported_function;
NAPI_CALL(env, napi_create_function(env,
"doSomethingUseful",
NAPI_AUTO_LENGTH,
DoSomethingUseful,
NULL,
&exported_function));
NAPI_CALL(env, napi_set_named_property(env,
result,
"doSomethingUseful",
exported_function));
return result;
}
```
```
// addon_node.c
#include <node_api.h>
#include "addon.h"
NAPI_MODULE_INIT() {
// This function body is expected to return a `napi_value`.
// The variables `napi_env env` and `napi_value exports` may be used within
// the body, as they are provided by the definition of `NAPI_MODULE_INIT()`.
return create_addon(env);
}
```
### Environment life cycle APIs
[Section 8.7](https://tc39.es/ecma262/#sec-agents) of the [ECMAScript Language Specification](https://tc39.github.io/ecma262/) defines the concept of an "Agent" as a self-contained environment in which JavaScript code runs. Multiple such Agents may be started and terminated either concurrently or in sequence by the process.
A Node.js environment corresponds to an ECMAScript Agent. In the main process, an environment is created at startup, and additional environments can be created on separate threads to serve as [worker threads](worker_threads). When Node.js is embedded in another application, the main thread of the application may also construct and destroy a Node.js environment multiple times during the life cycle of the application process such that each Node.js environment created by the application may, in turn, during its life cycle create and destroy additional environments as worker threads.
From the perspective of a native addon this means that the bindings it provides may be called multiple times, from multiple contexts, and even concurrently from multiple threads.
Native addons may need to allocate global state which they use during their entire life cycle such that the state must be unique to each instance of the addon.
To this end, Node-API provides a way to allocate data such that its life cycle is tied to the life cycle of the Agent.
####
`napi_set_instance_data`
Added in: v12.8.0, v10.20.0 N-API version: 6
```
napi_status napi_set_instance_data(napi_env env,
void* data,
napi_finalize finalize_cb,
void* finalize_hint);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] data`: The data item to make available to bindings of this instance.
* `[in] finalize_cb`: The function to call when the environment is being torn down. The function receives `data` so that it might free it. [`napi_finalize`](#napi_finalize) provides more details.
* `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection.
Returns `napi_ok` if the API succeeded.
This API associates `data` with the currently running Agent. `data` can later be retrieved using `napi_get_instance_data()`. Any existing data associated with the currently running Agent which was set by means of a previous call to `napi_set_instance_data()` will be overwritten. If a `finalize_cb` was provided by the previous call, it will not be called.
####
`napi_get_instance_data`
Added in: v12.8.0, v10.20.0 N-API version: 6
```
napi_status napi_get_instance_data(napi_env env,
void** data);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[out] data`: The data item that was previously associated with the currently running Agent by a call to `napi_set_instance_data()`.
Returns `napi_ok` if the API succeeded.
This API retrieves data that was previously associated with the currently running Agent via `napi_set_instance_data()`. If no data is set, the call will succeed and `data` will be set to `NULL`.
### Basic Node-API data types
Node-API exposes the following fundamental datatypes as abstractions that are consumed by the various APIs. These APIs should be treated as opaque, introspectable only with other Node-API calls.
####
`napi_status`
Added in: v8.0.0 N-API version: 1 Integral status code indicating the success or failure of a Node-API call. Currently, the following status codes are supported.
```
typedef enum {
napi_ok,
napi_invalid_arg,
napi_object_expected,
napi_string_expected,
napi_name_expected,
napi_function_expected,
napi_number_expected,
napi_boolean_expected,
napi_array_expected,
napi_generic_failure,
napi_pending_exception,
napi_cancelled,
napi_escape_called_twice,
napi_handle_scope_mismatch,
napi_callback_scope_mismatch,
napi_queue_full,
napi_closing,
napi_bigint_expected,
napi_date_expected,
napi_arraybuffer_expected,
napi_detachable_arraybuffer_expected,
napi_would_deadlock, /* unused */
} napi_status;
```
If additional information is required upon an API returning a failed status, it can be obtained by calling `napi_get_last_error_info`.
####
`napi_extended_error_info`
Added in: v8.0.0 N-API version: 1
```
typedef struct {
const char* error_message;
void* engine_reserved;
uint32_t engine_error_code;
napi_status error_code;
} napi_extended_error_info;
```
* `error_message`: UTF8-encoded string containing a VM-neutral description of the error.
* `engine_reserved`: Reserved for VM-specific error details. This is currently not implemented for any VM.
* `engine_error_code`: VM-specific error code. This is currently not implemented for any VM.
* `error_code`: The Node-API status code that originated with the last error.
See the [Error handling](#error-handling) section for additional information.
####
`napi_env`
`napi_env` is used to represent a context that the underlying Node-API implementation can use to persist VM-specific state. This structure is passed to native functions when they're invoked, and it must be passed back when making Node-API calls. Specifically, the same `napi_env` that was passed in when the initial native function was called must be passed to any subsequent nested Node-API calls. Caching the `napi_env` for the purpose of general reuse, and passing the `napi_env` between instances of the same addon running on different [`Worker`](worker_threads#class-worker) threads is not allowed. The `napi_env` becomes invalid when an instance of a native addon is unloaded. Notification of this event is delivered through the callbacks given to [`napi_add_env_cleanup_hook`](#napi_add_env_cleanup_hook) and [`napi_set_instance_data`](#napi_set_instance_data).
####
`napi_value`
This is an opaque pointer that is used to represent a JavaScript value.
####
`napi_threadsafe_function`
Added in: v10.6.0 N-API version: 4 This is an opaque pointer that represents a JavaScript function which can be called asynchronously from multiple threads via `napi_call_threadsafe_function()`.
####
`napi_threadsafe_function_release_mode`
Added in: v10.6.0 N-API version: 4 A value to be given to `napi_release_threadsafe_function()` to indicate whether the thread-safe function is to be closed immediately (`napi_tsfn_abort`) or merely released (`napi_tsfn_release`) and thus available for subsequent use via `napi_acquire_threadsafe_function()` and `napi_call_threadsafe_function()`.
```
typedef enum {
napi_tsfn_release,
napi_tsfn_abort
} napi_threadsafe_function_release_mode;
```
####
`napi_threadsafe_function_call_mode`
Added in: v10.6.0 N-API version: 4 A value to be given to `napi_call_threadsafe_function()` to indicate whether the call should block whenever the queue associated with the thread-safe function is full.
```
typedef enum {
napi_tsfn_nonblocking,
napi_tsfn_blocking
} napi_threadsafe_function_call_mode;
```
#### Node-API memory management types
#####
`napi_handle_scope`
This is an abstraction used to control and modify the lifetime of objects created within a particular scope. In general, Node-API values are created within the context of a handle scope. When a native method is called from JavaScript, a default handle scope will exist. If the user does not explicitly create a new handle scope, Node-API values will be created in the default handle scope. For any invocations of code outside the execution of a native method (for instance, during a libuv callback invocation), the module is required to create a scope before invoking any functions that can result in the creation of JavaScript values.
Handle scopes are created using [`napi_open_handle_scope`](#napi_open_handle_scope) and are destroyed using [`napi_close_handle_scope`](#napi_close_handle_scope). Closing the scope can indicate to the GC that all `napi_value`s created during the lifetime of the handle scope are no longer referenced from the current stack frame.
For more details, review the [Object lifetime management](#object-lifetime-management).
#####
`napi_escapable_handle_scope`
Added in: v8.0.0 N-API version: 1 Escapable handle scopes are a special type of handle scope to return values created within a particular handle scope to a parent scope.
#####
`napi_ref`
Added in: v8.0.0 N-API version: 1 This is the abstraction to use to reference a `napi_value`. This allows for users to manage the lifetimes of JavaScript values, including defining their minimum lifetimes explicitly.
For more details, review the [Object lifetime management](#object-lifetime-management).
#####
`napi_type_tag`
Added in: v14.8.0, v12.19.0 N-API version: 8 A 128-bit value stored as two unsigned 64-bit integers. It serves as a UUID with which JavaScript objects can be "tagged" in order to ensure that they are of a certain type. This is a stronger check than [`napi_instanceof`](#napi_instanceof), because the latter can report a false positive if the object's prototype has been manipulated. Type-tagging is most useful in conjunction with [`napi_wrap`](#napi_wrap) because it ensures that the pointer retrieved from a wrapped object can be safely cast to the native type corresponding to the type tag that had been previously applied to the JavaScript object.
```
typedef struct {
uint64_t lower;
uint64_t upper;
} napi_type_tag;
```
#####
`napi_async_cleanup_hook_handle`
Added in: v14.10.0, v12.19.0 An opaque value returned by [`napi_add_async_cleanup_hook`](#napi_add_async_cleanup_hook). It must be passed to [`napi_remove_async_cleanup_hook`](#napi_remove_async_cleanup_hook) when the chain of asynchronous cleanup events completes.
#### Node-API callback types
#####
`napi_callback_info`
Added in: v8.0.0 N-API version: 1 Opaque datatype that is passed to a callback function. It can be used for getting additional information about the context in which the callback was invoked.
#####
`napi_callback`
Added in: v8.0.0 N-API version: 1 Function pointer type for user-provided native functions which are to be exposed to JavaScript via Node-API. Callback functions should satisfy the following signature:
```
typedef napi_value (*napi_callback)(napi_env, napi_callback_info);
```
Unless for reasons discussed in [Object Lifetime Management](#object-lifetime-management), creating a handle and/or callback scope inside a `napi_callback` is not necessary.
#####
`napi_finalize`
Added in: v8.0.0 N-API version: 1 Function pointer type for add-on provided functions that allow the user to be notified when externally-owned data is ready to be cleaned up because the object with which it was associated with, has been garbage-collected. The user must provide a function satisfying the following signature which would get called upon the object's collection. Currently, `napi_finalize` can be used for finding out when objects that have external data are collected.
```
typedef void (*napi_finalize)(napi_env env,
void* finalize_data,
void* finalize_hint);
```
Unless for reasons discussed in [Object Lifetime Management](#object-lifetime-management), creating a handle and/or callback scope inside the function body is not necessary.
#####
`napi_async_execute_callback`
Added in: v8.0.0 N-API version: 1 Function pointer used with functions that support asynchronous operations. Callback functions must satisfy the following signature:
```
typedef void (*napi_async_execute_callback)(napi_env env, void* data);
```
Implementations of this function must avoid making Node-API calls that execute JavaScript or interact with JavaScript objects. Node-API calls should be in the `napi_async_complete_callback` instead. Do not use the `napi_env` parameter as it will likely result in execution of JavaScript.
#####
`napi_async_complete_callback`
Added in: v8.0.0 N-API version: 1 Function pointer used with functions that support asynchronous operations. Callback functions must satisfy the following signature:
```
typedef void (*napi_async_complete_callback)(napi_env env,
napi_status status,
void* data);
```
Unless for reasons discussed in [Object Lifetime Management](#object-lifetime-management), creating a handle and/or callback scope inside the function body is not necessary.
#####
`napi_threadsafe_function_call_js`
Added in: v10.6.0 N-API version: 4 Function pointer used with asynchronous thread-safe function calls. The callback will be called on the main thread. Its purpose is to use a data item arriving via the queue from one of the secondary threads to construct the parameters necessary for a call into JavaScript, usually via `napi_call_function`, and then make the call into JavaScript.
The data arriving from the secondary thread via the queue is given in the `data` parameter and the JavaScript function to call is given in the `js_callback` parameter.
Node-API sets up the environment prior to calling this callback, so it is sufficient to call the JavaScript function via `napi_call_function` rather than via `napi_make_callback`.
Callback functions must satisfy the following signature:
```
typedef void (*napi_threadsafe_function_call_js)(napi_env env,
napi_value js_callback,
void* context,
void* data);
```
* `[in] env`: The environment to use for API calls, or `NULL` if the thread-safe function is being torn down and `data` may need to be freed.
* `[in] js_callback`: The JavaScript function to call, or `NULL` if the thread-safe function is being torn down and `data` may need to be freed. It may also be `NULL` if the thread-safe function was created without `js_callback`.
* `[in] context`: The optional data with which the thread-safe function was created.
* `[in] data`: Data created by the secondary thread. It is the responsibility of the callback to convert this native data to JavaScript values (with Node-API functions) that can be passed as parameters when `js_callback` is invoked. This pointer is managed entirely by the threads and this callback. Thus this callback should free the data.
Unless for reasons discussed in [Object Lifetime Management](#object-lifetime-management), creating a handle and/or callback scope inside the function body is not necessary.
#####
`napi_async_cleanup_hook`
Added in: v14.10.0, v12.19.0 Function pointer used with [`napi_add_async_cleanup_hook`](#napi_add_async_cleanup_hook). It will be called when the environment is being torn down.
Callback functions must satisfy the following signature:
```
typedef void (*napi_async_cleanup_hook)(napi_async_cleanup_hook_handle handle,
void* data);
```
* `[in] handle`: The handle that must be passed to [`napi_remove_async_cleanup_hook`](#napi_remove_async_cleanup_hook) after completion of the asynchronous cleanup.
* `[in] data`: The data that was passed to [`napi_add_async_cleanup_hook`](#napi_add_async_cleanup_hook).
The body of the function should initiate the asynchronous cleanup actions at the end of which `handle` must be passed in a call to [`napi_remove_async_cleanup_hook`](#napi_remove_async_cleanup_hook).
### Error handling
Node-API uses both return values and JavaScript exceptions for error handling. The following sections explain the approach for each case.
#### Return values
All of the Node-API functions share the same error handling pattern. The return type of all API functions is `napi_status`.
The return value will be `napi_ok` if the request was successful and no uncaught JavaScript exception was thrown. If an error occurred AND an exception was thrown, the `napi_status` value for the error will be returned. If an exception was thrown, and no error occurred, `napi_pending_exception` will be returned.
In cases where a return value other than `napi_ok` or `napi_pending_exception` is returned, [`napi_is_exception_pending`](#napi_is_exception_pending) must be called to check if an exception is pending. See the section on exceptions for more details.
The full set of possible `napi_status` values is defined in `napi_api_types.h`.
The `napi_status` return value provides a VM-independent representation of the error which occurred. In some cases it is useful to be able to get more detailed information, including a string representing the error as well as VM (engine)-specific information.
In order to retrieve this information [`napi_get_last_error_info`](#napi_get_last_error_info) is provided which returns a `napi_extended_error_info` structure. The format of the `napi_extended_error_info` structure is as follows:
Added in: v8.0.0 N-API version: 1
```
typedef struct napi_extended_error_info {
const char* error_message;
void* engine_reserved;
uint32_t engine_error_code;
napi_status error_code;
};
```
* `error_message`: Textual representation of the error that occurred.
* `engine_reserved`: Opaque handle reserved for engine use only.
* `engine_error_code`: VM specific error code.
* `error_code`: Node-API status code for the last error.
[`napi_get_last_error_info`](#napi_get_last_error_info) returns the information for the last Node-API call that was made.
Do not rely on the content or format of any of the extended information as it is not subject to SemVer and may change at any time. It is intended only for logging purposes.
#####
`napi_get_last_error_info`
Added in: v8.0.0 N-API version: 1
```
napi_status
napi_get_last_error_info(napi_env env,
const napi_extended_error_info** result);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: The `napi_extended_error_info` structure with more information about the error.
Returns `napi_ok` if the API succeeded.
This API retrieves a `napi_extended_error_info` structure with information about the last error that occurred.
The content of the `napi_extended_error_info` returned is only valid up until a Node-API function is called on the same `env`. This includes a call to `napi_is_exception_pending` so it may often be necessary to make a copy of the information so that it can be used later. The pointer returned in `error_message` points to a statically-defined string so it is safe to use that pointer if you have copied it out of the `error_message` field (which will be overwritten) before another Node-API function was called.
Do not rely on the content or format of any of the extended information as it is not subject to SemVer and may change at any time. It is intended only for logging purposes.
This API can be called even if there is a pending JavaScript exception.
#### Exceptions
Any Node-API function call may result in a pending JavaScript exception. This is the case for any of the API functions, even those that may not cause the execution of JavaScript.
If the `napi_status` returned by a function is `napi_ok` then no exception is pending and no additional action is required. If the `napi_status` returned is anything other than `napi_ok` or `napi_pending_exception`, in order to try to recover and continue instead of simply returning immediately, [`napi_is_exception_pending`](#napi_is_exception_pending) must be called in order to determine if an exception is pending or not.
In many cases when a Node-API function is called and an exception is already pending, the function will return immediately with a `napi_status` of `napi_pending_exception`. However, this is not the case for all functions. Node-API allows a subset of the functions to be called to allow for some minimal cleanup before returning to JavaScript. In that case, `napi_status` will reflect the status for the function. It will not reflect previous pending exceptions. To avoid confusion, check the error status after every function call.
When an exception is pending one of two approaches can be employed.
The first approach is to do any appropriate cleanup and then return so that execution will return to JavaScript. As part of the transition back to JavaScript, the exception will be thrown at the point in the JavaScript code where the native method was invoked. The behavior of most Node-API calls is unspecified while an exception is pending, and many will simply return `napi_pending_exception`, so do as little as possible and then return to JavaScript where the exception can be handled.
The second approach is to try to handle the exception. There will be cases where the native code can catch the exception, take the appropriate action, and then continue. This is only recommended in specific cases where it is known that the exception can be safely handled. In these cases [`napi_get_and_clear_last_exception`](#napi_get_and_clear_last_exception) can be used to get and clear the exception. On success, result will contain the handle to the last JavaScript `Object` thrown. If it is determined, after retrieving the exception, the exception cannot be handled after all it can be re-thrown it with [`napi_throw`](#napi_throw) where error is the JavaScript value to be thrown.
The following utility functions are also available in case native code needs to throw an exception or determine if a `napi_value` is an instance of a JavaScript `Error` object: [`napi_throw_error`](#napi_throw_error), [`napi_throw_type_error`](#napi_throw_type_error), [`napi_throw_range_error`](#napi_throw_range_error), [`node_api_throw_syntax_error`](#node_api_throw_syntax_error) and [`napi_is_error`](#napi_is_error).
The following utility functions are also available in case native code needs to create an `Error` object: [`napi_create_error`](#napi_create_error), [`napi_create_type_error`](#napi_create_type_error), [`napi_create_range_error`](#napi_create_range_error) and [`node_api_create_syntax_error`](#node_api_create_syntax_error), where result is the `napi_value` that refers to the newly created JavaScript `Error` object.
The Node.js project is adding error codes to all of the errors generated internally. The goal is for applications to use these error codes for all error checking. The associated error messages will remain, but will only be meant to be used for logging and display with the expectation that the message can change without SemVer applying. In order to support this model with Node-API, both in internal functionality and for module specific functionality (as its good practice), the `throw_` and `create_` functions take an optional code parameter which is the string for the code to be added to the error object. If the optional parameter is `NULL` then no code will be associated with the error. If a code is provided, the name associated with the error is also updated to be:
```
originalName [code]
```
where `originalName` is the original name associated with the error and `code` is the code that was provided. For example, if the code is `'ERR_ERROR_1'` and a `TypeError` is being created the name will be:
```
TypeError [ERR_ERROR_1]
```
#####
`napi_throw`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_throw(napi_env env, napi_value error);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] error`: The JavaScript value to be thrown.
Returns `napi_ok` if the API succeeded.
This API throws the JavaScript value provided.
#####
`napi_throw_error`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_throw_error(napi_env env,
const char* code,
const char* msg);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] code`: Optional error code to be set on the error.
* `[in] msg`: C string representing the text to be associated with the error.
Returns `napi_ok` if the API succeeded.
This API throws a JavaScript `Error` with the text provided.
#####
`napi_throw_type_error`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_throw_type_error(napi_env env,
const char* code,
const char* msg);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] code`: Optional error code to be set on the error.
* `[in] msg`: C string representing the text to be associated with the error.
Returns `napi_ok` if the API succeeded.
This API throws a JavaScript `TypeError` with the text provided.
#####
`napi_throw_range_error`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_throw_range_error(napi_env env,
const char* code,
const char* msg);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] code`: Optional error code to be set on the error.
* `[in] msg`: C string representing the text to be associated with the error.
Returns `napi_ok` if the API succeeded.
This API throws a JavaScript `RangeError` with the text provided.
#####
`node_api_throw_syntax_error`
Added in: v17.2.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
```
NAPI_EXTERN napi_status node_api_throw_syntax_error(napi_env env,
const char* code,
const char* msg);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] code`: Optional error code to be set on the error.
* `[in] msg`: C string representing the text to be associated with the error.
Returns `napi_ok` if the API succeeded.
This API throws a JavaScript `SyntaxError` with the text provided.
#####
`napi_is_error`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_is_error(napi_env env,
napi_value value,
bool* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The `napi_value` to be checked.
* `[out] result`: Boolean value that is set to true if `napi_value` represents an error, false otherwise.
Returns `napi_ok` if the API succeeded.
This API queries a `napi_value` to check if it represents an error object.
#####
`napi_create_error`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_create_error(napi_env env,
napi_value code,
napi_value msg,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] code`: Optional `napi_value` with the string for the error code to be associated with the error.
* `[in] msg`: `napi_value` that references a JavaScript `string` to be used as the message for the `Error`.
* `[out] result`: `napi_value` representing the error created.
Returns `napi_ok` if the API succeeded.
This API returns a JavaScript `Error` with the text provided.
#####
`napi_create_type_error`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_create_type_error(napi_env env,
napi_value code,
napi_value msg,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] code`: Optional `napi_value` with the string for the error code to be associated with the error.
* `[in] msg`: `napi_value` that references a JavaScript `string` to be used as the message for the `Error`.
* `[out] result`: `napi_value` representing the error created.
Returns `napi_ok` if the API succeeded.
This API returns a JavaScript `TypeError` with the text provided.
#####
`napi_create_range_error`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_create_range_error(napi_env env,
napi_value code,
napi_value msg,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] code`: Optional `napi_value` with the string for the error code to be associated with the error.
* `[in] msg`: `napi_value` that references a JavaScript `string` to be used as the message for the `Error`.
* `[out] result`: `napi_value` representing the error created.
Returns `napi_ok` if the API succeeded.
This API returns a JavaScript `RangeError` with the text provided.
#####
`node_api_create_syntax_error`
Added in: v17.2.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
```
NAPI_EXTERN napi_status node_api_create_syntax_error(napi_env env,
napi_value code,
napi_value msg,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] code`: Optional `napi_value` with the string for the error code to be associated with the error.
* `[in] msg`: `napi_value` that references a JavaScript `string` to be used as the message for the `Error`.
* `[out] result`: `napi_value` representing the error created.
Returns `napi_ok` if the API succeeded.
This API returns a JavaScript `SyntaxError` with the text provided.
#####
`napi_get_and_clear_last_exception`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_and_clear_last_exception(napi_env env,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: The exception if one is pending, `NULL` otherwise.
Returns `napi_ok` if the API succeeded.
This API can be called even if there is a pending JavaScript exception.
#####
`napi_is_exception_pending`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_is_exception_pending(napi_env env, bool* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: Boolean value that is set to true if an exception is pending.
Returns `napi_ok` if the API succeeded.
This API can be called even if there is a pending JavaScript exception.
#####
`napi_fatal_exception`
Added in: v9.10.0 N-API version: 3
```
napi_status napi_fatal_exception(napi_env env, napi_value err);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] err`: The error that is passed to `'uncaughtException'`.
Trigger an `'uncaughtException'` in JavaScript. Useful if an async callback throws an exception with no way to recover.
#### Fatal errors
In the event of an unrecoverable error in a native addon, a fatal error can be thrown to immediately terminate the process.
#####
`napi_fatal_error`
Added in: v8.2.0 N-API version: 1
```
NAPI_NO_RETURN void napi_fatal_error(const char* location,
size_t location_len,
const char* message,
size_t message_len);
```
* `[in] location`: Optional location at which the error occurred.
* `[in] location_len`: The length of the location in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated.
* `[in] message`: The message associated with the error.
* `[in] message_len`: The length of the message in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated.
The function call does not return, the process will be terminated.
This API can be called even if there is a pending JavaScript exception.
### Object lifetime management
As Node-API calls are made, handles to objects in the heap for the underlying VM may be returned as `napi_values`. These handles must hold the objects 'live' until they are no longer required by the native code, otherwise the objects could be collected before the native code was finished using them.
As object handles are returned they are associated with a 'scope'. The lifespan for the default scope is tied to the lifespan of the native method call. The result is that, by default, handles remain valid and the objects associated with these handles will be held live for the lifespan of the native method call.
In many cases, however, it is necessary that the handles remain valid for either a shorter or longer lifespan than that of the native method. The sections which follow describe the Node-API functions that can be used to change the handle lifespan from the default.
#### Making handle lifespan shorter than that of the native method
It is often necessary to make the lifespan of handles shorter than the lifespan of a native method. For example, consider a native method that has a loop which iterates through the elements in a large array:
```
for (int i = 0; i < 1000000; i++) {
napi_value result;
napi_status status = napi_get_element(env, object, i, &result);
if (status != napi_ok) {
break;
}
// do something with element
}
```
This would result in a large number of handles being created, consuming substantial resources. In addition, even though the native code could only use the most recent handle, all of the associated objects would also be kept alive since they all share the same scope.
To handle this case, Node-API provides the ability to establish a new 'scope' to which newly created handles will be associated. Once those handles are no longer required, the scope can be 'closed' and any handles associated with the scope are invalidated. The methods available to open/close scopes are [`napi_open_handle_scope`](#napi_open_handle_scope) and [`napi_close_handle_scope`](#napi_close_handle_scope).
Node-API only supports a single nested hierarchy of scopes. There is only one active scope at any time, and all new handles will be associated with that scope while it is active. Scopes must be closed in the reverse order from which they are opened. In addition, all scopes created within a native method must be closed before returning from that method.
Taking the earlier example, adding calls to [`napi_open_handle_scope`](#napi_open_handle_scope) and [`napi_close_handle_scope`](#napi_close_handle_scope) would ensure that at most a single handle is valid throughout the execution of the loop:
```
for (int i = 0; i < 1000000; i++) {
napi_handle_scope scope;
napi_status status = napi_open_handle_scope(env, &scope);
if (status != napi_ok) {
break;
}
napi_value result;
status = napi_get_element(env, object, i, &result);
if (status != napi_ok) {
break;
}
// do something with element
status = napi_close_handle_scope(env, scope);
if (status != napi_ok) {
break;
}
}
```
When nesting scopes, there are cases where a handle from an inner scope needs to live beyond the lifespan of that scope. Node-API supports an 'escapable scope' in order to support this case. An escapable scope allows one handle to be 'promoted' so that it 'escapes' the current scope and the lifespan of the handle changes from the current scope to that of the outer scope.
The methods available to open/close escapable scopes are [`napi_open_escapable_handle_scope`](#napi_open_escapable_handle_scope) and [`napi_close_escapable_handle_scope`](#napi_close_escapable_handle_scope).
The request to promote a handle is made through [`napi_escape_handle`](#napi_escape_handle) which can only be called once.
#####
`napi_open_handle_scope`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_open_handle_scope(napi_env env,
napi_handle_scope* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: `napi_value` representing the new scope.
Returns `napi_ok` if the API succeeded.
This API opens a new scope.
#####
`napi_close_handle_scope`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_close_handle_scope(napi_env env,
napi_handle_scope scope);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] scope`: `napi_value` representing the scope to be closed.
Returns `napi_ok` if the API succeeded.
This API closes the scope passed in. Scopes must be closed in the reverse order from which they were created.
This API can be called even if there is a pending JavaScript exception.
#####
`napi_open_escapable_handle_scope`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status
napi_open_escapable_handle_scope(napi_env env,
napi_handle_scope* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: `napi_value` representing the new scope.
Returns `napi_ok` if the API succeeded.
This API opens a new scope from which one object can be promoted to the outer scope.
#####
`napi_close_escapable_handle_scope`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status
napi_close_escapable_handle_scope(napi_env env,
napi_handle_scope scope);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] scope`: `napi_value` representing the scope to be closed.
Returns `napi_ok` if the API succeeded.
This API closes the scope passed in. Scopes must be closed in the reverse order from which they were created.
This API can be called even if there is a pending JavaScript exception.
#####
`napi_escape_handle`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_escape_handle(napi_env env,
napi_escapable_handle_scope scope,
napi_value escapee,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] scope`: `napi_value` representing the current scope.
* `[in] escapee`: `napi_value` representing the JavaScript `Object` to be escaped.
* `[out] result`: `napi_value` representing the handle to the escaped `Object` in the outer scope.
Returns `napi_ok` if the API succeeded.
This API promotes the handle to the JavaScript object so that it is valid for the lifetime of the outer scope. It can only be called once per scope. If it is called more than once an error will be returned.
This API can be called even if there is a pending JavaScript exception.
#### References to objects with a lifespan longer than that of the native method
In some cases an addon will need to be able to create and reference objects with a lifespan longer than that of a single native method invocation. For example, to create a constructor and later use that constructor in a request to creates instances, it must be possible to reference the constructor object across many different instance creation requests. This would not be possible with a normal handle returned as a `napi_value` as described in the earlier section. The lifespan of a normal handle is managed by scopes and all scopes must be closed before the end of a native method.
Node-API provides methods to create persistent references to an object. Each persistent reference has an associated count with a value of 0 or higher. The count determines if the reference will keep the corresponding object live. References with a count of 0 do not prevent the object from being collected and are often called 'weak' references. Any count greater than 0 will prevent the object from being collected.
References can be created with an initial reference count. The count can then be modified through [`napi_reference_ref`](#napi_reference_ref) and [`napi_reference_unref`](#napi_reference_unref). If an object is collected while the count for a reference is 0, all subsequent calls to get the object associated with the reference [`napi_get_reference_value`](#napi_get_reference_value) will return `NULL` for the returned `napi_value`. An attempt to call [`napi_reference_ref`](#napi_reference_ref) for a reference whose object has been collected results in an error.
References must be deleted once they are no longer required by the addon. When a reference is deleted, it will no longer prevent the corresponding object from being collected. Failure to delete a persistent reference results in a 'memory leak' with both the native memory for the persistent reference and the corresponding object on the heap being retained forever.
There can be multiple persistent references created which refer to the same object, each of which will either keep the object live or not based on its individual count. Multiple persistent references to the same object can result in unexpectedly keeping alive native memory. The native structures for a persistent reference must be kept alive until finalizers for the referenced object are executed. If a new persistent reference is created for the same object, the finalizers for that object will not be run and the native memory pointed by the earlier persistent reference will not be freed. This can be avoided by calling `napi_delete_reference` in addition to `napi_reference_unref` when possible.
#####
`napi_create_reference`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_create_reference(napi_env env,
napi_value value,
uint32_t initial_refcount,
napi_ref* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing the `Object` to which we want a reference.
* `[in] initial_refcount`: Initial reference count for the new reference.
* `[out] result`: `napi_ref` pointing to the new reference.
Returns `napi_ok` if the API succeeded.
This API creates a new reference with the specified reference count to the `Object` passed in.
#####
`napi_delete_reference`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_delete_reference(napi_env env, napi_ref ref);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] ref`: `napi_ref` to be deleted.
Returns `napi_ok` if the API succeeded.
This API deletes the reference passed in.
This API can be called even if there is a pending JavaScript exception.
#####
`napi_reference_ref`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_reference_ref(napi_env env,
napi_ref ref,
uint32_t* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] ref`: `napi_ref` for which the reference count will be incremented.
* `[out] result`: The new reference count.
Returns `napi_ok` if the API succeeded.
This API increments the reference count for the reference passed in and returns the resulting reference count.
#####
`napi_reference_unref`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_reference_unref(napi_env env,
napi_ref ref,
uint32_t* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] ref`: `napi_ref` for which the reference count will be decremented.
* `[out] result`: The new reference count.
Returns `napi_ok` if the API succeeded.
This API decrements the reference count for the reference passed in and returns the resulting reference count.
#####
`napi_get_reference_value`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_get_reference_value(napi_env env,
napi_ref ref,
napi_value* result);
```
the `napi_value passed` in or out of these methods is a handle to the object to which the reference is related.
* `[in] env`: The environment that the API is invoked under.
* `[in] ref`: `napi_ref` for which we requesting the corresponding `Object`.
* `[out] result`: The `napi_value` for the `Object` referenced by the `napi_ref`.
Returns `napi_ok` if the API succeeded.
If still valid, this API returns the `napi_value` representing the JavaScript `Object` associated with the `napi_ref`. Otherwise, result will be `NULL`.
#### Cleanup on exit of the current Node.js instance
While a Node.js process typically releases all its resources when exiting, embedders of Node.js, or future Worker support, may require addons to register clean-up hooks that will be run once the current Node.js instance exits.
Node-API provides functions for registering and un-registering such callbacks. When those callbacks are run, all resources that are being held by the addon should be freed up.
#####
`napi_add_env_cleanup_hook`
Added in: v10.2.0 N-API version: 3
```
NODE_EXTERN napi_status napi_add_env_cleanup_hook(napi_env env,
void (*fun)(void* arg),
void* arg);
```
Registers `fun` as a function to be run with the `arg` parameter once the current Node.js environment exits.
A function can safely be specified multiple times with different `arg` values. In that case, it will be called multiple times as well. Providing the same `fun` and `arg` values multiple times is not allowed and will lead the process to abort.
The hooks will be called in reverse order, i.e. the most recently added one will be called first.
Removing this hook can be done by using [`napi_remove_env_cleanup_hook`](#napi_remove_env_cleanup_hook). Typically, that happens when the resource for which this hook was added is being torn down anyway.
For asynchronous cleanup, [`napi_add_async_cleanup_hook`](#napi_add_async_cleanup_hook) is available.
#####
`napi_remove_env_cleanup_hook`
Added in: v10.2.0 N-API version: 3
```
NAPI_EXTERN napi_status napi_remove_env_cleanup_hook(napi_env env,
void (*fun)(void* arg),
void* arg);
```
Unregisters `fun` as a function to be run with the `arg` parameter once the current Node.js environment exits. Both the argument and the function value need to be exact matches.
The function must have originally been registered with `napi_add_env_cleanup_hook`, otherwise the process will abort.
#####
`napi_add_async_cleanup_hook`
History
| Version | Changes |
| --- | --- |
| v14.8.0, v12.19.0 | Added in: v14.8.0, v12.19.0 |
| v14.10.0, v12.19.0 | Changed signature of the `hook` callback. |
N-API version: 8
```
NAPI_EXTERN napi_status napi_add_async_cleanup_hook(
napi_env env,
napi_async_cleanup_hook hook,
void* arg,
napi_async_cleanup_hook_handle* remove_handle);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] hook`: The function pointer to call at environment teardown.
* `[in] arg`: The pointer to pass to `hook` when it gets called.
* `[out] remove_handle`: Optional handle that refers to the asynchronous cleanup hook.
Registers `hook`, which is a function of type [`napi_async_cleanup_hook`](#napi_async_cleanup_hook), as a function to be run with the `remove_handle` and `arg` parameters once the current Node.js environment exits.
Unlike [`napi_add_env_cleanup_hook`](#napi_add_env_cleanup_hook), the hook is allowed to be asynchronous.
Otherwise, behavior generally matches that of [`napi_add_env_cleanup_hook`](#napi_add_env_cleanup_hook).
If `remove_handle` is not `NULL`, an opaque value will be stored in it that must later be passed to [`napi_remove_async_cleanup_hook`](#napi_remove_async_cleanup_hook), regardless of whether the hook has already been invoked. Typically, that happens when the resource for which this hook was added is being torn down anyway.
#####
`napi_remove_async_cleanup_hook`
History
| Version | Changes |
| --- | --- |
| v14.8.0, v12.19.0 | Added in: v14.8.0, v12.19.0 |
| v14.10.0, v12.19.0 | Removed `env` parameter. |
```
NAPI_EXTERN napi_status napi_remove_async_cleanup_hook(
napi_async_cleanup_hook_handle remove_handle);
```
* `[in] remove_handle`: The handle to an asynchronous cleanup hook that was created with [`napi_add_async_cleanup_hook`](#napi_add_async_cleanup_hook).
Unregisters the cleanup hook corresponding to `remove_handle`. This will prevent the hook from being executed, unless it has already started executing. This must be called on any `napi_async_cleanup_hook_handle` value obtained from [`napi_add_async_cleanup_hook`](#napi_add_async_cleanup_hook).
### Module registration
Node-API modules are registered in a manner similar to other modules except that instead of using the `NODE_MODULE` macro the following is used:
```
NAPI_MODULE(NODE_GYP_MODULE_NAME, Init)
```
The next difference is the signature for the `Init` method. For a Node-API module it is as follows:
```
napi_value Init(napi_env env, napi_value exports);
```
The return value from `Init` is treated as the `exports` object for the module. The `Init` method is passed an empty object via the `exports` parameter as a convenience. If `Init` returns `NULL`, the parameter passed as `exports` is exported by the module. Node-API modules cannot modify the `module` object but can specify anything as the `exports` property of the module.
To add the method `hello` as a function so that it can be called as a method provided by the addon:
```
napi_value Init(napi_env env, napi_value exports) {
napi_status status;
napi_property_descriptor desc = {
"hello",
NULL,
Method,
NULL,
NULL,
NULL,
napi_writable | napi_enumerable | napi_configurable,
NULL
};
status = napi_define_properties(env, exports, 1, &desc);
if (status != napi_ok) return NULL;
return exports;
}
```
To set a function to be returned by the `require()` for the addon:
```
napi_value Init(napi_env env, napi_value exports) {
napi_value method;
napi_status status;
status = napi_create_function(env, "exports", NAPI_AUTO_LENGTH, Method, NULL, &method);
if (status != napi_ok) return NULL;
return method;
}
```
To define a class so that new instances can be created (often used with [Object wrap](#object-wrap)):
```
// NOTE: partial example, not all referenced code is included
napi_value Init(napi_env env, napi_value exports) {
napi_status status;
napi_property_descriptor properties[] = {
{ "value", NULL, NULL, GetValue, SetValue, NULL, napi_writable | napi_configurable, NULL },
DECLARE_NAPI_METHOD("plusOne", PlusOne),
DECLARE_NAPI_METHOD("multiply", Multiply),
};
napi_value cons;
status =
napi_define_class(env, "MyObject", New, NULL, 3, properties, &cons);
if (status != napi_ok) return NULL;
status = napi_create_reference(env, cons, 1, &constructor);
if (status != napi_ok) return NULL;
status = napi_set_named_property(env, exports, "MyObject", cons);
if (status != napi_ok) return NULL;
return exports;
}
```
You can also use the `NAPI_MODULE_INIT` macro, which acts as a shorthand for `NAPI_MODULE` and defining an `Init` function:
```
NAPI_MODULE_INIT() {
napi_value answer;
napi_status result;
status = napi_create_int64(env, 42, &answer);
if (status != napi_ok) return NULL;
status = napi_set_named_property(env, exports, "answer", answer);
if (status != napi_ok) return NULL;
return exports;
}
```
All Node-API addons are context-aware, meaning they may be loaded multiple times. There are a few design considerations when declaring such a module. The documentation on [context-aware addons](addons#context-aware-addons) provides more details.
The variables `env` and `exports` will be available inside the function body following the macro invocation.
For more details on setting properties on objects, see the section on [Working with JavaScript properties](#working-with-javascript-properties).
For more details on building addon modules in general, refer to the existing API.
### Working with JavaScript values
Node-API exposes a set of APIs to create all types of JavaScript values. Some of these types are documented under [Section 6](https://tc39.github.io/ecma262/#sec-ecmascript-data-types-and-values) of the [ECMAScript Language Specification](https://tc39.github.io/ecma262/).
Fundamentally, these APIs are used to do one of the following:
1. Create a new JavaScript object
2. Convert from a primitive C type to a Node-API value
3. Convert from Node-API value to a primitive C type
4. Get global instances including `undefined` and `null`
Node-API values are represented by the type `napi_value`. Any Node-API call that requires a JavaScript value takes in a `napi_value`. In some cases, the API does check the type of the `napi_value` up-front. However, for better performance, it's better for the caller to make sure that the `napi_value` in question is of the JavaScript type expected by the API.
#### Enum types
#####
`napi_key_collection_mode`
Added in: v13.7.0, v12.17.0, v10.20.0 N-API version: 6
```
typedef enum {
napi_key_include_prototypes,
napi_key_own_only
} napi_key_collection_mode;
```
Describes the `Keys/Properties` filter enums:
`napi_key_collection_mode` limits the range of collected properties.
`napi_key_own_only` limits the collected properties to the given object only. `napi_key_include_prototypes` will include all keys of the objects's prototype chain as well.
#####
`napi_key_filter`
Added in: v13.7.0, v12.17.0, v10.20.0 N-API version: 6
```
typedef enum {
napi_key_all_properties = 0,
napi_key_writable = 1,
napi_key_enumerable = 1 << 1,
napi_key_configurable = 1 << 2,
napi_key_skip_strings = 1 << 3,
napi_key_skip_symbols = 1 << 4
} napi_key_filter;
```
Property filter bits. They can be or'ed to build a composite filter.
#####
`napi_key_conversion`
Added in: v13.7.0, v12.17.0, v10.20.0 N-API version: 6
```
typedef enum {
napi_key_keep_numbers,
napi_key_numbers_to_strings
} napi_key_conversion;
```
`napi_key_numbers_to_strings` will convert integer indices to strings. `napi_key_keep_numbers` will return numbers for integer indices.
#####
`napi_valuetype`
```
typedef enum {
// ES6 types (corresponds to typeof)
napi_undefined,
napi_null,
napi_boolean,
napi_number,
napi_string,
napi_symbol,
napi_object,
napi_function,
napi_external,
napi_bigint,
} napi_valuetype;
```
Describes the type of a `napi_value`. This generally corresponds to the types described in [Section 6.1](https://tc39.github.io/ecma262/#sec-ecmascript-language-types) of the ECMAScript Language Specification. In addition to types in that section, `napi_valuetype` can also represent `Function`s and `Object`s with external data.
A JavaScript value of type `napi_external` appears in JavaScript as a plain object such that no properties can be set on it, and no prototype.
#####
`napi_typedarray_type`
```
typedef enum {
napi_int8_array,
napi_uint8_array,
napi_uint8_clamped_array,
napi_int16_array,
napi_uint16_array,
napi_int32_array,
napi_uint32_array,
napi_float32_array,
napi_float64_array,
napi_bigint64_array,
napi_biguint64_array,
} napi_typedarray_type;
```
This represents the underlying binary scalar datatype of the `TypedArray`. Elements of this enum correspond to [Section 22.2](https://tc39.github.io/ecma262/#sec-typedarray-objects) of the [ECMAScript Language Specification](https://tc39.github.io/ecma262/).
#### Object creation functions
#####
`napi_create_array`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_array(napi_env env, napi_value* result)
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[out] result`: A `napi_value` representing a JavaScript `Array`.
Returns `napi_ok` if the API succeeded.
This API returns a Node-API value corresponding to a JavaScript `Array` type. JavaScript arrays are described in [Section 22.1](https://tc39.github.io/ecma262/#sec-array-objects) of the ECMAScript Language Specification.
#####
`napi_create_array_with_length`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_array_with_length(napi_env env,
size_t length,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] length`: The initial length of the `Array`.
* `[out] result`: A `napi_value` representing a JavaScript `Array`.
Returns `napi_ok` if the API succeeded.
This API returns a Node-API value corresponding to a JavaScript `Array` type. The `Array`'s length property is set to the passed-in length parameter. However, the underlying buffer is not guaranteed to be pre-allocated by the VM when the array is created. That behavior is left to the underlying VM implementation. If the buffer must be a contiguous block of memory that can be directly read and/or written via C, consider using [`napi_create_external_arraybuffer`](#napi_create_external_arraybuffer).
JavaScript arrays are described in [Section 22.1](https://tc39.github.io/ecma262/#sec-array-objects) of the ECMAScript Language Specification.
#####
`napi_create_arraybuffer`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_arraybuffer(napi_env env,
size_t byte_length,
void** data,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] length`: The length in bytes of the array buffer to create.
* `[out] data`: Pointer to the underlying byte buffer of the `ArrayBuffer`. `data` can optionally be ignored by passing `NULL`.
* `[out] result`: A `napi_value` representing a JavaScript `ArrayBuffer`.
Returns `napi_ok` if the API succeeded.
This API returns a Node-API value corresponding to a JavaScript `ArrayBuffer`. `ArrayBuffer`s are used to represent fixed-length binary data buffers. They are normally used as a backing-buffer for `TypedArray` objects. The `ArrayBuffer` allocated will have an underlying byte buffer whose size is determined by the `length` parameter that's passed in. The underlying buffer is optionally returned back to the caller in case the caller wants to directly manipulate the buffer. This buffer can only be written to directly from native code. To write to this buffer from JavaScript, a typed array or `DataView` object would need to be created.
JavaScript `ArrayBuffer` objects are described in [Section 24.1](https://tc39.github.io/ecma262/#sec-arraybuffer-objects) of the ECMAScript Language Specification.
#####
`napi_create_buffer`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_buffer(napi_env env,
size_t size,
void** data,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] size`: Size in bytes of the underlying buffer.
* `[out] data`: Raw pointer to the underlying buffer. `data` can optionally be ignored by passing `NULL`.
* `[out] result`: A `napi_value` representing a `node::Buffer`.
Returns `napi_ok` if the API succeeded.
This API allocates a `node::Buffer` object. While this is still a fully-supported data structure, in most cases using a `TypedArray` will suffice.
#####
`napi_create_buffer_copy`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_buffer_copy(napi_env env,
size_t length,
const void* data,
void** result_data,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] size`: Size in bytes of the input buffer (should be the same as the size of the new buffer).
* `[in] data`: Raw pointer to the underlying buffer to copy from.
* `[out] result_data`: Pointer to the new `Buffer`'s underlying data buffer. `result_data` can optionally be ignored by passing `NULL`.
* `[out] result`: A `napi_value` representing a `node::Buffer`.
Returns `napi_ok` if the API succeeded.
This API allocates a `node::Buffer` object and initializes it with data copied from the passed-in buffer. While this is still a fully-supported data structure, in most cases using a `TypedArray` will suffice.
#####
`napi_create_date`
Added in: v11.11.0, v10.17.0 N-API version: 5
```
napi_status napi_create_date(napi_env env,
double time,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] time`: ECMAScript time value in milliseconds since 01 January, 1970 UTC.
* `[out] result`: A `napi_value` representing a JavaScript `Date`.
Returns `napi_ok` if the API succeeded.
This API does not observe leap seconds; they are ignored, as ECMAScript aligns with POSIX time specification.
This API allocates a JavaScript `Date` object.
JavaScript `Date` objects are described in [Section 20.3](https://tc39.github.io/ecma262/#sec-date-objects) of the ECMAScript Language Specification.
#####
`napi_create_external`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_external(napi_env env,
void* data,
napi_finalize finalize_cb,
void* finalize_hint,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] data`: Raw pointer to the external data.
* `[in] finalize_cb`: Optional callback to call when the external value is being collected. [`napi_finalize`](#napi_finalize) provides more details.
* `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection.
* `[out] result`: A `napi_value` representing an external value.
Returns `napi_ok` if the API succeeded.
This API allocates a JavaScript value with external data attached to it. This is used to pass external data through JavaScript code, so it can be retrieved later by native code using [`napi_get_value_external`](#napi_get_value_external).
The API adds a `napi_finalize` callback which will be called when the JavaScript object just created is ready for garbage collection. It is similar to `napi_wrap()` except that:
* the native data cannot be retrieved later using `napi_unwrap()`,
* nor can it be removed later using `napi_remove_wrap()`, and
* the object created by the API can be used with `napi_wrap()`.
The created value is not an object, and therefore does not support additional properties. It is considered a distinct value type: calling `napi_typeof()` with an external value yields `napi_external`.
#####
`napi_create_external_arraybuffer`
Added in: v8.0.0 N-API version: 1
```
napi_status
napi_create_external_arraybuffer(napi_env env,
void* external_data,
size_t byte_length,
napi_finalize finalize_cb,
void* finalize_hint,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] external_data`: Pointer to the underlying byte buffer of the `ArrayBuffer`.
* `[in] byte_length`: The length in bytes of the underlying buffer.
* `[in] finalize_cb`: Optional callback to call when the `ArrayBuffer` is being collected. [`napi_finalize`](#napi_finalize) provides more details.
* `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection.
* `[out] result`: A `napi_value` representing a JavaScript `ArrayBuffer`.
Returns `napi_ok` if the API succeeded.
This API returns a Node-API value corresponding to a JavaScript `ArrayBuffer`. The underlying byte buffer of the `ArrayBuffer` is externally allocated and managed. The caller must ensure that the byte buffer remains valid until the finalize callback is called.
The API adds a `napi_finalize` callback which will be called when the JavaScript object just created is ready for garbage collection. It is similar to `napi_wrap()` except that:
* the native data cannot be retrieved later using `napi_unwrap()`,
* nor can it be removed later using `napi_remove_wrap()`, and
* the object created by the API can be used with `napi_wrap()`.
JavaScript `ArrayBuffer`s are described in [Section 24.1](https://tc39.github.io/ecma262/#sec-arraybuffer-objects) of the ECMAScript Language Specification.
#####
`napi_create_external_buffer`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_external_buffer(napi_env env,
size_t length,
void* data,
napi_finalize finalize_cb,
void* finalize_hint,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] length`: Size in bytes of the input buffer (should be the same as the size of the new buffer).
* `[in] data`: Raw pointer to the underlying buffer to expose to JavaScript.
* `[in] finalize_cb`: Optional callback to call when the `ArrayBuffer` is being collected. [`napi_finalize`](#napi_finalize) provides more details.
* `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection.
* `[out] result`: A `napi_value` representing a `node::Buffer`.
Returns `napi_ok` if the API succeeded.
This API allocates a `node::Buffer` object and initializes it with data backed by the passed in buffer. While this is still a fully-supported data structure, in most cases using a `TypedArray` will suffice.
The API adds a `napi_finalize` callback which will be called when the JavaScript object just created is ready for garbage collection. It is similar to `napi_wrap()` except that:
* the native data cannot be retrieved later using `napi_unwrap()`,
* nor can it be removed later using `napi_remove_wrap()`, and
* the object created by the API can be used with `napi_wrap()`.
For Node.js >=4 `Buffers` are `Uint8Array`s.
#####
`napi_create_object`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_object(napi_env env, napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: A `napi_value` representing a JavaScript `Object`.
Returns `napi_ok` if the API succeeded.
This API allocates a default JavaScript `Object`. It is the equivalent of doing `new Object()` in JavaScript.
The JavaScript `Object` type is described in [Section 6.1.7](https://tc39.github.io/ecma262/#sec-object-type) of the ECMAScript Language Specification.
#####
`napi_create_symbol`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_symbol(napi_env env,
napi_value description,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] description`: Optional `napi_value` which refers to a JavaScript `string` to be set as the description for the symbol.
* `[out] result`: A `napi_value` representing a JavaScript `symbol`.
Returns `napi_ok` if the API succeeded.
This API creates a JavaScript `symbol` value from a UTF8-encoded C string.
The JavaScript `symbol` type is described in [Section 19.4](https://tc39.github.io/ecma262/#sec-symbol-objects) of the ECMAScript Language Specification.
#####
`node_api_symbol_for`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
```
napi_status node_api_symbol_for(napi_env env,
const char* utf8description,
size_t length,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] utf8description`: UTF-8 C string representing the text to be used as the description for the symbol.
* `[in] length`: The length of the description string in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated.
* `[out] result`: A `napi_value` representing a JavaScript `symbol`.
Returns `napi_ok` if the API succeeded.
This API searches in the global registry for an existing symbol with the given description. If the symbol already exists it will be returned, otherwise a new symbol will be created in the registry.
The JavaScript `symbol` type is described in [Section 19.4](https://tc39.github.io/ecma262/#sec-symbol-objects) of the ECMAScript Language Specification.
#####
`napi_create_typedarray`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_typedarray(napi_env env,
napi_typedarray_type type,
size_t length,
napi_value arraybuffer,
size_t byte_offset,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] type`: Scalar datatype of the elements within the `TypedArray`.
* `[in] length`: Number of elements in the `TypedArray`.
* `[in] arraybuffer`: `ArrayBuffer` underlying the typed array.
* `[in] byte_offset`: The byte offset within the `ArrayBuffer` from which to start projecting the `TypedArray`.
* `[out] result`: A `napi_value` representing a JavaScript `TypedArray`.
Returns `napi_ok` if the API succeeded.
This API creates a JavaScript `TypedArray` object over an existing `ArrayBuffer`. `TypedArray` objects provide an array-like view over an underlying data buffer where each element has the same underlying binary scalar datatype.
It's required that `(length * size_of_element) + byte_offset` should be <= the size in bytes of the array passed in. If not, a `RangeError` exception is raised.
JavaScript `TypedArray` objects are described in [Section 22.2](https://tc39.github.io/ecma262/#sec-typedarray-objects) of the ECMAScript Language Specification.
#####
`napi_create_dataview`
Added in: v8.3.0 N-API version: 1
```
napi_status napi_create_dataview(napi_env env,
size_t byte_length,
napi_value arraybuffer,
size_t byte_offset,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] length`: Number of elements in the `DataView`.
* `[in] arraybuffer`: `ArrayBuffer` underlying the `DataView`.
* `[in] byte_offset`: The byte offset within the `ArrayBuffer` from which to start projecting the `DataView`.
* `[out] result`: A `napi_value` representing a JavaScript `DataView`.
Returns `napi_ok` if the API succeeded.
This API creates a JavaScript `DataView` object over an existing `ArrayBuffer`. `DataView` objects provide an array-like view over an underlying data buffer, but one which allows items of different size and type in the `ArrayBuffer`.
It is required that `byte_length + byte_offset` is less than or equal to the size in bytes of the array passed in. If not, a `RangeError` exception is raised.
JavaScript `DataView` objects are described in [Section 24.3](https://tc39.github.io/ecma262/#sec-dataview-objects) of the ECMAScript Language Specification.
#### Functions to convert from C types to Node-API
#####
`napi_create_int32`
Added in: v8.4.0 N-API version: 1
```
napi_status napi_create_int32(napi_env env, int32_t value, napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: Integer value to be represented in JavaScript.
* `[out] result`: A `napi_value` representing a JavaScript `number`.
Returns `napi_ok` if the API succeeded.
This API is used to convert from the C `int32_t` type to the JavaScript `number` type.
The JavaScript `number` type is described in [Section 6.1.6](https://tc39.github.io/ecma262/#sec-ecmascript-language-types-number-type) of the ECMAScript Language Specification.
#####
`napi_create_uint32`
Added in: v8.4.0 N-API version: 1
```
napi_status napi_create_uint32(napi_env env, uint32_t value, napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: Unsigned integer value to be represented in JavaScript.
* `[out] result`: A `napi_value` representing a JavaScript `number`.
Returns `napi_ok` if the API succeeded.
This API is used to convert from the C `uint32_t` type to the JavaScript `number` type.
The JavaScript `number` type is described in [Section 6.1.6](https://tc39.github.io/ecma262/#sec-ecmascript-language-types-number-type) of the ECMAScript Language Specification.
#####
`napi_create_int64`
Added in: v8.4.0 N-API version: 1
```
napi_status napi_create_int64(napi_env env, int64_t value, napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: Integer value to be represented in JavaScript.
* `[out] result`: A `napi_value` representing a JavaScript `number`.
Returns `napi_ok` if the API succeeded.
This API is used to convert from the C `int64_t` type to the JavaScript `number` type.
The JavaScript `number` type is described in [Section 6.1.6](https://tc39.github.io/ecma262/#sec-ecmascript-language-types-number-type) of the ECMAScript Language Specification. Note the complete range of `int64_t` cannot be represented with full precision in JavaScript. Integer values outside the range of [`Number.MIN_SAFE_INTEGER`](https://tc39.github.io/ecma262/#sec-number.min_safe_integer) `-(2**53 - 1)` - [`Number.MAX_SAFE_INTEGER`](https://tc39.github.io/ecma262/#sec-number.max_safe_integer) `(2**53 - 1)` will lose precision.
#####
`napi_create_double`
Added in: v8.4.0 N-API version: 1
```
napi_status napi_create_double(napi_env env, double value, napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: Double-precision value to be represented in JavaScript.
* `[out] result`: A `napi_value` representing a JavaScript `number`.
Returns `napi_ok` if the API succeeded.
This API is used to convert from the C `double` type to the JavaScript `number` type.
The JavaScript `number` type is described in [Section 6.1.6](https://tc39.github.io/ecma262/#sec-ecmascript-language-types-number-type) of the ECMAScript Language Specification.
#####
`napi_create_bigint_int64`
Added in: v10.7.0 N-API version: 6
```
napi_status napi_create_bigint_int64(napi_env env,
int64_t value,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: Integer value to be represented in JavaScript.
* `[out] result`: A `napi_value` representing a JavaScript `BigInt`.
Returns `napi_ok` if the API succeeded.
This API converts the C `int64_t` type to the JavaScript `BigInt` type.
#####
`napi_create_bigint_uint64`
Added in: v10.7.0 N-API version: 6
```
napi_status napi_create_bigint_uint64(napi_env env,
uint64_t value,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: Unsigned integer value to be represented in JavaScript.
* `[out] result`: A `napi_value` representing a JavaScript `BigInt`.
Returns `napi_ok` if the API succeeded.
This API converts the C `uint64_t` type to the JavaScript `BigInt` type.
#####
`napi_create_bigint_words`
Added in: v10.7.0 N-API version: 6
```
napi_status napi_create_bigint_words(napi_env env,
int sign_bit,
size_t word_count,
const uint64_t* words,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] sign_bit`: Determines if the resulting `BigInt` will be positive or negative.
* `[in] word_count`: The length of the `words` array.
* `[in] words`: An array of `uint64_t` little-endian 64-bit words.
* `[out] result`: A `napi_value` representing a JavaScript `BigInt`.
Returns `napi_ok` if the API succeeded.
This API converts an array of unsigned 64-bit words into a single `BigInt` value.
The resulting `BigInt` is calculated as: (–1)`sign_bit` (`words[0]` × (264)0 + `words[1]` × (264)1 + …)
#####
`napi_create_string_latin1`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_string_latin1(napi_env env,
const char* str,
size_t length,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] str`: Character buffer representing an ISO-8859-1-encoded string.
* `[in] length`: The length of the string in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated.
* `[out] result`: A `napi_value` representing a JavaScript `string`.
Returns `napi_ok` if the API succeeded.
This API creates a JavaScript `string` value from an ISO-8859-1-encoded C string. The native string is copied.
The JavaScript `string` type is described in [Section 6.1.4](https://tc39.github.io/ecma262/#sec-ecmascript-language-types-string-type) of the ECMAScript Language Specification.
#####
`napi_create_string_utf16`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_string_utf16(napi_env env,
const char16_t* str,
size_t length,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] str`: Character buffer representing a UTF16-LE-encoded string.
* `[in] length`: The length of the string in two-byte code units, or `NAPI_AUTO_LENGTH` if it is null-terminated.
* `[out] result`: A `napi_value` representing a JavaScript `string`.
Returns `napi_ok` if the API succeeded.
This API creates a JavaScript `string` value from a UTF16-LE-encoded C string. The native string is copied.
The JavaScript `string` type is described in [Section 6.1.4](https://tc39.github.io/ecma262/#sec-ecmascript-language-types-string-type) of the ECMAScript Language Specification.
#####
`napi_create_string_utf8`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_string_utf8(napi_env env,
const char* str,
size_t length,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] str`: Character buffer representing a UTF8-encoded string.
* `[in] length`: The length of the string in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated.
* `[out] result`: A `napi_value` representing a JavaScript `string`.
Returns `napi_ok` if the API succeeded.
This API creates a JavaScript `string` value from a UTF8-encoded C string. The native string is copied.
The JavaScript `string` type is described in [Section 6.1.4](https://tc39.github.io/ecma262/#sec-ecmascript-language-types-string-type) of the ECMAScript Language Specification.
#### Functions to convert from Node-API to C types
#####
`napi_get_array_length`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_array_length(napi_env env,
napi_value value,
uint32_t* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing the JavaScript `Array` whose length is being queried.
* `[out] result`: `uint32` representing length of the array.
Returns `napi_ok` if the API succeeded.
This API returns the length of an array.
`Array` length is described in [Section 22.1.4.1](https://tc39.github.io/ecma262/#sec-properties-of-array-instances-length) of the ECMAScript Language Specification.
#####
`napi_get_arraybuffer_info`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_arraybuffer_info(napi_env env,
napi_value arraybuffer,
void** data,
size_t* byte_length)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] arraybuffer`: `napi_value` representing the `ArrayBuffer` being queried.
* `[out] data`: The underlying data buffer of the `ArrayBuffer`. If byte\_length is `0`, this may be `NULL` or any other pointer value.
* `[out] byte_length`: Length in bytes of the underlying data buffer.
Returns `napi_ok` if the API succeeded.
This API is used to retrieve the underlying data buffer of an `ArrayBuffer` and its length.
*WARNING*: Use caution while using this API. The lifetime of the underlying data buffer is managed by the `ArrayBuffer` even after it's returned. A possible safe way to use this API is in conjunction with [`napi_create_reference`](#napi_create_reference), which can be used to guarantee control over the lifetime of the `ArrayBuffer`. It's also safe to use the returned data buffer within the same callback as long as there are no calls to other APIs that might trigger a GC.
#####
`napi_get_buffer_info`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_buffer_info(napi_env env,
napi_value value,
void** data,
size_t* length)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing the `node::Buffer` being queried.
* `[out] data`: The underlying data buffer of the `node::Buffer`. If length is `0`, this may be `NULL` or any other pointer value.
* `[out] length`: Length in bytes of the underlying data buffer.
Returns `napi_ok` if the API succeeded.
This API is used to retrieve the underlying data buffer of a `node::Buffer` and its length.
*Warning*: Use caution while using this API since the underlying data buffer's lifetime is not guaranteed if it's managed by the VM.
#####
`napi_get_prototype`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_prototype(napi_env env,
napi_value object,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] object`: `napi_value` representing JavaScript `Object` whose prototype to return. This returns the equivalent of `Object.getPrototypeOf` (which is not the same as the function's `prototype` property).
* `[out] result`: `napi_value` representing prototype of the given object.
Returns `napi_ok` if the API succeeded.
#####
`napi_get_typedarray_info`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_typedarray_info(napi_env env,
napi_value typedarray,
napi_typedarray_type* type,
size_t* length,
void** data,
napi_value* arraybuffer,
size_t* byte_offset)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] typedarray`: `napi_value` representing the `TypedArray` whose properties to query.
* `[out] type`: Scalar datatype of the elements within the `TypedArray`.
* `[out] length`: The number of elements in the `TypedArray`.
* `[out] data`: The data buffer underlying the `TypedArray` adjusted by the `byte_offset` value so that it points to the first element in the `TypedArray`. If the length of the array is `0`, this may be `NULL` or any other pointer value.
* `[out] arraybuffer`: The `ArrayBuffer` underlying the `TypedArray`.
* `[out] byte_offset`: The byte offset within the underlying native array at which the first element of the arrays is located. The value for the data parameter has already been adjusted so that data points to the first element in the array. Therefore, the first byte of the native array would be at `data - byte_offset`.
Returns `napi_ok` if the API succeeded.
This API returns various properties of a typed array.
Any of the out parameters may be `NULL` if that property is unneeded.
*Warning*: Use caution while using this API since the underlying data buffer is managed by the VM.
#####
`napi_get_dataview_info`
Added in: v8.3.0 N-API version: 1
```
napi_status napi_get_dataview_info(napi_env env,
napi_value dataview,
size_t* byte_length,
void** data,
napi_value* arraybuffer,
size_t* byte_offset)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] dataview`: `napi_value` representing the `DataView` whose properties to query.
* `[out] byte_length`: Number of bytes in the `DataView`.
* `[out] data`: The data buffer underlying the `DataView`. If byte\_length is `0`, this may be `NULL` or any other pointer value.
* `[out] arraybuffer`: `ArrayBuffer` underlying the `DataView`.
* `[out] byte_offset`: The byte offset within the data buffer from which to start projecting the `DataView`.
Returns `napi_ok` if the API succeeded.
Any of the out parameters may be `NULL` if that property is unneeded.
This API returns various properties of a `DataView`.
#####
`napi_get_date_value`
Added in: v11.11.0, v10.17.0 N-API version: 5
```
napi_status napi_get_date_value(napi_env env,
napi_value value,
double* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing a JavaScript `Date`.
* `[out] result`: Time value as a `double` represented as milliseconds since midnight at the beginning of 01 January, 1970 UTC.
This API does not observe leap seconds; they are ignored, as ECMAScript aligns with POSIX time specification.
Returns `napi_ok` if the API succeeded. If a non-date `napi_value` is passed in it returns `napi_date_expected`.
This API returns the C double primitive of time value for the given JavaScript `Date`.
#####
`napi_get_value_bool`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_value_bool(napi_env env, napi_value value, bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript `Boolean`.
* `[out] result`: C boolean primitive equivalent of the given JavaScript `Boolean`.
Returns `napi_ok` if the API succeeded. If a non-boolean `napi_value` is passed in it returns `napi_boolean_expected`.
This API returns the C boolean primitive equivalent of the given JavaScript `Boolean`.
#####
`napi_get_value_double`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_value_double(napi_env env,
napi_value value,
double* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript `number`.
* `[out] result`: C double primitive equivalent of the given JavaScript `number`.
Returns `napi_ok` if the API succeeded. If a non-number `napi_value` is passed in it returns `napi_number_expected`.
This API returns the C double primitive equivalent of the given JavaScript `number`.
#####
`napi_get_value_bigint_int64`
Added in: v10.7.0 N-API version: 6
```
napi_status napi_get_value_bigint_int64(napi_env env,
napi_value value,
int64_t* result,
bool* lossless);
```
* `[in] env`: The environment that the API is invoked under
* `[in] value`: `napi_value` representing JavaScript `BigInt`.
* `[out] result`: C `int64_t` primitive equivalent of the given JavaScript `BigInt`.
* `[out] lossless`: Indicates whether the `BigInt` value was converted losslessly.
Returns `napi_ok` if the API succeeded. If a non-`BigInt` is passed in it returns `napi_bigint_expected`.
This API returns the C `int64_t` primitive equivalent of the given JavaScript `BigInt`. If needed it will truncate the value, setting `lossless` to `false`.
#####
`napi_get_value_bigint_uint64`
Added in: v10.7.0 N-API version: 6
```
napi_status napi_get_value_bigint_uint64(napi_env env,
napi_value value,
uint64_t* result,
bool* lossless);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript `BigInt`.
* `[out] result`: C `uint64_t` primitive equivalent of the given JavaScript `BigInt`.
* `[out] lossless`: Indicates whether the `BigInt` value was converted losslessly.
Returns `napi_ok` if the API succeeded. If a non-`BigInt` is passed in it returns `napi_bigint_expected`.
This API returns the C `uint64_t` primitive equivalent of the given JavaScript `BigInt`. If needed it will truncate the value, setting `lossless` to `false`.
#####
`napi_get_value_bigint_words`
Added in: v10.7.0 N-API version: 6
```
napi_status napi_get_value_bigint_words(napi_env env,
napi_value value,
int* sign_bit,
size_t* word_count,
uint64_t* words);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript `BigInt`.
* `[out] sign_bit`: Integer representing if the JavaScript `BigInt` is positive or negative.
* `[in/out] word_count`: Must be initialized to the length of the `words` array. Upon return, it will be set to the actual number of words that would be needed to store this `BigInt`.
* `[out] words`: Pointer to a pre-allocated 64-bit word array.
Returns `napi_ok` if the API succeeded.
This API converts a single `BigInt` value into a sign bit, 64-bit little-endian array, and the number of elements in the array. `sign_bit` and `words` may be both set to `NULL`, in order to get only `word_count`.
#####
`napi_get_value_external`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_value_external(napi_env env,
napi_value value,
void** result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript external value.
* `[out] result`: Pointer to the data wrapped by the JavaScript external value.
Returns `napi_ok` if the API succeeded. If a non-external `napi_value` is passed in it returns `napi_invalid_arg`.
This API retrieves the external data pointer that was previously passed to `napi_create_external()`.
#####
`napi_get_value_int32`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_value_int32(napi_env env,
napi_value value,
int32_t* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript `number`.
* `[out] result`: C `int32` primitive equivalent of the given JavaScript `number`.
Returns `napi_ok` if the API succeeded. If a non-number `napi_value` is passed in `napi_number_expected`.
This API returns the C `int32` primitive equivalent of the given JavaScript `number`.
If the number exceeds the range of the 32 bit integer, then the result is truncated to the equivalent of the bottom 32 bits. This can result in a large positive number becoming a negative number if the value is > 231 - 1.
Non-finite number values (`NaN`, `+Infinity`, or `-Infinity`) set the result to zero.
#####
`napi_get_value_int64`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_value_int64(napi_env env,
napi_value value,
int64_t* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript `number`.
* `[out] result`: C `int64` primitive equivalent of the given JavaScript `number`.
Returns `napi_ok` if the API succeeded. If a non-number `napi_value` is passed in it returns `napi_number_expected`.
This API returns the C `int64` primitive equivalent of the given JavaScript `number`.
`number` values outside the range of [`Number.MIN_SAFE_INTEGER`](https://tc39.github.io/ecma262/#sec-number.min_safe_integer) `-(2**53 - 1)` - [`Number.MAX_SAFE_INTEGER`](https://tc39.github.io/ecma262/#sec-number.max_safe_integer) `(2**53 - 1)` will lose precision.
Non-finite number values (`NaN`, `+Infinity`, or `-Infinity`) set the result to zero.
#####
`napi_get_value_string_latin1`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_value_string_latin1(napi_env env,
napi_value value,
char* buf,
size_t bufsize,
size_t* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript string.
* `[in] buf`: Buffer to write the ISO-8859-1-encoded string into. If `NULL` is passed in, the length of the string in bytes and excluding the null terminator is returned in `result`.
* `[in] bufsize`: Size of the destination buffer. When this value is insufficient, the returned string is truncated and null-terminated.
* `[out] result`: Number of bytes copied into the buffer, excluding the null terminator.
Returns `napi_ok` if the API succeeded. If a non-`string` `napi_value` is passed in it returns `napi_string_expected`.
This API returns the ISO-8859-1-encoded string corresponding the value passed in.
#####
`napi_get_value_string_utf8`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_value_string_utf8(napi_env env,
napi_value value,
char* buf,
size_t bufsize,
size_t* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript string.
* `[in] buf`: Buffer to write the UTF8-encoded string into. If `NULL` is passed in, the length of the string in bytes and excluding the null terminator is returned in `result`.
* `[in] bufsize`: Size of the destination buffer. When this value is insufficient, the returned string is truncated and null-terminated.
* `[out] result`: Number of bytes copied into the buffer, excluding the null terminator.
Returns `napi_ok` if the API succeeded. If a non-`string` `napi_value` is passed in it returns `napi_string_expected`.
This API returns the UTF8-encoded string corresponding the value passed in.
#####
`napi_get_value_string_utf16`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_value_string_utf16(napi_env env,
napi_value value,
char16_t* buf,
size_t bufsize,
size_t* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript string.
* `[in] buf`: Buffer to write the UTF16-LE-encoded string into. If `NULL` is passed in, the length of the string in 2-byte code units and excluding the null terminator is returned.
* `[in] bufsize`: Size of the destination buffer. When this value is insufficient, the returned string is truncated and null-terminated.
* `[out] result`: Number of 2-byte code units copied into the buffer, excluding the null terminator.
Returns `napi_ok` if the API succeeded. If a non-`string` `napi_value` is passed in it returns `napi_string_expected`.
This API returns the UTF16-encoded string corresponding the value passed in.
#####
`napi_get_value_uint32`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_value_uint32(napi_env env,
napi_value value,
uint32_t* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: `napi_value` representing JavaScript `number`.
* `[out] result`: C primitive equivalent of the given `napi_value` as a `uint32_t`.
Returns `napi_ok` if the API succeeded. If a non-number `napi_value` is passed in it returns `napi_number_expected`.
This API returns the C primitive equivalent of the given `napi_value` as a `uint32_t`.
#### Functions to get global instances
#####
`napi_get_boolean`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_boolean(napi_env env, bool value, napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The value of the boolean to retrieve.
* `[out] result`: `napi_value` representing JavaScript `Boolean` singleton to retrieve.
Returns `napi_ok` if the API succeeded.
This API is used to return the JavaScript singleton object that is used to represent the given boolean value.
#####
`napi_get_global`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_global(napi_env env, napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: `napi_value` representing JavaScript `global` object.
Returns `napi_ok` if the API succeeded.
This API returns the `global` object.
#####
`napi_get_null`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_null(napi_env env, napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: `napi_value` representing JavaScript `null` object.
Returns `napi_ok` if the API succeeded.
This API returns the `null` object.
#####
`napi_get_undefined`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_undefined(napi_env env, napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: `napi_value` representing JavaScript Undefined value.
Returns `napi_ok` if the API succeeded.
This API returns the Undefined object.
### Working with JavaScript values and abstract operations
Node-API exposes a set of APIs to perform some abstract operations on JavaScript values. Some of these operations are documented under [Section 7](https://tc39.github.io/ecma262/#sec-abstract-operations) of the [ECMAScript Language Specification](https://tc39.github.io/ecma262/).
These APIs support doing one of the following:
1. Coerce JavaScript values to specific JavaScript types (such as `number` or `string`).
2. Check the type of a JavaScript value.
3. Check for equality between two JavaScript values.
####
`napi_coerce_to_bool`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_coerce_to_bool(napi_env env,
napi_value value,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to coerce.
* `[out] result`: `napi_value` representing the coerced JavaScript `Boolean`.
Returns `napi_ok` if the API succeeded.
This API implements the abstract operation `ToBoolean()` as defined in [Section 7.1.2](https://tc39.github.io/ecma262/#sec-toboolean) of the ECMAScript Language Specification.
####
`napi_coerce_to_number`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_coerce_to_number(napi_env env,
napi_value value,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to coerce.
* `[out] result`: `napi_value` representing the coerced JavaScript `number`.
Returns `napi_ok` if the API succeeded.
This API implements the abstract operation `ToNumber()` as defined in [Section 7.1.3](https://tc39.github.io/ecma262/#sec-tonumber) of the ECMAScript Language Specification. This function potentially runs JS code if the passed-in value is an object.
####
`napi_coerce_to_object`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_coerce_to_object(napi_env env,
napi_value value,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to coerce.
* `[out] result`: `napi_value` representing the coerced JavaScript `Object`.
Returns `napi_ok` if the API succeeded.
This API implements the abstract operation `ToObject()` as defined in [Section 7.1.13](https://tc39.github.io/ecma262/#sec-toobject) of the ECMAScript Language Specification.
####
`napi_coerce_to_string`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_coerce_to_string(napi_env env,
napi_value value,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to coerce.
* `[out] result`: `napi_value` representing the coerced JavaScript `string`.
Returns `napi_ok` if the API succeeded.
This API implements the abstract operation `ToString()` as defined in [Section 7.1.13](https://tc39.github.io/ecma262/#sec-toobject) of the ECMAScript Language Specification. This function potentially runs JS code if the passed-in value is an object.
####
`napi_typeof`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_typeof(napi_env env, napi_value value, napi_valuetype* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value whose type to query.
* `[out] result`: The type of the JavaScript value.
Returns `napi_ok` if the API succeeded.
* `napi_invalid_arg` if the type of `value` is not a known ECMAScript type and `value` is not an External value.
This API represents behavior similar to invoking the `typeof` Operator on the object as defined in [Section 12.5.5](https://tc39.github.io/ecma262/#sec-typeof-operator) of the ECMAScript Language Specification. However, there are some differences:
1. It has support for detecting an External value.
2. It detects `null` as a separate type, while ECMAScript `typeof` would detect `object`.
If `value` has a type that is invalid, an error is returned.
####
`napi_instanceof`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_instanceof(napi_env env,
napi_value object,
napi_value constructor,
bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] object`: The JavaScript value to check.
* `[in] constructor`: The JavaScript function object of the constructor function to check against.
* `[out] result`: Boolean that is set to true if `object instanceof constructor` is true.
Returns `napi_ok` if the API succeeded.
This API represents invoking the `instanceof` Operator on the object as defined in [Section 12.10.4](https://tc39.github.io/ecma262/#sec-instanceofoperator) of the ECMAScript Language Specification.
####
`napi_is_array`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_is_array(napi_env env, napi_value value, bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to check.
* `[out] result`: Whether the given object is an array.
Returns `napi_ok` if the API succeeded.
This API represents invoking the `IsArray` operation on the object as defined in [Section 7.2.2](https://tc39.github.io/ecma262/#sec-isarray) of the ECMAScript Language Specification.
####
`napi_is_arraybuffer`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_is_arraybuffer(napi_env env, napi_value value, bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to check.
* `[out] result`: Whether the given object is an `ArrayBuffer`.
Returns `napi_ok` if the API succeeded.
This API checks if the `Object` passed in is an array buffer.
####
`napi_is_buffer`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_is_buffer(napi_env env, napi_value value, bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to check.
* `[out] result`: Whether the given `napi_value` represents a `node::Buffer` object.
Returns `napi_ok` if the API succeeded.
This API checks if the `Object` passed in is a buffer.
####
`napi_is_date`
Added in: v11.11.0, v10.17.0 N-API version: 5
```
napi_status napi_is_date(napi_env env, napi_value value, bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to check.
* `[out] result`: Whether the given `napi_value` represents a JavaScript `Date` object.
Returns `napi_ok` if the API succeeded.
This API checks if the `Object` passed in is a date.
####
`napi_is_error`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_is_error(napi_env env, napi_value value, bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to check.
* `[out] result`: Whether the given `napi_value` represents an `Error` object.
Returns `napi_ok` if the API succeeded.
This API checks if the `Object` passed in is an `Error`.
####
`napi_is_typedarray`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_is_typedarray(napi_env env, napi_value value, bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to check.
* `[out] result`: Whether the given `napi_value` represents a `TypedArray`.
Returns `napi_ok` if the API succeeded.
This API checks if the `Object` passed in is a typed array.
####
`napi_is_dataview`
Added in: v8.3.0 N-API version: 1
```
napi_status napi_is_dataview(napi_env env, napi_value value, bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The JavaScript value to check.
* `[out] result`: Whether the given `napi_value` represents a `DataView`.
Returns `napi_ok` if the API succeeded.
This API checks if the `Object` passed in is a `DataView`.
####
`napi_strict_equals`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_strict_equals(napi_env env,
napi_value lhs,
napi_value rhs,
bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] lhs`: The JavaScript value to check.
* `[in] rhs`: The JavaScript value to check against.
* `[out] result`: Whether the two `napi_value` objects are equal.
Returns `napi_ok` if the API succeeded.
This API represents the invocation of the Strict Equality algorithm as defined in [Section 7.2.14](https://tc39.github.io/ecma262/#sec-strict-equality-comparison) of the ECMAScript Language Specification.
####
`napi_detach_arraybuffer`
Added in: v13.0.0, v12.16.0, v10.22.0 N-API version: 7
```
napi_status napi_detach_arraybuffer(napi_env env,
napi_value arraybuffer)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] arraybuffer`: The JavaScript `ArrayBuffer` to be detached.
Returns `napi_ok` if the API succeeded. If a non-detachable `ArrayBuffer` is passed in it returns `napi_detachable_arraybuffer_expected`.
Generally, an `ArrayBuffer` is non-detachable if it has been detached before. The engine may impose additional conditions on whether an `ArrayBuffer` is detachable. For example, V8 requires that the `ArrayBuffer` be external, that is, created with [`napi_create_external_arraybuffer`](#napi_create_external_arraybuffer).
This API represents the invocation of the `ArrayBuffer` detach operation as defined in [Section 24.1.1.3](https://tc39.es/ecma262/#sec-detacharraybuffer) of the ECMAScript Language Specification.
####
`napi_is_detached_arraybuffer`
Added in: v13.3.0, v12.16.0, v10.22.0 N-API version: 7
```
napi_status napi_is_detached_arraybuffer(napi_env env,
napi_value arraybuffer,
bool* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] arraybuffer`: The JavaScript `ArrayBuffer` to be checked.
* `[out] result`: Whether the `arraybuffer` is detached.
Returns `napi_ok` if the API succeeded.
The `ArrayBuffer` is considered detached if its internal data is `null`.
This API represents the invocation of the `ArrayBuffer` `IsDetachedBuffer` operation as defined in [Section 24.1.1.2](https://tc39.es/ecma262/#sec-isdetachedbuffer) of the ECMAScript Language Specification.
### Working with JavaScript properties
Node-API exposes a set of APIs to get and set properties on JavaScript objects. Some of these types are documented under [Section 7](https://tc39.github.io/ecma262/#sec-abstract-operations) of the [ECMAScript Language Specification](https://tc39.github.io/ecma262/).
Properties in JavaScript are represented as a tuple of a key and a value. Fundamentally, all property keys in Node-API can be represented in one of the following forms:
* Named: a simple UTF8-encoded string
* Integer-Indexed: an index value represented by `uint32_t`
* JavaScript value: these are represented in Node-API by `napi_value`. This can be a `napi_value` representing a `string`, `number`, or `symbol`.
Node-API values are represented by the type `napi_value`. Any Node-API call that requires a JavaScript value takes in a `napi_value`. However, it's the caller's responsibility to make sure that the `napi_value` in question is of the JavaScript type expected by the API.
The APIs documented in this section provide a simple interface to get and set properties on arbitrary JavaScript objects represented by `napi_value`.
For instance, consider the following JavaScript code snippet:
```
const obj = {};
obj.myProp = 123;
```
The equivalent can be done using Node-API values with the following snippet:
```
napi_status status = napi_generic_failure;
// const obj = {}
napi_value obj, value;
status = napi_create_object(env, &obj);
if (status != napi_ok) return status;
// Create a napi_value for 123
status = napi_create_int32(env, 123, &value);
if (status != napi_ok) return status;
// obj.myProp = 123
status = napi_set_named_property(env, obj, "myProp", value);
if (status != napi_ok) return status;
```
Indexed properties can be set in a similar manner. Consider the following JavaScript snippet:
```
const arr = [];
arr[123] = 'hello';
```
The equivalent can be done using Node-API values with the following snippet:
```
napi_status status = napi_generic_failure;
// const arr = [];
napi_value arr, value;
status = napi_create_array(env, &arr);
if (status != napi_ok) return status;
// Create a napi_value for 'hello'
status = napi_create_string_utf8(env, "hello", NAPI_AUTO_LENGTH, &value);
if (status != napi_ok) return status;
// arr[123] = 'hello';
status = napi_set_element(env, arr, 123, value);
if (status != napi_ok) return status;
```
Properties can be retrieved using the APIs described in this section. Consider the following JavaScript snippet:
```
const arr = [];
const value = arr[123];
```
The following is the approximate equivalent of the Node-API counterpart:
```
napi_status status = napi_generic_failure;
// const arr = []
napi_value arr, value;
status = napi_create_array(env, &arr);
if (status != napi_ok) return status;
// const value = arr[123]
status = napi_get_element(env, arr, 123, &value);
if (status != napi_ok) return status;
```
Finally, multiple properties can also be defined on an object for performance reasons. Consider the following JavaScript:
```
const obj = {};
Object.defineProperties(obj, {
'foo': { value: 123, writable: true, configurable: true, enumerable: true },
'bar': { value: 456, writable: true, configurable: true, enumerable: true }
});
```
The following is the approximate equivalent of the Node-API counterpart:
```
napi_status status = napi_status_generic_failure;
// const obj = {};
napi_value obj;
status = napi_create_object(env, &obj);
if (status != napi_ok) return status;
// Create napi_values for 123 and 456
napi_value fooValue, barValue;
status = napi_create_int32(env, 123, &fooValue);
if (status != napi_ok) return status;
status = napi_create_int32(env, 456, &barValue);
if (status != napi_ok) return status;
// Set the properties
napi_property_descriptor descriptors[] = {
{ "foo", NULL, NULL, NULL, NULL, fooValue, napi_writable | napi_configurable, NULL },
{ "bar", NULL, NULL, NULL, NULL, barValue, napi_writable | napi_configurable, NULL }
}
status = napi_define_properties(env,
obj,
sizeof(descriptors) / sizeof(descriptors[0]),
descriptors);
if (status != napi_ok) return status;
```
#### Structures
#####
`napi_property_attributes`
History
| Version | Changes |
| --- | --- |
| v14.12.0 | added `napi_default_method` and `napi_default_property`. |
```
typedef enum {
napi_default = 0,
napi_writable = 1 << 0,
napi_enumerable = 1 << 1,
napi_configurable = 1 << 2,
// Used with napi_define_class to distinguish static properties
// from instance properties. Ignored by napi_define_properties.
napi_static = 1 << 10,
// Default for class methods.
napi_default_method = napi_writable | napi_configurable,
// Default for object properties, like in JS obj[prop].
napi_default_jsproperty = napi_writable |
napi_enumerable |
napi_configurable,
} napi_property_attributes;
```
`napi_property_attributes` are flags used to control the behavior of properties set on a JavaScript object. Other than `napi_static` they correspond to the attributes listed in [Section 6.1.7.1](https://tc39.github.io/ecma262/#table-2) of the [ECMAScript Language Specification](https://tc39.github.io/ecma262/). They can be one or more of the following bitflags:
* `napi_default`: No explicit attributes are set on the property. By default, a property is read only, not enumerable and not configurable.
* `napi_writable`: The property is writable.
* `napi_enumerable`: The property is enumerable.
* `napi_configurable`: The property is configurable as defined in [Section 6.1.7.1](https://tc39.github.io/ecma262/#table-2) of the [ECMAScript Language Specification](https://tc39.github.io/ecma262/).
* `napi_static`: The property will be defined as a static property on a class as opposed to an instance property, which is the default. This is used only by [`napi_define_class`](#napi_define_class). It is ignored by `napi_define_properties`.
* `napi_default_method`: Like a method in a JS class, the property is configurable and writeable, but not enumerable.
* `napi_default_jsproperty`: Like a property set via assignment in JavaScript, the property is writable, enumerable, and configurable.
#####
`napi_property_descriptor`
```
typedef struct {
// One of utf8name or name should be NULL.
const char* utf8name;
napi_value name;
napi_callback method;
napi_callback getter;
napi_callback setter;
napi_value value;
napi_property_attributes attributes;
void* data;
} napi_property_descriptor;
```
* `utf8name`: Optional string describing the key for the property, encoded as UTF8. One of `utf8name` or `name` must be provided for the property.
* `name`: Optional `napi_value` that points to a JavaScript string or symbol to be used as the key for the property. One of `utf8name` or `name` must be provided for the property.
* `value`: The value that's retrieved by a get access of the property if the property is a data property. If this is passed in, set `getter`, `setter`, `method` and `data` to `NULL` (since these members won't be used).
* `getter`: A function to call when a get access of the property is performed. If this is passed in, set `value` and `method` to `NULL` (since these members won't be used). The given function is called implicitly by the runtime when the property is accessed from JavaScript code (or if a get on the property is performed using a Node-API call). [`napi_callback`](#napi_callback) provides more details.
* `setter`: A function to call when a set access of the property is performed. If this is passed in, set `value` and `method` to `NULL` (since these members won't be used). The given function is called implicitly by the runtime when the property is set from JavaScript code (or if a set on the property is performed using a Node-API call). [`napi_callback`](#napi_callback) provides more details.
* `method`: Set this to make the property descriptor object's `value` property to be a JavaScript function represented by `method`. If this is passed in, set `value`, `getter` and `setter` to `NULL` (since these members won't be used). [`napi_callback`](#napi_callback) provides more details.
* `attributes`: The attributes associated with the particular property. See [`napi_property_attributes`](#napi_property_attributes).
* `data`: The callback data passed into `method`, `getter` and `setter` if this function is invoked.
#### Functions
#####
`napi_get_property_names`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_property_names(napi_env env,
napi_value object,
napi_value* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object from which to retrieve the properties.
* `[out] result`: A `napi_value` representing an array of JavaScript values that represent the property names of the object. The API can be used to iterate over `result` using [`napi_get_array_length`](#napi_get_array_length) and [`napi_get_element`](#napi_get_element).
Returns `napi_ok` if the API succeeded.
This API returns the names of the enumerable properties of `object` as an array of strings. The properties of `object` whose key is a symbol will not be included.
#####
`napi_get_all_property_names`
Added in: v13.7.0, v12.17.0, v10.20.0 N-API version: 6
```
napi_get_all_property_names(napi_env env,
napi_value object,
napi_key_collection_mode key_mode,
napi_key_filter key_filter,
napi_key_conversion key_conversion,
napi_value* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object from which to retrieve the properties.
* `[in] key_mode`: Whether to retrieve prototype properties as well.
* `[in] key_filter`: Which properties to retrieve (enumerable/readable/writable).
* `[in] key_conversion`: Whether to convert numbered property keys to strings.
* `[out] result`: A `napi_value` representing an array of JavaScript values that represent the property names of the object. [`napi_get_array_length`](#napi_get_array_length) and [`napi_get_element`](#napi_get_element) can be used to iterate over `result`.
Returns `napi_ok` if the API succeeded.
This API returns an array containing the names of the available properties of this object.
#####
`napi_set_property`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_set_property(napi_env env,
napi_value object,
napi_value key,
napi_value value);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object on which to set the property.
* `[in] key`: The name of the property to set.
* `[in] value`: The property value.
Returns `napi_ok` if the API succeeded.
This API set a property on the `Object` passed in.
#####
`napi_get_property`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_property(napi_env env,
napi_value object,
napi_value key,
napi_value* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object from which to retrieve the property.
* `[in] key`: The name of the property to retrieve.
* `[out] result`: The value of the property.
Returns `napi_ok` if the API succeeded.
This API gets the requested property from the `Object` passed in.
#####
`napi_has_property`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_has_property(napi_env env,
napi_value object,
napi_value key,
bool* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object to query.
* `[in] key`: The name of the property whose existence to check.
* `[out] result`: Whether the property exists on the object or not.
Returns `napi_ok` if the API succeeded.
This API checks if the `Object` passed in has the named property.
#####
`napi_delete_property`
Added in: v8.2.0 N-API version: 1
```
napi_status napi_delete_property(napi_env env,
napi_value object,
napi_value key,
bool* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object to query.
* `[in] key`: The name of the property to delete.
* `[out] result`: Whether the property deletion succeeded or not. `result` can optionally be ignored by passing `NULL`.
Returns `napi_ok` if the API succeeded.
This API attempts to delete the `key` own property from `object`.
#####
`napi_has_own_property`
Added in: v8.2.0 N-API version: 1
```
napi_status napi_has_own_property(napi_env env,
napi_value object,
napi_value key,
bool* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object to query.
* `[in] key`: The name of the own property whose existence to check.
* `[out] result`: Whether the own property exists on the object or not.
Returns `napi_ok` if the API succeeded.
This API checks if the `Object` passed in has the named own property. `key` must be a `string` or a `symbol`, or an error will be thrown. Node-API will not perform any conversion between data types.
#####
`napi_set_named_property`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_set_named_property(napi_env env,
napi_value object,
const char* utf8Name,
napi_value value);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object on which to set the property.
* `[in] utf8Name`: The name of the property to set.
* `[in] value`: The property value.
Returns `napi_ok` if the API succeeded.
This method is equivalent to calling [`napi_set_property`](#napi_set_property) with a `napi_value` created from the string passed in as `utf8Name`.
#####
`napi_get_named_property`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_named_property(napi_env env,
napi_value object,
const char* utf8Name,
napi_value* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object from which to retrieve the property.
* `[in] utf8Name`: The name of the property to get.
* `[out] result`: The value of the property.
Returns `napi_ok` if the API succeeded.
This method is equivalent to calling [`napi_get_property`](#napi_get_property) with a `napi_value` created from the string passed in as `utf8Name`.
#####
`napi_has_named_property`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_has_named_property(napi_env env,
napi_value object,
const char* utf8Name,
bool* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object to query.
* `[in] utf8Name`: The name of the property whose existence to check.
* `[out] result`: Whether the property exists on the object or not.
Returns `napi_ok` if the API succeeded.
This method is equivalent to calling [`napi_has_property`](#napi_has_property) with a `napi_value` created from the string passed in as `utf8Name`.
#####
`napi_set_element`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_set_element(napi_env env,
napi_value object,
uint32_t index,
napi_value value);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object from which to set the properties.
* `[in] index`: The index of the property to set.
* `[in] value`: The property value.
Returns `napi_ok` if the API succeeded.
This API sets an element on the `Object` passed in.
#####
`napi_get_element`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_element(napi_env env,
napi_value object,
uint32_t index,
napi_value* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object from which to retrieve the property.
* `[in] index`: The index of the property to get.
* `[out] result`: The value of the property.
Returns `napi_ok` if the API succeeded.
This API gets the element at the requested index.
#####
`napi_has_element`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_has_element(napi_env env,
napi_value object,
uint32_t index,
bool* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object to query.
* `[in] index`: The index of the property whose existence to check.
* `[out] result`: Whether the property exists on the object or not.
Returns `napi_ok` if the API succeeded.
This API returns if the `Object` passed in has an element at the requested index.
#####
`napi_delete_element`
Added in: v8.2.0 N-API version: 1
```
napi_status napi_delete_element(napi_env env,
napi_value object,
uint32_t index,
bool* result);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object to query.
* `[in] index`: The index of the property to delete.
* `[out] result`: Whether the element deletion succeeded or not. `result` can optionally be ignored by passing `NULL`.
Returns `napi_ok` if the API succeeded.
This API attempts to delete the specified `index` from `object`.
#####
`napi_define_properties`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_define_properties(napi_env env,
napi_value object,
size_t property_count,
const napi_property_descriptor* properties);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object from which to retrieve the properties.
* `[in] property_count`: The number of elements in the `properties` array.
* `[in] properties`: The array of property descriptors.
Returns `napi_ok` if the API succeeded.
This method allows the efficient definition of multiple properties on a given object. The properties are defined using property descriptors (see [`napi_property_descriptor`](#napi_property_descriptor)). Given an array of such property descriptors, this API will set the properties on the object one at a time, as defined by `DefineOwnProperty()` (described in [Section 9.1.6](https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots-defineownproperty-p-desc) of the ECMA-262 specification).
#####
`napi_object_freeze`
Added in: v14.14.0, v12.20.0 N-API version: 8
```
napi_status napi_object_freeze(napi_env env,
napi_value object);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object to freeze.
Returns `napi_ok` if the API succeeded.
This method freezes a given object. This prevents new properties from being added to it, existing properties from being removed, prevents changing the enumerability, configurability, or writability of existing properties, and prevents the values of existing properties from being changed. It also prevents the object's prototype from being changed. This is described in [Section 19.1.2.6](https://tc39.es/ecma262/#sec-object.freeze) of the ECMA-262 specification.
#####
`napi_object_seal`
Added in: v14.14.0, v12.20.0 N-API version: 8
```
napi_status napi_object_seal(napi_env env,
napi_value object);
```
* `[in] env`: The environment that the Node-API call is invoked under.
* `[in] object`: The object to seal.
Returns `napi_ok` if the API succeeded.
This method seals a given object. This prevents new properties from being added to it, as well as marking all existing properties as non-configurable. This is described in [Section 19.1.2.20](https://tc39.es/ecma262/#sec-object.seal) of the ECMA-262 specification.
### Working with JavaScript functions
Node-API provides a set of APIs that allow JavaScript code to call back into native code. Node-APIs that support calling back into native code take in a callback functions represented by the `napi_callback` type. When the JavaScript VM calls back to native code, the `napi_callback` function provided is invoked. The APIs documented in this section allow the callback function to do the following:
* Get information about the context in which the callback was invoked.
* Get the arguments passed into the callback.
* Return a `napi_value` back from the callback.
Additionally, Node-API provides a set of functions which allow calling JavaScript functions from native code. One can either call a function like a regular JavaScript function call, or as a constructor function.
Any non-`NULL` data which is passed to this API via the `data` field of the `napi_property_descriptor` items can be associated with `object` and freed whenever `object` is garbage-collected by passing both `object` and the data to [`napi_add_finalizer`](#napi_add_finalizer).
####
`napi_call_function`
Added in: v8.0.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_call_function(napi_env env,
napi_value recv,
napi_value func,
size_t argc,
const napi_value* argv,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] recv`: The `this` value passed to the called function.
* `[in] func`: `napi_value` representing the JavaScript function to be invoked.
* `[in] argc`: The count of elements in the `argv` array.
* `[in] argv`: Array of `napi_values` representing JavaScript values passed in as arguments to the function.
* `[out] result`: `napi_value` representing the JavaScript object returned.
Returns `napi_ok` if the API succeeded.
This method allows a JavaScript function object to be called from a native add-on. This is the primary mechanism of calling back *from* the add-on's native code *into* JavaScript. For the special case of calling into JavaScript after an async operation, see [`napi_make_callback`](#napi_make_callback).
A sample use case might look as follows. Consider the following JavaScript snippet:
```
function AddTwo(num) {
return num + 2;
}
global.AddTwo = AddTwo;
```
Then, the above function can be invoked from a native add-on using the following code:
```
// Get the function named "AddTwo" on the global object
napi_value global, add_two, arg;
napi_status status = napi_get_global(env, &global);
if (status != napi_ok) return;
status = napi_get_named_property(env, global, "AddTwo", &add_two);
if (status != napi_ok) return;
// const arg = 1337
status = napi_create_int32(env, 1337, &arg);
if (status != napi_ok) return;
napi_value* argv = &arg;
size_t argc = 1;
// AddTwo(arg);
napi_value return_val;
status = napi_call_function(env, global, add_two, argc, argv, &return_val);
if (status != napi_ok) return;
// Convert the result back to a native type
int32_t result;
status = napi_get_value_int32(env, return_val, &result);
if (status != napi_ok) return;
```
####
`napi_create_function`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_create_function(napi_env env,
const char* utf8name,
size_t length,
napi_callback cb,
void* data,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] utf8Name`: Optional name of the function encoded as UTF8. This is visible within JavaScript as the new function object's `name` property.
* `[in] length`: The length of the `utf8name` in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated.
* `[in] cb`: The native function which should be called when this function object is invoked. [`napi_callback`](#napi_callback) provides more details.
* `[in] data`: User-provided data context. This will be passed back into the function when invoked later.
* `[out] result`: `napi_value` representing the JavaScript function object for the newly created function.
Returns `napi_ok` if the API succeeded.
This API allows an add-on author to create a function object in native code. This is the primary mechanism to allow calling *into* the add-on's native code *from* JavaScript.
The newly created function is not automatically visible from script after this call. Instead, a property must be explicitly set on any object that is visible to JavaScript, in order for the function to be accessible from script.
In order to expose a function as part of the add-on's module exports, set the newly created function on the exports object. A sample module might look as follows:
```
napi_value SayHello(napi_env env, napi_callback_info info) {
printf("Hello\n");
return NULL;
}
napi_value Init(napi_env env, napi_value exports) {
napi_status status;
napi_value fn;
status = napi_create_function(env, NULL, 0, SayHello, NULL, &fn);
if (status != napi_ok) return NULL;
status = napi_set_named_property(env, exports, "sayHello", fn);
if (status != napi_ok) return NULL;
return exports;
}
NAPI_MODULE(NODE_GYP_MODULE_NAME, Init)
```
Given the above code, the add-on can be used from JavaScript as follows:
```
const myaddon = require('./addon');
myaddon.sayHello();
```
The string passed to `require()` is the name of the target in `binding.gyp` responsible for creating the `.node` file.
Any non-`NULL` data which is passed to this API via the `data` parameter can be associated with the resulting JavaScript function (which is returned in the `result` parameter) and freed whenever the function is garbage-collected by passing both the JavaScript function and the data to [`napi_add_finalizer`](#napi_add_finalizer).
JavaScript `Function`s are described in [Section 19.2](https://tc39.github.io/ecma262/#sec-function-objects) of the ECMAScript Language Specification.
####
`napi_get_cb_info`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_cb_info(napi_env env,
napi_callback_info cbinfo,
size_t* argc,
napi_value* argv,
napi_value* thisArg,
void** data)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] cbinfo`: The callback info passed into the callback function.
* `[in-out] argc`: Specifies the length of the provided `argv` array and receives the actual count of arguments. `argc` can optionally be ignored by passing `NULL`.
* `[out] argv`: C array of `napi_value`s to which the arguments will be copied. If there are more arguments than the provided count, only the requested number of arguments are copied. If there are fewer arguments provided than claimed, the rest of `argv` is filled with `napi_value` values that represent `undefined`. `argv` can optionally be ignored by passing `NULL`.
* `[out] thisArg`: Receives the JavaScript `this` argument for the call. `thisArg` can optionally be ignored by passing `NULL`.
* `[out] data`: Receives the data pointer for the callback. `data` can optionally be ignored by passing `NULL`.
Returns `napi_ok` if the API succeeded.
This method is used within a callback function to retrieve details about the call like the arguments and the `this` pointer from a given callback info.
####
`napi_get_new_target`
Added in: v8.6.0 N-API version: 1
```
napi_status napi_get_new_target(napi_env env,
napi_callback_info cbinfo,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] cbinfo`: The callback info passed into the callback function.
* `[out] result`: The `new.target` of the constructor call.
Returns `napi_ok` if the API succeeded.
This API returns the `new.target` of the constructor call. If the current callback is not a constructor call, the result is `NULL`.
####
`napi_new_instance`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_new_instance(napi_env env,
napi_value cons,
size_t argc,
napi_value* argv,
napi_value* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] cons`: `napi_value` representing the JavaScript function to be invoked as a constructor.
* `[in] argc`: The count of elements in the `argv` array.
* `[in] argv`: Array of JavaScript values as `napi_value` representing the arguments to the constructor. If `argc` is zero this parameter may be omitted by passing in `NULL`.
* `[out] result`: `napi_value` representing the JavaScript object returned, which in this case is the constructed object.
This method is used to instantiate a new JavaScript value using a given `napi_value` that represents the constructor for the object. For example, consider the following snippet:
```
function MyObject(param) {
this.param = param;
}
const arg = 'hello';
const value = new MyObject(arg);
```
The following can be approximated in Node-API using the following snippet:
```
// Get the constructor function MyObject
napi_value global, constructor, arg, value;
napi_status status = napi_get_global(env, &global);
if (status != napi_ok) return;
status = napi_get_named_property(env, global, "MyObject", &constructor);
if (status != napi_ok) return;
// const arg = "hello"
status = napi_create_string_utf8(env, "hello", NAPI_AUTO_LENGTH, &arg);
if (status != napi_ok) return;
napi_value* argv = &arg;
size_t argc = 1;
// const value = new MyObject(arg)
status = napi_new_instance(env, constructor, argc, argv, &value);
```
Returns `napi_ok` if the API succeeded.
### Object wrap
Node-API offers a way to "wrap" C++ classes and instances so that the class constructor and methods can be called from JavaScript.
1. The [`napi_define_class`](#napi_define_class) API defines a JavaScript class with constructor, static properties and methods, and instance properties and methods that correspond to the C++ class.
2. When JavaScript code invokes the constructor, the constructor callback uses [`napi_wrap`](#napi_wrap) to wrap a new C++ instance in a JavaScript object, then returns the wrapper object.
3. When JavaScript code invokes a method or property accessor on the class, the corresponding `napi_callback` C++ function is invoked. For an instance callback, [`napi_unwrap`](#napi_unwrap) obtains the C++ instance that is the target of the call.
For wrapped objects it may be difficult to distinguish between a function called on a class prototype and a function called on an instance of a class. A common pattern used to address this problem is to save a persistent reference to the class constructor for later `instanceof` checks.
```
napi_value MyClass_constructor = NULL;
status = napi_get_reference_value(env, MyClass::es_constructor, &MyClass_constructor);
assert(napi_ok == status);
bool is_instance = false;
status = napi_instanceof(env, es_this, MyClass_constructor, &is_instance);
assert(napi_ok == status);
if (is_instance) {
// napi_unwrap() ...
} else {
// otherwise...
}
```
The reference must be freed once it is no longer needed.
There are occasions where `napi_instanceof()` is insufficient for ensuring that a JavaScript object is a wrapper for a certain native type. This is the case especially when wrapped JavaScript objects are passed back into the addon via static methods rather than as the `this` value of prototype methods. In such cases there is a chance that they may be unwrapped incorrectly.
```
const myAddon = require('./build/Release/my_addon.node');
// `openDatabase()` returns a JavaScript object that wraps a native database
// handle.
const dbHandle = myAddon.openDatabase();
// `query()` returns a JavaScript object that wraps a native query handle.
const queryHandle = myAddon.query(dbHandle, 'Gimme ALL the things!');
// There is an accidental error in the line below. The first parameter to
// `myAddon.queryHasRecords()` should be the database handle (`dbHandle`), not
// the query handle (`query`), so the correct condition for the while-loop
// should be
//
// myAddon.queryHasRecords(dbHandle, queryHandle)
//
while (myAddon.queryHasRecords(queryHandle, dbHandle)) {
// retrieve records
}
```
In the above example `myAddon.queryHasRecords()` is a method that accepts two arguments. The first is a database handle and the second is a query handle. Internally, it unwraps the first argument and casts the resulting pointer to a native database handle. It then unwraps the second argument and casts the resulting pointer to a query handle. If the arguments are passed in the wrong order, the casts will work, however, there is a good chance that the underlying database operation will fail, or will even cause an invalid memory access.
To ensure that the pointer retrieved from the first argument is indeed a pointer to a database handle and, similarly, that the pointer retrieved from the second argument is indeed a pointer to a query handle, the implementation of `queryHasRecords()` has to perform a type validation. Retaining the JavaScript class constructor from which the database handle was instantiated and the constructor from which the query handle was instantiated in `napi_ref`s can help, because `napi_instanceof()` can then be used to ensure that the instances passed into `queryHashRecords()` are indeed of the correct type.
Unfortunately, `napi_instanceof()` does not protect against prototype manipulation. For example, the prototype of the database handle instance can be set to the prototype of the constructor for query handle instances. In this case, the database handle instance can appear as a query handle instance, and it will pass the `napi_instanceof()` test for a query handle instance, while still containing a pointer to a database handle.
To this end, Node-API provides type-tagging capabilities.
A type tag is a 128-bit integer unique to the addon. Node-API provides the `napi_type_tag` structure for storing a type tag. When such a value is passed along with a JavaScript object stored in a `napi_value` to `napi_type_tag_object()`, the JavaScript object will be "marked" with the type tag. The "mark" is invisible on the JavaScript side. When a JavaScript object arrives into a native binding, `napi_check_object_type_tag()` can be used along with the original type tag to determine whether the JavaScript object was previously "marked" with the type tag. This creates a type-checking capability of a higher fidelity than `napi_instanceof()` can provide, because such type- tagging survives prototype manipulation and addon unloading/reloading.
Continuing the above example, the following skeleton addon implementation illustrates the use of `napi_type_tag_object()` and `napi_check_object_type_tag()`.
```
// This value is the type tag for a database handle. The command
//
// uuidgen | sed -r -e 's/-//g' -e 's/(.{16})(.*)/0x\1, 0x\2/'
//
// can be used to obtain the two values with which to initialize the structure.
static const napi_type_tag DatabaseHandleTypeTag = {
0x1edf75a38336451d, 0xa5ed9ce2e4c00c38
};
// This value is the type tag for a query handle.
static const napi_type_tag QueryHandleTypeTag = {
0x9c73317f9fad44a3, 0x93c3920bf3b0ad6a
};
static napi_value
openDatabase(napi_env env, napi_callback_info info) {
napi_status status;
napi_value result;
// Perform the underlying action which results in a database handle.
DatabaseHandle* dbHandle = open_database();
// Create a new, empty JS object.
status = napi_create_object(env, &result);
if (status != napi_ok) return NULL;
// Tag the object to indicate that it holds a pointer to a `DatabaseHandle`.
status = napi_type_tag_object(env, result, &DatabaseHandleTypeTag);
if (status != napi_ok) return NULL;
// Store the pointer to the `DatabaseHandle` structure inside the JS object.
status = napi_wrap(env, result, dbHandle, NULL, NULL, NULL);
if (status != napi_ok) return NULL;
return result;
}
// Later when we receive a JavaScript object purporting to be a database handle
// we can use `napi_check_object_type_tag()` to ensure that it is indeed such a
// handle.
static napi_value
query(napi_env env, napi_callback_info info) {
napi_status status;
size_t argc = 2;
napi_value argv[2];
bool is_db_handle;
status = napi_get_cb_info(env, info, &argc, argv, NULL, NULL);
if (status != napi_ok) return NULL;
// Check that the object passed as the first parameter has the previously
// applied tag.
status = napi_check_object_type_tag(env,
argv[0],
&DatabaseHandleTypeTag,
&is_db_handle);
if (status != napi_ok) return NULL;
// Throw a `TypeError` if it doesn't.
if (!is_db_handle) {
// Throw a TypeError.
return NULL;
}
}
```
####
`napi_define_class`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_define_class(napi_env env,
const char* utf8name,
size_t length,
napi_callback constructor,
void* data,
size_t property_count,
const napi_property_descriptor* properties,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] utf8name`: Name of the JavaScript constructor function; When wrapping a C++ class, we recommend for clarity that this name be the same as that of the C++ class.
* `[in] length`: The length of the `utf8name` in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated.
* `[in] constructor`: Callback function that handles constructing instances of the class. When wrapping a C++ class, this method must be a static member with the [`napi_callback`](#napi_callback) signature. A C++ class constructor cannot be used. [`napi_callback`](#napi_callback) provides more details.
* `[in] data`: Optional data to be passed to the constructor callback as the `data` property of the callback info.
* `[in] property_count`: Number of items in the `properties` array argument.
* `[in] properties`: Array of property descriptors describing static and instance data properties, accessors, and methods on the class See `napi_property_descriptor`.
* `[out] result`: A `napi_value` representing the constructor function for the class.
Returns `napi_ok` if the API succeeded.
Defines a JavaScript class, including:
* A JavaScript constructor function that has the class name. When wrapping a corresponding C++ class, the callback passed via `constructor` can be used to instantiate a new C++ class instance, which can then be placed inside the JavaScript object instance being constructed using [`napi_wrap`](#napi_wrap).
* Properties on the constructor function whose implementation can call corresponding *static* data properties, accessors, and methods of the C++ class (defined by property descriptors with the `napi_static` attribute).
* Properties on the constructor function's `prototype` object. When wrapping a C++ class, *non-static* data properties, accessors, and methods of the C++ class can be called from the static functions given in the property descriptors without the `napi_static` attribute after retrieving the C++ class instance placed inside the JavaScript object instance by using [`napi_unwrap`](#napi_unwrap).
When wrapping a C++ class, the C++ constructor callback passed via `constructor` should be a static method on the class that calls the actual class constructor, then wraps the new C++ instance in a JavaScript object, and returns the wrapper object. See [`napi_wrap`](#napi_wrap) for details.
The JavaScript constructor function returned from [`napi_define_class`](#napi_define_class) is often saved and used later to construct new instances of the class from native code, and/or to check whether provided values are instances of the class. In that case, to prevent the function value from being garbage-collected, a strong persistent reference to it can be created using [`napi_create_reference`](#napi_create_reference), ensuring that the reference count is kept >= 1.
Any non-`NULL` data which is passed to this API via the `data` parameter or via the `data` field of the `napi_property_descriptor` array items can be associated with the resulting JavaScript constructor (which is returned in the `result` parameter) and freed whenever the class is garbage-collected by passing both the JavaScript function and the data to [`napi_add_finalizer`](#napi_add_finalizer).
####
`napi_wrap`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_wrap(napi_env env,
napi_value js_object,
void* native_object,
napi_finalize finalize_cb,
void* finalize_hint,
napi_ref* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] js_object`: The JavaScript object that will be the wrapper for the native object.
* `[in] native_object`: The native instance that will be wrapped in the JavaScript object.
* `[in] finalize_cb`: Optional native callback that can be used to free the native instance when the JavaScript object is ready for garbage-collection. [`napi_finalize`](#napi_finalize) provides more details.
* `[in] finalize_hint`: Optional contextual hint that is passed to the finalize callback.
* `[out] result`: Optional reference to the wrapped object.
Returns `napi_ok` if the API succeeded.
Wraps a native instance in a JavaScript object. The native instance can be retrieved later using `napi_unwrap()`.
When JavaScript code invokes a constructor for a class that was defined using `napi_define_class()`, the `napi_callback` for the constructor is invoked. After constructing an instance of the native class, the callback must then call `napi_wrap()` to wrap the newly constructed instance in the already-created JavaScript object that is the `this` argument to the constructor callback. (That `this` object was created from the constructor function's `prototype`, so it already has definitions of all the instance properties and methods.)
Typically when wrapping a class instance, a finalize callback should be provided that simply deletes the native instance that is received as the `data` argument to the finalize callback.
The optional returned reference is initially a weak reference, meaning it has a reference count of 0. Typically this reference count would be incremented temporarily during async operations that require the instance to remain valid.
*Caution*: The optional returned reference (if obtained) should be deleted via [`napi_delete_reference`](#napi_delete_reference) ONLY in response to the finalize callback invocation. If it is deleted before then, then the finalize callback may never be invoked. Therefore, when obtaining a reference a finalize callback is also required in order to enable correct disposal of the reference.
Finalizer callbacks may be deferred, leaving a window where the object has been garbage collected (and the weak reference is invalid) but the finalizer hasn't been called yet. When using `napi_get_reference_value()` on weak references returned by `napi_wrap()`, you should still handle an empty result.
Calling `napi_wrap()` a second time on an object will return an error. To associate another native instance with the object, use `napi_remove_wrap()` first.
####
`napi_unwrap`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_unwrap(napi_env env,
napi_value js_object,
void** result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] js_object`: The object associated with the native instance.
* `[out] result`: Pointer to the wrapped native instance.
Returns `napi_ok` if the API succeeded.
Retrieves a native instance that was previously wrapped in a JavaScript object using `napi_wrap()`.
When JavaScript code invokes a method or property accessor on the class, the corresponding `napi_callback` is invoked. If the callback is for an instance method or accessor, then the `this` argument to the callback is the wrapper object; the wrapped C++ instance that is the target of the call can be obtained then by calling `napi_unwrap()` on the wrapper object.
####
`napi_remove_wrap`
Added in: v8.5.0 N-API version: 1
```
napi_status napi_remove_wrap(napi_env env,
napi_value js_object,
void** result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] js_object`: The object associated with the native instance.
* `[out] result`: Pointer to the wrapped native instance.
Returns `napi_ok` if the API succeeded.
Retrieves a native instance that was previously wrapped in the JavaScript object `js_object` using `napi_wrap()` and removes the wrapping. If a finalize callback was associated with the wrapping, it will no longer be called when the JavaScript object becomes garbage-collected.
####
`napi_type_tag_object`
Added in: v14.8.0, v12.19.0 N-API version: 8
```
napi_status napi_type_tag_object(napi_env env,
napi_value js_object,
const napi_type_tag* type_tag);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] js_object`: The JavaScript object to be marked.
* `[in] type_tag`: The tag with which the object is to be marked.
Returns `napi_ok` if the API succeeded.
Associates the value of the `type_tag` pointer with the JavaScript object. `napi_check_object_type_tag()` can then be used to compare the tag that was attached to the object with one owned by the addon to ensure that the object has the right type.
If the object already has an associated type tag, this API will return `napi_invalid_arg`.
####
`napi_check_object_type_tag`
Added in: v14.8.0, v12.19.0 N-API version: 8
```
napi_status napi_check_object_type_tag(napi_env env,
napi_value js_object,
const napi_type_tag* type_tag,
bool* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] js_object`: The JavaScript object whose type tag to examine.
* `[in] type_tag`: The tag with which to compare any tag found on the object.
* `[out] result`: Whether the type tag given matched the type tag on the object. `false` is also returned if no type tag was found on the object.
Returns `napi_ok` if the API succeeded.
Compares the pointer given as `type_tag` with any that can be found on `js_object`. If no tag is found on `js_object` or, if a tag is found but it does not match `type_tag`, then `result` is set to `false`. If a tag is found and it matches `type_tag`, then `result` is set to `true`.
####
`napi_add_finalizer`
Added in: v8.0.0 N-API version: 5
```
napi_status napi_add_finalizer(napi_env env,
napi_value js_object,
void* native_object,
napi_finalize finalize_cb,
void* finalize_hint,
napi_ref* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] js_object`: The JavaScript object to which the native data will be attached.
* `[in] native_object`: The native data that will be attached to the JavaScript object.
* `[in] finalize_cb`: Native callback that will be used to free the native data when the JavaScript object is ready for garbage-collection. [`napi_finalize`](#napi_finalize) provides more details.
* `[in] finalize_hint`: Optional contextual hint that is passed to the finalize callback.
* `[out] result`: Optional reference to the JavaScript object.
Returns `napi_ok` if the API succeeded.
Adds a `napi_finalize` callback which will be called when the JavaScript object in `js_object` is ready for garbage collection. This API is similar to `napi_wrap()` except that:
* the native data cannot be retrieved later using `napi_unwrap()`,
* nor can it be removed later using `napi_remove_wrap()`, and
* the API can be called multiple times with different data items in order to attach each of them to the JavaScript object, and
* the object manipulated by the API can be used with `napi_wrap()`.
*Caution*: The optional returned reference (if obtained) should be deleted via [`napi_delete_reference`](#napi_delete_reference) ONLY in response to the finalize callback invocation. If it is deleted before then, then the finalize callback may never be invoked. Therefore, when obtaining a reference a finalize callback is also required in order to enable correct disposal of the reference.
### Simple asynchronous operations
Addon modules often need to leverage async helpers from libuv as part of their implementation. This allows them to schedule work to be executed asynchronously so that their methods can return in advance of the work being completed. This allows them to avoid blocking overall execution of the Node.js application.
Node-API provides an ABI-stable interface for these supporting functions which covers the most common asynchronous use cases.
Node-API defines the `napi_async_work` structure which is used to manage asynchronous workers. Instances are created/deleted with [`napi_create_async_work`](#napi_create_async_work) and [`napi_delete_async_work`](#napi_delete_async_work).
The `execute` and `complete` callbacks are functions that will be invoked when the executor is ready to execute and when it completes its task respectively.
The `execute` function should avoid making any Node-API calls that could result in the execution of JavaScript or interaction with JavaScript objects. Most often, any code that needs to make Node-API calls should be made in `complete` callback instead. Avoid using the `napi_env` parameter in the execute callback as it will likely execute JavaScript.
These functions implement the following interfaces:
```
typedef void (*napi_async_execute_callback)(napi_env env,
void* data);
typedef void (*napi_async_complete_callback)(napi_env env,
napi_status status,
void* data);
```
When these methods are invoked, the `data` parameter passed will be the addon-provided `void*` data that was passed into the `napi_create_async_work` call.
Once created the async worker can be queued for execution using the [`napi_queue_async_work`](#napi_queue_async_work) function:
```
napi_status napi_queue_async_work(napi_env env,
napi_async_work work);
```
[`napi_cancel_async_work`](#napi_cancel_async_work) can be used if the work needs to be cancelled before the work has started execution.
After calling [`napi_cancel_async_work`](#napi_cancel_async_work), the `complete` callback will be invoked with a status value of `napi_cancelled`. The work should not be deleted before the `complete` callback invocation, even when it was cancelled.
####
`napi_create_async_work`
History
| Version | Changes |
| --- | --- |
| v8.6.0 | Added `async_resource` and `async_resource_name` parameters. |
| v8.0.0 | Added in: v8.0.0 |
N-API version: 1
```
napi_status napi_create_async_work(napi_env env,
napi_value async_resource,
napi_value async_resource_name,
napi_async_execute_callback execute,
napi_async_complete_callback complete,
void* data,
napi_async_work* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] async_resource`: An optional object associated with the async work that will be passed to possible `async_hooks` [`init` hooks](async_hooks#initasyncid-type-triggerasyncid-resource).
* `[in] async_resource_name`: Identifier for the kind of resource that is being provided for diagnostic information exposed by the `async_hooks` API.
* `[in] execute`: The native function which should be called to execute the logic asynchronously. The given function is called from a worker pool thread and can execute in parallel with the main event loop thread.
* `[in] complete`: The native function which will be called when the asynchronous logic is completed or is cancelled. The given function is called from the main event loop thread. [`napi_async_complete_callback`](#napi_async_complete_callback) provides more details.
* `[in] data`: User-provided data context. This will be passed back into the execute and complete functions.
* `[out] result`: `napi_async_work*` which is the handle to the newly created async work.
Returns `napi_ok` if the API succeeded.
This API allocates a work object that is used to execute logic asynchronously. It should be freed using [`napi_delete_async_work`](#napi_delete_async_work) once the work is no longer required.
`async_resource_name` should be a null-terminated, UTF-8-encoded string.
The `async_resource_name` identifier is provided by the user and should be representative of the type of async work being performed. It is also recommended to apply namespacing to the identifier, e.g. by including the module name. See the [`async_hooks` documentation](async_hooks#type) for more information.
####
`napi_delete_async_work`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_delete_async_work(napi_env env,
napi_async_work work);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] work`: The handle returned by the call to `napi_create_async_work`.
Returns `napi_ok` if the API succeeded.
This API frees a previously allocated work object.
This API can be called even if there is a pending JavaScript exception.
####
`napi_queue_async_work`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_queue_async_work(napi_env env,
napi_async_work work);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] work`: The handle returned by the call to `napi_create_async_work`.
Returns `napi_ok` if the API succeeded.
This API requests that the previously allocated work be scheduled for execution. Once it returns successfully, this API must not be called again with the same `napi_async_work` item or the result will be undefined.
####
`napi_cancel_async_work`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_cancel_async_work(napi_env env,
napi_async_work work);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] work`: The handle returned by the call to `napi_create_async_work`.
Returns `napi_ok` if the API succeeded.
This API cancels queued work if it has not yet been started. If it has already started executing, it cannot be cancelled and `napi_generic_failure` will be returned. If successful, the `complete` callback will be invoked with a status value of `napi_cancelled`. The work should not be deleted before the `complete` callback invocation, even if it has been successfully cancelled.
This API can be called even if there is a pending JavaScript exception.
### Custom asynchronous operations
The simple asynchronous work APIs above may not be appropriate for every scenario. When using any other asynchronous mechanism, the following APIs are necessary to ensure an asynchronous operation is properly tracked by the runtime.
####
`napi_async_init`
Added in: v8.6.0 N-API version: 1
```
napi_status napi_async_init(napi_env env,
napi_value async_resource,
napi_value async_resource_name,
napi_async_context* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] async_resource`: Object associated with the async work that will be passed to possible `async_hooks` [`init` hooks](async_hooks#initasyncid-type-triggerasyncid-resource) and can be accessed by [`async_hooks.executionAsyncResource()`](async_hooks#async_hooksexecutionasyncresource).
* `[in] async_resource_name`: Identifier for the kind of resource that is being provided for diagnostic information exposed by the `async_hooks` API.
* `[out] result`: The initialized async context.
Returns `napi_ok` if the API succeeded.
The `async_resource` object needs to be kept alive until [`napi_async_destroy`](#napi_async_destroy) to keep `async_hooks` related API acts correctly. In order to retain ABI compatibility with previous versions, `napi_async_context`s are not maintaining the strong reference to the `async_resource` objects to avoid introducing causing memory leaks. However, if the `async_resource` is garbage collected by JavaScript engine before the `napi_async_context` was destroyed by `napi_async_destroy`, calling `napi_async_context` related APIs like [`napi_open_callback_scope`](#napi_open_callback_scope) and [`napi_make_callback`](#napi_make_callback) can cause problems like loss of async context when using the `AsyncLocalStorage` API.
In order to retain ABI compatibility with previous versions, passing `NULL` for `async_resource` does not result in an error. However, this is not recommended as this will result poor results with `async_hooks` [`init` hooks](async_hooks#initasyncid-type-triggerasyncid-resource) and `async_hooks.executionAsyncResource()` as the resource is now required by the underlying `async_hooks` implementation in order to provide the linkage between async callbacks.
####
`napi_async_destroy`
Added in: v8.6.0 N-API version: 1
```
napi_status napi_async_destroy(napi_env env,
napi_async_context async_context);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] async_context`: The async context to be destroyed.
Returns `napi_ok` if the API succeeded.
This API can be called even if there is a pending JavaScript exception.
####
`napi_make_callback`
History
| Version | Changes |
| --- | --- |
| v8.6.0 | Added `async_context` parameter. |
| v8.0.0 | Added in: v8.0.0 |
N-API version: 1
```
NAPI_EXTERN napi_status napi_make_callback(napi_env env,
napi_async_context async_context,
napi_value recv,
napi_value func,
size_t argc,
const napi_value* argv,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] async_context`: Context for the async operation that is invoking the callback. This should normally be a value previously obtained from [`napi_async_init`](#napi_async_init). In order to retain ABI compatibility with previous versions, passing `NULL` for `async_context` does not result in an error. However, this results in incorrect operation of async hooks. Potential issues include loss of async context when using the `AsyncLocalStorage` API.
* `[in] recv`: The `this` value passed to the called function.
* `[in] func`: `napi_value` representing the JavaScript function to be invoked.
* `[in] argc`: The count of elements in the `argv` array.
* `[in] argv`: Array of JavaScript values as `napi_value` representing the arguments to the function. If `argc` is zero this parameter may be omitted by passing in `NULL`.
* `[out] result`: `napi_value` representing the JavaScript object returned.
Returns `napi_ok` if the API succeeded.
This method allows a JavaScript function object to be called from a native add-on. This API is similar to `napi_call_function`. However, it is used to call *from* native code back *into* JavaScript *after* returning from an async operation (when there is no other script on the stack). It is a fairly simple wrapper around `node::MakeCallback`.
Note it is *not* necessary to use `napi_make_callback` from within a `napi_async_complete_callback`; in that situation the callback's async context has already been set up, so a direct call to `napi_call_function` is sufficient and appropriate. Use of the `napi_make_callback` function may be required when implementing custom async behavior that does not use `napi_create_async_work`.
Any `process.nextTick`s or Promises scheduled on the microtask queue by JavaScript during the callback are ran before returning back to C/C++.
####
`napi_open_callback_scope`
Added in: v9.6.0 N-API version: 3
```
NAPI_EXTERN napi_status napi_open_callback_scope(napi_env env,
napi_value resource_object,
napi_async_context context,
napi_callback_scope* result)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] resource_object`: An object associated with the async work that will be passed to possible `async_hooks` [`init` hooks](async_hooks#initasyncid-type-triggerasyncid-resource). This parameter has been deprecated and is ignored at runtime. Use the `async_resource` parameter in [`napi_async_init`](#napi_async_init) instead.
* `[in] context`: Context for the async operation that is invoking the callback. This should be a value previously obtained from [`napi_async_init`](#napi_async_init).
* `[out] result`: The newly created scope.
There are cases (for example, resolving promises) where it is necessary to have the equivalent of the scope associated with a callback in place when making certain Node-API calls. If there is no other script on the stack the [`napi_open_callback_scope`](#napi_open_callback_scope) and [`napi_close_callback_scope`](#napi_close_callback_scope) functions can be used to open/close the required scope.
####
`napi_close_callback_scope`
Added in: v9.6.0 N-API version: 3
```
NAPI_EXTERN napi_status napi_close_callback_scope(napi_env env,
napi_callback_scope scope)
```
* `[in] env`: The environment that the API is invoked under.
* `[in] scope`: The scope to be closed.
This API can be called even if there is a pending JavaScript exception.
### Version management
####
`napi_get_node_version`
Added in: v8.4.0 N-API version: 1
```
typedef struct {
uint32_t major;
uint32_t minor;
uint32_t patch;
const char* release;
} napi_node_version;
napi_status napi_get_node_version(napi_env env,
const napi_node_version** version);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] version`: A pointer to version information for Node.js itself.
Returns `napi_ok` if the API succeeded.
This function fills the `version` struct with the major, minor, and patch version of Node.js that is currently running, and the `release` field with the value of [`process.release.name`](process#processrelease).
The returned buffer is statically allocated and does not need to be freed.
####
`napi_get_version`
Added in: v8.0.0 N-API version: 1
```
napi_status napi_get_version(napi_env env,
uint32_t* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: The highest version of Node-API supported.
Returns `napi_ok` if the API succeeded.
This API returns the highest Node-API version supported by the Node.js runtime. Node-API is planned to be additive such that newer releases of Node.js may support additional API functions. In order to allow an addon to use a newer function when running with versions of Node.js that support it, while providing fallback behavior when running with Node.js versions that don't support it:
* Call `napi_get_version()` to determine if the API is available.
* If available, dynamically load a pointer to the function using `uv_dlsym()`.
* Use the dynamically loaded pointer to invoke the function.
* If the function is not available, provide an alternate implementation that does not use the function.
### Memory management
####
`napi_adjust_external_memory`
Added in: v8.5.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_adjust_external_memory(napi_env env,
int64_t change_in_bytes,
int64_t* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] change_in_bytes`: The change in externally allocated memory that is kept alive by JavaScript objects.
* `[out] result`: The adjusted value
Returns `napi_ok` if the API succeeded.
This function gives V8 an indication of the amount of externally allocated memory that is kept alive by JavaScript objects (i.e. a JavaScript object that points to its own memory allocated by a native addon). Registering externally allocated memory will trigger global garbage collections more often than it would otherwise.
### Promises
Node-API provides facilities for creating `Promise` objects as described in [Section 25.4](https://tc39.github.io/ecma262/#sec-promise-objects) of the ECMA specification. It implements promises as a pair of objects. When a promise is created by `napi_create_promise()`, a "deferred" object is created and returned alongside the `Promise`. The deferred object is bound to the created `Promise` and is the only means to resolve or reject the `Promise` using `napi_resolve_deferred()` or `napi_reject_deferred()`. The deferred object that is created by `napi_create_promise()` is freed by `napi_resolve_deferred()` or `napi_reject_deferred()`. The `Promise` object may be returned to JavaScript where it can be used in the usual fashion.
For example, to create a promise and pass it to an asynchronous worker:
```
napi_deferred deferred;
napi_value promise;
napi_status status;
// Create the promise.
status = napi_create_promise(env, &deferred, &promise);
if (status != napi_ok) return NULL;
// Pass the deferred to a function that performs an asynchronous action.
do_something_asynchronous(deferred);
// Return the promise to JS
return promise;
```
The above function `do_something_asynchronous()` would perform its asynchronous action and then it would resolve or reject the deferred, thereby concluding the promise and freeing the deferred:
```
napi_deferred deferred;
napi_value undefined;
napi_status status;
// Create a value with which to conclude the deferred.
status = napi_get_undefined(env, &undefined);
if (status != napi_ok) return NULL;
// Resolve or reject the promise associated with the deferred depending on
// whether the asynchronous action succeeded.
if (asynchronous_action_succeeded) {
status = napi_resolve_deferred(env, deferred, undefined);
} else {
status = napi_reject_deferred(env, deferred, undefined);
}
if (status != napi_ok) return NULL;
// At this point the deferred has been freed, so we should assign NULL to it.
deferred = NULL;
```
####
`napi_create_promise`
Added in: v8.5.0 N-API version: 1
```
napi_status napi_create_promise(napi_env env,
napi_deferred* deferred,
napi_value* promise);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] deferred`: A newly created deferred object which can later be passed to `napi_resolve_deferred()` or `napi_reject_deferred()` to resolve resp. reject the associated promise.
* `[out] promise`: The JavaScript promise associated with the deferred object.
Returns `napi_ok` if the API succeeded.
This API creates a deferred object and a JavaScript promise.
####
`napi_resolve_deferred`
Added in: v8.5.0 N-API version: 1
```
napi_status napi_resolve_deferred(napi_env env,
napi_deferred deferred,
napi_value resolution);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] deferred`: The deferred object whose associated promise to resolve.
* `[in] resolution`: The value with which to resolve the promise.
This API resolves a JavaScript promise by way of the deferred object with which it is associated. Thus, it can only be used to resolve JavaScript promises for which the corresponding deferred object is available. This effectively means that the promise must have been created using `napi_create_promise()` and the deferred object returned from that call must have been retained in order to be passed to this API.
The deferred object is freed upon successful completion.
####
`napi_reject_deferred`
Added in: v8.5.0 N-API version: 1
```
napi_status napi_reject_deferred(napi_env env,
napi_deferred deferred,
napi_value rejection);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] deferred`: The deferred object whose associated promise to resolve.
* `[in] rejection`: The value with which to reject the promise.
This API rejects a JavaScript promise by way of the deferred object with which it is associated. Thus, it can only be used to reject JavaScript promises for which the corresponding deferred object is available. This effectively means that the promise must have been created using `napi_create_promise()` and the deferred object returned from that call must have been retained in order to be passed to this API.
The deferred object is freed upon successful completion.
####
`napi_is_promise`
Added in: v8.5.0 N-API version: 1
```
napi_status napi_is_promise(napi_env env,
napi_value value,
bool* is_promise);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] value`: The value to examine
* `[out] is_promise`: Flag indicating whether `promise` is a native promise object (that is, a promise object created by the underlying engine).
### Script execution
Node-API provides an API for executing a string containing JavaScript using the underlying JavaScript engine.
####
`napi_run_script`
Added in: v8.5.0 N-API version: 1
```
NAPI_EXTERN napi_status napi_run_script(napi_env env,
napi_value script,
napi_value* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] script`: A JavaScript string containing the script to execute.
* `[out] result`: The value resulting from having executed the script.
This function executes a string of JavaScript code and returns its result with the following caveats:
* Unlike `eval`, this function does not allow the script to access the current lexical scope, and therefore also does not allow to access the [module scope](modules#the-module-scope), meaning that pseudo-globals such as `require` will not be available.
* The script can access the [global scope](globals). Function and `var` declarations in the script will be added to the [`global`](globals#global) object. Variable declarations made using `let` and `const` will be visible globally, but will not be added to the [`global`](globals#global) object.
* The value of `this` is [`global`](globals#global) within the script.
### libuv event loop
Node-API provides a function for getting the current event loop associated with a specific `napi_env`.
####
`napi_get_uv_event_loop`
Added in: v9.3.0, v8.10.0 N-API version: 2
```
NAPI_EXTERN napi_status napi_get_uv_event_loop(napi_env env,
struct uv_loop_s** loop);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] loop`: The current libuv loop instance.
### Asynchronous thread-safe function calls
JavaScript functions can normally only be called from a native addon's main thread. If an addon creates additional threads, then Node-API functions that require a `napi_env`, `napi_value`, or `napi_ref` must not be called from those threads.
When an addon has additional threads and JavaScript functions need to be invoked based on the processing completed by those threads, those threads must communicate with the addon's main thread so that the main thread can invoke the JavaScript function on their behalf. The thread-safe function APIs provide an easy way to do this.
These APIs provide the type `napi_threadsafe_function` as well as APIs to create, destroy, and call objects of this type. `napi_create_threadsafe_function()` creates a persistent reference to a `napi_value` that holds a JavaScript function which can be called from multiple threads. The calls happen asynchronously. This means that values with which the JavaScript callback is to be called will be placed in a queue, and, for each value in the queue, a call will eventually be made to the JavaScript function.
Upon creation of a `napi_threadsafe_function` a `napi_finalize` callback can be provided. This callback will be invoked on the main thread when the thread-safe function is about to be destroyed. It receives the context and the finalize data given during construction, and provides an opportunity for cleaning up after the threads e.g. by calling `uv_thread_join()`. **Aside from the main loop thread, no threads should be using the thread-safe function after the finalize callback completes.**
The `context` given during the call to `napi_create_threadsafe_function()` can be retrieved from any thread with a call to `napi_get_threadsafe_function_context()`.
#### Calling a thread-safe function
`napi_call_threadsafe_function()` can be used for initiating a call into JavaScript. `napi_call_threadsafe_function()` accepts a parameter which controls whether the API behaves blockingly. If set to `napi_tsfn_nonblocking`, the API behaves non-blockingly, returning `napi_queue_full` if the queue was full, preventing data from being successfully added to the queue. If set to `napi_tsfn_blocking`, the API blocks until space becomes available in the queue. `napi_call_threadsafe_function()` never blocks if the thread-safe function was created with a maximum queue size of 0.
`napi_call_threadsafe_function()` should not be called with `napi_tsfn_blocking` from a JavaScript thread, because, if the queue is full, it may cause the JavaScript thread to deadlock.
The actual call into JavaScript is controlled by the callback given via the `call_js_cb` parameter. `call_js_cb` is invoked on the main thread once for each value that was placed into the queue by a successful call to `napi_call_threadsafe_function()`. If such a callback is not given, a default callback will be used, and the resulting JavaScript call will have no arguments. The `call_js_cb` callback receives the JavaScript function to call as a `napi_value` in its parameters, as well as the `void*` context pointer used when creating the `napi_threadsafe_function`, and the next data pointer that was created by one of the secondary threads. The callback can then use an API such as `napi_call_function()` to call into JavaScript.
The callback may also be invoked with `env` and `call_js_cb` both set to `NULL` to indicate that calls into JavaScript are no longer possible, while items remain in the queue that may need to be freed. This normally occurs when the Node.js process exits while there is a thread-safe function still active.
It is not necessary to call into JavaScript via `napi_make_callback()` because Node-API runs `call_js_cb` in a context appropriate for callbacks.
#### Reference counting of thread-safe functions
Threads can be added to and removed from a `napi_threadsafe_function` object during its existence. Thus, in addition to specifying an initial number of threads upon creation, `napi_acquire_threadsafe_function` can be called to indicate that a new thread will start making use of the thread-safe function. Similarly, `napi_release_threadsafe_function` can be called to indicate that an existing thread will stop making use of the thread-safe function.
`napi_threadsafe_function` objects are destroyed when every thread which uses the object has called `napi_release_threadsafe_function()` or has received a return status of `napi_closing` in response to a call to `napi_call_threadsafe_function`. The queue is emptied before the `napi_threadsafe_function` is destroyed. `napi_release_threadsafe_function()` should be the last API call made in conjunction with a given `napi_threadsafe_function`, because after the call completes, there is no guarantee that the `napi_threadsafe_function` is still allocated. For the same reason, do not use a thread-safe function after receiving a return value of `napi_closing` in response to a call to `napi_call_threadsafe_function`. Data associated with the `napi_threadsafe_function` can be freed in its `napi_finalize` callback which was passed to `napi_create_threadsafe_function()`. The parameter `initial_thread_count` of `napi_create_threadsafe_function` marks the initial number of acquisitions of the thread-safe functions, instead of calling `napi_acquire_threadsafe_function` multiple times at creation.
Once the number of threads making use of a `napi_threadsafe_function` reaches zero, no further threads can start making use of it by calling `napi_acquire_threadsafe_function()`. In fact, all subsequent API calls associated with it, except `napi_release_threadsafe_function()`, will return an error value of `napi_closing`.
The thread-safe function can be "aborted" by giving a value of `napi_tsfn_abort` to `napi_release_threadsafe_function()`. This will cause all subsequent APIs associated with the thread-safe function except `napi_release_threadsafe_function()` to return `napi_closing` even before its reference count reaches zero. In particular, `napi_call_threadsafe_function()` will return `napi_closing`, thus informing the threads that it is no longer possible to make asynchronous calls to the thread-safe function. This can be used as a criterion for terminating the thread. **Upon receiving a return value of `napi_closing` from `napi_call_threadsafe_function()` a thread must not use the thread-safe function anymore because it is no longer guaranteed to be allocated.**
#### Deciding whether to keep the process running
Similarly to libuv handles, thread-safe functions can be "referenced" and "unreferenced". A "referenced" thread-safe function will cause the event loop on the thread on which it is created to remain alive until the thread-safe function is destroyed. In contrast, an "unreferenced" thread-safe function will not prevent the event loop from exiting. The APIs `napi_ref_threadsafe_function` and `napi_unref_threadsafe_function` exist for this purpose.
Neither does `napi_unref_threadsafe_function` mark the thread-safe functions as able to be destroyed nor does `napi_ref_threadsafe_function` prevent it from being destroyed.
####
`napi_create_threadsafe_function`
History
| Version | Changes |
| --- | --- |
| v12.6.0, v10.17.0 | Made `func` parameter optional with custom `call_js_cb`. |
| v10.6.0 | Added in: v10.6.0 |
N-API version: 4
```
NAPI_EXTERN napi_status
napi_create_threadsafe_function(napi_env env,
napi_value func,
napi_value async_resource,
napi_value async_resource_name,
size_t max_queue_size,
size_t initial_thread_count,
void* thread_finalize_data,
napi_finalize thread_finalize_cb,
void* context,
napi_threadsafe_function_call_js call_js_cb,
napi_threadsafe_function* result);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] func`: An optional JavaScript function to call from another thread. It must be provided if `NULL` is passed to `call_js_cb`.
* `[in] async_resource`: An optional object associated with the async work that will be passed to possible `async_hooks` [`init` hooks](async_hooks#initasyncid-type-triggerasyncid-resource).
* `[in] async_resource_name`: A JavaScript string to provide an identifier for the kind of resource that is being provided for diagnostic information exposed by the `async_hooks` API.
* `[in] max_queue_size`: Maximum size of the queue. `0` for no limit.
* `[in] initial_thread_count`: The initial number of acquisitions, i.e. the initial number of threads, including the main thread, which will be making use of this function.
* `[in] thread_finalize_data`: Optional data to be passed to `thread_finalize_cb`.
* `[in] thread_finalize_cb`: Optional function to call when the `napi_threadsafe_function` is being destroyed.
* `[in] context`: Optional data to attach to the resulting `napi_threadsafe_function`.
* `[in] call_js_cb`: Optional callback which calls the JavaScript function in response to a call on a different thread. This callback will be called on the main thread. If not given, the JavaScript function will be called with no parameters and with `undefined` as its `this` value. [`napi_threadsafe_function_call_js`](#napi_threadsafe_function_call_js) provides more details.
* `[out] result`: The asynchronous thread-safe JavaScript function.
####
`napi_get_threadsafe_function_context`
Added in: v10.6.0 N-API version: 4
```
NAPI_EXTERN napi_status
napi_get_threadsafe_function_context(napi_threadsafe_function func,
void** result);
```
* `[in] func`: The thread-safe function for which to retrieve the context.
* `[out] result`: The location where to store the context.
This API may be called from any thread which makes use of `func`.
####
`napi_call_threadsafe_function`
History
| Version | Changes |
| --- | --- |
| v14.5.0 | Support for `napi_would_deadlock` has been reverted. |
| v14.1.0 | Return `napi_would_deadlock` when called with `napi_tsfn_blocking` from the main thread or a worker thread and the queue is full. |
| v10.6.0 | Added in: v10.6.0 |
N-API version: 4
```
NAPI_EXTERN napi_status
napi_call_threadsafe_function(napi_threadsafe_function func,
void* data,
napi_threadsafe_function_call_mode is_blocking);
```
* `[in] func`: The asynchronous thread-safe JavaScript function to invoke.
* `[in] data`: Data to send into JavaScript via the callback `call_js_cb` provided during the creation of the thread-safe JavaScript function.
* `[in] is_blocking`: Flag whose value can be either `napi_tsfn_blocking` to indicate that the call should block if the queue is full or `napi_tsfn_nonblocking` to indicate that the call should return immediately with a status of `napi_queue_full` whenever the queue is full.
This API should not be called with `napi_tsfn_blocking` from a JavaScript thread, because, if the queue is full, it may cause the JavaScript thread to deadlock.
This API will return `napi_closing` if `napi_release_threadsafe_function()` was called with `abort` set to `napi_tsfn_abort` from any thread. The value is only added to the queue if the API returns `napi_ok`.
This API may be called from any thread which makes use of `func`.
####
`napi_acquire_threadsafe_function`
Added in: v10.6.0 N-API version: 4
```
NAPI_EXTERN napi_status
napi_acquire_threadsafe_function(napi_threadsafe_function func);
```
* `[in] func`: The asynchronous thread-safe JavaScript function to start making use of.
A thread should call this API before passing `func` to any other thread-safe function APIs to indicate that it will be making use of `func`. This prevents `func` from being destroyed when all other threads have stopped making use of it.
This API may be called from any thread which will start making use of `func`.
####
`napi_release_threadsafe_function`
Added in: v10.6.0 N-API version: 4
```
NAPI_EXTERN napi_status
napi_release_threadsafe_function(napi_threadsafe_function func,
napi_threadsafe_function_release_mode mode);
```
* `[in] func`: The asynchronous thread-safe JavaScript function whose reference count to decrement.
* `[in] mode`: Flag whose value can be either `napi_tsfn_release` to indicate that the current thread will make no further calls to the thread-safe function, or `napi_tsfn_abort` to indicate that in addition to the current thread, no other thread should make any further calls to the thread-safe function. If set to `napi_tsfn_abort`, further calls to `napi_call_threadsafe_function()` will return `napi_closing`, and no further values will be placed in the queue.
A thread should call this API when it stops making use of `func`. Passing `func` to any thread-safe APIs after having called this API has undefined results, as `func` may have been destroyed.
This API may be called from any thread which will stop making use of `func`.
####
`napi_ref_threadsafe_function`
Added in: v10.6.0 N-API version: 4
```
NAPI_EXTERN napi_status
napi_ref_threadsafe_function(napi_env env, napi_threadsafe_function func);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] func`: The thread-safe function to reference.
This API is used to indicate that the event loop running on the main thread should not exit until `func` has been destroyed. Similar to [`uv_ref`](https://docs.libuv.org/en/v1.x/handle.html#c.uv_ref) it is also idempotent.
Neither does `napi_unref_threadsafe_function` mark the thread-safe functions as able to be destroyed nor does `napi_ref_threadsafe_function` prevent it from being destroyed. `napi_acquire_threadsafe_function` and `napi_release_threadsafe_function` are available for that purpose.
This API may only be called from the main thread.
####
`napi_unref_threadsafe_function`
Added in: v10.6.0 N-API version: 4
```
NAPI_EXTERN napi_status
napi_unref_threadsafe_function(napi_env env, napi_threadsafe_function func);
```
* `[in] env`: The environment that the API is invoked under.
* `[in] func`: The thread-safe function to unreference.
This API is used to indicate that the event loop running on the main thread may exit before `func` is destroyed. Similar to [`uv_unref`](https://docs.libuv.org/en/v1.x/handle.html#c.uv_unref) it is also idempotent.
This API may only be called from the main thread.
### Miscellaneous utilities
####
`node_api_get_module_file_name`
Added in: v15.9.0, v14.18.0, v12.22.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
```
NAPI_EXTERN napi_status
node_api_get_module_file_name(napi_env env, const char** result);
```
* `[in] env`: The environment that the API is invoked under.
* `[out] result`: A URL containing the absolute path of the location from which the add-on was loaded. For a file on the local file system it will start with `file://`. The string is null-terminated and owned by `env` and must thus not be modified or freed.
`result` may be an empty string if the add-on loading process fails to establish the add-on's file name during loading.
| programming_docs |
node None URL
---
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/url.js](https://github.com/nodejs/node/blob/v19.0.1/lib/url.js)
The `node:url` module provides utilities for URL resolution and parsing. It can be accessed using:
MJS modules
```
import url from 'node:url';
```
CJS modules
```
const url = require('node:url');
```
### URL strings and URL objects
A URL string is a structured string containing multiple meaningful components. When parsed, a URL object is returned containing properties for each of these components.
The `node:url` module provides two APIs for working with URLs: a legacy API that is Node.js specific, and a newer API that implements the same [WHATWG URL Standard](https://url.spec.whatwg.org/) used by web browsers.
A comparison between the WHATWG and legacy APIs is provided below. Above the URL `'https://user:[email protected]:8080/p/a/t/h?query=string#hash'`, properties of an object returned by the legacy `url.parse()` are shown. Below it are properties of a WHATWG `URL` object.
WHATWG URL's `origin` property includes `protocol` and `host`, but not `username` or `password`.
```
┌────────────────────────────────────────────────────────────────────────────────────────────────┐
│ href │
├──────────┬──┬─────────────────────┬────────────────────────┬───────────────────────────┬───────┤
│ protocol │ │ auth │ host │ path │ hash │
│ │ │ ├─────────────────┬──────┼──────────┬────────────────┤ │
│ │ │ │ hostname │ port │ pathname │ search │ │
│ │ │ │ │ │ ├─┬──────────────┤ │
│ │ │ │ │ │ │ │ query │ │
" https: // user : pass @ sub.example.com : 8080 /p/a/t/h ? query=string #hash "
│ │ │ │ │ hostname │ port │ │ │ │
│ │ │ │ ├─────────────────┴──────┤ │ │ │
│ protocol │ │ username │ password │ host │ │ │ │
├──────────┴──┼──────────┴──────────┼────────────────────────┤ │ │ │
│ origin │ │ origin │ pathname │ search │ hash │
├─────────────┴─────────────────────┴────────────────────────┴──────────┴────────────────┴───────┤
│ href │
└────────────────────────────────────────────────────────────────────────────────────────────────┘
(All spaces in the "" line should be ignored. They are purely for formatting.)
```
Parsing the URL string using the WHATWG API:
```
const myURL =
new URL('https://user:[email protected]:8080/p/a/t/h?query=string#hash');
```
Parsing the URL string using the legacy API:
MJS modules
```
import url from 'node:url';
const myURL =
url.parse('https://user:[email protected]:8080/p/a/t/h?query=string#hash');
```
CJS modules
```
const url = require('node:url');
const myURL =
url.parse('https://user:[email protected]:8080/p/a/t/h?query=string#hash');
```
#### Constructing a URL from component parts and getting the constructed string
It is possible to construct a WHATWG URL from component parts using either the property setters or a template literal string:
```
const myURL = new URL('https://example.org');
myURL.pathname = '/a/b/c';
myURL.search = '?d=e';
myURL.hash = '#fgh';
```
```
const pathname = '/a/b/c';
const search = '?d=e';
const hash = '#fgh';
const myURL = new URL(`https://example.org${pathname}${search}${hash}`);
```
To get the constructed URL string, use the `href` property accessor:
```
console.log(myURL.href);
```
### The WHATWG URL API
#### Class: `URL`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | The class is now available on the global object. |
| v7.0.0, v6.13.0 | Added in: v7.0.0, v6.13.0 |
Browser-compatible `URL` class, implemented by following the WHATWG URL Standard. [Examples of parsed URLs](https://url.spec.whatwg.org/#example-url-parsing) may be found in the Standard itself. The `URL` class is also available on the global object.
In accordance with browser conventions, all properties of `URL` objects are implemented as getters and setters on the class prototype, rather than as data properties on the object itself. Thus, unlike [legacy `urlObject`](#legacy-urlobject)s, using the `delete` keyword on any properties of `URL` objects (e.g. `delete myURL.protocol`, `delete myURL.pathname`, etc) has no effect but will still return `true`.
#####
`new URL(input[, base])`
* `input` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The absolute or relative input URL to parse. If `input` is relative, then `base` is required. If `input` is absolute, the `base` is ignored. If `input` is not a string, it is [converted to a string](https://tc39.es/ecma262/#sec-tostring) first.
* `base` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The base URL to resolve against if the `input` is not absolute. If `base` is not a string, it is [converted to a string](https://tc39.es/ecma262/#sec-tostring) first.
Creates a new `URL` object by parsing the `input` relative to the `base`. If `base` is passed as a string, it will be parsed equivalent to `new URL(base)`.
```
const myURL = new URL('/foo', 'https://example.org/');
// https://example.org/foo
```
The URL constructor is accessible as a property on the global object. It can also be imported from the built-in url module:
MJS modules
```
import { URL } from 'node:url';
console.log(URL === globalThis.URL); // Prints 'true'.
```
CJS modules
```
console.log(URL === require('node:url').URL); // Prints 'true'.
```
A `TypeError` will be thrown if the `input` or `base` are not valid URLs. Note that an effort will be made to coerce the given values into strings. For instance:
```
const myURL = new URL({ toString: () => 'https://example.org/' });
// https://example.org/
```
Unicode characters appearing within the host name of `input` will be automatically converted to ASCII using the [Punycode](https://tools.ietf.org/html/rfc5891#section-4.4) algorithm.
```
const myURL = new URL('https://測試');
// https://xn--g6w251d/
```
This feature is only available if the `node` executable was compiled with [ICU](intl#options-for-building-nodejs) enabled. If not, the domain names are passed through unchanged.
In cases where it is not known in advance if `input` is an absolute URL and a `base` is provided, it is advised to validate that the `origin` of the `URL` object is what is expected.
```
let myURL = new URL('http://Example.com/', 'https://example.org/');
// http://example.com/
myURL = new URL('https://Example.com/', 'https://example.org/');
// https://example.com/
myURL = new URL('foo://Example.com/', 'https://example.org/');
// foo://Example.com/
myURL = new URL('http:Example.com/', 'https://example.org/');
// http://example.com/
myURL = new URL('https:Example.com/', 'https://example.org/');
// https://example.org/Example.com/
myURL = new URL('foo:Example.com/', 'https://example.org/');
// foo:Example.com/
```
#####
`url.hash`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the fragment portion of the URL.
```
const myURL = new URL('https://example.org/foo#bar');
console.log(myURL.hash);
// Prints #bar
myURL.hash = 'baz';
console.log(myURL.href);
// Prints https://example.org/foo#baz
```
Invalid URL characters included in the value assigned to the `hash` property are [percent-encoded](#percent-encoding-in-urls). The selection of which characters to percent-encode may vary somewhat from what the [`url.parse()`](#urlparseurlstring-parsequerystring-slashesdenotehost) and [`url.format()`](#urlformaturlobject) methods would produce.
#####
`url.host`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the host portion of the URL.
```
const myURL = new URL('https://example.org:81/foo');
console.log(myURL.host);
// Prints example.org:81
myURL.host = 'example.com:82';
console.log(myURL.href);
// Prints https://example.com:82/foo
```
Invalid host values assigned to the `host` property are ignored.
#####
`url.hostname`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the host name portion of the URL. The key difference between `url.host` and `url.hostname` is that `url.hostname` does *not* include the port.
```
const myURL = new URL('https://example.org:81/foo');
console.log(myURL.hostname);
// Prints example.org
// Setting the hostname does not change the port
myURL.hostname = 'example.com:82';
console.log(myURL.href);
// Prints https://example.com:81/foo
// Use myURL.host to change the hostname and port
myURL.host = 'example.org:82';
console.log(myURL.href);
// Prints https://example.org:82/foo
```
Invalid host name values assigned to the `hostname` property are ignored.
#####
`url.href`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the serialized URL.
```
const myURL = new URL('https://example.org/foo');
console.log(myURL.href);
// Prints https://example.org/foo
myURL.href = 'https://example.com/bar';
console.log(myURL.href);
// Prints https://example.com/bar
```
Getting the value of the `href` property is equivalent to calling [`url.toString()`](#urltostring).
Setting the value of this property to a new value is equivalent to creating a new `URL` object using [`new URL(value)`](#new-urlinput-base). Each of the `URL` object's properties will be modified.
If the value assigned to the `href` property is not a valid URL, a `TypeError` will be thrown.
#####
`url.origin`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The scheme "gopher" is no longer special and `url.origin` now returns `'null'` for it. |
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets the read-only serialization of the URL's origin.
```
const myURL = new URL('https://example.org/foo/bar?baz');
console.log(myURL.origin);
// Prints https://example.org
```
```
const idnURL = new URL('https://測試');
console.log(idnURL.origin);
// Prints https://xn--g6w251d
console.log(idnURL.hostname);
// Prints xn--g6w251d
```
#####
`url.password`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the password portion of the URL.
```
const myURL = new URL('https://abc:[email protected]');
console.log(myURL.password);
// Prints xyz
myURL.password = '123';
console.log(myURL.href);
// Prints https://abc:[email protected]
```
Invalid URL characters included in the value assigned to the `password` property are [percent-encoded](#percent-encoding-in-urls). The selection of which characters to percent-encode may vary somewhat from what the [`url.parse()`](#urlparseurlstring-parsequerystring-slashesdenotehost) and [`url.format()`](#urlformaturlobject) methods would produce.
#####
`url.pathname`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the path portion of the URL.
```
const myURL = new URL('https://example.org/abc/xyz?123');
console.log(myURL.pathname);
// Prints /abc/xyz
myURL.pathname = '/abcdef';
console.log(myURL.href);
// Prints https://example.org/abcdef?123
```
Invalid URL characters included in the value assigned to the `pathname` property are [percent-encoded](#percent-encoding-in-urls). The selection of which characters to percent-encode may vary somewhat from what the [`url.parse()`](#urlparseurlstring-parsequerystring-slashesdenotehost) and [`url.format()`](#urlformaturlobject) methods would produce.
#####
`url.port`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The scheme "gopher" is no longer special. |
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the port portion of the URL.
The port value may be a number or a string containing a number in the range `0` to `65535` (inclusive). Setting the value to the default port of the `URL` objects given `protocol` will result in the `port` value becoming the empty string (`''`).
The port value can be an empty string in which case the port depends on the protocol/scheme:
| protocol | port |
| --- | --- |
| "ftp" | 21 |
| "file" | |
| "http" | 80 |
| "https" | 443 |
| "ws" | 80 |
| "wss" | 443 |
Upon assigning a value to the port, the value will first be converted to a string using `.toString()`.
If that string is invalid but it begins with a number, the leading number is assigned to `port`. If the number lies outside the range denoted above, it is ignored.
```
const myURL = new URL('https://example.org:8888');
console.log(myURL.port);
// Prints 8888
// Default ports are automatically transformed to the empty string
// (HTTPS protocol's default port is 443)
myURL.port = '443';
console.log(myURL.port);
// Prints the empty string
console.log(myURL.href);
// Prints https://example.org/
myURL.port = 1234;
console.log(myURL.port);
// Prints 1234
console.log(myURL.href);
// Prints https://example.org:1234/
// Completely invalid port strings are ignored
myURL.port = 'abcd';
console.log(myURL.port);
// Prints 1234
// Leading numbers are treated as a port number
myURL.port = '5678abcd';
console.log(myURL.port);
// Prints 5678
// Non-integers are truncated
myURL.port = 1234.5678;
console.log(myURL.port);
// Prints 1234
// Out-of-range numbers which are not represented in scientific notation
// will be ignored.
myURL.port = 1e10; // 10000000000, will be range-checked as described below
console.log(myURL.port);
// Prints 1234
```
Numbers which contain a decimal point, such as floating-point numbers or numbers in scientific notation, are not an exception to this rule. Leading numbers up to the decimal point will be set as the URL's port, assuming they are valid:
```
myURL.port = 4.567e21;
console.log(myURL.port);
// Prints 4 (because it is the leading number in the string '4.567e21')
```
#####
`url.protocol`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the protocol portion of the URL.
```
const myURL = new URL('https://example.org');
console.log(myURL.protocol);
// Prints https:
myURL.protocol = 'ftp';
console.log(myURL.href);
// Prints ftp://example.org/
```
Invalid URL protocol values assigned to the `protocol` property are ignored.
###### Special schemes
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The scheme "gopher" is no longer special. |
The [WHATWG URL Standard](https://url.spec.whatwg.org/) considers a handful of URL protocol schemes to be *special* in terms of how they are parsed and serialized. When a URL is parsed using one of these special protocols, the `url.protocol` property may be changed to another special protocol but cannot be changed to a non-special protocol, and vice versa.
For instance, changing from `http` to `https` works:
```
const u = new URL('http://example.org');
u.protocol = 'https';
console.log(u.href);
// https://example.org
```
However, changing from `http` to a hypothetical `fish` protocol does not because the new protocol is not special.
```
const u = new URL('http://example.org');
u.protocol = 'fish';
console.log(u.href);
// http://example.org
```
Likewise, changing from a non-special protocol to a special protocol is also not permitted:
```
const u = new URL('fish://example.org');
u.protocol = 'http';
console.log(u.href);
// fish://example.org
```
According to the WHATWG URL Standard, special protocol schemes are `ftp`, `file`, `http`, `https`, `ws`, and `wss`.
#####
`url.search`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the serialized query portion of the URL.
```
const myURL = new URL('https://example.org/abc?123');
console.log(myURL.search);
// Prints ?123
myURL.search = 'abc=xyz';
console.log(myURL.href);
// Prints https://example.org/abc?abc=xyz
```
Any invalid URL characters appearing in the value assigned the `search` property will be [percent-encoded](#percent-encoding-in-urls). The selection of which characters to percent-encode may vary somewhat from what the [`url.parse()`](#urlparseurlstring-parsequerystring-slashesdenotehost) and [`url.format()`](#urlformaturlobject) methods would produce.
#####
`url.searchParams`
* [<URLSearchParams>](url#class-urlsearchparams)
Gets the [`URLSearchParams`](#class-urlsearchparams) object representing the query parameters of the URL. This property is read-only but the `URLSearchParams` object it provides can be used to mutate the URL instance; to replace the entirety of query parameters of the URL, use the [`url.search`](#urlsearch) setter. See [`URLSearchParams`](#class-urlsearchparams) documentation for details.
Use care when using `.searchParams` to modify the `URL` because, per the WHATWG specification, the `URLSearchParams` object uses different rules to determine which characters to percent-encode. For instance, the `URL` object will not percent encode the ASCII tilde (`~`) character, while `URLSearchParams` will always encode it:
```
const myUrl = new URL('https://example.org/abc?foo=~bar');
console.log(myUrl.search); // prints ?foo=~bar
// Modify the URL via searchParams...
myUrl.searchParams.sort();
console.log(myUrl.search); // prints ?foo=%7Ebar
```
#####
`url.username`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Gets and sets the username portion of the URL.
```
const myURL = new URL('https://abc:[email protected]');
console.log(myURL.username);
// Prints abc
myURL.username = '123';
console.log(myURL.href);
// Prints https://123:[email protected]/
```
Any invalid URL characters appearing in the value assigned the `username` property will be [percent-encoded](#percent-encoding-in-urls). The selection of which characters to percent-encode may vary somewhat from what the [`url.parse()`](#urlparseurlstring-parsequerystring-slashesdenotehost) and [`url.format()`](#urlformaturlobject) methods would produce.
#####
`url.toString()`
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `toString()` method on the `URL` object returns the serialized URL. The value returned is equivalent to that of [`url.href`](#urlhref) and [`url.toJSON()`](#urltojson).
#####
`url.toJSON()`
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `toJSON()` method on the `URL` object returns the serialized URL. The value returned is equivalent to that of [`url.href`](#urlhref) and [`url.toString()`](#urltostring).
This method is automatically called when an `URL` object is serialized with [`JSON.stringify()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify).
```
const myURLs = [
new URL('https://www.example.com'),
new URL('https://test.example.org'),
];
console.log(JSON.stringify(myURLs));
// Prints ["https://www.example.com/","https://test.example.org/"]
```
#####
`URL.createObjectURL(blob)`
Added in: v16.7.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `blob` [<Blob>](buffer#class-blob)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Creates a `'blob:nodedata:...'` URL string that represents the given [<Blob>](buffer#class-blob) object and can be used to retrieve the `Blob` later.
```
const {
Blob,
resolveObjectURL,
} = require('node:buffer');
const blob = new Blob(['hello']);
const id = URL.createObjectURL(blob);
// later...
const otherBlob = resolveObjectURL(id);
console.log(otherBlob.size);
```
The data stored by the registered [<Blob>](buffer#class-blob) will be retained in memory until `URL.revokeObjectURL()` is called to remove it.
`Blob` objects are registered within the current thread. If using Worker Threads, `Blob` objects registered within one Worker will not be available to other workers or the main thread.
#####
`URL.revokeObjectURL(id)`
Added in: v16.7.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `id` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A `'blob:nodedata:...` URL string returned by a prior call to `URL.createObjectURL()`.
Removes the stored [<Blob>](buffer#class-blob) identified by the given ID. Attempting to revoke a ID that isn't registered will silently fail.
#### Class: `URLSearchParams`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | The class is now available on the global object. |
| v7.5.0, v6.13.0 | Added in: v7.5.0, v6.13.0 |
The `URLSearchParams` API provides read and write access to the query of a `URL`. The `URLSearchParams` class can also be used standalone with one of the four following constructors. The `URLSearchParams` class is also available on the global object.
The WHATWG `URLSearchParams` interface and the [`querystring`](querystring) module have similar purpose, but the purpose of the [`querystring`](querystring) module is more general, as it allows the customization of delimiter characters (`&` and `=`). On the other hand, this API is designed purely for URL query strings.
```
const myURL = new URL('https://example.org/?abc=123');
console.log(myURL.searchParams.get('abc'));
// Prints 123
myURL.searchParams.append('abc', 'xyz');
console.log(myURL.href);
// Prints https://example.org/?abc=123&abc=xyz
myURL.searchParams.delete('abc');
myURL.searchParams.set('a', 'b');
console.log(myURL.href);
// Prints https://example.org/?a=b
const newSearchParams = new URLSearchParams(myURL.searchParams);
// The above is equivalent to
// const newSearchParams = new URLSearchParams(myURL.search);
newSearchParams.append('a', 'c');
console.log(myURL.href);
// Prints https://example.org/?a=b
console.log(newSearchParams.toString());
// Prints a=b&a=c
// newSearchParams.toString() is implicitly called
myURL.search = newSearchParams;
console.log(myURL.href);
// Prints https://example.org/?a=b&a=c
newSearchParams.delete('a');
console.log(myURL.href);
// Prints https://example.org/?a=b&a=c
```
#####
`new URLSearchParams()`
Instantiate a new empty `URLSearchParams` object.
#####
`new URLSearchParams(string)`
* `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A query string
Parse the `string` as a query string, and use it to instantiate a new `URLSearchParams` object. A leading `'?'`, if present, is ignored.
```
let params;
params = new URLSearchParams('user=abc&query=xyz');
console.log(params.get('user'));
// Prints 'abc'
console.log(params.toString());
// Prints 'user=abc&query=xyz'
params = new URLSearchParams('?user=abc&query=xyz');
console.log(params.toString());
// Prints 'user=abc&query=xyz'
```
#####
`new URLSearchParams(obj)`
Added in: v7.10.0, v6.13.0 * `obj` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object representing a collection of key-value pairs
Instantiate a new `URLSearchParams` object with a query hash map. The key and value of each property of `obj` are always coerced to strings.
Unlike [`querystring`](querystring) module, duplicate keys in the form of array values are not allowed. Arrays are stringified using [`array.toString()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toString), which simply joins all array elements with commas.
```
const params = new URLSearchParams({
user: 'abc',
query: ['first', 'second']
});
console.log(params.getAll('query'));
// Prints [ 'first,second' ]
console.log(params.toString());
// Prints 'user=abc&query=first%2Csecond'
```
#####
`new URLSearchParams(iterable)`
Added in: v7.10.0, v6.13.0 * `iterable` [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) An iterable object whose elements are key-value pairs
Instantiate a new `URLSearchParams` object with an iterable map in a way that is similar to [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)'s constructor. `iterable` can be an `Array` or any iterable object. That means `iterable` can be another `URLSearchParams`, in which case the constructor will simply create a clone of the provided `URLSearchParams`. Elements of `iterable` are key-value pairs, and can themselves be any iterable object.
Duplicate keys are allowed.
```
let params;
// Using an array
params = new URLSearchParams([
['user', 'abc'],
['query', 'first'],
['query', 'second'],
]);
console.log(params.toString());
// Prints 'user=abc&query=first&query=second'
// Using a Map object
const map = new Map();
map.set('user', 'abc');
map.set('query', 'xyz');
params = new URLSearchParams(map);
console.log(params.toString());
// Prints 'user=abc&query=xyz'
// Using a generator function
function* getQueryPairs() {
yield ['user', 'abc'];
yield ['query', 'first'];
yield ['query', 'second'];
}
params = new URLSearchParams(getQueryPairs());
console.log(params.toString());
// Prints 'user=abc&query=first&query=second'
// Each key-value pair must have exactly two elements
new URLSearchParams([
['user', 'abc', 'error'],
]);
// Throws TypeError [ERR_INVALID_TUPLE]:
// Each query pair must be an iterable [name, value] tuple
```
#####
`urlSearchParams.append(name, value)`
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Append a new name-value pair to the query string.
#####
`urlSearchParams.delete(name)`
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Remove all name-value pairs whose name is `name`.
#####
`urlSearchParams.entries()`
* Returns: [<Iterator>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol)
Returns an ES6 `Iterator` over each of the name-value pairs in the query. Each item of the iterator is a JavaScript `Array`. The first item of the `Array` is the `name`, the second item of the `Array` is the `value`.
Alias for [`urlSearchParams[@@iterator]()`](#urlsearchparamssymboliterator).
#####
`urlSearchParams.forEach(fn[, thisArg])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `fn` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked for each name-value pair in the query
* `thisArg` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) To be used as `this` value for when `fn` is called
Iterates over each name-value pair in the query and invokes the given function.
```
const myURL = new URL('https://example.org/?a=b&c=d');
myURL.searchParams.forEach((value, name, searchParams) => {
console.log(name, value, myURL.searchParams === searchParams);
});
// Prints:
// a b true
// c d true
```
#####
`urlSearchParams.get(name)`
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) or `null` if there is no name-value pair with the given `name`.
Returns the value of the first name-value pair whose name is `name`. If there are no such pairs, `null` is returned.
#####
`urlSearchParams.getAll(name)`
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the values of all name-value pairs whose name is `name`. If there are no such pairs, an empty array is returned.
#####
`urlSearchParams.has(name)`
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if there is at least one name-value pair whose name is `name`.
#####
`urlSearchParams.keys()`
* Returns: [<Iterator>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol)
Returns an ES6 `Iterator` over the names of each name-value pair.
```
const params = new URLSearchParams('foo=bar&foo=baz');
for (const name of params.keys()) {
console.log(name);
}
// Prints:
// foo
// foo
```
#####
`urlSearchParams.set(name, value)`
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Sets the value in the `URLSearchParams` object associated with `name` to `value`. If there are any pre-existing name-value pairs whose names are `name`, set the first such pair's value to `value` and remove all others. If not, append the name-value pair to the query string.
```
const params = new URLSearchParams();
params.append('foo', 'bar');
params.append('foo', 'baz');
params.append('abc', 'def');
console.log(params.toString());
// Prints foo=bar&foo=baz&abc=def
params.set('foo', 'def');
params.set('xyz', 'opq');
console.log(params.toString());
// Prints foo=def&abc=def&xyz=opq
```
#####
`urlSearchParams.sort()`
Added in: v7.7.0, v6.13.0 Sort all existing name-value pairs in-place by their names. Sorting is done with a [stable sorting algorithm](https://en.wikipedia.org/wiki/Sorting_algorithm#Stability), so relative order between name-value pairs with the same name is preserved.
This method can be used, in particular, to increase cache hits.
```
const params = new URLSearchParams('query[]=abc&type=search&query[]=123');
params.sort();
console.log(params.toString());
// Prints query%5B%5D=abc&query%5B%5D=123&type=search
```
#####
`urlSearchParams.toString()`
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the search parameters serialized as a string, with characters percent-encoded where necessary.
#####
`urlSearchParams.values()`
* Returns: [<Iterator>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol)
Returns an ES6 `Iterator` over the values of each name-value pair.
#####
`urlSearchParams[Symbol.iterator]()`
* Returns: [<Iterator>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol)
Returns an ES6 `Iterator` over each of the name-value pairs in the query string. Each item of the iterator is a JavaScript `Array`. The first item of the `Array` is the `name`, the second item of the `Array` is the `value`.
Alias for [`urlSearchParams.entries()`](#urlsearchparamsentries).
```
const params = new URLSearchParams('foo=bar&xyz=baz');
for (const [name, value] of params) {
console.log(name, value);
}
// Prints:
// foo bar
// xyz baz
```
####
`url.domainToASCII(domain)`
Added in: v7.4.0, v6.13.0 * `domain` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the [Punycode](https://tools.ietf.org/html/rfc5891#section-4.4) ASCII serialization of the `domain`. If `domain` is an invalid domain, the empty string is returned.
It performs the inverse operation to [`url.domainToUnicode()`](#urldomaintounicodedomain).
This feature is only available if the `node` executable was compiled with [ICU](intl#options-for-building-nodejs) enabled. If not, the domain names are passed through unchanged.
MJS modules
```
import url from 'node:url';
console.log(url.domainToASCII('español.com'));
// Prints xn--espaol-zwa.com
console.log(url.domainToASCII('中文.com'));
// Prints xn--fiq228c.com
console.log(url.domainToASCII('xn--iñvalid.com'));
// Prints an empty string
```
CJS modules
```
const url = require('node:url');
console.log(url.domainToASCII('español.com'));
// Prints xn--espaol-zwa.com
console.log(url.domainToASCII('中文.com'));
// Prints xn--fiq228c.com
console.log(url.domainToASCII('xn--iñvalid.com'));
// Prints an empty string
```
####
`url.domainToUnicode(domain)`
Added in: v7.4.0, v6.13.0 * `domain` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the Unicode serialization of the `domain`. If `domain` is an invalid domain, the empty string is returned.
It performs the inverse operation to [`url.domainToASCII()`](#urldomaintoasciidomain).
This feature is only available if the `node` executable was compiled with [ICU](intl#options-for-building-nodejs) enabled. If not, the domain names are passed through unchanged.
MJS modules
```
import url from 'node:url';
console.log(url.domainToUnicode('xn--espaol-zwa.com'));
// Prints español.com
console.log(url.domainToUnicode('xn--fiq228c.com'));
// Prints 中文.com
console.log(url.domainToUnicode('xn--iñvalid.com'));
// Prints an empty string
```
CJS modules
```
const url = require('node:url');
console.log(url.domainToUnicode('xn--espaol-zwa.com'));
// Prints español.com
console.log(url.domainToUnicode('xn--fiq228c.com'));
// Prints 中文.com
console.log(url.domainToUnicode('xn--iñvalid.com'));
// Prints an empty string
```
####
`url.fileURLToPath(url)`
Added in: v10.12.0 * `url` [<URL>](url#the-whatwg-url-api) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The file URL string or URL object to convert to a path.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The fully-resolved platform-specific Node.js file path.
This function ensures the correct decodings of percent-encoded characters as well as ensuring a cross-platform valid absolute path string.
MJS modules
```
import { fileURLToPath } from 'node:url';
const __filename = fileURLToPath(import.meta.url);
new URL('file:///C:/path/').pathname; // Incorrect: /C:/path/
fileURLToPath('file:///C:/path/'); // Correct: C:\path\ (Windows)
new URL('file://nas/foo.txt').pathname; // Incorrect: /foo.txt
fileURLToPath('file://nas/foo.txt'); // Correct: \\nas\foo.txt (Windows)
new URL('file:///你好.txt').pathname; // Incorrect: /%E4%BD%A0%E5%A5%BD.txt
fileURLToPath('file:///你好.txt'); // Correct: /你好.txt (POSIX)
new URL('file:///hello world').pathname; // Incorrect: /hello%20world
fileURLToPath('file:///hello world'); // Correct: /hello world (POSIX)
```
CJS modules
```
const { fileURLToPath } = require('node:url');
new URL('file:///C:/path/').pathname; // Incorrect: /C:/path/
fileURLToPath('file:///C:/path/'); // Correct: C:\path\ (Windows)
new URL('file://nas/foo.txt').pathname; // Incorrect: /foo.txt
fileURLToPath('file://nas/foo.txt'); // Correct: \\nas\foo.txt (Windows)
new URL('file:///你好.txt').pathname; // Incorrect: /%E4%BD%A0%E5%A5%BD.txt
fileURLToPath('file:///你好.txt'); // Correct: /你好.txt (POSIX)
new URL('file:///hello world').pathname; // Incorrect: /hello%20world
fileURLToPath('file:///hello world'); // Correct: /hello world (POSIX)
```
####
`url.format(URL[, options])`
Added in: v7.6.0 * `URL` [<URL>](url#the-whatwg-url-api) A [WHATWG URL](#the-whatwg-url-api) object
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `auth` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the serialized URL string should include the username and password, `false` otherwise. **Default:** `true`.
+ `fragment` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the serialized URL string should include the fragment, `false` otherwise. **Default:** `true`.
+ `search` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the serialized URL string should include the search query, `false` otherwise. **Default:** `true`.
+ `unicode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if Unicode characters appearing in the host component of the URL string should be encoded directly as opposed to being Punycode encoded. **Default:** `false`.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns a customizable serialization of a URL `String` representation of a [WHATWG URL](#the-whatwg-url-api) object.
The URL object has both a `toString()` method and `href` property that return string serializations of the URL. These are not, however, customizable in any way. The `url.format(URL[, options])` method allows for basic customization of the output.
MJS modules
```
import url from 'node:url';
const myURL = new URL('https://a:b@測試?abc#foo');
console.log(myURL.href);
// Prints https://a:b@xn--g6w251d/?abc#foo
console.log(myURL.toString());
// Prints https://a:b@xn--g6w251d/?abc#foo
console.log(url.format(myURL, { fragment: false, unicode: true, auth: false }));
// Prints 'https://測試/?abc'
```
CJS modules
```
const url = require('node:url');
const myURL = new URL('https://a:b@測試?abc#foo');
console.log(myURL.href);
// Prints https://a:b@xn--g6w251d/?abc#foo
console.log(myURL.toString());
// Prints https://a:b@xn--g6w251d/?abc#foo
console.log(url.format(myURL, { fragment: false, unicode: true, auth: false }));
// Prints 'https://測試/?abc'
```
####
`url.pathToFileURL(path)`
Added in: v10.12.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The path to convert to a File URL.
* Returns: [<URL>](url#the-whatwg-url-api) The file URL object.
This function ensures that `path` is resolved absolutely, and that the URL control characters are correctly encoded when converting into a File URL.
MJS modules
```
import { pathToFileURL } from 'node:url';
new URL('/foo#1', 'file:'); // Incorrect: file:///foo#1
pathToFileURL('/foo#1'); // Correct: file:///foo%231 (POSIX)
new URL('/some/path%.c', 'file:'); // Incorrect: file:///some/path%.c
pathToFileURL('/some/path%.c'); // Correct: file:///some/path%25.c (POSIX)
```
CJS modules
```
const { pathToFileURL } = require('node:url');
new URL(__filename); // Incorrect: throws (POSIX)
new URL(__filename); // Incorrect: C:\... (Windows)
pathToFileURL(__filename); // Correct: file:///... (POSIX)
pathToFileURL(__filename); // Correct: file:///C:/... (Windows)
new URL('/foo#1', 'file:'); // Incorrect: file:///foo#1
pathToFileURL('/foo#1'); // Correct: file:///foo%231 (POSIX)
new URL('/some/path%.c', 'file:'); // Incorrect: file:///some/path%.c
pathToFileURL('/some/path%.c'); // Correct: file:///some/path%25.c (POSIX)
```
####
`url.urlToHttpOptions(url)`
Added in: v15.7.0, v14.18.0 * `url` [<URL>](url#the-whatwg-url-api) The [WHATWG URL](#the-whatwg-url-api) object to convert to an options object.
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Options object
+ `protocol` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Protocol to use.
+ `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A domain name or IP address of the server to issue the request to.
+ `hash` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The fragment portion of the URL.
+ `search` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The serialized query portion of the URL.
+ `pathname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The path portion of the URL.
+ `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Request path. Should include query string if any. E.G. `'/index.html?page=12'`. An exception is thrown when the request path contains illegal characters. Currently, only spaces are rejected but that may change in the future.
+ `href` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The serialized URL.
+ `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Port of remote server.
+ `auth` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Basic authentication i.e. `'user:password'` to compute an Authorization header.
This utility function converts a URL object into an ordinary options object as expected by the [`http.request()`](http#httprequestoptions-callback) and [`https.request()`](https#httpsrequestoptions-callback) APIs.
MJS modules
```
import { urlToHttpOptions } from 'node:url';
const myURL = new URL('https://a:b@測試?abc#foo');
console.log(urlToHttpOptions(myURL));
/*
{
protocol: 'https:',
hostname: 'xn--g6w251d',
hash: '#foo',
search: '?abc',
pathname: '/',
path: '/?abc',
href: 'https://a:b@xn--g6w251d/?abc#foo',
auth: 'a:b'
}
*/
```
CJS modules
```
const { urlToHttpOptions } = require('node:url');
const myURL = new URL('https://a:b@測試?abc#foo');
console.log(urlToHttpOptions(myUrl));
/*
{
protocol: 'https:',
hostname: 'xn--g6w251d',
hash: '#foo',
search: '?abc',
pathname: '/',
path: '/?abc',
href: 'https://a:b@xn--g6w251d/?abc#foo',
auth: 'a:b'
}
*/
```
### Legacy URL API
History
| Version | Changes |
| --- | --- |
| v15.13.0, v14.17.0 | Deprecation revoked. Status changed to "Legacy". |
| v11.0.0 | This API is deprecated. |
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use the WHATWG URL API instead.
#### Legacy `urlObject`
History
| Version | Changes |
| --- | --- |
| v15.13.0, v14.17.0 | Deprecation revoked. Status changed to "Legacy". |
| v11.0.0 | The Legacy URL API is deprecated. Use the WHATWG URL API. |
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use the WHATWG URL API instead.
The legacy `urlObject` (`require('node:url').Url` or `import { Url } from 'node:url'`) is created and returned by the `url.parse()` function.
#####
`urlObject.auth`
The `auth` property is the username and password portion of the URL, also referred to as *userinfo*. This string subset follows the `protocol` and double slashes (if present) and precedes the `host` component, delimited by `@`. The string is either the username, or it is the username and password separated by `:`.
For example: `'user:pass'`.
#####
`urlObject.hash`
The `hash` property is the fragment identifier portion of the URL including the leading `#` character.
For example: `'#hash'`.
#####
`urlObject.host`
The `host` property is the full lower-cased host portion of the URL, including the `port` if specified.
For example: `'sub.example.com:8080'`.
#####
`urlObject.hostname`
The `hostname` property is the lower-cased host name portion of the `host` component *without* the `port` included.
For example: `'sub.example.com'`.
#####
`urlObject.href`
The `href` property is the full URL string that was parsed with both the `protocol` and `host` components converted to lower-case.
For example: `'http://user:[email protected]:8080/p/a/t/h?query=string#hash'`.
#####
`urlObject.path`
The `path` property is a concatenation of the `pathname` and `search` components.
For example: `'/p/a/t/h?query=string'`.
No decoding of the `path` is performed.
#####
`urlObject.pathname`
The `pathname` property consists of the entire path section of the URL. This is everything following the `host` (including the `port`) and before the start of the `query` or `hash` components, delimited by either the ASCII question mark (`?`) or hash (`#`) characters.
For example: `'/p/a/t/h'`.
No decoding of the path string is performed.
#####
`urlObject.port`
The `port` property is the numeric port portion of the `host` component.
For example: `'8080'`.
#####
`urlObject.protocol`
The `protocol` property identifies the URL's lower-cased protocol scheme.
For example: `'http:'`.
#####
`urlObject.query`
The `query` property is either the query string without the leading ASCII question mark (`?`), or an object returned by the [`querystring`](querystring) module's `parse()` method. Whether the `query` property is a string or object is determined by the `parseQueryString` argument passed to `url.parse()`.
For example: `'query=string'` or `{'query': 'string'}`.
If returned as a string, no decoding of the query string is performed. If returned as an object, both keys and values are decoded.
#####
`urlObject.search`
The `search` property consists of the entire "query string" portion of the URL, including the leading ASCII question mark (`?`) character.
For example: `'?query=string'`.
No decoding of the query string is performed.
#####
`urlObject.slashes`
The `slashes` property is a `boolean` with a value of `true` if two ASCII forward-slash characters (`/`) are required following the colon in the `protocol`.
####
`url.format(urlObject)`
History
| Version | Changes |
| --- | --- |
| v17.0.0 | Now throws an `ERR_INVALID_URL` exception when Punycode conversion of a hostname introduces changes that could cause the URL to be re-parsed differently. |
| v15.13.0, v14.17.0 | Deprecation revoked. Status changed to "Legacy". |
| v11.0.0 | The Legacy URL API is deprecated. Use the WHATWG URL API. |
| v7.0.0 | URLs with a `file:` scheme will now always use the correct number of slashes regardless of `slashes` option. A falsy `slashes` option with no protocol is now also respected at all times. |
| v0.1.25 | Added in: v0.1.25 |
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use the WHATWG URL API instead.
* `urlObject` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A URL object (as returned by `url.parse()` or constructed otherwise). If a string, it is converted to an object by passing it to `url.parse()`.
The `url.format()` method returns a formatted URL string derived from `urlObject`.
```
const url = require('node:url');
url.format({
protocol: 'https',
hostname: 'example.com',
pathname: '/some/path',
query: {
page: 1,
format: 'json'
}
});
// => 'https://example.com/some/path?page=1&format=json'
```
If `urlObject` is not an object or a string, `url.format()` will throw a [`TypeError`](errors#class-typeerror).
The formatting process operates as follows:
* A new empty string `result` is created.
* If `urlObject.protocol` is a string, it is appended as-is to `result`.
* Otherwise, if `urlObject.protocol` is not `undefined` and is not a string, an [`Error`](errors#class-error) is thrown.
* For all string values of `urlObject.protocol` that *do not end* with an ASCII colon (`:`) character, the literal string `:` will be appended to `result`.
* If either of the following conditions is true, then the literal string `//` will be appended to `result`:
+ `urlObject.slashes` property is true;
+ `urlObject.protocol` begins with `http`, `https`, `ftp`, `gopher`, or `file`;
* If the value of the `urlObject.auth` property is truthy, and either `urlObject.host` or `urlObject.hostname` are not `undefined`, the value of `urlObject.auth` will be coerced into a string and appended to `result` followed by the literal string `@`.
* If the `urlObject.host` property is `undefined` then:
+ If the `urlObject.hostname` is a string, it is appended to `result`.
+ Otherwise, if `urlObject.hostname` is not `undefined` and is not a string, an [`Error`](errors#class-error) is thrown.
+ If the `urlObject.port` property value is truthy, and `urlObject.hostname` is not `undefined`:
- The literal string `:` is appended to `result`, and
- The value of `urlObject.port` is coerced to a string and appended to `result`.
* Otherwise, if the `urlObject.host` property value is truthy, the value of `urlObject.host` is coerced to a string and appended to `result`.
* If the `urlObject.pathname` property is a string that is not an empty string:
+ If the `urlObject.pathname` *does not start* with an ASCII forward slash (`/`), then the literal string `'/'` is appended to `result`.
+ The value of `urlObject.pathname` is appended to `result`.
* Otherwise, if `urlObject.pathname` is not `undefined` and is not a string, an [`Error`](errors#class-error) is thrown.
* If the `urlObject.search` property is `undefined` and if the `urlObject.query` property is an `Object`, the literal string `?` is appended to `result` followed by the output of calling the [`querystring`](querystring) module's `stringify()` method passing the value of `urlObject.query`.
* Otherwise, if `urlObject.search` is a string:
+ If the value of `urlObject.search` *does not start* with the ASCII question mark (`?`) character, the literal string `?` is appended to `result`.
+ The value of `urlObject.search` is appended to `result`.
* Otherwise, if `urlObject.search` is not `undefined` and is not a string, an [`Error`](errors#class-error) is thrown.
* If the `urlObject.hash` property is a string:
+ If the value of `urlObject.hash` *does not start* with the ASCII hash (`#`) character, the literal string `#` is appended to `result`.
+ The value of `urlObject.hash` is appended to `result`.
* Otherwise, if the `urlObject.hash` property is not `undefined` and is not a string, an [`Error`](errors#class-error) is thrown.
* `result` is returned.
####
`url.parse(urlString[, parseQueryString[, slashesDenoteHost]])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | Documentation-only deprecation. |
| v15.13.0, v14.17.0 | Deprecation revoked. Status changed to "Legacy". |
| v11.14.0 | The `pathname` property on the returned URL object is now `/` when there is no path and the protocol scheme is `ws:` or `wss:`. |
| v11.0.0 | The Legacy URL API is deprecated. Use the WHATWG URL API. |
| v9.0.0 | The `search` property on the returned URL object is now `null` when no query string is present. |
| v0.1.25 | Added in: v0.1.25 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use the WHATWG URL API instead.
* `urlString` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The URL string to parse.
* `parseQueryString` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, the `query` property will always be set to an object returned by the [`querystring`](querystring) module's `parse()` method. If `false`, the `query` property on the returned URL object will be an unparsed, undecoded string. **Default:** `false`.
* `slashesDenoteHost` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, the first token after the literal string `//` and preceding the next `/` will be interpreted as the `host`. For instance, given `//foo/bar`, the result would be `{host: 'foo', pathname: '/bar'}` rather than `{pathname: '//foo/bar'}`. **Default:** `false`.
The `url.parse()` method takes a URL string, parses it, and returns a URL object.
A `TypeError` is thrown if `urlString` is not a string.
A `URIError` is thrown if the `auth` property is present but cannot be decoded.
`url.parse()` uses a lenient, non-standard algorithm for parsing URL strings. It is prone to security issues such as [host name spoofing](https://hackerone.com/reports/678487) and incorrect handling of usernames and passwords. Do not use with untrusted input. CVEs are not issued for `url.parse()` vulnerabilities. Use the [WHATWG URL](#the-whatwg-url-api) API instead.
####
`url.resolve(from, to)`
History
| Version | Changes |
| --- | --- |
| v15.13.0, v14.17.0 | Deprecation revoked. Status changed to "Legacy". |
| v11.0.0 | The Legacy URL API is deprecated. Use the WHATWG URL API. |
| v6.6.0 | The `auth` fields are now kept intact when `from` and `to` refer to the same host. |
| v6.0.0 | The `auth` fields is cleared now the `to` parameter contains a hostname. |
| v6.5.0, v4.6.2 | The `port` field is copied correctly now. |
| v0.1.25 | Added in: v0.1.25 |
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use the WHATWG URL API instead.
* `from` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The base URL to use if `to` is a relative URL.
* `to` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The target URL to resolve.
The `url.resolve()` method resolves a target URL relative to a base URL in a manner similar to that of a web browser resolving an anchor tag.
```
const url = require('node:url');
url.resolve('/one/two/three', 'four'); // '/one/two/four'
url.resolve('http://example.com/', '/one'); // 'http://example.com/one'
url.resolve('http://example.com/one', '/two'); // 'http://example.com/two'
```
To achieve the same result using the WHATWG URL API:
```
function resolve(from, to) {
const resolvedUrl = new URL(to, new URL(from, 'resolve://'));
if (resolvedUrl.protocol === 'resolve:') {
// `from` is a relative URL.
const { pathname, search, hash } = resolvedUrl;
return pathname + search + hash;
}
return resolvedUrl.toString();
}
resolve('/one/two/three', 'four'); // '/one/two/four'
resolve('http://example.com/', '/one'); // 'http://example.com/one'
resolve('http://example.com/one', '/two'); // 'http://example.com/two'
```
### Percent-encoding in URLs
URLs are permitted to only contain a certain range of characters. Any character falling outside of that range must be encoded. How such characters are encoded, and which characters to encode depends entirely on where the character is located within the structure of the URL.
#### Legacy API
Within the Legacy API, spaces (`' '`) and the following characters will be automatically escaped in the properties of URL objects:
```
< > " ` \r \n \t { } | \ ^ '
```
For example, the ASCII space character (`' '`) is encoded as `%20`. The ASCII forward slash (`/`) character is encoded as `%3C`.
#### WHATWG API
The [WHATWG URL Standard](https://url.spec.whatwg.org/) uses a more selective and fine grained approach to selecting encoded characters than that used by the Legacy API.
The WHATWG algorithm defines four "percent-encode sets" that describe ranges of characters that must be percent-encoded:
* The *C0 control percent-encode set* includes code points in range U+0000 to U+001F (inclusive) and all code points greater than U+007E.
* The *fragment percent-encode set* includes the *C0 control percent-encode set* and code points U+0020, U+0022, U+003C, U+003E, and U+0060.
* The *path percent-encode set* includes the *C0 control percent-encode set* and code points U+0020, U+0022, U+0023, U+003C, U+003E, U+003F, U+0060, U+007B, and U+007D.
* The *userinfo encode set* includes the *path percent-encode set* and code points U+002F, U+003A, U+003B, U+003D, U+0040, U+005B, U+005C, U+005D, U+005E, and U+007C.
The *userinfo percent-encode set* is used exclusively for username and passwords encoded within the URL. The *path percent-encode set* is used for the path of most URLs. The *fragment percent-encode set* is used for URL fragments. The *C0 control percent-encode set* is used for host and path under certain specific conditions, in addition to all other cases.
When non-ASCII characters appear within a host name, the host name is encoded using the [Punycode](https://tools.ietf.org/html/rfc5891#section-4.4) algorithm. Note, however, that a host name *may* contain *both* Punycode encoded and percent-encoded characters:
```
const myURL = new URL('https://%CF%80.example.com/foo');
console.log(myURL.href);
// Prints https://xn--1xa.example.com/foo
console.log(myURL.origin);
// Prints https://xn--1xa.example.com
```
| programming_docs |
node None Cluster
-------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/cluster.js](https://github.com/nodejs/node/blob/v19.0.1/lib/cluster.js)
Clusters of Node.js processes can be used to run multiple instances of Node.js that can distribute workloads among their application threads. When process isolation is not needed, use the [`worker_threads`](worker_threads) module instead, which allows running multiple application threads within a single Node.js instance.
The cluster module allows easy creation of child processes that all share server ports.
MJS modules
```
import cluster from 'node:cluster';
import http from 'node:http';
import { cpus } from 'node:os';
import process from 'node:process';
const numCPUs = cpus().length;
if (cluster.isPrimary) {
console.log(`Primary ${process.pid} is running`);
// Fork workers.
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`worker ${worker.process.pid} died`);
});
} else {
// Workers can share any TCP connection
// In this case it is an HTTP server
http.createServer((req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
console.log(`Worker ${process.pid} started`);
}
```
CJS modules
```
const cluster = require('node:cluster');
const http = require('node:http');
const numCPUs = require('node:os').cpus().length;
const process = require('node:process');
if (cluster.isPrimary) {
console.log(`Primary ${process.pid} is running`);
// Fork workers.
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`worker ${worker.process.pid} died`);
});
} else {
// Workers can share any TCP connection
// In this case it is an HTTP server
http.createServer((req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
console.log(`Worker ${process.pid} started`);
}
```
Running Node.js will now share port 8000 between the workers:
```
$ node server.js
Primary 3596 is running
Worker 4324 started
Worker 4520 started
Worker 6056 started
Worker 5644 started
```
On Windows, it is not yet possible to set up a named pipe server in a worker.
### How it works
The worker processes are spawned using the [`child_process.fork()`](child_process#child_processforkmodulepath-args-options) method, so that they can communicate with the parent via IPC and pass server handles back and forth.
The cluster module supports two methods of distributing incoming connections.
The first one (and the default one on all platforms except Windows) is the round-robin approach, where the primary process listens on a port, accepts new connections and distributes them across the workers in a round-robin fashion, with some built-in smarts to avoid overloading a worker process.
The second approach is where the primary process creates the listen socket and sends it to interested workers. The workers then accept incoming connections directly.
The second approach should, in theory, give the best performance. In practice however, distribution tends to be very unbalanced due to operating system scheduler vagaries. Loads have been observed where over 70% of all connections ended up in just two processes, out of a total of eight.
Because `server.listen()` hands off most of the work to the primary process, there are three cases where the behavior between a normal Node.js process and a cluster worker differs:
1. `server.listen({fd: 7})` Because the message is passed to the primary, file descriptor 7 **in the parent** will be listened on, and the handle passed to the worker, rather than listening to the worker's idea of what the number 7 file descriptor references.
2. `server.listen(handle)` Listening on handles explicitly will cause the worker to use the supplied handle, rather than talk to the primary process.
3. `server.listen(0)` Normally, this will cause servers to listen on a random port. However, in a cluster, each worker will receive the same "random" port each time they do `listen(0)`. In essence, the port is random the first time, but predictable thereafter. To listen on a unique port, generate a port number based on the cluster worker ID.
Node.js does not provide routing logic. It is therefore important to design an application such that it does not rely too heavily on in-memory data objects for things like sessions and login.
Because workers are all separate processes, they can be killed or re-spawned depending on a program's needs, without affecting other workers. As long as there are some workers still alive, the server will continue to accept connections. If no workers are alive, existing connections will be dropped and new connections will be refused. Node.js does not automatically manage the number of workers, however. It is the application's responsibility to manage the worker pool based on its own needs.
Although a primary use case for the `node:cluster` module is networking, it can also be used for other use cases requiring worker processes.
### Class: `Worker`
Added in: v0.7.0 * Extends: [<EventEmitter>](events#class-eventemitter)
A `Worker` object contains all public information and method about a worker. In the primary it can be obtained using `cluster.workers`. In a worker it can be obtained using `cluster.worker`.
#### Event: `'disconnect'`
Added in: v0.7.7 Similar to the `cluster.on('disconnect')` event, but specific to this worker.
```
cluster.fork().on('disconnect', () => {
// Worker has disconnected
});
```
#### Event: `'error'`
Added in: v0.7.3 This event is the same as the one provided by [`child_process.fork()`](child_process#child_processforkmodulepath-args-options).
Within a worker, `process.on('error')` may also be used.
#### Event: `'exit'`
Added in: v0.11.2 * `code` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The exit code, if it exited normally.
* `signal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the signal (e.g. `'SIGHUP'`) that caused the process to be killed.
Similar to the `cluster.on('exit')` event, but specific to this worker.
MJS modules
```
import cluster from 'node:cluster';
if (cluster.isPrimary) {
const worker = cluster.fork();
worker.on('exit', (code, signal) => {
if (signal) {
console.log(`worker was killed by signal: ${signal}`);
} else if (code !== 0) {
console.log(`worker exited with error code: ${code}`);
} else {
console.log('worker success!');
}
});
}
```
CJS modules
```
const cluster = require('node:cluster');
if (cluster.isPrimary) {
const worker = cluster.fork();
worker.on('exit', (code, signal) => {
if (signal) {
console.log(`worker was killed by signal: ${signal}`);
} else if (code !== 0) {
console.log(`worker exited with error code: ${code}`);
} else {
console.log('worker success!');
}
});
}
```
#### Event: `'listening'`
Added in: v0.7.0 * `address` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Similar to the `cluster.on('listening')` event, but specific to this worker.
MJS modules
```
cluster.fork().on('listening', (address) => {
// Worker is listening
});
```
CJS modules
```
cluster.fork().on('listening', (address) => {
// Worker is listening
});
```
It is not emitted in the worker.
#### Event: `'message'`
Added in: v0.7.0 * `message` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `handle` [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Similar to the `'message'` event of `cluster`, but specific to this worker.
Within a worker, `process.on('message')` may also be used.
See [`process` event: `'message'`](process#event-message).
Here is an example using the message system. It keeps a count in the primary process of the number of HTTP requests received by the workers:
MJS modules
```
import cluster from 'node:cluster';
import http from 'node:http';
import { cpus } from 'node:os';
import process from 'node:process';
if (cluster.isPrimary) {
// Keep track of http requests
let numReqs = 0;
setInterval(() => {
console.log(`numReqs = ${numReqs}`);
}, 1000);
// Count requests
function messageHandler(msg) {
if (msg.cmd && msg.cmd === 'notifyRequest') {
numReqs += 1;
}
}
// Start workers and listen for messages containing notifyRequest
const numCPUs = cpus().length;
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
for (const id in cluster.workers) {
cluster.workers[id].on('message', messageHandler);
}
} else {
// Worker processes have a http server.
http.Server((req, res) => {
res.writeHead(200);
res.end('hello world\n');
// Notify primary about the request
process.send({ cmd: 'notifyRequest' });
}).listen(8000);
}
```
CJS modules
```
const cluster = require('node:cluster');
const http = require('node:http');
const process = require('node:process');
if (cluster.isPrimary) {
// Keep track of http requests
let numReqs = 0;
setInterval(() => {
console.log(`numReqs = ${numReqs}`);
}, 1000);
// Count requests
function messageHandler(msg) {
if (msg.cmd && msg.cmd === 'notifyRequest') {
numReqs += 1;
}
}
// Start workers and listen for messages containing notifyRequest
const numCPUs = require('node:os').cpus().length;
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
for (const id in cluster.workers) {
cluster.workers[id].on('message', messageHandler);
}
} else {
// Worker processes have a http server.
http.Server((req, res) => {
res.writeHead(200);
res.end('hello world\n');
// Notify primary about the request
process.send({ cmd: 'notifyRequest' });
}).listen(8000);
}
```
#### Event: `'online'`
Added in: v0.7.0 Similar to the `cluster.on('online')` event, but specific to this worker.
```
cluster.fork().on('online', () => {
// Worker is online
});
```
It is not emitted in the worker.
####
`worker.disconnect()`
History
| Version | Changes |
| --- | --- |
| v7.3.0 | This method now returns a reference to `worker`. |
| v0.7.7 | Added in: v0.7.7 |
* Returns: [<cluster.Worker>](cluster#class-worker) A reference to `worker`.
In a worker, this function will close all servers, wait for the `'close'` event on those servers, and then disconnect the IPC channel.
In the primary, an internal message is sent to the worker causing it to call `.disconnect()` on itself.
Causes `.exitedAfterDisconnect` to be set.
After a server is closed, it will no longer accept new connections, but connections may be accepted by any other listening worker. Existing connections will be allowed to close as usual. When no more connections exist, see [`server.close()`](net#event-close), the IPC channel to the worker will close allowing it to die gracefully.
The above applies *only* to server connections, client connections are not automatically closed by workers, and disconnect does not wait for them to close before exiting.
In a worker, `process.disconnect` exists, but it is not this function; it is [`disconnect()`](child_process#subprocessdisconnect).
Because long living server connections may block workers from disconnecting, it may be useful to send a message, so application specific actions may be taken to close them. It also may be useful to implement a timeout, killing a worker if the `'disconnect'` event has not been emitted after some time.
```
if (cluster.isPrimary) {
const worker = cluster.fork();
let timeout;
worker.on('listening', (address) => {
worker.send('shutdown');
worker.disconnect();
timeout = setTimeout(() => {
worker.kill();
}, 2000);
});
worker.on('disconnect', () => {
clearTimeout(timeout);
});
} else if (cluster.isWorker) {
const net = require('node:net');
const server = net.createServer((socket) => {
// Connections never end
});
server.listen(8000);
process.on('message', (msg) => {
if (msg === 'shutdown') {
// Initiate graceful close of any connections to server
}
});
}
```
####
`worker.exitedAfterDisconnect`
Added in: v6.0.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
This property is `true` if the worker exited due to `.disconnect()`. If the worker exited any other way, it is `false`. If the worker has not exited, it is `undefined`.
The boolean [`worker.exitedAfterDisconnect`](#workerexitedafterdisconnect) allows distinguishing between voluntary and accidental exit, the primary may choose not to respawn a worker based on this value.
```
cluster.on('exit', (worker, code, signal) => {
if (worker.exitedAfterDisconnect === true) {
console.log('Oh, it was just voluntary – no need to worry');
}
});
// kill worker
worker.kill();
```
####
`worker.id`
Added in: v0.8.0 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Each new worker is given its own unique id, this id is stored in the `id`.
While a worker is alive, this is the key that indexes it in `cluster.workers`.
####
`worker.isConnected()`
Added in: v0.11.14 This function returns `true` if the worker is connected to its primary via its IPC channel, `false` otherwise. A worker is connected to its primary after it has been created. It is disconnected after the `'disconnect'` event is emitted.
####
`worker.isDead()`
Added in: v0.11.14 This function returns `true` if the worker's process has terminated (either because of exiting or being signaled). Otherwise, it returns `false`.
MJS modules
```
import cluster from 'node:cluster';
import http from 'node:http';
import { cpus } from 'node:os';
import process from 'node:process';
const numCPUs = cpus().length;
if (cluster.isPrimary) {
console.log(`Primary ${process.pid} is running`);
// Fork workers.
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('fork', (worker) => {
console.log('worker is dead:', worker.isDead());
});
cluster.on('exit', (worker, code, signal) => {
console.log('worker is dead:', worker.isDead());
});
} else {
// Workers can share any TCP connection. In this case, it is an HTTP server.
http.createServer((req, res) => {
res.writeHead(200);
res.end(`Current process\n ${process.pid}`);
process.kill(process.pid);
}).listen(8000);
}
```
CJS modules
```
const cluster = require('node:cluster');
const http = require('node:http');
const numCPUs = require('node:os').cpus().length;
const process = require('node:process');
if (cluster.isPrimary) {
console.log(`Primary ${process.pid} is running`);
// Fork workers.
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('fork', (worker) => {
console.log('worker is dead:', worker.isDead());
});
cluster.on('exit', (worker, code, signal) => {
console.log('worker is dead:', worker.isDead());
});
} else {
// Workers can share any TCP connection. In this case, it is an HTTP server.
http.createServer((req, res) => {
res.writeHead(200);
res.end(`Current process\n ${process.pid}`);
process.kill(process.pid);
}).listen(8000);
}
```
####
`worker.kill([signal])`
Added in: v0.9.12 * `signal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the kill signal to send to the worker process. **Default:** `'SIGTERM'`
This function will kill the worker. In the primary worker, it does this by disconnecting the `worker.process`, and once disconnected, killing with `signal`. In the worker, it does it by killing the process with `signal`.
The `kill()` function kills the worker process without waiting for a graceful disconnect, it has the same behavior as `worker.process.kill()`.
This method is aliased as `worker.destroy()` for backwards compatibility.
In a worker, `process.kill()` exists, but it is not this function; it is [`kill()`](process#processkillpid-signal).
####
`worker.process`
Added in: v0.7.0 * [<ChildProcess>](child_process#class-childprocess)
All workers are created using [`child_process.fork()`](child_process#child_processforkmodulepath-args-options), the returned object from this function is stored as `.process`. In a worker, the global `process` is stored.
See: [Child Process module](child_process#child_processforkmodulepath-args-options).
Workers will call `process.exit(0)` if the `'disconnect'` event occurs on `process` and `.exitedAfterDisconnect` is not `true`. This protects against accidental disconnection.
####
`worker.send(message[, sendHandle[, options]][, callback])`
History
| Version | Changes |
| --- | --- |
| v4.0.0 | The `callback` parameter is supported now. |
| v0.7.0 | Added in: v0.7.0 |
* `message` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `sendHandle` [<Handle>](net#serverlistenhandle-backlog-callback)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The `options` argument, if present, is an object used to parameterize the sending of certain types of handles. `options` supports the following properties:
+ `keepOpen` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) A value that can be used when passing instances of `net.Socket`. When `true`, the socket is kept open in the sending process. **Default:** `false`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Send a message to a worker or primary, optionally with a handle.
In the primary, this sends a message to a specific worker. It is identical to [`ChildProcess.send()`](child_process#subprocesssendmessage-sendhandle-options-callback).
In a worker, this sends a message to the primary. It is identical to `process.send()`.
This example will echo back all messages from the primary:
```
if (cluster.isPrimary) {
const worker = cluster.fork();
worker.send('hi there');
} else if (cluster.isWorker) {
process.on('message', (msg) => {
process.send(msg);
});
}
```
### Event: `'disconnect'`
Added in: v0.7.9 * `worker` [<cluster.Worker>](cluster#class-worker)
Emitted after the worker IPC channel has disconnected. This can occur when a worker exits gracefully, is killed, or is disconnected manually (such as with `worker.disconnect()`).
There may be a delay between the `'disconnect'` and `'exit'` events. These events can be used to detect if the process is stuck in a cleanup or if there are long-living connections.
```
cluster.on('disconnect', (worker) => {
console.log(`The worker #${worker.id} has disconnected`);
});
```
### Event: `'exit'`
Added in: v0.7.9 * `worker` [<cluster.Worker>](cluster#class-worker)
* `code` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The exit code, if it exited normally.
* `signal` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the signal (e.g. `'SIGHUP'`) that caused the process to be killed.
When any of the workers die the cluster module will emit the `'exit'` event.
This can be used to restart the worker by calling [`.fork()`](#clusterforkenv) again.
```
cluster.on('exit', (worker, code, signal) => {
console.log('worker %d died (%s). restarting...',
worker.process.pid, signal || code);
cluster.fork();
});
```
See [`child_process` event: `'exit'`](child_process#event-exit).
### Event: `'fork'`
Added in: v0.7.0 * `worker` [<cluster.Worker>](cluster#class-worker)
When a new worker is forked the cluster module will emit a `'fork'` event. This can be used to log worker activity, and create a custom timeout.
```
const timeouts = [];
function errorMsg() {
console.error('Something must be wrong with the connection ...');
}
cluster.on('fork', (worker) => {
timeouts[worker.id] = setTimeout(errorMsg, 2000);
});
cluster.on('listening', (worker, address) => {
clearTimeout(timeouts[worker.id]);
});
cluster.on('exit', (worker, code, signal) => {
clearTimeout(timeouts[worker.id]);
errorMsg();
});
```
### Event: `'listening'`
Added in: v0.7.0 * `worker` [<cluster.Worker>](cluster#class-worker)
* `address` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
After calling `listen()` from a worker, when the `'listening'` event is emitted on the server, a `'listening'` event will also be emitted on `cluster` in the primary.
The event handler is executed with two arguments, the `worker` contains the worker object and the `address` object contains the following connection properties: `address`, `port`, and `addressType`. This is very useful if the worker is listening on more than one address.
```
cluster.on('listening', (worker, address) => {
console.log(
`A worker is now connected to ${address.address}:${address.port}`);
});
```
The `addressType` is one of:
* `4` (TCPv4)
* `6` (TCPv6)
* `-1` (Unix domain socket)
* `'udp4'` or `'udp6'` (UDPv4 or UDPv6)
### Event: `'message'`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | The `worker` parameter is passed now; see below for details. |
| v2.5.0 | Added in: v2.5.0 |
* `worker` [<cluster.Worker>](cluster#class-worker)
* `message` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `handle` [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Emitted when the cluster primary receives a message from any worker.
See [`child_process` event: `'message'`](child_process#event-message).
### Event: `'online'`
Added in: v0.7.0 * `worker` [<cluster.Worker>](cluster#class-worker)
After forking a new worker, the worker should respond with an online message. When the primary receives an online message it will emit this event. The difference between `'fork'` and `'online'` is that fork is emitted when the primary forks a worker, and `'online'` is emitted when the worker is running.
```
cluster.on('online', (worker) => {
console.log('Yay, the worker responded after it was forked');
});
```
### Event: `'setup'`
Added in: v0.7.1 * `settings` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Emitted every time [`.setupPrimary()`](#clustersetupprimarysettings) is called.
The `settings` object is the `cluster.settings` object at the time [`.setupPrimary()`](#clustersetupprimarysettings) was called and is advisory only, since multiple calls to [`.setupPrimary()`](#clustersetupprimarysettings) can be made in a single tick.
If accuracy is important, use `cluster.settings`.
###
`cluster.disconnect([callback])`
Added in: v0.7.7 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called when all workers are disconnected and handles are closed.
Calls `.disconnect()` on each worker in `cluster.workers`.
When they are disconnected all internal handles will be closed, allowing the primary process to die gracefully if no other event is waiting.
The method takes an optional callback argument which will be called when finished.
This can only be called from the primary process.
###
`cluster.fork([env])`
Added in: v0.6.0 * `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Key/value pairs to add to worker process environment.
* Returns: [<cluster.Worker>](cluster#class-worker)
Spawn a new worker process.
This can only be called from the primary process.
###
`cluster.isMaster`
Added in: v0.8.1Deprecated since: v16.0.0 Deprecated alias for [`cluster.isPrimary`](#clusterisprimary).
###
`cluster.isPrimary`
Added in: v16.0.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
True if the process is a primary. This is determined by the `process.env.NODE_UNIQUE_ID`. If `process.env.NODE_UNIQUE_ID` is undefined, then `isPrimary` is `true`.
###
`cluster.isWorker`
Added in: v0.6.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
True if the process is not a primary (it is the negation of `cluster.isPrimary`).
###
`cluster.schedulingPolicy`
Added in: v0.11.2 The scheduling policy, either `cluster.SCHED_RR` for round-robin or `cluster.SCHED_NONE` to leave it to the operating system. This is a global setting and effectively frozen once either the first worker is spawned, or [`.setupPrimary()`](#clustersetupprimarysettings) is called, whichever comes first.
`SCHED_RR` is the default on all operating systems except Windows. Windows will change to `SCHED_RR` once libuv is able to effectively distribute IOCP handles without incurring a large performance hit.
`cluster.schedulingPolicy` can also be set through the `NODE_CLUSTER_SCHED_POLICY` environment variable. Valid values are `'rr'` and `'none'`.
###
`cluster.settings`
History
| Version | Changes |
| --- | --- |
| v13.2.0, v12.16.0 | The `serialization` option is supported now. |
| v9.5.0 | The `cwd` option is supported now. |
| v9.4.0 | The `windowsHide` option is supported now. |
| v8.2.0 | The `inspectPort` option is supported now. |
| v6.4.0 | The `stdio` option is supported now. |
| v0.7.1 | Added in: v0.7.1 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `execArgv` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) List of string arguments passed to the Node.js executable. **Default:** `process.execArgv`.
+ `exec` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) File path to worker file. **Default:** `process.argv[1]`.
+ `args` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) String arguments passed to worker. **Default:** `process.argv.slice(2)`.
+ `cwd` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Current working directory of the worker process. **Default:** `undefined` (inherits from parent process).
+ `serialization` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specify the kind of serialization used for sending messages between processes. Possible values are `'json'` and `'advanced'`. See [Advanced serialization for `child_process`](child_process#advanced-serialization) for more details. **Default:** `false`.
+ `silent` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether or not to send output to parent's stdio. **Default:** `false`.
+ `stdio` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) Configures the stdio of forked processes. Because the cluster module relies on IPC to function, this configuration must contain an `'ipc'` entry. When this option is provided, it overrides `silent`.
+ `uid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the user identity of the process. (See [`setuid(2)`](http://man7.org/linux/man-pages/man2/setuid.2.html).)
+ `gid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the group identity of the process. (See [`setgid(2)`](http://man7.org/linux/man-pages/man2/setgid.2.html).)
+ `inspectPort` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Sets inspector port of worker. This can be a number, or a function that takes no arguments and returns a number. By default each worker gets its own port, incremented from the primary's `process.debugPort`.
+ `windowsHide` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Hide the forked processes console window that would normally be created on Windows systems. **Default:** `false`.
After calling [`.setupPrimary()`](#clustersetupprimarysettings) (or [`.fork()`](#clusterforkenv)) this settings object will contain the settings, including the default values.
This object is not intended to be changed or set manually.
###
`cluster.setupMaster([settings])`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Deprecated since: v16.0.0 |
| v6.4.0 | The `stdio` option is supported now. |
| v0.7.1 | Added in: v0.7.1 |
Deprecated alias for [`.setupPrimary()`](#clustersetupprimarysettings).
###
`cluster.setupPrimary([settings])`
Added in: v16.0.0 * `settings` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) See [`cluster.settings`](#clustersettings).
`setupPrimary` is used to change the default 'fork' behavior. Once called, the settings will be present in `cluster.settings`.
Any settings changes only affect future calls to [`.fork()`](#clusterforkenv) and have no effect on workers that are already running.
The only attribute of a worker that cannot be set via `.setupPrimary()` is the `env` passed to [`.fork()`](#clusterforkenv).
The defaults above apply to the first call only; the defaults for later calls are the current values at the time of `cluster.setupPrimary()` is called.
MJS modules
```
import cluster from 'node:cluster';
cluster.setupPrimary({
exec: 'worker.js',
args: ['--use', 'https'],
silent: true
});
cluster.fork(); // https worker
cluster.setupPrimary({
exec: 'worker.js',
args: ['--use', 'http']
});
cluster.fork(); // http worker
```
CJS modules
```
const cluster = require('node:cluster');
cluster.setupPrimary({
exec: 'worker.js',
args: ['--use', 'https'],
silent: true
});
cluster.fork(); // https worker
cluster.setupPrimary({
exec: 'worker.js',
args: ['--use', 'http']
});
cluster.fork(); // http worker
```
This can only be called from the primary process.
###
`cluster.worker`
Added in: v0.7.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
A reference to the current worker object. Not available in the primary process.
MJS modules
```
import cluster from 'node:cluster';
if (cluster.isPrimary) {
console.log('I am primary');
cluster.fork();
cluster.fork();
} else if (cluster.isWorker) {
console.log(`I am worker #${cluster.worker.id}`);
}
```
CJS modules
```
const cluster = require('node:cluster');
if (cluster.isPrimary) {
console.log('I am primary');
cluster.fork();
cluster.fork();
} else if (cluster.isWorker) {
console.log(`I am worker #${cluster.worker.id}`);
}
```
###
`cluster.workers`
Added in: v0.7.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
A hash that stores the active worker objects, keyed by `id` field. This makes it easy to loop through all the workers. It is only available in the primary process.
A worker is removed from `cluster.workers` after the worker has disconnected *and* exited. The order between these two events cannot be determined in advance. However, it is guaranteed that the removal from the `cluster.workers` list happens before the last `'disconnect'` or `'exit'` event is emitted.
MJS modules
```
import cluster from 'node:cluster';
for (const worker of Object.values(cluster.workers)) {
worker.send('big announcement to all workers');
}
```
CJS modules
```
const cluster = require('node:cluster');
for (const worker of Object.values(cluster.workers)) {
worker.send('big announcement to all workers');
}
```
| programming_docs |
node None Performance measurement APIs
----------------------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/perf\_hooks.js](https://github.com/nodejs/node/blob/v19.0.1/lib/perf_hooks.js)
This module provides an implementation of a subset of the W3C [Web Performance APIs](https://w3c.github.io/perf-timing-primer/) as well as additional APIs for Node.js-specific performance measurements.
Node.js supports the following [Web Performance APIs](https://w3c.github.io/perf-timing-primer/):
* [High Resolution Time](https://www.w3.org/TR/hr-time-2)
* [Performance Timeline](https://w3c.github.io/performance-timeline/)
* [User Timing](https://www.w3.org/TR/user-timing/)
* [Resource Timing](https://www.w3.org/TR/resource-timing-2/)
```
const { PerformanceObserver, performance } = require('node:perf_hooks');
const obs = new PerformanceObserver((items) => {
console.log(items.getEntries()[0].duration);
performance.clearMarks();
});
obs.observe({ type: 'measure' });
performance.measure('Start to Now');
performance.mark('A');
doSomeLongRunningProcess(() => {
performance.measure('A to Now', 'A');
performance.mark('B');
performance.measure('A to B', 'A', 'B');
});
```
###
`perf_hooks.performance`
Added in: v8.5.0 An object that can be used to collect performance metrics from the current Node.js instance. It is similar to [`window.performance`](https://developer.mozilla.org/en-US/docs/Web/API/Window/performance) in browsers.
####
`performance.clearMarks([name])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v8.5.0 | Added in: v8.5.0 |
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
If `name` is not provided, removes all `PerformanceMark` objects from the Performance Timeline. If `name` is provided, removes only the named mark.
####
`performance.clearMeasures([name])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v16.7.0 | Added in: v16.7.0 |
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
If `name` is not provided, removes all `PerformanceMeasure` objects from the Performance Timeline. If `name` is provided, removes only the named measure.
####
`performance.clearResourceTimings([name])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
If `name` is not provided, removes all `PerformanceResourceTiming` objects from the Resource Timeline. If `name` is provided, removes only the named resource.
####
`performance.eventLoopUtilization([utilization1[, utilization2]])`
Added in: v14.10.0, v12.19.0 * `utilization1` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The result of a previous call to `eventLoopUtilization()`.
* `utilization2` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The result of a previous call to `eventLoopUtilization()` prior to `utilization1`.
* Returns [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `idle` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `active` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `utilization` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `eventLoopUtilization()` method returns an object that contains the cumulative duration of time the event loop has been both idle and active as a high resolution milliseconds timer. The `utilization` value is the calculated Event Loop Utilization (ELU).
If bootstrapping has not yet finished on the main thread the properties have the value of `0`. The ELU is immediately available on [Worker threads](worker_threads#worker-threads) since bootstrap happens within the event loop.
Both `utilization1` and `utilization2` are optional parameters.
If `utilization1` is passed, then the delta between the current call's `active` and `idle` times, as well as the corresponding `utilization` value are calculated and returned (similar to [`process.hrtime()`](process#processhrtimetime)).
If `utilization1` and `utilization2` are both passed, then the delta is calculated between the two arguments. This is a convenience option because, unlike [`process.hrtime()`](process#processhrtimetime), calculating the ELU is more complex than a single subtraction.
ELU is similar to CPU utilization, except that it only measures event loop statistics and not CPU usage. It represents the percentage of time the event loop has spent outside the event loop's event provider (e.g. `epoll_wait`). No other CPU idle time is taken into consideration. The following is an example of how a mostly idle process will have a high ELU.
```
'use strict';
const { eventLoopUtilization } = require('node:perf_hooks').performance;
const { spawnSync } = require('node:child_process');
setImmediate(() => {
const elu = eventLoopUtilization();
spawnSync('sleep', ['5']);
console.log(eventLoopUtilization(elu).utilization);
});
```
Although the CPU is mostly idle while running this script, the value of `utilization` is `1`. This is because the call to [`child_process.spawnSync()`](child_process#child_processspawnsynccommand-args-options) blocks the event loop from proceeding.
Passing in a user-defined object instead of the result of a previous call to `eventLoopUtilization()` will lead to undefined behavior. The return values are not guaranteed to reflect any correct state of the event loop.
####
`performance.getEntries()`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v16.7.0 | Added in: v16.7.0 |
* Returns: [<PerformanceEntry[]>](perf_hooks#class-performanceentry)
Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime`. If you are only interested in performance entries of certain types or that have certain names, see `performance.getEntriesByType()` and `performance.getEntriesByName()`.
####
`performance.getEntriesByName(name[, type])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v16.7.0 | Added in: v16.7.0 |
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<PerformanceEntry[]>](perf_hooks#class-performanceentry)
Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.name` is equal to `name`, and optionally, whose `performanceEntry.entryType` is equal to `type`.
####
`performance.getEntriesByType(type)`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v16.7.0 | Added in: v16.7.0 |
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<PerformanceEntry[]>](perf_hooks#class-performanceentry)
Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.entryType` is equal to `type`.
####
`performance.mark([name[, options]])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v16.0.0 | Updated to conform to the User Timing Level 3 specification. |
| v8.5.0 | Added in: v8.5.0 |
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `detail` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Additional optional detail to include with the mark.
+ `startTime` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) An optional timestamp to be used as the mark time. **Default**: `performance.now()`.
Creates a new `PerformanceMark` entry in the Performance Timeline. A `PerformanceMark` is a subclass of `PerformanceEntry` whose `performanceEntry.entryType` is always `'mark'`, and whose `performanceEntry.duration` is always `0`. Performance marks are used to mark specific significant moments in the Performance Timeline.
The created `PerformanceMark` entry is put in the global Performance Timeline and can be queried with `performance.getEntries`, `performance.getEntriesByName`, and `performance.getEntriesByType`. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with `performance.clearMarks`.
####
`performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, global, cacheMode)`
Added in: v18.2.0, v16.17.0 * `timingInfo` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [Fetch Timing Info](https://fetch.spec.whatwg.org/#fetch-timing-info)
* `requestedUrl` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The resource url
* `initiatorType` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The initiator name, e.g: 'fetch'
* `global` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `cacheMode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The cache mode must be an empty string ('') or 'local'
*This property is an extension by Node.js. It is not available in Web browsers.*
Creates a new `PerformanceResourceTiming` entry in the Resource Timeline. A `PerformanceResourceTiming` is a subclass of `PerformanceEntry` whose `performanceEntry.entryType` is always `'resource'`. Performance resources are used to mark moments in the Resource Timeline.
The created `PerformanceMark` entry is put in the global Resource Timeline and can be queried with `performance.getEntries`, `performance.getEntriesByName`, and `performance.getEntriesByType`. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with `performance.clearResourceTimings`.
####
`performance.measure(name[, startMarkOrOptions[, endMark]])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v16.0.0 | Updated to conform to the User Timing Level 3 specification. |
| v13.13.0, v12.16.3 | Make `startMark` and `endMark` parameters optional. |
| v8.5.0 | Added in: v8.5.0 |
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `startMarkOrOptions` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Optional.
+ `detail` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Additional optional detail to include with the measure.
+ `duration` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Duration between start and end times.
+ `end` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Timestamp to be used as the end time, or a string identifying a previously recorded mark.
+ `start` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Timestamp to be used as the start time, or a string identifying a previously recorded mark.
* `endMark` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Optional. Must be omitted if `startMarkOrOptions` is an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object).
Creates a new `PerformanceMeasure` entry in the Performance Timeline. A `PerformanceMeasure` is a subclass of `PerformanceEntry` whose `performanceEntry.entryType` is always `'measure'`, and whose `performanceEntry.duration` measures the number of milliseconds elapsed since `startMark` and `endMark`.
The `startMark` argument may identify any *existing* `PerformanceMark` in the Performance Timeline, or *may* identify any of the timestamp properties provided by the `PerformanceNodeTiming` class. If the named `startMark` does not exist, an error is thrown.
The optional `endMark` argument must identify any *existing* `PerformanceMark` in the Performance Timeline or any of the timestamp properties provided by the `PerformanceNodeTiming` class. `endMark` will be `performance.now()` if no parameter is passed, otherwise if the named `endMark` does not exist, an error will be thrown.
The created `PerformanceMeasure` entry is put in the global Performance Timeline and can be queried with `performance.getEntries`, `performance.getEntriesByName`, and `performance.getEntriesByType`. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with `performance.clearMeasures`.
####
`performance.nodeTiming`
Added in: v8.5.0 * [<PerformanceNodeTiming>](perf_hooks#class-performancenodetiming)
*This property is an extension by Node.js. It is not available in Web browsers.*
An instance of the `PerformanceNodeTiming` class that provides performance metrics for specific Node.js operational milestones.
####
`performance.now()`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v8.5.0 | Added in: v8.5.0 |
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the current high resolution millisecond timestamp, where 0 represents the start of the current `node` process.
####
`performance.setResourceTimingBufferSize(maxSize)`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v18.8.0 | Added in: v18.8.0 |
Sets the global performance resource timing buffer size to the specified number of "resource" type performance entry objects.
By default the max buffer size is set to 250.
####
`performance.timeOrigin`
Added in: v8.5.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The [`timeOrigin`](https://w3c.github.io/hr-time/#dom-performance-timeorigin) specifies the high resolution millisecond timestamp at which the current `node` process began, measured in Unix time.
####
`performance.timerify(fn[, options])`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Added the histogram option. |
| v16.0.0 | Re-implemented to use pure-JavaScript and the ability to time async functions. |
| v8.5.0 | Added in: v8.5.0 |
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `histogram` [<RecordableHistogram>](perf_hooks#class-recordablehistogram-extends-histogram) A histogram object created using `perf_hooks.createHistogram()` that will record runtime durations in nanoseconds.
*This property is an extension by Node.js. It is not available in Web browsers.*
Wraps a function within a new function that measures the running time of the wrapped function. A `PerformanceObserver` must be subscribed to the `'function'` event type in order for the timing details to be accessed.
```
const {
performance,
PerformanceObserver
} = require('node:perf_hooks');
function someFunction() {
console.log('hello world');
}
const wrapped = performance.timerify(someFunction);
const obs = new PerformanceObserver((list) => {
console.log(list.getEntries()[0].duration);
performance.clearMarks();
performance.clearMeasures();
obs.disconnect();
});
obs.observe({ entryTypes: ['function'] });
// A performance timeline entry will be created
wrapped();
```
If the wrapped function returns a promise, a finally handler will be attached to the promise and the duration will be reported once the finally handler is invoked.
####
`performance.toJSON()`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `performance` object as the receiver. |
| v16.1.0 | Added in: v16.1.0 |
An object which is JSON representation of the `performance` object. It is similar to [`window.performance.toJSON`](https://developer.mozilla.org/en-US/docs/Web/API/Performance/toJSON) in browsers.
##### Event: `'resourcetimingbufferfull'`
Added in: v18.8.0 The `'resourcetimingbufferfull'` event is fired when the global performance resource timing buffer is full. Adjust resource timing buffer size with `performance.setResourceTimingBufferSize()` or clear the buffer with `performance.clearResourceTimings()` in the event listener to allow more entries to be added to the performance timeline buffer.
### Class: `PerformanceEntry`
Added in: v8.5.0 The constructor of this class is not exposed to users directly.
####
`performanceEntry.duration`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceEntry` object as the receiver. |
| v8.5.0 | Added in: v8.5.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The total number of milliseconds elapsed for this entry. This value will not be meaningful for all Performance Entry types.
####
`performanceEntry.entryType`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceEntry` object as the receiver. |
| v8.5.0 | Added in: v8.5.0 |
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The type of the performance entry. It may be one of:
* `'node'` (Node.js only)
* `'mark'` (available on the Web)
* `'measure'` (available on the Web)
* `'gc'` (Node.js only)
* `'function'` (Node.js only)
* `'http2'` (Node.js only)
* `'http'` (Node.js only)
####
`performanceEntry.name`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceEntry` object as the receiver. |
| v8.5.0 | Added in: v8.5.0 |
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The name of the performance entry.
####
`performanceEntry.startTime`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceEntry` object as the receiver. |
| v8.5.0 | Added in: v8.5.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp marking the starting time of the Performance Entry.
### Class: `PerformanceMark`
Added in: v18.2.0, v16.17.0 * Extends: [<PerformanceEntry>](perf_hooks#class-performanceentry)
Exposes marks created via the `Performance.mark()` method.
####
`performanceMark.detail`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceMark` object as the receiver. |
| v16.0.0 | Added in: v16.0.0 |
* [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Additional detail specified when creating with `Performance.mark()` method.
### Class: `PerformanceMeasure`
Added in: v18.2.0, v16.17.0 * Extends: [<PerformanceEntry>](perf_hooks#class-performanceentry)
Exposes measures created via the `Performance.measure()` method.
The constructor of this class is not exposed to users directly.
####
`performanceMeasure.detail`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceMeasure` object as the receiver. |
| v16.0.0 | Added in: v16.0.0 |
* [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Additional detail specified when creating with `Performance.measure()` method.
### Class: `PerformanceNodeEntry`
Added in: v19.0.0 * Extends: [<PerformanceEntry>](perf_hooks#class-performanceentry)
*This class is an extension by Node.js. It is not available in Web browsers.*
Provides detailed Node.js timing data.
The constructor of this class is not exposed to users directly.
####
`performanceNodeEntry.detail`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceNodeEntry` object as the receiver. |
| v16.0.0 | Added in: v16.0.0 |
* [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Additional detail specific to the `entryType`.
####
`performanceNodeEntry.flags`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Runtime deprecated. Now moved to the detail property when entryType is 'gc'. |
| v13.9.0, v12.17.0 | Added in: v13.9.0, v12.17.0 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `performanceNodeEntry.detail` instead.
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
When `performanceEntry.entryType` is equal to `'gc'`, the `performance.flags` property contains additional information about garbage collection operation. The value may be one of:
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE`
####
`performanceNodeEntry.kind`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Runtime deprecated. Now moved to the detail property when entryType is 'gc'. |
| v8.5.0 | Added in: v8.5.0 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use `performanceNodeEntry.detail` instead.
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
When `performanceEntry.entryType` is equal to `'gc'`, the `performance.kind` property identifies the type of garbage collection operation that occurred. The value may be one of:
* `perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB`
#### Garbage Collection ('gc') Details
When `performanceEntry.type` is equal to `'gc'`, the `performanceNodeEntry.detail` property will be an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) with two properties:
* `kind` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) One of:
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR`
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR`
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL`
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB`
* `flags` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) One of:
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO`
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED`
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED`
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING`
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE`
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY`
+ `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE`
#### HTTP ('http') Details
When `performanceEntry.type` is equal to `'http'`, the `performanceNodeEntry.detail` property will be an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) containing additional information.
If `performanceEntry.name` is equal to `HttpClient`, the `detail` will contain the following properties: `req`, `res`. And the `req` property will be an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) containing `method`, `url`, `headers`, the `res` property will be an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) containing `statusCode`, `statusMessage`, `headers`.
If `performanceEntry.name` is equal to `HttpRequest`, the `detail` will contain the following properties: `req`, `res`. And the `req` property will be an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) containing `method`, `url`, `headers`, the `res` property will be an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) containing `statusCode`, `statusMessage`, `headers`.
This could add additional memory overhead and should only be used for diagnostic purposes, not left turned on in production by default.
#### HTTP/2 ('http2') Details
When `performanceEntry.type` is equal to `'http2'`, the `performanceNodeEntry.detail` property will be an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) containing additional performance information.
If `performanceEntry.name` is equal to `Http2Stream`, the `detail` will contain the following properties:
* `bytesRead` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of `DATA` frame bytes received for this `Http2Stream`.
* `bytesWritten` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of `DATA` frame bytes sent for this `Http2Stream`.
* `id` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The identifier of the associated `Http2Stream`
* `timeToFirstByte` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first `DATA` frame.
* `timeToFirstByteSent` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and sending of the first `DATA` frame.
* `timeToFirstHeader` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first header.
If `performanceEntry.name` is equal to `Http2Session`, the `detail` will contain the following properties:
* `bytesRead` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes received for this `Http2Session`.
* `bytesWritten` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes sent for this `Http2Session`.
* `framesReceived` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of HTTP/2 frames received by the `Http2Session`.
* `framesSent` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of HTTP/2 frames sent by the `Http2Session`.
* `maxConcurrentStreams` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum number of streams concurrently open during the lifetime of the `Http2Session`.
* `pingRTT` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds elapsed since the transmission of a `PING` frame and the reception of its acknowledgment. Only present if a `PING` frame has been sent on the `Http2Session`.
* `streamAverageDuration` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The average duration (in milliseconds) for all `Http2Stream` instances.
* `streamCount` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of `Http2Stream` instances processed by the `Http2Session`.
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'server'` or `'client'` to identify the type of `Http2Session`.
#### Timerify ('function') Details
When `performanceEntry.type` is equal to `'function'`, the `performanceNodeEntry.detail` property will be an [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) listing the input arguments to the timed function.
#### Net ('net') Details
When `performanceEntry.type` is equal to `'net'`, the `performanceNodeEntry.detail` property will be an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) containing additional information.
If `performanceEntry.name` is equal to `connect`, the `detail` will contain the following properties: `host`, `port`.
#### DNS ('dns') Details
When `performanceEntry.type` is equal to `'dns'`, the `performanceNodeEntry.detail` property will be an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) containing additional information.
If `performanceEntry.name` is equal to `lookup`, the `detail` will contain the following properties: `hostname`, `family`, `hints`, `verbatim`, `addresses`.
If `performanceEntry.name` is equal to `lookupService`, the `detail` will contain the following properties: `host`, `port`, `hostname`, `service`.
If `performanceEntry.name` is equal to `queryxxx` or `getHostByAddr`, the `detail` will contain the following properties: `host`, `ttl`, `result`. The value of `result` is same as the result of `queryxxx` or `getHostByAddr`.
### Class: `PerformanceNodeTiming`
Added in: v8.5.0 * Extends: [<PerformanceEntry>](perf_hooks#class-performanceentry)
*This property is an extension by Node.js. It is not available in Web browsers.*
Provides timing details for Node.js itself. The constructor of this class is not exposed to users.
####
`performanceNodeTiming.bootstrapComplete`
Added in: v8.5.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp at which the Node.js process completed bootstrapping. If bootstrapping has not yet finished, the property has the value of -1.
####
`performanceNodeTiming.environment`
Added in: v8.5.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp at which the Node.js environment was initialized.
####
`performanceNodeTiming.idleTime`
Added in: v14.10.0, v12.19.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp of the amount of time the event loop has been idle within the event loop's event provider (e.g. `epoll_wait`). This does not take CPU usage into consideration. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of 0.
####
`performanceNodeTiming.loopExit`
Added in: v8.5.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp at which the Node.js event loop exited. If the event loop has not yet exited, the property has the value of -1. It can only have a value of not -1 in a handler of the [`'exit'`](process#event-exit) event.
####
`performanceNodeTiming.loopStart`
Added in: v8.5.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp at which the Node.js event loop started. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of -1.
####
`performanceNodeTiming.nodeStart`
Added in: v8.5.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp at which the Node.js process was initialized.
####
`performanceNodeTiming.v8Start`
Added in: v8.5.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp at which the V8 platform was initialized.
### Class: `PerformanceResourceTiming`
Added in: v18.2.0, v16.17.0 * Extends: [<PerformanceEntry>](perf_hooks#class-performanceentry)
Provides detailed network timing data regarding the loading of an application's resources.
The constructor of this class is not exposed to users directly.
####
`performanceResourceTiming.workerStart`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp at immediately before dispatching the `fetch` request. If the resource is not intercepted by a worker the property will always return 0.
####
`performanceResourceTiming.redirectStart`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp that represents the start time of the fetch which initiates the redirect.
####
`performanceResourceTiming.redirectEnd`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp that will be created immediately after receiving the last byte of the response of the last redirect.
####
`performanceResourceTiming.fetchStart`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp immediately before the Node.js starts to fetch the resource.
####
`performanceResourceTiming.domainLookupStart`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp immediately before the Node.js starts the domain name lookup for the resource.
####
`performanceResourceTiming.domainLookupEnd`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp representing the time immediately after the Node.js finished the domain name lookup for the resource.
####
`performanceResourceTiming.connectStart`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp representing the time immediately before Node.js starts to establish the connection to the server to retrieve the resource.
####
`performanceResourceTiming.connectEnd`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp representing the time immediately after Node.js finishes establishing the connection to the server to retrieve the resource.
####
`performanceResourceTiming.secureConnectionStart`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp representing the time immediately before Node.js starts the handshake process to secure the current connection.
####
`performanceResourceTiming.requestStart`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp representing the time immediately before Node.js receives the first byte of the response from the server.
####
`performanceResourceTiming.responseEnd`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The high resolution millisecond timestamp representing the time immediately after Node.js receives the last byte of the resource or immediately before the transport connection is closed, whichever comes first.
####
`performanceResourceTiming.transferSize`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
A number representing the size (in octets) of the fetched resource. The size includes the response header fields plus the response payload body.
####
`performanceResourceTiming.encodedBodySize`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
A number representing the size (in octets) received from the fetch (HTTP or cache), of the payload body, before removing any applied content-codings.
####
`performanceResourceTiming.decodedBodySize`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This property getter must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
A number representing the size (in octets) received from the fetch (HTTP or cache), of the message body, after removing any applied content-codings.
####
`performanceResourceTiming.toJSON()`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This method must be called with the `PerformanceResourceTiming` object as the receiver. |
| v18.2.0, v16.17.0 | Added in: v18.2.0, v16.17.0 |
Returns a `object` that is the JSON representation of the `PerformanceResourceTiming` object
### Class: `PerformanceObserver`
####
`new PerformanceObserver(callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.5.0 | Added in: v8.5.0 |
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `list` [<PerformanceObserverEntryList>](perf_hooks#class-performanceobserverentrylist)
+ `observer` [<PerformanceObserver>](perf_hooks#class-performanceobserver)
`PerformanceObserver` objects provide notifications when new `PerformanceEntry` instances have been added to the Performance Timeline.
```
const {
performance,
PerformanceObserver
} = require('node:perf_hooks');
const obs = new PerformanceObserver((list, observer) => {
console.log(list.getEntries());
performance.clearMarks();
performance.clearMeasures();
observer.disconnect();
});
obs.observe({ entryTypes: ['mark'], buffered: true });
performance.mark('test');
```
Because `PerformanceObserver` instances introduce their own additional performance overhead, instances should not be left subscribed to notifications indefinitely. Users should disconnect observers as soon as they are no longer needed.
The `callback` is invoked when a `PerformanceObserver` is notified about new `PerformanceEntry` instances. The callback receives a `PerformanceObserverEntryList` instance and a reference to the `PerformanceObserver`.
####
`performanceObserver.disconnect()`
Added in: v8.5.0 Disconnects the `PerformanceObserver` instance from all notifications.
####
`performanceObserver.observe(options)`
History
| Version | Changes |
| --- | --- |
| v16.7.0 | Updated to conform to Performance Timeline Level 2. The buffered option has been added back. |
| v16.0.0 | Updated to conform to User Timing Level 3. The buffered option has been removed. |
| v8.5.0 | Added in: v8.5.0 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A single [<PerformanceEntry>](perf_hooks#class-performanceentry) type. Must not be given if `entryTypes` is already specified.
+ `entryTypes` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) An array of strings identifying the types of [<PerformanceEntry>](perf_hooks#class-performanceentry) instances the observer is interested in. If not provided an error will be thrown.
+ `buffered` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If true, the observer callback is called with a list global `PerformanceEntry` buffered entries. If false, only `PerformanceEntry`s created after the time point are sent to the observer callback. **Default:** `false`.
Subscribes the [<PerformanceObserver>](perf_hooks#class-performanceobserver) instance to notifications of new [<PerformanceEntry>](perf_hooks#class-performanceentry) instances identified either by `options.entryTypes` or `options.type`:
```
const {
performance,
PerformanceObserver
} = require('node:perf_hooks');
const obs = new PerformanceObserver((list, observer) => {
// Called once asynchronously. `list` contains three items.
});
obs.observe({ type: 'mark' });
for (let n = 0; n < 3; n++)
performance.mark(`test${n}`);
```
### Class: `PerformanceObserverEntryList`
Added in: v8.5.0 The `PerformanceObserverEntryList` class is used to provide access to the `PerformanceEntry` instances passed to a `PerformanceObserver`. The constructor of this class is not exposed to users.
####
`performanceObserverEntryList.getEntries()`
Added in: v8.5.0 * Returns: [<PerformanceEntry[]>](perf_hooks#class-performanceentry)
Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime`.
```
const {
performance,
PerformanceObserver
} = require('node:perf_hooks');
const obs = new PerformanceObserver((perfObserverList, observer) => {
console.log(perfObserverList.getEntries());
/**
* [
* PerformanceEntry {
* name: 'test',
* entryType: 'mark',
* startTime: 81.465639,
* duration: 0
* },
* PerformanceEntry {
* name: 'meow',
* entryType: 'mark',
* startTime: 81.860064,
* duration: 0
* }
* ]
*/
performance.clearMarks();
performance.clearMeasures();
observer.disconnect();
});
obs.observe({ type: 'mark' });
performance.mark('test');
performance.mark('meow');
```
####
`performanceObserverEntryList.getEntriesByName(name[, type])`
Added in: v8.5.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<PerformanceEntry[]>](perf_hooks#class-performanceentry)
Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.name` is equal to `name`, and optionally, whose `performanceEntry.entryType` is equal to `type`.
```
const {
performance,
PerformanceObserver
} = require('node:perf_hooks');
const obs = new PerformanceObserver((perfObserverList, observer) => {
console.log(perfObserverList.getEntriesByName('meow'));
/**
* [
* PerformanceEntry {
* name: 'meow',
* entryType: 'mark',
* startTime: 98.545991,
* duration: 0
* }
* ]
*/
console.log(perfObserverList.getEntriesByName('nope')); // []
console.log(perfObserverList.getEntriesByName('test', 'mark'));
/**
* [
* PerformanceEntry {
* name: 'test',
* entryType: 'mark',
* startTime: 63.518931,
* duration: 0
* }
* ]
*/
console.log(perfObserverList.getEntriesByName('test', 'measure')); // []
performance.clearMarks();
performance.clearMeasures();
observer.disconnect();
});
obs.observe({ entryTypes: ['mark', 'measure'] });
performance.mark('test');
performance.mark('meow');
```
####
`performanceObserverEntryList.getEntriesByType(type)`
Added in: v8.5.0 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<PerformanceEntry[]>](perf_hooks#class-performanceentry)
Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.entryType` is equal to `type`.
```
const {
performance,
PerformanceObserver
} = require('node:perf_hooks');
const obs = new PerformanceObserver((perfObserverList, observer) => {
console.log(perfObserverList.getEntriesByType('mark'));
/**
* [
* PerformanceEntry {
* name: 'test',
* entryType: 'mark',
* startTime: 55.897834,
* duration: 0
* },
* PerformanceEntry {
* name: 'meow',
* entryType: 'mark',
* startTime: 56.350146,
* duration: 0
* }
* ]
*/
performance.clearMarks();
performance.clearMeasures();
observer.disconnect();
});
obs.observe({ type: 'mark' });
performance.mark('test');
performance.mark('meow');
```
###
`perf_hooks.createHistogram([options])`
Added in: v15.9.0, v14.18.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `lowest` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) The lowest discernible value. Must be an integer value greater than 0. **Default:** `1`.
+ `highest` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) The highest recordable value. Must be an integer value that is equal to or greater than two times `lowest`. **Default:** `Number.MAX_SAFE_INTEGER`.
+ `figures` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of accuracy digits. Must be a number between `1` and `5`. **Default:** `3`.
* Returns [<RecordableHistogram>](perf_hooks#class-recordablehistogram-extends-histogram)
Returns a [<RecordableHistogram>](perf_hooks#class-recordablehistogram-extends-histogram).
###
`perf_hooks.monitorEventLoopDelay([options])`
Added in: v11.10.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `resolution` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The sampling rate in milliseconds. Must be greater than zero. **Default:** `10`.
* Returns: [<IntervalHistogram>](perf_hooks#class-intervalhistogram-extends-histogram)
*This property is an extension by Node.js. It is not available in Web browsers.*
Creates an `IntervalHistogram` object that samples and reports the event loop delay over time. The delays will be reported in nanoseconds.
Using a timer to detect approximate event loop delay works because the execution of timers is tied specifically to the lifecycle of the libuv event loop. That is, a delay in the loop will cause a delay in the execution of the timer, and those delays are specifically what this API is intended to detect.
```
const { monitorEventLoopDelay } = require('node:perf_hooks');
const h = monitorEventLoopDelay({ resolution: 20 });
h.enable();
// Do something.
h.disable();
console.log(h.min);
console.log(h.max);
console.log(h.mean);
console.log(h.stddev);
console.log(h.percentiles);
console.log(h.percentile(50));
console.log(h.percentile(99));
```
### Class: `Histogram`
Added in: v11.10.0 ####
`histogram.count`
Added in: v17.4.0, v16.14.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The number of samples recorded by the histogram.
####
`histogram.countBigInt`
Added in: v17.4.0, v16.14.0 * [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The number of samples recorded by the histogram.
####
`histogram.exceeds`
Added in: v11.10.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold.
####
`histogram.exceedsBigInt`
Added in: v17.4.0, v16.14.0 * [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold.
####
`histogram.max`
Added in: v11.10.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The maximum recorded event loop delay.
####
`histogram.maxBigInt`
Added in: v17.4.0, v16.14.0 * [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The maximum recorded event loop delay.
####
`histogram.mean`
Added in: v11.10.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The mean of the recorded event loop delays.
####
`histogram.min`
Added in: v11.10.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The minimum recorded event loop delay.
####
`histogram.minBigInt`
Added in: v17.4.0, v16.14.0 * [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
The minimum recorded event loop delay.
####
`histogram.percentile(percentile)`
Added in: v11.10.0 * `percentile` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A percentile value in the range (0, 100].
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the value at the given percentile.
####
`histogram.percentileBigInt(percentile)`
Added in: v17.4.0, v16.14.0 * `percentile` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A percentile value in the range (0, 100].
* Returns: [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Returns the value at the given percentile.
####
`histogram.percentiles`
Added in: v11.10.0 * [<Map>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
Returns a `Map` object detailing the accumulated percentile distribution.
####
`histogram.percentilesBigInt`
Added in: v17.4.0, v16.14.0 * [<Map>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
Returns a `Map` object detailing the accumulated percentile distribution.
####
`histogram.reset()`
Added in: v11.10.0 Resets the collected histogram data.
####
`histogram.stddev`
Added in: v11.10.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The standard deviation of the recorded event loop delays.
### Class: `IntervalHistogram extends Histogram`
A `Histogram` that is periodically updated on a given interval.
####
`histogram.disable()`
Added in: v11.10.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Disables the update interval timer. Returns `true` if the timer was stopped, `false` if it was already stopped.
####
`histogram.enable()`
Added in: v11.10.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Enables the update interval timer. Returns `true` if the timer was started, `false` if it was already started.
#### Cloning an `IntervalHistogram`
[<IntervalHistogram>](perf_hooks#class-intervalhistogram-extends-histogram) instances can be cloned via [<MessagePort>](worker_threads#class-messageport). On the receiving end, the histogram is cloned as a plain [<Histogram>](perf_hooks#class-histogram) object that does not implement the `enable()` and `disable()` methods.
### Class: `RecordableHistogram extends Histogram`
Added in: v15.9.0, v14.18.0 ####
`histogram.add(other)`
Added in: v17.4.0, v16.14.0 * `other` [<RecordableHistogram>](perf_hooks#class-recordablehistogram-extends-histogram)
Adds the values from `other` to this histogram.
####
`histogram.record(val)`
Added in: v15.9.0, v14.18.0 * `val` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) The amount to record in the histogram.
####
`histogram.recordDelta()`
Added in: v15.9.0, v14.18.0 Calculates the amount of time (in nanoseconds) that has passed since the previous call to `recordDelta()` and records that amount in the histogram.
### Examples
#### Measuring the duration of async operations
The following example uses the [Async Hooks](async_hooks) and Performance APIs to measure the actual duration of a Timeout operation (including the amount of time it took to execute the callback).
```
'use strict';
const async_hooks = require('node:async_hooks');
const {
performance,
PerformanceObserver
} = require('node:perf_hooks');
const set = new Set();
const hook = async_hooks.createHook({
init(id, type) {
if (type === 'Timeout') {
performance.mark(`Timeout-${id}-Init`);
set.add(id);
}
},
destroy(id) {
if (set.has(id)) {
set.delete(id);
performance.mark(`Timeout-${id}-Destroy`);
performance.measure(`Timeout-${id}`,
`Timeout-${id}-Init`,
`Timeout-${id}-Destroy`);
}
}
});
hook.enable();
const obs = new PerformanceObserver((list, observer) => {
console.log(list.getEntries()[0]);
performance.clearMarks();
performance.clearMeasures();
observer.disconnect();
});
obs.observe({ entryTypes: ['measure'], buffered: true });
setTimeout(() => {}, 1000);
```
#### Measuring how long it takes to load dependencies
The following example measures the duration of `require()` operations to load dependencies:
```
'use strict';
const {
performance,
PerformanceObserver
} = require('node:perf_hooks');
const mod = require('node:module');
// Monkey patch the require function
mod.Module.prototype.require =
performance.timerify(mod.Module.prototype.require);
require = performance.timerify(require);
// Activate the observer
const obs = new PerformanceObserver((list) => {
const entries = list.getEntries();
entries.forEach((entry) => {
console.log(`require('${entry[0]}')`, entry.duration);
});
performance.clearMarks();
performance.clearMeasures();
obs.disconnect();
});
obs.observe({ entryTypes: ['function'], buffered: true });
require('some-module');
```
#### Measuring how long one HTTP round-trip takes
The following example is used to trace the time spent by HTTP client (`OutgoingMessage`) and HTTP request (`IncomingMessage`). For HTTP client, it means the time interval between starting the request and receiving the response, and for HTTP request, it means the time interval between receiving the request and sending the response:
```
'use strict';
const { PerformanceObserver } = require('node:perf_hooks');
const http = require('node:http');
const obs = new PerformanceObserver((items) => {
items.getEntries().forEach((item) => {
console.log(item);
});
});
obs.observe({ entryTypes: ['http'] });
const PORT = 8080;
http.createServer((req, res) => {
res.end('ok');
}).listen(PORT, () => {
http.get(`http://127.0.0.1:${PORT}`);
});
```
#### Measuring how long the `net.connect` (only for TCP) takes when the connection is successful
```
'use strict';
const { PerformanceObserver } = require('node:perf_hooks');
const net = require('node:net');
const obs = new PerformanceObserver((items) => {
items.getEntries().forEach((item) => {
console.log(item);
});
});
obs.observe({ entryTypes: ['net'] });
const PORT = 8080;
net.createServer((socket) => {
socket.destroy();
}).listen(PORT, () => {
net.connect(PORT);
});
```
#### Measuring how long the DNS takes when the request is successful
```
'use strict';
const { PerformanceObserver } = require('node:perf_hooks');
const dns = require('node:dns');
const obs = new PerformanceObserver((items) => {
items.getEntries().forEach((item) => {
console.log(item);
});
});
obs.observe({ entryTypes: ['dns'] });
dns.lookup('localhost', () => {});
dns.promises.resolve('localhost');
```
| programming_docs |
node None Modules: ECMAScript modules
---------------------------
History
| Version | Changes |
| --- | --- |
| v18.6.0, v16.17.0 | Add support for chaining loaders. |
| v17.1.0, v16.14.0 | Add support for import assertions. |
| v17.0.0, v16.12.0 | Consolidate loader hooks, removed `getFormat`, `getSource`, `transformSource`, and `getGlobalPreloadCode` hooks added `load` and `globalPreload` hooks allowed returning `format` from either `resolve` or `load` hooks. |
| v14.8.0 | Unflag Top-Level Await. |
| v15.3.0, v14.17.0, v12.22.0 | Stabilize modules implementation. |
| v14.13.0, v12.20.0 | Support for detection of CommonJS named exports. |
| v14.0.0, v13.14.0, v12.20.0 | Remove experimental modules warning. |
| v13.2.0, v12.17.0 | Loading ECMAScript modules no longer requires a command-line flag. |
| v12.0.0 | Add support for ES modules using `.js` file extension via `package.json` `"type"` field. |
| v8.5.0 | Added in: v8.5.0 |
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
### Introduction
ECMAScript modules are [the official standard format](https://tc39.github.io/ecma262/#sec-modules) to package JavaScript code for reuse. Modules are defined using a variety of [`import`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import) and [`export`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/export) statements.
The following example of an ES module exports a function:
```
// addTwo.mjs
function addTwo(num) {
return num + 2;
}
export { addTwo };
```
The following example of an ES module imports the function from `addTwo.mjs`:
```
// app.mjs
import { addTwo } from './addTwo.mjs';
// Prints: 6
console.log(addTwo(4));
```
Node.js fully supports ECMAScript modules as they are currently specified and provides interoperability between them and its original module format, [CommonJS](modules).
### Enabling
Node.js has two module systems: [CommonJS](modules) modules and ECMAScript modules.
Authors can tell Node.js to use the ECMAScript modules loader via the `.mjs` file extension, the `package.json` [`"type"`](packages#type) field, or the [`--input-type`](cli#--input-typetype) flag. Outside of those cases, Node.js will use the CommonJS module loader. See [Determining module system](packages#determining-module-system) for more details.
### Packages
This section was moved to [Modules: Packages](packages).
###
`import` Specifiers
#### Terminology
The *specifier* of an `import` statement is the string after the `from` keyword, e.g. `'node:path'` in `import { sep } from 'node:path'`. Specifiers are also used in `export from` statements, and as the argument to an `import()` expression.
There are three types of specifiers:
* *Relative specifiers* like `'./startup.js'` or `'../config.mjs'`. They refer to a path relative to the location of the importing file. *The file extension is always necessary for these.*
* *Bare specifiers* like `'some-package'` or `'some-package/shuffle'`. They can refer to the main entry point of a package by the package name, or a specific feature module within a package prefixed by the package name as per the examples respectively. *Including the file extension is only necessary for packages without an [`"exports"`](packages#exports) field.*
* *Absolute specifiers* like `'file:///opt/nodejs/config.js'`. They refer directly and explicitly to a full path.
Bare specifier resolutions are handled by the [Node.js module resolution algorithm](#resolver-algorithm-specification). All other specifier resolutions are always only resolved with the standard relative [URL](https://url.spec.whatwg.org/) resolution semantics.
Like in CommonJS, module files within packages can be accessed by appending a path to the package name unless the package's [`package.json`](packages#nodejs-packagejson-field-definitions) contains an [`"exports"`](packages#exports) field, in which case files within packages can only be accessed via the paths defined in [`"exports"`](packages#exports).
For details on these package resolution rules that apply to bare specifiers in the Node.js module resolution, see the [packages documentation](packages).
#### Mandatory file extensions
A file extension must be provided when using the `import` keyword to resolve relative or absolute specifiers. Directory indexes (e.g. `'./startup/index.js'`) must also be fully specified.
This behavior matches how `import` behaves in browser environments, assuming a typically configured server.
#### URLs
ES modules are resolved and cached as URLs. This means that special characters must be [percent-encoded](url#percent-encoding-in-urls), such as `#` with `%23` and `?` with `%3F`.
`file:`, `node:`, and `data:` URL schemes are supported. A specifier like `'https://example.com/app.js'` is not supported natively in Node.js unless using a [custom HTTPS loader](#https-loader).
#####
`file:` URLs
Modules are loaded multiple times if the `import` specifier used to resolve them has a different query or fragment.
```
import './foo.mjs?query=1'; // loads ./foo.mjs with query of "?query=1"
import './foo.mjs?query=2'; // loads ./foo.mjs with query of "?query=2"
```
The volume root may be referenced via `/`, `//`, or `file:///`. Given the differences between [URL](https://url.spec.whatwg.org/) and path resolution (such as percent encoding details), it is recommended to use [url.pathToFileURL](url#urlpathtofileurlpath) when importing a path.
#####
`data:` imports
Added in: v12.10.0 [`data:` URLs](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs) are supported for importing with the following MIME types:
* `text/javascript` for ES modules
* `application/json` for JSON
* `application/wasm` for Wasm
```
import 'data:text/javascript,console.log("hello!");';
import _ from 'data:application/json,"world!"' assert { type: 'json' };
```
`data:` URLs only resolve [bare specifiers](#terminology) for builtin modules and [absolute specifiers](#terminology). Resolving [relative specifiers](#terminology) does not work because `data:` is not a [special scheme](https://url.spec.whatwg.org/#special-scheme). For example, attempting to load `./foo` from `data:text/javascript,import "./foo";` fails to resolve because there is no concept of relative resolution for `data:` URLs.
#####
`node:` imports
History
| Version | Changes |
| --- | --- |
| v16.0.0, v14.18.0 | Added `node:` import support to `require(...)`. |
| v14.13.1, v12.20.0 | Added in: v14.13.1, v12.20.0 |
`node:` URLs are supported as an alternative means to load Node.js builtin modules. This URL scheme allows for builtin modules to be referenced by valid absolute URL strings.
```
import fs from 'node:fs/promises';
```
### Import assertions
Added in: v17.1.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
The [Import Assertions proposal](https://github.com/tc39/proposal-import-assertions) adds an inline syntax for module import statements to pass on more information alongside the module specifier.
```
import fooData from './foo.json' assert { type: 'json' };
const { default: barData } =
await import('./bar.json', { assert: { type: 'json' } });
```
Node.js supports the following `type` values, for which the assertion is mandatory:
| Assertion `type` | Needed for |
| --- | --- |
| `'json'` | [JSON modules](#json-modules) |
### Builtin modules
[Core modules](modules#core-modules) provide named exports of their public API. A default export is also provided which is the value of the CommonJS exports. The default export can be used for, among other things, modifying the named exports. Named exports of builtin modules are updated only by calling [`module.syncBuiltinESMExports()`](module#modulesyncbuiltinesmexports).
```
import EventEmitter from 'node:events';
const e = new EventEmitter();
```
```
import { readFile } from 'node:fs';
readFile('./foo.txt', (err, source) => {
if (err) {
console.error(err);
} else {
console.log(source);
}
});
```
```
import fs, { readFileSync } from 'node:fs';
import { syncBuiltinESMExports } from 'node:module';
import { Buffer } from 'node:buffer';
fs.readFileSync = () => Buffer.from('Hello, ESM');
syncBuiltinESMExports();
fs.readFileSync === readFileSync;
```
###
`import()` expressions
[Dynamic `import()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import) is supported in both CommonJS and ES modules. In CommonJS modules it can be used to load ES modules.
###
`import.meta`
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `import.meta` meta property is an `Object` that contains the following properties.
####
`import.meta.url`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The absolute `file:` URL of the module.
This is defined exactly the same as it is in browsers providing the URL of the current module file.
This enables useful patterns such as relative file loading:
```
import { readFileSync } from 'node:fs';
const buffer = readFileSync(new URL('./data.proto', import.meta.url));
```
####
`import.meta.resolve(specifier[, parent])`
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
This feature is only available with the `--experimental-import-meta-resolve` command flag enabled.
* `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The module specifier to resolve relative to `parent`.
* `parent` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) The absolute parent module URL to resolve from. If none is specified, the value of `import.meta.url` is used as the default.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Provides a module-relative resolution function scoped to each module, returning the URL string.
```
const dependencyAsset = await import.meta.resolve('component-lib/asset.css');
```
`import.meta.resolve` also accepts a second argument which is the parent module from which to resolve from:
```
await import.meta.resolve('./dep', import.meta.url);
```
This function is asynchronous because the ES module resolver in Node.js is allowed to be asynchronous.
### Interoperability with CommonJS
####
`import` statements
An `import` statement can reference an ES module or a CommonJS module. `import` statements are permitted only in ES modules, but dynamic [`import()`](#import-expressions) expressions are supported in CommonJS for loading ES modules.
When importing [CommonJS modules](#commonjs-namespaces), the `module.exports` object is provided as the default export. Named exports may be available, provided by static analysis as a convenience for better ecosystem compatibility.
####
`require`
The CommonJS module `require` always treats the files it references as CommonJS.
Using `require` to load an ES module is not supported because ES modules have asynchronous execution. Instead, use [`import()`](#import-expressions) to load an ES module from a CommonJS module.
#### CommonJS Namespaces
CommonJS modules consist of a `module.exports` object which can be of any type.
When importing a CommonJS module, it can be reliably imported using the ES module default import or its corresponding sugar syntax:
```
import { default as cjs } from 'cjs';
// The following import statement is "syntax sugar" (equivalent but sweeter)
// for `{ default as cjsSugar }` in the above import statement:
import cjsSugar from 'cjs';
console.log(cjs);
console.log(cjs === cjsSugar);
// Prints:
// <module.exports>
// true
```
The ECMAScript Module Namespace representation of a CommonJS module is always a namespace with a `default` export key pointing to the CommonJS `module.exports` value.
This Module Namespace Exotic Object can be directly observed either when using `import * as m from 'cjs'` or a dynamic import:
```
import * as m from 'cjs';
console.log(m);
console.log(m === await import('cjs'));
// Prints:
// [Module] { default: <module.exports> }
// true
```
For better compatibility with existing usage in the JS ecosystem, Node.js in addition attempts to determine the CommonJS named exports of every imported CommonJS module to provide them as separate ES module exports using a static analysis process.
For example, consider a CommonJS module written:
```
// cjs.cjs
exports.name = 'exported';
```
The preceding module supports named imports in ES modules:
```
import { name } from './cjs.cjs';
console.log(name);
// Prints: 'exported'
import cjs from './cjs.cjs';
console.log(cjs);
// Prints: { name: 'exported' }
import * as m from './cjs.cjs';
console.log(m);
// Prints: [Module] { default: { name: 'exported' }, name: 'exported' }
```
As can be seen from the last example of the Module Namespace Exotic Object being logged, the `name` export is copied off of the `module.exports` object and set directly on the ES module namespace when the module is imported.
Live binding updates or new exports added to `module.exports` are not detected for these named exports.
The detection of named exports is based on common syntax patterns but does not always correctly detect named exports. In these cases, using the default import form described above can be a better option.
Named exports detection covers many common export patterns, reexport patterns and build tool and transpiler outputs. See [cjs-module-lexer](https://github.com/nodejs/cjs-module-lexer/tree/1.2.2) for the exact semantics implemented.
#### Differences between ES modules and CommonJS
##### No `require`, `exports`, or `module.exports`
In most cases, the ES module `import` can be used to load CommonJS modules.
If needed, a `require` function can be constructed within an ES module using [`module.createRequire()`](module#modulecreaterequirefilename).
##### No `__filename` or `__dirname`
These CommonJS variables are not available in ES modules.
`__filename` and `__dirname` use cases can be replicated via [`import.meta.url`](#importmetaurl).
##### No Native Module Loading
Native modules are not currently supported with ES module imports.
They can instead be loaded with [`module.createRequire()`](module#modulecreaterequirefilename) or [`process.dlopen`](process#processdlopenmodule-filename-flags).
##### No `require.resolve`
Relative resolution can be handled via `new URL('./local', import.meta.url)`.
For a complete `require.resolve` replacement, there is a flagged experimental [`import.meta.resolve`](#importmetaresolvespecifier-parent) API.
Alternatively `module.createRequire()` can be used.
##### No `NODE_PATH`
`NODE_PATH` is not part of resolving `import` specifiers. Please use symlinks if this behavior is desired.
##### No `require.extensions`
`require.extensions` is not used by `import`. The expectation is that loader hooks can provide this workflow in the future.
##### No `require.cache`
`require.cache` is not used by `import` as the ES module loader has its own separate cache.
### JSON modules
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
JSON files can be referenced by `import`:
```
import packageConfig from './package.json' assert { type: 'json' };
```
The `assert { type: 'json' }` syntax is mandatory; see [Import Assertions](#import-assertions).
The imported JSON only exposes a `default` export. There is no support for named exports. A cache entry is created in the CommonJS cache to avoid duplication. The same object is returned in CommonJS if the JSON module has already been imported from the same path.
### Wasm modules
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Importing WebAssembly modules is supported under the `--experimental-wasm-modules` flag, allowing any `.wasm` files to be imported as normal modules while also supporting their module imports.
This integration is in line with the [ES Module Integration Proposal for WebAssembly](https://github.com/webassembly/esm-integration).
For example, an `index.mjs` containing:
```
import * as M from './module.wasm';
console.log(M);
```
executed under:
```
node --experimental-wasm-modules index.mjs
```
would provide the exports interface for the instantiation of `module.wasm`.
### Top-level `await`
Added in: v14.8.0 The `await` keyword may be used in the top level body of an ECMAScript module.
Assuming an `a.mjs` with
```
export const five = await Promise.resolve(5);
```
And a `b.mjs` with
```
import { five } from './a.mjs';
console.log(five); // Logs `5`
```
```
node b.mjs # works
```
If a top level `await` expression never resolves, the `node` process will exit with a `13` [status code](process#exit-codes).
```
import { spawn } from 'node:child_process';
import { execPath } from 'node:process';
spawn(execPath, [
'--input-type=module',
'--eval',
// Never-resolving Promise:
'await new Promise(() => {})',
]).once('exit', (code) => {
console.log(code); // Logs `13`
});
```
### HTTPS and HTTP imports
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Importing network based modules using `https:` and `http:` is supported under the `--experimental-network-imports` flag. This allows web browser-like imports to work in Node.js with a few differences due to application stability and security concerns that are different when running in a privileged environment instead of a browser sandbox.
#### Imports are limited to HTTP/1
Automatic protocol negotiation for HTTP/2 and HTTP/3 is not yet supported.
#### HTTP is limited to loopback addresses
`http:` is vulnerable to man-in-the-middle attacks and is not allowed to be used for addresses outside of the IPv4 address `127.0.0.0/8` (`127.0.0.1` to `127.255.255.255`) and the IPv6 address `::1`. Support for `http:` is intended to be used for local development.
#### Authentication is never sent to the destination server.
`Authorization`, `Cookie`, and `Proxy-Authorization` headers are not sent to the server. Avoid including user info in parts of imported URLs. A security model for safely using these on the server is being worked on.
#### CORS is never checked on the destination server
CORS is designed to allow a server to limit the consumers of an API to a specific set of hosts. This is not supported as it does not make sense for a server-based implementation.
#### Cannot load non-network dependencies
These modules cannot access other modules that are not over `http:` or `https:`. To still access local modules while avoiding the security concern, pass in references to the local dependencies:
```
// file.mjs
import worker_threads from 'node:worker_threads';
import { configure, resize } from 'https://example.com/imagelib.mjs';
configure({ worker_threads });
```
```
// https://example.com/imagelib.mjs
let worker_threads;
export function configure(opts) {
worker_threads = opts.worker_threads;
}
export function resize(img, size) {
// Perform resizing in worker_thread to avoid main thread blocking
}
```
#### Network-based loading is not enabled by default
For now, the `--experimental-network-imports` flag is required to enable loading resources over `http:` or `https:`. In the future, a different mechanism will be used to enforce this. Opt-in is required to prevent transitive dependencies inadvertently using potentially mutable state that could affect reliability of Node.js applications.
### Loaders
History
| Version | Changes |
| --- | --- |
| v18.6.0, v16.17.0 | Add support for chaining loaders. |
| v16.12.0 | Removed `getFormat`, `getSource`, `transformSource`, and `globalPreload`; added `load` hook and `getGlobalPreload` hook. |
| v8.8.0 | Added in: v8.8.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
> This API is currently being redesigned and will still change.
>
>
To customize the default module resolution, loader hooks can optionally be provided via a `--experimental-loader ./loader-name.mjs` argument to Node.js.
When hooks are used they apply to the entry point and all `import` calls. They won't apply to `require` calls; those still follow [CommonJS](modules) rules.
Loaders follow the pattern of `--require`:
```
node \
--experimental-loader unpkg \
--experimental-loader http-to-https \
--experimental-loader cache-buster
```
These are called in the following sequence: `cache-buster` calls `http-to-https` which calls `unpkg`.
#### Hooks
Hooks are part of a chain, even if that chain consists of only one custom (user-provided) hook and the default hook, which is always present. Hook functions nest: each one must always return a plain object, and chaining happens as a result of each function calling `next<hookName>()`, which is a reference to the subsequent loader's hook.
A hook that returns a value lacking a required property triggers an exception. A hook that returns without calling `next<hookName>()` *and* without returning `shortCircuit: true` also triggers an exception. These errors are to help prevent unintentional breaks in the chain.
#####
`resolve(specifier, context, nextResolve)`
History
| Version | Changes |
| --- | --- |
| v18.6.0, v16.17.0 | Add support for chaining resolve hooks. Each hook must either call `nextResolve()` or include a `shortCircuit` property set to `true` in its return. |
| v17.1.0, v16.14.0 | Add support for import assertions. |
> The loaders API is being redesigned. This hook may disappear or its signature may change. Do not rely on the API described below.
>
>
* `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `context` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `conditions` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Export conditions of the relevant `package.json`
+ `importAssertions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `parentURL` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) The module importing this one, or undefined if this is the Node.js entry point
* `nextResolve` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The subsequent `resolve` hook in the chain, or the Node.js default `resolve` hook after the last user-supplied `resolve` hook
+ `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `context` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) A hint to the load hook (it might be ignored) `'builtin' | 'commonjs' | 'json' | 'module' | 'wasm'`
+ `shortCircuit` [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) | [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) A signal that this hook intends to terminate the chain of `resolve` hooks. **Default:** `false`
+ `url` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The absolute URL to which this input resolves
The `resolve` hook chain is responsible for resolving file URL for a given module specifier and parent URL, and optionally its format (such as `'module'`) as a hint to the `load` hook. If a format is specified, the `load` hook is ultimately responsible for providing the final `format` value (and it is free to ignore the hint provided by `resolve`); if `resolve` provides a `format`, a custom `load` hook is required even if only to pass the value to the Node.js default `load` hook.
The module specifier is the string in an `import` statement or `import()` expression.
The parent URL is the URL of the module that imported this one, or `undefined` if this is the main entry point for the application.
The `conditions` property in `context` is an array of conditions for [package exports conditions](packages#conditional-exports) that apply to this resolution request. They can be used for looking up conditional mappings elsewhere or to modify the list when calling the default resolution logic.
The current [package exports conditions](packages#conditional-exports) are always in the `context.conditions` array passed into the hook. To guarantee *default Node.js module specifier resolution behavior* when calling `defaultResolve`, the `context.conditions` array passed to it *must* include *all* elements of the `context.conditions` array originally passed into the `resolve` hook.
```
export async function resolve(specifier, context, nextResolve) {
const { parentURL = null } = context;
if (Math.random() > 0.5) { // Some condition.
// For some or all specifiers, do some custom logic for resolving.
// Always return an object of the form {url: <string>}.
return {
shortCircuit: true,
url: parentURL ?
new URL(specifier, parentURL).href :
new URL(specifier).href,
};
}
if (Math.random() < 0.5) { // Another condition.
// When calling `defaultResolve`, the arguments can be modified. In this
// case it's adding another value for matching conditional exports.
return nextResolve(specifier, {
...context,
conditions: [...context.conditions, 'another-condition'],
});
}
// Defer to the next hook in the chain, which would be the
// Node.js default resolve if this is the last user-specified loader.
return nextResolve(specifier);
}
```
#####
`load(url, context, nextLoad)`
History
| Version | Changes |
| --- | --- |
| v18.6.0, v16.17.0 | Add support for chaining load hooks. Each hook must either call `nextLoad()` or include a `shortCircuit` property set to `true` in its return. |
> The loaders API is being redesigned. This hook may disappear or its signature may change. Do not rely on the API described below.
>
>
> In a previous version of this API, this was split across 3 separate, now deprecated, hooks (`getFormat`, `getSource`, and `transformSource`).
>
>
* `url` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The URL returned by the `resolve` chain
* `context` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `conditions` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Export conditions of the relevant `package.json`
+ `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) The format optionally supplied by the `resolve` hook chain
+ `importAssertions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `nextLoad` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The subsequent `load` hook in the chain, or the Node.js default `load` hook after the last user-supplied `load` hook
+ `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `context` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `shortCircuit` [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) | [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) A signal that this hook intends to terminate the chain of `resolve` hooks. **Default:** `false`
+ `source` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) The source for Node.js to evaluate
The `load` hook provides a way to define a custom method of determining how a URL should be interpreted, retrieved, and parsed. It is also in charge of validating the import assertion.
The final value of `format` must be one of the following:
| `format` | Description | Acceptable types for `source` returned by `load` |
| --- | --- | --- |
| `'builtin'` | Load a Node.js builtin module | Not applicable |
| `'commonjs'` | Load a Node.js CommonJS module | Not applicable |
| `'json'` | Load a JSON file | { [`string`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String), [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer), [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) } |
| `'module'` | Load an ES module | { [`string`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String), [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer), [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) } |
| `'wasm'` | Load a WebAssembly module | { [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer), [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) } |
The value of `source` is ignored for type `'builtin'` because currently it is not possible to replace the value of a Node.js builtin (core) module. The value of `source` is ignored for type `'commonjs'` because the CommonJS module loader does not provide a mechanism for the ES module loader to override the [CommonJS module return value](#commonjs-namespaces). This limitation might be overcome in the future.
> **Caveat**: The ESM `load` hook and namespaced exports from CommonJS modules are incompatible. Attempting to use them together will result in an empty object from the import. This may be addressed in the future.
>
>
> These types all correspond to classes defined in ECMAScript.
>
>
* The specific [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) object is a [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer).
* The specific [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) object is a [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array).
If the source value of a text-based format (i.e., `'json'`, `'module'`) is not a string, it is converted to a string using [`util.TextDecoder`](util#class-utiltextdecoder).
The `load` hook provides a way to define a custom method for retrieving the source code of an ES module specifier. This would allow a loader to potentially avoid reading files from disk. It could also be used to map an unrecognized format to a supported one, for example `yaml` to `module`.
```
export async function load(url, context, nextLoad) {
const { format } = context;
if (Math.random() > 0.5) { // Some condition
/*
For some or all URLs, do some custom logic for retrieving the source.
Always return an object of the form {
format: <string>,
source: <string|buffer>,
}.
*/
return {
format,
shortCircuit: true,
source: '...',
};
}
// Defer to the next hook in the chain.
return nextLoad(url);
}
```
In a more advanced scenario, this can also be used to transform an unsupported source to a supported one (see [Examples](#examples) below).
#####
`globalPreload()`
History
| Version | Changes |
| --- | --- |
| v18.6.0, v16.17.0 | Add support for chaining globalPreload hooks. |
> The loaders API is being redesigned. This hook may disappear or its signature may change. Do not rely on the API described below.
>
>
> In a previous version of this API, this hook was named `getGlobalPreloadCode`.
>
>
* `context` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Information to assist the preload code
+ `port` [<MessagePort>](worker_threads#class-messageport)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Code to run before application startup
Sometimes it might be necessary to run some code inside of the same global scope that the application runs in. This hook allows the return of a string that is run as a sloppy-mode script on startup.
Similar to how CommonJS wrappers work, the code runs in an implicit function scope. The only argument is a `require`-like function that can be used to load builtins like "fs": `getBuiltin(request: string)`.
If the code needs more advanced `require` features, it has to construct its own `require` using `module.createRequire()`.
```
export function globalPreload(context) {
return `\
globalThis.someInjectedProperty = 42;
console.log('I just set some globals!');
const { createRequire } = getBuiltin('module');
const { cwd } = getBuiltin('process');
const require = createRequire(cwd() + '/<preload>');
// [...]
`;
}
```
In order to allow communication between the application and the loader, another argument is provided to the preload code: `port`. This is available as a parameter to the loader hook and inside of the source text returned by the hook. Some care must be taken in order to properly call [`port.ref()`](https://nodejs.org/dist/latest-v17.x/docs/api/worker_threads.html#portref) and [`port.unref()`](https://nodejs.org/dist/latest-v17.x/docs/api/worker_threads.html#portunref) to prevent a process from being in a state where it won't close normally.
```
/**
* This example has the application context send a message to the loader
* and sends the message back to the application context
*/
export function globalPreload({ port }) {
port.onmessage = (evt) => {
port.postMessage(evt.data);
};
return `\
port.postMessage('console.log("I went to the Loader and back");');
port.onmessage = (evt) => {
eval(evt.data);
};
`;
}
```
#### Examples
The various loader hooks can be used together to accomplish wide-ranging customizations of the Node.js code loading and evaluation behaviors.
##### HTTPS loader
In current Node.js, specifiers starting with `https://` are experimental (see [HTTPS and HTTP imports](#https-and-http-imports)).
The loader below registers hooks to enable rudimentary support for such specifiers. While this may seem like a significant improvement to Node.js core functionality, there are substantial downsides to actually using this loader: performance is much slower than loading files from disk, there is no caching, and there is no security.
```
// https-loader.mjs
import { get } from 'node:https';
export function resolve(specifier, context, nextResolve) {
const { parentURL = null } = context;
// Normally Node.js would error on specifiers starting with 'https://', so
// this hook intercepts them and converts them into absolute URLs to be
// passed along to the later hooks below.
if (specifier.startsWith('https://')) {
return {
shortCircuit: true,
url: specifier
};
} else if (parentURL && parentURL.startsWith('https://')) {
return {
shortCircuit: true,
url: new URL(specifier, parentURL).href,
};
}
// Let Node.js handle all other specifiers.
return nextResolve(specifier);
}
export function load(url, context, nextLoad) {
// For JavaScript to be loaded over the network, we need to fetch and
// return it.
if (url.startsWith('https://')) {
return new Promise((resolve, reject) => {
get(url, (res) => {
let data = '';
res.on('data', (chunk) => data += chunk);
res.on('end', () => resolve({
// This example assumes all network-provided JavaScript is ES module
// code.
format: 'module',
shortCircuit: true,
source: data,
}));
}).on('error', (err) => reject(err));
});
}
// Let Node.js handle all other URLs.
return nextLoad(url);
}
```
```
// main.mjs
import { VERSION } from 'https://coffeescript.org/browser-compiler-modern/coffeescript.js';
console.log(VERSION);
```
With the preceding loader, running `node --experimental-loader ./https-loader.mjs ./main.mjs` prints the current version of CoffeeScript per the module at the URL in `main.mjs`.
##### Transpiler loader
Sources that are in formats Node.js doesn't understand can be converted into JavaScript using the [`load` hook](#loadurl-context-nextload). Before that hook gets called, however, a [`resolve` hook](#resolvespecifier-context-nextresolve) needs to tell Node.js not to throw an error on unknown file types.
This is less performant than transpiling source files before running Node.js; a transpiler loader should only be used for development and testing purposes.
```
// coffeescript-loader.mjs
import { readFile } from 'node:fs/promises';
import { dirname, extname, resolve as resolvePath } from 'node:path';
import { cwd } from 'node:process';
import { fileURLToPath, pathToFileURL } from 'node:url';
import CoffeeScript from 'coffeescript';
const baseURL = pathToFileURL(`${cwd()}/`).href;
// CoffeeScript files end in .coffee, .litcoffee, or .coffee.md.
const extensionsRegex = /\.coffee$|\.litcoffee$|\.coffee\.md$/;
export async function resolve(specifier, context, nextResolve) {
if (extensionsRegex.test(specifier)) {
const { parentURL = baseURL } = context;
// Node.js normally errors on unknown file extensions, so return a URL for
// specifiers ending in the CoffeeScript file extensions.
return {
shortCircuit: true,
url: new URL(specifier, parentURL).href
};
}
// Let Node.js handle all other specifiers.
return nextResolve(specifier);
}
export async function load(url, context, nextLoad) {
if (extensionsRegex.test(url)) {
// Now that we patched resolve to let CoffeeScript URLs through, we need to
// tell Node.js what format such URLs should be interpreted as. Because
// CoffeeScript transpiles into JavaScript, it should be one of the two
// JavaScript formats: 'commonjs' or 'module'.
// CoffeeScript files can be either CommonJS or ES modules, so we want any
// CoffeeScript file to be treated by Node.js the same as a .js file at the
// same location. To determine how Node.js would interpret an arbitrary .js
// file, search up the file system for the nearest parent package.json file
// and read its "type" field.
const format = await getPackageType(url);
// When a hook returns a format of 'commonjs', `source` is be ignored.
// To handle CommonJS files, a handler needs to be registered with
// `require.extensions` in order to process the files with the CommonJS
// loader. Avoiding the need for a separate CommonJS handler is a future
// enhancement planned for ES module loaders.
if (format === 'commonjs') {
return {
format,
shortCircuit: true,
};
}
const { source: rawSource } = await nextLoad(url, { ...context, format });
// This hook converts CoffeeScript source code into JavaScript source code
// for all imported CoffeeScript files.
const transformedSource = coffeeCompile(rawSource.toString(), url);
return {
format,
shortCircuit: true,
source: transformedSource,
};
}
// Let Node.js handle all other URLs.
return nextLoad(url);
}
async function getPackageType(url) {
// `url` is only a file path during the first iteration when passed the
// resolved url from the load() hook
// an actual file path from load() will contain a file extension as it's
// required by the spec
// this simple truthy check for whether `url` contains a file extension will
// work for most projects but does not cover some edge-cases (such as
// extensionless files or a url ending in a trailing space)
const isFilePath = !!extname(url);
// If it is a file path, get the directory it's in
const dir = isFilePath ?
dirname(fileURLToPath(url)) :
url;
// Compose a file path to a package.json in the same directory,
// which may or may not exist
const packagePath = resolvePath(dir, 'package.json');
// Try to read the possibly nonexistent package.json
const type = await readFile(packagePath, { encoding: 'utf8' })
.then((filestring) => JSON.parse(filestring).type)
.catch((err) => {
if (err?.code !== 'ENOENT') console.error(err);
});
// Ff package.json existed and contained a `type` field with a value, voila
if (type) return type;
// Otherwise, (if not at the root) continue checking the next directory up
// If at the root, stop and return false
return dir.length > 1 && getPackageType(resolvePath(dir, '..'));
}
```
```
# main.coffee
import { scream } from './scream.coffee'
console.log scream 'hello, world'
import { version } from 'node:process'
console.log "Brought to you by Node.js version #{version}"
```
```
# scream.coffee
export scream = (str) -> str.toUpperCase()
```
With the preceding loader, running `node --experimental-loader ./coffeescript-loader.mjs main.coffee` causes `main.coffee` to be turned into JavaScript after its source code is loaded from disk but before Node.js executes it; and so on for any `.coffee`, `.litcoffee` or `.coffee.md` files referenced via `import` statements of any loaded file.
### Resolution algorithm
#### Features
The resolver has the following properties:
* FileURL-based resolution as is used by ES modules
* Support for builtin module loading
* Relative and absolute URL resolution
* No default extensions
* No folder mains
* Bare specifier package resolution lookup through node\_modules
#### Resolver algorithm
The algorithm to load an ES module specifier is given through the **ESM\_RESOLVE** method below. It returns the resolved URL for a module specifier relative to a parentURL.
The algorithm to determine the module format of a resolved URL is provided by **ESM\_FORMAT**, which returns the unique module format for any file. The *"module"* format is returned for an ECMAScript Module, while the *"commonjs"* format is used to indicate loading through the legacy CommonJS loader. Additional formats such as *"addon"* can be extended in future updates.
In the following algorithms, all subroutine errors are propagated as errors of these top-level routines unless stated otherwise.
*defaultConditions* is the conditional environment name array, `["node", "import"]`.
The resolver can throw the following errors:
* *Invalid Module Specifier*: Module specifier is an invalid URL, package name or package subpath specifier.
* *Invalid Package Configuration*: package.json configuration is invalid or contains an invalid configuration.
* *Invalid Package Target*: Package exports or imports define a target module for the package that is an invalid type or string target.
* *Package Path Not Exported*: Package exports do not define or permit a target subpath in the package for the given module.
* *Package Import Not Defined*: Package imports do not define the specifier.
* *Module Not Found*: The package or module requested does not exist.
* *Unsupported Directory Import*: The resolved path corresponds to a directory, which is not a supported target for module imports.
#### Resolver Algorithm Specification
**ESM\_RESOLVE**(*specifier*, *parentURL*)
> 1. Let *resolved* be **undefined**.
> 2. If *specifier* is a valid URL, then
> 1. Set *resolved* to the result of parsing and reserializing *specifier* as a URL.
> 3. Otherwise, if *specifier* starts with *"/"*, *"./"*, or *"../"*, then
> 1. Set *resolved* to the URL resolution of *specifier* relative to *parentURL*.
> 4. Otherwise, if *specifier* starts with *"#"*, then
> 1. Set *resolved* to the result of **PACKAGE\_IMPORTS\_RESOLVE**(*specifier*, *parentURL*, *defaultConditions*).
> 5. Otherwise,
> 1. Note: *specifier* is now a bare specifier.
> 2. Set *resolved* the result of **PACKAGE\_RESOLVE**(*specifier*, *parentURL*).
> 6. Let *format* be **undefined**.
> 7. If *resolved* is a *"file:"* URL, then
> 1. If *resolved* contains any percent encodings of *"/"* or *"\"* (*"%2F"* and *"%5C"* respectively), then
> 1. Throw an *Invalid Module Specifier* error.
> 2. If the file at *resolved* is a directory, then
> 1. Throw an *Unsupported Directory Import* error.
> 3. If the file at *resolved* does not exist, then
> 1. Throw a *Module Not Found* error.
> 4. Set *resolved* to the real path of *resolved*, maintaining the same URL querystring and fragment components.
> 5. Set *format* to the result of **ESM\_FILE\_FORMAT**(*resolved*).
> 8. Otherwise,
> 1. Set *format* the module format of the content type associated with the URL *resolved*.
> 9. Load *resolved* as module format, *format*.
>
>
**PACKAGE\_RESOLVE**(*packageSpecifier*, *parentURL*)
> 1. Let *packageName* be **undefined**.
> 2. If *packageSpecifier* is an empty string, then
> 1. Throw an *Invalid Module Specifier* error.
> 3. If *packageSpecifier* is a Node.js builtin module name, then
> 1. Return the string *"node:"* concatenated with *packageSpecifier*.
> 4. If *packageSpecifier* does not start with *"@"*, then
> 1. Set *packageName* to the substring of *packageSpecifier* until the first *"/"* separator or the end of the string.
> 5. Otherwise,
> 1. If *packageSpecifier* does not contain a *"/"* separator, then
> 1. Throw an *Invalid Module Specifier* error.
> 2. Set *packageName* to the substring of *packageSpecifier* until the second *"/"* separator or the end of the string.
> 6. If *packageName* starts with *"."* or contains *"\"* or *"%"*, then
> 1. Throw an *Invalid Module Specifier* error.
> 7. Let *packageSubpath* be *"."* concatenated with the substring of *packageSpecifier* from the position at the length of *packageName*.
> 8. If *packageSubpath* ends in *"/"*, then
> 1. Throw an *Invalid Module Specifier* error.
> 9. Let *selfUrl* be the result of **PACKAGE\_SELF\_RESOLVE**(*packageName*, *packageSubpath*, *parentURL*).
> 10. If *selfUrl* is not **undefined**, return *selfUrl*.
> 11. While *parentURL* is not the file system root,
> 1. Let *packageURL* be the URL resolution of *"node\_modules/"* concatenated with *packageSpecifier*, relative to *parentURL*.
> 2. Set *parentURL* to the parent folder URL of *parentURL*.
> 3. If the folder at *packageURL* does not exist, then
> 1. Continue the next loop iteration.
> 4. Let *pjson* be the result of **READ\_PACKAGE\_JSON**(*packageURL*).
> 5. If *pjson* is not **null** and *pjson*.*exports* is not **null** or **undefined**, then
> 1. Return the result of **PACKAGE\_EXPORTS\_RESOLVE**(*packageURL*, *packageSubpath*, *pjson.exports*, *defaultConditions*).
> 6. Otherwise, if *packageSubpath* is equal to *"."*, then
> 1. If *pjson.main* is a string, then
> 1. Return the URL resolution of *main* in *packageURL*.
> 7. Otherwise,
> 1. Return the URL resolution of *packageSubpath* in *packageURL*.
> 12. Throw a *Module Not Found* error.
>
>
**PACKAGE\_SELF\_RESOLVE**(*packageName*, *packageSubpath*, *parentURL*)
> 1. Let *packageURL* be the result of **LOOKUP\_PACKAGE\_SCOPE**(*parentURL*).
> 2. If *packageURL* is **null**, then
> 1. Return **undefined**.
> 3. Let *pjson* be the result of **READ\_PACKAGE\_JSON**(*packageURL*).
> 4. If *pjson* is **null** or if *pjson*.*exports* is **null** or **undefined**, then
> 1. Return **undefined**.
> 5. If *pjson.name* is equal to *packageName*, then
> 1. Return the result of **PACKAGE\_EXPORTS\_RESOLVE**(*packageURL*, *packageSubpath*, *pjson.exports*, *defaultConditions*).
> 6. Otherwise, return **undefined**.
>
>
**PACKAGE\_EXPORTS\_RESOLVE**(*packageURL*, *subpath*, *exports*, *conditions*)
> 1. If *exports* is an Object with both a key starting with *"."* and a key not starting with *"."*, throw an *Invalid Package Configuration* error.
> 2. If *subpath* is equal to *"."*, then
> 1. Let *mainExport* be **undefined**.
> 2. If *exports* is a String or Array, or an Object containing no keys starting with *"."*, then
> 1. Set *mainExport* to *exports*.
> 3. Otherwise if *exports* is an Object containing a *"."* property, then
> 1. Set *mainExport* to *exports*[*"."*].
> 4. If *mainExport* is not **undefined**, then
> 1. Let *resolved* be the result of **PACKAGE\_TARGET\_RESOLVE**( *packageURL*, *mainExport*, **null**, **false**, *conditions*).
> 2. If *resolved* is not **null** or **undefined**, return *resolved*.
> 3. Otherwise, if *exports* is an Object and all keys of *exports* start with *"."*, then
> 1. Let *matchKey* be the string *"./"* concatenated with *subpath*.
> 2. Let *resolved* be the result of **PACKAGE\_IMPORTS\_EXPORTS\_RESOLVE**( *matchKey*, *exports*, *packageURL*, **false**, *conditions*).
> 3. If *resolved* is not **null** or **undefined**, return *resolved*.
> 4. Throw a *Package Path Not Exported* error.
>
>
**PACKAGE\_IMPORTS\_RESOLVE**(*specifier*, *parentURL*, *conditions*)
> 1. Assert: *specifier* begins with *"#"*.
> 2. If *specifier* is exactly equal to *"#"* or starts with *"#/"*, then
> 1. Throw an *Invalid Module Specifier* error.
> 3. Let *packageURL* be the result of **LOOKUP\_PACKAGE\_SCOPE**(*parentURL*).
> 4. If *packageURL* is not **null**, then
> 1. Let *pjson* be the result of **READ\_PACKAGE\_JSON**(*packageURL*).
> 2. If *pjson.imports* is a non-null Object, then
> 1. Let *resolved* be the result of **PACKAGE\_IMPORTS\_EXPORTS\_RESOLVE**( *specifier*, *pjson.imports*, *packageURL*, **true**, *conditions*).
> 2. If *resolved* is not **null** or **undefined**, return *resolved*.
> 5. Throw a *Package Import Not Defined* error.
>
>
**PACKAGE\_IMPORTS\_EXPORTS\_RESOLVE**(*matchKey*, *matchObj*, *packageURL*, *isImports*, *conditions*)
> 1. If *matchKey* is a key of *matchObj* and does not contain *"\*"*, then
> 1. Let *target* be the value of *matchObj*[*matchKey*].
> 2. Return the result of **PACKAGE\_TARGET\_RESOLVE**(*packageURL*, *target*, **null**, *isImports*, *conditions*).
> 2. Let *expansionKeys* be the list of keys of *matchObj* containing only a single *"\*"*, sorted by the sorting function **PATTERN\_KEY\_COMPARE** which orders in descending order of specificity.
> 3. For each key *expansionKey* in *expansionKeys*, do
> 1. Let *patternBase* be the substring of *expansionKey* up to but excluding the first *"\*"* character.
> 2. If *matchKey* starts with but is not equal to *patternBase*, then
> 1. Let *patternTrailer* be the substring of *expansionKey* from the index after the first *"\*"* character.
> 2. If *patternTrailer* has zero length, or if *matchKey* ends with *patternTrailer* and the length of *matchKey* is greater than or equal to the length of *expansionKey*, then
> 1. Let *target* be the value of *matchObj*[*expansionKey*].
> 2. Let *patternMatch* be the substring of *matchKey* starting at the index of the length of *patternBase* up to the length of *matchKey* minus the length of *patternTrailer*.
> 3. Return the result of **PACKAGE\_TARGET\_RESOLVE**(*packageURL*, *target*, *patternMatch*, *isImports*, *conditions*).
> 4. Return **null**.
>
>
**PATTERN\_KEY\_COMPARE**(*keyA*, *keyB*)
> 1. Assert: *keyA* ends with *"/"* or contains only a single *"\*"*.
> 2. Assert: *keyB* ends with *"/"* or contains only a single *"\*"*.
> 3. Let *baseLengthA* be the index of *"\*"* in *keyA* plus one, if *keyA* contains *"\*"*, or the length of *keyA* otherwise.
> 4. Let *baseLengthB* be the index of *"\*"* in *keyB* plus one, if *keyB* contains *"\*"*, or the length of *keyB* otherwise.
> 5. If *baseLengthA* is greater than *baseLengthB*, return -1.
> 6. If *baseLengthB* is greater than *baseLengthA*, return 1.
> 7. If *keyA* does not contain *"\*"*, return 1.
> 8. If *keyB* does not contain *"\*"*, return -1.
> 9. If the length of *keyA* is greater than the length of *keyB*, return -1.
> 10. If the length of *keyB* is greater than the length of *keyA*, return 1.
> 11. Return 0.
>
>
**PACKAGE\_TARGET\_RESOLVE**(*packageURL*, *target*, *patternMatch*, *isImports*, *conditions*)
> 1. If *target* is a String, then
> 1. If *target* does not start with *"./"*, then
> 1. If *isImports* is **false**, or if *target* starts with *"../"* or *"/"*, or if *target* is a valid URL, then
> 1. Throw an *Invalid Package Target* error.
> 2. If *patternMatch* is a String, then
> 1. Return **PACKAGE\_RESOLVE**(*target* with every instance of *"\*"* replaced by *patternMatch*, *packageURL* + *"/"*).
> 3. Return **PACKAGE\_RESOLVE**(*target*, *packageURL* + *"/"*).
> 2. If *target* split on *"/"* or *"\"* contains any *""*, *"."*, *".."*, or *"node\_modules"* segments after the first *"."* segment, case insensitive and including percent encoded variants, throw an *Invalid Package Target* error.
> 3. Let *resolvedTarget* be the URL resolution of the concatenation of *packageURL* and *target*.
> 4. Assert: *resolvedTarget* is contained in *packageURL*.
> 5. If *patternMatch* is **null**, then
> 1. Return *resolvedTarget*.
> 6. If *patternMatch* split on *"/"* or *"\"* contains any *""*, *"."*, *".."*, or *"node\_modules"* segments, case insensitive and including percent encoded variants, throw an *Invalid Module Specifier* error.
> 7. Return the URL resolution of *resolvedTarget* with every instance of *"\*"* replaced with *patternMatch*.
> 2. Otherwise, if *target* is a non-null Object, then
> 1. If *exports* contains any index property keys, as defined in ECMA-262 [6.1.7 Array Index](https://tc39.es/ecma262/#integer-index), throw an *Invalid Package Configuration* error.
> 2. For each property *p* of *target*, in object insertion order as,
> 1. If *p* equals *"default"* or *conditions* contains an entry for *p*, then
> 1. Let *targetValue* be the value of the *p* property in *target*.
> 2. Let *resolved* be the result of **PACKAGE\_TARGET\_RESOLVE**( *packageURL*, *targetValue*, *patternMatch*, *isImports*, *conditions*).
> 3. If *resolved* is equal to **undefined**, continue the loop.
> 4. Return *resolved*.
> 3. Return **undefined**.
> 3. Otherwise, if *target* is an Array, then
> 1. If \_target.length is zero, return **null**.
> 2. For each item *targetValue* in *target*, do
> 1. Let *resolved* be the result of **PACKAGE\_TARGET\_RESOLVE**( *packageURL*, *targetValue*, *patternMatch*, *isImports*, *conditions*), continuing the loop on any *Invalid Package Target* error.
> 2. If *resolved* is **undefined**, continue the loop.
> 3. Return *resolved*.
> 3. Return or throw the last fallback resolution **null** return or error.
> 4. Otherwise, if *target* is *null*, return **null**.
> 5. Otherwise throw an *Invalid Package Target* error.
>
>
**ESM\_FILE\_FORMAT**(*url*)
> 1. Assert: *url* corresponds to an existing file.
> 2. If *url* ends in *".mjs"*, then
> 1. Return *"module"*.
> 3. If *url* ends in *".cjs"*, then
> 1. Return *"commonjs"*.
> 4. If *url* ends in *".json"*, then
> 1. Return *"json"*.
> 5. Let *packageURL* be the result of **LOOKUP\_PACKAGE\_SCOPE**(*url*).
> 6. Let *pjson* be the result of **READ\_PACKAGE\_JSON**(*packageURL*).
> 7. If *pjson?.type* exists and is *"module"*, then
> 1. If *url* ends in *".js"*, then
> 1. Return *"module"*.
> 2. Throw an *Unsupported File Extension* error.
> 8. Otherwise,
> 1. Throw an *Unsupported File Extension* error.
>
>
**LOOKUP\_PACKAGE\_SCOPE**(*url*)
> 1. Let *scopeURL* be *url*.
> 2. While *scopeURL* is not the file system root,
> 1. Set *scopeURL* to the parent URL of *scopeURL*.
> 2. If *scopeURL* ends in a *"node\_modules"* path segment, return **null**.
> 3. Let *pjsonURL* be the resolution of *"package.json"* within *scopeURL*.
> 4. if the file at *pjsonURL* exists, then
> 1. Return *scopeURL*.
> 3. Return **null**.
>
>
**READ\_PACKAGE\_JSON**(*packageURL*)
> 1. Let *pjsonURL* be the resolution of *"package.json"* within *packageURL*.
> 2. If the file at *pjsonURL* does not exist, then
> 1. Return **null**.
> 3. If the file at *packageURL* does not parse as valid JSON, then
> 1. Throw an *Invalid Package Configuration* error.
> 4. Return the parsed JSON source of the file at *pjsonURL*.
>
>
#### Customizing ESM specifier resolution algorithm
The [Loaders API](#loaders) provides a mechanism for customizing the ESM specifier resolution algorithm. An example loader that provides CommonJS-style resolution for ESM specifiers is [commonjs-extension-resolution-loader](https://github.com/nodejs/loaders-test/tree/main/commonjs-extension-resolution-loader).
| programming_docs |
node None Trace events
------------
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
**Source Code:** [lib/trace\_events.js](https://github.com/nodejs/node/blob/v19.0.1/lib/trace_events.js)
The `node:trace_events` module provides a mechanism to centralize tracing information generated by V8, Node.js core, and userspace code.
Tracing can be enabled with the `--trace-event-categories` command-line flag or by using the `node:trace_events` module. The `--trace-event-categories` flag accepts a list of comma-separated category names.
The available categories are:
* `node`: An empty placeholder.
* `node.async_hooks`: Enables capture of detailed [`async_hooks`](async_hooks) trace data. The [`async_hooks`](async_hooks) events have a unique `asyncId` and a special `triggerId` `triggerAsyncId` property.
* `node.bootstrap`: Enables capture of Node.js bootstrap milestones.
* `node.console`: Enables capture of `console.time()` and `console.count()` output.
* `node.dns.native`: Enables capture of trace data for DNS queries.
* `node.net.native`: Enables capture of trace data for network.
* `node.environment`: Enables capture of Node.js Environment milestones.
* `node.fs.sync`: Enables capture of trace data for file system sync methods.
* `node.fs_dir.sync`: Enables capture of trace data for file system sync directory methods.
* `node.fs.async`: Enables capture of trace data for file system async methods.
* `node.fs_dir.async`: Enables capture of trace data for file system async directory methods.
* `node.perf`: Enables capture of [Performance API](perf_hooks) measurements.
+ `node.perf.usertiming`: Enables capture of only Performance API User Timing measures and marks.
+ `node.perf.timerify`: Enables capture of only Performance API timerify measurements.
* `node.promises.rejections`: Enables capture of trace data tracking the number of unhandled Promise rejections and handled-after-rejections.
* `node.vm.script`: Enables capture of trace data for the `node:vm` module's `runInNewContext()`, `runInContext()`, and `runInThisContext()` methods.
* `v8`: The [V8](v8) events are GC, compiling, and execution related.
* `node.http`: Enables capture of trace data for http request / response.
By default the `node`, `node.async_hooks`, and `v8` categories are enabled.
```
node --trace-event-categories v8,node,node.async_hooks server.js
```
Prior versions of Node.js required the use of the `--trace-events-enabled` flag to enable trace events. This requirement has been removed. However, the `--trace-events-enabled` flag *may* still be used and will enable the `node`, `node.async_hooks`, and `v8` trace event categories by default.
```
node --trace-events-enabled
# is equivalent to
node --trace-event-categories v8,node,node.async_hooks
```
Alternatively, trace events may be enabled using the `node:trace_events` module:
```
const trace_events = require('node:trace_events');
const tracing = trace_events.createTracing({ categories: ['node.perf'] });
tracing.enable(); // Enable trace event capture for the 'node.perf' category
// do work
tracing.disable(); // Disable trace event capture for the 'node.perf' category
```
Running Node.js with tracing enabled will produce log files that can be opened in the [`chrome://tracing`](https://www.chromium.org/developers/how-tos/trace-event-profiling-tool) tab of Chrome.
The logging file is by default called `node_trace.${rotation}.log`, where `${rotation}` is an incrementing log-rotation id. The filepath pattern can be specified with `--trace-event-file-pattern` that accepts a template string that supports `${rotation}` and `${pid}`:
```
node --trace-event-categories v8 --trace-event-file-pattern '${pid}-${rotation}.log' server.js
```
To guarantee that the log file is properly generated after signal events like `SIGINT`, `SIGTERM`, or `SIGBREAK`, make sure to have the appropriate handlers in your code, such as:
```
process.on('SIGINT', function onSigint() {
console.info('Received SIGINT.');
process.exit(130); // Or applicable exit code depending on OS and signal
});
```
The tracing system uses the same time source as the one used by `process.hrtime()`. However the trace-event timestamps are expressed in microseconds, unlike `process.hrtime()` which returns nanoseconds.
The features from this module are not available in [`Worker`](worker_threads#class-worker) threads.
### The `node:trace_events` module
Added in: v10.0.0 ####
`Tracing` object
Added in: v10.0.0 The `Tracing` object is used to enable or disable tracing for sets of categories. Instances are created using the `trace_events.createTracing()` method.
When created, the `Tracing` object is disabled. Calling the `tracing.enable()` method adds the categories to the set of enabled trace event categories. Calling `tracing.disable()` will remove the categories from the set of enabled trace event categories.
#####
`tracing.categories`
Added in: v10.0.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
A comma-separated list of the trace event categories covered by this `Tracing` object.
#####
`tracing.disable()`
Added in: v10.0.0 Disables this `Tracing` object.
Only trace event categories *not* covered by other enabled `Tracing` objects and *not* specified by the `--trace-event-categories` flag will be disabled.
```
const trace_events = require('node:trace_events');
const t1 = trace_events.createTracing({ categories: ['node', 'v8'] });
const t2 = trace_events.createTracing({ categories: ['node.perf', 'node'] });
t1.enable();
t2.enable();
// Prints 'node,node.perf,v8'
console.log(trace_events.getEnabledCategories());
t2.disable(); // Will only disable emission of the 'node.perf' category
// Prints 'node,v8'
console.log(trace_events.getEnabledCategories());
```
#####
`tracing.enable()`
Added in: v10.0.0 Enables this `Tracing` object for the set of categories covered by the `Tracing` object.
#####
`tracing.enabled`
Added in: v10.0.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` only if the `Tracing` object has been enabled.
####
`trace_events.createTracing(options)`
Added in: v10.0.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `categories` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) An array of trace category names. Values included in the array are coerced to a string when possible. An error will be thrown if the value cannot be coerced.
* Returns: [<Tracing>](tracing#tracing-object).
Creates and returns a `Tracing` object for the given set of `categories`.
```
const trace_events = require('node:trace_events');
const categories = ['node.perf', 'node.async_hooks'];
const tracing = trace_events.createTracing({ categories });
tracing.enable();
// do stuff
tracing.disable();
```
####
`trace_events.getEnabledCategories()`
Added in: v10.0.0 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns a comma-separated list of all currently-enabled trace event categories. The current set of enabled trace event categories is determined by the *union* of all currently-enabled `Tracing` objects and any categories enabled using the `--trace-event-categories` flag.
Given the file `test.js` below, the command `node --trace-event-categories node.perf test.js` will print `'node.async_hooks,node.perf'` to the console.
```
const trace_events = require('node:trace_events');
const t1 = trace_events.createTracing({ categories: ['node.async_hooks'] });
const t2 = trace_events.createTracing({ categories: ['node.perf'] });
const t3 = trace_events.createTracing({ categories: ['v8'] });
t1.enable();
t2.enable();
console.log(trace_events.getEnabledCategories());
```
### Examples
#### Collect trace events data by inspector
```
'use strict';
const { Session } = require('inspector');
const session = new Session();
session.connect();
function post(message, data) {
return new Promise((resolve, reject) => {
session.post(message, data, (err, result) => {
if (err)
reject(new Error(JSON.stringify(err)));
else
resolve(result);
});
});
}
async function collect() {
const data = [];
session.on('NodeTracing.dataCollected', (chunk) => data.push(chunk));
session.on('NodeTracing.tracingComplete', () => {
// done
});
const traceConfig = { includedCategories: ['v8'] };
await post('NodeTracing.start', { traceConfig });
// do something
setTimeout(() => {
post('NodeTracing.stop').then(() => {
session.disconnect();
console.log(data);
});
}, 1000);
}
collect();
```
node None V8
--
**Source Code:** [lib/v8.js](https://github.com/nodejs/node/blob/v19.0.1/lib/v8.js)
The `node:v8` module exposes APIs that are specific to the version of [V8](https://developers.google.com/v8/) built into the Node.js binary. It can be accessed using:
```
const v8 = require('node:v8');
```
###
`v8.cachedDataVersionTag()`
Added in: v8.0.0 * Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns an integer representing a version tag derived from the V8 version, command-line flags, and detected CPU features. This is useful for determining whether a [`vm.Script`](vm#new-vmscriptcode-options) `cachedData` buffer is compatible with this instance of V8.
```
console.log(v8.cachedDataVersionTag()); // 3947234607
// The value returned by v8.cachedDataVersionTag() is derived from the V8
// version, command-line flags, and detected CPU features. Test that the value
// does indeed update when flags are toggled.
v8.setFlagsFromString('--allow_natives_syntax');
console.log(v8.cachedDataVersionTag()); // 183726201
```
###
`v8.getHeapCodeStatistics()`
Added in: v12.8.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Get statistics about code and its metadata in the heap, see V8 [`GetHeapCodeAndMetadataStatistics`](https://v8docs.nodesource.com/node-13.2/d5/dda/classv8_1_1_isolate.html#a6079122af17612ef54ef3348ce170866) API. Returns an object with the following properties:
* `code_and_metadata_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `bytecode_and_metadata_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `external_script_source_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `cpu_profiler_metadata_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
```
{
code_and_metadata_size: 212208,
bytecode_and_metadata_size: 161368,
external_script_source_size: 1410794,
cpu_profiler_metadata_size: 0,
}
```
###
`v8.getHeapSnapshot()`
Added in: v11.13.0 * Returns: [<stream.Readable>](stream#class-streamreadable) A Readable Stream containing the V8 heap snapshot
Generates a snapshot of the current V8 heap and returns a Readable Stream that may be used to read the JSON serialized representation. This JSON stream format is intended to be used with tools such as Chrome DevTools. The JSON schema is undocumented and specific to the V8 engine. Therefore, the schema may change from one version of V8 to the next.
Creating a heap snapshot requires memory about twice the size of the heap at the time the snapshot is created. This results in the risk of OOM killers terminating the process.
Generating a snapshot is a synchronous operation which blocks the event loop for a duration depending on the heap size.
```
// Print heap snapshot to the console
const v8 = require('node:v8');
const stream = v8.getHeapSnapshot();
stream.pipe(process.stdout);
```
###
`v8.getHeapSpaceStatistics()`
History
| Version | Changes |
| --- | --- |
| v7.5.0 | Support values exceeding the 32-bit unsigned integer range. |
| v6.0.0 | Added in: v6.0.0 |
* Returns: [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns statistics about the V8 heap spaces, i.e. the segments which make up the V8 heap. Neither the ordering of heap spaces, nor the availability of a heap space can be guaranteed as the statistics are provided via the V8 [`GetHeapSpaceStatistics`](https://v8docs.nodesource.com/node-13.2/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4) function and may change from one V8 version to the next.
The value returned is an array of objects containing the following properties:
* `space_name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `space_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `space_used_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `space_available_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `physical_space_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
```
[
{
"space_name": "new_space",
"space_size": 2063872,
"space_used_size": 951112,
"space_available_size": 80824,
"physical_space_size": 2063872
},
{
"space_name": "old_space",
"space_size": 3090560,
"space_used_size": 2493792,
"space_available_size": 0,
"physical_space_size": 3090560
},
{
"space_name": "code_space",
"space_size": 1260160,
"space_used_size": 644256,
"space_available_size": 960,
"physical_space_size": 1260160
},
{
"space_name": "map_space",
"space_size": 1094160,
"space_used_size": 201608,
"space_available_size": 0,
"physical_space_size": 1094160
},
{
"space_name": "large_object_space",
"space_size": 0,
"space_used_size": 0,
"space_available_size": 1490980608,
"physical_space_size": 0
}
]
```
###
`v8.getHeapStatistics()`
History
| Version | Changes |
| --- | --- |
| v7.5.0 | Support values exceeding the 32-bit unsigned integer range. |
| v7.2.0 | Added `malloced_memory`, `peak_malloced_memory`, and `does_zap_garbage`. |
| v1.0.0 | Added in: v1.0.0 |
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns an object with the following properties:
* `total_heap_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `total_heap_size_executable` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `total_physical_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `total_available_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `used_heap_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `heap_size_limit` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `malloced_memory` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `peak_malloced_memory` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `does_zap_garbage` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `number_of_native_contexts` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `number_of_detached_contexts` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `total_global_handles_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `used_global_handles_size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `external_memory` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
`does_zap_garbage` is a 0/1 boolean, which signifies whether the `--zap_code_space` option is enabled or not. This makes V8 overwrite heap garbage with a bit pattern. The RSS footprint (resident set size) gets bigger because it continuously touches all heap pages and that makes them less likely to get swapped out by the operating system.
`number_of_native_contexts` The value of native\_context is the number of the top-level contexts currently active. Increase of this number over time indicates a memory leak.
`number_of_detached_contexts` The value of detached\_context is the number of contexts that were detached and not yet garbage collected. This number being non-zero indicates a potential memory leak.
`total_global_handles_size` The value of total\_global\_handles\_size is the total memory size of V8 global handles.
`used_global_handles_size` The value of used\_global\_handles\_size is the used memory size of V8 global handles.
`external_memory` The value of external\_memory is the memory size of array buffers and external strings.
```
{
total_heap_size: 7326976,
total_heap_size_executable: 4194304,
total_physical_size: 7326976,
total_available_size: 1152656,
used_heap_size: 3476208,
heap_size_limit: 1535115264,
malloced_memory: 16384,
peak_malloced_memory: 1127496,
does_zap_garbage: 0,
number_of_native_contexts: 1,
number_of_detached_contexts: 0,
total_global_handles_size: 8192,
used_global_handles_size: 3296,
external_memory: 318824
}
```
###
`v8.setFlagsFromString(flags)`
Added in: v1.0.0 * `flags` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `v8.setFlagsFromString()` method can be used to programmatically set V8 command-line flags. This method should be used with care. Changing settings after the VM has started may result in unpredictable behavior, including crashes and data loss; or it may simply do nothing.
The V8 options available for a version of Node.js may be determined by running `node --v8-options`.
Usage:
```
// Print GC events to stdout for one minute.
const v8 = require('node:v8');
v8.setFlagsFromString('--trace_gc');
setTimeout(() => { v8.setFlagsFromString('--notrace_gc'); }, 60e3);
```
###
`v8.stopCoverage()`
Added in: v15.1.0, v14.18.0, v12.22.0 The `v8.stopCoverage()` method allows the user to stop the coverage collection started by [`NODE_V8_COVERAGE`](cli#node_v8_coveragedir), so that V8 can release the execution count records and optimize code. This can be used in conjunction with [`v8.takeCoverage()`](#v8takecoverage) if the user wants to collect the coverage on demand.
###
`v8.takeCoverage()`
Added in: v15.1.0, v14.18.0, v12.22.0 The `v8.takeCoverage()` method allows the user to write the coverage started by [`NODE_V8_COVERAGE`](cli#node_v8_coveragedir) to disk on demand. This method can be invoked multiple times during the lifetime of the process. Each time the execution counter will be reset and a new coverage report will be written to the directory specified by [`NODE_V8_COVERAGE`](cli#node_v8_coveragedir).
When the process is about to exit, one last coverage will still be written to disk unless [`v8.stopCoverage()`](#v8stopcoverage) is invoked before the process exits.
###
`v8.writeHeapSnapshot([filename])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | An exception will now be thrown if the file could not be written. |
| v18.0.0 | Make the returned error codes consistent across all platforms. |
| v11.13.0 | Added in: v11.13.0 |
* `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The file path where the V8 heap snapshot is to be saved. If not specified, a file name with the pattern `'Heap-${yyyymmdd}-${hhmmss}-${pid}-${thread_id}.heapsnapshot'` will be generated, where `{pid}` will be the PID of the Node.js process, `{thread_id}` will be `0` when `writeHeapSnapshot()` is called from the main Node.js thread or the id of a worker thread.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The filename where the snapshot was saved.
Generates a snapshot of the current V8 heap and writes it to a JSON file. This file is intended to be used with tools such as Chrome DevTools. The JSON schema is undocumented and specific to the V8 engine, and may change from one version of V8 to the next.
A heap snapshot is specific to a single V8 isolate. When using [worker threads](worker_threads), a heap snapshot generated from the main thread will not contain any information about the workers, and vice versa.
Creating a heap snapshot requires memory about twice the size of the heap at the time the snapshot is created. This results in the risk of OOM killers terminating the process.
Generating a snapshot is a synchronous operation which blocks the event loop for a duration depending on the heap size.
```
const { writeHeapSnapshot } = require('node:v8');
const {
Worker,
isMainThread,
parentPort
} = require('node:worker_threads');
if (isMainThread) {
const worker = new Worker(__filename);
worker.once('message', (filename) => {
console.log(`worker heapdump: ${filename}`);
// Now get a heapdump for the main thread.
console.log(`main thread heapdump: ${writeHeapSnapshot()}`);
});
// Tell the worker to create a heapdump.
worker.postMessage('heapdump');
} else {
parentPort.once('message', (message) => {
if (message === 'heapdump') {
// Generate a heapdump for the worker
// and return the filename to the parent.
parentPort.postMessage(writeHeapSnapshot());
}
});
}
```
###
`v8.setHeapSnapshotNearHeapLimit(limit)`
Added in: v18.10.0, v16.18.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `limit` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The API is a no-op if `--heapsnapshot-near-heap-limit` is already set from the command line or the API is called more than once. `limit` must be a positive integer. See [`--heapsnapshot-near-heap-limit`](cli#--heapsnapshot-near-heap-limitmax_count) for more information.
### Serialization API
The serialization API provides means of serializing JavaScript values in a way that is compatible with the [HTML structured clone algorithm](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm).
The format is backward-compatible (i.e. safe to store to disk). Equal JavaScript values may result in different serialized output.
####
`v8.serialize(value)`
Added in: v8.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<Buffer>](buffer#class-buffer)
Uses a [`DefaultSerializer`](#class-v8defaultserializer) to serialize `value` into a buffer.
[`ERR_BUFFER_TOO_LARGE`](errors#err_buffer_too_large) will be thrown when trying to serialize a huge object which requires buffer larger than [`buffer.constants.MAX_LENGTH`](buffer#bufferconstantsmax_length).
####
`v8.deserialize(buffer)`
Added in: v8.0.0 * `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A buffer returned by [`serialize()`](#v8serializevalue).
Uses a [`DefaultDeserializer`](#class-v8defaultdeserializer) with default options to read a JS value from a buffer.
#### Class: `v8.Serializer`
Added in: v8.0.0 #####
`new Serializer()`
Creates a new `Serializer` object.
#####
`serializer.writeHeader()`
Writes out a header, which includes the serialization format version.
#####
`serializer.writeValue(value)`
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Serializes a JavaScript value and adds the serialized representation to the internal buffer.
This throws an error if `value` cannot be serialized.
#####
`serializer.releaseBuffer()`
* Returns: [<Buffer>](buffer#class-buffer)
Returns the stored internal buffer. This serializer should not be used once the buffer is released. Calling this method results in undefined behavior if a previous write has failed.
#####
`serializer.transferArrayBuffer(id, arrayBuffer)`
* `id` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A 32-bit unsigned integer.
* `arrayBuffer` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) An `ArrayBuffer` instance.
Marks an `ArrayBuffer` as having its contents transferred out of band. Pass the corresponding `ArrayBuffer` in the deserializing context to [`deserializer.transferArrayBuffer()`](#deserializertransferarraybufferid-arraybuffer).
#####
`serializer.writeUint32(value)`
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Write a raw 32-bit unsigned integer. For use inside of a custom [`serializer._writeHostObject()`](#serializer_writehostobjectobject).
#####
`serializer.writeUint64(hi, lo)`
* `hi` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `lo` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Write a raw 64-bit unsigned integer, split into high and low 32-bit parts. For use inside of a custom [`serializer._writeHostObject()`](#serializer_writehostobjectobject).
#####
`serializer.writeDouble(value)`
* `value` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Write a JS `number` value. For use inside of a custom [`serializer._writeHostObject()`](#serializer_writehostobjectobject).
#####
`serializer.writeRawBytes(buffer)`
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
Write raw bytes into the serializer's internal buffer. The deserializer will require a way to compute the length of the buffer. For use inside of a custom [`serializer._writeHostObject()`](#serializer_writehostobjectobject).
#####
`serializer._writeHostObject(object)`
* `object` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
This method is called to write some kind of host object, i.e. an object created by native C++ bindings. If it is not possible to serialize `object`, a suitable exception should be thrown.
This method is not present on the `Serializer` class itself but can be provided by subclasses.
#####
`serializer._getDataCloneError(message)`
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
This method is called to generate error objects that will be thrown when an object can not be cloned.
This method defaults to the [`Error`](errors#class-error) constructor and can be overridden on subclasses.
#####
`serializer._getSharedArrayBufferId(sharedArrayBuffer)`
* `sharedArrayBuffer` [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer)
This method is called when the serializer is going to serialize a `SharedArrayBuffer` object. It must return an unsigned 32-bit integer ID for the object, using the same ID if this `SharedArrayBuffer` has already been serialized. When deserializing, this ID will be passed to [`deserializer.transferArrayBuffer()`](#deserializertransferarraybufferid-arraybuffer).
If the object cannot be serialized, an exception should be thrown.
This method is not present on the `Serializer` class itself but can be provided by subclasses.
#####
`serializer._setTreatArrayBufferViewsAsHostObjects(flag)`
* `flag` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`
Indicate whether to treat `TypedArray` and `DataView` objects as host objects, i.e. pass them to [`serializer._writeHostObject()`](#serializer_writehostobjectobject).
#### Class: `v8.Deserializer`
Added in: v8.0.0 #####
`new Deserializer(buffer)`
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A buffer returned by [`serializer.releaseBuffer()`](#serializerreleasebuffer).
Creates a new `Deserializer` object.
#####
`deserializer.readHeader()`
Reads and validates a header (including the format version). May, for example, reject an invalid or unsupported wire format. In that case, an `Error` is thrown.
#####
`deserializer.readValue()`
Deserializes a JavaScript value from the buffer and returns it.
#####
`deserializer.transferArrayBuffer(id, arrayBuffer)`
* `id` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A 32-bit unsigned integer.
* `arrayBuffer` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) An `ArrayBuffer` instance.
Marks an `ArrayBuffer` as having its contents transferred out of band. Pass the corresponding `ArrayBuffer` in the serializing context to [`serializer.transferArrayBuffer()`](#serializertransferarraybufferid-arraybuffer) (or return the `id` from [`serializer._getSharedArrayBufferId()`](#serializer_getsharedarraybufferidsharedarraybuffer) in the case of `SharedArrayBuffer`s).
#####
`deserializer.getWireFormatVersion()`
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads the underlying wire format version. Likely mostly to be useful to legacy code reading old wire format versions. May not be called before `.readHeader()`.
#####
`deserializer.readUint32()`
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Read a raw 32-bit unsigned integer and return it. For use inside of a custom [`deserializer._readHostObject()`](#deserializer_readhostobject).
#####
`deserializer.readUint64()`
* Returns: [<integer[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Read a raw 64-bit unsigned integer and return it as an array `[hi, lo]` with two 32-bit unsigned integer entries. For use inside of a custom [`deserializer._readHostObject()`](#deserializer_readhostobject).
#####
`deserializer.readDouble()`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Read a JS `number` value. For use inside of a custom [`deserializer._readHostObject()`](#deserializer_readhostobject).
#####
`deserializer.readRawBytes(length)`
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: [<Buffer>](buffer#class-buffer)
Read raw bytes from the deserializer's internal buffer. The `length` parameter must correspond to the length of the buffer that was passed to [`serializer.writeRawBytes()`](#serializerwriterawbytesbuffer). For use inside of a custom [`deserializer._readHostObject()`](#deserializer_readhostobject).
#####
`deserializer._readHostObject()`
This method is called to read some kind of host object, i.e. an object that is created by native C++ bindings. If it is not possible to deserialize the data, a suitable exception should be thrown.
This method is not present on the `Deserializer` class itself but can be provided by subclasses.
#### Class: `v8.DefaultSerializer`
Added in: v8.0.0 A subclass of [`Serializer`](#class-v8serializer) that serializes `TypedArray` (in particular [`Buffer`](buffer)) and `DataView` objects as host objects, and only stores the part of their underlying `ArrayBuffer`s that they are referring to.
#### Class: `v8.DefaultDeserializer`
Added in: v8.0.0 A subclass of [`Deserializer`](#class-v8deserializer) corresponding to the format written by [`DefaultSerializer`](#class-v8defaultserializer).
### Promise hooks
The `promiseHooks` interface can be used to track promise lifecycle events. To track *all* async activity, see [`async_hooks`](async_hooks) which internally uses this module to produce promise lifecycle events in addition to events for other async resources. For request context management, see [`AsyncLocalStorage`](async_context#class-asynclocalstorage).
```
import { promiseHooks } from 'node:v8';
// There are four lifecycle events produced by promises:
// The `init` event represents the creation of a promise. This could be a
// direct creation such as with `new Promise(...)` or a continuation such
// as `then()` or `catch()`. It also happens whenever an async function is
// called or does an `await`. If a continuation promise is created, the
// `parent` will be the promise it is a continuation from.
function init(promise, parent) {
console.log('a promise was created', { promise, parent });
}
// The `settled` event happens when a promise receives a resolution or
// rejection value. This may happen synchronously such as when using
// `Promise.resolve()` on non-promise input.
function settled(promise) {
console.log('a promise resolved or rejected', { promise });
}
// The `before` event runs immediately before a `then()` or `catch()` handler
// runs or an `await` resumes execution.
function before(promise) {
console.log('a promise is about to call a then handler', { promise });
}
// The `after` event runs immediately after a `then()` handler runs or when
// an `await` begins after resuming from another.
function after(promise) {
console.log('a promise is done calling a then handler', { promise });
}
// Lifecycle hooks may be started and stopped individually
const stopWatchingInits = promiseHooks.onInit(init);
const stopWatchingSettleds = promiseHooks.onSettled(settled);
const stopWatchingBefores = promiseHooks.onBefore(before);
const stopWatchingAfters = promiseHooks.onAfter(after);
// Or they may be started and stopped in groups
const stopHookSet = promiseHooks.createHook({
init,
settled,
before,
after
});
// To stop a hook, call the function returned at its creation.
stopWatchingInits();
stopWatchingSettleds();
stopWatchingBefores();
stopWatchingAfters();
stopHookSet();
```
####
`promiseHooks.onInit(init)`
Added in: v17.1.0, v16.14.0 * `init` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`init` callback](#initpromise-parent) to call when a promise is created.
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Call to stop the hook.
**The `init` hook must be a plain function. Providing an async function will throw as it would produce an infinite microtask loop.**
MJS modules
```
import { promiseHooks } from 'node:v8';
const stop = promiseHooks.onInit((promise, parent) => {});
```
CJS modules
```
const { promiseHooks } = require('node:v8');
const stop = promiseHooks.onInit((promise, parent) => {});
```
####
`promiseHooks.onSettled(settled)`
Added in: v17.1.0, v16.14.0 * `settled` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`settled` callback](#settledpromise) to call when a promise is resolved or rejected.
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Call to stop the hook.
**The `settled` hook must be a plain function. Providing an async function will throw as it would produce an infinite microtask loop.**
MJS modules
```
import { promiseHooks } from 'node:v8';
const stop = promiseHooks.onSettled((promise) => {});
```
CJS modules
```
const { promiseHooks } = require('node:v8');
const stop = promiseHooks.onSettled((promise) => {});
```
####
`promiseHooks.onBefore(before)`
Added in: v17.1.0, v16.14.0 * `before` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`before` callback](#beforepromise) to call before a promise continuation executes.
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Call to stop the hook.
**The `before` hook must be a plain function. Providing an async function will throw as it would produce an infinite microtask loop.**
MJS modules
```
import { promiseHooks } from 'node:v8';
const stop = promiseHooks.onBefore((promise) => {});
```
CJS modules
```
const { promiseHooks } = require('node:v8');
const stop = promiseHooks.onBefore((promise) => {});
```
####
`promiseHooks.onAfter(after)`
Added in: v17.1.0, v16.14.0 * `after` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`after` callback](#afterpromise) to call after a promise continuation executes.
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Call to stop the hook.
**The `after` hook must be a plain function. Providing an async function will throw as it would produce an infinite microtask loop.**
MJS modules
```
import { promiseHooks } from 'node:v8';
const stop = promiseHooks.onAfter((promise) => {});
```
CJS modules
```
const { promiseHooks } = require('node:v8');
const stop = promiseHooks.onAfter((promise) => {});
```
####
`promiseHooks.createHook(callbacks)`
Added in: v17.1.0, v16.14.0 * `callbacks` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The [Hook Callbacks](#hook-callbacks) to register
+ `init` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`init` callback](#initpromise-parent).
+ `before` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`before` callback](#beforepromise).
+ `after` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`after` callback](#afterpromise).
+ `settled` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`settled` callback](#settledpromise).
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Used for disabling hooks
**The hook callbacks must be plain functions. Providing async functions will throw as it would produce an infinite microtask loop.**
Registers functions to be called for different lifetime events of each promise.
The callbacks `init()`/`before()`/`after()`/`settled()` are called for the respective events during a promise's lifetime.
All callbacks are optional. For example, if only promise creation needs to be tracked, then only the `init` callback needs to be passed. The specifics of all functions that can be passed to `callbacks` is in the [Hook Callbacks](#hook-callbacks) section.
MJS modules
```
import { promiseHooks } from 'node:v8';
const stopAll = promiseHooks.createHook({
init(promise, parent) {}
});
```
CJS modules
```
const { promiseHooks } = require('node:v8');
const stopAll = promiseHooks.createHook({
init(promise, parent) {}
});
```
#### Hook callbacks
Key events in the lifetime of a promise have been categorized into four areas: creation of a promise, before/after a continuation handler is called or around an await, and when the promise resolves or rejects.
While these hooks are similar to those of [`async_hooks`](async_hooks) they lack a `destroy` hook. Other types of async resources typically represent sockets or file descriptors which have a distinct "closed" state to express the `destroy` lifecycle event while promises remain usable for as long as code can still reach them. Garbage collection tracking is used to make promises fit into the `async_hooks` event model, however this tracking is very expensive and they may not necessarily ever even be garbage collected.
Because promises are asynchronous resources whose lifecycle is tracked via the promise hooks mechanism, the `init()`, `before()`, `after()`, and `settled()` callbacks *must not* be async functions as they create more promises which would produce an infinite loop.
While this API is used to feed promise events into [`async_hooks`](async_hooks), the ordering between the two is undefined. Both APIs are multi-tenant and therefore could produce events in any order relative to each other.
#####
`init(promise, parent)`
* `promise` [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) The promise being created.
* `parent` [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) The promise continued from, if applicable.
Called when a promise is constructed. This *does not* mean that corresponding `before`/`after` events will occur, only that the possibility exists. This will happen if a promise is created without ever getting a continuation.
#####
`before(promise)`
* `promise` [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Called before a promise continuation executes. This can be in the form of `then()`, `catch()`, or `finally()` handlers or an `await` resuming.
The `before` callback will be called 0 to N times. The `before` callback will typically be called 0 times if no continuation was ever made for the promise. The `before` callback may be called many times in the case where many continuations have been made from the same promise.
#####
`after(promise)`
* `promise` [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Called immediately after a promise continuation executes. This may be after a `then()`, `catch()`, or `finally()` handler or before an `await` after another `await`.
#####
`settled(promise)`
* `promise` [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Called when the promise receives a resolution or rejection value. This may occur synchronously in the case of `Promise.resolve()` or `Promise.reject()`.
### Startup Snapshot API
Added in: v18.6.0, v16.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
The `v8.startupSnapshot` interface can be used to add serialization and deserialization hooks for custom startup snapshots. Currently the startup snapshots can only be built into the Node.js binary from source.
```
$ cd /path/to/node
$ ./configure --node-snapshot-main=entry.js
$ make node
# This binary contains the result of the execution of entry.js
$ out/Release/node
```
In the example above, `entry.js` can use methods from the `v8.startupSnapshot` interface to specify how to save information for custom objects in the snapshot during serialization and how the information can be used to synchronize these objects during deserialization of the snapshot. For example, if the `entry.js` contains the following script:
```
'use strict';
const fs = require('fs');
const zlib = require('zlib');
const path = require('path');
const assert = require('assert');
const {
isBuildingSnapshot,
addSerializeCallback,
addDeserializeCallback,
setDeserializeMainFunction
} = require('v8').startupSnapshot;
const filePath = path.resolve(__dirname, '../x1024.txt');
const storage = {};
assert(isBuildingSnapshot());
addSerializeCallback(({ filePath }) => {
storage[filePath] = zlib.gzipSync(fs.readFileSync(filePath));
}, { filePath });
addDeserializeCallback(({ filePath }) => {
storage[filePath] = zlib.gunzipSync(storage[filePath]);
}, { filePath });
setDeserializeMainFunction(({ filePath }) => {
console.log(storage[filePath].toString());
}, { filePath });
```
The resulted binary will simply print the data deserialized from the snapshot during start up:
```
$ out/Release/node
# Prints content of ./test/fixtures/x1024.txt
```
Currently the API is only available to a Node.js instance launched from the default snapshot, that is, the application deserialized from a user-land snapshot cannot use these APIs again.
####
`v8.startupSnapshot.addSerializeCallback(callback[, data])`
Added in: v18.6.0, v16.17.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Callback to be invoked before serialization.
* `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Optional data that will be passed to the `callback` when it gets called.
Add a callback that will be called when the Node.js instance is about to get serialized into a snapshot and exit. This can be used to release resources that should not or cannot be serialized or to convert user data into a form more suitable for serialization.
####
`v8.startupSnapshot.addDeserializeCallback(callback[, data])`
Added in: v18.6.0, v16.17.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Callback to be invoked after the snapshot is deserialized.
* `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Optional data that will be passed to the `callback` when it gets called.
Add a callback that will be called when the Node.js instance is deserialized from a snapshot. The `callback` and the `data` (if provided) will be serialized into the snapshot, they can be used to re-initialize the state of the application or to re-acquire resources that the application needs when the application is restarted from the snapshot.
####
`v8.startupSnapshot.setDeserializeMainFunction(callback[, data])`
Added in: v18.6.0, v16.17.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Callback to be invoked as the entry point after the snapshot is deserialized.
* `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Optional data that will be passed to the `callback` when it gets called.
This sets the entry point of the Node.js application when it is deserialized from a snapshot. This can be called only once in the snapshot building script. If called, the deserialized application no longer needs an additional entry point script to start up and will simply invoke the callback along with the deserialized data (if provided), otherwise an entry point script still needs to be provided to the deserialized application.
####
`v8.startupSnapshot.isBuildingSnapshot()`
Added in: v18.6.0, v16.17.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns true if the Node.js instance is run to build a snapshot.
| programming_docs |
node None Inspector
---------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/inspector.js](https://github.com/nodejs/node/blob/v19.0.1/lib/inspector.js)
The `node:inspector` module provides an API for interacting with the V8 inspector.
It can be accessed using:
MJS modules
```
import * as inspector from 'node:inspector/promises';
```
CJS modules
```
const inspector = require('node:inspector/promises');
```
or
MJS modules
```
import * as inspector from 'node:inspector';
```
CJS modules
```
const inspector = require('node:inspector');
```
### Promises API
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Added in: v19.0.0 #### Class: `inspector.Session`
* Extends: [<EventEmitter>](events#class-eventemitter)
The `inspector.Session` is used for dispatching messages to the V8 inspector back-end and receiving message responses and notifications.
#####
`new inspector.Session()`
Added in: v8.0.0 Create a new instance of the `inspector.Session` class. The inspector session needs to be connected through [`session.connect()`](#sessionconnect) before the messages can be dispatched to the inspector backend.
##### Event: `'inspectorNotification'`
Added in: v8.0.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The notification message object
Emitted when any notification from the V8 Inspector is received.
```
session.on('inspectorNotification', (message) => console.log(message.method));
// Debugger.paused
// Debugger.resumed
```
It is also possible to subscribe only to notifications with specific method:
##### Event: `<inspector-protocol-method>`;
Added in: v8.0.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The notification message object
Emitted when an inspector notification is received that has its method field set to the `<inspector-protocol-method>` value.
The following snippet installs a listener on the [`'Debugger.paused'`](https://chromedevtools.github.io/devtools-protocol/v8/Debugger#event-paused) event, and prints the reason for program suspension whenever program execution is suspended (through breakpoints, for example):
```
session.on('Debugger.paused', ({ params }) => {
console.log(params.hitBreakpoints);
});
// [ '/the/file/that/has/the/breakpoint.js:11:0' ]
```
#####
`session.connect()`
Added in: v8.0.0 Connects a session to the inspector back-end.
#####
`session.connectToMainThread()`
Added in: v12.11.0 Connects a session to the main thread inspector back-end. An exception will be thrown if this API was not called on a Worker thread.
#####
`session.disconnect()`
Added in: v8.0.0 Immediately close the session. All pending message callbacks will be called with an error. [`session.connect()`](#sessionconnect) will need to be called to be able to send messages again. Reconnected session will lose all inspector state, such as enabled agents or configured breakpoints.
#####
`session.post(method[, params])`
Added in: v19.0.0 * `method` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `params` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Posts a message to the inspector back-end.
```
import { Session } from 'node:inspector/promises';
try {
const session = new Session();
session.connect();
const result = await session.post('Runtime.evaluate', { expression: '2 + 2' });
console.log(result);
} catch (error) {
console.error(error);
}
// Output: { type: 'number', value: 4, description: '4' }
```
The latest version of the V8 inspector protocol is published on the [Chrome DevTools Protocol Viewer](https://chromedevtools.github.io/devtools-protocol/v8/).
Node.js inspector supports all the Chrome DevTools Protocol domains declared by V8. Chrome DevTools Protocol domain provides an interface for interacting with one of the runtime agents used to inspect the application state and listen to the run-time events.
##### Example usage
Apart from the debugger, various V8 Profilers are available through the DevTools protocol.
###### CPU profiler
Here's an example showing how to use the [CPU Profiler](https://chromedevtools.github.io/devtools-protocol/v8/Profiler):
```
import { Session } from 'node:inspector/promises';
import fs from 'node:fs';
const session = new Session();
session.connect();
await session.post('Profiler.enable');
await session.post('Profiler.start');
// Invoke business logic under measurement here...
// some time later...
const { profile } = await session.post('Profiler.stop');
// Write profile to disk, upload, etc.
fs.writeFileSync('./profile.cpuprofile', JSON.stringify(profile));
```
###### Heap profiler
Here's an example showing how to use the [Heap Profiler](https://chromedevtools.github.io/devtools-protocol/v8/HeapProfiler):
```
import { Session } from 'node:inspector/promises';
import fs from 'node:fs';
const session = new Session();
const fd = fs.openSync('profile.heapsnapshot', 'w');
session.connect();
session.on('HeapProfiler.addHeapSnapshotChunk', (m) => {
fs.writeSync(fd, m.params.chunk);
});
const result = await session.post('HeapProfiler.takeHeapSnapshot', null);
console.log('HeapProfiler.takeHeapSnapshot done:', result);
session.disconnect();
fs.closeSync(fd);
```
### Callback API
#### Class: `inspector.Session`
* Extends: [<EventEmitter>](events#class-eventemitter)
The `inspector.Session` is used for dispatching messages to the V8 inspector back-end and receiving message responses and notifications.
#####
`new inspector.Session()`
Added in: v8.0.0 Create a new instance of the `inspector.Session` class. The inspector session needs to be connected through [`session.connect()`](#sessionconnect) before the messages can be dispatched to the inspector backend.
##### Event: `'inspectorNotification'`
Added in: v8.0.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The notification message object
Emitted when any notification from the V8 Inspector is received.
```
session.on('inspectorNotification', (message) => console.log(message.method));
// Debugger.paused
// Debugger.resumed
```
It is also possible to subscribe only to notifications with specific method:
##### Event: `<inspector-protocol-method>`;
Added in: v8.0.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The notification message object
Emitted when an inspector notification is received that has its method field set to the `<inspector-protocol-method>` value.
The following snippet installs a listener on the [`'Debugger.paused'`](https://chromedevtools.github.io/devtools-protocol/v8/Debugger#event-paused) event, and prints the reason for program suspension whenever program execution is suspended (through breakpoints, for example):
```
session.on('Debugger.paused', ({ params }) => {
console.log(params.hitBreakpoints);
});
// [ '/the/file/that/has/the/breakpoint.js:11:0' ]
```
#####
`session.connect()`
Added in: v8.0.0 Connects a session to the inspector back-end.
#####
`session.connectToMainThread()`
Added in: v12.11.0 Connects a session to the main thread inspector back-end. An exception will be thrown if this API was not called on a Worker thread.
#####
`session.disconnect()`
Added in: v8.0.0 Immediately close the session. All pending message callbacks will be called with an error. [`session.connect()`](#sessionconnect) will need to be called to be able to send messages again. Reconnected session will lose all inspector state, such as enabled agents or configured breakpoints.
#####
`session.post(method[, params][, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.0.0 | Added in: v8.0.0 |
* `method` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `params` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Posts a message to the inspector back-end. `callback` will be notified when a response is received. `callback` is a function that accepts two optional arguments: error and message-specific result.
```
session.post('Runtime.evaluate', { expression: '2 + 2' },
(error, { result }) => console.log(result));
// Output: { type: 'number', value: 4, description: '4' }
```
The latest version of the V8 inspector protocol is published on the [Chrome DevTools Protocol Viewer](https://chromedevtools.github.io/devtools-protocol/v8/).
Node.js inspector supports all the Chrome DevTools Protocol domains declared by V8. Chrome DevTools Protocol domain provides an interface for interacting with one of the runtime agents used to inspect the application state and listen to the run-time events.
##### Example usage
Apart from the debugger, various V8 Profilers are available through the DevTools protocol.
###### CPU profiler
Here's an example showing how to use the [CPU Profiler](https://chromedevtools.github.io/devtools-protocol/v8/Profiler):
```
const inspector = require('node:inspector');
const fs = require('node:fs');
const session = new inspector.Session();
session.connect();
session.post('Profiler.enable', () => {
session.post('Profiler.start', () => {
// Invoke business logic under measurement here...
// some time later...
session.post('Profiler.stop', (err, { profile }) => {
// Write profile to disk, upload, etc.
if (!err) {
fs.writeFileSync('./profile.cpuprofile', JSON.stringify(profile));
}
});
});
});
```
###### Heap profiler
Here's an example showing how to use the [Heap Profiler](https://chromedevtools.github.io/devtools-protocol/v8/HeapProfiler):
```
const inspector = require('node:inspector');
const fs = require('node:fs');
const session = new inspector.Session();
const fd = fs.openSync('profile.heapsnapshot', 'w');
session.connect();
session.on('HeapProfiler.addHeapSnapshotChunk', (m) => {
fs.writeSync(fd, m.params.chunk);
});
session.post('HeapProfiler.takeHeapSnapshot', null, (err, r) => {
console.log('HeapProfiler.takeHeapSnapshot done:', err, r);
session.disconnect();
fs.closeSync(fd);
});
```
### Common Objects
####
`inspector.close()`
History
| Version | Changes |
| --- | --- |
| v18.10.0 | The API is exposed in the worker threads. |
| v9.0.0 | Added in: v9.0.0 |
Deactivate the inspector. Blocks until there are no active connections.
####
`inspector.console`
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object to send messages to the remote inspector console.
```
require('node:inspector').console.log('a message');
```
The inspector console does not have API parity with Node.js console.
####
`inspector.open([port[, host[, wait]]])`
* `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Port to listen on for inspector connections. Optional. **Default:** what was specified on the CLI.
* `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host to listen on for inspector connections. Optional. **Default:** what was specified on the CLI.
* `wait` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Block until a client has connected. Optional. **Default:** `false`.
Activate inspector on host and port. Equivalent to `node --inspect=[[host:]port]`, but can be done programmatically after node has started.
If wait is `true`, will block until a client has connected to the inspect port and flow control has been passed to the debugger client.
See the [security warning](cli#warning-binding-inspector-to-a-public-ipport-combination-is-insecure) regarding the `host` parameter usage.
####
`inspector.url()`
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
Return the URL of the active inspector, or `undefined` if there is none.
```
$ node --inspect -p 'inspector.url()'
Debugger listening on ws://127.0.0.1:9229/166e272e-7a30-4d09-97ce-f1c012b43c34
For help, see: https://nodejs.org/en/docs/inspector
ws://127.0.0.1:9229/166e272e-7a30-4d09-97ce-f1c012b43c34
$ node --inspect=localhost:3000 -p 'inspector.url()'
Debugger listening on ws://localhost:3000/51cf8d0e-3c36-4c59-8efd-54519839e56a
For help, see: https://nodejs.org/en/docs/inspector
ws://localhost:3000/51cf8d0e-3c36-4c59-8efd-54519839e56a
$ node -p 'inspector.url()'
undefined
```
####
`inspector.waitForDebugger()`
Added in: v12.7.0 Blocks until a client (existing or connected later) has sent `Runtime.runIfWaitingForDebugger` command.
An exception will be thrown if there is no active inspector.
node None HTTP/2
------
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Requests with the `host` header (with or without `:authority`) can now be sent/received. |
| v15.3.0, v14.17.0 | It is possible to abort a request with an AbortSignal. |
| v10.10.0 | HTTP/2 is now Stable. Previously, it had been Experimental. |
| v8.4.0 | Added in: v8.4.0 |
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/http2.js](https://github.com/nodejs/node/blob/v19.0.1/lib/http2.js)
The `node:http2` module provides an implementation of the [HTTP/2](https://tools.ietf.org/html/rfc7540) protocol. It can be accessed using:
```
const http2 = require('node:http2');
```
### Determining if crypto support is unavailable
It is possible for Node.js to be built without including support for the `node:crypto` module. In such cases, attempting to `import` from `node:http2` or calling `require('node:http2')` will result in an error being thrown.
When using CommonJS, the error thrown can be caught using try/catch:
```
let http2;
try {
http2 = require('node:http2');
} catch (err) {
console.log('http2 support is disabled!');
}
```
When using the lexical ESM `import` keyword, the error can only be caught if a handler for `process.on('uncaughtException')` is registered *before* any attempt to load the module is made (using, for instance, a preload module).
When using ESM, if there is a chance that the code may be run on a build of Node.js where crypto support is not enabled, consider using the [`import()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import) function instead of the lexical `import` keyword:
```
let http2;
try {
http2 = await import('node:http2');
} catch (err) {
console.log('http2 support is disabled!');
}
```
### Core API
The Core API provides a low-level interface designed specifically around support for HTTP/2 protocol features. It is specifically *not* designed for compatibility with the existing [HTTP/1](http) module API. However, the [Compatibility API](#compatibility-api) is.
The `http2` Core API is much more symmetric between client and server than the `http` API. For instance, most events, like `'error'`, `'connect'` and `'stream'`, can be emitted either by client-side code or server-side code.
#### Server-side example
The following illustrates a simple HTTP/2 server using the Core API. Since there are no browsers known that support [unencrypted HTTP/2](https://http2.github.io/faq/#does-http2-require-encryption), the use of [`http2.createSecureServer()`](#http2createsecureserveroptions-onrequesthandler) is necessary when communicating with browser clients.
```
const http2 = require('node:http2');
const fs = require('node:fs');
const server = http2.createSecureServer({
key: fs.readFileSync('localhost-privkey.pem'),
cert: fs.readFileSync('localhost-cert.pem')
});
server.on('error', (err) => console.error(err));
server.on('stream', (stream, headers) => {
// stream is a Duplex
stream.respond({
'content-type': 'text/html; charset=utf-8',
':status': 200
});
stream.end('<h1>Hello World</h1>');
});
server.listen(8443);
```
To generate the certificate and key for this example, run:
```
openssl req -x509 -newkey rsa:2048 -nodes -sha256 -subj '/CN=localhost' \
-keyout localhost-privkey.pem -out localhost-cert.pem
```
#### Client-side example
The following illustrates an HTTP/2 client:
```
const http2 = require('node:http2');
const fs = require('node:fs');
const client = http2.connect('https://localhost:8443', {
ca: fs.readFileSync('localhost-cert.pem')
});
client.on('error', (err) => console.error(err));
const req = client.request({ ':path': '/' });
req.on('response', (headers, flags) => {
for (const name in headers) {
console.log(`${name}: ${headers[name]}`);
}
});
req.setEncoding('utf8');
let data = '';
req.on('data', (chunk) => { data += chunk; });
req.on('end', () => {
console.log(`\n${data}`);
client.close();
});
req.end();
```
#### Class: `Http2Session`
Added in: v8.4.0 * Extends: [<EventEmitter>](events#class-eventemitter)
Instances of the `http2.Http2Session` class represent an active communications session between an HTTP/2 client and server. Instances of this class are *not* intended to be constructed directly by user code.
Each `Http2Session` instance will exhibit slightly different behaviors depending on whether it is operating as a server or a client. The `http2session.type` property can be used to determine the mode in which an `Http2Session` is operating. On the server side, user code should rarely have occasion to work with the `Http2Session` object directly, with most actions typically taken through interactions with either the `Http2Server` or `Http2Stream` objects.
User code will not create `Http2Session` instances directly. Server-side `Http2Session` instances are created by the `Http2Server` instance when a new HTTP/2 connection is received. Client-side `Http2Session` instances are created using the `http2.connect()` method.
#####
`Http2Session` and sockets
Every `Http2Session` instance is associated with exactly one [`net.Socket`](net#class-netsocket) or [`tls.TLSSocket`](tls#class-tlstlssocket) when it is created. When either the `Socket` or the `Http2Session` are destroyed, both will be destroyed.
Because of the specific serialization and processing requirements imposed by the HTTP/2 protocol, it is not recommended for user code to read data from or write data to a `Socket` instance bound to a `Http2Session`. Doing so can put the HTTP/2 session into an indeterminate state causing the session and the socket to become unusable.
Once a `Socket` has been bound to an `Http2Session`, user code should rely solely on the API of the `Http2Session`.
##### Event: `'close'`
Added in: v8.4.0 The `'close'` event is emitted once the `Http2Session` has been destroyed. Its listener does not expect any arguments.
##### Event: `'connect'`
Added in: v8.4.0 * `session` [<Http2Session>](http2#class-http2session)
* `socket` [<net.Socket>](net#class-netsocket)
The `'connect'` event is emitted once the `Http2Session` has been successfully connected to the remote peer and communication may begin.
User code will typically not listen for this event directly.
##### Event: `'error'`
Added in: v8.4.0 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
The `'error'` event is emitted when an error occurs during the processing of an `Http2Session`.
##### Event: `'frameError'`
Added in: v8.4.0 * `type` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The frame type.
* `code` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The error code.
* `id` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The stream id (or `0` if the frame isn't associated with a stream).
The `'frameError'` event is emitted when an error occurs while attempting to send a frame on the session. If the frame that could not be sent is associated with a specific `Http2Stream`, an attempt to emit a `'frameError'` event on the `Http2Stream` is made.
If the `'frameError'` event is associated with a stream, the stream will be closed and destroyed immediately following the `'frameError'` event. If the event is not associated with a stream, the `Http2Session` will be shut down immediately following the `'frameError'` event.
##### Event: `'goaway'`
Added in: v8.4.0 * `errorCode` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The HTTP/2 error code specified in the `GOAWAY` frame.
* `lastStreamID` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The ID of the last stream the remote peer successfully processed (or `0` if no ID is specified).
* `opaqueData` [<Buffer>](buffer#class-buffer) If additional opaque data was included in the `GOAWAY` frame, a `Buffer` instance will be passed containing that data.
The `'goaway'` event is emitted when a `GOAWAY` frame is received.
The `Http2Session` instance will be shut down automatically when the `'goaway'` event is emitted.
##### Event: `'localSettings'`
Added in: v8.4.0 * `settings` [<HTTP/2 Settings Object>](http2#settings-object) A copy of the `SETTINGS` frame received.
The `'localSettings'` event is emitted when an acknowledgment `SETTINGS` frame has been received.
When using `http2session.settings()` to submit new settings, the modified settings do not take effect until the `'localSettings'` event is emitted.
```
session.settings({ enablePush: false });
session.on('localSettings', (settings) => {
/* Use the new settings */
});
```
##### Event: `'ping'`
Added in: v10.12.0 * `payload` [<Buffer>](buffer#class-buffer) The `PING` frame 8-byte payload
The `'ping'` event is emitted whenever a `PING` frame is received from the connected peer.
##### Event: `'remoteSettings'`
Added in: v8.4.0 * `settings` [<HTTP/2 Settings Object>](http2#settings-object) A copy of the `SETTINGS` frame received.
The `'remoteSettings'` event is emitted when a new `SETTINGS` frame is received from the connected peer.
```
session.on('remoteSettings', (settings) => {
/* Use the new settings */
});
```
##### Event: `'stream'`
Added in: v8.4.0 * `stream` [<Http2Stream>](http2#class-http2stream) A reference to the stream
* `headers` [<HTTP/2 Headers Object>](http2#headers-object) An object describing the headers
* `flags` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The associated numeric flags
* `rawHeaders` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) An array containing the raw header names followed by their respective values.
The `'stream'` event is emitted when a new `Http2Stream` is created.
```
const http2 = require('node:http2');
session.on('stream', (stream, headers, flags) => {
const method = headers[':method'];
const path = headers[':path'];
// ...
stream.respond({
':status': 200,
'content-type': 'text/plain; charset=utf-8'
});
stream.write('hello ');
stream.end('world');
});
```
On the server side, user code will typically not listen for this event directly, and would instead register a handler for the `'stream'` event emitted by the `net.Server` or `tls.Server` instances returned by `http2.createServer()` and `http2.createSecureServer()`, respectively, as in the example below:
```
const http2 = require('node:http2');
// Create an unencrypted HTTP/2 server
const server = http2.createServer();
server.on('stream', (stream, headers) => {
stream.respond({
'content-type': 'text/html; charset=utf-8',
':status': 200
});
stream.on('error', (error) => console.error(error));
stream.end('<h1>Hello World</h1>');
});
server.listen(80);
```
Even though HTTP/2 streams and network sockets are not in a 1:1 correspondence, a network error will destroy each individual stream and must be handled on the stream level, as shown above.
##### Event: `'timeout'`
Added in: v8.4.0 After the `http2session.setTimeout()` method is used to set the timeout period for this `Http2Session`, the `'timeout'` event is emitted if there is no activity on the `Http2Session` after the configured number of milliseconds. Its listener does not expect any arguments.
```
session.setTimeout(2000);
session.on('timeout', () => { /* .. */ });
```
#####
`http2session.alpnProtocol`
Added in: v9.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
Value will be `undefined` if the `Http2Session` is not yet connected to a socket, `h2c` if the `Http2Session` is not connected to a `TLSSocket`, or will return the value of the connected `TLSSocket`'s own `alpnProtocol` property.
#####
`http2session.close([callback])`
Added in: v9.4.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Gracefully closes the `Http2Session`, allowing any existing streams to complete on their own and preventing new `Http2Stream` instances from being created. Once closed, `http2session.destroy()` *might* be called if there are no open `Http2Stream` instances.
If specified, the `callback` function is registered as a handler for the `'close'` event.
#####
`http2session.closed`
Added in: v9.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Will be `true` if this `Http2Session` instance has been closed, otherwise `false`.
#####
`http2session.connecting`
Added in: v10.0.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Will be `true` if this `Http2Session` instance is still connecting, will be set to `false` before emitting `connect` event and/or calling the `http2.connect` callback.
#####
`http2session.destroy([error][, code])`
Added in: v8.4.0 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) An `Error` object if the `Http2Session` is being destroyed due to an error.
* `code` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The HTTP/2 error code to send in the final `GOAWAY` frame. If unspecified, and `error` is not undefined, the default is `INTERNAL_ERROR`, otherwise defaults to `NO_ERROR`.
Immediately terminates the `Http2Session` and the associated `net.Socket` or `tls.TLSSocket`.
Once destroyed, the `Http2Session` will emit the `'close'` event. If `error` is not undefined, an `'error'` event will be emitted immediately before the `'close'` event.
If there are any remaining open `Http2Streams` associated with the `Http2Session`, those will also be destroyed.
#####
`http2session.destroyed`
Added in: v8.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Will be `true` if this `Http2Session` instance has been destroyed and must no longer be used, otherwise `false`.
#####
`http2session.encrypted`
Added in: v9.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
Value is `undefined` if the `Http2Session` session socket has not yet been connected, `true` if the `Http2Session` is connected with a `TLSSocket`, and `false` if the `Http2Session` is connected to any other kind of socket or stream.
#####
`http2session.goaway([code[, lastStreamID[, opaqueData]]])`
Added in: v9.4.0 * `code` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) An HTTP/2 error code
* `lastStreamID` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The numeric ID of the last processed `Http2Stream`
* `opaqueData` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A `TypedArray` or `DataView` instance containing additional data to be carried within the `GOAWAY` frame.
Transmits a `GOAWAY` frame to the connected peer *without* shutting down the `Http2Session`.
#####
`http2session.localSettings`
Added in: v8.4.0 * [<HTTP/2 Settings Object>](http2#settings-object)
A prototype-less object describing the current local settings of this `Http2Session`. The local settings are local to *this* `Http2Session` instance.
#####
`http2session.originSet`
Added in: v9.4.0 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
If the `Http2Session` is connected to a `TLSSocket`, the `originSet` property will return an `Array` of origins for which the `Http2Session` may be considered authoritative.
The `originSet` property is only available when using a secure TLS connection.
#####
`http2session.pendingSettingsAck`
Added in: v8.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Indicates whether the `Http2Session` is currently waiting for acknowledgment of a sent `SETTINGS` frame. Will be `true` after calling the `http2session.settings()` method. Will be `false` once all sent `SETTINGS` frames have been acknowledged.
#####
`http2session.ping([payload, ]callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.9.3 | Added in: v8.9.3 |
* `payload` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Optional ping payload.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Sends a `PING` frame to the connected HTTP/2 peer. A `callback` function must be provided. The method will return `true` if the `PING` was sent, `false` otherwise.
The maximum number of outstanding (unacknowledged) pings is determined by the `maxOutstandingPings` configuration option. The default maximum is 10.
If provided, the `payload` must be a `Buffer`, `TypedArray`, or `DataView` containing 8 bytes of data that will be transmitted with the `PING` and returned with the ping acknowledgment.
The callback will be invoked with three arguments: an error argument that will be `null` if the `PING` was successfully acknowledged, a `duration` argument that reports the number of milliseconds elapsed since the ping was sent and the acknowledgment was received, and a `Buffer` containing the 8-byte `PING` payload.
```
session.ping(Buffer.from('abcdefgh'), (err, duration, payload) => {
if (!err) {
console.log(`Ping acknowledged in ${duration} milliseconds`);
console.log(`With payload '${payload.toString()}'`);
}
});
```
If the `payload` argument is not specified, the default payload will be the 64-bit timestamp (little endian) marking the start of the `PING` duration.
#####
`http2session.ref()`
Added in: v9.4.0 Calls [`ref()`](net#socketref) on this `Http2Session` instance's underlying [`net.Socket`](net#class-netsocket).
#####
`http2session.remoteSettings`
Added in: v8.4.0 * [<HTTP/2 Settings Object>](http2#settings-object)
A prototype-less object describing the current remote settings of this `Http2Session`. The remote settings are set by the *connected* HTTP/2 peer.
#####
`http2session.setLocalWindowSize(windowSize)`
Added in: v15.3.0, v14.18.0 * `windowSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Sets the local endpoint's window size. The `windowSize` is the total window size to set, not the delta.
```
const http2 = require('node:http2');
const server = http2.createServer();
const expectedWindowSize = 2 ** 20;
server.on('connect', (session) => {
// Set local window size to be 2 ** 20
session.setLocalWindowSize(expectedWindowSize);
});
```
#####
`http2session.setTimeout(msecs, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.4.0 | Added in: v8.4.0 |
* `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Used to set a callback function that is called when there is no activity on the `Http2Session` after `msecs` milliseconds. The given `callback` is registered as a listener on the `'timeout'` event.
#####
`http2session.socket`
Added in: v8.4.0 * [<net.Socket>](net#class-netsocket) | [<tls.TLSSocket>](tls#class-tlstlssocket)
Returns a `Proxy` object that acts as a `net.Socket` (or `tls.TLSSocket`) but limits available methods to ones safe to use with HTTP/2.
`destroy`, `emit`, `end`, `pause`, `read`, `resume`, and `write` will throw an error with code `ERR_HTTP2_NO_SOCKET_MANIPULATION`. See [`Http2Session` and Sockets](#http2session-and-sockets) for more information.
`setTimeout` method will be called on this `Http2Session`.
All other interactions will be routed directly to the socket.
#####
`http2session.state`
Added in: v8.4.0 Provides miscellaneous information about the current state of the `Http2Session`.
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `effectiveLocalWindowSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The current local (receive) flow control window size for the `Http2Session`.
+ `effectiveRecvDataLength` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The current number of bytes that have been received since the last flow control `WINDOW_UPDATE`.
+ `nextStreamID` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The numeric identifier to be used the next time a new `Http2Stream` is created by this `Http2Session`.
+ `localWindowSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes that the remote peer can send without receiving a `WINDOW_UPDATE`.
+ `lastProcStreamID` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The numeric id of the `Http2Stream` for which a `HEADERS` or `DATA` frame was most recently received.
+ `remoteWindowSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes that this `Http2Session` may send without receiving a `WINDOW_UPDATE`.
+ `outboundQueueSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of frames currently within the outbound queue for this `Http2Session`.
+ `deflateDynamicTableSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The current size in bytes of the outbound header compression state table.
+ `inflateDynamicTableSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The current size in bytes of the inbound header compression state table.
An object describing the current status of this `Http2Session`.
#####
`http2session.settings([settings][, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.4.0 | Added in: v8.4.0 |
* `settings` [<HTTP/2 Settings Object>](http2#settings-object)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Callback that is called once the session is connected or right away if the session is already connected.
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
+ `settings` [<HTTP/2 Settings Object>](http2#settings-object) The updated `settings` object.
+ `duration` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Updates the current local settings for this `Http2Session` and sends a new `SETTINGS` frame to the connected HTTP/2 peer.
Once called, the `http2session.pendingSettingsAck` property will be `true` while the session is waiting for the remote peer to acknowledge the new settings.
The new settings will not become effective until the `SETTINGS` acknowledgment is received and the `'localSettings'` event is emitted. It is possible to send multiple `SETTINGS` frames while acknowledgment is still pending.
#####
`http2session.type`
Added in: v8.4.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `http2session.type` will be equal to `http2.constants.NGHTTP2_SESSION_SERVER` if this `Http2Session` instance is a server, and `http2.constants.NGHTTP2_SESSION_CLIENT` if the instance is a client.
#####
`http2session.unref()`
Added in: v9.4.0 Calls [`unref()`](net#socketunref) on this `Http2Session` instance's underlying [`net.Socket`](net#class-netsocket).
#### Class: `ServerHttp2Session`
Added in: v8.4.0 * Extends: [<Http2Session>](http2#class-http2session)
#####
`serverhttp2session.altsvc(alt, originOrStream)`
Added in: v9.4.0 * `alt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A description of the alternative service configuration as defined by [RFC 7838](https://tools.ietf.org/html/rfc7838).
* `originOrStream` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Either a URL string specifying the origin (or an `Object` with an `origin` property) or the numeric identifier of an active `Http2Stream` as given by the `http2stream.id` property.
Submits an `ALTSVC` frame (as defined by [RFC 7838](https://tools.ietf.org/html/rfc7838)) to the connected client.
```
const http2 = require('node:http2');
const server = http2.createServer();
server.on('session', (session) => {
// Set altsvc for origin https://example.org:80
session.altsvc('h2=":8000"', 'https://example.org:80');
});
server.on('stream', (stream) => {
// Set altsvc for a specific stream
stream.session.altsvc('h2=":8000"', stream.id);
});
```
Sending an `ALTSVC` frame with a specific stream ID indicates that the alternate service is associated with the origin of the given `Http2Stream`.
The `alt` and origin string *must* contain only ASCII bytes and are strictly interpreted as a sequence of ASCII bytes. The special value `'clear'` may be passed to clear any previously set alternative service for a given domain.
When a string is passed for the `originOrStream` argument, it will be parsed as a URL and the origin will be derived. For instance, the origin for the HTTP URL `'https://example.org/foo/bar'` is the ASCII string `'https://example.org'`. An error will be thrown if either the given string cannot be parsed as a URL or if a valid origin cannot be derived.
A `URL` object, or any object with an `origin` property, may be passed as `originOrStream`, in which case the value of the `origin` property will be used. The value of the `origin` property *must* be a properly serialized ASCII origin.
##### Specifying alternative services
The format of the `alt` parameter is strictly defined by [RFC 7838](https://tools.ietf.org/html/rfc7838) as an ASCII string containing a comma-delimited list of "alternative" protocols associated with a specific host and port.
For example, the value `'h2="example.org:81"'` indicates that the HTTP/2 protocol is available on the host `'example.org'` on TCP/IP port 81. The host and port *must* be contained within the quote (`"`) characters.
Multiple alternatives may be specified, for instance: `'h2="example.org:81", h2=":82"'`.
The protocol identifier (`'h2'` in the examples) may be any valid [ALPN Protocol ID](https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml#alpn-protocol-ids).
The syntax of these values is not validated by the Node.js implementation and are passed through as provided by the user or received from the peer.
#####
`serverhttp2session.origin(...origins)`
Added in: v10.12.0 * `origins` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) One or more URL Strings passed as separate arguments.
Submits an `ORIGIN` frame (as defined by [RFC 8336](https://tools.ietf.org/html/rfc8336)) to the connected client to advertise the set of origins for which the server is capable of providing authoritative responses.
```
const http2 = require('node:http2');
const options = getSecureOptionsSomehow();
const server = http2.createSecureServer(options);
server.on('stream', (stream) => {
stream.respond();
stream.end('ok');
});
server.on('session', (session) => {
session.origin('https://example.com', 'https://example.org');
});
```
When a string is passed as an `origin`, it will be parsed as a URL and the origin will be derived. For instance, the origin for the HTTP URL `'https://example.org/foo/bar'` is the ASCII string `'https://example.org'`. An error will be thrown if either the given string cannot be parsed as a URL or if a valid origin cannot be derived.
A `URL` object, or any object with an `origin` property, may be passed as an `origin`, in which case the value of the `origin` property will be used. The value of the `origin` property *must* be a properly serialized ASCII origin.
Alternatively, the `origins` option may be used when creating a new HTTP/2 server using the `http2.createSecureServer()` method:
```
const http2 = require('node:http2');
const options = getSecureOptionsSomehow();
options.origins = ['https://example.com', 'https://example.org'];
const server = http2.createSecureServer(options);
server.on('stream', (stream) => {
stream.respond();
stream.end('ok');
});
```
#### Class: `ClientHttp2Session`
Added in: v8.4.0 * Extends: [<Http2Session>](http2#class-http2session)
##### Event: `'altsvc'`
Added in: v9.4.0 * `alt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `origin` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `streamId` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `'altsvc'` event is emitted whenever an `ALTSVC` frame is received by the client. The event is emitted with the `ALTSVC` value, origin, and stream ID. If no `origin` is provided in the `ALTSVC` frame, `origin` will be an empty string.
```
const http2 = require('node:http2');
const client = http2.connect('https://example.org');
client.on('altsvc', (alt, origin, streamId) => {
console.log(alt);
console.log(origin);
console.log(streamId);
});
```
##### Event: `'origin'`
Added in: v10.12.0 * `origins` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `'origin'` event is emitted whenever an `ORIGIN` frame is received by the client. The event is emitted with an array of `origin` strings. The `http2session.originSet` will be updated to include the received origins.
```
const http2 = require('node:http2');
const client = http2.connect('https://example.org');
client.on('origin', (origins) => {
for (let n = 0; n < origins.length; n++)
console.log(origins[n]);
});
```
The `'origin'` event is only emitted when using a secure TLS connection.
#####
`clienthttp2session.request(headers[, options])`
Added in: v8.4.0 * `headers` [<HTTP/2 Headers Object>](http2#headers-object)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `endStream` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the `Http2Stream` *writable* side should be closed initially, such as when sending a `GET` request that should not expect a payload body.
+ `exclusive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true` and `parent` identifies a parent Stream, the created stream is made the sole direct dependency of the parent, with all other existing dependents made a dependent of the newly created stream. **Default:** `false`.
+ `parent` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the numeric identifier of a stream the newly created stream is dependent on.
+ `weight` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the relative dependency of a stream in relation to other streams with the same `parent`. The value is a number between `1` and `256` (inclusive).
+ `waitForTrailers` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the `Http2Stream` will emit the `'wantTrailers'` event after the final `DATA` frame has been sent.
+ `signal` [<AbortSignal>](globals#class-abortsignal) An AbortSignal that may be used to abort an ongoing request.
* Returns: [<ClientHttp2Stream>](http2#class-clienthttp2stream)
For HTTP/2 Client `Http2Session` instances only, the `http2session.request()` creates and returns an `Http2Stream` instance that can be used to send an HTTP/2 request to the connected server.
When a `ClientHttp2Session` is first created, the socket may not yet be connected. if `clienthttp2session.request()` is called during this time, the actual request will be deferred until the socket is ready to go. If the `session` is closed before the actual request be executed, an `ERR_HTTP2_GOAWAY_SESSION` is thrown.
This method is only available if `http2session.type` is equal to `http2.constants.NGHTTP2_SESSION_CLIENT`.
```
const http2 = require('node:http2');
const clientSession = http2.connect('https://localhost:1234');
const {
HTTP2_HEADER_PATH,
HTTP2_HEADER_STATUS
} = http2.constants;
const req = clientSession.request({ [HTTP2_HEADER_PATH]: '/' });
req.on('response', (headers) => {
console.log(headers[HTTP2_HEADER_STATUS]);
req.on('data', (chunk) => { /* .. */ });
req.on('end', () => { /* .. */ });
});
```
When the `options.waitForTrailers` option is set, the `'wantTrailers'` event is emitted immediately after queuing the last chunk of payload data to be sent. The `http2stream.sendTrailers()` method can then be called to send trailing headers to the peer.
When `options.waitForTrailers` is set, the `Http2Stream` will not automatically close when the final `DATA` frame is transmitted. User code must call either `http2stream.sendTrailers()` or `http2stream.close()` to close the `Http2Stream`.
When `options.signal` is set with an `AbortSignal` and then `abort` on the corresponding `AbortController` is called, the request will emit an `'error'` event with an `AbortError` error.
The `:method` and `:path` pseudo-headers are not specified within `headers`, they respectively default to:
* `:method` = `'GET'`
* `:path` = `/`
#### Class: `Http2Stream`
Added in: v8.4.0 * Extends: [<stream.Duplex>](stream#class-streamduplex)
Each instance of the `Http2Stream` class represents a bidirectional HTTP/2 communications stream over an `Http2Session` instance. Any single `Http2Session` may have up to 231-1 `Http2Stream` instances over its lifetime.
User code will not construct `Http2Stream` instances directly. Rather, these are created, managed, and provided to user code through the `Http2Session` instance. On the server, `Http2Stream` instances are created either in response to an incoming HTTP request (and handed off to user code via the `'stream'` event), or in response to a call to the `http2stream.pushStream()` method. On the client, `Http2Stream` instances are created and returned when either the `http2session.request()` method is called, or in response to an incoming `'push'` event.
The `Http2Stream` class is a base for the [`ServerHttp2Stream`](#class-serverhttp2stream) and [`ClientHttp2Stream`](#class-clienthttp2stream) classes, each of which is used specifically by either the Server or Client side, respectively.
All `Http2Stream` instances are [`Duplex`](stream#class-streamduplex) streams. The `Writable` side of the `Duplex` is used to send data to the connected peer, while the `Readable` side is used to receive data sent by the connected peer.
The default text character encoding for an `Http2Stream` is UTF-8. When using an `Http2Stream` to send text, use the `'content-type'` header to set the character encoding.
```
stream.respond({
'content-type': 'text/html; charset=utf-8',
':status': 200
});
```
#####
`Http2Stream` Lifecycle
###### Creation
On the server side, instances of [`ServerHttp2Stream`](#class-serverhttp2stream) are created either when:
* A new HTTP/2 `HEADERS` frame with a previously unused stream ID is received;
* The `http2stream.pushStream()` method is called.
On the client side, instances of [`ClientHttp2Stream`](#class-clienthttp2stream) are created when the `http2session.request()` method is called.
On the client, the `Http2Stream` instance returned by `http2session.request()` may not be immediately ready for use if the parent `Http2Session` has not yet been fully established. In such cases, operations called on the `Http2Stream` will be buffered until the `'ready'` event is emitted. User code should rarely, if ever, need to handle the `'ready'` event directly. The ready status of an `Http2Stream` can be determined by checking the value of `http2stream.id`. If the value is `undefined`, the stream is not yet ready for use.
###### Destruction
All [`Http2Stream`](#class-http2stream) instances are destroyed either when:
* An `RST_STREAM` frame for the stream is received by the connected peer, and (for client streams only) pending data has been read.
* The `http2stream.close()` method is called, and (for client streams only) pending data has been read.
* The `http2stream.destroy()` or `http2session.destroy()` methods are called.
When an `Http2Stream` instance is destroyed, an attempt will be made to send an `RST_STREAM` frame to the connected peer.
When the `Http2Stream` instance is destroyed, the `'close'` event will be emitted. Because `Http2Stream` is an instance of `stream.Duplex`, the `'end'` event will also be emitted if the stream data is currently flowing. The `'error'` event may also be emitted if `http2stream.destroy()` was called with an `Error` passed as the first argument.
After the `Http2Stream` has been destroyed, the `http2stream.destroyed` property will be `true` and the `http2stream.rstCode` property will specify the `RST_STREAM` error code. The `Http2Stream` instance is no longer usable once destroyed.
##### Event: `'aborted'`
Added in: v8.4.0 The `'aborted'` event is emitted whenever a `Http2Stream` instance is abnormally aborted in mid-communication. Its listener does not expect any arguments.
The `'aborted'` event will only be emitted if the `Http2Stream` writable side has not been ended.
##### Event: `'close'`
Added in: v8.4.0 The `'close'` event is emitted when the `Http2Stream` is destroyed. Once this event is emitted, the `Http2Stream` instance is no longer usable.
The HTTP/2 error code used when closing the stream can be retrieved using the `http2stream.rstCode` property. If the code is any value other than `NGHTTP2_NO_ERROR` (`0`), an `'error'` event will have also been emitted.
##### Event: `'error'`
Added in: v8.4.0 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
The `'error'` event is emitted when an error occurs during the processing of an `Http2Stream`.
##### Event: `'frameError'`
Added in: v8.4.0 * `type` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The frame type.
* `code` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The error code.
* `id` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The stream id (or `0` if the frame isn't associated with a stream).
The `'frameError'` event is emitted when an error occurs while attempting to send a frame. When invoked, the handler function will receive an integer argument identifying the frame type, and an integer argument identifying the error code. The `Http2Stream` instance will be destroyed immediately after the `'frameError'` event is emitted.
##### Event: `'ready'`
Added in: v8.4.0 The `'ready'` event is emitted when the `Http2Stream` has been opened, has been assigned an `id`, and can be used. The listener does not expect any arguments.
##### Event: `'timeout'`
Added in: v8.4.0 The `'timeout'` event is emitted after no activity is received for this `Http2Stream` within the number of milliseconds set using `http2stream.setTimeout()`. Its listener does not expect any arguments.
##### Event: `'trailers'`
Added in: v8.4.0 * `headers` [<HTTP/2 Headers Object>](http2#headers-object) An object describing the headers
* `flags` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The associated numeric flags
The `'trailers'` event is emitted when a block of headers associated with trailing header fields is received. The listener callback is passed the [HTTP/2 Headers Object](#headers-object) and flags associated with the headers.
This event might not be emitted if `http2stream.end()` is called before trailers are received and the incoming data is not being read or listened for.
```
stream.on('trailers', (headers, flags) => {
console.log(headers);
});
```
##### Event: `'wantTrailers'`
Added in: v10.0.0 The `'wantTrailers'` event is emitted when the `Http2Stream` has queued the final `DATA` frame to be sent on a frame and the `Http2Stream` is ready to send trailing headers. When initiating a request or response, the `waitForTrailers` option must be set for this event to be emitted.
#####
`http2stream.aborted`
Added in: v8.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Set to `true` if the `Http2Stream` instance was aborted abnormally. When set, the `'aborted'` event will have been emitted.
#####
`http2stream.bufferSize`
Added in: v11.2.0, v10.16.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
This property shows the number of characters currently buffered to be written. See [`net.Socket.bufferSize`](net#socketbuffersize) for details.
#####
`http2stream.close(code[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.4.0 | Added in: v8.4.0 |
* `code` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Unsigned 32-bit integer identifying the error code. **Default:** `http2.constants.NGHTTP2_NO_ERROR` (`0x00`).
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) An optional function registered to listen for the `'close'` event.
Closes the `Http2Stream` instance by sending an `RST_STREAM` frame to the connected HTTP/2 peer.
#####
`http2stream.closed`
Added in: v9.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Set to `true` if the `Http2Stream` instance has been closed.
#####
`http2stream.destroyed`
Added in: v8.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Set to `true` if the `Http2Stream` instance has been destroyed and is no longer usable.
#####
`http2stream.endAfterHeaders`
Added in: v10.11.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Set to `true` if the `END_STREAM` flag was set in the request or response HEADERS frame received, indicating that no additional data should be received and the readable side of the `Http2Stream` will be closed.
#####
`http2stream.id`
Added in: v8.4.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
The numeric stream identifier of this `Http2Stream` instance. Set to `undefined` if the stream identifier has not yet been assigned.
#####
`http2stream.pending`
Added in: v9.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Set to `true` if the `Http2Stream` instance has not yet been assigned a numeric stream identifier.
#####
`http2stream.priority(options)`
Added in: v8.4.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `exclusive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true` and `parent` identifies a parent Stream, this stream is made the sole direct dependency of the parent, with all other existing dependents made a dependent of this stream. **Default:** `false`.
+ `parent` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the numeric identifier of a stream this stream is dependent on.
+ `weight` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the relative dependency of a stream in relation to other streams with the same `parent`. The value is a number between `1` and `256` (inclusive).
+ `silent` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, changes the priority locally without sending a `PRIORITY` frame to the connected peer.
Updates the priority for this `Http2Stream` instance.
#####
`http2stream.rstCode`
Added in: v8.4.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Set to the `RST_STREAM` [error code](#error-codes-for-rst_stream-and-goaway) reported when the `Http2Stream` is destroyed after either receiving an `RST_STREAM` frame from the connected peer, calling `http2stream.close()`, or `http2stream.destroy()`. Will be `undefined` if the `Http2Stream` has not been closed.
#####
`http2stream.sentHeaders`
Added in: v9.5.0 * [<HTTP/2 Headers Object>](http2#headers-object)
An object containing the outbound headers sent for this `Http2Stream`.
#####
`http2stream.sentInfoHeaders`
Added in: v9.5.0 * [<HTTP/2 Headers Object[]>](http2#headers-object)
An array of objects containing the outbound informational (additional) headers sent for this `Http2Stream`.
#####
`http2stream.sentTrailers`
Added in: v9.5.0 * [<HTTP/2 Headers Object>](http2#headers-object)
An object containing the outbound trailers sent for this `HttpStream`.
#####
`http2stream.session`
Added in: v8.4.0 * [<Http2Session>](http2#class-http2session)
A reference to the `Http2Session` instance that owns this `Http2Stream`. The value will be `undefined` after the `Http2Stream` instance is destroyed.
#####
`http2stream.setTimeout(msecs, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.4.0 | Added in: v8.4.0 |
* `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
```
const http2 = require('node:http2');
const client = http2.connect('http://example.org:8000');
const { NGHTTP2_CANCEL } = http2.constants;
const req = client.request({ ':path': '/' });
// Cancel the stream if there's no activity after 5 seconds
req.setTimeout(5000, () => req.close(NGHTTP2_CANCEL));
```
#####
`http2stream.state`
Added in: v8.4.0 Provides miscellaneous information about the current state of the `Http2Stream`.
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `localWindowSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes the connected peer may send for this `Http2Stream` without receiving a `WINDOW_UPDATE`.
+ `state` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A flag indicating the low-level current state of the `Http2Stream` as determined by `nghttp2`.
+ `localClose` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `1` if this `Http2Stream` has been closed locally.
+ `remoteClose` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `1` if this `Http2Stream` has been closed remotely.
+ `sumDependencyWeight` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The sum weight of all `Http2Stream` instances that depend on this `Http2Stream` as specified using `PRIORITY` frames.
+ `weight` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The priority weight of this `Http2Stream`.
A current state of this `Http2Stream`.
#####
`http2stream.sendTrailers(headers)`
Added in: v10.0.0 * `headers` [<HTTP/2 Headers Object>](http2#headers-object)
Sends a trailing `HEADERS` frame to the connected HTTP/2 peer. This method will cause the `Http2Stream` to be immediately closed and must only be called after the `'wantTrailers'` event has been emitted. When sending a request or sending a response, the `options.waitForTrailers` option must be set in order to keep the `Http2Stream` open after the final `DATA` frame so that trailers can be sent.
```
const http2 = require('node:http2');
const server = http2.createServer();
server.on('stream', (stream) => {
stream.respond(undefined, { waitForTrailers: true });
stream.on('wantTrailers', () => {
stream.sendTrailers({ xyz: 'abc' });
});
stream.end('Hello World');
});
```
The HTTP/1 specification forbids trailers from containing HTTP/2 pseudo-header fields (e.g. `':method'`, `':path'`, etc).
#### Class: `ClientHttp2Stream`
Added in: v8.4.0 * Extends [<Http2Stream>](http2#class-http2stream)
The `ClientHttp2Stream` class is an extension of `Http2Stream` that is used exclusively on HTTP/2 Clients. `Http2Stream` instances on the client provide events such as `'response'` and `'push'` that are only relevant on the client.
##### Event: `'continue'`
Added in: v8.5.0 Emitted when the server sends a `100 Continue` status, usually because the request contained `Expect: 100-continue`. This is an instruction that the client should send the request body.
##### Event: `'headers'`
Added in: v8.4.0 * `headers` [<HTTP/2 Headers Object>](http2#headers-object)
* `flags` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `'headers'` event is emitted when an additional block of headers is received for a stream, such as when a block of `1xx` informational headers is received. The listener callback is passed the [HTTP/2 Headers Object](#headers-object) and flags associated with the headers.
```
stream.on('headers', (headers, flags) => {
console.log(headers);
});
```
##### Event: `'push'`
Added in: v8.4.0 * `headers` [<HTTP/2 Headers Object>](http2#headers-object)
* `flags` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `'push'` event is emitted when response headers for a Server Push stream are received. The listener callback is passed the [HTTP/2 Headers Object](#headers-object) and flags associated with the headers.
```
stream.on('push', (headers, flags) => {
console.log(headers);
});
```
##### Event: `'response'`
Added in: v8.4.0 * `headers` [<HTTP/2 Headers Object>](http2#headers-object)
* `flags` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `'response'` event is emitted when a response `HEADERS` frame has been received for this stream from the connected HTTP/2 server. The listener is invoked with two arguments: an `Object` containing the received [HTTP/2 Headers Object](#headers-object), and flags associated with the headers.
```
const http2 = require('node:http2');
const client = http2.connect('https://localhost');
const req = client.request({ ':path': '/' });
req.on('response', (headers, flags) => {
console.log(headers[':status']);
});
```
#### Class: `ServerHttp2Stream`
Added in: v8.4.0 * Extends: [<Http2Stream>](http2#class-http2stream)
The `ServerHttp2Stream` class is an extension of [`Http2Stream`](#class-http2stream) that is used exclusively on HTTP/2 Servers. `Http2Stream` instances on the server provide additional methods such as `http2stream.pushStream()` and `http2stream.respond()` that are only relevant on the server.
#####
`http2stream.additionalHeaders(headers)`
Added in: v8.4.0 * `headers` [<HTTP/2 Headers Object>](http2#headers-object)
Sends an additional informational `HEADERS` frame to the connected HTTP/2 peer.
#####
`http2stream.headersSent`
Added in: v8.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
True if headers were sent, false otherwise (read-only).
#####
`http2stream.pushAllowed`
Added in: v8.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Read-only property mapped to the `SETTINGS_ENABLE_PUSH` flag of the remote client's most recent `SETTINGS` frame. Will be `true` if the remote peer accepts push streams, `false` otherwise. Settings are the same for every `Http2Stream` in the same `Http2Session`.
#####
`http2stream.pushStream(headers[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.4.0 | Added in: v8.4.0 |
* `headers` [<HTTP/2 Headers Object>](http2#headers-object)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `exclusive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true` and `parent` identifies a parent Stream, the created stream is made the sole direct dependency of the parent, with all other existing dependents made a dependent of the newly created stream. **Default:** `false`.
+ `parent` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the numeric identifier of a stream the newly created stream is dependent on.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Callback that is called once the push stream has been initiated.
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `pushStream` [<ServerHttp2Stream>](http2#class-serverhttp2stream) The returned `pushStream` object.
+ `headers` [<HTTP/2 Headers Object>](http2#headers-object) Headers object the `pushStream` was initiated with.
Initiates a push stream. The callback is invoked with the new `Http2Stream` instance created for the push stream passed as the second argument, or an `Error` passed as the first argument.
```
const http2 = require('node:http2');
const server = http2.createServer();
server.on('stream', (stream) => {
stream.respond({ ':status': 200 });
stream.pushStream({ ':path': '/' }, (err, pushStream, headers) => {
if (err) throw err;
pushStream.respond({ ':status': 200 });
pushStream.end('some pushed data');
});
stream.end('some data');
});
```
Setting the weight of a push stream is not allowed in the `HEADERS` frame. Pass a `weight` value to `http2stream.priority` with the `silent` option set to `true` to enable server-side bandwidth balancing between concurrent streams.
Calling `http2stream.pushStream()` from within a pushed stream is not permitted and will throw an error.
#####
`http2stream.respond([headers[, options]])`
History
| Version | Changes |
| --- | --- |
| v14.5.0, v12.19.0 | Allow explicitly setting date headers. |
| v8.4.0 | Added in: v8.4.0 |
* `headers` [<HTTP/2 Headers Object>](http2#headers-object)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `endStream` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Set to `true` to indicate that the response will not include payload data.
+ `waitForTrailers` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the `Http2Stream` will emit the `'wantTrailers'` event after the final `DATA` frame has been sent.
```
const http2 = require('node:http2');
const server = http2.createServer();
server.on('stream', (stream) => {
stream.respond({ ':status': 200 });
stream.end('some data');
});
```
Initiates a response. When the `options.waitForTrailers` option is set, the `'wantTrailers'` event will be emitted immediately after queuing the last chunk of payload data to be sent. The `http2stream.sendTrailers()` method can then be used to sent trailing header fields to the peer.
When `options.waitForTrailers` is set, the `Http2Stream` will not automatically close when the final `DATA` frame is transmitted. User code must call either `http2stream.sendTrailers()` or `http2stream.close()` to close the `Http2Stream`.
```
const http2 = require('node:http2');
const server = http2.createServer();
server.on('stream', (stream) => {
stream.respond({ ':status': 200 }, { waitForTrailers: true });
stream.on('wantTrailers', () => {
stream.sendTrailers({ ABC: 'some value to send' });
});
stream.end('some data');
});
```
#####
`http2stream.respondWithFD(fd[, headers[, options]])`
History
| Version | Changes |
| --- | --- |
| v14.5.0, v12.19.0 | Allow explicitly setting date headers. |
| v12.12.0 | The `fd` option may now be a `FileHandle`. |
| v10.0.0 | Any readable file descriptor, not necessarily for a regular file, is supported now. |
| v8.4.0 | Added in: v8.4.0 |
* `fd` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<FileHandle>](fs#class-filehandle) A readable file descriptor.
* `headers` [<HTTP/2 Headers Object>](http2#headers-object)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `statCheck` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `waitForTrailers` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the `Http2Stream` will emit the `'wantTrailers'` event after the final `DATA` frame has been sent.
+ `offset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The offset position at which to begin reading.
+ `length` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The amount of data from the fd to send.
Initiates a response whose data is read from the given file descriptor. No validation is performed on the given file descriptor. If an error occurs while attempting to read data using the file descriptor, the `Http2Stream` will be closed using an `RST_STREAM` frame using the standard `INTERNAL_ERROR` code.
When used, the `Http2Stream` object's `Duplex` interface will be closed automatically.
```
const http2 = require('node:http2');
const fs = require('node:fs');
const server = http2.createServer();
server.on('stream', (stream) => {
const fd = fs.openSync('/some/file', 'r');
const stat = fs.fstatSync(fd);
const headers = {
'content-length': stat.size,
'last-modified': stat.mtime.toUTCString(),
'content-type': 'text/plain; charset=utf-8'
};
stream.respondWithFD(fd, headers);
stream.on('close', () => fs.closeSync(fd));
});
```
The optional `options.statCheck` function may be specified to give user code an opportunity to set additional content headers based on the `fs.Stat` details of the given fd. If the `statCheck` function is provided, the `http2stream.respondWithFD()` method will perform an `fs.fstat()` call to collect details on the provided file descriptor.
The `offset` and `length` options may be used to limit the response to a specific range subset. This can be used, for instance, to support HTTP Range requests.
The file descriptor or `FileHandle` is not closed when the stream is closed, so it will need to be closed manually once it is no longer needed. Using the same file descriptor concurrently for multiple streams is not supported and may result in data loss. Re-using a file descriptor after a stream has finished is supported.
When the `options.waitForTrailers` option is set, the `'wantTrailers'` event will be emitted immediately after queuing the last chunk of payload data to be sent. The `http2stream.sendTrailers()` method can then be used to sent trailing header fields to the peer.
When `options.waitForTrailers` is set, the `Http2Stream` will not automatically close when the final `DATA` frame is transmitted. User code *must* call either `http2stream.sendTrailers()` or `http2stream.close()` to close the `Http2Stream`.
```
const http2 = require('node:http2');
const fs = require('node:fs');
const server = http2.createServer();
server.on('stream', (stream) => {
const fd = fs.openSync('/some/file', 'r');
const stat = fs.fstatSync(fd);
const headers = {
'content-length': stat.size,
'last-modified': stat.mtime.toUTCString(),
'content-type': 'text/plain; charset=utf-8'
};
stream.respondWithFD(fd, headers, { waitForTrailers: true });
stream.on('wantTrailers', () => {
stream.sendTrailers({ ABC: 'some value to send' });
});
stream.on('close', () => fs.closeSync(fd));
});
```
#####
`http2stream.respondWithFile(path[, headers[, options]])`
History
| Version | Changes |
| --- | --- |
| v14.5.0, v12.19.0 | Allow explicitly setting date headers. |
| v10.0.0 | Any readable file, not necessarily a regular file, is supported now. |
| v8.4.0 | Added in: v8.4.0 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<URL>](url#the-whatwg-url-api)
* `headers` [<HTTP/2 Headers Object>](http2#headers-object)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `statCheck` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `onError` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Callback function invoked in the case of an error before send.
+ `waitForTrailers` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the `Http2Stream` will emit the `'wantTrailers'` event after the final `DATA` frame has been sent.
+ `offset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The offset position at which to begin reading.
+ `length` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The amount of data from the fd to send.
Sends a regular file as the response. The `path` must specify a regular file or an `'error'` event will be emitted on the `Http2Stream` object.
When used, the `Http2Stream` object's `Duplex` interface will be closed automatically.
The optional `options.statCheck` function may be specified to give user code an opportunity to set additional content headers based on the `fs.Stat` details of the given file:
If an error occurs while attempting to read the file data, the `Http2Stream` will be closed using an `RST_STREAM` frame using the standard `INTERNAL_ERROR` code. If the `onError` callback is defined, then it will be called. Otherwise the stream will be destroyed.
Example using a file path:
```
const http2 = require('node:http2');
const server = http2.createServer();
server.on('stream', (stream) => {
function statCheck(stat, headers) {
headers['last-modified'] = stat.mtime.toUTCString();
}
function onError(err) {
// stream.respond() can throw if the stream has been destroyed by
// the other side.
try {
if (err.code === 'ENOENT') {
stream.respond({ ':status': 404 });
} else {
stream.respond({ ':status': 500 });
}
} catch (err) {
// Perform actual error handling.
console.log(err);
}
stream.end();
}
stream.respondWithFile('/some/file',
{ 'content-type': 'text/plain; charset=utf-8' },
{ statCheck, onError });
});
```
The `options.statCheck` function may also be used to cancel the send operation by returning `false`. For instance, a conditional request may check the stat results to determine if the file has been modified to return an appropriate `304` response:
```
const http2 = require('node:http2');
const server = http2.createServer();
server.on('stream', (stream) => {
function statCheck(stat, headers) {
// Check the stat here...
stream.respond({ ':status': 304 });
return false; // Cancel the send operation
}
stream.respondWithFile('/some/file',
{ 'content-type': 'text/plain; charset=utf-8' },
{ statCheck });
});
```
The `content-length` header field will be automatically set.
The `offset` and `length` options may be used to limit the response to a specific range subset. This can be used, for instance, to support HTTP Range requests.
The `options.onError` function may also be used to handle all the errors that could happen before the delivery of the file is initiated. The default behavior is to destroy the stream.
When the `options.waitForTrailers` option is set, the `'wantTrailers'` event will be emitted immediately after queuing the last chunk of payload data to be sent. The `http2stream.sendTrailers()` method can then be used to sent trailing header fields to the peer.
When `options.waitForTrailers` is set, the `Http2Stream` will not automatically close when the final `DATA` frame is transmitted. User code must call either `http2stream.sendTrailers()` or `http2stream.close()` to close the `Http2Stream`.
```
const http2 = require('node:http2');
const server = http2.createServer();
server.on('stream', (stream) => {
stream.respondWithFile('/some/file',
{ 'content-type': 'text/plain; charset=utf-8' },
{ waitForTrailers: true });
stream.on('wantTrailers', () => {
stream.sendTrailers({ ABC: 'some value to send' });
});
});
```
#### Class: `Http2Server`
Added in: v8.4.0 * Extends: [<net.Server>](net#class-netserver)
Instances of `Http2Server` are created using the `http2.createServer()` function. The `Http2Server` class is not exported directly by the `node:http2` module.
##### Event: `'checkContinue'`
Added in: v8.5.0 * `request` [<http2.Http2ServerRequest>](http2#class-http2http2serverrequest)
* `response` [<http2.Http2ServerResponse>](http2#class-http2http2serverresponse)
If a [`'request'`](#event-request) listener is registered or [`http2.createServer()`](#http2createserveroptions-onrequesthandler) is supplied a callback function, the `'checkContinue'` event is emitted each time a request with an HTTP `Expect: 100-continue` is received. If this event is not listened for, the server will automatically respond with a status `100 Continue` as appropriate.
Handling this event involves calling [`response.writeContinue()`](#responsewritecontinue) if the client should continue to send the request body, or generating an appropriate HTTP response (e.g. 400 Bad Request) if the client should not continue to send the request body.
When this event is emitted and handled, the [`'request'`](#event-request) event will not be emitted.
##### Event: `'connection'`
Added in: v8.4.0 * `socket` [<stream.Duplex>](stream#class-streamduplex)
This event is emitted when a new TCP stream is established. `socket` is typically an object of type [`net.Socket`](net#class-netsocket). Usually users will not want to access this event.
This event can also be explicitly emitted by users to inject connections into the HTTP server. In that case, any [`Duplex`](stream#class-streamduplex) stream can be passed.
##### Event: `'request'`
Added in: v8.4.0 * `request` [<http2.Http2ServerRequest>](http2#class-http2http2serverrequest)
* `response` [<http2.Http2ServerResponse>](http2#class-http2http2serverresponse)
Emitted each time there is a request. There may be multiple requests per session. See the [Compatibility API](#compatibility-api).
##### Event: `'session'`
Added in: v8.4.0 * `session` [<ServerHttp2Session>](http2#class-serverhttp2session)
The `'session'` event is emitted when a new `Http2Session` is created by the `Http2Server`.
##### Event: `'sessionError'`
Added in: v8.4.0 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
* `session` [<ServerHttp2Session>](http2#class-serverhttp2session)
The `'sessionError'` event is emitted when an `'error'` event is emitted by an `Http2Session` object associated with the `Http2Server`.
##### Event: `'stream'`
Added in: v8.4.0 * `stream` [<Http2Stream>](http2#class-http2stream) A reference to the stream
* `headers` [<HTTP/2 Headers Object>](http2#headers-object) An object describing the headers
* `flags` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The associated numeric flags
* `rawHeaders` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) An array containing the raw header names followed by their respective values.
The `'stream'` event is emitted when a `'stream'` event has been emitted by an `Http2Session` associated with the server.
See also [`Http2Session`'s `'stream'` event](#event-stream).
```
const http2 = require('node:http2');
const {
HTTP2_HEADER_METHOD,
HTTP2_HEADER_PATH,
HTTP2_HEADER_STATUS,
HTTP2_HEADER_CONTENT_TYPE
} = http2.constants;
const server = http2.createServer();
server.on('stream', (stream, headers, flags) => {
const method = headers[HTTP2_HEADER_METHOD];
const path = headers[HTTP2_HEADER_PATH];
// ...
stream.respond({
[HTTP2_HEADER_STATUS]: 200,
[HTTP2_HEADER_CONTENT_TYPE]: 'text/plain; charset=utf-8'
});
stream.write('hello ');
stream.end('world');
});
```
##### Event: `'timeout'`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The default timeout changed from 120s to 0 (no timeout). |
| v8.4.0 | Added in: v8.4.0 |
The `'timeout'` event is emitted when there is no activity on the Server for a given number of milliseconds set using `http2server.setTimeout()`. **Default:** 0 (no timeout)
#####
`server.close([callback])`
Added in: v8.4.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Stops the server from establishing new sessions. This does not prevent new request streams from being created due to the persistent nature of HTTP/2 sessions. To gracefully shut down the server, call [`http2session.close()`](#http2sessionclosecallback) on all active sessions.
If `callback` is provided, it is not invoked until all active sessions have been closed, although the server has already stopped allowing new sessions. See [`net.Server.close()`](net#serverclosecallback) for more details.
#####
`server.setTimeout([msecs][, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v13.0.0 | The default timeout changed from 120s to 0 (no timeout). |
| v8.4.0 | Added in: v8.4.0 |
* `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** 0 (no timeout)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<Http2Server>](http2#class-http2server)
Used to set the timeout value for http2 server requests, and sets a callback function that is called when there is no activity on the `Http2Server` after `msecs` milliseconds.
The given callback is registered as a listener on the `'timeout'` event.
In case if `callback` is not a function, a new `ERR_INVALID_ARG_TYPE` error will be thrown.
#####
`server.timeout`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The default timeout changed from 120s to 0 (no timeout). |
| v8.4.0 | Added in: v8.4.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Timeout in milliseconds. **Default:** 0 (no timeout)
The number of milliseconds of inactivity before a socket is presumed to have timed out.
A value of `0` will disable the timeout behavior on incoming connections.
The socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections.
#####
`server.updateSettings([settings])`
Added in: v15.1.0, v14.17.0 * `settings` [<HTTP/2 Settings Object>](http2#settings-object)
Used to update the server with the provided settings.
Throws `ERR_HTTP2_INVALID_SETTING_VALUE` for invalid `settings` values.
Throws `ERR_INVALID_ARG_TYPE` for invalid `settings` argument.
#### Class: `Http2SecureServer`
Added in: v8.4.0 * Extends: [<tls.Server>](tls#class-tlsserver)
Instances of `Http2SecureServer` are created using the `http2.createSecureServer()` function. The `Http2SecureServer` class is not exported directly by the `node:http2` module.
##### Event: `'checkContinue'`
Added in: v8.5.0 * `request` [<http2.Http2ServerRequest>](http2#class-http2http2serverrequest)
* `response` [<http2.Http2ServerResponse>](http2#class-http2http2serverresponse)
If a [`'request'`](#event-request) listener is registered or [`http2.createSecureServer()`](#http2createsecureserveroptions-onrequesthandler) is supplied a callback function, the `'checkContinue'` event is emitted each time a request with an HTTP `Expect: 100-continue` is received. If this event is not listened for, the server will automatically respond with a status `100 Continue` as appropriate.
Handling this event involves calling [`response.writeContinue()`](#responsewritecontinue) if the client should continue to send the request body, or generating an appropriate HTTP response (e.g. 400 Bad Request) if the client should not continue to send the request body.
When this event is emitted and handled, the [`'request'`](#event-request) event will not be emitted.
##### Event: `'connection'`
Added in: v8.4.0 * `socket` [<stream.Duplex>](stream#class-streamduplex)
This event is emitted when a new TCP stream is established, before the TLS handshake begins. `socket` is typically an object of type [`net.Socket`](net#class-netsocket). Usually users will not want to access this event.
This event can also be explicitly emitted by users to inject connections into the HTTP server. In that case, any [`Duplex`](stream#class-streamduplex) stream can be passed.
##### Event: `'request'`
Added in: v8.4.0 * `request` [<http2.Http2ServerRequest>](http2#class-http2http2serverrequest)
* `response` [<http2.Http2ServerResponse>](http2#class-http2http2serverresponse)
Emitted each time there is a request. There may be multiple requests per session. See the [Compatibility API](#compatibility-api).
##### Event: `'session'`
Added in: v8.4.0 * `session` [<ServerHttp2Session>](http2#class-serverhttp2session)
The `'session'` event is emitted when a new `Http2Session` is created by the `Http2SecureServer`.
##### Event: `'sessionError'`
Added in: v8.4.0 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
* `session` [<ServerHttp2Session>](http2#class-serverhttp2session)
The `'sessionError'` event is emitted when an `'error'` event is emitted by an `Http2Session` object associated with the `Http2SecureServer`.
##### Event: `'stream'`
Added in: v8.4.0 * `stream` [<Http2Stream>](http2#class-http2stream) A reference to the stream
* `headers` [<HTTP/2 Headers Object>](http2#headers-object) An object describing the headers
* `flags` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The associated numeric flags
* `rawHeaders` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) An array containing the raw header names followed by their respective values.
The `'stream'` event is emitted when a `'stream'` event has been emitted by an `Http2Session` associated with the server.
See also [`Http2Session`'s `'stream'` event](#event-stream).
```
const http2 = require('node:http2');
const {
HTTP2_HEADER_METHOD,
HTTP2_HEADER_PATH,
HTTP2_HEADER_STATUS,
HTTP2_HEADER_CONTENT_TYPE
} = http2.constants;
const options = getOptionsSomehow();
const server = http2.createSecureServer(options);
server.on('stream', (stream, headers, flags) => {
const method = headers[HTTP2_HEADER_METHOD];
const path = headers[HTTP2_HEADER_PATH];
// ...
stream.respond({
[HTTP2_HEADER_STATUS]: 200,
[HTTP2_HEADER_CONTENT_TYPE]: 'text/plain; charset=utf-8'
});
stream.write('hello ');
stream.end('world');
});
```
##### Event: `'timeout'`
Added in: v8.4.0 The `'timeout'` event is emitted when there is no activity on the Server for a given number of milliseconds set using `http2secureServer.setTimeout()`. **Default:** 2 minutes.
##### Event: `'unknownProtocol'`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | This event will only be emitted if the client did not transmit an ALPN extension during the TLS handshake. |
| v8.4.0 | Added in: v8.4.0 |
* `socket` [<stream.Duplex>](stream#class-streamduplex)
The `'unknownProtocol'` event is emitted when a connecting client fails to negotiate an allowed protocol (i.e. HTTP/2 or HTTP/1.1). The event handler receives the socket for handling. If no listener is registered for this event, the connection is terminated. A timeout may be specified using the `'unknownProtocolTimeout'` option passed to [`http2.createSecureServer()`](#http2createsecureserveroptions-onrequesthandler).
In earlier versions of Node.js, this event would be emitted if `allowHTTP1` is `false` and, during the TLS handshake, the client either does not send an ALPN extension or sends an ALPN extension that does not include HTTP/2 (`h2`). Newer versions of Node.js only emit this event if `allowHTTP1` is `false` and the client does not send an ALPN extension. If the client sends an ALPN extension that does not include HTTP/2 (or HTTP/1.1 if `allowHTTP1` is `true`), the TLS handshake will fail and no secure connection will be established.
See the [Compatibility API](#compatibility-api).
#####
`server.close([callback])`
Added in: v8.4.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Stops the server from establishing new sessions. This does not prevent new request streams from being created due to the persistent nature of HTTP/2 sessions. To gracefully shut down the server, call [`http2session.close()`](#http2sessionclosecallback) on all active sessions.
If `callback` is provided, it is not invoked until all active sessions have been closed, although the server has already stopped allowing new sessions. See [`tls.Server.close()`](tls#serverclosecallback) for more details.
#####
`server.setTimeout([msecs][, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.4.0 | Added in: v8.4.0 |
* `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `120000` (2 minutes)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<Http2SecureServer>](http2#class-http2secureserver)
Used to set the timeout value for http2 secure server requests, and sets a callback function that is called when there is no activity on the `Http2SecureServer` after `msecs` milliseconds.
The given callback is registered as a listener on the `'timeout'` event.
In case if `callback` is not a function, a new `ERR_INVALID_ARG_TYPE` error will be thrown.
#####
`server.timeout`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The default timeout changed from 120s to 0 (no timeout). |
| v8.4.0 | Added in: v8.4.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Timeout in milliseconds. **Default:** 0 (no timeout)
The number of milliseconds of inactivity before a socket is presumed to have timed out.
A value of `0` will disable the timeout behavior on incoming connections.
The socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections.
#####
`server.updateSettings([settings])`
Added in: v15.1.0, v14.17.0 * `settings` [<HTTP/2 Settings Object>](http2#settings-object)
Used to update the server with the provided settings.
Throws `ERR_HTTP2_INVALID_SETTING_VALUE` for invalid `settings` values.
Throws `ERR_INVALID_ARG_TYPE` for invalid `settings` argument.
####
`http2.createServer([options][, onRequestHandler])`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The `PADDING_STRATEGY_CALLBACK` has been made equivalent to providing `PADDING_STRATEGY_ALIGNED` and `selectPadding` has been removed. |
| v13.3.0, v12.16.0 | Added `maxSessionRejectedStreams` option with a default of 100. |
| v13.3.0, v12.16.0 | Added `maxSessionInvalidFrames` option with a default of 1000. |
| v12.4.0 | The `options` parameter now supports `net.createServer()` options. |
| v15.10.0, v14.16.0, v12.21.0, v10.24.0 | Added `unknownProtocolTimeout` option with a default of 10000. |
| v14.4.0, v12.18.0, v10.21.0 | Added `maxSettings` option with a default of 32. |
| v9.6.0 | Added the `Http1IncomingMessage` and `Http1ServerResponse` option. |
| v8.9.3 | Added the `maxOutstandingPings` option with a default limit of 10. |
| v8.9.3 | Added the `maxHeaderListPairs` option with a default limit of 128 header pairs. |
| v8.4.0 | Added in: v8.4.0 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `maxDeflateDynamicTableSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum dynamic table size for deflating header fields. **Default:** `4Kib`.
+ `maxSettings` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of settings entries per `SETTINGS` frame. The minimum value allowed is `1`. **Default:** `32`.
+ `maxSessionMemory`[<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum memory that the `Http2Session` is permitted to use. The value is expressed in terms of number of megabytes, e.g. `1` equal 1 megabyte. The minimum value allowed is `1`. This is a credit based limit, existing `Http2Stream`s may cause this limit to be exceeded, but new `Http2Stream` instances will be rejected while this limit is exceeded. The current number of `Http2Stream` sessions, the current memory use of the header compression tables, current data queued to be sent, and unacknowledged `PING` and `SETTINGS` frames are all counted towards the current limit. **Default:** `10`.
+ `maxHeaderListPairs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of header entries. This is similar to [`server.maxHeadersCount`](http#servermaxheaderscount) or [`request.maxHeadersCount`](http#requestmaxheaderscount) in the `node:http` module. The minimum value is `4`. **Default:** `128`.
+ `maxOutstandingPings` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of outstanding, unacknowledged pings. **Default:** `10`.
+ `maxSendHeaderBlockLength` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum allowed size for a serialized, compressed block of headers. Attempts to send headers that exceed this limit will result in a `'frameError'` event being emitted and the stream being closed and destroyed. While this sets the maximum allowed size to the entire block of headers, `nghttp2` (the internal http2 library) has a limit of `65536` for each decompressed key/value pair.
+ `paddingStrategy` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The strategy used for determining the amount of padding to use for `HEADERS` and `DATA` frames. **Default:** `http2.constants.PADDING_STRATEGY_NONE`. Value may be one of:
- `http2.constants.PADDING_STRATEGY_NONE`: No padding is applied.
- `http2.constants.PADDING_STRATEGY_MAX`: The maximum amount of padding, determined by the internal implementation, is applied.
- `http2.constants.PADDING_STRATEGY_ALIGNED`: Attempts to apply enough padding to ensure that the total frame length, including the 9-byte header, is a multiple of 8. For each frame, there is a maximum allowed number of padding bytes that is determined by current flow control state and settings. If this maximum is less than the calculated amount needed to ensure alignment, the maximum is used and the total frame length is not necessarily aligned at 8 bytes.
+ `peerMaxConcurrentStreams` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of concurrent streams for the remote peer as if a `SETTINGS` frame had been received. Will be overridden if the remote peer sets its own value for `maxConcurrentStreams`. **Default:** `100`.
+ `maxSessionInvalidFrames` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of invalid frames that will be tolerated before the session is closed. **Default:** `1000`.
+ `maxSessionRejectedStreams` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of rejected upon creation streams that will be tolerated before the session is closed. Each rejection is associated with an `NGHTTP2_ENHANCE_YOUR_CALM` error that should tell the peer to not open any more streams, continuing to open streams is therefore regarded as a sign of a misbehaving peer. **Default:** `100`.
+ `settings` [<HTTP/2 Settings Object>](http2#settings-object) The initial settings to send to the remote peer upon connection.
+ `Http1IncomingMessage` [<http.IncomingMessage>](http#class-httpincomingmessage) Specifies the `IncomingMessage` class to used for HTTP/1 fallback. Useful for extending the original `http.IncomingMessage`. **Default:** `http.IncomingMessage`.
+ `Http1ServerResponse` [<http.ServerResponse>](http#class-httpserverresponse) Specifies the `ServerResponse` class to used for HTTP/1 fallback. Useful for extending the original `http.ServerResponse`. **Default:** `http.ServerResponse`.
+ `Http2ServerRequest` [<http2.Http2ServerRequest>](http2#class-http2http2serverrequest) Specifies the `Http2ServerRequest` class to use. Useful for extending the original `Http2ServerRequest`. **Default:** `Http2ServerRequest`.
+ `Http2ServerResponse` [<http2.Http2ServerResponse>](http2#class-http2http2serverresponse) Specifies the `Http2ServerResponse` class to use. Useful for extending the original `Http2ServerResponse`. **Default:** `Http2ServerResponse`.
+ `unknownProtocolTimeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies a timeout in milliseconds that a server should wait when an [`'unknownProtocol'`](#event-unknownprotocol) is emitted. If the socket has not been destroyed by that time the server will destroy it. **Default:** `10000`.
+ ...: Any [`net.createServer()`](net#netcreateserveroptions-connectionlistener) option can be provided.
* `onRequestHandler` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) See [Compatibility API](#compatibility-api)
* Returns: [<Http2Server>](http2#class-http2server)
Returns a `net.Server` instance that creates and manages `Http2Session` instances.
Since there are no browsers known that support [unencrypted HTTP/2](https://http2.github.io/faq/#does-http2-require-encryption), the use of [`http2.createSecureServer()`](#http2createsecureserveroptions-onrequesthandler) is necessary when communicating with browser clients.
```
const http2 = require('node:http2');
// Create an unencrypted HTTP/2 server.
// Since there are no browsers known that support
// unencrypted HTTP/2, the use of `http2.createSecureServer()`
// is necessary when communicating with browser clients.
const server = http2.createServer();
server.on('stream', (stream, headers) => {
stream.respond({
'content-type': 'text/html; charset=utf-8',
':status': 200
});
stream.end('<h1>Hello World</h1>');
});
server.listen(80);
```
####
`http2.createSecureServer(options[, onRequestHandler])`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The `PADDING_STRATEGY_CALLBACK` has been made equivalent to providing `PADDING_STRATEGY_ALIGNED` and `selectPadding` has been removed. |
| v13.3.0, v12.16.0 | Added `maxSessionRejectedStreams` option with a default of 100. |
| v13.3.0, v12.16.0 | Added `maxSessionInvalidFrames` option with a default of 1000. |
| v15.10.0, v14.16.0, v12.21.0, v10.24.0 | Added `unknownProtocolTimeout` option with a default of 10000. |
| v14.4.0, v12.18.0, v10.21.0 | Added `maxSettings` option with a default of 32. |
| v10.12.0 | Added the `origins` option to automatically send an `ORIGIN` frame on `Http2Session` startup. |
| v8.9.3 | Added the `maxOutstandingPings` option with a default limit of 10. |
| v8.9.3 | Added the `maxHeaderListPairs` option with a default limit of 128 header pairs. |
| v8.4.0 | Added in: v8.4.0 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `allowHTTP1` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Incoming client connections that do not support HTTP/2 will be downgraded to HTTP/1.x when set to `true`. See the [`'unknownProtocol'`](#event-unknownprotocol) event. See [ALPN negotiation](#alpn-negotiation). **Default:** `false`.
+ `maxDeflateDynamicTableSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum dynamic table size for deflating header fields. **Default:** `4Kib`.
+ `maxSettings` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of settings entries per `SETTINGS` frame. The minimum value allowed is `1`. **Default:** `32`.
+ `maxSessionMemory`[<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum memory that the `Http2Session` is permitted to use. The value is expressed in terms of number of megabytes, e.g. `1` equal 1 megabyte. The minimum value allowed is `1`. This is a credit based limit, existing `Http2Stream`s may cause this limit to be exceeded, but new `Http2Stream` instances will be rejected while this limit is exceeded. The current number of `Http2Stream` sessions, the current memory use of the header compression tables, current data queued to be sent, and unacknowledged `PING` and `SETTINGS` frames are all counted towards the current limit. **Default:** `10`.
+ `maxHeaderListPairs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of header entries. This is similar to [`server.maxHeadersCount`](http#servermaxheaderscount) or [`request.maxHeadersCount`](http#requestmaxheaderscount) in the `node:http` module. The minimum value is `4`. **Default:** `128`.
+ `maxOutstandingPings` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of outstanding, unacknowledged pings. **Default:** `10`.
+ `maxSendHeaderBlockLength` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum allowed size for a serialized, compressed block of headers. Attempts to send headers that exceed this limit will result in a `'frameError'` event being emitted and the stream being closed and destroyed.
+ `paddingStrategy` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Strategy used for determining the amount of padding to use for `HEADERS` and `DATA` frames. **Default:** `http2.constants.PADDING_STRATEGY_NONE`. Value may be one of:
- `http2.constants.PADDING_STRATEGY_NONE`: No padding is applied.
- `http2.constants.PADDING_STRATEGY_MAX`: The maximum amount of padding, determined by the internal implementation, is applied.
- `http2.constants.PADDING_STRATEGY_ALIGNED`: Attempts to apply enough padding to ensure that the total frame length, including the 9-byte header, is a multiple of 8. For each frame, there is a maximum allowed number of padding bytes that is determined by current flow control state and settings. If this maximum is less than the calculated amount needed to ensure alignment, the maximum is used and the total frame length is not necessarily aligned at 8 bytes.
+ `peerMaxConcurrentStreams` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of concurrent streams for the remote peer as if a `SETTINGS` frame had been received. Will be overridden if the remote peer sets its own value for `maxConcurrentStreams`. **Default:** `100`.
+ `maxSessionInvalidFrames` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of invalid frames that will be tolerated before the session is closed. **Default:** `1000`.
+ `maxSessionRejectedStreams` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of rejected upon creation streams that will be tolerated before the session is closed. Each rejection is associated with an `NGHTTP2_ENHANCE_YOUR_CALM` error that should tell the peer to not open any more streams, continuing to open streams is therefore regarded as a sign of a misbehaving peer. **Default:** `100`.
+ `settings` [<HTTP/2 Settings Object>](http2#settings-object) The initial settings to send to the remote peer upon connection.
+ ...: Any [`tls.createServer()`](tls#tlscreateserveroptions-secureconnectionlistener) options can be provided. For servers, the identity options (`pfx` or `key`/`cert`) are usually required.
+ `origins` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) An array of origin strings to send within an `ORIGIN` frame immediately following creation of a new server `Http2Session`.
+ `unknownProtocolTimeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies a timeout in milliseconds that a server should wait when an [`'unknownProtocol'`](#event-unknownprotocol) event is emitted. If the socket has not been destroyed by that time the server will destroy it. **Default:** `10000`.
* `onRequestHandler` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) See [Compatibility API](#compatibility-api)
* Returns: [<Http2SecureServer>](http2#class-http2secureserver)
Returns a `tls.Server` instance that creates and manages `Http2Session` instances.
```
const http2 = require('node:http2');
const fs = require('node:fs');
const options = {
key: fs.readFileSync('server-key.pem'),
cert: fs.readFileSync('server-cert.pem')
};
// Create a secure HTTP/2 server
const server = http2.createSecureServer(options);
server.on('stream', (stream, headers) => {
stream.respond({
'content-type': 'text/html; charset=utf-8',
':status': 200
});
stream.end('<h1>Hello World</h1>');
});
server.listen(80);
```
####
`http2.connect(authority[, options][, listener])`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The `PADDING_STRATEGY_CALLBACK` has been made equivalent to providing `PADDING_STRATEGY_ALIGNED` and `selectPadding` has been removed. |
| v15.10.0, v14.16.0, v12.21.0, v10.24.0 | Added `unknownProtocolTimeout` option with a default of 10000. |
| v14.4.0, v12.18.0, v10.21.0 | Added `maxSettings` option with a default of 32. |
| v8.9.3 | Added the `maxOutstandingPings` option with a default limit of 10. |
| v8.9.3 | Added the `maxHeaderListPairs` option with a default limit of 128 header pairs. |
| v8.4.0 | Added in: v8.4.0 |
* `authority` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) The remote HTTP/2 server to connect to. This must be in the form of a minimal, valid URL with the `http://` or `https://` prefix, host name, and IP port (if a non-default port is used). Userinfo (user ID and password), path, querystring, and fragment details in the URL will be ignored.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `maxDeflateDynamicTableSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum dynamic table size for deflating header fields. **Default:** `4Kib`.
+ `maxSettings` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of settings entries per `SETTINGS` frame. The minimum value allowed is `1`. **Default:** `32`.
+ `maxSessionMemory`[<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum memory that the `Http2Session` is permitted to use. The value is expressed in terms of number of megabytes, e.g. `1` equal 1 megabyte. The minimum value allowed is `1`. This is a credit based limit, existing `Http2Stream`s may cause this limit to be exceeded, but new `Http2Stream` instances will be rejected while this limit is exceeded. The current number of `Http2Stream` sessions, the current memory use of the header compression tables, current data queued to be sent, and unacknowledged `PING` and `SETTINGS` frames are all counted towards the current limit. **Default:** `10`.
+ `maxHeaderListPairs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of header entries. This is similar to [`server.maxHeadersCount`](http#servermaxheaderscount) or [`request.maxHeadersCount`](http#requestmaxheaderscount) in the `node:http` module. The minimum value is `1`. **Default:** `128`.
+ `maxOutstandingPings` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of outstanding, unacknowledged pings. **Default:** `10`.
+ `maxReservedRemoteStreams` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of reserved push streams the client will accept at any given time. Once the current number of currently reserved push streams exceeds reaches this limit, new push streams sent by the server will be automatically rejected. The minimum allowed value is 0. The maximum allowed value is 232-1. A negative value sets this option to the maximum allowed value. **Default:** `200`.
+ `maxSendHeaderBlockLength` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum allowed size for a serialized, compressed block of headers. Attempts to send headers that exceed this limit will result in a `'frameError'` event being emitted and the stream being closed and destroyed.
+ `paddingStrategy` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Strategy used for determining the amount of padding to use for `HEADERS` and `DATA` frames. **Default:** `http2.constants.PADDING_STRATEGY_NONE`. Value may be one of:
- `http2.constants.PADDING_STRATEGY_NONE`: No padding is applied.
- `http2.constants.PADDING_STRATEGY_MAX`: The maximum amount of padding, determined by the internal implementation, is applied.
- `http2.constants.PADDING_STRATEGY_ALIGNED`: Attempts to apply enough padding to ensure that the total frame length, including the 9-byte header, is a multiple of 8. For each frame, there is a maximum allowed number of padding bytes that is determined by current flow control state and settings. If this maximum is less than the calculated amount needed to ensure alignment, the maximum is used and the total frame length is not necessarily aligned at 8 bytes.
+ `peerMaxConcurrentStreams` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets the maximum number of concurrent streams for the remote peer as if a `SETTINGS` frame had been received. Will be overridden if the remote peer sets its own value for `maxConcurrentStreams`. **Default:** `100`.
+ `protocol` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The protocol to connect with, if not set in the `authority`. Value may be either `'http:'` or `'https:'`. **Default:** `'https:'`
+ `settings` [<HTTP/2 Settings Object>](http2#settings-object) The initial settings to send to the remote peer upon connection.
+ `createConnection` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) An optional callback that receives the `URL` instance passed to `connect` and the `options` object, and returns any [`Duplex`](stream#class-streamduplex) stream that is to be used as the connection for this session.
+ ...: Any [`net.connect()`](net#netconnect) or [`tls.connect()`](tls#tlsconnectoptions-callback) options can be provided.
+ `unknownProtocolTimeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies a timeout in milliseconds that a server should wait when an [`'unknownProtocol'`](#event-unknownprotocol) event is emitted. If the socket has not been destroyed by that time the server will destroy it. **Default:** `10000`.
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Will be registered as a one-time listener of the [`'connect'`](#event-connect) event.
* Returns: [<ClientHttp2Session>](http2#class-clienthttp2session)
Returns a `ClientHttp2Session` instance.
```
const http2 = require('node:http2');
const client = http2.connect('https://localhost:1234');
/* Use the client */
client.close();
```
####
`http2.constants`
Added in: v8.4.0 ##### Error codes for `RST_STREAM` and `GOAWAY`
| Value | Name | Constant |
| --- | --- | --- |
| `0x00` | No Error | `http2.constants.NGHTTP2_NO_ERROR` |
| `0x01` | Protocol Error | `http2.constants.NGHTTP2_PROTOCOL_ERROR` |
| `0x02` | Internal Error | `http2.constants.NGHTTP2_INTERNAL_ERROR` |
| `0x03` | Flow Control Error | `http2.constants.NGHTTP2_FLOW_CONTROL_ERROR` |
| `0x04` | Settings Timeout | `http2.constants.NGHTTP2_SETTINGS_TIMEOUT` |
| `0x05` | Stream Closed | `http2.constants.NGHTTP2_STREAM_CLOSED` |
| `0x06` | Frame Size Error | `http2.constants.NGHTTP2_FRAME_SIZE_ERROR` |
| `0x07` | Refused Stream | `http2.constants.NGHTTP2_REFUSED_STREAM` |
| `0x08` | Cancel | `http2.constants.NGHTTP2_CANCEL` |
| `0x09` | Compression Error | `http2.constants.NGHTTP2_COMPRESSION_ERROR` |
| `0x0a` | Connect Error | `http2.constants.NGHTTP2_CONNECT_ERROR` |
| `0x0b` | Enhance Your Calm | `http2.constants.NGHTTP2_ENHANCE_YOUR_CALM` |
| `0x0c` | Inadequate Security | `http2.constants.NGHTTP2_INADEQUATE_SECURITY` |
| `0x0d` | HTTP/1.1 Required | `http2.constants.NGHTTP2_HTTP_1_1_REQUIRED` |
The `'timeout'` event is emitted when there is no activity on the Server for a given number of milliseconds set using `http2server.setTimeout()`.
####
`http2.getDefaultSettings()`
Added in: v8.4.0 * Returns: [<HTTP/2 Settings Object>](http2#settings-object)
Returns an object containing the default settings for an `Http2Session` instance. This method returns a new object instance every time it is called so instances returned may be safely modified for use.
####
`http2.getPackedSettings([settings])`
Added in: v8.4.0 * `settings` [<HTTP/2 Settings Object>](http2#settings-object)
* Returns: [<Buffer>](buffer#class-buffer)
Returns a `Buffer` instance containing serialized representation of the given HTTP/2 settings as specified in the [HTTP/2](https://tools.ietf.org/html/rfc7540) specification. This is intended for use with the `HTTP2-Settings` header field.
```
const http2 = require('node:http2');
const packed = http2.getPackedSettings({ enablePush: false });
console.log(packed.toString('base64'));
// Prints: AAIAAAAA
```
####
`http2.getUnpackedSettings(buf)`
Added in: v8.4.0 * `buf` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) The packed settings.
* Returns: [<HTTP/2 Settings Object>](http2#settings-object)
Returns a [HTTP/2 Settings Object](#settings-object) containing the deserialized settings from the given `Buffer` as generated by `http2.getPackedSettings()`.
####
`http2.sensitiveHeaders`
Added in: v15.0.0, v14.18.0 * [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
This symbol can be set as a property on the HTTP/2 headers object with an array value in order to provide a list of headers considered sensitive. See [Sensitive headers](#sensitive-headers) for more details.
#### Headers object
Headers are represented as own-properties on JavaScript objects. The property keys will be serialized to lower-case. Property values should be strings (if they are not they will be coerced to strings) or an `Array` of strings (in order to send more than one value per header field).
```
const headers = {
':status': '200',
'content-type': 'text-plain',
'ABC': ['has', 'more', 'than', 'one', 'value']
};
stream.respond(headers);
```
Header objects passed to callback functions will have a `null` prototype. This means that normal JavaScript object methods such as `Object.prototype.toString()` and `Object.prototype.hasOwnProperty()` will not work.
For incoming headers:
* The `:status` header is converted to `number`.
* Duplicates of `:status`, `:method`, `:authority`, `:scheme`, `:path`, `:protocol`, `age`, `authorization`, `access-control-allow-credentials`, `access-control-max-age`, `access-control-request-method`, `content-encoding`, `content-language`, `content-length`, `content-location`, `content-md5`, `content-range`, `content-type`, `date`, `dnt`, `etag`, `expires`, `from`, `host`, `if-match`, `if-modified-since`, `if-none-match`, `if-range`, `if-unmodified-since`, `last-modified`, `location`, `max-forwards`, `proxy-authorization`, `range`, `referer`,`retry-after`, `tk`, `upgrade-insecure-requests`, `user-agent` or `x-content-type-options` are discarded.
* `set-cookie` is always an array. Duplicates are added to the array.
* For duplicate `cookie` headers, the values are joined together with '; '.
* For all other headers, the values are joined together with ', '.
```
const http2 = require('node:http2');
const server = http2.createServer();
server.on('stream', (stream, headers) => {
console.log(headers[':path']);
console.log(headers.ABC);
});
```
##### Sensitive headers
HTTP2 headers can be marked as sensitive, which means that the HTTP/2 header compression algorithm will never index them. This can make sense for header values with low entropy and that may be considered valuable to an attacker, for example `Cookie` or `Authorization`. To achieve this, add the header name to the `[http2.sensitiveHeaders]` property as an array:
```
const headers = {
':status': '200',
'content-type': 'text-plain',
'cookie': 'some-cookie',
'other-sensitive-header': 'very secret data',
[http2.sensitiveHeaders]: ['cookie', 'other-sensitive-header']
};
stream.respond(headers);
```
For some headers, such as `Authorization` and short `Cookie` headers, this flag is set automatically.
This property is also set for received headers. It will contain the names of all headers marked as sensitive, including ones marked that way automatically.
#### Settings object
History
| Version | Changes |
| --- | --- |
| v12.12.0 | The `maxConcurrentStreams` setting is stricter. |
| v8.9.3 | The `maxHeaderListSize` setting is now strictly enforced. |
| v8.4.0 | Added in: v8.4.0 |
The `http2.getDefaultSettings()`, `http2.getPackedSettings()`, `http2.createServer()`, `http2.createSecureServer()`, `http2session.settings()`, `http2session.localSettings`, and `http2session.remoteSettings` APIs either return or receive as input an object that defines configuration settings for an `Http2Session` object. These objects are ordinary JavaScript objects containing the following properties.
* `headerTableSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the maximum number of bytes used for header compression. The minimum allowed value is 0. The maximum allowed value is 232-1. **Default:** `4096`.
* `enablePush` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Specifies `true` if HTTP/2 Push Streams are to be permitted on the `Http2Session` instances. **Default:** `true`.
* `initialWindowSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the *sender's* initial window size in bytes for stream-level flow control. The minimum allowed value is 0. The maximum allowed value is 232-1. **Default:** `65535`.
* `maxFrameSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the size in bytes of the largest frame payload. The minimum allowed value is 16,384. The maximum allowed value is 224-1. **Default:** `16384`.
* `maxConcurrentStreams` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the maximum number of concurrent streams permitted on an `Http2Session`. There is no default value which implies, at least theoretically, 232-1 streams may be open concurrently at any given time in an `Http2Session`. The minimum value is 0. The maximum allowed value is 232-1. **Default:** `4294967295`.
* `maxHeaderListSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the maximum size (uncompressed octets) of header list that will be accepted. The minimum allowed value is 0. The maximum allowed value is 232-1. **Default:** `65535`.
* `maxHeaderSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Alias for `maxHeaderListSize`.
* `enableConnectProtocol`[<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Specifies `true` if the "Extended Connect Protocol" defined by [RFC 8441](https://tools.ietf.org/html/rfc8441) is to be enabled. This setting is only meaningful if sent by the server. Once the `enableConnectProtocol` setting has been enabled for a given `Http2Session`, it cannot be disabled. **Default:** `false`.
All additional properties on the settings object are ignored.
#### Error handling
There are several types of error conditions that may arise when using the `node:http2` module:
Validation errors occur when an incorrect argument, option, or setting value is passed in. These will always be reported by a synchronous `throw`.
State errors occur when an action is attempted at an incorrect time (for instance, attempting to send data on a stream after it has closed). These will be reported using either a synchronous `throw` or via an `'error'` event on the `Http2Stream`, `Http2Session` or HTTP/2 Server objects, depending on where and when the error occurs.
Internal errors occur when an HTTP/2 session fails unexpectedly. These will be reported via an `'error'` event on the `Http2Session` or HTTP/2 Server objects.
Protocol errors occur when various HTTP/2 protocol constraints are violated. These will be reported using either a synchronous `throw` or via an `'error'` event on the `Http2Stream`, `Http2Session` or HTTP/2 Server objects, depending on where and when the error occurs.
#### Invalid character handling in header names and values
The HTTP/2 implementation applies stricter handling of invalid characters in HTTP header names and values than the HTTP/1 implementation.
Header field names are *case-insensitive* and are transmitted over the wire strictly as lower-case strings. The API provided by Node.js allows header names to be set as mixed-case strings (e.g. `Content-Type`) but will convert those to lower-case (e.g. `content-type`) upon transmission.
Header field-names *must only* contain one or more of the following ASCII characters: `a`-`z`, `A`-`Z`, `0`-`9`, `!`, `#`, `$`, `%`, `&`, `'`, `*`, `+`, `-`, `.`, `^`, `_`, ``` (backtick), `|`, and `~`.
Using invalid characters within an HTTP header field name will cause the stream to be closed with a protocol error being reported.
Header field values are handled with more leniency but *should* not contain new-line or carriage return characters and *should* be limited to US-ASCII characters, per the requirements of the HTTP specification.
#### Push streams on the client
To receive pushed streams on the client, set a listener for the `'stream'` event on the `ClientHttp2Session`:
```
const http2 = require('node:http2');
const client = http2.connect('http://localhost');
client.on('stream', (pushedStream, requestHeaders) => {
pushedStream.on('push', (responseHeaders) => {
// Process response headers
});
pushedStream.on('data', (chunk) => { /* handle pushed data */ });
});
const req = client.request({ ':path': '/' });
```
#### Supporting the `CONNECT` method
The `CONNECT` method is used to allow an HTTP/2 server to be used as a proxy for TCP/IP connections.
A simple TCP Server:
```
const net = require('node:net');
const server = net.createServer((socket) => {
let name = '';
socket.setEncoding('utf8');
socket.on('data', (chunk) => name += chunk);
socket.on('end', () => socket.end(`hello ${name}`));
});
server.listen(8000);
```
An HTTP/2 CONNECT proxy:
```
const http2 = require('node:http2');
const { NGHTTP2_REFUSED_STREAM } = http2.constants;
const net = require('node:net');
const proxy = http2.createServer();
proxy.on('stream', (stream, headers) => {
if (headers[':method'] !== 'CONNECT') {
// Only accept CONNECT requests
stream.close(NGHTTP2_REFUSED_STREAM);
return;
}
const auth = new URL(`tcp://${headers[':authority']}`);
// It's a very good idea to verify that hostname and port are
// things this proxy should be connecting to.
const socket = net.connect(auth.port, auth.hostname, () => {
stream.respond();
socket.pipe(stream);
stream.pipe(socket);
});
socket.on('error', (error) => {
stream.close(http2.constants.NGHTTP2_CONNECT_ERROR);
});
});
proxy.listen(8001);
```
An HTTP/2 CONNECT client:
```
const http2 = require('node:http2');
const client = http2.connect('http://localhost:8001');
// Must not specify the ':path' and ':scheme' headers
// for CONNECT requests or an error will be thrown.
const req = client.request({
':method': 'CONNECT',
':authority': `localhost:${port}`
});
req.on('response', (headers) => {
console.log(headers[http2.constants.HTTP2_HEADER_STATUS]);
});
let data = '';
req.setEncoding('utf8');
req.on('data', (chunk) => data += chunk);
req.on('end', () => {
console.log(`The server says: ${data}`);
client.close();
});
req.end('Jane');
```
#### The extended `CONNECT` protocol
[RFC 8441](https://tools.ietf.org/html/rfc8441) defines an "Extended CONNECT Protocol" extension to HTTP/2 that may be used to bootstrap the use of an `Http2Stream` using the `CONNECT` method as a tunnel for other communication protocols (such as WebSockets).
The use of the Extended CONNECT Protocol is enabled by HTTP/2 servers by using the `enableConnectProtocol` setting:
```
const http2 = require('node:http2');
const settings = { enableConnectProtocol: true };
const server = http2.createServer({ settings });
```
Once the client receives the `SETTINGS` frame from the server indicating that the extended CONNECT may be used, it may send `CONNECT` requests that use the `':protocol'` HTTP/2 pseudo-header:
```
const http2 = require('node:http2');
const client = http2.connect('http://localhost:8080');
client.on('remoteSettings', (settings) => {
if (settings.enableConnectProtocol) {
const req = client.request({ ':method': 'CONNECT', ':protocol': 'foo' });
// ...
}
});
```
### Compatibility API
The Compatibility API has the goal of providing a similar developer experience of HTTP/1 when using HTTP/2, making it possible to develop applications that support both [HTTP/1](http) and HTTP/2. This API targets only the **public API** of the [HTTP/1](http). However many modules use internal methods or state, and those *are not supported* as it is a completely different implementation.
The following example creates an HTTP/2 server using the compatibility API:
```
const http2 = require('node:http2');
const server = http2.createServer((req, res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, { 'Content-Type': 'text/plain; charset=utf-8' });
res.end('ok');
});
```
In order to create a mixed [HTTPS](https) and HTTP/2 server, refer to the [ALPN negotiation](#alpn-negotiation) section. Upgrading from non-tls HTTP/1 servers is not supported.
The HTTP/2 compatibility API is composed of [`Http2ServerRequest`](#class-http2http2serverrequest) and [`Http2ServerResponse`](#class-http2http2serverresponse). They aim at API compatibility with HTTP/1, but they do not hide the differences between the protocols. As an example, the status message for HTTP codes is ignored.
#### ALPN negotiation
ALPN negotiation allows supporting both [HTTPS](https) and HTTP/2 over the same socket. The `req` and `res` objects can be either HTTP/1 or HTTP/2, and an application **must** restrict itself to the public API of [HTTP/1](http), and detect if it is possible to use the more advanced features of HTTP/2.
The following example creates a server that supports both protocols:
```
const { createSecureServer } = require('node:http2');
const { readFileSync } = require('node:fs');
const cert = readFileSync('./cert.pem');
const key = readFileSync('./key.pem');
const server = createSecureServer(
{ cert, key, allowHTTP1: true },
onRequest
).listen(4443);
function onRequest(req, res) {
// Detects if it is a HTTPS request or HTTP/2
const { socket: { alpnProtocol } } = req.httpVersion === '2.0' ?
req.stream.session : req;
res.writeHead(200, { 'content-type': 'application/json' });
res.end(JSON.stringify({
alpnProtocol,
httpVersion: req.httpVersion
}));
}
```
The `'request'` event works identically on both [HTTPS](https) and HTTP/2.
#### Class: `http2.Http2ServerRequest`
Added in: v8.4.0 * Extends: [<stream.Readable>](stream#class-streamreadable)
A `Http2ServerRequest` object is created by [`http2.Server`](#class-http2server) or [`http2.SecureServer`](#class-http2secureserver) and passed as the first argument to the [`'request'`](#event-request) event. It may be used to access a request status, headers, and data.
##### Event: `'aborted'`
Added in: v8.4.0 The `'aborted'` event is emitted whenever a `Http2ServerRequest` instance is abnormally aborted in mid-communication.
The `'aborted'` event will only be emitted if the `Http2ServerRequest` writable side has not been ended.
##### Event: `'close'`
Added in: v8.4.0 Indicates that the underlying [`Http2Stream`](#class-http2stream) was closed. Just like `'end'`, this event occurs only once per response.
#####
`request.aborted`
Added in: v10.1.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `request.aborted` property will be `true` if the request has been aborted.
#####
`request.authority`
Added in: v8.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The request authority pseudo header field. Because HTTP/2 allows requests to set either `:authority` or `host`, this value is derived from `req.headers[':authority']` if present. Otherwise, it is derived from `req.headers['host']`.
#####
`request.complete`
Added in: v12.10.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `request.complete` property will be `true` if the request has been completed, aborted, or destroyed.
#####
`request.connection`
Added in: v8.4.0Deprecated since: v13.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Use [`request.socket`](#requestsocket).
* [<net.Socket>](net#class-netsocket) | [<tls.TLSSocket>](tls#class-tlstlssocket)
See [`request.socket`](#requestsocket).
#####
`request.destroy([error])`
Added in: v8.4.0 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Calls `destroy()` on the [`Http2Stream`](#class-http2stream) that received the [`Http2ServerRequest`](#class-http2http2serverrequest). If `error` is provided, an `'error'` event is emitted and `error` is passed as an argument to any listeners on the event.
It does nothing if the stream was already destroyed.
#####
`request.headers`
Added in: v8.4.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The request/response headers object.
Key-value pairs of header names and values. Header names are lower-cased.
```
// Prints something like:
//
// { 'user-agent': 'curl/7.22.0',
// host: '127.0.0.1:8000',
// accept: '*/*' }
console.log(request.headers);
```
See [HTTP/2 Headers Object](#headers-object).
In HTTP/2, the request path, host name, protocol, and method are represented as special headers prefixed with the `:` character (e.g. `':path'`). These special headers will be included in the `request.headers` object. Care must be taken not to inadvertently modify these special headers or errors may occur. For instance, removing all headers from the request will cause errors to occur:
```
removeAllHeaders(request.headers);
assert(request.url); // Fails because the :path header has been removed
```
#####
`request.httpVersion`
Added in: v8.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
In case of server request, the HTTP version sent by the client. In the case of client response, the HTTP version of the connected-to server. Returns `'2.0'`.
Also `message.httpVersionMajor` is the first integer and `message.httpVersionMinor` is the second.
#####
`request.method`
Added in: v8.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The request method as a string. Read-only. Examples: `'GET'`, `'DELETE'`.
#####
`request.rawHeaders`
Added in: v8.4.0 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The raw request/response headers list exactly as they were received.
The keys and values are in the same list. It is *not* a list of tuples. So, the even-numbered offsets are key values, and the odd-numbered offsets are the associated values.
Header names are not lowercased, and duplicates are not merged.
```
// Prints something like:
//
// [ 'user-agent',
// 'this is invalid because there can be only one',
// 'User-Agent',
// 'curl/7.22.0',
// 'Host',
// '127.0.0.1:8000',
// 'ACCEPT',
// '*/*' ]
console.log(request.rawHeaders);
```
#####
`request.rawTrailers`
Added in: v8.4.0 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The raw request/response trailer keys and values exactly as they were received. Only populated at the `'end'` event.
#####
`request.scheme`
Added in: v8.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The request scheme pseudo header field indicating the scheme portion of the target URL.
#####
`request.setTimeout(msecs, callback)`
Added in: v8.4.0 * `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<http2.Http2ServerRequest>](http2#class-http2http2serverrequest)
Sets the [`Http2Stream`](#class-http2stream)'s timeout value to `msecs`. If a callback is provided, then it is added as a listener on the `'timeout'` event on the response object.
If no `'timeout'` listener is added to the request, the response, or the server, then [`Http2Stream`](#class-http2stream)s are destroyed when they time out. If a handler is assigned to the request, the response, or the server's `'timeout'` events, timed out sockets must be handled explicitly.
#####
`request.socket`
Added in: v8.4.0 * [<net.Socket>](net#class-netsocket) | [<tls.TLSSocket>](tls#class-tlstlssocket)
Returns a `Proxy` object that acts as a `net.Socket` (or `tls.TLSSocket`) but applies getters, setters, and methods based on HTTP/2 logic.
`destroyed`, `readable`, and `writable` properties will be retrieved from and set on `request.stream`.
`destroy`, `emit`, `end`, `on` and `once` methods will be called on `request.stream`.
`setTimeout` method will be called on `request.stream.session`.
`pause`, `read`, `resume`, and `write` will throw an error with code `ERR_HTTP2_NO_SOCKET_MANIPULATION`. See [`Http2Session` and Sockets](#http2session-and-sockets) for more information.
All other interactions will be routed directly to the socket. With TLS support, use [`request.socket.getPeerCertificate()`](tls#tlssocketgetpeercertificatedetailed) to obtain the client's authentication details.
#####
`request.stream`
Added in: v8.4.0 * [<Http2Stream>](http2#class-http2stream)
The [`Http2Stream`](#class-http2stream) object backing the request.
#####
`request.trailers`
Added in: v8.4.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The request/response trailers object. Only populated at the `'end'` event.
#####
`request.url`
Added in: v8.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Request URL string. This contains only the URL that is present in the actual HTTP request. If the request is:
```
GET /status?name=ryan HTTP/1.1
Accept: text/plain
```
Then `request.url` will be:
```
'/status?name=ryan'
```
To parse the url into its parts, `new URL()` can be used:
```
$ node
> new URL('/status?name=ryan', 'http://example.com')
URL {
href: 'http://example.com/status?name=ryan',
origin: 'http://example.com',
protocol: 'http:',
username: '',
password: '',
host: 'example.com',
hostname: 'example.com',
port: '',
pathname: '/status',
search: '?name=ryan',
searchParams: URLSearchParams { 'name' => 'ryan' },
hash: ''
}
```
#### Class: `http2.Http2ServerResponse`
Added in: v8.4.0 * Extends: [<Stream>](stream#stream)
This object is created internally by an HTTP server, not by the user. It is passed as the second parameter to the [`'request'`](#event-request) event.
##### Event: `'close'`
Added in: v8.4.0 Indicates that the underlying [`Http2Stream`](#class-http2stream) was terminated before [`response.end()`](#responseenddata-encoding-callback) was called or able to flush.
##### Event: `'finish'`
Added in: v8.4.0 Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the HTTP/2 multiplexing for transmission over the network. It does not imply that the client has received anything yet.
After this event, no more events will be emitted on the response object.
#####
`response.addTrailers(headers)`
Added in: v8.4.0 * `headers` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
This method adds HTTP trailing headers (a header but at the end of the message) to the response.
Attempting to set a header field name or value that contains invalid characters will result in a [`TypeError`](errors#class-typeerror) being thrown.
#####
`response.connection`
Added in: v8.4.0Deprecated since: v13.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Use [`response.socket`](#responsesocket).
* [<net.Socket>](net#class-netsocket) | [<tls.TLSSocket>](tls#class-tlstlssocket)
See [`response.socket`](#responsesocket).
#####
`response.createPushResponse(headers, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v8.4.0 | Added in: v8.4.0 |
* `headers` [<HTTP/2 Headers Object>](http2#headers-object) An object describing the headers
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called once `http2stream.pushStream()` is finished, or either when the attempt to create the pushed `Http2Stream` has failed or has been rejected, or the state of `Http2ServerRequest` is closed prior to calling the `http2stream.pushStream()` method
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `res` [<http2.Http2ServerResponse>](http2#class-http2http2serverresponse) The newly-created `Http2ServerResponse` object
Call [`http2stream.pushStream()`](#http2streampushstreamheaders-options-callback) with the given headers, and wrap the given [`Http2Stream`](#class-http2stream) on a newly created `Http2ServerResponse` as the callback parameter if successful. When `Http2ServerRequest` is closed, the callback is called with an error `ERR_HTTP2_INVALID_STREAM`.
#####
`response.end([data[, encoding]][, callback])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | This method now returns a reference to `ServerResponse`. |
| v8.4.0 | Added in: v8.4.0 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
This method signals to the server that all of the response headers and body have been sent; that server should consider this message complete. The method, `response.end()`, MUST be called on each response.
If `data` is specified, it is equivalent to calling [`response.write(data, encoding)`](http#responsewritechunk-encoding-callback) followed by `response.end(callback)`.
If `callback` is specified, it will be called when the response stream is finished.
#####
`response.finished`
Added in: v8.4.0Deprecated since: v13.4.0, v12.16.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Use [`response.writableEnded`](#responsewritableended).
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Boolean value that indicates whether the response has completed. Starts as `false`. After [`response.end()`](#responseenddata-encoding-callback) executes, the value will be `true`.
#####
`response.getHeader(name)`
Added in: v8.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Reads out a header that has already been queued but not sent to the client. The name is case-insensitive.
```
const contentType = response.getHeader('content-type');
```
#####
`response.getHeaderNames()`
Added in: v8.4.0 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns an array containing the unique names of the current outgoing headers. All header names are lowercase.
```
response.setHeader('Foo', 'bar');
response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']);
const headerNames = response.getHeaderNames();
// headerNames === ['foo', 'set-cookie']
```
#####
`response.getHeaders()`
Added in: v8.4.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related http module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase.
The object returned by the `response.getHeaders()` method *does not* prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and *will not work*.
```
response.setHeader('Foo', 'bar');
response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']);
const headers = response.getHeaders();
// headers === { foo: 'bar', 'set-cookie': ['foo=bar', 'bar=baz'] }
```
#####
`response.hasHeader(name)`
Added in: v8.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the header identified by `name` is currently set in the outgoing headers. The header name matching is case-insensitive.
```
const hasContentType = response.hasHeader('content-type');
```
#####
`response.headersSent`
Added in: v8.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
True if headers were sent, false otherwise (read-only).
#####
`response.removeHeader(name)`
Added in: v8.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Removes a header that has been queued for implicit sending.
```
response.removeHeader('Content-Encoding');
```
####
`response.req`
Added in: v15.7.0 * [<http2.Http2ServerRequest>](http2#class-http2http2serverrequest)
A reference to the original HTTP2 `request` object.
#####
`response.sendDate`
Added in: v8.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
When true, the Date header will be automatically generated and sent in the response if it is not already present in the headers. Defaults to true.
This should only be disabled for testing; HTTP requires the Date header in responses.
#####
`response.setHeader(name, value)`
Added in: v8.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here to send multiple headers with the same name.
```
response.setHeader('Content-Type', 'text/html; charset=utf-8');
```
or
```
response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']);
```
Attempting to set a header field name or value that contains invalid characters will result in a [`TypeError`](errors#class-typeerror) being thrown.
When headers have been set with [`response.setHeader()`](#responsesetheadername-value), they will be merged with any headers passed to [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers), with the headers passed to [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) given precedence.
```
// Returns content-type = text/plain
const server = http2.createServer((req, res) => {
res.setHeader('Content-Type', 'text/html; charset=utf-8');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, { 'Content-Type': 'text/plain; charset=utf-8' });
res.end('ok');
});
```
#####
`response.setTimeout(msecs[, callback])`
Added in: v8.4.0 * `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<http2.Http2ServerResponse>](http2#class-http2http2serverresponse)
Sets the [`Http2Stream`](#class-http2stream)'s timeout value to `msecs`. If a callback is provided, then it is added as a listener on the `'timeout'` event on the response object.
If no `'timeout'` listener is added to the request, the response, or the server, then [`Http2Stream`](#class-http2stream)s are destroyed when they time out. If a handler is assigned to the request, the response, or the server's `'timeout'` events, timed out sockets must be handled explicitly.
#####
`response.socket`
Added in: v8.4.0 * [<net.Socket>](net#class-netsocket) | [<tls.TLSSocket>](tls#class-tlstlssocket)
Returns a `Proxy` object that acts as a `net.Socket` (or `tls.TLSSocket`) but applies getters, setters, and methods based on HTTP/2 logic.
`destroyed`, `readable`, and `writable` properties will be retrieved from and set on `response.stream`.
`destroy`, `emit`, `end`, `on` and `once` methods will be called on `response.stream`.
`setTimeout` method will be called on `response.stream.session`.
`pause`, `read`, `resume`, and `write` will throw an error with code `ERR_HTTP2_NO_SOCKET_MANIPULATION`. See [`Http2Session` and Sockets](#http2session-and-sockets) for more information.
All other interactions will be routed directly to the socket.
```
const http2 = require('node:http2');
const server = http2.createServer((req, res) => {
const ip = req.socket.remoteAddress;
const port = req.socket.remotePort;
res.end(`Your IP address is ${ip} and your source port is ${port}.`);
}).listen(3000);
```
#####
`response.statusCode`
Added in: v8.4.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
When using implicit headers (not calling [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) explicitly), this property controls the status code that will be sent to the client when the headers get flushed.
```
response.statusCode = 404;
```
After response header was sent to the client, this property indicates the status code which was sent out.
#####
`response.statusMessage`
Added in: v8.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Status message is not supported by HTTP/2 (RFC 7540 8.1.2.4). It returns an empty string.
#####
`response.stream`
Added in: v8.4.0 * [<Http2Stream>](http2#class-http2stream)
The [`Http2Stream`](#class-http2stream) object backing the response.
#####
`response.writableEnded`
Added in: v12.9.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` after [`response.end()`](#responseenddata-encoding-callback) has been called. This property does not indicate whether the data has been flushed, for this use [`writable.writableFinished`](stream#writablewritablefinished) instead.
#####
`response.write(chunk[, encoding][, callback])`
Added in: v8.4.0 * `chunk` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If this method is called and [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) has not been called, it will switch to implicit header mode and flush the implicit headers.
This sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.
In the `node:http` module, the response body is omitted when the request is a HEAD request. Similarly, the `204` and `304` responses *must not* include a message body.
`chunk` can be a string or a buffer. If `chunk` is a string, the second parameter specifies how to encode it into a byte stream. By default the `encoding` is `'utf8'`. `callback` will be called when this chunk of data is flushed.
This is the raw HTTP body and has nothing to do with higher-level multi-part body encodings that may be used.
The first time [`response.write()`](#responsewritechunk-encoding-callback) is called, it will send the buffered header information and the first chunk of the body to the client. The second time [`response.write()`](#responsewritechunk-encoding-callback) is called, Node.js assumes data will be streamed, and sends the new data separately. That is, the response is buffered up to the first chunk of the body.
Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in user memory. `'drain'` will be emitted when the buffer is free again.
#####
`response.writeContinue()`
Added in: v8.4.0 Sends a status `100 Continue` to the client, indicating that the request body should be sent. See the [`'checkContinue'`](#event-checkcontinue) event on `Http2Server` and `Http2SecureServer`.
####
`response.writeEarlyHints(links)`
Added in: v18.11.0 * `links` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)
Sends a status `103 Early Hints` to the client with a Link header, indicating that the user agent can preload/preconnect the linked resources. The `links` can be a string or an array of strings containing the values of the `Link` header.
**Example**
```
const earlyHintsLink = '</styles.css>; rel=preload; as=style';
response.writeEarlyHints(earlyHintsLink);
const earlyHintsLinks = [
'</styles.css>; rel=preload; as=style',
'</scripts.js>; rel=preload; as=script',
];
response.writeEarlyHints(earlyHintsLinks);
```
#####
`response.writeHead(statusCode[, statusMessage][, headers])`
History
| Version | Changes |
| --- | --- |
| v11.10.0, v10.17.0 | Return `this` from `writeHead()` to allow chaining with `end()`. |
| v8.4.0 | Added in: v8.4.0 |
* `statusCode` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `statusMessage` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `headers` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)
* Returns: [<http2.Http2ServerResponse>](http2#class-http2http2serverresponse)
Sends a response header to the request. The status code is a 3-digit HTTP status code, like `404`. The last argument, `headers`, are the response headers.
Returns a reference to the `Http2ServerResponse`, so that calls can be chained.
For compatibility with [HTTP/1](http), a human-readable `statusMessage` may be passed as the second argument. However, because the `statusMessage` has no meaning within HTTP/2, the argument will have no effect and a process warning will be emitted.
```
const body = 'hello world';
response.writeHead(200, {
'Content-Length': Buffer.byteLength(body),
'Content-Type': 'text/plain; charset=utf-8',
});
```
`Content-Length` is given in bytes not characters. The `Buffer.byteLength()` API may be used to determine the number of bytes in a given encoding. On outbound messages, Node.js does not check if Content-Length and the length of the body being transmitted are equal or not. However, when receiving messages, Node.js will automatically reject messages when the `Content-Length` does not match the actual payload size.
This method may be called at most one time on a message before [`response.end()`](#responseenddata-encoding-callback) is called.
If [`response.write()`](#responsewritechunk-encoding-callback) or [`response.end()`](#responseenddata-encoding-callback) are called before calling this, the implicit/mutable headers will be calculated and call this function.
When headers have been set with [`response.setHeader()`](#responsesetheadername-value), they will be merged with any headers passed to [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers), with the headers passed to [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) given precedence.
```
// Returns content-type = text/plain
const server = http2.createServer((req, res) => {
res.setHeader('Content-Type', 'text/html; charset=utf-8');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, { 'Content-Type': 'text/plain; charset=utf-8' });
res.end('ok');
});
```
Attempting to set a header field name or value that contains invalid characters will result in a [`TypeError`](errors#class-typeerror) being thrown.
### Collecting HTTP/2 performance metrics
The [Performance Observer](perf_hooks) API can be used to collect basic performance metrics for each `Http2Session` and `Http2Stream` instance.
```
const { PerformanceObserver } = require('node:perf_hooks');
const obs = new PerformanceObserver((items) => {
const entry = items.getEntries()[0];
console.log(entry.entryType); // prints 'http2'
if (entry.name === 'Http2Session') {
// Entry contains statistics about the Http2Session
} else if (entry.name === 'Http2Stream') {
// Entry contains statistics about the Http2Stream
}
});
obs.observe({ entryTypes: ['http2'] });
```
The `entryType` property of the `PerformanceEntry` will be equal to `'http2'`.
The `name` property of the `PerformanceEntry` will be equal to either `'Http2Stream'` or `'Http2Session'`.
If `name` is equal to `Http2Stream`, the `PerformanceEntry` will contain the following additional properties:
* `bytesRead` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of `DATA` frame bytes received for this `Http2Stream`.
* `bytesWritten` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of `DATA` frame bytes sent for this `Http2Stream`.
* `id` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The identifier of the associated `Http2Stream`
* `timeToFirstByte` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first `DATA` frame.
* `timeToFirstByteSent` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and sending of the first `DATA` frame.
* `timeToFirstHeader` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first header.
If `name` is equal to `Http2Session`, the `PerformanceEntry` will contain the following additional properties:
* `bytesRead` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes received for this `Http2Session`.
* `bytesWritten` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes sent for this `Http2Session`.
* `framesReceived` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of HTTP/2 frames received by the `Http2Session`.
* `framesSent` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of HTTP/2 frames sent by the `Http2Session`.
* `maxConcurrentStreams` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum number of streams concurrently open during the lifetime of the `Http2Session`.
* `pingRTT` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds elapsed since the transmission of a `PING` frame and the reception of its acknowledgment. Only present if a `PING` frame has been sent on the `Http2Session`.
* `streamAverageDuration` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The average duration (in milliseconds) for all `Http2Stream` instances.
* `streamCount` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of `Http2Stream` instances processed by the `Http2Session`.
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'server'` or `'client'` to identify the type of `Http2Session`.
### Note on `:authority` and `host`
HTTP/2 requires requests to have either the `:authority` pseudo-header or the `host` header. Prefer `:authority` when constructing an HTTP/2 request directly, and `host` when converting from HTTP/1 (in proxies, for instance).
The compatibility API falls back to `host` if `:authority` is not present. See [`request.authority`](#requestauthority) for more information. However, if you don't use the compatibility API (or use `req.headers` directly), you need to implement any fall-back behavior yourself.
| programming_docs |
node None Stream[[src]](https://github.com/nodejs/node/blob/6ac3a22f89ae43402d41166baf44266e60595fcb/lib/stream.js#L53)
-------------------------------------------------------------------------------------------------------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/stream.js](https://github.com/nodejs/node/blob/v19.0.1/lib/stream.js)
A stream is an abstract interface for working with streaming data in Node.js. The `node:stream` module provides an API for implementing the stream interface.
There are many stream objects provided by Node.js. For instance, a [request to an HTTP server](http#class-httpincomingmessage) and [`process.stdout`](process#processstdout) are both stream instances.
Streams can be readable, writable, or both. All streams are instances of [`EventEmitter`](events#class-eventemitter).
To access the `node:stream` module:
```
const stream = require('node:stream');
```
The `node:stream` module is useful for creating new types of stream instances. It is usually not necessary to use the `node:stream` module to consume streams.
### Organization of this document
This document contains two primary sections and a third section for notes. The first section explains how to use existing streams within an application. The second section explains how to create new types of streams.
### Types of streams
There are four fundamental stream types within Node.js:
* [`Writable`](#class-streamwritable): streams to which data can be written (for example, [`fs.createWriteStream()`](fs#fscreatewritestreampath-options)).
* [`Readable`](#class-streamreadable): streams from which data can be read (for example, [`fs.createReadStream()`](fs#fscreatereadstreampath-options)).
* [`Duplex`](#class-streamduplex): streams that are both `Readable` and `Writable` (for example, [`net.Socket`](net#class-netsocket)).
* [`Transform`](#class-streamtransform): `Duplex` streams that can modify or transform the data as it is written and read (for example, [`zlib.createDeflate()`](zlib#zlibcreatedeflateoptions)).
Additionally, this module includes the utility functions [`stream.pipeline()`](#streampipelinesource-transforms-destination-callback), [`stream.finished()`](#streamfinishedstream-options-callback), [`stream.Readable.from()`](#streamreadablefromiterable-options) and [`stream.addAbortSignal()`](#streamaddabortsignalsignal-stream).
#### Streams Promises API
Added in: v15.0.0 The `stream/promises` API provides an alternative set of asynchronous utility functions for streams that return `Promise` objects rather than using callbacks. The API is accessible via `require('node:stream/promises')` or `require('node:stream').promises`.
#### Object mode
All streams created by Node.js APIs operate exclusively on strings and `Buffer` (or `Uint8Array`) objects. It is possible, however, for stream implementations to work with other types of JavaScript values (with the exception of `null`, which serves a special purpose within streams). Such streams are considered to operate in "object mode".
Stream instances are switched into object mode using the `objectMode` option when the stream is created. Attempting to switch an existing stream into object mode is not safe.
#### Buffering
Both [`Writable`](#class-streamwritable) and [`Readable`](#class-streamreadable) streams will store data in an internal buffer.
The amount of data potentially buffered depends on the `highWaterMark` option passed into the stream's constructor. For normal streams, the `highWaterMark` option specifies a [total number of bytes](#highwatermark-discrepancy-after-calling-readablesetencoding). For streams operating in object mode, the `highWaterMark` specifies a total number of objects.
Data is buffered in `Readable` streams when the implementation calls [`stream.push(chunk)`](#readablepushchunk-encoding). If the consumer of the Stream does not call [`stream.read()`](#readablereadsize), the data will sit in the internal queue until it is consumed.
Once the total size of the internal read buffer reaches the threshold specified by `highWaterMark`, the stream will temporarily stop reading data from the underlying resource until the data currently buffered can be consumed (that is, the stream will stop calling the internal [`readable._read()`](#readable_readsize) method that is used to fill the read buffer).
Data is buffered in `Writable` streams when the [`writable.write(chunk)`](#writablewritechunk-encoding-callback) method is called repeatedly. While the total size of the internal write buffer is below the threshold set by `highWaterMark`, calls to `writable.write()` will return `true`. Once the size of the internal buffer reaches or exceeds the `highWaterMark`, `false` will be returned.
A key goal of the `stream` API, particularly the [`stream.pipe()`](#readablepipedestination-options) method, is to limit the buffering of data to acceptable levels such that sources and destinations of differing speeds will not overwhelm the available memory.
The `highWaterMark` option is a threshold, not a limit: it dictates the amount of data that a stream buffers before it stops asking for more data. It does not enforce a strict memory limitation in general. Specific stream implementations may choose to enforce stricter limits but doing so is optional.
Because [`Duplex`](#class-streamduplex) and [`Transform`](#class-streamtransform) streams are both `Readable` and `Writable`, each maintains *two* separate internal buffers used for reading and writing, allowing each side to operate independently of the other while maintaining an appropriate and efficient flow of data. For example, [`net.Socket`](net#class-netsocket) instances are [`Duplex`](#class-streamduplex) streams whose `Readable` side allows consumption of data received *from* the socket and whose `Writable` side allows writing data *to* the socket. Because data may be written to the socket at a faster or slower rate than data is received, each side should operate (and buffer) independently of the other.
The mechanics of the internal buffering are an internal implementation detail and may be changed at any time. However, for certain advanced implementations, the internal buffers can be retrieved using `writable.writableBuffer` or `readable.readableBuffer`. Use of these undocumented properties is discouraged.
### API for stream consumers
Almost all Node.js applications, no matter how simple, use streams in some manner. The following is an example of using streams in a Node.js application that implements an HTTP server:
```
const http = require('node:http');
const server = http.createServer((req, res) => {
// `req` is an http.IncomingMessage, which is a readable stream.
// `res` is an http.ServerResponse, which is a writable stream.
let body = '';
// Get the data as utf8 strings.
// If an encoding is not set, Buffer objects will be received.
req.setEncoding('utf8');
// Readable streams emit 'data' events once a listener is added.
req.on('data', (chunk) => {
body += chunk;
});
// The 'end' event indicates that the entire body has been received.
req.on('end', () => {
try {
const data = JSON.parse(body);
// Write back something interesting to the user:
res.write(typeof data);
res.end();
} catch (er) {
// uh oh! bad json!
res.statusCode = 400;
return res.end(`error: ${er.message}`);
}
});
});
server.listen(1337);
// $ curl localhost:1337 -d "{}"
// object
// $ curl localhost:1337 -d "\"foo\""
// string
// $ curl localhost:1337 -d "not json"
// error: Unexpected token o in JSON at position 1
```
[`Writable`](#class-streamwritable) streams (such as `res` in the example) expose methods such as `write()` and `end()` that are used to write data onto the stream.
[`Readable`](#class-streamreadable) streams use the [`EventEmitter`](events#class-eventemitter) API for notifying application code when data is available to be read off the stream. That available data can be read from the stream in multiple ways.
Both [`Writable`](#class-streamwritable) and [`Readable`](#class-streamreadable) streams use the [`EventEmitter`](events#class-eventemitter) API in various ways to communicate the current state of the stream.
[`Duplex`](#class-streamduplex) and [`Transform`](#class-streamtransform) streams are both [`Writable`](#class-streamwritable) and [`Readable`](#class-streamreadable).
Applications that are either writing data to or consuming data from a stream are not required to implement the stream interfaces directly and will generally have no reason to call `require('node:stream')`.
Developers wishing to implement new types of streams should refer to the section [API for stream implementers](#api-for-stream-implementers).
#### Writable streams
Writable streams are an abstraction for a *destination* to which data is written.
Examples of [`Writable`](#class-streamwritable) streams include:
* [HTTP requests, on the client](http#class-httpclientrequest)
* [HTTP responses, on the server](http#class-httpserverresponse)
* [fs write streams](fs#class-fswritestream)
* [zlib streams](zlib)
* [crypto streams](crypto)
* [TCP sockets](net#class-netsocket)
* [child process stdin](child_process#subprocessstdin)
* [`process.stdout`](process#processstdout), [`process.stderr`](process#processstderr)
Some of these examples are actually [`Duplex`](#class-streamduplex) streams that implement the [`Writable`](#class-streamwritable) interface.
All [`Writable`](#class-streamwritable) streams implement the interface defined by the `stream.Writable` class.
While specific instances of [`Writable`](#class-streamwritable) streams may differ in various ways, all `Writable` streams follow the same fundamental usage pattern as illustrated in the example below:
```
const myStream = getWritableStreamSomehow();
myStream.write('some data');
myStream.write('some more data');
myStream.end('done writing data');
```
##### Class: `stream.Writable`
Added in: v0.9.4 ###### Event: `'close'`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Add `emitClose` option to specify if `'close'` is emitted on destroy. |
| v0.9.4 | Added in: v0.9.4 |
The `'close'` event is emitted when the stream and any of its underlying resources (a file descriptor, for example) have been closed. The event indicates that no more events will be emitted, and no further computation will occur.
A [`Writable`](#class-streamwritable) stream will always emit the `'close'` event if it is created with the `emitClose` option.
###### Event: `'drain'`
Added in: v0.9.4 If a call to [`stream.write(chunk)`](#writablewritechunk-encoding-callback) returns `false`, the `'drain'` event will be emitted when it is appropriate to resume writing data to the stream.
```
// Write the data to the supplied writable stream one million times.
// Be attentive to back-pressure.
function writeOneMillionTimes(writer, data, encoding, callback) {
let i = 1000000;
write();
function write() {
let ok = true;
do {
i--;
if (i === 0) {
// Last time!
writer.write(data, encoding, callback);
} else {
// See if we should continue, or wait.
// Don't pass the callback, because we're not done yet.
ok = writer.write(data, encoding);
}
} while (i > 0 && ok);
if (i > 0) {
// Had to stop early!
// Write some more once it drains.
writer.once('drain', write);
}
}
}
```
###### Event: `'error'`
Added in: v0.9.4 * [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
The `'error'` event is emitted if an error occurred while writing or piping data. The listener callback is passed a single `Error` argument when called.
The stream is closed when the `'error'` event is emitted unless the [`autoDestroy`](#new-streamwritableoptions) option was set to `false` when creating the stream.
After `'error'`, no further events other than `'close'` *should* be emitted (including `'error'` events).
###### Event: `'finish'`
Added in: v0.9.4 The `'finish'` event is emitted after the [`stream.end()`](#writableendchunk-encoding-callback) method has been called, and all data has been flushed to the underlying system.
```
const writer = getWritableStreamSomehow();
for (let i = 0; i < 100; i++) {
writer.write(`hello, #${i}!\n`);
}
writer.on('finish', () => {
console.log('All writes are now complete.');
});
writer.end('This is the end\n');
```
###### Event: `'pipe'`
Added in: v0.9.4 * `src` [<stream.Readable>](stream#class-streamreadable) source stream that is piping to this writable
The `'pipe'` event is emitted when the [`stream.pipe()`](#readablepipedestination-options) method is called on a readable stream, adding this writable to its set of destinations.
```
const writer = getWritableStreamSomehow();
const reader = getReadableStreamSomehow();
writer.on('pipe', (src) => {
console.log('Something is piping into the writer.');
assert.equal(src, reader);
});
reader.pipe(writer);
```
###### Event: `'unpipe'`
Added in: v0.9.4 * `src` [<stream.Readable>](stream#class-streamreadable) The source stream that [unpiped](#readableunpipedestination) this writable
The `'unpipe'` event is emitted when the [`stream.unpipe()`](#readableunpipedestination) method is called on a [`Readable`](#class-streamreadable) stream, removing this [`Writable`](#class-streamwritable) from its set of destinations.
This is also emitted in case this [`Writable`](#class-streamwritable) stream emits an error when a [`Readable`](#class-streamreadable) stream pipes into it.
```
const writer = getWritableStreamSomehow();
const reader = getReadableStreamSomehow();
writer.on('unpipe', (src) => {
console.log('Something has stopped piping into the writer.');
assert.equal(src, reader);
});
reader.pipe(writer);
reader.unpipe(writer);
```
######
`writable.cork()`
Added in: v0.11.2 The `writable.cork()` method forces all written data to be buffered in memory. The buffered data will be flushed when either the [`stream.uncork()`](#writableuncork) or [`stream.end()`](#writableendchunk-encoding-callback) methods are called.
The primary intent of `writable.cork()` is to accommodate a situation in which several small chunks are written to the stream in rapid succession. Instead of immediately forwarding them to the underlying destination, `writable.cork()` buffers all the chunks until `writable.uncork()` is called, which will pass them all to `writable._writev()`, if present. This prevents a head-of-line blocking situation where data is being buffered while waiting for the first small chunk to be processed. However, use of `writable.cork()` without implementing `writable._writev()` may have an adverse effect on throughput.
See also: [`writable.uncork()`](#writableuncork), [`writable._writev()`](#writable_writevchunks-callback).
######
`writable.destroy([error])`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | Work as a no-op on a stream that has already been destroyed. |
| v8.0.0 | Added in: v8.0.0 |
* `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) Optional, an error to emit with `'error'` event.
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Destroy the stream. Optionally emit an `'error'` event, and emit a `'close'` event (unless `emitClose` is set to `false`). After this call, the writable stream has ended and subsequent calls to `write()` or `end()` will result in an `ERR_STREAM_DESTROYED` error. This is a destructive and immediate way to destroy a stream. Previous calls to `write()` may not have drained, and may trigger an `ERR_STREAM_DESTROYED` error. Use `end()` instead of destroy if data should flush before close, or wait for the `'drain'` event before destroying the stream.
```
const { Writable } = require('node:stream');
const myStream = new Writable();
const fooErr = new Error('foo error');
myStream.destroy(fooErr);
myStream.on('error', (fooErr) => console.error(fooErr.message)); // foo error
```
```
const { Writable } = require('node:stream');
const myStream = new Writable();
myStream.destroy();
myStream.on('error', function wontHappen() {});
```
```
const { Writable } = require('node:stream');
const myStream = new Writable();
myStream.destroy();
myStream.write('foo', (error) => console.error(error.code));
// ERR_STREAM_DESTROYED
```
Once `destroy()` has been called any further calls will be a no-op and no further errors except from `_destroy()` may be emitted as `'error'`.
Implementors should not override this method, but instead implement [`writable._destroy()`](#writable_destroyerr-callback).
######
`writable.closed`
Added in: v18.0.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` after `'close'` has been emitted.
######
`writable.destroyed`
Added in: v8.0.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` after [`writable.destroy()`](#writabledestroyerror) has been called.
```
const { Writable } = require('node:stream');
const myStream = new Writable();
console.log(myStream.destroyed); // false
myStream.destroy();
console.log(myStream.destroyed); // true
```
######
`writable.end([chunk[, encoding]][, callback])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The `callback` is invoked before 'finish' or on error. |
| v14.0.0 | The `callback` is invoked if 'finish' or 'error' is emitted. |
| v10.0.0 | This method now returns a reference to `writable`. |
| v8.0.0 | The `chunk` argument can now be a `Uint8Array` instance. |
| v0.9.4 | Added in: v0.9.4 |
* `chunk` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Optional data to write. For streams not operating in object mode, `chunk` must be a string, `Buffer` or `Uint8Array`. For object mode streams, `chunk` may be any JavaScript value other than `null`.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The encoding if `chunk` is a string
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Callback for when the stream is finished.
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Calling the `writable.end()` method signals that no more data will be written to the [`Writable`](#class-streamwritable). The optional `chunk` and `encoding` arguments allow one final additional chunk of data to be written immediately before closing the stream.
Calling the [`stream.write()`](#writablewritechunk-encoding-callback) method after calling [`stream.end()`](#writableendchunk-encoding-callback) will raise an error.
```
// Write 'hello, ' and then end with 'world!'.
const fs = require('node:fs');
const file = fs.createWriteStream('example.txt');
file.write('hello, ');
file.end('world!');
// Writing more now is not allowed!
```
######
`writable.setDefaultEncoding(encoding)`
History
| Version | Changes |
| --- | --- |
| v6.1.0 | This method now returns a reference to `writable`. |
| v0.11.15 | Added in: v0.11.15 |
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The new default encoding
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
The `writable.setDefaultEncoding()` method sets the default `encoding` for a [`Writable`](#class-streamwritable) stream.
######
`writable.uncork()`
Added in: v0.11.2 The `writable.uncork()` method flushes all data buffered since [`stream.cork()`](#writablecork) was called.
When using [`writable.cork()`](#writablecork) and `writable.uncork()` to manage the buffering of writes to a stream, defer calls to `writable.uncork()` using `process.nextTick()`. Doing so allows batching of all `writable.write()` calls that occur within a given Node.js event loop phase.
```
stream.cork();
stream.write('some ');
stream.write('data ');
process.nextTick(() => stream.uncork());
```
If the [`writable.cork()`](#writablecork) method is called multiple times on a stream, the same number of calls to `writable.uncork()` must be called to flush the buffered data.
```
stream.cork();
stream.write('some ');
stream.cork();
stream.write('data ');
process.nextTick(() => {
stream.uncork();
// The data will not be flushed until uncork() is called a second time.
stream.uncork();
});
```
See also: [`writable.cork()`](#writablecork).
######
`writable.writable`
Added in: v11.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` if it is safe to call [`writable.write()`](#writablewritechunk-encoding-callback), which means the stream has not been destroyed, errored, or ended.
######
`writable.writableAborted`
Added in: v18.0.0, v16.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns whether the stream was destroyed or errored before emitting `'finish'`.
######
`writable.writableEnded`
Added in: v12.9.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` after [`writable.end()`](#writableendchunk-encoding-callback) has been called. This property does not indicate whether the data has been flushed, for this use [`writable.writableFinished`](#writablewritablefinished) instead.
######
`writable.writableCorked`
Added in: v13.2.0, v12.16.0 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Number of times [`writable.uncork()`](#writableuncork) needs to be called in order to fully uncork the stream.
######
`writable.errored`
Added in: v18.0.0 * [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Returns error if the stream has been destroyed with an error.
######
`writable.writableFinished`
Added in: v12.6.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is set to `true` immediately before the [`'finish'`](#event-finish) event is emitted.
######
`writable.writableHighWaterMark`
Added in: v9.3.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Return the value of `highWaterMark` passed when creating this `Writable`.
######
`writable.writableLength`
Added in: v9.4.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
This property contains the number of bytes (or objects) in the queue ready to be written. The value provides introspection data regarding the status of the `highWaterMark`.
######
`writable.writableNeedDrain`
Added in: v15.2.0, v14.17.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` if the stream's buffer has been full and stream will emit `'drain'`.
######
`writable.writableObjectMode`
Added in: v12.3.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Getter for the property `objectMode` of a given `Writable` stream.
######
`writable.write(chunk[, encoding][, callback])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The `chunk` argument can now be a `Uint8Array` instance. |
| v6.0.0 | Passing `null` as the `chunk` parameter will always be considered invalid now, even in object mode. |
| v0.9.4 | Added in: v0.9.4 |
* `chunk` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Optional data to write. For streams not operating in object mode, `chunk` must be a string, `Buffer` or `Uint8Array`. For object mode streams, `chunk` may be any JavaScript value other than `null`.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) The encoding, if `chunk` is a string. **Default:** `'utf8'`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Callback for when this chunk of data is flushed.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `false` if the stream wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`.
The `writable.write()` method writes some data to the stream, and calls the supplied `callback` once the data has been fully handled. If an error occurs, the `callback` will be called with the error as its first argument. The `callback` is called asynchronously and before `'error'` is emitted.
The return value is `true` if the internal buffer is less than the `highWaterMark` configured when the stream was created after admitting `chunk`. If `false` is returned, further attempts to write data to the stream should stop until the [`'drain'`](#event-drain) event is emitted.
While a stream is not draining, calls to `write()` will buffer `chunk`, and return false. Once all currently buffered chunks are drained (accepted for delivery by the operating system), the `'drain'` event will be emitted. Once `write()` returns false, do not write more chunks until the `'drain'` event is emitted. While calling `write()` on a stream that is not draining is allowed, Node.js will buffer all written chunks until maximum memory usage occurs, at which point it will abort unconditionally. Even before it aborts, high memory usage will cause poor garbage collector performance and high RSS (which is not typically released back to the system, even after the memory is no longer required). Since TCP sockets may never drain if the remote peer does not read the data, writing a socket that is not draining may lead to a remotely exploitable vulnerability.
Writing data while the stream is not draining is particularly problematic for a [`Transform`](#class-streamtransform), because the `Transform` streams are paused by default until they are piped or a `'data'` or `'readable'` event handler is added.
If the data to be written can be generated or fetched on demand, it is recommended to encapsulate the logic into a [`Readable`](#class-streamreadable) and use [`stream.pipe()`](#readablepipedestination-options). However, if calling `write()` is preferred, it is possible to respect backpressure and avoid memory issues using the [`'drain'`](#event-drain) event:
```
function write(data, cb) {
if (!stream.write(data)) {
stream.once('drain', cb);
} else {
process.nextTick(cb);
}
}
// Wait for cb to be called before doing any other write.
write('hello', () => {
console.log('Write completed, do more writes now.');
});
```
A `Writable` stream in object mode will always ignore the `encoding` argument.
#### Readable streams
Readable streams are an abstraction for a *source* from which data is consumed.
Examples of `Readable` streams include:
* [HTTP responses, on the client](http#class-httpincomingmessage)
* [HTTP requests, on the server](http#class-httpincomingmessage)
* [fs read streams](fs#class-fsreadstream)
* [zlib streams](zlib)
* [crypto streams](crypto)
* [TCP sockets](net#class-netsocket)
* [child process stdout and stderr](child_process#subprocessstdout)
* [`process.stdin`](process#processstdin)
All [`Readable`](#class-streamreadable) streams implement the interface defined by the `stream.Readable` class.
##### Two reading modes
`Readable` streams effectively operate in one of two modes: flowing and paused. These modes are separate from [object mode](#object-mode). A [`Readable`](#class-streamreadable) stream can be in object mode or not, regardless of whether it is in flowing mode or paused mode.
* In flowing mode, data is read from the underlying system automatically and provided to an application as quickly as possible using events via the [`EventEmitter`](events#class-eventemitter) interface.
* In paused mode, the [`stream.read()`](#readablereadsize) method must be called explicitly to read chunks of data from the stream.
All [`Readable`](#class-streamreadable) streams begin in paused mode but can be switched to flowing mode in one of the following ways:
* Adding a [`'data'`](#event-data) event handler.
* Calling the [`stream.resume()`](#readableresume) method.
* Calling the [`stream.pipe()`](#readablepipedestination-options) method to send the data to a [`Writable`](#class-streamwritable).
The `Readable` can switch back to paused mode using one of the following:
* If there are no pipe destinations, by calling the [`stream.pause()`](#readablepause) method.
* If there are pipe destinations, by removing all pipe destinations. Multiple pipe destinations may be removed by calling the [`stream.unpipe()`](#readableunpipedestination) method.
The important concept to remember is that a `Readable` will not generate data until a mechanism for either consuming or ignoring that data is provided. If the consuming mechanism is disabled or taken away, the `Readable` will *attempt* to stop generating the data.
For backward compatibility reasons, removing [`'data'`](#event-data) event handlers will **not** automatically pause the stream. Also, if there are piped destinations, then calling [`stream.pause()`](#readablepause) will not guarantee that the stream will *remain* paused once those destinations drain and ask for more data.
If a [`Readable`](#class-streamreadable) is switched into flowing mode and there are no consumers available to handle the data, that data will be lost. This can occur, for instance, when the `readable.resume()` method is called without a listener attached to the `'data'` event, or when a `'data'` event handler is removed from the stream.
Adding a [`'readable'`](#event-readable) event handler automatically makes the stream stop flowing, and the data has to be consumed via [`readable.read()`](#readablereadsize). If the [`'readable'`](#event-readable) event handler is removed, then the stream will start flowing again if there is a [`'data'`](#event-data) event handler.
##### Three states
The "two modes" of operation for a `Readable` stream are a simplified abstraction for the more complicated internal state management that is happening within the `Readable` stream implementation.
Specifically, at any given point in time, every `Readable` is in one of three possible states:
* `readable.readableFlowing === null`
* `readable.readableFlowing === false`
* `readable.readableFlowing === true`
When `readable.readableFlowing` is `null`, no mechanism for consuming the stream's data is provided. Therefore, the stream will not generate data. While in this state, attaching a listener for the `'data'` event, calling the `readable.pipe()` method, or calling the `readable.resume()` method will switch `readable.readableFlowing` to `true`, causing the `Readable` to begin actively emitting events as data is generated.
Calling `readable.pause()`, `readable.unpipe()`, or receiving backpressure will cause the `readable.readableFlowing` to be set as `false`, temporarily halting the flowing of events but *not* halting the generation of data. While in this state, attaching a listener for the `'data'` event will not switch `readable.readableFlowing` to `true`.
```
const { PassThrough, Writable } = require('node:stream');
const pass = new PassThrough();
const writable = new Writable();
pass.pipe(writable);
pass.unpipe(writable);
// readableFlowing is now false.
pass.on('data', (chunk) => { console.log(chunk.toString()); });
pass.write('ok'); // Will not emit 'data'.
pass.resume(); // Must be called to make stream emit 'data'.
```
While `readable.readableFlowing` is `false`, data may be accumulating within the stream's internal buffer.
##### Choose one API style
The `Readable` stream API evolved across multiple Node.js versions and provides multiple methods of consuming stream data. In general, developers should choose *one* of the methods of consuming data and *should never* use multiple methods to consume data from a single stream. Specifically, using a combination of `on('data')`, `on('readable')`, `pipe()`, or async iterators could lead to unintuitive behavior.
##### Class: `stream.Readable`
Added in: v0.9.4 ###### Event: `'close'`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Add `emitClose` option to specify if `'close'` is emitted on destroy. |
| v0.9.4 | Added in: v0.9.4 |
The `'close'` event is emitted when the stream and any of its underlying resources (a file descriptor, for example) have been closed. The event indicates that no more events will be emitted, and no further computation will occur.
A [`Readable`](#class-streamreadable) stream will always emit the `'close'` event if it is created with the `emitClose` option.
###### Event: `'data'`
Added in: v0.9.4 * `chunk` [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The chunk of data. For streams that are not operating in object mode, the chunk will be either a string or `Buffer`. For streams that are in object mode, the chunk can be any JavaScript value other than `null`.
The `'data'` event is emitted whenever the stream is relinquishing ownership of a chunk of data to a consumer. This may occur whenever the stream is switched in flowing mode by calling `readable.pipe()`, `readable.resume()`, or by attaching a listener callback to the `'data'` event. The `'data'` event will also be emitted whenever the `readable.read()` method is called and a chunk of data is available to be returned.
Attaching a `'data'` event listener to a stream that has not been explicitly paused will switch the stream into flowing mode. Data will then be passed as soon as it is available.
The listener callback will be passed the chunk of data as a string if a default encoding has been specified for the stream using the `readable.setEncoding()` method; otherwise the data will be passed as a `Buffer`.
```
const readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
console.log(`Received ${chunk.length} bytes of data.`);
});
```
###### Event: `'end'`
Added in: v0.9.4 The `'end'` event is emitted when there is no more data to be consumed from the stream.
The `'end'` event **will not be emitted** unless the data is completely consumed. This can be accomplished by switching the stream into flowing mode, or by calling [`stream.read()`](#readablereadsize) repeatedly until all data has been consumed.
```
const readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
console.log(`Received ${chunk.length} bytes of data.`);
});
readable.on('end', () => {
console.log('There will be no more data.');
});
```
###### Event: `'error'`
Added in: v0.9.4 * [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
The `'error'` event may be emitted by a `Readable` implementation at any time. Typically, this may occur if the underlying stream is unable to generate data due to an underlying internal failure, or when a stream implementation attempts to push an invalid chunk of data.
The listener callback will be passed a single `Error` object.
###### Event: `'pause'`
Added in: v0.9.4 The `'pause'` event is emitted when [`stream.pause()`](#readablepause) is called and `readableFlowing` is not `false`.
###### Event: `'readable'`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | The `'readable'` is always emitted in the next tick after `.push()` is called. |
| v10.0.0 | Using `'readable'` requires calling `.read()`. |
| v0.9.4 | Added in: v0.9.4 |
The `'readable'` event is emitted when there is data available to be read from the stream or when the end of the stream has been reached. Effectively, the `'readable'` event indicates that the stream has new information. If data is available, [`stream.read()`](#readablereadsize) will return that data.
```
const readable = getReadableStreamSomehow();
readable.on('readable', function() {
// There is some data to read now.
let data;
while ((data = this.read()) !== null) {
console.log(data);
}
});
```
If the end of the stream has been reached, calling [`stream.read()`](#readablereadsize) will return `null` and trigger the `'end'` event. This is also true if there never was any data to be read. For instance, in the following example, `foo.txt` is an empty file:
```
const fs = require('node:fs');
const rr = fs.createReadStream('foo.txt');
rr.on('readable', () => {
console.log(`readable: ${rr.read()}`);
});
rr.on('end', () => {
console.log('end');
});
```
The output of running this script is:
```
$ node test.js
readable: null
end
```
In some cases, attaching a listener for the `'readable'` event will cause some amount of data to be read into an internal buffer.
In general, the `readable.pipe()` and `'data'` event mechanisms are easier to understand than the `'readable'` event. However, handling `'readable'` might result in increased throughput.
If both `'readable'` and [`'data'`](#event-data) are used at the same time, `'readable'` takes precedence in controlling the flow, i.e. `'data'` will be emitted only when [`stream.read()`](#readablereadsize) is called. The `readableFlowing` property would become `false`. If there are `'data'` listeners when `'readable'` is removed, the stream will start flowing, i.e. `'data'` events will be emitted without calling `.resume()`.
###### Event: `'resume'`
Added in: v0.9.4 The `'resume'` event is emitted when [`stream.resume()`](#readableresume) is called and `readableFlowing` is not `true`.
######
`readable.destroy([error])`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | Work as a no-op on a stream that has already been destroyed. |
| v8.0.0 | Added in: v8.0.0 |
* `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) Error which will be passed as payload in `'error'` event
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Destroy the stream. Optionally emit an `'error'` event, and emit a `'close'` event (unless `emitClose` is set to `false`). After this call, the readable stream will release any internal resources and subsequent calls to `push()` will be ignored.
Once `destroy()` has been called any further calls will be a no-op and no further errors except from `_destroy()` may be emitted as `'error'`.
Implementors should not override this method, but instead implement [`readable._destroy()`](#readable_destroyerr-callback).
######
`readable.closed`
Added in: v18.0.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` after `'close'` has been emitted.
######
`readable.destroyed`
Added in: v8.0.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` after [`readable.destroy()`](#readabledestroyerror) has been called.
######
`readable.isPaused()`
Added in: v0.11.14 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `readable.isPaused()` method returns the current operating state of the `Readable`. This is used primarily by the mechanism that underlies the `readable.pipe()` method. In most typical cases, there will be no reason to use this method directly.
```
const readable = new stream.Readable();
readable.isPaused(); // === false
readable.pause();
readable.isPaused(); // === true
readable.resume();
readable.isPaused(); // === false
```
######
`readable.pause()`
Added in: v0.9.4 * Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
The `readable.pause()` method will cause a stream in flowing mode to stop emitting [`'data'`](#event-data) events, switching out of flowing mode. Any data that becomes available will remain in the internal buffer.
```
const readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
console.log(`Received ${chunk.length} bytes of data.`);
readable.pause();
console.log('There will be no additional data for 1 second.');
setTimeout(() => {
console.log('Now data will start flowing again.');
readable.resume();
}, 1000);
});
```
The `readable.pause()` method has no effect if there is a `'readable'` event listener.
######
`readable.pipe(destination[, options])`
Added in: v0.9.4 * `destination` [<stream.Writable>](stream#class-streamwritable) The destination for writing data
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Pipe options
+ `end` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) End the writer when the reader ends. **Default:** `true`.
* Returns: [<stream.Writable>](stream#class-streamwritable) The *destination*, allowing for a chain of pipes if it is a [`Duplex`](#class-streamduplex) or a [`Transform`](#class-streamtransform) stream
The `readable.pipe()` method attaches a [`Writable`](#class-streamwritable) stream to the `readable`, causing it to switch automatically into flowing mode and push all of its data to the attached [`Writable`](#class-streamwritable). The flow of data will be automatically managed so that the destination `Writable` stream is not overwhelmed by a faster `Readable` stream.
The following example pipes all of the data from the `readable` into a file named `file.txt`:
```
const fs = require('node:fs');
const readable = getReadableStreamSomehow();
const writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt'.
readable.pipe(writable);
```
It is possible to attach multiple `Writable` streams to a single `Readable` stream.
The `readable.pipe()` method returns a reference to the *destination* stream making it possible to set up chains of piped streams:
```
const fs = require('node:fs');
const zlib = require('node:zlib');
const r = fs.createReadStream('file.txt');
const z = zlib.createGzip();
const w = fs.createWriteStream('file.txt.gz');
r.pipe(z).pipe(w);
```
By default, [`stream.end()`](#writableendchunk-encoding-callback) is called on the destination `Writable` stream when the source `Readable` stream emits [`'end'`](#event-end), so that the destination is no longer writable. To disable this default behavior, the `end` option can be passed as `false`, causing the destination stream to remain open:
```
reader.pipe(writer, { end: false });
reader.on('end', () => {
writer.end('Goodbye\n');
});
```
One important caveat is that if the `Readable` stream emits an error during processing, the `Writable` destination *is not closed* automatically. If an error occurs, it will be necessary to *manually* close each stream in order to prevent memory leaks.
The [`process.stderr`](process#processstderr) and [`process.stdout`](process#processstdout) `Writable` streams are never closed until the Node.js process exits, regardless of the specified options.
######
`readable.read([size])`
Added in: v0.9.4 * `size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optional argument to specify how much data to read.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
The `readable.read()` method reads data out of the internal buffer and returns it. If no data is available to be read, `null` is returned. By default, the data is returned as a `Buffer` object unless an encoding has been specified using the `readable.setEncoding()` method or the stream is operating in object mode.
The optional `size` argument specifies a specific number of bytes to read. If `size` bytes are not available to be read, `null` will be returned *unless* the stream has ended, in which case all of the data remaining in the internal buffer will be returned.
If the `size` argument is not specified, all of the data contained in the internal buffer will be returned.
The `size` argument must be less than or equal to 1 GiB.
The `readable.read()` method should only be called on `Readable` streams operating in paused mode. In flowing mode, `readable.read()` is called automatically until the internal buffer is fully drained.
```
const readable = getReadableStreamSomehow();
// 'readable' may be triggered multiple times as data is buffered in
readable.on('readable', () => {
let chunk;
console.log('Stream is readable (new data received in buffer)');
// Use a loop to make sure we read all currently available data
while (null !== (chunk = readable.read())) {
console.log(`Read ${chunk.length} bytes of data...`);
}
});
// 'end' will be triggered once when there is no more data available
readable.on('end', () => {
console.log('Reached end of stream.');
});
```
Each call to `readable.read()` returns a chunk of data, or `null`. The chunks are not concatenated. A `while` loop is necessary to consume all data currently in the buffer. When reading a large file `.read()` may return `null`, having consumed all buffered content so far, but there is still more data to come not yet buffered. In this case a new `'readable'` event will be emitted when there is more data in the buffer. Finally the `'end'` event will be emitted when there is no more data to come.
Therefore to read a file's whole contents from a `readable`, it is necessary to collect chunks across multiple `'readable'` events:
```
const chunks = [];
readable.on('readable', () => {
let chunk;
while (null !== (chunk = readable.read())) {
chunks.push(chunk);
}
});
readable.on('end', () => {
const content = chunks.join('');
});
```
A `Readable` stream in object mode will always return a single item from a call to [`readable.read(size)`](#readablereadsize), regardless of the value of the `size` argument.
If the `readable.read()` method returns a chunk of data, a `'data'` event will also be emitted.
Calling [`stream.read([size])`](#readablereadsize) after the [`'end'`](#event-end) event has been emitted will return `null`. No runtime error will be raised.
######
`readable.readable`
Added in: v11.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` if it is safe to call [`readable.read()`](#readablereadsize), which means the stream has not been destroyed or emitted `'error'` or `'end'`.
######
`readable.readableAborted`
Added in: v16.8.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns whether the stream was destroyed or errored before emitting `'end'`.
######
`readable.readableDidRead`
Added in: v16.7.0, v14.18.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns whether `'data'` has been emitted.
######
`readable.readableEncoding`
Added in: v12.7.0 * [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Getter for the property `encoding` of a given `Readable` stream. The `encoding` property can be set using the [`readable.setEncoding()`](#readablesetencodingencoding) method.
######
`readable.readableEnded`
Added in: v12.9.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Becomes `true` when [`'end'`](#event-end) event is emitted.
######
`readable.errored`
Added in: v18.0.0 * [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
Returns error if the stream has been destroyed with an error.
######
`readable.readableFlowing`
Added in: v9.4.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
This property reflects the current state of a `Readable` stream as described in the [Three states](#three-states) section.
######
`readable.readableHighWaterMark`
Added in: v9.3.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the value of `highWaterMark` passed when creating this `Readable`.
######
`readable.readableLength`
Added in: v9.4.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
This property contains the number of bytes (or objects) in the queue ready to be read. The value provides introspection data regarding the status of the `highWaterMark`.
######
`readable.readableObjectMode`
Added in: v12.3.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Getter for the property `objectMode` of a given `Readable` stream.
######
`readable.resume()`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | The `resume()` has no effect if there is a `'readable'` event listening. |
| v0.9.4 | Added in: v0.9.4 |
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
The `readable.resume()` method causes an explicitly paused `Readable` stream to resume emitting [`'data'`](#event-data) events, switching the stream into flowing mode.
The `readable.resume()` method can be used to fully consume the data from a stream without actually processing any of that data:
```
getReadableStreamSomehow()
.resume()
.on('end', () => {
console.log('Reached the end, but did not read anything.');
});
```
The `readable.resume()` method has no effect if there is a `'readable'` event listener.
######
`readable.setEncoding(encoding)`
Added in: v0.9.4 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The encoding to use.
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
The `readable.setEncoding()` method sets the character encoding for data read from the `Readable` stream.
By default, no encoding is assigned and stream data will be returned as `Buffer` objects. Setting an encoding causes the stream data to be returned as strings of the specified encoding rather than as `Buffer` objects. For instance, calling `readable.setEncoding('utf8')` will cause the output data to be interpreted as UTF-8 data, and passed as strings. Calling `readable.setEncoding('hex')` will cause the data to be encoded in hexadecimal string format.
The `Readable` stream will properly handle multi-byte characters delivered through the stream that would otherwise become improperly decoded if simply pulled from the stream as `Buffer` objects.
```
const readable = getReadableStreamSomehow();
readable.setEncoding('utf8');
readable.on('data', (chunk) => {
assert.equal(typeof chunk, 'string');
console.log('Got %d characters of string data:', chunk.length);
});
```
######
`readable.unpipe([destination])`
Added in: v0.9.4 * `destination` [<stream.Writable>](stream#class-streamwritable) Optional specific stream to unpipe
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
The `readable.unpipe()` method detaches a `Writable` stream previously attached using the [`stream.pipe()`](#readablepipedestination-options) method.
If the `destination` is not specified, then *all* pipes are detached.
If the `destination` is specified, but no pipe is set up for it, then the method does nothing.
```
const fs = require('node:fs');
const readable = getReadableStreamSomehow();
const writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt',
// but only for the first second.
readable.pipe(writable);
setTimeout(() => {
console.log('Stop writing to file.txt.');
readable.unpipe(writable);
console.log('Manually close the file stream.');
writable.end();
}, 1000);
```
######
`readable.unshift(chunk[, encoding])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The `chunk` argument can now be a `Uint8Array` instance. |
| v0.9.11 | Added in: v0.9.11 |
* `chunk` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Chunk of data to unshift onto the read queue. For streams not operating in object mode, `chunk` must be a string, `Buffer`, `Uint8Array`, or `null`. For object mode streams, `chunk` may be any JavaScript value.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Encoding of string chunks. Must be a valid `Buffer` encoding, such as `'utf8'` or `'ascii'`.
Passing `chunk` as `null` signals the end of the stream (EOF) and behaves the same as `readable.push(null)`, after which no more data can be written. The EOF signal is put at the end of the buffer and any buffered data will still be flushed.
The `readable.unshift()` method pushes a chunk of data back into the internal buffer. This is useful in certain situations where a stream is being consumed by code that needs to "un-consume" some amount of data that it has optimistically pulled out of the source, so that the data can be passed on to some other party.
The `stream.unshift(chunk)` method cannot be called after the [`'end'`](#event-end) event has been emitted or a runtime error will be thrown.
Developers using `stream.unshift()` often should consider switching to use of a [`Transform`](#class-streamtransform) stream instead. See the [API for stream implementers](#api-for-stream-implementers) section for more information.
```
// Pull off a header delimited by \n\n.
// Use unshift() if we get too much.
// Call the callback with (error, header, stream).
const { StringDecoder } = require('node:string_decoder');
function parseHeader(stream, callback) {
stream.on('error', callback);
stream.on('readable', onReadable);
const decoder = new StringDecoder('utf8');
let header = '';
function onReadable() {
let chunk;
while (null !== (chunk = stream.read())) {
const str = decoder.write(chunk);
if (str.includes('\n\n')) {
// Found the header boundary.
const split = str.split(/\n\n/);
header += split.shift();
const remaining = split.join('\n\n');
const buf = Buffer.from(remaining, 'utf8');
stream.removeListener('error', callback);
// Remove the 'readable' listener before unshifting.
stream.removeListener('readable', onReadable);
if (buf.length)
stream.unshift(buf);
// Now the body of the message can be read from the stream.
callback(null, header, stream);
return;
}
// Still reading the header.
header += str;
}
}
}
```
Unlike [`stream.push(chunk)`](#readablepushchunk-encoding), `stream.unshift(chunk)` will not end the reading process by resetting the internal reading state of the stream. This can cause unexpected results if `readable.unshift()` is called during a read (i.e. from within a [`stream._read()`](#readable_readsize) implementation on a custom stream). Following the call to `readable.unshift()` with an immediate [`stream.push('')`](#readablepushchunk-encoding) will reset the reading state appropriately, however it is best to simply avoid calling `readable.unshift()` while in the process of performing a read.
######
`readable.wrap(stream)`
Added in: v0.9.4 * `stream` [<Stream>](stream#stream) An "old style" readable stream
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Prior to Node.js 0.10, streams did not implement the entire `node:stream` module API as it is currently defined. (See [Compatibility](#compatibility-with-older-nodejs-versions) for more information.)
When using an older Node.js library that emits [`'data'`](#event-data) events and has a [`stream.pause()`](#readablepause) method that is advisory only, the `readable.wrap()` method can be used to create a [`Readable`](#class-streamreadable) stream that uses the old stream as its data source.
It will rarely be necessary to use `readable.wrap()` but the method has been provided as a convenience for interacting with older Node.js applications and libraries.
```
const { OldReader } = require('./old-api-module.js');
const { Readable } = require('node:stream');
const oreader = new OldReader();
const myReader = new Readable().wrap(oreader);
myReader.on('readable', () => {
myReader.read(); // etc.
});
```
######
`readable[Symbol.asyncIterator]()`
History
| Version | Changes |
| --- | --- |
| v11.14.0 | Symbol.asyncIterator support is no longer experimental. |
| v10.0.0 | Added in: v10.0.0 |
* Returns: [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface) to fully consume the stream.
```
const fs = require('node:fs');
async function print(readable) {
readable.setEncoding('utf8');
let data = '';
for await (const chunk of readable) {
data += chunk;
}
console.log(data);
}
print(fs.createReadStream('file')).catch(console.error);
```
If the loop terminates with a `break`, `return`, or a `throw`, the stream will be destroyed. In other terms, iterating over a stream will consume the stream fully. The stream will be read in chunks of size equal to the `highWaterMark` option. In the code example above, data will be in a single chunk if the file has less then 64 KiB of data because no `highWaterMark` option is provided to [`fs.createReadStream()`](fs#fscreatereadstreampath-options).
######
`readable.iterator([options])`
Added in: v16.3.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `destroyOnReturn` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When set to `false`, calling `return` on the async iterator, or exiting a `for await...of` iteration using a `break`, `return`, or `throw` will not destroy the stream. **Default:** `true`.
* Returns: [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface) to consume the stream.
The iterator created by this method gives users the option to cancel the destruction of the stream if the `for await...of` loop is exited by `return`, `break`, or `throw`, or if the iterator should destroy the stream if the stream emitted an error during iteration.
```
const { Readable } = require('node:stream');
async function printIterator(readable) {
for await (const chunk of readable.iterator({ destroyOnReturn: false })) {
console.log(chunk); // 1
break;
}
console.log(readable.destroyed); // false
for await (const chunk of readable.iterator({ destroyOnReturn: false })) {
console.log(chunk); // Will print 2 and then 3
}
console.log(readable.destroyed); // True, stream was totally consumed
}
async function printSymbolAsyncIterator(readable) {
for await (const chunk of readable) {
console.log(chunk); // 1
break;
}
console.log(readable.destroyed); // true
}
async function showBoth() {
await printIterator(Readable.from([1, 2, 3]));
await printSymbolAsyncIterator(Readable.from([1, 2, 3]));
}
showBoth();
```
######
`readable.map(fn[, options])`
Added in: v17.4.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) a function to map over every chunk in the stream.
+ `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) a chunk of data from the stream.
+ `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `signal` [<AbortSignal>](globals#class-abortsignal) aborted if the stream is destroyed allowing to abort the `fn` call early.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the maximum concurrent invocation of `fn` to call on the stream at once. **Default:** `1`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Readable>](stream#class-streamreadable) a stream mapped with the function `fn`.
This method allows mapping over the stream. The `fn` function will be called for every chunk in the stream. If the `fn` function returns a promise - that promise will be `await`ed before being passed to the result stream.
```
import { Readable } from 'node:stream';
import { Resolver } from 'node:dns/promises';
// With a synchronous mapper.
for await (const chunk of Readable.from([1, 2, 3, 4]).map((x) => x * 2)) {
console.log(chunk); // 2, 4, 6, 8
}
// With an asynchronous mapper, making at most 2 queries at a time.
const resolver = new Resolver();
const dnsResults = Readable.from([
'nodejs.org',
'openjsf.org',
'www.linuxfoundation.org',
]).map((domain) => resolver.resolve4(domain), { concurrency: 2 });
for await (const result of dnsResults) {
console.log(result); // Logs the DNS result of resolver.resolve4.
}
```
######
`readable.filter(fn[, options])`
Added in: v17.4.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) a function to filter chunks from the stream.
+ `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) a chunk of data from the stream.
+ `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `signal` [<AbortSignal>](globals#class-abortsignal) aborted if the stream is destroyed allowing to abort the `fn` call early.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the maximum concurrent invocation of `fn` to call on the stream at once. **Default:** `1`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Readable>](stream#class-streamreadable) a stream filtered with the predicate `fn`.
This method allows filtering the stream. For each chunk in the stream the `fn` function will be called and if it returns a truthy value, the chunk will be passed to the result stream. If the `fn` function returns a promise - that promise will be `await`ed.
```
import { Readable } from 'node:stream';
import { Resolver } from 'node:dns/promises';
// With a synchronous predicate.
for await (const chunk of Readable.from([1, 2, 3, 4]).filter((x) => x > 2)) {
console.log(chunk); // 3, 4
}
// With an asynchronous predicate, making at most 2 queries at a time.
const resolver = new Resolver();
const dnsResults = Readable.from([
'nodejs.org',
'openjsf.org',
'www.linuxfoundation.org',
]).filter(async (domain) => {
const { address } = await resolver.resolve4(domain, { ttl: true });
return address.ttl > 60;
}, { concurrency: 2 });
for await (const result of dnsResults) {
// Logs domains with more than 60 seconds on the resolved dns record.
console.log(result);
}
```
######
`readable.forEach(fn[, options])`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) a function to call on each chunk of the stream.
+ `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) a chunk of data from the stream.
+ `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `signal` [<AbortSignal>](globals#class-abortsignal) aborted if the stream is destroyed allowing to abort the `fn` call early.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the maximum concurrent invocation of `fn` to call on the stream at once. **Default:** `1`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) a promise for when the stream has finished.
This method allows iterating a stream. For each chunk in the stream the `fn` function will be called. If the `fn` function returns a promise - that promise will be `await`ed.
This method is different from `for await...of` loops in that it can optionally process chunks concurrently. In addition, a `forEach` iteration can only be stopped by having passed a `signal` option and aborting the related `AbortController` while `for await...of` can be stopped with `break` or `return`. In either case the stream will be destroyed.
This method is different from listening to the [`'data'`](#event-data) event in that it uses the [`readable`](#class-streamreadable) event in the underlying machinary and can limit the number of concurrent `fn` calls.
```
import { Readable } from 'node:stream';
import { Resolver } from 'node:dns/promises';
// With a synchronous predicate.
for await (const chunk of Readable.from([1, 2, 3, 4]).filter((x) => x > 2)) {
console.log(chunk); // 3, 4
}
// With an asynchronous predicate, making at most 2 queries at a time.
const resolver = new Resolver();
const dnsResults = Readable.from([
'nodejs.org',
'openjsf.org',
'www.linuxfoundation.org',
]).map(async (domain) => {
const { address } = await resolver.resolve4(domain, { ttl: true });
return address;
}, { concurrency: 2 });
await dnsResults.forEach((result) => {
// Logs result, similar to `for await (const result of dnsResults)`
console.log(result);
});
console.log('done'); // Stream has finished
```
######
`readable.toArray([options])`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows cancelling the toArray operation if the signal is aborted.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) a promise containing an array with the contents of the stream.
This method allows easily obtaining the contents of a stream.
As this method reads the entire stream into memory, it negates the benefits of streams. It's intended for interoperability and convenience, not as the primary way to consume streams.
```
import { Readable } from 'node:stream';
import { Resolver } from 'node:dns/promises';
await Readable.from([1, 2, 3, 4]).toArray(); // [1, 2, 3, 4]
// Make dns queries concurrently using .map and collect
// the results into an array using toArray
const dnsResults = await Readable.from([
'nodejs.org',
'openjsf.org',
'www.linuxfoundation.org',
]).map(async (domain) => {
const { address } = await resolver.resolve4(domain, { ttl: true });
return address;
}, { concurrency: 2 }).toArray();
```
######
`readable.some(fn[, options])`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) a function to call on each chunk of the stream.
+ `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) a chunk of data from the stream.
+ `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `signal` [<AbortSignal>](globals#class-abortsignal) aborted if the stream is destroyed allowing to abort the `fn` call early.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the maximum concurrent invocation of `fn` to call on the stream at once. **Default:** `1`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) a promise evaluating to `true` if `fn` returned a truthy value for at least one of the chunks.
This method is similar to `Array.prototype.some` and calls `fn` on each chunk in the stream until the awaited return value is `true` (or any truthy value). Once an `fn` call on a chunk awaited return value is truthy, the stream is destroyed and the promise is fulfilled with `true`. If none of the `fn` calls on the chunks return a truthy value, the promise is fulfilled with `false`.
```
import { Readable } from 'node:stream';
import { stat } from 'node:fs/promises';
// With a synchronous predicate.
await Readable.from([1, 2, 3, 4]).some((x) => x > 2); // true
await Readable.from([1, 2, 3, 4]).some((x) => x < 0); // false
// With an asynchronous predicate, making at most 2 file checks at a time.
const anyBigFile = await Readable.from([
'file1',
'file2',
'file3',
]).some(async (fileName) => {
const stats = await stat(fileName);
return stat.size > 1024 * 1024;
}, { concurrency: 2 });
console.log(anyBigFile); // `true` if any file in the list is bigger than 1MB
console.log('done'); // Stream has finished
```
######
`readable.find(fn[, options])`
Added in: v17.5.0, v16.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) a function to call on each chunk of the stream.
+ `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) a chunk of data from the stream.
+ `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `signal` [<AbortSignal>](globals#class-abortsignal) aborted if the stream is destroyed allowing to abort the `fn` call early.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the maximum concurrent invocation of `fn` to call on the stream at once. **Default:** `1`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) a promise evaluating to the first chunk for which `fn` evaluated with a truthy value, or `undefined` if no element was found.
This method is similar to `Array.prototype.find` and calls `fn` on each chunk in the stream to find a chunk with a truthy value for `fn`. Once an `fn` call's awaited return value is truthy, the stream is destroyed and the promise is fulfilled with value for which `fn` returned a truthy value. If all of the `fn` calls on the chunks return a falsy value, the promise is fulfilled with `undefined`.
```
import { Readable } from 'node:stream';
import { stat } from 'node:fs/promises';
// With a synchronous predicate.
await Readable.from([1, 2, 3, 4]).find((x) => x > 2); // 3
await Readable.from([1, 2, 3, 4]).find((x) => x > 0); // 1
await Readable.from([1, 2, 3, 4]).find((x) => x > 10); // undefined
// With an asynchronous predicate, making at most 2 file checks at a time.
const foundBigFile = await Readable.from([
'file1',
'file2',
'file3',
]).find(async (fileName) => {
const stats = await stat(fileName);
return stat.size > 1024 * 1024;
}, { concurrency: 2 });
console.log(foundBigFile); // File name of large file, if any file in the list is bigger than 1MB
console.log('done'); // Stream has finished
```
######
`readable.every(fn[, options])`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) a function to call on each chunk of the stream.
+ `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) a chunk of data from the stream.
+ `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `signal` [<AbortSignal>](globals#class-abortsignal) aborted if the stream is destroyed allowing to abort the `fn` call early.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the maximum concurrent invocation of `fn` to call on the stream at once. **Default:** `1`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) a promise evaluating to `true` if `fn` returned a truthy value for all of the chunks.
This method is similar to `Array.prototype.every` and calls `fn` on each chunk in the stream to check if all awaited return values are truthy value for `fn`. Once an `fn` call on a chunk awaited return value is falsy, the stream is destroyed and the promise is fulfilled with `false`. If all of the `fn` calls on the chunks return a truthy value, the promise is fulfilled with `true`.
```
import { Readable } from 'node:stream';
import { stat } from 'node:fs/promises';
// With a synchronous predicate.
await Readable.from([1, 2, 3, 4]).every((x) => x > 2); // false
await Readable.from([1, 2, 3, 4]).every((x) => x > 0); // true
// With an asynchronous predicate, making at most 2 file checks at a time.
const allBigFiles = await Readable.from([
'file1',
'file2',
'file3',
]).every(async (fileName) => {
const stats = await stat(fileName);
return stat.size > 1024 * 1024;
}, { concurrency: 2 });
// `true` if all files in the list are bigger than 1MiB
console.log(allBigFiles);
console.log('done'); // Stream has finished
```
######
`readable.flatMap(fn[, options])`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncGeneratorFunction>](https://tc39.es/proposal-async-iteration/#sec-asyncgeneratorfunction-constructor) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) a function to map over every chunk in the stream.
+ `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) a chunk of data from the stream.
+ `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `signal` [<AbortSignal>](globals#class-abortsignal) aborted if the stream is destroyed allowing to abort the `fn` call early.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the maximum concurrent invocation of `fn` to call on the stream at once. **Default:** `1`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Readable>](stream#class-streamreadable) a stream flat-mapped with the function `fn`.
This method returns a new stream by applying the given callback to each chunk of the stream and then flattening the result.
It is possible to return a stream or another iterable or async iterable from `fn` and the result streams will be merged (flattened) into the returned stream.
```
import { Readable } from 'node:stream';
import { createReadStream } from 'node:fs';
// With a synchronous mapper.
for await (const chunk of Readable.from([1, 2, 3, 4]).flatMap((x) => [x, x])) {
console.log(chunk); // 1, 1, 2, 2, 3, 3, 4, 4
}
// With an asynchronous mapper, combine the contents of 4 files
const concatResult = Readable.from([
'./1.mjs',
'./2.mjs',
'./3.mjs',
'./4.mjs',
]).flatMap((fileName) => createReadStream(fileName));
for await (const result of concatResult) {
// This will contain the contents (all chunks) of all 4 files
console.log(result);
}
```
######
`readable.drop(limit[, options])`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `limit` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the number of chunks to drop from the readable.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Readable>](stream#class-streamreadable) a stream with `limit` chunks dropped.
This method returns a new stream with the first `limit` chunks dropped.
```
import { Readable } from 'node:stream';
await Readable.from([1, 2, 3, 4]).drop(2).toArray(); // [3, 4]
```
######
`readable.take(limit[, options])`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `limit` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the number of chunks to take from the readable.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Readable>](stream#class-streamreadable) a stream with `limit` chunks taken.
This method returns a new stream with the first `limit` chunks.
```
import { Readable } from 'node:stream';
await Readable.from([1, 2, 3, 4]).take(2).toArray(); // [1, 2]
```
######
`readable.asIndexedPairs([options])`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Readable>](stream#class-streamreadable) a stream of indexed pairs.
This method returns a new stream with chunks of the underlying stream paired with a counter in the form `[index, chunk]`. The first index value is 0 and it increases by 1 for each chunk produced.
```
import { Readable } from 'node:stream';
const pairs = await Readable.from(['a', 'b', 'c']).asIndexedPairs().toArray();
console.log(pairs); // [[0, 'a'], [1, 'b'], [2, 'c']]
```
######
`readable.reduce(fn[, initial[, options]])`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) a reducer function to call over every chunk in the stream.
+ `previous` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the value obtained from the last call to `fn` or the `initial` value if specified or the first chunk of the stream otherwise.
+ `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) a chunk of data from the stream.
+ `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `signal` [<AbortSignal>](globals#class-abortsignal) aborted if the stream is destroyed allowing to abort the `fn` call early.
* `initial` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the initial value to use in the reduction.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows destroying the stream if the signal is aborted.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) a promise for the final value of the reduction.
This method calls `fn` on each chunk of the stream in order, passing it the result from the calculation on the previous element. It returns a promise for the final value of the reduction.
The reducer function iterates the stream element-by-element which means that there is no `concurrency` parameter or parallelism. To perform a `reduce` concurrently, it can be chained to the [`readable.map`](#readablemapfn-options) method.
If no `initial` value is supplied the first chunk of the stream is used as the initial value. If the stream is empty, the promise is rejected with a `TypeError` with the `ERR_INVALID_ARGS` code property.
```
import { Readable } from 'node:stream';
const ten = await Readable.from([1, 2, 3, 4]).reduce((previous, data) => {
return previous + data;
});
console.log(ten); // 10
```
#### Duplex and transform streams
##### Class: `stream.Duplex`
History
| Version | Changes |
| --- | --- |
| v6.8.0 | Instances of `Duplex` now return `true` when checking `instanceof stream.Writable`. |
| v0.9.4 | Added in: v0.9.4 |
Duplex streams are streams that implement both the [`Readable`](#class-streamreadable) and [`Writable`](#class-streamwritable) interfaces.
Examples of `Duplex` streams include:
* [TCP sockets](net#class-netsocket)
* [zlib streams](zlib)
* [crypto streams](crypto)
######
`duplex.allowHalfOpen`
Added in: v0.9.4 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If `false` then the stream will automatically end the writable side when the readable side ends. Set initially by the `allowHalfOpen` constructor option, which defaults to `true`.
This can be changed manually to change the half-open behavior of an existing `Duplex` stream instance, but must be changed before the `'end'` event is emitted.
##### Class: `stream.Transform`
Added in: v0.9.4 Transform streams are [`Duplex`](#class-streamduplex) streams where the output is in some way related to the input. Like all [`Duplex`](#class-streamduplex) streams, `Transform` streams implement both the [`Readable`](#class-streamreadable) and [`Writable`](#class-streamwritable) interfaces.
Examples of `Transform` streams include:
* [zlib streams](zlib)
* [crypto streams](crypto)
######
`transform.destroy([error])`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | Work as a no-op on a stream that has already been destroyed. |
| v8.0.0 | Added in: v8.0.0 |
* `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Destroy the stream, and optionally emit an `'error'` event. After this call, the transform stream would release any internal resources. Implementors should not override this method, but instead implement [`readable._destroy()`](#readable_destroyerr-callback). The default implementation of `_destroy()` for `Transform` also emit `'close'` unless `emitClose` is set in false.
Once `destroy()` has been called, any further calls will be a no-op and no further errors except from `_destroy()` may be emitted as `'error'`.
####
`stream.finished(stream[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v15.11.0 | The `signal` option was added. |
| v14.0.0 | The `finished(stream, cb)` will wait for the `'close'` event before invoking the callback. The implementation tries to detect legacy streams and only apply this behavior to streams which are expected to emit `'close'`. |
| v14.0.0 | Emitting `'close'` before `'end'` on a `Readable` stream will cause an `ERR_STREAM_PREMATURE_CLOSE` error. |
| v14.0.0 | Callback will be invoked on streams which have already finished before the call to `finished(stream, cb)`. |
| v10.0.0 | Added in: v10.0.0 |
* `stream` [<Stream>](stream#stream) A readable and/or writable stream.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `error` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `false`, then a call to `emit('error', err)` is not treated as finished. **Default:** `true`.
+ `readable` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When set to `false`, the callback will be called when the stream ends even though the stream might still be readable. **Default:** `true`.
+ `writable` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When set to `false`, the callback will be called when the stream ends even though the stream might still be writable. **Default:** `true`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) allows aborting the wait for the stream finish. The underlying stream will *not* be aborted if the signal is aborted. The callback will get called with an `AbortError`. All registered listeners added by this function will also be removed.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function that takes an optional error argument.
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A cleanup function which removes all registered listeners.
A function to get notified when a stream is no longer readable, writable or has experienced an error or a premature close event.
```
const { finished } = require('node:stream');
const fs = require('node:fs');
const rs = fs.createReadStream('archive.tar');
finished(rs, (err) => {
if (err) {
console.error('Stream failed.', err);
} else {
console.log('Stream is done reading.');
}
});
rs.resume(); // Drain the stream.
```
Especially useful in error handling scenarios where a stream is destroyed prematurely (like an aborted HTTP request), and will not emit `'end'` or `'finish'`.
The `finished` API provides promise version:
```
const { finished } = require('node:stream/promises');
const fs = require('node:fs');
const rs = fs.createReadStream('archive.tar');
async function run() {
await finished(rs);
console.log('Stream is done reading.');
}
run().catch(console.error);
rs.resume(); // Drain the stream.
```
`stream.finished()` leaves dangling event listeners (in particular `'error'`, `'end'`, `'finish'` and `'close'`) after `callback` has been invoked. The reason for this is so that unexpected `'error'` events (due to incorrect stream implementations) do not cause unexpected crashes. If this is unwanted behavior then the returned cleanup function needs to be invoked in the callback:
```
const cleanup = finished(rs, (err) => {
cleanup();
// ...
});
```
####
`stream.pipeline(source[, ...transforms], destination, callback)`
####
`stream.pipeline(streams, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v14.0.0 | The `pipeline(..., cb)` will wait for the `'close'` event before invoking the callback. The implementation tries to detect legacy streams and only apply this behavior to streams which are expected to emit `'close'`. |
| v13.10.0 | Add support for async generators. |
| v10.0.0 | Added in: v10.0.0 |
* `streams` [<Stream[]>](stream#stream) | [<Iterable[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) | [<AsyncIterable[]>](https://tc39.github.io/ecma262/#sec-asynciterable-interface) | [<Function[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `source` [<Stream>](stream#stream) | [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) | [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ Returns: [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) | [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface)
* `...transforms` [<Stream>](stream#stream) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `source` [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface)
+ Returns: [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface)
* `destination` [<Stream>](stream#stream) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `source` [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface)
+ Returns: [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface) | [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called when the pipeline is fully done.
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `val` Resolved value of `Promise` returned by `destination`.
* Returns: [<Stream>](stream#stream)
A module method to pipe between streams and generators forwarding errors and properly cleaning up and provide a callback when the pipeline is complete.
```
const { pipeline } = require('node:stream');
const fs = require('node:fs');
const zlib = require('node:zlib');
// Use the pipeline API to easily pipe a series of streams
// together and get notified when the pipeline is fully done.
// A pipeline to gzip a potentially huge tar file efficiently:
pipeline(
fs.createReadStream('archive.tar'),
zlib.createGzip(),
fs.createWriteStream('archive.tar.gz'),
(err) => {
if (err) {
console.error('Pipeline failed.', err);
} else {
console.log('Pipeline succeeded.');
}
}
);
```
The `pipeline` API provides a promise version, which can also receive an options argument as the last parameter with a `signal` [<AbortSignal>](globals#class-abortsignal) property. When the signal is aborted, `destroy` will be called on the underlying pipeline, with an `AbortError`.
```
const { pipeline } = require('node:stream/promises');
const fs = require('node:fs');
const zlib = require('node:zlib');
async function run() {
await pipeline(
fs.createReadStream('archive.tar'),
zlib.createGzip(),
fs.createWriteStream('archive.tar.gz')
);
console.log('Pipeline succeeded.');
}
run().catch(console.error);
```
To use an `AbortSignal`, pass it inside an options object, as the last argument:
```
const { pipeline } = require('node:stream/promises');
const fs = require('node:fs');
const zlib = require('node:zlib');
async function run() {
const ac = new AbortController();
const signal = ac.signal;
setTimeout(() => ac.abort(), 1);
await pipeline(
fs.createReadStream('archive.tar'),
zlib.createGzip(),
fs.createWriteStream('archive.tar.gz'),
{ signal },
);
}
run().catch(console.error); // AbortError
```
The `pipeline` API also supports async generators:
```
const { pipeline } = require('node:stream/promises');
const fs = require('node:fs');
async function run() {
await pipeline(
fs.createReadStream('lowercase.txt'),
async function* (source, { signal }) {
source.setEncoding('utf8'); // Work with strings rather than `Buffer`s.
for await (const chunk of source) {
yield await processChunk(chunk, { signal });
}
},
fs.createWriteStream('uppercase.txt')
);
console.log('Pipeline succeeded.');
}
run().catch(console.error);
```
Remember to handle the `signal` argument passed into the async generator. Especially in the case where the async generator is the source for the pipeline (i.e. first argument) or the pipeline will never complete.
```
const { pipeline } = require('node:stream/promises');
const fs = require('node:fs');
async function run() {
await pipeline(
async function* ({ signal }) {
await someLongRunningfn({ signal });
yield 'asd';
},
fs.createWriteStream('uppercase.txt')
);
console.log('Pipeline succeeded.');
}
run().catch(console.error);
```
`stream.pipeline()` will call `stream.destroy(err)` on all streams except:
* `Readable` streams which have emitted `'end'` or `'close'`.
* `Writable` streams which have emitted `'finish'` or `'close'`.
`stream.pipeline()` leaves dangling event listeners on the streams after the `callback` has been invoked. In the case of reuse of streams after failure, this can cause event listener leaks and swallowed errors. If the last stream is readable, dangling event listeners will be removed so that the last stream can be consumed later.
`stream.pipeline()` closes all the streams when an error is raised. The `IncomingRequest` usage with `pipeline` could lead to an unexpected behavior once it would destroy the socket without sending the expected response. See the example below:
```
const fs = require('node:fs');
const http = require('node:http');
const { pipeline } = require('node:stream');
const server = http.createServer((req, res) => {
const fileStream = fs.createReadStream('./fileNotExist.txt');
pipeline(fileStream, res, (err) => {
if (err) {
console.log(err); // No such file
// this message can't be sent once `pipeline` already destroyed the socket
return res.end('error!!!');
}
});
});
```
####
`stream.compose(...streams)`
Added in: v16.9.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - `stream.compose` is experimental.
* `streams` [<Stream[]>](stream#stream) | [<Iterable[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) | [<AsyncIterable[]>](https://tc39.github.io/ecma262/#sec-asynciterable-interface) | [<Function[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<stream.Duplex>](stream#class-streamduplex)
Combines two or more streams into a `Duplex` stream that writes to the first stream and reads from the last. Each provided stream is piped into the next, using `stream.pipeline`. If any of the streams error then all are destroyed, including the outer `Duplex` stream.
Because `stream.compose` returns a new stream that in turn can (and should) be piped into other streams, it enables composition. In contrast, when passing streams to `stream.pipeline`, typically the first stream is a readable stream and the last a writable stream, forming a closed circuit.
If passed a `Function` it must be a factory method taking a `source` `Iterable`.
```
import { compose, Transform } from 'node:stream';
const removeSpaces = new Transform({
transform(chunk, encoding, callback) {
callback(null, String(chunk).replace(' ', ''));
}
});
async function* toUpper(source) {
for await (const chunk of source) {
yield String(chunk).toUpperCase();
}
}
let res = '';
for await (const buf of compose(removeSpaces, toUpper).end('hello world')) {
res += buf;
}
console.log(res); // prints 'HELLOWORLD'
```
`stream.compose` can be used to convert async iterables, generators and functions into streams.
* `AsyncIterable` converts into a readable `Duplex`. Cannot yield `null`.
* `AsyncGeneratorFunction` converts into a readable/writable transform `Duplex`. Must take a source `AsyncIterable` as first parameter. Cannot yield `null`.
* `AsyncFunction` converts into a writable `Duplex`. Must return either `null` or `undefined`.
```
import { compose } from 'node:stream';
import { finished } from 'node:stream/promises';
// Convert AsyncIterable into readable Duplex.
const s1 = compose(async function*() {
yield 'Hello';
yield 'World';
}());
// Convert AsyncGenerator into transform Duplex.
const s2 = compose(async function*(source) {
for await (const chunk of source) {
yield String(chunk).toUpperCase();
}
});
let res = '';
// Convert AsyncFunction into writable Duplex.
const s3 = compose(async function(source) {
for await (const chunk of source) {
res += chunk;
}
});
await finished(compose(s1, s2, s3));
console.log(res); // prints 'HELLOWORLD'
```
####
`stream.Readable.from(iterable[, options])`
Added in: v12.3.0, v10.17.0 * `iterable` [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) Object implementing the `Symbol.asyncIterator` or `Symbol.iterator` iterable protocol. Emits an 'error' event if a null value is passed.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Options provided to `new stream.Readable([options])`. By default, `Readable.from()` will set `options.objectMode` to `true`, unless this is explicitly opted out by setting `options.objectMode` to `false`.
* Returns: [<stream.Readable>](stream#class-streamreadable)
A utility method for creating readable streams out of iterators.
```
const { Readable } = require('node:stream');
async function * generate() {
yield 'hello';
yield 'streams';
}
const readable = Readable.from(generate());
readable.on('data', (chunk) => {
console.log(chunk);
});
```
Calling `Readable.from(string)` or `Readable.from(buffer)` will not have the strings or buffers be iterated to match the other streams semantics for performance reasons.
####
`stream.Readable.fromWeb(readableStream[, options])`
Added in: v17.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `readableStream` [<ReadableStream>](webstreams#class-readablestream)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `objectMode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
+ `signal` [<AbortSignal>](globals#class-abortsignal)
* Returns: [<stream.Readable>](stream#class-streamreadable)
####
`stream.Readable.isDisturbed(stream)`
Added in: v16.8.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `stream` [<stream.Readable>](stream#class-streamreadable) | [<ReadableStream>](webstreams#class-readablestream)
* Returns: `boolean`
Returns whether the stream has been read from or cancelled.
####
`stream.isErrored(stream)`
Added in: v17.3.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `stream` [<Readable>](stream#class-streamreadable) | [<Writable>](stream#class-streamwritable) | [<Duplex>](stream#class-streamduplex) | [<WritableStream>](webstreams#class-writablestream) | [<ReadableStream>](webstreams#class-readablestream)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns whether the stream has encountered an error.
####
`stream.isReadable(stream)`
Added in: v17.4.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `stream` [<Readable>](stream#class-streamreadable) | [<Duplex>](stream#class-streamduplex) | [<ReadableStream>](webstreams#class-readablestream)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns whether the stream is readable.
####
`stream.Readable.toWeb(streamReadable[, options])`
Added in: v17.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `streamReadable` [<stream.Readable>](stream#class-streamreadable)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `strategy` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
- `size` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<ReadableStream>](webstreams#class-readablestream)
####
`stream.Writable.fromWeb(writableStream[, options])`
Added in: v17.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `writableStream` [<WritableStream>](webstreams#class-writablestream)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `decodeStrings` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `objectMode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
+ `signal` [<AbortSignal>](globals#class-abortsignal)
* Returns: [<stream.Writable>](stream#class-streamwritable)
####
`stream.Writable.toWeb(streamWritable)`
Added in: v17.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `streamWritable` [<stream.Writable>](stream#class-streamwritable)
* Returns: [<WritableStream>](webstreams#class-writablestream)
####
`stream.Duplex.from(src)`
Added in: v16.8.0 * `src` [<Stream>](stream#stream) | [<Blob>](buffer#class-blob) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Iterable>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) | [<AsyncIterable>](https://tc39.github.io/ecma262/#sec-asynciterable-interface) | [<AsyncGeneratorFunction>](https://tc39.es/proposal-async-iteration/#sec-asyncgeneratorfunction-constructor) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) | [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
A utility method for creating duplex streams.
* `Stream` converts writable stream into writable `Duplex` and readable stream to `Duplex`.
* `Blob` converts into readable `Duplex`.
* `string` converts into readable `Duplex`.
* `ArrayBuffer` converts into readable `Duplex`.
* `AsyncIterable` converts into a readable `Duplex`. Cannot yield `null`.
* `AsyncGeneratorFunction` converts into a readable/writable transform `Duplex`. Must take a source `AsyncIterable` as first parameter. Cannot yield `null`.
* `AsyncFunction` converts into a writable `Duplex`. Must return either `null` or `undefined`
* `Object ({ writable, readable })` converts `readable` and `writable` into `Stream` and then combines them into `Duplex` where the `Duplex` will write to the `writable` and read from the `readable`.
* `Promise` converts into readable `Duplex`. Value `null` is ignored.
* Returns: [<stream.Duplex>](stream#class-streamduplex)
####
`stream.Duplex.fromWeb(pair[, options])`
Added in: v17.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `pair` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `readable` [<ReadableStream>](webstreams#class-readablestream)
+ `writable` [<WritableStream>](webstreams#class-writablestream)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `allowHalfOpen` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
+ `decodeStrings` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `objectMode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
+ `signal` [<AbortSignal>](globals#class-abortsignal)
* Returns: [<stream.Duplex>](stream#class-streamduplex)
MJS modules
```
import { Duplex } from 'node:stream';
import {
ReadableStream,
WritableStream
} from 'node:stream/web';
const readable = new ReadableStream({
start(controller) {
controller.enqueue('world');
},
});
const writable = new WritableStream({
write(chunk) {
console.log('writable', chunk);
}
});
const pair = {
readable,
writable
};
const duplex = Duplex.fromWeb(pair, { encoding: 'utf8', objectMode: true });
duplex.write('hello');
for await (const chunk of duplex) {
console.log('readable', chunk);
}
```
CJS modules
```
const { Duplex } = require('node:stream');
const {
ReadableStream,
WritableStream
} = require('node:stream/web');
const readable = new ReadableStream({
start(controller) {
controller.enqueue('world');
},
});
const writable = new WritableStream({
write(chunk) {
console.log('writable', chunk);
}
});
const pair = {
readable,
writable
};
const duplex = Duplex.fromWeb(pair, { encoding: 'utf8', objectMode: true });
duplex.write('hello');
duplex.once('readable', () => console.log('readable', duplex.read()));
```
####
`stream.Duplex.toWeb(streamDuplex)`
Added in: v17.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `streamDuplex` [<stream.Duplex>](stream#class-streamduplex)
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `readable` [<ReadableStream>](webstreams#class-readablestream)
+ `writable` [<WritableStream>](webstreams#class-writablestream)
MJS modules
```
import { Duplex } from 'node:stream';
const duplex = Duplex({
objectMode: true,
read() {
this.push('world');
this.push(null);
},
write(chunk, encoding, callback) {
console.log('writable', chunk);
callback();
}
});
const { readable, writable } = Duplex.toWeb(duplex);
writable.getWriter().write('hello');
const { value } = await readable.getReader().read();
console.log('readable', value);
```
CJS modules
```
const { Duplex } = require('node:stream');
const duplex = Duplex({
objectMode: true,
read() {
this.push('world');
this.push(null);
},
write(chunk, encoding, callback) {
console.log('writable', chunk);
callback();
}
});
const { readable, writable } = Duplex.toWeb(duplex);
writable.getWriter().write('hello');
readable.getReader().read().then((result) => {
console.log('readable', result.value);
});
```
####
`stream.addAbortSignal(signal, stream)`
Added in: v15.4.0 * `signal` [<AbortSignal>](globals#class-abortsignal) A signal representing possible cancellation
* `stream` [<Stream>](stream#stream) a stream to attach a signal to
Attaches an AbortSignal to a readable or writeable stream. This lets code control stream destruction using an `AbortController`.
Calling `abort` on the `AbortController` corresponding to the passed `AbortSignal` will behave the same way as calling `.destroy(new AbortError())` on the stream.
```
const fs = require('node:fs');
const controller = new AbortController();
const read = addAbortSignal(
controller.signal,
fs.createReadStream(('object.json'))
);
// Later, abort the operation closing the stream
controller.abort();
```
Or using an `AbortSignal` with a readable stream as an async iterable:
```
const controller = new AbortController();
setTimeout(() => controller.abort(), 10_000); // set a timeout
const stream = addAbortSignal(
controller.signal,
fs.createReadStream(('object.json'))
);
(async () => {
try {
for await (const chunk of stream) {
await process(chunk);
}
} catch (e) {
if (e.name === 'AbortError') {
// The operation was cancelled
} else {
throw e;
}
}
})();
```
### API for stream implementers
The `node:stream` module API has been designed to make it possible to easily implement streams using JavaScript's prototypal inheritance model.
First, a stream developer would declare a new JavaScript class that extends one of the four basic stream classes (`stream.Writable`, `stream.Readable`, `stream.Duplex`, or `stream.Transform`), making sure they call the appropriate parent class constructor:
```
const { Writable } = require('node:stream');
class MyWritable extends Writable {
constructor({ highWaterMark, ...options }) {
super({ highWaterMark });
// ...
}
}
```
When extending streams, keep in mind what options the user can and should provide before forwarding these to the base constructor. For example, if the implementation makes assumptions in regard to the `autoDestroy` and `emitClose` options, do not allow the user to override these. Be explicit about what options are forwarded instead of implicitly forwarding all options.
The new stream class must then implement one or more specific methods, depending on the type of stream being created, as detailed in the chart below:
| Use-case | Class | Method(s) to implement |
| --- | --- | --- |
| Reading only | [`Readable`](#class-streamreadable) | [`_read()`](#readable_readsize) |
| Writing only | [`Writable`](#class-streamwritable) | [`_write()`](#writable_writechunk-encoding-callback), [`_writev()`](#writable_writevchunks-callback), [`_final()`](#writable_finalcallback) |
| Reading and writing | [`Duplex`](#class-streamduplex) | [`_read()`](#readable_readsize), [`_write()`](#writable_writechunk-encoding-callback), [`_writev()`](#writable_writevchunks-callback), [`_final()`](#writable_finalcallback) |
| Operate on written data, then read the result | [`Transform`](#class-streamtransform) | [`_transform()`](#transform_transformchunk-encoding-callback), [`_flush()`](#transform_flushcallback), [`_final()`](#writable_finalcallback) |
The implementation code for a stream should *never* call the "public" methods of a stream that are intended for use by consumers (as described in the [API for stream consumers](#api-for-stream-consumers) section). Doing so may lead to adverse side effects in application code consuming the stream.
Avoid overriding public methods such as `write()`, `end()`, `cork()`, `uncork()`, `read()` and `destroy()`, or emitting internal events such as `'error'`, `'data'`, `'end'`, `'finish'` and `'close'` through `.emit()`. Doing so can break current and future stream invariants leading to behavior and/or compatibility issues with other streams, stream utilities, and user expectations.
#### Simplified construction
Added in: v1.2.0 For many simple cases, it is possible to create a stream without relying on inheritance. This can be accomplished by directly creating instances of the `stream.Writable`, `stream.Readable`, `stream.Duplex`, or `stream.Transform` objects and passing appropriate methods as constructor options.
```
const { Writable } = require('node:stream');
const myWritable = new Writable({
construct(callback) {
// Initialize state and load resources...
},
write(chunk, encoding, callback) {
// ...
},
destroy() {
// Free resources...
}
});
```
#### Implementing a writable stream
The `stream.Writable` class is extended to implement a [`Writable`](#class-streamwritable) stream.
Custom `Writable` streams *must* call the `new stream.Writable([options])` constructor and implement the `writable._write()` and/or `writable._writev()` method.
#####
`new stream.Writable([options])`
History
| Version | Changes |
| --- | --- |
| v15.5.0 | support passing in an AbortSignal. |
| v14.0.0 | Change `autoDestroy` option default to `true`. |
| v11.2.0, v10.16.0 | Add `autoDestroy` option to automatically `destroy()` the stream when it emits `'finish'` or errors. |
| v10.0.0 | Add `emitClose` option to specify if `'close'` is emitted on destroy. |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Buffer level when [`stream.write()`](#writablewritechunk-encoding-callback) starts returning `false`. **Default:** `16384` (16 KiB), or `16` for `objectMode` streams.
+ `decodeStrings` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether to encode `string`s passed to [`stream.write()`](#writablewritechunk-encoding-callback) to `Buffer`s (with the encoding specified in the [`stream.write()`](#writablewritechunk-encoding-callback) call) before passing them to [`stream._write()`](#writable_writechunk-encoding-callback). Other types of data are not converted (i.e. `Buffer`s are not decoded into `string`s). Setting to false will prevent `string`s from being converted. **Default:** `true`.
+ `defaultEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The default encoding that is used when no encoding is specified as an argument to [`stream.write()`](#writablewritechunk-encoding-callback). **Default:** `'utf8'`.
+ `objectMode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether or not the [`stream.write(anyObj)`](#writablewritechunk-encoding-callback) is a valid operation. When set, it becomes possible to write JavaScript values other than string, `Buffer` or `Uint8Array` if supported by the stream implementation. **Default:** `false`.
+ `emitClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether or not the stream should emit `'close'` after it has been destroyed. **Default:** `true`.
+ `write` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._write()`](#writable_writechunk-encoding-callback) method.
+ `writev` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._writev()`](#writable_writevchunks-callback) method.
+ `destroy` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._destroy()`](#writable_destroyerr-callback) method.
+ `final` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._final()`](#writable_finalcallback) method.
+ `construct` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._construct()`](#writable_constructcallback) method.
+ `autoDestroy` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether this stream should automatically call `.destroy()` on itself after ending. **Default:** `true`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) A signal representing possible cancellation.
```
const { Writable } = require('node:stream');
class MyWritable extends Writable {
constructor(options) {
// Calls the stream.Writable() constructor.
super(options);
// ...
}
}
```
Or, when using pre-ES6 style constructors:
```
const { Writable } = require('node:stream');
const util = require('node:util');
function MyWritable(options) {
if (!(this instanceof MyWritable))
return new MyWritable(options);
Writable.call(this, options);
}
util.inherits(MyWritable, Writable);
```
Or, using the simplified constructor approach:
```
const { Writable } = require('node:stream');
const myWritable = new Writable({
write(chunk, encoding, callback) {
// ...
},
writev(chunks, callback) {
// ...
}
});
```
Calling `abort` on the `AbortController` corresponding to the passed `AbortSignal` will behave the same way as calling `.destroy(new AbortError())` on the writeable stream.
```
const { Writable } = require('node:stream');
const controller = new AbortController();
const myWritable = new Writable({
write(chunk, encoding, callback) {
// ...
},
writev(chunks, callback) {
// ...
},
signal: controller.signal
});
// Later, abort the operation closing the stream
controller.abort();
```
#####
`writable._construct(callback)`
Added in: v15.0.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Call this function (optionally with an error argument) when the stream has finished initializing.
The `_construct()` method MUST NOT be called directly. It may be implemented by child classes, and if so, will be called by the internal `Writable` class methods only.
This optional function will be called in a tick after the stream constructor has returned, delaying any `_write()`, `_final()` and `_destroy()` calls until `callback` is called. This is useful to initialize state or asynchronously initialize resources before the stream can be used.
```
const { Writable } = require('node:stream');
const fs = require('node:fs');
class WriteStream extends Writable {
constructor(filename) {
super();
this.filename = filename;
this.fd = null;
}
_construct(callback) {
fs.open(this.filename, (err, fd) => {
if (err) {
callback(err);
} else {
this.fd = fd;
callback();
}
});
}
_write(chunk, encoding, callback) {
fs.write(this.fd, chunk, callback);
}
_destroy(err, callback) {
if (this.fd) {
fs.close(this.fd, (er) => callback(er || err));
} else {
callback(err);
}
}
}
```
#####
`writable._write(chunk, encoding, callback)`
History
| Version | Changes |
| --- | --- |
| v12.11.0 | \_write() is optional when providing \_writev(). |
* `chunk` [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The `Buffer` to be written, converted from the `string` passed to [`stream.write()`](#writablewritechunk-encoding-callback). If the stream's `decodeStrings` option is `false` or the stream is operating in object mode, the chunk will not be converted & will be whatever was passed to [`stream.write()`](#writablewritechunk-encoding-callback).
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If the chunk is a string, then `encoding` is the character encoding of that string. If chunk is a `Buffer`, or if the stream is operating in object mode, `encoding` may be ignored.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Call this function (optionally with an error argument) when processing is complete for the supplied chunk.
All `Writable` stream implementations must provide a [`writable._write()`](#writable_writechunk-encoding-callback) and/or [`writable._writev()`](#writable_writevchunks-callback) method to send data to the underlying resource.
[`Transform`](#class-streamtransform) streams provide their own implementation of the [`writable._write()`](#writable_writechunk-encoding-callback).
This function MUST NOT be called by application code directly. It should be implemented by child classes, and called by the internal `Writable` class methods only.
The `callback` function must be called synchronously inside of `writable._write()` or asynchronously (i.e. different tick) to signal either that the write completed successfully or failed with an error. The first argument passed to the `callback` must be the `Error` object if the call failed or `null` if the write succeeded.
All calls to `writable.write()` that occur between the time `writable._write()` is called and the `callback` is called will cause the written data to be buffered. When the `callback` is invoked, the stream might emit a [`'drain'`](#event-drain) event. If a stream implementation is capable of processing multiple chunks of data at once, the `writable._writev()` method should be implemented.
If the `decodeStrings` property is explicitly set to `false` in the constructor options, then `chunk` will remain the same object that is passed to `.write()`, and may be a string rather than a `Buffer`. This is to support implementations that have an optimized handling for certain string data encodings. In that case, the `encoding` argument will indicate the character encoding of the string. Otherwise, the `encoding` argument can be safely ignored.
The `writable._write()` method is prefixed with an underscore because it is internal to the class that defines it, and should never be called directly by user programs.
#####
`writable._writev(chunks, callback)`
* `chunks` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The data to be written. The value is an array of [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) that each represent a discrete chunk of data to write. The properties of these objects are:
+ `chunk` [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A buffer instance or string containing the data to be written. The `chunk` will be a string if the `Writable` was created with the `decodeStrings` option set to `false` and a string was passed to `write()`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The character encoding of the `chunk`. If `chunk` is a `Buffer`, the `encoding` will be `'buffer'`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function (optionally with an error argument) to be invoked when processing is complete for the supplied chunks.
This function MUST NOT be called by application code directly. It should be implemented by child classes, and called by the internal `Writable` class methods only.
The `writable._writev()` method may be implemented in addition or alternatively to `writable._write()` in stream implementations that are capable of processing multiple chunks of data at once. If implemented and if there is buffered data from previous writes, `_writev()` will be called instead of `_write()`.
The `writable._writev()` method is prefixed with an underscore because it is internal to the class that defines it, and should never be called directly by user programs.
#####
`writable._destroy(err, callback)`
Added in: v8.0.0 * `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) A possible error.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function that takes an optional error argument.
The `_destroy()` method is called by [`writable.destroy()`](#writabledestroyerror). It can be overridden by child classes but it **must not** be called directly. Furthermore, the `callback` should not be mixed with async/await once it is executed when a promise is resolved.
#####
`writable._final(callback)`
Added in: v8.0.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Call this function (optionally with an error argument) when finished writing any remaining data.
The `_final()` method **must not** be called directly. It may be implemented by child classes, and if so, will be called by the internal `Writable` class methods only.
This optional function will be called before the stream closes, delaying the `'finish'` event until `callback` is called. This is useful to close resources or write buffered data before a stream ends.
##### Errors while writing
Errors occurring during the processing of the [`writable._write()`](#writable_writechunk-encoding-callback), [`writable._writev()`](#writable_writevchunks-callback) and [`writable._final()`](#writable_finalcallback) methods must be propagated by invoking the callback and passing the error as the first argument. Throwing an `Error` from within these methods or manually emitting an `'error'` event results in undefined behavior.
If a `Readable` stream pipes into a `Writable` stream when `Writable` emits an error, the `Readable` stream will be unpiped.
```
const { Writable } = require('node:stream');
const myWritable = new Writable({
write(chunk, encoding, callback) {
if (chunk.toString().indexOf('a') >= 0) {
callback(new Error('chunk is invalid'));
} else {
callback();
}
}
});
```
##### An example writable stream
The following illustrates a rather simplistic (and somewhat pointless) custom `Writable` stream implementation. While this specific `Writable` stream instance is not of any real particular usefulness, the example illustrates each of the required elements of a custom [`Writable`](#class-streamwritable) stream instance:
```
const { Writable } = require('node:stream');
class MyWritable extends Writable {
_write(chunk, encoding, callback) {
if (chunk.toString().indexOf('a') >= 0) {
callback(new Error('chunk is invalid'));
} else {
callback();
}
}
}
```
##### Decoding buffers in a writable stream
Decoding buffers is a common task, for instance, when using transformers whose input is a string. This is not a trivial process when using multi-byte characters encoding, such as UTF-8. The following example shows how to decode multi-byte strings using `StringDecoder` and [`Writable`](#class-streamwritable).
```
const { Writable } = require('node:stream');
const { StringDecoder } = require('node:string_decoder');
class StringWritable extends Writable {
constructor(options) {
super(options);
this._decoder = new StringDecoder(options && options.defaultEncoding);
this.data = '';
}
_write(chunk, encoding, callback) {
if (encoding === 'buffer') {
chunk = this._decoder.write(chunk);
}
this.data += chunk;
callback();
}
_final(callback) {
this.data += this._decoder.end();
callback();
}
}
const euro = [[0xE2, 0x82], [0xAC]].map(Buffer.from);
const w = new StringWritable();
w.write('currency: ');
w.write(euro[0]);
w.end(euro[1]);
console.log(w.data); // currency: €
```
#### Implementing a readable stream
The `stream.Readable` class is extended to implement a [`Readable`](#class-streamreadable) stream.
Custom `Readable` streams *must* call the `new stream.Readable([options])` constructor and implement the [`readable._read()`](#readable_readsize) method.
#####
`new stream.Readable([options])`
History
| Version | Changes |
| --- | --- |
| v15.5.0 | support passing in an AbortSignal. |
| v14.0.0 | Change `autoDestroy` option default to `true`. |
| v11.2.0, v10.16.0 | Add `autoDestroy` option to automatically `destroy()` the stream when it emits `'end'` or errors. |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum [number of bytes](#highwatermark-discrepancy-after-calling-readablesetencoding) to store in the internal buffer before ceasing to read from the underlying resource. **Default:** `16384` (16 KiB), or `16` for `objectMode` streams.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If specified, then buffers will be decoded to strings using the specified encoding. **Default:** `null`.
+ `objectMode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether this stream should behave as a stream of objects. Meaning that [`stream.read(n)`](#readablereadsize) returns a single value instead of a `Buffer` of size `n`. **Default:** `false`.
+ `emitClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether or not the stream should emit `'close'` after it has been destroyed. **Default:** `true`.
+ `read` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._read()`](#readable_readsize) method.
+ `destroy` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._destroy()`](#readable_destroyerr-callback) method.
+ `construct` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._construct()`](#readable_constructcallback) method.
+ `autoDestroy` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether this stream should automatically call `.destroy()` on itself after ending. **Default:** `true`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) A signal representing possible cancellation.
```
const { Readable } = require('node:stream');
class MyReadable extends Readable {
constructor(options) {
// Calls the stream.Readable(options) constructor.
super(options);
// ...
}
}
```
Or, when using pre-ES6 style constructors:
```
const { Readable } = require('node:stream');
const util = require('node:util');
function MyReadable(options) {
if (!(this instanceof MyReadable))
return new MyReadable(options);
Readable.call(this, options);
}
util.inherits(MyReadable, Readable);
```
Or, using the simplified constructor approach:
```
const { Readable } = require('node:stream');
const myReadable = new Readable({
read(size) {
// ...
}
});
```
Calling `abort` on the `AbortController` corresponding to the passed `AbortSignal` will behave the same way as calling `.destroy(new AbortError())` on the readable created.
```
const { Readable } = require('node:stream');
const controller = new AbortController();
const read = new Readable({
read(size) {
// ...
},
signal: controller.signal
});
// Later, abort the operation closing the stream
controller.abort();
```
#####
`readable._construct(callback)`
Added in: v15.0.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Call this function (optionally with an error argument) when the stream has finished initializing.
The `_construct()` method MUST NOT be called directly. It may be implemented by child classes, and if so, will be called by the internal `Readable` class methods only.
This optional function will be scheduled in the next tick by the stream constructor, delaying any `_read()` and `_destroy()` calls until `callback` is called. This is useful to initialize state or asynchronously initialize resources before the stream can be used.
```
const { Readable } = require('node:stream');
const fs = require('node:fs');
class ReadStream extends Readable {
constructor(filename) {
super();
this.filename = filename;
this.fd = null;
}
_construct(callback) {
fs.open(this.filename, (err, fd) => {
if (err) {
callback(err);
} else {
this.fd = fd;
callback();
}
});
}
_read(n) {
const buf = Buffer.alloc(n);
fs.read(this.fd, buf, 0, n, null, (err, bytesRead) => {
if (err) {
this.destroy(err);
} else {
this.push(bytesRead > 0 ? buf.slice(0, bytesRead) : null);
}
});
}
_destroy(err, callback) {
if (this.fd) {
fs.close(this.fd, (er) => callback(er || err));
} else {
callback(err);
}
}
}
```
#####
`readable._read(size)`
Added in: v0.9.4 * `size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to read asynchronously
This function MUST NOT be called by application code directly. It should be implemented by child classes, and called by the internal `Readable` class methods only.
All `Readable` stream implementations must provide an implementation of the [`readable._read()`](#readable_readsize) method to fetch data from the underlying resource.
When [`readable._read()`](#readable_readsize) is called, if data is available from the resource, the implementation should begin pushing that data into the read queue using the [`this.push(dataChunk)`](#readablepushchunk-encoding) method. `_read()` will be called again after each call to [`this.push(dataChunk)`](#readablepushchunk-encoding) once the stream is ready to accept more data. `_read()` may continue reading from the resource and pushing data until `readable.push()` returns `false`. Only when `_read()` is called again after it has stopped should it resume pushing additional data into the queue.
Once the [`readable._read()`](#readable_readsize) method has been called, it will not be called again until more data is pushed through the [`readable.push()`](#readablepushchunk-encoding) method. Empty data such as empty buffers and strings will not cause [`readable._read()`](#readable_readsize) to be called.
The `size` argument is advisory. For implementations where a "read" is a single operation that returns data can use the `size` argument to determine how much data to fetch. Other implementations may ignore this argument and simply provide data whenever it becomes available. There is no need to "wait" until `size` bytes are available before calling [`stream.push(chunk)`](#readablepushchunk-encoding).
The [`readable._read()`](#readable_readsize) method is prefixed with an underscore because it is internal to the class that defines it, and should never be called directly by user programs.
#####
`readable._destroy(err, callback)`
Added in: v8.0.0 * `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) A possible error.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function that takes an optional error argument.
The `_destroy()` method is called by [`readable.destroy()`](#readabledestroyerror). It can be overridden by child classes but it **must not** be called directly.
#####
`readable.push(chunk[, encoding])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The `chunk` argument can now be a `Uint8Array` instance. |
* `chunk` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Chunk of data to push into the read queue. For streams not operating in object mode, `chunk` must be a string, `Buffer` or `Uint8Array`. For object mode streams, `chunk` may be any JavaScript value.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Encoding of string chunks. Must be a valid `Buffer` encoding, such as `'utf8'` or `'ascii'`.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if additional chunks of data may continue to be pushed; `false` otherwise.
When `chunk` is a `Buffer`, `Uint8Array`, or `string`, the `chunk` of data will be added to the internal queue for users of the stream to consume. Passing `chunk` as `null` signals the end of the stream (EOF), after which no more data can be written.
When the `Readable` is operating in paused mode, the data added with `readable.push()` can be read out by calling the [`readable.read()`](#readablereadsize) method when the [`'readable'`](#event-readable) event is emitted.
When the `Readable` is operating in flowing mode, the data added with `readable.push()` will be delivered by emitting a `'data'` event.
The `readable.push()` method is designed to be as flexible as possible. For example, when wrapping a lower-level source that provides some form of pause/resume mechanism, and a data callback, the low-level source can be wrapped by the custom `Readable` instance:
```
// `_source` is an object with readStop() and readStart() methods,
// and an `ondata` member that gets called when it has data, and
// an `onend` member that gets called when the data is over.
class SourceWrapper extends Readable {
constructor(options) {
super(options);
this._source = getLowLevelSourceObject();
// Every time there's data, push it into the internal buffer.
this._source.ondata = (chunk) => {
// If push() returns false, then stop reading from source.
if (!this.push(chunk))
this._source.readStop();
};
// When the source ends, push the EOF-signaling `null` chunk.
this._source.onend = () => {
this.push(null);
};
}
// _read() will be called when the stream wants to pull more data in.
// The advisory size argument is ignored in this case.
_read(size) {
this._source.readStart();
}
}
```
The `readable.push()` method is used to push the content into the internal buffer. It can be driven by the [`readable._read()`](#readable_readsize) method.
For streams not operating in object mode, if the `chunk` parameter of `readable.push()` is `undefined`, it will be treated as empty string or buffer. See [`readable.push('')`](#readablepush) for more information.
##### Errors while reading
Errors occurring during processing of the [`readable._read()`](#readable_readsize) must be propagated through the [`readable.destroy(err)`](#readable_destroyerr-callback) method. Throwing an `Error` from within [`readable._read()`](#readable_readsize) or manually emitting an `'error'` event results in undefined behavior.
```
const { Readable } = require('node:stream');
const myReadable = new Readable({
read(size) {
const err = checkSomeErrorCondition();
if (err) {
this.destroy(err);
} else {
// Do some work.
}
}
});
```
##### An example counting stream
The following is a basic example of a `Readable` stream that emits the numerals from 1 to 1,000,000 in ascending order, and then ends.
```
const { Readable } = require('node:stream');
class Counter extends Readable {
constructor(opt) {
super(opt);
this._max = 1000000;
this._index = 1;
}
_read() {
const i = this._index++;
if (i > this._max)
this.push(null);
else {
const str = String(i);
const buf = Buffer.from(str, 'ascii');
this.push(buf);
}
}
}
```
#### Implementing a duplex stream
A [`Duplex`](#class-streamduplex) stream is one that implements both [`Readable`](#class-streamreadable) and [`Writable`](#class-streamwritable), such as a TCP socket connection.
Because JavaScript does not have support for multiple inheritance, the `stream.Duplex` class is extended to implement a [`Duplex`](#class-streamduplex) stream (as opposed to extending the `stream.Readable` *and* `stream.Writable` classes).
The `stream.Duplex` class prototypically inherits from `stream.Readable` and parasitically from `stream.Writable`, but `instanceof` will work properly for both base classes due to overriding [`Symbol.hasInstance`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/hasInstance) on `stream.Writable`.
Custom `Duplex` streams *must* call the `new stream.Duplex([options])` constructor and implement *both* the [`readable._read()`](#readable_readsize) and `writable._write()` methods.
#####
`new stream.Duplex(options)`
History
| Version | Changes |
| --- | --- |
| v8.4.0 | The `readableHighWaterMark` and `writableHighWaterMark` options are supported now. |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Passed to both `Writable` and `Readable` constructors. Also has the following fields:
+ `allowHalfOpen` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `false`, then the stream will automatically end the writable side when the readable side ends. **Default:** `true`.
+ `readable` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Sets whether the `Duplex` should be readable. **Default:** `true`.
+ `writable` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Sets whether the `Duplex` should be writable. **Default:** `true`.
+ `readableObjectMode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Sets `objectMode` for readable side of the stream. Has no effect if `objectMode` is `true`. **Default:** `false`.
+ `writableObjectMode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Sets `objectMode` for writable side of the stream. Has no effect if `objectMode` is `true`. **Default:** `false`.
+ `readableHighWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets `highWaterMark` for the readable side of the stream. Has no effect if `highWaterMark` is provided.
+ `writableHighWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Sets `highWaterMark` for the writable side of the stream. Has no effect if `highWaterMark` is provided.
```
const { Duplex } = require('node:stream');
class MyDuplex extends Duplex {
constructor(options) {
super(options);
// ...
}
}
```
Or, when using pre-ES6 style constructors:
```
const { Duplex } = require('node:stream');
const util = require('node:util');
function MyDuplex(options) {
if (!(this instanceof MyDuplex))
return new MyDuplex(options);
Duplex.call(this, options);
}
util.inherits(MyDuplex, Duplex);
```
Or, using the simplified constructor approach:
```
const { Duplex } = require('node:stream');
const myDuplex = new Duplex({
read(size) {
// ...
},
write(chunk, encoding, callback) {
// ...
}
});
```
When using pipeline:
```
const { Transform, pipeline } = require('node:stream');
const fs = require('node:fs');
pipeline(
fs.createReadStream('object.json')
.setEncoding('utf8'),
new Transform({
decodeStrings: false, // Accept string input rather than Buffers
construct(callback) {
this.data = '';
callback();
},
transform(chunk, encoding, callback) {
this.data += chunk;
callback();
},
flush(callback) {
try {
// Make sure is valid json.
JSON.parse(this.data);
this.push(this.data);
callback();
} catch (err) {
callback(err);
}
}
}),
fs.createWriteStream('valid-object.json'),
(err) => {
if (err) {
console.error('failed', err);
} else {
console.log('completed');
}
}
);
```
##### An example duplex stream
The following illustrates a simple example of a `Duplex` stream that wraps a hypothetical lower-level source object to which data can be written, and from which data can be read, albeit using an API that is not compatible with Node.js streams. The following illustrates a simple example of a `Duplex` stream that buffers incoming written data via the [`Writable`](#class-streamwritable) interface that is read back out via the [`Readable`](#class-streamreadable) interface.
```
const { Duplex } = require('node:stream');
const kSource = Symbol('source');
class MyDuplex extends Duplex {
constructor(source, options) {
super(options);
this[kSource] = source;
}
_write(chunk, encoding, callback) {
// The underlying source only deals with strings.
if (Buffer.isBuffer(chunk))
chunk = chunk.toString();
this[kSource].writeSomeData(chunk);
callback();
}
_read(size) {
this[kSource].fetchSomeData(size, (data, encoding) => {
this.push(Buffer.from(data, encoding));
});
}
}
```
The most important aspect of a `Duplex` stream is that the `Readable` and `Writable` sides operate independently of one another despite co-existing within a single object instance.
##### Object mode duplex streams
For `Duplex` streams, `objectMode` can be set exclusively for either the `Readable` or `Writable` side using the `readableObjectMode` and `writableObjectMode` options respectively.
In the following example, for instance, a new `Transform` stream (which is a type of [`Duplex`](#class-streamduplex) stream) is created that has an object mode `Writable` side that accepts JavaScript numbers that are converted to hexadecimal strings on the `Readable` side.
```
const { Transform } = require('node:stream');
// All Transform streams are also Duplex Streams.
const myTransform = new Transform({
writableObjectMode: true,
transform(chunk, encoding, callback) {
// Coerce the chunk to a number if necessary.
chunk |= 0;
// Transform the chunk into something else.
const data = chunk.toString(16);
// Push the data onto the readable queue.
callback(null, '0'.repeat(data.length % 2) + data);
}
});
myTransform.setEncoding('ascii');
myTransform.on('data', (chunk) => console.log(chunk));
myTransform.write(1);
// Prints: 01
myTransform.write(10);
// Prints: 0a
myTransform.write(100);
// Prints: 64
```
#### Implementing a transform stream
A [`Transform`](#class-streamtransform) stream is a [`Duplex`](#class-streamduplex) stream where the output is computed in some way from the input. Examples include <zlib> streams or <crypto> streams that compress, encrypt, or decrypt data.
There is no requirement that the output be the same size as the input, the same number of chunks, or arrive at the same time. For example, a `Hash` stream will only ever have a single chunk of output which is provided when the input is ended. A `zlib` stream will produce output that is either much smaller or much larger than its input.
The `stream.Transform` class is extended to implement a [`Transform`](#class-streamtransform) stream.
The `stream.Transform` class prototypically inherits from `stream.Duplex` and implements its own versions of the `writable._write()` and [`readable._read()`](#readable_readsize) methods. Custom `Transform` implementations *must* implement the [`transform._transform()`](#transform_transformchunk-encoding-callback) method and *may* also implement the [`transform._flush()`](#transform_flushcallback) method.
Care must be taken when using `Transform` streams in that data written to the stream can cause the `Writable` side of the stream to become paused if the output on the `Readable` side is not consumed.
#####
`new stream.Transform([options])`
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Passed to both `Writable` and `Readable` constructors. Also has the following fields:
+ `transform` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._transform()`](#transform_transformchunk-encoding-callback) method.
+ `flush` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Implementation for the [`stream._flush()`](#transform_flushcallback) method.
```
const { Transform } = require('node:stream');
class MyTransform extends Transform {
constructor(options) {
super(options);
// ...
}
}
```
Or, when using pre-ES6 style constructors:
```
const { Transform } = require('node:stream');
const util = require('node:util');
function MyTransform(options) {
if (!(this instanceof MyTransform))
return new MyTransform(options);
Transform.call(this, options);
}
util.inherits(MyTransform, Transform);
```
Or, using the simplified constructor approach:
```
const { Transform } = require('node:stream');
const myTransform = new Transform({
transform(chunk, encoding, callback) {
// ...
}
});
```
##### Event: `'end'`
The [`'end'`](#event-end) event is from the `stream.Readable` class. The `'end'` event is emitted after all data has been output, which occurs after the callback in [`transform._flush()`](#transform_flushcallback) has been called. In the case of an error, `'end'` should not be emitted.
##### Event: `'finish'`
The [`'finish'`](#event-finish) event is from the `stream.Writable` class. The `'finish'` event is emitted after [`stream.end()`](#writableendchunk-encoding-callback) is called and all chunks have been processed by [`stream._transform()`](#transform_transformchunk-encoding-callback). In the case of an error, `'finish'` should not be emitted.
#####
`transform._flush(callback)`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function (optionally with an error argument and data) to be called when remaining data has been flushed.
This function MUST NOT be called by application code directly. It should be implemented by child classes, and called by the internal `Readable` class methods only.
In some cases, a transform operation may need to emit an additional bit of data at the end of the stream. For example, a `zlib` compression stream will store an amount of internal state used to optimally compress the output. When the stream ends, however, that additional data needs to be flushed so that the compressed data will be complete.
Custom [`Transform`](#class-streamtransform) implementations *may* implement the `transform._flush()` method. This will be called when there is no more written data to be consumed, but before the [`'end'`](#event-end) event is emitted signaling the end of the [`Readable`](#class-streamreadable) stream.
Within the `transform._flush()` implementation, the `transform.push()` method may be called zero or more times, as appropriate. The `callback` function must be called when the flush operation is complete.
The `transform._flush()` method is prefixed with an underscore because it is internal to the class that defines it, and should never be called directly by user programs.
#####
`transform._transform(chunk, encoding, callback)`
* `chunk` [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The `Buffer` to be transformed, converted from the `string` passed to [`stream.write()`](#writablewritechunk-encoding-callback). If the stream's `decodeStrings` option is `false` or the stream is operating in object mode, the chunk will not be converted & will be whatever was passed to [`stream.write()`](#writablewritechunk-encoding-callback).
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If the chunk is a string, then this is the encoding type. If chunk is a buffer, then this is the special value `'buffer'`. Ignore it in that case.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function (optionally with an error argument and data) to be called after the supplied `chunk` has been processed.
This function MUST NOT be called by application code directly. It should be implemented by child classes, and called by the internal `Readable` class methods only.
All `Transform` stream implementations must provide a `_transform()` method to accept input and produce output. The `transform._transform()` implementation handles the bytes being written, computes an output, then passes that output off to the readable portion using the `transform.push()` method.
The `transform.push()` method may be called zero or more times to generate output from a single input chunk, depending on how much is to be output as a result of the chunk.
It is possible that no output is generated from any given chunk of input data.
The `callback` function must be called only when the current chunk is completely consumed. The first argument passed to the `callback` must be an `Error` object if an error occurred while processing the input or `null` otherwise. If a second argument is passed to the `callback`, it will be forwarded on to the `transform.push()` method. In other words, the following are equivalent:
```
transform.prototype._transform = function(data, encoding, callback) {
this.push(data);
callback();
};
transform.prototype._transform = function(data, encoding, callback) {
callback(null, data);
};
```
The `transform._transform()` method is prefixed with an underscore because it is internal to the class that defines it, and should never be called directly by user programs.
`transform._transform()` is never called in parallel; streams implement a queue mechanism, and to receive the next chunk, `callback` must be called, either synchronously or asynchronously.
##### Class: `stream.PassThrough`
The `stream.PassThrough` class is a trivial implementation of a [`Transform`](#class-streamtransform) stream that simply passes the input bytes across to the output. Its purpose is primarily for examples and testing, but there are some use cases where `stream.PassThrough` is useful as a building block for novel sorts of streams.
### Additional notes
#### Streams compatibility with async generators and async iterators
With the support of async generators and iterators in JavaScript, async generators are effectively a first-class language-level stream construct at this point.
Some common interop cases of using Node.js streams with async generators and async iterators are provided below.
##### Consuming readable streams with async iterators
```
(async function() {
for await (const chunk of readable) {
console.log(chunk);
}
})();
```
Async iterators register a permanent error handler on the stream to prevent any unhandled post-destroy errors.
##### Creating readable streams with async generators
A Node.js readable stream can be created from an asynchronous generator using the `Readable.from()` utility method:
```
const { Readable } = require('node:stream');
const ac = new AbortController();
const signal = ac.signal;
async function * generate() {
yield 'a';
await someLongRunningFn({ signal });
yield 'b';
yield 'c';
}
const readable = Readable.from(generate());
readable.on('close', () => {
ac.abort();
});
readable.on('data', (chunk) => {
console.log(chunk);
});
```
##### Piping to writable streams from async iterators
When writing to a writable stream from an async iterator, ensure correct handling of backpressure and errors. [`stream.pipeline()`](#streampipelinesource-transforms-destination-callback) abstracts away the handling of backpressure and backpressure-related errors:
```
const fs = require('node:fs');
const { pipeline } = require('node:stream');
const { pipeline: pipelinePromise } = require('node:stream/promises');
const writable = fs.createWriteStream('./file');
const ac = new AbortController();
const signal = ac.signal;
const iterator = createIterator({ signal });
// Callback Pattern
pipeline(iterator, writable, (err, value) => {
if (err) {
console.error(err);
} else {
console.log(value, 'value returned');
}
}).on('close', () => {
ac.abort();
});
// Promise Pattern
pipelinePromise(iterator, writable)
.then((value) => {
console.log(value, 'value returned');
})
.catch((err) => {
console.error(err);
ac.abort();
});
```
#### Compatibility with older Node.js versions
Prior to Node.js 0.10, the `Readable` stream interface was simpler, but also less powerful and less useful.
* Rather than waiting for calls to the [`stream.read()`](#readablereadsize) method, [`'data'`](#event-data) events would begin emitting immediately. Applications that would need to perform some amount of work to decide how to handle data were required to store read data into buffers so the data would not be lost.
* The [`stream.pause()`](#readablepause) method was advisory, rather than guaranteed. This meant that it was still necessary to be prepared to receive [`'data'`](#event-data) events *even when the stream was in a paused state*.
In Node.js 0.10, the [`Readable`](#class-streamreadable) class was added. For backward compatibility with older Node.js programs, `Readable` streams switch into "flowing mode" when a [`'data'`](#event-data) event handler is added, or when the [`stream.resume()`](#readableresume) method is called. The effect is that, even when not using the new [`stream.read()`](#readablereadsize) method and [`'readable'`](#event-readable) event, it is no longer necessary to worry about losing [`'data'`](#event-data) chunks.
While most applications will continue to function normally, this introduces an edge case in the following conditions:
* No [`'data'`](#event-data) event listener is added.
* The [`stream.resume()`](#readableresume) method is never called.
* The stream is not piped to any writable destination.
For example, consider the following code:
```
// WARNING! BROKEN!
net.createServer((socket) => {
// We add an 'end' listener, but never consume the data.
socket.on('end', () => {
// It will never get here.
socket.end('The message was received but was not processed.\n');
});
}).listen(1337);
```
Prior to Node.js 0.10, the incoming message data would be simply discarded. However, in Node.js 0.10 and beyond, the socket remains paused forever.
The workaround in this situation is to call the [`stream.resume()`](#readableresume) method to begin the flow of data:
```
// Workaround.
net.createServer((socket) => {
socket.on('end', () => {
socket.end('The message was received but was not processed.\n');
});
// Start the flow of data, discarding it.
socket.resume();
}).listen(1337);
```
In addition to new `Readable` streams switching into flowing mode, pre-0.10 style streams can be wrapped in a `Readable` class using the [`readable.wrap()`](#readablewrapstream) method.
####
`readable.read(0)`
There are some cases where it is necessary to trigger a refresh of the underlying readable stream mechanisms, without actually consuming any data. In such cases, it is possible to call `readable.read(0)`, which will always return `null`.
If the internal read buffer is below the `highWaterMark`, and the stream is not currently reading, then calling `stream.read(0)` will trigger a low-level [`stream._read()`](#readable_readsize) call.
While most applications will almost never need to do this, there are situations within Node.js where this is done, particularly in the `Readable` stream class internals.
####
`readable.push('')`
Use of `readable.push('')` is not recommended.
Pushing a zero-byte string, `Buffer`, or `Uint8Array` to a stream that is not in object mode has an interesting side effect. Because it *is* a call to [`readable.push()`](#readablepushchunk-encoding), the call will end the reading process. However, because the argument is an empty string, no data is added to the readable buffer so there is nothing for a user to consume.
####
`highWaterMark` discrepancy after calling `readable.setEncoding()`
The use of `readable.setEncoding()` will change the behavior of how the `highWaterMark` operates in non-object mode.
Typically, the size of the current buffer is measured against the `highWaterMark` in *bytes*. However, after `setEncoding()` is called, the comparison function will begin to measure the buffer's size in *characters*.
This is not a problem in common cases with `latin1` or `ascii`. But it is advised to be mindful about this behavior when working with strings that could contain multi-byte characters.
| programming_docs |
node None Web Streams API
---------------
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Use of this API no longer emit a runtime warning. |
| v16.5.0 | Added in: v16.5.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
An implementation of the [WHATWG Streams Standard](https://streams.spec.whatwg.org/).
### Overview
The [WHATWG Streams Standard](https://streams.spec.whatwg.org/) (or "web streams") defines an API for handling streaming data. It is similar to the Node.js [Streams](stream) API but emerged later and has become the "standard" API for streaming data across many JavaScript environments.
There are three primary types of objects:
* `ReadableStream` - Represents a source of streaming data.
* `WritableStream` - Represents a destination for streaming data.
* `TransformStream` - Represents an algorithm for transforming streaming data.
#### Example `ReadableStream`
This example creates a simple `ReadableStream` that pushes the current `performance.now()` timestamp once every second forever. An async iterable is used to read the data from the stream.
MJS modules
```
import {
ReadableStream
} from 'node:stream/web';
import {
setInterval as every
} from 'node:timers/promises';
import {
performance
} from 'node:perf_hooks';
const SECOND = 1000;
const stream = new ReadableStream({
async start(controller) {
for await (const _ of every(SECOND))
controller.enqueue(performance.now());
}
});
for await (const value of stream)
console.log(value);
```
CJS modules
```
const {
ReadableStream
} = require('node:stream/web');
const {
setInterval: every
} = require('node:timers/promises');
const {
performance
} = require('node:perf_hooks');
const SECOND = 1000;
const stream = new ReadableStream({
async start(controller) {
for await (const _ of every(SECOND))
controller.enqueue(performance.now());
}
});
(async () => {
for await (const value of stream)
console.log(value);
})();
```
### API
#### Class: `ReadableStream`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
#####
`new ReadableStream([underlyingSource [, strategy]])`
Added in: v16.5.0 * `underlyingSource` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `start` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that is invoked immediately when the `ReadableStream` is created.
- `controller` [<ReadableStreamDefaultController>](webstreams#class-readablestreamdefaultcontroller) | [<ReadableByteStreamController>](webstreams#class-readablebytestreamcontroller)
- Returns: `undefined` or a promise fulfilled with `undefined`.
+ `pull` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that is called repeatedly when the `ReadableStream` internal queue is not full. The operation may be sync or async. If async, the function will not be called again until the previously returned promise is fulfilled.
- `controller` [<ReadableStreamDefaultController>](webstreams#class-readablestreamdefaultcontroller) | [<ReadableByteStreamController>](webstreams#class-readablebytestreamcontroller)
- Returns: A promise fulfilled with `undefined`.
+ `cancel` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that is called when the `ReadableStream` is canceled.
- `reason` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
- Returns: A promise fulfilled with `undefined`.
+ `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'bytes'` or `undefined`.
+ `autoAllocateChunkSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Used only when `type` is equal to `'bytes'`.
* `strategy` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum internal queue size before backpressure is applied.
+ `size` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function used to identify the size of each chunk of data.
- `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
- Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
#####
`readableStream.locked`
Added in: v16.5.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Set to `true` if there is an active reader for this [<ReadableStream>](webstreams#class-readablestream).
The `readableStream.locked` property is `false` by default, and is switched to `true` while there is an active reader consuming the stream's data.
#####
`readableStream.cancel([reason])`
Added in: v16.5.0 * `reason` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: A promise fulfilled with `undefined` once cancelation has been completed.
#####
`readableStream.getReader([options])`
Added in: v16.5.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) `'byob'` or `undefined`
* Returns: [<ReadableStreamDefaultReader>](webstreams#class-readablestreamdefaultreader) | [<ReadableStreamBYOBReader>](webstreams#class-readablestreambyobreader)
MJS modules
```
import { ReadableStream } from 'node:stream/web';
const stream = new ReadableStream();
const reader = stream.getReader();
console.log(await reader.read());
```
CJS modules
```
const { ReadableStream } = require('node:stream/web');
const stream = new ReadableStream();
const reader = stream.getReader();
reader.read().then(console.log);
```
Causes the `readableStream.locked` to be `true`.
#####
`readableStream.pipeThrough(transform[, options])`
Added in: v16.5.0 * `transform` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `readable` [<ReadableStream>](webstreams#class-readablestream) The `ReadableStream` to which `transform.writable` will push the potentially modified data is receives from this `ReadableStream`.
+ `writable` [<WritableStream>](webstreams#class-writablestream) The `WritableStream` to which this `ReadableStream`'s data will be written.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `preventAbort` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, errors in this `ReadableStream` will not cause `transform.writable` to be aborted.
+ `preventCancel` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, errors in the destination `transform.writable` do not cause this `ReadableStream` to be canceled.
+ `preventClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, closing this `ReadableStream` does not cause `transform.writable` to be closed.
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows the transfer of data to be canceled using an [<AbortController>](globals#class-abortcontroller).
* Returns: [<ReadableStream>](webstreams#class-readablestream) From `transform.readable`.
Connects this [<ReadableStream>](webstreams#class-readablestream) to the pair of [<ReadableStream>](webstreams#class-readablestream) and [<WritableStream>](webstreams#class-writablestream) provided in the `transform` argument such that the data from this [<ReadableStream>](webstreams#class-readablestream) is written in to `transform.writable`, possibly transformed, then pushed to `transform.readable`. Once the pipeline is configured, `transform.readable` is returned.
Causes the `readableStream.locked` to be `true` while the pipe operation is active.
MJS modules
```
import {
ReadableStream,
TransformStream,
} from 'node:stream/web';
const stream = new ReadableStream({
start(controller) {
controller.enqueue('a');
},
});
const transform = new TransformStream({
transform(chunk, controller) {
controller.enqueue(chunk.toUpperCase());
}
});
const transformedStream = stream.pipeThrough(transform);
for await (const chunk of transformedStream)
console.log(chunk);
```
CJS modules
```
const {
ReadableStream,
TransformStream,
} = require('node:stream/web');
const stream = new ReadableStream({
start(controller) {
controller.enqueue('a');
},
});
const transform = new TransformStream({
transform(chunk, controller) {
controller.enqueue(chunk.toUpperCase());
}
});
const transformedStream = stream.pipeThrough(transform);
(async () => {
for await (const chunk of transformedStream)
console.log(chunk);
})();
```
#####
`readableStream.pipeTo(destination, options)`
Added in: v16.5.0 * `destination` [<WritableStream>](webstreams#class-writablestream) A [<WritableStream>](webstreams#class-writablestream) to which this `ReadableStream`'s data will be written.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `preventAbort` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, errors in this `ReadableStream` will not cause `destination` to be aborted.
+ `preventCancel` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, errors in the `destination` will not cause this `ReadableStream` to be canceled.
+ `preventClose` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, closing this `ReadableStream` does not cause `destination` to be closed.
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows the transfer of data to be canceled using an [<AbortController>](globals#class-abortcontroller).
* Returns: A promise fulfilled with `undefined`
Causes the `readableStream.locked` to be `true` while the pipe operation is active.
#####
`readableStream.tee()`
History
| Version | Changes |
| --- | --- |
| v18.10.0, v16.18.0 | Support teeing a readable byte stream. |
| v16.5.0 | Added in: v16.5.0 |
* Returns: [<ReadableStream[]>](webstreams#class-readablestream)
Returns a pair of new [<ReadableStream>](webstreams#class-readablestream) instances to which this `ReadableStream`'s data will be forwarded. Each will receive the same data.
Causes the `readableStream.locked` to be `true`.
#####
`readableStream.values([options])`
Added in: v16.5.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `preventCancel` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, prevents the [<ReadableStream>](webstreams#class-readablestream) from being closed when the async iterator abruptly terminates. **Default**: `false`.
Creates and returns an async iterator usable for consuming this `ReadableStream`'s data.
Causes the `readableStream.locked` to be `true` while the async iterator is active.
```
import { Buffer } from 'node:buffer';
const stream = new ReadableStream(getSomeSource());
for await (const chunk of stream.values({ preventCancel: true }))
console.log(Buffer.from(chunk).toString());
```
##### Async Iteration
The [<ReadableStream>](webstreams#class-readablestream) object supports the async iterator protocol using `for await` syntax.
```
import { Buffer } from 'node:buffer';
const stream = new ReadableStream(getSomeSource());
for await (const chunk of stream)
console.log(Buffer.from(chunk).toString());
```
The async iterator will consume the [<ReadableStream>](webstreams#class-readablestream) until it terminates.
By default, if the async iterator exits early (via either a `break`, `return`, or a `throw`), the [<ReadableStream>](webstreams#class-readablestream) will be closed. To prevent automatic closing of the [<ReadableStream>](webstreams#class-readablestream), use the `readableStream.values()` method to acquire the async iterator and set the `preventCancel` option to `true`.
The [<ReadableStream>](webstreams#class-readablestream) must not be locked (that is, it must not have an existing active reader). During the async iteration, the [<ReadableStream>](webstreams#class-readablestream) will be locked.
##### Transferring with `postMessage()`
A [<ReadableStream>](webstreams#class-readablestream) instance can be transferred using a [<MessagePort>](worker_threads#class-messageport).
```
const stream = new ReadableStream(getReadableSourceSomehow());
const { port1, port2 } = new MessageChannel();
port1.onmessage = ({ data }) => {
data.getReader().read().then((chunk) => {
console.log(chunk);
});
};
port2.postMessage(stream, [stream]);
```
#### Class: `ReadableStreamDefaultReader`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
By default, calling `readableStream.getReader()` with no arguments will return an instance of `ReadableStreamDefaultReader`. The default reader treats the chunks of data passed through the stream as opaque values, which allows the [<ReadableStream>](webstreams#class-readablestream) to work with generally any JavaScript value.
#####
`new ReadableStreamDefaultReader(stream)`
Added in: v16.5.0 * `stream` [<ReadableStream>](webstreams#class-readablestream)
Creates a new [<ReadableStreamDefaultReader>](webstreams#class-readablestreamdefaultreader) that is locked to the given [<ReadableStream>](webstreams#class-readablestream).
#####
`readableStreamDefaultReader.cancel([reason])`
Added in: v16.5.0 * `reason` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: A promise fulfilled with `undefined`.
Cancels the [<ReadableStream>](webstreams#class-readablestream) and returns a promise that is fulfilled when the underlying stream has been canceled.
#####
`readableStreamDefaultReader.closed`
Added in: v16.5.0 * Type: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfilled with `undefined` when the associated [<ReadableStream>](webstreams#class-readablestream) is closed or rejected if the stream errors or the reader's lock is released before the stream finishes closing.
#####
`readableStreamDefaultReader.read()`
Added in: v16.5.0 * Returns: A promise fulfilled with an object:
+ `value` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
+ `done` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Requests the next chunk of data from the underlying [<ReadableStream>](webstreams#class-readablestream) and returns a promise that is fulfilled with the data once it is available.
#####
`readableStreamDefaultReader.releaseLock()`
Added in: v16.5.0 Releases this reader's lock on the underlying [<ReadableStream>](webstreams#class-readablestream).
#### Class: `ReadableStreamBYOBReader`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
The `ReadableStreamBYOBReader` is an alternative consumer for byte-oriented [<ReadableStream>](webstreams#class-readablestream)s (those that are created with `underlyingSource.type` set equal to `'bytes'` when the `ReadableStream` was created).
The `BYOB` is short for "bring your own buffer". This is a pattern that allows for more efficient reading of byte-oriented data that avoids extraneous copying.
```
import {
open
} from 'node:fs/promises';
import {
ReadableStream
} from 'node:stream/web';
import { Buffer } from 'node:buffer';
class Source {
type = 'bytes';
autoAllocateChunkSize = 1024;
async start(controller) {
this.file = await open(new URL(import.meta.url));
this.controller = controller;
}
async pull(controller) {
const view = controller.byobRequest?.view;
const {
bytesRead,
} = await this.file.read({
buffer: view,
offset: view.byteOffset,
length: view.byteLength
});
if (bytesRead === 0) {
await this.file.close();
this.controller.close();
}
controller.byobRequest.respond(bytesRead);
}
}
const stream = new ReadableStream(new Source());
async function read(stream) {
const reader = stream.getReader({ mode: 'byob' });
const chunks = [];
let result;
do {
result = await reader.read(Buffer.alloc(100));
if (result.value !== undefined)
chunks.push(Buffer.from(result.value));
} while (!result.done);
return Buffer.concat(chunks);
}
const data = await read(stream);
console.log(Buffer.from(data).toString());
```
#####
`new ReadableStreamBYOBReader(stream)`
Added in: v16.5.0 * `stream` [<ReadableStream>](webstreams#class-readablestream)
Creates a new `ReadableStreamBYOBReader` that is locked to the given [<ReadableStream>](webstreams#class-readablestream).
#####
`readableStreamBYOBReader.cancel([reason])`
Added in: v16.5.0 * `reason` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: A promise fulfilled with `undefined`.
Cancels the [<ReadableStream>](webstreams#class-readablestream) and returns a promise that is fulfilled when the underlying stream has been canceled.
#####
`readableStreamBYOBReader.closed`
Added in: v16.5.0 * Type: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfilled with `undefined` when the associated [<ReadableStream>](webstreams#class-readablestream) is closed or rejected if the stream errors or the reader's lock is released before the stream finishes closing.
#####
`readableStreamBYOBReader.read(view)`
Added in: v16.5.0 * `view` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* Returns: A promise fulfilled with an object:
+ `value` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
+ `done` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Requests the next chunk of data from the underlying [<ReadableStream>](webstreams#class-readablestream) and returns a promise that is fulfilled with the data once it is available.
Do not pass a pooled [<Buffer>](buffer#class-buffer) object instance in to this method. Pooled `Buffer` objects are created using `Buffer.allocUnsafe()`, or `Buffer.from()`, or are often returned by various `node:fs` module callbacks. These types of `Buffer`s use a shared underlying [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) object that contains all of the data from all of the pooled `Buffer` instances. When a `Buffer`, [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), or [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) is passed in to `readableStreamBYOBReader.read()`, the view's underlying `ArrayBuffer` is *detached*, invalidating all existing views that may exist on that `ArrayBuffer`. This can have disastrous consequences for your application.
#####
`readableStreamBYOBReader.releaseLock()`
Added in: v16.5.0 Releases this reader's lock on the underlying [<ReadableStream>](webstreams#class-readablestream).
#### Class: `ReadableStreamDefaultController`
Added in: v16.5.0 Every [<ReadableStream>](webstreams#class-readablestream) has a controller that is responsible for the internal state and management of the stream's queue. The `ReadableStreamDefaultController` is the default controller implementation for `ReadableStream`s that are not byte-oriented.
#####
`readableStreamDefaultController.close()`
Added in: v16.5.0 Closes the [<ReadableStream>](webstreams#class-readablestream) to which this controller is associated.
#####
`readableStreamDefaultController.desiredSize`
Added in: v16.5.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the amount of data remaining to fill the [<ReadableStream>](webstreams#class-readablestream)'s queue.
#####
`readableStreamDefaultController.enqueue(chunk)`
Added in: v16.5.0 * `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Appends a new chunk of data to the [<ReadableStream>](webstreams#class-readablestream)'s queue.
#####
`readableStreamDefaultController.error(error)`
Added in: v16.5.0 * `error` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Signals an error that causes the [<ReadableStream>](webstreams#class-readablestream) to error and close.
#### Class: `ReadableByteStreamController`
History
| Version | Changes |
| --- | --- |
| v18.10.0 | Support handling a BYOB pull request from a released reader. |
| v16.5.0 | Added in: v16.5.0 |
Every [<ReadableStream>](webstreams#class-readablestream) has a controller that is responsible for the internal state and management of the stream's queue. The `ReadableByteStreamController` is for byte-oriented `ReadableStream`s.
#####
`readableByteStreamController.byobRequest`
Added in: v16.5.0 * Type: [<ReadableStreamBYOBRequest>](webstreams#class-readablestreambyobrequest)
#####
`readableByteStreamController.close()`
Added in: v16.5.0 Closes the [<ReadableStream>](webstreams#class-readablestream) to which this controller is associated.
#####
`readableByteStreamController.desiredSize`
Added in: v16.5.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the amount of data remaining to fill the [<ReadableStream>](webstreams#class-readablestream)'s queue.
#####
`readableByteStreamController.enqueue(chunk)`
Added in: v16.5.0 * `chunk`: [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
Appends a new chunk of data to the [<ReadableStream>](webstreams#class-readablestream)'s queue.
#####
`readableByteStreamController.error(error)`
Added in: v16.5.0 * `error` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Signals an error that causes the [<ReadableStream>](webstreams#class-readablestream) to error and close.
#### Class: `ReadableStreamBYOBRequest`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
When using `ReadableByteStreamController` in byte-oriented streams, and when using the `ReadableStreamBYOBReader`, the `readableByteStreamController.byobRequest` property provides access to a `ReadableStreamBYOBRequest` instance that represents the current read request. The object is used to gain access to the `ArrayBuffer`/`TypedArray` that has been provided for the read request to fill, and provides methods for signaling that the data has been provided.
#####
`readableStreamBYOBRequest.respond(bytesWritten)`
Added in: v16.5.0 * `bytesWritten` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Signals that a `bytesWritten` number of bytes have been written to `readableStreamBYOBRequest.view`.
#####
`readableStreamBYOBRequest.respondWithNewView(view)`
Added in: v16.5.0 * `view` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
Signals that the request has been fulfilled with bytes written to a new `Buffer`, `TypedArray`, or `DataView`.
#####
`readableStreamBYOBRequest.view`
Added in: v16.5.0 * Type: [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
#### Class: `WritableStream`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
The `WritableStream` is a destination to which stream data is sent.
```
import {
WritableStream
} from 'node:stream/web';
const stream = new WritableStream({
write(chunk) {
console.log(chunk);
}
});
await stream.getWriter().write('Hello World');
```
#####
`new WritableStream([underlyingSink[, strategy]])`
Added in: v16.5.0 * `underlyingSink` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `start` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that is invoked immediately when the `WritableStream` is created.
- `controller` [<WritableStreamDefaultController>](webstreams#class-writablestreamdefaultcontroller)
- Returns: `undefined` or a promise fulfilled with `undefined`.
+ `write` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that is invoked when a chunk of data has been written to the `WritableStream`.
- `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
- `controller` [<WritableStreamDefaultController>](webstreams#class-writablestreamdefaultcontroller)
- Returns: A promise fulfilled with `undefined`.
+ `close` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that is called when the `WritableStream` is closed.
- Returns: A promise fulfilled with `undefined`.
+ `abort` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that is called to abruptly close the `WritableStream`.
- `reason` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
- Returns: A promise fulfilled with `undefined`.
+ `type` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The `type` option is reserved for future use and *must* be undefined.
* `strategy` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum internal queue size before backpressure is applied.
+ `size` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function used to identify the size of each chunk of data.
- `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
- Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
#####
`writableStream.abort([reason])`
Added in: v16.5.0 * `reason` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: A promise fulfilled with `undefined`.
Abruptly terminates the `WritableStream`. All queued writes will be canceled with their associated promises rejected.
#####
`writableStream.close()`
Added in: v16.5.0 * Returns: A promise fulfilled with `undefined`.
Closes the `WritableStream` when no additional writes are expected.
#####
`writableStream.getWriter()`
Added in: v16.5.0 * Returns: [<WritableStreamDefaultWriter>](webstreams#class-writablestreamdefaultwriter)
Creates and creates a new writer instance that can be used to write data into the `WritableStream`.
#####
`writableStream.locked`
Added in: v16.5.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `writableStream.locked` property is `false` by default, and is switched to `true` while there is an active writer attached to this `WritableStream`.
##### Transferring with postMessage()
A [<WritableStream>](webstreams#class-writablestream) instance can be transferred using a [<MessagePort>](worker_threads#class-messageport).
```
const stream = new WritableStream(getWritableSinkSomehow());
const { port1, port2 } = new MessageChannel();
port1.onmessage = ({ data }) => {
data.getWriter().write('hello');
};
port2.postMessage(stream, [stream]);
```
#### Class: `WritableStreamDefaultWriter`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
#####
`new WritableStreamDefaultWriter(stream)`
Added in: v16.5.0 * `stream` [<WritableStream>](webstreams#class-writablestream)
Creates a new `WritableStreamDefaultWriter` that is locked to the given `WritableStream`.
#####
`writableStreamDefaultWriter.abort([reason])`
Added in: v16.5.0 * `reason` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: A promise fulfilled with `undefined`.
Abruptly terminates the `WritableStream`. All queued writes will be canceled with their associated promises rejected.
#####
`writableStreamDefaultWriter.close()`
Added in: v16.5.0 * Returns: A promise fulfilled with `undefined`.
Closes the `WritableStream` when no additional writes are expected.
#####
`writableStreamDefaultWriter.closed`
Added in: v16.5.0 * Type: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfilled with `undefined` when the associated [<WritableStream>](webstreams#class-writablestream) is closed or rejected if the stream errors or the writer's lock is released before the stream finishes closing.
#####
`writableStreamDefaultWriter.desiredSize`
Added in: v16.5.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The amount of data required to fill the [<WritableStream>](webstreams#class-writablestream)'s queue.
#####
`writableStreamDefaultWriter.ready`
Added in: v16.5.0 * type: A promise that is fulfilled with `undefined` when the writer is ready to be used.
#####
`writableStreamDefaultWriter.releaseLock()`
Added in: v16.5.0 Releases this writer's lock on the underlying [<ReadableStream>](webstreams#class-readablestream).
#####
`writableStreamDefaultWriter.write([chunk])`
Added in: v16.5.0 * `chunk`: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: A promise fulfilled with `undefined`.
Appends a new chunk of data to the [<WritableStream>](webstreams#class-writablestream)'s queue.
#### Class: `WritableStreamDefaultController`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
The `WritableStreamDefaultController` manage's the [<WritableStream>](webstreams#class-writablestream)'s internal state.
#####
`writableStreamDefaultController.error(error)`
Added in: v16.5.0 * `error` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Called by user-code to signal that an error has occurred while processing the `WritableStream` data. When called, the [<WritableStream>](webstreams#class-writablestream) will be aborted, with currently pending writes canceled.
#####
`writableStreamDefaultController.signal`
* Type: [<AbortSignal>](globals#class-abortsignal) An `AbortSignal` that can be used to cancel pending write or close operations when a [<WritableStream>](webstreams#class-writablestream) is aborted.
#### Class: `TransformStream`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
A `TransformStream` consists of a [<ReadableStream>](webstreams#class-readablestream) and a [<WritableStream>](webstreams#class-writablestream) that are connected such that the data written to the `WritableStream` is received, and potentially transformed, before being pushed into the `ReadableStream`'s queue.
```
import {
TransformStream
} from 'node:stream/web';
const transform = new TransformStream({
transform(chunk, controller) {
controller.enqueue(chunk.toUpperCase());
}
});
await Promise.all([
transform.writable.getWriter().write('A'),
transform.readable.getReader().read(),
]);
```
#####
`new TransformStream([transformer[, writableStrategy[, readableStrategy]]])`
Added in: v16.5.0 * `transformer` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `start` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that is invoked immediately when the `TransformStream` is created.
- `controller` [<TransformStreamDefaultController>](webstreams#class-transformstreamdefaultcontroller)
- Returns: `undefined` or a promise fulfilled with `undefined`
+ `transform` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that receives, and potentially modifies, a chunk of data written to `transformStream.writable`, before forwarding that on to `transformStream.readable`.
- `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
- `controller` [<TransformStreamDefaultController>](webstreams#class-transformstreamdefaultcontroller)
- Returns: A promise fulfilled with `undefined`.
+ `flush` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function that is called immediately before the writable side of the `TransformStream` is closed, signaling the end of the transformation process.
- `controller` [<TransformStreamDefaultController>](webstreams#class-transformstreamdefaultcontroller)
- Returns: A promise fulfilled with `undefined`.
+ `readableType` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the `readableType` option is reserved for future use and *must* be `undefined`.
+ `writableType` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the `writableType` option is reserved for future use and *must* be `undefined`.
* `writableStrategy` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum internal queue size before backpressure is applied.
+ `size` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function used to identify the size of each chunk of data.
- `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
- Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `readableStrategy` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum internal queue size before backpressure is applied.
+ `size` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A user-defined function used to identify the size of each chunk of data.
- `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
- Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
#####
`transformStream.readable`
Added in: v16.5.0 * Type: [<ReadableStream>](webstreams#class-readablestream)
#####
`transformStream.writable`
Added in: v16.5.0 * Type: [<WritableStream>](webstreams#class-writablestream)
##### Transferring with postMessage()
A [<TransformStream>](webstreams#class-transformstream) instance can be transferred using a [<MessagePort>](worker_threads#class-messageport).
```
const stream = new TransformStream();
const { port1, port2 } = new MessageChannel();
port1.onmessage = ({ data }) => {
const { writable, readable } = data;
// ...
};
port2.postMessage(stream, [stream]);
```
#### Class: `TransformStreamDefaultController`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
The `TransformStreamDefaultController` manages the internal state of the `TransformStream`.
#####
`transformStreamDefaultController.desiredSize`
Added in: v16.5.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The amount of data required to fill the readable side's queue.
#####
`transformStreamDefaultController.enqueue([chunk])`
Added in: v16.5.0 * `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Appends a chunk of data to the readable side's queue.
#####
`transformStreamDefaultController.error([reason])`
Added in: v16.5.0 * `reason` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Signals to both the readable and writable side that an error has occurred while processing the transform data, causing both sides to be abruptly closed.
#####
`transformStreamDefaultController.terminate()`
Added in: v16.5.0 Closes the readable side of the transport and causes the writable side to be abruptly closed with an error.
#### Class: `ByteLengthQueuingStrategy`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
#####
`new ByteLengthQueuingStrategy(options)`
Added in: v16.5.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
#####
`byteLengthQueuingStrategy.highWaterMark`
Added in: v16.5.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
#####
`byteLengthQueuingStrategy.size`
Added in: v16.5.0 * Type: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
+ Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
#### Class: `CountQueuingStrategy`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.5.0 | Added in: v16.5.0 |
#####
`new CountQueuingStrategy(options)`
Added in: v16.5.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `highWaterMark` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
#####
`countQueuingStrategy.highWaterMark`
Added in: v16.5.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
#####
`countQueuingStrategy.size`
Added in: v16.5.0 * Type: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `chunk` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
+ Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
#### Class: `TextEncoderStream`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.6.0 | Added in: v16.6.0 |
#####
`new TextEncoderStream()`
Added in: v16.6.0 Creates a new `TextEncoderStream` instance.
#####
`textEncoderStream.encoding`
Added in: v16.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The encoding supported by the `TextEncoderStream` instance.
#####
`textEncoderStream.readable`
Added in: v16.6.0 * Type: [<ReadableStream>](webstreams#class-readablestream)
#####
`textEncoderStream.writable`
Added in: v16.6.0 * Type: [<WritableStream>](webstreams#class-writablestream)
#### Class: `TextDecoderStream`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v16.6.0 | Added in: v16.6.0 |
#####
`new TextDecoderStream([encoding[, options]])`
Added in: v16.6.0 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Identifies the `encoding` that this `TextDecoder` instance supports. **Default:** `'utf-8'`.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `fatal` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if decoding failures are fatal.
+ `ignoreBOM` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the `TextDecoderStream` will include the byte order mark in the decoded result. When `false`, the byte order mark will be removed from the output. This option is only used when `encoding` is `'utf-8'`, `'utf-16be'`, or `'utf-16le'`. **Default:** `false`.
Creates a new `TextDecoderStream` instance.
#####
`textDecoderStream.encoding`
Added in: v16.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The encoding supported by the `TextDecoderStream` instance.
#####
`textDecoderStream.fatal`
Added in: v16.6.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The value will be `true` if decoding errors result in a `TypeError` being thrown.
#####
`textDecoderStream.ignoreBOM`
Added in: v16.6.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The value will be `true` if the decoding result will include the byte order mark.
#####
`textDecoderStream.readable`
Added in: v16.6.0 * Type: [<ReadableStream>](webstreams#class-readablestream)
#####
`textDecoderStream.writable`
Added in: v16.6.0 * Type: [<WritableStream>](webstreams#class-writablestream)
#### Class: `CompressionStream`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v17.0.0 | Added in: v17.0.0 |
#####
`new CompressionStream(format)`
Added in: v17.0.0 * `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) One of either `'deflate'` or `'gzip'`.
#####
`compressionStream.readable`
Added in: v17.0.0 * Type: [<ReadableStream>](webstreams#class-readablestream)
#####
`compressionStream.writable`
Added in: v17.0.0 * Type: [<WritableStream>](webstreams#class-writablestream)
#### Class: `DecompressionStream`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | This class is now exposed on the global object. |
| v17.0.0 | Added in: v17.0.0 |
#####
`new DecompressionStream(format)`
Added in: v17.0.0 * `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) One of either `'deflate'` or `'gzip'`.
#####
`decompressionStream.readable`
Added in: v17.0.0 * Type: [<ReadableStream>](webstreams#class-readablestream)
#####
`decompressionStream.writable`
Added in: v17.0.0 * Type: [<WritableStream>](webstreams#class-writablestream)
#### Utility Consumers
Added in: v16.7.0 The utility consumer functions provide common options for consuming streams.
They are accessed using:
MJS modules
```
import {
arrayBuffer,
blob,
buffer,
json,
text,
} from 'node:stream/consumers';
```
CJS modules
```
const {
arrayBuffer,
blob,
buffer,
json,
text,
} = require('node:stream/consumers');
```
#####
`streamConsumers.arrayBuffer(stream)`
Added in: v16.7.0 * `stream` [<ReadableStream>](webstreams#class-readablestream) | [<stream.Readable>](stream#class-streamreadable) | [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with an `ArrayBuffer` containing the full contents of the stream.
MJS modules
```
import { buffer as arrayBuffer } from 'node:stream/consumers';
import { Readable } from 'node:stream';
import { TextEncoder } from 'node:util';
const encoder = new TextEncoder();
const dataArray = encoder.encode('hello world from consumers!');
const readable = Readable.from(dataArray);
const data = await arrayBuffer(readable);
console.log(`from readable: ${data.byteLength}`);
```
CJS modules
```
const { arrayBuffer } = require('node:stream/consumers');
const { Readable } = require('stream');
const { TextEncoder } = require('util');
const encoder = new TextEncoder();
const dataArray = encoder.encode(['hello world from consumers!']);
const readable = Readable.from(dataArray);
arrayBuffer(readable).then((data) => {
console.log(`from readable: ${data.byteLength}`);
});
```
#####
`streamConsumers.blob(stream)`
Added in: v16.7.0 * `stream` [<ReadableStream>](webstreams#class-readablestream) | [<stream.Readable>](stream#class-streamreadable) | [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with a [<Blob>](buffer#class-blob) containing the full contents of the stream.
MJS modules
```
import { blob } from 'node:stream/consumers';
const dataBlob = new Blob(['hello world from consumers!']);
const readable = dataBlob.stream();
const data = await blob(readable);
console.log(`from readable: ${data.size}`);
```
CJS modules
```
const { blob } = require('node:stream/consumers');
const dataBlob = new Blob(['hello world from consumers!']);
const readable = dataBlob.stream();
blob(readable).then((data) => {
console.log(`from readable: ${data.size}`);
});
```
#####
`streamConsumers.buffer(stream)`
Added in: v16.7.0 * `stream` [<ReadableStream>](webstreams#class-readablestream) | [<stream.Readable>](stream#class-streamreadable) | [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with a [<Buffer>](buffer#class-buffer) containing the full contents of the stream.
MJS modules
```
import { buffer } from 'node:stream/consumers';
import { Readable } from 'node:stream';
import { Buffer } from 'node:buffer';
const dataBuffer = Buffer.from('hello world from consumers!');
const readable = Readable.from(dataBuffer);
const data = await buffer(readable);
console.log(`from readable: ${data.length}`);
```
CJS modules
```
const { buffer } = require('node:stream/consumers');
const { Readable } = require('node:stream');
const { Buffer } = require('node:buffer');
const dataBuffer = Buffer.from('hello world from consumers!');
const readable = Readable.from(dataBuffer);
buffer(readable).then((data) => {
console.log(`from readable: ${data.length}`);
});
```
#####
`streamConsumers.json(stream)`
Added in: v16.7.0 * `stream` [<ReadableStream>](webstreams#class-readablestream) | [<stream.Readable>](stream#class-streamreadable) | [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with the contents of the stream parsed as a UTF-8 encoded string that is then passed through `JSON.parse()`.
MJS modules
```
import { json } from 'node:stream/consumers';
import { Readable } from 'node:stream';
const items = Array.from(
{
length: 100
},
() => ({
message: 'hello world from consumers!'
})
);
const readable = Readable.from(JSON.stringify(items));
const data = await json(readable);
console.log(`from readable: ${data.length}`);
```
CJS modules
```
const { json } = require('node:stream/consumers');
const { Readable } = require('node:stream');
const items = Array.from(
{
length: 100
},
() => ({
message: 'hello world from consumers!'
})
);
const readable = Readable.from(JSON.stringify(items));
json(readable).then((data) => {
console.log(`from readable: ${data.length}`);
});
```
#####
`streamConsumers.text(stream)`
Added in: v16.7.0 * `stream` [<ReadableStream>](webstreams#class-readablestream) | [<stream.Readable>](stream#class-streamreadable) | [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with the contents of the stream parsed as a UTF-8 encoded string.
MJS modules
```
import { json, text, blob, buffer } from 'node:stream/consumers';
import { Readable } from 'node:stream';
const readable = Readable.from('Hello world from consumers!');
const data = await text(readable);
console.log(`from readable: ${data.length}`);
```
CJS modules
```
const { text } = require('node:stream/consumers');
const { Readable } = require('node:stream');
const readable = Readable.from('Hello world from consumers!');
text(readable).then((data) => {
console.log(`from readable: ${data.length}`);
});
```
| programming_docs |
node None Test runner
-----------
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
**Source Code:** [lib/test.js](https://github.com/nodejs/node/blob/v19.0.1/lib/test.js)
The `node:test` module facilitates the creation of JavaScript tests that report results in [TAP](https://testanything.org/) format. To access it:
MJS modules
```
import test from 'node:test';
```
CJS modules
```
const test = require('node:test');
```
This module is only available under the `node:` scheme. The following will not work:
MJS modules
```
import test from 'test';
```
CJS modules
```
const test = require('test');
```
Tests created via the `test` module consist of a single function that is processed in one of three ways:
1. A synchronous function that is considered failing if it throws an exception, and is considered passing otherwise.
2. A function that returns a `Promise` that is considered failing if the `Promise` rejects, and is considered passing if the `Promise` resolves.
3. A function that receives a callback function. If the callback receives any truthy value as its first argument, the test is considered failing. If a falsy value is passed as the first argument to the callback, the test is considered passing. If the test function receives a callback function and also returns a `Promise`, the test will fail.
The following example illustrates how tests are written using the `test` module.
```
test('synchronous passing test', (t) => {
// This test passes because it does not throw an exception.
assert.strictEqual(1, 1);
});
test('synchronous failing test', (t) => {
// This test fails because it throws an exception.
assert.strictEqual(1, 2);
});
test('asynchronous passing test', async (t) => {
// This test passes because the Promise returned by the async
// function is not rejected.
assert.strictEqual(1, 1);
});
test('asynchronous failing test', async (t) => {
// This test fails because the Promise returned by the async
// function is rejected.
assert.strictEqual(1, 2);
});
test('failing test using Promises', (t) => {
// Promises can be used directly as well.
return new Promise((resolve, reject) => {
setImmediate(() => {
reject(new Error('this will cause the test to fail'));
});
});
});
test('callback passing test', (t, done) => {
// done() is the callback function. When the setImmediate() runs, it invokes
// done() with no arguments.
setImmediate(done);
});
test('callback failing test', (t, done) => {
// When the setImmediate() runs, done() is invoked with an Error object and
// the test fails.
setImmediate(() => {
done(new Error('callback failure'));
});
});
```
As a test file executes, TAP is written to the standard output of the Node.js process. This output can be interpreted by any test harness that understands the TAP format. If any tests fail, the process exit code is set to `1`.
### Subtests
The test context's `test()` method allows subtests to be created. This method behaves identically to the top level `test()` function. The following example demonstrates the creation of a top level test with two subtests.
```
test('top level test', async (t) => {
await t.test('subtest 1', (t) => {
assert.strictEqual(1, 1);
});
await t.test('subtest 2', (t) => {
assert.strictEqual(2, 2);
});
});
```
In this example, `await` is used to ensure that both subtests have completed. This is necessary because parent tests do not wait for their subtests to complete. Any subtests that are still outstanding when their parent finishes are cancelled and treated as failures. Any subtest failures cause the parent test to fail.
### Skipping tests
Individual tests can be skipped by passing the `skip` option to the test, or by calling the test context's `skip()` method. Both of these options support including a message that is displayed in the TAP output as shown in the following example.
```
// The skip option is used, but no message is provided.
test('skip option', { skip: true }, (t) => {
// This code is never executed.
});
// The skip option is used, and a message is provided.
test('skip option with message', { skip: 'this is skipped' }, (t) => {
// This code is never executed.
});
test('skip() method', (t) => {
// Make sure to return here as well if the test contains additional logic.
t.skip();
});
test('skip() method with message', (t) => {
// Make sure to return here as well if the test contains additional logic.
t.skip('this is skipped');
});
```
###
`describe`/`it` syntax
Running tests can also be done using `describe` to declare a suite and `it` to declare a test. A suite is used to organize and group related tests together. `it` is an alias for `test`, except there is no test context passed, since nesting is done using suites.
```
describe('A thing', () => {
it('should work', () => {
assert.strictEqual(1, 1);
});
it('should be ok', () => {
assert.strictEqual(2, 2);
});
describe('a nested thing', () => {
it('should work', () => {
assert.strictEqual(3, 3);
});
});
});
```
`describe` and `it` are imported from the `node:test` module.
MJS modules
```
import { describe, it } from 'node:test';
```
CJS modules
```
const { describe, it } = require('node:test');
```
####
`only` tests
If Node.js is started with the [`--test-only`](cli#--test-only) command-line option, it is possible to skip all top level tests except for a selected subset by passing the `only` option to the tests that should be run. When a test with the `only` option set is run, all subtests are also run. The test context's `runOnly()` method can be used to implement the same behavior at the subtest level.
```
// Assume Node.js is run with the --test-only command-line option.
// The 'only' option is set, so this test is run.
test('this test is run', { only: true }, async (t) => {
// Within this test, all subtests are run by default.
await t.test('running subtest');
// The test context can be updated to run subtests with the 'only' option.
t.runOnly(true);
await t.test('this subtest is now skipped');
await t.test('this subtest is run', { only: true });
// Switch the context back to execute all tests.
t.runOnly(false);
await t.test('this subtest is now run');
// Explicitly do not run these tests.
await t.test('skipped subtest 3', { only: false });
await t.test('skipped subtest 4', { skip: true });
});
// The 'only' option is not set, so this test is skipped.
test('this test is not run', () => {
// This code is not run.
throw new Error('fail');
});
```
### Filtering tests by name
The [`--test-name-pattern`](cli#--test-name-pattern) command-line option can be used to only run tests whose name matches the provided pattern. Test name patterns are interpreted as JavaScript regular expressions. The `--test-name-pattern` option can be specified multiple times in order to run nested tests. For each test that is executed, any corresponding test hooks, such as `beforeEach()`, are also run.
Given the following test file, starting Node.js with the `--test-name-pattern="test [1-3]"` option would cause the test runner to execute `test 1`, `test 2`, and `test 3`. If `test 1` did not match the test name pattern, then its subtests would not execute, despite matching the pattern. The same set of tests could also be executed by passing `--test-name-pattern` multiple times (e.g. `--test-name-pattern="test 1"`, `--test-name-pattern="test 2"`, etc.).
```
test('test 1', async (t) => {
await t.test('test 2');
await t.test('test 3');
});
test('Test 4', async (t) => {
await t.test('Test 5');
await t.test('test 6');
});
```
Test name patterns can also be specified using regular expression literals. This allows regular expression flags to be used. In the previous example, starting Node.js with `--test-name-pattern="/test [4-5]/i"` would match `Test 4` and `Test 5` because the pattern is case-insensitive.
Test name patterns do not change the set of files that the test runner executes.
### Extraneous asynchronous activity
Once a test function finishes executing, the TAP results are output as quickly as possible while maintaining the order of the tests. However, it is possible for the test function to generate asynchronous activity that outlives the test itself. The test runner handles this type of activity, but does not delay the reporting of test results in order to accommodate it.
In the following example, a test completes with two `setImmediate()` operations still outstanding. The first `setImmediate()` attempts to create a new subtest. Because the parent test has already finished and output its results, the new subtest is immediately marked as failed, and reported in the top level of the file's TAP output.
The second `setImmediate()` creates an `uncaughtException` event. `uncaughtException` and `unhandledRejection` events originating from a completed test are handled by the `test` module and reported as diagnostic warnings in the top level of the file's TAP output.
```
test('a test that creates asynchronous activity', (t) => {
setImmediate(() => {
t.test('subtest that is created too late', (t) => {
throw new Error('error1');
});
});
setImmediate(() => {
throw new Error('error2');
});
// The test finishes after this line.
});
```
### Running tests from the command line
The Node.js test runner can be invoked from the command line by passing the [`--test`](cli#--test) flag:
```
node --test
```
By default, Node.js will recursively search the current directory for JavaScript source files matching a specific naming convention. Matching files are executed as test files. More information on the expected test file naming convention and behavior can be found in the [test runner execution model](#test-runner-execution-model) section.
Alternatively, one or more paths can be provided as the final argument(s) to the Node.js command, as shown below.
```
node --test test1.js test2.mjs custom_test_dir/
```
In this example, the test runner will execute the files `test1.js` and `test2.mjs`. The test runner will also recursively search the `custom_test_dir/` directory for test files to execute.
#### Test runner execution model
When searching for test files to execute, the test runner behaves as follows:
* Any files explicitly provided by the user are executed.
* If the user did not explicitly specify any paths, the current working directory is recursively searched for files as specified in the following steps.
* `node_modules` directories are skipped unless explicitly provided by the user.
* If a directory named `test` is encountered, the test runner will search it recursively for all all `.js`, `.cjs`, and `.mjs` files. All of these files are treated as test files, and do not need to match the specific naming convention detailed below. This is to accommodate projects that place all of their tests in a single `test` directory.
* In all other directories, `.js`, `.cjs`, and `.mjs` files matching the following patterns are treated as test files:
+ `^test$` - Files whose basename is the string `'test'`. Examples: `test.js`, `test.cjs`, `test.mjs`.
+ `^test-.+` - Files whose basename starts with the string `'test-'` followed by one or more characters. Examples: `test-example.js`, `test-another-example.mjs`.
+ `.+[\.\-\_]test$` - Files whose basename ends with `.test`, `-test`, or `_test`, preceded by one or more characters. Examples: `example.test.js`, `example-test.cjs`, `example_test.mjs`.
+ Other file types understood by Node.js such as `.node` and `.json` are not automatically executed by the test runner, but are supported if explicitly provided on the command line.
Each matching test file is executed in a separate child process. If the child process finishes with an exit code of 0, the test is considered passing. Otherwise, the test is considered to be a failure. Test files must be executable by Node.js, but are not required to use the `node:test` module internally.
###
`run([options])`
Added in: v18.9.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for running tests. The following properties are supported:
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If a number is provided, then that many files would run in parallel. If truthy, it would run (number of cpu cores - 1) files in parallel. If falsy, it would only run one file at a time. If unspecified, subtests inherit this value from their parent. **Default:** `true`.
+ `files`: [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) An array containing the list of files to run. **Default** matching files from [test runner execution model](#test-runner-execution-model).
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows aborting an in-progress test execution.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A number of milliseconds the test execution will fail after. If unspecified, subtests inherit this value from their parent. **Default:** `Infinity`.
+ `inspectPort` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Sets inspector port of test child process. This can be a number, or a function that takes no arguments and returns a number. If a nullish value is provided, each process gets its own port, incremented from the primary's `process.debugPort`. **Default:** `undefined`.
* Returns: [<TapStream>](test#class-tapstream)
```
run({ files: [path.resolve('./tests/test.js')] })
.pipe(process.stdout);
```
###
`test([name][, options][, fn])`
History
| Version | Changes |
| --- | --- |
| v18.0.0, v16.17.0 | Added in: v18.0.0, v16.17.0 |
| v18.8.0, v16.18.0 | Add a `signal` option. |
| v18.7.0, v16.17.0 | Add a `timeout` option. |
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the test, which is displayed when reporting test results. **Default:** The `name` property of `fn`, or `'<anonymous>'` if `fn` does not have a name.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the test. The following properties are supported:
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If a number is provided, then that many tests would run in parallel. If truthy, it would run (number of cpu cores - 1) tests in parallel. For subtests, it will be `Infinity` tests in parallel. If falsy, it would only run one test at a time. If unspecified, subtests inherit this value from their parent. **Default:** `false`.
+ `only` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If truthy, and the test context is configured to run `only` tests, then this test will be run. Otherwise, the test is skipped. **Default:** `false`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows aborting an in-progress test.
+ `skip` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If truthy, the test is skipped. If a string is provided, that string is displayed in the test results as the reason for skipping the test. **Default:** `false`.
+ `todo` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If truthy, the test marked as `TODO`. If a string is provided, that string is displayed in the test results as the reason why the test is `TODO`. **Default:** `false`.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A number of milliseconds the test will fail after. If unspecified, subtests inherit this value from their parent. **Default:** `Infinity`.
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The function under test. The first argument to this function is a [`TestContext`](#class-testcontext) object. If the test uses callbacks, the callback function is passed as the second argument. **Default:** A no-op function.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Resolved with `undefined` once the test completes.
The `test()` function is the value imported from the `test` module. Each invocation of this function results in the creation of a test point in the TAP output.
The `TestContext` object passed to the `fn` argument can be used to perform actions related to the current test. Examples include skipping the test, adding additional TAP diagnostic information, or creating subtests.
`test()` returns a `Promise` that resolves once the test completes. The return value can usually be discarded for top level tests. However, the return value from subtests should be used to prevent the parent test from finishing first and cancelling the subtest as shown in the following example.
```
test('top level test', async (t) => {
// The setTimeout() in the following subtest would cause it to outlive its
// parent test if 'await' is removed on the next line. Once the parent test
// completes, it will cancel any outstanding subtests.
await t.test('longer running subtest', async (t) => {
return new Promise((resolve, reject) => {
setTimeout(resolve, 1000);
});
});
});
```
The `timeout` option can be used to fail the test if it takes longer than `timeout` milliseconds to complete. However, it is not a reliable mechanism for canceling tests because a running test might block the application thread and thus prevent the scheduled cancellation.
###
`describe([name][, options][, fn])`
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the suite, which is displayed when reporting test results. **Default:** The `name` property of `fn`, or `'<anonymous>'` if `fn` does not have a name.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the suite. supports the same options as `test([name][, options][, fn])`.
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The function under suite declaring all subtests and subsuites. The first argument to this function is a [`SuiteContext`](#class-suitecontext) object. **Default:** A no-op function.
* Returns: `undefined`.
The `describe()` function imported from the `node:test` module. Each invocation of this function results in the creation of a Subtest and a test point in the TAP output. After invocation of top level `describe` functions, all top level tests and suites will execute.
###
`describe.skip([name][, options][, fn])`
Shorthand for skipping a suite, same as [`describe([name], { skip: true }[, fn])`](#describename-options-fn).
###
`describe.todo([name][, options][, fn])`
Shorthand for marking a suite as `TODO`, same as [`describe([name], { todo: true }[, fn])`](#describename-options-fn).
###
`it([name][, options][, fn])`
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the test, which is displayed when reporting test results. **Default:** The `name` property of `fn`, or `'<anonymous>'` if `fn` does not have a name.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the suite. supports the same options as `test([name][, options][, fn])`.
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The function under test. If the test uses callbacks, the callback function is passed as an argument. **Default:** A no-op function.
* Returns: `undefined`.
The `it()` function is the value imported from the `node:test` module. Each invocation of this function results in the creation of a test point in the TAP output.
###
`it.skip([name][, options][, fn])`
Shorthand for skipping a test, same as [`it([name], { skip: true }[, fn])`](#testname-options-fn).
###
`it.todo([name][, options][, fn])`
Shorthand for marking a test as `TODO`, same as [`it([name], { todo: true }[, fn])`](#testname-options-fn).
###
`before([fn][, options])`
Added in: v18.8.0, v16.18.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The hook function. If the hook uses callbacks, the callback function is passed as the second argument. **Default:** A no-op function.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the hook. The following properties are supported:
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows aborting an in-progress hook.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. **Default:** `Infinity`.
This function is used to create a hook running before running a suite.
```
describe('tests', async () => {
before(() => console.log('about to run some test'));
it('is a subtest', () => {
assert.ok('some relevant assertion here');
});
});
```
###
`after([fn][, options])`
Added in: v18.8.0, v16.18.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The hook function. If the hook uses callbacks, the callback function is passed as the second argument. **Default:** A no-op function.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the hook. The following properties are supported:
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows aborting an in-progress hook.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. **Default:** `Infinity`.
This function is used to create a hook running after running a suite.
```
describe('tests', async () => {
after(() => console.log('finished running tests'));
it('is a subtest', () => {
assert.ok('some relevant assertion here');
});
});
```
###
`beforeEach([fn][, options])`
Added in: v18.8.0, v16.18.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The hook function. If the hook uses callbacks, the callback function is passed as the second argument. **Default:** A no-op function.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the hook. The following properties are supported:
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows aborting an in-progress hook.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. **Default:** `Infinity`.
This function is used to create a hook running before each subtest of the current suite.
```
describe('tests', async () => {
beforeEach(() => t.diagnostic('about to run a test'));
it('is a subtest', () => {
assert.ok('some relevant assertion here');
});
});
```
###
`afterEach([fn][, options])`
Added in: v18.8.0, v16.18.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The hook function. If the hook uses callbacks, the callback function is passed as the second argument. **Default:** A no-op function.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the hook. The following properties are supported:
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows aborting an in-progress hook.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. **Default:** `Infinity`.
This function is used to create a hook running after each subtest of the current test.
```
describe('tests', async () => {
afterEach(() => t.diagnostic('about to run a test'));
it('is a subtest', () => {
assert.ok('some relevant assertion here');
});
});
```
### Class: `TapStream`
Added in: v18.9.0 * Extends [<ReadableStream>](webstreams#class-readablestream)
A successful call to [`run()`](#runoptions) method will return a new [<TapStream>](test#class-tapstream) object, streaming a [TAP](https://testanything.org/) output `TapStream` will emit events, in the order of the tests definition
#### Event: `'test:diagnostic'`
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The diagnostic message.
Emitted when [`context.diagnostic`](#contextdiagnosticmessage) is called.
#### Event: `'test:fail'`
* `data` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `duration` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The test duration.
+ `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) The failure casing test to fail.
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The test name.
+ `testNumber` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The ordinal number of the test.
+ `todo` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Present if [`context.todo`](#contexttodomessage) is called
+ `skip` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Present if [`context.skip`](#contextskipmessage) is called
Emitted when a test fails.
#### Event: `'test:pass'`
* `data` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `duration` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The test duration.
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The test name.
+ `testNumber` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The ordinal number of the test.
+ `todo` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Present if [`context.todo`](#contexttodomessage) is called
+ `skip` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Present if [`context.skip`](#contextskipmessage) is called
Emitted when a test passes.
### Class: `TestContext`
Added in: v18.0.0, v16.17.0 An instance of `TestContext` is passed to each test function in order to interact with the test runner. However, the `TestContext` constructor is not exposed as part of the API.
####
`context.beforeEach([fn][, options])`
Added in: v18.8.0, v16.18.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The hook function. The first argument to this function is a [`TestContext`](#class-testcontext) object. If the hook uses callbacks, the callback function is passed as the second argument. **Default:** A no-op function.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the hook. The following properties are supported:
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows aborting an in-progress hook.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. **Default:** `Infinity`.
This function is used to create a hook running before each subtest of the current test.
```
test('top level test', async (t) => {
t.beforeEach((t) => t.diagnostic(`about to run ${t.name}`));
await t.test(
'This is a subtest',
(t) => {
assert.ok('some relevant assertion here');
}
);
});
```
####
`context.afterEach([fn][, options])`
Added in: v18.8.0, v16.18.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The hook function. The first argument to this function is a [`TestContext`](#class-testcontext) object. If the hook uses callbacks, the callback function is passed as the second argument. **Default:** A no-op function.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the hook. The following properties are supported:
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows aborting an in-progress hook.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. **Default:** `Infinity`.
This function is used to create a hook running after each subtest of the current test.
```
test('top level test', async (t) => {
t.afterEach((t) => t.diagnostic(`finished running ${t.name}`));
await t.test(
'This is a subtest',
(t) => {
assert.ok('some relevant assertion here');
}
);
});
```
####
`context.diagnostic(message)`
Added in: v18.0.0, v16.17.0 * `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Message to be displayed as a TAP diagnostic.
This function is used to write TAP diagnostics to the output. Any diagnostic information is included at the end of the test's results. This function does not return a value.
```
test('top level test', (t) => {
t.diagnostic('A diagnostic message');
});
```
####
`context.name`
Added in: v18.8.0, v16.18.0 The name of the test.
####
`context.runOnly(shouldRunOnlyTests)`
Added in: v18.0.0, v16.17.0 * `shouldRunOnlyTests` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether or not to run `only` tests.
If `shouldRunOnlyTests` is truthy, the test context will only run tests that have the `only` option set. Otherwise, all tests are run. If Node.js was not started with the [`--test-only`](cli#--test-only) command-line option, this function is a no-op.
```
test('top level test', (t) => {
// The test context can be set to run subtests with the 'only' option.
t.runOnly(true);
return Promise.all([
t.test('this subtest is now skipped'),
t.test('this subtest is run', { only: true }),
]);
});
```
####
`context.signal`
Added in: v18.7.0, v16.17.0 * [<AbortSignal>](globals#class-abortsignal) Can be used to abort test subtasks when the test has been aborted.
```
test('top level test', async (t) => {
await fetch('some/uri', { signal: t.signal });
});
```
####
`context.skip([message])`
Added in: v18.0.0, v16.17.0 * `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Optional skip message to be displayed in TAP output.
This function causes the test's output to indicate the test as skipped. If `message` is provided, it is included in the TAP output. Calling `skip()` does not terminate execution of the test function. This function does not return a value.
```
test('top level test', (t) => {
// Make sure to return here as well if the test contains additional logic.
t.skip('this is skipped');
});
```
####
`context.todo([message])`
Added in: v18.0.0, v16.17.0 * `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Optional `TODO` message to be displayed in TAP output.
This function adds a `TODO` directive to the test's output. If `message` is provided, it is included in the TAP output. Calling `todo()` does not terminate execution of the test function. This function does not return a value.
```
test('top level test', (t) => {
// This test is marked as `TODO`
t.todo('this is a todo');
});
```
####
`context.test([name][, options][, fn])`
History
| Version | Changes |
| --- | --- |
| v18.0.0, v16.17.0 | Added in: v18.0.0, v16.17.0 |
| v18.8.0, v16.18.0 | Add a `signal` option. |
| v18.7.0, v16.17.0 | Add a `timeout` option. |
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the subtest, which is displayed when reporting test results. **Default:** The `name` property of `fn`, or `'<anonymous>'` if `fn` does not have a name.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Configuration options for the subtest. The following properties are supported:
+ `concurrency` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of tests that can be run at the same time. If unspecified, subtests inherit this value from their parent. **Default:** `1`.
+ `only` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If truthy, and the test context is configured to run `only` tests, then this test will be run. Otherwise, the test is skipped. **Default:** `false`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows aborting an in-progress test.
+ `skip` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If truthy, the test is skipped. If a string is provided, that string is displayed in the test results as the reason for skipping the test. **Default:** `false`.
+ `todo` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If truthy, the test marked as `TODO`. If a string is provided, that string is displayed in the test results as the reason why the test is `TODO`. **Default:** `false`.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A number of milliseconds the test will fail after. If unspecified, subtests inherit this value from their parent. **Default:** `Infinity`.
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<AsyncFunction>](https://tc39.es/ecma262/#sec-async-function-constructor) The function under test. The first argument to this function is a [`TestContext`](#class-testcontext) object. If the test uses callbacks, the callback function is passed as the second argument. **Default:** A no-op function.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Resolved with `undefined` once the test completes.
This function is used to create subtests under the current test. This function behaves in the same fashion as the top level [`test()`](#testname-options-fn) function.
```
test('top level test', async (t) => {
await t.test(
'This is a subtest',
{ only: false, skip: false, concurrency: 1, todo: false },
(t) => {
assert.ok('some relevant assertion here');
}
);
});
```
### Class: `SuiteContext`
Added in: v18.7.0, v16.17.0 An instance of `SuiteContext` is passed to each suite function in order to interact with the test runner. However, the `SuiteContext` constructor is not exposed as part of the API.
####
`context.name`
Added in: v18.8.0, v16.18.0 The name of the suite.
####
`context.signal`
Added in: v18.7.0, v16.17.0 * [<AbortSignal>](globals#class-abortsignal) Can be used to abort test subtasks when the test has been aborted.
| programming_docs |
node None Command-line API
----------------
Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options.
To view this documentation as a manual page in a terminal, run `man node`.
### Synopsis
`node [options] [V8 options] [<program-entry-point> | -e "script" | -] [--] [arguments]`
`node inspect [<program-entry-point> | -e "script" | <host>:<port>] …`
`node --v8-options`
Execute without arguments to start the [REPL](repl).
For more info about `node inspect`, see the <debugger> documentation.
### Program entry point
The program entry point is a specifier-like string. If the string is not an absolute path, it's resolved as a relative path from the current working directory. That path is then resolved by [CommonJS](modules) module loader. If no corresponding file is found, an error is thrown.
If a file is found, its path will be passed to the [ECMAScript module loader](esm#loaders) under any of the following conditions:
* The program was started with a command-line flag that forces the entry point to be loaded with ECMAScript module loader.
* The file has an `.mjs` extension.
* The file does not have a `.cjs` extension, and the nearest parent `package.json` file contains a top-level [`"type"`](packages#type) field with a value of `"module"`.
Otherwise, the file is loaded using the CommonJS module loader. See [Modules loaders](packages#modules-loaders) for more details.
#### ECMAScript modules loader entry point caveat
When loading [ECMAScript module loader](esm#loaders) loads the program entry point, the `node` command will only accept as input only files with `.js`, `.mjs`, or `.cjs` extensions; and with `.wasm` extensions when [`--experimental-wasm-modules`](#--experimental-wasm-modules) is enabled.
### Options
History
| Version | Changes |
| --- | --- |
| v10.12.0 | Underscores instead of dashes are now allowed for Node.js options as well, in addition to V8 options. |
All options, including V8 options, allow words to be separated by both dashes (`-`) or underscores (`_`). For example, `--pending-deprecation` is equivalent to `--pending_deprecation`.
If an option that takes a single value (such as `--max-http-header-size`) is passed more than once, then the last passed value is used. Options from the command line take precedence over options passed through the [`NODE_OPTIONS`](#node_optionsoptions) environment variable.
####
`-`
Added in: v8.0.0 Alias for stdin. Analogous to the use of `-` in other command-line utilities, meaning that the script is read from stdin, and the rest of the options are passed to that script.
####
`--`
Added in: v6.11.0 Indicate the end of node options. Pass the rest of the arguments to the script. If no script filename or eval/print script is supplied prior to this, then the next argument is used as a script filename.
####
`--abort-on-uncaught-exception`
Added in: v0.10.8 Aborting instead of exiting causes a core file to be generated for post-mortem analysis using a debugger (such as `lldb`, `gdb`, and `mdb`).
If this flag is passed, the behavior can still be set to not abort through [`process.setUncaughtExceptionCaptureCallback()`](process#processsetuncaughtexceptioncapturecallbackfn) (and through usage of the `node:domain` module that uses it).
####
`--build-snapshot`
Added in: v18.8.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Generates a snapshot blob when the process exits and writes it to disk, which can be loaded later with `--snapshot-blob`.
When building the snapshot, if `--snapshot-blob` is not specified, the generated blob will be written, by default, to `snapshot.blob` in the current working directory. Otherwise it will be written to the path specified by `--snapshot-blob`.
```
$ echo "globalThis.foo = 'I am from the snapshot'" > snapshot.js
# Run snapshot.js to intialize the application and snapshot the
# state of it into snapshot.blob.
$ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js
$ echo "console.log(globalThis.foo)" > index.js
# Load the generated snapshot and start the application from index.js.
$ node --snapshot-blob snapshot.blob index.js
I am from the snapshot
```
The [`v8.startupSnapshot` API](v8#startup-snapshot-api) can be used to specify an entry point at snapshot building time, thus avoiding the need of an additional entry script at deserialization time:
```
$ echo "require('v8').startupSnapshot.setDeserializeMainFunction(() => console.log('I am from the snapshot'))" > snapshot.js
$ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js
$ node --snapshot-blob snapshot.blob
I am from the snapshot
```
For more information, check out the [`v8.startupSnapshot` API](v8#startup-snapshot-api) documentation.
Currently the support for run-time snapshot is experimental in that:
1. User-land modules are not yet supported in the snapshot, so only one single file can be snapshotted. Users can bundle their applications into a single script with their bundler of choice before building a snapshot, however.
2. Only a subset of the built-in modules work in the snapshot, though the Node.js core test suite checks that a few fairly complex applications can be snapshotted. Support for more modules are being added. If any crashes or buggy behaviors occur when building a snapshot, please file a report in the [Node.js issue tracker](https://github.com/nodejs/node/issues) and link to it in the [tracking issue for user-land snapshots](https://github.com/nodejs/node/issues/44014).
####
`--completion-bash`
Added in: v10.12.0 Print source-able bash completion script for Node.js.
```
$ node --completion-bash > node_bash_completion
$ source node_bash_completion
```
####
`-C=condition`, `--conditions=condition`
Added in: v14.9.0, v12.19.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Enable experimental support for custom [conditional exports](packages#conditional-exports) resolution conditions.
Any number of custom string condition names are permitted.
The default Node.js conditions of `"node"`, `"default"`, `"import"`, and `"require"` will always apply as defined.
For example, to run a module with "development" resolutions:
```
$ node -C=development app.js
```
####
`--cpu-prof`
Added in: v12.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Starts the V8 CPU profiler on start up, and writes the CPU profile to disk before exit.
If `--cpu-prof-dir` is not specified, the generated profile is placed in the current working directory.
If `--cpu-prof-name` is not specified, the generated profile is named `CPU.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.cpuprofile`.
```
$ node --cpu-prof index.js
$ ls *.cpuprofile
CPU.20190409.202950.15293.0.0.cpuprofile
```
####
`--cpu-prof-dir`
Added in: v12.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Specify the directory where the CPU profiles generated by `--cpu-prof` will be placed.
The default value is controlled by the [`--diagnostic-dir`](#--diagnostic-dirdirectory) command-line option.
####
`--cpu-prof-interval`
Added in: v12.2.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Specify the sampling interval in microseconds for the CPU profiles generated by `--cpu-prof`. The default is 1000 microseconds.
####
`--cpu-prof-name`
Added in: v12.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Specify the file name of the CPU profile generated by `--cpu-prof`.
####
`--diagnostic-dir=directory`
Set the directory to which all diagnostic output files are written. Defaults to current working directory.
Affects the default output directory of:
* [`--cpu-prof-dir`](#--cpu-prof-dir)
* [`--heap-prof-dir`](#--heap-prof-dir)
* [`--redirect-warnings`](#--redirect-warningsfile)
####
`--disable-proto=mode`
Added in: v13.12.0, v12.17.0 Disable the `Object.prototype.__proto__` property. If `mode` is `delete`, the property is removed entirely. If `mode` is `throw`, accesses to the property throw an exception with the code `ERR_PROTO_ACCESS`.
####
`--disallow-code-generation-from-strings`
Added in: v9.8.0 Make built-in language features like `eval` and `new Function` that generate code from strings throw an exception instead. This does not affect the Node.js `node:vm` module.
####
`--dns-result-order=order`
History
| Version | Changes |
| --- | --- |
| v17.0.0 | Changed default value to `verbatim`. |
| v16.4.0, v14.18.0 | Added in: v16.4.0, v14.18.0 |
Set the default value of `verbatim` in [`dns.lookup()`](dns#dnslookuphostname-options-callback) and [`dnsPromises.lookup()`](dns#dnspromiseslookuphostname-options). The value could be:
* `ipv4first`: sets default `verbatim` `false`.
* `verbatim`: sets default `verbatim` `true`.
The default is `verbatim` and [`dns.setDefaultResultOrder()`](dns#dnssetdefaultresultorderorder) have higher priority than `--dns-result-order`.
####
`--enable-fips`
Added in: v6.0.0 Enable FIPS-compliant crypto at startup. (Requires Node.js to be built against FIPS-compatible OpenSSL.)
####
`--enable-source-maps`
History
| Version | Changes |
| --- | --- |
| v15.11.0, v14.18.0 | This API is no longer experimental. |
| v12.12.0 | Added in: v12.12.0 |
Enable [Source Map v3](https://sourcemaps.info/spec.html) support for stack traces.
When using a transpiler, such as TypeScript, stack traces thrown by an application reference the transpiled code, not the original source position. `--enable-source-maps` enables caching of Source Maps and makes a best effort to report stack traces relative to the original source file.
Overriding `Error.prepareStackTrace` prevents `--enable-source-maps` from modifying the stack trace.
Note, enabling source maps can introduce latency to your application when `Error.stack` is accessed. If you access `Error.stack` frequently in your application, take into account the performance implications of `--enable-source-maps`.
####
`--experimental-import-meta-resolve`
Added in: v13.9.0, v12.16.2 Enable experimental `import.meta.resolve()` support.
####
`--experimental-loader=module`
History
| Version | Changes |
| --- | --- |
| v12.11.1 | This flag was renamed from `--loader` to `--experimental-loader`. |
| v8.8.0 | Added in: v8.8.0 |
Specify the `module` of a custom experimental [ECMAScript module loader](esm#loaders). `module` may be any string accepted as an [`import` specifier](esm#import-specifiers).
####
`--experimental-network-imports`
Added in: v17.6.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Enable experimental support for the `https:` protocol in `import` specifiers.
####
`--experimental-policy`
Added in: v11.8.0 Use the specified file as a security policy.
####
`--no-experimental-fetch`
Added in: v18.0.0 Disable experimental support for the [Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API).
####
`--no-experimental-global-webcrypto`
Added in: v19.0.0 Disable exposition of [Web Crypto API](webcrypto) on the global scope.
####
`--no-experimental-global-customevent`
Added in: v19.0.0 Disable exposition of [CustomEvent Web API](https://dom.spec.whatwg.org/#customevent) on the global scope.
####
`--no-experimental-repl-await`
Added in: v16.6.0 Use this flag to disable top-level await in REPL.
####
`--experimental-shadow-realm`
Added in: v19.0.0 Use this flag to enable [ShadowRealm](https://github.com/tc39/proposal-shadowrealm) support.
####
`--experimental-vm-modules`
Added in: v9.6.0 Enable experimental ES Module support in the `node:vm` module.
####
`--experimental-wasi-unstable-preview1`
History
| Version | Changes |
| --- | --- |
| v13.6.0 | changed from `--experimental-wasi-unstable-preview0` to `--experimental-wasi-unstable-preview1`. |
| v13.3.0, v12.16.0 | Added in: v13.3.0, v12.16.0 |
Enable experimental WebAssembly System Interface (WASI) support.
####
`--experimental-wasm-modules`
Added in: v12.3.0 Enable experimental WebAssembly module support.
####
`--force-context-aware`
Added in: v12.12.0 Disable loading native addons that are not [context-aware](addons#context-aware-addons).
####
`--force-fips`
Added in: v6.0.0 Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.) (Same requirements as `--enable-fips`.)
####
`--frozen-intrinsics`
Added in: v11.12.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Enable experimental frozen intrinsics like `Array` and `Object`.
Only the root context is supported. There is no guarantee that `globalThis.Array` is indeed the default intrinsic reference. Code may break under this flag.
To allow polyfills to be added, [`--require`](#-r---require-module) and [`--import`](#--importmodule) both run before freezing intrinsics.
####
`--force-node-api-uncaught-exceptions-policy`
Added in: v18.3.0, v16.17.0 Enforces `uncaughtException` event on Node-API asynchronous callbacks.
To prevent from an existing add-on from crashing the process, this flag is not enabled by default. In the future, this flag will be enabled by default to enforce the correct behavior.
####
`--heapsnapshot-near-heap-limit=max_count`
Added in: v15.1.0, v14.18.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Writes a V8 heap snapshot to disk when the V8 heap usage is approaching the heap limit. `count` should be a non-negative integer (in which case Node.js will write no more than `max_count` snapshots to disk).
When generating snapshots, garbage collection may be triggered and bring the heap usage down. Therefore multiple snapshots may be written to disk before the Node.js instance finally runs out of memory. These heap snapshots can be compared to determine what objects are being allocated during the time consecutive snapshots are taken. It's not guaranteed that Node.js will write exactly `max_count` snapshots to disk, but it will try its best to generate at least one and up to `max_count` snapshots before the Node.js instance runs out of memory when `max_count` is greater than `0`.
Generating V8 snapshots takes time and memory (both memory managed by the V8 heap and native memory outside the V8 heap). The bigger the heap is, the more resources it needs. Node.js will adjust the V8 heap to accommodate the additional V8 heap memory overhead, and try its best to avoid using up all the memory available to the process. When the process uses more memory than the system deems appropriate, the process may be terminated abruptly by the system, depending on the system configuration.
```
$ node --max-old-space-size=100 --heapsnapshot-near-heap-limit=3 index.js
Wrote snapshot to Heap.20200430.100036.49580.0.001.heapsnapshot
Wrote snapshot to Heap.20200430.100037.49580.0.002.heapsnapshot
Wrote snapshot to Heap.20200430.100038.49580.0.003.heapsnapshot
<--- Last few GCs --->
[49580:0x110000000] 4826 ms: Mark-sweep 130.6 (147.8) -> 130.5 (147.8) MB, 27.4 / 0.0 ms (average mu = 0.126, current mu = 0.034) allocation failure scavenge might not succeed
[49580:0x110000000] 4845 ms: Mark-sweep 130.6 (147.8) -> 130.6 (147.8) MB, 18.8 / 0.0 ms (average mu = 0.088, current mu = 0.031) allocation failure scavenge might not succeed
<--- JS stacktrace --->
FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory
....
```
####
`--heapsnapshot-signal=signal`
Added in: v12.0.0 Enables a signal handler that causes the Node.js process to write a heap dump when the specified signal is received. `signal` must be a valid signal name. Disabled by default.
```
$ node --heapsnapshot-signal=SIGUSR2 index.js &
$ ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
node 1 5.5 6.1 787252 247004 ? Ssl 16:43 0:02 node --heapsnapshot-signal=SIGUSR2 index.js
$ kill -USR2 1
$ ls
Heap.20190718.133405.15554.0.001.heapsnapshot
```
####
`--heap-prof`
Added in: v12.4.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Starts the V8 heap profiler on start up, and writes the heap profile to disk before exit.
If `--heap-prof-dir` is not specified, the generated profile is placed in the current working directory.
If `--heap-prof-name` is not specified, the generated profile is named `Heap.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.heapprofile`.
```
$ node --heap-prof index.js
$ ls *.heapprofile
Heap.20190409.202950.15293.0.001.heapprofile
```
####
`--heap-prof-dir`
Added in: v12.4.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Specify the directory where the heap profiles generated by `--heap-prof` will be placed.
The default value is controlled by the [`--diagnostic-dir`](#--diagnostic-dirdirectory) command-line option.
####
`--heap-prof-interval`
Added in: v12.4.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Specify the average sampling interval in bytes for the heap profiles generated by `--heap-prof`. The default is 512 \* 1024 bytes.
####
`--heap-prof-name`
Added in: v12.4.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Specify the file name of the heap profile generated by `--heap-prof`.
####
`--icu-data-dir=file`
Added in: v0.11.15 Specify ICU data load path. (Overrides `NODE_ICU_DATA`.)
####
`--import=module`
Added in: v19.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Preload the specified module at startup.
Follows [ECMAScript module](esm#modules-ecmascript-modules) resolution rules. Use [`--require`](#-r---require-module) to load a [CommonJS module](modules). Modules preloaded with `--require` will run before modules preloaded with `--import`.
####
`--input-type=type`
Added in: v12.0.0 This configures Node.js to interpret string input as CommonJS or as an ES module. String input is input via `--eval`, `--print`, or `STDIN`.
Valid values are `"commonjs"` and `"module"`. The default is `"commonjs"`.
The REPL does not support this option.
####
`--inspect-brk[=[host:]port]`
Added in: v7.6.0 Activate inspector on `host:port` and break at start of user script. Default `host:port` is `127.0.0.1:9229`.
####
`--inspect-port=[host:]port`
Added in: v7.6.0 Set the `host:port` to be used when the inspector is activated. Useful when activating the inspector by sending the `SIGUSR1` signal.
Default host is `127.0.0.1`.
See the [security warning](#warning-binding-inspector-to-a-public-ipport-combination-is-insecure) below regarding the `host` parameter usage.
####
`--inspect[=[host:]port]`
Added in: v6.3.0 Activate inspector on `host:port`. Default is `127.0.0.1:9229`.
V8 inspector integration allows tools such as Chrome DevTools and IDEs to debug and profile Node.js instances. The tools attach to Node.js instances via a tcp port and communicate using the [Chrome DevTools Protocol](https://chromedevtools.github.io/devtools-protocol/).
##### Warning: binding inspector to a public IP:port combination is insecure
Binding the inspector to a public IP (including `0.0.0.0`) with an open port is insecure, as it allows external hosts to connect to the inspector and perform a [remote code execution](https://www.owasp.org/index.php/Code_Injection) attack.
If specifying a host, make sure that either:
* The host is not accessible from public networks.
* A firewall disallows unwanted connections on the port.
**More specifically, `--inspect=0.0.0.0` is insecure if the port (`9229` by default) is not firewall-protected.**
See the [debugging security implications](https://nodejs.org/en/docs/guides/debugging-getting-started/#security-implications) section for more information.
####
`--inspect-publish-uid=stderr,http`
Specify ways of the inspector web socket url exposure.
By default inspector websocket url is available in stderr and under `/json/list` endpoint on `http://host:port/json/list`.
####
`--insecure-http-parser`
Added in: v13.4.0, v12.15.0, v10.19.0 Use an insecure HTTP parser that accepts invalid HTTP headers. This may allow interoperability with non-conformant HTTP implementations. It may also allow request smuggling and other HTTP attacks that rely on invalid headers being accepted. Avoid using this option.
####
`--jitless`
Added in: v12.0.0 Disable [runtime allocation of executable memory](https://v8.dev/blog/jitless). This may be required on some platforms for security reasons. It can also reduce attack surface on other platforms, but the performance impact may be severe.
This flag is inherited from V8 and is subject to change upstream. It may disappear in a non-semver-major release.
####
`--max-http-header-size=size`
History
| Version | Changes |
| --- | --- |
| v13.13.0 | Change maximum default size of HTTP headers from 8 KiB to 16 KiB. |
| v11.6.0, v10.15.0 | Added in: v11.6.0, v10.15.0 |
Specify the maximum size, in bytes, of HTTP headers. Defaults to 16 KiB.
####
`--napi-modules`
Added in: v7.10.0 This option is a no-op. It is kept for compatibility.
####
`--no-addons`
Added in: v16.10.0, v14.19.0 Disable the `node-addons` exports condition as well as disable loading native addons. When `--no-addons` is specified, calling `process.dlopen` or requiring a native C++ addon will fail and throw an exception.
####
`--no-deprecation`
Added in: v0.8.0 Silence deprecation warnings.
####
`--no-extra-info-on-fatal-exception`
Added in: v17.0.0 Hide extra information on fatal exception that causes exit.
####
`--no-force-async-hooks-checks`
Added in: v9.0.0 Disables runtime checks for `async_hooks`. These will still be enabled dynamically when `async_hooks` is enabled.
####
`--no-global-search-paths`
Added in: v16.10.0 Do not search modules from global paths like `$HOME/.node_modules` and `$NODE_PATH`.
####
`--no-warnings`
Added in: v6.0.0 Silence all process warnings (including deprecations).
####
`--node-memory-debug`
Added in: v15.0.0, v14.18.0 Enable extra debug checks for memory leaks in Node.js internals. This is usually only useful for developers debugging Node.js itself.
####
`--openssl-config=file`
Added in: v6.9.0 Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built against FIPS-enabled OpenSSL.
####
`--openssl-shared-config`
Added in: v18.5.0, v16.17.0 Enable OpenSSL default configuration section, `openssl_conf` to be read from the OpenSSL configuration file. The default configuration file is named `openssl.cnf` but this can be changed using the environment variable `OPENSSL_CONF`, or by using the command line option `--openssl-config`. The location of the default OpenSSL configuration file depends on how OpenSSL is being linked to Node.js. Sharing the OpenSSL configuration may have unwanted implications and it is recommended to use a configuration section specific to Node.js which is `nodejs_conf` and is default when this option is not used.
####
`--openssl-legacy-provider`
Added in: v17.0.0, v16.17.0 Enable OpenSSL 3.0 legacy provider. For more information please see [OSSL\_PROVIDER-legacy](https://www.openssl.org/docs/man3.0/man7/OSSL_PROVIDER-legacy.html).
####
`--pending-deprecation`
Added in: v8.0.0 Emit pending deprecation warnings.
Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned *off* by default and will not be emitted unless either the `--pending-deprecation` command-line flag, or the `NODE_PENDING_DEPRECATION=1` environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.
####
`--policy-integrity=sri`
Added in: v12.7.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Instructs Node.js to error prior to running any code if the policy does not have the specified integrity. It expects a [Subresource Integrity](https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity) string as a parameter.
####
`--preserve-symlinks`
Added in: v6.3.0 Instructs the module loader to preserve symbolic links when resolving and caching modules.
By default, when Node.js loads a module from a path that is symbolically linked to a different on-disk location, Node.js will dereference the link and use the actual on-disk "real path" of the module as both an identifier and as a root path to locate other dependency modules. In most cases, this default behavior is acceptable. However, when using symbolically linked peer dependencies, as illustrated in the example below, the default behavior causes an exception to be thrown if `moduleA` attempts to require `moduleB` as a peer dependency:
```
{appDir}
├── app
│ ├── index.js
│ └── node_modules
│ ├── moduleA -> {appDir}/moduleA
│ └── moduleB
│ ├── index.js
│ └── package.json
└── moduleA
├── index.js
└── package.json
```
The `--preserve-symlinks` command-line flag instructs Node.js to use the symlink path for modules as opposed to the real path, allowing symbolically linked peer dependencies to be found.
Note, however, that using `--preserve-symlinks` can have other side effects. Specifically, symbolically linked *native* modules can fail to load if those are linked from more than one location in the dependency tree (Node.js would see those as two separate modules and would attempt to load the module multiple times, causing an exception to be thrown).
The `--preserve-symlinks` flag does not apply to the main module, which allows `node --preserve-symlinks node_module/.bin/<foo>` to work. To apply the same behavior for the main module, also use `--preserve-symlinks-main`.
####
`--preserve-symlinks-main`
Added in: v10.2.0 Instructs the module loader to preserve symbolic links when resolving and caching the main module (`require.main`).
This flag exists so that the main module can be opted-in to the same behavior that `--preserve-symlinks` gives to all other imports; they are separate flags, however, for backward compatibility with older Node.js versions.
`--preserve-symlinks-main` does not imply `--preserve-symlinks`; use `--preserve-symlinks-main` in addition to `--preserve-symlinks` when it is not desirable to follow symlinks before resolving relative paths.
See [`--preserve-symlinks`](#--preserve-symlinks) for more information.
####
`--prof`
Added in: v2.0.0 Generate V8 profiler output.
####
`--prof-process`
Added in: v5.2.0 Process V8 profiler output generated using the V8 option `--prof`.
####
`--redirect-warnings=file`
Added in: v8.0.0 Write process warnings to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead.
The `file` name may be an absolute path. If it is not, the default directory it will be written to is controlled by the [`--diagnostic-dir`](#--diagnostic-dirdirectory) command-line option.
####
`--report-compact`
Added in: v13.12.0, v12.17.0 Write reports in a compact format, single-line JSON, more easily consumable by log processing systems than the default multi-line format designed for human consumption.
####
`--report-dir=directory`, `report-directory=directory`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This option is no longer experimental. |
| v12.0.0 | Changed from `--diagnostic-report-directory` to `--report-directory`. |
| v11.8.0 | Added in: v11.8.0 |
Location at which the report will be generated.
####
`--report-filename=filename`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This option is no longer experimental. |
| v12.0.0 | changed from `--diagnostic-report-filename` to `--report-filename`. |
| v11.8.0 | Added in: v11.8.0 |
Name of the file to which the report will be written.
If the filename is set to `'stdout'` or `'stderr'`, the report is written to the stdout or stderr of the process respectively.
####
`--report-on-fatalerror`
History
| Version | Changes |
| --- | --- |
| v14.0.0, v13.14.0, v12.17.0 | This option is no longer experimental. |
| v12.0.0 | changed from `--diagnostic-report-on-fatalerror` to `--report-on-fatalerror`. |
| v11.8.0 | Added in: v11.8.0 |
Enables the report to be triggered on fatal errors (internal errors within the Node.js runtime such as out of memory) that lead to termination of the application. Useful to inspect various diagnostic data elements such as heap, stack, event loop state, resource consumption etc. to reason about the fatal error.
####
`--report-on-signal`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This option is no longer experimental. |
| v12.0.0 | changed from `--diagnostic-report-on-signal` to `--report-on-signal`. |
| v11.8.0 | Added in: v11.8.0 |
Enables report to be generated upon receiving the specified (or predefined) signal to the running Node.js process. The signal to trigger the report is specified through `--report-signal`.
####
`--report-signal=signal`
History
| Version | Changes |
| --- | --- |
| v13.12.0, v12.17.0 | This option is no longer experimental. |
| v12.0.0 | changed from `--diagnostic-report-signal` to `--report-signal`. |
| v11.8.0 | Added in: v11.8.0 |
Sets or resets the signal for report generation (not supported on Windows). Default signal is `SIGUSR2`.
####
`--report-uncaught-exception`
History
| Version | Changes |
| --- | --- |
| v18.8.0, v16.18.0 | Report is not generated if the uncaught exception is handled. |
| v13.12.0, v12.17.0 | This option is no longer experimental. |
| v12.0.0 | changed from `--diagnostic-report-uncaught-exception` to `--report-uncaught-exception`. |
| v11.8.0 | Added in: v11.8.0 |
Enables report to be generated when the process exits due to an uncaught exception. Useful when inspecting the JavaScript stack in conjunction with native stack and other runtime environment data.
####
`--secure-heap=n`
Added in: v15.6.0 Initializes an OpenSSL secure heap of `n` bytes. When initialized, the secure heap is used for selected types of allocations within OpenSSL during key generation and other operations. This is useful, for instance, to prevent sensitive information from leaking due to pointer overruns or underruns.
The secure heap is a fixed size and cannot be resized at runtime so, if used, it is important to select a large enough heap to cover all application uses.
The heap size given must be a power of two. Any value less than 2 will disable the secure heap.
The secure heap is disabled by default.
The secure heap is not available on Windows.
See [`CRYPTO_secure_malloc_init`](https://www.openssl.org/docs/man1.1.0/man3/CRYPTO_secure_malloc_init.html) for more details.
####
`--secure-heap-min=n`
Added in: v15.6.0 When using `--secure-heap`, the `--secure-heap-min` flag specifies the minimum allocation from the secure heap. The minimum value is `2`. The maximum value is the lesser of `--secure-heap` or `2147483647`. The value given must be a power of two.
####
`--snapshot-blob=path`
Added in: v18.8.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
When used with `--build-snapshot`, `--snapshot-blob` specifies the path where the generated snapshot blob will be written to. If not specified, the generated blob will be written, by default, to `snapshot.blob` in the current working directory.
When used without `--build-snapshot`, `--snapshot-blob` specifies the path to the blob that will be used to restore the application state.
When loading a snapshot, Node.js checks that:
1. The version, architecture and platform of the running Node.js binary are exactly the same as that of the binary that generates the snapshot.
2. The V8 flags and CPU features are compatible with that of the binary that generates the snapshot.
If they don't match, Node.js would refuse to load the snapshot and exit with 1.
####
`--test`
Added in: v18.1.0, v16.17.0 Starts the Node.js command line test runner. This flag cannot be combined with `--check`, `--eval`, `--interactive`, or the inspector. See the documentation on [running tests from the command line](test#running-tests-from-the-command-line) for more details.
####
`--test-name-pattern`
Added in: v18.11.0 A regular expression that configures the test runner to only execute tests whose name matches the provided pattern. See the documentation on [filtering tests by name](test#filtering-tests-by-name) for more details.
####
`--test-only`
Added in: v18.0.0, v16.17.0 Configures the test runner to only execute top level tests that have the `only` option set.
####
`--throw-deprecation`
Added in: v0.11.14 Throw errors for deprecations.
####
`--title=title`
Added in: v10.7.0 Set `process.title` on startup.
####
`--tls-cipher-list=list`
Added in: v4.0.0 Specify an alternative default TLS cipher list. Requires Node.js to be built with crypto support (default).
####
`--tls-keylog=file`
Added in: v13.2.0, v12.16.0 Log TLS key material to a file. The key material is in NSS `SSLKEYLOGFILE` format and can be used by software (such as Wireshark) to decrypt the TLS traffic.
####
`--tls-max-v1.2`
Added in: v12.0.0, v10.20.0 Set [`tls.DEFAULT_MAX_VERSION`](tls#tlsdefault_max_version) to 'TLSv1.2'. Use to disable support for TLSv1.3.
####
`--tls-max-v1.3`
Added in: v12.0.0 Set default [`tls.DEFAULT_MAX_VERSION`](tls#tlsdefault_max_version) to 'TLSv1.3'. Use to enable support for TLSv1.3.
####
`--tls-min-v1.0`
Added in: v12.0.0, v10.20.0 Set default [`tls.DEFAULT_MIN_VERSION`](tls#tlsdefault_min_version) to 'TLSv1'. Use for compatibility with old TLS clients or servers.
####
`--tls-min-v1.1`
Added in: v12.0.0, v10.20.0 Set default [`tls.DEFAULT_MIN_VERSION`](tls#tlsdefault_min_version) to 'TLSv1.1'. Use for compatibility with old TLS clients or servers.
####
`--tls-min-v1.2`
Added in: v12.2.0, v10.20.0 Set default [`tls.DEFAULT_MIN_VERSION`](tls#tlsdefault_min_version) to 'TLSv1.2'. This is the default for 12.x and later, but the option is supported for compatibility with older Node.js versions.
####
`--tls-min-v1.3`
Added in: v12.0.0 Set default [`tls.DEFAULT_MIN_VERSION`](tls#tlsdefault_min_version) to 'TLSv1.3'. Use to disable support for TLSv1.2, which is not as secure as TLSv1.3.
####
`--trace-atomics-wait`
Added in: v14.3.0Deprecated since: v18.8.0, v16.18.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
Print short summaries of calls to [`Atomics.wait()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics/wait) to stderr. The output could look like this:
```
(node:15701) [Thread 0] Atomics.wait(<address> + 0, 1, inf) started
(node:15701) [Thread 0] Atomics.wait(<address> + 0, 1, inf) did not wait because the values mismatched
(node:15701) [Thread 0] Atomics.wait(<address> + 0, 0, 10) started
(node:15701) [Thread 0] Atomics.wait(<address> + 0, 0, 10) timed out
(node:15701) [Thread 0] Atomics.wait(<address> + 4, 0, inf) started
(node:15701) [Thread 1] Atomics.wait(<address> + 4, -1, inf) started
(node:15701) [Thread 0] Atomics.wait(<address> + 4, 0, inf) was woken up by another thread
(node:15701) [Thread 1] Atomics.wait(<address> + 4, -1, inf) was woken up by another thread
```
The fields here correspond to:
* The thread id as given by [`worker_threads.threadId`](worker_threads#workerthreadid)
* The base address of the `SharedArrayBuffer` in question, as well as the byte offset corresponding to the index passed to `Atomics.wait()`
* The expected value that was passed to `Atomics.wait()`
* The timeout passed to `Atomics.wait`
####
`--trace-deprecation`
Added in: v0.8.0 Print stack traces for deprecations.
####
`--trace-event-categories`
Added in: v7.7.0 A comma separated list of categories that should be traced when trace event tracing is enabled using `--trace-events-enabled`.
####
`--trace-event-file-pattern`
Added in: v9.8.0 Template string specifying the filepath for the trace event data, it supports `${rotation}` and `${pid}`.
####
`--trace-events-enabled`
Added in: v7.7.0 Enables the collection of trace event tracing information.
####
`--trace-exit`
Added in: v13.5.0, v12.16.0 Prints a stack trace whenever an environment is exited proactively, i.e. invoking `process.exit()`.
####
`--trace-sigint`
Added in: v13.9.0, v12.17.0 Prints a stack trace on SIGINT.
####
`--trace-sync-io`
Added in: v2.1.0 Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop.
####
`--trace-tls`
Added in: v12.2.0 Prints TLS packet trace information to `stderr`. This can be used to debug TLS connection problems.
####
`--trace-uncaught`
Added in: v13.1.0 Print stack traces for uncaught exceptions; usually, the stack trace associated with the creation of an `Error` is printed, whereas this makes Node.js also print the stack trace associated with throwing the value (which does not need to be an `Error` instance).
Enabling this option may affect garbage collection behavior negatively.
####
`--trace-warnings`
Added in: v6.0.0 Print stack traces for process warnings (including deprecations).
####
`--track-heap-objects`
Added in: v2.4.0 Track heap object allocations for heap snapshots.
####
`--unhandled-rejections=mode`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Changed default mode to `throw`. Previously, a warning was emitted. |
| v12.0.0, v10.17.0 | Added in: v12.0.0, v10.17.0 |
Using this flag allows to change what should happen when an unhandled rejection occurs. One of the following modes can be chosen:
* `throw`: Emit [`unhandledRejection`](process#event-unhandledrejection). If this hook is not set, raise the unhandled rejection as an uncaught exception. This is the default.
* `strict`: Raise the unhandled rejection as an uncaught exception. If the exception is handled, [`unhandledRejection`](process#event-unhandledrejection) is emitted.
* `warn`: Always trigger a warning, no matter if the [`unhandledRejection`](process#event-unhandledrejection) hook is set or not but do not print the deprecation warning.
* `warn-with-error-code`: Emit [`unhandledRejection`](process#event-unhandledrejection). If this hook is not set, trigger a warning, and set the process exit code to 1.
* `none`: Silence all warnings.
If a rejection happens during the command line entry point's ES module static loading phase, it will always raise it as an uncaught exception.
####
`--update-assert-snapshot`
Added in: v18.8.0 Updates snapshot files used by [`assert.snapshot()`](assert#assertsnapshotvalue-name).
####
`--use-bundled-ca`, `--use-openssl-ca`
Added in: v6.11.0 Use bundled Mozilla CA store as supplied by current Node.js version or use OpenSSL's default CA store. The default store is selectable at build-time.
The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms.
Using OpenSSL store allows for external modifications of the store. For most Linux and BSD distributions, this store is maintained by the distribution maintainers and system administrators. OpenSSL CA store location is dependent on configuration of the OpenSSL library but this can be altered at runtime using environment variables.
See `SSL_CERT_DIR` and `SSL_CERT_FILE`.
####
`--use-largepages=mode`
Added in: v13.6.0, v12.17.0 Re-map the Node.js static code to large memory pages at startup. If supported on the target system, this will cause the Node.js static code to be moved onto 2 MiB pages instead of 4 KiB pages.
The following values are valid for `mode`:
* `off`: No mapping will be attempted. This is the default.
* `on`: If supported by the OS, mapping will be attempted. Failure to map will be ignored and a message will be printed to standard error.
* `silent`: If supported by the OS, mapping will be attempted. Failure to map will be ignored and will not be reported.
####
`--v8-options`
Added in: v0.1.3 Print V8 command-line options.
####
`--v8-pool-size=num`
Added in: v5.10.0 Set V8's thread pool size which will be used to allocate background jobs.
If set to `0` then V8 will choose an appropriate size of the thread pool based on the number of online processors.
If the value provided is larger than V8's maximum, then the largest value will be chosen.
####
`--watch`
Added in: v18.11.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Starts Node.js in watch mode. When in watch mode, changes in the watched files cause the Node.js process to restart. By default, watch mode will watch the entry point and any required or imported module. Use `--watch-path` to specify what paths to watch.
This flag cannot be combined with `--check`, `--eval`, `--interactive`, or the REPL.
```
$ node --watch index.js
```
####
`--watch-path`
Added in: v18.11.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Starts Node.js in watch mode and specifies what paths to watch. When in watch mode, changes in the watched paths cause the Node.js process to restart. This will turn off watching of required or imported modules, even when used in combination with `--watch`.
This flag cannot be combined with `--check`, `--eval`, `--interactive`, or the REPL.
```
$ node --watch-path=./src --watch-path=./tests index.js
```
This option is only supported on macOS and Windows. An `ERR_FEATURE_UNAVAILABLE_ON_PLATFORM` exception will be thrown when the option is used on a platform that does not support it.
####
`--zero-fill-buffers`
Added in: v6.0.0 Automatically zero-fills all newly allocated [`Buffer`](buffer#class-buffer) and [`SlowBuffer`](buffer#class-slowbuffer) instances.
####
`-c`, `--check`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | The `--require` option is now supported when checking a file. |
| v5.0.0, v4.2.0 | Added in: v5.0.0, v4.2.0 |
Syntax check the script without executing.
####
`-e`, `--eval "script"`
History
| Version | Changes |
| --- | --- |
| v5.11.0 | Built-in libraries are now available as predefined variables. |
| v0.5.2 | Added in: v0.5.2 |
Evaluate the following argument as JavaScript. The modules which are predefined in the REPL can also be used in `script`.
On Windows, using `cmd.exe` a single quote will not work correctly because it only recognizes double `"` for quoting. In Powershell or Git bash, both `'` and `"` are usable.
####
`-h`, `--help`
Added in: v0.1.3 Print node command-line options. The output of this option is less detailed than this document.
####
`-i`, `--interactive`
Added in: v0.7.7 Opens the REPL even if stdin does not appear to be a terminal.
####
`-p`, `--print "script"`
History
| Version | Changes |
| --- | --- |
| v5.11.0 | Built-in libraries are now available as predefined variables. |
| v0.6.4 | Added in: v0.6.4 |
Identical to `-e` but prints the result.
####
`-r`, `--require module`
Added in: v1.6.0 Preload the specified module at startup.
Follows `require()`'s module resolution rules. `module` may be either a path to a file, or a node module name.
Only CommonJS modules are supported. Use [`--import`](#--importmodule) to preload an [ECMAScript module](esm#modules-ecmascript-modules). Modules preloaded with `--require` will run before modules preloaded with `--import`.
####
`-v`, `--version`
Added in: v0.1.3 Print node's version.
### Environment variables
####
`FORCE_COLOR=[1, 2, 3]`
The `FORCE_COLOR` environment variable is used to enable ANSI colorized output. The value may be:
* `1`, `true`, or the empty string `''` indicate 16-color support,
* `2` to indicate 256-color support, or
* `3` to indicate 16 million-color support.
When `FORCE_COLOR` is used and set to a supported value, both the `NO_COLOR`, and `NODE_DISABLE_COLORS` environment variables are ignored.
Any other value will result in colorized output being disabled.
####
`NODE_DEBUG=module[,…]`
Added in: v0.1.32 `','`-separated list of core modules that should print debug information.
####
`NODE_DEBUG_NATIVE=module[,…]`
`','`-separated list of core C++ modules that should print debug information.
####
`NODE_DISABLE_COLORS=1`
Added in: v0.3.0 When set, colors will not be used in the REPL.
####
`NODE_EXTRA_CA_CERTS=file`
Added in: v7.3.0 When set, the well known "root" CAs (like VeriSign) will be extended with the extra certificates in `file`. The file should consist of one or more trusted certificates in PEM format. A message will be emitted (once) with [`process.emitWarning()`](process#processemitwarningwarning-options) if the file is missing or malformed, but any errors are otherwise ignored.
Neither the well known nor extra certificates are used when the `ca` options property is explicitly specified for a TLS or HTTPS client or server.
This environment variable is ignored when `node` runs as setuid root or has Linux file capabilities set.
The `NODE_EXTRA_CA_CERTS` environment variable is only read when the Node.js process is first launched. Changing the value at runtime using `process.env.NODE_EXTRA_CA_CERTS` has no effect on the current process.
####
`NODE_ICU_DATA=file`
Added in: v0.11.15 Data path for ICU (`Intl` object) data. Will extend linked-in data when compiled with small-icu support.
####
`NODE_NO_WARNINGS=1`
Added in: v6.11.0 When set to `1`, process warnings are silenced.
####
`NODE_OPTIONS=options...`
Added in: v8.0.0 A space-separated list of command-line options. `options...` are interpreted before command-line options, so command-line options will override or compound after anything in `options...`. Node.js will exit with an error if an option that is not allowed in the environment is used, such as `-p` or a script file.
If an option value contains a space, it can be escaped using double quotes:
```
NODE_OPTIONS='--require "./my path/file.js"'
```
A singleton flag passed as a command-line option will override the same flag passed into `NODE_OPTIONS`:
```
# The inspector will be available on port 5555
NODE_OPTIONS='--inspect=localhost:4444' node --inspect=localhost:5555
```
A flag that can be passed multiple times will be treated as if its `NODE_OPTIONS` instances were passed first, and then its command-line instances afterwards:
```
NODE_OPTIONS='--require "./a.js"' node --require "./b.js"
# is equivalent to:
node --require "./a.js" --require "./b.js"
```
Node.js options that are allowed are:
* `--conditions`, `-C`
* `--diagnostic-dir`
* `--disable-proto`
* `--dns-result-order`
* `--enable-fips`
* `--enable-source-maps`
* `--experimental-abortcontroller`
* `--experimental-import-meta-resolve`
* `--experimental-json-modules`
* `--experimental-loader`
* `--experimental-modules`
* `--experimental-network-imports`
* `--experimental-policy`
* `--experimental-shadow-realm`
* `--experimental-specifier-resolution`
* `--experimental-top-level-await`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-wasm-modules`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
* `--frozen-intrinsics`
* `--heapsnapshot-near-heap-limit`
* `--heapsnapshot-signal`
* `--http-parser`
* `--icu-data-dir`
* `--import`
* `--input-type`
* `--insecure-http-parser`
* `--inspect-brk`
* `--inspect-port`, `--debug-port`
* `--inspect-publish-uid`
* `--inspect`
* `--max-http-header-size`
* `--napi-modules`
* `--no-addons`
* `--no-deprecation`
* `--no-experimental-fetch`
* `--no-experimental-global-customevent`
* `--no-experimental-global-webcrypto`
* `--no-experimental-repl-await`
* `--no-extra-info-on-fatal-exception`
* `--no-force-async-hooks-checks`
* `--no-global-search-paths`
* `--no-warnings`
* `--node-memory-debug`
* `--openssl-config`
* `--openssl-legacy-provider`
* `--openssl-shared-config`
* `--pending-deprecation`
* `--policy-integrity`
* `--preserve-symlinks-main`
* `--preserve-symlinks`
* `--prof-process`
* `--redirect-warnings`
* `--report-compact`
* `--report-dir`, `--report-directory`
* `--report-filename`
* `--report-on-fatalerror`
* `--report-on-signal`
* `--report-signal`
* `--report-uncaught-exception`
* `--require`, `-r`
* `--secure-heap-min`
* `--secure-heap`
* `--snapshot-blob`
* `--test-only`
* `--throw-deprecation`
* `--title`
* `--tls-cipher-list`
* `--tls-keylog`
* `--tls-max-v1.2`
* `--tls-max-v1.3`
* `--tls-min-v1.0`
* `--tls-min-v1.1`
* `--tls-min-v1.2`
* `--tls-min-v1.3`
* `--trace-atomics-wait`
* `--trace-deprecation`
* `--trace-event-categories`
* `--trace-event-file-pattern`
* `--trace-events-enabled`
* `--trace-exit`
* `--trace-sigint`
* `--trace-sync-io`
* `--trace-tls`
* `--trace-uncaught`
* `--trace-warnings`
* `--track-heap-objects`
* `--unhandled-rejections`
* `--update-assert-snapshot`
* `--use-bundled-ca`
* `--use-largepages`
* `--use-openssl-ca`
* `--v8-pool-size`
* `--watch-path`
* `--watch`
* `--zero-fill-buffers`
V8 options that are allowed are:
* `--abort-on-uncaught-exception`
* `--disallow-code-generation-from-strings`
* `--huge-max-old-generation-size`
* `--interpreted-frames-native-stack`
* `--jitless`
* `--max-old-space-size`
* `--perf-basic-prof-only-functions`
* `--perf-basic-prof`
* `--perf-prof-unwinding-info`
* `--perf-prof`
* `--stack-trace-limit`
`--perf-basic-prof-only-functions`, `--perf-basic-prof`, `--perf-prof-unwinding-info`, and `--perf-prof` are only available on Linux.
####
`NODE_PATH=path[:…]`
Added in: v0.1.32 `':'`-separated list of directories prefixed to the module search path.
On Windows, this is a `';'`-separated list instead.
####
`NODE_PENDING_DEPRECATION=1`
Added in: v8.0.0 When set to `1`, emit pending deprecation warnings.
Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned *off* by default and will not be emitted unless either the `--pending-deprecation` command-line flag, or the `NODE_PENDING_DEPRECATION=1` environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.
####
`NODE_PENDING_PIPE_INSTANCES=instances`
Set the number of pending pipe instance handles when the pipe server is waiting for connections. This setting applies to Windows only.
####
`NODE_PRESERVE_SYMLINKS=1`
Added in: v7.1.0 When set to `1`, instructs the module loader to preserve symbolic links when resolving and caching modules.
####
`NODE_REDIRECT_WARNINGS=file`
Added in: v8.0.0 When set, process warnings will be emitted to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead. This is equivalent to using the `--redirect-warnings=file` command-line flag.
####
`NODE_REPL_HISTORY=file`
Added in: v3.0.0 Path to the file used to store the persistent REPL history. The default path is `~/.node_repl_history`, which is overridden by this variable. Setting the value to an empty string (`''` or `' '`) disables persistent REPL history.
####
`NODE_REPL_EXTERNAL_MODULE=file`
Added in: v13.0.0, v12.16.0 Path to a Node.js module which will be loaded in place of the built-in REPL. Overriding this value to an empty string (`''`) will use the built-in REPL.
####
`NODE_SKIP_PLATFORM_CHECK=value`
Added in: v14.5.0 If `value` equals `'1'`, the check for a supported platform is skipped during Node.js startup. Node.js might not execute correctly. Any issues encountered on unsupported platforms will not be fixed.
####
`NODE_TLS_REJECT_UNAUTHORIZED=value`
If `value` equals `'0'`, certificate validation is disabled for TLS connections. This makes TLS, and HTTPS by extension, insecure. The use of this environment variable is strongly discouraged.
####
`NODE_V8_COVERAGE=dir`
When set, Node.js will begin outputting [V8 JavaScript code coverage](https://v8project.blogspot.com/2017/12/javascript-code-coverage.html) and [Source Map](https://sourcemaps.info/spec.html) data to the directory provided as an argument (coverage information is written as JSON to files with a `coverage` prefix).
`NODE_V8_COVERAGE` will automatically propagate to subprocesses, making it easier to instrument applications that call the `child_process.spawn()` family of functions. `NODE_V8_COVERAGE` can be set to an empty string, to prevent propagation.
##### Coverage output
Coverage is output as an array of [ScriptCoverage](https://chromedevtools.github.io/devtools-protocol/tot/Profiler#type-ScriptCoverage) objects on the top-level key `result`:
```
{
"result": [
{
"scriptId": "67",
"url": "internal/tty.js",
"functions": []
}
]
}
```
##### Source map cache
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
If found, source map data is appended to the top-level key `source-map-cache` on the JSON coverage object.
`source-map-cache` is an object with keys representing the files source maps were extracted from, and values which include the raw source-map URL (in the key `url`), the parsed Source Map v3 information (in the key `data`), and the line lengths of the source file (in the key `lineLengths`).
```
{
"result": [
{
"scriptId": "68",
"url": "file:///absolute/path/to/source.js",
"functions": []
}
],
"source-map-cache": {
"file:///absolute/path/to/source.js": {
"url": "./path-to-map.json",
"data": {
"version": 3,
"sources": [
"file:///absolute/path/to/original.js"
],
"names": [
"Foo",
"console",
"info"
],
"mappings": "MAAMA,IACJC,YAAaC",
"sourceRoot": "./"
},
"lineLengths": [
13,
62,
38,
27
]
}
}
}
```
####
`NO_COLOR=<any>`
[`NO_COLOR`](https://no-color.org) is an alias for `NODE_DISABLE_COLORS`. The value of the environment variable is arbitrary.
####
`OPENSSL_CONF=file`
Added in: v6.11.0 Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with `./configure --openssl-fips`.
If the [`--openssl-config`](#--openssl-configfile) command-line option is used, the environment variable is ignored.
####
`SSL_CERT_DIR=dir`
Added in: v7.7.0 If `--use-openssl-ca` is enabled, this overrides and sets OpenSSL's directory containing trusted certificates.
Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.
####
`SSL_CERT_FILE=file`
Added in: v7.7.0 If `--use-openssl-ca` is enabled, this overrides and sets OpenSSL's file containing trusted certificates.
Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.
####
`TZ`
History
| Version | Changes |
| --- | --- |
| v16.2.0 | Changing the TZ variable using process.env.TZ = changes the timezone on Windows as well. |
| v13.0.0 | Changing the TZ variable using process.env.TZ = changes the timezone on POSIX systems. |
| v0.0.1 | Added in: v0.0.1 |
The `TZ` environment variable is used to specify the timezone configuration.
While Node.js does not support all of the various [ways that `TZ` is handled in other environments](https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html), it does support basic [timezone IDs](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones) (such as `'Etc/UTC'`, `'Europe/Paris'`, or `'America/New_York'`). It may support a few other abbreviations or aliases, but these are strongly discouraged and not guaranteed.
```
$ TZ=Europe/Dublin node -pe "new Date().toString()"
Wed May 12 2021 20:30:48 GMT+0100 (Irish Standard Time)
```
####
`UV_THREADPOOL_SIZE=size`
Set the number of threads used in libuv's threadpool to `size` threads.
Asynchronous system APIs are used by Node.js whenever possible, but where they do not exist, libuv's threadpool is used to create asynchronous node APIs based on synchronous system APIs. Node.js APIs that use the threadpool are:
* all `fs` APIs, other than the file watcher APIs and those that are explicitly synchronous
* asynchronous crypto APIs such as `crypto.pbkdf2()`, `crypto.scrypt()`, `crypto.randomBytes()`, `crypto.randomFill()`, `crypto.generateKeyPair()`
* `dns.lookup()`
* all `zlib` APIs, other than those that are explicitly synchronous
Because libuv's threadpool has a fixed size, it means that if for whatever reason any of these APIs takes a long time, other (seemingly unrelated) APIs that run in libuv's threadpool will experience degraded performance. In order to mitigate this issue, one potential solution is to increase the size of libuv's threadpool by setting the `'UV_THREADPOOL_SIZE'` environment variable to a value greater than `4` (its current default value). For more information, see the [libuv threadpool documentation](https://docs.libuv.org/en/latest/threadpool.html).
### Useful V8 options
V8 has its own set of CLI options. Any V8 CLI option that is provided to `node` will be passed on to V8 to handle. V8's options have *no stability guarantee*. The V8 team themselves don't consider them to be part of their formal API, and reserve the right to change them at any time. Likewise, they are not covered by the Node.js stability guarantees. Many of the V8 options are of interest only to V8 developers. Despite this, there is a small set of V8 options that are widely applicable to Node.js, and they are documented here:
####
`--max-old-space-size=SIZE` (in megabytes)
Sets the max memory size of V8's old memory section. As memory consumption approaches the limit, V8 will spend more time on garbage collection in an effort to free unused memory.
On a machine with 2 GiB of memory, consider setting this to 1536 (1.5 GiB) to leave some memory for other uses and avoid swapping.
```
$ node --max-old-space-size=1536 index.js
```
####
`--max-semi-space-size=SIZE` (in megabytes)
Sets the maximum [semi-space](https://www.memorymanagement.org/glossary/s.html#semi.space) size for V8's [scavenge garbage collector](https://v8.dev/blog/orinoco-parallel-scavenger) in MiB (megabytes). Increasing the max size of a semi-space may improve throughput for Node.js at the cost of more memory consumption.
Since the young generation size of the V8 heap is three times (see [`YoungGenerationSizeFromSemiSpaceSize`](https://chromium.googlesource.com/v8/v8.git/+/refs/tags/10.3.129/src/heap/heap.cc#328) in V8) the size of the semi-space, an increase of 1 MiB to semi-space applies to each of the three individual semi-spaces and causes the heap size to increase by 3 MiB. The throughput improvement depends on your workload (see [#42511](https://github.com/nodejs/node/issues/42511)).
The default value is 16 MiB for 64-bit systems and 8 MiB for 32-bit systems. To get the best configuration for your application, you should try different max-semi-space-size values when running benchmarks for your application.
For example, benchmark on a 64-bit systems:
```
for MiB in 16 32 64 128; do
node --max-semi-space-size=$MiB index.js
done
```
| programming_docs |
node None HTTP
----
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/http.js](https://github.com/nodejs/node/blob/v19.0.1/lib/http.js)
To use the HTTP server and client one must `require('node:http')`.
The HTTP interfaces in Node.js are designed to support many features of the protocol which have been traditionally difficult to use. In particular, large, possibly chunk-encoded, messages. The interface is careful to never buffer entire requests or responses, so the user is able to stream data.
HTTP message headers are represented by an object like this:
```
{ 'content-length': '123',
'content-type': 'text/plain',
'connection': 'keep-alive',
'host': 'example.com',
'accept': '*/*' }
```
Keys are lowercased. Values are not modified.
In order to support the full spectrum of possible HTTP applications, the Node.js HTTP API is very low-level. It deals with stream handling and message parsing only. It parses a message into headers and body but it does not parse the actual headers or the body.
See [`message.headers`](#messageheaders) for details on how duplicate headers are handled.
The raw headers as they were received are retained in the `rawHeaders` property, which is an array of `[key, value, key2, value2, ...]`. For example, the previous message header object might have a `rawHeaders` list like the following:
```
[ 'ConTent-Length', '123456',
'content-LENGTH', '123',
'content-type', 'text/plain',
'CONNECTION', 'keep-alive',
'Host', 'example.com',
'accepT', '*/*' ]
```
### Class: `http.Agent`
Added in: v0.3.4 An `Agent` is responsible for managing connection persistence and reuse for HTTP clients. It maintains a queue of pending requests for a given host and port, reusing a single socket connection for each until the queue is empty, at which time the socket is either destroyed or put into a pool where it is kept to be used again for requests to the same host and port. Whether it is destroyed or pooled depends on the `keepAlive` [option](#new-agentoptions).
Pooled connections have TCP Keep-Alive enabled for them, but servers may still close idle connections, in which case they will be removed from the pool and a new connection will be made when a new HTTP request is made for that host and port. Servers may also refuse to allow multiple requests over the same connection, in which case the connection will have to be remade for every request and cannot be pooled. The `Agent` will still make the requests to that server, but each one will occur over a new connection.
When a connection is closed by the client or the server, it is removed from the pool. Any unused sockets in the pool will be unrefed so as not to keep the Node.js process running when there are no outstanding requests. (see [`socket.unref()`](net#socketunref)).
It is good practice, to [`destroy()`](#agentdestroy) an `Agent` instance when it is no longer in use, because unused sockets consume OS resources.
Sockets are removed from an agent when the socket emits either a `'close'` event or an `'agentRemove'` event. When intending to keep one HTTP request open for a long time without keeping it in the agent, something like the following may be done:
```
http.get(options, (res) => {
// Do stuff
}).on('socket', (socket) => {
socket.emit('agentRemove');
});
```
An agent may also be used for an individual request. By providing `{agent: false}` as an option to the `http.get()` or `http.request()` functions, a one-time use `Agent` with default options will be used for the client connection.
`agent:false`:
```
http.get({
hostname: 'localhost',
port: 80,
path: '/',
agent: false // Create a new agent just for this one request
}, (res) => {
// Do stuff with response
});
```
####
`new Agent([options])`
History
| Version | Changes |
| --- | --- |
| v15.6.0, v14.17.0 | Change the default scheduling from 'fifo' to 'lifo'. |
| v14.5.0, v12.20.0 | Add `scheduling` option to specify the free socket scheduling strategy. |
| v14.5.0, v12.19.0 | Add `maxTotalSockets` option to agent constructor. |
| v0.3.4 | Added in: v0.3.4 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Set of configurable options to set on the agent. Can have the following fields:
+ `keepAlive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Keep sockets around even when there are no outstanding requests, so they can be used for future requests without having to reestablish a TCP connection. Not to be confused with the `keep-alive` value of the `Connection` header. The `Connection: keep-alive` header is always sent when using an agent except when the `Connection` header is explicitly specified or when the `keepAlive` and `maxSockets` options are respectively set to `false` and `Infinity`, in which case `Connection: close` will be used. **Default:** `false`.
+ `keepAliveMsecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) When using the `keepAlive` option, specifies the [initial delay](net#socketsetkeepaliveenable-initialdelay) for TCP Keep-Alive packets. Ignored when the `keepAlive` option is `false` or `undefined`. **Default:** `1000`.
+ `maxSockets` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Maximum number of sockets to allow per host. If the same host opens multiple concurrent connections, each request will use new socket until the `maxSockets` value is reached. If the host attempts to open more connections than `maxSockets`, the additional requests will enter into a pending request queue, and will enter active connection state when an existing connection terminates. This makes sure there are at most `maxSockets` active connections at any point in time, from a given host. **Default:** `Infinity`.
+ `maxTotalSockets` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Maximum number of sockets allowed for all hosts in total. Each request will use a new socket until the maximum is reached. **Default:** `Infinity`.
+ `maxFreeSockets` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Maximum number of sockets per host to leave open in a free state. Only relevant if `keepAlive` is set to `true`. **Default:** `256`.
+ `scheduling` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Scheduling strategy to apply when picking the next free socket to use. It can be `'fifo'` or `'lifo'`. The main difference between the two scheduling strategies is that `'lifo'` selects the most recently used socket, while `'fifo'` selects the least recently used socket. In case of a low rate of request per second, the `'lifo'` scheduling will lower the risk of picking a socket that might have been closed by the server due to inactivity. In case of a high rate of request per second, the `'fifo'` scheduling will maximize the number of open sockets, while the `'lifo'` scheduling will keep it as low as possible. **Default:** `'lifo'`.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Socket timeout in milliseconds. This will set the timeout when the socket is created.
`options` in [`socket.connect()`](net#socketconnectoptions-connectlistener) are also supported.
The default [`http.globalAgent`](#httpglobalagent) that is used by [`http.request()`](#httprequestoptions-callback) has all of these values set to their respective defaults.
To configure any of them, a custom [`http.Agent`](#class-httpagent) instance must be created.
```
const http = require('node:http');
const keepAliveAgent = new http.Agent({ keepAlive: true });
options.agent = keepAliveAgent;
http.request(options, onResponseCallback);
```
####
`agent.createConnection(options[, callback])`
Added in: v0.11.4 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Options containing connection details. Check [`net.createConnection()`](net#netcreateconnectionoptions-connectlistener) for the format of the options
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Callback function that receives the created socket
* Returns: [<stream.Duplex>](stream#class-streamduplex)
Produces a socket/stream to be used for HTTP requests.
By default, this function is the same as [`net.createConnection()`](net#netcreateconnectionoptions-connectlistener). However, custom agents may override this method in case greater flexibility is desired.
A socket/stream can be supplied in one of two ways: by returning the socket/stream from this function, or by passing the socket/stream to `callback`.
This method is guaranteed to return an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specifies a socket type other than [<net.Socket>](net#class-netsocket).
`callback` has a signature of `(err, stream)`.
####
`agent.keepSocketAlive(socket)`
Added in: v8.1.0 * `socket` [<stream.Duplex>](stream#class-streamduplex)
Called when `socket` is detached from a request and could be persisted by the `Agent`. Default behavior is to:
```
socket.setKeepAlive(true, this.keepAliveMsecs);
socket.unref();
return true;
```
This method can be overridden by a particular `Agent` subclass. If this method returns a falsy value, the socket will be destroyed instead of persisting it for use with the next request.
The `socket` argument can be an instance of [<net.Socket>](net#class-netsocket), a subclass of [<stream.Duplex>](stream#class-streamduplex).
####
`agent.reuseSocket(socket, request)`
Added in: v8.1.0 * `socket` [<stream.Duplex>](stream#class-streamduplex)
* `request` [<http.ClientRequest>](http#class-httpclientrequest)
Called when `socket` is attached to `request` after being persisted because of the keep-alive options. Default behavior is to:
```
socket.ref();
```
This method can be overridden by a particular `Agent` subclass.
The `socket` argument can be an instance of [<net.Socket>](net#class-netsocket), a subclass of [<stream.Duplex>](stream#class-streamduplex).
####
`agent.destroy()`
Added in: v0.11.4 Destroy any sockets that are currently in use by the agent.
It is usually not necessary to do this. However, if using an agent with `keepAlive` enabled, then it is best to explicitly shut down the agent when it is no longer needed. Otherwise, sockets might stay open for quite a long time before the server terminates them.
####
`agent.freeSockets`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | The property now has a `null` prototype. |
| v0.11.4 | Added in: v0.11.4 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
An object which contains arrays of sockets currently awaiting use by the agent when `keepAlive` is enabled. Do not modify.
Sockets in the `freeSockets` list will be automatically destroyed and removed from the array on `'timeout'`.
####
`agent.getName([options])`
History
| Version | Changes |
| --- | --- |
| v17.7.0, v16.15.0 | The `options` parameter is now optional. |
| v0.11.4 | Added in: v0.11.4 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A set of options providing information for name generation
+ `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A domain name or IP address of the server to issue the request to
+ `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Port of remote server
+ `localAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Local interface to bind for network connections when issuing the request
+ `family` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Must be 4 or 6 if this doesn't equal `undefined`.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Get a unique name for a set of request options, to determine whether a connection can be reused. For an HTTP agent, this returns `host:port:localAddress` or `host:port:localAddress:family`. For an HTTPS agent, the name includes the CA, cert, ciphers, and other HTTPS/TLS-specific options that determine socket reusability.
####
`agent.maxFreeSockets`
Added in: v0.11.7 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
By default set to 256. For agents with `keepAlive` enabled, this sets the maximum number of sockets that will be left open in the free state.
####
`agent.maxSockets`
Added in: v0.3.6 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
By default set to `Infinity`. Determines how many concurrent sockets the agent can have open per origin. Origin is the returned value of [`agent.getName()`](#agentgetnameoptions).
####
`agent.maxTotalSockets`
Added in: v14.5.0, v12.19.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
By default set to `Infinity`. Determines how many concurrent sockets the agent can have open. Unlike `maxSockets`, this parameter applies across all origins.
####
`agent.requests`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | The property now has a `null` prototype. |
| v0.5.9 | Added in: v0.5.9 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
An object which contains queues of requests that have not yet been assigned to sockets. Do not modify.
####
`agent.sockets`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | The property now has a `null` prototype. |
| v0.3.6 | Added in: v0.3.6 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
An object which contains arrays of sockets currently in use by the agent. Do not modify.
### Class: `http.ClientRequest`
Added in: v0.1.17 * Extends: [<http.OutgoingMessage>](http#class-httpoutgoingmessage)
This object is created internally and returned from [`http.request()`](#httprequestoptions-callback). It represents an *in-progress* request whose header has already been queued. The header is still mutable using the [`setHeader(name, value)`](#requestsetheadername-value), [`getHeader(name)`](#requestgetheadername), [`removeHeader(name)`](#requestremoveheadername) API. The actual header will be sent along with the first data chunk or when calling [`request.end()`](#requestenddata-encoding-callback).
To get the response, add a listener for [`'response'`](#event-response) to the request object. [`'response'`](#event-response) will be emitted from the request object when the response headers have been received. The [`'response'`](#event-response) event is executed with one argument which is an instance of [`http.IncomingMessage`](#class-httpincomingmessage).
During the [`'response'`](#event-response) event, one can add listeners to the response object; particularly to listen for the `'data'` event.
If no [`'response'`](#event-response) handler is added, then the response will be entirely discarded. However, if a [`'response'`](#event-response) event handler is added, then the data from the response object **must** be consumed, either by calling `response.read()` whenever there is a `'readable'` event, or by adding a `'data'` handler, or by calling the `.resume()` method. Until the data is consumed, the `'end'` event will not fire. Also, until the data is read it will consume memory that can eventually lead to a 'process out of memory' error.
For backward compatibility, `res` will only emit `'error'` if there is an `'error'` listener registered.
Set `Content-Length` header to limit the response body size. Mismatching the `Content-Length` header value will result in an [`Error`][] being thrown, identified by `code:` [`'ERR_HTTP_CONTENT_LENGTH_MISMATCH'`](errors#err_http_content_length_mismatch).
`Content-Length` value should be in bytes, not characters. Use [`Buffer.byteLength()`](buffer#static-method-bufferbytelengthstring-encoding) to determine the length of the body in bytes.
#### Event: `'abort'`
Added in: v1.4.1Deprecated since: v17.0.0, v16.12.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Listen for the `'close'` event instead.
Emitted when the request has been aborted by the client. This event is only emitted on the first call to `abort()`.
#### Event: `'close'`
Added in: v0.5.4 Indicates that the request is completed, or its underlying connection was terminated prematurely (before the response completion).
#### Event: `'connect'`
Added in: v0.7.0 * `response` [<http.IncomingMessage>](http#class-httpincomingmessage)
* `socket` [<stream.Duplex>](stream#class-streamduplex)
* `head` [<Buffer>](buffer#class-buffer)
Emitted each time a server responds to a request with a `CONNECT` method. If this event is not being listened for, clients receiving a `CONNECT` method will have their connections closed.
This event is guaranteed to be passed an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specifies a socket type other than [<net.Socket>](net#class-netsocket).
A client and server pair demonstrating how to listen for the `'connect'` event:
```
const http = require('node:http');
const net = require('node:net');
const { URL } = require('node:url');
// Create an HTTP tunneling proxy
const proxy = http.createServer((req, res) => {
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('okay');
});
proxy.on('connect', (req, clientSocket, head) => {
// Connect to an origin server
const { port, hostname } = new URL(`http://${req.url}`);
const serverSocket = net.connect(port || 80, hostname, () => {
clientSocket.write('HTTP/1.1 200 Connection Established\r\n' +
'Proxy-agent: Node.js-Proxy\r\n' +
'\r\n');
serverSocket.write(head);
serverSocket.pipe(clientSocket);
clientSocket.pipe(serverSocket);
});
});
// Now that proxy is running
proxy.listen(1337, '127.0.0.1', () => {
// Make a request to a tunneling proxy
const options = {
port: 1337,
host: '127.0.0.1',
method: 'CONNECT',
path: 'www.google.com:80'
};
const req = http.request(options);
req.end();
req.on('connect', (res, socket, head) => {
console.log('got connected!');
// Make a request over an HTTP tunnel
socket.write('GET / HTTP/1.1\r\n' +
'Host: www.google.com:80\r\n' +
'Connection: close\r\n' +
'\r\n');
socket.on('data', (chunk) => {
console.log(chunk.toString());
});
socket.on('end', () => {
proxy.close();
});
});
});
```
#### Event: `'continue'`
Added in: v0.3.2 Emitted when the server sends a '100 Continue' HTTP response, usually because the request contained 'Expect: 100-continue'. This is an instruction that the client should send the request body.
#### Event: `'finish'`
Added in: v0.3.6 Emitted when the request has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network. It does not imply that the server has received anything yet.
#### Event: `'information'`
Added in: v10.0.0 * `info` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `httpVersion` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `httpVersionMajor` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `httpVersionMinor` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `statusCode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `statusMessage` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `headers` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `rawHeaders` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Emitted when the server sends a 1xx intermediate response (excluding 101 Upgrade). The listeners of this event will receive an object containing the HTTP version, status code, status message, key-value headers object, and array with the raw header names followed by their respective values.
```
const http = require('node:http');
const options = {
host: '127.0.0.1',
port: 8080,
path: '/length_request'
};
// Make a request
const req = http.request(options);
req.end();
req.on('information', (info) => {
console.log(`Got information prior to main response: ${info.statusCode}`);
});
```
101 Upgrade statuses do not fire this event due to their break from the traditional HTTP request/response chain, such as web sockets, in-place TLS upgrades, or HTTP 2.0. To be notified of 101 Upgrade notices, listen for the [`'upgrade'`](#event-upgrade) event instead.
#### Event: `'response'`
Added in: v0.1.0 * `response` [<http.IncomingMessage>](http#class-httpincomingmessage)
Emitted when a response is received to this request. This event is emitted only once.
#### Event: `'socket'`
Added in: v0.5.3 * `socket` [<stream.Duplex>](stream#class-streamduplex)
This event is guaranteed to be passed an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specifies a socket type other than [<net.Socket>](net#class-netsocket).
#### Event: `'timeout'`
Added in: v0.7.8 Emitted when the underlying socket times out from inactivity. This only notifies that the socket has been idle. The request must be destroyed manually.
See also: [`request.setTimeout()`](#requestsettimeouttimeout-callback).
#### Event: `'upgrade'`
Added in: v0.1.94 * `response` [<http.IncomingMessage>](http#class-httpincomingmessage)
* `socket` [<stream.Duplex>](stream#class-streamduplex)
* `head` [<Buffer>](buffer#class-buffer)
Emitted each time a server responds to a request with an upgrade. If this event is not being listened for and the response status code is 101 Switching Protocols, clients receiving an upgrade header will have their connections closed.
This event is guaranteed to be passed an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specifies a socket type other than [<net.Socket>](net#class-netsocket).
A client server pair demonstrating how to listen for the `'upgrade'` event.
```
const http = require('node:http');
// Create an HTTP server
const server = http.createServer((req, res) => {
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('okay');
});
server.on('upgrade', (req, socket, head) => {
socket.write('HTTP/1.1 101 Web Socket Protocol Handshake\r\n' +
'Upgrade: WebSocket\r\n' +
'Connection: Upgrade\r\n' +
'\r\n');
socket.pipe(socket); // echo back
});
// Now that server is running
server.listen(1337, '127.0.0.1', () => {
// make a request
const options = {
port: 1337,
host: '127.0.0.1',
headers: {
'Connection': 'Upgrade',
'Upgrade': 'websocket'
}
};
const req = http.request(options);
req.end();
req.on('upgrade', (res, socket, upgradeHead) => {
console.log('got upgraded!');
socket.end();
process.exit(0);
});
});
```
####
`request.abort()`
Added in: v0.3.8Deprecated since: v14.1.0, v13.14.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`request.destroy()`](#requestdestroyerror) instead.
Marks the request as aborting. Calling this will cause remaining data in the response to be dropped and the socket to be destroyed.
####
`request.aborted`
History
| Version | Changes |
| --- | --- |
| v17.0.0, v16.12.0 | Deprecated since: v17.0.0, v16.12.0 |
| v11.0.0 | The `aborted` property is no longer a timestamp number. |
| v0.11.14 | Added in: v0.11.14 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Check [`request.destroyed`](#requestdestroyed) instead.
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `request.aborted` property will be `true` if the request has been aborted.
####
`request.connection`
Added in: v0.3.0Deprecated since: v13.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Use [`request.socket`](#requestsocket).
* [<stream.Duplex>](stream#class-streamduplex)
See [`request.socket`](#requestsocket).
####
`request.cork()`
Added in: v13.2.0, v12.16.0 See [`writable.cork()`](stream#writablecork).
####
`request.end([data[, encoding]][, callback])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | This method now returns a reference to `ClientRequest`. |
| v0.1.90 | Added in: v0.1.90 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Finishes sending the request. If any parts of the body are unsent, it will flush them to the stream. If the request is chunked, this will send the terminating `'0\r\n\r\n'`.
If `data` is specified, it is equivalent to calling [`request.write(data, encoding)`](#requestwritechunk-encoding-callback) followed by `request.end(callback)`.
If `callback` is specified, it will be called when the request stream is finished.
####
`request.destroy([error])`
History
| Version | Changes |
| --- | --- |
| v14.5.0 | The function returns `this` for consistency with other Readable streams. |
| v0.3.0 | Added in: v0.3.0 |
* `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) Optional, an error to emit with `'error'` event.
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Destroy the request. Optionally emit an `'error'` event, and emit a `'close'` event. Calling this will cause remaining data in the response to be dropped and the socket to be destroyed.
See [`writable.destroy()`](stream#writabledestroyerror) for further details.
#####
`request.destroyed`
Added in: v14.1.0, v13.14.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` after [`request.destroy()`](#requestdestroyerror) has been called.
See [`writable.destroyed`](stream#writabledestroyed) for further details.
####
`request.finished`
Added in: v0.0.1Deprecated since: v13.4.0, v12.16.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Use [`request.writableEnded`](#requestwritableended).
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `request.finished` property will be `true` if [`request.end()`](#requestenddata-encoding-callback) has been called. `request.end()` will automatically be called if the request was initiated via [`http.get()`](#httpgetoptions-callback).
####
`request.flushHeaders()`
Added in: v1.6.0 Flushes the request headers.
For efficiency reasons, Node.js normally buffers the request headers until `request.end()` is called or the first chunk of request data is written. It then tries to pack the request headers and data into a single TCP packet.
That's usually desired (it saves a TCP round-trip), but not when the first data is not sent until possibly much later. `request.flushHeaders()` bypasses the optimization and kickstarts the request.
####
`request.getHeader(name)`
Added in: v1.6.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Reads out a header on the request. The name is case-insensitive. The type of the return value depends on the arguments provided to [`request.setHeader()`](#requestsetheadername-value).
```
request.setHeader('content-type', 'text/html');
request.setHeader('Content-Length', Buffer.byteLength(body));
request.setHeader('Cookie', ['type=ninja', 'language=javascript']);
const contentType = request.getHeader('Content-Type');
// 'contentType' is 'text/html'
const contentLength = request.getHeader('Content-Length');
// 'contentLength' is of type number
const cookie = request.getHeader('Cookie');
// 'cookie' is of type string[]
```
####
`request.getHeaderNames()`
Added in: v7.7.0 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns an array containing the unique names of the current outgoing headers. All header names are lowercase.
```
request.setHeader('Foo', 'bar');
request.setHeader('Cookie', ['foo=bar', 'bar=baz']);
const headerNames = request.getHeaderNames();
// headerNames === ['foo', 'cookie']
```
####
`request.getHeaders()`
Added in: v7.7.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related http module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase.
The object returned by the `request.getHeaders()` method *does not* prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and *will not work*.
```
request.setHeader('Foo', 'bar');
request.setHeader('Cookie', ['foo=bar', 'bar=baz']);
const headers = request.getHeaders();
// headers === { foo: 'bar', 'cookie': ['foo=bar', 'bar=baz'] }
```
####
`request.getRawHeaderNames()`
Added in: v15.13.0, v14.17.0 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns an array containing the unique names of the current outgoing raw headers. Header names are returned with their exact casing being set.
```
request.setHeader('Foo', 'bar');
request.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']);
const headerNames = request.getRawHeaderNames();
// headerNames === ['Foo', 'Set-Cookie']
```
####
`request.hasHeader(name)`
Added in: v7.7.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the header identified by `name` is currently set in the outgoing headers. The header name matching is case-insensitive.
```
const hasContentType = request.hasHeader('content-type');
```
####
`request.maxHeadersCount`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `2000`
Limits maximum response headers count. If set to 0, no limit will be applied.
####
`request.path`
Added in: v0.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The request path.
####
`request.method`
Added in: v0.1.97 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The request method.
####
`request.host`
Added in: v14.5.0, v12.19.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The request host.
####
`request.protocol`
Added in: v14.5.0, v12.19.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The request protocol.
####
`request.removeHeader(name)`
Added in: v1.6.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Removes a header that's already defined into headers object.
```
request.removeHeader('Content-Type');
```
####
`request.reusedSocket`
Added in: v13.0.0, v12.16.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Whether the request is send through a reused socket.
When sending request through a keep-alive enabled agent, the underlying socket might be reused. But if server closes connection at unfortunate time, client may run into a 'ECONNRESET' error.
```
const http = require('node:http');
// Server has a 5 seconds keep-alive timeout by default
http
.createServer((req, res) => {
res.write('hello\n');
res.end();
})
.listen(3000);
setInterval(() => {
// Adapting a keep-alive agent
http.get('http://localhost:3000', { agent }, (res) => {
res.on('data', (data) => {
// Do nothing
});
});
}, 5000); // Sending request on 5s interval so it's easy to hit idle timeout
```
By marking a request whether it reused socket or not, we can do automatic error retry base on it.
```
const http = require('node:http');
const agent = new http.Agent({ keepAlive: true });
function retriableRequest() {
const req = http
.get('http://localhost:3000', { agent }, (res) => {
// ...
})
.on('error', (err) => {
// Check if retry is needed
if (req.reusedSocket && err.code === 'ECONNRESET') {
retriableRequest();
}
});
}
retriableRequest();
```
####
`request.setHeader(name, value)`
Added in: v1.6.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Sets a single header value for headers object. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here to send multiple headers with the same name. Non-string values will be stored without modification. Therefore, [`request.getHeader()`](#requestgetheadername) may return non-string values. However, the non-string values will be converted to strings for network transmission.
```
request.setHeader('Content-Type', 'application/json');
```
or
```
request.setHeader('Cookie', ['type=ninja', 'language=javascript']);
```
When the value is a string an exception will be thrown if it contains characters outside the `latin1` encoding.
If you need to pass UTF-8 characters in the value please encode the value using the [RFC 8187](https://www.rfc-editor.org/rfc/rfc8187.txt) standard.
```
const filename = 'Rock 🎵.txt';
request.setHeader('Content-Disposition', `attachment; filename*=utf-8''${encodeURIComponent(filename)}`);
```
####
`request.setNoDelay([noDelay])`
Added in: v0.5.9 * `noDelay` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Once a socket is assigned to this request and is connected [`socket.setNoDelay()`](net#socketsetnodelaynodelay) will be called.
####
`request.setSocketKeepAlive([enable][, initialDelay])`
Added in: v0.5.9 * `enable` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
* `initialDelay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Once a socket is assigned to this request and is connected [`socket.setKeepAlive()`](net#socketsetkeepaliveenable-initialdelay) will be called.
####
`request.setTimeout(timeout[, callback])`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | Consistently set socket timeout only when the socket connects. |
| v0.5.9 | Added in: v0.5.9 |
* `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Milliseconds before a request times out.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Optional function to be called when a timeout occurs. Same as binding to the `'timeout'` event.
* Returns: [<http.ClientRequest>](http#class-httpclientrequest)
Once a socket is assigned to this request and is connected [`socket.setTimeout()`](net#socketsettimeouttimeout-callback) will be called.
####
`request.socket`
Added in: v0.3.0 * [<stream.Duplex>](stream#class-streamduplex)
Reference to the underlying socket. Usually users will not want to access this property. In particular, the socket will not emit `'readable'` events because of how the protocol parser attaches to the socket.
```
const http = require('node:http');
const options = {
host: 'www.google.com',
};
const req = http.get(options);
req.end();
req.once('response', (res) => {
const ip = req.socket.localAddress;
const port = req.socket.localPort;
console.log(`Your IP address is ${ip} and your source port is ${port}.`);
// Consume response object
});
```
This property is guaranteed to be an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specified a socket type other than [<net.Socket>](net#class-netsocket).
####
`request.uncork()`
Added in: v13.2.0, v12.16.0 See [`writable.uncork()`](stream#writableuncork).
####
`request.writableEnded`
Added in: v12.9.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` after [`request.end()`](#requestenddata-encoding-callback) has been called. This property does not indicate whether the data has been flushed, for this use [`request.writableFinished`](#requestwritablefinished) instead.
####
`request.writableFinished`
Added in: v12.7.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` if all data has been flushed to the underlying system, immediately before the [`'finish'`](#event-finish) event is emitted.
####
`request.write(chunk[, encoding][, callback])`
Added in: v0.1.29 * `chunk` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Sends a chunk of the body. This method can be called multiple times. If no `Content-Length` is set, data will automatically be encoded in HTTP Chunked transfer encoding, so that server knows when the data ends. The `Transfer-Encoding: chunked` header is added. Calling [`request.end()`](#requestenddata-encoding-callback) is necessary to finish sending the request.
The `encoding` argument is optional and only applies when `chunk` is a string. Defaults to `'utf8'`.
The `callback` argument is optional and will be called when this chunk of data is flushed, but only if the chunk is non-empty.
Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in user memory. `'drain'` will be emitted when the buffer is free again.
When `write` function is called with empty string or buffer, it does nothing and waits for more input.
### Class: `http.Server`
Added in: v0.1.17 * Extends: [<net.Server>](net#class-netserver)
#### Event: `'checkContinue'`
Added in: v0.3.0 * `request` [<http.IncomingMessage>](http#class-httpincomingmessage)
* `response` [<http.ServerResponse>](http#class-httpserverresponse)
Emitted each time a request with an HTTP `Expect: 100-continue` is received. If this event is not listened for, the server will automatically respond with a `100 Continue` as appropriate.
Handling this event involves calling [`response.writeContinue()`](#responsewritecontinue) if the client should continue to send the request body, or generating an appropriate HTTP response (e.g. 400 Bad Request) if the client should not continue to send the request body.
When this event is emitted and handled, the [`'request'`](#event-request) event will not be emitted.
#### Event: `'checkExpectation'`
Added in: v5.5.0 * `request` [<http.IncomingMessage>](http#class-httpincomingmessage)
* `response` [<http.ServerResponse>](http#class-httpserverresponse)
Emitted each time a request with an HTTP `Expect` header is received, where the value is not `100-continue`. If this event is not listened for, the server will automatically respond with a `417 Expectation Failed` as appropriate.
When this event is emitted and handled, the [`'request'`](#event-request) event will not be emitted.
#### Event: `'clientError'`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | The default behavior will return a 431 Request Header Fields Too Large if a HPE\_HEADER\_OVERFLOW error occurs. |
| v9.4.0 | The `rawPacket` is the current buffer that just parsed. Adding this buffer to the error object of `'clientError'` event is to make it possible that developers can log the broken packet. |
| v6.0.0 | The default action of calling `.destroy()` on the `socket` will no longer take place if there are listeners attached for `'clientError'`. |
| v0.1.94 | Added in: v0.1.94 |
* `exception` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
* `socket` [<stream.Duplex>](stream#class-streamduplex)
If a client connection emits an `'error'` event, it will be forwarded here. Listener of this event is responsible for closing/destroying the underlying socket. For example, one may wish to more gracefully close the socket with a custom HTTP response instead of abruptly severing the connection.
This event is guaranteed to be passed an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specifies a socket type other than [<net.Socket>](net#class-netsocket).
Default behavior is to try close the socket with a HTTP '400 Bad Request', or a HTTP '431 Request Header Fields Too Large' in the case of a [`HPE_HEADER_OVERFLOW`](errors#hpe_header_overflow) error. If the socket is not writable or headers of the current attached [`http.ServerResponse`](#class-httpserverresponse) has been sent, it is immediately destroyed.
`socket` is the [`net.Socket`](net#class-netsocket) object that the error originated from.
```
const http = require('node:http');
const server = http.createServer((req, res) => {
res.end();
});
server.on('clientError', (err, socket) => {
socket.end('HTTP/1.1 400 Bad Request\r\n\r\n');
});
server.listen(8000);
```
When the `'clientError'` event occurs, there is no `request` or `response` object, so any HTTP response sent, including response headers and payload, *must* be written directly to the `socket` object. Care must be taken to ensure the response is a properly formatted HTTP response message.
`err` is an instance of `Error` with two extra columns:
* `bytesParsed`: the bytes count of request packet that Node.js may have parsed correctly;
* `rawPacket`: the raw packet of current request.
In some cases, the client has already received the response and/or the socket has already been destroyed, like in case of `ECONNRESET` errors. Before trying to send data to the socket, it is better to check that it is still writable.
```
server.on('clientError', (err, socket) => {
if (err.code === 'ECONNRESET' || !socket.writable) {
return;
}
socket.end('HTTP/1.1 400 Bad Request\r\n\r\n');
});
```
#### Event: `'close'`
Added in: v0.1.4 Emitted when the server closes.
#### Event: `'connect'`
Added in: v0.7.0 * `request` [<http.IncomingMessage>](http#class-httpincomingmessage) Arguments for the HTTP request, as it is in the [`'request'`](#event-request) event
* `socket` [<stream.Duplex>](stream#class-streamduplex) Network socket between the server and client
* `head` [<Buffer>](buffer#class-buffer) The first packet of the tunneling stream (may be empty)
Emitted each time a client requests an HTTP `CONNECT` method. If this event is not listened for, then clients requesting a `CONNECT` method will have their connections closed.
This event is guaranteed to be passed an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specifies a socket type other than [<net.Socket>](net#class-netsocket).
After this event is emitted, the request's socket will not have a `'data'` event listener, meaning it will need to be bound in order to handle data sent to the server on that socket.
#### Event: `'connection'`
Added in: v0.1.0 * `socket` [<stream.Duplex>](stream#class-streamduplex)
This event is emitted when a new TCP stream is established. `socket` is typically an object of type [`net.Socket`](net#class-netsocket). Usually users will not want to access this event. In particular, the socket will not emit `'readable'` events because of how the protocol parser attaches to the socket. The `socket` can also be accessed at `request.socket`.
This event can also be explicitly emitted by users to inject connections into the HTTP server. In that case, any [`Duplex`](stream#class-streamduplex) stream can be passed.
If `socket.setTimeout()` is called here, the timeout will be replaced with `server.keepAliveTimeout` when the socket has served a request (if `server.keepAliveTimeout` is non-zero).
This event is guaranteed to be passed an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specifies a socket type other than [<net.Socket>](net#class-netsocket).
#### Event: `'dropRequest'`
Added in: v18.7.0, v16.17.0 * `request` [<http.IncomingMessage>](http#class-httpincomingmessage) Arguments for the HTTP request, as it is in the [`'request'`](#event-request) event
* `socket` [<stream.Duplex>](stream#class-streamduplex) Network socket between the server and client
When the number of requests on a socket reaches the threshold of `server.maxRequestsPerSocket`, the server will drop new requests and emit `'dropRequest'` event instead, then send `503` to client.
#### Event: `'request'`
Added in: v0.1.0 * `request` [<http.IncomingMessage>](http#class-httpincomingmessage)
* `response` [<http.ServerResponse>](http#class-httpserverresponse)
Emitted each time there is a request. There may be multiple requests per connection (in the case of HTTP Keep-Alive connections).
#### Event: `'upgrade'`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Not listening to this event no longer causes the socket to be destroyed if a client sends an Upgrade header. |
| v0.1.94 | Added in: v0.1.94 |
* `request` [<http.IncomingMessage>](http#class-httpincomingmessage) Arguments for the HTTP request, as it is in the [`'request'`](#event-request) event
* `socket` [<stream.Duplex>](stream#class-streamduplex) Network socket between the server and client
* `head` [<Buffer>](buffer#class-buffer) The first packet of the upgraded stream (may be empty)
Emitted each time a client requests an HTTP upgrade. Listening to this event is optional and clients cannot insist on a protocol change.
After this event is emitted, the request's socket will not have a `'data'` event listener, meaning it will need to be bound in order to handle data sent to the server on that socket.
This event is guaranteed to be passed an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specifies a socket type other than [<net.Socket>](net#class-netsocket).
####
`server.close([callback])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | The method closes idle connections before returning. |
| v0.1.90 | Added in: v0.1.90 |
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Stops the server from accepting new connections and closes all connections connected to this server which are not sending a request or waiting for a response. See [`net.Server.close()`](net#serverclosecallback).
####
`server.closeAllConnections()`
Added in: v18.2.0 Closes all connections connected to this server.
####
`server.closeIdleConnections()`
Added in: v18.2.0 Closes all connections connected to this server which are not sending a request or waiting for a response.
####
`server.headersTimeout`
Added in: v11.3.0, v10.14.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `60000`
Limit the amount of time the parser will wait to receive the complete HTTP headers.
If the timeout expires, the server responds with status 408 without forwarding the request to the request listener and then closes the connection.
It must be set to a non-zero value (e.g. 120 seconds) to protect against potential Denial-of-Service attacks in case the server is deployed without a reverse proxy in front.
####
`server.listen()`
Starts the HTTP server listening for connections. This method is identical to [`server.listen()`](net#serverlisten) from [`net.Server`](net#class-netserver).
####
`server.listening`
Added in: v5.7.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Indicates whether or not the server is listening for connections.
####
`server.maxHeadersCount`
Added in: v0.7.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `2000`
Limits maximum incoming headers count. If set to 0, no limit will be applied.
####
`server.requestTimeout`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | The default request timeout changed from no timeout to 300s (5 minutes). |
| v14.11.0 | Added in: v14.11.0 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `300000`
Sets the timeout value in milliseconds for receiving the entire request from the client.
If the timeout expires, the server responds with status 408 without forwarding the request to the request listener and then closes the connection.
It must be set to a non-zero value (e.g. 120 seconds) to protect against potential Denial-of-Service attacks in case the server is deployed without a reverse proxy in front.
####
`server.setTimeout([msecs][, callback])`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The default timeout changed from 120s to 0 (no timeout). |
| v0.9.12 | Added in: v0.9.12 |
* `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** 0 (no timeout)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<http.Server>](http#class-httpserver)
Sets the timeout value for sockets, and emits a `'timeout'` event on the Server object, passing the socket as an argument, if a timeout occurs.
If there is a `'timeout'` event listener on the Server object, then it will be called with the timed-out socket as an argument.
By default, the Server does not timeout sockets. However, if a callback is assigned to the Server's `'timeout'` event, timeouts must be handled explicitly.
####
`server.maxRequestsPerSocket`
Added in: v16.10.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Requests per socket. **Default:** 0 (no limit)
The maximum number of requests socket can handle before closing keep alive connection.
A value of `0` will disable the limit.
When the limit is reached it will set the `Connection` header value to `close`, but will not actually close the connection, subsequent requests sent after the limit is reached will get `503 Service Unavailable` as a response.
####
`server.timeout`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The default timeout changed from 120s to 0 (no timeout). |
| v0.9.12 | Added in: v0.9.12 |
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Timeout in milliseconds. **Default:** 0 (no timeout)
The number of milliseconds of inactivity before a socket is presumed to have timed out.
A value of `0` will disable the timeout behavior on incoming connections.
The socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections.
####
`server.keepAliveTimeout`
Added in: v8.0.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Timeout in milliseconds. **Default:** `5000` (5 seconds).
The number of milliseconds of inactivity a server needs to wait for additional incoming data, after it has finished writing the last response, before a socket will be destroyed. If the server receives new data before the keep-alive timeout has fired, it will reset the regular inactivity timeout, i.e., [`server.timeout`](#servertimeout).
A value of `0` will disable the keep-alive timeout behavior on incoming connections. A value of `0` makes the http server behave similarly to Node.js versions prior to 8.0.0, which did not have a keep-alive timeout.
The socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections.
### Class: `http.ServerResponse`
Added in: v0.1.17 * Extends: [<http.OutgoingMessage>](http#class-httpoutgoingmessage)
This object is created internally by an HTTP server, not by the user. It is passed as the second parameter to the [`'request'`](#event-request) event.
#### Event: `'close'`
Added in: v0.6.7 Indicates that the response is completed, or its underlying connection was terminated prematurely (before the response completion).
#### Event: `'finish'`
Added in: v0.3.6 Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network. It does not imply that the client has received anything yet.
####
`response.addTrailers(headers)`
Added in: v0.3.0 * `headers` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
This method adds HTTP trailing headers (a header but at the end of the message) to the response.
Trailers will **only** be emitted if chunked encoding is used for the response; if it is not (e.g. if the request was HTTP/1.0), they will be silently discarded.
HTTP requires the `Trailer` header to be sent in order to emit trailers, with a list of the header fields in its value. E.g.,
```
response.writeHead(200, { 'Content-Type': 'text/plain',
'Trailer': 'Content-MD5' });
response.write(fileData);
response.addTrailers({ 'Content-MD5': '7895bf4b8828b55ceaf47747b4bca667' });
response.end();
```
Attempting to set a header field name or value that contains invalid characters will result in a [`TypeError`](errors#class-typeerror) being thrown.
####
`response.connection`
Added in: v0.3.0Deprecated since: v13.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Use [`response.socket`](#responsesocket).
* [<stream.Duplex>](stream#class-streamduplex)
See [`response.socket`](#responsesocket).
####
`response.cork()`
Added in: v13.2.0, v12.16.0 See [`writable.cork()`](stream#writablecork).
####
`response.end([data[, encoding]][, callback])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | This method now returns a reference to `ServerResponse`. |
| v0.1.90 | Added in: v0.1.90 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
This method signals to the server that all of the response headers and body have been sent; that server should consider this message complete. The method, `response.end()`, MUST be called on each response.
If `data` is specified, it is similar in effect to calling [`response.write(data, encoding)`](#responsewritechunk-encoding-callback) followed by `response.end(callback)`.
If `callback` is specified, it will be called when the response stream is finished.
####
`response.finished`
Added in: v0.0.2Deprecated since: v13.4.0, v12.16.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Use [`response.writableEnded`](#responsewritableended).
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `response.finished` property will be `true` if [`response.end()`](#responseenddata-encoding-callback) has been called.
####
`response.flushHeaders()`
Added in: v1.6.0 Flushes the response headers. See also: [`request.flushHeaders()`](#requestflushheaders).
####
`response.getHeader(name)`
Added in: v0.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Reads out a header that's already been queued but not sent to the client. The name is case-insensitive. The type of the return value depends on the arguments provided to [`response.setHeader()`](#responsesetheadername-value).
```
response.setHeader('Content-Type', 'text/html');
response.setHeader('Content-Length', Buffer.byteLength(body));
response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']);
const contentType = response.getHeader('content-type');
// contentType is 'text/html'
const contentLength = response.getHeader('Content-Length');
// contentLength is of type number
const setCookie = response.getHeader('set-cookie');
// setCookie is of type string[]
```
####
`response.getHeaderNames()`
Added in: v7.7.0 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns an array containing the unique names of the current outgoing headers. All header names are lowercase.
```
response.setHeader('Foo', 'bar');
response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']);
const headerNames = response.getHeaderNames();
// headerNames === ['foo', 'set-cookie']
```
####
`response.getHeaders()`
Added in: v7.7.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related http module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase.
The object returned by the `response.getHeaders()` method *does not* prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and *will not work*.
```
response.setHeader('Foo', 'bar');
response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']);
const headers = response.getHeaders();
// headers === { foo: 'bar', 'set-cookie': ['foo=bar', 'bar=baz'] }
```
####
`response.hasHeader(name)`
Added in: v7.7.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the header identified by `name` is currently set in the outgoing headers. The header name matching is case-insensitive.
```
const hasContentType = response.hasHeader('content-type');
```
####
`response.headersSent`
Added in: v0.9.3 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Boolean (read-only). True if headers were sent, false otherwise.
####
`response.removeHeader(name)`
Added in: v0.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Removes a header that's queued for implicit sending.
```
response.removeHeader('Content-Encoding');
```
####
`response.req`
Added in: v15.7.0 * [<http.IncomingMessage>](http#class-httpincomingmessage)
A reference to the original HTTP `request` object.
####
`response.sendDate`
Added in: v0.7.5 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
When true, the Date header will be automatically generated and sent in the response if it is not already present in the headers. Defaults to true.
This should only be disabled for testing; HTTP requires the Date header in responses.
####
`response.setHeader(name, value)`
Added in: v0.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<http.ServerResponse>](http#class-httpserverresponse)
Returns the response object.
Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here to send multiple headers with the same name. Non-string values will be stored without modification. Therefore, [`response.getHeader()`](#responsegetheadername) may return non-string values. However, the non-string values will be converted to strings for network transmission. The same response object is returned to the caller, to enable call chaining.
```
response.setHeader('Content-Type', 'text/html');
```
or
```
response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']);
```
Attempting to set a header field name or value that contains invalid characters will result in a [`TypeError`](errors#class-typeerror) being thrown.
When headers have been set with [`response.setHeader()`](#responsesetheadername-value), they will be merged with any headers passed to [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers), with the headers passed to [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) given precedence.
```
// Returns content-type = text/plain
const server = http.createServer((req, res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('ok');
});
```
If [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) method is called and this method has not been called, it will directly write the supplied header values onto the network channel without caching internally, and the [`response.getHeader()`](#responsegetheadername) on the header will not yield the expected result. If progressive population of headers is desired with potential future retrieval and modification, use [`response.setHeader()`](#responsesetheadername-value) instead of [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers).
####
`response.setTimeout(msecs[, callback])`
Added in: v0.9.12 * `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<http.ServerResponse>](http#class-httpserverresponse)
Sets the Socket's timeout value to `msecs`. If a callback is provided, then it is added as a listener on the `'timeout'` event on the response object.
If no `'timeout'` listener is added to the request, the response, or the server, then sockets are destroyed when they time out. If a handler is assigned to the request, the response, or the server's `'timeout'` events, timed out sockets must be handled explicitly.
####
`response.socket`
Added in: v0.3.0 * [<stream.Duplex>](stream#class-streamduplex)
Reference to the underlying socket. Usually users will not want to access this property. In particular, the socket will not emit `'readable'` events because of how the protocol parser attaches to the socket. After `response.end()`, the property is nulled.
```
const http = require('node:http');
const server = http.createServer((req, res) => {
const ip = res.socket.remoteAddress;
const port = res.socket.remotePort;
res.end(`Your IP address is ${ip} and your source port is ${port}.`);
}).listen(3000);
```
This property is guaranteed to be an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specified a socket type other than [<net.Socket>](net#class-netsocket).
####
`response.statusCode`
Added in: v0.4.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `200`
When using implicit headers (not calling [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) explicitly), this property controls the status code that will be sent to the client when the headers get flushed.
```
response.statusCode = 404;
```
After response header was sent to the client, this property indicates the status code which was sent out.
####
`response.statusMessage`
Added in: v0.11.8 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
When using implicit headers (not calling [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) explicitly), this property controls the status message that will be sent to the client when the headers get flushed. If this is left as `undefined` then the standard message for the status code will be used.
```
response.statusMessage = 'Not found';
```
After response header was sent to the client, this property indicates the status message which was sent out.
####
`response.uncork()`
Added in: v13.2.0, v12.16.0 See [`writable.uncork()`](stream#writableuncork).
####
`response.writableEnded`
Added in: v12.9.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` after [`response.end()`](#responseenddata-encoding-callback) has been called. This property does not indicate whether the data has been flushed, for this use [`response.writableFinished`](#responsewritablefinished) instead.
####
`response.writableFinished`
Added in: v12.7.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` if all data has been flushed to the underlying system, immediately before the [`'finish'`](#event-finish) event is emitted.
####
`response.write(chunk[, encoding][, callback])`
Added in: v0.1.29 * `chunk` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'utf8'`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If this method is called and [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) has not been called, it will switch to implicit header mode and flush the implicit headers.
This sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.
In the `node:http` module, the response body is omitted when the request is a HEAD request. Similarly, the `204` and `304` responses *must not* include a message body.
`chunk` can be a string or a buffer. If `chunk` is a string, the second parameter specifies how to encode it into a byte stream. `callback` will be called when this chunk of data is flushed.
This is the raw HTTP body and has nothing to do with higher-level multi-part body encodings that may be used.
The first time [`response.write()`](#responsewritechunk-encoding-callback) is called, it will send the buffered header information and the first chunk of the body to the client. The second time [`response.write()`](#responsewritechunk-encoding-callback) is called, Node.js assumes data will be streamed, and sends the new data separately. That is, the response is buffered up to the first chunk of the body.
Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in user memory. `'drain'` will be emitted when the buffer is free again.
####
`response.writeContinue()`
Added in: v0.3.0 Sends an HTTP/1.1 100 Continue message to the client, indicating that the request body should be sent. See the [`'checkContinue'`](#event-checkcontinue) event on `Server`.
####
`response.writeEarlyHints(hints[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.11.0 | Allow passing hints as an object. |
| v18.11.0 | Added in: v18.11.0 |
* `hints` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Sends an HTTP/1.1 103 Early Hints message to the client with a Link header, indicating that the user agent can preload/preconnect the linked resources. The `hints` is an object containing the values of headers to be sent with early hints message. The optional `callback` argument will be called when the response message has been written.
**Example**
```
const earlyHintsLink = '</styles.css>; rel=preload; as=style';
response.writeEarlyHints({
'link': earlyHintsLink,
});
const earlyHintsLinks = [
'</styles.css>; rel=preload; as=style',
'</scripts.js>; rel=preload; as=script',
];
response.writeEarlyHints({
'link': earlyHintsLinks,
'x-trace-id': 'id for diagnostics'
});
const earlyHintsCallback = () => console.log('early hints message sent');
response.writeEarlyHints(earlyHintsLinks, earlyHintsCallback);
```
####
`response.writeHead(statusCode[, statusMessage][, headers])`
History
| Version | Changes |
| --- | --- |
| v14.14.0 | Allow passing headers as an array. |
| v11.10.0, v10.17.0 | Return `this` from `writeHead()` to allow chaining with `end()`. |
| v5.11.0, v4.4.5 | A `RangeError` is thrown if `statusCode` is not a number in the range `[100, 999]`. |
| v0.1.30 | Added in: v0.1.30 |
* `statusCode` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `statusMessage` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `headers` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)
* Returns: [<http.ServerResponse>](http#class-httpserverresponse)
Sends a response header to the request. The status code is a 3-digit HTTP status code, like `404`. The last argument, `headers`, are the response headers. Optionally one can give a human-readable `statusMessage` as the second argument.
`headers` may be an `Array` where the keys and values are in the same list. It is *not* a list of tuples. So, the even-numbered offsets are key values, and the odd-numbered offsets are the associated values. The array is in the same format as `request.rawHeaders`.
Returns a reference to the `ServerResponse`, so that calls can be chained.
```
const body = 'hello world';
response
.writeHead(200, {
'Content-Length': Buffer.byteLength(body),
'Content-Type': 'text/plain'
})
.end(body);
```
This method must only be called once on a message and it must be called before [`response.end()`](#responseenddata-encoding-callback) is called.
If [`response.write()`](#responsewritechunk-encoding-callback) or [`response.end()`](#responseenddata-encoding-callback) are called before calling this, the implicit/mutable headers will be calculated and call this function.
When headers have been set with [`response.setHeader()`](#responsesetheadername-value), they will be merged with any headers passed to [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers), with the headers passed to [`response.writeHead()`](#responsewriteheadstatuscode-statusmessage-headers) given precedence.
If this method is called and [`response.setHeader()`](#responsesetheadername-value) has not been called, it will directly write the supplied header values onto the network channel without caching internally, and the [`response.getHeader()`](#responsegetheadername) on the header will not yield the expected result. If progressive population of headers is desired with potential future retrieval and modification, use [`response.setHeader()`](#responsesetheadername-value) instead.
```
// Returns content-type = text/plain
const server = http.createServer((req, res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('ok');
});
```
`Content-Length` is read in bytes, not characters. Use [`Buffer.byteLength()`](buffer#static-method-bufferbytelengthstring-encoding) to determine the length of the body in bytes. Node.js will check whether `Content-Length` and the length of the body which has been transmitted are equal or not.
Attempting to set a header field name or value that contains invalid characters will result in a [`Error`][] being thrown.
####
`response.writeProcessing()`
Added in: v10.0.0 Sends a HTTP/1.1 102 Processing message to the client, indicating that the request body should be sent.
### Class: `http.IncomingMessage`
History
| Version | Changes |
| --- | --- |
| v15.5.0 | The `destroyed` value returns `true` after the incoming data is consumed. |
| v13.1.0, v12.16.0 | The `readableHighWaterMark` value mirrors that of the socket. |
| v0.1.17 | Added in: v0.1.17 |
* Extends: [<stream.Readable>](stream#class-streamreadable)
An `IncomingMessage` object is created by [`http.Server`](#class-httpserver) or [`http.ClientRequest`](#class-httpclientrequest) and passed as the first argument to the [`'request'`](#event-request) and [`'response'`](#event-response) event respectively. It may be used to access response status, headers, and data.
Different from its `socket` value which is a subclass of [<stream.Duplex>](stream#class-streamduplex), the `IncomingMessage` itself extends [<stream.Readable>](stream#class-streamreadable) and is created separately to parse and emit the incoming HTTP headers and payload, as the underlying socket may be reused multiple times in case of keep-alive.
#### Event: `'aborted'`
Added in: v0.3.8Deprecated since: v17.0.0, v16.12.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Listen for `'close'` event instead.
Emitted when the request has been aborted.
#### Event: `'close'`
History
| Version | Changes |
| --- | --- |
| v16.0.0 | The close event is now emitted when the request has been completed and not when the underlying socket is closed. |
| v0.4.2 | Added in: v0.4.2 |
Emitted when the request has been completed.
####
`message.aborted`
Added in: v10.1.0Deprecated since: v17.0.0, v16.12.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Check `message.destroyed` from [<stream.Readable>](stream#class-streamreadable).
* [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `message.aborted` property will be `true` if the request has been aborted.
####
`message.complete`
Added in: v0.3.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `message.complete` property will be `true` if a complete HTTP message has been received and successfully parsed.
This property is particularly useful as a means of determining if a client or server fully transmitted a message before a connection was terminated:
```
const req = http.request({
host: '127.0.0.1',
port: 8080,
method: 'POST'
}, (res) => {
res.resume();
res.on('end', () => {
if (!res.complete)
console.error(
'The connection was terminated while the message was still being sent');
});
});
```
####
`message.connection`
Added in: v0.1.90Deprecated since: v16.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. Use [`message.socket`](#messagesocket).
Alias for [`message.socket`](#messagesocket).
####
`message.destroy([error])`
History
| Version | Changes |
| --- | --- |
| v14.5.0, v12.19.0 | The function returns `this` for consistency with other Readable streams. |
| v0.3.0 | Added in: v0.3.0 |
* `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Calls `destroy()` on the socket that received the `IncomingMessage`. If `error` is provided, an `'error'` event is emitted on the socket and `error` is passed as an argument to any listeners on the event.
####
`message.headers`
History
| Version | Changes |
| --- | --- |
| v15.1.0 | `message.headers` is now lazily computed using an accessor property on the prototype and is no longer enumerable. |
| v0.1.5 | Added in: v0.1.5 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The request/response headers object.
Key-value pairs of header names and values. Header names are lower-cased.
```
// Prints something like:
//
// { 'user-agent': 'curl/7.22.0',
// host: '127.0.0.1:8000',
// accept: '*/*' }
console.log(request.headers);
```
Duplicates in raw headers are handled in the following ways, depending on the header name:
* Duplicates of `age`, `authorization`, `content-length`, `content-type`, `etag`, `expires`, `from`, `host`, `if-modified-since`, `if-unmodified-since`, `last-modified`, `location`, `max-forwards`, `proxy-authorization`, `referer`, `retry-after`, `server`, or `user-agent` are discarded.
* `set-cookie` is always an array. Duplicates are added to the array.
* For duplicate `cookie` headers, the values are joined together with `;` .
* For all other headers, the values are joined together with `,` .
####
`message.headersDistinct`
Added in: v18.3.0, v16.17.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Similar to [`message.headers`](#messageheaders), but there is no join logic and the values are always arrays of strings, even for headers received just once.
```
// Prints something like:
//
// { 'user-agent': ['curl/7.22.0'],
// host: ['127.0.0.1:8000'],
// accept: ['*/*'] }
console.log(request.headersDistinct);
```
####
`message.httpVersion`
Added in: v0.1.1 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
In case of server request, the HTTP version sent by the client. In the case of client response, the HTTP version of the connected-to server. Probably either `'1.1'` or `'1.0'`.
Also `message.httpVersionMajor` is the first integer and `message.httpVersionMinor` is the second.
####
`message.method`
Added in: v0.1.1 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
**Only valid for request obtained from [`http.Server`](#class-httpserver).**
The request method as a string. Read only. Examples: `'GET'`, `'DELETE'`.
####
`message.rawHeaders`
Added in: v0.11.6 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The raw request/response headers list exactly as they were received.
The keys and values are in the same list. It is *not* a list of tuples. So, the even-numbered offsets are key values, and the odd-numbered offsets are the associated values.
Header names are not lowercased, and duplicates are not merged.
```
// Prints something like:
//
// [ 'user-agent',
// 'this is invalid because there can be only one',
// 'User-Agent',
// 'curl/7.22.0',
// 'Host',
// '127.0.0.1:8000',
// 'ACCEPT',
// '*/*' ]
console.log(request.rawHeaders);
```
####
`message.rawTrailers`
Added in: v0.11.6 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The raw request/response trailer keys and values exactly as they were received. Only populated at the `'end'` event.
####
`message.setTimeout(msecs[, callback])`
Added in: v0.5.9 * `msecs` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<http.IncomingMessage>](http#class-httpincomingmessage)
Calls `message.socket.setTimeout(msecs, callback)`.
####
`message.socket`
Added in: v0.3.0 * [<stream.Duplex>](stream#class-streamduplex)
The [`net.Socket`](net#class-netsocket) object associated with the connection.
With HTTPS support, use [`request.socket.getPeerCertificate()`](tls#tlssocketgetpeercertificatedetailed) to obtain the client's authentication details.
This property is guaranteed to be an instance of the [<net.Socket>](net#class-netsocket) class, a subclass of [<stream.Duplex>](stream#class-streamduplex), unless the user specified a socket type other than [<net.Socket>](net#class-netsocket) or internally nulled.
####
`message.statusCode`
Added in: v0.1.1 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
**Only valid for response obtained from [`http.ClientRequest`](#class-httpclientrequest).**
The 3-digit HTTP response status code. E.G. `404`.
####
`message.statusMessage`
Added in: v0.11.10 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
**Only valid for response obtained from [`http.ClientRequest`](#class-httpclientrequest).**
The HTTP response status message (reason phrase). E.G. `OK` or `Internal Server Error`.
####
`message.trailers`
Added in: v0.3.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The request/response trailers object. Only populated at the `'end'` event.
####
`message.trailersDistinct`
Added in: v18.3.0, v16.17.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Similar to [`message.trailers`](#messagetrailers), but there is no join logic and the values are always arrays of strings, even for headers received just once. Only populated at the `'end'` event.
####
`message.url`
Added in: v0.1.90 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
**Only valid for request obtained from [`http.Server`](#class-httpserver).**
Request URL string. This contains only the URL that is present in the actual HTTP request. Take the following request:
```
GET /status?name=ryan HTTP/1.1
Accept: text/plain
```
To parse the URL into its parts:
```
new URL(request.url, `http://${request.headers.host}`);
```
When `request.url` is `'/status?name=ryan'` and `request.headers.host` is `'localhost:3000'`:
```
$ node
> new URL(request.url, `http://${request.headers.host}`)
URL {
href: 'http://localhost:3000/status?name=ryan',
origin: 'http://localhost:3000',
protocol: 'http:',
username: '',
password: '',
host: 'localhost:3000',
hostname: 'localhost',
port: '3000',
pathname: '/status',
search: '?name=ryan',
searchParams: URLSearchParams { 'name' => 'ryan' },
hash: ''
}
```
### Class: `http.OutgoingMessage`
Added in: v0.1.17 * Extends: [<Stream>](stream#stream)
This class serves as the parent class of [`http.ClientRequest`](#class-httpclientrequest) and [`http.ServerResponse`](#class-httpserverresponse). It is an abstract outgoing message from the perspective of the participants of an HTTP transaction.
#### Event: `'drain'`
Added in: v0.3.6 Emitted when the buffer of the message is free again.
#### Event: `'finish'`
Added in: v0.1.17 Emitted when the transmission is finished successfully.
#### Event: `'prefinish'`
Added in: v0.11.6 Emitted after `outgoingMessage.end()` is called. When the event is emitted, all data has been processed but not necessarily completely flushed.
####
`outgoingMessage.addTrailers(headers)`
Added in: v0.3.0 * `headers` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Adds HTTP trailers (headers but at the end of the message) to the message.
Trailers will **only** be emitted if the message is chunked encoded. If not, the trailers will be silently discarded.
HTTP requires the `Trailer` header to be sent to emit trailers, with a list of header field names in its value, e.g.
```
message.writeHead(200, { 'Content-Type': 'text/plain',
'Trailer': 'Content-MD5' });
message.write(fileData);
message.addTrailers({ 'Content-MD5': '7895bf4b8828b55ceaf47747b4bca667' });
message.end();
```
Attempting to set a header field name or value that contains invalid characters will result in a `TypeError` being thrown.
####
`outgoingMessage.appendHeader(name, value)`
Added in: v18.3.0, v16.17.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Header name
* `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Header value
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Append a single header value for the header object.
If the value is an array, this is equivalent of calling this method multiple times.
If there were no previous value for the header, this is equivalent of calling [`outgoingMessage.setHeader(name, value)`](#outgoingmessagesetheadername-value).
Depending of the value of `options.uniqueHeaders` when the client request or the server were created, this will end up in the header being sent multiple times or a single time with values joined using `;` .
####
`outgoingMessage.connection`
Added in: v0.3.0Deprecated since: v15.12.0, v14.17.1
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`outgoingMessage.socket`](#outgoingmessagesocket) instead.
Alias of [`outgoingMessage.socket`](#outgoingmessagesocket).
####
`outgoingMessage.cork()`
Added in: v13.2.0, v12.16.0 See [`writable.cork()`](stream#writablecork).
####
`outgoingMessage.destroy([error])`
Added in: v0.3.0 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) Optional, an error to emit with `error` event
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Destroys the message. Once a socket is associated with the message and is connected, that socket will be destroyed as well.
####
`outgoingMessage.end(chunk[, encoding][, callback])`
History
| Version | Changes |
| --- | --- |
| v0.11.6 | add `callback` argument. |
| v0.1.90 | Added in: v0.1.90 |
* `chunk` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Optional, **Default**: `utf8`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Optional
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Finishes the outgoing message. If any parts of the body are unsent, it will flush them to the underlying system. If the message is chunked, it will send the terminating chunk `0\r\n\r\n`, and send the trailers (if any).
If `chunk` is specified, it is equivalent to calling `outgoingMessage.write(chunk, encoding)`, followed by `outgoingMessage.end(callback)`.
If `callback` is provided, it will be called when the message is finished (equivalent to a listener of the `'finish'` event).
####
`outgoingMessage.flushHeaders()`
Added in: v1.6.0 Flushes the message headers.
For efficiency reason, Node.js normally buffers the message headers until `outgoingMessage.end()` is called or the first chunk of message data is written. It then tries to pack the headers and data into a single TCP packet.
It is usually desired (it saves a TCP round-trip), but not when the first data is not sent until possibly much later. `outgoingMessage.flushHeaders()` bypasses the optimization and kickstarts the message.
####
`outgoingMessage.getHeader(name)`
Added in: v0.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of header
* Returns [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
Gets the value of the HTTP header with the given name. If that header is not set, the returned value will be `undefined`.
####
`outgoingMessage.getHeaderNames()`
Added in: v7.7.0 * Returns [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns an array containing the unique names of the current outgoing headers. All names are lowercase.
####
`outgoingMessage.getHeaders()`
Added in: v7.7.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related HTTP module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase.
The object returned by the `outgoingMessage.getHeaders()` method does not prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and will not work.
```
outgoingMessage.setHeader('Foo', 'bar');
outgoingMessage.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']);
const headers = outgoingMessage.getHeaders();
// headers === { foo: 'bar', 'set-cookie': ['foo=bar', 'bar=baz'] }
```
####
`outgoingMessage.hasHeader(name)`
Added in: v7.7.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the header identified by `name` is currently set in the outgoing headers. The header name is case-insensitive.
```
const hasContentType = outgoingMessage.hasHeader('content-type');
```
####
`outgoingMessage.headersSent`
Added in: v0.9.3 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Read-only. `true` if the headers were sent, otherwise `false`.
####
`outgoingMessage.pipe()`
Added in: v9.0.0 Overrides the `stream.pipe()` method inherited from the legacy `Stream` class which is the parent class of `http.OutgoingMessage`.
Calling this method will throw an `Error` because `outgoingMessage` is a write-only stream.
####
`outgoingMessage.removeHeader(name)`
Added in: v0.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Header name
Removes a header that is queued for implicit sending.
```
outgoingMessage.removeHeader('Content-Encoding');
```
####
`outgoingMessage.setHeader(name, value)`
Added in: v0.4.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Header name
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Header value
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Sets a single header value. If the header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings to send multiple headers with the same name.
####
`outgoingMessage.setTimeout(msesc[, callback])`
Added in: v0.9.12 * `msesc` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Optional function to be called when a timeout occurs. Same as binding to the `timeout` event.
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)
Once a socket is associated with the message and is connected, [`socket.setTimeout()`](net#socketsettimeouttimeout-callback) will be called with `msecs` as the first parameter.
####
`outgoingMessage.socket`
Added in: v0.3.0 * [<stream.Duplex>](stream#class-streamduplex)
Reference to the underlying socket. Usually, users will not want to access this property.
After calling `outgoingMessage.end()`, this property will be nulled.
####
`outgoingMessage.uncork()`
Added in: v13.2.0, v12.16.0 See [`writable.uncork()`](stream#writableuncork)
####
`outgoingMessage.writableCorked`
Added in: v13.2.0, v12.16.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The number of times `outgoingMessage.cork()` has been called.
####
`outgoingMessage.writableEnded`
Added in: v12.9.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` if `outgoingMessage.end()` has been called. This property does not indicate whether the data has been flushed. For that purpose, use `message.writableFinished` instead.
####
`outgoingMessage.writableFinished`
Added in: v12.7.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` if all data has been flushed to the underlying system.
####
`outgoingMessage.writableHighWaterMark`
Added in: v12.9.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `highWaterMark` of the underlying socket if assigned. Otherwise, the default buffer level when [`writable.write()`](stream#writablewritechunk-encoding-callback) starts returning false (`16384`).
####
`outgoingMessage.writableLength`
Added in: v12.9.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The number of buffered bytes.
####
`outgoingMessage.writableObjectMode`
Added in: v12.9.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Always `false`.
####
`outgoingMessage.write(chunk[, encoding][, callback])`
History
| Version | Changes |
| --- | --- |
| v0.11.6 | The `callback` argument was added. |
| v0.1.29 | Added in: v0.1.29 |
* `chunk` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default**: `utf8`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Sends a chunk of the body. This method can be called multiple times.
The `encoding` argument is only relevant when `chunk` is a string. Defaults to `'utf8'`.
The `callback` argument is optional and will be called when this chunk of data is flushed.
Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in the user memory. The `'drain'` event will be emitted when the buffer is free again.
###
`http.METHODS`
Added in: v0.11.8 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
A list of the HTTP methods that are supported by the parser.
###
`http.STATUS_CODES`
Added in: v0.1.22 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
A collection of all the standard HTTP response status codes, and the short description of each. For example, `http.STATUS_CODES[404] === 'Not Found'`.
###
`http.createServer([options][, requestListener])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | The `requestTimeout`, `headersTimeout`, `keepAliveTimeout`, and `connectionsCheckingInterval` options are supported now. |
| v18.0.0 | The `noDelay` option now defaults to `true`. |
| v17.7.0, v16.15.0 | The `noDelay`, `keepAlive` and `keepAliveInitialDelay` options are supported now. |
| v13.3.0 | The `maxHeaderSize` option is supported now. |
| v13.8.0, v12.15.0, v10.19.0 | The `insecureHTTPParser` option is supported now. |
| v9.6.0, v8.12.0 | The `options` argument is supported now. |
| v0.1.13 | Added in: v0.1.13 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `IncomingMessage` [<http.IncomingMessage>](http#class-httpincomingmessage) Specifies the `IncomingMessage` class to be used. Useful for extending the original `IncomingMessage`. **Default:** `IncomingMessage`.
+ `ServerResponse` [<http.ServerResponse>](http#class-httpserverresponse) Specifies the `ServerResponse` class to be used. Useful for extending the original `ServerResponse`. **Default:** `ServerResponse`.
+ `requestTimeout`: Sets the timeout value in milliseconds for receiving the entire request from the client. See [`server.requestTimeout`](#serverrequesttimeout) for more information. **Default:** `300000`.
+ `headersTimeout`: Sets the timeout value in milliseconds for receiving the complete HTTP headers from the client. See [`server.headersTimeout`](#serverheaderstimeout) for more information. **Default:** `60000`.
+ `keepAliveTimeout`: The number of milliseconds of inactivity a server needs to wait for additional incoming data, after it has finished writing the last response, before a socket will be destroyed. See [`server.keepAliveTimeout`](#serverkeepalivetimeout) for more information. **Default:** `5000`.
+ `connectionsCheckingInterval`: Sets the interval value in milliseconds to check for request and headers timeout in incomplete requests. **Default:** `30000`.
+ `insecureHTTPParser` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Use an insecure HTTP parser that accepts invalid HTTP headers when `true`. Using the insecure parser should be avoided. See [`--insecure-http-parser`](cli#--insecure-http-parser) for more information. **Default:** `false`
+ `maxHeaderSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optionally overrides the value of [`--max-http-header-size`](cli#--max-http-header-sizesize) for requests received by this server, i.e. the maximum length of request headers in bytes. **Default:** 16384 (16 KiB).
+ `noDelay` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `true`, it disables the use of Nagle's algorithm immediately after a new incoming connection is received. **Default:** `true`.
+ `keepAlive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `true`, it enables keep-alive functionality on the socket immediately after a new incoming connection is received, similarly on what is done in [`socket.setKeepAlive([enable][, initialDelay])`][`socket.setKeepAlive(enable, initialDelay)`]. **Default:** `false`.
+ `keepAliveInitialDelay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If set to a positive number, it sets the initial delay before the first keepalive probe is sent on an idle socket. **Default:** `0`.
+ `uniqueHeaders` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) A list of response headers that should be sent only once. If the header's value is an array, the items will be joined using `;` .
* `requestListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<http.Server>](http#class-httpserver)
Returns a new instance of [`http.Server`](#class-httpserver).
The `requestListener` is a function which is automatically added to the [`'request'`](#event-request) event.
```
const http = require('node:http');
// Create a local server to receive data from
const server = http.createServer((req, res) => {
res.writeHead(200, { 'Content-Type': 'application/json' });
res.end(JSON.stringify({
data: 'Hello World!'
}));
});
server.listen(8000);
```
```
const http = require('node:http');
// Create a local server to receive data from
const server = http.createServer();
// Listen to the request event
server.on('request', (request, res) => {
res.writeHead(200, { 'Content-Type': 'application/json' });
res.end(JSON.stringify({
data: 'Hello World!'
}));
});
server.listen(8000);
```
###
`http.get(options[, callback])`
###
`http.get(url[, options][, callback])`
History
| Version | Changes |
| --- | --- |
| v10.9.0 | The `url` parameter can now be passed along with a separate `options` object. |
| v7.5.0 | The `options` parameter can be a WHATWG `URL` object. |
| v0.3.6 | Added in: v0.3.6 |
* `url` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Accepts the same `options` as [`http.request()`](#httprequestoptions-callback), with the `method` always set to `GET`. Properties that are inherited from the prototype are ignored.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<http.ClientRequest>](http#class-httpclientrequest)
Since most requests are GET requests without bodies, Node.js provides this convenience method. The only difference between this method and [`http.request()`](#httprequestoptions-callback) is that it sets the method to GET and calls `req.end()` automatically. The callback must take care to consume the response data for reasons stated in [`http.ClientRequest`](#class-httpclientrequest) section.
The `callback` is invoked with a single argument that is an instance of [`http.IncomingMessage`](#class-httpincomingmessage).
JSON fetching example:
```
http.get('http://localhost:8000/', (res) => {
const { statusCode } = res;
const contentType = res.headers['content-type'];
let error;
// Any 2xx status code signals a successful response but
// here we're only checking for 200.
if (statusCode !== 200) {
error = new Error('Request Failed.\n' +
`Status Code: ${statusCode}`);
} else if (!/^application\/json/.test(contentType)) {
error = new Error('Invalid content-type.\n' +
`Expected application/json but received ${contentType}`);
}
if (error) {
console.error(error.message);
// Consume response data to free up memory
res.resume();
return;
}
res.setEncoding('utf8');
let rawData = '';
res.on('data', (chunk) => { rawData += chunk; });
res.on('end', () => {
try {
const parsedData = JSON.parse(rawData);
console.log(parsedData);
} catch (e) {
console.error(e.message);
}
});
}).on('error', (e) => {
console.error(`Got error: ${e.message}`);
});
// Create a local server to receive data from
const server = http.createServer((req, res) => {
res.writeHead(200, { 'Content-Type': 'application/json' });
res.end(JSON.stringify({
data: 'Hello World!'
}));
});
server.listen(8000);
```
###
`http.globalAgent`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | The agent now uses HTTP Keep-Alive by default. |
| v0.5.9 | Added in: v0.5.9 |
* [<http.Agent>](http#class-httpagent)
Global instance of `Agent` which is used as the default for all HTTP client requests.
###
`http.maxHeaderSize`
Added in: v11.6.0, v10.15.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Read-only property specifying the maximum allowed size of HTTP headers in bytes. Defaults to 16 KiB. Configurable using the [`--max-http-header-size`](cli#--max-http-header-sizesize) CLI option.
This can be overridden for servers and client requests by passing the `maxHeaderSize` option.
###
`http.request(options[, callback])`
###
`http.request(url[, options][, callback])`
History
| Version | Changes |
| --- | --- |
| v16.7.0, v14.18.0 | When using a `URL` object parsed username and password will now be properly URI decoded. |
| v15.3.0, v14.17.0 | It is possible to abort a request with an AbortSignal. |
| v13.3.0 | The `maxHeaderSize` option is supported now. |
| v13.8.0, v12.15.0, v10.19.0 | The `insecureHTTPParser` option is supported now. |
| v10.9.0 | The `url` parameter can now be passed along with a separate `options` object. |
| v7.5.0 | The `options` parameter can be a WHATWG `URL` object. |
| v0.3.6 | Added in: v0.3.6 |
* `url` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `agent` [<http.Agent>](http#class-httpagent) | [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Controls [`Agent`](#class-httpagent) behavior. Possible values:
- `undefined` (default): use [`http.globalAgent`](#httpglobalagent) for this host and port.
- `Agent` object: explicitly use the passed in `Agent`.
- `false`: causes a new `Agent` with default values to be used.
+ `auth` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Basic authentication (`'user:password'`) to compute an Authorization header.
+ `createConnection` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A function that produces a socket/stream to use for the request when the `agent` option is not used. This can be used to avoid creating a custom `Agent` class just to override the default `createConnection` function. See [`agent.createConnection()`](#agentcreateconnectionoptions-callback) for more details. Any [`Duplex`](stream#class-streamduplex) stream is a valid return value.
+ `defaultPort` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Default port for the protocol. **Default:** `agent.defaultPort` if an `Agent` is used, else `undefined`.
+ `family` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) IP address family to use when resolving `host` or `hostname`. Valid values are `4` or `6`. When unspecified, both IP v4 and v6 will be used.
+ `headers` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object containing request headers.
+ `hints` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optional [`dns.lookup()` hints](dns#supported-getaddrinfo-flags).
+ `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A domain name or IP address of the server to issue the request to. **Default:** `'localhost'`.
+ `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Alias for `host`. To support [`url.parse()`](url#urlparseurlstring-parsequerystring-slashesdenotehost), `hostname` will be used if both `host` and `hostname` are specified.
+ `insecureHTTPParser` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Use an insecure HTTP parser that accepts invalid HTTP headers when `true`. Using the insecure parser should be avoided. See [`--insecure-http-parser`](cli#--insecure-http-parser) for more information. **Default:** `false`
+ `localAddress` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Local interface to bind for network connections.
+ `localPort` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Local port to connect from.
+ `lookup` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Custom lookup function. **Default:** [`dns.lookup()`](dns#dnslookuphostname-options-callback).
+ `maxHeaderSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optionally overrides the value of [`--max-http-header-size`](cli#--max-http-header-sizesize) (the maximum length of response headers in bytes) for responses received from the server. **Default:** 16384 (16 KiB).
+ `method` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A string specifying the HTTP request method. **Default:** `'GET'`.
+ `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Request path. Should include query string if any. E.G. `'/index.html?page=12'`. An exception is thrown when the request path contains illegal characters. Currently, only spaces are rejected but that may change in the future. **Default:** `'/'`.
+ `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Port of remote server. **Default:** `defaultPort` if set, else `80`.
+ `protocol` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Protocol to use. **Default:** `'http:'`.
+ `setHost` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type): Specifies whether or not to automatically add the `Host` header. Defaults to `true`.
+ `signal` [<AbortSignal>](globals#class-abortsignal): An AbortSignal that may be used to abort an ongoing request.
+ `socketPath` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Unix domain socket. Cannot be used if one of `host` or `port` is specified, as those specify a TCP Socket.
+ `timeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type): A number specifying the socket timeout in milliseconds. This will set the timeout before the socket is connected.
+ `uniqueHeaders` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) A list of request headers that should be sent only once. If the header's value is an array, the items will be joined using `;` .
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<http.ClientRequest>](http#class-httpclientrequest)
`options` in [`socket.connect()`](net#socketconnectoptions-connectlistener) are also supported.
Node.js maintains several connections per server to make HTTP requests. This function allows one to transparently issue requests.
`url` can be a string or a [`URL`](url#the-whatwg-url-api) object. If `url` is a string, it is automatically parsed with [`new URL()`](url#new-urlinput-base). If it is a [`URL`](url#the-whatwg-url-api) object, it will be automatically converted to an ordinary `options` object.
If both `url` and `options` are specified, the objects are merged, with the `options` properties taking precedence.
The optional `callback` parameter will be added as a one-time listener for the [`'response'`](#event-response) event.
`http.request()` returns an instance of the [`http.ClientRequest`](#class-httpclientrequest) class. The `ClientRequest` instance is a writable stream. If one needs to upload a file with a POST request, then write to the `ClientRequest` object.
```
const http = require('node:http');
const postData = JSON.stringify({
'msg': 'Hello World!'
});
const options = {
hostname: 'www.google.com',
port: 80,
path: '/upload',
method: 'POST',
headers: {
'Content-Type': 'application/json',
'Content-Length': Buffer.byteLength(postData)
}
};
const req = http.request(options, (res) => {
console.log(`STATUS: ${res.statusCode}`);
console.log(`HEADERS: ${JSON.stringify(res.headers)}`);
res.setEncoding('utf8');
res.on('data', (chunk) => {
console.log(`BODY: ${chunk}`);
});
res.on('end', () => {
console.log('No more data in response.');
});
});
req.on('error', (e) => {
console.error(`problem with request: ${e.message}`);
});
// Write data to request body
req.write(postData);
req.end();
```
In the example `req.end()` was called. With `http.request()` one must always call `req.end()` to signify the end of the request - even if there is no data being written to the request body.
If any error is encountered during the request (be that with DNS resolution, TCP level errors, or actual HTTP parse errors) an `'error'` event is emitted on the returned request object. As with all `'error'` events, if no listeners are registered the error will be thrown.
There are a few special headers that should be noted.
* Sending a 'Connection: keep-alive' will notify Node.js that the connection to the server should be persisted until the next request.
* Sending a 'Content-Length' header will disable the default chunked encoding.
* Sending an 'Expect' header will immediately send the request headers. Usually, when sending 'Expect: 100-continue', both a timeout and a listener for the `'continue'` event should be set. See RFC 2616 Section 8.2.3 for more information.
* Sending an Authorization header will override using the `auth` option to compute basic authentication.
Example using a [`URL`](url#the-whatwg-url-api) as `options`:
```
const options = new URL('http://abc:[email protected]');
const req = http.request(options, (res) => {
// ...
});
```
In a successful request, the following events will be emitted in the following order:
* `'socket'`
* `'response'`
+ `'data'` any number of times, on the `res` object (`'data'` will not be emitted at all if the response body is empty, for instance, in most redirects)
+ `'end'` on the `res` object
* `'close'`
In the case of a connection error, the following events will be emitted:
* `'socket'`
* `'error'`
* `'close'`
In the case of a premature connection close before the response is received, the following events will be emitted in the following order:
* `'socket'`
* `'error'` with an error with message `'Error: socket hang up'` and code `'ECONNRESET'`
* `'close'`
In the case of a premature connection close after the response is received, the following events will be emitted in the following order:
* `'socket'`
* `'response'`
+ `'data'` any number of times, on the `res` object
* (connection closed here)
* `'aborted'` on the `res` object
* `'error'` on the `res` object with an error with message `'Error: aborted'` and code `'ECONNRESET'`.
* `'close'`
* `'close'` on the `res` object
If `req.destroy()` is called before a socket is assigned, the following events will be emitted in the following order:
* (`req.destroy()` called here)
* `'error'` with an error with message `'Error: socket hang up'` and code `'ECONNRESET'`
* `'close'`
If `req.destroy()` is called before the connection succeeds, the following events will be emitted in the following order:
* `'socket'`
* (`req.destroy()` called here)
* `'error'` with an error with message `'Error: socket hang up'` and code `'ECONNRESET'`
* `'close'`
If `req.destroy()` is called after the response is received, the following events will be emitted in the following order:
* `'socket'`
* `'response'`
+ `'data'` any number of times, on the `res` object
* (`req.destroy()` called here)
* `'aborted'` on the `res` object
* `'error'` on the `res` object with an error with message `'Error: aborted'` and code `'ECONNRESET'`.
* `'close'`
* `'close'` on the `res` object
If `req.abort()` is called before a socket is assigned, the following events will be emitted in the following order:
* (`req.abort()` called here)
* `'abort'`
* `'close'`
If `req.abort()` is called before the connection succeeds, the following events will be emitted in the following order:
* `'socket'`
* (`req.abort()` called here)
* `'abort'`
* `'error'` with an error with message `'Error: socket hang up'` and code `'ECONNRESET'`
* `'close'`
If `req.abort()` is called after the response is received, the following events will be emitted in the following order:
* `'socket'`
* `'response'`
+ `'data'` any number of times, on the `res` object
* (`req.abort()` called here)
* `'abort'`
* `'aborted'` on the `res` object
* `'error'` on the `res` object with an error with message `'Error: aborted'` and code `'ECONNRESET'`.
* `'close'`
* `'close'` on the `res` object
Setting the `timeout` option or using the `setTimeout()` function will not abort the request or do anything besides add a `'timeout'` event.
Passing an `AbortSignal` and then calling `abort` on the corresponding `AbortController` will behave the same way as calling `.destroy()` on the request itself.
###
`http.validateHeaderName(name)`
Added in: v14.3.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Performs the low-level validations on the provided `name` that are done when `res.setHeader(name, value)` is called.
Passing illegal value as `name` will result in a [`TypeError`](errors#class-typeerror) being thrown, identified by `code: 'ERR_INVALID_HTTP_TOKEN'`.
It is not necessary to use this method before passing headers to an HTTP request or response. The HTTP module will automatically validate such headers. Examples:
Example:
```
const { validateHeaderName } = require('node:http');
try {
validateHeaderName('');
} catch (err) {
err instanceof TypeError; // --> true
err.code; // --> 'ERR_INVALID_HTTP_TOKEN'
err.message; // --> 'Header name must be a valid HTTP token [""]'
}
```
###
`http.validateHeaderValue(name, value)`
Added in: v14.3.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Performs the low-level validations on the provided `value` that are done when `res.setHeader(name, value)` is called.
Passing illegal value as `value` will result in a [`TypeError`](errors#class-typeerror) being thrown.
* Undefined value error is identified by `code: 'ERR_HTTP_INVALID_HEADER_VALUE'`.
* Invalid value character error is identified by `code: 'ERR_INVALID_CHAR'`.
It is not necessary to use this method before passing headers to an HTTP request or response. The HTTP module will automatically validate such headers.
Examples:
```
const { validateHeaderValue } = require('node:http');
try {
validateHeaderValue('x-my-header', undefined);
} catch (err) {
err instanceof TypeError; // --> true
err.code === 'ERR_HTTP_INVALID_HEADER_VALUE'; // --> true
err.message; // --> 'Invalid value "undefined" for header "x-my-header"'
}
try {
validateHeaderValue('x-my-header', 'oʊmɪɡə');
} catch (err) {
err instanceof TypeError; // --> true
err.code === 'ERR_INVALID_CHAR'; // --> true
err.message; // --> 'Invalid character in header content ["x-my-header"]'
}
```
###
`http.setMaxIdleHTTPParsers`
Added in: v18.8.0, v16.18.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Set the maximum number of idle HTTP parsers. **Default:** `1000`.
| programming_docs |
node None Timers
------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/timers.js](https://github.com/nodejs/node/blob/v19.0.1/lib/timers.js)
The `timer` module exposes a global API for scheduling functions to be called at some future period of time. Because the timer functions are globals, there is no need to call `require('node:timers')` to use the API.
The timer functions within Node.js implement a similar API as the timers API provided by Web Browsers but use a different internal implementation that is built around the Node.js [Event Loop](https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/#setimmediate-vs-settimeout).
### Class: `Immediate`
This object is created internally and is returned from [`setImmediate()`](#setimmediatecallback-args). It can be passed to [`clearImmediate()`](#clearimmediateimmediate) in order to cancel the scheduled actions.
By default, when an immediate is scheduled, the Node.js event loop will continue running as long as the immediate is active. The `Immediate` object returned by [`setImmediate()`](#setimmediatecallback-args) exports both `immediate.ref()` and `immediate.unref()` functions that can be used to control this default behavior.
####
`immediate.hasRef()`
Added in: v11.0.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If true, the `Immediate` object will keep the Node.js event loop active.
####
`immediate.ref()`
Added in: v9.7.0 * Returns: [<Immediate>](timers#class-immediate) a reference to `immediate`
When called, requests that the Node.js event loop *not* exit so long as the `Immediate` is active. Calling `immediate.ref()` multiple times will have no effect.
By default, all `Immediate` objects are "ref'ed", making it normally unnecessary to call `immediate.ref()` unless `immediate.unref()` had been called previously.
####
`immediate.unref()`
Added in: v9.7.0 * Returns: [<Immediate>](timers#class-immediate) a reference to `immediate`
When called, the active `Immediate` object will not require the Node.js event loop to remain active. If there is no other activity keeping the event loop running, the process may exit before the `Immediate` object's callback is invoked. Calling `immediate.unref()` multiple times will have no effect.
### Class: `Timeout`
This object is created internally and is returned from [`setTimeout()`](#settimeoutcallback-delay-args) and [`setInterval()`](#setintervalcallback-delay-args). It can be passed to either [`clearTimeout()`](#cleartimeouttimeout) or [`clearInterval()`](#clearintervaltimeout) in order to cancel the scheduled actions.
By default, when a timer is scheduled using either [`setTimeout()`](#settimeoutcallback-delay-args) or [`setInterval()`](#setintervalcallback-delay-args), the Node.js event loop will continue running as long as the timer is active. Each of the `Timeout` objects returned by these functions export both `timeout.ref()` and `timeout.unref()` functions that can be used to control this default behavior.
####
`timeout.close()`
Added in: v0.9.1
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy: Use [`clearTimeout()`](#cleartimeouttimeout) instead.
* Returns: [<Timeout>](timers#class-timeout) a reference to `timeout`
Cancels the timeout.
####
`timeout.hasRef()`
Added in: v11.0.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If true, the `Timeout` object will keep the Node.js event loop active.
####
`timeout.ref()`
Added in: v0.9.1 * Returns: [<Timeout>](timers#class-timeout) a reference to `timeout`
When called, requests that the Node.js event loop *not* exit so long as the `Timeout` is active. Calling `timeout.ref()` multiple times will have no effect.
By default, all `Timeout` objects are "ref'ed", making it normally unnecessary to call `timeout.ref()` unless `timeout.unref()` had been called previously.
####
`timeout.refresh()`
Added in: v10.2.0 * Returns: [<Timeout>](timers#class-timeout) a reference to `timeout`
Sets the timer's start time to the current time, and reschedules the timer to call its callback at the previously specified duration adjusted to the current time. This is useful for refreshing a timer without allocating a new JavaScript object.
Using this on a timer that has already called its callback will reactivate the timer.
####
`timeout.unref()`
Added in: v0.9.1 * Returns: [<Timeout>](timers#class-timeout) a reference to `timeout`
When called, the active `Timeout` object will not require the Node.js event loop to remain active. If there is no other activity keeping the event loop running, the process may exit before the `Timeout` object's callback is invoked. Calling `timeout.unref()` multiple times will have no effect.
####
`timeout[Symbol.toPrimitive]()`
Added in: v14.9.0, v12.19.0 * Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) a number that can be used to reference this `timeout`
Coerce a `Timeout` to a primitive. The primitive can be used to clear the `Timeout`. The primitive can only be used in the same thread where the timeout was created. Therefore, to use it across [`worker_threads`](worker_threads) it must first be passed to the correct thread. This allows enhanced compatibility with browser `setTimeout()` and `setInterval()` implementations.
### Scheduling timers
A timer in Node.js is an internal construct that calls a given function after a certain period of time. When a timer's function is called varies depending on which method was used to create the timer and what other work the Node.js event loop is doing.
####
`setImmediate(callback[, ...args])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.9.1 | Added in: v0.9.1 |
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to call at the end of this turn of the Node.js [Event Loop](https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/#setimmediate-vs-settimeout)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Optional arguments to pass when the `callback` is called.
* Returns: [<Immediate>](timers#class-immediate) for use with [`clearImmediate()`](#clearimmediateimmediate)
Schedules the "immediate" execution of the `callback` after I/O events' callbacks.
When multiple calls to `setImmediate()` are made, the `callback` functions are queued for execution in the order in which they are created. The entire callback queue is processed every event loop iteration. If an immediate timer is queued from inside an executing callback, that timer will not be triggered until the next event loop iteration.
If `callback` is not a function, a [`TypeError`](errors#class-typeerror) will be thrown.
This method has a custom variant for promises that is available using [`timersPromises.setImmediate()`](#timerspromisessetimmediatevalue-options).
####
`setInterval(callback[, delay[, ...args]])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.0.1 | Added in: v0.0.1 |
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to call when the timer elapses.
* `delay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds to wait before calling the `callback`. **Default:** `1`.
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Optional arguments to pass when the `callback` is called.
* Returns: [<Timeout>](timers#class-timeout) for use with [`clearInterval()`](#clearintervaltimeout)
Schedules repeated execution of `callback` every `delay` milliseconds.
When `delay` is larger than `2147483647` or less than `1`, the `delay` will be set to `1`. Non-integer delays are truncated to an integer.
If `callback` is not a function, a [`TypeError`](errors#class-typeerror) will be thrown.
This method has a custom variant for promises that is available using [`timersPromises.setInterval()`](#timerspromisessetintervaldelay-value-options).
####
`setTimeout(callback[, delay[, ...args]])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.0.1 | Added in: v0.0.1 |
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to call when the timer elapses.
* `delay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds to wait before calling the `callback`. **Default:** `1`.
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Optional arguments to pass when the `callback` is called.
* Returns: [<Timeout>](timers#class-timeout) for use with [`clearTimeout()`](#cleartimeouttimeout)
Schedules execution of a one-time `callback` after `delay` milliseconds.
The `callback` will likely not be invoked in precisely `delay` milliseconds. Node.js makes no guarantees about the exact timing of when callbacks will fire, nor of their ordering. The callback will be called as close as possible to the time specified.
When `delay` is larger than `2147483647` or less than `1`, the `delay` will be set to `1`. Non-integer delays are truncated to an integer.
If `callback` is not a function, a [`TypeError`](errors#class-typeerror) will be thrown.
This method has a custom variant for promises that is available using [`timersPromises.setTimeout()`](#timerspromisessettimeoutdelay-value-options).
### Cancelling timers
The [`setImmediate()`](#setimmediatecallback-args), [`setInterval()`](#setintervalcallback-delay-args), and [`setTimeout()`](#settimeoutcallback-delay-args) methods each return objects that represent the scheduled timers. These can be used to cancel the timer and prevent it from triggering.
For the promisified variants of [`setImmediate()`](#setimmediatecallback-args) and [`setTimeout()`](#settimeoutcallback-delay-args), an [`AbortController`](globals#class-abortcontroller) may be used to cancel the timer. When canceled, the returned Promises will be rejected with an `'AbortError'`.
For `setImmediate()`:
```
const { setImmediate: setImmediatePromise } = require('node:timers/promises');
const ac = new AbortController();
const signal = ac.signal;
setImmediatePromise('foobar', { signal })
.then(console.log)
.catch((err) => {
if (err.name === 'AbortError')
console.log('The immediate was aborted');
});
ac.abort();
```
For `setTimeout()`:
```
const { setTimeout: setTimeoutPromise } = require('node:timers/promises');
const ac = new AbortController();
const signal = ac.signal;
setTimeoutPromise(1000, 'foobar', { signal })
.then(console.log)
.catch((err) => {
if (err.name === 'AbortError')
console.log('The timeout was aborted');
});
ac.abort();
```
####
`clearImmediate(immediate)`
Added in: v0.9.1 * `immediate` [<Immediate>](timers#class-immediate) An `Immediate` object as returned by [`setImmediate()`](#setimmediatecallback-args).
Cancels an `Immediate` object created by [`setImmediate()`](#setimmediatecallback-args).
####
`clearInterval(timeout)`
Added in: v0.0.1 * `timeout` [<Timeout>](timers#class-timeout) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A `Timeout` object as returned by [`setInterval()`](#setintervalcallback-delay-args) or the [primitive](#timeoutsymboltoprimitive) of the `Timeout` object as a string or a number.
Cancels a `Timeout` object created by [`setInterval()`](#setintervalcallback-delay-args).
####
`clearTimeout(timeout)`
Added in: v0.0.1 * `timeout` [<Timeout>](timers#class-timeout) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A `Timeout` object as returned by [`setTimeout()`](#settimeoutcallback-delay-args) or the [primitive](#timeoutsymboltoprimitive) of the `Timeout` object as a string or a number.
Cancels a `Timeout` object created by [`setTimeout()`](#settimeoutcallback-delay-args).
### Timers Promises API
History
| Version | Changes |
| --- | --- |
| v16.0.0 | Graduated from experimental. |
| v15.0.0 | Added in: v15.0.0 |
The `timers/promises` API provides an alternative set of timer functions that return `Promise` objects. The API is accessible via `require('node:timers/promises')`.
MJS modules
```
import {
setTimeout,
setImmediate,
setInterval,
} from 'timers/promises';
```
CJS modules
```
const {
setTimeout,
setImmediate,
setInterval,
} = require('node:timers/promises');
```
####
`timersPromises.setTimeout([delay[, value[, options]]])`
Added in: v15.0.0 * `delay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds to wait before fulfilling the promise. **Default:** `1`.
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) A value with which the promise is fulfilled.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ref` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Set to `false` to indicate that the scheduled `Timeout` should not require the Node.js event loop to remain active. **Default:** `true`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) An optional `AbortSignal` that can be used to cancel the scheduled `Timeout`.
MJS modules
```
import {
setTimeout,
} from 'timers/promises';
const res = await setTimeout(100, 'result');
console.log(res); // Prints 'result'
```
CJS modules
```
const {
setTimeout,
} = require('node:timers/promises');
setTimeout(100, 'result').then((res) => {
console.log(res); // Prints 'result'
});
```
####
`timersPromises.setImmediate([value[, options]])`
Added in: v15.0.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) A value with which the promise is fulfilled.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ref` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Set to `false` to indicate that the scheduled `Immediate` should not require the Node.js event loop to remain active. **Default:** `true`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) An optional `AbortSignal` that can be used to cancel the scheduled `Immediate`.
MJS modules
```
import {
setImmediate,
} from 'timers/promises';
const res = await setImmediate('result');
console.log(res); // Prints 'result'
```
CJS modules
```
const {
setImmediate,
} = require('node:timers/promises');
setImmediate('result').then((res) => {
console.log(res); // Prints 'result'
});
```
####
`timersPromises.setInterval([delay[, value[, options]]])`
Added in: v15.9.0 Returns an async iterator that generates values in an interval of `delay` ms.
* `delay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds to wait between iterations. **Default:** `1`.
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) A value with which the iterator returns.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ref` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Set to `false` to indicate that the scheduled `Timeout` between iterations should not require the Node.js event loop to remain active. **Default:** `true`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) An optional `AbortSignal` that can be used to cancel the scheduled `Timeout` between operations.
MJS modules
```
import {
setInterval,
} from 'timers/promises';
const interval = 100;
for await (const startTime of setInterval(interval, Date.now())) {
const now = Date.now();
console.log(now);
if ((now - startTime) > 1000)
break;
}
console.log(Date.now());
```
CJS modules
```
const {
setInterval,
} = require('node:timers/promises');
const interval = 100;
(async function() {
for await (const startTime of setInterval(interval, Date.now())) {
const now = Date.now();
console.log(now);
if ((now - startTime) > 1000)
break;
}
console.log(Date.now());
})();
```
####
`timersPromises.scheduler.wait(delay[, options])`
Added in: v17.3.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `delay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds to wait before resolving the promise.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) An optional `AbortSignal` that can be used to cancel waiting.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
An experimental API defined by the [Scheduling APIs](https://github.com/WICG/scheduling-apis) draft specification being developed as a standard Web Platform API.
Calling `timersPromises.scheduler.wait(delay, options)` is roughly equivalent to calling `timersPromises.setTimeout(delay, undefined, options)` except that the `ref` option is not supported.
```
import { scheduler } from 'node:timers/promises';
await scheduler.wait(1000); // Wait one second before continuing
```
####
`timersPromises.scheduler.yield()`
Added in: v17.3.0, v16.14.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
An experimental API defined by the [Scheduling APIs](https://github.com/WICG/scheduling-apis) draft specification being developed as a standard Web Platform API.
Calling `timersPromises.scheduler.yield()` is equivalent to calling `timersPromises.setImmediate()` with no arguments.
node None DNS
---
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/dns.js](https://github.com/nodejs/node/blob/v19.0.1/lib/dns.js)
The `node:dns` module enables name resolution. For example, use it to look up IP addresses of host names.
Although named for the [Domain Name System (DNS)](https://en.wikipedia.org/wiki/Domain_Name_System), it does not always use the DNS protocol for lookups. [`dns.lookup()`](#dnslookuphostname-options-callback) uses the operating system facilities to perform name resolution. It may not need to perform any network communication. To perform name resolution the way other applications on the same system do, use [`dns.lookup()`](#dnslookuphostname-options-callback).
```
const dns = require('node:dns');
dns.lookup('example.org', (err, address, family) => {
console.log('address: %j family: IPv%s', address, family);
});
// address: "93.184.216.34" family: IPv4
```
All other functions in the `node:dns` module connect to an actual DNS server to perform name resolution. They will always use the network to perform DNS queries. These functions do not use the same set of configuration files used by [`dns.lookup()`](#dnslookuphostname-options-callback) (e.g. `/etc/hosts`). Use these functions to always perform DNS queries, bypassing other name-resolution facilities.
```
const dns = require('node:dns');
dns.resolve4('archive.org', (err, addresses) => {
if (err) throw err;
console.log(`addresses: ${JSON.stringify(addresses)}`);
addresses.forEach((a) => {
dns.reverse(a, (err, hostnames) => {
if (err) {
throw err;
}
console.log(`reverse for ${a}: ${JSON.stringify(hostnames)}`);
});
});
});
```
See the [Implementation considerations section](#implementation-considerations) for more information.
### Class: `dns.Resolver`
Added in: v8.3.0 An independent resolver for DNS requests.
Creating a new resolver uses the default server settings. Setting the servers used for a resolver using [`resolver.setServers()`](#dnssetserversservers) does not affect other resolvers:
```
const { Resolver } = require('node:dns');
const resolver = new Resolver();
resolver.setServers(['4.4.4.4']);
// This request will use the server at 4.4.4.4, independent of global settings.
resolver.resolve4('example.org', (err, addresses) => {
// ...
});
```
The following methods from the `node:dns` module are available:
* [`resolver.getServers()`](#dnsgetservers)
* [`resolver.resolve()`](#dnsresolvehostname-rrtype-callback)
* [`resolver.resolve4()`](#dnsresolve4hostname-options-callback)
* [`resolver.resolve6()`](#dnsresolve6hostname-options-callback)
* [`resolver.resolveAny()`](#dnsresolveanyhostname-callback)
* [`resolver.resolveCaa()`](#dnsresolvecaahostname-callback)
* [`resolver.resolveCname()`](#dnsresolvecnamehostname-callback)
* [`resolver.resolveMx()`](#dnsresolvemxhostname-callback)
* [`resolver.resolveNaptr()`](#dnsresolvenaptrhostname-callback)
* [`resolver.resolveNs()`](#dnsresolvenshostname-callback)
* [`resolver.resolvePtr()`](#dnsresolveptrhostname-callback)
* [`resolver.resolveSoa()`](#dnsresolvesoahostname-callback)
* [`resolver.resolveSrv()`](#dnsresolvesrvhostname-callback)
* [`resolver.resolveTxt()`](#dnsresolvetxthostname-callback)
* [`resolver.reverse()`](#dnsreverseip-callback)
* [`resolver.setServers()`](#dnssetserversservers)
####
`Resolver([options])`
History
| Version | Changes |
| --- | --- |
| v16.7.0, v14.18.0 | The `options` object now accepts a `tries` option. |
| v12.18.3 | The constructor now accepts an `options` object. The single supported option is `timeout`. |
| v8.3.0 | Added in: v8.3.0 |
Create a new resolver.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `timeout` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Query timeout in milliseconds, or `-1` to use the default timeout.
+ `tries` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of tries the resolver will try contacting each name server before giving up. **Default:** `4`
####
`resolver.cancel()`
Added in: v8.3.0 Cancel all outstanding DNS queries made by this resolver. The corresponding callbacks will be called with an error with code `ECANCELLED`.
####
`resolver.setLocalAddress([ipv4][, ipv6])`
Added in: v15.1.0, v14.17.0 * `ipv4` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A string representation of an IPv4 address. **Default:** `'0.0.0.0'`
* `ipv6` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A string representation of an IPv6 address. **Default:** `'::0'`
The resolver instance will send its requests from the specified IP address. This allows programs to specify outbound interfaces when used on multi-homed systems.
If a v4 or v6 address is not specified, it is set to the default and the operating system will choose a local address automatically.
The resolver will use the v4 local address when making requests to IPv4 DNS servers, and the v6 local address when making requests to IPv6 DNS servers. The `rrtype` of resolution requests has no impact on the local address used.
###
`dns.getServers()`
Added in: v0.11.3 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns an array of IP address strings, formatted according to [RFC 5952](https://tools.ietf.org/html/rfc5952#section-6), that are currently configured for DNS resolution. A string will include a port section if a custom port is used.
```
[
'4.4.4.4',
'2001:4860:4860::8888',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053',
]
```
###
`dns.lookup(hostname[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.4.0 | For compatibility with `node:net`, when passing an option object the `family` option can be the string `'IPv4'` or the string `'IPv6'`. |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v17.0.0 | The `verbatim` options defaults to `true` now. |
| v8.5.0 | The `verbatim` option is supported now. |
| v1.2.0 | The `all` option is supported now. |
| v0.1.90 | Added in: v0.1.90 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `family` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The record family. Must be `4`, `6`, or `0`. For backward compatibility reasons,`'IPv4'` and `'IPv6'` are interpreted as `4` and `6` respectively. The value `0` indicates that IPv4 and IPv6 addresses are both returned. **Default:** `0`.
+ `hints` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) One or more [supported `getaddrinfo` flags](#supported-getaddrinfo-flags). Multiple flags may be passed by bitwise `OR`ing their values.
+ `all` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the callback returns all resolved addresses in an array. Otherwise, returns a single address. **Default:** `false`.
+ `verbatim` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the callback receives IPv4 and IPv6 addresses in the order the DNS resolver returned them. When `false`, IPv4 addresses are placed before IPv6 addresses. **Default:** `true` (addresses are not reordered). Default value is configurable using [`dns.setDefaultResultOrder()`](#dnssetdefaultresultorderorder) or [`--dns-result-order`](cli#--dns-result-orderorder).
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A string representation of an IPv4 or IPv6 address.
+ `family` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `4` or `6`, denoting the family of `address`, or `0` if the address is not an IPv4 or IPv6 address. `0` is a likely indicator of a bug in the name resolution service used by the operating system.
Resolves a host name (e.g. `'nodejs.org'`) into the first found A (IPv4) or AAAA (IPv6) record. All `option` properties are optional. If `options` is an integer, then it must be `4` or `6` – if `options` is `0` or not provided, then IPv4 and IPv6 addresses are both returned if found.
With the `all` option set to `true`, the arguments for `callback` change to `(err, addresses)`, with `addresses` being an array of objects with the properties `address` and `family`.
On error, `err` is an [`Error`](errors#class-error) object, where `err.code` is the error code. Keep in mind that `err.code` will be set to `'ENOTFOUND'` not only when the host name does not exist but also when the lookup fails in other ways such as no available file descriptors.
`dns.lookup()` does not necessarily have anything to do with the DNS protocol. The implementation uses an operating system facility that can associate names with addresses and vice versa. This implementation can have subtle but important consequences on the behavior of any Node.js program. Please take some time to consult the [Implementation considerations section](#implementation-considerations) before using `dns.lookup()`.
Example usage:
```
const dns = require('node:dns');
const options = {
family: 6,
hints: dns.ADDRCONFIG | dns.V4MAPPED,
};
dns.lookup('example.com', options, (err, address, family) =>
console.log('address: %j family: IPv%s', address, family));
// address: "2606:2800:220:1:248:1893:25c8:1946" family: IPv6
// When options.all is true, the result will be an Array.
options.all = true;
dns.lookup('example.com', options, (err, addresses) =>
console.log('addresses: %j', addresses));
// addresses: [{"address":"2606:2800:220:1:248:1893:25c8:1946","family":6}]
```
If this method is invoked as its [`util.promisify()`](util#utilpromisifyoriginal)ed version, and `all` is not set to `true`, it returns a `Promise` for an `Object` with `address` and `family` properties.
#### Supported getaddrinfo flags
History
| Version | Changes |
| --- | --- |
| v13.13.0, v12.17.0 | Added support for the `dns.ALL` flag. |
The following flags can be passed as hints to [`dns.lookup()`](#dnslookuphostname-options-callback).
* `dns.ADDRCONFIG`: Limits returned address types to the types of non-loopback addresses configured on the system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured.
* `dns.V4MAPPED`: If the IPv6 family was specified, but no IPv6 addresses were found, then return IPv4 mapped IPv6 addresses. It is not supported on some operating systems (e.g. FreeBSD 10.1).
* `dns.ALL`: If `dns.V4MAPPED` is specified, return resolved IPv6 addresses as well as IPv4 mapped IPv6 addresses.
###
`dns.lookupService(address, port, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.11.14 | Added in: v0.11.14 |
* `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) e.g. `example.com`
+ `service` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) e.g. `http`
Resolves the given `address` and `port` into a host name and service using the operating system's underlying `getnameinfo` implementation.
If `address` is not a valid IP address, a `TypeError` will be thrown. The `port` will be coerced to a number. If it is not a legal port, a `TypeError` will be thrown.
On an error, `err` is an [`Error`](errors#class-error) object, where `err.code` is the error code.
```
const dns = require('node:dns');
dns.lookupService('127.0.0.1', 22, (err, hostname, service) => {
console.log(hostname, service);
// Prints: localhost ssh
});
```
If this method is invoked as its [`util.promisify()`](util#utilpromisifyoriginal)ed version, it returns a `Promise` for an `Object` with `hostname` and `service` properties.
###
`dns.resolve(hostname[, rrtype], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.1.27 | Added in: v0.1.27 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host name to resolve.
* `rrtype` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Resource record type. **Default:** `'A'`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `records` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Uses the DNS protocol to resolve a host name (e.g. `'nodejs.org'`) into an array of the resource records. The `callback` function has arguments `(err, records)`. When successful, `records` will be an array of resource records. The type and structure of individual results varies based on `rrtype`:
| `rrtype` | `records` contains | Result type | Shorthand method |
| --- | --- | --- | --- |
| `'A'` | IPv4 addresses (default) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dns.resolve4()`](#dnsresolve4hostname-options-callback) |
| `'AAAA'` | IPv6 addresses | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dns.resolve6()`](#dnsresolve6hostname-options-callback) |
| `'ANY'` | any records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dns.resolveAny()`](#dnsresolveanyhostname-callback) |
| `'CAA'` | CA authorization records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dns.resolveCaa()`](#dnsresolvecaahostname-callback) |
| `'CNAME'` | canonical name records | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dns.resolveCname()`](#dnsresolvecnamehostname-callback) |
| `'MX'` | mail exchange records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dns.resolveMx()`](#dnsresolvemxhostname-callback) |
| `'NAPTR'` | name authority pointer records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dns.resolveNaptr()`](#dnsresolvenaptrhostname-callback) |
| `'NS'` | name server records | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dns.resolveNs()`](#dnsresolvenshostname-callback) |
| `'PTR'` | pointer records | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dns.resolvePtr()`](#dnsresolveptrhostname-callback) |
| `'SOA'` | start of authority records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dns.resolveSoa()`](#dnsresolvesoahostname-callback) |
| `'SRV'` | service records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dns.resolveSrv()`](#dnsresolvesrvhostname-callback) |
| `'TXT'` | text records | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dns.resolveTxt()`](#dnsresolvetxthostname-callback) |
On error, `err` is an [`Error`](errors#class-error) object, where `err.code` is one of the [DNS error codes](#error-codes).
###
`dns.resolve4(hostname[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v7.2.0 | This method now supports passing `options`, specifically `options.ttl`. |
| v0.1.16 | Added in: v0.1.16 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host name to resolve.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ttl` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Retrieves the Time-To-Live value (TTL) of each record. When `true`, the callback receives an array of `{ address: '1.2.3.4', ttl: 60 }` objects rather than an array of strings, with the TTL expressed in seconds.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `addresses` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Uses the DNS protocol to resolve a IPv4 addresses (`A` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of IPv4 addresses (e.g. `['74.125.79.104', '74.125.79.105', '74.125.79.106']`).
###
`dns.resolve6(hostname[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v7.2.0 | This method now supports passing `options`, specifically `options.ttl`. |
| v0.1.16 | Added in: v0.1.16 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host name to resolve.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ttl` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Retrieve the Time-To-Live value (TTL) of each record. When `true`, the callback receives an array of `{ address: '0:1:2:3:4:5:6:7', ttl: 60 }` objects rather than an array of strings, with the TTL expressed in seconds.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `addresses` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Uses the DNS protocol to resolve IPv6 addresses (`AAAA` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of IPv6 addresses.
###
`dns.resolveAny(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `ret` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Uses the DNS protocol to resolve all records (also known as `ANY` or `*` query). The `ret` argument passed to the `callback` function will be an array containing various types of records. Each object has a property `type` that indicates the type of the current record. And depending on the `type`, additional properties will be present on the object:
| Type | Properties |
| --- | --- |
| `'A'` | `address`/`ttl` |
| `'AAAA'` | `address`/`ttl` |
| `'CNAME'` | `value` |
| `'MX'` | Refer to [`dns.resolveMx()`](#dnsresolvemxhostname-callback) |
| `'NAPTR'` | Refer to [`dns.resolveNaptr()`](#dnsresolvenaptrhostname-callback) |
| `'NS'` | `value` |
| `'PTR'` | `value` |
| `'SOA'` | Refer to [`dns.resolveSoa()`](#dnsresolvesoahostname-callback) |
| `'SRV'` | Refer to [`dns.resolveSrv()`](#dnsresolvesrvhostname-callback) |
| `'TXT'` | This type of record contains an array property called `entries` which refers to [`dns.resolveTxt()`](#dnsresolvetxthostname-callback), e.g. `{ entries: ['...'], type: 'TXT' }` |
Here is an example of the `ret` object passed to the callback:
```
[ { type: 'A', address: '127.0.0.1', ttl: 299 },
{ type: 'CNAME', value: 'example.com' },
{ type: 'MX', exchange: 'alt4.aspmx.l.example.com', priority: 50 },
{ type: 'NS', value: 'ns1.example.com' },
{ type: 'TXT', entries: [ 'v=spf1 include:_spf.example.com ~all' ] },
{ type: 'SOA',
nsname: 'ns1.example.com',
hostmaster: 'admin.example.com',
serial: 156696742,
refresh: 900,
retry: 900,
expire: 1800,
minttl: 60 } ]
```
DNS server operators may choose not to respond to `ANY` queries. It may be better to call individual methods like [`dns.resolve4()`](#dnsresolve4hostname-options-callback), [`dns.resolveMx()`](#dnsresolvemxhostname-callback), and so on. For more details, see [RFC 8482](https://tools.ietf.org/html/rfc8482).
###
`dns.resolveCname(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.3.2 | Added in: v0.3.2 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `addresses` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve `CNAME` records for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of canonical name records available for the `hostname` (e.g. `['bar.example.com']`).
###
`dns.resolveCaa(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v15.0.0, v14.17.0 | Added in: v15.0.0, v14.17.0 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `records` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Uses the DNS protocol to resolve `CAA` records for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of certification authority authorization records available for the `hostname` (e.g. `[{critical: 0, iodef: 'mailto:[email protected]'}, {critical: 128, issue: 'pki.example.com'}]`).
###
`dns.resolveMx(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.1.27 | Added in: v0.1.27 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `addresses` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Uses the DNS protocol to resolve mail exchange records (`MX` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of objects containing both a `priority` and `exchange` property (e.g. `[{priority: 10, exchange: 'mx.example.com'}, ...]`).
###
`dns.resolveNaptr(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.9.12 | Added in: v0.9.12 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `addresses` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Uses the DNS protocol to resolve regular expression-based records (`NAPTR` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of objects with the following properties:
* `flags`
* `service`
* `regexp`
* `replacement`
* `order`
* `preference`
```
{
flags: 's',
service: 'SIP+D2U',
regexp: '',
replacement: '_sip._udp.example.com',
order: 30,
preference: 100
}
```
###
`dns.resolveNs(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.1.90 | Added in: v0.1.90 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `addresses` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve name server records (`NS` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of name server records available for `hostname` (e.g. `['ns1.example.com', 'ns2.example.com']`).
###
`dns.resolvePtr(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v6.0.0 | Added in: v6.0.0 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `addresses` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve pointer records (`PTR` records) for the `hostname`. The `addresses` argument passed to the `callback` function will be an array of strings containing the reply records.
###
`dns.resolveSoa(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.11.10 | Added in: v0.11.10 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `address` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Uses the DNS protocol to resolve a start of authority record (`SOA` record) for the `hostname`. The `address` argument passed to the `callback` function will be an object with the following properties:
* `nsname`
* `hostmaster`
* `serial`
* `refresh`
* `retry`
* `expire`
* `minttl`
```
{
nsname: 'ns.example.com',
hostmaster: 'root.example.com',
serial: 2013101809,
refresh: 10000,
retry: 2400,
expire: 604800,
minttl: 3600
}
```
###
`dns.resolveSrv(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.1.27 | Added in: v0.1.27 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `addresses` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Uses the DNS protocol to resolve service records (`SRV` records) for the `hostname`. The `addresses` argument passed to the `callback` function will be an array of objects with the following properties:
* `priority`
* `weight`
* `port`
* `name`
```
{
priority: 10,
weight: 5,
port: 21223,
name: 'service.example.com'
}
```
###
`dns.resolveTxt(hostname, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.1.27 | Added in: v0.1.27 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `records` [<string[][]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve text queries (`TXT` records) for the `hostname`. The `records` argument passed to the `callback` function is a two-dimensional array of the text records available for `hostname` (e.g. `[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]`). Each sub-array contains TXT chunks of one record. Depending on the use case, these could be either joined together or treated separately.
###
`dns.reverse(ip, callback)`
Added in: v0.1.16 * `ip` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `hostnames` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an array of host names.
On error, `err` is an [`Error`](errors#class-error) object, where `err.code` is one of the [DNS error codes](#error-codes).
###
`dns.setDefaultResultOrder(order)`
Added in: v16.4.0, v14.18.0 * `order` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) must be `'ipv4first'` or `'verbatim'`.
Set the default value of `verbatim` in [`dns.lookup()`](#dnslookuphostname-options-callback) and [`dnsPromises.lookup()`](#dnspromiseslookuphostname-options). The value could be:
* `ipv4first`: sets default `verbatim` `false`.
* `verbatim`: sets default `verbatim` `true`.
The default is `ipv4first` and [`dns.setDefaultResultOrder()`](#dnssetdefaultresultorderorder) have higher priority than [`--dns-result-order`](cli#--dns-result-orderorder). When using [worker threads](worker_threads), [`dns.setDefaultResultOrder()`](#dnssetdefaultresultorderorder) from the main thread won't affect the default dns orders in workers.
###
`dns.setServers(servers)`
Added in: v0.11.3 * `servers` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) array of [RFC 5952](https://tools.ietf.org/html/rfc5952#section-6) formatted addresses
Sets the IP address and port of servers to be used when performing DNS resolution. The `servers` argument is an array of [RFC 5952](https://tools.ietf.org/html/rfc5952#section-6) formatted addresses. If the port is the IANA default DNS port (53) it can be omitted.
```
dns.setServers([
'4.4.4.4',
'[2001:4860:4860::8888]',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053',
]);
```
An error will be thrown if an invalid address is provided.
The `dns.setServers()` method must not be called while a DNS query is in progress.
The [`dns.setServers()`](#dnssetserversservers) method affects only [`dns.resolve()`](#dnsresolvehostname-rrtype-callback), `dns.resolve*()` and [`dns.reverse()`](#dnsreverseip-callback) (and specifically *not* [`dns.lookup()`](#dnslookuphostname-options-callback)).
This method works much like [resolve.conf](https://man7.org/linux/man-pages/man5/resolv.conf.5.html). That is, if attempting to resolve with the first server provided results in a `NOTFOUND` error, the `resolve()` method will *not* attempt to resolve with subsequent servers provided. Fallback DNS servers will only be used if the earlier ones time out or result in some other error.
### DNS promises API
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Exposed as `require('dns/promises')`. |
| v11.14.0, v10.17.0 | This API is no longer experimental. |
| v10.6.0 | Added in: v10.6.0 |
The `dns.promises` API provides an alternative set of asynchronous DNS methods that return `Promise` objects rather than using callbacks. The API is accessible via `require('node:dns').promises` or `require('node:dns/promises')`.
#### Class: `dnsPromises.Resolver`
Added in: v10.6.0 An independent resolver for DNS requests.
Creating a new resolver uses the default server settings. Setting the servers used for a resolver using [`resolver.setServers()`](#dnspromisessetserversservers) does not affect other resolvers:
```
const { Resolver } = require('node:dns').promises;
const resolver = new Resolver();
resolver.setServers(['4.4.4.4']);
// This request will use the server at 4.4.4.4, independent of global settings.
resolver.resolve4('example.org').then((addresses) => {
// ...
});
// Alternatively, the same code can be written using async-await style.
(async function() {
const addresses = await resolver.resolve4('example.org');
})();
```
The following methods from the `dnsPromises` API are available:
* [`resolver.getServers()`](#dnspromisesgetservers)
* [`resolver.resolve()`](#dnspromisesresolvehostname-rrtype)
* [`resolver.resolve4()`](#dnspromisesresolve4hostname-options)
* [`resolver.resolve6()`](#dnspromisesresolve6hostname-options)
* [`resolver.resolveAny()`](#dnspromisesresolveanyhostname)
* [`resolver.resolveCaa()`](#dnspromisesresolvecaahostname)
* [`resolver.resolveCname()`](#dnspromisesresolvecnamehostname)
* [`resolver.resolveMx()`](#dnspromisesresolvemxhostname)
* [`resolver.resolveNaptr()`](#dnspromisesresolvenaptrhostname)
* [`resolver.resolveNs()`](#dnspromisesresolvenshostname)
* [`resolver.resolvePtr()`](#dnspromisesresolveptrhostname)
* [`resolver.resolveSoa()`](#dnspromisesresolvesoahostname)
* [`resolver.resolveSrv()`](#dnspromisesresolvesrvhostname)
* [`resolver.resolveTxt()`](#dnspromisesresolvetxthostname)
* [`resolver.reverse()`](#dnspromisesreverseip)
* [`resolver.setServers()`](#dnspromisessetserversservers)
####
`resolver.cancel()`
Added in: v15.3.0, v14.17.0 Cancel all outstanding DNS queries made by this resolver. The corresponding promises will be rejected with an error with the code `ECANCELLED`.
####
`dnsPromises.getServers()`
Added in: v10.6.0 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns an array of IP address strings, formatted according to [RFC 5952](https://tools.ietf.org/html/rfc5952#section-6), that are currently configured for DNS resolution. A string will include a port section if a custom port is used.
```
[
'4.4.4.4',
'2001:4860:4860::8888',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053',
]
```
####
`dnsPromises.lookup(hostname[, options])`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `family` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The record family. Must be `4`, `6`, or `0`. The value `0` indicates that IPv4 and IPv6 addresses are both returned. **Default:** `0`.
+ `hints` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) One or more [supported `getaddrinfo` flags](#supported-getaddrinfo-flags). Multiple flags may be passed by bitwise `OR`ing their values.
+ `all` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the `Promise` is resolved with all addresses in an array. Otherwise, returns a single address. **Default:** `false`.
+ `verbatim` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the `Promise` is resolved with IPv4 and IPv6 addresses in the order the DNS resolver returned them. When `false`, IPv4 addresses are placed before IPv6 addresses. **Default:** currently `false` (addresses are reordered) but this is expected to change in the not too distant future. Default value is configurable using [`dns.setDefaultResultOrder()`](#dnssetdefaultresultorderorder) or [`--dns-result-order`](cli#--dns-result-orderorder). New code should use `{ verbatim: true }`.
Resolves a host name (e.g. `'nodejs.org'`) into the first found A (IPv4) or AAAA (IPv6) record. All `option` properties are optional. If `options` is an integer, then it must be `4` or `6` – if `options` is not provided, then IPv4 and IPv6 addresses are both returned if found.
With the `all` option set to `true`, the `Promise` is resolved with `addresses` being an array of objects with the properties `address` and `family`.
On error, the `Promise` is rejected with an [`Error`](errors#class-error) object, where `err.code` is the error code. Keep in mind that `err.code` will be set to `'ENOTFOUND'` not only when the host name does not exist but also when the lookup fails in other ways such as no available file descriptors.
[`dnsPromises.lookup()`](#dnspromiseslookuphostname-options) does not necessarily have anything to do with the DNS protocol. The implementation uses an operating system facility that can associate names with addresses and vice versa. This implementation can have subtle but important consequences on the behavior of any Node.js program. Please take some time to consult the [Implementation considerations section](#implementation-considerations) before using `dnsPromises.lookup()`.
Example usage:
```
const dns = require('node:dns');
const dnsPromises = dns.promises;
const options = {
family: 6,
hints: dns.ADDRCONFIG | dns.V4MAPPED,
};
dnsPromises.lookup('example.com', options).then((result) => {
console.log('address: %j family: IPv%s', result.address, result.family);
// address: "2606:2800:220:1:248:1893:25c8:1946" family: IPv6
});
// When options.all is true, the result will be an Array.
options.all = true;
dnsPromises.lookup('example.com', options).then((result) => {
console.log('addresses: %j', result);
// addresses: [{"address":"2606:2800:220:1:248:1893:25c8:1946","family":6}]
});
```
####
`dnsPromises.lookupService(address, port)`
Added in: v10.6.0 * `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Resolves the given `address` and `port` into a host name and service using the operating system's underlying `getnameinfo` implementation.
If `address` is not a valid IP address, a `TypeError` will be thrown. The `port` will be coerced to a number. If it is not a legal port, a `TypeError` will be thrown.
On error, the `Promise` is rejected with an [`Error`](errors#class-error) object, where `err.code` is the error code.
```
const dnsPromises = require('node:dns').promises;
dnsPromises.lookupService('127.0.0.1', 22).then((result) => {
console.log(result.hostname, result.service);
// Prints: localhost ssh
});
```
####
`dnsPromises.resolve(hostname[, rrtype])`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host name to resolve.
* `rrtype` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Resource record type. **Default:** `'A'`.
Uses the DNS protocol to resolve a host name (e.g. `'nodejs.org'`) into an array of the resource records. When successful, the `Promise` is resolved with an array of resource records. The type and structure of individual results vary based on `rrtype`:
| `rrtype` | `records` contains | Result type | Shorthand method |
| --- | --- | --- | --- |
| `'A'` | IPv4 addresses (default) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dnsPromises.resolve4()`](#dnspromisesresolve4hostname-options) |
| `'AAAA'` | IPv6 addresses | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dnsPromises.resolve6()`](#dnspromisesresolve6hostname-options) |
| `'ANY'` | any records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dnsPromises.resolveAny()`](#dnspromisesresolveanyhostname) |
| `'CAA'` | CA authorization records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dnsPromises.resolveCaa()`](#dnspromisesresolvecaahostname) |
| `'CNAME'` | canonical name records | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dnsPromises.resolveCname()`](#dnspromisesresolvecnamehostname) |
| `'MX'` | mail exchange records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dnsPromises.resolveMx()`](#dnspromisesresolvemxhostname) |
| `'NAPTR'` | name authority pointer records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dnsPromises.resolveNaptr()`](#dnspromisesresolvenaptrhostname) |
| `'NS'` | name server records | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dnsPromises.resolveNs()`](#dnspromisesresolvenshostname) |
| `'PTR'` | pointer records | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dnsPromises.resolvePtr()`](#dnspromisesresolveptrhostname) |
| `'SOA'` | start of authority records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dnsPromises.resolveSoa()`](#dnspromisesresolvesoahostname) |
| `'SRV'` | service records | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [`dnsPromises.resolveSrv()`](#dnspromisesresolvesrvhostname) |
| `'TXT'` | text records | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [`dnsPromises.resolveTxt()`](#dnspromisesresolvetxthostname) |
On error, the `Promise` is rejected with an [`Error`](errors#class-error) object, where `err.code` is one of the [DNS error codes](#error-codes).
####
`dnsPromises.resolve4(hostname[, options])`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host name to resolve.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ttl` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Retrieve the Time-To-Live value (TTL) of each record. When `true`, the `Promise` is resolved with an array of `{ address: '1.2.3.4', ttl: 60 }` objects rather than an array of strings, with the TTL expressed in seconds.
Uses the DNS protocol to resolve IPv4 addresses (`A` records) for the `hostname`. On success, the `Promise` is resolved with an array of IPv4 addresses (e.g. `['74.125.79.104', '74.125.79.105', '74.125.79.106']`).
####
`dnsPromises.resolve6(hostname[, options])`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host name to resolve.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ttl` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Retrieve the Time-To-Live value (TTL) of each record. When `true`, the `Promise` is resolved with an array of `{ address: '0:1:2:3:4:5:6:7', ttl: 60 }` objects rather than an array of strings, with the TTL expressed in seconds.
Uses the DNS protocol to resolve IPv6 addresses (`AAAA` records) for the `hostname`. On success, the `Promise` is resolved with an array of IPv6 addresses.
####
`dnsPromises.resolveAny(hostname)`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve all records (also known as `ANY` or `*` query). On success, the `Promise` is resolved with an array containing various types of records. Each object has a property `type` that indicates the type of the current record. And depending on the `type`, additional properties will be present on the object:
| Type | Properties |
| --- | --- |
| `'A'` | `address`/`ttl` |
| `'AAAA'` | `address`/`ttl` |
| `'CNAME'` | `value` |
| `'MX'` | Refer to [`dnsPromises.resolveMx()`](#dnspromisesresolvemxhostname) |
| `'NAPTR'` | Refer to [`dnsPromises.resolveNaptr()`](#dnspromisesresolvenaptrhostname) |
| `'NS'` | `value` |
| `'PTR'` | `value` |
| `'SOA'` | Refer to [`dnsPromises.resolveSoa()`](#dnspromisesresolvesoahostname) |
| `'SRV'` | Refer to [`dnsPromises.resolveSrv()`](#dnspromisesresolvesrvhostname) |
| `'TXT'` | This type of record contains an array property called `entries` which refers to [`dnsPromises.resolveTxt()`](#dnspromisesresolvetxthostname), e.g. `{ entries: ['...'], type: 'TXT' }` |
Here is an example of the result object:
```
[ { type: 'A', address: '127.0.0.1', ttl: 299 },
{ type: 'CNAME', value: 'example.com' },
{ type: 'MX', exchange: 'alt4.aspmx.l.example.com', priority: 50 },
{ type: 'NS', value: 'ns1.example.com' },
{ type: 'TXT', entries: [ 'v=spf1 include:_spf.example.com ~all' ] },
{ type: 'SOA',
nsname: 'ns1.example.com',
hostmaster: 'admin.example.com',
serial: 156696742,
refresh: 900,
retry: 900,
expire: 1800,
minttl: 60 } ]
```
####
`dnsPromises.resolveCaa(hostname)`
Added in: v15.0.0, v14.17.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve `CAA` records for the `hostname`. On success, the `Promise` is resolved with an array of objects containing available certification authority authorization records available for the `hostname` (e.g. `[{critical: 0, iodef: 'mailto:[email protected]'},{critical: 128, issue: 'pki.example.com'}]`).
####
`dnsPromises.resolveCname(hostname)`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve `CNAME` records for the `hostname`. On success, the `Promise` is resolved with an array of canonical name records available for the `hostname` (e.g. `['bar.example.com']`).
####
`dnsPromises.resolveMx(hostname)`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve mail exchange records (`MX` records) for the `hostname`. On success, the `Promise` is resolved with an array of objects containing both a `priority` and `exchange` property (e.g. `[{priority: 10, exchange: 'mx.example.com'}, ...]`).
####
`dnsPromises.resolveNaptr(hostname)`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve regular expression-based records (`NAPTR` records) for the `hostname`. On success, the `Promise` is resolved with an array of objects with the following properties:
* `flags`
* `service`
* `regexp`
* `replacement`
* `order`
* `preference`
```
{
flags: 's',
service: 'SIP+D2U',
regexp: '',
replacement: '_sip._udp.example.com',
order: 30,
preference: 100
}
```
####
`dnsPromises.resolveNs(hostname)`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve name server records (`NS` records) for the `hostname`. On success, the `Promise` is resolved with an array of name server records available for `hostname` (e.g. `['ns1.example.com', 'ns2.example.com']`).
####
`dnsPromises.resolvePtr(hostname)`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve pointer records (`PTR` records) for the `hostname`. On success, the `Promise` is resolved with an array of strings containing the reply records.
####
`dnsPromises.resolveSoa(hostname)`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve a start of authority record (`SOA` record) for the `hostname`. On success, the `Promise` is resolved with an object with the following properties:
* `nsname`
* `hostmaster`
* `serial`
* `refresh`
* `retry`
* `expire`
* `minttl`
```
{
nsname: 'ns.example.com',
hostmaster: 'root.example.com',
serial: 2013101809,
refresh: 10000,
retry: 2400,
expire: 604800,
minttl: 3600
}
```
####
`dnsPromises.resolveSrv(hostname)`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve service records (`SRV` records) for the `hostname`. On success, the `Promise` is resolved with an array of objects with the following properties:
* `priority`
* `weight`
* `port`
* `name`
```
{
priority: 10,
weight: 5,
port: 21223,
name: 'service.example.com'
}
```
####
`dnsPromises.resolveTxt(hostname)`
Added in: v10.6.0 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Uses the DNS protocol to resolve text queries (`TXT` records) for the `hostname`. On success, the `Promise` is resolved with a two-dimensional array of the text records available for `hostname` (e.g. `[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]`). Each sub-array contains TXT chunks of one record. Depending on the use case, these could be either joined together or treated separately.
####
`dnsPromises.reverse(ip)`
Added in: v10.6.0 * `ip` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an array of host names.
On error, the `Promise` is rejected with an [`Error`](errors#class-error) object, where `err.code` is one of the [DNS error codes](#error-codes).
####
`dnsPromises.setDefaultResultOrder(order)`
Added in: v16.4.0, v14.18.0 * `order` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) must be `'ipv4first'` or `'verbatim'`.
Set the default value of `verbatim` in [`dns.lookup()`](#dnslookuphostname-options-callback) and [`dnsPromises.lookup()`](#dnspromiseslookuphostname-options). The value could be:
* `ipv4first`: sets default `verbatim` `false`.
* `verbatim`: sets default `verbatim` `true`.
The default is `ipv4first` and [`dnsPromises.setDefaultResultOrder()`](#dnspromisessetdefaultresultorderorder) have higher priority than [`--dns-result-order`](cli#--dns-result-orderorder). When using [worker threads](worker_threads), [`dnsPromises.setDefaultResultOrder()`](#dnspromisessetdefaultresultorderorder) from the main thread won't affect the default dns orders in workers.
####
`dnsPromises.setServers(servers)`
Added in: v10.6.0 * `servers` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) array of [RFC 5952](https://tools.ietf.org/html/rfc5952#section-6) formatted addresses
Sets the IP address and port of servers to be used when performing DNS resolution. The `servers` argument is an array of [RFC 5952](https://tools.ietf.org/html/rfc5952#section-6) formatted addresses. If the port is the IANA default DNS port (53) it can be omitted.
```
dnsPromises.setServers([
'4.4.4.4',
'[2001:4860:4860::8888]',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053',
]);
```
An error will be thrown if an invalid address is provided.
The `dnsPromises.setServers()` method must not be called while a DNS query is in progress.
This method works much like [resolve.conf](https://man7.org/linux/man-pages/man5/resolv.conf.5.html). That is, if attempting to resolve with the first server provided results in a `NOTFOUND` error, the `resolve()` method will *not* attempt to resolve with subsequent servers provided. Fallback DNS servers will only be used if the earlier ones time out or result in some other error.
### Error codes
Each DNS query can return one of the following error codes:
* `dns.NODATA`: DNS server returned an answer with no data.
* `dns.FORMERR`: DNS server claims query was misformatted.
* `dns.SERVFAIL`: DNS server returned general failure.
* `dns.NOTFOUND`: Domain name not found.
* `dns.NOTIMP`: DNS server does not implement the requested operation.
* `dns.REFUSED`: DNS server refused query.
* `dns.BADQUERY`: Misformatted DNS query.
* `dns.BADNAME`: Misformatted host name.
* `dns.BADFAMILY`: Unsupported address family.
* `dns.BADRESP`: Misformatted DNS reply.
* `dns.CONNREFUSED`: Could not contact DNS servers.
* `dns.TIMEOUT`: Timeout while contacting DNS servers.
* `dns.EOF`: End of file.
* `dns.FILE`: Error reading file.
* `dns.NOMEM`: Out of memory.
* `dns.DESTRUCTION`: Channel is being destroyed.
* `dns.BADSTR`: Misformatted string.
* `dns.BADFLAGS`: Illegal flags specified.
* `dns.NONAME`: Given host name is not numeric.
* `dns.BADHINTS`: Illegal hints flags specified.
* `dns.NOTINITIALIZED`: c-ares library initialization not yet performed.
* `dns.LOADIPHLPAPI`: Error loading `iphlpapi.dll`.
* `dns.ADDRGETNETWORKPARAMS`: Could not find `GetNetworkParams` function.
* `dns.CANCELLED`: DNS query cancelled.
The `dnsPromises` API also exports the above error codes, e.g., `dnsPromises.NODATA`.
### Implementation considerations
Although [`dns.lookup()`](#dnslookuphostname-options-callback) and the various `dns.resolve*()/dns.reverse()` functions have the same goal of associating a network name with a network address (or vice versa), their behavior is quite different. These differences can have subtle but significant consequences on the behavior of Node.js programs.
####
`dns.lookup()`
Under the hood, [`dns.lookup()`](#dnslookuphostname-options-callback) uses the same operating system facilities as most other programs. For instance, [`dns.lookup()`](#dnslookuphostname-options-callback) will almost always resolve a given name the same way as the `ping` command. On most POSIX-like operating systems, the behavior of the [`dns.lookup()`](#dnslookuphostname-options-callback) function can be modified by changing settings in [`nsswitch.conf(5)`](http://man7.org/linux/man-pages/man5/nsswitch.conf.5.html) and/or [`resolv.conf(5)`](http://man7.org/linux/man-pages/man5/resolv.conf.5.html), but changing these files will change the behavior of all other programs running on the same operating system.
Though the call to `dns.lookup()` will be asynchronous from JavaScript's perspective, it is implemented as a synchronous call to [`getaddrinfo(3)`](http://man7.org/linux/man-pages/man3/getaddrinfo.3.html) that runs on libuv's threadpool. This can have surprising negative performance implications for some applications, see the [`UV_THREADPOOL_SIZE`](cli#uv_threadpool_sizesize) documentation for more information.
Various networking APIs will call `dns.lookup()` internally to resolve host names. If that is an issue, consider resolving the host name to an address using `dns.resolve()` and using the address instead of a host name. Also, some networking APIs (such as [`socket.connect()`](net#socketconnectoptions-connectlistener) and [`dgram.createSocket()`](dgram#dgramcreatesocketoptions-callback)) allow the default resolver, `dns.lookup()`, to be replaced.
####
`dns.resolve()`, `dns.resolve*()`, and `dns.reverse()`
These functions are implemented quite differently than [`dns.lookup()`](#dnslookuphostname-options-callback). They do not use [`getaddrinfo(3)`](http://man7.org/linux/man-pages/man3/getaddrinfo.3.html) and they *always* perform a DNS query on the network. This network communication is always done asynchronously and does not use libuv's threadpool.
As a result, these functions cannot have the same negative impact on other processing that happens on libuv's threadpool that [`dns.lookup()`](#dnslookuphostname-options-callback) can have.
They do not use the same set of configuration files that [`dns.lookup()`](#dnslookuphostname-options-callback) uses. For instance, they do not use the configuration from `/etc/hosts`.
| programming_docs |
node None VM (executing JavaScript)
-------------------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/vm.js](https://github.com/nodejs/node/blob/v19.0.1/lib/vm.js)
The `node:vm` module enables compiling and running code within V8 Virtual Machine contexts.
**The `node:vm` module is not a security mechanism. Do not use it to run untrusted code.**
JavaScript code can be compiled and run immediately or compiled, saved, and run later.
A common use case is to run the code in a different V8 Context. This means invoked code has a different global object than the invoking code.
One can provide the context by [*contextifying*](#what-does-it-mean-to-contextify-an-object) an object. The invoked code treats any property in the context like a global variable. Any changes to global variables caused by the invoked code are reflected in the context object.
```
const vm = require('node:vm');
const x = 1;
const context = { x: 2 };
vm.createContext(context); // Contextify the object.
const code = 'x += 40; var y = 17;';
// `x` and `y` are global variables in the context.
// Initially, x has the value 2 because that is the value of context.x.
vm.runInContext(code, context);
console.log(context.x); // 42
console.log(context.y); // 17
console.log(x); // 1; y is not defined.
```
### Class: `vm.Script`
Added in: v0.3.1 Instances of the `vm.Script` class contain precompiled scripts that can be executed in specific contexts.
####
`new vm.Script(code[, options])`
History
| Version | Changes |
| --- | --- |
| v17.0.0, v16.12.0 | Added support for import assertions to the `importModuleDynamically` parameter. |
| v10.6.0 | The `produceCachedData` is deprecated in favour of `script.createCachedData()`. |
| v5.7.0 | The `cachedData` and `produceCachedData` options are supported now. |
| v0.3.1 | Added in: v0.3.1 |
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The JavaScript code to compile.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specifies the filename used in stack traces produced by this script. **Default:** `'evalmachine.<anonymous>'`.
+ `lineOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the line number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `columnOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the first-line column number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `cachedData` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Provides an optional `Buffer` or `TypedArray`, or `DataView` with V8's code cache data for the supplied source. When supplied, the `cachedDataRejected` value will be set to either `true` or `false` depending on acceptance of the data by V8.
+ `produceCachedData` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true` and no `cachedData` is present, V8 will attempt to produce code cache data for `code`. Upon success, a `Buffer` with V8's code cache data will be produced and stored in the `cachedData` property of the returned `vm.Script` instance. The `cachedDataProduced` value will be set to either `true` or `false` depending on whether code cache data is produced successfully. This option is **deprecated** in favor of `script.createCachedData()`. **Default:** `false`.
+ `importModuleDynamically` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called during evaluation of this module when `import()` is called. If this option is not specified, calls to `import()` will reject with [`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`](errors#err_vm_dynamic_import_callback_missing). This option is part of the experimental modules API. We do not recommend using it in a production environment.
- `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) specifier passed to `import()`
- `script` [<vm.Script>](vm#class-vmscript)
- `importAssertions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The `"assert"` value passed to the [`optionsExpression`](https://tc39.es/proposal-import-assertions/#sec-evaluate-import-call) optional parameter, or an empty object if no value was provided.
- Returns: [<Module Namespace Object>](https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects) | [<vm.Module>](vm#class-vmmodule) Returning a `vm.Module` is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain `then` function exports.
If `options` is a string, then it specifies the filename.
Creating a new `vm.Script` object compiles `code` but does not run it. The compiled `vm.Script` can be run later multiple times. The `code` is not bound to any global object; rather, it is bound before each run, just for that run.
####
`script.cachedDataRejected`
Added in: v5.7.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
When `cachedData` is supplied to create the `vm.Script`, this value will be set to either `true` or `false` depending on acceptance of the data by V8. Otherwise the value is `undefined`.
####
`script.createCachedData()`
Added in: v10.6.0 * Returns: [<Buffer>](buffer#class-buffer)
Creates a code cache that can be used with the `Script` constructor's `cachedData` option. Returns a `Buffer`. This method may be called at any time and any number of times.
The code cache of the `Script` doesn't contain any JavaScript observable states. The code cache is safe to be saved along side the script source and used to construct new `Script` instances multiple times.
Functions in the `Script` source can be marked as lazily compiled and they are not compiled at construction of the `Script`. These functions are going to be compiled when they are invoked the first time. The code cache serializes the metadata that V8 currently knows about the `Script` that it can use to speed up future compilations.
```
const script = new vm.Script(`
function add(a, b) {
return a + b;
}
const x = add(1, 2);
`);
const cacheWithoutAdd = script.createCachedData();
// In `cacheWithoutAdd` the function `add()` is marked for full compilation
// upon invocation.
script.runInThisContext();
const cacheWithAdd = script.createCachedData();
// `cacheWithAdd` contains fully compiled function `add()`.
```
####
`script.runInContext(contextifiedObject[, options])`
History
| Version | Changes |
| --- | --- |
| v6.3.0 | The `breakOnSigint` option is supported now. |
| v0.3.1 | Added in: v0.3.1 |
* `contextifiedObject` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A [contextified](#what-does-it-mean-to-contextify-an-object) object as returned by the `vm.createContext()` method.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `displayErrors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, if an [`Error`](errors#class-error) occurs while compiling the `code`, the line of code causing the error is attached to the stack trace. **Default:** `true`.
+ `timeout` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the number of milliseconds to execute `code` before terminating execution. If execution is terminated, an [`Error`](errors#class-error) will be thrown. This value must be a strictly positive integer.
+ `breakOnSigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, receiving `SIGINT` (`Ctrl`+`C`) will terminate execution and throw an [`Error`](errors#class-error). Existing handlers for the event that have been attached via `process.on('SIGINT')` are disabled during script execution, but continue to work after that. **Default:** `false`.
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the result of the very last statement executed in the script.
Runs the compiled code contained by the `vm.Script` object within the given `contextifiedObject` and returns the result. Running code does not have access to local scope.
The following example compiles code that increments a global variable, sets the value of another global variable, then execute the code multiple times. The globals are contained in the `context` object.
```
const vm = require('node:vm');
const context = {
animal: 'cat',
count: 2
};
const script = new vm.Script('count += 1; name = "kitty";');
vm.createContext(context);
for (let i = 0; i < 10; ++i) {
script.runInContext(context);
}
console.log(context);
// Prints: { animal: 'cat', count: 12, name: 'kitty' }
```
Using the `timeout` or `breakOnSigint` options will result in new event loops and corresponding threads being started, which have a non-zero performance overhead.
####
`script.runInNewContext([contextObject[, options]])`
History
| Version | Changes |
| --- | --- |
| v14.6.0 | The `microtaskMode` option is supported now. |
| v10.0.0 | The `contextCodeGeneration` option is supported now. |
| v6.3.0 | The `breakOnSigint` option is supported now. |
| v0.3.1 | Added in: v0.3.1 |
* `contextObject` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object that will be [contextified](#what-does-it-mean-to-contextify-an-object). If `undefined`, a new object will be created.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `displayErrors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, if an [`Error`](errors#class-error) occurs while compiling the `code`, the line of code causing the error is attached to the stack trace. **Default:** `true`.
+ `timeout` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the number of milliseconds to execute `code` before terminating execution. If execution is terminated, an [`Error`](errors#class-error) will be thrown. This value must be a strictly positive integer.
+ `breakOnSigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, receiving `SIGINT` (`Ctrl`+`C`) will terminate execution and throw an [`Error`](errors#class-error). Existing handlers for the event that have been attached via `process.on('SIGINT')` are disabled during script execution, but continue to work after that. **Default:** `false`.
+ `contextName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Human-readable name of the newly created context. **Default:** `'VM Context i'`, where `i` is an ascending numerical index of the created context.
+ `contextOrigin` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) [Origin](https://developer.mozilla.org/en-US/docs/Glossary/Origin) corresponding to the newly created context for display purposes. The origin should be formatted like a URL, but with only the scheme, host, and port (if necessary), like the value of the [`url.origin`](url#urlorigin) property of a [`URL`](url#class-url) object. Most notably, this string should omit the trailing slash, as that denotes a path. **Default:** `''`.
+ `contextCodeGeneration` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `strings` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to false any calls to `eval` or function constructors (`Function`, `GeneratorFunction`, etc) will throw an `EvalError`. **Default:** `true`.
- `wasm` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to false any attempt to compile a WebAssembly module will throw a `WebAssembly.CompileError`. **Default:** `true`.
+ `microtaskMode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If set to `afterEvaluate`, microtasks (tasks scheduled through `Promise`s and `async function`s) will be run immediately after the script has run. They are included in the `timeout` and `breakOnSigint` scopes in that case.
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the result of the very last statement executed in the script.
First contextifies the given `contextObject`, runs the compiled code contained by the `vm.Script` object within the created context, and returns the result. Running code does not have access to local scope.
The following example compiles code that sets a global variable, then executes the code multiple times in different contexts. The globals are set on and contained within each individual `context`.
```
const vm = require('node:vm');
const script = new vm.Script('globalVar = "set"');
const contexts = [{}, {}, {}];
contexts.forEach((context) => {
script.runInNewContext(context);
});
console.log(contexts);
// Prints: [{ globalVar: 'set' }, { globalVar: 'set' }, { globalVar: 'set' }]
```
####
`script.runInThisContext([options])`
History
| Version | Changes |
| --- | --- |
| v6.3.0 | The `breakOnSigint` option is supported now. |
| v0.3.1 | Added in: v0.3.1 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `displayErrors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, if an [`Error`](errors#class-error) occurs while compiling the `code`, the line of code causing the error is attached to the stack trace. **Default:** `true`.
+ `timeout` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the number of milliseconds to execute `code` before terminating execution. If execution is terminated, an [`Error`](errors#class-error) will be thrown. This value must be a strictly positive integer.
+ `breakOnSigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, receiving `SIGINT` (`Ctrl`+`C`) will terminate execution and throw an [`Error`](errors#class-error). Existing handlers for the event that have been attached via `process.on('SIGINT')` are disabled during script execution, but continue to work after that. **Default:** `false`.
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the result of the very last statement executed in the script.
Runs the compiled code contained by the `vm.Script` within the context of the current `global` object. Running code does not have access to local scope, but *does* have access to the current `global` object.
The following example compiles code that increments a `global` variable then executes that code multiple times:
```
const vm = require('node:vm');
global.globalVar = 0;
const script = new vm.Script('globalVar += 1', { filename: 'myfile.vm' });
for (let i = 0; i < 1000; ++i) {
script.runInThisContext();
}
console.log(globalVar);
// 1000
```
### Class: `vm.Module`
Added in: v13.0.0, v12.16.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
This feature is only available with the `--experimental-vm-modules` command flag enabled.
The `vm.Module` class provides a low-level interface for using ECMAScript modules in VM contexts. It is the counterpart of the `vm.Script` class that closely mirrors [Module Record](https://www.ecma-international.org/ecma-262/#sec-abstract-module-records)s as defined in the ECMAScript specification.
Unlike `vm.Script` however, every `vm.Module` object is bound to a context from its creation. Operations on `vm.Module` objects are intrinsically asynchronous, in contrast with the synchronous nature of `vm.Script` objects. The use of 'async' functions can help with manipulating `vm.Module` objects.
Using a `vm.Module` object requires three distinct steps: creation/parsing, linking, and evaluation. These three steps are illustrated in the following example.
This implementation lies at a lower level than the [ECMAScript Module loader](esm#modules-ecmascript-modules). There is also no way to interact with the Loader yet, though support is planned.
MJS modules
```
import vm from 'node:vm';
const contextifiedObject = vm.createContext({
secret: 42,
print: console.log,
});
// Step 1
//
// Create a Module by constructing a new `vm.SourceTextModule` object. This
// parses the provided source text, throwing a `SyntaxError` if anything goes
// wrong. By default, a Module is created in the top context. But here, we
// specify `contextifiedObject` as the context this Module belongs to.
//
// Here, we attempt to obtain the default export from the module "foo", and
// put it into local binding "secret".
const bar = new vm.SourceTextModule(`
import s from 'foo';
s;
print(s);
`, { context: contextifiedObject });
// Step 2
//
// "Link" the imported dependencies of this Module to it.
//
// The provided linking callback (the "linker") accepts two arguments: the
// parent module (`bar` in this case) and the string that is the specifier of
// the imported module. The callback is expected to return a Module that
// corresponds to the provided specifier, with certain requirements documented
// in `module.link()`.
//
// If linking has not started for the returned Module, the same linker
// callback will be called on the returned Module.
//
// Even top-level Modules without dependencies must be explicitly linked. The
// callback provided would never be called, however.
//
// The link() method returns a Promise that will be resolved when all the
// Promises returned by the linker resolve.
//
// Note: This is a contrived example in that the linker function creates a new
// "foo" module every time it is called. In a full-fledged module system, a
// cache would probably be used to avoid duplicated modules.
async function linker(specifier, referencingModule) {
if (specifier === 'foo') {
return new vm.SourceTextModule(`
// The "secret" variable refers to the global variable we added to
// "contextifiedObject" when creating the context.
export default secret;
`, { context: referencingModule.context });
// Using `contextifiedObject` instead of `referencingModule.context`
// here would work as well.
}
throw new Error(`Unable to resolve dependency: ${specifier}`);
}
await bar.link(linker);
// Step 3
//
// Evaluate the Module. The evaluate() method returns a promise which will
// resolve after the module has finished evaluating.
// Prints 42.
await bar.evaluate();
```
CJS modules
```
const vm = require('node:vm');
const contextifiedObject = vm.createContext({
secret: 42,
print: console.log,
});
(async () => {
// Step 1
//
// Create a Module by constructing a new `vm.SourceTextModule` object. This
// parses the provided source text, throwing a `SyntaxError` if anything goes
// wrong. By default, a Module is created in the top context. But here, we
// specify `contextifiedObject` as the context this Module belongs to.
//
// Here, we attempt to obtain the default export from the module "foo", and
// put it into local binding "secret".
const bar = new vm.SourceTextModule(`
import s from 'foo';
s;
print(s);
`, { context: contextifiedObject });
// Step 2
//
// "Link" the imported dependencies of this Module to it.
//
// The provided linking callback (the "linker") accepts two arguments: the
// parent module (`bar` in this case) and the string that is the specifier of
// the imported module. The callback is expected to return a Module that
// corresponds to the provided specifier, with certain requirements documented
// in `module.link()`.
//
// If linking has not started for the returned Module, the same linker
// callback will be called on the returned Module.
//
// Even top-level Modules without dependencies must be explicitly linked. The
// callback provided would never be called, however.
//
// The link() method returns a Promise that will be resolved when all the
// Promises returned by the linker resolve.
//
// Note: This is a contrived example in that the linker function creates a new
// "foo" module every time it is called. In a full-fledged module system, a
// cache would probably be used to avoid duplicated modules.
async function linker(specifier, referencingModule) {
if (specifier === 'foo') {
return new vm.SourceTextModule(`
// The "secret" variable refers to the global variable we added to
// "contextifiedObject" when creating the context.
export default secret;
`, { context: referencingModule.context });
// Using `contextifiedObject` instead of `referencingModule.context`
// here would work as well.
}
throw new Error(`Unable to resolve dependency: ${specifier}`);
}
await bar.link(linker);
// Step 3
//
// Evaluate the Module. The evaluate() method returns a promise which will
// resolve after the module has finished evaluating.
// Prints 42.
await bar.evaluate();
})();
```
####
`module.dependencySpecifiers`
* [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The specifiers of all dependencies of this module. The returned array is frozen to disallow any changes to it.
Corresponds to the `[[RequestedModules]]` field of [Cyclic Module Record](https://tc39.es/ecma262/#sec-cyclic-module-records)s in the ECMAScript specification.
####
`module.error`
* [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
If the `module.status` is `'errored'`, this property contains the exception thrown by the module during evaluation. If the status is anything else, accessing this property will result in a thrown exception.
The value `undefined` cannot be used for cases where there is not a thrown exception due to possible ambiguity with `throw undefined;`.
Corresponds to the `[[EvaluationError]]` field of [Cyclic Module Record](https://tc39.es/ecma262/#sec-cyclic-module-records)s in the ECMAScript specification.
####
`module.evaluate([options])`
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `timeout` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the number of milliseconds to evaluate before terminating execution. If execution is interrupted, an [`Error`](errors#class-error) will be thrown. This value must be a strictly positive integer.
+ `breakOnSigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, receiving `SIGINT` (`Ctrl`+`C`) will terminate execution and throw an [`Error`](errors#class-error). Existing handlers for the event that have been attached via `process.on('SIGINT')` are disabled during script execution, but continue to work after that. **Default:** `false`.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) Fulfills with `undefined` upon success.
Evaluate the module.
This must be called after the module has been linked; otherwise it will reject. It could be called also when the module has already been evaluated, in which case it will either do nothing if the initial evaluation ended in success (`module.status` is `'evaluated'`) or it will re-throw the exception that the initial evaluation resulted in (`module.status` is `'errored'`).
This method cannot be called while the module is being evaluated (`module.status` is `'evaluating'`).
Corresponds to the [Evaluate() concrete method](https://tc39.es/ecma262/#sec-moduleevaluation) field of [Cyclic Module Record](https://tc39.es/ecma262/#sec-cyclic-module-records)s in the ECMAScript specification.
####
`module.identifier`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The identifier of the current module, as set in the constructor.
####
`module.link(linker)`
* `linker` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The specifier of the requested module:
```
import foo from 'foo';
// ^^^^^ the module specifier
```
+ `referencingModule` [<vm.Module>](vm#class-vmmodule) The `Module` object `link()` is called on.
+ `extra` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `assert` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The data from the assertion:
```
import foo from 'foo' assert { name: 'value' };
// ^^^^^^^^^^^^^^^^^ the assertion
```
Per ECMA-262, hosts are expected to ignore assertions that they do not support, as opposed to, for example, triggering an error if an unsupported assertion is present.
+ Returns: [<vm.Module>](vm#class-vmmodule) | [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Link module dependencies. This method must be called before evaluation, and can only be called once per module.
The function is expected to return a `Module` object or a `Promise` that eventually resolves to a `Module` object. The returned `Module` must satisfy the following two invariants:
* It must belong to the same context as the parent `Module`.
* Its `status` must not be `'errored'`.
If the returned `Module`'s `status` is `'unlinked'`, this method will be recursively called on the returned `Module` with the same provided `linker` function.
`link()` returns a `Promise` that will either get resolved when all linking instances resolve to a valid `Module`, or rejected if the linker function either throws an exception or returns an invalid `Module`.
The linker function roughly corresponds to the implementation-defined [HostResolveImportedModule](https://tc39.es/ecma262/#sec-hostresolveimportedmodule) abstract operation in the ECMAScript specification, with a few key differences:
* The linker function is allowed to be asynchronous while [HostResolveImportedModule](https://tc39.es/ecma262/#sec-hostresolveimportedmodule) is synchronous.
The actual [HostResolveImportedModule](https://tc39.es/ecma262/#sec-hostresolveimportedmodule) implementation used during module linking is one that returns the modules linked during linking. Since at that point all modules would have been fully linked already, the [HostResolveImportedModule](https://tc39.es/ecma262/#sec-hostresolveimportedmodule) implementation is fully synchronous per specification.
Corresponds to the [Link() concrete method](https://tc39.es/ecma262/#sec-moduledeclarationlinking) field of [Cyclic Module Record](https://tc39.es/ecma262/#sec-cyclic-module-records)s in the ECMAScript specification.
####
`module.namespace`
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The namespace object of the module. This is only available after linking (`module.link()`) has completed.
Corresponds to the [GetModuleNamespace](https://tc39.es/ecma262/#sec-getmodulenamespace) abstract operation in the ECMAScript specification.
####
`module.status`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The current status of the module. Will be one of:
* `'unlinked'`: `module.link()` has not yet been called.
* `'linking'`: `module.link()` has been called, but not all Promises returned by the linker function have been resolved yet.
* `'linked'`: The module has been linked successfully, and all of its dependencies are linked, but `module.evaluate()` has not yet been called.
* `'evaluating'`: The module is being evaluated through a `module.evaluate()` on itself or a parent module.
* `'evaluated'`: The module has been successfully evaluated.
* `'errored'`: The module has been evaluated, but an exception was thrown.
Other than `'errored'`, this status string corresponds to the specification's [Cyclic Module Record](https://tc39.es/ecma262/#sec-cyclic-module-records)'s `[[Status]]` field. `'errored'` corresponds to `'evaluated'` in the specification, but with `[[EvaluationError]]` set to a value that is not `undefined`.
### Class: `vm.SourceTextModule`
Added in: v9.6.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
This feature is only available with the `--experimental-vm-modules` command flag enabled.
* Extends: [<vm.Module>](vm#class-vmmodule)
The `vm.SourceTextModule` class provides the [Source Text Module Record](https://tc39.es/ecma262/#sec-source-text-module-records) as defined in the ECMAScript specification.
####
`new vm.SourceTextModule(code[, options])`
History
| Version | Changes |
| --- | --- |
| v17.0.0, v16.12.0 | Added support for import assertions to the `importModuleDynamically` parameter. |
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) JavaScript Module code to parse
* `options`
+ `identifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) String used in stack traces. **Default:** `'vm:module(i)'` where `i` is a context-specific ascending index.
+ `cachedData` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Provides an optional `Buffer` or `TypedArray`, or `DataView` with V8's code cache data for the supplied source. The `code` must be the same as the module from which this `cachedData` was created.
+ `context` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The [contextified](#what-does-it-mean-to-contextify-an-object) object as returned by the `vm.createContext()` method, to compile and evaluate this `Module` in.
+ `lineOffset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the line number offset that is displayed in stack traces produced by this `Module`. **Default:** `0`.
+ `columnOffset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the first-line column number offset that is displayed in stack traces produced by this `Module`. **Default:** `0`.
+ `initializeImportMeta` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called during evaluation of this `Module` to initialize the `import.meta`.
- `meta` [<import.meta>](esm#importmeta)
- `module` [<vm.SourceTextModule>](vm#class-vmsourcetextmodule)
+ `importModuleDynamically` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called during evaluation of this module when `import()` is called. If this option is not specified, calls to `import()` will reject with [`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`](errors#err_vm_dynamic_import_callback_missing).
- `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) specifier passed to `import()`
- `module` [<vm.Module>](vm#class-vmmodule)
- `importAssertions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The `"assert"` value passed to the [`optionsExpression`](https://tc39.es/proposal-import-assertions/#sec-evaluate-import-call) optional parameter, or an empty object if no value was provided.
- Returns: [<Module Namespace Object>](https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects) | [<vm.Module>](vm#class-vmmodule) Returning a `vm.Module` is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain `then` function exports.
Creates a new `SourceTextModule` instance.
Properties assigned to the `import.meta` object that are objects may allow the module to access information outside the specified `context`. Use `vm.runInContext()` to create objects in a specific context.
MJS modules
```
import vm from 'node:vm';
const contextifiedObject = vm.createContext({ secret: 42 });
const module = new vm.SourceTextModule(
'Object.getPrototypeOf(import.meta.prop).secret = secret;',
{
initializeImportMeta(meta) {
// Note: this object is created in the top context. As such,
// Object.getPrototypeOf(import.meta.prop) points to the
// Object.prototype in the top context rather than that in
// the contextified object.
meta.prop = {};
}
});
// Since module has no dependencies, the linker function will never be called.
await module.link(() => {});
await module.evaluate();
// Now, Object.prototype.secret will be equal to 42.
//
// To fix this problem, replace
// meta.prop = {};
// above with
// meta.prop = vm.runInContext('{}', contextifiedObject);
```
CJS modules
```
const vm = require('node:vm');
const contextifiedObject = vm.createContext({ secret: 42 });
(async () => {
const module = new vm.SourceTextModule(
'Object.getPrototypeOf(import.meta.prop).secret = secret;',
{
initializeImportMeta(meta) {
// Note: this object is created in the top context. As such,
// Object.getPrototypeOf(import.meta.prop) points to the
// Object.prototype in the top context rather than that in
// the contextified object.
meta.prop = {};
}
});
// Since module has no dependencies, the linker function will never be called.
await module.link(() => {});
await module.evaluate();
// Now, Object.prototype.secret will be equal to 42.
//
// To fix this problem, replace
// meta.prop = {};
// above with
// meta.prop = vm.runInContext('{}', contextifiedObject);
})();
```
####
`sourceTextModule.createCachedData()`
Added in: v13.7.0, v12.17.0 * Returns: [<Buffer>](buffer#class-buffer)
Creates a code cache that can be used with the `SourceTextModule` constructor's `cachedData` option. Returns a `Buffer`. This method may be called any number of times before the module has been evaluated.
The code cache of the `SourceTextModule` doesn't contain any JavaScript observable states. The code cache is safe to be saved along side the script source and used to construct new `SourceTextModule` instances multiple times.
Functions in the `SourceTextModule` source can be marked as lazily compiled and they are not compiled at construction of the `SourceTextModule`. These functions are going to be compiled when they are invoked the first time. The code cache serializes the metadata that V8 currently knows about the `SourceTextModule` that it can use to speed up future compilations.
```
// Create an initial module
const module = new vm.SourceTextModule('const a = 1;');
// Create cached data from this module
const cachedData = module.createCachedData();
// Create a new module using the cached data. The code must be the same.
const module2 = new vm.SourceTextModule('const a = 1;', { cachedData });
```
### Class: `vm.SyntheticModule`
Added in: v13.0.0, v12.16.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
This feature is only available with the `--experimental-vm-modules` command flag enabled.
* Extends: [<vm.Module>](vm#class-vmmodule)
The `vm.SyntheticModule` class provides the [Synthetic Module Record](https://heycam.github.io/webidl/#synthetic-module-records) as defined in the WebIDL specification. The purpose of synthetic modules is to provide a generic interface for exposing non-JavaScript sources to ECMAScript module graphs.
```
const vm = require('node:vm');
const source = '{ "a": 1 }';
const module = new vm.SyntheticModule(['default'], function() {
const obj = JSON.parse(source);
this.setExport('default', obj);
});
// Use `module` in linking...
```
####
`new vm.SyntheticModule(exportNames, evaluateCallback[, options])`
Added in: v13.0.0, v12.16.0 * `exportNames` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Array of names that will be exported from the module.
* `evaluateCallback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called when the module is evaluated.
* `options`
+ `identifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) String used in stack traces. **Default:** `'vm:module(i)'` where `i` is a context-specific ascending index.
+ `context` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The [contextified](#what-does-it-mean-to-contextify-an-object) object as returned by the `vm.createContext()` method, to compile and evaluate this `Module` in.
Creates a new `SyntheticModule` instance.
Objects assigned to the exports of this instance may allow importers of the module to access information outside the specified `context`. Use `vm.runInContext()` to create objects in a specific context.
####
`syntheticModule.setExport(name, value)`
Added in: v13.0.0, v12.16.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the export to set.
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The value to set the export to.
This method is used after the module is linked to set the values of exports. If it is called before the module is linked, an [`ERR_VM_MODULE_STATUS`](errors#err_vm_module_status) error will be thrown.
MJS modules
```
import vm from 'node:vm';
const m = new vm.SyntheticModule(['x'], () => {
m.setExport('x', 1);
});
await m.link(() => {});
await m.evaluate();
assert.strictEqual(m.namespace.x, 1);
```
CJS modules
```
const vm = require('node:vm');
(async () => {
const m = new vm.SyntheticModule(['x'], () => {
m.setExport('x', 1);
});
await m.link(() => {});
await m.evaluate();
assert.strictEqual(m.namespace.x, 1);
})();
```
###
`vm.compileFunction(code[, params[, options]])`
History
| Version | Changes |
| --- | --- |
| v17.0.0, v16.12.0 | Added support for import assertions to the `importModuleDynamically` parameter. |
| v15.9.0 | Added `importModuleDynamically` option again. |
| v14.3.0 | Removal of `importModuleDynamically` due to compatibility issues. |
| v14.1.0, v13.14.0 | The `importModuleDynamically` option is now supported. |
| v10.10.0 | Added in: v10.10.0 |
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The body of the function to compile.
* `params` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) An array of strings containing all parameters for the function.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specifies the filename used in stack traces produced by this script. **Default:** `''`.
+ `lineOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the line number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `columnOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the first-line column number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `cachedData` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Provides an optional `Buffer` or `TypedArray`, or `DataView` with V8's code cache data for the supplied source.
+ `produceCachedData` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Specifies whether to produce new cache data. **Default:** `false`.
+ `parsingContext` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The [contextified](#what-does-it-mean-to-contextify-an-object) object in which the said function should be compiled in.
+ `contextExtensions` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An array containing a collection of context extensions (objects wrapping the current scope) to be applied while compiling. **Default:** `[]`.
+ `importModuleDynamically` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called during evaluation of this module when `import()` is called. If this option is not specified, calls to `import()` will reject with [`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`](errors#err_vm_dynamic_import_callback_missing). This option is part of the experimental modules API, and should not be considered stable.
- `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) specifier passed to `import()`
- `function` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
- `importAssertions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The `"assert"` value passed to the [`optionsExpression`](https://tc39.es/proposal-import-assertions/#sec-evaluate-import-call) optional parameter, or an empty object if no value was provided.
- Returns: [<Module Namespace Object>](https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects) | [<vm.Module>](vm#class-vmmodule) Returning a `vm.Module` is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain `then` function exports.
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Compiles the given code into the provided context (if no context is supplied, the current context is used), and returns it wrapped inside a function with the given `params`.
###
`vm.createContext([contextObject[, options]])`
History
| Version | Changes |
| --- | --- |
| v14.6.0 | The `microtaskMode` option is supported now. |
| v10.0.0 | The first argument can no longer be a function. |
| v10.0.0 | The `codeGeneration` option is supported now. |
| v0.3.1 | Added in: v0.3.1 |
* `contextObject` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Human-readable name of the newly created context. **Default:** `'VM Context i'`, where `i` is an ascending numerical index of the created context.
+ `origin` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) [Origin](https://developer.mozilla.org/en-US/docs/Glossary/Origin) corresponding to the newly created context for display purposes. The origin should be formatted like a URL, but with only the scheme, host, and port (if necessary), like the value of the [`url.origin`](url#urlorigin) property of a [`URL`](url#class-url) object. Most notably, this string should omit the trailing slash, as that denotes a path. **Default:** `''`.
+ `codeGeneration` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `strings` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to false any calls to `eval` or function constructors (`Function`, `GeneratorFunction`, etc) will throw an `EvalError`. **Default:** `true`.
- `wasm` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to false any attempt to compile a WebAssembly module will throw a `WebAssembly.CompileError`. **Default:** `true`.
+ `microtaskMode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If set to `afterEvaluate`, microtasks (tasks scheduled through `Promise`s and `async function`s) will be run immediately after a script has run through [`script.runInContext()`](#scriptrunincontextcontextifiedobject-options). They are included in the `timeout` and `breakOnSigint` scopes in that case.
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) contextified object.
If given a `contextObject`, the `vm.createContext()` method will [prepare that object](#what-does-it-mean-to-contextify-an-object) so that it can be used in calls to [`vm.runInContext()`](#vmrunincontextcode-contextifiedobject-options) or [`script.runInContext()`](#scriptrunincontextcontextifiedobject-options). Inside such scripts, the `contextObject` will be the global object, retaining all of its existing properties but also having the built-in objects and functions any standard [global object](https://es5.github.io/#x15.1) has. Outside of scripts run by the vm module, global variables will remain unchanged.
```
const vm = require('node:vm');
global.globalVar = 3;
const context = { globalVar: 1 };
vm.createContext(context);
vm.runInContext('globalVar *= 2;', context);
console.log(context);
// Prints: { globalVar: 2 }
console.log(global.globalVar);
// Prints: 3
```
If `contextObject` is omitted (or passed explicitly as `undefined`), a new, empty [contextified](#what-does-it-mean-to-contextify-an-object) object will be returned.
The `vm.createContext()` method is primarily useful for creating a single context that can be used to run multiple scripts. For instance, if emulating a web browser, the method can be used to create a single context representing a window's global object, then run all `<script>` tags together within that context.
The provided `name` and `origin` of the context are made visible through the Inspector API.
###
`vm.isContext(object)`
Added in: v0.11.7 * `object` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the given `object` object has been [contextified](#what-does-it-mean-to-contextify-an-object) using [`vm.createContext()`](#vmcreatecontextcontextobject-options).
###
`vm.measureMemory([options])`
Added in: v13.10.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Measure the memory known to V8 and used by all contexts known to the current V8 isolate, or the main context.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Optional.
+ `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'summary'` or `'detailed'`. In summary mode, only the memory measured for the main context will be returned. In detailed mode, the memory measured for all contexts known to the current V8 isolate will be returned. **Default:** `'summary'`
+ `execution` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `'default'` or `'eager'`. With default execution, the promise will not resolve until after the next scheduled garbage collection starts, which may take a while (or never if the program exits before the next GC). With eager execution, the GC will be started right away to measure the memory. **Default:** `'default'`
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) If the memory is successfully measured the promise will resolve with an object containing information about the memory usage.
The format of the object that the returned Promise may resolve with is specific to the V8 engine and may change from one version of V8 to the next.
The returned result is different from the statistics returned by `v8.getHeapSpaceStatistics()` in that `vm.measureMemory()` measure the memory reachable by each V8 specific contexts in the current instance of the V8 engine, while the result of `v8.getHeapSpaceStatistics()` measure the memory occupied by each heap space in the current V8 instance.
```
const vm = require('node:vm');
// Measure the memory used by the main context.
vm.measureMemory({ mode: 'summary' })
// This is the same as vm.measureMemory()
.then((result) => {
// The current format is:
// {
// total: {
// jsMemoryEstimate: 2418479, jsMemoryRange: [ 2418479, 2745799 ]
// }
// }
console.log(result);
});
const context = vm.createContext({ a: 1 });
vm.measureMemory({ mode: 'detailed', execution: 'eager' })
.then((result) => {
// Reference the context here so that it won't be GC'ed
// until the measurement is complete.
console.log(context.a);
// {
// total: {
// jsMemoryEstimate: 2574732,
// jsMemoryRange: [ 2574732, 2904372 ]
// },
// current: {
// jsMemoryEstimate: 2438996,
// jsMemoryRange: [ 2438996, 2768636 ]
// },
// other: [
// {
// jsMemoryEstimate: 135736,
// jsMemoryRange: [ 135736, 465376 ]
// }
// ]
// }
console.log(result);
});
```
###
`vm.runInContext(code, contextifiedObject[, options])`
History
| Version | Changes |
| --- | --- |
| v17.0.0, v16.12.0 | Added support for import assertions to the `importModuleDynamically` parameter. |
| v6.3.0 | The `breakOnSigint` option is supported now. |
| v0.3.1 | Added in: v0.3.1 |
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The JavaScript code to compile and run.
* `contextifiedObject` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The [contextified](#what-does-it-mean-to-contextify-an-object) object that will be used as the `global` when the `code` is compiled and run.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specifies the filename used in stack traces produced by this script. **Default:** `'evalmachine.<anonymous>'`.
+ `lineOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the line number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `columnOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the first-line column number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `displayErrors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, if an [`Error`](errors#class-error) occurs while compiling the `code`, the line of code causing the error is attached to the stack trace. **Default:** `true`.
+ `timeout` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the number of milliseconds to execute `code` before terminating execution. If execution is terminated, an [`Error`](errors#class-error) will be thrown. This value must be a strictly positive integer.
+ `breakOnSigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, receiving `SIGINT` (`Ctrl`+`C`) will terminate execution and throw an [`Error`](errors#class-error). Existing handlers for the event that have been attached via `process.on('SIGINT')` are disabled during script execution, but continue to work after that. **Default:** `false`.
+ `cachedData` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Provides an optional `Buffer` or `TypedArray`, or `DataView` with V8's code cache data for the supplied source.
+ `importModuleDynamically` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called during evaluation of this module when `import()` is called. If this option is not specified, calls to `import()` will reject with [`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`](errors#err_vm_dynamic_import_callback_missing). This option is part of the experimental modules API. We do not recommend using it in a production environment.
- `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) specifier passed to `import()`
- `script` [<vm.Script>](vm#class-vmscript)
- `importAssertions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The `"assert"` value passed to the [`optionsExpression`](https://tc39.es/proposal-import-assertions/#sec-evaluate-import-call) optional parameter, or an empty object if no value was provided.
- Returns: [<Module Namespace Object>](https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects) | [<vm.Module>](vm#class-vmmodule) Returning a `vm.Module` is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain `then` function exports.
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the result of the very last statement executed in the script.
The `vm.runInContext()` method compiles `code`, runs it within the context of the `contextifiedObject`, then returns the result. Running code does not have access to the local scope. The `contextifiedObject` object *must* have been previously [contextified](#what-does-it-mean-to-contextify-an-object) using the [`vm.createContext()`](#vmcreatecontextcontextobject-options) method.
If `options` is a string, then it specifies the filename.
The following example compiles and executes different scripts using a single [contextified](#what-does-it-mean-to-contextify-an-object) object:
```
const vm = require('node:vm');
const contextObject = { globalVar: 1 };
vm.createContext(contextObject);
for (let i = 0; i < 10; ++i) {
vm.runInContext('globalVar *= 2;', contextObject);
}
console.log(contextObject);
// Prints: { globalVar: 1024 }
```
###
`vm.runInNewContext(code[, contextObject[, options]])`
History
| Version | Changes |
| --- | --- |
| v17.0.0, v16.12.0 | Added support for import assertions to the `importModuleDynamically` parameter. |
| v14.6.0 | The `microtaskMode` option is supported now. |
| v10.0.0 | The `contextCodeGeneration` option is supported now. |
| v6.3.0 | The `breakOnSigint` option is supported now. |
| v0.3.1 | Added in: v0.3.1 |
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The JavaScript code to compile and run.
* `contextObject` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object that will be [contextified](#what-does-it-mean-to-contextify-an-object). If `undefined`, a new object will be created.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specifies the filename used in stack traces produced by this script. **Default:** `'evalmachine.<anonymous>'`.
+ `lineOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the line number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `columnOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the first-line column number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `displayErrors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, if an [`Error`](errors#class-error) occurs while compiling the `code`, the line of code causing the error is attached to the stack trace. **Default:** `true`.
+ `timeout` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the number of milliseconds to execute `code` before terminating execution. If execution is terminated, an [`Error`](errors#class-error) will be thrown. This value must be a strictly positive integer.
+ `breakOnSigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, receiving `SIGINT` (`Ctrl`+`C`) will terminate execution and throw an [`Error`](errors#class-error). Existing handlers for the event that have been attached via `process.on('SIGINT')` are disabled during script execution, but continue to work after that. **Default:** `false`.
+ `contextName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Human-readable name of the newly created context. **Default:** `'VM Context i'`, where `i` is an ascending numerical index of the created context.
+ `contextOrigin` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) [Origin](https://developer.mozilla.org/en-US/docs/Glossary/Origin) corresponding to the newly created context for display purposes. The origin should be formatted like a URL, but with only the scheme, host, and port (if necessary), like the value of the [`url.origin`](url#urlorigin) property of a [`URL`](url#class-url) object. Most notably, this string should omit the trailing slash, as that denotes a path. **Default:** `''`.
+ `contextCodeGeneration` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
- `strings` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to false any calls to `eval` or function constructors (`Function`, `GeneratorFunction`, etc) will throw an `EvalError`. **Default:** `true`.
- `wasm` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to false any attempt to compile a WebAssembly module will throw a `WebAssembly.CompileError`. **Default:** `true`.
+ `cachedData` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Provides an optional `Buffer` or `TypedArray`, or `DataView` with V8's code cache data for the supplied source.
+ `importModuleDynamically` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called during evaluation of this module when `import()` is called. If this option is not specified, calls to `import()` will reject with [`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`](errors#err_vm_dynamic_import_callback_missing). This option is part of the experimental modules API. We do not recommend using it in a production environment.
- `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) specifier passed to `import()`
- `script` [<vm.Script>](vm#class-vmscript)
- `importAssertions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The `"assert"` value passed to the [`optionsExpression`](https://tc39.es/proposal-import-assertions/#sec-evaluate-import-call) optional parameter, or an empty object if no value was provided.
- Returns: [<Module Namespace Object>](https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects) | [<vm.Module>](vm#class-vmmodule) Returning a `vm.Module` is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain `then` function exports.
+ `microtaskMode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If set to `afterEvaluate`, microtasks (tasks scheduled through `Promise`s and `async function`s) will be run immediately after the script has run. They are included in the `timeout` and `breakOnSigint` scopes in that case.
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the result of the very last statement executed in the script.
The `vm.runInNewContext()` first contextifies the given `contextObject` (or creates a new `contextObject` if passed as `undefined`), compiles the `code`, runs it within the created context, then returns the result. Running code does not have access to the local scope.
If `options` is a string, then it specifies the filename.
The following example compiles and executes code that increments a global variable and sets a new one. These globals are contained in the `contextObject`.
```
const vm = require('node:vm');
const contextObject = {
animal: 'cat',
count: 2
};
vm.runInNewContext('count += 1; name = "kitty"', contextObject);
console.log(contextObject);
// Prints: { animal: 'cat', count: 3, name: 'kitty' }
```
###
`vm.runInThisContext(code[, options])`
History
| Version | Changes |
| --- | --- |
| v17.0.0, v16.12.0 | Added support for import assertions to the `importModuleDynamically` parameter. |
| v6.3.0 | The `breakOnSigint` option is supported now. |
| v0.3.1 | Added in: v0.3.1 |
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The JavaScript code to compile and run.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Specifies the filename used in stack traces produced by this script. **Default:** `'evalmachine.<anonymous>'`.
+ `lineOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the line number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `columnOffset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the first-line column number offset that is displayed in stack traces produced by this script. **Default:** `0`.
+ `displayErrors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, if an [`Error`](errors#class-error) occurs while compiling the `code`, the line of code causing the error is attached to the stack trace. **Default:** `true`.
+ `timeout` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the number of milliseconds to execute `code` before terminating execution. If execution is terminated, an [`Error`](errors#class-error) will be thrown. This value must be a strictly positive integer.
+ `breakOnSigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, receiving `SIGINT` (`Ctrl`+`C`) will terminate execution and throw an [`Error`](errors#class-error). Existing handlers for the event that have been attached via `process.on('SIGINT')` are disabled during script execution, but continue to work after that. **Default:** `false`.
+ `cachedData` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Provides an optional `Buffer` or `TypedArray`, or `DataView` with V8's code cache data for the supplied source.
+ `importModuleDynamically` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Called during evaluation of this module when `import()` is called. If this option is not specified, calls to `import()` will reject with [`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`](errors#err_vm_dynamic_import_callback_missing). This option is part of the experimental modules API. We do not recommend using it in a production environment.
- `specifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) specifier passed to `import()`
- `script` [<vm.Script>](vm#class-vmscript)
- `importAssertions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The `"assert"` value passed to the [`optionsExpression`](https://tc39.es/proposal-import-assertions/#sec-evaluate-import-call) optional parameter, or an empty object if no value was provided.
- Returns: [<Module Namespace Object>](https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects) | [<vm.Module>](vm#class-vmmodule) Returning a `vm.Module` is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain `then` function exports.
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) the result of the very last statement executed in the script.
`vm.runInThisContext()` compiles `code`, runs it within the context of the current `global` and returns the result. Running code does not have access to local scope, but does have access to the current `global` object.
If `options` is a string, then it specifies the filename.
The following example illustrates using both `vm.runInThisContext()` and the JavaScript [`eval()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval) function to run the same code:
```
const vm = require('node:vm');
let localVar = 'initial value';
const vmResult = vm.runInThisContext('localVar = "vm";');
console.log(`vmResult: '${vmResult}', localVar: '${localVar}'`);
// Prints: vmResult: 'vm', localVar: 'initial value'
const evalResult = eval('localVar = "eval";');
console.log(`evalResult: '${evalResult}', localVar: '${localVar}'`);
// Prints: evalResult: 'eval', localVar: 'eval'
```
Because `vm.runInThisContext()` does not have access to the local scope, `localVar` is unchanged. In contrast, [`eval()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval) *does* have access to the local scope, so the value `localVar` is changed. In this way `vm.runInThisContext()` is much like an [indirect `eval()` call](https://es5.github.io/#x10.4.2), e.g. `(0,eval)('code')`.
### Example: Running an HTTP server within a VM
When using either [`script.runInThisContext()`](#scriptruninthiscontextoptions) or [`vm.runInThisContext()`](#vmruninthiscontextcode-options), the code is executed within the current V8 global context. The code passed to this VM context will have its own isolated scope.
In order to run a simple web server using the `node:http` module the code passed to the context must either call `require('node:http')` on its own, or have a reference to the `node:http` module passed to it. For instance:
```
'use strict';
const vm = require('node:vm');
const code = `
((require) => {
const http = require('node:http');
http.createServer((request, response) => {
response.writeHead(200, { 'Content-Type': 'text/plain' });
response.end('Hello World\\n');
}).listen(8124);
console.log('Server running at http://127.0.0.1:8124/');
})`;
vm.runInThisContext(code)(require);
```
The `require()` in the above case shares the state with the context it is passed from. This may introduce risks when untrusted code is executed, e.g. altering objects in the context in unwanted ways.
### What does it mean to "contextify" an object?
All JavaScript executed within Node.js runs within the scope of a "context". According to the [V8 Embedder's Guide](https://v8.dev/docs/embed#contexts):
> In V8, a context is an execution environment that allows separate, unrelated, JavaScript applications to run in a single instance of V8. You must explicitly specify the context in which you want any JavaScript code to be run.
>
>
When the method `vm.createContext()` is called, the `contextObject` argument (or a newly-created object if `contextObject` is `undefined`) is associated internally with a new instance of a V8 Context. This V8 Context provides the `code` run using the `node:vm` module's methods with an isolated global environment within which it can operate. The process of creating the V8 Context and associating it with the `contextObject` is what this document refers to as "contextifying" the object.
### Timeout interactions with asynchronous tasks and Promises
`Promise`s and `async function`s can schedule tasks run by the JavaScript engine asynchronously. By default, these tasks are run after all JavaScript functions on the current stack are done executing. This allows escaping the functionality of the `timeout` and `breakOnSigint` options.
For example, the following code executed by `vm.runInNewContext()` with a timeout of 5 milliseconds schedules an infinite loop to run after a promise resolves. The scheduled loop is never interrupted by the timeout:
```
const vm = require('node:vm');
function loop() {
console.log('entering loop');
while (1) console.log(Date.now());
}
vm.runInNewContext(
'Promise.resolve().then(() => loop());',
{ loop, console },
{ timeout: 5 }
);
// This is printed *before* 'entering loop' (!)
console.log('done executing');
```
This can be addressed by passing `microtaskMode: 'afterEvaluate'` to the code that creates the `Context`:
```
const vm = require('node:vm');
function loop() {
while (1) console.log(Date.now());
}
vm.runInNewContext(
'Promise.resolve().then(() => loop());',
{ loop, console },
{ timeout: 5, microtaskMode: 'afterEvaluate' }
);
```
In this case, the microtask scheduled through `promise.then()` will be run before returning from `vm.runInNewContext()`, and will be interrupted by the `timeout` functionality. This applies only to code running in a `vm.Context`, so e.g. [`vm.runInThisContext()`](#vmruninthiscontextcode-options) does not take this option.
Promise callbacks are entered into the microtask queue of the context in which they were created. For example, if `() => loop()` is replaced with just `loop` in the above example, then `loop` will be pushed into the global microtask queue, because it is a function from the outer (main) context, and thus will also be able to escape the timeout.
If asynchronous scheduling functions such as `process.nextTick()`, `queueMicrotask()`, `setTimeout()`, `setImmediate()`, etc. are made available inside a `vm.Context`, functions passed to them will be added to global queues, which are shared by all contexts. Therefore, callbacks passed to those functions are not controllable through the timeout either.
| programming_docs |
node None Async hooks
-----------
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
**Source Code:** [lib/async\_hooks.js](https://github.com/nodejs/node/blob/v19.0.1/lib/async_hooks.js)
The `node:async_hooks` module provides an API to track asynchronous resources. It can be accessed using:
MJS modules
```
import async_hooks from 'node:async_hooks';
```
CJS modules
```
const async_hooks = require('node:async_hooks');
```
### Terminology
An asynchronous resource represents an object with an associated callback. This callback may be called multiple times, such as the `'connection'` event in `net.createServer()`, or just a single time like in `fs.open()`. A resource can also be closed before the callback is called. `AsyncHook` does not explicitly distinguish between these different cases but will represent them as the abstract concept that is a resource.
If [`Worker`](worker_threads#class-worker)s are used, each thread has an independent `async_hooks` interface, and each thread will use a new set of async IDs.
### Overview
Following is a simple overview of the public API.
MJS modules
```
import async_hooks from 'node:async_hooks';
// Return the ID of the current execution context.
const eid = async_hooks.executionAsyncId();
// Return the ID of the handle responsible for triggering the callback of the
// current execution scope to call.
const tid = async_hooks.triggerAsyncId();
// Create a new AsyncHook instance. All of these callbacks are optional.
const asyncHook =
async_hooks.createHook({ init, before, after, destroy, promiseResolve });
// Allow callbacks of this AsyncHook instance to call. This is not an implicit
// action after running the constructor, and must be explicitly run to begin
// executing callbacks.
asyncHook.enable();
// Disable listening for new asynchronous events.
asyncHook.disable();
//
// The following are the callbacks that can be passed to createHook().
//
// init() is called during object construction. The resource may not have
// completed construction when this callback runs. Therefore, all fields of the
// resource referenced by "asyncId" may not have been populated.
function init(asyncId, type, triggerAsyncId, resource) { }
// before() is called just before the resource's callback is called. It can be
// called 0-N times for handles (such as TCPWrap), and will be called exactly 1
// time for requests (such as FSReqCallback).
function before(asyncId) { }
// after() is called just after the resource's callback has finished.
function after(asyncId) { }
// destroy() is called when the resource is destroyed.
function destroy(asyncId) { }
// promiseResolve() is called only for promise resources, when the
// resolve() function passed to the Promise constructor is invoked
// (either directly or through other means of resolving a promise).
function promiseResolve(asyncId) { }
```
CJS modules
```
const async_hooks = require('node:async_hooks');
// Return the ID of the current execution context.
const eid = async_hooks.executionAsyncId();
// Return the ID of the handle responsible for triggering the callback of the
// current execution scope to call.
const tid = async_hooks.triggerAsyncId();
// Create a new AsyncHook instance. All of these callbacks are optional.
const asyncHook =
async_hooks.createHook({ init, before, after, destroy, promiseResolve });
// Allow callbacks of this AsyncHook instance to call. This is not an implicit
// action after running the constructor, and must be explicitly run to begin
// executing callbacks.
asyncHook.enable();
// Disable listening for new asynchronous events.
asyncHook.disable();
//
// The following are the callbacks that can be passed to createHook().
//
// init() is called during object construction. The resource may not have
// completed construction when this callback runs. Therefore, all fields of the
// resource referenced by "asyncId" may not have been populated.
function init(asyncId, type, triggerAsyncId, resource) { }
// before() is called just before the resource's callback is called. It can be
// called 0-N times for handles (such as TCPWrap), and will be called exactly 1
// time for requests (such as FSReqCallback).
function before(asyncId) { }
// after() is called just after the resource's callback has finished.
function after(asyncId) { }
// destroy() is called when the resource is destroyed.
function destroy(asyncId) { }
// promiseResolve() is called only for promise resources, when the
// resolve() function passed to the Promise constructor is invoked
// (either directly or through other means of resolving a promise).
function promiseResolve(asyncId) { }
```
###
`async_hooks.createHook(callbacks)`
Added in: v8.1.0 * `callbacks` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The [Hook Callbacks](#hook-callbacks) to register
+ `init` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`init` callback](#initasyncid-type-triggerasyncid-resource).
+ `before` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`before` callback](#beforeasyncid).
+ `after` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`after` callback](#afterasyncid).
+ `destroy` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`destroy` callback](#destroyasyncid).
+ `promiseResolve` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The [`promiseResolve` callback](#promiseresolveasyncid).
* Returns: [<AsyncHook>](async_hooks#async_hookscreatehookcallbacks) Instance used for disabling and enabling hooks
Registers functions to be called for different lifetime events of each async operation.
The callbacks `init()`/`before()`/`after()`/`destroy()` are called for the respective asynchronous event during a resource's lifetime.
All callbacks are optional. For example, if only resource cleanup needs to be tracked, then only the `destroy` callback needs to be passed. The specifics of all functions that can be passed to `callbacks` is in the [Hook Callbacks](#hook-callbacks) section.
MJS modules
```
import { createHook } from 'node:async_hooks';
const asyncHook = createHook({
init(asyncId, type, triggerAsyncId, resource) { },
destroy(asyncId) { }
});
```
CJS modules
```
const async_hooks = require('node:async_hooks');
const asyncHook = async_hooks.createHook({
init(asyncId, type, triggerAsyncId, resource) { },
destroy(asyncId) { }
});
```
The callbacks will be inherited via the prototype chain:
```
class MyAsyncCallbacks {
init(asyncId, type, triggerAsyncId, resource) { }
destroy(asyncId) {}
}
class MyAddedCallbacks extends MyAsyncCallbacks {
before(asyncId) { }
after(asyncId) { }
}
const asyncHook = async_hooks.createHook(new MyAddedCallbacks());
```
Because promises are asynchronous resources whose lifecycle is tracked via the async hooks mechanism, the `init()`, `before()`, `after()`, and `destroy()` callbacks *must not* be async functions that return promises.
#### Error handling
If any `AsyncHook` callbacks throw, the application will print the stack trace and exit. The exit path does follow that of an uncaught exception, but all `'uncaughtException'` listeners are removed, thus forcing the process to exit. The `'exit'` callbacks will still be called unless the application is run with `--abort-on-uncaught-exception`, in which case a stack trace will be printed and the application exits, leaving a core file.
The reason for this error handling behavior is that these callbacks are running at potentially volatile points in an object's lifetime, for example during class construction and destruction. Because of this, it is deemed necessary to bring down the process quickly in order to prevent an unintentional abort in the future. This is subject to change in the future if a comprehensive analysis is performed to ensure an exception can follow the normal control flow without unintentional side effects.
#### Printing in `AsyncHook` callbacks
Because printing to the console is an asynchronous operation, `console.log()` will cause `AsyncHook` callbacks to be called. Using `console.log()` or similar asynchronous operations inside an `AsyncHook` callback function will cause an infinite recursion. An easy solution to this when debugging is to use a synchronous logging operation such as `fs.writeFileSync(file, msg, flag)`. This will print to the file and will not invoke `AsyncHook` recursively because it is synchronous.
MJS modules
```
import { writeFileSync } from 'node:fs';
import { format } from 'node:util';
function debug(...args) {
// Use a function like this one when debugging inside an AsyncHook callback
writeFileSync('log.out', `${format(...args)}\n`, { flag: 'a' });
}
```
CJS modules
```
const fs = require('node:fs');
const util = require('node:util');
function debug(...args) {
// Use a function like this one when debugging inside an AsyncHook callback
fs.writeFileSync('log.out', `${util.format(...args)}\n`, { flag: 'a' });
}
```
If an asynchronous operation is needed for logging, it is possible to keep track of what caused the asynchronous operation using the information provided by `AsyncHook` itself. The logging should then be skipped when it was the logging itself that caused the `AsyncHook` callback to be called. By doing this, the otherwise infinite recursion is broken.
### Class: `AsyncHook`
The class `AsyncHook` exposes an interface for tracking lifetime events of asynchronous operations.
####
`asyncHook.enable()`
* Returns: [<AsyncHook>](async_hooks#async_hookscreatehookcallbacks) A reference to `asyncHook`.
Enable the callbacks for a given `AsyncHook` instance. If no callbacks are provided, enabling is a no-op.
The `AsyncHook` instance is disabled by default. If the `AsyncHook` instance should be enabled immediately after creation, the following pattern can be used.
MJS modules
```
import { createHook } from 'node:async_hooks';
const hook = createHook(callbacks).enable();
```
CJS modules
```
const async_hooks = require('node:async_hooks');
const hook = async_hooks.createHook(callbacks).enable();
```
####
`asyncHook.disable()`
* Returns: [<AsyncHook>](async_hooks#async_hookscreatehookcallbacks) A reference to `asyncHook`.
Disable the callbacks for a given `AsyncHook` instance from the global pool of `AsyncHook` callbacks to be executed. Once a hook has been disabled it will not be called again until enabled.
For API consistency `disable()` also returns the `AsyncHook` instance.
#### Hook callbacks
Key events in the lifetime of asynchronous events have been categorized into four areas: instantiation, before/after the callback is called, and when the instance is destroyed.
#####
`init(asyncId, type, triggerAsyncId, resource)`
* `asyncId` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A unique ID for the async resource.
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The type of the async resource.
* `triggerAsyncId` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The unique ID of the async resource in whose execution context this async resource was created.
* `resource` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Reference to the resource representing the async operation, needs to be released during *destroy*.
Called when a class is constructed that has the *possibility* to emit an asynchronous event. This *does not* mean the instance must call `before`/`after` before `destroy` is called, only that the possibility exists.
This behavior can be observed by doing something like opening a resource then closing it before the resource can be used. The following snippet demonstrates this.
MJS modules
```
import { createServer } from 'node:net';
createServer().listen(function() { this.close(); });
// OR
clearTimeout(setTimeout(() => {}, 10));
```
CJS modules
```
require('node:net').createServer().listen(function() { this.close(); });
// OR
clearTimeout(setTimeout(() => {}, 10));
```
Every new resource is assigned an ID that is unique within the scope of the current Node.js instance.
######
`type`
The `type` is a string identifying the type of resource that caused `init` to be called. Generally, it will correspond to the name of the resource's constructor.
Valid values are:
```
FSEVENTWRAP, FSREQCALLBACK, GETADDRINFOREQWRAP, GETNAMEINFOREQWRAP, HTTPINCOMINGMESSAGE,
HTTPCLIENTREQUEST, JSSTREAM, PIPECONNECTWRAP, PIPEWRAP, PROCESSWRAP, QUERYWRAP,
SHUTDOWNWRAP, SIGNALWRAP, STATWATCHER, TCPCONNECTWRAP, TCPSERVERWRAP, TCPWRAP,
TTYWRAP, UDPSENDWRAP, UDPWRAP, WRITEWRAP, ZLIB, SSLCONNECTION, PBKDF2REQUEST,
RANDOMBYTESREQUEST, TLSWRAP, Microtask, Timeout, Immediate, TickObject
```
These values can change in any Node.js release. Furthermore users of [`AsyncResource`](async_context#class-asyncresource) likely provide other values.
There is also the `PROMISE` resource type, which is used to track `Promise` instances and asynchronous work scheduled by them.
Users are able to define their own `type` when using the public embedder API.
It is possible to have type name collisions. Embedders are encouraged to use unique prefixes, such as the npm package name, to prevent collisions when listening to the hooks.
######
`triggerAsyncId`
`triggerAsyncId` is the `asyncId` of the resource that caused (or "triggered") the new resource to initialize and that caused `init` to call. This is different from `async_hooks.executionAsyncId()` that only shows *when* a resource was created, while `triggerAsyncId` shows *why* a resource was created.
The following is a simple demonstration of `triggerAsyncId`:
MJS modules
```
import { createHook, executionAsyncId } from 'node:async_hooks';
import { stdout } from 'node:process';
import net from 'node:net';
createHook({
init(asyncId, type, triggerAsyncId) {
const eid = executionAsyncId();
fs.writeSync(
stdout.fd,
`${type}(${asyncId}): trigger: ${triggerAsyncId} execution: ${eid}\n`);
}
}).enable();
net.createServer((conn) => {}).listen(8080);
```
CJS modules
```
const { createHook, executionAsyncId } = require('node:async_hooks');
const { stdout } = require('node:process');
const net = require('node:net');
createHook({
init(asyncId, type, triggerAsyncId) {
const eid = executionAsyncId();
fs.writeSync(
stdout.fd,
`${type}(${asyncId}): trigger: ${triggerAsyncId} execution: ${eid}\n`);
}
}).enable();
net.createServer((conn) => {}).listen(8080);
```
Output when hitting the server with `nc localhost 8080`:
```
TCPSERVERWRAP(5): trigger: 1 execution: 1
TCPWRAP(7): trigger: 5 execution: 0
```
The `TCPSERVERWRAP` is the server which receives the connections.
The `TCPWRAP` is the new connection from the client. When a new connection is made, the `TCPWrap` instance is immediately constructed. This happens outside of any JavaScript stack. (An `executionAsyncId()` of `0` means that it is being executed from C++ with no JavaScript stack above it.) With only that information, it would be impossible to link resources together in terms of what caused them to be created, so `triggerAsyncId` is given the task of propagating what resource is responsible for the new resource's existence.
######
`resource`
`resource` is an object that represents the actual async resource that has been initialized. This can contain useful information that can vary based on the value of `type`. For instance, for the `GETADDRINFOREQWRAP` resource type, `resource` provides the host name used when looking up the IP address for the host in `net.Server.listen()`. The API for accessing this information is not supported, but using the Embedder API, users can provide and document their own resource objects. For example, such a resource object could contain the SQL query being executed.
In some cases the resource object is reused for performance reasons, it is thus not safe to use it as a key in a `WeakMap` or add properties to it.
###### Asynchronous context example
The following is an example with additional information about the calls to `init` between the `before` and `after` calls, specifically what the callback to `listen()` will look like. The output formatting is slightly more elaborate to make calling context easier to see.
```
const async_hooks = require('node:async_hooks');
const fs = require('node:fs');
const net = require('node:net');
const { fd } = process.stdout;
let indent = 0;
async_hooks.createHook({
init(asyncId, type, triggerAsyncId) {
const eid = async_hooks.executionAsyncId();
const indentStr = ' '.repeat(indent);
fs.writeSync(
fd,
`${indentStr}${type}(${asyncId}):` +
` trigger: ${triggerAsyncId} execution: ${eid}\n`);
},
before(asyncId) {
const indentStr = ' '.repeat(indent);
fs.writeSync(fd, `${indentStr}before: ${asyncId}\n`);
indent += 2;
},
after(asyncId) {
indent -= 2;
const indentStr = ' '.repeat(indent);
fs.writeSync(fd, `${indentStr}after: ${asyncId}\n`);
},
destroy(asyncId) {
const indentStr = ' '.repeat(indent);
fs.writeSync(fd, `${indentStr}destroy: ${asyncId}\n`);
},
}).enable();
net.createServer(() => {}).listen(8080, () => {
// Let's wait 10ms before logging the server started.
setTimeout(() => {
console.log('>>>', async_hooks.executionAsyncId());
}, 10);
});
```
Output from only starting the server:
```
TCPSERVERWRAP(5): trigger: 1 execution: 1
TickObject(6): trigger: 5 execution: 1
before: 6
Timeout(7): trigger: 6 execution: 6
after: 6
destroy: 6
before: 7
>>> 7
TickObject(8): trigger: 7 execution: 7
after: 7
before: 8
after: 8
```
As illustrated in the example, `executionAsyncId()` and `execution` each specify the value of the current execution context; which is delineated by calls to `before` and `after`.
Only using `execution` to graph resource allocation results in the following:
```
root(1)
^
|
TickObject(6)
^
|
Timeout(7)
```
The `TCPSERVERWRAP` is not part of this graph, even though it was the reason for `console.log()` being called. This is because binding to a port without a host name is a *synchronous* operation, but to maintain a completely asynchronous API the user's callback is placed in a `process.nextTick()`. Which is why `TickObject` is present in the output and is a 'parent' for `.listen()` callback.
The graph only shows *when* a resource was created, not *why*, so to track the *why* use `triggerAsyncId`. Which can be represented with the following graph:
```
bootstrap(1)
|
˅
TCPSERVERWRAP(5)
|
˅
TickObject(6)
|
˅
Timeout(7)
```
#####
`before(asyncId)`
* `asyncId` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
When an asynchronous operation is initiated (such as a TCP server receiving a new connection) or completes (such as writing data to disk) a callback is called to notify the user. The `before` callback is called just before said callback is executed. `asyncId` is the unique identifier assigned to the resource about to execute the callback.
The `before` callback will be called 0 to N times. The `before` callback will typically be called 0 times if the asynchronous operation was cancelled or, for example, if no connections are received by a TCP server. Persistent asynchronous resources like a TCP server will typically call the `before` callback multiple times, while other operations like `fs.open()` will call it only once.
#####
`after(asyncId)`
* `asyncId` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Called immediately after the callback specified in `before` is completed.
If an uncaught exception occurs during execution of the callback, then `after` will run *after* the `'uncaughtException'` event is emitted or a `domain`'s handler runs.
#####
`destroy(asyncId)`
* `asyncId` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Called after the resource corresponding to `asyncId` is destroyed. It is also called asynchronously from the embedder API `emitDestroy()`.
Some resources depend on garbage collection for cleanup, so if a reference is made to the `resource` object passed to `init` it is possible that `destroy` will never be called, causing a memory leak in the application. If the resource does not depend on garbage collection, then this will not be an issue.
#####
`promiseResolve(asyncId)`
Added in: v8.6.0 * `asyncId` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Called when the `resolve` function passed to the `Promise` constructor is invoked (either directly or through other means of resolving a promise).
`resolve()` does not do any observable synchronous work.
The `Promise` is not necessarily fulfilled or rejected at this point if the `Promise` was resolved by assuming the state of another `Promise`.
```
new Promise((resolve) => resolve(true)).then((a) => {});
```
calls the following callbacks:
```
init for PROMISE with id 5, trigger id: 1
promise resolve 5 # corresponds to resolve(true)
init for PROMISE with id 6, trigger id: 5 # the Promise returned by then()
before 6 # the then() callback is entered
promise resolve 6 # the then() callback resolves the promise by returning
after 6
```
####
`async_hooks.executionAsyncResource()`
Added in: v13.9.0, v12.17.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The resource representing the current execution. Useful to store data within the resource.
Resource objects returned by `executionAsyncResource()` are most often internal Node.js handle objects with undocumented APIs. Using any functions or properties on the object is likely to crash your application and should be avoided.
Using `executionAsyncResource()` in the top-level execution context will return an empty object as there is no handle or request object to use, but having an object representing the top-level can be helpful.
MJS modules
```
import { open } from 'node:fs';
import { executionAsyncId, executionAsyncResource } from 'node:async_hooks';
console.log(executionAsyncId(), executionAsyncResource()); // 1 {}
open(new URL(import.meta.url), 'r', (err, fd) => {
console.log(executionAsyncId(), executionAsyncResource()); // 7 FSReqWrap
});
```
CJS modules
```
const { open } = require('node:fs');
const { executionAsyncId, executionAsyncResource } = require('node:async_hooks');
console.log(executionAsyncId(), executionAsyncResource()); // 1 {}
open(__filename, 'r', (err, fd) => {
console.log(executionAsyncId(), executionAsyncResource()); // 7 FSReqWrap
});
```
This can be used to implement continuation local storage without the use of a tracking `Map` to store the metadata:
MJS modules
```
import { createServer } from 'node:http';
import {
executionAsyncId,
executionAsyncResource,
createHook
} from 'async_hooks';
const sym = Symbol('state'); // Private symbol to avoid pollution
createHook({
init(asyncId, type, triggerAsyncId, resource) {
const cr = executionAsyncResource();
if (cr) {
resource[sym] = cr[sym];
}
}
}).enable();
const server = createServer((req, res) => {
executionAsyncResource()[sym] = { state: req.url };
setTimeout(function() {
res.end(JSON.stringify(executionAsyncResource()[sym]));
}, 100);
}).listen(3000);
```
CJS modules
```
const { createServer } = require('node:http');
const {
executionAsyncId,
executionAsyncResource,
createHook
} = require('node:async_hooks');
const sym = Symbol('state'); // Private symbol to avoid pollution
createHook({
init(asyncId, type, triggerAsyncId, resource) {
const cr = executionAsyncResource();
if (cr) {
resource[sym] = cr[sym];
}
}
}).enable();
const server = createServer((req, res) => {
executionAsyncResource()[sym] = { state: req.url };
setTimeout(function() {
res.end(JSON.stringify(executionAsyncResource()[sym]));
}, 100);
}).listen(3000);
```
####
`async_hooks.executionAsyncId()`
History
| Version | Changes |
| --- | --- |
| v8.2.0 | Renamed from `currentId`. |
| v8.1.0 | Added in: v8.1.0 |
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The `asyncId` of the current execution context. Useful to track when something calls.
MJS modules
```
import { executionAsyncId } from 'node:async_hooks';
console.log(executionAsyncId()); // 1 - bootstrap
fs.open(path, 'r', (err, fd) => {
console.log(executionAsyncId()); // 6 - open()
});
```
CJS modules
```
const async_hooks = require('node:async_hooks');
console.log(async_hooks.executionAsyncId()); // 1 - bootstrap
fs.open(path, 'r', (err, fd) => {
console.log(async_hooks.executionAsyncId()); // 6 - open()
});
```
The ID returned from `executionAsyncId()` is related to execution timing, not causality (which is covered by `triggerAsyncId()`):
```
const server = net.createServer((conn) => {
// Returns the ID of the server, not of the new connection, because the
// callback runs in the execution scope of the server's MakeCallback().
async_hooks.executionAsyncId();
}).listen(port, () => {
// Returns the ID of a TickObject (process.nextTick()) because all
// callbacks passed to .listen() are wrapped in a nextTick().
async_hooks.executionAsyncId();
});
```
Promise contexts may not get precise `executionAsyncIds` by default. See the section on [promise execution tracking](#promise-execution-tracking).
####
`async_hooks.triggerAsyncId()`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The ID of the resource responsible for calling the callback that is currently being executed.
```
const server = net.createServer((conn) => {
// The resource that caused (or triggered) this callback to be called
// was that of the new connection. Thus the return value of triggerAsyncId()
// is the asyncId of "conn".
async_hooks.triggerAsyncId();
}).listen(port, () => {
// Even though all callbacks passed to .listen() are wrapped in a nextTick()
// the callback itself exists because the call to the server's .listen()
// was made. So the return value would be the ID of the server.
async_hooks.triggerAsyncId();
});
```
Promise contexts may not get valid `triggerAsyncId`s by default. See the section on [promise execution tracking](#promise-execution-tracking).
####
`async_hooks.asyncWrapProviders`
Added in: v17.2.0, v16.14.0 * Returns: A map of provider types to the corresponding numeric id. This map contains all the event types that might be emitted by the `async_hooks.init()` event.
This feature suppresses the deprecated usage of `process.binding('async_wrap').Providers`. See: [DEP0111](deprecations#dep0111-processbinding)
### Promise execution tracking
By default, promise executions are not assigned `asyncId`s due to the relatively expensive nature of the [promise introspection API](https://docs.google.com/document/d/1rda3yKGHimKIhg5YeoAmCOtyURgsbTH_qaYR79FELlk/edit) provided by V8. This means that programs using promises or `async`/`await` will not get correct execution and trigger ids for promise callback contexts by default.
MJS modules
```
import { executionAsyncId, triggerAsyncId } from 'node:async_hooks';
Promise.resolve(1729).then(() => {
console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`);
});
// produces:
// eid 1 tid 0
```
CJS modules
```
const { executionAsyncId, triggerAsyncId } = require('node:async_hooks');
Promise.resolve(1729).then(() => {
console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`);
});
// produces:
// eid 1 tid 0
```
Observe that the `then()` callback claims to have executed in the context of the outer scope even though there was an asynchronous hop involved. Also, the `triggerAsyncId` value is `0`, which means that we are missing context about the resource that caused (triggered) the `then()` callback to be executed.
Installing async hooks via `async_hooks.createHook` enables promise execution tracking:
MJS modules
```
import { createHook, executionAsyncId, triggerAsyncId } from 'node:async_hooks';
createHook({ init() {} }).enable(); // forces PromiseHooks to be enabled.
Promise.resolve(1729).then(() => {
console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`);
});
// produces:
// eid 7 tid 6
```
CJS modules
```
const { createHook, executionAsyncId, triggerAsyncId } = require('node:async_hooks');
createHook({ init() {} }).enable(); // forces PromiseHooks to be enabled.
Promise.resolve(1729).then(() => {
console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`);
});
// produces:
// eid 7 tid 6
```
In this example, adding any actual hook function enabled the tracking of promises. There are two promises in the example above; the promise created by `Promise.resolve()` and the promise returned by the call to `then()`. In the example above, the first promise got the `asyncId` `6` and the latter got `asyncId` `7`. During the execution of the `then()` callback, we are executing in the context of promise with `asyncId` `7`. This promise was triggered by async resource `6`.
Another subtlety with promises is that `before` and `after` callbacks are run only on chained promises. That means promises not created by `then()`/`catch()` will not have the `before` and `after` callbacks fired on them. For more details see the details of the V8 [PromiseHooks](https://docs.google.com/document/d/1rda3yKGHimKIhg5YeoAmCOtyURgsbTH_qaYR79FELlk/edit) API.
### JavaScript embedder API
Library developers that handle their own asynchronous resources performing tasks like I/O, connection pooling, or managing callback queues may use the `AsyncResource` JavaScript API so that all the appropriate callbacks are called.
#### Class: `AsyncResource`
The documentation for this class has moved [`AsyncResource`](async_context#class-asyncresource).
### Class: `AsyncLocalStorage`
The documentation for this class has moved [`AsyncLocalStorage`](async_context#class-asynclocalstorage).
| programming_docs |
node None Asynchronous context tracking
-----------------------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/async\_hooks.js](https://github.com/nodejs/node/blob/v19.0.1/lib/async_hooks.js)
### Introduction
These classes are used to associate state and propagate it throughout callbacks and promise chains. They allow storing data throughout the lifetime of a web request or any other asynchronous duration. It is similar to thread-local storage in other languages.
The `AsyncLocalStorage` and `AsyncResource` classes are part of the `node:async_hooks` module:
MJS modules
```
import { AsyncLocalStorage, AsyncResource } from 'node:async_hooks';
```
CJS modules
```
const { AsyncLocalStorage, AsyncResource } = require('node:async_hooks');
```
### Class: `AsyncLocalStorage`
History
| Version | Changes |
| --- | --- |
| v16.4.0 | AsyncLocalStorage is now Stable. Previously, it had been Experimental. |
| v13.10.0, v12.17.0 | Added in: v13.10.0, v12.17.0 |
This class creates stores that stay coherent through asynchronous operations.
While you can create your own implementation on top of the `node:async_hooks` module, `AsyncLocalStorage` should be preferred as it is a performant and memory safe implementation that involves significant optimizations that are non-obvious to implement.
The following example uses `AsyncLocalStorage` to build a simple logger that assigns IDs to incoming HTTP requests and includes them in messages logged within each request.
MJS modules
```
import http from 'node:http';
import { AsyncLocalStorage } from 'node:async_hooks';
const asyncLocalStorage = new AsyncLocalStorage();
function logWithId(msg) {
const id = asyncLocalStorage.getStore();
console.log(`${id !== undefined ? id : '-'}:`, msg);
}
let idSeq = 0;
http.createServer((req, res) => {
asyncLocalStorage.run(idSeq++, () => {
logWithId('start');
// Imagine any chain of async operations here
setImmediate(() => {
logWithId('finish');
res.end();
});
});
}).listen(8080);
http.get('http://localhost:8080');
http.get('http://localhost:8080');
// Prints:
// 0: start
// 1: start
// 0: finish
// 1: finish
```
CJS modules
```
const http = require('node:http');
const { AsyncLocalStorage } = require('node:async_hooks');
const asyncLocalStorage = new AsyncLocalStorage();
function logWithId(msg) {
const id = asyncLocalStorage.getStore();
console.log(`${id !== undefined ? id : '-'}:`, msg);
}
let idSeq = 0;
http.createServer((req, res) => {
asyncLocalStorage.run(idSeq++, () => {
logWithId('start');
// Imagine any chain of async operations here
setImmediate(() => {
logWithId('finish');
res.end();
});
});
}).listen(8080);
http.get('http://localhost:8080');
http.get('http://localhost:8080');
// Prints:
// 0: start
// 1: start
// 0: finish
// 1: finish
```
Each instance of `AsyncLocalStorage` maintains an independent storage context. Multiple instances can safely exist simultaneously without risk of interfering with each other's data.
####
`new AsyncLocalStorage()`
Added in: v13.10.0, v12.17.0 Creates a new instance of `AsyncLocalStorage`. Store is only provided within a `run()` call or after an `enterWith()` call.
####
`asyncLocalStorage.disable()`
Added in: v13.10.0, v12.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Disables the instance of `AsyncLocalStorage`. All subsequent calls to `asyncLocalStorage.getStore()` will return `undefined` until `asyncLocalStorage.run()` or `asyncLocalStorage.enterWith()` is called again.
When calling `asyncLocalStorage.disable()`, all current contexts linked to the instance will be exited.
Calling `asyncLocalStorage.disable()` is required before the `asyncLocalStorage` can be garbage collected. This does not apply to stores provided by the `asyncLocalStorage`, as those objects are garbage collected along with the corresponding async resources.
Use this method when the `asyncLocalStorage` is not in use anymore in the current process.
####
`asyncLocalStorage.getStore()`
Added in: v13.10.0, v12.17.0 * Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Returns the current store. If called outside of an asynchronous context initialized by calling `asyncLocalStorage.run()` or `asyncLocalStorage.enterWith()`, it returns `undefined`.
####
`asyncLocalStorage.enterWith(store)`
Added in: v13.11.0, v12.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `store` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Transitions into the context for the remainder of the current synchronous execution and then persists the store through any following asynchronous calls.
Example:
```
const store = { id: 1 };
// Replaces previous store with the given store object
asyncLocalStorage.enterWith(store);
asyncLocalStorage.getStore(); // Returns the store object
someAsyncOperation(() => {
asyncLocalStorage.getStore(); // Returns the same object
});
```
This transition will continue for the *entire* synchronous execution. This means that if, for example, the context is entered within an event handler subsequent event handlers will also run within that context unless specifically bound to another context with an `AsyncResource`. That is why `run()` should be preferred over `enterWith()` unless there are strong reasons to use the latter method.
```
const store = { id: 1 };
emitter.on('my-event', () => {
asyncLocalStorage.enterWith(store);
});
emitter.on('my-event', () => {
asyncLocalStorage.getStore(); // Returns the same object
});
asyncLocalStorage.getStore(); // Returns undefined
emitter.emit('my-event');
asyncLocalStorage.getStore(); // Returns the same object
```
####
`asyncLocalStorage.run(store, callback[, ...args])`
Added in: v13.10.0, v12.17.0 * `store` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Runs a function synchronously within a context and returns its return value. The store is not accessible outside of the callback function. The store is accessible to any asynchronous operations created within the callback.
The optional `args` are passed to the callback function.
If the callback function throws an error, the error is thrown by `run()` too. The stacktrace is not impacted by this call and the context is exited.
Example:
```
const store = { id: 2 };
try {
asyncLocalStorage.run(store, () => {
asyncLocalStorage.getStore(); // Returns the store object
setTimeout(() => {
asyncLocalStorage.getStore(); // Returns the store object
}, 200);
throw new Error();
});
} catch (e) {
asyncLocalStorage.getStore(); // Returns undefined
// The error will be caught here
}
```
####
`asyncLocalStorage.exit(callback[, ...args])`
Added in: v13.10.0, v12.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Runs a function synchronously outside of a context and returns its return value. The store is not accessible within the callback function or the asynchronous operations created within the callback. Any `getStore()` call done within the callback function will always return `undefined`.
The optional `args` are passed to the callback function.
If the callback function throws an error, the error is thrown by `exit()` too. The stacktrace is not impacted by this call and the context is re-entered.
Example:
```
// Within a call to run
try {
asyncLocalStorage.getStore(); // Returns the store object or value
asyncLocalStorage.exit(() => {
asyncLocalStorage.getStore(); // Returns undefined
throw new Error();
});
} catch (e) {
asyncLocalStorage.getStore(); // Returns the same object or value
// The error will be caught here
}
```
#### Usage with `async/await`
If, within an async function, only one `await` call is to run within a context, the following pattern should be used:
```
async function fn() {
await asyncLocalStorage.run(new Map(), () => {
asyncLocalStorage.getStore().set('key', value);
return foo(); // The return value of foo will be awaited
});
}
```
In this example, the store is only available in the callback function and the functions called by `foo`. Outside of `run`, calling `getStore` will return `undefined`.
#### Troubleshooting: Context loss
In most cases, `AsyncLocalStorage` works without issues. In rare situations, the current store is lost in one of the asynchronous operations.
If your code is callback-based, it is enough to promisify it with [`util.promisify()`](util#utilpromisifyoriginal) so it starts working with native promises.
If you need to use a callback-based API or your code assumes a custom thenable implementation, use the [`AsyncResource`](#class-asyncresource) class to associate the asynchronous operation with the correct execution context. Find the function call responsible for the context loss by logging the content of `asyncLocalStorage.getStore()` after the calls you suspect are responsible for the loss. When the code logs `undefined`, the last callback called is probably responsible for the context loss.
### Class: `AsyncResource`
History
| Version | Changes |
| --- | --- |
| v16.4.0 | AsyncResource is now Stable. Previously, it had been Experimental. |
The class `AsyncResource` is designed to be extended by the embedder's async resources. Using this, users can easily trigger the lifetime events of their own resources.
The `init` hook will trigger when an `AsyncResource` is instantiated.
The following is an overview of the `AsyncResource` API.
MJS modules
```
import { AsyncResource, executionAsyncId } from 'node:async_hooks';
// AsyncResource() is meant to be extended. Instantiating a
// new AsyncResource() also triggers init. If triggerAsyncId is omitted then
// async_hook.executionAsyncId() is used.
const asyncResource = new AsyncResource(
type, { triggerAsyncId: executionAsyncId(), requireManualDestroy: false }
);
// Run a function in the execution context of the resource. This will
// * establish the context of the resource
// * trigger the AsyncHooks before callbacks
// * call the provided function `fn` with the supplied arguments
// * trigger the AsyncHooks after callbacks
// * restore the original execution context
asyncResource.runInAsyncScope(fn, thisArg, ...args);
// Call AsyncHooks destroy callbacks.
asyncResource.emitDestroy();
// Return the unique ID assigned to the AsyncResource instance.
asyncResource.asyncId();
// Return the trigger ID for the AsyncResource instance.
asyncResource.triggerAsyncId();
```
CJS modules
```
const { AsyncResource, executionAsyncId } = require('node:async_hooks');
// AsyncResource() is meant to be extended. Instantiating a
// new AsyncResource() also triggers init. If triggerAsyncId is omitted then
// async_hook.executionAsyncId() is used.
const asyncResource = new AsyncResource(
type, { triggerAsyncId: executionAsyncId(), requireManualDestroy: false }
);
// Run a function in the execution context of the resource. This will
// * establish the context of the resource
// * trigger the AsyncHooks before callbacks
// * call the provided function `fn` with the supplied arguments
// * trigger the AsyncHooks after callbacks
// * restore the original execution context
asyncResource.runInAsyncScope(fn, thisArg, ...args);
// Call AsyncHooks destroy callbacks.
asyncResource.emitDestroy();
// Return the unique ID assigned to the AsyncResource instance.
asyncResource.asyncId();
// Return the trigger ID for the AsyncResource instance.
asyncResource.triggerAsyncId();
```
####
`new AsyncResource(type[, options])`
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The type of async event.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `triggerAsyncId` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The ID of the execution context that created this async event. **Default:** `executionAsyncId()`.
+ `requireManualDestroy` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `true`, disables `emitDestroy` when the object is garbage collected. This usually does not need to be set (even if `emitDestroy` is called manually), unless the resource's `asyncId` is retrieved and the sensitive API's `emitDestroy` is called with it. When set to `false`, the `emitDestroy` call on garbage collection will only take place if there is at least one active `destroy` hook. **Default:** `false`.
Example usage:
```
class DBQuery extends AsyncResource {
constructor(db) {
super('DBQuery');
this.db = db;
}
getInfo(query, callback) {
this.db.get(query, (err, data) => {
this.runInAsyncScope(callback, null, err, data);
});
}
close() {
this.db = null;
this.emitDestroy();
}
}
```
#### Static method: `AsyncResource.bind(fn[, type[, thisArg]])`
History
| Version | Changes |
| --- | --- |
| v17.8.0, v16.15.0 | Changed the default when `thisArg` is undefined to use `this` from the caller. |
| v16.0.0 | Added optional thisArg. |
| v14.8.0, v12.19.0 | Added in: v14.8.0, v12.19.0 |
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to bind to the current execution context.
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) An optional name to associate with the underlying `AsyncResource`.
* `thisArg` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Binds the given function to the current execution context.
The returned function will have an `asyncResource` property referencing the `AsyncResource` to which the function is bound.
####
`asyncResource.bind(fn[, thisArg])`
History
| Version | Changes |
| --- | --- |
| v17.8.0, v16.15.0 | Changed the default when `thisArg` is undefined to use `this` from the caller. |
| v16.0.0 | Added optional thisArg. |
| v14.8.0, v12.19.0 | Added in: v14.8.0, v12.19.0 |
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to bind to the current `AsyncResource`.
* `thisArg` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Binds the given function to execute to this `AsyncResource`'s scope.
The returned function will have an `asyncResource` property referencing the `AsyncResource` to which the function is bound.
####
`asyncResource.runInAsyncScope(fn[, thisArg, ...args])`
Added in: v9.6.0 * `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to call in the execution context of this async resource.
* `thisArg` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The receiver to be used for the function call.
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Optional arguments to pass to the function.
Call the provided function with the provided arguments in the execution context of the async resource. This will establish the context, trigger the AsyncHooks before callbacks, call the function, trigger the AsyncHooks after callbacks, and then restore the original execution context.
####
`asyncResource.emitDestroy()`
* Returns: [<AsyncResource>](async_hooks#class-asyncresource) A reference to `asyncResource`.
Call all `destroy` hooks. This should only ever be called once. An error will be thrown if it is called more than once. This **must** be manually called. If the resource is left to be collected by the GC then the `destroy` hooks will never be called.
####
`asyncResource.asyncId()`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The unique `asyncId` assigned to the resource.
####
`asyncResource.triggerAsyncId()`
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The same `triggerAsyncId` that is passed to the `AsyncResource` constructor.
#### Using `AsyncResource` for a `Worker` thread pool
The following example shows how to use the `AsyncResource` class to properly provide async tracking for a [`Worker`](worker_threads#class-worker) pool. Other resource pools, such as database connection pools, can follow a similar model.
Assuming that the task is adding two numbers, using a file named `task_processor.js` with the following content:
MJS modules
```
import { parentPort } from 'node:worker_threads';
parentPort.on('message', (task) => {
parentPort.postMessage(task.a + task.b);
});
```
CJS modules
```
const { parentPort } = require('node:worker_threads');
parentPort.on('message', (task) => {
parentPort.postMessage(task.a + task.b);
});
```
a Worker pool around it could use the following structure:
MJS modules
```
import { AsyncResource } from 'node:async_hooks';
import { EventEmitter } from 'node:events';
import path from 'node:path';
import { Worker } from 'node:worker_threads';
const kTaskInfo = Symbol('kTaskInfo');
const kWorkerFreedEvent = Symbol('kWorkerFreedEvent');
class WorkerPoolTaskInfo extends AsyncResource {
constructor(callback) {
super('WorkerPoolTaskInfo');
this.callback = callback;
}
done(err, result) {
this.runInAsyncScope(this.callback, null, err, result);
this.emitDestroy(); // `TaskInfo`s are used only once.
}
}
export default class WorkerPool extends EventEmitter {
constructor(numThreads) {
super();
this.numThreads = numThreads;
this.workers = [];
this.freeWorkers = [];
this.tasks = [];
for (let i = 0; i < numThreads; i++)
this.addNewWorker();
// Any time the kWorkerFreedEvent is emitted, dispatch
// the next task pending in the queue, if any.
this.on(kWorkerFreedEvent, () => {
if (this.tasks.length > 0) {
const { task, callback } = this.tasks.shift();
this.runTask(task, callback);
}
});
}
addNewWorker() {
const worker = new Worker(new URL('task_processer.js', import.meta.url));
worker.on('message', (result) => {
// In case of success: Call the callback that was passed to `runTask`,
// remove the `TaskInfo` associated with the Worker, and mark it as free
// again.
worker[kTaskInfo].done(null, result);
worker[kTaskInfo] = null;
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
});
worker.on('error', (err) => {
// In case of an uncaught exception: Call the callback that was passed to
// `runTask` with the error.
if (worker[kTaskInfo])
worker[kTaskInfo].done(err, null);
else
this.emit('error', err);
// Remove the worker from the list and start a new Worker to replace the
// current one.
this.workers.splice(this.workers.indexOf(worker), 1);
this.addNewWorker();
});
this.workers.push(worker);
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
}
runTask(task, callback) {
if (this.freeWorkers.length === 0) {
// No free threads, wait until a worker thread becomes free.
this.tasks.push({ task, callback });
return;
}
const worker = this.freeWorkers.pop();
worker[kTaskInfo] = new WorkerPoolTaskInfo(callback);
worker.postMessage(task);
}
close() {
for (const worker of this.workers) worker.terminate();
}
}
```
CJS modules
```
const { AsyncResource } = require('node:async_hooks');
const { EventEmitter } = require('node:events');
const path = require('node:path');
const { Worker } = require('node:worker_threads');
const kTaskInfo = Symbol('kTaskInfo');
const kWorkerFreedEvent = Symbol('kWorkerFreedEvent');
class WorkerPoolTaskInfo extends AsyncResource {
constructor(callback) {
super('WorkerPoolTaskInfo');
this.callback = callback;
}
done(err, result) {
this.runInAsyncScope(this.callback, null, err, result);
this.emitDestroy(); // `TaskInfo`s are used only once.
}
}
class WorkerPool extends EventEmitter {
constructor(numThreads) {
super();
this.numThreads = numThreads;
this.workers = [];
this.freeWorkers = [];
this.tasks = [];
for (let i = 0; i < numThreads; i++)
this.addNewWorker();
// Any time the kWorkerFreedEvent is emitted, dispatch
// the next task pending in the queue, if any.
this.on(kWorkerFreedEvent, () => {
if (this.tasks.length > 0) {
const { task, callback } = this.tasks.shift();
this.runTask(task, callback);
}
});
}
addNewWorker() {
const worker = new Worker(path.resolve(__dirname, 'task_processor.js'));
worker.on('message', (result) => {
// In case of success: Call the callback that was passed to `runTask`,
// remove the `TaskInfo` associated with the Worker, and mark it as free
// again.
worker[kTaskInfo].done(null, result);
worker[kTaskInfo] = null;
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
});
worker.on('error', (err) => {
// In case of an uncaught exception: Call the callback that was passed to
// `runTask` with the error.
if (worker[kTaskInfo])
worker[kTaskInfo].done(err, null);
else
this.emit('error', err);
// Remove the worker from the list and start a new Worker to replace the
// current one.
this.workers.splice(this.workers.indexOf(worker), 1);
this.addNewWorker();
});
this.workers.push(worker);
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
}
runTask(task, callback) {
if (this.freeWorkers.length === 0) {
// No free threads, wait until a worker thread becomes free.
this.tasks.push({ task, callback });
return;
}
const worker = this.freeWorkers.pop();
worker[kTaskInfo] = new WorkerPoolTaskInfo(callback);
worker.postMessage(task);
}
close() {
for (const worker of this.workers) worker.terminate();
}
}
module.exports = WorkerPool;
```
Without the explicit tracking added by the `WorkerPoolTaskInfo` objects, it would appear that the callbacks are associated with the individual `Worker` objects. However, the creation of the `Worker`s is not associated with the creation of the tasks and does not provide information about when tasks were scheduled.
This pool could be used as follows:
MJS modules
```
import WorkerPool from './worker_pool.js';
import os from 'node:os';
const pool = new WorkerPool(os.cpus().length);
let finished = 0;
for (let i = 0; i < 10; i++) {
pool.runTask({ a: 42, b: 100 }, (err, result) => {
console.log(i, err, result);
if (++finished === 10)
pool.close();
});
}
```
CJS modules
```
const WorkerPool = require('./worker_pool.js');
const os = require('node:os');
const pool = new WorkerPool(os.cpus().length);
let finished = 0;
for (let i = 0; i < 10; i++) {
pool.runTask({ a: 42, b: 100 }, (err, result) => {
console.log(i, err, result);
if (++finished === 10)
pool.close();
});
}
```
#### Integrating `AsyncResource` with `EventEmitter`
Event listeners triggered by an [`EventEmitter`](events#class-eventemitter) may be run in a different execution context than the one that was active when `eventEmitter.on()` was called.
The following example shows how to use the `AsyncResource` class to properly associate an event listener with the correct execution context. The same approach can be applied to a [`Stream`](stream#stream) or a similar event-driven class.
MJS modules
```
import { createServer } from 'node:http';
import { AsyncResource, executionAsyncId } from 'node:async_hooks';
const server = createServer((req, res) => {
req.on('close', AsyncResource.bind(() => {
// Execution context is bound to the current outer scope.
}));
req.on('close', () => {
// Execution context is bound to the scope that caused 'close' to emit.
});
res.end();
}).listen(3000);
```
CJS modules
```
const { createServer } = require('node:http');
const { AsyncResource, executionAsyncId } = require('node:async_hooks');
const server = createServer((req, res) => {
req.on('close', AsyncResource.bind(() => {
// Execution context is bound to the current outer scope.
}));
req.on('close', () => {
// Execution context is bound to the scope that caused 'close' to emit.
});
res.end();
}).listen(3000);
```
| programming_docs |
node None Console
-------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/console.js](https://github.com/nodejs/node/blob/v19.0.1/lib/console.js)
The `node:console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers.
The module exports two specific components:
* A `Console` class with methods such as `console.log()`, `console.error()`, and `console.warn()` that can be used to write to any Node.js stream.
* A global `console` instance configured to write to [`process.stdout`](process#processstdout) and [`process.stderr`](process#processstderr). The global `console` can be used without calling `require('node:console')`.
***Warning***: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [note on process I/O](process#a-note-on-process-io) for more information.
Example using the global `console`:
```
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
```
Example using the `Console` class:
```
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
```
### Class: `Console`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | Errors that occur while writing to the underlying streams will now be ignored by default. |
The `Console` class can be used to create a simple logger with configurable output streams and can be accessed using either `require('node:console').Console` or `console.Console` (or their destructured counterparts):
```
const { Console } = require('node:console');
```
```
const { Console } = console;
```
####
`new Console(stdout[, stderr][, ignoreErrors])`
####
`new Console(options)`
History
| Version | Changes |
| --- | --- |
| v14.2.0, v12.17.0 | The `groupIndentation` option was introduced. |
| v11.7.0 | The `inspectOptions` option is introduced. |
| v10.0.0 | The `Console` constructor now supports an `options` argument, and the `colorMode` option was introduced. |
| v8.0.0 | The `ignoreErrors` option was introduced. |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `stdout` [<stream.Writable>](stream#class-streamwritable)
+ `stderr` [<stream.Writable>](stream#class-streamwritable)
+ `ignoreErrors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Ignore errors when writing to the underlying streams. **Default:** `true`.
+ `colorMode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Set color support for this `Console` instance. Setting to `true` enables coloring while inspecting values. Setting to `false` disables coloring while inspecting values. Setting to `'auto'` makes color support depend on the value of the `isTTY` property and the value returned by `getColorDepth()` on the respective stream. This option can not be used, if `inspectOptions.colors` is set as well. **Default:** `'auto'`.
+ `inspectOptions` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Specifies options that are passed along to [`util.inspect()`](util#utilinspectobject-options).
+ `groupIndentation` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Set group indentation. **Default:** `2`.
Creates a new `Console` with one or two writable stream instances. `stdout` is a writable stream to print log or info output. `stderr` is used for warning or error output. If `stderr` is not provided, `stdout` is used for `stderr`.
```
const output = fs.createWriteStream('./stdout.log');
const errorOutput = fs.createWriteStream('./stderr.log');
// Custom simple logger
const logger = new Console({ stdout: output, stderr: errorOutput });
// use it like console
const count = 5;
logger.log('count: %d', count);
// In stdout.log: count 5
```
The global `console` is a special `Console` whose output is sent to [`process.stdout`](process#processstdout) and [`process.stderr`](process#processstderr). It is equivalent to calling:
```
new Console({ stdout: process.stdout, stderr: process.stderr });
```
####
`console.assert(value[, ...message])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | The implementation is now spec compliant and does not throw anymore. |
| v0.1.101 | Added in: v0.1.101 |
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The value tested for being truthy.
* `...message` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) All arguments besides `value` are used as error message.
`console.assert()` writes a message if `value` is [falsy](https://developer.mozilla.org/en-US/docs/Glossary/Falsy) or omitted. It only writes a message and does not otherwise affect execution. The output always starts with `"Assertion failed"`. If provided, `message` is formatted using [`util.format()`](util#utilformatformat-args).
If `value` is [truthy](https://developer.mozilla.org/en-US/docs/Glossary/Truthy), nothing happens.
```
console.assert(true, 'does nothing');
console.assert(false, 'Whoops %s work', 'didn\'t');
// Assertion failed: Whoops didn't work
console.assert();
// Assertion failed
```
####
`console.clear()`
Added in: v8.3.0 When `stdout` is a TTY, calling `console.clear()` will attempt to clear the TTY. When `stdout` is not a TTY, this method does nothing.
The specific operation of `console.clear()` can vary across operating systems and terminal types. For most Linux operating systems, `console.clear()` operates similarly to the `clear` shell command. On Windows, `console.clear()` will clear only the output in the current terminal viewport for the Node.js binary.
####
`console.count([label])`
Added in: v8.3.0 * `label` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The display label for the counter. **Default:** `'default'`.
Maintains an internal counter specific to `label` and outputs to `stdout` the number of times `console.count()` has been called with the given `label`.
```
> console.count()
default: 1
undefined
> console.count('default')
default: 2
undefined
> console.count('abc')
abc: 1
undefined
> console.count('xyz')
xyz: 1
undefined
> console.count('abc')
abc: 2
undefined
> console.count()
default: 3
undefined
>
```
####
`console.countReset([label])`
Added in: v8.3.0 * `label` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The display label for the counter. **Default:** `'default'`.
Resets the internal counter specific to `label`.
```
> console.count('abc');
abc: 1
undefined
> console.countReset('abc');
undefined
> console.count('abc');
abc: 1
undefined
>
```
####
`console.debug(data[, ...args])`
History
| Version | Changes |
| --- | --- |
| v8.10.0 | `console.debug` is now an alias for `console.log`. |
| v8.0.0 | Added in: v8.0.0 |
* `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
The `console.debug()` function is an alias for [`console.log()`](#consolelogdata-args).
####
`console.dir(obj[, options])`
Added in: v0.1.101 * `obj` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `showHidden` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true` then the object's non-enumerable and symbol properties will be shown too. **Default:** `false`.
+ `depth` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Tells [`util.inspect()`](util#utilinspectobject-options) how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. To make it recurse indefinitely, pass `null`. **Default:** `2`.
+ `colors` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, then the output will be styled with ANSI color codes. Colors are customizable; see [customizing `util.inspect()` colors](util#customizing-utilinspect-colors). **Default:** `false`.
Uses [`util.inspect()`](util#utilinspectobject-options) on `obj` and prints the resulting string to `stdout`. This function bypasses any custom `inspect()` function defined on `obj`.
####
`console.dirxml(...data)`
History
| Version | Changes |
| --- | --- |
| v9.3.0 | `console.dirxml` now calls `console.log` for its arguments. |
| v8.0.0 | Added in: v8.0.0 |
* `...data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
This method calls `console.log()` passing it the arguments received. This method does not produce any XML formatting.
####
`console.error([data][, ...args])`
Added in: v0.1.100 * `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Prints to `stderr` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](util#utilformatformat-args)).
```
const code = 5;
console.error('error #%d', code);
// Prints: error #5, to stderr
console.error('error', code);
// Prints: error 5, to stderr
```
If formatting elements (e.g. `%d`) are not found in the first string then [`util.inspect()`](util#utilinspectobject-options) is called on each argument and the resulting string values are concatenated. See [`util.format()`](util#utilformatformat-args) for more information.
####
`console.group([...label])`
Added in: v8.5.0 * `...label` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Increases indentation of subsequent lines by spaces for `groupIndentation` length.
If one or more `label`s are provided, those are printed first without the additional indentation.
####
`console.groupCollapsed()`
Added in: v8.5.0 An alias for [`console.group()`](#consolegrouplabel).
####
`console.groupEnd()`
Added in: v8.5.0 Decreases indentation of subsequent lines by spaces for `groupIndentation` length.
####
`console.info([data][, ...args])`
Added in: v0.1.100 * `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
The `console.info()` function is an alias for [`console.log()`](#consolelogdata-args).
####
`console.log([data][, ...args])`
Added in: v0.1.100 * `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](util#utilformatformat-args)).
```
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
```
See [`util.format()`](util#utilformatformat-args) for more information.
####
`console.table(tabularData[, properties])`
Added in: v10.0.0 * `tabularData` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `properties` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Alternate properties for constructing the table.
Try to construct a table with the columns of the properties of `tabularData` (or use `properties`) and rows of `tabularData` and log it. Falls back to just logging the argument if it can't be parsed as tabular.
```
// These can't be parsed as tabular data
console.table(Symbol());
// Symbol()
console.table(undefined);
// undefined
console.table([{ a: 1, b: 'Y' }, { a: 'Z', b: 2 }]);
// ┌─────────┬─────┬─────┐
// │ (index) │ a │ b │
// ├─────────┼─────┼─────┤
// │ 0 │ 1 │ 'Y' │
// │ 1 │ 'Z' │ 2 │
// └─────────┴─────┴─────┘
console.table([{ a: 1, b: 'Y' }, { a: 'Z', b: 2 }], ['a']);
// ┌─────────┬─────┐
// │ (index) │ a │
// ├─────────┼─────┤
// │ 0 │ 1 │
// │ 1 │ 'Z' │
// └─────────┴─────┘
```
####
`console.time([label])`
Added in: v0.1.104 * `label` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'default'`
Starts a timer that can be used to compute the duration of an operation. Timers are identified by a unique `label`. Use the same `label` when calling [`console.timeEnd()`](#consoletimeendlabel) to stop the timer and output the elapsed time in suitable time units to `stdout`. For example, if the elapsed time is 3869ms, `console.timeEnd()` displays "3.869s".
####
`console.timeEnd([label])`
History
| Version | Changes |
| --- | --- |
| v13.0.0 | The elapsed time is displayed with a suitable time unit. |
| v6.0.0 | This method no longer supports multiple calls that don't map to individual `console.time()` calls; see below for details. |
| v0.1.104 | Added in: v0.1.104 |
* `label` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'default'`
Stops a timer that was previously started by calling [`console.time()`](#consoletimelabel) and prints the result to `stdout`:
```
console.time('bunch-of-stuff');
// Do a bunch of stuff.
console.timeEnd('bunch-of-stuff');
// Prints: bunch-of-stuff: 225.438ms
```
####
`console.timeLog([label][, ...data])`
Added in: v10.7.0 * `label` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'default'`
* `...data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
For a timer that was previously started by calling [`console.time()`](#consoletimelabel), prints the elapsed time and other `data` arguments to `stdout`:
```
console.time('process');
const value = expensiveProcess1(); // Returns 42
console.timeLog('process', value);
// Prints "process: 365.227ms 42".
doExpensiveProcess2(value);
console.timeEnd('process');
```
####
`console.trace([message][, ...args])`
Added in: v0.1.104 * `message` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Prints to `stderr` the string `'Trace: '`, followed by the [`util.format()`](util#utilformatformat-args) formatted message and stack trace to the current position in the code.
```
console.trace('Show me');
// Prints: (stack trace will vary based on where trace is called)
// Trace: Show me
// at repl:2:9
// at REPLServer.defaultEval (repl.js:248:27)
// at bound (domain.js:287:14)
// at REPLServer.runBound [as eval] (domain.js:300:12)
// at REPLServer.<anonymous> (repl.js:412:12)
// at emitOne (events.js:82:20)
// at REPLServer.emit (events.js:169:7)
// at REPLServer.Interface._onLine (readline.js:210:10)
// at REPLServer.Interface._line (readline.js:549:8)
// at REPLServer.Interface._ttyWrite (readline.js:826:14)
```
####
`console.warn([data][, ...args])`
Added in: v0.1.100 * `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
The `console.warn()` function is an alias for [`console.error()`](#consoleerrordata-args).
### Inspector only methods
The following methods are exposed by the V8 engine in the general API but do not display anything unless used in conjunction with the [inspector](debugger) (`--inspect` flag).
####
`console.profile([label])`
Added in: v8.0.0 * `label` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
This method does not display anything unless used in the inspector. The `console.profile()` method starts a JavaScript CPU profile with an optional label until [`console.profileEnd()`](#consoleprofileendlabel) is called. The profile is then added to the **Profile** panel of the inspector.
```
console.profile('MyLabel');
// Some code
console.profileEnd('MyLabel');
// Adds the profile 'MyLabel' to the Profiles panel of the inspector.
```
####
`console.profileEnd([label])`
Added in: v8.0.0 * `label` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
This method does not display anything unless used in the inspector. Stops the current JavaScript CPU profiling session if one has been started and prints the report to the **Profiles** panel of the inspector. See [`console.profile()`](#consoleprofilelabel) for an example.
If this method is called without a label, the most recently started profile is stopped.
####
`console.timeStamp([label])`
Added in: v8.0.0 * `label` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
This method does not display anything unless used in the inspector. The `console.timeStamp()` method adds an event with the label `'label'` to the **Timeline** panel of the inspector.
node None Worker threads
--------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/worker\_threads.js](https://github.com/nodejs/node/blob/v19.0.1/lib/worker_threads.js)
The `node:worker_threads` module enables the use of threads that execute JavaScript in parallel. To access it:
```
const worker = require('node:worker_threads');
```
Workers (threads) are useful for performing CPU-intensive JavaScript operations. They do not help much with I/O-intensive work. The Node.js built-in asynchronous I/O operations are more efficient than Workers can be.
Unlike `child_process` or `cluster`, `worker_threads` can share memory. They do so by transferring `ArrayBuffer` instances or sharing `SharedArrayBuffer` instances.
```
const {
Worker, isMainThread, parentPort, workerData
} = require('node:worker_threads');
if (isMainThread) {
module.exports = function parseJSAsync(script) {
return new Promise((resolve, reject) => {
const worker = new Worker(__filename, {
workerData: script
});
worker.on('message', resolve);
worker.on('error', reject);
worker.on('exit', (code) => {
if (code !== 0)
reject(new Error(`Worker stopped with exit code ${code}`));
});
});
};
} else {
const { parse } = require('some-js-parsing-library');
const script = workerData;
parentPort.postMessage(parse(script));
}
```
The above example spawns a Worker thread for each `parseJSAsync()` call. In practice, use a pool of Workers for these kinds of tasks. Otherwise, the overhead of creating Workers would likely exceed their benefit.
When implementing a worker pool, use the [`AsyncResource`](async_hooks#class-asyncresource) API to inform diagnostic tools (e.g. to provide asynchronous stack traces) about the correlation between tasks and their outcomes. See ["Using `AsyncResource` for a `Worker` thread pool"](async_context#using-asyncresource-for-a-worker-thread-pool) in the `async_hooks` documentation for an example implementation.
Worker threads inherit non-process-specific options by default. Refer to [`Worker constructor options`](#new-workerfilename-options) to know how to customize worker thread options, specifically `argv` and `execArgv` options.
###
`worker.getEnvironmentData(key)`
History
| Version | Changes |
| --- | --- |
| v17.5.0, v16.15.0 | No longer experimental. |
| v15.12.0, v14.18.0 | Added in: v15.12.0, v14.18.0 |
* `key` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Any arbitrary, cloneable JavaScript value that can be used as a [<Map>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) key.
* Returns: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Within a worker thread, `worker.getEnvironmentData()` returns a clone of data passed to the spawning thread's `worker.setEnvironmentData()`. Every new `Worker` receives its own copy of the environment data automatically.
```
const {
Worker,
isMainThread,
setEnvironmentData,
getEnvironmentData,
} = require('node:worker_threads');
if (isMainThread) {
setEnvironmentData('Hello', 'World!');
const worker = new Worker(__filename);
} else {
console.log(getEnvironmentData('Hello')); // Prints 'World!'.
}
```
###
`worker.isMainThread`
Added in: v10.5.0 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` if this code is not running inside of a [`Worker`](#class-worker) thread.
```
const { Worker, isMainThread } = require('node:worker_threads');
if (isMainThread) {
// This re-loads the current file inside a Worker instance.
new Worker(__filename);
} else {
console.log('Inside Worker!');
console.log(isMainThread); // Prints 'false'.
}
```
###
`worker.markAsUntransferable(object)`
Added in: v14.5.0, v12.19.0 Mark an object as not transferable. If `object` occurs in the transfer list of a [`port.postMessage()`](#portpostmessagevalue-transferlist) call, it is ignored.
In particular, this makes sense for objects that can be cloned, rather than transferred, and which are used by other objects on the sending side. For example, Node.js marks the `ArrayBuffer`s it uses for its [`Buffer` pool](buffer#static-method-bufferallocunsafesize) with this.
This operation cannot be undone.
```
const { MessageChannel, markAsUntransferable } = require('node:worker_threads');
const pooledBuffer = new ArrayBuffer(8);
const typedArray1 = new Uint8Array(pooledBuffer);
const typedArray2 = new Float64Array(pooledBuffer);
markAsUntransferable(pooledBuffer);
const { port1 } = new MessageChannel();
port1.postMessage(typedArray1, [ typedArray1.buffer ]);
// The following line prints the contents of typedArray1 -- it still owns
// its memory and has been cloned, not transferred. Without
// `markAsUntransferable()`, this would print an empty Uint8Array.
// typedArray2 is intact as well.
console.log(typedArray1);
console.log(typedArray2);
```
There is no equivalent to this API in browsers.
###
`worker.moveMessagePortToContext(port, contextifiedSandbox)`
Added in: v11.13.0 * `port` [<MessagePort>](worker_threads#class-messageport) The message port to transfer.
* `contextifiedSandbox` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A [contextified](vm#what-does-it-mean-to-contextify-an-object) object as returned by the `vm.createContext()` method.
* Returns: [<MessagePort>](worker_threads#class-messageport)
Transfer a `MessagePort` to a different [`vm`](vm) Context. The original `port` object is rendered unusable, and the returned `MessagePort` instance takes its place.
The returned `MessagePort` is an object in the target context and inherits from its global `Object` class. Objects passed to the [`port.onmessage()`](https://developer.mozilla.org/en-US/docs/Web/API/MessagePort/onmessage) listener are also created in the target context and inherit from its global `Object` class.
However, the created `MessagePort` no longer inherits from [`EventTarget`](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget), and only [`port.onmessage()`](https://developer.mozilla.org/en-US/docs/Web/API/MessagePort/onmessage) can be used to receive events using it.
###
`worker.parentPort`
Added in: v10.5.0 * [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<MessagePort>](worker_threads#class-messageport)
If this thread is a [`Worker`](#class-worker), this is a [`MessagePort`](#class-messageport) allowing communication with the parent thread. Messages sent using `parentPort.postMessage()` are available in the parent thread using `worker.on('message')`, and messages sent from the parent thread using `worker.postMessage()` are available in this thread using `parentPort.on('message')`.
```
const { Worker, isMainThread, parentPort } = require('node:worker_threads');
if (isMainThread) {
const worker = new Worker(__filename);
worker.once('message', (message) => {
console.log(message); // Prints 'Hello, world!'.
});
worker.postMessage('Hello, world!');
} else {
// When a message from the parent thread is received, send it back:
parentPort.once('message', (message) => {
parentPort.postMessage(message);
});
}
```
###
`worker.receiveMessageOnPort(port)`
History
| Version | Changes |
| --- | --- |
| v15.12.0 | The port argument can also refer to a `BroadcastChannel` now. |
| v12.3.0 | Added in: v12.3.0 |
* `port` [<MessagePort>](worker_threads#class-messageport) | [<BroadcastChannel>](worker_threads#class-broadcastchannel-extends-eventtarget)
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
Receive a single message from a given `MessagePort`. If no message is available, `undefined` is returned, otherwise an object with a single `message` property that contains the message payload, corresponding to the oldest message in the `MessagePort`'s queue.
```
const { MessageChannel, receiveMessageOnPort } = require('node:worker_threads');
const { port1, port2 } = new MessageChannel();
port1.postMessage({ hello: 'world' });
console.log(receiveMessageOnPort(port2));
// Prints: { message: { hello: 'world' } }
console.log(receiveMessageOnPort(port2));
// Prints: undefined
```
When this function is used, no `'message'` event is emitted and the `onmessage` listener is not invoked.
###
`worker.resourceLimits`
Added in: v13.2.0, v12.16.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `maxYoungGenerationSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `maxOldGenerationSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `codeRangeSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `stackSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Provides the set of JS engine resource constraints inside this Worker thread. If the `resourceLimits` option was passed to the [`Worker`](#class-worker) constructor, this matches its values.
If this is used in the main thread, its value is an empty object.
###
`worker.SHARE_ENV`
Added in: v11.14.0 * [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
A special value that can be passed as the `env` option of the [`Worker`](#class-worker) constructor, to indicate that the current thread and the Worker thread should share read and write access to the same set of environment variables.
```
const { Worker, SHARE_ENV } = require('node:worker_threads');
new Worker('process.env.SET_IN_WORKER = "foo"', { eval: true, env: SHARE_ENV })
.on('exit', () => {
console.log(process.env.SET_IN_WORKER); // Prints 'foo'.
});
```
###
`worker.setEnvironmentData(key[, value])`
History
| Version | Changes |
| --- | --- |
| v17.5.0, v16.15.0 | No longer experimental. |
| v15.12.0, v14.18.0 | Added in: v15.12.0, v14.18.0 |
* `key` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Any arbitrary, cloneable JavaScript value that can be used as a [<Map>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) key.
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Any arbitrary, cloneable JavaScript value that will be cloned and passed automatically to all new `Worker` instances. If `value` is passed as `undefined`, any previously set value for the `key` will be deleted.
The `worker.setEnvironmentData()` API sets the content of `worker.getEnvironmentData()` in the current thread and all new `Worker` instances spawned from the current context.
###
`worker.threadId`
Added in: v10.5.0 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
An integer identifier for the current thread. On the corresponding worker object (if there is any), it is available as [`worker.threadId`](#workerthreadid_1). This value is unique for each [`Worker`](#class-worker) instance inside a single process.
###
`worker.workerData`
Added in: v10.5.0 An arbitrary JavaScript value that contains a clone of the data passed to this thread's `Worker` constructor.
The data is cloned as if using [`postMessage()`](#portpostmessagevalue-transferlist), according to the [HTML structured clone algorithm](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm).
```
const { Worker, isMainThread, workerData } = require('node:worker_threads');
if (isMainThread) {
const worker = new Worker(__filename, { workerData: 'Hello, world!' });
} else {
console.log(workerData); // Prints 'Hello, world!'.
}
```
### Class: `BroadcastChannel extends EventTarget`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | No longer experimental. |
| v15.4.0 | Added in: v15.4.0 |
Instances of `BroadcastChannel` allow asynchronous one-to-many communication with all other `BroadcastChannel` instances bound to the same channel name.
```
'use strict';
const {
isMainThread,
BroadcastChannel,
Worker
} = require('node:worker_threads');
const bc = new BroadcastChannel('hello');
if (isMainThread) {
let c = 0;
bc.onmessage = (event) => {
console.log(event.data);
if (++c === 10) bc.close();
};
for (let n = 0; n < 10; n++)
new Worker(__filename);
} else {
bc.postMessage('hello from every worker');
bc.close();
}
```
####
`new BroadcastChannel(name)`
Added in: v15.4.0 * `name` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The name of the channel to connect to. Any JavaScript value that can be converted to a string using ``${name}`` is permitted.
####
`broadcastChannel.close()`
Added in: v15.4.0 Closes the `BroadcastChannel` connection.
####
`broadcastChannel.onmessage`
Added in: v15.4.0 * Type: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked with a single `MessageEvent` argument when a message is received.
####
`broadcastChannel.onmessageerror`
Added in: v15.4.0 * Type: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked with a received message cannot be deserialized.
####
`broadcastChannel.postMessage(message)`
Added in: v15.4.0 * `message` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Any cloneable JavaScript value.
####
`broadcastChannel.ref()`
Added in: v15.4.0 Opposite of `unref()`. Calling `ref()` on a previously `unref()`ed BroadcastChannel does *not* let the program exit if it's the only active handle left (the default behavior). If the port is `ref()`ed, calling `ref()` again has no effect.
####
`broadcastChannel.unref()`
Added in: v15.4.0 Calling `unref()` on a BroadcastChannel allows the thread to exit if this is the only active handle in the event system. If the BroadcastChannel is already `unref()`ed calling `unref()` again has no effect.
### Class: `MessageChannel`
Added in: v10.5.0 Instances of the `worker.MessageChannel` class represent an asynchronous, two-way communications channel. The `MessageChannel` has no methods of its own. `new MessageChannel()` yields an object with `port1` and `port2` properties, which refer to linked [`MessagePort`](#class-messageport) instances.
```
const { MessageChannel } = require('node:worker_threads');
const { port1, port2 } = new MessageChannel();
port1.on('message', (message) => console.log('received', message));
port2.postMessage({ foo: 'bar' });
// Prints: received { foo: 'bar' } from the `port1.on('message')` listener
```
### Class: `MessagePort`
History
| Version | Changes |
| --- | --- |
| v14.7.0 | This class now inherits from `EventTarget` rather than from `EventEmitter`. |
| v10.5.0 | Added in: v10.5.0 |
* Extends: [<EventTarget>](events#class-eventtarget)
Instances of the `worker.MessagePort` class represent one end of an asynchronous, two-way communications channel. It can be used to transfer structured data, memory regions and other `MessagePort`s between different [`Worker`](#class-worker)s.
This implementation matches [browser `MessagePort`](https://developer.mozilla.org/en-US/docs/Web/API/MessagePort)s.
#### Event: `'close'`
Added in: v10.5.0 The `'close'` event is emitted once either side of the channel has been disconnected.
```
const { MessageChannel } = require('node:worker_threads');
const { port1, port2 } = new MessageChannel();
// Prints:
// foobar
// closed!
port2.on('message', (message) => console.log(message));
port2.on('close', () => console.log('closed!'));
port1.postMessage('foobar');
port1.close();
```
#### Event: `'message'`
Added in: v10.5.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The transmitted value
The `'message'` event is emitted for any incoming message, containing the cloned input of [`port.postMessage()`](#portpostmessagevalue-transferlist).
Listeners on this event receive a clone of the `value` parameter as passed to `postMessage()` and no further arguments.
#### Event: `'messageerror'`
Added in: v14.5.0, v12.19.0 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) An Error object
The `'messageerror'` event is emitted when deserializing a message failed.
Currently, this event is emitted when there is an error occurring while instantiating the posted JS object on the receiving end. Such situations are rare, but can happen, for instance, when certain Node.js API objects are received in a `vm.Context` (where Node.js APIs are currently unavailable).
####
`port.close()`
Added in: v10.5.0 Disables further sending of messages on either side of the connection. This method can be called when no further communication will happen over this `MessagePort`.
The [`'close'` event](#event-close) is emitted on both `MessagePort` instances that are part of the channel.
####
`port.postMessage(value[, transferList])`
History
| Version | Changes |
| --- | --- |
| v15.6.0 | Added `X509Certificate` to the list of cloneable types. |
| v15.0.0 | Added `CryptoKey` to the list of cloneable types. |
| v15.14.0, v14.18.0 | Add 'BlockList' to the list of cloneable types. |
| v15.9.0, v14.18.0 | Add 'Histogram' types to the list of cloneable types. |
| v14.5.0, v12.19.0 | Added `KeyObject` to the list of cloneable types. |
| v14.5.0, v12.19.0 | Added `FileHandle` to the list of transferable types. |
| v10.5.0 | Added in: v10.5.0 |
* `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `transferList` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Sends a JavaScript value to the receiving side of this channel. `value` is transferred in a way which is compatible with the [HTML structured clone algorithm](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm).
In particular, the significant differences to `JSON` are:
* `value` may contain circular references.
* `value` may contain instances of builtin JS types such as `RegExp`s, `BigInt`s, `Map`s, `Set`s, etc.
* `value` may contain typed arrays, both using `ArrayBuffer`s and `SharedArrayBuffer`s.
* `value` may contain [`WebAssembly.Module`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Module) instances.
* `value` may not contain native (C++-backed) objects other than:
+ [<CryptoKey>](webcrypto#class-cryptokey)s,
+ [<FileHandle>](fs#class-filehandle)s,
+ [<Histogram>](perf_hooks#class-histogram)s,
+ [<KeyObject>](crypto#class-keyobject)s,
+ [<MessagePort>](worker_threads#class-messageport)s,
+ [<net.BlockList>](net#class-netblocklist)s,
+ [<net.SocketAddress>](net#class-netsocketaddress)es,
+ [<X509Certificate>](crypto#class-x509certificate)s.
```
const { MessageChannel } = require('node:worker_threads');
const { port1, port2 } = new MessageChannel();
port1.on('message', (message) => console.log(message));
const circularData = {};
circularData.foo = circularData;
// Prints: { foo: [Circular] }
port2.postMessage(circularData);
```
`transferList` may be a list of [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer), [`MessagePort`](#class-messageport), and [`FileHandle`](fs#class-filehandle) objects. After transferring, they are not usable on the sending side of the channel anymore (even if they are not contained in `value`). Unlike with [child processes](child_process), transferring handles such as network sockets is currently not supported.
If `value` contains [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) instances, those are accessible from either thread. They cannot be listed in `transferList`.
`value` may still contain `ArrayBuffer` instances that are not in `transferList`; in that case, the underlying memory is copied rather than moved.
```
const { MessageChannel } = require('node:worker_threads');
const { port1, port2 } = new MessageChannel();
port1.on('message', (message) => console.log(message));
const uint8Array = new Uint8Array([ 1, 2, 3, 4 ]);
// This posts a copy of `uint8Array`:
port2.postMessage(uint8Array);
// This does not copy data, but renders `uint8Array` unusable:
port2.postMessage(uint8Array, [ uint8Array.buffer ]);
// The memory for the `sharedUint8Array` is accessible from both the
// original and the copy received by `.on('message')`:
const sharedUint8Array = new Uint8Array(new SharedArrayBuffer(4));
port2.postMessage(sharedUint8Array);
// This transfers a freshly created message port to the receiver.
// This can be used, for example, to create communication channels between
// multiple `Worker` threads that are children of the same parent thread.
const otherChannel = new MessageChannel();
port2.postMessage({ port: otherChannel.port1 }, [ otherChannel.port1 ]);
```
The message object is cloned immediately, and can be modified after posting without having side effects.
For more information on the serialization and deserialization mechanisms behind this API, see the [serialization API of the `node:v8` module](v8#serialization-api).
##### Considerations when transferring TypedArrays and Buffers
All `TypedArray` and `Buffer` instances are views over an underlying `ArrayBuffer`. That is, it is the `ArrayBuffer` that actually stores the raw data while the `TypedArray` and `Buffer` objects provide a way of viewing and manipulating the data. It is possible and common for multiple views to be created over the same `ArrayBuffer` instance. Great care must be taken when using a transfer list to transfer an `ArrayBuffer` as doing so causes all `TypedArray` and `Buffer` instances that share that same `ArrayBuffer` to become unusable.
```
const ab = new ArrayBuffer(10);
const u1 = new Uint8Array(ab);
const u2 = new Uint16Array(ab);
console.log(u2.length); // prints 5
port.postMessage(u1, [u1.buffer]);
console.log(u2.length); // prints 0
```
For `Buffer` instances, specifically, whether the underlying `ArrayBuffer` can be transferred or cloned depends entirely on how instances were created, which often cannot be reliably determined.
An `ArrayBuffer` can be marked with [`markAsUntransferable()`](#workermarkasuntransferableobject) to indicate that it should always be cloned and never transferred.
Depending on how a `Buffer` instance was created, it may or may not own its underlying `ArrayBuffer`. An `ArrayBuffer` must not be transferred unless it is known that the `Buffer` instance owns it. In particular, for `Buffer`s created from the internal `Buffer` pool (using, for instance `Buffer.from()` or `Buffer.allocUnsafe()`), transferring them is not possible and they are always cloned, which sends a copy of the entire `Buffer` pool. This behavior may come with unintended higher memory usage and possible security concerns.
See [`Buffer.allocUnsafe()`](buffer#static-method-bufferallocunsafesize) for more details on `Buffer` pooling.
The `ArrayBuffer`s for `Buffer` instances created using `Buffer.alloc()` or `Buffer.allocUnsafeSlow()` can always be transferred but doing so renders all other existing views of those `ArrayBuffer`s unusable.
##### Considerations when cloning objects with prototypes, classes, and accessors
Because object cloning uses the [HTML structured clone algorithm](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm), non-enumerable properties, property accessors, and object prototypes are not preserved. In particular, [`Buffer`](buffer) objects will be read as plain [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)s on the receiving side, and instances of JavaScript classes will be cloned as plain JavaScript objects.
```
const b = Symbol('b');
class Foo {
#a = 1;
constructor() {
this[b] = 2;
this.c = 3;
}
get d() { return 4; }
}
const { port1, port2 } = new MessageChannel();
port1.onmessage = ({ data }) => console.log(data);
port2.postMessage(new Foo());
// Prints: { c: 3 }
```
This limitation extends to many built-in objects, such as the global `URL` object:
```
const { port1, port2 } = new MessageChannel();
port1.onmessage = ({ data }) => console.log(data);
port2.postMessage(new URL('https://example.org'));
// Prints: { }
```
####
`port.hasRef()`
Added in: v18.1.0, v16.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
If true, the `MessagePort` object will keep the Node.js event loop active.
####
`port.ref()`
Added in: v10.5.0 Opposite of `unref()`. Calling `ref()` on a previously `unref()`ed port does *not* let the program exit if it's the only active handle left (the default behavior). If the port is `ref()`ed, calling `ref()` again has no effect.
If listeners are attached or removed using `.on('message')`, the port is `ref()`ed and `unref()`ed automatically depending on whether listeners for the event exist.
####
`port.start()`
Added in: v10.5.0 Starts receiving messages on this `MessagePort`. When using this port as an event emitter, this is called automatically once `'message'` listeners are attached.
This method exists for parity with the Web `MessagePort` API. In Node.js, it is only useful for ignoring messages when no event listener is present. Node.js also diverges in its handling of `.onmessage`. Setting it automatically calls `.start()`, but unsetting it lets messages queue up until a new handler is set or the port is discarded.
####
`port.unref()`
Added in: v10.5.0 Calling `unref()` on a port allows the thread to exit if this is the only active handle in the event system. If the port is already `unref()`ed calling `unref()` again has no effect.
If listeners are attached or removed using `.on('message')`, the port is `ref()`ed and `unref()`ed automatically depending on whether listeners for the event exist.
### Class: `Worker`
Added in: v10.5.0 * Extends: [<EventEmitter>](events#class-eventemitter)
The `Worker` class represents an independent JavaScript execution thread. Most Node.js APIs are available inside of it.
Notable differences inside a Worker environment are:
* The [`process.stdin`](process#processstdin), [`process.stdout`](process#processstdout), and [`process.stderr`](process#processstderr) streams may be redirected by the parent thread.
* The [`require('node:worker_threads').isMainThread`](#workerismainthread) property is set to `false`.
* The [`require('node:worker_threads').parentPort`](#workerparentport) message port is available.
* [`process.exit()`](process#processexitcode) does not stop the whole program, just the single thread, and [`process.abort()`](process#processabort) is not available.
* [`process.chdir()`](process#processchdirdirectory) and `process` methods that set group or user ids are not available.
* [`process.env`](process#processenv) is a copy of the parent thread's environment variables, unless otherwise specified. Changes to one copy are not visible in other threads, and are not visible to native add-ons (unless [`worker.SHARE_ENV`](#workershare_env) is passed as the `env` option to the [`Worker`](#class-worker) constructor).
* [`process.title`](process#processtitle) cannot be modified.
* Signals are not delivered through [`process.on('...')`](process#signal-events).
* Execution may stop at any point as a result of [`worker.terminate()`](#workerterminate) being invoked.
* IPC channels from parent processes are not accessible.
* The [`trace_events`](tracing) module is not supported.
* Native add-ons can only be loaded from multiple threads if they fulfill [certain conditions](addons#worker-support).
Creating `Worker` instances inside of other `Worker`s is possible.
Like [Web Workers](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API) and the [`node:cluster` module](cluster), two-way communication can be achieved through inter-thread message passing. Internally, a `Worker` has a built-in pair of [`MessagePort`](#class-messageport)s that are already associated with each other when the `Worker` is created. While the `MessagePort` object on the parent side is not directly exposed, its functionalities are exposed through [`worker.postMessage()`](#workerpostmessagevalue-transferlist) and the [`worker.on('message')`](#event-message_1) event on the `Worker` object for the parent thread.
To create custom messaging channels (which is encouraged over using the default global channel because it facilitates separation of concerns), users can create a `MessageChannel` object on either thread and pass one of the `MessagePort`s on that `MessageChannel` to the other thread through a pre-existing channel, such as the global one.
See [`port.postMessage()`](#portpostmessagevalue-transferlist) for more information on how messages are passed, and what kind of JavaScript values can be successfully transported through the thread barrier.
```
const assert = require('node:assert');
const {
Worker, MessageChannel, MessagePort, isMainThread, parentPort
} = require('node:worker_threads');
if (isMainThread) {
const worker = new Worker(__filename);
const subChannel = new MessageChannel();
worker.postMessage({ hereIsYourPort: subChannel.port1 }, [subChannel.port1]);
subChannel.port2.on('message', (value) => {
console.log('received:', value);
});
} else {
parentPort.once('message', (value) => {
assert(value.hereIsYourPort instanceof MessagePort);
value.hereIsYourPort.postMessage('the worker is sending this');
value.hereIsYourPort.close();
});
}
```
####
`new Worker(filename[, options])`
History
| Version | Changes |
| --- | --- |
| v14.9.0 | The `filename` parameter can be a WHATWG `URL` object using `data:` protocol. |
| v14.9.0 | The `trackUnmanagedFds` option was set to `true` by default. |
| v14.6.0, v12.19.0 | The `trackUnmanagedFds` option was introduced. |
| v13.13.0, v12.17.0 | The `transferList` option was introduced. |
| v13.12.0, v12.17.0 | The `filename` parameter can be a WHATWG `URL` object using `file:` protocol. |
| v13.4.0, v12.16.0 | The `argv` option was introduced. |
| v13.2.0, v12.16.0 | The `resourceLimits` option was introduced. |
| v10.5.0 | Added in: v10.5.0 |
* `filename` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<URL>](url#the-whatwg-url-api) The path to the Worker's main script or module. Must be either an absolute path or a relative path (i.e. relative to the current working directory) starting with `./` or `../`, or a WHATWG `URL` object using `file:` or `data:` protocol. When using a [`data:` URL](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs), the data is interpreted based on MIME type using the [ECMAScript module loader](esm#data-imports). If `options.eval` is `true`, this is a string containing JavaScript code rather than a path.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `argv` [<any[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) List of arguments which would be stringified and appended to `process.argv` in the worker. This is mostly similar to the `workerData` but the values are available on the global `process.argv` as if they were passed as CLI options to the script.
+ `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) If set, specifies the initial value of `process.env` inside the Worker thread. As a special value, [`worker.SHARE_ENV`](#workershare_env) may be used to specify that the parent thread and the child thread should share their environment variables; in that case, changes to one thread's `process.env` object affect the other thread as well. **Default:** `process.env`.
+ `eval` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true` and the first argument is a `string`, interpret the first argument to the constructor as a script that is executed once the worker is online.
+ `execArgv` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) List of node CLI options passed to the worker. V8 options (such as `--max-old-space-size`) and options that affect the process (such as `--title`) are not supported. If set, this is provided as [`process.execArgv`](process#processexecargv) inside the worker. By default, options are inherited from the parent thread.
+ `stdin` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If this is set to `true`, then `worker.stdin` provides a writable stream whose contents appear as `process.stdin` inside the Worker. By default, no data is provided.
+ `stdout` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If this is set to `true`, then `worker.stdout` is not automatically piped through to `process.stdout` in the parent.
+ `stderr` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If this is set to `true`, then `worker.stderr` is not automatically piped through to `process.stderr` in the parent.
+ `workerData` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Any JavaScript value that is cloned and made available as [`require('node:worker_threads').workerData`](#workerworkerdata). The cloning occurs as described in the [HTML structured clone algorithm](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm), and an error is thrown if the object cannot be cloned (e.g. because it contains `function`s).
+ `trackUnmanagedFds` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If this is set to `true`, then the Worker tracks raw file descriptors managed through [`fs.open()`](fs#fsopenpath-flags-mode-callback) and [`fs.close()`](fs#fsclosefd-callback), and closes them when the Worker exits, similar to other resources like network sockets or file descriptors managed through the [`FileHandle`](fs#class-filehandle) API. This option is automatically inherited by all nested `Worker`s. **Default:** `true`.
+ `transferList` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) If one or more `MessagePort`-like objects are passed in `workerData`, a `transferList` is required for those items or [`ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST`](errors#err_missing_message_port_in_transfer_list) is thrown. See [`port.postMessage()`](#portpostmessagevalue-transferlist) for more information.
+ `resourceLimits` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An optional set of resource limits for the new JS engine instance. Reaching these limits leads to termination of the `Worker` instance. These limits only affect the JS engine, and no external data, including no `ArrayBuffer`s. Even if these limits are set, the process may still abort if it encounters a global out-of-memory situation.
- `maxOldGenerationSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum size of the main heap in MB. If the command-line argument [`--max-old-space-size`](cli#--max-old-space-sizesize-in-megabytes) is set, it overrides this setting.
- `maxYoungGenerationSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum size of a heap space for recently created objects. If the command-line argument [`--max-semi-space-size`](cli#--max-semi-space-sizesize-in-megabytes) is set, it overrides this setting.
- `codeRangeSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The size of a pre-allocated memory range used for generated code.
- `stackSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The default maximum stack size for the thread. Small values may lead to unusable Worker instances. **Default:** `4`.
#### Event: `'error'`
Added in: v10.5.0 * `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
The `'error'` event is emitted if the worker thread throws an uncaught exception. In that case, the worker is terminated.
#### Event: `'exit'`
Added in: v10.5.0 * `exitCode` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `'exit'` event is emitted once the worker has stopped. If the worker exited by calling [`process.exit()`](process#processexitcode), the `exitCode` parameter is the passed exit code. If the worker was terminated, the `exitCode` parameter is `1`.
This is the final event emitted by any `Worker` instance.
#### Event: `'message'`
Added in: v10.5.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The transmitted value
The `'message'` event is emitted when the worker thread has invoked [`require('node:worker_threads').parentPort.postMessage()`](#workerpostmessagevalue-transferlist). See the [`port.on('message')`](#event-message) event for more details.
All messages sent from the worker thread are emitted before the [`'exit'` event](#event-exit) is emitted on the `Worker` object.
#### Event: `'messageerror'`
Added in: v14.5.0, v12.19.0 * `error` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) An Error object
The `'messageerror'` event is emitted when deserializing a message failed.
#### Event: `'online'`
Added in: v10.5.0 The `'online'` event is emitted when the worker thread has started executing JavaScript code.
####
`worker.getHeapSnapshot()`
Added in: v13.9.0, v12.17.0 * Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) A promise for a Readable Stream containing a V8 heap snapshot
Returns a readable stream for a V8 snapshot of the current state of the Worker. See [`v8.getHeapSnapshot()`](v8#v8getheapsnapshot) for more details.
If the Worker thread is no longer running, which may occur before the [`'exit'` event](#event-exit) is emitted, the returned `Promise` is rejected immediately with an [`ERR_WORKER_NOT_RUNNING`](errors#err_worker_not_running) error.
####
`worker.performance`
Added in: v15.1.0, v14.17.0, v12.22.0 An object that can be used to query performance information from a worker instance. Similar to [`perf_hooks.performance`](perf_hooks#perf_hooksperformance).
#####
`performance.eventLoopUtilization([utilization1[, utilization2]])`
Added in: v15.1.0, v14.17.0, v12.22.0 * `utilization1` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The result of a previous call to `eventLoopUtilization()`.
* `utilization2` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The result of a previous call to `eventLoopUtilization()` prior to `utilization1`.
* Returns [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `idle` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `active` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `utilization` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The same call as [`perf_hooks` `eventLoopUtilization()`](perf_hooks#performanceeventlooputilizationutilization1-utilization2), except the values of the worker instance are returned.
One difference is that, unlike the main thread, bootstrapping within a worker is done within the event loop. So the event loop utilization is immediately available once the worker's script begins execution.
An `idle` time that does not increase does not indicate that the worker is stuck in bootstrap. The following examples shows how the worker's entire lifetime never accumulates any `idle` time, but is still be able to process messages.
```
const { Worker, isMainThread, parentPort } = require('node:worker_threads');
if (isMainThread) {
const worker = new Worker(__filename);
setInterval(() => {
worker.postMessage('hi');
console.log(worker.performance.eventLoopUtilization());
}, 100).unref();
return;
}
parentPort.on('message', () => console.log('msg')).unref();
(function r(n) {
if (--n < 0) return;
const t = Date.now();
while (Date.now() - t < 300);
setImmediate(r, n);
})(10);
```
The event loop utilization of a worker is available only after the [`'online'` event](#event-online) emitted, and if called before this, or after the [`'exit'` event](#event-exit), then all properties have the value of `0`.
####
`worker.postMessage(value[, transferList])`
Added in: v10.5.0 * `value` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* `transferList` [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Send a message to the worker that is received via [`require('node:worker_threads').parentPort.on('message')`](#event-message). See [`port.postMessage()`](#portpostmessagevalue-transferlist) for more details.
####
`worker.ref()`
Added in: v10.5.0 Opposite of `unref()`, calling `ref()` on a previously `unref()`ed worker does *not* let the program exit if it's the only active handle left (the default behavior). If the worker is `ref()`ed, calling `ref()` again has no effect.
####
`worker.resourceLimits`
Added in: v13.2.0, v12.16.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `maxYoungGenerationSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `maxOldGenerationSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `codeRangeSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `stackSizeMb` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Provides the set of JS engine resource constraints for this Worker thread. If the `resourceLimits` option was passed to the [`Worker`](#class-worker) constructor, this matches its values.
If the worker has stopped, the return value is an empty object.
####
`worker.stderr`
Added in: v10.5.0 * [<stream.Readable>](stream#class-streamreadable)
This is a readable stream which contains data written to [`process.stderr`](process#processstderr) inside the worker thread. If `stderr: true` was not passed to the [`Worker`](#class-worker) constructor, then data is piped to the parent thread's [`process.stderr`](process#processstderr) stream.
####
`worker.stdin`
Added in: v10.5.0 * [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<stream.Writable>](stream#class-streamwritable)
If `stdin: true` was passed to the [`Worker`](#class-worker) constructor, this is a writable stream. The data written to this stream will be made available in the worker thread as [`process.stdin`](process#processstdin).
####
`worker.stdout`
Added in: v10.5.0 * [<stream.Readable>](stream#class-streamreadable)
This is a readable stream which contains data written to [`process.stdout`](process#processstdout) inside the worker thread. If `stdout: true` was not passed to the [`Worker`](#class-worker) constructor, then data is piped to the parent thread's [`process.stdout`](process#processstdout) stream.
####
`worker.terminate()`
History
| Version | Changes |
| --- | --- |
| v12.5.0 | This function now returns a Promise. Passing a callback is deprecated, and was useless up to this version, as the Worker was actually terminated synchronously. Terminating is now a fully asynchronous operation. |
| v10.5.0 | Added in: v10.5.0 |
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Stop all JavaScript execution in the worker thread as soon as possible. Returns a Promise for the exit code that is fulfilled when the [`'exit'` event](#event-exit) is emitted.
####
`worker.threadId`
Added in: v10.5.0 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
An integer identifier for the referenced thread. Inside the worker thread, it is available as [`require('node:worker_threads').threadId`](#workerthreadid). This value is unique for each `Worker` instance inside a single process.
####
`worker.unref()`
Added in: v10.5.0 Calling `unref()` on a worker allows the thread to exit if this is the only active handle in the event system. If the worker is already `unref()`ed calling `unref()` again has no effect.
### Notes
#### Synchronous blocking of stdio
`Worker`s utilize message passing via [<MessagePort>](worker_threads#class-messageport) to implement interactions with `stdio`. This means that `stdio` output originating from a `Worker` can get blocked by synchronous code on the receiving end that is blocking the Node.js event loop.
MJS modules
```
import {
Worker,
isMainThread,
} from 'worker_threads';
if (isMainThread) {
new Worker(new URL(import.meta.url));
for (let n = 0; n < 1e10; n++) {
// Looping to simulate work.
}
} else {
// This output will be blocked by the for loop in the main thread.
console.log('foo');
}
```
CJS modules
```
'use strict';
const {
Worker,
isMainThread,
} = require('node:worker_threads');
if (isMainThread) {
new Worker(__filename);
for (let n = 0; n < 1e10; n++) {
// Looping to simulate work.
}
} else {
// This output will be blocked by the for loop in the main thread.
console.log('foo');
}
```
#### Launching worker threads from preload scripts
Take care when launching worker threads from preload scripts (scripts loaded and run using the `-r` command line flag). Unless the `execArgv` option is explicitly set, new Worker threads automatically inherit the command line flags from the running process and will preload the same preload scripts as the main thread. If the preload script unconditionally launches a worker thread, every thread spawned will spawn another until the application crashes.
| programming_docs |
node None Errors
------
Applications running in Node.js will generally experience four categories of errors:
* Standard JavaScript errors such as [<EvalError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/EvalError), [<SyntaxError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SyntaxError), [<RangeError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RangeError), [<ReferenceError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ReferenceError), [<TypeError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError), and [<URIError>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/URIError).
* System errors triggered by underlying operating system constraints such as attempting to open a file that does not exist or attempting to send data over a closed socket.
* User-specified errors triggered by application code.
* `AssertionError`s are a special class of error that can be triggered when Node.js detects an exceptional logic violation that should never occur. These are raised typically by the `node:assert` module.
All JavaScript and system errors raised by Node.js inherit from, or are instances of, the standard JavaScript [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) class and are guaranteed to provide *at least* the properties available on that class.
### Error propagation and interception
Node.js supports several mechanisms for propagating and handling errors that occur while an application is running. How these errors are reported and handled depends entirely on the type of `Error` and the style of the API that is called.
All JavaScript errors are handled as exceptions that *immediately* generate and throw an error using the standard JavaScript `throw` mechanism. These are handled using the [`try…catch` construct](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try...catch) provided by the JavaScript language.
```
// Throws with a ReferenceError because z is not defined.
try {
const m = 1;
const n = m + z;
} catch (err) {
// Handle the error here.
}
```
Any use of the JavaScript `throw` mechanism will raise an exception that *must* be handled using `try…catch` or the Node.js process will exit immediately.
With few exceptions, *Synchronous* APIs (any blocking method that does not accept a `callback` function, such as [`fs.readFileSync`](fs#fsreadfilesyncpath-options)), will use `throw` to report errors.
Errors that occur within *Asynchronous APIs* may be reported in multiple ways:
* Most asynchronous methods that accept a `callback` function will accept an `Error` object passed as the first argument to that function. If that first argument is not `null` and is an instance of `Error`, then an error occurred that should be handled.
```
const fs = require('node:fs');
fs.readFile('a file that does not exist', (err, data) => {
if (err) {
console.error('There was an error reading the file!', err);
return;
}
// Otherwise handle the data
});
```
* When an asynchronous method is called on an object that is an [`EventEmitter`](events#class-eventemitter), errors can be routed to that object's `'error'` event.
```
const net = require('node:net');
const connection = net.connect('localhost');
// Adding an 'error' event handler to a stream:
connection.on('error', (err) => {
// If the connection is reset by the server, or if it can't
// connect at all, or on any sort of error encountered by
// the connection, the error will be sent here.
console.error(err);
});
connection.pipe(process.stdout);
```
* A handful of typically asynchronous methods in the Node.js API may still use the `throw` mechanism to raise exceptions that must be handled using `try…catch`. There is no comprehensive list of such methods; please refer to the documentation of each method to determine the appropriate error handling mechanism required.
The use of the `'error'` event mechanism is most common for [stream-based](stream) and [event emitter-based](events#class-eventemitter) APIs, which themselves represent a series of asynchronous operations over time (as opposed to a single operation that may pass or fail).
For *all* [`EventEmitter`](events#class-eventemitter) objects, if an `'error'` event handler is not provided, the error will be thrown, causing the Node.js process to report an uncaught exception and crash unless either: The [`domain`](domain) module is used appropriately or a handler has been registered for the [`'uncaughtException'`](process#event-uncaughtexception) event.
```
const EventEmitter = require('node:events');
const ee = new EventEmitter();
setImmediate(() => {
// This will crash the process because no 'error' event
// handler has been added.
ee.emit('error', new Error('This will crash'));
});
```
Errors generated in this way *cannot* be intercepted using `try…catch` as they are thrown *after* the calling code has already exited.
Developers must refer to the documentation for each method to determine exactly how errors raised by those methods are propagated.
#### Error-first callbacks
Most asynchronous methods exposed by the Node.js core API follow an idiomatic pattern referred to as an *error-first callback*. With this pattern, a callback function is passed to the method as an argument. When the operation either completes or an error is raised, the callback function is called with the `Error` object (if any) passed as the first argument. If no error was raised, the first argument will be passed as `null`.
```
const fs = require('node:fs');
function errorFirstCallback(err, data) {
if (err) {
console.error('There was an error', err);
return;
}
console.log(data);
}
fs.readFile('/some/file/that/does-not-exist', errorFirstCallback);
fs.readFile('/some/file/that/does-exist', errorFirstCallback);
```
The JavaScript `try…catch` mechanism **cannot** be used to intercept errors generated by asynchronous APIs. A common mistake for beginners is to try to use `throw` inside an error-first callback:
```
// THIS WILL NOT WORK:
const fs = require('node:fs');
try {
fs.readFile('/some/file/that/does-not-exist', (err, data) => {
// Mistaken assumption: throwing here...
if (err) {
throw err;
}
});
} catch (err) {
// This will not catch the throw!
console.error(err);
}
```
This will not work because the callback function passed to `fs.readFile()` is called asynchronously. By the time the callback has been called, the surrounding code, including the `try…catch` block, will have already exited. Throwing an error inside the callback **can crash the Node.js process** in most cases. If [domains](domain) are enabled, or a handler has been registered with `process.on('uncaughtException')`, such errors can be intercepted.
### Class: `Error`
A generic JavaScript [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) object that does not denote any specific circumstance of why the error occurred. `Error` objects capture a "stack trace" detailing the point in the code at which the `Error` was instantiated, and may provide a text description of the error.
All errors generated by Node.js, including all system and JavaScript errors, will either be instances of, or inherit from, the `Error` class.
####
`new Error(message[, options])`
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cause` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The error that caused the newly created error.
Creates a new `Error` object and sets the `error.message` property to the provided text message. If an object is passed as `message`, the text message is generated by calling `String(message)`. If the `cause` option is provided, it is assigned to the `error.cause` property. The `error.stack` property will represent the point in the code at which `new Error()` was called. Stack traces are dependent on [V8's stack trace API](https://v8.dev/docs/stack-trace-api). Stack traces extend only to either (a) the beginning of *synchronous code execution*, or (b) the number of frames given by the property `Error.stackTraceLimit`, whichever is smaller.
####
`Error.captureStackTrace(targetObject[, constructorOpt])`
* `targetObject` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `constructorOpt` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Creates a `.stack` property on `targetObject`, which when accessed returns a string representing the location in the code at which `Error.captureStackTrace()` was called.
```
const myObject = {};
Error.captureStackTrace(myObject);
myObject.stack; // Similar to `new Error().stack`
```
The first line of the trace will be prefixed with `${myObject.name}: ${myObject.message}`.
The optional `constructorOpt` argument accepts a function. If given, all frames above `constructorOpt`, including `constructorOpt`, will be omitted from the generated stack trace.
The `constructorOpt` argument is useful for hiding implementation details of error generation from the user. For instance:
```
function MyError() {
Error.captureStackTrace(this, MyError);
}
// Without passing MyError to captureStackTrace, the MyError
// frame would show up in the .stack property. By passing
// the constructor, we omit that frame, and retain all frames below it.
new MyError().stack;
```
####
`Error.stackTraceLimit`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `Error.stackTraceLimit` property specifies the number of stack frames collected by a stack trace (whether generated by `new Error().stack` or `Error.captureStackTrace(obj)`).
The default value is `10` but may be set to any valid JavaScript number. Changes will affect any stack trace captured *after* the value has been changed.
If set to a non-number value, or set to a negative number, stack traces will not capture any frames.
####
`error.cause`
Added in: v16.9.0 * [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
If present, the `error.cause` property is the underlying cause of the `Error`. It is used when catching an error and throwing a new one with a different message or code in order to still have access to the original error.
The `error.cause` property is typically set by calling `new Error(message, { cause })`. It is not set by the constructor if the `cause` option is not provided.
This property allows errors to be chained. When serializing `Error` objects, [`util.inspect()`](util#utilinspectobject-options) recursively serializes `error.cause` if it is set.
```
const cause = new Error('The remote HTTP server responded with a 500 status');
const symptom = new Error('The message failed to send', { cause });
console.log(symptom);
// Prints:
// Error: The message failed to send
// at REPL2:1:17
// at Script.runInThisContext (node:vm:130:12)
// ... 7 lines matching cause stack trace ...
// at [_line] [as _line] (node:internal/readline/interface:886:18) {
// [cause]: Error: The remote HTTP server responded with a 500 status
// at REPL1:1:15
// at Script.runInThisContext (node:vm:130:12)
// at REPLServer.defaultEval (node:repl:574:29)
// at bound (node:domain:426:15)
// at REPLServer.runBound [as eval] (node:domain:437:12)
// at REPLServer.onLine (node:repl:902:10)
// at REPLServer.emit (node:events:549:35)
// at REPLServer.emit (node:domain:482:12)
// at [_onLine] [as _onLine] (node:internal/readline/interface:425:12)
// at [_line] [as _line] (node:internal/readline/interface:886:18)
```
####
`error.code`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `error.code` property is a string label that identifies the kind of error. `error.code` is the most stable way to identify an error. It will only change between major versions of Node.js. In contrast, `error.message` strings may change between any versions of Node.js. See [Node.js error codes](#nodejs-error-codes) for details about specific codes.
####
`error.message`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `error.message` property is the string description of the error as set by calling `new Error(message)`. The `message` passed to the constructor will also appear in the first line of the stack trace of the `Error`, however changing this property after the `Error` object is created *may not* change the first line of the stack trace (for example, when `error.stack` is read before this property is changed).
```
const err = new Error('The message');
console.error(err.message);
// Prints: The message
```
####
`error.stack`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `error.stack` property is a string describing the point in the code at which the `Error` was instantiated.
```
Error: Things keep happening!
at /home/gbusey/file.js:525:2
at Frobnicator.refrobulate (/home/gbusey/business-logic.js:424:21)
at Actor.<anonymous> (/home/gbusey/actors.js:400:8)
at increaseSynergy (/home/gbusey/actors.js:701:6)
```
The first line is formatted as `<error class name>: <error message>`, and is followed by a series of stack frames (each line beginning with "at "). Each frame describes a call site within the code that lead to the error being generated. V8 attempts to display a name for each function (by variable name, function name, or object method name), but occasionally it will not be able to find a suitable name. If V8 cannot determine a name for the function, only location information will be displayed for that frame. Otherwise, the determined function name will be displayed with location information appended in parentheses.
Frames are only generated for JavaScript functions. If, for example, execution synchronously passes through a C++ addon function called `cheetahify` which itself calls a JavaScript function, the frame representing the `cheetahify` call will not be present in the stack traces:
```
const cheetahify = require('./native-binding.node');
function makeFaster() {
// `cheetahify()` *synchronously* calls speedy.
cheetahify(function speedy() {
throw new Error('oh no!');
});
}
makeFaster();
// will throw:
// /home/gbusey/file.js:6
// throw new Error('oh no!');
// ^
// Error: oh no!
// at speedy (/home/gbusey/file.js:6:11)
// at makeFaster (/home/gbusey/file.js:5:3)
// at Object.<anonymous> (/home/gbusey/file.js:10:1)
// at Module._compile (module.js:456:26)
// at Object.Module._extensions..js (module.js:474:10)
// at Module.load (module.js:356:32)
// at Function.Module._load (module.js:312:12)
// at Function.Module.runMain (module.js:497:10)
// at startup (node.js:119:16)
// at node.js:906:3
```
The location information will be one of:
* `native`, if the frame represents a call internal to V8 (as in `[].forEach`).
* `plain-filename.js:line:column`, if the frame represents a call internal to Node.js.
* `/absolute/path/to/file.js:line:column`, if the frame represents a call in a user program (using CommonJS module system), or its dependencies.
* `<transport-protocol>:///url/to/module/file.mjs:line:column`, if the frame represents a call in a user program (using ES module system), or its dependencies.
The string representing the stack trace is lazily generated when the `error.stack` property is **accessed**.
The number of frames captured by the stack trace is bounded by the smaller of `Error.stackTraceLimit` or the number of available frames on the current event loop tick.
### Class: `AssertionError`
* Extends: [<errors.Error>](errors#class-error)
Indicates the failure of an assertion. For details, see [`Class: assert.AssertionError`](assert#class-assertassertionerror).
### Class: `RangeError`
* Extends: [<errors.Error>](errors#class-error)
Indicates that a provided argument was not within the set or range of acceptable values for a function; whether that is a numeric range, or outside the set of options for a given function parameter.
```
require('node:net').connect(-1);
// Throws "RangeError: "port" option should be >= 0 and < 65536: -1"
```
Node.js will generate and throw `RangeError` instances *immediately* as a form of argument validation.
### Class: `ReferenceError`
* Extends: [<errors.Error>](errors#class-error)
Indicates that an attempt is being made to access a variable that is not defined. Such errors commonly indicate typos in code, or an otherwise broken program.
While client code may generate and propagate these errors, in practice, only V8 will do so.
```
doesNotExist;
// Throws ReferenceError, doesNotExist is not a variable in this program.
```
Unless an application is dynamically generating and running code, `ReferenceError` instances indicate a bug in the code or its dependencies.
### Class: `SyntaxError`
* Extends: [<errors.Error>](errors#class-error)
Indicates that a program is not valid JavaScript. These errors may only be generated and propagated as a result of code evaluation. Code evaluation may happen as a result of `eval`, `Function`, `require`, or <vm>. These errors are almost always indicative of a broken program.
```
try {
require('node:vm').runInThisContext('binary ! isNotOk');
} catch (err) {
// 'err' will be a SyntaxError.
}
```
`SyntaxError` instances are unrecoverable in the context that created them – they may only be caught by other contexts.
### Class: `SystemError`
* Extends: [<errors.Error>](errors#class-error)
Node.js generates system errors when exceptions occur within its runtime environment. These usually occur when an application violates an operating system constraint. For example, a system error will occur if an application attempts to read a file that does not exist.
* `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If present, the address to which a network connection failed
* `code` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The string error code
* `dest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If present, the file path destination when reporting a file system error
* `errno` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The system-provided error number
* `info` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) If present, extra details about the error condition
* `message` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A system-provided human-readable description of the error
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If present, the file path when reporting a file system error
* `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If present, the network connection port that is not available
* `syscall` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the system call that triggered the error
####
`error.address`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
If present, `error.address` is a string describing the address to which a network connection failed.
####
`error.code`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `error.code` property is a string representing the error code.
####
`error.dest`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
If present, `error.dest` is the file path destination when reporting a file system error.
####
`error.errno`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `error.errno` property is a negative number which corresponds to the error code defined in [`libuv Error handling`](https://docs.libuv.org/en/v1.x/errors.html).
On Windows the error number provided by the system will be normalized by libuv.
To get the string representation of the error code, use [`util.getSystemErrorName(error.errno)`](util#utilgetsystemerrornameerr).
####
`error.info`
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
If present, `error.info` is an object with details about the error condition.
####
`error.message`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
`error.message` is a system-provided human-readable description of the error.
####
`error.path`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
If present, `error.path` is a string containing a relevant invalid pathname.
####
`error.port`
* [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
If present, `error.port` is the network connection port that is not available.
####
`error.syscall`
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `error.syscall` property is a string describing the [syscall](https://man7.org/linux/man-pages/man2/syscalls.2.html) that failed.
#### Common system errors
This is a list of system errors commonly-encountered when writing a Node.js program. For a comprehensive list, see the [`errno`(3) man page](https://man7.org/linux/man-pages/man3/errno.3.html).
* `EACCES` (Permission denied): An attempt was made to access a file in a way forbidden by its file access permissions.
* `EADDRINUSE` (Address already in use): An attempt to bind a server ([`net`](net), [`http`](http), or [`https`](https)) to a local address failed due to another server on the local system already occupying that address.
* `ECONNREFUSED` (Connection refused): No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service that is inactive on the foreign host.
* `ECONNRESET` (Connection reset by peer): A connection was forcibly closed by a peer. This normally results from a loss of the connection on the remote socket due to a timeout or reboot. Commonly encountered via the [`http`](http) and [`net`](net) modules.
* `EEXIST` (File exists): An existing file was the target of an operation that required that the target not exist.
* `EISDIR` (Is a directory): An operation expected a file, but the given pathname was a directory.
* `EMFILE` (Too many open files in system): Maximum number of [file descriptors](https://en.wikipedia.org/wiki/File_descriptor) allowable on the system has been reached, and requests for another descriptor cannot be fulfilled until at least one has been closed. This is encountered when opening many files at once in parallel, especially on systems (in particular, macOS) where there is a low file descriptor limit for processes. To remedy a low limit, run `ulimit -n 2048` in the same shell that will run the Node.js process.
* `ENOENT` (No such file or directory): Commonly raised by [`fs`](fs) operations to indicate that a component of the specified pathname does not exist. No entity (file or directory) could be found by the given path.
* `ENOTDIR` (Not a directory): A component of the given pathname existed, but was not a directory as expected. Commonly raised by [`fs.readdir`](fs#fsreaddirpath-options-callback).
* `ENOTEMPTY` (Directory not empty): A directory with entries was the target of an operation that requires an empty directory, usually [`fs.unlink`](fs#fsunlinkpath-callback).
* `ENOTFOUND` (DNS lookup failed): Indicates a DNS failure of either `EAI_NODATA` or `EAI_NONAME`. This is not a standard POSIX error.
* `EPERM` (Operation not permitted): An attempt was made to perform an operation that requires elevated privileges.
* `EPIPE` (Broken pipe): A write on a pipe, socket, or FIFO for which there is no process to read the data. Commonly encountered at the [`net`](net) and [`http`](http) layers, indicative that the remote side of the stream being written to has been closed.
* `ETIMEDOUT` (Operation timed out): A connect or send request failed because the connected party did not properly respond after a period of time. Usually encountered by [`http`](http) or [`net`](net). Often a sign that a `socket.end()` was not properly called.
### Class: `TypeError`
* Extends [<errors.Error>](errors#class-error)
Indicates that a provided argument is not an allowable type. For example, passing a function to a parameter which expects a string would be a `TypeError`.
```
require('node:url').parse(() => { });
// Throws TypeError, since it expected a string.
```
Node.js will generate and throw `TypeError` instances *immediately* as a form of argument validation.
### Exceptions vs. errors
A JavaScript exception is a value that is thrown as a result of an invalid operation or as the target of a `throw` statement. While it is not required that these values are instances of `Error` or classes which inherit from `Error`, all exceptions thrown by Node.js or the JavaScript runtime *will* be instances of `Error`.
Some exceptions are *unrecoverable* at the JavaScript layer. Such exceptions will *always* cause the Node.js process to crash. Examples include `assert()` checks or `abort()` calls in the C++ layer.
### OpenSSL errors
Errors originating in `crypto` or `tls` are of class `Error`, and in addition to the standard `.code` and `.message` properties, may have some additional OpenSSL-specific properties.
####
`error.opensslErrorStack`
An array of errors that can give context to where in the OpenSSL library an error originates from.
####
`error.function`
The OpenSSL function the error originates in.
####
`error.library`
The OpenSSL library the error originates in.
####
`error.reason`
A human-readable string describing the reason for the error.
### Node.js error codes
####
`ABORT_ERR`
Added in: v15.0.0 Used when an operation has been aborted (typically using an `AbortController`).
APIs *not* using `AbortSignal`s typically do not raise an error with this code.
This code does not use the regular `ERR_*` convention Node.js errors use in order to be compatible with the web platform's `AbortError`.
####
`ERR_AMBIGUOUS_ARGUMENT`
A function argument is being used in a way that suggests that the function signature may be misunderstood. This is thrown by the `node:assert` module when the `message` parameter in `assert.throws(block, message)` matches the error message thrown by `block` because that usage suggests that the user believes `message` is the expected message rather than the message the `AssertionError` will display if `block` does not throw.
####
`ERR_ARG_NOT_ITERABLE`
An iterable argument (i.e. a value that works with `for...of` loops) was required, but not provided to a Node.js API.
####
`ERR_ASSERTION`
A special type of error that can be triggered whenever Node.js detects an exceptional logic violation that should never occur. These are raised typically by the `node:assert` module.
####
`ERR_ASSERT_SNAPSHOT_NOT_SUPPORTED`
An attempt was made to use `assert.snapshot()` in an environment that does not support snapshots, such as the REPL, or when using `node --eval`.
####
`ERR_ASYNC_CALLBACK`
An attempt was made to register something that is not a function as an `AsyncHooks` callback.
####
`ERR_ASYNC_TYPE`
The type of an asynchronous resource was invalid. Users are also able to define their own types if using the public embedder API.
####
`ERR_BROTLI_COMPRESSION_FAILED`
Data passed to a Brotli stream was not successfully compressed.
####
`ERR_BROTLI_INVALID_PARAM`
An invalid parameter key was passed during construction of a Brotli stream.
####
`ERR_BUFFER_CONTEXT_NOT_AVAILABLE`
An attempt was made to create a Node.js `Buffer` instance from addon or embedder code, while in a JS engine Context that is not associated with a Node.js instance. The data passed to the `Buffer` method will have been released by the time the method returns.
When encountering this error, a possible alternative to creating a `Buffer` instance is to create a normal `Uint8Array`, which only differs in the prototype of the resulting object. `Uint8Array`s are generally accepted in all Node.js core APIs where `Buffer`s are; they are available in all Contexts.
####
`ERR_BUFFER_OUT_OF_BOUNDS`
An operation outside the bounds of a `Buffer` was attempted.
####
`ERR_BUFFER_TOO_LARGE`
An attempt has been made to create a `Buffer` larger than the maximum allowed size.
####
`ERR_CANNOT_WATCH_SIGINT`
Node.js was unable to watch for the `SIGINT` signal.
####
`ERR_CHILD_CLOSED_BEFORE_REPLY`
A child process was closed before the parent received a reply.
####
`ERR_CHILD_PROCESS_IPC_REQUIRED`
Used when a child process is being forked without specifying an IPC channel.
####
`ERR_CHILD_PROCESS_STDIO_MAXBUFFER`
Used when the main process is trying to read data from the child process's STDERR/STDOUT, and the data's length is longer than the `maxBuffer` option.
####
`ERR_CLOSED_MESSAGE_PORT`
There was an attempt to use a `MessagePort` instance in a closed state, usually after `.close()` has been called.
####
`ERR_CONSOLE_WRITABLE_STREAM`
`Console` was instantiated without `stdout` stream, or `Console` has a non-writable `stdout` or `stderr` stream.
####
`ERR_CONSTRUCT_CALL_INVALID`
A class constructor was called that is not callable.
####
`ERR_CONSTRUCT_CALL_REQUIRED`
A constructor for a class was called without `new`.
####
`ERR_CONTEXT_NOT_INITIALIZED`
The vm context passed into the API is not yet initialized. This could happen when an error occurs (and is caught) during the creation of the context, for example, when the allocation fails or the maximum call stack size is reached when the context is created.
####
`ERR_CRYPTO_CUSTOM_ENGINE_NOT_SUPPORTED`
A client certificate engine was requested that is not supported by the version of OpenSSL being used.
####
`ERR_CRYPTO_ECDH_INVALID_FORMAT`
An invalid value for the `format` argument was passed to the `crypto.ECDH()` class `getPublicKey()` method.
####
`ERR_CRYPTO_ECDH_INVALID_PUBLIC_KEY`
An invalid value for the `key` argument has been passed to the `crypto.ECDH()` class `computeSecret()` method. It means that the public key lies outside of the elliptic curve.
####
`ERR_CRYPTO_ENGINE_UNKNOWN`
An invalid crypto engine identifier was passed to [`require('node:crypto').setEngine()`](crypto#cryptosetengineengine-flags).
####
`ERR_CRYPTO_FIPS_FORCED`
The [`--force-fips`](cli#--force-fips) command-line argument was used but there was an attempt to enable or disable FIPS mode in the `node:crypto` module.
####
`ERR_CRYPTO_FIPS_UNAVAILABLE`
An attempt was made to enable or disable FIPS mode, but FIPS mode was not available.
####
`ERR_CRYPTO_HASH_FINALIZED`
[`hash.digest()`](crypto#hashdigestencoding) was called multiple times. The `hash.digest()` method must be called no more than one time per instance of a `Hash` object.
####
`ERR_CRYPTO_HASH_UPDATE_FAILED`
[`hash.update()`](crypto#hashupdatedata-inputencoding) failed for any reason. This should rarely, if ever, happen.
####
`ERR_CRYPTO_INCOMPATIBLE_KEY`
The given crypto keys are incompatible with the attempted operation.
####
`ERR_CRYPTO_INCOMPATIBLE_KEY_OPTIONS`
The selected public or private key encoding is incompatible with other options.
####
`ERR_CRYPTO_INITIALIZATION_FAILED`
Added in: v15.0.0 Initialization of the crypto subsystem failed.
####
`ERR_CRYPTO_INVALID_AUTH_TAG`
Added in: v15.0.0 An invalid authentication tag was provided.
####
`ERR_CRYPTO_INVALID_COUNTER`
Added in: v15.0.0 An invalid counter was provided for a counter-mode cipher.
####
`ERR_CRYPTO_INVALID_CURVE`
Added in: v15.0.0 An invalid elliptic-curve was provided.
####
`ERR_CRYPTO_INVALID_DIGEST`
An invalid [crypto digest algorithm](crypto#cryptogethashes) was specified.
####
`ERR_CRYPTO_INVALID_IV`
Added in: v15.0.0 An invalid initialization vector was provided.
####
`ERR_CRYPTO_INVALID_JWK`
Added in: v15.0.0 An invalid JSON Web Key was provided.
####
`ERR_CRYPTO_INVALID_KEY_OBJECT_TYPE`
The given crypto key object's type is invalid for the attempted operation.
####
`ERR_CRYPTO_INVALID_KEYLEN`
Added in: v15.0.0 An invalid key length was provided.
####
`ERR_CRYPTO_INVALID_KEYPAIR`
Added in: v15.0.0 An invalid key pair was provided.
####
`ERR_CRYPTO_INVALID_KEYTYPE`
Added in: v15.0.0 An invalid key type was provided.
####
`ERR_CRYPTO_INVALID_MESSAGELEN`
Added in: v15.0.0 An invalid message length was provided.
####
`ERR_CRYPTO_INVALID_SCRYPT_PARAMS`
Added in: v15.0.0 Invalid scrypt algorithm parameters were provided.
####
`ERR_CRYPTO_INVALID_STATE`
A crypto method was used on an object that was in an invalid state. For instance, calling [`cipher.getAuthTag()`](crypto#ciphergetauthtag) before calling `cipher.final()`.
####
`ERR_CRYPTO_INVALID_TAG_LENGTH`
Added in: v15.0.0 An invalid authentication tag length was provided.
####
`ERR_CRYPTO_JOB_INIT_FAILED`
Added in: v15.0.0 Initialization of an asynchronous crypto operation failed.
####
`ERR_CRYPTO_JWK_UNSUPPORTED_CURVE`
Key's Elliptic Curve is not registered for use in the [JSON Web Key Elliptic Curve Registry](https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve).
####
`ERR_CRYPTO_JWK_UNSUPPORTED_KEY_TYPE`
Key's Asymmetric Key Type is not registered for use in the [JSON Web Key Types Registry](https://www.iana.org/assignments/jose/jose.xhtml#web-key-types).
####
`ERR_CRYPTO_OPERATION_FAILED`
Added in: v15.0.0 A crypto operation failed for an otherwise unspecified reason.
####
`ERR_CRYPTO_PBKDF2_ERROR`
The PBKDF2 algorithm failed for unspecified reasons. OpenSSL does not provide more details and therefore neither does Node.js.
####
`ERR_CRYPTO_SCRYPT_INVALID_PARAMETER`
One or more [`crypto.scrypt()`](crypto#cryptoscryptpassword-salt-keylen-options-callback) or [`crypto.scryptSync()`](crypto#cryptoscryptsyncpassword-salt-keylen-options) parameters are outside their legal range.
####
`ERR_CRYPTO_SCRYPT_NOT_SUPPORTED`
Node.js was compiled without `scrypt` support. Not possible with the official release binaries but can happen with custom builds, including distro builds.
####
`ERR_CRYPTO_SIGN_KEY_REQUIRED`
A signing `key` was not provided to the [`sign.sign()`](crypto#signsignprivatekey-outputencoding) method.
####
`ERR_CRYPTO_TIMING_SAFE_EQUAL_LENGTH`
[`crypto.timingSafeEqual()`](crypto#cryptotimingsafeequala-b) was called with `Buffer`, `TypedArray`, or `DataView` arguments of different lengths.
####
`ERR_CRYPTO_UNKNOWN_CIPHER`
An unknown cipher was specified.
####
`ERR_CRYPTO_UNKNOWN_DH_GROUP`
An unknown Diffie-Hellman group name was given. See [`crypto.getDiffieHellman()`](crypto#cryptogetdiffiehellmangroupname) for a list of valid group names.
####
`ERR_CRYPTO_UNSUPPORTED_OPERATION`
Added in: v15.0.0, v14.18.0 An attempt to invoke an unsupported crypto operation was made.
####
`ERR_DEBUGGER_ERROR`
Added in: v16.4.0, v14.17.4 An error occurred with the <debugger>.
####
`ERR_DEBUGGER_STARTUP_ERROR`
Added in: v16.4.0, v14.17.4 The <debugger> timed out waiting for the required host/port to be free.
####
`ERR_DLOPEN_DISABLED`
Added in: v16.10.0, v14.19.0 Loading native addons has been disabled using [`--no-addons`](cli#--no-addons).
####
`ERR_DLOPEN_FAILED`
Added in: v15.0.0 A call to `process.dlopen()` failed.
####
`ERR_DIR_CLOSED`
The [`fs.Dir`](fs#class-fsdir) was previously closed.
####
`ERR_DIR_CONCURRENT_OPERATION`
Added in: v14.3.0 A synchronous read or close call was attempted on an [`fs.Dir`](fs#class-fsdir) which has ongoing asynchronous operations.
####
`ERR_DNS_SET_SERVERS_FAILED`
`c-ares` failed to set the DNS server.
####
`ERR_DOMAIN_CALLBACK_NOT_AVAILABLE`
The `node:domain` module was not usable since it could not establish the required error handling hooks, because [`process.setUncaughtExceptionCaptureCallback()`](process#processsetuncaughtexceptioncapturecallbackfn) had been called at an earlier point in time.
####
`ERR_DOMAIN_CANNOT_SET_UNCAUGHT_EXCEPTION_CAPTURE`
[`process.setUncaughtExceptionCaptureCallback()`](process#processsetuncaughtexceptioncapturecallbackfn) could not be called because the `node:domain` module has been loaded at an earlier point in time.
The stack trace is extended to include the point in time at which the `node:domain` module had been loaded.
####
`ERR_DUPLICATE_STARTUP_SNAPSHOT_MAIN_FUNCTION`
[`v8.startupSnapshot.setDeserializeMainFunction()`](v8#v8startupsnapshotsetdeserializemainfunctioncallback-data) could not be called because it had already been called before.
####
`ERR_ENCODING_INVALID_ENCODED_DATA`
Data provided to `TextDecoder()` API was invalid according to the encoding provided.
####
`ERR_ENCODING_NOT_SUPPORTED`
Encoding provided to `TextDecoder()` API was not one of the [WHATWG Supported Encodings](util#whatwg-supported-encodings).
####
`ERR_EVAL_ESM_CANNOT_PRINT`
`--print` cannot be used with ESM input.
####
`ERR_EVENT_RECURSION`
Thrown when an attempt is made to recursively dispatch an event on `EventTarget`.
####
`ERR_EXECUTION_ENVIRONMENT_NOT_AVAILABLE`
The JS execution context is not associated with a Node.js environment. This may occur when Node.js is used as an embedded library and some hooks for the JS engine are not set up properly.
####
`ERR_FALSY_VALUE_REJECTION`
A `Promise` that was callbackified via `util.callbackify()` was rejected with a falsy value.
####
`ERR_FEATURE_UNAVAILABLE_ON_PLATFORM`
Added in: v14.0.0 Used when a feature that is not available to the current platform which is running Node.js is used.
####
`ERR_FS_CP_DIR_TO_NON_DIR`
An attempt was made to copy a directory to a non-directory (file, symlink, etc.) using [`fs.cp()`](fs#fscpsrc-dest-options-callback).
####
`ERR_FS_CP_EEXIST`
An attempt was made to copy over a file that already existed with [`fs.cp()`](fs#fscpsrc-dest-options-callback), with the `force` and `errorOnExist` set to `true`.
####
`ERR_FS_CP_EINVAL`
When using [`fs.cp()`](fs#fscpsrc-dest-options-callback), `src` or `dest` pointed to an invalid path.
####
`ERR_HTTP_CONTENT_LENGTH_MISMATCH`
Response body size doesn't match with the specified content-length header value.
####
`ERR_FS_CP_FIFO_PIPE`
An attempt was made to copy a named pipe with [`fs.cp()`](fs#fscpsrc-dest-options-callback).
####
`ERR_FS_CP_NON_DIR_TO_DIR`
An attempt was made to copy a non-directory (file, symlink, etc.) to a directory using [`fs.cp()`](fs#fscpsrc-dest-options-callback).
####
`ERR_FS_CP_SOCKET`
An attempt was made to copy to a socket with [`fs.cp()`](fs#fscpsrc-dest-options-callback).
####
`ERR_FS_CP_SYMLINK_TO_SUBDIRECTORY`
When using [`fs.cp()`](fs#fscpsrc-dest-options-callback), a symlink in `dest` pointed to a subdirectory of `src`.
####
`ERR_FS_CP_UNKNOWN`
An attempt was made to copy to an unknown file type with [`fs.cp()`](fs#fscpsrc-dest-options-callback).
####
`ERR_FS_EISDIR`
Path is a directory.
####
`ERR_FS_FILE_TOO_LARGE`
An attempt has been made to read a file whose size is larger than the maximum allowed size for a `Buffer`.
####
`ERR_FS_INVALID_SYMLINK_TYPE`
An invalid symlink type was passed to the [`fs.symlink()`](fs#fssymlinktarget-path-type-callback) or [`fs.symlinkSync()`](fs#fssymlinksynctarget-path-type) methods.
####
`ERR_HTTP_HEADERS_SENT`
An attempt was made to add more headers after the headers had already been sent.
####
`ERR_HTTP_INVALID_HEADER_VALUE`
An invalid HTTP header value was specified.
####
`ERR_HTTP_INVALID_STATUS_CODE`
Status code was outside the regular status code range (100-999).
####
`ERR_HTTP_REQUEST_TIMEOUT`
The client has not sent the entire request within the allowed time.
####
`ERR_HTTP_SOCKET_ENCODING`
Changing the socket encoding is not allowed per [RFC 7230 Section 3](https://tools.ietf.org/html/rfc7230#section-3).
####
`ERR_HTTP_TRAILER_INVALID`
The `Trailer` header was set even though the transfer encoding does not support that.
####
`ERR_HTTP2_ALTSVC_INVALID_ORIGIN`
HTTP/2 ALTSVC frames require a valid origin.
####
`ERR_HTTP2_ALTSVC_LENGTH`
HTTP/2 ALTSVC frames are limited to a maximum of 16,382 payload bytes.
####
`ERR_HTTP2_CONNECT_AUTHORITY`
For HTTP/2 requests using the `CONNECT` method, the `:authority` pseudo-header is required.
####
`ERR_HTTP2_CONNECT_PATH`
For HTTP/2 requests using the `CONNECT` method, the `:path` pseudo-header is forbidden.
####
`ERR_HTTP2_CONNECT_SCHEME`
For HTTP/2 requests using the `CONNECT` method, the `:scheme` pseudo-header is forbidden.
####
`ERR_HTTP2_ERROR`
A non-specific HTTP/2 error has occurred.
####
`ERR_HTTP2_GOAWAY_SESSION`
New HTTP/2 Streams may not be opened after the `Http2Session` has received a `GOAWAY` frame from the connected peer.
####
`ERR_HTTP2_HEADER_SINGLE_VALUE`
Multiple values were provided for an HTTP/2 header field that was required to have only a single value.
####
`ERR_HTTP2_HEADERS_AFTER_RESPOND`
An additional headers was specified after an HTTP/2 response was initiated.
####
`ERR_HTTP2_HEADERS_SENT`
An attempt was made to send multiple response headers.
####
`ERR_HTTP2_INFO_STATUS_NOT_ALLOWED`
Informational HTTP status codes (`1xx`) may not be set as the response status code on HTTP/2 responses.
####
`ERR_HTTP2_INVALID_CONNECTION_HEADERS`
HTTP/1 connection specific headers are forbidden to be used in HTTP/2 requests and responses.
####
`ERR_HTTP2_INVALID_HEADER_VALUE`
An invalid HTTP/2 header value was specified.
####
`ERR_HTTP2_INVALID_INFO_STATUS`
An invalid HTTP informational status code has been specified. Informational status codes must be an integer between `100` and `199` (inclusive).
####
`ERR_HTTP2_INVALID_ORIGIN`
HTTP/2 `ORIGIN` frames require a valid origin.
####
`ERR_HTTP2_INVALID_PACKED_SETTINGS_LENGTH`
Input `Buffer` and `Uint8Array` instances passed to the `http2.getUnpackedSettings()` API must have a length that is a multiple of six.
####
`ERR_HTTP2_INVALID_PSEUDOHEADER`
Only valid HTTP/2 pseudoheaders (`:status`, `:path`, `:authority`, `:scheme`, and `:method`) may be used.
####
`ERR_HTTP2_INVALID_SESSION`
An action was performed on an `Http2Session` object that had already been destroyed.
####
`ERR_HTTP2_INVALID_SETTING_VALUE`
An invalid value has been specified for an HTTP/2 setting.
####
`ERR_HTTP2_INVALID_STREAM`
An operation was performed on a stream that had already been destroyed.
####
`ERR_HTTP2_MAX_PENDING_SETTINGS_ACK`
Whenever an HTTP/2 `SETTINGS` frame is sent to a connected peer, the peer is required to send an acknowledgment that it has received and applied the new `SETTINGS`. By default, a maximum number of unacknowledged `SETTINGS` frames may be sent at any given time. This error code is used when that limit has been reached.
####
`ERR_HTTP2_NESTED_PUSH`
An attempt was made to initiate a new push stream from within a push stream. Nested push streams are not permitted.
####
`ERR_HTTP2_NO_MEM`
Out of memory when using the `http2session.setLocalWindowSize(windowSize)` API.
####
`ERR_HTTP2_NO_SOCKET_MANIPULATION`
An attempt was made to directly manipulate (read, write, pause, resume, etc.) a socket attached to an `Http2Session`.
####
`ERR_HTTP2_ORIGIN_LENGTH`
HTTP/2 `ORIGIN` frames are limited to a length of 16382 bytes.
####
`ERR_HTTP2_OUT_OF_STREAMS`
The number of streams created on a single HTTP/2 session reached the maximum limit.
####
`ERR_HTTP2_PAYLOAD_FORBIDDEN`
A message payload was specified for an HTTP response code for which a payload is forbidden.
####
`ERR_HTTP2_PING_CANCEL`
An HTTP/2 ping was canceled.
####
`ERR_HTTP2_PING_LENGTH`
HTTP/2 ping payloads must be exactly 8 bytes in length.
####
`ERR_HTTP2_PSEUDOHEADER_NOT_ALLOWED`
An HTTP/2 pseudo-header has been used inappropriately. Pseudo-headers are header key names that begin with the `:` prefix.
####
`ERR_HTTP2_PUSH_DISABLED`
An attempt was made to create a push stream, which had been disabled by the client.
####
`ERR_HTTP2_SEND_FILE`
An attempt was made to use the `Http2Stream.prototype.responseWithFile()` API to send a directory.
####
`ERR_HTTP2_SEND_FILE_NOSEEK`
An attempt was made to use the `Http2Stream.prototype.responseWithFile()` API to send something other than a regular file, but `offset` or `length` options were provided.
####
`ERR_HTTP2_SESSION_ERROR`
The `Http2Session` closed with a non-zero error code.
####
`ERR_HTTP2_SETTINGS_CANCEL`
The `Http2Session` settings canceled.
####
`ERR_HTTP2_SOCKET_BOUND`
An attempt was made to connect a `Http2Session` object to a `net.Socket` or `tls.TLSSocket` that had already been bound to another `Http2Session` object.
####
`ERR_HTTP2_SOCKET_UNBOUND`
An attempt was made to use the `socket` property of an `Http2Session` that has already been closed.
####
`ERR_HTTP2_STATUS_101`
Use of the `101` Informational status code is forbidden in HTTP/2.
####
`ERR_HTTP2_STATUS_INVALID`
An invalid HTTP status code has been specified. Status codes must be an integer between `100` and `599` (inclusive).
####
`ERR_HTTP2_STREAM_CANCEL`
An `Http2Stream` was destroyed before any data was transmitted to the connected peer.
####
`ERR_HTTP2_STREAM_ERROR`
A non-zero error code was been specified in an `RST_STREAM` frame.
####
`ERR_HTTP2_STREAM_SELF_DEPENDENCY`
When setting the priority for an HTTP/2 stream, the stream may be marked as a dependency for a parent stream. This error code is used when an attempt is made to mark a stream and dependent of itself.
####
`ERR_HTTP2_TOO_MANY_INVALID_FRAMES`
The limit of acceptable invalid HTTP/2 protocol frames sent by the peer, as specified through the `maxSessionInvalidFrames` option, has been exceeded.
####
`ERR_HTTP2_TRAILERS_ALREADY_SENT`
Trailing headers have already been sent on the `Http2Stream`.
####
`ERR_HTTP2_TRAILERS_NOT_READY`
The `http2stream.sendTrailers()` method cannot be called until after the `'wantTrailers'` event is emitted on an `Http2Stream` object. The `'wantTrailers'` event will only be emitted if the `waitForTrailers` option is set for the `Http2Stream`.
####
`ERR_HTTP2_UNSUPPORTED_PROTOCOL`
`http2.connect()` was passed a URL that uses any protocol other than `http:` or `https:`.
####
`ERR_ILLEGAL_CONSTRUCTOR`
An attempt was made to construct an object using a non-public constructor.
####
`ERR_IMPORT_ASSERTION_TYPE_FAILED`
Added in: v17.1.0, v16.14.0 An import assertion has failed, preventing the specified module to be imported.
####
`ERR_IMPORT_ASSERTION_TYPE_MISSING`
Added in: v17.1.0, v16.14.0 An import assertion is missing, preventing the specified module to be imported.
####
`ERR_IMPORT_ASSERTION_TYPE_UNSUPPORTED`
Added in: v17.1.0, v16.14.0 An import assertion is not supported by this version of Node.js.
####
`ERR_INCOMPATIBLE_OPTION_PAIR`
An option pair is incompatible with each other and cannot be used at the same time.
####
`ERR_INPUT_TYPE_NOT_ALLOWED`
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
The `--input-type` flag was used to attempt to execute a file. This flag can only be used with input via `--eval`, `--print`, or `STDIN`.
####
`ERR_INSPECTOR_ALREADY_ACTIVATED`
While using the `node:inspector` module, an attempt was made to activate the inspector when it already started to listen on a port. Use `inspector.close()` before activating it on a different address.
####
`ERR_INSPECTOR_ALREADY_CONNECTED`
While using the `node:inspector` module, an attempt was made to connect when the inspector was already connected.
####
`ERR_INSPECTOR_CLOSED`
While using the `node:inspector` module, an attempt was made to use the inspector after the session had already closed.
####
`ERR_INSPECTOR_COMMAND`
An error occurred while issuing a command via the `node:inspector` module.
####
`ERR_INSPECTOR_NOT_ACTIVE`
The `inspector` is not active when `inspector.waitForDebugger()` is called.
####
`ERR_INSPECTOR_NOT_AVAILABLE`
The `node:inspector` module is not available for use.
####
`ERR_INSPECTOR_NOT_CONNECTED`
While using the `node:inspector` module, an attempt was made to use the inspector before it was connected.
####
`ERR_INSPECTOR_NOT_WORKER`
An API was called on the main thread that can only be used from the worker thread.
####
`ERR_INTERNAL_ASSERTION`
There was a bug in Node.js or incorrect usage of Node.js internals. To fix the error, open an issue at <https://github.com/nodejs/node/issues>.
####
`ERR_INVALID_ADDRESS_FAMILY`
The provided address family is not understood by the Node.js API.
####
`ERR_INVALID_ARG_TYPE`
An argument of the wrong type was passed to a Node.js API.
####
`ERR_INVALID_ARG_VALUE`
An invalid or unsupported value was passed for a given argument.
####
`ERR_INVALID_ASYNC_ID`
An invalid `asyncId` or `triggerAsyncId` was passed using `AsyncHooks`. An id less than -1 should never happen.
####
`ERR_INVALID_BUFFER_SIZE`
A swap was performed on a `Buffer` but its size was not compatible with the operation.
####
`ERR_INVALID_CHAR`
Invalid characters were detected in headers.
####
`ERR_INVALID_CURSOR_POS`
A cursor on a given stream cannot be moved to a specified row without a specified column.
####
`ERR_INVALID_FD`
A file descriptor ('fd') was not valid (e.g. it was a negative value).
####
`ERR_INVALID_FD_TYPE`
A file descriptor ('fd') type was not valid.
####
`ERR_INVALID_FILE_URL_HOST`
A Node.js API that consumes `file:` URLs (such as certain functions in the [`fs`](fs) module) encountered a file URL with an incompatible host. This situation can only occur on Unix-like systems where only `localhost` or an empty host is supported.
####
`ERR_INVALID_FILE_URL_PATH`
A Node.js API that consumes `file:` URLs (such as certain functions in the [`fs`](fs) module) encountered a file URL with an incompatible path. The exact semantics for determining whether a path can be used is platform-dependent.
####
`ERR_INVALID_HANDLE_TYPE`
An attempt was made to send an unsupported "handle" over an IPC communication channel to a child process. See [`subprocess.send()`](child_process#subprocesssendmessage-sendhandle-options-callback) and [`process.send()`](process#processsendmessage-sendhandle-options-callback) for more information.
####
`ERR_INVALID_HTTP_TOKEN`
An invalid HTTP token was supplied.
####
`ERR_INVALID_IP_ADDRESS`
An IP address is not valid.
####
`ERR_INVALID_MODULE`
Added in: v15.0.0, v14.18.0 An attempt was made to load a module that does not exist or was otherwise not valid.
####
`ERR_INVALID_MODULE_SPECIFIER`
The imported module string is an invalid URL, package name, or package subpath specifier.
####
`ERR_INVALID_OBJECT_DEFINE_PROPERTY`
An error occurred while setting an invalid attribute on the property of an object.
####
`ERR_INVALID_PACKAGE_CONFIG`
An invalid [`package.json`](packages#nodejs-packagejson-field-definitions) file failed parsing.
####
`ERR_INVALID_PACKAGE_TARGET`
The `package.json` [`"exports"`](packages#exports) field contains an invalid target mapping value for the attempted module resolution.
####
`ERR_INVALID_PERFORMANCE_MARK`
While using the Performance Timing API (`perf_hooks`), a performance mark is invalid.
####
`ERR_INVALID_PROTOCOL`
An invalid `options.protocol` was passed to `http.request()`.
####
`ERR_INVALID_REPL_EVAL_CONFIG`
Both `breakEvalOnSigint` and `eval` options were set in the [`REPL`](repl) config, which is not supported.
####
`ERR_INVALID_REPL_INPUT`
The input may not be used in the [`REPL`](repl). The conditions under which this error is used are described in the [`REPL`](repl) documentation.
####
`ERR_INVALID_RETURN_PROPERTY`
Thrown in case a function option does not provide a valid value for one of its returned object properties on execution.
####
`ERR_INVALID_RETURN_PROPERTY_VALUE`
Thrown in case a function option does not provide an expected value type for one of its returned object properties on execution.
####
`ERR_INVALID_RETURN_VALUE`
Thrown in case a function option does not return an expected value type on execution, such as when a function is expected to return a promise.
####
`ERR_INVALID_STATE`
Added in: v15.0.0 Indicates that an operation cannot be completed due to an invalid state. For instance, an object may have already been destroyed, or may be performing another operation.
####
`ERR_INVALID_SYNC_FORK_INPUT`
A `Buffer`, `TypedArray`, `DataView`, or `string` was provided as stdio input to an asynchronous fork. See the documentation for the [`child_process`](child_process) module for more information.
####
`ERR_INVALID_THIS`
A Node.js API function was called with an incompatible `this` value.
```
const urlSearchParams = new URLSearchParams('foo=bar&baz=new');
const buf = Buffer.alloc(1);
urlSearchParams.has.call(buf, 'foo');
// Throws a TypeError with code 'ERR_INVALID_THIS'
```
####
`ERR_INVALID_TRANSFER_OBJECT`
An invalid transfer object was passed to `postMessage()`.
####
`ERR_INVALID_TUPLE`
An element in the `iterable` provided to the [WHATWG](url#the-whatwg-url-api) [`URLSearchParams` constructor](url#new-urlsearchparamsiterable) did not represent a `[name, value]` tuple – that is, if an element is not iterable, or does not consist of exactly two elements.
####
`ERR_INVALID_URI`
An invalid URI was passed.
####
`ERR_INVALID_URL`
An invalid URL was passed to the [WHATWG](url#the-whatwg-url-api) [`URL` constructor](url#new-urlinput-base) or the legacy [`url.parse()`](url#urlparseurlstring-parsequerystring-slashesdenotehost) to be parsed. The thrown error object typically has an additional property `'input'` that contains the URL that failed to parse.
####
`ERR_INVALID_URL_SCHEME`
An attempt was made to use a URL of an incompatible scheme (protocol) for a specific purpose. It is only used in the [WHATWG URL API](url#the-whatwg-url-api) support in the [`fs`](fs) module (which only accepts URLs with `'file'` scheme), but may be used in other Node.js APIs as well in the future.
####
`ERR_IPC_CHANNEL_CLOSED`
An attempt was made to use an IPC communication channel that was already closed.
####
`ERR_IPC_DISCONNECTED`
An attempt was made to disconnect an IPC communication channel that was already disconnected. See the documentation for the [`child_process`](child_process) module for more information.
####
`ERR_IPC_ONE_PIPE`
An attempt was made to create a child Node.js process using more than one IPC communication channel. See the documentation for the [`child_process`](child_process) module for more information.
####
`ERR_IPC_SYNC_FORK`
An attempt was made to open an IPC communication channel with a synchronously forked Node.js process. See the documentation for the [`child_process`](child_process) module for more information.
####
`ERR_LOADER_CHAIN_INCOMPLETE`
Added in: v18.6.0, v16.17.0 An ESM loader hook returned without calling `next()` and without explicitly signaling a short circuit.
####
`ERR_MANIFEST_ASSERT_INTEGRITY`
An attempt was made to load a resource, but the resource did not match the integrity defined by the policy manifest. See the documentation for [policy](permissions#policies) manifests for more information.
####
`ERR_MANIFEST_DEPENDENCY_MISSING`
An attempt was made to load a resource, but the resource was not listed as a dependency from the location that attempted to load it. See the documentation for [policy](permissions#policies) manifests for more information.
####
`ERR_MANIFEST_INTEGRITY_MISMATCH`
An attempt was made to load a policy manifest, but the manifest had multiple entries for a resource which did not match each other. Update the manifest entries to match in order to resolve this error. See the documentation for [policy](permissions#policies) manifests for more information.
####
`ERR_MANIFEST_INVALID_RESOURCE_FIELD`
A policy manifest resource had an invalid value for one of its fields. Update the manifest entry to match in order to resolve this error. See the documentation for [policy](permissions#policies) manifests for more information.
####
`ERR_MANIFEST_INVALID_SPECIFIER`
A policy manifest resource had an invalid value for one of its dependency mappings. Update the manifest entry to match to resolve this error. See the documentation for [policy](permissions#policies) manifests for more information.
####
`ERR_MANIFEST_PARSE_POLICY`
An attempt was made to load a policy manifest, but the manifest was unable to be parsed. See the documentation for [policy](permissions#policies) manifests for more information.
####
`ERR_MANIFEST_TDZ`
An attempt was made to read from a policy manifest, but the manifest initialization has not yet taken place. This is likely a bug in Node.js.
####
`ERR_MANIFEST_UNKNOWN_ONERROR`
A policy manifest was loaded, but had an unknown value for its "onerror" behavior. See the documentation for [policy](permissions#policies) manifests for more information.
####
`ERR_MEMORY_ALLOCATION_FAILED`
An attempt was made to allocate memory (usually in the C++ layer) but it failed.
####
`ERR_MESSAGE_TARGET_CONTEXT_UNAVAILABLE`
Added in: v14.5.0, v12.19.0 A message posted to a [`MessagePort`](worker_threads#class-messageport) could not be deserialized in the target <vm> `Context`. Not all Node.js objects can be successfully instantiated in any context at this time, and attempting to transfer them using `postMessage()` can fail on the receiving side in that case.
####
`ERR_METHOD_NOT_IMPLEMENTED`
A method is required but not implemented.
####
`ERR_MISSING_ARGS`
A required argument of a Node.js API was not passed. This is only used for strict compliance with the API specification (which in some cases may accept `func(undefined)` but not `func()`). In most native Node.js APIs, `func(undefined)` and `func()` are treated identically, and the [`ERR_INVALID_ARG_TYPE`](#err_invalid_arg_type) error code may be used instead.
####
`ERR_MISSING_OPTION`
For APIs that accept options objects, some options might be mandatory. This code is thrown if a required option is missing.
####
`ERR_MISSING_PASSPHRASE`
An attempt was made to read an encrypted key without specifying a passphrase.
####
`ERR_MISSING_PLATFORM_FOR_WORKER`
The V8 platform used by this instance of Node.js does not support creating Workers. This is caused by lack of embedder support for Workers. In particular, this error will not occur with standard builds of Node.js.
####
`ERR_MISSING_TRANSFERABLE_IN_TRANSFER_LIST`
Added in: v15.0.0 An object that needs to be explicitly listed in the `transferList` argument is in the object passed to a [`postMessage()`](worker_threads#portpostmessagevalue-transferlist) call, but is not provided in the `transferList` for that call. Usually, this is a `MessagePort`.
In Node.js versions prior to v15.0.0, the error code being used here was [`ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST`](#err_missing_message_port_in_transfer_list). However, the set of transferable object types has been expanded to cover more types than `MessagePort`.
####
`ERR_MODULE_NOT_FOUND`
A module file could not be resolved by the ECMAScript modules loader while attempting an `import` operation or when loading the program entry point.
####
`ERR_MULTIPLE_CALLBACK`
A callback was called more than once.
A callback is almost always meant to only be called once as the query can either be fulfilled or rejected but not both at the same time. The latter would be possible by calling a callback more than once.
####
`ERR_NAPI_CONS_FUNCTION`
While using `Node-API`, a constructor passed was not a function.
####
`ERR_NAPI_INVALID_DATAVIEW_ARGS`
While calling `napi_create_dataview()`, a given `offset` was outside the bounds of the dataview or `offset + length` was larger than a length of given `buffer`.
####
`ERR_NAPI_INVALID_TYPEDARRAY_ALIGNMENT`
While calling `napi_create_typedarray()`, the provided `offset` was not a multiple of the element size.
####
`ERR_NAPI_INVALID_TYPEDARRAY_LENGTH`
While calling `napi_create_typedarray()`, `(length * size_of_element) + byte_offset` was larger than the length of given `buffer`.
####
`ERR_NAPI_TSFN_CALL_JS`
An error occurred while invoking the JavaScript portion of the thread-safe function.
####
`ERR_NAPI_TSFN_GET_UNDEFINED`
An error occurred while attempting to retrieve the JavaScript `undefined` value.
####
`ERR_NAPI_TSFN_START_IDLE_LOOP`
On the main thread, values are removed from the queue associated with the thread-safe function in an idle loop. This error indicates that an error has occurred when attempting to start the loop.
####
`ERR_NAPI_TSFN_STOP_IDLE_LOOP`
Once no more items are left in the queue, the idle loop must be suspended. This error indicates that the idle loop has failed to stop.
####
`ERR_NOT_BUILDING_SNAPSHOT`
An attempt was made to use operations that can only be used when building V8 startup snapshot even though Node.js isn't building one.
####
`ERR_NO_CRYPTO`
An attempt was made to use crypto features while Node.js was not compiled with OpenSSL crypto support.
####
`ERR_NO_ICU`
An attempt was made to use features that require [ICU](intl#internationalization-support), but Node.js was not compiled with ICU support.
####
`ERR_NON_CONTEXT_AWARE_DISABLED`
A non-context-aware native addon was loaded in a process that disallows them.
####
`ERR_OUT_OF_RANGE`
A given value is out of the accepted range.
####
`ERR_PACKAGE_IMPORT_NOT_DEFINED`
The `package.json` [`"imports"`](packages#imports) field does not define the given internal package specifier mapping.
####
`ERR_PACKAGE_PATH_NOT_EXPORTED`
The `package.json` [`"exports"`](packages#exports) field does not export the requested subpath. Because exports are encapsulated, private internal modules that are not exported cannot be imported through the package resolution, unless using an absolute URL.
####
`ERR_PARSE_ARGS_INVALID_OPTION_VALUE`
Added in: v18.3.0, v16.17.0 When `strict` set to `true`, thrown by [`util.parseArgs()`](util#utilparseargsconfig) if a [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) value is provided for an option of type [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type), or if a [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) value is provided for an option of type [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type).
####
`ERR_PARSE_ARGS_UNEXPECTED_POSITIONAL`
Added in: v18.3.0, v16.17.0 Thrown by [`util.parseArgs()`](util#utilparseargsconfig), when a positional argument is provided and `allowPositionals` is set to `false`.
####
`ERR_PARSE_ARGS_UNKNOWN_OPTION`
Added in: v18.3.0, v16.17.0 When `strict` set to `true`, thrown by [`util.parseArgs()`](util#utilparseargsconfig) if an argument is not configured in `options`.
####
`ERR_PERFORMANCE_INVALID_TIMESTAMP`
An invalid timestamp value was provided for a performance mark or measure.
####
`ERR_PERFORMANCE_MEASURE_INVALID_OPTIONS`
Invalid options were provided for a performance measure.
####
`ERR_PROTO_ACCESS`
Accessing `Object.prototype.__proto__` has been forbidden using [`--disable-proto=throw`](cli#--disable-protomode). [`Object.getPrototypeOf`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getPrototypeOf) and [`Object.setPrototypeOf`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/setPrototypeOf) should be used to get and set the prototype of an object.
####
`ERR_REQUIRE_ESM`
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
An attempt was made to `require()` an [ES Module](esm).
####
`ERR_SCRIPT_EXECUTION_INTERRUPTED`
Script execution was interrupted by `SIGINT` (For example, `Ctrl`+`C` was pressed.)
####
`ERR_SCRIPT_EXECUTION_TIMEOUT`
Script execution timed out, possibly due to bugs in the script being executed.
####
`ERR_SERVER_ALREADY_LISTEN`
The [`server.listen()`](net#serverlisten) method was called while a `net.Server` was already listening. This applies to all instances of `net.Server`, including HTTP, HTTPS, and HTTP/2 `Server` instances.
####
`ERR_SERVER_NOT_RUNNING`
The [`server.close()`](net#serverclosecallback) method was called when a `net.Server` was not running. This applies to all instances of `net.Server`, including HTTP, HTTPS, and HTTP/2 `Server` instances.
####
`ERR_SOCKET_ALREADY_BOUND`
An attempt was made to bind a socket that has already been bound.
####
`ERR_SOCKET_BAD_BUFFER_SIZE`
An invalid (negative) size was passed for either the `recvBufferSize` or `sendBufferSize` options in [`dgram.createSocket()`](dgram#dgramcreatesocketoptions-callback).
####
`ERR_SOCKET_BAD_PORT`
An API function expecting a port >= 0 and < 65536 received an invalid value.
####
`ERR_SOCKET_BAD_TYPE`
An API function expecting a socket type (`udp4` or `udp6`) received an invalid value.
####
`ERR_SOCKET_BUFFER_SIZE`
While using [`dgram.createSocket()`](dgram#dgramcreatesocketoptions-callback), the size of the receive or send `Buffer` could not be determined.
####
`ERR_SOCKET_CLOSED`
An attempt was made to operate on an already closed socket.
####
`ERR_SOCKET_DGRAM_IS_CONNECTED`
A [`dgram.connect()`](dgram#socketconnectport-address-callback) call was made on an already connected socket.
####
`ERR_SOCKET_DGRAM_NOT_CONNECTED`
A [`dgram.disconnect()`](dgram#socketdisconnect) or [`dgram.remoteAddress()`](dgram#socketremoteaddress) call was made on a disconnected socket.
####
`ERR_SOCKET_DGRAM_NOT_RUNNING`
A call was made and the UDP subsystem was not running.
####
`ERR_SRI_PARSE`
A string was provided for a Subresource Integrity check, but was unable to be parsed. Check the format of integrity attributes by looking at the [Subresource Integrity specification](https://www.w3.org/TR/SRI/#the-integrity-attribute).
####
`ERR_STREAM_ALREADY_FINISHED`
A stream method was called that cannot complete because the stream was finished.
####
`ERR_STREAM_CANNOT_PIPE`
An attempt was made to call [`stream.pipe()`](stream#readablepipedestination-options) on a [`Writable`](stream#class-streamwritable) stream.
####
`ERR_STREAM_DESTROYED`
A stream method was called that cannot complete because the stream was destroyed using `stream.destroy()`.
####
`ERR_STREAM_NULL_VALUES`
An attempt was made to call [`stream.write()`](stream#writablewritechunk-encoding-callback) with a `null` chunk.
####
`ERR_STREAM_PREMATURE_CLOSE`
An error returned by `stream.finished()` and `stream.pipeline()`, when a stream or a pipeline ends non gracefully with no explicit error.
####
`ERR_STREAM_PUSH_AFTER_EOF`
An attempt was made to call [`stream.push()`](stream#readablepushchunk-encoding) after a `null`(EOF) had been pushed to the stream.
####
`ERR_STREAM_UNSHIFT_AFTER_END_EVENT`
An attempt was made to call [`stream.unshift()`](stream#readableunshiftchunk-encoding) after the `'end'` event was emitted.
####
`ERR_STREAM_WRAP`
Prevents an abort if a string decoder was set on the Socket or if the decoder is in `objectMode`.
```
const Socket = require('node:net').Socket;
const instance = new Socket();
instance.setEncoding('utf8');
```
####
`ERR_STREAM_WRITE_AFTER_END`
An attempt was made to call [`stream.write()`](stream#writablewritechunk-encoding-callback) after `stream.end()` has been called.
####
`ERR_STRING_TOO_LONG`
An attempt has been made to create a string longer than the maximum allowed length.
####
`ERR_SYNTHETIC`
An artificial error object used to capture the call stack for diagnostic reports.
####
`ERR_SYSTEM_ERROR`
An unspecified or non-specific system error has occurred within the Node.js process. The error object will have an `err.info` object property with additional details.
####
`ERR_TEST_FAILURE`
This error represents a failed test. Additional information about the failure is available via the `cause` property. The `failureType` property specifies what the test was doing when the failure occurred.
####
`ERR_TLS_CERT_ALTNAME_FORMAT`
This error is thrown by `checkServerIdentity` if a user-supplied `subjectaltname` property violates encoding rules. Certificate objects produced by Node.js itself always comply with encoding rules and will never cause this error.
####
`ERR_TLS_CERT_ALTNAME_INVALID`
While using TLS, the host name/IP of the peer did not match any of the `subjectAltNames` in its certificate.
####
`ERR_TLS_DH_PARAM_SIZE`
While using TLS, the parameter offered for the Diffie-Hellman (`DH`) key-agreement protocol is too small. By default, the key length must be greater than or equal to 1024 bits to avoid vulnerabilities, even though it is strongly recommended to use 2048 bits or larger for stronger security.
####
`ERR_TLS_HANDSHAKE_TIMEOUT`
A TLS/SSL handshake timed out. In this case, the server must also abort the connection.
####
`ERR_TLS_INVALID_CONTEXT`
Added in: v13.3.0 The context must be a `SecureContext`.
####
`ERR_TLS_INVALID_PROTOCOL_METHOD`
The specified `secureProtocol` method is invalid. It is either unknown, or disabled because it is insecure.
####
`ERR_TLS_INVALID_PROTOCOL_VERSION`
Valid TLS protocol versions are `'TLSv1'`, `'TLSv1.1'`, or `'TLSv1.2'`.
####
`ERR_TLS_INVALID_STATE`
Added in: v13.10.0, v12.17.0 The TLS socket must be connected and securely established. Ensure the 'secure' event is emitted before continuing.
####
`ERR_TLS_PROTOCOL_VERSION_CONFLICT`
Attempting to set a TLS protocol `minVersion` or `maxVersion` conflicts with an attempt to set the `secureProtocol` explicitly. Use one mechanism or the other.
####
`ERR_TLS_PSK_SET_IDENTIY_HINT_FAILED`
Failed to set PSK identity hint. Hint may be too long.
####
`ERR_TLS_RENEGOTIATION_DISABLED`
An attempt was made to renegotiate TLS on a socket instance with TLS disabled.
####
`ERR_TLS_REQUIRED_SERVER_NAME`
While using TLS, the `server.addContext()` method was called without providing a host name in the first parameter.
####
`ERR_TLS_SESSION_ATTACK`
An excessive amount of TLS renegotiations is detected, which is a potential vector for denial-of-service attacks.
####
`ERR_TLS_SNI_FROM_SERVER`
An attempt was made to issue Server Name Indication from a TLS server-side socket, which is only valid from a client.
####
`ERR_TRACE_EVENTS_CATEGORY_REQUIRED`
The `trace_events.createTracing()` method requires at least one trace event category.
####
`ERR_TRACE_EVENTS_UNAVAILABLE`
The `node:trace_events` module could not be loaded because Node.js was compiled with the `--without-v8-platform` flag.
####
`ERR_TRANSFORM_ALREADY_TRANSFORMING`
A `Transform` stream finished while it was still transforming.
####
`ERR_TRANSFORM_WITH_LENGTH_0`
A `Transform` stream finished with data still in the write buffer.
####
`ERR_TTY_INIT_FAILED`
The initialization of a TTY failed due to a system error.
####
`ERR_UNAVAILABLE_DURING_EXIT`
Function was called within a [`process.on('exit')`](process#event-exit) handler that shouldn't be called within [`process.on('exit')`](process#event-exit) handler.
####
`ERR_UNCAUGHT_EXCEPTION_CAPTURE_ALREADY_SET`
[`process.setUncaughtExceptionCaptureCallback()`](process#processsetuncaughtexceptioncapturecallbackfn) was called twice, without first resetting the callback to `null`.
This error is designed to prevent accidentally overwriting a callback registered from another module.
####
`ERR_UNESCAPED_CHARACTERS`
A string that contained unescaped characters was received.
####
`ERR_UNHANDLED_ERROR`
An unhandled error occurred (for instance, when an `'error'` event is emitted by an [`EventEmitter`](events#class-eventemitter) but an `'error'` handler is not registered).
####
`ERR_UNKNOWN_BUILTIN_MODULE`
Used to identify a specific kind of internal Node.js error that should not typically be triggered by user code. Instances of this error point to an internal bug within the Node.js binary itself.
####
`ERR_UNKNOWN_CREDENTIAL`
A Unix group or user identifier that does not exist was passed.
####
`ERR_UNKNOWN_ENCODING`
An invalid or unknown encoding option was passed to an API.
####
`ERR_UNKNOWN_FILE_EXTENSION`
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
An attempt was made to load a module with an unknown or unsupported file extension.
####
`ERR_UNKNOWN_MODULE_FORMAT`
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
An attempt was made to load a module with an unknown or unsupported format.
####
`ERR_UNKNOWN_SIGNAL`
An invalid or unknown process signal was passed to an API expecting a valid signal (such as [`subprocess.kill()`](child_process#subprocesskillsignal)).
####
`ERR_UNSUPPORTED_DIR_IMPORT`
`import` a directory URL is unsupported. Instead, [self-reference a package using its name](packages#self-referencing-a-package-using-its-name) and [define a custom subpath](packages#subpath-exports) in the [`"exports"`](packages#exports) field of the [`package.json`](packages#nodejs-packagejson-field-definitions) file.
```
import './'; // unsupported
import './index.js'; // supported
import 'package-name'; // supported
```
####
`ERR_UNSUPPORTED_ESM_URL_SCHEME`
`import` with URL schemes other than `file` and `data` is unsupported.
####
`ERR_USE_AFTER_CLOSE`
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
An attempt was made to use something that was already closed.
####
`ERR_VALID_PERFORMANCE_ENTRY_TYPE`
While using the Performance Timing API (`perf_hooks`), no valid performance entry types are found.
####
`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`
A dynamic import callback was not specified.
####
`ERR_VM_MODULE_ALREADY_LINKED`
The module attempted to be linked is not eligible for linking, because of one of the following reasons:
* It has already been linked (`linkingStatus` is `'linked'`)
* It is being linked (`linkingStatus` is `'linking'`)
* Linking has failed for this module (`linkingStatus` is `'errored'`)
####
`ERR_VM_MODULE_CACHED_DATA_REJECTED`
The `cachedData` option passed to a module constructor is invalid.
####
`ERR_VM_MODULE_CANNOT_CREATE_CACHED_DATA`
Cached data cannot be created for modules which have already been evaluated.
####
`ERR_VM_MODULE_DIFFERENT_CONTEXT`
The module being returned from the linker function is from a different context than the parent module. Linked modules must share the same context.
####
`ERR_VM_MODULE_LINK_FAILURE`
The module was unable to be linked due to a failure.
####
`ERR_VM_MODULE_NOT_MODULE`
The fulfilled value of a linking promise is not a `vm.Module` object.
####
`ERR_VM_MODULE_STATUS`
The current module's status does not allow for this operation. The specific meaning of the error depends on the specific function.
####
`ERR_WASI_ALREADY_STARTED`
The WASI instance has already started.
####
`ERR_WASI_NOT_STARTED`
The WASI instance has not been started.
####
`ERR_WEBASSEMBLY_RESPONSE`
Added in: v18.1.0 The `Response` that has been passed to `WebAssembly.compileStreaming` or to `WebAssembly.instantiateStreaming` is not a valid WebAssembly response.
####
`ERR_WORKER_INIT_FAILED`
The `Worker` initialization failed.
####
`ERR_WORKER_INVALID_EXEC_ARGV`
The `execArgv` option passed to the `Worker` constructor contains invalid flags.
####
`ERR_WORKER_NOT_RUNNING`
An operation failed because the `Worker` instance is not currently running.
####
`ERR_WORKER_OUT_OF_MEMORY`
The `Worker` instance terminated because it reached its memory limit.
####
`ERR_WORKER_PATH`
The path for the main script of a worker is neither an absolute path nor a relative path starting with `./` or `../`.
####
`ERR_WORKER_UNSERIALIZABLE_ERROR`
All attempts at serializing an uncaught exception from a worker thread failed.
####
`ERR_WORKER_UNSUPPORTED_OPERATION`
The requested functionality is not supported in worker threads.
####
`ERR_ZLIB_INITIALIZATION_FAILED`
Creation of a [`zlib`](zlib) object failed due to incorrect configuration.
####
`HPE_HEADER_OVERFLOW`
History
| Version | Changes |
| --- | --- |
| v11.4.0, v10.15.0 | Max header size in `http_parser` was set to 8 KiB. |
Too much HTTP header data was received. In order to protect against malicious or malconfigured clients, if more than 8 KiB of HTTP header data is received then HTTP parsing will abort without a request or response object being created, and an `Error` with this code will be emitted.
####
`HPE_UNEXPECTED_CONTENT_LENGTH`
Server is sending both a `Content-Length` header and `Transfer-Encoding: chunked`.
`Transfer-Encoding: chunked` allows the server to maintain an HTTP persistent connection for dynamically generated content. In this case, the `Content-Length` HTTP header cannot be used.
Use `Content-Length` or `Transfer-Encoding: chunked`.
####
`MODULE_NOT_FOUND`
History
| Version | Changes |
| --- | --- |
| v12.0.0 | Added `requireStack` property. |
A module file could not be resolved by the CommonJS modules loader while attempting a [`require()`](modules#requireid) operation or when loading the program entry point.
### Legacy Node.js error codes
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated. These error codes are either inconsistent, or have been removed.
####
`ERR_CANNOT_TRANSFER_OBJECT`
The value passed to `postMessage()` contained an object that is not supported for transferring.
####
`ERR_CRYPTO_HASH_DIGEST_NO_UTF16`
Added in: v9.0.0Removed in: v12.12.0 The UTF-16 encoding was used with [`hash.digest()`](crypto#hashdigestencoding). While the `hash.digest()` method does allow an `encoding` argument to be passed in, causing the method to return a string rather than a `Buffer`, the UTF-16 encoding (e.g. `ucs` or `utf16le`) is not supported.
####
`ERR_HTTP2_FRAME_ERROR`
Added in: v9.0.0Removed in: v10.0.0 Used when a failure occurs sending an individual frame on the HTTP/2 session.
####
`ERR_HTTP2_HEADERS_OBJECT`
Added in: v9.0.0Removed in: v10.0.0 Used when an HTTP/2 Headers Object is expected.
####
`ERR_HTTP2_HEADER_REQUIRED`
Added in: v9.0.0Removed in: v10.0.0 Used when a required header is missing in an HTTP/2 message.
####
`ERR_HTTP2_INFO_HEADERS_AFTER_RESPOND`
Added in: v9.0.0Removed in: v10.0.0 HTTP/2 informational headers must only be sent *prior* to calling the `Http2Stream.prototype.respond()` method.
####
`ERR_HTTP2_STREAM_CLOSED`
Added in: v9.0.0Removed in: v10.0.0 Used when an action has been performed on an HTTP/2 Stream that has already been closed.
####
`ERR_HTTP_INVALID_CHAR`
Added in: v9.0.0Removed in: v10.0.0 Used when an invalid character is found in an HTTP response status message (reason phrase).
####
`ERR_INDEX_OUT_OF_RANGE`
Added in: v10.0.0Removed in: v11.0.0 A given index was out of the accepted range (e.g. negative offsets).
####
`ERR_INVALID_OPT_VALUE`
Added in: v8.0.0Removed in: v15.0.0 An invalid or unexpected value was passed in an options object.
####
`ERR_INVALID_OPT_VALUE_ENCODING`
Added in: v9.0.0Removed in: v15.0.0 An invalid or unknown file encoding was passed.
####
`ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST`
Removed in: v15.0.0 This error code was replaced by [`ERR_MISSING_TRANSFERABLE_IN_TRANSFER_LIST`](#err_missing_transferable_in_transfer_list) in Node.js v15.0.0, because it is no longer accurate as other types of transferable objects also exist now.
####
`ERR_NAPI_CONS_PROTOTYPE_OBJECT`
Added in: v9.0.0Removed in: v10.0.0 Used by the `Node-API` when `Constructor.prototype` is not an object.
####
`ERR_NETWORK_IMPORT_BAD_RESPONSE`
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Response was received but was invalid when importing a module over the network.
####
`ERR_NETWORK_IMPORT_DISALLOWED`
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
A network module attempted to load another module that it is not allowed to load. Likely this restriction is for security reasons.
####
`ERR_NO_LONGER_SUPPORTED`
A Node.js API was called in an unsupported manner, such as `Buffer.write(string, encoding, offset[, length])`.
####
`ERR_OPERATION_FAILED`
Added in: v15.0.0 An operation failed. This is typically used to signal the general failure of an asynchronous operation.
####
`ERR_OUTOFMEMORY`
Added in: v9.0.0Removed in: v10.0.0 Used generically to identify that an operation caused an out of memory condition.
####
`ERR_PARSE_HISTORY_DATA`
Added in: v9.0.0Removed in: v10.0.0 The `node:repl` module was unable to parse data from the REPL history file.
####
`ERR_SOCKET_CANNOT_SEND`
Added in: v9.0.0Removed in: v14.0.0 Data could not be sent on a socket.
####
`ERR_STDERR_CLOSE`
History
| Version | Changes |
| --- | --- |
| v10.12.0 | Rather than emitting an error, `process.stderr.end()` now only closes the stream side but not the underlying resource, making this error obsolete. |
| v10.12.0 | Removed in: v10.12.0 |
An attempt was made to close the `process.stderr` stream. By design, Node.js does not allow `stdout` or `stderr` streams to be closed by user code.
####
`ERR_STDOUT_CLOSE`
History
| Version | Changes |
| --- | --- |
| v10.12.0 | Rather than emitting an error, `process.stderr.end()` now only closes the stream side but not the underlying resource, making this error obsolete. |
| v10.12.0 | Removed in: v10.12.0 |
An attempt was made to close the `process.stdout` stream. By design, Node.js does not allow `stdout` or `stderr` streams to be closed by user code.
####
`ERR_STREAM_READ_NOT_IMPLEMENTED`
Added in: v9.0.0Removed in: v10.0.0 Used when an attempt is made to use a readable stream that has not implemented [`readable._read()`](stream#readable_readsize).
####
`ERR_TLS_RENEGOTIATION_FAILED`
Added in: v9.0.0Removed in: v10.0.0 Used when a TLS renegotiation request has failed in a non-specific way.
####
`ERR_TRANSFERRING_EXTERNALIZED_SHAREDARRAYBUFFER`
Added in: v10.5.0Removed in: v14.0.0 A `SharedArrayBuffer` whose memory is not managed by the JavaScript engine or by Node.js was encountered during serialization. Such a `SharedArrayBuffer` cannot be serialized.
This can only happen when native addons create `SharedArrayBuffer`s in "externalized" mode, or put existing `SharedArrayBuffer` into externalized mode.
####
`ERR_UNKNOWN_STDIN_TYPE`
Added in: v8.0.0Removed in: v11.7.0 An attempt was made to launch a Node.js process with an unknown `stdin` file type. This error is usually an indication of a bug within Node.js itself, although it is possible for user code to trigger it.
####
`ERR_UNKNOWN_STREAM_TYPE`
Added in: v8.0.0Removed in: v11.7.0 An attempt was made to launch a Node.js process with an unknown `stdout` or `stderr` file type. This error is usually an indication of a bug within Node.js itself, although it is possible for user code to trigger it.
####
`ERR_V8BREAKITERATOR`
The V8 `BreakIterator` API was used but the full ICU data set is not installed.
####
`ERR_VALUE_OUT_OF_RANGE`
Added in: v9.0.0Removed in: v10.0.0 Used when a given value is out of the accepted range.
####
`ERR_VM_MODULE_NOT_LINKED`
The module must be successfully linked before instantiation.
####
`ERR_VM_MODULE_LINKING_ERRORED`
Added in: v10.0.0Removed in: v18.1.0, v16.17.0 The linker function returned a module for which linking has failed.
####
`ERR_WORKER_UNSUPPORTED_EXTENSION`
Added in: v11.0.0Removed in: v16.9.0 The pathname used for the main script of a worker has an unknown file extension.
####
`ERR_ZLIB_BINDING_CLOSED`
Added in: v9.0.0Removed in: v10.0.0 Used when an attempt is made to use a `zlib` object after it has already been closed.
####
`ERR_CPU_USAGE`
Removed in: v15.0.0 The native call from `process.cpuUsage` could not be processed.
| programming_docs |
node None C++ embedder API
----------------
Node.js provides a number of C++ APIs that can be used to execute JavaScript in a Node.js environment from other C++ software.
The documentation for these APIs can be found in [src/node.h](https://github.com/nodejs/node/blob/HEAD/src/node.h) in the Node.js source tree. In addition to the APIs exposed by Node.js, some required concepts are provided by the V8 embedder API.
Because using Node.js as an embedded library is different from writing code that is executed by Node.js, breaking changes do not follow typical Node.js [deprecation policy](deprecations) and may occur on each semver-major release without prior warning.
### Example embedding application
The following sections will provide an overview over how to use these APIs to create an application from scratch that will perform the equivalent of `node -e <code>`, i.e. that will take a piece of JavaScript and run it in a Node.js-specific environment.
The full code can be found [in the Node.js source tree](https://github.com/nodejs/node/blob/HEAD/test/embedding/embedtest.cc).
#### Setting up per-process state
Node.js requires some per-process state management in order to run:
* Arguments parsing for Node.js [CLI options](cli),
* V8 per-process requirements, such as a `v8::Platform` instance.
The following example shows how these can be set up. Some class names are from the `node` and `v8` C++ namespaces, respectively.
```
int main(int argc, char** argv) {
argv = uv_setup_args(argc, argv);
std::vector<std::string> args(argv, argv + argc);
// Parse Node.js CLI options, and print any errors that have occurred while
// trying to parse them.
std::unique_ptr<node::InitializationResult> result =
node::InitializeOncePerProcess(args, {
node::ProcessInitializationFlags::kNoInitializeV8,
node::ProcessInitializationFlags::kNoInitializeNodeV8Platform
});
for (const std::string& error : result->errors())
fprintf(stderr, "%s: %s\n", args[0].c_str(), error.c_str());
if (result->early_return() != 0) {
return result->exit_code();
}
// Create a v8::Platform instance. `MultiIsolatePlatform::Create()` is a way
// to create a v8::Platform instance that Node.js can use when creating
// Worker threads. When no `MultiIsolatePlatform` instance is present,
// Worker threads are disabled.
std::unique_ptr<MultiIsolatePlatform> platform =
MultiIsolatePlatform::Create(4);
V8::InitializePlatform(platform.get());
V8::Initialize();
// See below for the contents of this function.
int ret = RunNodeInstance(
platform.get(), result->args(), result->exec_args());
V8::Dispose();
V8::DisposePlatform();
node::TearDownOncePerProcess();
return ret;
}
```
#### Per-instance state
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The `CommonEnvironmentSetup` and `SpinEventLoop` utilities were added. |
Node.js has a concept of a “Node.js instance”, that is commonly being referred to as `node::Environment`. Each `node::Environment` is associated with:
* Exactly one `v8::Isolate`, i.e. one JS Engine instance,
* Exactly one `uv_loop_t`, i.e. one event loop, and
* A number of `v8::Context`s, but exactly one main `v8::Context`.
* One `node::IsolateData` instance that contains information that could be shared by multiple `node::Environment`s that use the same `v8::Isolate`. Currently, no testing if performed for this scenario.
In order to set up a `v8::Isolate`, an `v8::ArrayBuffer::Allocator` needs to be provided. One possible choice is the default Node.js allocator, which can be created through `node::ArrayBufferAllocator::Create()`. Using the Node.js allocator allows minor performance optimizations when addons use the Node.js C++ `Buffer` API, and is required in order to track `ArrayBuffer` memory in [`process.memoryUsage()`](process#processmemoryusage).
Additionally, each `v8::Isolate` that is used for a Node.js instance needs to be registered and unregistered with the `MultiIsolatePlatform` instance, if one is being used, in order for the platform to know which event loop to use for tasks scheduled by the `v8::Isolate`.
The `node::NewIsolate()` helper function creates a `v8::Isolate`, sets it up with some Node.js-specific hooks (e.g. the Node.js error handler), and registers it with the platform automatically.
```
int RunNodeInstance(MultiIsolatePlatform* platform,
const std::vector<std::string>& args,
const std::vector<std::string>& exec_args) {
int exit_code = 0;
// Setup up a libuv event loop, v8::Isolate, and Node.js Environment.
std::vector<std::string> errors;
std::unique_ptr<CommonEnvironmentSetup> setup =
CommonEnvironmentSetup::Create(platform, &errors, args, exec_args);
if (!setup) {
for (const std::string& err : errors)
fprintf(stderr, "%s: %s\n", args[0].c_str(), err.c_str());
return 1;
}
Isolate* isolate = setup->isolate();
Environment* env = setup->env();
{
Locker locker(isolate);
Isolate::Scope isolate_scope(isolate);
HandleScope handle_scope(isolate);
// The v8::Context needs to be entered when node::CreateEnvironment() and
// node::LoadEnvironment() are being called.
Context::Scope context_scope(setup->context());
// Set up the Node.js instance for execution, and run code inside of it.
// There is also a variant that takes a callback and provides it with
// the `require` and `process` objects, so that it can manually compile
// and run scripts as needed.
// The `require` function inside this script does *not* access the file
// system, and can only load built-in Node.js modules.
// `module.createRequire()` is being used to create one that is able to
// load files from the disk, and uses the standard CommonJS file loader
// instead of the internal-only `require` function.
MaybeLocal<Value> loadenv_ret = node::LoadEnvironment(
env,
"const publicRequire ="
" require('node:module').createRequire(process.cwd() + '/');"
"globalThis.require = publicRequire;"
"require('node:vm').runInThisContext(process.argv[1]);");
if (loadenv_ret.IsEmpty()) // There has been a JS exception.
return 1;
exit_code = node::SpinEventLoop(env).FromMaybe(1);
// node::Stop() can be used to explicitly stop the event loop and keep
// further JavaScript from running. It can be called from any thread,
// and will act like worker.terminate() if called from another thread.
node::Stop(env);
}
return exit_code;
}
```
node None Query string
------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/querystring.js](https://github.com/nodejs/node/blob/v19.0.1/lib/querystring.js)
The `node:querystring` module provides utilities for parsing and formatting URL query strings. It can be accessed using:
```
const querystring = require('node:querystring');
```
`querystring` is more performant than [<URLSearchParams>](url#class-urlsearchparams) but is not a standardized API. Use [<URLSearchParams>](url#class-urlsearchparams) when performance is not critical or when compatibility with browser code is desirable.
###
`querystring.decode()`
Added in: v0.1.99 The `querystring.decode()` function is an alias for `querystring.parse()`.
###
`querystring.encode()`
Added in: v0.1.99 The `querystring.encode()` function is an alias for `querystring.stringify()`.
###
`querystring.escape(str)`
Added in: v0.1.25 * `str` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `querystring.escape()` method performs URL percent-encoding on the given `str` in a manner that is optimized for the specific requirements of URL query strings.
The `querystring.escape()` method is used by `querystring.stringify()` and is generally not expected to be used directly. It is exported primarily to allow application code to provide a replacement percent-encoding implementation if necessary by assigning `querystring.escape` to an alternative function.
###
`querystring.parse(str[, sep[, eq[, options]]])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | Multiple empty entries are now parsed correctly (e.g. `&=&=`). |
| v6.0.0 | The returned object no longer inherits from `Object.prototype`. |
| v6.0.0, v4.2.4 | The `eq` parameter may now have a length of more than `1`. |
| v0.1.25 | Added in: v0.1.25 |
* `str` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The URL query string to parse
* `sep` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The substring used to delimit key and value pairs in the query string. **Default:** `'&'`.
* `eq` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type). The substring used to delimit keys and values in the query string. **Default:** `'='`.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `decodeURIComponent` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to use when decoding percent-encoded characters in the query string. **Default:** `querystring.unescape()`.
+ `maxKeys` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the maximum number of keys to parse. Specify `0` to remove key counting limitations. **Default:** `1000`.
The `querystring.parse()` method parses a URL query string (`str`) into a collection of key and value pairs.
For example, the query string `'foo=bar&abc=xyz&abc=123'` is parsed into:
```
{
foo: 'bar',
abc: ['xyz', '123']
}
```
The object returned by the `querystring.parse()` method *does not* prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and *will not work*.
By default, percent-encoded characters within the query string will be assumed to use UTF-8 encoding. If an alternative character encoding is used, then an alternative `decodeURIComponent` option will need to be specified:
```
// Assuming gbkDecodeURIComponent function already exists...
querystring.parse('w=%D6%D0%CE%C4&foo=bar', null, null,
{ decodeURIComponent: gbkDecodeURIComponent });
```
###
`querystring.stringify(obj[, sep[, eq[, options]]])`
Added in: v0.1.25 * `obj` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The object to serialize into a URL query string
* `sep` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The substring used to delimit key and value pairs in the query string. **Default:** `'&'`.
* `eq` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type). The substring used to delimit keys and values in the query string. **Default:** `'='`.
* `options`
+ `encodeURIComponent` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The function to use when converting URL-unsafe characters to percent-encoding in the query string. **Default:** `querystring.escape()`.
The `querystring.stringify()` method produces a URL query string from a given `obj` by iterating through the object's "own properties".
It serializes the following types of values passed in `obj`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) | [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<bigint[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) | [<boolean[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) The numeric values must be finite. Any other input values will be coerced to empty strings.
```
querystring.stringify({ foo: 'bar', baz: ['qux', 'quux'], corge: '' });
// Returns 'foo=bar&baz=qux&baz=quux&corge='
querystring.stringify({ foo: 'bar', baz: 'qux' }, ';', ':');
// Returns 'foo:bar;baz:qux'
```
By default, characters requiring percent-encoding within the query string will be encoded as UTF-8. If an alternative encoding is required, then an alternative `encodeURIComponent` option will need to be specified:
```
// Assuming gbkEncodeURIComponent function already exists,
querystring.stringify({ w: '中文', foo: 'bar' }, null, null,
{ encodeURIComponent: gbkEncodeURIComponent });
```
###
`querystring.unescape(str)`
Added in: v0.1.25 * `str` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `querystring.unescape()` method performs decoding of URL percent-encoded characters on the given `str`.
The `querystring.unescape()` method is used by `querystring.parse()` and is generally not expected to be used directly. It is exported primarily to allow application code to provide a replacement decoding implementation if necessary by assigning `querystring.unescape` to an alternative function.
By default, the `querystring.unescape()` method will attempt to use the JavaScript built-in `decodeURIComponent()` method to decode. If that fails, a safer equivalent that does not throw on malformed URLs will be used.
node None OS
--
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/os.js](https://github.com/nodejs/node/blob/v19.0.1/lib/os.js)
The `node:os` module provides operating system-related utility methods and properties. It can be accessed using:
```
const os = require('node:os');
```
###
`os.EOL`
Added in: v0.7.8 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The operating system-specific end-of-line marker.
* `\n` on POSIX
* `\r\n` on Windows
###
`os.arch()`
Added in: v0.5.0 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the operating system CPU architecture for which the Node.js binary was compiled. Possible values are `'arm'`, `'arm64'`, `'ia32'`, `'mips'`, `'mipsel'`, `'ppc'`, `'ppc64'`, `'s390'`, `'s390x'`, and `'x64'`.
The return value is equivalent to [`process.arch`](process#processarch).
###
`os.constants`
Added in: v6.3.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Contains commonly used operating system-specific constants for error codes, process signals, and so on. The specific constants defined are described in [OS constants](#os-constants).
###
`os.cpus()`
Added in: v0.3.3 * Returns: [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns an array of objects containing information about each logical CPU core.
The properties included on each object include:
* `model` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `speed` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) (in MHz)
* `times` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `user` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds the CPU has spent in user mode.
+ `nice` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds the CPU has spent in nice mode.
+ `sys` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds the CPU has spent in sys mode.
+ `idle` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds the CPU has spent in idle mode.
+ `irq` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds the CPU has spent in irq mode.
```
[
{
model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times: {
user: 252020,
nice: 0,
sys: 30340,
idle: 1070356870,
irq: 0
}
},
{
model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times: {
user: 306960,
nice: 0,
sys: 26980,
idle: 1071569080,
irq: 0
}
},
{
model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times: {
user: 248450,
nice: 0,
sys: 21750,
idle: 1070919370,
irq: 0
}
},
{
model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times: {
user: 256880,
nice: 0,
sys: 19430,
idle: 1070905480,
irq: 20
}
},
]
```
`nice` values are POSIX-only. On Windows, the `nice` values of all processors are always 0.
###
`os.devNull`
Added in: v16.3.0, v14.18.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The platform-specific file path of the null device.
* `\\.\nul` on Windows
* `/dev/null` on POSIX
###
`os.endianness()`
Added in: v0.9.4 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns a string identifying the endianness of the CPU for which the Node.js binary was compiled.
Possible values are `'BE'` for big endian and `'LE'` for little endian.
###
`os.freemem()`
Added in: v0.3.3 * Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the amount of free system memory in bytes as an integer.
###
`os.getPriority([pid])`
Added in: v10.10.0 * `pid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The process ID to retrieve scheduling priority for. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the scheduling priority for the process specified by `pid`. If `pid` is not provided or is `0`, the priority of the current process is returned.
###
`os.homedir()`
Added in: v2.3.0 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the string path of the current user's home directory.
On POSIX, it uses the `$HOME` environment variable if defined. Otherwise it uses the [effective UID](https://en.wikipedia.org/wiki/User_identifier#Effective_user_ID) to look up the user's home directory.
On Windows, it uses the `USERPROFILE` environment variable if defined. Otherwise it uses the path to the profile directory of the current user.
###
`os.hostname()`
Added in: v0.3.3 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the host name of the operating system as a string.
###
`os.loadavg()`
Added in: v0.3.3 * Returns: [<number[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns an array containing the 1, 5, and 15 minute load averages.
The load average is a measure of system activity calculated by the operating system and expressed as a fractional number.
The load average is a Unix-specific concept. On Windows, the return value is always `[0, 0, 0]`.
###
`os.networkInterfaces()`
History
| Version | Changes |
| --- | --- |
| v18.4.0 | The `family` property now returns a string instead of a number. |
| v18.0.0 | The `family` property now returns a number instead of a string. |
| v0.6.0 | Added in: v0.6.0 |
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns an object containing network interfaces that have been assigned a network address.
Each key on the returned object identifies a network interface. The associated value is an array of objects that each describe an assigned network address.
The properties available on the assigned network address object include:
* `address` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The assigned IPv4 or IPv6 address
* `netmask` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The IPv4 or IPv6 network mask
* `family` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Either `IPv4` or `IPv6`
* `mac` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The MAC address of the network interface
* `internal` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the network interface is a loopback or similar interface that is not remotely accessible; otherwise `false`
* `scopeid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The numeric IPv6 scope ID (only specified when `family` is `IPv6`)
* `cidr` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The assigned IPv4 or IPv6 address with the routing prefix in CIDR notation. If the `netmask` is invalid, this property is set to `null`.
```
{
lo: [
{
address: '127.0.0.1',
netmask: '255.0.0.0',
family: 'IPv4',
mac: '00:00:00:00:00:00',
internal: true,
cidr: '127.0.0.1/8'
},
{
address: '::1',
netmask: 'ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff',
family: 'IPv6',
mac: '00:00:00:00:00:00',
scopeid: 0,
internal: true,
cidr: '::1/128'
}
],
eth0: [
{
address: '192.168.1.108',
netmask: '255.255.255.0',
family: 'IPv4',
mac: '01:02:03:0a:0b:0c',
internal: false,
cidr: '192.168.1.108/24'
},
{
address: 'fe80::a00:27ff:fe4e:66a1',
netmask: 'ffff:ffff:ffff:ffff::',
family: 'IPv6',
mac: '01:02:03:0a:0b:0c',
scopeid: 1,
internal: false,
cidr: 'fe80::a00:27ff:fe4e:66a1/64'
}
]
}
```
###
`os.platform()`
Added in: v0.5.0 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns a string identifying the operating system platform for which the Node.js binary was compiled. The value is set at compile time. Possible values are `'aix'`, `'darwin'`, `'freebsd'`,`'linux'`, `'openbsd'`, `'sunos'`, and `'win32'`.
The return value is equivalent to [`process.platform`](process#processplatform).
The value `'android'` may also be returned if Node.js is built on the Android operating system. [Android support is experimental](https://github.com/nodejs/node/blob/HEAD/BUILDING.md#androidandroid-based-devices-eg-firefox-os).
###
`os.release()`
Added in: v0.3.3 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the operating system as a string.
On POSIX systems, the operating system release is determined by calling [`uname(3)`](https://linux.die.net/man/3/uname). On Windows, `GetVersionExW()` is used. See <https://en.wikipedia.org/wiki/Uname#Examples> for more information.
###
`os.setPriority([pid, ]priority)`
Added in: v10.10.0 * `pid` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The process ID to set scheduling priority for. **Default:** `0`.
* `priority` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The scheduling priority to assign to the process.
Attempts to set the scheduling priority for the process specified by `pid`. If `pid` is not provided or is `0`, the process ID of the current process is used.
The `priority` input must be an integer between `-20` (high priority) and `19` (low priority). Due to differences between Unix priority levels and Windows priority classes, `priority` is mapped to one of six priority constants in `os.constants.priority`. When retrieving a process priority level, this range mapping may cause the return value to be slightly different on Windows. To avoid confusion, set `priority` to one of the priority constants.
On Windows, setting priority to `PRIORITY_HIGHEST` requires elevated user privileges. Otherwise the set priority will be silently reduced to `PRIORITY_HIGH`.
###
`os.tmpdir()`
History
| Version | Changes |
| --- | --- |
| v2.0.0 | This function is now cross-platform consistent and no longer returns a path with a trailing slash on any platform. |
| v0.9.9 | Added in: v0.9.9 |
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the operating system's default directory for temporary files as a string.
###
`os.totalmem()`
Added in: v0.3.3 * Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the total amount of system memory in bytes as an integer.
###
`os.type()`
Added in: v0.3.3 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the operating system name as returned by [`uname(3)`](https://linux.die.net/man/3/uname). For example, it returns `'Linux'` on Linux, `'Darwin'` on macOS, and `'Windows_NT'` on Windows.
See <https://en.wikipedia.org/wiki/Uname#Examples> for additional information about the output of running [`uname(3)`](https://linux.die.net/man/3/uname) on various operating systems.
###
`os.uptime()`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | The result of this function no longer contains a fraction component on Windows. |
| v0.3.3 | Added in: v0.3.3 |
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the system uptime in number of seconds.
###
`os.userInfo([options])`
Added in: v6.0.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Character encoding used to interpret resulting strings. If `encoding` is set to `'buffer'`, the `username`, `shell`, and `homedir` values will be `Buffer` instances. **Default:** `'utf8'`.
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns information about the currently effective user. On POSIX platforms, this is typically a subset of the password file. The returned object includes the `username`, `uid`, `gid`, `shell`, and `homedir`. On Windows, the `uid` and `gid` fields are `-1`, and `shell` is `null`.
The value of `homedir` returned by `os.userInfo()` is provided by the operating system. This differs from the result of `os.homedir()`, which queries environment variables for the home directory before falling back to the operating system response.
Throws a [`SystemError`](errors#class-systemerror) if a user has no `username` or `homedir`.
###
`os.version()`
Added in: v13.11.0, v12.17.0 * Returns [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns a string identifying the kernel version.
On POSIX systems, the operating system release is determined by calling [`uname(3)`](https://linux.die.net/man/3/uname). On Windows, `RtlGetVersion()` is used, and if it is not available, `GetVersionExW()` will be used. See <https://en.wikipedia.org/wiki/Uname#Examples> for more information.
###
`os.machine()`
Added in: v18.9.0, v16.18.0 * Returns [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the machine type as a string, such as `arm`, `aarch64`, `mips`, `mips64`, `ppc64`, `ppc64le`, `s390`, `s390x`, `i386`, `i686`, `x86_64`.
On POSIX systems, the machine type is determined by calling [`uname(3)`](https://linux.die.net/man/3/uname). On Windows, `RtlGetVersion()` is used, and if it is not available, `GetVersionExW()` will be used. See <https://en.wikipedia.org/wiki/Uname#Examples> for more information.
### OS constants
The following constants are exported by `os.constants`.
Not all constants will be available on every operating system.
#### Signal constants
History
| Version | Changes |
| --- | --- |
| v5.11.0 | Added support for `SIGINFO`. |
The following signal constants are exported by `os.constants.signals`.
| Constant | Description |
| --- | --- |
| `SIGHUP` | Sent to indicate when a controlling terminal is closed or a parent process exits. |
| `SIGINT` | Sent to indicate when a user wishes to interrupt a process (`Ctrl`+`C`). |
| `SIGQUIT` | Sent to indicate when a user wishes to terminate a process and perform a core dump. |
| `SIGILL` | Sent to a process to notify that it has attempted to perform an illegal, malformed, unknown, or privileged instruction. |
| `SIGTRAP` | Sent to a process when an exception has occurred. |
| `SIGABRT` | Sent to a process to request that it abort. |
| `SIGIOT` | Synonym for `SIGABRT` |
| `SIGBUS` | Sent to a process to notify that it has caused a bus error. |
| `SIGFPE` | Sent to a process to notify that it has performed an illegal arithmetic operation. |
| `SIGKILL` | Sent to a process to terminate it immediately. |
| `SIGUSR1` `SIGUSR2` | Sent to a process to identify user-defined conditions. |
| `SIGSEGV` | Sent to a process to notify of a segmentation fault. |
| `SIGPIPE` | Sent to a process when it has attempted to write to a disconnected pipe. |
| `SIGALRM` | Sent to a process when a system timer elapses. |
| `SIGTERM` | Sent to a process to request termination. |
| `SIGCHLD` | Sent to a process when a child process terminates. |
| `SIGSTKFLT` | Sent to a process to indicate a stack fault on a coprocessor. |
| `SIGCONT` | Sent to instruct the operating system to continue a paused process. |
| `SIGSTOP` | Sent to instruct the operating system to halt a process. |
| `SIGTSTP` | Sent to a process to request it to stop. |
| `SIGBREAK` | Sent to indicate when a user wishes to interrupt a process. |
| `SIGTTIN` | Sent to a process when it reads from the TTY while in the background. |
| `SIGTTOU` | Sent to a process when it writes to the TTY while in the background. |
| `SIGURG` | Sent to a process when a socket has urgent data to read. |
| `SIGXCPU` | Sent to a process when it has exceeded its limit on CPU usage. |
| `SIGXFSZ` | Sent to a process when it grows a file larger than the maximum allowed. |
| `SIGVTALRM` | Sent to a process when a virtual timer has elapsed. |
| `SIGPROF` | Sent to a process when a system timer has elapsed. |
| `SIGWINCH` | Sent to a process when the controlling terminal has changed its size. |
| `SIGIO` | Sent to a process when I/O is available. |
| `SIGPOLL` | Synonym for `SIGIO` |
| `SIGLOST` | Sent to a process when a file lock has been lost. |
| `SIGPWR` | Sent to a process to notify of a power failure. |
| `SIGINFO` | Synonym for `SIGPWR` |
| `SIGSYS` | Sent to a process to notify of a bad argument. |
| `SIGUNUSED` | Synonym for `SIGSYS` |
#### Error constants
The following error constants are exported by `os.constants.errno`.
##### POSIX error constants
| Constant | Description |
| --- | --- |
| `E2BIG` | Indicates that the list of arguments is longer than expected. |
| `EACCES` | Indicates that the operation did not have sufficient permissions. |
| `EADDRINUSE` | Indicates that the network address is already in use. |
| `EADDRNOTAVAIL` | Indicates that the network address is currently unavailable for use. |
| `EAFNOSUPPORT` | Indicates that the network address family is not supported. |
| `EAGAIN` | Indicates that there is no data available and to try the operation again later. |
| `EALREADY` | Indicates that the socket already has a pending connection in progress. |
| `EBADF` | Indicates that a file descriptor is not valid. |
| `EBADMSG` | Indicates an invalid data message. |
| `EBUSY` | Indicates that a device or resource is busy. |
| `ECANCELED` | Indicates that an operation was canceled. |
| `ECHILD` | Indicates that there are no child processes. |
| `ECONNABORTED` | Indicates that the network connection has been aborted. |
| `ECONNREFUSED` | Indicates that the network connection has been refused. |
| `ECONNRESET` | Indicates that the network connection has been reset. |
| `EDEADLK` | Indicates that a resource deadlock has been avoided. |
| `EDESTADDRREQ` | Indicates that a destination address is required. |
| `EDOM` | Indicates that an argument is out of the domain of the function. |
| `EDQUOT` | Indicates that the disk quota has been exceeded. |
| `EEXIST` | Indicates that the file already exists. |
| `EFAULT` | Indicates an invalid pointer address. |
| `EFBIG` | Indicates that the file is too large. |
| `EHOSTUNREACH` | Indicates that the host is unreachable. |
| `EIDRM` | Indicates that the identifier has been removed. |
| `EILSEQ` | Indicates an illegal byte sequence. |
| `EINPROGRESS` | Indicates that an operation is already in progress. |
| `EINTR` | Indicates that a function call was interrupted. |
| `EINVAL` | Indicates that an invalid argument was provided. |
| `EIO` | Indicates an otherwise unspecified I/O error. |
| `EISCONN` | Indicates that the socket is connected. |
| `EISDIR` | Indicates that the path is a directory. |
| `ELOOP` | Indicates too many levels of symbolic links in a path. |
| `EMFILE` | Indicates that there are too many open files. |
| `EMLINK` | Indicates that there are too many hard links to a file. |
| `EMSGSIZE` | Indicates that the provided message is too long. |
| `EMULTIHOP` | Indicates that a multihop was attempted. |
| `ENAMETOOLONG` | Indicates that the filename is too long. |
| `ENETDOWN` | Indicates that the network is down. |
| `ENETRESET` | Indicates that the connection has been aborted by the network. |
| `ENETUNREACH` | Indicates that the network is unreachable. |
| `ENFILE` | Indicates too many open files in the system. |
| `ENOBUFS` | Indicates that no buffer space is available. |
| `ENODATA` | Indicates that no message is available on the stream head read queue. |
| `ENODEV` | Indicates that there is no such device. |
| `ENOENT` | Indicates that there is no such file or directory. |
| `ENOEXEC` | Indicates an exec format error. |
| `ENOLCK` | Indicates that there are no locks available. |
| `ENOLINK` | Indications that a link has been severed. |
| `ENOMEM` | Indicates that there is not enough space. |
| `ENOMSG` | Indicates that there is no message of the desired type. |
| `ENOPROTOOPT` | Indicates that a given protocol is not available. |
| `ENOSPC` | Indicates that there is no space available on the device. |
| `ENOSR` | Indicates that there are no stream resources available. |
| `ENOSTR` | Indicates that a given resource is not a stream. |
| `ENOSYS` | Indicates that a function has not been implemented. |
| `ENOTCONN` | Indicates that the socket is not connected. |
| `ENOTDIR` | Indicates that the path is not a directory. |
| `ENOTEMPTY` | Indicates that the directory is not empty. |
| `ENOTSOCK` | Indicates that the given item is not a socket. |
| `ENOTSUP` | Indicates that a given operation is not supported. |
| `ENOTTY` | Indicates an inappropriate I/O control operation. |
| `ENXIO` | Indicates no such device or address. |
| `EOPNOTSUPP` | Indicates that an operation is not supported on the socket. Although `ENOTSUP` and `EOPNOTSUPP` have the same value on Linux, according to POSIX.1 these error values should be distinct.) |
| `EOVERFLOW` | Indicates that a value is too large to be stored in a given data type. |
| `EPERM` | Indicates that the operation is not permitted. |
| `EPIPE` | Indicates a broken pipe. |
| `EPROTO` | Indicates a protocol error. |
| `EPROTONOSUPPORT` | Indicates that a protocol is not supported. |
| `EPROTOTYPE` | Indicates the wrong type of protocol for a socket. |
| `ERANGE` | Indicates that the results are too large. |
| `EROFS` | Indicates that the file system is read only. |
| `ESPIPE` | Indicates an invalid seek operation. |
| `ESRCH` | Indicates that there is no such process. |
| `ESTALE` | Indicates that the file handle is stale. |
| `ETIME` | Indicates an expired timer. |
| `ETIMEDOUT` | Indicates that the connection timed out. |
| `ETXTBSY` | Indicates that a text file is busy. |
| `EWOULDBLOCK` | Indicates that the operation would block. |
| `EXDEV` | Indicates an improper link. |
##### Windows-specific error constants
The following error codes are specific to the Windows operating system.
| Constant | Description |
| --- | --- |
| `WSAEINTR` | Indicates an interrupted function call. |
| `WSAEBADF` | Indicates an invalid file handle. |
| `WSAEACCES` | Indicates insufficient permissions to complete the operation. |
| `WSAEFAULT` | Indicates an invalid pointer address. |
| `WSAEINVAL` | Indicates that an invalid argument was passed. |
| `WSAEMFILE` | Indicates that there are too many open files. |
| `WSAEWOULDBLOCK` | Indicates that a resource is temporarily unavailable. |
| `WSAEINPROGRESS` | Indicates that an operation is currently in progress. |
| `WSAEALREADY` | Indicates that an operation is already in progress. |
| `WSAENOTSOCK` | Indicates that the resource is not a socket. |
| `WSAEDESTADDRREQ` | Indicates that a destination address is required. |
| `WSAEMSGSIZE` | Indicates that the message size is too long. |
| `WSAEPROTOTYPE` | Indicates the wrong protocol type for the socket. |
| `WSAENOPROTOOPT` | Indicates a bad protocol option. |
| `WSAEPROTONOSUPPORT` | Indicates that the protocol is not supported. |
| `WSAESOCKTNOSUPPORT` | Indicates that the socket type is not supported. |
| `WSAEOPNOTSUPP` | Indicates that the operation is not supported. |
| `WSAEPFNOSUPPORT` | Indicates that the protocol family is not supported. |
| `WSAEAFNOSUPPORT` | Indicates that the address family is not supported. |
| `WSAEADDRINUSE` | Indicates that the network address is already in use. |
| `WSAEADDRNOTAVAIL` | Indicates that the network address is not available. |
| `WSAENETDOWN` | Indicates that the network is down. |
| `WSAENETUNREACH` | Indicates that the network is unreachable. |
| `WSAENETRESET` | Indicates that the network connection has been reset. |
| `WSAECONNABORTED` | Indicates that the connection has been aborted. |
| `WSAECONNRESET` | Indicates that the connection has been reset by the peer. |
| `WSAENOBUFS` | Indicates that there is no buffer space available. |
| `WSAEISCONN` | Indicates that the socket is already connected. |
| `WSAENOTCONN` | Indicates that the socket is not connected. |
| `WSAESHUTDOWN` | Indicates that data cannot be sent after the socket has been shutdown. |
| `WSAETOOMANYREFS` | Indicates that there are too many references. |
| `WSAETIMEDOUT` | Indicates that the connection has timed out. |
| `WSAECONNREFUSED` | Indicates that the connection has been refused. |
| `WSAELOOP` | Indicates that a name cannot be translated. |
| `WSAENAMETOOLONG` | Indicates that a name was too long. |
| `WSAEHOSTDOWN` | Indicates that a network host is down. |
| `WSAEHOSTUNREACH` | Indicates that there is no route to a network host. |
| `WSAENOTEMPTY` | Indicates that the directory is not empty. |
| `WSAEPROCLIM` | Indicates that there are too many processes. |
| `WSAEUSERS` | Indicates that the user quota has been exceeded. |
| `WSAEDQUOT` | Indicates that the disk quota has been exceeded. |
| `WSAESTALE` | Indicates a stale file handle reference. |
| `WSAEREMOTE` | Indicates that the item is remote. |
| `WSASYSNOTREADY` | Indicates that the network subsystem is not ready. |
| `WSAVERNOTSUPPORTED` | Indicates that the `winsock.dll` version is out of range. |
| `WSANOTINITIALISED` | Indicates that successful WSAStartup has not yet been performed. |
| `WSAEDISCON` | Indicates that a graceful shutdown is in progress. |
| `WSAENOMORE` | Indicates that there are no more results. |
| `WSAECANCELLED` | Indicates that an operation has been canceled. |
| `WSAEINVALIDPROCTABLE` | Indicates that the procedure call table is invalid. |
| `WSAEINVALIDPROVIDER` | Indicates an invalid service provider. |
| `WSAEPROVIDERFAILEDINIT` | Indicates that the service provider failed to initialized. |
| `WSASYSCALLFAILURE` | Indicates a system call failure. |
| `WSASERVICE_NOT_FOUND` | Indicates that a service was not found. |
| `WSATYPE_NOT_FOUND` | Indicates that a class type was not found. |
| `WSA_E_NO_MORE` | Indicates that there are no more results. |
| `WSA_E_CANCELLED` | Indicates that the call was canceled. |
| `WSAEREFUSED` | Indicates that a database query was refused. |
#### dlopen constants
If available on the operating system, the following constants are exported in `os.constants.dlopen`. See [`dlopen(3)`](http://man7.org/linux/man-pages/man3/dlopen.3.html) for detailed information.
| Constant | Description |
| --- | --- |
| `RTLD_LAZY` | Perform lazy binding. Node.js sets this flag by default. |
| `RTLD_NOW` | Resolve all undefined symbols in the library before dlopen(3) returns. |
| `RTLD_GLOBAL` | Symbols defined by the library will be made available for symbol resolution of subsequently loaded libraries. |
| `RTLD_LOCAL` | The converse of `RTLD_GLOBAL`. This is the default behavior if neither flag is specified. |
| `RTLD_DEEPBIND` | Make a self-contained library use its own symbols in preference to symbols from previously loaded libraries. |
#### Priority constants
Added in: v10.10.0 The following process scheduling constants are exported by `os.constants.priority`.
| Constant | Description |
| --- | --- |
| `PRIORITY_LOW` | The lowest process scheduling priority. This corresponds to `IDLE_PRIORITY_CLASS` on Windows, and a nice value of `19` on all other platforms. |
| `PRIORITY_BELOW_NORMAL` | The process scheduling priority above `PRIORITY_LOW` and below `PRIORITY_NORMAL`. This corresponds to `BELOW_NORMAL_PRIORITY_CLASS` on Windows, and a nice value of `10` on all other platforms. |
| `PRIORITY_NORMAL` | The default process scheduling priority. This corresponds to `NORMAL_PRIORITY_CLASS` on Windows, and a nice value of `0` on all other platforms. |
| `PRIORITY_ABOVE_NORMAL` | The process scheduling priority above `PRIORITY_NORMAL` and below `PRIORITY_HIGH`. This corresponds to `ABOVE_NORMAL_PRIORITY_CLASS` on Windows, and a nice value of `-7` on all other platforms. |
| `PRIORITY_HIGH` | The process scheduling priority above `PRIORITY_ABOVE_NORMAL` and below `PRIORITY_HIGHEST`. This corresponds to `HIGH_PRIORITY_CLASS` on Windows, and a nice value of `-14` on all other platforms. |
| `PRIORITY_HIGHEST` | The highest process scheduling priority. This corresponds to `REALTIME_PRIORITY_CLASS` on Windows, and a nice value of `-20` on all other platforms. |
#### libuv constants
| Constant | Description |
| --- | --- |
| `UV_UDP_REUSEADDR` | |
| programming_docs |
node None Buffer
------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/buffer.js](https://github.com/nodejs/node/blob/v19.0.1/lib/buffer.js)
`Buffer` objects are used to represent a fixed-length sequence of bytes. Many Node.js APIs support `Buffer`s.
The `Buffer` class is a subclass of JavaScript's [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) class and extends it with methods that cover additional use cases. Node.js APIs accept plain [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)s wherever `Buffer`s are supported as well.
While the `Buffer` class is available within the global scope, it is still recommended to explicitly reference it via an import or require statement.
MJS modules
```
import { Buffer } from 'node:buffer';
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);
// Creates a Buffer of length 10,
// filled with bytes which all have the value `1`.
const buf2 = Buffer.alloc(10, 1);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using fill(), write(), or other functions that fill the Buffer's
// contents.
const buf3 = Buffer.allocUnsafe(10);
// Creates a Buffer containing the bytes [1, 2, 3].
const buf4 = Buffer.from([1, 2, 3]);
// Creates a Buffer containing the bytes [1, 1, 1, 1] – the entries
// are all truncated using `(value & 255)` to fit into the range 0–255.
const buf5 = Buffer.from([257, 257.5, -255, '1']);
// Creates a Buffer containing the UTF-8-encoded bytes for the string 'tést':
// [0x74, 0xc3, 0xa9, 0x73, 0x74] (in hexadecimal notation)
// [116, 195, 169, 115, 116] (in decimal notation)
const buf6 = Buffer.from('tést');
// Creates a Buffer containing the Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf7 = Buffer.from('tést', 'latin1');
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);
// Creates a Buffer of length 10,
// filled with bytes which all have the value `1`.
const buf2 = Buffer.alloc(10, 1);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using fill(), write(), or other functions that fill the Buffer's
// contents.
const buf3 = Buffer.allocUnsafe(10);
// Creates a Buffer containing the bytes [1, 2, 3].
const buf4 = Buffer.from([1, 2, 3]);
// Creates a Buffer containing the bytes [1, 1, 1, 1] – the entries
// are all truncated using `(value & 255)` to fit into the range 0–255.
const buf5 = Buffer.from([257, 257.5, -255, '1']);
// Creates a Buffer containing the UTF-8-encoded bytes for the string 'tést':
// [0x74, 0xc3, 0xa9, 0x73, 0x74] (in hexadecimal notation)
// [116, 195, 169, 115, 116] (in decimal notation)
const buf6 = Buffer.from('tést');
// Creates a Buffer containing the Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf7 = Buffer.from('tést', 'latin1');
```
### Buffers and character encodings
History
| Version | Changes |
| --- | --- |
| v15.7.0, v14.18.0 | Introduced `base64url` encoding. |
| v6.4.0 | Introduced `latin1` as an alias for `binary`. |
| v5.0.0 | Removed the deprecated `raw` and `raws` encodings. |
When converting between `Buffer`s and strings, a character encoding may be specified. If no character encoding is specified, UTF-8 will be used as the default.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('hello world', 'utf8');
console.log(buf.toString('hex'));
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// Prints: aGVsbG8gd29ybGQ=
console.log(Buffer.from('fhqwhgads', 'utf8'));
// Prints: <Buffer 66 68 71 77 68 67 61 64 73>
console.log(Buffer.from('fhqwhgads', 'utf16le'));
// Prints: <Buffer 66 00 68 00 71 00 77 00 68 00 67 00 61 00 64 00 73 00>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('hello world', 'utf8');
console.log(buf.toString('hex'));
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// Prints: aGVsbG8gd29ybGQ=
console.log(Buffer.from('fhqwhgads', 'utf8'));
// Prints: <Buffer 66 68 71 77 68 67 61 64 73>
console.log(Buffer.from('fhqwhgads', 'utf16le'));
// Prints: <Buffer 66 00 68 00 71 00 77 00 68 00 67 00 61 00 64 00 73 00>
```
Node.js buffers accept all case variations of encoding strings that they receive. For example, UTF-8 can be specified as `'utf8'`, `'UTF8'`, or `'uTf8'`.
The character encodings currently supported by Node.js are the following:
* `'utf8'` (alias: `'utf-8'`): Multi-byte encoded Unicode characters. Many web pages and other document formats use [UTF-8](https://en.wikipedia.org/wiki/UTF-8). This is the default character encoding. When decoding a `Buffer` into a string that does not exclusively contain valid UTF-8 data, the Unicode replacement character `U+FFFD` � will be used to represent those errors.
* `'utf16le'` (alias: `'utf-16le'`): Multi-byte encoded Unicode characters. Unlike `'utf8'`, each character in the string will be encoded using either 2 or 4 bytes. Node.js only supports the [little-endian](https://en.wikipedia.org/wiki/Endianness) variant of [UTF-16](https://en.wikipedia.org/wiki/UTF-16).
* `'latin1'`: Latin-1 stands for [ISO-8859-1](https://en.wikipedia.org/wiki/ISO-8859-1). This character encoding only supports the Unicode characters from `U+0000` to `U+00FF`. Each character is encoded using a single byte. Characters that do not fit into that range are truncated and will be mapped to characters in that range.
Converting a `Buffer` into a string using one of the above is referred to as decoding, and converting a string into a `Buffer` is referred to as encoding.
Node.js also supports the following binary-to-text encodings. For binary-to-text encodings, the naming convention is reversed: Converting a `Buffer` into a string is typically referred to as encoding, and converting a string into a `Buffer` as decoding.
* `'base64'`: [Base64](https://en.wikipedia.org/wiki/Base64) encoding. When creating a `Buffer` from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in [RFC 4648, Section 5](https://tools.ietf.org/html/rfc4648#section-5). Whitespace characters such as spaces, tabs, and new lines contained within the base64-encoded string are ignored.
* `'base64url'`: [base64url](https://tools.ietf.org/html/rfc4648#section-5) encoding as specified in [RFC 4648, Section 5](https://tools.ietf.org/html/rfc4648#section-5). When creating a `Buffer` from a string, this encoding will also correctly accept regular base64-encoded strings. When encoding a `Buffer` to a string, this encoding will omit padding.
* `'hex'`: Encode each byte as two hexadecimal characters. Data truncation may occur when decoding strings that do not exclusively consist of an even number of hexadecimal characters. See below for an example.
The following legacy character encodings are also supported:
* `'ascii'`: For 7-bit [ASCII](https://en.wikipedia.org/wiki/ASCII) data only. When encoding a string into a `Buffer`, this is equivalent to using `'latin1'`. When decoding a `Buffer` into a string, using this encoding will additionally unset the highest bit of each byte before decoding as `'latin1'`. Generally, there should be no reason to use this encoding, as `'utf8'` (or, if the data is known to always be ASCII-only, `'latin1'`) will be a better choice when encoding or decoding ASCII-only text. It is only provided for legacy compatibility.
* `'binary'`: Alias for `'latin1'`. See [binary strings](https://developer.mozilla.org/en-US/docs/Web/API/DOMString/Binary) for more background on this topic. The name of this encoding can be very misleading, as all of the encodings listed here convert between strings and binary data. For converting between strings and `Buffer`s, typically `'utf8'` is the right choice.
* `'ucs2'`, `'ucs-2'`: Aliases of `'utf16le'`. UCS-2 used to refer to a variant of UTF-16 that did not support characters that had code points larger than U+FFFF. In Node.js, these code points are always supported.
MJS modules
```
import { Buffer } from 'node:buffer';
Buffer.from('1ag123', 'hex');
// Prints <Buffer 1a>, data truncated when first non-hexadecimal value
// ('g') encountered.
Buffer.from('1a7', 'hex');
// Prints <Buffer 1a>, data truncated when data ends in single digit ('7').
Buffer.from('1634', 'hex');
// Prints <Buffer 16 34>, all data represented.
```
CJS modules
```
const { Buffer } = require('node:buffer');
Buffer.from('1ag123', 'hex');
// Prints <Buffer 1a>, data truncated when first non-hexadecimal value
// ('g') encountered.
Buffer.from('1a7', 'hex');
// Prints <Buffer 1a>, data truncated when data ends in single digit ('7').
Buffer.from('1634', 'hex');
// Prints <Buffer 16 34>, all data represented.
```
Modern Web browsers follow the [WHATWG Encoding Standard](https://encoding.spec.whatwg.org/) which aliases both `'latin1'` and `'ISO-8859-1'` to `'win-1252'`. This means that while doing something like `http.get()`, if the returned charset is one of those listed in the WHATWG specification it is possible that the server actually returned `'win-1252'`-encoded data, and using `'latin1'` encoding may incorrectly decode the characters.
### Buffers and TypedArrays
History
| Version | Changes |
| --- | --- |
| v3.0.0 | The `Buffer`s class now inherits from `Uint8Array`. |
`Buffer` instances are also JavaScript [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) and [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) instances. All [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) methods are available on `Buffer`s. There are, however, subtle incompatibilities between the `Buffer` API and the [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) API.
In particular:
* While [`TypedArray.prototype.slice()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/slice) creates a copy of part of the `TypedArray`, [`Buffer.prototype.slice()`](#bufslicestart-end) creates a view over the existing `Buffer` without copying. This behavior can be surprising, and only exists for legacy compatibility. [`TypedArray.prototype.subarray()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/subarray) can be used to achieve the behavior of [`Buffer.prototype.slice()`](#bufslicestart-end) on both `Buffer`s and other `TypedArray`s and should be preferred.
* [`buf.toString()`](#buftostringencoding-start-end) is incompatible with its `TypedArray` equivalent.
* A number of methods, e.g. [`buf.indexOf()`](#bufindexofvalue-byteoffset-encoding), support additional arguments.
There are two ways to create new [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) instances from a `Buffer`:
* Passing a `Buffer` to a [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) constructor will copy the `Buffer`s contents, interpreted as an array of integers, and not as a byte sequence of the target type.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4]);
const uint32array = new Uint32Array(buf);
console.log(uint32array);
// Prints: Uint32Array(4) [ 1, 2, 3, 4 ]
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4]);
const uint32array = new Uint32Array(buf);
console.log(uint32array);
// Prints: Uint32Array(4) [ 1, 2, 3, 4 ]
```
* Passing the `Buffer`s underlying [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) will create a [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) that shares its memory with the `Buffer`.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('hello', 'utf16le');
const uint16array = new Uint16Array(
buf.buffer,
buf.byteOffset,
buf.length / Uint16Array.BYTES_PER_ELEMENT);
console.log(uint16array);
// Prints: Uint16Array(5) [ 104, 101, 108, 108, 111 ]
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('hello', 'utf16le');
const uint16array = new Uint16Array(
buf.buffer,
buf.byteOffset,
buf.length / Uint16Array.BYTES_PER_ELEMENT);
console.log(uint16array);
// Prints: Uint16Array(5) [ 104, 101, 108, 108, 111 ]
```
It is possible to create a new `Buffer` that shares the same allocated memory as a [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) instance by using the `TypedArray` object's `.buffer` property in the same way. [`Buffer.from()`](#static-method-bufferfromarraybuffer-byteoffset-length) behaves like `new Uint8Array()` in this context.
MJS modules
```
import { Buffer } from 'node:buffer';
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`.
const buf1 = Buffer.from(arr);
// Shares memory with `arr`.
const buf2 = Buffer.from(arr.buffer);
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>
arr[1] = 6000;
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`.
const buf1 = Buffer.from(arr);
// Shares memory with `arr`.
const buf2 = Buffer.from(arr.buffer);
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>
arr[1] = 6000;
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
```
When creating a `Buffer` using a [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray)'s `.buffer`, it is possible to use only a portion of the underlying [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) by passing in `byteOffset` and `length` parameters.
MJS modules
```
import { Buffer } from 'node:buffer';
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
console.log(buf.length);
// Prints: 16
```
CJS modules
```
const { Buffer } = require('node:buffer');
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
console.log(buf.length);
// Prints: 16
```
The `Buffer.from()` and [`TypedArray.from()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/from) have different signatures and implementations. Specifically, the [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) variants accept a second argument that is a mapping function that is invoked on every element of the typed array:
* `TypedArray.from(source[, mapFn[, thisArg]])`
The `Buffer.from()` method, however, does not support the use of a mapping function:
* [`Buffer.from(array)`](#static-method-bufferfromarray)
* [`Buffer.from(buffer)`](#static-method-bufferfrombuffer)
* [`Buffer.from(arrayBuffer[, byteOffset[, length]])`](#static-method-bufferfromarraybuffer-byteoffset-length)
* [`Buffer.from(string[, encoding])`](#static-method-bufferfromstring-encoding)
### Buffers and iteration
`Buffer` instances can be iterated over using `for..of` syntax:
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3]);
for (const b of buf) {
console.log(b);
}
// Prints:
// 1
// 2
// 3
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3]);
for (const b of buf) {
console.log(b);
}
// Prints:
// 1
// 2
// 3
```
Additionally, the [`buf.values()`](#bufvalues), [`buf.keys()`](#bufkeys), and [`buf.entries()`](#bufentries) methods can be used to create iterators.
### Class: `Blob`
History
| Version | Changes |
| --- | --- |
| v18.0.0, v16.17.0 | No longer experimental. |
| v15.7.0, v14.18.0 | Added in: v15.7.0, v14.18.0 |
A [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob) encapsulates immutable, raw data that can be safely shared across multiple worker threads.
####
`new buffer.Blob([sources[, options]])`
History
| Version | Changes |
| --- | --- |
| v16.7.0 | Added the standard `endings` option to replace line-endings, and removed the non-standard `encoding` option. |
| v15.7.0, v14.18.0 | Added in: v15.7.0, v14.18.0 |
* `sources` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Blob[]>](buffer#class-blob) An array of string, [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer), [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView), or [<Blob>](buffer#class-blob) objects, or any mix of such objects, that will be stored within the `Blob`.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `endings` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) One of either `'transparent'` or `'native'`. When set to `'native'`, line endings in string source parts will be converted to the platform native line-ending as specified by `require('node:os').EOL`.
+ `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The Blob content-type. The intent is for `type` to convey the MIME media type of the data, however no validation of the type format is performed.
Creates a new `Blob` object containing a concatenation of the given sources.
[<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer), [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView), and [<Buffer>](buffer#class-buffer) sources are copied into the 'Blob' and can therefore be safely modified after the 'Blob' is created.
String sources are encoded as UTF-8 byte sequences and copied into the Blob. Unmatched surrogate pairs within each string part will be replaced by Unicode U+FFFD replacement characters.
####
`blob.arrayBuffer()`
Added in: v15.7.0, v14.18.0 * Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Returns a promise that fulfills with an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) containing a copy of the `Blob` data.
####
`blob.size`
Added in: v15.7.0, v14.18.0 The total size of the `Blob` in bytes.
####
`blob.slice([start[, end[, type]]])`
Added in: v15.7.0, v14.18.0 * `start` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The starting index.
* `end` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The ending index.
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The content-type for the new `Blob`
Creates and returns a new `Blob` containing a subset of this `Blob` objects data. The original `Blob` is not altered.
####
`blob.stream()`
Added in: v16.7.0 * Returns: [<ReadableStream>](webstreams#class-readablestream)
Returns a new `ReadableStream` that allows the content of the `Blob` to be read.
####
`blob.text()`
Added in: v15.7.0, v14.18.0 * Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Returns a promise that fulfills with the contents of the `Blob` decoded as a UTF-8 string.
####
`blob.type`
Added in: v15.7.0, v14.18.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The content-type of the `Blob`.
####
`Blob` objects and `MessageChannel`
Once a [<Blob>](buffer#class-blob) object is created, it can be sent via `MessagePort` to multiple destinations without transferring or immediately copying the data. The data contained by the `Blob` is copied only when the `arrayBuffer()` or `text()` methods are called.
MJS modules
```
import { Blob, Buffer } from 'node:buffer';
import { setTimeout as delay } from 'node:timers/promises';
const blob = new Blob(['hello there']);
const mc1 = new MessageChannel();
const mc2 = new MessageChannel();
mc1.port1.onmessage = async ({ data }) => {
console.log(await data.arrayBuffer());
mc1.port1.close();
};
mc2.port1.onmessage = async ({ data }) => {
await delay(1000);
console.log(await data.arrayBuffer());
mc2.port1.close();
};
mc1.port2.postMessage(blob);
mc2.port2.postMessage(blob);
// The Blob is still usable after posting.
blob.text().then(console.log);
```
CJS modules
```
const { Blob, Buffer } = require('node:buffer');
const { setTimeout: delay } = require('node:timers/promises');
const blob = new Blob(['hello there']);
const mc1 = new MessageChannel();
const mc2 = new MessageChannel();
mc1.port1.onmessage = async ({ data }) => {
console.log(await data.arrayBuffer());
mc1.port1.close();
};
mc2.port1.onmessage = async ({ data }) => {
await delay(1000);
console.log(await data.arrayBuffer());
mc2.port1.close();
};
mc1.port2.postMessage(blob);
mc2.port2.postMessage(blob);
// The Blob is still usable after posting.
blob.text().then(console.log);
```
### Class: `Buffer`
The `Buffer` class is a global type for dealing with binary data directly. It can be constructed in a variety of ways.
#### Static method: `Buffer.alloc(size[, fill[, encoding]])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Throw ERR\_INVALID\_ARG\_VALUE instead of ERR\_INVALID\_OPT\_VALUE for invalid input arguments. |
| v10.0.0 | Attempting to fill a non-zero length buffer with a zero length buffer triggers a thrown exception. |
| v10.0.0 | Specifying an invalid string for `fill` triggers a thrown exception. |
| v8.9.3 | Specifying an invalid string for `fill` now results in a zero-filled buffer. |
| v5.10.0 | Added in: v5.10.0 |
* `size` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The desired length of the new `Buffer`.
* `fill` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A value to pre-fill the new `Buffer` with. **Default:** `0`.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If `fill` is a string, this is its encoding. **Default:** `'utf8'`.
Allocates a new `Buffer` of `size` bytes. If `fill` is `undefined`, the `Buffer` will be zero-filled.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(5);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(5);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00>
```
If `size` is larger than [`buffer.constants.MAX_LENGTH`](#bufferconstantsmax_length) or smaller than 0, [`ERR_INVALID_ARG_VALUE`](errors#err_invalid_arg_value) is thrown.
If `fill` is specified, the allocated `Buffer` will be initialized by calling [`buf.fill(fill)`](#buffillvalue-offset-end-encoding).
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(5, 'a');
console.log(buf);
// Prints: <Buffer 61 61 61 61 61>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(5, 'a');
console.log(buf);
// Prints: <Buffer 61 61 61 61 61>
```
If both `fill` and `encoding` are specified, the allocated `Buffer` will be initialized by calling [`buf.fill(fill, encoding)`](#buffillvalue-offset-end-encoding).
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
```
Calling [`Buffer.alloc()`](#static-method-bufferallocsize-fill-encoding) can be measurably slower than the alternative [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize) but ensures that the newly created `Buffer` instance contents will never contain sensitive data from previous allocations, including data that might not have been allocated for `Buffer`s.
A `TypeError` will be thrown if `size` is not a number.
#### Static method: `Buffer.allocUnsafe(size)`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Throw ERR\_INVALID\_ARG\_VALUE instead of ERR\_INVALID\_OPT\_VALUE for invalid input arguments. |
| v7.0.0 | Passing a negative `size` will now throw an error. |
| v5.10.0 | Added in: v5.10.0 |
* `size` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The desired length of the new `Buffer`.
Allocates a new `Buffer` of `size` bytes. If `size` is larger than [`buffer.constants.MAX_LENGTH`](#bufferconstantsmax_length) or smaller than 0, [`ERR_INVALID_ARG_VALUE`](errors#err_invalid_arg_value) is thrown.
The underlying memory for `Buffer` instances created in this way is *not initialized*. The contents of the newly created `Buffer` are unknown and *may contain sensitive data*. Use [`Buffer.alloc()`](#static-method-bufferallocsize-fill-encoding) instead to initialize `Buffer` instances with zeroes.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(10);
console.log(buf);
// Prints (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>
buf.fill(0);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(10);
console.log(buf);
// Prints (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>
buf.fill(0);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
```
A `TypeError` will be thrown if `size` is not a number.
The `Buffer` module pre-allocates an internal `Buffer` instance of size [`Buffer.poolSize`](#class-property-bufferpoolsize) that is used as a pool for the fast allocation of new `Buffer` instances created using [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize), [`Buffer.from(array)`](#static-method-bufferfromarray), [`Buffer.concat()`](#static-method-bufferconcatlist-totallength), and the deprecated `new Buffer(size)` constructor only when `size` is less than or equal to `Buffer.poolSize >> 1` (floor of [`Buffer.poolSize`](#class-property-bufferpoolsize) divided by two).
Use of this pre-allocated internal memory pool is a key difference between calling `Buffer.alloc(size, fill)` vs. `Buffer.allocUnsafe(size).fill(fill)`. Specifically, `Buffer.alloc(size, fill)` will *never* use the internal `Buffer` pool, while `Buffer.allocUnsafe(size).fill(fill)` *will* use the internal `Buffer` pool if `size` is less than or equal to half [`Buffer.poolSize`](#class-property-bufferpoolsize). The difference is subtle but can be important when an application requires the additional performance that [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize) provides.
#### Static method: `Buffer.allocUnsafeSlow(size)`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Throw ERR\_INVALID\_ARG\_VALUE instead of ERR\_INVALID\_OPT\_VALUE for invalid input arguments. |
| v5.12.0 | Added in: v5.12.0 |
* `size` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The desired length of the new `Buffer`.
Allocates a new `Buffer` of `size` bytes. If `size` is larger than [`buffer.constants.MAX_LENGTH`](#bufferconstantsmax_length) or smaller than 0, [`ERR_INVALID_ARG_VALUE`](errors#err_invalid_arg_value) is thrown. A zero-length `Buffer` is created if `size` is 0.
The underlying memory for `Buffer` instances created in this way is *not initialized*. The contents of the newly created `Buffer` are unknown and *may contain sensitive data*. Use [`buf.fill(0)`](#buffillvalue-offset-end-encoding) to initialize such `Buffer` instances with zeroes.
When using [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize) to allocate new `Buffer` instances, allocations under 4 KiB are sliced from a single pre-allocated `Buffer`. This allows applications to avoid the garbage collection overhead of creating many individually allocated `Buffer` instances. This approach improves both performance and memory usage by eliminating the need to track and clean up as many individual `ArrayBuffer` objects.
However, in the case where a developer may need to retain a small chunk of memory from a pool for an indeterminate amount of time, it may be appropriate to create an un-pooled `Buffer` instance using `Buffer.allocUnsafeSlow()` and then copying out the relevant bits.
MJS modules
```
import { Buffer } from 'node:buffer';
// Need to keep around a few small chunks of memory.
const store = [];
socket.on('readable', () => {
let data;
while (null !== (data = readable.read())) {
// Allocate for retained data.
const sb = Buffer.allocUnsafeSlow(10);
// Copy the data into the new allocation.
data.copy(sb, 0, 0, 10);
store.push(sb);
}
});
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Need to keep around a few small chunks of memory.
const store = [];
socket.on('readable', () => {
let data;
while (null !== (data = readable.read())) {
// Allocate for retained data.
const sb = Buffer.allocUnsafeSlow(10);
// Copy the data into the new allocation.
data.copy(sb, 0, 0, 10);
store.push(sb);
}
});
```
A `TypeError` will be thrown if `size` is not a number.
#### Static method: `Buffer.byteLength(string[, encoding])`
History
| Version | Changes |
| --- | --- |
| v7.0.0 | Passing invalid input will now throw an error. |
| v5.10.0 | The `string` parameter can now be any `TypedArray`, `DataView` or `ArrayBuffer`. |
| v0.1.90 | Added in: v0.1.90 |
* `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) A value to calculate the length of.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If `string` is a string, this is its encoding. **Default:** `'utf8'`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes contained within `string`.
Returns the byte length of a string when encoded using `encoding`. This is not the same as [`String.prototype.length`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length), which does not account for the encoding that is used to convert the string into bytes.
For `'base64'`, `'base64url'`, and `'hex'`, this function assumes valid input. For strings that contain non-base64/hex-encoded data (e.g. whitespace), the return value might be greater than the length of a `Buffer` created from the string.
MJS modules
```
import { Buffer } from 'node:buffer';
const str = '\u00bd + \u00bc = \u00be';
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
```
CJS modules
```
const { Buffer } = require('node:buffer');
const str = '\u00bd + \u00bc = \u00be';
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
```
When `string` is a `Buffer`/[`DataView`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)/[`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray)/[`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)/ [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer), the byte length as reported by `.byteLength` is returned.
#### Static method: `Buffer.compare(buf1, buf2)`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The arguments can now be `Uint8Array`s. |
| v0.11.13 | Added in: v0.11.13 |
* `buf1` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
* `buf2` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Either `-1`, `0`, or `1`, depending on the result of the comparison. See [`buf.compare()`](#bufcomparetarget-targetstart-targetend-sourcestart-sourceend) for details.
Compares `buf1` to `buf2`, typically for the purpose of sorting arrays of `Buffer` instances. This is equivalent to calling [`buf1.compare(buf2)`](#bufcomparetarget-targetstart-targetend-sourcestart-sourceend).
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];
console.log(arr.sort(Buffer.compare));
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1].)
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];
console.log(arr.sort(Buffer.compare));
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1].)
```
#### Static method: `Buffer.concat(list[, totalLength])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The elements of `list` can now be `Uint8Array`s. |
| v0.7.11 | Added in: v0.7.11 |
* `list` [<Buffer[]>](buffer#class-buffer) | [<Uint8Array[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) List of `Buffer` or [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) instances to concatenate.
* `totalLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Total length of the `Buffer` instances in `list` when concatenated.
* Returns: [<Buffer>](buffer#class-buffer)
Returns a new `Buffer` which is the result of concatenating all the `Buffer` instances in the `list` together.
If the list has no items, or if the `totalLength` is 0, then a new zero-length `Buffer` is returned.
If `totalLength` is not provided, it is calculated from the `Buffer` instances in `list` by adding their lengths.
If `totalLength` is provided, it is coerced to an unsigned integer. If the combined length of the `Buffer`s in `list` exceeds `totalLength`, the result is truncated to `totalLength`.
MJS modules
```
import { Buffer } from 'node:buffer';
// Create a single `Buffer` from a list of three `Buffer` instances.
const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;
console.log(totalLength);
// Prints: 42
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA.length);
// Prints: 42
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Create a single `Buffer` from a list of three `Buffer` instances.
const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;
console.log(totalLength);
// Prints: 42
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA.length);
// Prints: 42
```
`Buffer.concat()` may also use the internal `Buffer` pool like [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize) does.
#### Static method: `Buffer.from(array)`
Added in: v5.10.0 * `array` [<integer[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Allocates a new `Buffer` using an `array` of bytes in the range `0` – `255`. Array entries outside that range will be truncated to fit into it.
MJS modules
```
import { Buffer } from 'node:buffer';
// Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'.
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'.
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
```
A `TypeError` will be thrown if `array` is not an `Array` or another type appropriate for `Buffer.from()` variants.
`Buffer.from(array)` and [`Buffer.from(string)`](#static-method-bufferfromstring-encoding) may also use the internal `Buffer` pool like [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize) does.
#### Static method: `Buffer.from(arrayBuffer[, byteOffset[, length]])`
Added in: v5.10.0 * `arrayBuffer` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) An [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer), [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer), for example the `.buffer` property of a [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray).
* `byteOffset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Index of first byte to expose. **Default:** `0`.
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to expose. **Default:** `arrayBuffer.byteLength - byteOffset`.
This creates a view of the [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) without copying the underlying memory. For example, when passed a reference to the `.buffer` property of a [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) instance, the newly created `Buffer` will share the same allocated memory as the [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray)'s underlying `ArrayBuffer`.
MJS modules
```
import { Buffer } from 'node:buffer';
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);
console.log(buf);
// Prints: <Buffer 88 13 a0 0f>
// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;
console.log(buf);
// Prints: <Buffer 88 13 70 17>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);
console.log(buf);
// Prints: <Buffer 88 13 a0 0f>
// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;
console.log(buf);
// Prints: <Buffer 88 13 70 17>
```
The optional `byteOffset` and `length` arguments specify a memory range within the `arrayBuffer` that will be shared by the `Buffer`.
MJS modules
```
import { Buffer } from 'node:buffer';
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
console.log(buf.length);
// Prints: 2
```
CJS modules
```
const { Buffer } = require('node:buffer');
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
console.log(buf.length);
// Prints: 2
```
A `TypeError` will be thrown if `arrayBuffer` is not an [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) or a [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) or another type appropriate for `Buffer.from()` variants.
It is important to remember that a backing `ArrayBuffer` can cover a range of memory that extends beyond the bounds of a `TypedArray` view. A new `Buffer` created using the `buffer` property of a `TypedArray` may extend beyond the range of the `TypedArray`:
MJS modules
```
import { Buffer } from 'node:buffer';
const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 elements
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 elements
console.log(arrA.buffer === arrB.buffer); // true
const buf = Buffer.from(arrB.buffer);
console.log(buf);
// Prints: <Buffer 63 64 65 66>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 elements
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 elements
console.log(arrA.buffer === arrB.buffer); // true
const buf = Buffer.from(arrB.buffer);
console.log(buf);
// Prints: <Buffer 63 64 65 66>
```
#### Static method: `Buffer.from(buffer)`
Added in: v5.10.0 * `buffer` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) An existing `Buffer` or [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) from which to copy data.
Copies the passed `buffer` data onto a new `Buffer` instance.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
// Prints: auffer
console.log(buf2.toString());
// Prints: buffer
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
// Prints: auffer
console.log(buf2.toString());
// Prints: buffer
```
A `TypeError` will be thrown if `buffer` is not a `Buffer` or another type appropriate for `Buffer.from()` variants.
#### Static method: `Buffer.from(object[, offsetOrEncoding[, length]])`
Added in: v8.2.0 * `object` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object supporting `Symbol.toPrimitive` or `valueOf()`.
* `offsetOrEncoding` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A byte-offset or encoding.
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A length.
For objects whose `valueOf()` function returns a value not strictly equal to `object`, returns `Buffer.from(object.valueOf(), offsetOrEncoding, length)`.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from(new String('this is a test'));
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from(new String('this is a test'));
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
```
For objects that support `Symbol.toPrimitive`, returns `Buffer.from(object[Symbol.toPrimitive]('string'), offsetOrEncoding)`.
MJS modules
```
import { Buffer } from 'node:buffer';
class Foo {
[Symbol.toPrimitive]() {
return 'this is a test';
}
}
const buf = Buffer.from(new Foo(), 'utf8');
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
```
CJS modules
```
const { Buffer } = require('node:buffer');
class Foo {
[Symbol.toPrimitive]() {
return 'this is a test';
}
}
const buf = Buffer.from(new Foo(), 'utf8');
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
```
A `TypeError` will be thrown if `object` does not have the mentioned methods or is not of another type appropriate for `Buffer.from()` variants.
#### Static method: `Buffer.from(string[, encoding])`
Added in: v5.10.0 * `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A string to encode.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The encoding of `string`. **Default:** `'utf8'`.
Creates a new `Buffer` containing `string`. The `encoding` parameter identifies the character encoding to be used when converting `string` into bytes.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf1.toString());
// Prints: this is a tést
console.log(buf2.toString());
// Prints: this is a tést
console.log(buf1.toString('latin1'));
// Prints: this is a tést
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf1.toString());
// Prints: this is a tést
console.log(buf2.toString());
// Prints: this is a tést
console.log(buf1.toString('latin1'));
// Prints: this is a tést
```
A `TypeError` will be thrown if `string` is not a string or another type appropriate for `Buffer.from()` variants.
#### Static method: `Buffer.isBuffer(obj)`
Added in: v0.1.101 * `obj` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if `obj` is a `Buffer`, `false` otherwise.
MJS modules
```
import { Buffer } from 'node:buffer';
Buffer.isBuffer(Buffer.alloc(10)); // true
Buffer.isBuffer(Buffer.from('foo')); // true
Buffer.isBuffer('a string'); // false
Buffer.isBuffer([]); // false
Buffer.isBuffer(new Uint8Array(1024)); // false
```
CJS modules
```
const { Buffer } = require('node:buffer');
Buffer.isBuffer(Buffer.alloc(10)); // true
Buffer.isBuffer(Buffer.from('foo')); // true
Buffer.isBuffer('a string'); // false
Buffer.isBuffer([]); // false
Buffer.isBuffer(new Uint8Array(1024)); // false
```
#### Static method: `Buffer.isEncoding(encoding)`
Added in: v0.9.1 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A character encoding name to check.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if `encoding` is the name of a supported character encoding, or `false` otherwise.
MJS modules
```
import { Buffer } from 'node:buffer';
console.log(Buffer.isEncoding('utf8'));
// Prints: true
console.log(Buffer.isEncoding('hex'));
// Prints: true
console.log(Buffer.isEncoding('utf/8'));
// Prints: false
console.log(Buffer.isEncoding(''));
// Prints: false
```
CJS modules
```
const { Buffer } = require('node:buffer');
console.log(Buffer.isEncoding('utf8'));
// Prints: true
console.log(Buffer.isEncoding('hex'));
// Prints: true
console.log(Buffer.isEncoding('utf/8'));
// Prints: false
console.log(Buffer.isEncoding(''));
// Prints: false
```
#### Class property: `Buffer.poolSize`
Added in: v0.11.3 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `8192`
This is the size (in bytes) of pre-allocated internal `Buffer` instances used for pooling. This value may be modified.
####
`buf[index]`
* `index` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The index operator `[index]` can be used to get and set the octet at position `index` in `buf`. The values refer to individual bytes, so the legal value range is between `0x00` and `0xFF` (hex) or `0` and `255` (decimal).
This operator is inherited from `Uint8Array`, so its behavior on out-of-bounds access is the same as `Uint8Array`. In other words, `buf[index]` returns `undefined` when `index` is negative or greater or equal to `buf.length`, and `buf[index] = value` does not modify the buffer if `index` is negative or `>= buf.length`.
MJS modules
```
import { Buffer } from 'node:buffer';
// Copy an ASCII string into a `Buffer` one byte at a time.
// (This only works for ASCII-only strings. In general, one should use
// `Buffer.from()` to perform this conversion.)
const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);
for (let i = 0; i < str.length; i++) {
buf[i] = str.charCodeAt(i);
}
console.log(buf.toString('utf8'));
// Prints: Node.js
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Copy an ASCII string into a `Buffer` one byte at a time.
// (This only works for ASCII-only strings. In general, one should use
// `Buffer.from()` to perform this conversion.)
const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);
for (let i = 0; i < str.length; i++) {
buf[i] = str.charCodeAt(i);
}
console.log(buf.toString('utf8'));
// Prints: Node.js
```
####
`buf.buffer`
* [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) The underlying `ArrayBuffer` object based on which this `Buffer` object is created.
This `ArrayBuffer` is not guaranteed to correspond exactly to the original `Buffer`. See the notes on `buf.byteOffset` for details.
MJS modules
```
import { Buffer } from 'node:buffer';
const arrayBuffer = new ArrayBuffer(16);
const buffer = Buffer.from(arrayBuffer);
console.log(buffer.buffer === arrayBuffer);
// Prints: true
```
CJS modules
```
const { Buffer } = require('node:buffer');
const arrayBuffer = new ArrayBuffer(16);
const buffer = Buffer.from(arrayBuffer);
console.log(buffer.buffer === arrayBuffer);
// Prints: true
```
####
`buf.byteOffset`
* [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The `byteOffset` of the `Buffer`s underlying `ArrayBuffer` object.
When setting `byteOffset` in `Buffer.from(ArrayBuffer, byteOffset, length)`, or sometimes when allocating a `Buffer` smaller than `Buffer.poolSize`, the buffer does not start from a zero offset on the underlying `ArrayBuffer`.
This can cause problems when accessing the underlying `ArrayBuffer` directly using `buf.buffer`, as other parts of the `ArrayBuffer` may be unrelated to the `Buffer` object itself.
A common issue when creating a `TypedArray` object that shares its memory with a `Buffer` is that in this case one needs to specify the `byteOffset` correctly:
MJS modules
```
import { Buffer } from 'node:buffer';
// Create a buffer smaller than `Buffer.poolSize`.
const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
// When casting the Node.js Buffer to an Int8Array, use the byteOffset
// to refer only to the part of `nodeBuffer.buffer` that contains the memory
// for `nodeBuffer`.
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Create a buffer smaller than `Buffer.poolSize`.
const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
// When casting the Node.js Buffer to an Int8Array, use the byteOffset
// to refer only to the part of `nodeBuffer.buffer` that contains the memory
// for `nodeBuffer`.
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
```
####
`buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The `target` parameter can now be a `Uint8Array`. |
| v5.11.0 | Additional parameters for specifying offsets are supported now. |
| v0.11.13 | Added in: v0.11.13 |
* `target` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) A `Buffer` or [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) with which to compare `buf`.
* `targetStart` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The offset within `target` at which to begin comparison. **Default:** `0`.
* `targetEnd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The offset within `target` at which to end comparison (not inclusive). **Default:** `target.length`.
* `sourceStart` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The offset within `buf` at which to begin comparison. **Default:** `0`.
* `sourceEnd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The offset within `buf` at which to end comparison (not inclusive). **Default:** [`buf.length`](#buflength).
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Compares `buf` with `target` and returns a number indicating whether `buf` comes before, after, or is the same as `target` in sort order. Comparison is based on the actual sequence of bytes in each `Buffer`.
* `0` is returned if `target` is the same as `buf`
* `1` is returned if `target` should come *before* `buf` when sorted.
* `-1` is returned if `target` should come *after* `buf` when sorted.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
console.log(buf1.compare(buf1));
// Prints: 0
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: -1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: 1
console.log([buf1, buf2, buf3].sort(Buffer.compare));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2].)
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
console.log(buf1.compare(buf1));
// Prints: 0
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: -1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: 1
console.log([buf1, buf2, buf3].sort(Buffer.compare));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2].)
```
The optional `targetStart`, `targetEnd`, `sourceStart`, and `sourceEnd` arguments can be used to limit the comparison to specific ranges within `target` and `buf` respectively.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: 0
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: -1
console.log(buf1.compare(buf2, 5, 6, 5));
// Prints: 1
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: 0
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: -1
console.log(buf1.compare(buf2, 5, 6, 5));
// Prints: 1
```
[`ERR_OUT_OF_RANGE`](errors#err_out_of_range) is thrown if `targetStart < 0`, `sourceStart < 0`, `targetEnd > target.byteLength`, or `sourceEnd > source.byteLength`.
####
`buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])`
Added in: v0.1.90 * `target` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) A `Buffer` or [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) to copy into.
* `targetStart` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The offset within `target` at which to begin writing. **Default:** `0`.
* `sourceStart` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The offset within `buf` from which to begin copying. **Default:** `0`.
* `sourceEnd` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The offset within `buf` at which to stop copying (not inclusive). **Default:** [`buf.length`](#buflength).
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes copied.
Copies data from a region of `buf` to a region in `target`, even if the `target` memory region overlaps with `buf`.
[`TypedArray.prototype.set()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/set) performs the same operation, and is available for all TypedArrays, including Node.js `Buffer`s, although it takes different function arguments.
MJS modules
```
import { Buffer } from 'node:buffer';
// Create two `Buffer` instances.
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
// Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`.
buf1.copy(buf2, 8, 16, 20);
// This is equivalent to:
// buf2.set(buf1.subarray(16, 20), 8);
console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Create two `Buffer` instances.
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
// Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`.
buf1.copy(buf2, 8, 16, 20);
// This is equivalent to:
// buf2.set(buf1.subarray(16, 20), 8);
console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
```
MJS modules
```
import { Buffer } from 'node:buffer';
// Create a `Buffer` and copy data from one region to an overlapping region
// within the same `Buffer`.
const buf = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf[i] = i + 97;
}
buf.copy(buf, 0, 4, 10);
console.log(buf.toString());
// Prints: efghijghijklmnopqrstuvwxyz
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Create a `Buffer` and copy data from one region to an overlapping region
// within the same `Buffer`.
const buf = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf[i] = i + 97;
}
buf.copy(buf, 0, 4, 10);
console.log(buf.toString());
// Prints: efghijghijklmnopqrstuvwxyz
```
####
`buf.entries()`
Added in: v1.1.0 * Returns: [<Iterator>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol)
Creates and returns an [iterator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) of `[index, byte]` pairs from the contents of `buf`.
MJS modules
```
import { Buffer } from 'node:buffer';
// Log the entire contents of a `Buffer`.
const buf = Buffer.from('buffer');
for (const pair of buf.entries()) {
console.log(pair);
}
// Prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Log the entire contents of a `Buffer`.
const buf = Buffer.from('buffer');
for (const pair of buf.entries()) {
console.log(pair);
}
// Prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
```
####
`buf.equals(otherBuffer)`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The arguments can now be `Uint8Array`s. |
| v0.11.13 | Added in: v0.11.13 |
* `otherBuffer` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) A `Buffer` or [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) with which to compare `buf`.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if both `buf` and `otherBuffer` have exactly the same bytes, `false` otherwise. Equivalent to [`buf.compare(otherBuffer) === 0`](#bufcomparetarget-targetstart-targetend-sourcestart-sourceend).
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');
console.log(buf1.equals(buf2));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');
console.log(buf1.equals(buf2));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
```
####
`buf.fill(value[, offset[, end]][, encoding])`
History
| Version | Changes |
| --- | --- |
| v11.0.0 | Throws `ERR_OUT_OF_RANGE` instead of `ERR_INDEX_OUT_OF_RANGE`. |
| v10.0.0 | Negative `end` values throw an `ERR_INDEX_OUT_OF_RANGE` error. |
| v10.0.0 | Attempting to fill a non-zero length buffer with a zero length buffer triggers a thrown exception. |
| v10.0.0 | Specifying an invalid string for `value` triggers a thrown exception. |
| v5.7.0 | The `encoding` parameter is supported now. |
| v0.5.0 | Added in: v0.5.0 |
* `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The value with which to fill `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to fill `buf`. **Default:** `0`.
* `end` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Where to stop filling `buf` (not inclusive). **Default:** [`buf.length`](#buflength).
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The encoding for `value` if `value` is a string. **Default:** `'utf8'`.
* Returns: [<Buffer>](buffer#class-buffer) A reference to `buf`.
Fills `buf` with the specified `value`. If the `offset` and `end` are not given, the entire `buf` will be filled:
MJS modules
```
import { Buffer } from 'node:buffer';
// Fill a `Buffer` with the ASCII character 'h'.
const b = Buffer.allocUnsafe(50).fill('h');
console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Fill a `Buffer` with the ASCII character 'h'.
const b = Buffer.allocUnsafe(50).fill('h');
console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
```
`value` is coerced to a `uint32` value if it is not a string, `Buffer`, or integer. If the resulting integer is greater than `255` (decimal), `buf` will be filled with `value & 255`.
If the final write of a `fill()` operation falls on a multi-byte character, then only the bytes of that character that fit into `buf` are written:
MJS modules
```
import { Buffer } from 'node:buffer';
// Fill a `Buffer` with character that takes up two bytes in UTF-8.
console.log(Buffer.allocUnsafe(5).fill('\u0222'));
// Prints: <Buffer c8 a2 c8 a2 c8>
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Fill a `Buffer` with character that takes up two bytes in UTF-8.
console.log(Buffer.allocUnsafe(5).fill('\u0222'));
// Prints: <Buffer c8 a2 c8 a2 c8>
```
If `value` contains invalid characters, it is truncated; if no valid fill data remains, an exception is thrown:
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(5);
console.log(buf.fill('a'));
// Prints: <Buffer 61 61 61 61 61>
console.log(buf.fill('aazz', 'hex'));
// Prints: <Buffer aa aa aa aa aa>
console.log(buf.fill('zz', 'hex'));
// Throws an exception.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(5);
console.log(buf.fill('a'));
// Prints: <Buffer 61 61 61 61 61>
console.log(buf.fill('aazz', 'hex'));
// Prints: <Buffer aa aa aa aa aa>
console.log(buf.fill('zz', 'hex'));
// Throws an exception.
```
####
`buf.includes(value[, byteOffset][, encoding])`
Added in: v5.3.0 * `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) What to search for.
* `byteOffset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Where to begin searching in `buf`. If negative, then offset is calculated from the end of `buf`. **Default:** `0`.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If `value` is a string, this is its encoding. **Default:** `'utf8'`.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if `value` was found in `buf`, `false` otherwise.
Equivalent to [`buf.indexOf() !== -1`](#bufindexofvalue-byteoffset-encoding).
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('this is a buffer');
console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
console.log(buf.includes(97));
// Prints: true (97 is the decimal ASCII value for 'a')
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: true
console.log(buf.includes('this', 4));
// Prints: false
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('this is a buffer');
console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
console.log(buf.includes(97));
// Prints: true (97 is the decimal ASCII value for 'a')
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: true
console.log(buf.includes('this', 4));
// Prints: false
```
####
`buf.indexOf(value[, byteOffset][, encoding])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The `value` can now be a `Uint8Array`. |
| v5.7.0, v4.4.0 | When `encoding` is being passed, the `byteOffset` parameter is no longer required. |
| v1.5.0 | Added in: v1.5.0 |
* `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) What to search for.
* `byteOffset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Where to begin searching in `buf`. If negative, then offset is calculated from the end of `buf`. **Default:** `0`.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If `value` is a string, this is the encoding used to determine the binary representation of the string that will be searched for in `buf`. **Default:** `'utf8'`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The index of the first occurrence of `value` in `buf`, or `-1` if `buf` does not contain `value`.
If `value` is:
* a string, `value` is interpreted according to the character encoding in `encoding`.
* a `Buffer` or [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array), `value` will be used in its entirety. To compare a partial `Buffer`, use [`buf.subarray`](#bufsubarraystart-end).
* a number, `value` will be interpreted as an unsigned 8-bit integer value between `0` and `255`.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('this is a buffer');
console.log(buf.indexOf('this'));
// Prints: 0
console.log(buf.indexOf('is'));
// Prints: 2
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
console.log(buf.indexOf(97));
// Prints: 8 (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
// Prints: 8
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
// Prints: 6
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('this is a buffer');
console.log(buf.indexOf('this'));
// Prints: 0
console.log(buf.indexOf('is'));
// Prints: 2
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
console.log(buf.indexOf(97));
// Prints: 8 (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
// Prints: 8
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
// Prints: 6
```
If `value` is not a string, number, or `Buffer`, this method will throw a `TypeError`. If `value` is a number, it will be coerced to a valid byte value, an integer between 0 and 255.
If `byteOffset` is not a number, it will be coerced to a number. If the result of coercion is `NaN` or `0`, then the entire buffer will be searched. This behavior matches [`String.prototype.indexOf()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf).
MJS modules
```
import { Buffer } from 'node:buffer';
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
// Passing a byteOffset that coerces to NaN or 0.
// Prints: 1, searching the whole buffer.
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
```
CJS modules
```
const { Buffer } = require('node:buffer');
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
// Passing a byteOffset that coerces to NaN or 0.
// Prints: 1, searching the whole buffer.
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
```
If `value` is an empty string or empty `Buffer` and `byteOffset` is less than `buf.length`, `byteOffset` will be returned. If `value` is empty and `byteOffset` is at least `buf.length`, `buf.length` will be returned.
####
`buf.keys()`
Added in: v1.1.0 * Returns: [<Iterator>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol)
Creates and returns an [iterator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) of `buf` keys (indices).
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('buffer');
for (const key of buf.keys()) {
console.log(key);
}
// Prints:
// 0
// 1
// 2
// 3
// 4
// 5
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('buffer');
for (const key of buf.keys()) {
console.log(key);
}
// Prints:
// 0
// 1
// 2
// 3
// 4
// 5
```
####
`buf.lastIndexOf(value[, byteOffset][, encoding])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The `value` can now be a `Uint8Array`. |
| v6.0.0 | Added in: v6.0.0 |
* `value` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) What to search for.
* `byteOffset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Where to begin searching in `buf`. If negative, then offset is calculated from the end of `buf`. **Default:** `buf.length - 1`.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If `value` is a string, this is the encoding used to determine the binary representation of the string that will be searched for in `buf`. **Default:** `'utf8'`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The index of the last occurrence of `value` in `buf`, or `-1` if `buf` does not contain `value`.
Identical to [`buf.indexOf()`](#bufindexofvalue-byteoffset-encoding), except the last occurrence of `value` is found rather than the first occurrence.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('this buffer is a buffer');
console.log(buf.lastIndexOf('this'));
// Prints: 0
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 17
console.log(buf.lastIndexOf(97));
// Prints: 15 (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 5));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 4));
// Prints: -1
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
// Prints: 4
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('this buffer is a buffer');
console.log(buf.lastIndexOf('this'));
// Prints: 0
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 17
console.log(buf.lastIndexOf(97));
// Prints: 15 (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 5));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 4));
// Prints: -1
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
// Prints: 4
```
If `value` is not a string, number, or `Buffer`, this method will throw a `TypeError`. If `value` is a number, it will be coerced to a valid byte value, an integer between 0 and 255.
If `byteOffset` is not a number, it will be coerced to a number. Any arguments that coerce to `NaN`, like `{}` or `undefined`, will search the whole buffer. This behavior matches [`String.prototype.lastIndexOf()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/lastIndexOf).
MJS modules
```
import { Buffer } from 'node:buffer';
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
// Passing a byteOffset that coerces to NaN.
// Prints: 1, searching the whole buffer.
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
// Passing a byteOffset that coerces to 0.
// Prints: -1, equivalent to passing 0.
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
```
CJS modules
```
const { Buffer } = require('node:buffer');
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
// Passing a byteOffset that coerces to NaN.
// Prints: 1, searching the whole buffer.
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
// Passing a byteOffset that coerces to 0.
// Prints: -1, equivalent to passing 0.
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
```
If `value` is an empty string or empty `Buffer`, `byteOffset` will be returned.
####
`buf.length`
Added in: v0.1.90 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the number of bytes in `buf`.
MJS modules
```
import { Buffer } from 'node:buffer';
// Create a `Buffer` and write a shorter string to it using UTF-8.
const buf = Buffer.alloc(1234);
console.log(buf.length);
// Prints: 1234
buf.write('some string', 0, 'utf8');
console.log(buf.length);
// Prints: 1234
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Create a `Buffer` and write a shorter string to it using UTF-8.
const buf = Buffer.alloc(1234);
console.log(buf.length);
// Prints: 1234
buf.write('some string', 0, 'utf8');
console.log(buf.length);
// Prints: 1234
```
####
`buf.parent`
Deprecated since: v8.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`buf.buffer`](#bufbuffer) instead.
The `buf.parent` property is a deprecated alias for `buf.buffer`.
####
`buf.readBigInt64BE([offset])`
Added in: v12.0.0, v10.20.0 * `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Reads a signed, big-endian 64-bit integer from `buf` at the specified `offset`.
Integers read from a `Buffer` are interpreted as two's complement signed values.
####
`buf.readBigInt64LE([offset])`
Added in: v12.0.0, v10.20.0 * `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Reads a signed, little-endian 64-bit integer from `buf` at the specified `offset`.
Integers read from a `Buffer` are interpreted as two's complement signed values.
####
`buf.readBigUInt64BE([offset])`
History
| Version | Changes |
| --- | --- |
| v14.10.0, v12.19.0 | This function is also available as `buf.readBigUint64BE()`. |
| v12.0.0, v10.20.0 | Added in: v12.0.0, v10.20.0 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Reads an unsigned, big-endian 64-bit integer from `buf` at the specified `offset`.
This function is also available under the `readBigUint64BE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64BE(0));
// Prints: 4294967295n
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64BE(0));
// Prints: 4294967295n
```
####
`buf.readBigUInt64LE([offset])`
History
| Version | Changes |
| --- | --- |
| v14.10.0, v12.19.0 | This function is also available as `buf.readBigUint64LE()`. |
| v12.0.0, v10.20.0 | Added in: v12.0.0, v10.20.0 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Reads an unsigned, little-endian 64-bit integer from `buf` at the specified `offset`.
This function is also available under the `readBigUint64LE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64LE(0));
// Prints: 18446744069414584320n
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64LE(0));
// Prints: 18446744069414584320n
```
####
`buf.readDoubleBE([offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads a 64-bit, big-endian double from `buf` at the specified `offset`.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
```
####
`buf.readDoubleLE([offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads a 64-bit, little-endian double from `buf` at the specified `offset`.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleLE(0));
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE(1));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleLE(0));
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE(1));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readFloatBE([offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads a 32-bit, big-endian float from `buf` at the specified `offset`.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
```
####
`buf.readFloatLE([offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads a 32-bit, little-endian float from `buf` at the specified `offset`.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatLE(0));
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE(1));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatLE(0));
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE(1));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readInt8([offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.0 | Added in: v0.5.0 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads a signed 8-bit integer from `buf` at the specified `offset`.
Integers read from a `Buffer` are interpreted as two's complement signed values.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([-1, 5]);
console.log(buf.readInt8(0));
// Prints: -1
console.log(buf.readInt8(1));
// Prints: 5
console.log(buf.readInt8(2));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([-1, 5]);
console.log(buf.readInt8(0));
// Prints: -1
console.log(buf.readInt8(1));
// Prints: 5
console.log(buf.readInt8(2));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readInt16BE([offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads a signed, big-endian 16-bit integer from `buf` at the specified `offset`.
Integers read from a `Buffer` are interpreted as two's complement signed values.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16BE(0));
// Prints: 5
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16BE(0));
// Prints: 5
```
####
`buf.readInt16LE([offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads a signed, little-endian 16-bit integer from `buf` at the specified `offset`.
Integers read from a `Buffer` are interpreted as two's complement signed values.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readInt32BE([offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads a signed, big-endian 32-bit integer from `buf` at the specified `offset`.
Integers read from a `Buffer` are interpreted as two's complement signed values.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32BE(0));
// Prints: 5
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32BE(0));
// Prints: 5
```
####
`buf.readInt32LE([offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads a signed, little-endian 32-bit integer from `buf` at the specified `offset`.
Integers read from a `Buffer` are interpreted as two's complement signed values.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32LE(0));
// Prints: 83886080
console.log(buf.readInt32LE(1));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32LE(0));
// Prints: 83886080
console.log(buf.readInt32LE(1));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readIntBE(offset, byteLength)`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to read. Must satisfy `0 < byteLength <= 6`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads `byteLength` number of bytes from `buf` at the specified `offset` and interprets the result as a big-endian, two's complement signed value supporting up to 48 bits of accuracy.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
console.log(buf.readIntBE(1, 0).toString(16));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
console.log(buf.readIntBE(1, 0).toString(16));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readIntLE(offset, byteLength)`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to read. Must satisfy `0 < byteLength <= 6`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads `byteLength` number of bytes from `buf` at the specified `offset` and interprets the result as a little-endian, two's complement signed value supporting up to 48 bits of accuracy.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntLE(0, 6).toString(16));
// Prints: -546f87a9cbee
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntLE(0, 6).toString(16));
// Prints: -546f87a9cbee
```
####
`buf.readUInt8([offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.readUint8()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.0 | Added in: v0.5.0 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads an unsigned 8-bit integer from `buf` at the specified `offset`.
This function is also available under the `readUint8` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, -2]);
console.log(buf.readUInt8(0));
// Prints: 1
console.log(buf.readUInt8(1));
// Prints: 254
console.log(buf.readUInt8(2));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, -2]);
console.log(buf.readUInt8(0));
// Prints: 1
console.log(buf.readUInt8(1));
// Prints: 254
console.log(buf.readUInt8(2));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readUInt16BE([offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.readUint16BE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads an unsigned, big-endian 16-bit integer from `buf` at the specified `offset`.
This function is also available under the `readUint16BE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16BE(0).toString(16));
// Prints: 1234
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 3456
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16BE(0).toString(16));
// Prints: 1234
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 3456
```
####
`buf.readUInt16LE([offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.readUint16LE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads an unsigned, little-endian 16-bit integer from `buf` at the specified `offset`.
This function is also available under the `readUint16LE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(2).toString(16));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(2).toString(16));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readUInt32BE([offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.readUint32BE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads an unsigned, big-endian 32-bit integer from `buf` at the specified `offset`.
This function is also available under the `readUint32BE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
```
####
`buf.readUInt32LE([offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.readUint32LE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads an unsigned, little-endian 32-bit integer from `buf` at the specified `offset`.
This function is also available under the `readUint32LE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32LE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(1).toString(16));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32LE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(1).toString(16));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readUIntBE(offset, byteLength)`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.readUintBE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to read. Must satisfy `0 < byteLength <= 6`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads `byteLength` number of bytes from `buf` at the specified `offset` and interprets the result as an unsigned big-endian integer supporting up to 48 bits of accuracy.
This function is also available under the `readUintBE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readUIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readUIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
```
####
`buf.readUIntLE(offset, byteLength)`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.readUintLE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to read. Must satisfy `0 < byteLength <= 6`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Reads `byteLength` number of bytes from `buf` at the specified `offset` and interprets the result as an unsigned, little-endian integer supporting up to 48 bits of accuracy.
This function is also available under the `readUintLE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
```
####
`buf.subarray([start[, end]])`
Added in: v3.0.0 * `start` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Where the new `Buffer` will start. **Default:** `0`.
* `end` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Where the new `Buffer` will end (not inclusive). **Default:** [`buf.length`](#buflength).
* Returns: [<Buffer>](buffer#class-buffer)
Returns a new `Buffer` that references the same memory as the original, but offset and cropped by the `start` and `end` indices.
Specifying `end` greater than [`buf.length`](#buflength) will return the same result as that of `end` equal to [`buf.length`](#buflength).
This method is inherited from [`TypedArray.prototype.subarray()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/subarray).
Modifying the new `Buffer` slice will modify the memory in the original `Buffer` because the allocated memory of the two objects overlap.
MJS modules
```
import { Buffer } from 'node:buffer';
// Create a `Buffer` with the ASCII alphabet, take a slice, and modify one byte
// from the original `Buffer`.
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
const buf2 = buf1.subarray(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: abc
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: !bc
```
CJS modules
```
const { Buffer } = require('node:buffer');
// Create a `Buffer` with the ASCII alphabet, take a slice, and modify one byte
// from the original `Buffer`.
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
const buf2 = buf1.subarray(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: abc
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: !bc
```
Specifying negative indexes causes the slice to be generated relative to the end of `buf` rather than the beginning.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('buffer');
console.log(buf.subarray(-6, -1).toString());
// Prints: buffe
// (Equivalent to buf.subarray(0, 5).)
console.log(buf.subarray(-6, -2).toString());
// Prints: buff
// (Equivalent to buf.subarray(0, 4).)
console.log(buf.subarray(-5, -2).toString());
// Prints: uff
// (Equivalent to buf.subarray(1, 4).)
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('buffer');
console.log(buf.subarray(-6, -1).toString());
// Prints: buffe
// (Equivalent to buf.subarray(0, 5).)
console.log(buf.subarray(-6, -2).toString());
// Prints: buff
// (Equivalent to buf.subarray(0, 4).)
console.log(buf.subarray(-5, -2).toString());
// Prints: uff
// (Equivalent to buf.subarray(1, 4).)
```
####
`buf.slice([start[, end]])`
History
| Version | Changes |
| --- | --- |
| v17.5.0, v16.15.0 | The buf.slice() method has been deprecated. |
| v7.0.0 | All offsets are now coerced to integers before doing any calculations with them. |
| v7.1.0, v6.9.2 | Coercing the offsets to integers now handles values outside the 32-bit integer range properly. |
| v0.3.0 | Added in: v0.3.0 |
* `start` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Where the new `Buffer` will start. **Default:** `0`.
* `end` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Where the new `Buffer` will end (not inclusive). **Default:** [`buf.length`](#buflength).
* Returns: [<Buffer>](buffer#class-buffer)
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`buf.subarray`](#bufsubarraystart-end) instead.
Returns a new `Buffer` that references the same memory as the original, but offset and cropped by the `start` and `end` indices.
This method is not compatible with the `Uint8Array.prototype.slice()`, which is a superclass of `Buffer`. To copy the slice, use `Uint8Array.prototype.slice()`.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('buffer');
const copiedBuf = Uint8Array.prototype.slice.call(buf);
copiedBuf[0]++;
console.log(copiedBuf.toString());
// Prints: cuffer
console.log(buf.toString());
// Prints: buffer
// With buf.slice(), the original buffer is modified.
const notReallyCopiedBuf = buf.slice();
notReallyCopiedBuf[0]++;
console.log(notReallyCopiedBuf.toString());
// Prints: cuffer
console.log(buf.toString());
// Also prints: cuffer (!)
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('buffer');
const copiedBuf = Uint8Array.prototype.slice.call(buf);
copiedBuf[0]++;
console.log(copiedBuf.toString());
// Prints: cuffer
console.log(buf.toString());
// Prints: buffer
// With buf.slice(), the original buffer is modified.
const notReallyCopiedBuf = buf.slice();
notReallyCopiedBuf[0]++;
console.log(notReallyCopiedBuf.toString());
// Prints: cuffer
console.log(buf.toString());
// Also prints: cuffer (!)
```
####
`buf.swap16()`
Added in: v5.10.0 * Returns: [<Buffer>](buffer#class-buffer) A reference to `buf`.
Interprets `buf` as an array of unsigned 16-bit integers and swaps the byte order *in-place*. Throws [`ERR_INVALID_BUFFER_SIZE`](errors#err_invalid_buffer_size) if [`buf.length`](#buflength) is not a multiple of 2.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf1.swap16();
console.log(buf1);
// Prints: <Buffer 02 01 04 03 06 05 08 07>
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap16();
// Throws ERR_INVALID_BUFFER_SIZE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf1.swap16();
console.log(buf1);
// Prints: <Buffer 02 01 04 03 06 05 08 07>
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap16();
// Throws ERR_INVALID_BUFFER_SIZE.
```
One convenient use of `buf.swap16()` is to perform a fast in-place conversion between UTF-16 little-endian and UTF-16 big-endian:
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('This is little-endian UTF-16', 'utf16le');
buf.swap16(); // Convert to big-endian UTF-16 text.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('This is little-endian UTF-16', 'utf16le');
buf.swap16(); // Convert to big-endian UTF-16 text.
```
####
`buf.swap32()`
Added in: v5.10.0 * Returns: [<Buffer>](buffer#class-buffer) A reference to `buf`.
Interprets `buf` as an array of unsigned 32-bit integers and swaps the byte order *in-place*. Throws [`ERR_INVALID_BUFFER_SIZE`](errors#err_invalid_buffer_size) if [`buf.length`](#buflength) is not a multiple of 4.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf1.swap32();
console.log(buf1);
// Prints: <Buffer 04 03 02 01 08 07 06 05>
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap32();
// Throws ERR_INVALID_BUFFER_SIZE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf1.swap32();
console.log(buf1);
// Prints: <Buffer 04 03 02 01 08 07 06 05>
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap32();
// Throws ERR_INVALID_BUFFER_SIZE.
```
####
`buf.swap64()`
Added in: v6.3.0 * Returns: [<Buffer>](buffer#class-buffer) A reference to `buf`.
Interprets `buf` as an array of 64-bit numbers and swaps byte order *in-place*. Throws [`ERR_INVALID_BUFFER_SIZE`](errors#err_invalid_buffer_size) if [`buf.length`](#buflength) is not a multiple of 8.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf1.swap64();
console.log(buf1);
// Prints: <Buffer 08 07 06 05 04 03 02 01>
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap64();
// Throws ERR_INVALID_BUFFER_SIZE.
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf1.swap64();
console.log(buf1);
// Prints: <Buffer 08 07 06 05 04 03 02 01>
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap64();
// Throws ERR_INVALID_BUFFER_SIZE.
```
####
`buf.toJSON()`
Added in: v0.9.2 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns a JSON representation of `buf`. [`JSON.stringify()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify) implicitly calls this function when stringifying a `Buffer` instance.
`Buffer.from()` accepts objects in the format returned from this method. In particular, `Buffer.from(buf.toJSON())` works like `Buffer.from(buf)`.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);
console.log(json);
// Prints: {"type":"Buffer","data":[1,2,3,4,5]}
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer' ?
Buffer.from(value) :
value;
});
console.log(copy);
// Prints: <Buffer 01 02 03 04 05>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);
console.log(json);
// Prints: {"type":"Buffer","data":[1,2,3,4,5]}
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer' ?
Buffer.from(value) :
value;
});
console.log(copy);
// Prints: <Buffer 01 02 03 04 05>
```
####
`buf.toString([encoding[, start[, end]]])`
Added in: v0.1.90 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The character encoding to use. **Default:** `'utf8'`.
* `start` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The byte offset to start decoding at. **Default:** `0`.
* `end` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The byte offset to stop decoding at (not inclusive). **Default:** [`buf.length`](#buflength).
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Decodes `buf` to a string according to the specified character encoding in `encoding`. `start` and `end` may be passed to decode only a subset of `buf`.
If `encoding` is `'utf8'` and a byte sequence in the input is not valid UTF-8, then each invalid byte is replaced with the replacement character `U+FFFD`.
The maximum length of a string instance (in UTF-16 code units) is available as [`buffer.constants.MAX_STRING_LENGTH`](#bufferconstantsmax_string_length).
MJS modules
```
import { Buffer } from 'node:buffer';
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
console.log(buf1.toString('utf8'));
// Prints: abcdefghijklmnopqrstuvwxyz
console.log(buf1.toString('utf8', 0, 5));
// Prints: abcde
const buf2 = Buffer.from('tést');
console.log(buf2.toString('hex'));
// Prints: 74c3a97374
console.log(buf2.toString('utf8', 0, 3));
// Prints: té
console.log(buf2.toString(undefined, 0, 3));
// Prints: té
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
console.log(buf1.toString('utf8'));
// Prints: abcdefghijklmnopqrstuvwxyz
console.log(buf1.toString('utf8', 0, 5));
// Prints: abcde
const buf2 = Buffer.from('tést');
console.log(buf2.toString('hex'));
// Prints: 74c3a97374
console.log(buf2.toString('utf8', 0, 3));
// Prints: té
console.log(buf2.toString(undefined, 0, 3));
// Prints: té
```
####
`buf.values()`
Added in: v1.1.0 * Returns: [<Iterator>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol)
Creates and returns an [iterator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) for `buf` values (bytes). This function is called automatically when a `Buffer` is used in a `for..of` statement.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.from('buffer');
for (const value of buf.values()) {
console.log(value);
}
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (const value of buf) {
console.log(value);
}
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.from('buffer');
for (const value of buf.values()) {
console.log(value);
}
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (const value of buf) {
console.log(value);
}
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
```
####
`buf.write(string[, offset[, length]][, encoding])`
Added in: v0.1.90 * `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) String to write to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write `string`. **Default:** `0`.
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Maximum number of bytes to write (written bytes will not exceed `buf.length - offset`). **Default:** `buf.length - offset`.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The character encoding of `string`. **Default:** `'utf8'`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes written.
Writes `string` to `buf` at `offset` according to the character encoding in `encoding`. The `length` parameter is the number of bytes to write. If `buf` did not contain enough space to fit the entire string, only part of `string` will be written. However, partially encoded characters will not be written.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
// Prints: 12 bytes: ½ + ¼ = ¾
const buffer = Buffer.alloc(10);
const length = buffer.write('abcd', 8);
console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
// Prints: 2 bytes : ab
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
// Prints: 12 bytes: ½ + ¼ = ¾
const buffer = Buffer.alloc(10);
const length = buffer.write('abcd', 8);
console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
// Prints: 2 bytes : ab
```
####
`buf.writeBigInt64BE(value[, offset])`
Added in: v12.0.0, v10.20.0 * `value` [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as big-endian.
`value` is interpreted and written as a two's complement signed integer.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64BE(0x0102030405060708n, 0);
console.log(buf);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64BE(0x0102030405060708n, 0);
console.log(buf);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
```
####
`buf.writeBigInt64LE(value[, offset])`
Added in: v12.0.0, v10.20.0 * `value` [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as little-endian.
`value` is interpreted and written as a two's complement signed integer.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64LE(0x0102030405060708n, 0);
console.log(buf);
// Prints: <Buffer 08 07 06 05 04 03 02 01>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64LE(0x0102030405060708n, 0);
console.log(buf);
// Prints: <Buffer 08 07 06 05 04 03 02 01>
```
####
`buf.writeBigUInt64BE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v14.10.0, v12.19.0 | This function is also available as `buf.writeBigUint64BE()`. |
| v12.0.0, v10.20.0 | Added in: v12.0.0, v10.20.0 |
* `value` [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as big-endian.
This function is also available under the `writeBigUint64BE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(8);
buf.writeBigUInt64BE(0xdecafafecacefaden, 0);
console.log(buf);
// Prints: <Buffer de ca fa fe ca ce fa de>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(8);
buf.writeBigUInt64BE(0xdecafafecacefaden, 0);
console.log(buf);
// Prints: <Buffer de ca fa fe ca ce fa de>
```
####
`buf.writeBigUInt64LE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v14.10.0, v12.19.0 | This function is also available as `buf.writeBigUint64LE()`. |
| v12.0.0, v10.20.0 | Added in: v12.0.0, v10.20.0 |
* `value` [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as little-endian
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(8);
buf.writeBigUInt64LE(0xdecafafecacefaden, 0);
console.log(buf);
// Prints: <Buffer de fa ce ca fe fa ca de>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(8);
buf.writeBigUInt64LE(0xdecafafecacefaden, 0);
console.log(buf);
// Prints: <Buffer de fa ce ca fe fa ca de>
```
This function is also available under the `writeBigUint64LE` alias.
####
`buf.writeDoubleBE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `value` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a JavaScript number. Behavior is undefined when `value` is anything other than a JavaScript number.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleBE(123.456, 0);
console.log(buf);
// Prints: <Buffer 40 5e dd 2f 1a 9f be 77>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleBE(123.456, 0);
console.log(buf);
// Prints: <Buffer 40 5e dd 2f 1a 9f be 77>
```
####
`buf.writeDoubleLE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `value` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a JavaScript number. Behavior is undefined when `value` is anything other than a JavaScript number.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleLE(123.456, 0);
console.log(buf);
// Prints: <Buffer 77 be 9f 1a 2f dd 5e 40>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleLE(123.456, 0);
console.log(buf);
// Prints: <Buffer 77 be 9f 1a 2f dd 5e 40>
```
####
`buf.writeFloatBE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `value` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as big-endian. Behavior is undefined when `value` is anything other than a JavaScript number.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(4);
buf.writeFloatBE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer 4f 4a fe bb>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(4);
buf.writeFloatBE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer 4f 4a fe bb>
```
####
`buf.writeFloatLE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `value` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as little-endian. Behavior is undefined when `value` is anything other than a JavaScript number.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(4);
buf.writeFloatLE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer bb fe 4a 4f>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(4);
buf.writeFloatLE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer bb fe 4a 4f>
```
####
`buf.writeInt8(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.0 | Added in: v0.5.0 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset`. `value` must be a valid signed 8-bit integer. Behavior is undefined when `value` is anything other than a signed 8-bit integer.
`value` is interpreted and written as a two's complement signed integer.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(2);
buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);
console.log(buf);
// Prints: <Buffer 02 fe>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(2);
buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);
console.log(buf);
// Prints: <Buffer 02 fe>
```
####
`buf.writeInt16BE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a valid signed 16-bit integer. Behavior is undefined when `value` is anything other than a signed 16-bit integer.
The `value` is interpreted and written as a two's complement signed integer.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(2);
buf.writeInt16BE(0x0102, 0);
console.log(buf);
// Prints: <Buffer 01 02>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(2);
buf.writeInt16BE(0x0102, 0);
console.log(buf);
// Prints: <Buffer 01 02>
```
####
`buf.writeInt16LE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a valid signed 16-bit integer. Behavior is undefined when `value` is anything other than a signed 16-bit integer.
The `value` is interpreted and written as a two's complement signed integer.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(2);
buf.writeInt16LE(0x0304, 0);
console.log(buf);
// Prints: <Buffer 04 03>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(2);
buf.writeInt16LE(0x0304, 0);
console.log(buf);
// Prints: <Buffer 04 03>
```
####
`buf.writeInt32BE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a valid signed 32-bit integer. Behavior is undefined when `value` is anything other than a signed 32-bit integer.
The `value` is interpreted and written as a two's complement signed integer.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(4);
buf.writeInt32BE(0x01020304, 0);
console.log(buf);
// Prints: <Buffer 01 02 03 04>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(4);
buf.writeInt32BE(0x01020304, 0);
console.log(buf);
// Prints: <Buffer 01 02 03 04>
```
####
`buf.writeInt32LE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a valid signed 32-bit integer. Behavior is undefined when `value` is anything other than a signed 32-bit integer.
The `value` is interpreted and written as a two's complement signed integer.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(4);
buf.writeInt32LE(0x05060708, 0);
console.log(buf);
// Prints: <Buffer 08 07 06 05>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(4);
buf.writeInt32LE(0x05060708, 0);
console.log(buf);
// Prints: <Buffer 08 07 06 05>
```
####
`buf.writeIntBE(value, offset, byteLength)`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to write. Must satisfy `0 < byteLength <= 6`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `byteLength` bytes of `value` to `buf` at the specified `offset` as big-endian. Supports up to 48 bits of accuracy. Behavior is undefined when `value` is anything other than a signed integer.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(6);
buf.writeIntBE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(6);
buf.writeIntBE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
```
####
`buf.writeIntLE(value, offset, byteLength)`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. |
| v0.11.15 | Added in: v0.11.15 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to write. Must satisfy `0 < byteLength <= 6`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `byteLength` bytes of `value` to `buf` at the specified `offset` as little-endian. Supports up to 48 bits of accuracy. Behavior is undefined when `value` is anything other than a signed integer.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(6);
buf.writeIntLE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer ab 90 78 56 34 12>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(6);
buf.writeIntLE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer ab 90 78 56 34 12>
```
####
`buf.writeUInt8(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.writeUint8()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.0 | Added in: v0.5.0 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset`. `value` must be a valid unsigned 8-bit integer. Behavior is undefined when `value` is anything other than an unsigned 8-bit integer.
This function is also available under the `writeUint8` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);
console.log(buf);
// Prints: <Buffer 03 04 23 42>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);
console.log(buf);
// Prints: <Buffer 03 04 23 42>
```
####
`buf.writeUInt16BE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.writeUint16BE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a valid unsigned 16-bit integer. Behavior is undefined when `value` is anything other than an unsigned 16-bit integer.
This function is also available under the `writeUint16BE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer de ad be ef>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer de ad be ef>
```
####
`buf.writeUInt16LE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.writeUint16LE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a valid unsigned 16-bit integer. Behavior is undefined when `value` is anything other than an unsigned 16-bit integer.
This function is also available under the `writeUint16LE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer ad de ef be>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer ad de ef be>
```
####
`buf.writeUInt32BE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.writeUint32BE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a valid unsigned 32-bit integer. Behavior is undefined when `value` is anything other than an unsigned 32-bit integer.
This function is also available under the `writeUint32BE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32BE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer fe ed fa ce>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32BE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer fe ed fa ce>
```
####
`buf.writeUInt32LE(value[, offset])`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.writeUint32LE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a valid unsigned 32-bit integer. Behavior is undefined when `value` is anything other than an unsigned 32-bit integer.
This function is also available under the `writeUint32LE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32LE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer ce fa ed fe>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32LE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer ce fa ed fe>
```
####
`buf.writeUIntBE(value, offset, byteLength)`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.writeUintBE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to write. Must satisfy `0 < byteLength <= 6`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `byteLength` bytes of `value` to `buf` at the specified `offset` as big-endian. Supports up to 48 bits of accuracy. Behavior is undefined when `value` is anything other than an unsigned integer.
This function is also available under the `writeUintBE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
```
####
`buf.writeUIntLE(value, offset, byteLength)`
History
| Version | Changes |
| --- | --- |
| v14.9.0, v12.19.0 | This function is also available as `buf.writeUintLE()`. |
| v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. |
| v0.5.5 | Added in: v0.5.5 |
* `value` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number to be written to `buf`.
* `offset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to write. Must satisfy `0 < byteLength <= 6`.
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `offset` plus the number of bytes written.
Writes `byteLength` bytes of `value` to `buf` at the specified `offset` as little-endian. Supports up to 48 bits of accuracy. Behavior is undefined when `value` is anything other than an unsigned integer.
This function is also available under the `writeUintLE` alias.
MJS modules
```
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(6);
buf.writeUIntLE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer ab 90 78 56 34 12>
```
CJS modules
```
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(6);
buf.writeUIntLE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer ab 90 78 56 34 12>
```
####
`new Buffer(array)`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. |
| v7.2.1 | Calling this constructor no longer emits a deprecation warning. |
| v7.0.0 | Calling this constructor emits a deprecation warning now. |
| v6.0.0 | Deprecated since: v6.0.0 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Buffer.from(array)`](#static-method-bufferfromarray) instead.
* `array` [<integer[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) An array of bytes to copy from.
See [`Buffer.from(array)`](#static-method-bufferfromarray).
####
`new Buffer(arrayBuffer[, byteOffset[, length]])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. |
| v7.2.1 | Calling this constructor no longer emits a deprecation warning. |
| v7.0.0 | Calling this constructor emits a deprecation warning now. |
| v6.0.0 | The `byteOffset` and `length` parameters are supported now. |
| v6.0.0 | Deprecated since: v6.0.0 |
| v3.0.0 | Added in: v3.0.0 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Buffer.from(arrayBuffer[, byteOffset[, length]])`](#static-method-bufferfromarraybuffer-byteoffset-length) instead.
* `arrayBuffer` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) An [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer), [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) or the `.buffer` property of a [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray).
* `byteOffset` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Index of first byte to expose. **Default:** `0`.
* `length` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Number of bytes to expose. **Default:** `arrayBuffer.byteLength - byteOffset`.
See [`Buffer.from(arrayBuffer[, byteOffset[, length]])`](#static-method-bufferfromarraybuffer-byteoffset-length).
####
`new Buffer(buffer)`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. |
| v7.2.1 | Calling this constructor no longer emits a deprecation warning. |
| v7.0.0 | Calling this constructor emits a deprecation warning now. |
| v6.0.0 | Deprecated since: v6.0.0 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Buffer.from(buffer)`](#static-method-bufferfrombuffer) instead.
* `buffer` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) An existing `Buffer` or [`Uint8Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) from which to copy data.
See [`Buffer.from(buffer)`](#static-method-bufferfrombuffer).
####
`new Buffer(size)`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. |
| v8.0.0 | The `new Buffer(size)` will return zero-filled memory by default. |
| v7.2.1 | Calling this constructor no longer emits a deprecation warning. |
| v7.0.0 | Calling this constructor emits a deprecation warning now. |
| v6.0.0 | Deprecated since: v6.0.0 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Buffer.alloc()`](#static-method-bufferallocsize-fill-encoding) instead (also see [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize)).
* `size` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The desired length of the new `Buffer`.
See [`Buffer.alloc()`](#static-method-bufferallocsize-fill-encoding) and [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize). This variant of the constructor is equivalent to [`Buffer.alloc()`](#static-method-bufferallocsize-fill-encoding).
####
`new Buffer(string[, encoding])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. |
| v7.2.1 | Calling this constructor no longer emits a deprecation warning. |
| v7.0.0 | Calling this constructor emits a deprecation warning now. |
| v6.0.0 | Deprecated since: v6.0.0 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Buffer.from(string[, encoding])`](#static-method-bufferfromstring-encoding) instead.
* `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) String to encode.
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The encoding of `string`. **Default:** `'utf8'`.
See [`Buffer.from(string[, encoding])`](#static-method-bufferfromstring-encoding).
###
`node:buffer` module APIs
While, the `Buffer` object is available as a global, there are additional `Buffer`-related APIs that are available only via the `node:buffer` module accessed using `require('node:buffer')`.
####
`buffer.atob(data)`
Added in: v15.13.0, v14.17.0
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy. Use `Buffer.from(data, 'base64')` instead.
* `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The Base64-encoded input string.
Decodes a string of Base64-encoded data into bytes, and encodes those bytes into a string using Latin-1 (ISO-8859-1).
The `data` may be any JavaScript-value that can be coerced into a string.
**This function is only provided for compatibility with legacy web platform APIs and should never be used in new code, because they use strings to represent binary data and predate the introduction of typed arrays in JavaScript. For code running using Node.js APIs, converting between base64-encoded strings and binary data should be performed using `Buffer.from(str, 'base64')` and `buf.toString('base64')`.**
####
`buffer.btoa(data)`
Added in: v15.13.0, v14.17.0
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy. Use `buf.toString('base64')` instead.
* `data` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) An ASCII (Latin1) string.
Decodes a string into bytes using Latin-1 (ISO-8859), and encodes those bytes into a string using Base64.
The `data` may be any JavaScript-value that can be coerced into a string.
**This function is only provided for compatibility with legacy web platform APIs and should never be used in new code, because they use strings to represent binary data and predate the introduction of typed arrays in JavaScript. For code running using Node.js APIs, converting between base64-encoded strings and binary data should be performed using `Buffer.from(str, 'base64')` and `buf.toString('base64')`.**
####
`buffer.INSPECT_MAX_BYTES`
Added in: v0.5.4 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `50`
Returns the maximum number of bytes that will be returned when `buf.inspect()` is called. This can be overridden by user modules. See [`util.inspect()`](util#utilinspectobject-options) for more details on `buf.inspect()` behavior.
####
`buffer.kMaxLength`
Added in: v3.0.0 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The largest size allowed for a single `Buffer` instance.
An alias for [`buffer.constants.MAX_LENGTH`](#bufferconstantsmax_length).
####
`buffer.kStringMaxLength`
Added in: v3.0.0 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The largest length allowed for a single `string` instance.
An alias for [`buffer.constants.MAX_STRING_LENGTH`](#bufferconstantsmax_string_length).
####
`buffer.resolveObjectURL(id)`
Added in: v16.7.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
* `id` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A `'blob:nodedata:...` URL string returned by a prior call to `URL.createObjectURL()`.
* Returns: [<Blob>](buffer#class-blob)
Resolves a `'blob:nodedata:...'` an associated [<Blob>](buffer#class-blob) object registered using a prior call to `URL.createObjectURL()`.
####
`buffer.transcode(source, fromEnc, toEnc)`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The `source` parameter can now be a `Uint8Array`. |
| v7.1.0 | Added in: v7.1.0 |
* `source` [<Buffer>](buffer#class-buffer) | [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) A `Buffer` or `Uint8Array` instance.
* `fromEnc` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The current encoding.
* `toEnc` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) To target encoding.
* Returns: [<Buffer>](buffer#class-buffer)
Re-encodes the given `Buffer` or `Uint8Array` instance from one character encoding to another. Returns a new `Buffer` instance.
Throws if the `fromEnc` or `toEnc` specify invalid character encodings or if conversion from `fromEnc` to `toEnc` is not permitted.
Encodings supported by `buffer.transcode()` are: `'ascii'`, `'utf8'`, `'utf16le'`, `'ucs2'`, `'latin1'`, and `'binary'`.
The transcoding process will use substitution characters if a given byte sequence cannot be adequately represented in the target encoding. For instance:
MJS modules
```
import { Buffer, transcode } from 'node:buffer';
const newBuf = transcode(Buffer.from('€'), 'utf8', 'ascii');
console.log(newBuf.toString('ascii'));
// Prints: '?'
```
CJS modules
```
const { Buffer, transcode } = require('node:buffer');
const newBuf = transcode(Buffer.from('€'), 'utf8', 'ascii');
console.log(newBuf.toString('ascii'));
// Prints: '?'
```
Because the Euro (`€`) sign is not representable in US-ASCII, it is replaced with `?` in the transcoded `Buffer`.
#### Class: `SlowBuffer`
Deprecated since: v6.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Buffer.allocUnsafeSlow()`](#static-method-bufferallocunsafeslowsize) instead.
See [`Buffer.allocUnsafeSlow()`](#static-method-bufferallocunsafeslowsize). This was never a class in the sense that the constructor always returned a `Buffer` instance, rather than a `SlowBuffer` instance.
#####
`new SlowBuffer(size)`
Deprecated since: v6.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`Buffer.allocUnsafeSlow()`](#static-method-bufferallocunsafeslowsize) instead.
* `size` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The desired length of the new `SlowBuffer`.
See [`Buffer.allocUnsafeSlow()`](#static-method-bufferallocunsafeslowsize).
#### Buffer constants
Added in: v8.2.0 #####
`buffer.constants.MAX_LENGTH`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Value is changed to 232 on 64-bit architectures. |
| v14.0.0 | Value is changed from 231 - 1 to 232 - 1 on 64-bit architectures. |
| v8.2.0 | Added in: v8.2.0 |
* [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The largest size allowed for a single `Buffer` instance.
On 32-bit architectures, this value currently is 230 - 1 (about 1 GiB).
On 64-bit architectures, this value currently is 232 (about 4 GiB).
It reflects [`v8::TypedArray::kMaxLength`](https://v8.github.io/api/head/classv8_1_1TypedArray.html#a54a48f4373da0850663c4393d843b9b0) under the hood.
This value is also available as [`buffer.kMaxLength`](#bufferkmaxlength).
#####
`buffer.constants.MAX_STRING_LENGTH`
Added in: v8.2.0 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The largest length allowed for a single `string` instance.
Represents the largest `length` that a `string` primitive can have, counted in UTF-16 code units.
This value may depend on the JS engine that is being used.
###
`Buffer.from()`, `Buffer.alloc()`, and `Buffer.allocUnsafe()`
In versions of Node.js prior to 6.0.0, `Buffer` instances were created using the `Buffer` constructor function, which allocates the returned `Buffer` differently based on what arguments are provided:
* Passing a number as the first argument to `Buffer()` (e.g. `new Buffer(10)`) allocates a new `Buffer` object of the specified size. Prior to Node.js 8.0.0, the memory allocated for such `Buffer` instances is *not* initialized and *can contain sensitive data*. Such `Buffer` instances *must* be subsequently initialized by using either [`buf.fill(0)`](#buffillvalue-offset-end-encoding) or by writing to the entire `Buffer` before reading data from the `Buffer`. While this behavior is *intentional* to improve performance, development experience has demonstrated that a more explicit distinction is required between creating a fast-but-uninitialized `Buffer` versus creating a slower-but-safer `Buffer`. Since Node.js 8.0.0, `Buffer(num)` and `new Buffer(num)` return a `Buffer` with initialized memory.
* Passing a string, array, or `Buffer` as the first argument copies the passed object's data into the `Buffer`.
* Passing an [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) or a [`SharedArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) returns a `Buffer` that shares allocated memory with the given array buffer.
Because the behavior of `new Buffer()` is different depending on the type of the first argument, security and reliability issues can be inadvertently introduced into applications when argument validation or `Buffer` initialization is not performed.
For example, if an attacker can cause an application to receive a number where a string is expected, the application may call `new Buffer(100)` instead of `new Buffer("100")`, leading it to allocate a 100 byte buffer instead of allocating a 3 byte buffer with content `"100"`. This is commonly possible using JSON API calls. Since JSON distinguishes between numeric and string types, it allows injection of numbers where a naively written application that does not validate its input sufficiently might expect to always receive a string. Before Node.js 8.0.0, the 100 byte buffer might contain arbitrary pre-existing in-memory data, so may be used to expose in-memory secrets to a remote attacker. Since Node.js 8.0.0, exposure of memory cannot occur because the data is zero-filled. However, other attacks are still possible, such as causing very large buffers to be allocated by the server, leading to performance degradation or crashing on memory exhaustion.
To make the creation of `Buffer` instances more reliable and less error-prone, the various forms of the `new Buffer()` constructor have been **deprecated** and replaced by separate `Buffer.from()`, [`Buffer.alloc()`](#static-method-bufferallocsize-fill-encoding), and [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize) methods.
*Developers should migrate all existing uses of the `new Buffer()` constructors to one of these new APIs.*
* [`Buffer.from(array)`](#static-method-bufferfromarray) returns a new `Buffer` that *contains a copy* of the provided octets.
* [`Buffer.from(arrayBuffer[, byteOffset[, length]])`](#static-method-bufferfromarraybuffer-byteoffset-length) returns a new `Buffer` that *shares the same allocated memory* as the given [`ArrayBuffer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer).
* [`Buffer.from(buffer)`](#static-method-bufferfrombuffer) returns a new `Buffer` that *contains a copy* of the contents of the given `Buffer`.
* [`Buffer.from(string[, encoding])`](#static-method-bufferfromstring-encoding) returns a new `Buffer` that *contains a copy* of the provided string.
* [`Buffer.alloc(size[, fill[, encoding]])`](#static-method-bufferallocsize-fill-encoding) returns a new initialized `Buffer` of the specified size. This method is slower than [`Buffer.allocUnsafe(size)`](#static-method-bufferallocunsafesize) but guarantees that newly created `Buffer` instances never contain old data that is potentially sensitive. A `TypeError` will be thrown if `size` is not a number.
* [`Buffer.allocUnsafe(size)`](#static-method-bufferallocunsafesize) and [`Buffer.allocUnsafeSlow(size)`](#static-method-bufferallocunsafeslowsize) each return a new uninitialized `Buffer` of the specified `size`. Because the `Buffer` is uninitialized, the allocated segment of memory might contain old data that is potentially sensitive.
`Buffer` instances returned by [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize) and [`Buffer.from(array)`](#static-method-bufferfromarray) *may* be allocated off a shared internal memory pool if `size` is less than or equal to half [`Buffer.poolSize`](#class-property-bufferpoolsize). Instances returned by [`Buffer.allocUnsafeSlow()`](#static-method-bufferallocunsafeslowsize) *never* use the shared internal memory pool.
#### The `--zero-fill-buffers` command-line option
Added in: v5.10.0 Node.js can be started using the `--zero-fill-buffers` command-line option to cause all newly-allocated `Buffer` instances to be zero-filled upon creation by default. Without the option, buffers created with [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize), [`Buffer.allocUnsafeSlow()`](#static-method-bufferallocunsafeslowsize), and `new SlowBuffer(size)` are not zero-filled. Use of this flag can have a measurable negative impact on performance. Use the `--zero-fill-buffers` option only when necessary to enforce that newly allocated `Buffer` instances cannot contain old data that is potentially sensitive.
```
$ node --zero-fill-buffers
> Buffer.allocUnsafe(5);
<Buffer 00 00 00 00 00>
```
#### What makes `Buffer.allocUnsafe()` and `Buffer.allocUnsafeSlow()` "unsafe"?
When calling [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize) and [`Buffer.allocUnsafeSlow()`](#static-method-bufferallocunsafeslowsize), the segment of allocated memory is *uninitialized* (it is not zeroed-out). While this design makes the allocation of memory quite fast, the allocated segment of memory might contain old data that is potentially sensitive. Using a `Buffer` created by [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize) without *completely* overwriting the memory can allow this old data to be leaked when the `Buffer` memory is read.
While there are clear performance advantages to using [`Buffer.allocUnsafe()`](#static-method-bufferallocunsafesize), extra care *must* be taken in order to avoid introducing security vulnerabilities into an application.
| programming_docs |
node None Crypto
------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/crypto.js](https://github.com/nodejs/node/blob/v19.0.1/lib/crypto.js)
The `node:crypto` module provides cryptographic functionality that includes a set of wrappers for OpenSSL's hash, HMAC, cipher, decipher, sign, and verify functions.
MJS modules
```
const { createHmac } = await import('node:crypto');
const secret = 'abcdefg';
const hash = createHmac('sha256', secret)
.update('I love cupcakes')
.digest('hex');
console.log(hash);
// Prints:
// c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e
```
CJS modules
```
const crypto = require('node:crypto');
const secret = 'abcdefg';
const hash = crypto.createHmac('sha256', secret)
.update('I love cupcakes')
.digest('hex');
console.log(hash);
// Prints:
// c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e
```
### Determining if crypto support is unavailable
It is possible for Node.js to be built without including support for the `node:crypto` module. In such cases, attempting to `import` from `crypto` or calling `require('node:crypto')` will result in an error being thrown.
When using CommonJS, the error thrown can be caught using try/catch:
```
let crypto;
try {
crypto = require('node:crypto');
} catch (err) {
console.log('crypto support is disabled!');
}
```
When using the lexical ESM `import` keyword, the error can only be caught if a handler for `process.on('uncaughtException')` is registered *before* any attempt to load the module is made (using, for instance, a preload module).
When using ESM, if there is a chance that the code may be run on a build of Node.js where crypto support is not enabled, consider using the [`import()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import) function instead of the lexical `import` keyword:
```
let crypto;
try {
crypto = await import('node:crypto');
} catch (err) {
console.log('crypto support is disabled!');
}
```
### Class: `Certificate`
Added in: v0.11.8 SPKAC is a Certificate Signing Request mechanism originally implemented by Netscape and was specified formally as part of [HTML5's `keygen` element](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/keygen).
`<keygen>` is deprecated since [HTML 5.2](https://www.w3.org/TR/html52/changes.html#features-removed) and new projects should not use this element anymore.
The `node:crypto` module provides the `Certificate` class for working with SPKAC data. The most common usage is handling output generated by the HTML5 `<keygen>` element. Node.js uses [OpenSSL's SPKAC implementation](https://www.openssl.org/docs/man1.1.0/apps/openssl-spkac.html) internally.
#### Static method: `Certificate.exportChallenge(spkac[, encoding])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The spkac argument can be an ArrayBuffer. Limited the size of the spkac argument to a maximum of 2\*\*31 - 1 bytes. |
| v9.0.0 | Added in: v9.0.0 |
* `spkac` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `spkac` string.
* Returns: [<Buffer>](buffer#class-buffer) The challenge component of the `spkac` data structure, which includes a public key and a challenge.
MJS modules
```
const { Certificate } = await import('node:crypto');
const spkac = getSpkacSomehow();
const challenge = Certificate.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
```
CJS modules
```
const { Certificate } = require('node:crypto');
const spkac = getSpkacSomehow();
const challenge = Certificate.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
```
#### Static method: `Certificate.exportPublicKey(spkac[, encoding])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The spkac argument can be an ArrayBuffer. Limited the size of the spkac argument to a maximum of 2\*\*31 - 1 bytes. |
| v9.0.0 | Added in: v9.0.0 |
* `spkac` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `spkac` string.
* Returns: [<Buffer>](buffer#class-buffer) The public key component of the `spkac` data structure, which includes a public key and a challenge.
MJS modules
```
const { Certificate } = await import('node:crypto');
const spkac = getSpkacSomehow();
const publicKey = Certificate.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
```
CJS modules
```
const { Certificate } = require('node:crypto');
const spkac = getSpkacSomehow();
const publicKey = Certificate.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
```
#### Static method: `Certificate.verifySpkac(spkac[, encoding])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The spkac argument can be an ArrayBuffer. Added encoding. Limited the size of the spkac argument to a maximum of 2\*\*31 - 1 bytes. |
| v9.0.0 | Added in: v9.0.0 |
* `spkac` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `spkac` string.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the given `spkac` data structure is valid, `false` otherwise.
MJS modules
```
import { Buffer } from 'node:buffer';
const { Certificate } = await import('node:crypto');
const spkac = getSpkacSomehow();
console.log(Certificate.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
```
CJS modules
```
const { Certificate } = require('node:crypto');
const { Buffer } = require('node:buffer');
const spkac = getSpkacSomehow();
console.log(Certificate.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
```
#### Legacy API
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
As a legacy interface, it is possible to create new instances of the `crypto.Certificate` class as illustrated in the examples below.
#####
`new crypto.Certificate()`
Instances of the `Certificate` class can be created using the `new` keyword or by calling `crypto.Certificate()` as a function:
MJS modules
```
const { Certificate } = await import('node:crypto');
const cert1 = new Certificate();
const cert2 = Certificate();
```
CJS modules
```
const { Certificate } = require('node:crypto');
const cert1 = new Certificate();
const cert2 = Certificate();
```
#####
`certificate.exportChallenge(spkac[, encoding])`
Added in: v0.11.8 * `spkac` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `spkac` string.
* Returns: [<Buffer>](buffer#class-buffer) The challenge component of the `spkac` data structure, which includes a public key and a challenge.
MJS modules
```
const { Certificate } = await import('node:crypto');
const cert = Certificate();
const spkac = getSpkacSomehow();
const challenge = cert.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
```
CJS modules
```
const { Certificate } = require('node:crypto');
const cert = Certificate();
const spkac = getSpkacSomehow();
const challenge = cert.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
```
#####
`certificate.exportPublicKey(spkac[, encoding])`
Added in: v0.11.8 * `spkac` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `spkac` string.
* Returns: [<Buffer>](buffer#class-buffer) The public key component of the `spkac` data structure, which includes a public key and a challenge.
MJS modules
```
const { Certificate } = await import('node:crypto');
const cert = Certificate();
const spkac = getSpkacSomehow();
const publicKey = cert.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
```
CJS modules
```
const { Certificate } = require('node:crypto');
const cert = Certificate();
const spkac = getSpkacSomehow();
const publicKey = cert.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
```
#####
`certificate.verifySpkac(spkac[, encoding])`
Added in: v0.11.8 * `spkac` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `spkac` string.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the given `spkac` data structure is valid, `false` otherwise.
MJS modules
```
import { Buffer } from 'node:buffer';
const { Certificate } = await import('node:crypto');
const cert = Certificate();
const spkac = getSpkacSomehow();
console.log(cert.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
```
CJS modules
```
const { Certificate } = require('node:crypto');
const { Buffer } = require('node:buffer');
const cert = Certificate();
const spkac = getSpkacSomehow();
console.log(cert.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
```
### Class: `Cipher`
Added in: v0.1.94 * Extends: [<stream.Transform>](stream#class-streamtransform)
Instances of the `Cipher` class are used to encrypt data. The class can be used in one of two ways:
* As a <stream> that is both readable and writable, where plain unencrypted data is written to produce encrypted data on the readable side, or
* Using the [`cipher.update()`](#cipherupdatedata-inputencoding-outputencoding) and [`cipher.final()`](#cipherfinaloutputencoding) methods to produce the encrypted data.
The [`crypto.createCipher()`](#cryptocreatecipheralgorithm-password-options) or [`crypto.createCipheriv()`](#cryptocreatecipherivalgorithm-key-iv-options) methods are used to create `Cipher` instances. `Cipher` objects are not to be created directly using the `new` keyword.
Example: Using `Cipher` objects as streams:
MJS modules
```
const {
scrypt,
randomFill,
createCipheriv
} = await import('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// First, we'll generate the key. The key length is dependent on the algorithm.
// In this case for aes192, it is 24 bytes (192 bits).
scrypt(password, 'salt', 24, (err, key) => {
if (err) throw err;
// Then, we'll generate a random initialization vector
randomFill(new Uint8Array(16), (err, iv) => {
if (err) throw err;
// Once we have the key and iv, we can create and use the cipher...
const cipher = createCipheriv(algorithm, key, iv);
let encrypted = '';
cipher.setEncoding('hex');
cipher.on('data', (chunk) => encrypted += chunk);
cipher.on('end', () => console.log(encrypted));
cipher.write('some clear text data');
cipher.end();
});
});
```
CJS modules
```
const {
scrypt,
randomFill,
createCipheriv
} = require('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// First, we'll generate the key. The key length is dependent on the algorithm.
// In this case for aes192, it is 24 bytes (192 bits).
scrypt(password, 'salt', 24, (err, key) => {
if (err) throw err;
// Then, we'll generate a random initialization vector
randomFill(new Uint8Array(16), (err, iv) => {
if (err) throw err;
// Once we have the key and iv, we can create and use the cipher...
const cipher = createCipheriv(algorithm, key, iv);
let encrypted = '';
cipher.setEncoding('hex');
cipher.on('data', (chunk) => encrypted += chunk);
cipher.on('end', () => console.log(encrypted));
cipher.write('some clear text data');
cipher.end();
});
});
```
Example: Using `Cipher` and piped streams:
MJS modules
```
import {
createReadStream,
createWriteStream,
} from 'node:fs';
import {
pipeline
} from 'node:stream';
const {
scrypt,
randomFill,
createCipheriv
} = await import('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// First, we'll generate the key. The key length is dependent on the algorithm.
// In this case for aes192, it is 24 bytes (192 bits).
scrypt(password, 'salt', 24, (err, key) => {
if (err) throw err;
// Then, we'll generate a random initialization vector
randomFill(new Uint8Array(16), (err, iv) => {
if (err) throw err;
const cipher = createCipheriv(algorithm, key, iv);
const input = createReadStream('test.js');
const output = createWriteStream('test.enc');
pipeline(input, cipher, output, (err) => {
if (err) throw err;
});
});
});
```
CJS modules
```
const {
createReadStream,
createWriteStream,
} = require('node:fs');
const {
pipeline
} = require('node:stream');
const {
scrypt,
randomFill,
createCipheriv,
} = require('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// First, we'll generate the key. The key length is dependent on the algorithm.
// In this case for aes192, it is 24 bytes (192 bits).
scrypt(password, 'salt', 24, (err, key) => {
if (err) throw err;
// Then, we'll generate a random initialization vector
randomFill(new Uint8Array(16), (err, iv) => {
if (err) throw err;
const cipher = createCipheriv(algorithm, key, iv);
const input = createReadStream('test.js');
const output = createWriteStream('test.enc');
pipeline(input, cipher, output, (err) => {
if (err) throw err;
});
});
});
```
Example: Using the [`cipher.update()`](#cipherupdatedata-inputencoding-outputencoding) and [`cipher.final()`](#cipherfinaloutputencoding) methods:
MJS modules
```
const {
scrypt,
randomFill,
createCipheriv
} = await import('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// First, we'll generate the key. The key length is dependent on the algorithm.
// In this case for aes192, it is 24 bytes (192 bits).
scrypt(password, 'salt', 24, (err, key) => {
if (err) throw err;
// Then, we'll generate a random initialization vector
randomFill(new Uint8Array(16), (err, iv) => {
if (err) throw err;
const cipher = createCipheriv(algorithm, key, iv);
let encrypted = cipher.update('some clear text data', 'utf8', 'hex');
encrypted += cipher.final('hex');
console.log(encrypted);
});
});
```
CJS modules
```
const {
scrypt,
randomFill,
createCipheriv,
} = require('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// First, we'll generate the key. The key length is dependent on the algorithm.
// In this case for aes192, it is 24 bytes (192 bits).
scrypt(password, 'salt', 24, (err, key) => {
if (err) throw err;
// Then, we'll generate a random initialization vector
randomFill(new Uint8Array(16), (err, iv) => {
if (err) throw err;
const cipher = createCipheriv(algorithm, key, iv);
let encrypted = cipher.update('some clear text data', 'utf8', 'hex');
encrypted += cipher.final('hex');
console.log(encrypted);
});
});
```
####
`cipher.final([outputEncoding])`
Added in: v0.1.94 * `outputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Any remaining enciphered contents. If `outputEncoding` is specified, a string is returned. If an `outputEncoding` is not provided, a [`Buffer`](buffer) is returned.
Once the `cipher.final()` method has been called, the `Cipher` object can no longer be used to encrypt data. Attempts to call `cipher.final()` more than once will result in an error being thrown.
####
`cipher.getAuthTag()`
Added in: v1.0.0 * Returns: [<Buffer>](buffer#class-buffer) When using an authenticated encryption mode (`GCM`, `CCM`, `OCB`, and `chacha20-poly1305` are currently supported), the `cipher.getAuthTag()` method returns a [`Buffer`](buffer) containing the *authentication tag* that has been computed from the given data.
The `cipher.getAuthTag()` method should only be called after encryption has been completed using the [`cipher.final()`](#cipherfinaloutputencoding) method.
If the `authTagLength` option was set during the `cipher` instance's creation, this function will return exactly `authTagLength` bytes.
####
`cipher.setAAD(buffer[, options])`
Added in: v1.0.0 * `buffer` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.transform` options](stream#new-streamtransformoptions)
+ `plaintextLength` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The string encoding to use when `buffer` is a string.
* Returns: [<Cipher>](crypto#class-cipher) for method chaining.
When using an authenticated encryption mode (`GCM`, `CCM`, `OCB`, and `chacha20-poly1305` are currently supported), the `cipher.setAAD()` method sets the value used for the *additional authenticated data* (AAD) input parameter.
The `plaintextLength` option is optional for `GCM` and `OCB`. When using `CCM`, the `plaintextLength` option must be specified and its value must match the length of the plaintext in bytes. See [CCM mode](#ccm-mode).
The `cipher.setAAD()` method must be called before [`cipher.update()`](#cipherupdatedata-inputencoding-outputencoding).
####
`cipher.setAutoPadding([autoPadding])`
Added in: v0.7.1 * `autoPadding` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
* Returns: [<Cipher>](crypto#class-cipher) for method chaining.
When using block encryption algorithms, the `Cipher` class will automatically add padding to the input data to the appropriate block size. To disable the default padding call `cipher.setAutoPadding(false)`.
When `autoPadding` is `false`, the length of the entire input data must be a multiple of the cipher's block size or [`cipher.final()`](#cipherfinaloutputencoding) will throw an error. Disabling automatic padding is useful for non-standard padding, for instance using `0x0` instead of PKCS padding.
The `cipher.setAutoPadding()` method must be called before [`cipher.final()`](#cipherfinaloutputencoding).
####
`cipher.update(data[, inputEncoding][, outputEncoding])`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | The default `inputEncoding` changed from `binary` to `utf8`. |
| v0.1.94 | Added in: v0.1.94 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `inputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the data.
* `outputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Updates the cipher with `data`. If the `inputEncoding` argument is given, the `data` argument is a string using the specified encoding. If the `inputEncoding` argument is not given, `data` must be a [`Buffer`](buffer), `TypedArray`, or `DataView`. If `data` is a [`Buffer`](buffer), `TypedArray`, or `DataView`, then `inputEncoding` is ignored.
The `outputEncoding` specifies the output format of the enciphered data. If the `outputEncoding` is specified, a string using the specified encoding is returned. If no `outputEncoding` is provided, a [`Buffer`](buffer) is returned.
The `cipher.update()` method can be called multiple times with new data until [`cipher.final()`](#cipherfinaloutputencoding) is called. Calling `cipher.update()` after [`cipher.final()`](#cipherfinaloutputencoding) will result in an error being thrown.
### Class: `Decipher`
Added in: v0.1.94 * Extends: [<stream.Transform>](stream#class-streamtransform)
Instances of the `Decipher` class are used to decrypt data. The class can be used in one of two ways:
* As a <stream> that is both readable and writable, where plain encrypted data is written to produce unencrypted data on the readable side, or
* Using the [`decipher.update()`](#decipherupdatedata-inputencoding-outputencoding) and [`decipher.final()`](#decipherfinaloutputencoding) methods to produce the unencrypted data.
The [`crypto.createDecipher()`](#cryptocreatedecipheralgorithm-password-options) or [`crypto.createDecipheriv()`](#cryptocreatedecipherivalgorithm-key-iv-options) methods are used to create `Decipher` instances. `Decipher` objects are not to be created directly using the `new` keyword.
Example: Using `Decipher` objects as streams:
MJS modules
```
import { Buffer } from 'node:buffer';
const {
scryptSync,
createDecipheriv
} = await import('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Key length is dependent on the algorithm. In this case for aes192, it is
// 24 bytes (192 bits).
// Use the async `crypto.scrypt()` instead.
const key = scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.
const decipher = createDecipheriv(algorithm, key, iv);
let decrypted = '';
decipher.on('readable', () => {
let chunk;
while (null !== (chunk = decipher.read())) {
decrypted += chunk.toString('utf8');
}
});
decipher.on('end', () => {
console.log(decrypted);
// Prints: some clear text data
});
// Encrypted with same algorithm, key and iv.
const encrypted =
'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa';
decipher.write(encrypted, 'hex');
decipher.end();
```
CJS modules
```
const {
scryptSync,
createDecipheriv,
} = require('node:crypto');
const { Buffer } = require('node:buffer');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Key length is dependent on the algorithm. In this case for aes192, it is
// 24 bytes (192 bits).
// Use the async `crypto.scrypt()` instead.
const key = scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.
const decipher = createDecipheriv(algorithm, key, iv);
let decrypted = '';
decipher.on('readable', () => {
let chunk;
while (null !== (chunk = decipher.read())) {
decrypted += chunk.toString('utf8');
}
});
decipher.on('end', () => {
console.log(decrypted);
// Prints: some clear text data
});
// Encrypted with same algorithm, key and iv.
const encrypted =
'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa';
decipher.write(encrypted, 'hex');
decipher.end();
```
Example: Using `Decipher` and piped streams:
MJS modules
```
import {
createReadStream,
createWriteStream,
} from 'node:fs';
import { Buffer } from 'node:buffer';
const {
scryptSync,
createDecipheriv
} = await import('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.
const decipher = createDecipheriv(algorithm, key, iv);
const input = createReadStream('test.enc');
const output = createWriteStream('test.js');
input.pipe(decipher).pipe(output);
```
CJS modules
```
const {
createReadStream,
createWriteStream,
} = require('node:fs');
const {
scryptSync,
createDecipheriv,
} = require('node:crypto');
const { Buffer } = require('node:buffer');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.
const decipher = createDecipheriv(algorithm, key, iv);
const input = createReadStream('test.enc');
const output = createWriteStream('test.js');
input.pipe(decipher).pipe(output);
```
Example: Using the [`decipher.update()`](#decipherupdatedata-inputencoding-outputencoding) and [`decipher.final()`](#decipherfinaloutputencoding) methods:
MJS modules
```
import { Buffer } from 'node:buffer';
const {
scryptSync,
createDecipheriv
} = await import('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.
const decipher = createDecipheriv(algorithm, key, iv);
// Encrypted using same algorithm, key and iv.
const encrypted =
'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa';
let decrypted = decipher.update(encrypted, 'hex', 'utf8');
decrypted += decipher.final('utf8');
console.log(decrypted);
// Prints: some clear text data
```
CJS modules
```
const {
scryptSync,
createDecipheriv,
} = require('node:crypto');
const { Buffer } = require('node:buffer');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.
const decipher = createDecipheriv(algorithm, key, iv);
// Encrypted using same algorithm, key and iv.
const encrypted =
'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa';
let decrypted = decipher.update(encrypted, 'hex', 'utf8');
decrypted += decipher.final('utf8');
console.log(decrypted);
// Prints: some clear text data
```
####
`decipher.final([outputEncoding])`
Added in: v0.1.94 * `outputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Any remaining deciphered contents. If `outputEncoding` is specified, a string is returned. If an `outputEncoding` is not provided, a [`Buffer`](buffer) is returned.
Once the `decipher.final()` method has been called, the `Decipher` object can no longer be used to decrypt data. Attempts to call `decipher.final()` more than once will result in an error being thrown.
####
`decipher.setAAD(buffer[, options])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The buffer argument can be a string or ArrayBuffer and is limited to no more than 2 \*\* 31 - 1 bytes. |
| v7.2.0 | This method now returns a reference to `decipher`. |
| v1.0.0 | Added in: v1.0.0 |
* `buffer` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.transform` options](stream#new-streamtransformoptions)
+ `plaintextLength` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) String encoding to use when `buffer` is a string.
* Returns: [<Decipher>](crypto#class-decipher) for method chaining.
When using an authenticated encryption mode (`GCM`, `CCM`, `OCB`, and `chacha20-poly1305` are currently supported), the `decipher.setAAD()` method sets the value used for the *additional authenticated data* (AAD) input parameter.
The `options` argument is optional for `GCM`. When using `CCM`, the `plaintextLength` option must be specified and its value must match the length of the ciphertext in bytes. See [CCM mode](#ccm-mode).
The `decipher.setAAD()` method must be called before [`decipher.update()`](#decipherupdatedata-inputencoding-outputencoding).
When passing a string as the `buffer`, please consider [caveats when using strings as inputs to cryptographic APIs](#using-strings-as-inputs-to-cryptographic-apis).
####
`decipher.setAuthTag(buffer[, encoding])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The buffer argument can be a string or ArrayBuffer and is limited to no more than 2 \*\* 31 - 1 bytes. |
| v11.0.0 | This method now throws if the GCM tag length is invalid. |
| v7.2.0 | This method now returns a reference to `decipher`. |
| v1.0.0 | Added in: v1.0.0 |
* `buffer` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) String encoding to use when `buffer` is a string.
* Returns: [<Decipher>](crypto#class-decipher) for method chaining.
When using an authenticated encryption mode (`GCM`, `CCM`, `OCB`, and `chacha20-poly1305` are currently supported), the `decipher.setAuthTag()` method is used to pass in the received *authentication tag*. If no tag is provided, or if the cipher text has been tampered with, [`decipher.final()`](#decipherfinaloutputencoding) will throw, indicating that the cipher text should be discarded due to failed authentication. If the tag length is invalid according to [NIST SP 800-38D](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf) or does not match the value of the `authTagLength` option, `decipher.setAuthTag()` will throw an error.
The `decipher.setAuthTag()` method must be called before [`decipher.update()`](#decipherupdatedata-inputencoding-outputencoding) for `CCM` mode or before [`decipher.final()`](#decipherfinaloutputencoding) for `GCM` and `OCB` modes and `chacha20-poly1305`. `decipher.setAuthTag()` can only be called once.
When passing a string as the authentication tag, please consider [caveats when using strings as inputs to cryptographic APIs](#using-strings-as-inputs-to-cryptographic-apis).
####
`decipher.setAutoPadding([autoPadding])`
Added in: v0.7.1 * `autoPadding` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`
* Returns: [<Decipher>](crypto#class-decipher) for method chaining.
When data has been encrypted without standard block padding, calling `decipher.setAutoPadding(false)` will disable automatic padding to prevent [`decipher.final()`](#decipherfinaloutputencoding) from checking for and removing padding.
Turning auto padding off will only work if the input data's length is a multiple of the ciphers block size.
The `decipher.setAutoPadding()` method must be called before [`decipher.final()`](#decipherfinaloutputencoding).
####
`decipher.update(data[, inputEncoding][, outputEncoding])`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | The default `inputEncoding` changed from `binary` to `utf8`. |
| v0.1.94 | Added in: v0.1.94 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `inputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `data` string.
* `outputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Updates the decipher with `data`. If the `inputEncoding` argument is given, the `data` argument is a string using the specified encoding. If the `inputEncoding` argument is not given, `data` must be a [`Buffer`](buffer). If `data` is a [`Buffer`](buffer) then `inputEncoding` is ignored.
The `outputEncoding` specifies the output format of the enciphered data. If the `outputEncoding` is specified, a string using the specified encoding is returned. If no `outputEncoding` is provided, a [`Buffer`](buffer) is returned.
The `decipher.update()` method can be called multiple times with new data until [`decipher.final()`](#decipherfinaloutputencoding) is called. Calling `decipher.update()` after [`decipher.final()`](#decipherfinaloutputencoding) will result in an error being thrown.
### Class: `DiffieHellman`
Added in: v0.5.0 The `DiffieHellman` class is a utility for creating Diffie-Hellman key exchanges.
Instances of the `DiffieHellman` class can be created using the [`crypto.createDiffieHellman()`](#cryptocreatediffiehellmanprime-primeencoding-generator-generatorencoding) function.
MJS modules
```
import assert from 'node:assert';
const {
createDiffieHellman
} = await import('node:crypto');
// Generate Alice's keys...
const alice = createDiffieHellman(2048);
const aliceKey = alice.generateKeys();
// Generate Bob's keys...
const bob = createDiffieHellman(alice.getPrime(), alice.getGenerator());
const bobKey = bob.generateKeys();
// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);
// OK
assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
```
CJS modules
```
const assert = require('node:assert');
const {
createDiffieHellman,
} = require('node:crypto');
// Generate Alice's keys...
const alice = createDiffieHellman(2048);
const aliceKey = alice.generateKeys();
// Generate Bob's keys...
const bob = createDiffieHellman(alice.getPrime(), alice.getGenerator());
const bobKey = bob.generateKeys();
// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);
// OK
assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
```
####
`diffieHellman.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])`
Added in: v0.5.0 * `otherPublicKey` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `inputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of an `otherPublicKey` string.
* `outputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Computes the shared secret using `otherPublicKey` as the other party's public key and returns the computed shared secret. The supplied key is interpreted using the specified `inputEncoding`, and secret is encoded using specified `outputEncoding`. If the `inputEncoding` is not provided, `otherPublicKey` is expected to be a [`Buffer`](buffer), `TypedArray`, or `DataView`.
If `outputEncoding` is given a string is returned; otherwise, a [`Buffer`](buffer) is returned.
####
`diffieHellman.generateKeys([encoding])`
Added in: v0.5.0 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Generates private and public Diffie-Hellman key values, and returns the public key in the specified `encoding`. This key should be transferred to the other party. If `encoding` is provided a string is returned; otherwise a [`Buffer`](buffer) is returned.
####
`diffieHellman.getGenerator([encoding])`
Added in: v0.5.0 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the Diffie-Hellman generator in the specified `encoding`. If `encoding` is provided a string is returned; otherwise a [`Buffer`](buffer) is returned.
####
`diffieHellman.getPrime([encoding])`
Added in: v0.5.0 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the Diffie-Hellman prime in the specified `encoding`. If `encoding` is provided a string is returned; otherwise a [`Buffer`](buffer) is returned.
####
`diffieHellman.getPrivateKey([encoding])`
Added in: v0.5.0 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the Diffie-Hellman private key in the specified `encoding`. If `encoding` is provided a string is returned; otherwise a [`Buffer`](buffer) is returned.
####
`diffieHellman.getPublicKey([encoding])`
Added in: v0.5.0 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the Diffie-Hellman public key in the specified `encoding`. If `encoding` is provided a string is returned; otherwise a [`Buffer`](buffer) is returned.
####
`diffieHellman.setPrivateKey(privateKey[, encoding])`
Added in: v0.5.0 * `privateKey` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `privateKey` string.
Sets the Diffie-Hellman private key. If the `encoding` argument is provided, `privateKey` is expected to be a string. If no `encoding` is provided, `privateKey` is expected to be a [`Buffer`](buffer), `TypedArray`, or `DataView`.
####
`diffieHellman.setPublicKey(publicKey[, encoding])`
Added in: v0.5.0 * `publicKey` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `publicKey` string.
Sets the Diffie-Hellman public key. If the `encoding` argument is provided, `publicKey` is expected to be a string. If no `encoding` is provided, `publicKey` is expected to be a [`Buffer`](buffer), `TypedArray`, or `DataView`.
####
`diffieHellman.verifyError`
Added in: v0.11.12 A bit field containing any warnings and/or errors resulting from a check performed during initialization of the `DiffieHellman` object.
The following values are valid for this property (as defined in `node:constants` module):
* `DH_CHECK_P_NOT_SAFE_PRIME`
* `DH_CHECK_P_NOT_PRIME`
* `DH_UNABLE_TO_CHECK_GENERATOR`
* `DH_NOT_SUITABLE_GENERATOR`
### Class: `DiffieHellmanGroup`
Added in: v0.7.5 The `DiffieHellmanGroup` class takes a well-known modp group as its argument. It works the same as `DiffieHellman`, except that it does not allow changing its keys after creation. In other words, it does not implement `setPublicKey()` or `setPrivateKey()` methods.
MJS modules
```
const { createDiffieHellmanGroup } = await import('node:crypto');
const dh = createDiffieHellmanGroup('modp16');
```
CJS modules
```
const { createDiffieHellmanGroup } = require('node:crypto');
const dh = createDiffieHellmanGroup('modp16');
```
The following groups are supported:
* `'modp14'` (2048 bits, [RFC 3526](https://www.rfc-editor.org/rfc/rfc3526.txt) Section 3)
* `'modp15'` (3072 bits, [RFC 3526](https://www.rfc-editor.org/rfc/rfc3526.txt) Section 4)
* `'modp16'` (4096 bits, [RFC 3526](https://www.rfc-editor.org/rfc/rfc3526.txt) Section 5)
* `'modp17'` (6144 bits, [RFC 3526](https://www.rfc-editor.org/rfc/rfc3526.txt) Section 6)
* `'modp18'` (8192 bits, [RFC 3526](https://www.rfc-editor.org/rfc/rfc3526.txt) Section 7)
The following groups are still supported but deprecated (see [Caveats](#support-for-weak-or-compromised-algorithms)):
* `'modp1'` (768 bits, [RFC 2409](https://www.rfc-editor.org/rfc/rfc2409.txt) Section 6.1)
* `'modp2'` (1024 bits, [RFC 2409](https://www.rfc-editor.org/rfc/rfc2409.txt) Section 6.2)
* `'modp5'` (1536 bits, [RFC 3526](https://www.rfc-editor.org/rfc/rfc3526.txt) Section 2)
These deprecated groups might be removed in future versions of Node.js.
### Class: `ECDH`
Added in: v0.11.14 The `ECDH` class is a utility for creating Elliptic Curve Diffie-Hellman (ECDH) key exchanges.
Instances of the `ECDH` class can be created using the [`crypto.createECDH()`](#cryptocreateecdhcurvename) function.
MJS modules
```
import assert from 'node:assert';
const {
createECDH
} = await import('node:crypto');
// Generate Alice's keys...
const alice = createECDH('secp521r1');
const aliceKey = alice.generateKeys();
// Generate Bob's keys...
const bob = createECDH('secp521r1');
const bobKey = bob.generateKeys();
// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);
assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
// OK
```
CJS modules
```
const assert = require('node:assert');
const {
createECDH,
} = require('node:crypto');
// Generate Alice's keys...
const alice = createECDH('secp521r1');
const aliceKey = alice.generateKeys();
// Generate Bob's keys...
const bob = createECDH('secp521r1');
const bobKey = bob.generateKeys();
// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);
assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
// OK
```
#### Static method: `ECDH.convertKey(key, curve[, inputEncoding[, outputEncoding[, format]]])`
Added in: v10.0.0 * `key` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `curve` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `inputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `key` string.
* `outputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'uncompressed'`
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Converts the EC Diffie-Hellman public key specified by `key` and `curve` to the format specified by `format`. The `format` argument specifies point encoding and can be `'compressed'`, `'uncompressed'` or `'hybrid'`. The supplied key is interpreted using the specified `inputEncoding`, and the returned key is encoded using the specified `outputEncoding`.
Use [`crypto.getCurves()`](#cryptogetcurves) to obtain a list of available curve names. On recent OpenSSL releases, `openssl ecparam -list_curves` will also display the name and description of each available elliptic curve.
If `format` is not specified the point will be returned in `'uncompressed'` format.
If the `inputEncoding` is not provided, `key` is expected to be a [`Buffer`](buffer), `TypedArray`, or `DataView`.
Example (uncompressing a key):
MJS modules
```
const {
createECDH,
ECDH
} = await import('node:crypto');
const ecdh = createECDH('secp256k1');
ecdh.generateKeys();
const compressedKey = ecdh.getPublicKey('hex', 'compressed');
const uncompressedKey = ECDH.convertKey(compressedKey,
'secp256k1',
'hex',
'hex',
'uncompressed');
// The converted key and the uncompressed public key should be the same
console.log(uncompressedKey === ecdh.getPublicKey('hex'));
```
CJS modules
```
const {
createECDH,
ECDH,
} = require('node:crypto');
const ecdh = createECDH('secp256k1');
ecdh.generateKeys();
const compressedKey = ecdh.getPublicKey('hex', 'compressed');
const uncompressedKey = ECDH.convertKey(compressedKey,
'secp256k1',
'hex',
'hex',
'uncompressed');
// The converted key and the uncompressed public key should be the same
console.log(uncompressedKey === ecdh.getPublicKey('hex'));
```
####
`ecdh.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Changed error format to better support invalid public key error. |
| v6.0.0 | The default `inputEncoding` changed from `binary` to `utf8`. |
| v0.11.14 | Added in: v0.11.14 |
* `otherPublicKey` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `inputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `otherPublicKey` string.
* `outputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Computes the shared secret using `otherPublicKey` as the other party's public key and returns the computed shared secret. The supplied key is interpreted using specified `inputEncoding`, and the returned secret is encoded using the specified `outputEncoding`. If the `inputEncoding` is not provided, `otherPublicKey` is expected to be a [`Buffer`](buffer), `TypedArray`, or `DataView`.
If `outputEncoding` is given a string will be returned; otherwise a [`Buffer`](buffer) is returned.
`ecdh.computeSecret` will throw an `ERR_CRYPTO_ECDH_INVALID_PUBLIC_KEY` error when `otherPublicKey` lies outside of the elliptic curve. Since `otherPublicKey` is usually supplied from a remote user over an insecure network, be sure to handle this exception accordingly.
####
`ecdh.generateKeys([encoding[, format]])`
Added in: v0.11.14 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'uncompressed'`
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Generates private and public EC Diffie-Hellman key values, and returns the public key in the specified `format` and `encoding`. This key should be transferred to the other party.
The `format` argument specifies point encoding and can be `'compressed'` or `'uncompressed'`. If `format` is not specified, the point will be returned in `'uncompressed'` format.
If `encoding` is provided a string is returned; otherwise a [`Buffer`](buffer) is returned.
####
`ecdh.getPrivateKey([encoding])`
Added in: v0.11.14 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The EC Diffie-Hellman in the specified `encoding`.
If `encoding` is specified, a string is returned; otherwise a [`Buffer`](buffer) is returned.
####
`ecdh.getPublicKey([encoding][, format])`
Added in: v0.11.14 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* `format` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) **Default:** `'uncompressed'`
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The EC Diffie-Hellman public key in the specified `encoding` and `format`.
The `format` argument specifies point encoding and can be `'compressed'` or `'uncompressed'`. If `format` is not specified the point will be returned in `'uncompressed'` format.
If `encoding` is specified, a string is returned; otherwise a [`Buffer`](buffer) is returned.
####
`ecdh.setPrivateKey(privateKey[, encoding])`
Added in: v0.11.14 * `privateKey` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `privateKey` string.
Sets the EC Diffie-Hellman private key. If `encoding` is provided, `privateKey` is expected to be a string; otherwise `privateKey` is expected to be a [`Buffer`](buffer), `TypedArray`, or `DataView`.
If `privateKey` is not valid for the curve specified when the `ECDH` object was created, an error is thrown. Upon setting the private key, the associated public point (key) is also generated and set in the `ECDH` object.
####
`ecdh.setPublicKey(publicKey[, encoding])`
Added in: v0.11.14Deprecated since: v5.2.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
* `publicKey` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `publicKey` string.
Sets the EC Diffie-Hellman public key. If `encoding` is provided `publicKey` is expected to be a string; otherwise a [`Buffer`](buffer), `TypedArray`, or `DataView` is expected.
There is not normally a reason to call this method because `ECDH` only requires a private key and the other party's public key to compute the shared secret. Typically either [`ecdh.generateKeys()`](#ecdhgeneratekeysencoding-format) or [`ecdh.setPrivateKey()`](#ecdhsetprivatekeyprivatekey-encoding) will be called. The [`ecdh.setPrivateKey()`](#ecdhsetprivatekeyprivatekey-encoding) method attempts to generate the public point/key associated with the private key being set.
Example (obtaining a shared secret):
MJS modules
```
const {
createECDH,
createHash
} = await import('node:crypto');
const alice = createECDH('secp256k1');
const bob = createECDH('secp256k1');
// This is a shortcut way of specifying one of Alice's previous private
// keys. It would be unwise to use such a predictable private key in a real
// application.
alice.setPrivateKey(
createHash('sha256').update('alice', 'utf8').digest()
);
// Bob uses a newly generated cryptographically strong
// pseudorandom key pair
bob.generateKeys();
const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
// aliceSecret and bobSecret should be the same shared secret value
console.log(aliceSecret === bobSecret);
```
CJS modules
```
const {
createECDH,
createHash,
} = require('node:crypto');
const alice = createECDH('secp256k1');
const bob = createECDH('secp256k1');
// This is a shortcut way of specifying one of Alice's previous private
// keys. It would be unwise to use such a predictable private key in a real
// application.
alice.setPrivateKey(
createHash('sha256').update('alice', 'utf8').digest()
);
// Bob uses a newly generated cryptographically strong
// pseudorandom key pair
bob.generateKeys();
const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
// aliceSecret and bobSecret should be the same shared secret value
console.log(aliceSecret === bobSecret);
```
### Class: `Hash`
Added in: v0.1.92 * Extends: [<stream.Transform>](stream#class-streamtransform)
The `Hash` class is a utility for creating hash digests of data. It can be used in one of two ways:
* As a <stream> that is both readable and writable, where data is written to produce a computed hash digest on the readable side, or
* Using the [`hash.update()`](#hashupdatedata-inputencoding) and [`hash.digest()`](#hashdigestencoding) methods to produce the computed hash.
The [`crypto.createHash()`](#cryptocreatehashalgorithm-options) method is used to create `Hash` instances. `Hash` objects are not to be created directly using the `new` keyword.
Example: Using `Hash` objects as streams:
MJS modules
```
const {
createHash
} = await import('node:crypto');
const hash = createHash('sha256');
hash.on('readable', () => {
// Only one element is going to be produced by the
// hash stream.
const data = hash.read();
if (data) {
console.log(data.toString('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
}
});
hash.write('some data to hash');
hash.end();
```
CJS modules
```
const {
createHash,
} = require('node:crypto');
const hash = createHash('sha256');
hash.on('readable', () => {
// Only one element is going to be produced by the
// hash stream.
const data = hash.read();
if (data) {
console.log(data.toString('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
}
});
hash.write('some data to hash');
hash.end();
```
Example: Using `Hash` and piped streams:
MJS modules
```
import { createReadStream } from 'node:fs';
import { stdout } from 'node:process';
const { createHash } = await import('node:crypto');
const hash = createHash('sha256');
const input = createReadStream('test.js');
input.pipe(hash).setEncoding('hex').pipe(stdout);
```
CJS modules
```
const { createReadStream } = require('node:fs');
const { createHash } = require('node:crypto');
const { stdout } = require('node:process');
const hash = createHash('sha256');
const input = createReadStream('test.js');
input.pipe(hash).setEncoding('hex').pipe(stdout);
```
Example: Using the [`hash.update()`](#hashupdatedata-inputencoding) and [`hash.digest()`](#hashdigestencoding) methods:
MJS modules
```
const {
createHash
} = await import('node:crypto');
const hash = createHash('sha256');
hash.update('some data to hash');
console.log(hash.digest('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
```
CJS modules
```
const {
createHash,
} = require('node:crypto');
const hash = createHash('sha256');
hash.update('some data to hash');
console.log(hash.digest('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
```
####
`hash.copy([options])`
Added in: v13.1.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.transform` options](stream#new-streamtransformoptions)
* Returns: [<Hash>](crypto#class-hash)
Creates a new `Hash` object that contains a deep copy of the internal state of the current `Hash` object.
The optional `options` argument controls stream behavior. For XOF hash functions such as `'shake256'`, the `outputLength` option can be used to specify the desired output length in bytes.
An error is thrown when an attempt is made to copy the `Hash` object after its [`hash.digest()`](#hashdigestencoding) method has been called.
MJS modules
```
// Calculate a rolling hash.
const {
createHash
} = await import('node:crypto');
const hash = createHash('sha256');
hash.update('one');
console.log(hash.copy().digest('hex'));
hash.update('two');
console.log(hash.copy().digest('hex'));
hash.update('three');
console.log(hash.copy().digest('hex'));
// Etc.
```
CJS modules
```
// Calculate a rolling hash.
const {
createHash,
} = require('node:crypto');
const hash = createHash('sha256');
hash.update('one');
console.log(hash.copy().digest('hex'));
hash.update('two');
console.log(hash.copy().digest('hex'));
hash.update('three');
console.log(hash.copy().digest('hex'));
// Etc.
```
####
`hash.digest([encoding])`
Added in: v0.1.92 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Calculates the digest of all of the data passed to be hashed (using the [`hash.update()`](#hashupdatedata-inputencoding) method). If `encoding` is provided a string will be returned; otherwise a [`Buffer`](buffer) is returned.
The `Hash` object can not be used again after `hash.digest()` method has been called. Multiple calls will cause an error to be thrown.
####
`hash.update(data[, inputEncoding])`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | The default `inputEncoding` changed from `binary` to `utf8`. |
| v0.1.92 | Added in: v0.1.92 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `inputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `data` string.
Updates the hash content with the given `data`, the encoding of which is given in `inputEncoding`. If `encoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a [`Buffer`](buffer), `TypedArray`, or `DataView`, then `inputEncoding` is ignored.
This can be called many times with new data as it is streamed.
### Class: `Hmac`
Added in: v0.1.94 * Extends: [<stream.Transform>](stream#class-streamtransform)
The `Hmac` class is a utility for creating cryptographic HMAC digests. It can be used in one of two ways:
* As a <stream> that is both readable and writable, where data is written to produce a computed HMAC digest on the readable side, or
* Using the [`hmac.update()`](#hmacupdatedata-inputencoding) and [`hmac.digest()`](#hmacdigestencoding) methods to produce the computed HMAC digest.
The [`crypto.createHmac()`](#cryptocreatehmacalgorithm-key-options) method is used to create `Hmac` instances. `Hmac` objects are not to be created directly using the `new` keyword.
Example: Using `Hmac` objects as streams:
MJS modules
```
const {
createHmac
} = await import('node:crypto');
const hmac = createHmac('sha256', 'a secret');
hmac.on('readable', () => {
// Only one element is going to be produced by the
// hash stream.
const data = hmac.read();
if (data) {
console.log(data.toString('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
}
});
hmac.write('some data to hash');
hmac.end();
```
CJS modules
```
const {
createHmac,
} = require('node:crypto');
const hmac = createHmac('sha256', 'a secret');
hmac.on('readable', () => {
// Only one element is going to be produced by the
// hash stream.
const data = hmac.read();
if (data) {
console.log(data.toString('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
}
});
hmac.write('some data to hash');
hmac.end();
```
Example: Using `Hmac` and piped streams:
MJS modules
```
import { createReadStream } from 'node:fs';
import { stdout } from 'node:process';
const {
createHmac
} = await import('node:crypto');
const hmac = createHmac('sha256', 'a secret');
const input = createReadStream('test.js');
input.pipe(hmac).pipe(stdout);
```
CJS modules
```
const {
createReadStream,
} = require('node:fs');
const {
createHmac,
} = require('node:crypto');
const { stdout } = require('node:process');
const hmac = createHmac('sha256', 'a secret');
const input = createReadStream('test.js');
input.pipe(hmac).pipe(stdout);
```
Example: Using the [`hmac.update()`](#hmacupdatedata-inputencoding) and [`hmac.digest()`](#hmacdigestencoding) methods:
MJS modules
```
const {
createHmac
} = await import('node:crypto');
const hmac = createHmac('sha256', 'a secret');
hmac.update('some data to hash');
console.log(hmac.digest('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
```
CJS modules
```
const {
createHmac,
} = require('node:crypto');
const hmac = createHmac('sha256', 'a secret');
hmac.update('some data to hash');
console.log(hmac.digest('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
```
####
`hmac.digest([encoding])`
Added in: v0.1.94 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Calculates the HMAC digest of all of the data passed using [`hmac.update()`](#hmacupdatedata-inputencoding). If `encoding` is provided a string is returned; otherwise a [`Buffer`](buffer) is returned;
The `Hmac` object can not be used again after `hmac.digest()` has been called. Multiple calls to `hmac.digest()` will result in an error being thrown.
####
`hmac.update(data[, inputEncoding])`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | The default `inputEncoding` changed from `binary` to `utf8`. |
| v0.1.94 | Added in: v0.1.94 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `inputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `data` string.
Updates the `Hmac` content with the given `data`, the encoding of which is given in `inputEncoding`. If `encoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a [`Buffer`](buffer), `TypedArray`, or `DataView`, then `inputEncoding` is ignored.
This can be called many times with new data as it is streamed.
### Class: `KeyObject`
History
| Version | Changes |
| --- | --- |
| v14.5.0, v12.19.0 | Instances of this class can now be passed to worker threads using `postMessage`. |
| v11.13.0 | This class is now exported. |
| v11.6.0 | Added in: v11.6.0 |
Node.js uses a `KeyObject` class to represent a symmetric or asymmetric key, and each kind of key exposes different functions. The [`crypto.createSecretKey()`](#cryptocreatesecretkeykey-encoding), [`crypto.createPublicKey()`](#cryptocreatepublickeykey) and [`crypto.createPrivateKey()`](#cryptocreateprivatekeykey) methods are used to create `KeyObject` instances. `KeyObject` objects are not to be created directly using the `new` keyword.
Most applications should consider using the new `KeyObject` API instead of passing keys as strings or `Buffer`s due to improved security features.
`KeyObject` instances can be passed to other threads via [`postMessage()`](worker_threads#portpostmessagevalue-transferlist). The receiver obtains a cloned `KeyObject`, and the `KeyObject` does not need to be listed in the `transferList` argument.
#### Static method: `KeyObject.from(key)`
Added in: v15.0.0 * `key` [<CryptoKey>](webcrypto#class-cryptokey)
* Returns: [<KeyObject>](crypto#class-keyobject)
Example: Converting a `CryptoKey` instance to a `KeyObject`:
MJS modules
```
const { webcrypto, KeyObject } = await import('node:crypto');
const { subtle } = webcrypto;
const key = await subtle.generateKey({
name: 'HMAC',
hash: 'SHA-256',
length: 256
}, true, ['sign', 'verify']);
const keyObject = KeyObject.from(key);
console.log(keyObject.symmetricKeySize);
// Prints: 32 (symmetric key size in bytes)
```
CJS modules
```
const {
webcrypto: {
subtle,
},
KeyObject,
} = require('node:crypto');
(async function() {
const key = await subtle.generateKey({
name: 'HMAC',
hash: 'SHA-256',
length: 256
}, true, ['sign', 'verify']);
const keyObject = KeyObject.from(key);
console.log(keyObject.symmetricKeySize);
// Prints: 32 (symmetric key size in bytes)
})();
```
####
`keyObject.asymmetricKeyDetails`
History
| Version | Changes |
| --- | --- |
| v16.9.0 | Expose `RSASSA-PSS-params` sequence parameters for RSA-PSS keys. |
| v15.7.0 | Added in: v15.7.0 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `modulusLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Key size in bits (RSA, DSA).
+ `publicExponent`: [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) Public exponent (RSA).
+ `hashAlgorithm`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the message digest (RSA-PSS).
+ `mgf1HashAlgorithm`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the message digest used by MGF1 (RSA-PSS).
+ `saltLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Minimal salt length in bytes (RSA-PSS).
+ `divisorLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Size of `q` in bits (DSA).
+ `namedCurve`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the curve (EC).
This property exists only on asymmetric keys. Depending on the type of the key, this object contains information about the key. None of the information obtained through this property can be used to uniquely identify a key or to compromise the security of the key.
For RSA-PSS keys, if the key material contains a `RSASSA-PSS-params` sequence, the `hashAlgorithm`, `mgf1HashAlgorithm`, and `saltLength` properties will be set.
Other key details might be exposed via this API using additional attributes.
####
`keyObject.asymmetricKeyType`
History
| Version | Changes |
| --- | --- |
| v13.9.0, v12.17.0 | Added support for `'dh'`. |
| v12.0.0 | Added support for `'rsa-pss'`. |
| v12.0.0 | This property now returns `undefined` for KeyObject instances of unrecognized type instead of aborting. |
| v12.0.0 | Added support for `'x25519'` and `'x448'`. |
| v12.0.0 | Added support for `'ed25519'` and `'ed448'`. |
| v11.6.0 | Added in: v11.6.0 |
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
For asymmetric keys, this property represents the type of the key. Supported key types are:
* `'rsa'` (OID 1.2.840.113549.1.1.1)
* `'rsa-pss'` (OID 1.2.840.113549.1.1.10)
* `'dsa'` (OID 1.2.840.10040.4.1)
* `'ec'` (OID 1.2.840.10045.2.1)
* `'x25519'` (OID 1.3.101.110)
* `'x448'` (OID 1.3.101.111)
* `'ed25519'` (OID 1.3.101.112)
* `'ed448'` (OID 1.3.101.113)
* `'dh'` (OID 1.2.840.113549.1.3.1)
This property is `undefined` for unrecognized `KeyObject` types and symmetric keys.
####
`keyObject.export([options])`
History
| Version | Changes |
| --- | --- |
| v15.9.0 | Added support for `'jwk'` format. |
| v11.6.0 | Added in: v11.6.0 |
* `options`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
For symmetric keys, the following encoding options can be used:
* `format`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'buffer'` (default) or `'jwk'`.
For public keys, the following encoding options can be used:
* `type`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'pkcs1'` (RSA only) or `'spki'`.
* `format`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'pem'`, `'der'`, or `'jwk'`.
For private keys, the following encoding options can be used:
* `type`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'pkcs1'` (RSA only), `'pkcs8'` or `'sec1'` (EC only).
* `format`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'pem'`, `'der'`, or `'jwk'`.
* `cipher`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) If specified, the private key will be encrypted with the given `cipher` and `passphrase` using PKCS#5 v2.0 password based encryption.
* `passphrase`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) The passphrase to use for encryption, see `cipher`.
The result type depends on the selected encoding format, when PEM the result is a string, when DER it will be a buffer containing the data encoded as DER, when [JWK](https://tools.ietf.org/html/rfc7517) it will be an object.
When [JWK](https://tools.ietf.org/html/rfc7517) encoding format was selected, all other encoding options are ignored.
PKCS#1, SEC1, and PKCS#8 type keys can be encrypted by using a combination of the `cipher` and `format` options. The PKCS#8 `type` can be used with any `format` to encrypt any key algorithm (RSA, EC, or DH) by specifying a `cipher`. PKCS#1 and SEC1 can only be encrypted by specifying a `cipher` when the PEM `format` is used. For maximum compatibility, use PKCS#8 for encrypted private keys. Since PKCS#8 defines its own encryption mechanism, PEM-level encryption is not supported when encrypting a PKCS#8 key. See [RFC 5208](https://www.rfc-editor.org/rfc/rfc5208.txt) for PKCS#8 encryption and [RFC 1421](https://www.rfc-editor.org/rfc/rfc1421.txt) for PKCS#1 and SEC1 encryption.
####
`keyObject.equals(otherKeyObject)`
Added in: v17.7.0, v16.15.0 * `otherKeyObject`: [<KeyObject>](crypto#class-keyobject) A `KeyObject` with which to compare `keyObject`.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` or `false` depending on whether the keys have exactly the same type, value, and parameters. This method is not [constant time](https://en.wikipedia.org/wiki/Timing_attack).
####
`keyObject.symmetricKeySize`
Added in: v11.6.0 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
For secret keys, this property represents the size of the key in bytes. This property is `undefined` for asymmetric keys.
####
`keyObject.type`
Added in: v11.6.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Depending on the type of this `KeyObject`, this property is either `'secret'` for secret (symmetric) keys, `'public'` for public (asymmetric) keys or `'private'` for private (asymmetric) keys.
### Class: `Sign`
Added in: v0.1.92 * Extends: [<stream.Writable>](stream#class-streamwritable)
The `Sign` class is a utility for generating signatures. It can be used in one of two ways:
* As a writable <stream>, where data to be signed is written and the [`sign.sign()`](#signsignprivatekey-outputencoding) method is used to generate and return the signature, or
* Using the [`sign.update()`](#signupdatedata-inputencoding) and [`sign.sign()`](#signsignprivatekey-outputencoding) methods to produce the signature.
The [`crypto.createSign()`](#cryptocreatesignalgorithm-options) method is used to create `Sign` instances. The argument is the string name of the hash function to use. `Sign` objects are not to be created directly using the `new` keyword.
Example: Using `Sign` and [`Verify`](#class-verify) objects as streams:
MJS modules
```
const {
generateKeyPairSync,
createSign,
createVerify
} = await import('node:crypto');
const { privateKey, publicKey } = generateKeyPairSync('ec', {
namedCurve: 'sect239k1'
});
const sign = createSign('SHA256');
sign.write('some data to sign');
sign.end();
const signature = sign.sign(privateKey, 'hex');
const verify = createVerify('SHA256');
verify.write('some data to sign');
verify.end();
console.log(verify.verify(publicKey, signature, 'hex'));
// Prints: true
```
CJS modules
```
const {
generateKeyPairSync,
createSign,
createVerify,
} = require('node:crypto');
const { privateKey, publicKey } = generateKeyPairSync('ec', {
namedCurve: 'sect239k1'
});
const sign = createSign('SHA256');
sign.write('some data to sign');
sign.end();
const signature = sign.sign(privateKey, 'hex');
const verify = createVerify('SHA256');
verify.write('some data to sign');
verify.end();
console.log(verify.verify(publicKey, signature, 'hex'));
// Prints: true
```
Example: Using the [`sign.update()`](#signupdatedata-inputencoding) and [`verify.update()`](#verifyupdatedata-inputencoding) methods:
MJS modules
```
const {
generateKeyPairSync,
createSign,
createVerify
} = await import('node:crypto');
const { privateKey, publicKey } = generateKeyPairSync('rsa', {
modulusLength: 2048,
});
const sign = createSign('SHA256');
sign.update('some data to sign');
sign.end();
const signature = sign.sign(privateKey);
const verify = createVerify('SHA256');
verify.update('some data to sign');
verify.end();
console.log(verify.verify(publicKey, signature));
// Prints: true
```
CJS modules
```
const {
generateKeyPairSync,
createSign,
createVerify,
} = require('node:crypto');
const { privateKey, publicKey } = generateKeyPairSync('rsa', {
modulusLength: 2048,
});
const sign = createSign('SHA256');
sign.update('some data to sign');
sign.end();
const signature = sign.sign(privateKey);
const verify = createVerify('SHA256');
verify.update('some data to sign');
verify.end();
console.log(verify.verify(publicKey, signature));
// Prints: true
```
####
`sign.sign(privateKey[, outputEncoding])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The privateKey can also be an ArrayBuffer and CryptoKey. |
| v13.2.0, v12.16.0 | This function now supports IEEE-P1363 DSA and ECDSA signatures. |
| v12.0.0 | This function now supports RSA-PSS keys. |
| v11.6.0 | This function now supports key objects. |
| v8.0.0 | Support for RSASSA-PSS and additional options was added. |
| v0.1.92 | Added in: v0.1.92 |
* `privateKey` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
+ `dsaEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `padding` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `saltLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `outputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the return value.
* Returns: [<Buffer>](buffer#class-buffer) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Calculates the signature on all the data passed through using either [`sign.update()`](#signupdatedata-inputencoding) or [`sign.write()`](stream#writablewritechunk-encoding-callback).
If `privateKey` is not a [`KeyObject`](#class-keyobject), this function behaves as if `privateKey` had been passed to [`crypto.createPrivateKey()`](#cryptocreateprivatekeykey). If it is an object, the following additional properties can be passed:
* `dsaEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) For DSA and ECDSA, this option specifies the format of the generated signature. It can be one of the following:
+ `'der'` (default): DER-encoded ASN.1 signature structure encoding `(r, s)`.
+ `'ieee-p1363'`: Signature format `r || s` as proposed in IEEE-P1363.
* `padding` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optional padding value for RSA, one of the following:
+ `crypto.constants.RSA_PKCS1_PADDING` (default)
+ `crypto.constants.RSA_PKCS1_PSS_PADDING``RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function used to sign the message as specified in section 3.1 of [RFC 4055](https://www.rfc-editor.org/rfc/rfc4055.txt), unless an MGF1 hash function has been specified as part of the key in compliance with section 3.3 of [RFC 4055](https://www.rfc-editor.org/rfc/rfc4055.txt).
* `saltLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Salt length for when padding is `RSA_PKCS1_PSS_PADDING`. The special value `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest size, `crypto.constants.RSA_PSS_SALTLEN_MAX_SIGN` (default) sets it to the maximum permissible value.
If `outputEncoding` is provided a string is returned; otherwise a [`Buffer`](buffer) is returned.
The `Sign` object can not be again used after `sign.sign()` method has been called. Multiple calls to `sign.sign()` will result in an error being thrown.
####
`sign.update(data[, inputEncoding])`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | The default `inputEncoding` changed from `binary` to `utf8`. |
| v0.1.92 | Added in: v0.1.92 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `inputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `data` string.
Updates the `Sign` content with the given `data`, the encoding of which is given in `inputEncoding`. If `encoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a [`Buffer`](buffer), `TypedArray`, or `DataView`, then `inputEncoding` is ignored.
This can be called many times with new data as it is streamed.
### Class: `Verify`
Added in: v0.1.92 * Extends: [<stream.Writable>](stream#class-streamwritable)
The `Verify` class is a utility for verifying signatures. It can be used in one of two ways:
* As a writable <stream> where written data is used to validate against the supplied signature, or
* Using the [`verify.update()`](#verifyupdatedata-inputencoding) and [`verify.verify()`](#verifyverifyobject-signature-signatureencoding) methods to verify the signature.
The [`crypto.createVerify()`](#cryptocreateverifyalgorithm-options) method is used to create `Verify` instances. `Verify` objects are not to be created directly using the `new` keyword.
See [`Sign`](#class-sign) for examples.
####
`verify.update(data[, inputEncoding])`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | The default `inputEncoding` changed from `binary` to `utf8`. |
| v0.1.92 | Added in: v0.1.92 |
* `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `inputEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `data` string.
Updates the `Verify` content with the given `data`, the encoding of which is given in `inputEncoding`. If `inputEncoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a [`Buffer`](buffer), `TypedArray`, or `DataView`, then `inputEncoding` is ignored.
This can be called many times with new data as it is streamed.
####
`verify.verify(object, signature[, signatureEncoding])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The object can also be an ArrayBuffer and CryptoKey. |
| v13.2.0, v12.16.0 | This function now supports IEEE-P1363 DSA and ECDSA signatures. |
| v12.0.0 | This function now supports RSA-PSS keys. |
| v11.7.0 | The key can now be a private key. |
| v8.0.0 | Support for RSASSA-PSS and additional options was added. |
| v0.1.92 | Added in: v0.1.92 |
* `object` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
+ `dsaEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `padding` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `saltLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `signature` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `signatureEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `signature` string.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` or `false` depending on the validity of the signature for the data and public key.
Verifies the provided data using the given `object` and `signature`.
If `object` is not a [`KeyObject`](#class-keyobject), this function behaves as if `object` had been passed to [`crypto.createPublicKey()`](#cryptocreatepublickeykey). If it is an object, the following additional properties can be passed:
* `dsaEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) For DSA and ECDSA, this option specifies the format of the signature. It can be one of the following:
+ `'der'` (default): DER-encoded ASN.1 signature structure encoding `(r, s)`.
+ `'ieee-p1363'`: Signature format `r || s` as proposed in IEEE-P1363.
* `padding` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optional padding value for RSA, one of the following:
+ `crypto.constants.RSA_PKCS1_PADDING` (default)
+ `crypto.constants.RSA_PKCS1_PSS_PADDING``RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function used to verify the message as specified in section 3.1 of [RFC 4055](https://www.rfc-editor.org/rfc/rfc4055.txt), unless an MGF1 hash function has been specified as part of the key in compliance with section 3.3 of [RFC 4055](https://www.rfc-editor.org/rfc/rfc4055.txt).
* `saltLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Salt length for when padding is `RSA_PKCS1_PSS_PADDING`. The special value `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest size, `crypto.constants.RSA_PSS_SALTLEN_AUTO` (default) causes it to be determined automatically.
The `signature` argument is the previously calculated signature for the data, in the `signatureEncoding`. If a `signatureEncoding` is specified, the `signature` is expected to be a string; otherwise `signature` is expected to be a [`Buffer`](buffer), `TypedArray`, or `DataView`.
The `verify` object can not be used again after `verify.verify()` has been called. Multiple calls to `verify.verify()` will result in an error being thrown.
Because public keys can be derived from private keys, a private key may be passed instead of a public key.
### Class: `X509Certificate`
Added in: v15.6.0 Encapsulates an X509 certificate and provides read-only access to its information.
MJS modules
```
const { X509Certificate } = await import('node:crypto');
const x509 = new X509Certificate('{... pem encoded cert ...}');
console.log(x509.subject);
```
CJS modules
```
const { X509Certificate } = require('node:crypto');
const x509 = new X509Certificate('{... pem encoded cert ...}');
console.log(x509.subject);
```
####
`new X509Certificate(buffer)`
Added in: v15.6.0 * `buffer` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<Buffer>](buffer#class-buffer) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A PEM or DER encoded X509 Certificate.
####
`x509.ca`
Added in: v15.6.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Will be `true` if this is a Certificate Authority (CA) certificate.
####
`x509.checkEmail(email[, options])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | The subject option now defaults to `'default'`. |
| v17.5.0, v16.15.0 | The subject option can now be set to `'default'`. |
| v17.5.0, v16.14.1 | The `wildcards`, `partialWildcards`, `multiLabelWildcards`, and `singleLabelSubdomains` options have been removed since they had no effect. |
| v15.6.0 | Added in: v15.6.0 |
* `email` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `subject` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) `'default'`, `'always'`, or `'never'`. **Default:** `'default'`.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Returns `email` if the certificate matches, `undefined` if it does not.
Checks whether the certificate matches the given email address.
If the `'subject'` option is undefined or set to `'default'`, the certificate subject is only considered if the subject alternative name extension either does not exist or does not contain any email addresses.
If the `'subject'` option is set to `'always'` and if the subject alternative name extension either does not exist or does not contain a matching email address, the certificate subject is considered.
If the `'subject'` option is set to `'never'`, the certificate subject is never considered, even if the certificate contains no subject alternative names.
####
`x509.checkHost(name[, options])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | The subject option now defaults to `'default'`. |
| v17.5.0, v16.15.0 | The subject option can now be set to `'default'`. |
| v15.6.0 | Added in: v15.6.0 |
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `subject` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) `'default'`, `'always'`, or `'never'`. **Default:** `'default'`.
+ `wildcards` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`.
+ `partialWildcards` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `true`.
+ `multiLabelWildcards` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`.
+ `singleLabelSubdomains` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Returns a subject name that matches `name`, or `undefined` if no subject name matches `name`.
Checks whether the certificate matches the given host name.
If the certificate matches the given host name, the matching subject name is returned. The returned name might be an exact match (e.g., `foo.example.com`) or it might contain wildcards (e.g., `*.example.com`). Because host name comparisons are case-insensitive, the returned subject name might also differ from the given `name` in capitalization.
If the `'subject'` option is undefined or set to `'default'`, the certificate subject is only considered if the subject alternative name extension either does not exist or does not contain any DNS names. This behavior is consistent with [RFC 2818](https://www.rfc-editor.org/rfc/rfc2818.txt) ("HTTP Over TLS").
If the `'subject'` option is set to `'always'` and if the subject alternative name extension either does not exist or does not contain a matching DNS name, the certificate subject is considered.
If the `'subject'` option is set to `'never'`, the certificate subject is never considered, even if the certificate contains no subject alternative names.
####
`x509.checkIP(ip)`
History
| Version | Changes |
| --- | --- |
| v17.5.0, v16.14.1 | The `options` argument has been removed since it had no effect. |
| v15.6.0 | Added in: v15.6.0 |
* `ip` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) Returns `ip` if the certificate matches, `undefined` if it does not.
Checks whether the certificate matches the given IP address (IPv4 or IPv6).
Only [RFC 5280](https://www.rfc-editor.org/rfc/rfc5280.txt) `iPAddress` subject alternative names are considered, and they must match the given `ip` address exactly. Other subject alternative names as well as the subject field of the certificate are ignored.
####
`x509.checkIssued(otherCert)`
Added in: v15.6.0 * `otherCert` [<X509Certificate>](crypto#class-x509certificate)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Checks whether this certificate was issued by the given `otherCert`.
####
`x509.checkPrivateKey(privateKey)`
Added in: v15.6.0 * `privateKey` [<KeyObject>](crypto#class-keyobject) A private key.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Checks whether the public key for this certificate is consistent with the given private key.
####
`x509.fingerprint`
Added in: v15.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The SHA-1 fingerprint of this certificate.
Because SHA-1 is cryptographically broken and because the security of SHA-1 is significantly worse than that of algorithms that are commonly used to sign certificates, consider using [`x509.fingerprint256`](#x509fingerprint256) instead.
####
`x509.fingerprint256`
Added in: v15.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The SHA-256 fingerprint of this certificate.
####
`x509.fingerprint512`
Added in: v17.2.0, v16.14.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The SHA-512 fingerprint of this certificate.
Because computing the SHA-256 fingerprint is usually faster and because it is only half the size of the SHA-512 fingerprint, [`x509.fingerprint256`](#x509fingerprint256) may be a better choice. While SHA-512 presumably provides a higher level of security in general, the security of SHA-256 matches that of most algorithms that are commonly used to sign certificates.
####
`x509.infoAccess`
History
| Version | Changes |
| --- | --- |
| v17.3.1, v16.13.2 | Parts of this string may be encoded as JSON string literals in response to CVE-2021-44532. |
| v15.6.0 | Added in: v15.6.0 |
* Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
A textual representation of the certificate's authority information access extension.
This is a line feed separated list of access descriptions. Each line begins with the access method and the kind of the access location, followed by a colon and the value associated with the access location.
After the prefix denoting the access method and the kind of the access location, the remainder of each line might be enclosed in quotes to indicate that the value is a JSON string literal. For backward compatibility, Node.js only uses JSON string literals within this property when necessary to avoid ambiguity. Third-party code should be prepared to handle both possible entry formats.
####
`x509.issuer`
Added in: v15.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The issuer identification included in this certificate.
####
`x509.issuerCertificate`
Added in: v15.9.0 * Type: [<X509Certificate>](crypto#class-x509certificate)
The issuer certificate or `undefined` if the issuer certificate is not available.
####
`x509.keyUsage`
Added in: v15.6.0 * Type: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
An array detailing the key usages for this certificate.
####
`x509.publicKey`
Added in: v15.6.0 * Type: [<KeyObject>](crypto#class-keyobject)
The public key [<KeyObject>](crypto#class-keyobject) for this certificate.
####
`x509.raw`
Added in: v15.6.0 * Type: [<Buffer>](buffer#class-buffer)
A `Buffer` containing the DER encoding of this certificate.
####
`x509.serialNumber`
Added in: v15.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The serial number of this certificate.
Serial numbers are assigned by certificate authorities and do not uniquely identify certificates. Consider using [`x509.fingerprint256`](#x509fingerprint256) as a unique identifier instead.
####
`x509.subject`
Added in: v15.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The complete subject of this certificate.
####
`x509.subjectAltName`
History
| Version | Changes |
| --- | --- |
| v17.3.1, v16.13.2 | Parts of this string may be encoded as JSON string literals in response to CVE-2021-44532. |
| v15.6.0 | Added in: v15.6.0 |
* Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The subject alternative name specified for this certificate.
This is a comma-separated list of subject alternative names. Each entry begins with a string identifying the kind of the subject alternative name followed by a colon and the value associated with the entry.
Earlier versions of Node.js incorrectly assumed that it is safe to split this property at the two-character sequence `', '` (see [CVE-2021-44532](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-44532)). However, both malicious and legitimate certificates can contain subject alternative names that include this sequence when represented as a string.
After the prefix denoting the type of the entry, the remainder of each entry might be enclosed in quotes to indicate that the value is a JSON string literal. For backward compatibility, Node.js only uses JSON string literals within this property when necessary to avoid ambiguity. Third-party code should be prepared to handle both possible entry formats.
####
`x509.toJSON()`
Added in: v15.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
There is no standard JSON encoding for X509 certificates. The `toJSON()` method returns a string containing the PEM encoded certificate.
####
`x509.toLegacyObject()`
Added in: v15.6.0 * Type: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns information about this certificate using the legacy [certificate object](tls#certificate-object) encoding.
####
`x509.toString()`
Added in: v15.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the PEM-encoded certificate.
####
`x509.validFrom`
Added in: v15.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The date/time from which this certificate is considered valid.
####
`x509.validTo`
Added in: v15.6.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The date/time until which this certificate is considered valid.
####
`x509.verify(publicKey)`
Added in: v15.6.0 * `publicKey` [<KeyObject>](crypto#class-keyobject) A public key.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Verifies that this certificate was signed by the given public key. Does not perform any other validation checks on the certificate.
###
`node:crypto` module methods and properties
####
`crypto.constants`
Added in: v6.3.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
An object containing commonly used constants for crypto and security related operations. The specific constants currently defined are described in [Crypto constants](#crypto-constants).
####
`crypto.DEFAULT_ENCODING`
Added in: v0.9.3Deprecated since: v10.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
The default encoding to use for functions that can take either strings or [buffers](buffer). The default value is `'buffer'`, which makes methods default to [`Buffer`](buffer) objects.
The `crypto.DEFAULT_ENCODING` mechanism is provided for backward compatibility with legacy programs that expect `'latin1'` to be the default encoding.
New applications should expect the default to be `'buffer'`.
This property is deprecated.
####
`crypto.fips`
Added in: v6.0.0Deprecated since: v10.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
Property for checking and controlling whether a FIPS compliant crypto provider is currently in use. Setting to true requires a FIPS build of Node.js.
This property is deprecated. Please use `crypto.setFips()` and `crypto.getFips()` instead.
####
`crypto.checkPrime(candidate[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v15.8.0 | Added in: v15.8.0 |
* `candidate` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<Buffer>](buffer#class-buffer) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) A possible prime encoded as a sequence of big endian octets of arbitrary length.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `checks` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of Miller-Rabin probabilistic primality iterations to perform. When the value is `0` (zero), a number of checks is used that yields a false positive rate of at most 2-64 for random input. Care must be used when selecting a number of checks. Refer to the OpenSSL documentation for the [`BN_is_prime_ex`](https://www.openssl.org/docs/man1.1.1/man3/BN_is_prime_ex.html) function `nchecks` options for more details. **Default:** `0`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) Set to an [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) object if an error occurred during check.
+ `result` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the candidate is a prime with an error probability less than `0.25 ** options.checks`.
Checks the primality of the `candidate`.
####
`crypto.checkPrimeSync(candidate[, options])`
Added in: v15.8.0 * `candidate` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<Buffer>](buffer#class-buffer) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) A possible prime encoded as a sequence of big endian octets of arbitrary length.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `checks` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of Miller-Rabin probabilistic primality iterations to perform. When the value is `0` (zero), a number of checks is used that yields a false positive rate of at most 2-64 for random input. Care must be used when selecting a number of checks. Refer to the OpenSSL documentation for the [`BN_is_prime_ex`](https://www.openssl.org/docs/man1.1.1/man3/BN_is_prime_ex.html) function `nchecks` options for more details. **Default:** `0`
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the candidate is a prime with an error probability less than `0.25 ** options.checks`.
Checks the primality of the `candidate`.
####
`crypto.createCipher(algorithm, password[, options])`
History
| Version | Changes |
| --- | --- |
| v17.9.0, v16.17.0 | The `authTagLength` option is now optional when using the `chacha20-poly1305` cipher and defaults to 16 bytes. |
| v15.0.0 | The password argument can be an ArrayBuffer and is limited to a maximum of 2 \*\* 31 - 1 bytes. |
| v10.10.0 | Ciphers in OCB mode are now supported. |
| v10.2.0 | The `authTagLength` option can now be used to produce shorter authentication tags in GCM mode and defaults to 16 bytes. |
| v10.0.0 | Deprecated since: v10.0.0 |
| v0.1.94 | Added in: v0.1.94 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`crypto.createCipheriv()`](#cryptocreatecipherivalgorithm-key-iv-options) instead.
* `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `password` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.transform` options](stream#new-streamtransformoptions)
* Returns: [<Cipher>](crypto#class-cipher)
Creates and returns a `Cipher` object that uses the given `algorithm` and `password`.
The `options` argument controls stream behavior and is optional except when a cipher in CCM or OCB mode (e.g. `'aes-128-ccm'`) is used. In that case, the `authTagLength` option is required and specifies the length of the authentication tag in bytes, see [CCM mode](#ccm-mode). In GCM mode, the `authTagLength` option is not required but can be used to set the length of the authentication tag that will be returned by `getAuthTag()` and defaults to 16 bytes. For `chacha20-poly1305`, the `authTagLength` option defaults to 16 bytes.
The `algorithm` is dependent on OpenSSL, examples are `'aes192'`, etc. On recent OpenSSL releases, `openssl list -cipher-algorithms` will display the available cipher algorithms.
The `password` is used to derive the cipher key and initialization vector (IV). The value must be either a `'latin1'` encoded string, a [`Buffer`](buffer), a `TypedArray`, or a `DataView`.
**This function is semantically insecure for all supported ciphers and fatally flawed for ciphers in counter mode (such as CTR, GCM, or CCM).**
The implementation of `crypto.createCipher()` derives keys using the OpenSSL function [`EVP_BytesToKey`](https://www.openssl.org/docs/man1.1.0/crypto/EVP_BytesToKey.html) with the digest algorithm set to MD5, one iteration, and no salt. The lack of salt allows dictionary attacks as the same password always creates the same key. The low iteration count and non-cryptographically secure hash algorithm allow passwords to be tested very rapidly.
In line with OpenSSL's recommendation to use a more modern algorithm instead of [`EVP_BytesToKey`](https://www.openssl.org/docs/man1.1.0/crypto/EVP_BytesToKey.html) it is recommended that developers derive a key and IV on their own using [`crypto.scrypt()`](#cryptoscryptpassword-salt-keylen-options-callback) and to use [`crypto.createCipheriv()`](#cryptocreatecipherivalgorithm-key-iv-options) to create the `Cipher` object. Users should not use ciphers with counter mode (e.g. CTR, GCM, or CCM) in `crypto.createCipher()`. A warning is emitted when they are used in order to avoid the risk of IV reuse that causes vulnerabilities. For the case when IV is reused in GCM, see [Nonce-Disrespecting Adversaries](https://github.com/nonce-disrespect/nonce-disrespect) for details.
####
`crypto.createCipheriv(algorithm, key, iv[, options])`
History
| Version | Changes |
| --- | --- |
| v17.9.0, v16.17.0 | The `authTagLength` option is now optional when using the `chacha20-poly1305` cipher and defaults to 16 bytes. |
| v15.0.0 | The password and iv arguments can be an ArrayBuffer and are each limited to a maximum of 2 \*\* 31 - 1 bytes. |
| v11.6.0 | The `key` argument can now be a `KeyObject`. |
| v11.2.0, v10.17.0 | The cipher `chacha20-poly1305` (the IETF variant of ChaCha20-Poly1305) is now supported. |
| v10.10.0 | Ciphers in OCB mode are now supported. |
| v10.2.0 | The `authTagLength` option can now be used to produce shorter authentication tags in GCM mode and defaults to 16 bytes. |
| v9.9.0 | The `iv` parameter may now be `null` for ciphers which do not need an initialization vector. |
| v0.1.94 | Added in: v0.1.94 |
* `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `key` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
* `iv` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.transform` options](stream#new-streamtransformoptions)
* Returns: [<Cipher>](crypto#class-cipher)
Creates and returns a `Cipher` object, with the given `algorithm`, `key` and initialization vector (`iv`).
The `options` argument controls stream behavior and is optional except when a cipher in CCM or OCB mode (e.g. `'aes-128-ccm'`) is used. In that case, the `authTagLength` option is required and specifies the length of the authentication tag in bytes, see [CCM mode](#ccm-mode). In GCM mode, the `authTagLength` option is not required but can be used to set the length of the authentication tag that will be returned by `getAuthTag()` and defaults to 16 bytes. For `chacha20-poly1305`, the `authTagLength` option defaults to 16 bytes.
The `algorithm` is dependent on OpenSSL, examples are `'aes192'`, etc. On recent OpenSSL releases, `openssl list -cipher-algorithms` will display the available cipher algorithms.
The `key` is the raw key used by the `algorithm` and `iv` is an [initialization vector](https://en.wikipedia.org/wiki/Initialization_vector). Both arguments must be `'utf8'` encoded strings, [Buffers](buffer), `TypedArray`, or `DataView`s. The `key` may optionally be a [`KeyObject`](#class-keyobject) of type `secret`. If the cipher does not need an initialization vector, `iv` may be `null`.
When passing strings for `key` or `iv`, please consider [caveats when using strings as inputs to cryptographic APIs](#using-strings-as-inputs-to-cryptographic-apis).
Initialization vectors should be unpredictable and unique; ideally, they will be cryptographically random. They do not have to be secret: IVs are typically just added to ciphertext messages unencrypted. It may sound contradictory that something has to be unpredictable and unique, but does not have to be secret; remember that an attacker must not be able to predict ahead of time what a given IV will be.
####
`crypto.createDecipher(algorithm, password[, options])`
History
| Version | Changes |
| --- | --- |
| v17.9.0, v16.17.0 | The `authTagLength` option is now optional when using the `chacha20-poly1305` cipher and defaults to 16 bytes. |
| v10.10.0 | Ciphers in OCB mode are now supported. |
| v10.0.0 | Deprecated since: v10.0.0 |
| v0.1.94 | Added in: v0.1.94 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`crypto.createDecipheriv()`](#cryptocreatedecipherivalgorithm-key-iv-options) instead.
* `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `password` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.transform` options](stream#new-streamtransformoptions)
* Returns: [<Decipher>](crypto#class-decipher)
Creates and returns a `Decipher` object that uses the given `algorithm` and `password` (key).
The `options` argument controls stream behavior and is optional except when a cipher in CCM or OCB mode (e.g. `'aes-128-ccm'`) is used. In that case, the `authTagLength` option is required and specifies the length of the authentication tag in bytes, see [CCM mode](#ccm-mode). For `chacha20-poly1305`, the `authTagLength` option defaults to 16 bytes.
**This function is semantically insecure for all supported ciphers and fatally flawed for ciphers in counter mode (such as CTR, GCM, or CCM).**
The implementation of `crypto.createDecipher()` derives keys using the OpenSSL function [`EVP_BytesToKey`](https://www.openssl.org/docs/man1.1.0/crypto/EVP_BytesToKey.html) with the digest algorithm set to MD5, one iteration, and no salt. The lack of salt allows dictionary attacks as the same password always creates the same key. The low iteration count and non-cryptographically secure hash algorithm allow passwords to be tested very rapidly.
In line with OpenSSL's recommendation to use a more modern algorithm instead of [`EVP_BytesToKey`](https://www.openssl.org/docs/man1.1.0/crypto/EVP_BytesToKey.html) it is recommended that developers derive a key and IV on their own using [`crypto.scrypt()`](#cryptoscryptpassword-salt-keylen-options-callback) and to use [`crypto.createDecipheriv()`](#cryptocreatedecipherivalgorithm-key-iv-options) to create the `Decipher` object.
####
`crypto.createDecipheriv(algorithm, key, iv[, options])`
History
| Version | Changes |
| --- | --- |
| v17.9.0, v16.17.0 | The `authTagLength` option is now optional when using the `chacha20-poly1305` cipher and defaults to 16 bytes. |
| v11.6.0 | The `key` argument can now be a `KeyObject`. |
| v11.2.0, v10.17.0 | The cipher `chacha20-poly1305` (the IETF variant of ChaCha20-Poly1305) is now supported. |
| v10.10.0 | Ciphers in OCB mode are now supported. |
| v10.2.0 | The `authTagLength` option can now be used to restrict accepted GCM authentication tag lengths. |
| v9.9.0 | The `iv` parameter may now be `null` for ciphers which do not need an initialization vector. |
| v0.1.94 | Added in: v0.1.94 |
* `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `key` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
* `iv` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.transform` options](stream#new-streamtransformoptions)
* Returns: [<Decipher>](crypto#class-decipher)
Creates and returns a `Decipher` object that uses the given `algorithm`, `key` and initialization vector (`iv`).
The `options` argument controls stream behavior and is optional except when a cipher in CCM or OCB mode (e.g. `'aes-128-ccm'`) is used. In that case, the `authTagLength` option is required and specifies the length of the authentication tag in bytes, see [CCM mode](#ccm-mode). In GCM mode, the `authTagLength` option is not required but can be used to restrict accepted authentication tags to those with the specified length. For `chacha20-poly1305`, the `authTagLength` option defaults to 16 bytes.
The `algorithm` is dependent on OpenSSL, examples are `'aes192'`, etc. On recent OpenSSL releases, `openssl list -cipher-algorithms` will display the available cipher algorithms.
The `key` is the raw key used by the `algorithm` and `iv` is an [initialization vector](https://en.wikipedia.org/wiki/Initialization_vector). Both arguments must be `'utf8'` encoded strings, [Buffers](buffer), `TypedArray`, or `DataView`s. The `key` may optionally be a [`KeyObject`](#class-keyobject) of type `secret`. If the cipher does not need an initialization vector, `iv` may be `null`.
When passing strings for `key` or `iv`, please consider [caveats when using strings as inputs to cryptographic APIs](#using-strings-as-inputs-to-cryptographic-apis).
Initialization vectors should be unpredictable and unique; ideally, they will be cryptographically random. They do not have to be secret: IVs are typically just added to ciphertext messages unencrypted. It may sound contradictory that something has to be unpredictable and unique, but does not have to be secret; remember that an attacker must not be able to predict ahead of time what a given IV will be.
####
`crypto.createDiffieHellman(prime[, primeEncoding][, generator][, generatorEncoding])`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | The `prime` argument can be any `TypedArray` or `DataView` now. |
| v8.0.0 | The `prime` argument can be a `Uint8Array` now. |
| v6.0.0 | The default for the encoding parameters changed from `binary` to `utf8`. |
| v0.11.12 | Added in: v0.11.12 |
* `prime` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `primeEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `prime` string.
* `generator` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) **Default:** `2`
* `generatorEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The [encoding](buffer#buffers-and-character-encodings) of the `generator` string.
* Returns: [<DiffieHellman>](crypto#class-diffiehellman)
Creates a `DiffieHellman` key exchange object using the supplied `prime` and an optional specific `generator`.
The `generator` argument can be a number, string, or [`Buffer`](buffer). If `generator` is not specified, the value `2` is used.
If `primeEncoding` is specified, `prime` is expected to be a string; otherwise a [`Buffer`](buffer), `TypedArray`, or `DataView` is expected.
If `generatorEncoding` is specified, `generator` is expected to be a string; otherwise a number, [`Buffer`](buffer), `TypedArray`, or `DataView` is expected.
####
`crypto.createDiffieHellman(primeLength[, generator])`
Added in: v0.5.0 * `primeLength` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `generator` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `2`
* Returns: [<DiffieHellman>](crypto#class-diffiehellman)
Creates a `DiffieHellman` key exchange object and generates a prime of `primeLength` bits using an optional specific numeric `generator`. If `generator` is not specified, the value `2` is used.
####
`crypto.createDiffieHellmanGroup(name)`
Added in: v0.9.3 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<DiffieHellmanGroup>](crypto#class-diffiehellmangroup)
An alias for [`crypto.getDiffieHellman()`](#cryptogetdiffiehellmangroupname)
####
`crypto.createECDH(curveName)`
Added in: v0.11.14 * `curveName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<ECDH>](crypto#class-ecdh)
Creates an Elliptic Curve Diffie-Hellman (`ECDH`) key exchange object using a predefined curve specified by the `curveName` string. Use [`crypto.getCurves()`](#cryptogetcurves) to obtain a list of available curve names. On recent OpenSSL releases, `openssl ecparam -list_curves` will also display the name and description of each available elliptic curve.
####
`crypto.createHash(algorithm[, options])`
History
| Version | Changes |
| --- | --- |
| v12.8.0 | The `outputLength` option was added for XOF hash functions. |
| v0.1.92 | Added in: v0.1.92 |
* `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.transform` options](stream#new-streamtransformoptions)
* Returns: [<Hash>](crypto#class-hash)
Creates and returns a `Hash` object that can be used to generate hash digests using the given `algorithm`. Optional `options` argument controls stream behavior. For XOF hash functions such as `'shake256'`, the `outputLength` option can be used to specify the desired output length in bytes.
The `algorithm` is dependent on the available algorithms supported by the version of OpenSSL on the platform. Examples are `'sha256'`, `'sha512'`, etc. On recent releases of OpenSSL, `openssl list -digest-algorithms` will display the available digest algorithms.
Example: generating the sha256 sum of a file
MJS modules
```
import {
createReadStream
} from 'node:fs';
import { argv } from 'node:process';
const {
createHash
} = await import('node:crypto');
const filename = argv[2];
const hash = createHash('sha256');
const input = createReadStream(filename);
input.on('readable', () => {
// Only one element is going to be produced by the
// hash stream.
const data = input.read();
if (data)
hash.update(data);
else {
console.log(`${hash.digest('hex')} ${filename}`);
}
});
```
CJS modules
```
const {
createReadStream,
} = require('node:fs');
const {
createHash,
} = require('node:crypto');
const { argv } = require('node:process');
const filename = argv[2];
const hash = createHash('sha256');
const input = createReadStream(filename);
input.on('readable', () => {
// Only one element is going to be produced by the
// hash stream.
const data = input.read();
if (data)
hash.update(data);
else {
console.log(`${hash.digest('hex')} ${filename}`);
}
});
```
####
`crypto.createHmac(algorithm, key[, options])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The key can also be an ArrayBuffer or CryptoKey. The encoding option was added. The key cannot contain more than 2 \*\* 32 - 1 bytes. |
| v11.6.0 | The `key` argument can now be a `KeyObject`. |
| v0.1.94 | Added in: v0.1.94 |
* `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `key` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.transform` options](stream#new-streamtransformoptions)
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The string encoding to use when `key` is a string.
* Returns: [<Hmac>](crypto#class-hmac)
Creates and returns an `Hmac` object that uses the given `algorithm` and `key`. Optional `options` argument controls stream behavior.
The `algorithm` is dependent on the available algorithms supported by the version of OpenSSL on the platform. Examples are `'sha256'`, `'sha512'`, etc. On recent releases of OpenSSL, `openssl list -digest-algorithms` will display the available digest algorithms.
The `key` is the HMAC key used to generate the cryptographic HMAC hash. If it is a [`KeyObject`](#class-keyobject), its type must be `secret`.
Example: generating the sha256 HMAC of a file
MJS modules
```
import {
createReadStream
} from 'node:fs';
import { argv } from 'node:process';
const {
createHmac
} = await import('node:crypto');
const filename = argv[2];
const hmac = createHmac('sha256', 'a secret');
const input = createReadStream(filename);
input.on('readable', () => {
// Only one element is going to be produced by the
// hash stream.
const data = input.read();
if (data)
hmac.update(data);
else {
console.log(`${hmac.digest('hex')} ${filename}`);
}
});
```
CJS modules
```
const {
createReadStream,
} = require('node:fs');
const {
createHmac,
} = require('node:crypto');
const { argv } = require('node:process');
const filename = argv[2];
const hmac = createHmac('sha256', 'a secret');
const input = createReadStream(filename);
input.on('readable', () => {
// Only one element is going to be produced by the
// hash stream.
const data = input.read();
if (data)
hmac.update(data);
else {
console.log(`${hmac.digest('hex')} ${filename}`);
}
});
```
####
`crypto.createPrivateKey(key)`
History
| Version | Changes |
| --- | --- |
| v15.12.0 | The key can also be a JWK object. |
| v15.0.0 | The key can also be an ArrayBuffer. The encoding option was added. The key cannot contain more than 2 \*\* 32 - 1 bytes. |
| v11.6.0 | Added in: v11.6.0 |
* `key` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
+ `key`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The key material, either in PEM, DER, or JWK format.
+ `format`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'pem'`, `'der'`, or '`'jwk'`. **Default:** `'pem'`.
+ `type`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'pkcs1'`, `'pkcs8'` or `'sec1'`. This option is required only if the `format` is `'der'` and ignored otherwise.
+ `passphrase`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) The passphrase to use for decryption.
+ `encoding`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The string encoding to use when `key` is a string.
* Returns: [<KeyObject>](crypto#class-keyobject)
Creates and returns a new key object containing a private key. If `key` is a string or `Buffer`, `format` is assumed to be `'pem'`; otherwise, `key` must be an object with the properties described above.
If the private key is encrypted, a `passphrase` must be specified. The length of the passphrase is limited to 1024 bytes.
####
`crypto.createPublicKey(key)`
History
| Version | Changes |
| --- | --- |
| v15.12.0 | The key can also be a JWK object. |
| v15.0.0 | The key can also be an ArrayBuffer. The encoding option was added. The key cannot contain more than 2 \*\* 32 - 1 bytes. |
| v11.13.0 | The `key` argument can now be a `KeyObject` with type `private`. |
| v11.7.0 | The `key` argument can now be a private key. |
| v11.6.0 | Added in: v11.6.0 |
* `key` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
+ `key`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The key material, either in PEM, DER, or JWK format.
+ `format`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'pem'`, `'der'`, or `'jwk'`. **Default:** `'pem'`.
+ `type`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'pkcs1'` or `'spki'`. This option is required only if the `format` is `'der'` and ignored otherwise.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The string encoding to use when `key` is a string.
* Returns: [<KeyObject>](crypto#class-keyobject)
Creates and returns a new key object containing a public key. If `key` is a string or `Buffer`, `format` is assumed to be `'pem'`; if `key` is a `KeyObject` with type `'private'`, the public key is derived from the given private key; otherwise, `key` must be an object with the properties described above.
If the format is `'pem'`, the `'key'` may also be an X.509 certificate.
Because public keys can be derived from private keys, a private key may be passed instead of a public key. In that case, this function behaves as if [`crypto.createPrivateKey()`](#cryptocreateprivatekeykey) had been called, except that the type of the returned `KeyObject` will be `'public'` and that the private key cannot be extracted from the returned `KeyObject`. Similarly, if a `KeyObject` with type `'private'` is given, a new `KeyObject` with type `'public'` will be returned and it will be impossible to extract the private key from the returned object.
####
`crypto.createSecretKey(key[, encoding])`
History
| Version | Changes |
| --- | --- |
| v18.8.0, v16.18.0 | The key can now be zero-length. |
| v15.0.0 | The key can also be an ArrayBuffer or string. The encoding argument was added. The key cannot contain more than 2 \*\* 32 - 1 bytes. |
| v11.6.0 | Added in: v11.6.0 |
* `key` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The string encoding when `key` is a string.
* Returns: [<KeyObject>](crypto#class-keyobject)
Creates and returns a new key object containing a secret key for symmetric encryption or `Hmac`.
####
`crypto.createSign(algorithm[, options])`
Added in: v0.1.92 * `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.Writable` options](stream#new-streamwritableoptions)
* Returns: [<Sign>](crypto#class-sign)
Creates and returns a `Sign` object that uses the given `algorithm`. Use [`crypto.getHashes()`](#cryptogethashes) to obtain the names of the available digest algorithms. Optional `options` argument controls the `stream.Writable` behavior.
In some cases, a `Sign` instance can be created using the name of a signature algorithm, such as `'RSA-SHA256'`, instead of a digest algorithm. This will use the corresponding digest algorithm. This does not work for all signature algorithms, such as `'ecdsa-with-SHA256'`, so it is best to always use digest algorithm names.
####
`crypto.createVerify(algorithm[, options])`
Added in: v0.1.92 * `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) [`stream.Writable` options](stream#new-streamwritableoptions)
* Returns: [<Verify>](crypto#class-verify)
Creates and returns a `Verify` object that uses the given algorithm. Use [`crypto.getHashes()`](#cryptogethashes) to obtain an array of names of the available signing algorithms. Optional `options` argument controls the `stream.Writable` behavior.
In some cases, a `Verify` instance can be created using the name of a signature algorithm, such as `'RSA-SHA256'`, instead of a digest algorithm. This will use the corresponding digest algorithm. This does not work for all signature algorithms, such as `'ecdsa-with-SHA256'`, so it is best to always use digest algorithm names.
####
`crypto.diffieHellman(options)`
Added in: v13.9.0, v12.17.0 * `options`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `privateKey`: [<KeyObject>](crypto#class-keyobject)
+ `publicKey`: [<KeyObject>](crypto#class-keyobject)
* Returns: [<Buffer>](buffer#class-buffer)
Computes the Diffie-Hellman secret based on a `privateKey` and a `publicKey`. Both keys must have the same `asymmetricKeyType`, which must be one of `'dh'` (for Diffie-Hellman), `'ec'` (for ECDH), `'x448'`, or `'x25519'` (for ECDH-ES).
####
`crypto.generateKey(type, options, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v15.0.0 | Added in: v15.0.0 |
* `type`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The intended use of the generated secret key. Currently accepted values are `'hmac'` and `'aes'`.
* `options`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `length`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The bit length of the key to generate. This must be a value greater than 0.
- If `type` is `'hmac'`, the minimum is 8, and the maximum length is 231-1. If the value is not a multiple of 8, the generated key will be truncated to `Math.floor(length / 8)`.
- If `type` is `'aes'`, the length must be one of `128`, `192`, or `256`.
* `callback`: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err`: [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `key`: [<KeyObject>](crypto#class-keyobject)
Asynchronously generates a new random secret key of the given `length`. The `type` will determine which validations will be performed on the `length`.
MJS modules
```
const {
generateKey
} = await import('node:crypto');
generateKey('hmac', { length: 64 }, (err, key) => {
if (err) throw err;
console.log(key.export().toString('hex')); // 46e..........620
});
```
CJS modules
```
const {
generateKey,
} = require('node:crypto');
generateKey('hmac', { length: 64 }, (err, key) => {
if (err) throw err;
console.log(key.export().toString('hex')); // 46e..........620
});
```
####
`crypto.generateKeyPair(type, options, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v16.10.0 | Add ability to define `RSASSA-PSS-params` sequence parameters for RSA-PSS keys pairs. |
| v13.9.0, v12.17.0 | Add support for Diffie-Hellman. |
| v12.0.0 | Add support for RSA-PSS key pairs. |
| v12.0.0 | Add ability to generate X25519 and X448 key pairs. |
| v12.0.0 | Add ability to generate Ed25519 and Ed448 key pairs. |
| v11.6.0 | The `generateKeyPair` and `generateKeyPairSync` functions now produce key objects if no encoding was specified. |
| v10.12.0 | Added in: v10.12.0 |
* `type`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'rsa'`, `'rsa-pss'`, `'dsa'`, `'ec'`, `'ed25519'`, `'ed448'`, `'x25519'`, `'x448'`, or `'dh'`.
* `options`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `modulusLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Key size in bits (RSA, DSA).
+ `publicExponent`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Public exponent (RSA). **Default:** `0x10001`.
+ `hashAlgorithm`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the message digest (RSA-PSS).
+ `mgf1HashAlgorithm`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the message digest used by MGF1 (RSA-PSS).
+ `saltLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Minimal salt length in bytes (RSA-PSS).
+ `divisorLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Size of `q` in bits (DSA).
+ `namedCurve`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the curve to use (EC).
+ `prime`: [<Buffer>](buffer#class-buffer) The prime parameter (DH).
+ `primeLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Prime length in bits (DH).
+ `generator`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Custom generator (DH). **Default:** `2`.
+ `groupName`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Diffie-Hellman group name (DH). See [`crypto.getDiffieHellman()`](#cryptogetdiffiehellmangroupname).
+ `publicKeyEncoding`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) See [`keyObject.export()`](#keyobjectexportoptions).
+ `privateKeyEncoding`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) See [`keyObject.export()`](#keyobjectexportoptions).
* `callback`: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err`: [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `publicKey`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<KeyObject>](crypto#class-keyobject)
+ `privateKey`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<KeyObject>](crypto#class-keyobject)
Generates a new asymmetric key pair of the given `type`. RSA, RSA-PSS, DSA, EC, Ed25519, Ed448, X25519, X448, and DH are currently supported.
If a `publicKeyEncoding` or `privateKeyEncoding` was specified, this function behaves as if [`keyObject.export()`](#keyobjectexportoptions) had been called on its result. Otherwise, the respective part of the key is returned as a [`KeyObject`](#class-keyobject).
It is recommended to encode public keys as `'spki'` and private keys as `'pkcs8'` with encryption for long-term storage:
MJS modules
```
const {
generateKeyPair
} = await import('node:crypto');
generateKeyPair('rsa', {
modulusLength: 4096,
publicKeyEncoding: {
type: 'spki',
format: 'pem'
},
privateKeyEncoding: {
type: 'pkcs8',
format: 'pem',
cipher: 'aes-256-cbc',
passphrase: 'top secret'
}
}, (err, publicKey, privateKey) => {
// Handle errors and use the generated key pair.
});
```
CJS modules
```
const {
generateKeyPair,
} = require('node:crypto');
generateKeyPair('rsa', {
modulusLength: 4096,
publicKeyEncoding: {
type: 'spki',
format: 'pem'
},
privateKeyEncoding: {
type: 'pkcs8',
format: 'pem',
cipher: 'aes-256-cbc',
passphrase: 'top secret'
}
}, (err, publicKey, privateKey) => {
// Handle errors and use the generated key pair.
});
```
On completion, `callback` will be called with `err` set to `undefined` and `publicKey` / `privateKey` representing the generated key pair.
If this method is invoked as its [`util.promisify()`](util#utilpromisifyoriginal)ed version, it returns a `Promise` for an `Object` with `publicKey` and `privateKey` properties.
####
`crypto.generateKeyPairSync(type, options)`
History
| Version | Changes |
| --- | --- |
| v16.10.0 | Add ability to define `RSASSA-PSS-params` sequence parameters for RSA-PSS keys pairs. |
| v13.9.0, v12.17.0 | Add support for Diffie-Hellman. |
| v12.0.0 | Add support for RSA-PSS key pairs. |
| v12.0.0 | Add ability to generate X25519 and X448 key pairs. |
| v12.0.0 | Add ability to generate Ed25519 and Ed448 key pairs. |
| v11.6.0 | The `generateKeyPair` and `generateKeyPairSync` functions now produce key objects if no encoding was specified. |
| v10.12.0 | Added in: v10.12.0 |
* `type`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'rsa'`, `'rsa-pss'`, `'dsa'`, `'ec'`, `'ed25519'`, `'ed448'`, `'x25519'`, `'x448'`, or `'dh'`.
* `options`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `modulusLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Key size in bits (RSA, DSA).
+ `publicExponent`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Public exponent (RSA). **Default:** `0x10001`.
+ `hashAlgorithm`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the message digest (RSA-PSS).
+ `mgf1HashAlgorithm`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the message digest used by MGF1 (RSA-PSS).
+ `saltLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Minimal salt length in bytes (RSA-PSS).
+ `divisorLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Size of `q` in bits (DSA).
+ `namedCurve`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of the curve to use (EC).
+ `prime`: [<Buffer>](buffer#class-buffer) The prime parameter (DH).
+ `primeLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Prime length in bits (DH).
+ `generator`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Custom generator (DH). **Default:** `2`.
+ `groupName`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Diffie-Hellman group name (DH). See [`crypto.getDiffieHellman()`](#cryptogetdiffiehellmangroupname).
+ `publicKeyEncoding`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) See [`keyObject.export()`](#keyobjectexportoptions).
+ `privateKeyEncoding`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) See [`keyObject.export()`](#keyobjectexportoptions).
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `publicKey`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<KeyObject>](crypto#class-keyobject)
+ `privateKey`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<KeyObject>](crypto#class-keyobject)
Generates a new asymmetric key pair of the given `type`. RSA, RSA-PSS, DSA, EC, Ed25519, Ed448, X25519, X448, and DH are currently supported.
If a `publicKeyEncoding` or `privateKeyEncoding` was specified, this function behaves as if [`keyObject.export()`](#keyobjectexportoptions) had been called on its result. Otherwise, the respective part of the key is returned as a [`KeyObject`](#class-keyobject).
When encoding public keys, it is recommended to use `'spki'`. When encoding private keys, it is recommended to use `'pkcs8'` with a strong passphrase, and to keep the passphrase confidential.
MJS modules
```
const {
generateKeyPairSync
} = await import('node:crypto');
const {
publicKey,
privateKey,
} = generateKeyPairSync('rsa', {
modulusLength: 4096,
publicKeyEncoding: {
type: 'spki',
format: 'pem'
},
privateKeyEncoding: {
type: 'pkcs8',
format: 'pem',
cipher: 'aes-256-cbc',
passphrase: 'top secret'
}
});
```
CJS modules
```
const {
generateKeyPairSync,
} = require('node:crypto');
const {
publicKey,
privateKey,
} = generateKeyPairSync('rsa', {
modulusLength: 4096,
publicKeyEncoding: {
type: 'spki',
format: 'pem'
},
privateKeyEncoding: {
type: 'pkcs8',
format: 'pem',
cipher: 'aes-256-cbc',
passphrase: 'top secret'
}
});
```
The return value `{ publicKey, privateKey }` represents the generated key pair. When PEM encoding was selected, the respective key will be a string, otherwise it will be a buffer containing the data encoded as DER.
####
`crypto.generateKeySync(type, options)`
Added in: v15.0.0 * `type`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The intended use of the generated secret key. Currently accepted values are `'hmac'` and `'aes'`.
* `options`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `length`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The bit length of the key to generate.
- If `type` is `'hmac'`, the minimum is 8, and the maximum length is 231-1. If the value is not a multiple of 8, the generated key will be truncated to `Math.floor(length / 8)`.
- If `type` is `'aes'`, the length must be one of `128`, `192`, or `256`.
* Returns: [<KeyObject>](crypto#class-keyobject)
Synchronously generates a new random secret key of the given `length`. The `type` will determine which validations will be performed on the `length`.
MJS modules
```
const {
generateKeySync
} = await import('node:crypto');
const key = generateKeySync('hmac', { length: 64 });
console.log(key.export().toString('hex')); // e89..........41e
```
CJS modules
```
const {
generateKeySync,
} = require('node:crypto');
const key = generateKeySync('hmac', { length: 64 });
console.log(key.export().toString('hex')); // e89..........41e
```
####
`crypto.generatePrime(size[, options[, callback]])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v15.8.0 | Added in: v15.8.0 |
* `size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The size (in bits) of the prime to generate.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `add` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<Buffer>](buffer#class-buffer) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
+ `rem` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<Buffer>](buffer#class-buffer) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
+ `safe` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`.
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the generated prime is returned as a `bigint`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `prime` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Generates a pseudorandom prime of `size` bits.
If `options.safe` is `true`, the prime will be a safe prime -- that is, `(prime - 1) / 2` will also be a prime.
The `options.add` and `options.rem` parameters can be used to enforce additional requirements, e.g., for Diffie-Hellman:
* If `options.add` and `options.rem` are both set, the prime will satisfy the condition that `prime % add = rem`.
* If only `options.add` is set and `options.safe` is not `true`, the prime will satisfy the condition that `prime % add = 1`.
* If only `options.add` is set and `options.safe` is set to `true`, the prime will instead satisfy the condition that `prime % add = 3`. This is necessary because `prime % add = 1` for `options.add > 2` would contradict the condition enforced by `options.safe`.
* `options.rem` is ignored if `options.add` is not given.
Both `options.add` and `options.rem` must be encoded as big-endian sequences if given as an `ArrayBuffer`, `SharedArrayBuffer`, `TypedArray`, `Buffer`, or `DataView`.
By default, the prime is encoded as a big-endian sequence of octets in an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer). If the `bigint` option is `true`, then a [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) is provided.
####
`crypto.generatePrimeSync(size[, options])`
Added in: v15.8.0 * `size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The size (in bits) of the prime to generate.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `add` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<Buffer>](buffer#class-buffer) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
+ `rem` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<SharedArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<Buffer>](buffer#class-buffer) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
+ `safe` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) **Default:** `false`.
+ `bigint` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the generated prime is returned as a `bigint`.
* Returns: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
Generates a pseudorandom prime of `size` bits.
If `options.safe` is `true`, the prime will be a safe prime -- that is, `(prime - 1) / 2` will also be a prime.
The `options.add` and `options.rem` parameters can be used to enforce additional requirements, e.g., for Diffie-Hellman:
* If `options.add` and `options.rem` are both set, the prime will satisfy the condition that `prime % add = rem`.
* If only `options.add` is set and `options.safe` is not `true`, the prime will satisfy the condition that `prime % add = 1`.
* If only `options.add` is set and `options.safe` is set to `true`, the prime will instead satisfy the condition that `prime % add = 3`. This is necessary because `prime % add = 1` for `options.add > 2` would contradict the condition enforced by `options.safe`.
* `options.rem` is ignored if `options.add` is not given.
Both `options.add` and `options.rem` must be encoded as big-endian sequences if given as an `ArrayBuffer`, `SharedArrayBuffer`, `TypedArray`, `Buffer`, or `DataView`.
By default, the prime is encoded as a big-endian sequence of octets in an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer). If the `bigint` option is `true`, then a [<bigint>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) is provided.
####
`crypto.getCipherInfo(nameOrNid[, options])`
Added in: v15.0.0 * `nameOrNid`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The name or nid of the cipher to query.
* `options`: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `keyLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A test key length.
+ `ivLength`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A test IV length.
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the cipher
+ `nid` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The nid of the cipher
+ `blockSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The block size of the cipher in bytes. This property is omitted when `mode` is `'stream'`.
+ `ivLength` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The expected or default initialization vector length in bytes. This property is omitted if the cipher does not use an initialization vector.
+ `keyLength` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The expected or default key length in bytes.
+ `mode` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The cipher mode. One of `'cbc'`, `'ccm'`, `'cfb'`, `'ctr'`, `'ecb'`, `'gcm'`, `'ocb'`, `'ofb'`, `'stream'`, `'wrap'`, `'xts'`.
Returns information about a given cipher.
Some ciphers accept variable length keys and initialization vectors. By default, the `crypto.getCipherInfo()` method will return the default values for these ciphers. To test if a given key length or iv length is acceptable for given cipher, use the `keyLength` and `ivLength` options. If the given values are unacceptable, `undefined` will be returned.
####
`crypto.getCiphers()`
Added in: v0.9.3 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) An array with the names of the supported cipher algorithms.
MJS modules
```
const {
getCiphers
} = await import('node:crypto');
console.log(getCiphers()); // ['aes-128-cbc', 'aes-128-ccm', ...]
```
CJS modules
```
const {
getCiphers,
} = require('node:crypto');
console.log(getCiphers()); // ['aes-128-cbc', 'aes-128-ccm', ...]
```
####
`crypto.getCurves()`
Added in: v2.3.0 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) An array with the names of the supported elliptic curves.
MJS modules
```
const {
getCurves
} = await import('node:crypto');
console.log(getCurves()); // ['Oakley-EC2N-3', 'Oakley-EC2N-4', ...]
```
CJS modules
```
const {
getCurves,
} = require('node:crypto');
console.log(getCurves()); // ['Oakley-EC2N-3', 'Oakley-EC2N-4', ...]
```
####
`crypto.getDiffieHellman(groupName)`
Added in: v0.7.5 * `groupName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<DiffieHellmanGroup>](crypto#class-diffiehellmangroup)
Creates a predefined `DiffieHellmanGroup` key exchange object. The supported groups are listed in the documentation for [`DiffieHellmanGroup`](#class-diffiehellmangroup).
The returned object mimics the interface of objects created by [`crypto.createDiffieHellman()`](#cryptocreatediffiehellmanprime-primeencoding-generator-generatorencoding), but will not allow changing the keys (with [`diffieHellman.setPublicKey()`](#diffiehellmansetpublickeypublickey-encoding), for example). The advantage of using this method is that the parties do not have to generate nor exchange a group modulus beforehand, saving both processor and communication time.
Example (obtaining a shared secret):
MJS modules
```
const {
getDiffieHellman
} = await import('node:crypto');
const alice = getDiffieHellman('modp14');
const bob = getDiffieHellman('modp14');
alice.generateKeys();
bob.generateKeys();
const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
/* aliceSecret and bobSecret should be the same */
console.log(aliceSecret === bobSecret);
```
CJS modules
```
const {
getDiffieHellman,
} = require('node:crypto');
const alice = getDiffieHellman('modp14');
const bob = getDiffieHellman('modp14');
alice.generateKeys();
bob.generateKeys();
const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
/* aliceSecret and bobSecret should be the same */
console.log(aliceSecret === bobSecret);
```
####
`crypto.getFips()`
Added in: v10.0.0 * Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) `1` if and only if a FIPS compliant crypto provider is currently in use, `0` otherwise. A future semver-major release may change the return type of this API to a [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type).
####
`crypto.getHashes()`
Added in: v0.9.3 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) An array of the names of the supported hash algorithms, such as `'RSA-SHA256'`. Hash algorithms are also called "digest" algorithms.
MJS modules
```
const {
getHashes
} = await import('node:crypto');
console.log(getHashes()); // ['DSA', 'DSA-SHA', 'DSA-SHA1', ...]
```
CJS modules
```
const {
getHashes,
} = require('node:crypto');
console.log(getHashes()); // ['DSA', 'DSA-SHA', 'DSA-SHA1', ...]
```
####
`crypto.getRandomValues(typedArray)`
Added in: v17.4.0 * `typedArray` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
* Returns: [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) Returns `typedArray`.
A convenient alias for [`crypto.webcrypto.getRandomValues()`](webcrypto#cryptogetrandomvaluestypedarray). This implementation is not compliant with the Web Crypto spec, to write web-compatible code use [`crypto.webcrypto.getRandomValues()`](webcrypto#cryptogetrandomvaluestypedarray) instead.
####
`crypto.hkdf(digest, ikm, salt, info, keylen, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v18.8.0, v16.18.0 | The input keying material can now be zero-length. |
| v15.0.0 | Added in: v15.0.0 |
* `digest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The digest algorithm to use.
* `ikm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) The input keying material. Must be provided but can be zero-length.
* `salt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The salt value. Must be provided but can be zero-length.
* `info` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Additional info value. Must be provided but can be zero-length, and cannot be more than 1024 bytes.
* `keylen` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The length of the key to generate. Must be greater than 0. The maximum allowable value is `255` times the number of bytes produced by the selected digest function (e.g. `sha512` generates 64-byte hashes, making the maximum HKDF output 16320 bytes).
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `derivedKey` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
HKDF is a simple key derivation function defined in RFC 5869. The given `ikm`, `salt` and `info` are used with the `digest` to derive a key of `keylen` bytes.
The supplied `callback` function is called with two arguments: `err` and `derivedKey`. If an errors occurs while deriving the key, `err` will be set; otherwise `err` will be `null`. The successfully generated `derivedKey` will be passed to the callback as an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer). An error will be thrown if any of the input arguments specify invalid values or types.
MJS modules
```
import { Buffer } from 'node:buffer';
const {
hkdf
} = await import('node:crypto');
hkdf('sha512', 'key', 'salt', 'info', 64, (err, derivedKey) => {
if (err) throw err;
console.log(Buffer.from(derivedKey).toString('hex')); // '24156e2...5391653'
});
```
CJS modules
```
const {
hkdf,
} = require('node:crypto');
const { Buffer } = require('node:buffer');
hkdf('sha512', 'key', 'salt', 'info', 64, (err, derivedKey) => {
if (err) throw err;
console.log(Buffer.from(derivedKey).toString('hex')); // '24156e2...5391653'
});
```
####
`crypto.hkdfSync(digest, ikm, salt, info, keylen)`
History
| Version | Changes |
| --- | --- |
| v18.8.0, v16.18.0 | The input keying material can now be zero-length. |
| v15.0.0 | Added in: v15.0.0 |
* `digest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The digest algorithm to use.
* `ikm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) The input keying material. Must be provided but can be zero-length.
* `salt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The salt value. Must be provided but can be zero-length.
* `info` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Additional info value. Must be provided but can be zero-length, and cannot be more than 1024 bytes.
* `keylen` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The length of the key to generate. Must be greater than 0. The maximum allowable value is `255` times the number of bytes produced by the selected digest function (e.g. `sha512` generates 64-byte hashes, making the maximum HKDF output 16320 bytes).
* Returns: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
Provides a synchronous HKDF key derivation function as defined in RFC 5869. The given `ikm`, `salt` and `info` are used with the `digest` to derive a key of `keylen` bytes.
The successfully generated `derivedKey` will be returned as an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer).
An error will be thrown if any of the input arguments specify invalid values or types, or if the derived key cannot be generated.
MJS modules
```
import { Buffer } from 'node:buffer';
const {
hkdfSync
} = await import('node:crypto');
const derivedKey = hkdfSync('sha512', 'key', 'salt', 'info', 64);
console.log(Buffer.from(derivedKey).toString('hex')); // '24156e2...5391653'
```
CJS modules
```
const {
hkdfSync,
} = require('node:crypto');
const { Buffer } = require('node:buffer');
const derivedKey = hkdfSync('sha512', 'key', 'salt', 'info', 64);
console.log(Buffer.from(derivedKey).toString('hex')); // '24156e2...5391653'
```
####
`crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v15.0.0 | The password and salt arguments can also be ArrayBuffer instances. |
| v14.0.0 | The `iterations` parameter is now restricted to positive values. Earlier releases treated other values as one. |
| v8.0.0 | The `digest` parameter is always required now. |
| v6.0.0 | Calling this function without passing the `digest` parameter is deprecated now and will emit a warning. |
| v6.0.0 | The default encoding for `password` if it is a string changed from `binary` to `utf8`. |
| v0.5.5 | Added in: v0.5.5 |
* `password` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `salt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `iterations` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `keylen` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `digest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `derivedKey` [<Buffer>](buffer#class-buffer)
Provides an asynchronous Password-Based Key Derivation Function 2 (PBKDF2) implementation. A selected HMAC digest algorithm specified by `digest` is applied to derive a key of the requested byte length (`keylen`) from the `password`, `salt` and `iterations`.
The supplied `callback` function is called with two arguments: `err` and `derivedKey`. If an error occurs while deriving the key, `err` will be set; otherwise `err` will be `null`. By default, the successfully generated `derivedKey` will be passed to the callback as a [`Buffer`](buffer). An error will be thrown if any of the input arguments specify invalid values or types.
The `iterations` argument must be a number set as high as possible. The higher the number of iterations, the more secure the derived key will be, but will take a longer amount of time to complete.
The `salt` should be as unique as possible. It is recommended that a salt is random and at least 16 bytes long. See [NIST SP 800-132](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-132.pdf) for details.
When passing strings for `password` or `salt`, please consider [caveats when using strings as inputs to cryptographic APIs](#using-strings-as-inputs-to-cryptographic-apis).
MJS modules
```
const {
pbkdf2
} = await import('node:crypto');
pbkdf2('secret', 'salt', 100000, 64, 'sha512', (err, derivedKey) => {
if (err) throw err;
console.log(derivedKey.toString('hex')); // '3745e48...08d59ae'
});
```
CJS modules
```
const {
pbkdf2,
} = require('node:crypto');
pbkdf2('secret', 'salt', 100000, 64, 'sha512', (err, derivedKey) => {
if (err) throw err;
console.log(derivedKey.toString('hex')); // '3745e48...08d59ae'
});
```
The `crypto.DEFAULT_ENCODING` property can be used to change the way the `derivedKey` is passed to the callback. This property, however, has been deprecated and use should be avoided.
MJS modules
```
import crypto from 'node:crypto';
crypto.DEFAULT_ENCODING = 'hex';
crypto.pbkdf2('secret', 'salt', 100000, 512, 'sha512', (err, derivedKey) => {
if (err) throw err;
console.log(derivedKey); // '3745e48...aa39b34'
});
```
CJS modules
```
const crypto = require('node:crypto');
crypto.DEFAULT_ENCODING = 'hex';
crypto.pbkdf2('secret', 'salt', 100000, 512, 'sha512', (err, derivedKey) => {
if (err) throw err;
console.log(derivedKey); // '3745e48...aa39b34'
});
```
An array of supported digest functions can be retrieved using [`crypto.getHashes()`](#cryptogethashes).
This API uses libuv's threadpool, which can have surprising and negative performance implications for some applications; see the [`UV_THREADPOOL_SIZE`](cli#uv_threadpool_sizesize) documentation for more information.
####
`crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)`
History
| Version | Changes |
| --- | --- |
| v14.0.0 | The `iterations` parameter is now restricted to positive values. Earlier releases treated other values as one. |
| v6.0.0 | Calling this function without passing the `digest` parameter is deprecated now and will emit a warning. |
| v6.0.0 | The default encoding for `password` if it is a string changed from `binary` to `utf8`. |
| v0.9.3 | Added in: v0.9.3 |
* `password` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `salt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `iterations` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `keylen` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `digest` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<Buffer>](buffer#class-buffer)
Provides a synchronous Password-Based Key Derivation Function 2 (PBKDF2) implementation. A selected HMAC digest algorithm specified by `digest` is applied to derive a key of the requested byte length (`keylen`) from the `password`, `salt` and `iterations`.
If an error occurs an `Error` will be thrown, otherwise the derived key will be returned as a [`Buffer`](buffer).
The `iterations` argument must be a number set as high as possible. The higher the number of iterations, the more secure the derived key will be, but will take a longer amount of time to complete.
The `salt` should be as unique as possible. It is recommended that a salt is random and at least 16 bytes long. See [NIST SP 800-132](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-132.pdf) for details.
When passing strings for `password` or `salt`, please consider [caveats when using strings as inputs to cryptographic APIs](#using-strings-as-inputs-to-cryptographic-apis).
MJS modules
```
const {
pbkdf2Sync
} = await import('node:crypto');
const key = pbkdf2Sync('secret', 'salt', 100000, 64, 'sha512');
console.log(key.toString('hex')); // '3745e48...08d59ae'
```
CJS modules
```
const {
pbkdf2Sync,
} = require('node:crypto');
const key = pbkdf2Sync('secret', 'salt', 100000, 64, 'sha512');
console.log(key.toString('hex')); // '3745e48...08d59ae'
```
The `crypto.DEFAULT_ENCODING` property may be used to change the way the `derivedKey` is returned. This property, however, is deprecated and use should be avoided.
MJS modules
```
import crypto from 'node:crypto';
crypto.DEFAULT_ENCODING = 'hex';
const key = crypto.pbkdf2Sync('secret', 'salt', 100000, 512, 'sha512');
console.log(key); // '3745e48...aa39b34'
```
CJS modules
```
const crypto = require('node:crypto');
crypto.DEFAULT_ENCODING = 'hex';
const key = crypto.pbkdf2Sync('secret', 'salt', 100000, 512, 'sha512');
console.log(key); // '3745e48...aa39b34'
```
An array of supported digest functions can be retrieved using [`crypto.getHashes()`](#cryptogethashes).
####
`crypto.privateDecrypt(privateKey, buffer)`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Added string, ArrayBuffer, and CryptoKey as allowable key types. The oaepLabel can be an ArrayBuffer. The buffer can be a string or ArrayBuffer. All types that accept buffers are limited to a maximum of 2 \*\* 31 - 1 bytes. |
| v12.11.0 | The `oaepLabel` option was added. |
| v12.9.0 | The `oaepHash` option was added. |
| v11.6.0 | This function now supports key objects. |
| v0.11.14 | Added in: v0.11.14 |
* `privateKey` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
+ `oaepHash` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The hash function to use for OAEP padding and MGF1. **Default:** `'sha1'`
+ `oaepLabel` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The label to use for OAEP padding. If not specified, no label is used.
+ `padding` [<crypto.constants>](crypto#cryptoconstants) An optional padding value defined in `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING`, `crypto.constants.RSA_PKCS1_PADDING`, or `crypto.constants.RSA_PKCS1_OAEP_PADDING`.
* `buffer` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* Returns: [<Buffer>](buffer#class-buffer) A new `Buffer` with the decrypted content.
Decrypts `buffer` with `privateKey`. `buffer` was previously encrypted using the corresponding public key, for example using [`crypto.publicEncrypt()`](#cryptopublicencryptkey-buffer).
If `privateKey` is not a [`KeyObject`](#class-keyobject), this function behaves as if `privateKey` had been passed to [`crypto.createPrivateKey()`](#cryptocreateprivatekeykey). If it is an object, the `padding` property can be passed. Otherwise, this function uses `RSA_PKCS1_OAEP_PADDING`.
####
`crypto.privateEncrypt(privateKey, buffer)`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Added string, ArrayBuffer, and CryptoKey as allowable key types. The passphrase can be an ArrayBuffer. The buffer can be a string or ArrayBuffer. All types that accept buffers are limited to a maximum of 2 \*\* 31 - 1 bytes. |
| v11.6.0 | This function now supports key objects. |
| v1.1.0 | Added in: v1.1.0 |
* `privateKey` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
+ `key` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey) A PEM encoded private key.
+ `passphrase` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) An optional passphrase for the private key.
+ `padding` [<crypto.constants>](crypto#cryptoconstants) An optional padding value defined in `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING` or `crypto.constants.RSA_PKCS1_PADDING`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The string encoding to use when `buffer`, `key`, or `passphrase` are strings.
* `buffer` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* Returns: [<Buffer>](buffer#class-buffer) A new `Buffer` with the encrypted content.
Encrypts `buffer` with `privateKey`. The returned data can be decrypted using the corresponding public key, for example using [`crypto.publicDecrypt()`](#cryptopublicdecryptkey-buffer).
If `privateKey` is not a [`KeyObject`](#class-keyobject), this function behaves as if `privateKey` had been passed to [`crypto.createPrivateKey()`](#cryptocreateprivatekeykey). If it is an object, the `padding` property can be passed. Otherwise, this function uses `RSA_PKCS1_PADDING`.
####
`crypto.publicDecrypt(key, buffer)`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Added string, ArrayBuffer, and CryptoKey as allowable key types. The passphrase can be an ArrayBuffer. The buffer can be a string or ArrayBuffer. All types that accept buffers are limited to a maximum of 2 \*\* 31 - 1 bytes. |
| v11.6.0 | This function now supports key objects. |
| v1.1.0 | Added in: v1.1.0 |
* `key` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
+ `passphrase` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) An optional passphrase for the private key.
+ `padding` [<crypto.constants>](crypto#cryptoconstants) An optional padding value defined in `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING` or `crypto.constants.RSA_PKCS1_PADDING`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The string encoding to use when `buffer`, `key`, or `passphrase` are strings.
* `buffer` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* Returns: [<Buffer>](buffer#class-buffer) A new `Buffer` with the decrypted content.
Decrypts `buffer` with `key`.`buffer` was previously encrypted using the corresponding private key, for example using [`crypto.privateEncrypt()`](#cryptoprivateencryptprivatekey-buffer).
If `key` is not a [`KeyObject`](#class-keyobject), this function behaves as if `key` had been passed to [`crypto.createPublicKey()`](#cryptocreatepublickeykey). If it is an object, the `padding` property can be passed. Otherwise, this function uses `RSA_PKCS1_PADDING`.
Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key.
####
`crypto.publicEncrypt(key, buffer)`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | Added string, ArrayBuffer, and CryptoKey as allowable key types. The oaepLabel and passphrase can be ArrayBuffers. The buffer can be a string or ArrayBuffer. All types that accept buffers are limited to a maximum of 2 \*\* 31 - 1 bytes. |
| v12.11.0 | The `oaepLabel` option was added. |
| v12.9.0 | The `oaepHash` option was added. |
| v11.6.0 | This function now supports key objects. |
| v0.11.14 | Added in: v0.11.14 |
* `key` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
+ `key` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey) A PEM encoded public or private key, [<KeyObject>](crypto#class-keyobject), or [<CryptoKey>](webcrypto#class-cryptokey).
+ `oaepHash` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The hash function to use for OAEP padding and MGF1. **Default:** `'sha1'`
+ `oaepLabel` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The label to use for OAEP padding. If not specified, no label is used.
+ `passphrase` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) An optional passphrase for the private key.
+ `padding` [<crypto.constants>](crypto#cryptoconstants) An optional padding value defined in `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING`, `crypto.constants.RSA_PKCS1_PADDING`, or `crypto.constants.RSA_PKCS1_OAEP_PADDING`.
+ `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The string encoding to use when `buffer`, `key`, `oaepLabel`, or `passphrase` are strings.
* `buffer` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* Returns: [<Buffer>](buffer#class-buffer) A new `Buffer` with the encrypted content.
Encrypts the content of `buffer` with `key` and returns a new [`Buffer`](buffer) with encrypted content. The returned data can be decrypted using the corresponding private key, for example using [`crypto.privateDecrypt()`](#cryptoprivatedecryptprivatekey-buffer).
If `key` is not a [`KeyObject`](#class-keyobject), this function behaves as if `key` had been passed to [`crypto.createPublicKey()`](#cryptocreatepublickeykey). If it is an object, the `padding` property can be passed. Otherwise, this function uses `RSA_PKCS1_OAEP_PADDING`.
Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key.
####
`crypto.randomBytes(size[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v9.0.0 | Passing `null` as the `callback` argument now throws `ERR_INVALID_CALLBACK`. |
| v0.5.8 | Added in: v0.5.8 |
* `size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bytes to generate. The `size` must not be larger than `2**31 - 1`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `buf` [<Buffer>](buffer#class-buffer)
* Returns: [<Buffer>](buffer#class-buffer) if the `callback` function is not provided.
Generates cryptographically strong pseudorandom data. The `size` argument is a number indicating the number of bytes to generate.
If a `callback` function is provided, the bytes are generated asynchronously and the `callback` function is invoked with two arguments: `err` and `buf`. If an error occurs, `err` will be an `Error` object; otherwise it is `null`. The `buf` argument is a [`Buffer`](buffer) containing the generated bytes.
MJS modules
```
// Asynchronous
const {
randomBytes
} = await import('node:crypto');
randomBytes(256, (err, buf) => {
if (err) throw err;
console.log(`${buf.length} bytes of random data: ${buf.toString('hex')}`);
});
```
CJS modules
```
// Asynchronous
const {
randomBytes,
} = require('node:crypto');
randomBytes(256, (err, buf) => {
if (err) throw err;
console.log(`${buf.length} bytes of random data: ${buf.toString('hex')}`);
});
```
If the `callback` function is not provided, the random bytes are generated synchronously and returned as a [`Buffer`](buffer). An error will be thrown if there is a problem generating the bytes.
MJS modules
```
// Synchronous
const {
randomBytes
} = await import('node:crypto');
const buf = randomBytes(256);
console.log(
`${buf.length} bytes of random data: ${buf.toString('hex')}`);
```
CJS modules
```
// Synchronous
const {
randomBytes,
} = require('node:crypto');
const buf = randomBytes(256);
console.log(
`${buf.length} bytes of random data: ${buf.toString('hex')}`);
```
The `crypto.randomBytes()` method will not complete until there is sufficient entropy available. This should normally never take longer than a few milliseconds. The only time when generating the random bytes may conceivably block for a longer period of time is right after boot, when the whole system is still low on entropy.
This API uses libuv's threadpool, which can have surprising and negative performance implications for some applications; see the [`UV_THREADPOOL_SIZE`](cli#uv_threadpool_sizesize) documentation for more information.
The asynchronous version of `crypto.randomBytes()` is carried out in a single threadpool request. To minimize threadpool task length variation, partition large `randomBytes` requests when doing so as part of fulfilling a client request.
####
`crypto.randomFillSync(buffer[, offset][, size])`
History
| Version | Changes |
| --- | --- |
| v9.0.0 | The `buffer` argument may be any `TypedArray` or `DataView`. |
| v7.10.0, v6.13.0 | Added in: v7.10.0, v6.13.0 |
* `buffer` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Must be supplied. The size of the provided `buffer` must not be larger than `2**31 - 1`.
* `offset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
* `size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.length - offset`. The `size` must not be larger than `2**31 - 1`.
* Returns: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) The object passed as `buffer` argument.
Synchronous version of [`crypto.randomFill()`](#cryptorandomfillbuffer-offset-size-callback).
MJS modules
```
import { Buffer } from 'node:buffer';
const { randomFillSync } = await import('node:crypto');
const buf = Buffer.alloc(10);
console.log(randomFillSync(buf).toString('hex'));
randomFillSync(buf, 5);
console.log(buf.toString('hex'));
// The above is equivalent to the following:
randomFillSync(buf, 5, 5);
console.log(buf.toString('hex'));
```
CJS modules
```
const { randomFillSync } = require('node:crypto');
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(10);
console.log(randomFillSync(buf).toString('hex'));
randomFillSync(buf, 5);
console.log(buf.toString('hex'));
// The above is equivalent to the following:
randomFillSync(buf, 5, 5);
console.log(buf.toString('hex'));
```
Any `ArrayBuffer`, `TypedArray` or `DataView` instance may be passed as `buffer`.
MJS modules
```
import { Buffer } from 'node:buffer';
const { randomFillSync } = await import('node:crypto');
const a = new Uint32Array(10);
console.log(Buffer.from(randomFillSync(a).buffer,
a.byteOffset, a.byteLength).toString('hex'));
const b = new DataView(new ArrayBuffer(10));
console.log(Buffer.from(randomFillSync(b).buffer,
b.byteOffset, b.byteLength).toString('hex'));
const c = new ArrayBuffer(10);
console.log(Buffer.from(randomFillSync(c)).toString('hex'));
```
CJS modules
```
const { randomFillSync } = require('node:crypto');
const { Buffer } = require('node:buffer');
const a = new Uint32Array(10);
console.log(Buffer.from(randomFillSync(a).buffer,
a.byteOffset, a.byteLength).toString('hex'));
const b = new DataView(new ArrayBuffer(10));
console.log(Buffer.from(randomFillSync(b).buffer,
b.byteOffset, b.byteLength).toString('hex'));
const c = new ArrayBuffer(10);
console.log(Buffer.from(randomFillSync(c)).toString('hex'));
```
####
`crypto.randomFill(buffer[, offset][, size], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v9.0.0 | The `buffer` argument may be any `TypedArray` or `DataView`. |
| v7.10.0, v6.13.0 | Added in: v7.10.0, v6.13.0 |
* `buffer` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) Must be supplied. The size of the provided `buffer` must not be larger than `2**31 - 1`.
* `offset` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `0`
* `size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) **Default:** `buffer.length - offset`. The `size` must not be larger than `2**31 - 1`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) `function(err, buf) {}`.
This function is similar to [`crypto.randomBytes()`](#cryptorandombytessize-callback) but requires the first argument to be a [`Buffer`](buffer) that will be filled. It also requires that a callback is passed in.
If the `callback` function is not provided, an error will be thrown.
MJS modules
```
import { Buffer } from 'node:buffer';
const { randomFill } = await import('node:crypto');
const buf = Buffer.alloc(10);
randomFill(buf, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
randomFill(buf, 5, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
// The above is equivalent to the following:
randomFill(buf, 5, 5, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
```
CJS modules
```
const { randomFill } = require('node:crypto');
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(10);
randomFill(buf, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
randomFill(buf, 5, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
// The above is equivalent to the following:
randomFill(buf, 5, 5, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
```
Any `ArrayBuffer`, `TypedArray`, or `DataView` instance may be passed as `buffer`.
While this includes instances of `Float32Array` and `Float64Array`, this function should not be used to generate random floating-point numbers. The result may contain `+Infinity`, `-Infinity`, and `NaN`, and even if the array contains finite numbers only, they are not drawn from a uniform random distribution and have no meaningful lower or upper bounds.
MJS modules
```
import { Buffer } from 'node:buffer';
const { randomFill } = await import('node:crypto');
const a = new Uint32Array(10);
randomFill(a, (err, buf) => {
if (err) throw err;
console.log(Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength)
.toString('hex'));
});
const b = new DataView(new ArrayBuffer(10));
randomFill(b, (err, buf) => {
if (err) throw err;
console.log(Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength)
.toString('hex'));
});
const c = new ArrayBuffer(10);
randomFill(c, (err, buf) => {
if (err) throw err;
console.log(Buffer.from(buf).toString('hex'));
});
```
CJS modules
```
const { randomFill } = require('node:crypto');
const { Buffer } = require('node:buffer');
const a = new Uint32Array(10);
randomFill(a, (err, buf) => {
if (err) throw err;
console.log(Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength)
.toString('hex'));
});
const b = new DataView(new ArrayBuffer(10));
randomFill(b, (err, buf) => {
if (err) throw err;
console.log(Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength)
.toString('hex'));
});
const c = new ArrayBuffer(10);
randomFill(c, (err, buf) => {
if (err) throw err;
console.log(Buffer.from(buf).toString('hex'));
});
```
This API uses libuv's threadpool, which can have surprising and negative performance implications for some applications; see the [`UV_THREADPOOL_SIZE`](cli#uv_threadpool_sizesize) documentation for more information.
The asynchronous version of `crypto.randomFill()` is carried out in a single threadpool request. To minimize threadpool task length variation, partition large `randomFill` requests when doing so as part of fulfilling a client request.
####
`crypto.randomInt([min, ]max[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v14.10.0, v12.19.0 | Added in: v14.10.0, v12.19.0 |
* `min` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Start of random range (inclusive). **Default:** `0`.
* `max` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) End of random range (exclusive).
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) `function(err, n) {}`.
Return a random integer `n` such that `min <= n < max`. This implementation avoids [modulo bias](https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle#Modulo_bias).
The range (`max - min`) must be less than 248. `min` and `max` must be [safe integers](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isSafeInteger).
If the `callback` function is not provided, the random integer is generated synchronously.
MJS modules
```
// Asynchronous
const {
randomInt
} = await import('node:crypto');
randomInt(3, (err, n) => {
if (err) throw err;
console.log(`Random number chosen from (0, 1, 2): ${n}`);
});
```
CJS modules
```
// Asynchronous
const {
randomInt,
} = require('node:crypto');
randomInt(3, (err, n) => {
if (err) throw err;
console.log(`Random number chosen from (0, 1, 2): ${n}`);
});
```
MJS modules
```
// Synchronous
const {
randomInt
} = await import('node:crypto');
const n = randomInt(3);
console.log(`Random number chosen from (0, 1, 2): ${n}`);
```
CJS modules
```
// Synchronous
const {
randomInt,
} = require('node:crypto');
const n = randomInt(3);
console.log(`Random number chosen from (0, 1, 2): ${n}`);
```
MJS modules
```
// With `min` argument
const {
randomInt
} = await import('node:crypto');
const n = randomInt(1, 7);
console.log(`The dice rolled: ${n}`);
```
CJS modules
```
// With `min` argument
const {
randomInt,
} = require('node:crypto');
const n = randomInt(1, 7);
console.log(`The dice rolled: ${n}`);
```
####
`crypto.randomUUID([options])`
Added in: v15.6.0, v14.17.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `disableEntropyCache` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) By default, to improve performance, Node.js generates and caches enough random data to generate up to 128 random UUIDs. To generate a UUID without using the cache, set `disableEntropyCache` to `true`. **Default:** `false`.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Generates a random [RFC 4122](https://www.rfc-editor.org/rfc/rfc4122.txt) version 4 UUID. The UUID is generated using a cryptographic pseudorandom number generator.
####
`crypto.scrypt(password, salt, keylen[, options], callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v15.0.0 | The password and salt arguments can also be ArrayBuffer instances. |
| v12.8.0, v10.17.0 | The `maxmem` value can now be any safe integer. |
| v10.9.0 | The `cost`, `blockSize` and `parallelization` option names have been added. |
| v10.5.0 | Added in: v10.5.0 |
* `password` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `salt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `keylen` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cost` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) CPU/memory cost parameter. Must be a power of two greater than one. **Default:** `16384`.
+ `blockSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Block size parameter. **Default:** `8`.
+ `parallelization` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Parallelization parameter. **Default:** `1`.
+ `N` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Alias for `cost`. Only one of both may be specified.
+ `r` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Alias for `blockSize`. Only one of both may be specified.
+ `p` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Alias for `parallelization`. Only one of both may be specified.
+ `maxmem` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Memory upper bound. It is an error when (approximately) `128 * N * r > maxmem`. **Default:** `32 * 1024 * 1024`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `derivedKey` [<Buffer>](buffer#class-buffer)
Provides an asynchronous [scrypt](https://en.wikipedia.org/wiki/Scrypt) implementation. Scrypt is a password-based key derivation function that is designed to be expensive computationally and memory-wise in order to make brute-force attacks unrewarding.
The `salt` should be as unique as possible. It is recommended that a salt is random and at least 16 bytes long. See [NIST SP 800-132](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-132.pdf) for details.
When passing strings for `password` or `salt`, please consider [caveats when using strings as inputs to cryptographic APIs](#using-strings-as-inputs-to-cryptographic-apis).
The `callback` function is called with two arguments: `err` and `derivedKey`. `err` is an exception object when key derivation fails, otherwise `err` is `null`. `derivedKey` is passed to the callback as a [`Buffer`](buffer).
An exception is thrown when any of the input arguments specify invalid values or types.
MJS modules
```
const {
scrypt
} = await import('node:crypto');
// Using the factory defaults.
scrypt('password', 'salt', 64, (err, derivedKey) => {
if (err) throw err;
console.log(derivedKey.toString('hex')); // '3745e48...08d59ae'
});
// Using a custom N parameter. Must be a power of two.
scrypt('password', 'salt', 64, { N: 1024 }, (err, derivedKey) => {
if (err) throw err;
console.log(derivedKey.toString('hex')); // '3745e48...aa39b34'
});
```
CJS modules
```
const {
scrypt,
} = require('node:crypto');
// Using the factory defaults.
scrypt('password', 'salt', 64, (err, derivedKey) => {
if (err) throw err;
console.log(derivedKey.toString('hex')); // '3745e48...08d59ae'
});
// Using a custom N parameter. Must be a power of two.
scrypt('password', 'salt', 64, { N: 1024 }, (err, derivedKey) => {
if (err) throw err;
console.log(derivedKey.toString('hex')); // '3745e48...aa39b34'
});
```
####
`crypto.scryptSync(password, salt, keylen[, options])`
History
| Version | Changes |
| --- | --- |
| v12.8.0, v10.17.0 | The `maxmem` value can now be any safe integer. |
| v10.9.0 | The `cost`, `blockSize` and `parallelization` option names have been added. |
| v10.5.0 | Added in: v10.5.0 |
* `password` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `salt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `keylen` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `cost` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) CPU/memory cost parameter. Must be a power of two greater than one. **Default:** `16384`.
+ `blockSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Block size parameter. **Default:** `8`.
+ `parallelization` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Parallelization parameter. **Default:** `1`.
+ `N` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Alias for `cost`. Only one of both may be specified.
+ `r` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Alias for `blockSize`. Only one of both may be specified.
+ `p` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Alias for `parallelization`. Only one of both may be specified.
+ `maxmem` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Memory upper bound. It is an error when (approximately) `128 * N * r > maxmem`. **Default:** `32 * 1024 * 1024`.
* Returns: [<Buffer>](buffer#class-buffer)
Provides a synchronous [scrypt](https://en.wikipedia.org/wiki/Scrypt) implementation. Scrypt is a password-based key derivation function that is designed to be expensive computationally and memory-wise in order to make brute-force attacks unrewarding.
The `salt` should be as unique as possible. It is recommended that a salt is random and at least 16 bytes long. See [NIST SP 800-132](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-132.pdf) for details.
When passing strings for `password` or `salt`, please consider [caveats when using strings as inputs to cryptographic APIs](#using-strings-as-inputs-to-cryptographic-apis).
An exception is thrown when key derivation fails, otherwise the derived key is returned as a [`Buffer`](buffer).
An exception is thrown when any of the input arguments specify invalid values or types.
MJS modules
```
const {
scryptSync
} = await import('node:crypto');
// Using the factory defaults.
const key1 = scryptSync('password', 'salt', 64);
console.log(key1.toString('hex')); // '3745e48...08d59ae'
// Using a custom N parameter. Must be a power of two.
const key2 = scryptSync('password', 'salt', 64, { N: 1024 });
console.log(key2.toString('hex')); // '3745e48...aa39b34'
```
CJS modules
```
const {
scryptSync,
} = require('node:crypto');
// Using the factory defaults.
const key1 = scryptSync('password', 'salt', 64);
console.log(key1.toString('hex')); // '3745e48...08d59ae'
// Using a custom N parameter. Must be a power of two.
const key2 = scryptSync('password', 'salt', 64, { N: 1024 });
console.log(key2.toString('hex')); // '3745e48...aa39b34'
```
####
`crypto.secureHeapUsed()`
Added in: v15.6.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `total` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The total allocated secure heap size as specified using the `--secure-heap=n` command-line flag.
+ `min` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The minimum allocation from the secure heap as specified using the `--secure-heap-min` command-line flag.
+ `used` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The total number of bytes currently allocated from the secure heap.
+ `utilization` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The calculated ratio of `used` to `total` allocated bytes.
####
`crypto.setEngine(engine[, flags])`
Added in: v0.11.11 * `engine` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `flags` [<crypto.constants>](crypto#cryptoconstants) **Default:** `crypto.constants.ENGINE_METHOD_ALL`
Load and set the `engine` for some or all OpenSSL functions (selected by flags).
`engine` could be either an id or a path to the engine's shared library.
The optional `flags` argument uses `ENGINE_METHOD_ALL` by default. The `flags` is a bit field taking one of or a mix of the following flags (defined in `crypto.constants`):
* `crypto.constants.ENGINE_METHOD_RSA`
* `crypto.constants.ENGINE_METHOD_DSA`
* `crypto.constants.ENGINE_METHOD_DH`
* `crypto.constants.ENGINE_METHOD_RAND`
* `crypto.constants.ENGINE_METHOD_EC`
* `crypto.constants.ENGINE_METHOD_CIPHERS`
* `crypto.constants.ENGINE_METHOD_DIGESTS`
* `crypto.constants.ENGINE_METHOD_PKEY_METHS`
* `crypto.constants.ENGINE_METHOD_PKEY_ASN1_METHS`
* `crypto.constants.ENGINE_METHOD_ALL`
* `crypto.constants.ENGINE_METHOD_NONE`
####
`crypto.setFips(bool)`
Added in: v10.0.0 * `bool` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` to enable FIPS mode.
Enables the FIPS compliant crypto provider in a FIPS-enabled Node.js build. Throws an error if FIPS mode is not available.
####
`crypto.sign(algorithm, data, key[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v15.12.0 | Optional callback argument added. |
| v13.2.0, v12.16.0 | This function now supports IEEE-P1363 DSA and ECDSA signatures. |
| v12.0.0 | Added in: v12.0.0 |
* `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
* `data` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `key` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `signature` [<Buffer>](buffer#class-buffer)
* Returns: [<Buffer>](buffer#class-buffer) if the `callback` function is not provided.
Calculates and returns the signature for `data` using the given private key and algorithm. If `algorithm` is `null` or `undefined`, then the algorithm is dependent upon the key type (especially Ed25519 and Ed448).
If `key` is not a [`KeyObject`](#class-keyobject), this function behaves as if `key` had been passed to [`crypto.createPrivateKey()`](#cryptocreateprivatekeykey). If it is an object, the following additional properties can be passed:
* `dsaEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) For DSA and ECDSA, this option specifies the format of the generated signature. It can be one of the following:
+ `'der'` (default): DER-encoded ASN.1 signature structure encoding `(r, s)`.
+ `'ieee-p1363'`: Signature format `r || s` as proposed in IEEE-P1363.
* `padding` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optional padding value for RSA, one of the following:
+ `crypto.constants.RSA_PKCS1_PADDING` (default)
+ `crypto.constants.RSA_PKCS1_PSS_PADDING``RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function used to sign the message as specified in section 3.1 of [RFC 4055](https://www.rfc-editor.org/rfc/rfc4055.txt).
* `saltLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Salt length for when padding is `RSA_PKCS1_PSS_PADDING`. The special value `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest size, `crypto.constants.RSA_PSS_SALTLEN_MAX_SIGN` (default) sets it to the maximum permissible value.
If the `callback` function is provided this function uses libuv's threadpool.
####
`crypto.subtle`
Added in: v17.4.0 * Type: [<SubtleCrypto>](webcrypto#class-subtlecrypto)
A convenient alias for [`crypto.webcrypto.subtle`](webcrypto#class-subtlecrypto).
####
`crypto.timingSafeEqual(a, b)`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The a and b arguments can also be ArrayBuffer. |
| v6.6.0 | Added in: v6.6.0 |
* `a` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `b` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
This function compares the underlying bytes that represent the given `ArrayBuffer`, `TypedArray`, or `DataView` instances using a constant-time algorithm.
This function does not leak timing information that would allow an attacker to guess one of the values. This is suitable for comparing HMAC digests or secret values like authentication cookies or [capability urls](https://www.w3.org/TR/capability-urls/).
`a` and `b` must both be `Buffer`s, `TypedArray`s, or `DataView`s, and they must have the same byte length. An error is thrown if `a` and `b` have different byte lengths.
If at least one of `a` and `b` is a `TypedArray` with more than one byte per entry, such as `Uint16Array`, the result will be computed using the platform byte order.
**When both of the inputs are `Float32Array`s or `Float64Array`s, this function might return unexpected results due to IEEE 754 encoding of floating-point numbers. In particular, neither `x === y` nor `Object.is(x, y)` implies that the byte representations of two floating-point numbers `x` and `y` are equal.**
Use of `crypto.timingSafeEqual` does not guarantee that the *surrounding* code is timing-safe. Care should be taken to ensure that the surrounding code does not introduce timing vulnerabilities.
####
`crypto.verify(algorithm, data, key, signature[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v15.12.0 | Optional callback argument added. |
| v15.0.0 | The data, key, and signature arguments can also be ArrayBuffer. |
| v13.2.0, v12.16.0 | This function now supports IEEE-P1363 DSA and ECDSA signatures. |
| v12.0.0 | Added in: v12.0.0 |
* `algorithm` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
* `data` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `key` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) | [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<KeyObject>](crypto#class-keyobject) | [<CryptoKey>](webcrypto#class-cryptokey)
* `signature` [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `result` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` or `false` depending on the validity of the signature for the data and public key if the `callback` function is not provided.
Verifies the given signature for `data` using the given key and algorithm. If `algorithm` is `null` or `undefined`, then the algorithm is dependent upon the key type (especially Ed25519 and Ed448).
If `key` is not a [`KeyObject`](#class-keyobject), this function behaves as if `key` had been passed to [`crypto.createPublicKey()`](#cryptocreatepublickeykey). If it is an object, the following additional properties can be passed:
* `dsaEncoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) For DSA and ECDSA, this option specifies the format of the signature. It can be one of the following:
+ `'der'` (default): DER-encoded ASN.1 signature structure encoding `(r, s)`.
+ `'ieee-p1363'`: Signature format `r || s` as proposed in IEEE-P1363.
* `padding` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optional padding value for RSA, one of the following:
+ `crypto.constants.RSA_PKCS1_PADDING` (default)
+ `crypto.constants.RSA_PKCS1_PSS_PADDING``RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function used to sign the message as specified in section 3.1 of [RFC 4055](https://www.rfc-editor.org/rfc/rfc4055.txt).
* `saltLength` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Salt length for when padding is `RSA_PKCS1_PSS_PADDING`. The special value `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest size, `crypto.constants.RSA_PSS_SALTLEN_MAX_SIGN` (default) sets it to the maximum permissible value.
The `signature` argument is the previously calculated signature for the `data`.
Because public keys can be derived from private keys, a private key or a public key may be passed for `key`.
If the `callback` function is provided this function uses libuv's threadpool.
####
`crypto.webcrypto`
Added in: v15.0.0 Type: [<Crypto>](webcrypto#class-crypto) An implementation of the Web Crypto API standard.
See the [Web Crypto API documentation](webcrypto) for details.
### Notes
#### Using strings as inputs to cryptographic APIs
For historical reasons, many cryptographic APIs provided by Node.js accept strings as inputs where the underlying cryptographic algorithm works on byte sequences. These instances include plaintexts, ciphertexts, symmetric keys, initialization vectors, passphrases, salts, authentication tags, and additional authenticated data.
When passing strings to cryptographic APIs, consider the following factors.
* Not all byte sequences are valid UTF-8 strings. Therefore, when a byte sequence of length `n` is derived from a string, its entropy is generally lower than the entropy of a random or pseudorandom `n` byte sequence. For example, no UTF-8 string will result in the byte sequence `c0 af`. Secret keys should almost exclusively be random or pseudorandom byte sequences.
* Similarly, when converting random or pseudorandom byte sequences to UTF-8 strings, subsequences that do not represent valid code points may be replaced by the Unicode replacement character (`U+FFFD`). The byte representation of the resulting Unicode string may, therefore, not be equal to the byte sequence that the string was created from.
```
const original = [0xc0, 0xaf];
const bytesAsString = Buffer.from(original).toString('utf8');
const stringAsBytes = Buffer.from(bytesAsString, 'utf8');
console.log(stringAsBytes);
// Prints '<Buffer ef bf bd ef bf bd>'.
```
The outputs of ciphers, hash functions, signature algorithms, and key derivation functions are pseudorandom byte sequences and should not be used as Unicode strings.
* When strings are obtained from user input, some Unicode characters can be represented in multiple equivalent ways that result in different byte sequences. For example, when passing a user passphrase to a key derivation function, such as PBKDF2 or scrypt, the result of the key derivation function depends on whether the string uses composed or decomposed characters. Node.js does not normalize character representations. Developers should consider using [`String.prototype.normalize()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize) on user inputs before passing them to cryptographic APIs.
#### Legacy streams API (prior to Node.js 0.10)
The Crypto module was added to Node.js before there was the concept of a unified Stream API, and before there were [`Buffer`](buffer) objects for handling binary data. As such, the many of the `crypto` defined classes have methods not typically found on other Node.js classes that implement the [streams](stream) API (e.g. `update()`, `final()`, or `digest()`). Also, many methods accepted and returned `'latin1'` encoded strings by default rather than `Buffer`s. This default was changed after Node.js v0.8 to use [`Buffer`](buffer) objects by default instead.
#### Support for weak or compromised algorithms
The `node:crypto` module still supports some algorithms which are already compromised and are not currently recommended for use. The API also allows the use of ciphers and hashes with a small key size that are too weak for safe use.
Users should take full responsibility for selecting the crypto algorithm and key size according to their security requirements.
Based on the recommendations of [NIST SP 800-131A](https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-131Ar1.pdf):
* MD5 and SHA-1 are no longer acceptable where collision resistance is required such as digital signatures.
* The key used with RSA, DSA, and DH algorithms is recommended to have at least 2048 bits and that of the curve of ECDSA and ECDH at least 224 bits, to be safe to use for several years.
* The DH groups of `modp1`, `modp2` and `modp5` have a key size smaller than 2048 bits and are not recommended.
See the reference for other recommendations and details.
Some algorithms that have known weaknesses and are of little relevance in practice are only available through the [legacy provider](cli#--openssl-legacy-provider), which is not enabled by default.
#### CCM mode
CCM is one of the supported [AEAD algorithms](https://en.wikipedia.org/wiki/Authenticated_encryption). Applications which use this mode must adhere to certain restrictions when using the cipher API:
* The authentication tag length must be specified during cipher creation by setting the `authTagLength` option and must be one of 4, 6, 8, 10, 12, 14 or 16 bytes.
* The length of the initialization vector (nonce) `N` must be between 7 and 13 bytes (`7 ≤ N ≤ 13`).
* The length of the plaintext is limited to `2 ** (8 * (15 - N))` bytes.
* When decrypting, the authentication tag must be set via `setAuthTag()` before calling `update()`. Otherwise, decryption will fail and `final()` will throw an error in compliance with section 2.6 of [RFC 3610](https://www.rfc-editor.org/rfc/rfc3610.txt).
* Using stream methods such as `write(data)`, `end(data)` or `pipe()` in CCM mode might fail as CCM cannot handle more than one chunk of data per instance.
* When passing additional authenticated data (AAD), the length of the actual message in bytes must be passed to `setAAD()` via the `plaintextLength` option. Many crypto libraries include the authentication tag in the ciphertext, which means that they produce ciphertexts of the length `plaintextLength + authTagLength`. Node.js does not include the authentication tag, so the ciphertext length is always `plaintextLength`. This is not necessary if no AAD is used.
* As CCM processes the whole message at once, `update()` must be called exactly once.
* Even though calling `update()` is sufficient to encrypt/decrypt the message, applications *must* call `final()` to compute or verify the authentication tag.
MJS modules
```
import { Buffer } from 'node:buffer';
const {
createCipheriv,
createDecipheriv,
randomBytes
} = await import('node:crypto');
const key = 'keykeykeykeykeykeykeykey';
const nonce = randomBytes(12);
const aad = Buffer.from('0123456789', 'hex');
const cipher = createCipheriv('aes-192-ccm', key, nonce, {
authTagLength: 16
});
const plaintext = 'Hello world';
cipher.setAAD(aad, {
plaintextLength: Buffer.byteLength(plaintext)
});
const ciphertext = cipher.update(plaintext, 'utf8');
cipher.final();
const tag = cipher.getAuthTag();
// Now transmit { ciphertext, nonce, tag }.
const decipher = createDecipheriv('aes-192-ccm', key, nonce, {
authTagLength: 16
});
decipher.setAuthTag(tag);
decipher.setAAD(aad, {
plaintextLength: ciphertext.length
});
const receivedPlaintext = decipher.update(ciphertext, null, 'utf8');
try {
decipher.final();
} catch (err) {
throw new Error('Authentication failed!', { cause: err });
}
console.log(receivedPlaintext);
```
CJS modules
```
const { Buffer } = require('node:buffer');
const {
createCipheriv,
createDecipheriv,
randomBytes,
} = require('node:crypto');
const key = 'keykeykeykeykeykeykeykey';
const nonce = randomBytes(12);
const aad = Buffer.from('0123456789', 'hex');
const cipher = createCipheriv('aes-192-ccm', key, nonce, {
authTagLength: 16
});
const plaintext = 'Hello world';
cipher.setAAD(aad, {
plaintextLength: Buffer.byteLength(plaintext)
});
const ciphertext = cipher.update(plaintext, 'utf8');
cipher.final();
const tag = cipher.getAuthTag();
// Now transmit { ciphertext, nonce, tag }.
const decipher = createDecipheriv('aes-192-ccm', key, nonce, {
authTagLength: 16
});
decipher.setAuthTag(tag);
decipher.setAAD(aad, {
plaintextLength: ciphertext.length
});
const receivedPlaintext = decipher.update(ciphertext, null, 'utf8');
try {
decipher.final();
} catch (err) {
throw new Error('Authentication failed!', { cause: err });
}
console.log(receivedPlaintext);
```
### Crypto constants
The following constants exported by `crypto.constants` apply to various uses of the `node:crypto`, `node:tls`, and `node:https` modules and are generally specific to OpenSSL.
#### OpenSSL options
See the [list of SSL OP Flags](https://wiki.openssl.org/index.php/List_of_SSL_OP_Flags#Table_of_Options) for details.
| Constant | Description |
| --- | --- |
| `SSL_OP_ALL` | Applies multiple bug workarounds within OpenSSL. See <https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html> for detail. |
| `SSL_OP_ALLOW_NO_DHE_KEX` | Instructs OpenSSL to allow a non-[EC]DHE-based key exchange mode for TLS v1.3 |
| `SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION` | Allows legacy insecure renegotiation between OpenSSL and unpatched clients or servers. See <https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html>. |
| `SSL_OP_CIPHER_SERVER_PREFERENCE` | Attempts to use the server's preferences instead of the client's when selecting a cipher. Behavior depends on protocol version. See <https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html>. |
| `SSL_OP_CISCO_ANYCONNECT` | Instructs OpenSSL to use Cisco's "speshul" version of DTLS\_BAD\_VER. |
| `SSL_OP_COOKIE_EXCHANGE` | Instructs OpenSSL to turn on cookie exchange. |
| `SSL_OP_CRYPTOPRO_TLSEXT_BUG` | Instructs OpenSSL to add server-hello extension from an early version of the cryptopro draft. |
| `SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS` | Instructs OpenSSL to disable a SSL 3.0/TLS 1.0 vulnerability workaround added in OpenSSL 0.9.6d. |
| `SSL_OP_EPHEMERAL_RSA` | Instructs OpenSSL to always use the tmp\_rsa key when performing RSA operations. |
| `SSL_OP_LEGACY_SERVER_CONNECT` | Allows initial connection to servers that do not support RI. |
| `SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER` | |
| `SSL_OP_MICROSOFT_SESS_ID_BUG` | |
| `SSL_OP_MSIE_SSLV2_RSA_PADDING` | Instructs OpenSSL to disable the workaround for a man-in-the-middle protocol-version vulnerability in the SSL 2.0 server implementation. |
| `SSL_OP_NETSCAPE_CA_DN_BUG` | |
| `SSL_OP_NETSCAPE_CHALLENGE_BUG` | |
| `SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG` | |
| `SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG` | |
| `SSL_OP_NO_COMPRESSION` | Instructs OpenSSL to disable support for SSL/TLS compression. |
| `SSL_OP_NO_ENCRYPT_THEN_MAC` | Instructs OpenSSL to disable encrypt-then-MAC. |
| `SSL_OP_NO_QUERY_MTU` | |
| `SSL_OP_NO_RENEGOTIATION` | Instructs OpenSSL to disable renegotiation. |
| `SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION` | Instructs OpenSSL to always start a new session when performing renegotiation. |
| `SSL_OP_NO_SSLv2` | Instructs OpenSSL to turn off SSL v2 |
| `SSL_OP_NO_SSLv3` | Instructs OpenSSL to turn off SSL v3 |
| `SSL_OP_NO_TICKET` | Instructs OpenSSL to disable use of RFC4507bis tickets. |
| `SSL_OP_NO_TLSv1` | Instructs OpenSSL to turn off TLS v1 |
| `SSL_OP_NO_TLSv1_1` | Instructs OpenSSL to turn off TLS v1.1 |
| `SSL_OP_NO_TLSv1_2` | Instructs OpenSSL to turn off TLS v1.2 |
| `SSL_OP_NO_TLSv1_3` | Instructs OpenSSL to turn off TLS v1.3 |
| `SSL_OP_PKCS1_CHECK_1` | |
| `SSL_OP_PKCS1_CHECK_2` | |
| `SSL_OP_PRIORITIZE_CHACHA` | Instructs OpenSSL server to prioritize ChaCha20-Poly1305 when the client does. This option has no effect if `SSL_OP_CIPHER_SERVER_PREFERENCE` is not enabled. |
| `SSL_OP_SINGLE_DH_USE` | Instructs OpenSSL to always create a new key when using temporary/ephemeral DH parameters. |
| `SSL_OP_SINGLE_ECDH_USE` | Instructs OpenSSL to always create a new key when using temporary/ephemeral ECDH parameters. |
| `SSL_OP_SSLEAY_080_CLIENT_DH_BUG` | |
| `SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG` | |
| `SSL_OP_TLS_BLOCK_PADDING_BUG` | |
| `SSL_OP_TLS_D5_BUG` | |
| `SSL_OP_TLS_ROLLBACK_BUG` | Instructs OpenSSL to disable version rollback attack detection. |
#### OpenSSL engine constants
| Constant | Description |
| --- | --- |
| `ENGINE_METHOD_RSA` | Limit engine usage to RSA |
| `ENGINE_METHOD_DSA` | Limit engine usage to DSA |
| `ENGINE_METHOD_DH` | Limit engine usage to DH |
| `ENGINE_METHOD_RAND` | Limit engine usage to RAND |
| `ENGINE_METHOD_EC` | Limit engine usage to EC |
| `ENGINE_METHOD_CIPHERS` | Limit engine usage to CIPHERS |
| `ENGINE_METHOD_DIGESTS` | Limit engine usage to DIGESTS |
| `ENGINE_METHOD_PKEY_METHS` | Limit engine usage to PKEY\_METHDS |
| `ENGINE_METHOD_PKEY_ASN1_METHS` | Limit engine usage to PKEY\_ASN1\_METHS |
| `ENGINE_METHOD_ALL` | |
| `ENGINE_METHOD_NONE` | |
#### Other OpenSSL constants
| Constant | Description |
| --- | --- |
| `DH_CHECK_P_NOT_SAFE_PRIME` | |
| `DH_CHECK_P_NOT_PRIME` | |
| `DH_UNABLE_TO_CHECK_GENERATOR` | |
| `DH_NOT_SUITABLE_GENERATOR` | |
| `ALPN_ENABLED` | |
| `RSA_PKCS1_PADDING` | |
| `RSA_SSLV23_PADDING` | |
| `RSA_NO_PADDING` | |
| `RSA_PKCS1_OAEP_PADDING` | |
| `RSA_X931_PADDING` | |
| `RSA_PKCS1_PSS_PADDING` | |
| `RSA_PSS_SALTLEN_DIGEST` | Sets the salt length for `RSA_PKCS1_PSS_PADDING` to the digest size when signing or verifying. |
| `RSA_PSS_SALTLEN_MAX_SIGN` | Sets the salt length for `RSA_PKCS1_PSS_PADDING` to the maximum permissible value when signing data. |
| `RSA_PSS_SALTLEN_AUTO` | Causes the salt length for `RSA_PKCS1_PSS_PADDING` to be determined automatically when verifying a signature. |
| `POINT_CONVERSION_COMPRESSED` | |
| `POINT_CONVERSION_UNCOMPRESSED` | |
| `POINT_CONVERSION_HYBRID` | |
#### Node.js crypto constants
| Constant | Description |
| --- | --- |
| `defaultCoreCipherList` | Specifies the built-in default cipher list used by Node.js. |
| `defaultCipherList` | Specifies the active default cipher list used by the current Node.js process. |
| programming_docs |
node None Readline
--------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/readline.js](https://github.com/nodejs/node/blob/v19.0.1/lib/readline.js)
The `node:readline` module provides an interface for reading data from a [Readable](stream#readable-streams) stream (such as [`process.stdin`](process#processstdin)) one line at a time.
To use the promise-based APIs:
MJS modules
```
import * as readline from 'node:readline/promises';
```
CJS modules
```
const readline = require('node:readline/promises');
```
To use the callback and sync APIs:
MJS modules
```
import * as readline from 'node:readline';
```
CJS modules
```
const readline = require('node:readline');
```
The following simple example illustrates the basic use of the `node:readline` module.
MJS modules
```
import * as readline from 'node:readline/promises';
import { stdin as input, stdout as output } from 'node:process';
const rl = readline.createInterface({ input, output });
const answer = await rl.question('What do you think of Node.js? ');
console.log(`Thank you for your valuable feedback: ${answer}`);
rl.close();
```
CJS modules
```
const readline = require('node:readline');
const { stdin: input, stdout: output } = require('node:process');
const rl = readline.createInterface({ input, output });
rl.question('What do you think of Node.js? ', (answer) => {
// TODO: Log the answer in a database
console.log(`Thank you for your valuable feedback: ${answer}`);
rl.close();
});
```
Once this code is invoked, the Node.js application will not terminate until the `readline.Interface` is closed because the interface waits for data to be received on the `input` stream.
### Class: `InterfaceConstructor`
Added in: v0.1.104 * Extends: [<EventEmitter>](events#class-eventemitter)
Instances of the `InterfaceConstructor` class are constructed using the `readlinePromises.createInterface()` or `readline.createInterface()` method. Every instance is associated with a single `input` [Readable](stream#readable-streams) stream and a single `output` [Writable](stream#writable-streams) stream. The `output` stream is used to print prompts for user input that arrives on, and is read from, the `input` stream.
#### Event: `'close'`
Added in: v0.1.98 The `'close'` event is emitted when one of the following occur:
* The `rl.close()` method is called and the `InterfaceConstructor` instance has relinquished control over the `input` and `output` streams;
* The `input` stream receives its `'end'` event;
* The `input` stream receives `Ctrl`+`D` to signal end-of-transmission (EOT);
* The `input` stream receives `Ctrl`+`C` to signal `SIGINT` and there is no `'SIGINT'` event listener registered on the `InterfaceConstructor` instance.
The listener function is called without passing any arguments.
The `InterfaceConstructor` instance is finished once the `'close'` event is emitted.
#### Event: `'line'`
Added in: v0.1.98 The `'line'` event is emitted whenever the `input` stream receives an end-of-line input (`\n`, `\r`, or `\r\n`). This usually occurs when the user presses `Enter` or `Return`.
The `'line'` event is also emitted if new data has been read from a stream and that stream ends without a final end-of-line marker.
The listener function is called with a string containing the single line of received input.
```
rl.on('line', (input) => {
console.log(`Received: ${input}`);
});
```
#### Event: `'history'`
Added in: v15.8.0, v14.18.0 The `'history'` event is emitted whenever the history array has changed.
The listener function is called with an array containing the history array. It will reflect all changes, added lines and removed lines due to `historySize` and `removeHistoryDuplicates`.
The primary purpose is to allow a listener to persist the history. It is also possible for the listener to change the history object. This could be useful to prevent certain lines to be added to the history, like a password.
```
rl.on('history', (history) => {
console.log(`Received: ${history}`);
});
```
#### Event: `'pause'`
Added in: v0.7.5 The `'pause'` event is emitted when one of the following occur:
* The `input` stream is paused.
* The `input` stream is not paused and receives the `'SIGCONT'` event. (See events [`'SIGTSTP'`](#event-sigtstp) and [`'SIGCONT'`](#event-sigcont).)
The listener function is called without passing any arguments.
```
rl.on('pause', () => {
console.log('Readline paused.');
});
```
#### Event: `'resume'`
Added in: v0.7.5 The `'resume'` event is emitted whenever the `input` stream is resumed.
The listener function is called without passing any arguments.
```
rl.on('resume', () => {
console.log('Readline resumed.');
});
```
#### Event: `'SIGCONT'`
Added in: v0.7.5 The `'SIGCONT'` event is emitted when a Node.js process previously moved into the background using `Ctrl`+`Z` (i.e. `SIGTSTP`) is then brought back to the foreground using [`fg(1p)`](http://man7.org/linux/man-pages/man1/fg.1p.html).
If the `input` stream was paused *before* the `SIGTSTP` request, this event will not be emitted.
The listener function is invoked without passing any arguments.
```
rl.on('SIGCONT', () => {
// `prompt` will automatically resume the stream
rl.prompt();
});
```
The `'SIGCONT'` event is *not* supported on Windows.
#### Event: `'SIGINT'`
Added in: v0.3.0 The `'SIGINT'` event is emitted whenever the `input` stream receives a `Ctrl+C` input, known typically as `SIGINT`. If there are no `'SIGINT'` event listeners registered when the `input` stream receives a `SIGINT`, the `'pause'` event will be emitted.
The listener function is invoked without passing any arguments.
```
rl.on('SIGINT', () => {
rl.question('Are you sure you want to exit? ', (answer) => {
if (answer.match(/^y(es)?$/i)) rl.pause();
});
});
```
#### Event: `'SIGTSTP'`
Added in: v0.7.5 The `'SIGTSTP'` event is emitted when the `input` stream receives a `Ctrl`+`Z` input, typically known as `SIGTSTP`. If there are no `'SIGTSTP'` event listeners registered when the `input` stream receives a `SIGTSTP`, the Node.js process will be sent to the background.
When the program is resumed using [`fg(1p)`](http://man7.org/linux/man-pages/man1/fg.1p.html), the `'pause'` and `'SIGCONT'` events will be emitted. These can be used to resume the `input` stream.
The `'pause'` and `'SIGCONT'` events will not be emitted if the `input` was paused before the process was sent to the background.
The listener function is invoked without passing any arguments.
```
rl.on('SIGTSTP', () => {
// This will override SIGTSTP and prevent the program from going to the
// background.
console.log('Caught SIGTSTP.');
});
```
The `'SIGTSTP'` event is *not* supported on Windows.
####
`rl.close()`
Added in: v0.1.98 The `rl.close()` method closes the `InterfaceConstructor` instance and relinquishes control over the `input` and `output` streams. When called, the `'close'` event will be emitted.
Calling `rl.close()` does not immediately stop other events (including `'line'`) from being emitted by the `InterfaceConstructor` instance.
####
`rl.pause()`
Added in: v0.3.4 The `rl.pause()` method pauses the `input` stream, allowing it to be resumed later if necessary.
Calling `rl.pause()` does not immediately pause other events (including `'line'`) from being emitted by the `InterfaceConstructor` instance.
####
`rl.prompt([preserveCursor])`
Added in: v0.1.98 * `preserveCursor` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, prevents the cursor placement from being reset to `0`.
The `rl.prompt()` method writes the `InterfaceConstructor` instances configured `prompt` to a new line in `output` in order to provide a user with a new location at which to provide input.
When called, `rl.prompt()` will resume the `input` stream if it has been paused.
If the `InterfaceConstructor` was created with `output` set to `null` or `undefined` the prompt is not written.
####
`rl.resume()`
Added in: v0.3.4 The `rl.resume()` method resumes the `input` stream if it has been paused.
####
`rl.setPrompt(prompt)`
Added in: v0.1.98 * `prompt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `rl.setPrompt()` method sets the prompt that will be written to `output` whenever `rl.prompt()` is called.
####
`rl.getPrompt()`
Added in: v15.3.0, v14.17.0 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) the current prompt string
The `rl.getPrompt()` method returns the current prompt used by `rl.prompt()`.
####
`rl.write(data[, key])`
Added in: v0.1.98 * `data` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `key` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ctrl` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` to indicate the `Ctrl` key.
+ `meta` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` to indicate the `Meta` key.
+ `shift` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` to indicate the `Shift` key.
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The name of the a key.
The `rl.write()` method will write either `data` or a key sequence identified by `key` to the `output`. The `key` argument is supported only if `output` is a [TTY](tty) text terminal. See [TTY keybindings](#tty-keybindings) for a list of key combinations.
If `key` is specified, `data` is ignored.
When called, `rl.write()` will resume the `input` stream if it has been paused.
If the `InterfaceConstructor` was created with `output` set to `null` or `undefined` the `data` and `key` are not written.
```
rl.write('Delete this!');
// Simulate Ctrl+U to delete the line written previously
rl.write(null, { ctrl: true, name: 'u' });
```
The `rl.write()` method will write the data to the `readline` `Interface`'s `input` *as if it were provided by the user*.
####
`rl[Symbol.asyncIterator]()`
History
| Version | Changes |
| --- | --- |
| v11.4.0, v10.16.0 | Added in: v11.4.0, v10.16.0 |
| v11.14.0, v10.17.0 | Symbol.asyncIterator support is no longer experimental. |
* Returns: [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface)
Create an `AsyncIterator` object that iterates through each line in the input stream as a string. This method allows asynchronous iteration of `InterfaceConstructor` objects through `for await...of` loops.
Errors in the input stream are not forwarded.
If the loop is terminated with `break`, `throw`, or `return`, [`rl.close()`](#rlclose) will be called. In other words, iterating over a `InterfaceConstructor` will always consume the input stream fully.
Performance is not on par with the traditional `'line'` event API. Use `'line'` instead for performance-sensitive applications.
```
async function processLineByLine() {
const rl = readline.createInterface({
// ...
});
for await (const line of rl) {
// Each line in the readline input will be successively available here as
// `line`.
}
}
```
`readline.createInterface()` will start to consume the input stream once invoked. Having asynchronous operations between interface creation and asynchronous iteration may result in missed lines.
####
`rl.line`
History
| Version | Changes |
| --- | --- |
| v15.8.0, v14.18.0 | Value will always be a string, never undefined. |
| v0.1.98 | Added in: v0.1.98 |
* [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The current input data being processed by node.
This can be used when collecting input from a TTY stream to retrieve the current value that has been processed thus far, prior to the `line` event being emitted. Once the `line` event has been emitted, this property will be an empty string.
Be aware that modifying the value during the instance runtime may have unintended consequences if `rl.cursor` is not also controlled.
**If not using a TTY stream for input, use the [`'line'`](#event-line) event.**
One possible use case would be as follows:
```
const values = ['lorem ipsum', 'dolor sit amet'];
const rl = readline.createInterface(process.stdin);
const showResults = debounce(() => {
console.log(
'\n',
values.filter((val) => val.startsWith(rl.line)).join(' ')
);
}, 300);
process.stdin.on('keypress', (c, k) => {
showResults();
});
```
####
`rl.cursor`
Added in: v0.1.98 * [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
The cursor position relative to `rl.line`.
This will track where the current cursor lands in the input string, when reading input from a TTY stream. The position of cursor determines the portion of the input string that will be modified as input is processed, as well as the column where the terminal caret will be rendered.
####
`rl.getCursorPos()`
Added in: v13.5.0, v12.16.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `rows` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the row of the prompt the cursor currently lands on
+ `cols` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) the screen column the cursor currently lands on
Returns the real position of the cursor in relation to the input prompt + string. Long input (wrapping) strings, as well as multiple line prompts are included in the calculations.
### Promises API
Added in: v17.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
#### Class: `readlinePromises.Interface`
Added in: v17.0.0 * Extends: [<readline.InterfaceConstructor>](readline#class-interfaceconstructor)
Instances of the `readlinePromises.Interface` class are constructed using the `readlinePromises.createInterface()` method. Every instance is associated with a single `input` [Readable](stream#readable-streams) stream and a single `output` [Writable](stream#writable-streams) stream. The `output` stream is used to print prompts for user input that arrives on, and is read from, the `input` stream.
#####
`rl.question(query[, options])`
Added in: v17.0.0 * `query` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A statement or query to write to `output`, prepended to the prompt.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) Optionally allows the `question()` to be canceled using an `AbortSignal`.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) A promise that is fulfilled with the user's input in response to the `query`.
The `rl.question()` method displays the `query` by writing it to the `output`, waits for user input to be provided on `input`, then invokes the `callback` function passing the provided input as the first argument.
When called, `rl.question()` will resume the `input` stream if it has been paused.
If the `readlinePromises.Interface` was created with `output` set to `null` or `undefined` the `query` is not written.
If the question is called after `rl.close()`, it returns a rejected promise.
Example usage:
```
const answer = await rl.question('What is your favorite food? ');
console.log(`Oh, so your favorite food is ${answer}`);
```
Using an `AbortSignal` to cancel a question.
```
const signal = AbortSignal.timeout(10_000);
signal.addEventListener('abort', () => {
console.log('The food question timed out');
}, { once: true });
const answer = await rl.question('What is your favorite food? ', { signal });
console.log(`Oh, so your favorite food is ${answer}`);
```
#### Class: `readlinePromises.Readline`
Added in: v17.0.0 #####
`new readlinePromises.Readline(stream[, options])`
Added in: v17.0.0 * `stream` [<stream.Writable>](stream#class-streamwritable) A [TTY](tty) stream.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `autoCommit` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, no need to call `rl.commit()`.
#####
`rl.clearLine(dir)`
Added in: v17.0.0 * `dir` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `-1`: to the left from cursor
+ `1`: to the right from cursor
+ `0`: the entire line
* Returns: this
The `rl.clearLine()` method adds to the internal list of pending action an action that clears current line of the associated `stream` in a specified direction identified by `dir`. Call `rl.commit()` to see the effect of this method, unless `autoCommit: true` was passed to the constructor.
#####
`rl.clearScreenDown()`
Added in: v17.0.0 * Returns: this
The `rl.clearScreenDown()` method adds to the internal list of pending action an action that clears the associated stream from the current position of the cursor down. Call `rl.commit()` to see the effect of this method, unless `autoCommit: true` was passed to the constructor.
#####
`rl.commit()`
Added in: v17.0.0 * Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
The `rl.commit()` method sends all the pending actions to the associated `stream` and clears the internal list of pending actions.
#####
`rl.cursorTo(x[, y])`
Added in: v17.0.0 * `x` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `y` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: this
The `rl.cursorTo()` method adds to the internal list of pending action an action that moves cursor to the specified position in the associated `stream`. Call `rl.commit()` to see the effect of this method, unless `autoCommit: true` was passed to the constructor.
#####
`rl.moveCursor(dx, dy)`
Added in: v17.0.0 * `dx` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `dy` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: this
The `rl.moveCursor()` method adds to the internal list of pending action an action that moves the cursor *relative* to its current position in the associated `stream`. Call `rl.commit()` to see the effect of this method, unless `autoCommit: true` was passed to the constructor.
#####
`rl.rollback()`
Added in: v17.0.0 * Returns: this
The `rl.rollback` methods clears the internal list of pending actions without sending it to the associated `stream`.
####
`readlinePromises.createInterface(options)`
Added in: v17.0.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `input` [<stream.Readable>](stream#class-streamreadable) The [Readable](stream#readable-streams) stream to listen to. This option is *required*.
+ `output` [<stream.Writable>](stream#class-streamwritable) The [Writable](stream#writable-streams) stream to write readline data to.
+ `completer` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) An optional function used for Tab autocompletion.
+ `terminal` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the `input` and `output` streams should be treated like a TTY, and have ANSI/VT100 escape codes written to it. **Default:** checking `isTTY` on the `output` stream upon instantiation.
+ `history` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Initial list of history lines. This option makes sense only if `terminal` is set to `true` by the user or by an internal `output` check, otherwise the history caching mechanism is not initialized at all. **Default:** `[]`.
+ `historySize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Maximum number of history lines retained. To disable the history set this value to `0`. This option makes sense only if `terminal` is set to `true` by the user or by an internal `output` check, otherwise the history caching mechanism is not initialized at all. **Default:** `30`.
+ `removeHistoryDuplicates` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, when a new input line added to the history list duplicates an older one, this removes the older line from the list. **Default:** `false`.
+ `prompt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The prompt string to use. **Default:** `'> '`.
+ `crlfDelay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If the delay between `\r` and `\n` exceeds `crlfDelay` milliseconds, both `\r` and `\n` will be treated as separate end-of-line input. `crlfDelay` will be coerced to a number no less than `100`. It can be set to `Infinity`, in which case `\r` followed by `\n` will always be considered a single newline (which may be reasonable for [reading files](#example-read-file-stream-line-by-line) with `\r\n` line delimiter). **Default:** `100`.
+ `escapeCodeTimeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The duration `readlinePromises` will wait for a character (when reading an ambiguous key sequence in milliseconds one that can both form a complete key sequence using the input read so far and can take additional input to complete a longer key sequence). **Default:** `500`.
+ `tabSize` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of spaces a tab is equal to (minimum 1). **Default:** `8`.
* Returns: [<readlinePromises.Interface>](readline#class-readlinepromisesinterface)
The `readlinePromises.createInterface()` method creates a new `readlinePromises.Interface` instance.
```
const readlinePromises = require('node:readline/promises');
const rl = readlinePromises.createInterface({
input: process.stdin,
output: process.stdout
});
```
Once the `readlinePromises.Interface` instance is created, the most common case is to listen for the `'line'` event:
```
rl.on('line', (line) => {
console.log(`Received: ${line}`);
});
```
If `terminal` is `true` for this instance then the `output` stream will get the best compatibility if it defines an `output.columns` property and emits a `'resize'` event on the `output` if or when the columns ever change ([`process.stdout`](process#processstdout) does this automatically when it is a TTY).
##### Use of the `completer` function
The `completer` function takes the current line entered by the user as an argument, and returns an `Array` with 2 entries:
* An `Array` with matching entries for the completion.
* The substring that was used for the matching.
For instance: `[[substr1, substr2, ...], originalsubstring]`.
```
function completer(line) {
const completions = '.help .error .exit .quit .q'.split(' ');
const hits = completions.filter((c) => c.startsWith(line));
// Show all completions if none found
return [hits.length ? hits : completions, line];
}
```
The `completer` function can also returns a [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise), or be asynchronous:
```
async function completer(linePartial) {
await someAsyncWork();
return [['123'], linePartial];
}
```
### Callback API
Added in: v0.1.104 #### Class: `readline.Interface`
History
| Version | Changes |
| --- | --- |
| v17.0.0 | The class `readline.Interface` now inherits from `Interface`. |
| v0.1.104 | Added in: v0.1.104 |
* Extends: [<readline.InterfaceConstructor>](readline#class-interfaceconstructor)
Instances of the `readline.Interface` class are constructed using the `readline.createInterface()` method. Every instance is associated with a single `input` [Readable](stream#readable-streams) stream and a single `output` [Writable](stream#writable-streams) stream. The `output` stream is used to print prompts for user input that arrives on, and is read from, the `input` stream.
#####
`rl.question(query[, options], callback)`
Added in: v0.3.3 * `query` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A statement or query to write to `output`, prepended to the prompt.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) Optionally allows the `question()` to be canceled using an `AbortController`.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function that is invoked with the user's input in response to the `query`.
The `rl.question()` method displays the `query` by writing it to the `output`, waits for user input to be provided on `input`, then invokes the `callback` function passing the provided input as the first argument.
When called, `rl.question()` will resume the `input` stream if it has been paused.
If the `readline.Interface` was created with `output` set to `null` or `undefined` the `query` is not written.
The `callback` function passed to `rl.question()` does not follow the typical pattern of accepting an `Error` object or `null` as the first argument. The `callback` is called with the provided answer as the only argument.
An error will be thrown if calling `rl.question()` after `rl.close()`.
Example usage:
```
rl.question('What is your favorite food? ', (answer) => {
console.log(`Oh, so your favorite food is ${answer}`);
});
```
Using an `AbortController` to cancel a question.
```
const ac = new AbortController();
const signal = ac.signal;
rl.question('What is your favorite food? ', { signal }, (answer) => {
console.log(`Oh, so your favorite food is ${answer}`);
});
signal.addEventListener('abort', () => {
console.log('The food question timed out');
}, { once: true });
setTimeout(() => ac.abort(), 10000);
```
####
`readline.clearLine(stream, dir[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v12.7.0 | The stream's write() callback and return value are exposed. |
| v0.7.7 | Added in: v0.7.7 |
* `stream` [<stream.Writable>](stream#class-streamwritable)
* `dir` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `-1`: to the left from cursor
+ `1`: to the right from cursor
+ `0`: the entire line
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked once the operation completes.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `false` if `stream` wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`.
The `readline.clearLine()` method clears current line of given [TTY](tty) stream in a specified direction identified by `dir`.
####
`readline.clearScreenDown(stream[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v12.7.0 | The stream's write() callback and return value are exposed. |
| v0.7.7 | Added in: v0.7.7 |
* `stream` [<stream.Writable>](stream#class-streamwritable)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked once the operation completes.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `false` if `stream` wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`.
The `readline.clearScreenDown()` method clears the given [TTY](tty) stream from the current position of the cursor down.
####
`readline.createInterface(options)`
History
| Version | Changes |
| --- | --- |
| v15.14.0, v14.18.0 | The `signal` option is supported now. |
| v15.8.0, v14.18.0 | The `history` option is supported now. |
| v13.9.0 | The `tabSize` option is supported now. |
| v8.3.0, v6.11.4 | Remove max limit of `crlfDelay` option. |
| v6.6.0 | The `crlfDelay` option is supported now. |
| v6.3.0 | The `prompt` option is supported now. |
| v6.0.0 | The `historySize` option can be `0` now. |
| v0.1.98 | Added in: v0.1.98 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `input` [<stream.Readable>](stream#class-streamreadable) The [Readable](stream#readable-streams) stream to listen to. This option is *required*.
+ `output` [<stream.Writable>](stream#class-streamwritable) The [Writable](stream#writable-streams) stream to write readline data to.
+ `completer` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) An optional function used for Tab autocompletion.
+ `terminal` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the `input` and `output` streams should be treated like a TTY, and have ANSI/VT100 escape codes written to it. **Default:** checking `isTTY` on the `output` stream upon instantiation.
+ `history` [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Initial list of history lines. This option makes sense only if `terminal` is set to `true` by the user or by an internal `output` check, otherwise the history caching mechanism is not initialized at all. **Default:** `[]`.
+ `historySize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Maximum number of history lines retained. To disable the history set this value to `0`. This option makes sense only if `terminal` is set to `true` by the user or by an internal `output` check, otherwise the history caching mechanism is not initialized at all. **Default:** `30`.
+ `removeHistoryDuplicates` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, when a new input line added to the history list duplicates an older one, this removes the older line from the list. **Default:** `false`.
+ `prompt` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The prompt string to use. **Default:** `'> '`.
+ `crlfDelay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) If the delay between `\r` and `\n` exceeds `crlfDelay` milliseconds, both `\r` and `\n` will be treated as separate end-of-line input. `crlfDelay` will be coerced to a number no less than `100`. It can be set to `Infinity`, in which case `\r` followed by `\n` will always be considered a single newline (which may be reasonable for [reading files](#example-read-file-stream-line-by-line) with `\r\n` line delimiter). **Default:** `100`.
+ `escapeCodeTimeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The duration `readline` will wait for a character (when reading an ambiguous key sequence in milliseconds one that can both form a complete key sequence using the input read so far and can take additional input to complete a longer key sequence). **Default:** `500`.
+ `tabSize` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of spaces a tab is equal to (minimum 1). **Default:** `8`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) Allows closing the interface using an AbortSignal. Aborting the signal will internally call `close` on the interface.
* Returns: [<readline.Interface>](readline#class-readlineinterface)
The `readline.createInterface()` method creates a new `readline.Interface` instance.
```
const readline = require('node:readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
```
Once the `readline.Interface` instance is created, the most common case is to listen for the `'line'` event:
```
rl.on('line', (line) => {
console.log(`Received: ${line}`);
});
```
If `terminal` is `true` for this instance then the `output` stream will get the best compatibility if it defines an `output.columns` property and emits a `'resize'` event on the `output` if or when the columns ever change ([`process.stdout`](process#processstdout) does this automatically when it is a TTY).
When creating a `readline.Interface` using `stdin` as input, the program will not terminate until it receives an [EOF character](https://en.wikipedia.org/wiki/End-of-file#EOF_character). To exit without waiting for user input, call `process.stdin.unref()`.
##### Use of the `completer` function
The `completer` function takes the current line entered by the user as an argument, and returns an `Array` with 2 entries:
* An `Array` with matching entries for the completion.
* The substring that was used for the matching.
For instance: `[[substr1, substr2, ...], originalsubstring]`.
```
function completer(line) {
const completions = '.help .error .exit .quit .q'.split(' ');
const hits = completions.filter((c) => c.startsWith(line));
// Show all completions if none found
return [hits.length ? hits : completions, line];
}
```
The `completer` function can be called asynchronously if it accepts two arguments:
```
function completer(linePartial, callback) {
callback(null, [['123'], linePartial]);
}
```
####
`readline.cursorTo(stream, x[, y][, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v12.7.0 | The stream's write() callback and return value are exposed. |
| v0.7.7 | Added in: v0.7.7 |
* `stream` [<stream.Writable>](stream#class-streamwritable)
* `x` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `y` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked once the operation completes.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `false` if `stream` wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`.
The `readline.cursorTo()` method moves cursor to the specified position in a given [TTY](tty) `stream`.
####
`readline.moveCursor(stream, dx, dy[, callback])`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v12.7.0 | The stream's write() callback and return value are exposed. |
| v0.7.7 | Added in: v0.7.7 |
* `stream` [<stream.Writable>](stream#class-streamwritable)
* `dx` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `dy` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked once the operation completes.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `false` if `stream` wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`.
The `readline.moveCursor()` method moves the cursor *relative* to its current position in a given [TTY](tty) `stream`.
###
`readline.emitKeypressEvents(stream[, interface])`
Added in: v0.7.7 * `stream` [<stream.Readable>](stream#class-streamreadable)
* `interface` [<readline.InterfaceConstructor>](readline#class-interfaceconstructor)
The `readline.emitKeypressEvents()` method causes the given [Readable](stream#readable-streams) stream to begin emitting `'keypress'` events corresponding to received input.
Optionally, `interface` specifies a `readline.Interface` instance for which autocompletion is disabled when copy-pasted input is detected.
If the `stream` is a [TTY](tty), then it must be in raw mode.
This is automatically called by any readline instance on its `input` if the `input` is a terminal. Closing the `readline` instance does not stop the `input` from emitting `'keypress'` events.
```
readline.emitKeypressEvents(process.stdin);
if (process.stdin.isTTY)
process.stdin.setRawMode(true);
```
### Example: Tiny CLI
The following example illustrates the use of `readline.Interface` class to implement a small command-line interface:
```
const readline = require('node:readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout,
prompt: 'OHAI> '
});
rl.prompt();
rl.on('line', (line) => {
switch (line.trim()) {
case 'hello':
console.log('world!');
break;
default:
console.log(`Say what? I might have heard '${line.trim()}'`);
break;
}
rl.prompt();
}).on('close', () => {
console.log('Have a great day!');
process.exit(0);
});
```
### Example: Read file stream line-by-Line
A common use case for `readline` is to consume an input file one line at a time. The easiest way to do so is leveraging the [`fs.ReadStream`](fs#class-fsreadstream) API as well as a `for await...of` loop:
```
const fs = require('node:fs');
const readline = require('node:readline');
async function processLineByLine() {
const fileStream = fs.createReadStream('input.txt');
const rl = readline.createInterface({
input: fileStream,
crlfDelay: Infinity
});
// Note: we use the crlfDelay option to recognize all instances of CR LF
// ('\r\n') in input.txt as a single line break.
for await (const line of rl) {
// Each line in input.txt will be successively available here as `line`.
console.log(`Line from file: ${line}`);
}
}
processLineByLine();
```
Alternatively, one could use the [`'line'`](#event-line) event:
```
const fs = require('node:fs');
const readline = require('node:readline');
const rl = readline.createInterface({
input: fs.createReadStream('sample.txt'),
crlfDelay: Infinity
});
rl.on('line', (line) => {
console.log(`Line from file: ${line}`);
});
```
Currently, `for await...of` loop can be a bit slower. If `async` / `await` flow and speed are both essential, a mixed approach can be applied:
```
const { once } = require('node:events');
const { createReadStream } = require('node:fs');
const { createInterface } = require('node:readline');
(async function processLineByLine() {
try {
const rl = createInterface({
input: createReadStream('big-file.txt'),
crlfDelay: Infinity
});
rl.on('line', (line) => {
// Process the line.
});
await once(rl, 'close');
console.log('File processed.');
} catch (err) {
console.error(err);
}
})();
```
### TTY keybindings
| Keybindings | Description | Notes |
| --- | --- | --- |
| `Ctrl`+`Shift`+`Backspace` | Delete line left | Doesn't work on Linux, Mac and Windows |
| `Ctrl`+`Shift`+`Delete` | Delete line right | Doesn't work on Mac |
| `Ctrl`+`C` | Emit `SIGINT` or close the readline instance | |
| `Ctrl`+`H` | Delete left | |
| `Ctrl`+`D` | Delete right or close the readline instance in case the current line is empty / EOF | Doesn't work on Windows |
| `Ctrl`+`U` | Delete from the current position to the line start | |
| `Ctrl`+`K` | Delete from the current position to the end of line | |
| `Ctrl`+`Y` | Yank (Recall) the previously deleted text | Only works with text deleted by `Ctrl`+`U` or `Ctrl`+`K` |
| `Meta`+`Y` | Cycle among previously deleted lines | Only available when the last keystroke is `Ctrl`+`Y` |
| `Ctrl`+`A` | Go to start of line | |
| `Ctrl`+`E` | Go to end of line | |
| `Ctrl`+`B` | Back one character | |
| `Ctrl`+`F` | Forward one character | |
| `Ctrl`+`L` | Clear screen | |
| `Ctrl`+`N` | Next history item | |
| `Ctrl`+`P` | Previous history item | |
| `Ctrl`+`-` | Undo previous change | Any keystroke that emits key code `0x1F` will do this action. In many terminals, for example `xterm`, this is bound to `Ctrl`+`-`. |
| `Ctrl`+`6` | Redo previous change | Many terminals don't have a default redo keystroke. We choose key code `0x1E` to perform redo. In `xterm`, it is bound to `Ctrl`+`6` by default. |
| `Ctrl`+`Z` | Moves running process into background. Type `fg` and press `Enter` to return. | Doesn't work on Windows |
| `Ctrl`+`W` or `Ctrl` +`Backspace` | Delete backward to a word boundary | `Ctrl`+`Backspace` Doesn't work on Linux, Mac and Windows |
| `Ctrl`+`Delete` | Delete forward to a word boundary | Doesn't work on Mac |
| `Ctrl`+`Left arrow` or `Meta`+`B` | Word left | `Ctrl`+`Left arrow` Doesn't work on Mac |
| `Ctrl`+`Right arrow` or `Meta`+`F` | Word right | `Ctrl`+`Right arrow` Doesn't work on Mac |
| `Meta`+`D` or `Meta` +`Delete` | Delete word right | `Meta`+`Delete` Doesn't work on windows |
| `Meta`+`Backspace` | Delete word left | Doesn't work on Mac |
| programming_docs |
node None Events
------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/events.js](https://github.com/nodejs/node/blob/v19.0.1/lib/events.js)
Much of the Node.js core API is built around an idiomatic asynchronous event-driven architecture in which certain kinds of objects (called "emitters") emit named events that cause `Function` objects ("listeners") to be called.
For instance: a [`net.Server`](net#class-netserver) object emits an event each time a peer connects to it; a [`fs.ReadStream`](fs#class-fsreadstream) emits an event when the file is opened; a <stream> emits an event whenever data is available to be read.
All objects that emit events are instances of the `EventEmitter` class. These objects expose an `eventEmitter.on()` function that allows one or more functions to be attached to named events emitted by the object. Typically, event names are camel-cased strings but any valid JavaScript property key can be used.
When the `EventEmitter` object emits an event, all of the functions attached to that specific event are called *synchronously*. Any values returned by the called listeners are *ignored* and discarded.
The following example shows a simple `EventEmitter` instance with a single listener. The `eventEmitter.on()` method is used to register listeners, while the `eventEmitter.emit()` method is used to trigger the event.
MJS modules
```
import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');
```
CJS modules
```
const EventEmitter = require('node:events');
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');
```
### Passing arguments and `this` to listeners
The `eventEmitter.emit()` method allows an arbitrary set of arguments to be passed to the listener functions. Keep in mind that when an ordinary listener function is called, the standard `this` keyword is intentionally set to reference the `EventEmitter` instance to which the listener is attached.
```
const myEmitter = new MyEmitter();
myEmitter.on('event', function(a, b) {
console.log(a, b, this, this === myEmitter);
// Prints:
// a b MyEmitter {
// domain: null,
// _events: { event: [Function] },
// _eventsCount: 1,
// _maxListeners: undefined } true
});
myEmitter.emit('event', 'a', 'b');
```
It is possible to use ES6 Arrow Functions as listeners, however, when doing so, the `this` keyword will no longer reference the `EventEmitter` instance:
```
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
console.log(a, b, this);
// Prints: a b {}
});
myEmitter.emit('event', 'a', 'b');
```
### Asynchronous vs. synchronous
The `EventEmitter` calls all listeners synchronously in the order in which they were registered. This ensures the proper sequencing of events and helps avoid race conditions and logic errors. When appropriate, listener functions can switch to an asynchronous mode of operation using the `setImmediate()` or `process.nextTick()` methods:
```
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
setImmediate(() => {
console.log('this happens asynchronously');
});
});
myEmitter.emit('event', 'a', 'b');
```
### Handling events only once
When a listener is registered using the `eventEmitter.on()` method, that listener is invoked *every time* the named event is emitted.
```
const myEmitter = new MyEmitter();
let m = 0;
myEmitter.on('event', () => {
console.log(++m);
});
myEmitter.emit('event');
// Prints: 1
myEmitter.emit('event');
// Prints: 2
```
Using the `eventEmitter.once()` method, it is possible to register a listener that is called at most once for a particular event. Once the event is emitted, the listener is unregistered and *then* called.
```
const myEmitter = new MyEmitter();
let m = 0;
myEmitter.once('event', () => {
console.log(++m);
});
myEmitter.emit('event');
// Prints: 1
myEmitter.emit('event');
// Ignored
```
### Error events
When an error occurs within an `EventEmitter` instance, the typical action is for an `'error'` event to be emitted. These are treated as special cases within Node.js.
If an `EventEmitter` does *not* have at least one listener registered for the `'error'` event, and an `'error'` event is emitted, the error is thrown, a stack trace is printed, and the Node.js process exits.
```
const myEmitter = new MyEmitter();
myEmitter.emit('error', new Error('whoops!'));
// Throws and crashes Node.js
```
To guard against crashing the Node.js process the [`domain`](domain) module can be used. (Note, however, that the `node:domain` module is deprecated.)
As a best practice, listeners should always be added for the `'error'` events.
```
const myEmitter = new MyEmitter();
myEmitter.on('error', (err) => {
console.error('whoops! there was an error');
});
myEmitter.emit('error', new Error('whoops!'));
// Prints: whoops! there was an error
```
It is possible to monitor `'error'` events without consuming the emitted error by installing a listener using the symbol `events.errorMonitor`.
MJS modules
```
import { EventEmitter, errorMonitor } from 'node:events';
const myEmitter = new EventEmitter();
myEmitter.on(errorMonitor, (err) => {
MyMonitoringTool.log(err);
});
myEmitter.emit('error', new Error('whoops!'));
// Still throws and crashes Node.js
```
CJS modules
```
const { EventEmitter, errorMonitor } = require('node:events');
const myEmitter = new EventEmitter();
myEmitter.on(errorMonitor, (err) => {
MyMonitoringTool.log(err);
});
myEmitter.emit('error', new Error('whoops!'));
// Still throws and crashes Node.js
```
### Capture rejections of promises
Using `async` functions with event handlers is problematic, because it can lead to an unhandled rejection in case of a thrown exception:
```
const ee = new EventEmitter();
ee.on('something', async (value) => {
throw new Error('kaboom');
});
```
The `captureRejections` option in the `EventEmitter` constructor or the global setting change this behavior, installing a `.then(undefined, handler)` handler on the `Promise`. This handler routes the exception asynchronously to the [`Symbol.for('nodejs.rejection')`](#emittersymbolfornodejsrejectionerr-eventname-args) method if there is one, or to [`'error'`](#error-events) event handler if there is none.
```
const ee1 = new EventEmitter({ captureRejections: true });
ee1.on('something', async (value) => {
throw new Error('kaboom');
});
ee1.on('error', console.log);
const ee2 = new EventEmitter({ captureRejections: true });
ee2.on('something', async (value) => {
throw new Error('kaboom');
});
ee2[Symbol.for('nodejs.rejection')] = console.log;
```
Setting `events.captureRejections = true` will change the default for all new instances of `EventEmitter`.
MJS modules
```
import { EventEmitter } from 'node:events';
EventEmitter.captureRejections = true;
const ee1 = new EventEmitter();
ee1.on('something', async (value) => {
throw new Error('kaboom');
});
ee1.on('error', console.log);
```
CJS modules
```
const events = require('node:events');
events.captureRejections = true;
const ee1 = new events.EventEmitter();
ee1.on('something', async (value) => {
throw new Error('kaboom');
});
ee1.on('error', console.log);
```
The `'error'` events that are generated by the `captureRejections` behavior do not have a catch handler to avoid infinite error loops: the recommendation is to **not use `async` functions as `'error'` event handlers**.
### Class: `EventEmitter`
History
| Version | Changes |
| --- | --- |
| v13.4.0, v12.16.0 | Added captureRejections option. |
| v0.1.26 | Added in: v0.1.26 |
The `EventEmitter` class is defined and exposed by the `node:events` module:
MJS modules
```
import { EventEmitter } from 'node:events';
```
CJS modules
```
const EventEmitter = require('node:events');
```
All `EventEmitter`s emit the event `'newListener'` when new listeners are added and `'removeListener'` when existing listeners are removed.
It supports the following option:
* `captureRejections` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) It enables [automatic capturing of promise rejection](#capture-rejections-of-promises). **Default:** `false`.
#### Event: `'newListener'`
Added in: v0.1.26 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The name of the event being listened for
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The event handler function
The `EventEmitter` instance will emit its own `'newListener'` event *before* a listener is added to its internal array of listeners.
Listeners registered for the `'newListener'` event are passed the event name and a reference to the listener being added.
The fact that the event is triggered before adding the listener has a subtle but important side effect: any *additional* listeners registered to the same `name` *within* the `'newListener'` callback are inserted *before* the listener that is in the process of being added.
```
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
// Only do this once so we don't loop forever
myEmitter.once('newListener', (event, listener) => {
if (event === 'event') {
// Insert a new listener in front
myEmitter.on('event', () => {
console.log('B');
});
}
});
myEmitter.on('event', () => {
console.log('A');
});
myEmitter.emit('event');
// Prints:
// B
// A
```
#### Event: `'removeListener'`
History
| Version | Changes |
| --- | --- |
| v6.1.0, v4.7.0 | For listeners attached using `.once()`, the `listener` argument now yields the original listener function. |
| v0.9.3 | Added in: v0.9.3 |
* `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The event name
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The event handler function
The `'removeListener'` event is emitted *after* the `listener` is removed.
####
`emitter.addListener(eventName, listener)`
Added in: v0.1.26 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Alias for `emitter.on(eventName, listener)`.
####
`emitter.emit(eventName[, ...args])`
Added in: v0.1.26 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Synchronously calls each of the listeners registered for the event named `eventName`, in the order they were registered, passing the supplied arguments to each.
Returns `true` if the event had listeners, `false` otherwise.
MJS modules
```
import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();
// First listener
myEmitter.on('event', function firstListener() {
console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
const parameters = args.join(', ');
console.log(`event with parameters ${parameters} in third listener`);
});
console.log(myEmitter.listeners('event'));
myEmitter.emit('event', 1, 2, 3, 4, 5);
// Prints:
// [
// [Function: firstListener],
// [Function: secondListener],
// [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener
```
CJS modules
```
const EventEmitter = require('node:events');
const myEmitter = new EventEmitter();
// First listener
myEmitter.on('event', function firstListener() {
console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
const parameters = args.join(', ');
console.log(`event with parameters ${parameters} in third listener`);
});
console.log(myEmitter.listeners('event'));
myEmitter.emit('event', 1, 2, 3, 4, 5);
// Prints:
// [
// [Function: firstListener],
// [Function: secondListener],
// [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener
```
####
`emitter.eventNames()`
Added in: v6.0.0 * Returns: [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)
Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or `Symbol`s.
MJS modules
```
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});
const sym = Symbol('symbol');
myEE.on(sym, () => {});
console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]
```
CJS modules
```
const EventEmitter = require('node:events');
const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});
const sym = Symbol('symbol');
myEE.on(sym, () => {});
console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]
```
####
`emitter.getMaxListeners()`
Added in: v1.0.0 * Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the current max listener value for the `EventEmitter` which is either set by [`emitter.setMaxListeners(n)`](#emittersetmaxlistenersn) or defaults to [`events.defaultMaxListeners`](#eventsdefaultmaxlisteners).
####
`emitter.listenerCount(eventName)`
Added in: v3.2.0 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The name of the event being listened for
* Returns: [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the number of listeners listening to the event named `eventName`.
####
`emitter.listeners(eventName)`
History
| Version | Changes |
| --- | --- |
| v7.0.0 | For listeners attached using `.once()` this returns the original listeners instead of wrapper functions now. |
| v0.1.26 | Added in: v0.1.26 |
* `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
* Returns: [<Function[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Returns a copy of the array of listeners for the event named `eventName`.
```
server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
```
####
`emitter.off(eventName, listener)`
Added in: v10.0.0 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<EventEmitter>](events#class-eventemitter)
Alias for [`emitter.removeListener()`](#emitterremovelistenereventname-listener).
####
`emitter.on(eventName, listener)`
Added in: v0.1.101 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The name of the event.
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The callback function
* Returns: [<EventEmitter>](events#class-eventemitter)
Adds the `listener` function to the end of the listeners array for the event named `eventName`. No checks are made to see if the `listener` has already been added. Multiple calls passing the same combination of `eventName` and `listener` will result in the `listener` being added, and called, multiple times.
```
server.on('connection', (stream) => {
console.log('someone connected!');
});
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The `emitter.prependListener()` method can be used as an alternative to add the event listener to the beginning of the listeners array.
```
const myEE = new EventEmitter();
myEE.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
```
####
`emitter.once(eventName, listener)`
Added in: v0.3.0 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The name of the event.
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The callback function
* Returns: [<EventEmitter>](events#class-eventemitter)
Adds a **one-time** `listener` function for the event named `eventName`. The next time `eventName` is triggered, this listener is removed and then invoked.
```
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The `emitter.prependOnceListener()` method can be used as an alternative to add the event listener to the beginning of the listeners array.
```
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
```
####
`emitter.prependListener(eventName, listener)`
Added in: v6.0.0 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The name of the event.
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The callback function
* Returns: [<EventEmitter>](events#class-eventemitter)
Adds the `listener` function to the *beginning* of the listeners array for the event named `eventName`. No checks are made to see if the `listener` has already been added. Multiple calls passing the same combination of `eventName` and `listener` will result in the `listener` being added, and called, multiple times.
```
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
####
`emitter.prependOnceListener(eventName, listener)`
Added in: v6.0.0 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The name of the event.
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The callback function
* Returns: [<EventEmitter>](events#class-eventemitter)
Adds a **one-time** `listener` function for the event named `eventName` to the *beginning* of the listeners array. The next time `eventName` is triggered, this listener is removed, and then invoked.
```
server.prependOnceListener('connection', (stream) => {
console.log('Ah, we have our first user!');
});
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
####
`emitter.removeAllListeners([eventName])`
Added in: v0.1.26 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
* Returns: [<EventEmitter>](events#class-eventemitter)
Removes all listeners, or those of the specified `eventName`.
It is bad practice to remove listeners added elsewhere in the code, particularly when the `EventEmitter` instance was created by some other component or module (e.g. sockets or file streams).
Returns a reference to the `EventEmitter`, so that calls can be chained.
####
`emitter.removeListener(eventName, listener)`
Added in: v0.1.26 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<EventEmitter>](events#class-eventemitter)
Removes the specified `listener` from the listener array for the event named `eventName`.
```
const callback = (stream) => {
console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);
```
`removeListener()` will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified `eventName`, then `removeListener()` must be called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any `removeListener()` or `removeAllListeners()` calls *after* emitting and *before* the last listener finishes execution will not remove them from `emit()` in progress. Subsequent events behave as expected.
```
const myEmitter = new MyEmitter();
const callbackA = () => {
console.log('A');
myEmitter.removeListener('event', callbackB);
};
const callbackB = () => {
console.log('B');
};
myEmitter.on('event', callbackA);
myEmitter.on('event', callbackB);
// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
// A
// B
// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
// A
```
Because listeners are managed using an internal array, calling this will change the position indices of any listener registered *after* the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the `emitter.listeners()` method will need to be recreated.
When a single function has been added as a handler multiple times for a single event (as in the example below), `removeListener()` will remove the most recently added instance. In the example the `once('ping')` listener is removed:
```
const ee = new EventEmitter();
function pong() {
console.log('pong');
}
ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);
ee.emit('ping');
ee.emit('ping');
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
####
`emitter.setMaxListeners(n)`
Added in: v0.3.5 * `n` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* Returns: [<EventEmitter>](events#class-eventemitter)
By default `EventEmitter`s will print a warning if more than `10` listeners are added for a particular event. This is a useful default that helps finding memory leaks. The `emitter.setMaxListeners()` method allows the limit to be modified for this specific `EventEmitter` instance. The value can be set to `Infinity` (or `0`) to indicate an unlimited number of listeners.
Returns a reference to the `EventEmitter`, so that calls can be chained.
####
`emitter.rawListeners(eventName)`
Added in: v9.4.0 * `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
* Returns: [<Function[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Returns a copy of the array of listeners for the event named `eventName`, including any wrappers (such as those created by `.once()`).
```
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));
// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];
// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();
// Logs "log once" to the console and removes the listener
logFnWrapper();
emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');
// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
```
####
`emitter[Symbol.for('nodejs.rejection')](err, eventName[, ...args])`
History
| Version | Changes |
| --- | --- |
| v17.4.0, v16.14.0 | No longer experimental. |
| v13.4.0, v12.16.0 | Added in: v13.4.0, v12.16.0 |
* `err` Error
* `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
The `Symbol.for('nodejs.rejection')` method is called in case a promise rejection happens when emitting an event and [`captureRejections`](#capture-rejections-of-promises) is enabled on the emitter. It is possible to use [`events.captureRejectionSymbol`](#eventscapturerejectionsymbol) in place of `Symbol.for('nodejs.rejection')`.
MJS modules
```
import { EventEmitter, captureRejectionSymbol } from 'node:events';
class MyClass extends EventEmitter {
constructor() {
super({ captureRejections: true });
}
[captureRejectionSymbol](err, event, ...args) {
console.log('rejection happened for', event, 'with', err, ...args);
this.destroy(err);
}
destroy(err) {
// Tear the resource down here.
}
}
```
CJS modules
```
const { EventEmitter, captureRejectionSymbol } = require('node:events');
class MyClass extends EventEmitter {
constructor() {
super({ captureRejections: true });
}
[captureRejectionSymbol](err, event, ...args) {
console.log('rejection happened for', event, 'with', err, ...args);
this.destroy(err);
}
destroy(err) {
// Tear the resource down here.
}
}
```
###
`events.defaultMaxListeners`
Added in: v0.11.2 By default, a maximum of `10` listeners can be registered for any single event. This limit can be changed for individual `EventEmitter` instances using the [`emitter.setMaxListeners(n)`](#emittersetmaxlistenersn) method. To change the default for *all* `EventEmitter` instances, the `events.defaultMaxListeners` property can be used. If this value is not a positive number, a `RangeError` is thrown.
Take caution when setting the `events.defaultMaxListeners` because the change affects *all* `EventEmitter` instances, including those created before the change is made. However, calling [`emitter.setMaxListeners(n)`](#emittersetmaxlistenersn) still has precedence over `events.defaultMaxListeners`.
This is not a hard limit. The `EventEmitter` instance will allow more listeners to be added but will output a trace warning to stderr indicating that a "possible EventEmitter memory leak" has been detected. For any single `EventEmitter`, the `emitter.getMaxListeners()` and `emitter.setMaxListeners()` methods can be used to temporarily avoid this warning:
```
emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', () => {
// do stuff
emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});
```
The [`--trace-warnings`](cli#--trace-warnings) command-line flag can be used to display the stack trace for such warnings.
The emitted warning can be inspected with [`process.on('warning')`](process#event-warning) and will have the additional `emitter`, `type`, and `count` properties, referring to the event emitter instance, the event's name and the number of attached listeners, respectively. Its `name` property is set to `'MaxListenersExceededWarning'`.
###
`events.errorMonitor`
Added in: v13.6.0, v12.17.0 This symbol shall be used to install a listener for only monitoring `'error'` events. Listeners installed using this symbol are called before the regular `'error'` listeners are called.
Installing a listener using this symbol does not change the behavior once an `'error'` event is emitted. Therefore, the process will still crash if no regular `'error'` listener is installed.
###
`events.getEventListeners(emitterOrTarget, eventName)`
Added in: v15.2.0, v14.17.0 * `emitterOrTarget` [<EventEmitter>](events#class-eventemitter) | [<EventTarget>](events#class-eventtarget)
* `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type)
* Returns: [<Function[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Returns a copy of the array of listeners for the event named `eventName`.
For `EventEmitter`s this behaves exactly the same as calling `.listeners` on the emitter.
For `EventTarget`s this is the only way to get the event listeners for the event target. This is useful for debugging and diagnostic purposes.
MJS modules
```
import { getEventListeners, EventEmitter } from 'node:events';
{
const ee = new EventEmitter();
const listener = () => console.log('Events are fun');
ee.on('foo', listener);
getEventListeners(ee, 'foo'); // [listener]
}
{
const et = new EventTarget();
const listener = () => console.log('Events are fun');
et.addEventListener('foo', listener);
getEventListeners(et, 'foo'); // [listener]
}
```
CJS modules
```
const { getEventListeners, EventEmitter } = require('node:events');
{
const ee = new EventEmitter();
const listener = () => console.log('Events are fun');
ee.on('foo', listener);
getEventListeners(ee, 'foo'); // [listener]
}
{
const et = new EventTarget();
const listener = () => console.log('Events are fun');
et.addEventListener('foo', listener);
getEventListeners(et, 'foo'); // [listener]
}
```
###
`events.once(emitter, name[, options])`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The `signal` option is supported now. |
| v11.13.0, v10.16.0 | Added in: v11.13.0, v10.16.0 |
* `emitter` [<EventEmitter>](events#class-eventemitter)
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) Can be used to cancel waiting for the event.
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
Creates a `Promise` that is fulfilled when the `EventEmitter` emits the given event or that is rejected if the `EventEmitter` emits `'error'` while waiting. The `Promise` will resolve with an array of all the arguments emitted to the given event.
This method is intentionally generic and works with the web platform [EventTarget](https://dom.spec.whatwg.org/#interface-eventtarget) interface, which has no special `'error'` event semantics and does not listen to the `'error'` event.
MJS modules
```
import { once, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
process.nextTick(() => {
ee.emit('myevent', 42);
});
const [value] = await once(ee, 'myevent');
console.log(value);
const err = new Error('kaboom');
process.nextTick(() => {
ee.emit('error', err);
});
try {
await once(ee, 'myevent');
} catch (err) {
console.log('error happened', err);
}
```
CJS modules
```
const { once, EventEmitter } = require('node:events');
async function run() {
const ee = new EventEmitter();
process.nextTick(() => {
ee.emit('myevent', 42);
});
const [value] = await once(ee, 'myevent');
console.log(value);
const err = new Error('kaboom');
process.nextTick(() => {
ee.emit('error', err);
});
try {
await once(ee, 'myevent');
} catch (err) {
console.log('error happened', err);
}
}
run();
```
The special handling of the `'error'` event is only used when `events.once()` is used to wait for another event. If `events.once()` is used to wait for the '`error'` event itself, then it is treated as any other kind of event without special handling:
MJS modules
```
import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
once(ee, 'error')
.then(([err]) => console.log('ok', err.message))
.catch((err) => console.log('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boom
```
CJS modules
```
const { EventEmitter, once } = require('node:events');
const ee = new EventEmitter();
once(ee, 'error')
.then(([err]) => console.log('ok', err.message))
.catch((err) => console.log('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boom
```
An [<AbortSignal>](globals#class-abortsignal) can be used to cancel waiting for the event:
MJS modules
```
import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
const ac = new AbortController();
async function foo(emitter, event, signal) {
try {
await once(emitter, event, { signal });
console.log('event emitted!');
} catch (error) {
if (error.name === 'AbortError') {
console.error('Waiting for the event was canceled!');
} else {
console.error('There was an error', error.message);
}
}
}
foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
```
CJS modules
```
const { EventEmitter, once } = require('node:events');
const ee = new EventEmitter();
const ac = new AbortController();
async function foo(emitter, event, signal) {
try {
await once(emitter, event, { signal });
console.log('event emitted!');
} catch (error) {
if (error.name === 'AbortError') {
console.error('Waiting for the event was canceled!');
} else {
console.error('There was an error', error.message);
}
}
}
foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
```
#### Awaiting multiple events emitted on `process.nextTick()`
There is an edge case worth noting when using the `events.once()` function to await multiple events emitted on in the same batch of `process.nextTick()` operations, or whenever multiple events are emitted synchronously. Specifically, because the `process.nextTick()` queue is drained before the `Promise` microtask queue, and because `EventEmitter` emits all events synchronously, it is possible for `events.once()` to miss an event.
MJS modules
```
import { EventEmitter, once } from 'node:events';
import process from 'node:process';
const myEE = new EventEmitter();
async function foo() {
await once(myEE, 'bar');
console.log('bar');
// This Promise will never resolve because the 'foo' event will
// have already been emitted before the Promise is created.
await once(myEE, 'foo');
console.log('foo');
}
process.nextTick(() => {
myEE.emit('bar');
myEE.emit('foo');
});
foo().then(() => console.log('done'));
```
CJS modules
```
const { EventEmitter, once } = require('node:events');
const myEE = new EventEmitter();
async function foo() {
await once(myEE, 'bar');
console.log('bar');
// This Promise will never resolve because the 'foo' event will
// have already been emitted before the Promise is created.
await once(myEE, 'foo');
console.log('foo');
}
process.nextTick(() => {
myEE.emit('bar');
myEE.emit('foo');
});
foo().then(() => console.log('done'));
```
To catch both events, create each of the Promises *before* awaiting either of them, then it becomes possible to use `Promise.all()`, `Promise.race()`, or `Promise.allSettled()`:
MJS modules
```
import { EventEmitter, once } from 'node:events';
import process from 'node:process';
const myEE = new EventEmitter();
async function foo() {
await Promise.all([once(myEE, 'bar'), once(myEE, 'foo')]);
console.log('foo', 'bar');
}
process.nextTick(() => {
myEE.emit('bar');
myEE.emit('foo');
});
foo().then(() => console.log('done'));
```
CJS modules
```
const { EventEmitter, once } = require('node:events');
const myEE = new EventEmitter();
async function foo() {
await Promise.all([once(myEE, 'bar'), once(myEE, 'foo')]);
console.log('foo', 'bar');
}
process.nextTick(() => {
myEE.emit('bar');
myEE.emit('foo');
});
foo().then(() => console.log('done'));
```
###
`events.captureRejections`
History
| Version | Changes |
| --- | --- |
| v17.4.0, v16.14.0 | No longer experimental. |
| v13.4.0, v12.16.0 | Added in: v13.4.0, v12.16.0 |
Value: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Change the default `captureRejections` option on all new `EventEmitter` objects.
###
`events.captureRejectionSymbol`
History
| Version | Changes |
| --- | --- |
| v17.4.0, v16.14.0 | No longer experimental. |
| v13.4.0, v12.16.0 | Added in: v13.4.0, v12.16.0 |
Value: `Symbol.for('nodejs.rejection')`
See how to write a custom [rejection handler](#emittersymbolfornodejsrejectionerr-eventname-args).
###
`events.listenerCount(emitter, eventName)`
Added in: v0.9.12Deprecated since: v3.2.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`emitter.listenerCount()`](#emitterlistenercounteventname) instead.
* `emitter` [<EventEmitter>](events#class-eventemitter) The emitter to query
* `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The event name
A class method that returns the number of listeners for the given `eventName` registered on the given `emitter`.
MJS modules
```
import { EventEmitter, listenerCount } from 'node:events';
const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2
```
CJS modules
```
const { EventEmitter, listenerCount } = require('node:events');
const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2
```
###
`events.on(emitter, eventName[, options])`
Added in: v13.6.0, v12.16.0 * `emitter` [<EventEmitter>](events#class-eventemitter)
* `eventName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The name of the event being listened for
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `signal` [<AbortSignal>](globals#class-abortsignal) Can be used to cancel awaiting events.
* Returns: [<AsyncIterator>](https://tc39.github.io/ecma262/#sec-asynciterator-interface) that iterates `eventName` events emitted by the `emitter`
MJS modules
```
import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo')) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
```
CJS modules
```
const { on, EventEmitter } = require('node:events');
(async () => {
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo')) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();
```
Returns an `AsyncIterator` that iterates `eventName` events. It will throw if the `EventEmitter` emits `'error'`. It removes all listeners when exiting the loop. The `value` returned by each iteration is an array composed of the emitted event arguments.
An [<AbortSignal>](globals#class-abortsignal) can be used to cancel waiting on events:
MJS modules
```
import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ac = new AbortController();
(async () => {
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo', { signal: ac.signal })) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();
process.nextTick(() => ac.abort());
```
CJS modules
```
const { on, EventEmitter } = require('node:events');
const ac = new AbortController();
(async () => {
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo', { signal: ac.signal })) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();
process.nextTick(() => ac.abort());
```
###
`events.setMaxListeners(n[, ...eventTargets])`
Added in: v15.4.0 * `n` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A non-negative number. The maximum number of listeners per `EventTarget` event.
* `...eventsTargets` [<EventTarget[]>](events#class-eventtarget) | [<EventEmitter[]>](events#class-eventemitter) Zero or more [<EventTarget>](events#class-eventtarget) or [<EventEmitter>](events#class-eventemitter) instances. If none are specified, `n` is set as the default max for all newly created [<EventTarget>](events#class-eventtarget) and [<EventEmitter>](events#class-eventemitter) objects.
MJS modules
```
import { setMaxListeners, EventEmitter } from 'node:events';
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);
```
CJS modules
```
const {
setMaxListeners,
EventEmitter
} = require('node:events');
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);
```
### Class: `events.EventEmitterAsyncResource extends EventEmitter`
Added in: v17.4.0, v16.14.0 Integrates `EventEmitter` with [<AsyncResource>](async_hooks#class-asyncresource) for `EventEmitter`s that require manual async tracking. Specifically, all events emitted by instances of `events.EventEmitterAsyncResource` will run within its [async context](async_context).
MJS modules
```
import { EventEmitterAsyncResource, EventEmitter } from 'node:events';
import { notStrictEqual, strictEqual } from 'node:assert';
import { executionAsyncId, triggerAsyncId } from 'node:async_hooks';
// Async tracking tooling will identify this as 'Q'.
const ee1 = new EventEmitterAsyncResource({ name: 'Q' });
// 'foo' listeners will run in the EventEmitters async context.
ee1.on('foo', () => {
strictEqual(executionAsyncId(), ee1.asyncId);
strictEqual(triggerAsyncId(), ee1.triggerAsyncId);
});
const ee2 = new EventEmitter();
// 'foo' listeners on ordinary EventEmitters that do not track async
// context, however, run in the same async context as the emit().
ee2.on('foo', () => {
notStrictEqual(executionAsyncId(), ee2.asyncId);
notStrictEqual(triggerAsyncId(), ee2.triggerAsyncId);
});
Promise.resolve().then(() => {
ee1.emit('foo');
ee2.emit('foo');
});
```
CJS modules
```
const { EventEmitterAsyncResource, EventEmitter } = require('node:events');
const { notStrictEqual, strictEqual } = require('node:assert');
const { executionAsyncId, triggerAsyncId } = require('node:async_hooks');
// Async tracking tooling will identify this as 'Q'.
const ee1 = new EventEmitterAsyncResource({ name: 'Q' });
// 'foo' listeners will run in the EventEmitters async context.
ee1.on('foo', () => {
strictEqual(executionAsyncId(), ee1.asyncId);
strictEqual(triggerAsyncId(), ee1.triggerAsyncId);
});
const ee2 = new EventEmitter();
// 'foo' listeners on ordinary EventEmitters that do not track async
// context, however, run in the same async context as the emit().
ee2.on('foo', () => {
notStrictEqual(executionAsyncId(), ee2.asyncId);
notStrictEqual(triggerAsyncId(), ee2.triggerAsyncId);
});
Promise.resolve().then(() => {
ee1.emit('foo');
ee2.emit('foo');
});
```
The `EventEmitterAsyncResource` class has the same methods and takes the same options as `EventEmitter` and `AsyncResource` themselves.
####
`new events.EventEmitterAsyncResource(options)`
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `captureRejections` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) It enables [automatic capturing of promise rejection](#capture-rejections-of-promises). **Default:** `false`.
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The type of async event. **Default::** [`new.target.name`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new.target).
+ `triggerAsyncId` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The ID of the execution context that created this async event. **Default:** `executionAsyncId()`.
+ `requireManualDestroy` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `true`, disables `emitDestroy` when the object is garbage collected. This usually does not need to be set (even if `emitDestroy` is called manually), unless the resource's `asyncId` is retrieved and the sensitive API's `emitDestroy` is called with it. When set to `false`, the `emitDestroy` call on garbage collection will only take place if there is at least one active `destroy` hook. **Default:** `false`.
####
`eventemitterasyncresource.asyncId`
* Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The unique `asyncId` assigned to the resource.
####
`eventemitterasyncresource.asyncResource`
* Type: The underlying [<AsyncResource>](async_hooks#class-asyncresource).
The returned `AsyncResource` object has an additional `eventEmitter` property that provides a reference to this `EventEmitterAsyncResource`.
####
`eventemitterasyncresource.emitDestroy()`
Call all `destroy` hooks. This should only ever be called once. An error will be thrown if it is called more than once. This **must** be manually called. If the resource is left to be collected by the GC then the `destroy` hooks will never be called.
####
`eventemitterasyncresource.triggerAsyncId`
* Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The same `triggerAsyncId` that is passed to the `AsyncResource` constructor.
###
`EventTarget` and `Event` API
History
| Version | Changes |
| --- | --- |
| v16.0.0 | changed EventTarget error handling. |
| v15.4.0 | No longer experimental. |
| v15.0.0 | The `EventTarget` and `Event` classes are now available as globals. |
| v14.5.0 | Added in: v14.5.0 |
The `EventTarget` and `Event` objects are a Node.js-specific implementation of the [`EventTarget` Web API](https://dom.spec.whatwg.org/#eventtarget) that are exposed by some Node.js core APIs.
```
const target = new EventTarget();
target.addEventListener('foo', (event) => {
console.log('foo event happened!');
});
```
#### Node.js `EventTarget` vs. DOM `EventTarget`
There are two key differences between the Node.js `EventTarget` and the [`EventTarget` Web API](https://dom.spec.whatwg.org/#eventtarget):
1. Whereas DOM `EventTarget` instances *may* be hierarchical, there is no concept of hierarchy and event propagation in Node.js. That is, an event dispatched to an `EventTarget` does not propagate through a hierarchy of nested target objects that may each have their own set of handlers for the event.
2. In the Node.js `EventTarget`, if an event listener is an async function or returns a `Promise`, and the returned `Promise` rejects, the rejection is automatically captured and handled the same way as a listener that throws synchronously (see [`EventTarget` error handling](#eventtarget-error-handling) for details).
####
`NodeEventTarget` vs. `EventEmitter`
The `NodeEventTarget` object implements a modified subset of the `EventEmitter` API that allows it to closely *emulate* an `EventEmitter` in certain situations. A `NodeEventTarget` is *not* an instance of `EventEmitter` and cannot be used in place of an `EventEmitter` in most cases.
1. Unlike `EventEmitter`, any given `listener` can be registered at most once per event `type`. Attempts to register a `listener` multiple times are ignored.
2. The `NodeEventTarget` does not emulate the full `EventEmitter` API. Specifically the `prependListener()`, `prependOnceListener()`, `rawListeners()`, `setMaxListeners()`, `getMaxListeners()`, and `errorMonitor` APIs are not emulated. The `'newListener'` and `'removeListener'` events will also not be emitted.
3. The `NodeEventTarget` does not implement any special default behavior for events with type `'error'`.
4. The `NodeEventTarget` supports `EventListener` objects as well as functions as handlers for all event types.
#### Event listener
Event listeners registered for an event `type` may either be JavaScript functions or objects with a `handleEvent` property whose value is a function.
In either case, the handler function is invoked with the `event` argument passed to the `eventTarget.dispatchEvent()` function.
Async functions may be used as event listeners. If an async handler function rejects, the rejection is captured and handled as described in [`EventTarget` error handling](#eventtarget-error-handling).
An error thrown by one handler function does not prevent the other handlers from being invoked.
The return value of a handler function is ignored.
Handlers are always invoked in the order they were added.
Handler functions may mutate the `event` object.
```
function handler1(event) {
console.log(event.type); // Prints 'foo'
event.a = 1;
}
async function handler2(event) {
console.log(event.type); // Prints 'foo'
console.log(event.a); // Prints 1
}
const handler3 = {
handleEvent(event) {
console.log(event.type); // Prints 'foo'
}
};
const handler4 = {
async handleEvent(event) {
console.log(event.type); // Prints 'foo'
}
};
const target = new EventTarget();
target.addEventListener('foo', handler1);
target.addEventListener('foo', handler2);
target.addEventListener('foo', handler3);
target.addEventListener('foo', handler4, { once: true });
```
####
`EventTarget` error handling
When a registered event listener throws (or returns a Promise that rejects), by default the error is treated as an uncaught exception on `process.nextTick()`. This means uncaught exceptions in `EventTarget`s will terminate the Node.js process by default.
Throwing within an event listener will *not* stop the other registered handlers from being invoked.
The `EventTarget` does not implement any special default handling for `'error'` type events like `EventEmitter`.
Currently errors are first forwarded to the `process.on('error')` event before reaching `process.on('uncaughtException')`. This behavior is deprecated and will change in a future release to align `EventTarget` with other Node.js APIs. Any code relying on the `process.on('error')` event should be aligned with the new behavior.
#### Class: `Event`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The `Event` class is now available through the global object. |
| v14.5.0 | Added in: v14.5.0 |
The `Event` object is an adaptation of the [`Event` Web API](https://dom.spec.whatwg.org/#event). Instances are created internally by Node.js.
#####
`event.bubbles`
Added in: v14.5.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Always returns `false`.
This is not used in Node.js and is provided purely for completeness.
#####
`event.cancelBubble()`
Added in: v14.5.0 Alias for `event.stopPropagation()`. This is not used in Node.js and is provided purely for completeness.
#####
`event.cancelable`
Added in: v14.5.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) True if the event was created with the `cancelable` option.
#####
`event.composed`
Added in: v14.5.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Always returns `false`.
This is not used in Node.js and is provided purely for completeness.
#####
`event.composedPath()`
Added in: v14.5.0 Returns an array containing the current `EventTarget` as the only entry or empty if the event is not being dispatched. This is not used in Node.js and is provided purely for completeness.
#####
`event.currentTarget`
Added in: v14.5.0 * Type: [<EventTarget>](events#class-eventtarget) The `EventTarget` dispatching the event.
Alias for `event.target`.
#####
`event.defaultPrevented`
Added in: v14.5.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Is `true` if `cancelable` is `true` and `event.preventDefault()` has been called.
#####
`event.eventPhase`
Added in: v14.5.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Returns `0` while an event is not being dispatched, `2` while it is being dispatched.
This is not used in Node.js and is provided purely for completeness.
#####
`event.isTrusted`
Added in: v14.5.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The [<AbortSignal>](globals#class-abortsignal) `"abort"` event is emitted with `isTrusted` set to `true`. The value is `false` in all other cases.
#####
`event.preventDefault()`
Added in: v14.5.0 Sets the `defaultPrevented` property to `true` if `cancelable` is `true`.
#####
`event.returnValue`
Added in: v14.5.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) True if the event has not been canceled.
This is not used in Node.js and is provided purely for completeness.
#####
`event.srcElement`
Added in: v14.5.0 * Type: [<EventTarget>](events#class-eventtarget) The `EventTarget` dispatching the event.
Alias for `event.target`.
#####
`event.stopImmediatePropagation()`
Added in: v14.5.0 Stops the invocation of event listeners after the current one completes.
#####
`event.stopPropagation()`
Added in: v14.5.0 This is not used in Node.js and is provided purely for completeness.
#####
`event.target`
Added in: v14.5.0 * Type: [<EventTarget>](events#class-eventtarget) The `EventTarget` dispatching the event.
#####
`event.timeStamp`
Added in: v14.5.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The millisecond timestamp when the `Event` object was created.
#####
`event.type`
Added in: v14.5.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The event type identifier.
#### Class: `EventTarget`
History
| Version | Changes |
| --- | --- |
| v15.0.0 | The `EventTarget` class is now available through the global object. |
| v14.5.0 | Added in: v14.5.0 |
#####
`eventTarget.addEventListener(type, listener[, options])`
History
| Version | Changes |
| --- | --- |
| v15.4.0 | add support for `signal` option. |
| v14.5.0 | Added in: v14.5.0 |
* `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<EventListener>](events#event-listener)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `once` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, the listener is automatically removed when it is first invoked. **Default:** `false`.
+ `passive` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) When `true`, serves as a hint that the listener will not call the `Event` object's `preventDefault()` method. **Default:** `false`.
+ `capture` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Not directly used by Node.js. Added for API completeness. **Default:** `false`.
+ `signal` [<AbortSignal>](globals#class-abortsignal) The listener will be removed when the given AbortSignal object's `abort()` method is called.
Adds a new handler for the `type` event. Any given `listener` is added only once per `type` and per `capture` option value.
If the `once` option is `true`, the `listener` is removed after the next time a `type` event is dispatched.
The `capture` option is not used by Node.js in any functional way other than tracking registered event listeners per the `EventTarget` specification. Specifically, the `capture` option is used as part of the key when registering a `listener`. Any individual `listener` may be added once with `capture = false`, and once with `capture = true`.
```
function handler(event) {}
const target = new EventTarget();
target.addEventListener('foo', handler, { capture: true }); // first
target.addEventListener('foo', handler, { capture: false }); // second
// Removes the second instance of handler
target.removeEventListener('foo', handler);
// Removes the first instance of handler
target.removeEventListener('foo', handler, { capture: true });
```
#####
`eventTarget.dispatchEvent(event)`
Added in: v14.5.0 * `event` [<Event>](events#class-event)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if either event's `cancelable` attribute value is false or its `preventDefault()` method was not invoked, otherwise `false`.
Dispatches the `event` to the list of handlers for `event.type`.
The registered event listeners is synchronously invoked in the order they were registered.
#####
`eventTarget.removeEventListener(type, listener)`
Added in: v14.5.0 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<EventListener>](events#event-listener)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `capture` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Removes the `listener` from the list of handlers for event `type`.
#### Class: `CustomEvent`
Added in: v18.7.0, v16.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
* Extends: [<Event>](events#class-event)
The `CustomEvent` object is an adaptation of the [`CustomEvent` Web API](https://dom.spec.whatwg.org/#customevent). Instances are created internally by Node.js.
#####
`event.detail`
Added in: v18.7.0, v16.17.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
* Type: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) Returns custom data passed when initializing.
Read-only.
#### Class: `NodeEventTarget`
Added in: v14.5.0 * Extends: [<EventTarget>](events#class-eventtarget)
The `NodeEventTarget` is a Node.js-specific extension to `EventTarget` that emulates a subset of the `EventEmitter` API.
#####
`nodeEventTarget.addListener(type, listener[, options])`
Added in: v14.5.0 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<EventListener>](events#event-listener)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `once` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
* Returns: [<EventTarget>](events#class-eventtarget) this
Node.js-specific extension to the `EventTarget` class that emulates the equivalent `EventEmitter` API. The only difference between `addListener()` and `addEventListener()` is that `addListener()` will return a reference to the `EventTarget`.
#####
`nodeEventTarget.eventNames()`
Added in: v14.5.0 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Node.js-specific extension to the `EventTarget` class that returns an array of event `type` names for which event listeners are registered.
#####
`nodeEventTarget.listenerCount(type)`
Added in: v14.5.0 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Node.js-specific extension to the `EventTarget` class that returns the number of event listeners registered for the `type`.
#####
`nodeEventTarget.off(type, listener)`
Added in: v14.5.0 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<EventListener>](events#event-listener)
* Returns: [<EventTarget>](events#class-eventtarget) this
Node.js-specific alias for `eventTarget.removeListener()`.
#####
`nodeEventTarget.on(type, listener[, options])`
Added in: v14.5.0 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<EventListener>](events#event-listener)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `once` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
* Returns: [<EventTarget>](events#class-eventtarget) this
Node.js-specific alias for `eventTarget.addListener()`.
#####
`nodeEventTarget.once(type, listener[, options])`
Added in: v14.5.0 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<EventListener>](events#event-listener)
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* Returns: [<EventTarget>](events#class-eventtarget) this
Node.js-specific extension to the `EventTarget` class that adds a `once` listener for the given event `type`. This is equivalent to calling `on` with the `once` option set to `true`.
#####
`nodeEventTarget.removeAllListeners([type])`
Added in: v14.5.0 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<EventTarget>](events#class-eventtarget) this
Node.js-specific extension to the `EventTarget` class. If `type` is specified, removes all registered listeners for `type`, otherwise removes all registered listeners.
#####
`nodeEventTarget.removeListener(type, listener)`
Added in: v14.5.0 * `type` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `listener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) | [<EventListener>](events#event-listener)
* Returns: [<EventTarget>](events#class-eventtarget) this
Node.js-specific extension to the `EventTarget` class that removes the `listener` for the given `type`. The only difference between `removeListener()` and `removeEventListener()` is that `removeListener()` will return a reference to the `EventTarget`.
| programming_docs |
node None Punycode
--------
Deprecated since: v7.0.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
**Source Code:** [lib/punycode.js](https://github.com/nodejs/node/blob/v19.0.1/lib/punycode.js)
**The version of the punycode module bundled in Node.js is being deprecated.** In a future major version of Node.js this module will be removed. Users currently depending on the `punycode` module should switch to using the userland-provided [Punycode.js](https://github.com/bestiejs/punycode.js) module instead. For punycode-based URL encoding, see [`url.domainToASCII`](url#urldomaintoasciidomain) or, more generally, the [WHATWG URL API](url#the-whatwg-url-api).
The `punycode` module is a bundled version of the [Punycode.js](https://github.com/bestiejs/punycode.js) module. It can be accessed using:
```
const punycode = require('punycode');
```
[Punycode](https://tools.ietf.org/html/rfc3492) is a character encoding scheme defined by RFC 3492 that is primarily intended for use in Internationalized Domain Names. Because host names in URLs are limited to ASCII characters only, Domain Names that contain non-ASCII characters must be converted into ASCII using the Punycode scheme. For instance, the Japanese character that translates into the English word, `'example'` is `'例'`. The Internationalized Domain Name, `'例.com'` (equivalent to `'example.com'`) is represented by Punycode as the ASCII string `'xn--fsq.com'`.
The `punycode` module provides a simple implementation of the Punycode standard.
The `punycode` module is a third-party dependency used by Node.js and made available to developers as a convenience. Fixes or other modifications to the module must be directed to the [Punycode.js](https://github.com/bestiejs/punycode.js) project.
###
`punycode.decode(string)`
Added in: v0.5.1 * `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `punycode.decode()` method converts a [Punycode](https://tools.ietf.org/html/rfc3492) string of ASCII-only characters to the equivalent string of Unicode codepoints.
```
punycode.decode('maana-pta'); // 'mañana'
punycode.decode('--dqo34k'); // '☃-⌘'
```
###
`punycode.encode(string)`
Added in: v0.5.1 * `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `punycode.encode()` method converts a string of Unicode codepoints to a [Punycode](https://tools.ietf.org/html/rfc3492) string of ASCII-only characters.
```
punycode.encode('mañana'); // 'maana-pta'
punycode.encode('☃-⌘'); // '--dqo34k'
```
###
`punycode.toASCII(domain)`
Added in: v0.6.1 * `domain` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `punycode.toASCII()` method converts a Unicode string representing an Internationalized Domain Name to [Punycode](https://tools.ietf.org/html/rfc3492). Only the non-ASCII parts of the domain name will be converted. Calling `punycode.toASCII()` on a string that already only contains ASCII characters will have no effect.
```
// encode domain names
punycode.toASCII('mañana.com'); // 'xn--maana-pta.com'
punycode.toASCII('☃-⌘.com'); // 'xn----dqo34k.com'
punycode.toASCII('example.com'); // 'example.com'
```
###
`punycode.toUnicode(domain)`
Added in: v0.6.1 * `domain` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `punycode.toUnicode()` method converts a string representing a domain name containing [Punycode](https://tools.ietf.org/html/rfc3492) encoded characters into Unicode. Only the [Punycode](https://tools.ietf.org/html/rfc3492) encoded parts of the domain name are be converted.
```
// decode domain names
punycode.toUnicode('xn--maana-pta.com'); // 'mañana.com'
punycode.toUnicode('xn----dqo34k.com'); // '☃-⌘.com'
punycode.toUnicode('example.com'); // 'example.com'
```
###
`punycode.ucs2`
Added in: v0.7.0 ####
`punycode.ucs2.decode(string)`
Added in: v0.7.0 * `string` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `punycode.ucs2.decode()` method returns an array containing the numeric codepoint values of each Unicode symbol in the string.
```
punycode.ucs2.decode('abc'); // [0x61, 0x62, 0x63]
// surrogate pair for U+1D306 tetragram for centre:
punycode.ucs2.decode('\uD834\uDF06'); // [0x1D306]
```
####
`punycode.ucs2.encode(codePoints)`
Added in: v0.7.0 * `codePoints` [<integer[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The `punycode.ucs2.encode()` method returns a string based on an array of numeric code point values.
```
punycode.ucs2.encode([0x61, 0x62, 0x63]); // 'abc'
punycode.ucs2.encode([0x1D306]); // '\uD834\uDF06'
```
###
`punycode.version`
Added in: v0.6.1 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns a string identifying the current [Punycode.js](https://github.com/bestiejs/punycode.js) version number.
node None Diagnostic report
-----------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
Delivers a JSON-formatted diagnostic summary, written to a file.
The report is intended for development, test, and production use, to capture and preserve information for problem determination. It includes JavaScript and native stack traces, heap statistics, platform information, resource usage etc. With the report option enabled, diagnostic reports can be triggered on unhandled exceptions, fatal errors and user signals, in addition to triggering programmatically through API calls.
A complete example report that was generated on an uncaught exception is provided below for reference.
```
{
"header": {
"reportVersion": 1,
"event": "exception",
"trigger": "Exception",
"filename": "report.20181221.005011.8974.0.001.json",
"dumpEventTime": "2018-12-21T00:50:11Z",
"dumpEventTimeStamp": "1545371411331",
"processId": 8974,
"cwd": "/home/nodeuser/project/node",
"commandLine": [
"/home/nodeuser/project/node/out/Release/node",
"--report-uncaught-exception",
"/home/nodeuser/project/node/test/report/test-exception.js",
"child"
],
"nodejsVersion": "v12.0.0-pre",
"glibcVersionRuntime": "2.17",
"glibcVersionCompiler": "2.17",
"wordSize": "64 bit",
"arch": "x64",
"platform": "linux",
"componentVersions": {
"node": "12.0.0-pre",
"v8": "7.1.302.28-node.5",
"uv": "1.24.1",
"zlib": "1.2.11",
"ares": "1.15.0",
"modules": "68",
"nghttp2": "1.34.0",
"napi": "3",
"llhttp": "1.0.1",
"openssl": "1.1.0j"
},
"release": {
"name": "node"
},
"osName": "Linux",
"osRelease": "3.10.0-862.el7.x86_64",
"osVersion": "#1 SMP Wed Mar 21 18:14:51 EDT 2018",
"osMachine": "x86_64",
"cpus": [
{
"model": "Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz",
"speed": 2700,
"user": 88902660,
"nice": 0,
"sys": 50902570,
"idle": 241732220,
"irq": 0
},
{
"model": "Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz",
"speed": 2700,
"user": 88902660,
"nice": 0,
"sys": 50902570,
"idle": 241732220,
"irq": 0
}
],
"networkInterfaces": [
{
"name": "en0",
"internal": false,
"mac": "13:10:de:ad:be:ef",
"address": "10.0.0.37",
"netmask": "255.255.255.0",
"family": "IPv4"
}
],
"host": "test_machine"
},
"javascriptStack": {
"message": "Error: *** test-exception.js: throwing uncaught Error",
"stack": [
"at myException (/home/nodeuser/project/node/test/report/test-exception.js:9:11)",
"at Object.<anonymous> (/home/nodeuser/project/node/test/report/test-exception.js:12:3)",
"at Module._compile (internal/modules/cjs/loader.js:718:30)",
"at Object.Module._extensions..js (internal/modules/cjs/loader.js:729:10)",
"at Module.load (internal/modules/cjs/loader.js:617:32)",
"at tryModuleLoad (internal/modules/cjs/loader.js:560:12)",
"at Function.Module._load (internal/modules/cjs/loader.js:552:3)",
"at Function.Module.runMain (internal/modules/cjs/loader.js:771:12)",
"at executeUserCode (internal/bootstrap/node.js:332:15)"
]
},
"nativeStack": [
{
"pc": "0x000055b57f07a9ef",
"symbol": "report::GetNodeReport(v8::Isolate*, node::Environment*, char const*, char const*, v8::Local<v8::String>, std::ostream&) [./node]"
},
{
"pc": "0x000055b57f07cf03",
"symbol": "report::GetReport(v8::FunctionCallbackInfo<v8::Value> const&) [./node]"
},
{
"pc": "0x000055b57f1bccfd",
"symbol": " [./node]"
},
{
"pc": "0x000055b57f1be048",
"symbol": "v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*) [./node]"
},
{
"pc": "0x000055b57feeda0e",
"symbol": " [./node]"
}
],
"javascriptHeap": {
"totalMemory": 5660672,
"executableMemory": 524288,
"totalCommittedMemory": 5488640,
"availableMemory": 4341379928,
"totalGlobalHandlesMemory": 8192,
"usedGlobalHandlesMemory": 3136,
"usedMemory": 4816432,
"memoryLimit": 4345298944,
"mallocedMemory": 254128,
"externalMemory": 315644,
"peakMallocedMemory": 98752,
"nativeContextCount": 1,
"detachedContextCount": 0,
"doesZapGarbage": 0,
"heapSpaces": {
"read_only_space": {
"memorySize": 524288,
"committedMemory": 39208,
"capacity": 515584,
"used": 30504,
"available": 485080
},
"new_space": {
"memorySize": 2097152,
"committedMemory": 2019312,
"capacity": 1031168,
"used": 985496,
"available": 45672
},
"old_space": {
"memorySize": 2273280,
"committedMemory": 1769008,
"capacity": 1974640,
"used": 1725488,
"available": 249152
},
"code_space": {
"memorySize": 696320,
"committedMemory": 184896,
"capacity": 152128,
"used": 152128,
"available": 0
},
"map_space": {
"memorySize": 536576,
"committedMemory": 344928,
"capacity": 327520,
"used": 327520,
"available": 0
},
"large_object_space": {
"memorySize": 0,
"committedMemory": 0,
"capacity": 1520590336,
"used": 0,
"available": 1520590336
},
"new_large_object_space": {
"memorySize": 0,
"committedMemory": 0,
"capacity": 0,
"used": 0,
"available": 0
}
}
},
"resourceUsage": {
"userCpuSeconds": 0.069595,
"kernelCpuSeconds": 0.019163,
"cpuConsumptionPercent": 0.000000,
"maxRss": 18079744,
"pageFaults": {
"IORequired": 0,
"IONotRequired": 4610
},
"fsActivity": {
"reads": 0,
"writes": 0
}
},
"uvthreadResourceUsage": {
"userCpuSeconds": 0.068457,
"kernelCpuSeconds": 0.019127,
"cpuConsumptionPercent": 0.000000,
"fsActivity": {
"reads": 0,
"writes": 0
}
},
"libuv": [
{
"type": "async",
"is_active": true,
"is_referenced": false,
"address": "0x0000000102910900",
"details": ""
},
{
"type": "timer",
"is_active": false,
"is_referenced": false,
"address": "0x00007fff5fbfeab0",
"repeat": 0,
"firesInMsFromNow": 94403548320796,
"expired": true
},
{
"type": "check",
"is_active": true,
"is_referenced": false,
"address": "0x00007fff5fbfeb48"
},
{
"type": "idle",
"is_active": false,
"is_referenced": true,
"address": "0x00007fff5fbfebc0"
},
{
"type": "prepare",
"is_active": false,
"is_referenced": false,
"address": "0x00007fff5fbfec38"
},
{
"type": "check",
"is_active": false,
"is_referenced": false,
"address": "0x00007fff5fbfecb0"
},
{
"type": "async",
"is_active": true,
"is_referenced": false,
"address": "0x000000010188f2e0"
},
{
"type": "tty",
"is_active": false,
"is_referenced": true,
"address": "0x000055b581db0e18",
"width": 204,
"height": 55,
"fd": 17,
"writeQueueSize": 0,
"readable": true,
"writable": true
},
{
"type": "signal",
"is_active": true,
"is_referenced": false,
"address": "0x000055b581d80010",
"signum": 28,
"signal": "SIGWINCH"
},
{
"type": "tty",
"is_active": true,
"is_referenced": true,
"address": "0x000055b581df59f8",
"width": 204,
"height": 55,
"fd": 19,
"writeQueueSize": 0,
"readable": true,
"writable": true
},
{
"type": "loop",
"is_active": true,
"address": "0x000055fc7b2cb180",
"loopIdleTimeSeconds": 22644.8
}
],
"workers": [],
"environmentVariables": {
"REMOTEHOST": "REMOVED",
"MANPATH": "/opt/rh/devtoolset-3/root/usr/share/man:",
"XDG_SESSION_ID": "66126",
"HOSTNAME": "test_machine",
"HOST": "test_machine",
"TERM": "xterm-256color",
"SHELL": "/bin/csh",
"SSH_CLIENT": "REMOVED",
"PERL5LIB": "/opt/rh/devtoolset-3/root//usr/lib64/perl5/vendor_perl:/opt/rh/devtoolset-3/root/usr/lib/perl5:/opt/rh/devtoolset-3/root//usr/share/perl5/vendor_perl",
"OLDPWD": "/home/nodeuser/project/node/src",
"JAVACONFDIRS": "/opt/rh/devtoolset-3/root/etc/java:/etc/java",
"SSH_TTY": "/dev/pts/0",
"PCP_DIR": "/opt/rh/devtoolset-3/root",
"GROUP": "normaluser",
"USER": "nodeuser",
"LD_LIBRARY_PATH": "/opt/rh/devtoolset-3/root/usr/lib64:/opt/rh/devtoolset-3/root/usr/lib",
"HOSTTYPE": "x86_64-linux",
"XDG_CONFIG_DIRS": "/opt/rh/devtoolset-3/root/etc/xdg:/etc/xdg",
"MAIL": "/var/spool/mail/nodeuser",
"PATH": "/home/nodeuser/project/node:/opt/rh/devtoolset-3/root/usr/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin",
"PWD": "/home/nodeuser/project/node",
"LANG": "en_US.UTF-8",
"PS1": "\\u@\\h : \\[\\e[31m\\]\\w\\[\\e[m\\] > ",
"SHLVL": "2",
"HOME": "/home/nodeuser",
"OSTYPE": "linux",
"VENDOR": "unknown",
"PYTHONPATH": "/opt/rh/devtoolset-3/root/usr/lib64/python2.7/site-packages:/opt/rh/devtoolset-3/root/usr/lib/python2.7/site-packages",
"MACHTYPE": "x86_64",
"LOGNAME": "nodeuser",
"XDG_DATA_DIRS": "/opt/rh/devtoolset-3/root/usr/share:/usr/local/share:/usr/share",
"LESSOPEN": "||/usr/bin/lesspipe.sh %s",
"INFOPATH": "/opt/rh/devtoolset-3/root/usr/share/info",
"XDG_RUNTIME_DIR": "/run/user/50141",
"_": "./node"
},
"userLimits": {
"core_file_size_blocks": {
"soft": "",
"hard": "unlimited"
},
"data_seg_size_kbytes": {
"soft": "unlimited",
"hard": "unlimited"
},
"file_size_blocks": {
"soft": "unlimited",
"hard": "unlimited"
},
"max_locked_memory_bytes": {
"soft": "unlimited",
"hard": 65536
},
"max_memory_size_kbytes": {
"soft": "unlimited",
"hard": "unlimited"
},
"open_files": {
"soft": "unlimited",
"hard": 4096
},
"stack_size_bytes": {
"soft": "unlimited",
"hard": "unlimited"
},
"cpu_time_seconds": {
"soft": "unlimited",
"hard": "unlimited"
},
"max_user_processes": {
"soft": "unlimited",
"hard": 4127290
},
"virtual_memory_kbytes": {
"soft": "unlimited",
"hard": "unlimited"
}
},
"sharedObjects": [
"/lib64/libdl.so.2",
"/lib64/librt.so.1",
"/lib64/libstdc++.so.6",
"/lib64/libm.so.6",
"/lib64/libgcc_s.so.1",
"/lib64/libpthread.so.0",
"/lib64/libc.so.6",
"/lib64/ld-linux-x86-64.so.2"
]
}
```
### Usage
```
node --report-uncaught-exception --report-on-signal \
--report-on-fatalerror app.js
```
* `--report-uncaught-exception` Enables report to be generated on un-caught exceptions. Useful when inspecting JavaScript stack in conjunction with native stack and other runtime environment data.
* `--report-on-signal` Enables report to be generated upon receiving the specified (or predefined) signal to the running Node.js process. (See below on how to modify the signal that triggers the report.) Default signal is `SIGUSR2`. Useful when a report needs to be triggered from another program. Application monitors may leverage this feature to collect report at regular intervals and plot rich set of internal runtime data to their views.
Signal based report generation is not supported in Windows.
Under normal circumstances, there is no need to modify the report triggering signal. However, if `SIGUSR2` is already used for other purposes, then this flag helps to change the signal for report generation and preserve the original meaning of `SIGUSR2` for the said purposes.
* `--report-on-fatalerror` Enables the report to be triggered on fatal errors (internal errors within the Node.js runtime, such as out of memory) that leads to termination of the application. Useful to inspect various diagnostic data elements such as heap, stack, event loop state, resource consumption etc. to reason about the fatal error.
* `--report-compact` Write reports in a compact format, single-line JSON, more easily consumable by log processing systems than the default multi-line format designed for human consumption.
* `--report-directory` Location at which the report will be generated.
* `--report-filename` Name of the file to which the report will be written.
* `--report-signal` Sets or resets the signal for report generation (not supported on Windows). Default signal is `SIGUSR2`.
A report can also be triggered via an API call from a JavaScript application:
```
process.report.writeReport();
```
This function takes an optional additional argument `filename`, which is the name of a file into which the report is written.
```
process.report.writeReport('./foo.json');
```
This function takes an optional additional argument `err` which is an `Error` object that will be used as the context for the JavaScript stack printed in the report. When using report to handle errors in a callback or an exception handler, this allows the report to include the location of the original error as well as where it was handled.
```
try {
process.chdir('/non-existent-path');
} catch (err) {
process.report.writeReport(err);
}
// Any other code
```
If both filename and error object are passed to `writeReport()` the error object must be the second parameter.
```
try {
process.chdir('/non-existent-path');
} catch (err) {
process.report.writeReport(filename, err);
}
// Any other code
```
The content of the diagnostic report can be returned as a JavaScript Object via an API call from a JavaScript application:
```
const report = process.report.getReport();
console.log(typeof report === 'object'); // true
// Similar to process.report.writeReport() output
console.log(JSON.stringify(report, null, 2));
```
This function takes an optional additional argument `err`, which is an `Error` object that will be used as the context for the JavaScript stack printed in the report.
```
const report = process.report.getReport(new Error('custom error'));
console.log(typeof report === 'object'); // true
```
The API versions are useful when inspecting the runtime state from within the application, in expectation of self-adjusting the resource consumption, load balancing, monitoring etc.
The content of the report consists of a header section containing the event type, date, time, PID, and Node.js version, sections containing JavaScript and native stack traces, a section containing V8 heap information, a section containing `libuv` handle information, and an OS platform information section showing CPU and memory usage and system limits. An example report can be triggered using the Node.js REPL:
```
$ node
> process.report.writeReport();
Writing Node.js report to file: report.20181126.091102.8480.0.001.json
Node.js report completed
>
```
When a report is written, start and end messages are issued to stderr and the filename of the report is returned to the caller. The default filename includes the date, time, PID, and a sequence number. The sequence number helps in associating the report dump with the runtime state if generated multiple times for the same Node.js process.
### Configuration
Additional runtime configuration of report generation is available via the following properties of `process.report`:
`reportOnFatalError` triggers diagnostic reporting on fatal errors when `true`. Defaults to `false`.
`reportOnSignal` triggers diagnostic reporting on signal when `true`. This is not supported on Windows. Defaults to `false`.
`reportOnUncaughtException` triggers diagnostic reporting on uncaught exception when `true`. Defaults to `false`.
`signal` specifies the POSIX signal identifier that will be used to intercept external triggers for report generation. Defaults to `'SIGUSR2'`.
`filename` specifies the name of the output file in the file system. Special meaning is attached to `stdout` and `stderr`. Usage of these will result in report being written to the associated standard streams. In cases where standard streams are used, the value in `directory` is ignored. URLs are not supported. Defaults to a composite filename that contains timestamp, PID, and sequence number.
`directory` specifies the filesystem directory where the report will be written. URLs are not supported. Defaults to the current working directory of the Node.js process.
```
// Trigger report only on uncaught exceptions.
process.report.reportOnFatalError = false;
process.report.reportOnSignal = false;
process.report.reportOnUncaughtException = true;
// Trigger report for both internal errors as well as external signal.
process.report.reportOnFatalError = true;
process.report.reportOnSignal = true;
process.report.reportOnUncaughtException = false;
// Change the default signal to 'SIGQUIT' and enable it.
process.report.reportOnFatalError = false;
process.report.reportOnUncaughtException = false;
process.report.reportOnSignal = true;
process.report.signal = 'SIGQUIT';
```
Configuration on module initialization is also available via environment variables:
```
NODE_OPTIONS="--report-uncaught-exception \
--report-on-fatalerror --report-on-signal \
--report-signal=SIGUSR2 --report-filename=./report.json \
--report-directory=/home/nodeuser"
```
Specific API documentation can be found under [`process API documentation`](process) section.
### Interaction with workers
History
| Version | Changes |
| --- | --- |
| v13.9.0, v12.16.2 | Workers are now included in the report. |
[`Worker`](worker_threads) threads can create reports in the same way that the main thread does.
Reports will include information on any Workers that are children of the current thread as part of the `workers` section, with each Worker generating a report in the standard report format.
The thread which is generating the report will wait for the reports from Worker threads to finish. However, the latency for this will usually be low, as both running JavaScript and the event loop are interrupted to generate the report.
| programming_docs |
node None TTY
---
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/tty.js](https://github.com/nodejs/node/blob/v19.0.1/lib/tty.js)
The `node:tty` module provides the `tty.ReadStream` and `tty.WriteStream` classes. In most cases, it will not be necessary or possible to use this module directly. However, it can be accessed using:
```
const tty = require('node:tty');
```
When Node.js detects that it is being run with a text terminal ("TTY") attached, [`process.stdin`](process#processstdin) will, by default, be initialized as an instance of `tty.ReadStream` and both [`process.stdout`](process#processstdout) and [`process.stderr`](process#processstderr) will, by default, be instances of `tty.WriteStream`. The preferred method of determining whether Node.js is being run within a TTY context is to check that the value of the `process.stdout.isTTY` property is `true`:
```
$ node -p -e "Boolean(process.stdout.isTTY)"
true
$ node -p -e "Boolean(process.stdout.isTTY)" | cat
false
```
In most cases, there should be little to no reason for an application to manually create instances of the `tty.ReadStream` and `tty.WriteStream` classes.
### Class: `tty.ReadStream`
Added in: v0.5.8 * Extends: [<net.Socket>](net#class-netsocket)
Represents the readable side of a TTY. In normal circumstances [`process.stdin`](process#processstdin) will be the only `tty.ReadStream` instance in a Node.js process and there should be no reason to create additional instances.
####
`readStream.isRaw`
Added in: v0.7.7 A `boolean` that is `true` if the TTY is currently configured to operate as a raw device. Defaults to `false`.
####
`readStream.isTTY`
Added in: v0.5.8 A `boolean` that is always `true` for `tty.ReadStream` instances.
####
`readStream.setRawMode(mode)`
Added in: v0.7.7 * `mode` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, configures the `tty.ReadStream` to operate as a raw device. If `false`, configures the `tty.ReadStream` to operate in its default mode. The `readStream.isRaw` property will be set to the resulting mode.
* Returns: [<this>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this) The read stream instance.
Allows configuration of `tty.ReadStream` so that it operates as a raw device.
When in raw mode, input is always available character-by-character, not including modifiers. Additionally, all special processing of characters by the terminal is disabled, including echoing input characters. `Ctrl`+`C` will no longer cause a `SIGINT` when in this mode.
### Class: `tty.WriteStream`
Added in: v0.5.8 * Extends: [<net.Socket>](net#class-netsocket)
Represents the writable side of a TTY. In normal circumstances, [`process.stdout`](process#processstdout) and [`process.stderr`](process#processstderr) will be the only `tty.WriteStream` instances created for a Node.js process and there should be no reason to create additional instances.
#### Event: `'resize'`
Added in: v0.7.7 The `'resize'` event is emitted whenever either of the `writeStream.columns` or `writeStream.rows` properties have changed. No arguments are passed to the listener callback when called.
```
process.stdout.on('resize', () => {
console.log('screen size has changed!');
console.log(`${process.stdout.columns}x${process.stdout.rows}`);
});
```
####
`writeStream.clearLine(dir[, callback])`
History
| Version | Changes |
| --- | --- |
| v12.7.0 | The stream's write() callback and return value are exposed. |
| v0.7.7 | Added in: v0.7.7 |
* `dir` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
+ `-1`: to the left from cursor
+ `1`: to the right from cursor
+ `0`: the entire line
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked once the operation completes.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `false` if the stream wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`.
`writeStream.clearLine()` clears the current line of this `WriteStream` in a direction identified by `dir`.
####
`writeStream.clearScreenDown([callback])`
History
| Version | Changes |
| --- | --- |
| v12.7.0 | The stream's write() callback and return value are exposed. |
| v0.7.7 | Added in: v0.7.7 |
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked once the operation completes.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `false` if the stream wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`.
`writeStream.clearScreenDown()` clears this `WriteStream` from the current cursor down.
####
`writeStream.columns`
Added in: v0.7.7 A `number` specifying the number of columns the TTY currently has. This property is updated whenever the `'resize'` event is emitted.
####
`writeStream.cursorTo(x[, y][, callback])`
History
| Version | Changes |
| --- | --- |
| v12.7.0 | The stream's write() callback and return value are exposed. |
| v0.7.7 | Added in: v0.7.7 |
* `x` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `y` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked once the operation completes.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `false` if the stream wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`.
`writeStream.cursorTo()` moves this `WriteStream`'s cursor to the specified position.
####
`writeStream.getColorDepth([env])`
Added in: v9.9.0 * `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object containing the environment variables to check. This enables simulating the usage of a specific terminal. **Default:** `process.env`.
* Returns: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns:
* `1` for 2,
* `4` for 16,
* `8` for 256,
* `24` for 16,777,216 colors supported.
Use this to determine what colors the terminal supports. Due to the nature of colors in terminals it is possible to either have false positives or false negatives. It depends on process information and the environment variables that may lie about what terminal is used. It is possible to pass in an `env` object to simulate the usage of a specific terminal. This can be useful to check how specific environment settings behave.
To enforce a specific color support, use one of the below environment settings.
* 2 colors: `FORCE_COLOR = 0` (Disables colors)
* 16 colors: `FORCE_COLOR = 1`
* 256 colors: `FORCE_COLOR = 2`
* 16,777,216 colors: `FORCE_COLOR = 3`
Disabling color support is also possible by using the `NO_COLOR` and `NODE_DISABLE_COLORS` environment variables.
####
`writeStream.getWindowSize()`
Added in: v0.7.7 * Returns: [<number[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
`writeStream.getWindowSize()` returns the size of the TTY corresponding to this `WriteStream`. The array is of the type `[numColumns, numRows]` where `numColumns` and `numRows` represent the number of columns and rows in the corresponding TTY.
####
`writeStream.hasColors([count][, env])`
Added in: v11.13.0, v10.16.0 * `count` [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of colors that are requested (minimum 2). **Default:** 16.
* `env` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object containing the environment variables to check. This enables simulating the usage of a specific terminal. **Default:** `process.env`.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Returns `true` if the `writeStream` supports at least as many colors as provided in `count`. Minimum support is 2 (black and white).
This has the same false positives and negatives as described in [`writeStream.getColorDepth()`](#writestreamgetcolordepthenv).
```
process.stdout.hasColors();
// Returns true or false depending on if `stdout` supports at least 16 colors.
process.stdout.hasColors(256);
// Returns true or false depending on if `stdout` supports at least 256 colors.
process.stdout.hasColors({ TMUX: '1' });
// Returns true.
process.stdout.hasColors(2 ** 24, { TMUX: '1' });
// Returns false (the environment setting pretends to support 2 ** 8 colors).
```
####
`writeStream.isTTY`
Added in: v0.5.8 A `boolean` that is always `true`.
####
`writeStream.moveCursor(dx, dy[, callback])`
History
| Version | Changes |
| --- | --- |
| v12.7.0 | The stream's write() callback and return value are exposed. |
| v0.7.7 | Added in: v0.7.7 |
* `dx` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `dy` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Invoked once the operation completes.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `false` if the stream wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`.
`writeStream.moveCursor()` moves this `WriteStream`'s cursor *relative* to its current position.
####
`writeStream.rows`
Added in: v0.7.7 A `number` specifying the number of rows the TTY currently has. This property is updated whenever the `'resize'` event is emitted.
###
`tty.isatty(fd)`
Added in: v0.5.8 * `fd` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) A numeric file descriptor
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `tty.isatty()` method returns `true` if the given `fd` is associated with a TTY and `false` if it is not, including whenever `fd` is not a non-negative integer.
node None C++ addons
----------
*Addons* are dynamically-linked shared objects written in C++. The [`require()`](modules#requireid) function can load addons as ordinary Node.js modules. Addons provide an interface between JavaScript and C/C++ libraries.
There are three options for implementing addons: Node-API, nan, or direct use of internal V8, libuv, and Node.js libraries. Unless there is a need for direct access to functionality which is not exposed by Node-API, use Node-API. Refer to [C/C++ addons with Node-API](n-api) for more information on Node-API.
When not using Node-API, implementing addons is complicated, involving knowledge of several components and APIs:
* [V8](https://v8.dev/): the C++ library Node.js uses to provide the JavaScript implementation. V8 provides the mechanisms for creating objects, calling functions, etc. V8's API is documented mostly in the `v8.h` header file (`deps/v8/include/v8.h` in the Node.js source tree), which is also available [online](https://v8docs.nodesource.com/).
* [libuv](https://github.com/libuv/libuv): The C library that implements the Node.js event loop, its worker threads and all of the asynchronous behaviors of the platform. It also serves as a cross-platform abstraction library, giving easy, POSIX-like access across all major operating systems to many common system tasks, such as interacting with the filesystem, sockets, timers, and system events. libuv also provides a threading abstraction similar to POSIX threads for more sophisticated asynchronous addons that need to move beyond the standard event loop. Addon authors should avoid blocking the event loop with I/O or other time-intensive tasks by offloading work via libuv to non-blocking system operations, worker threads, or a custom use of libuv threads.
* Internal Node.js libraries. Node.js itself exports C++ APIs that addons can use, the most important of which is the `node::ObjectWrap` class.
* Node.js includes other statically linked libraries including OpenSSL. These other libraries are located in the `deps/` directory in the Node.js source tree. Only the libuv, OpenSSL, V8, and zlib symbols are purposefully re-exported by Node.js and may be used to various extents by addons. See [Linking to libraries included with Node.js](#linking-to-libraries-included-with-nodejs) for additional information.
All of the following examples are available for [download](https://github.com/nodejs/node-addon-examples) and may be used as the starting-point for an addon.
### Hello world
This "Hello world" example is a simple addon, written in C++, that is the equivalent of the following JavaScript code:
```
module.exports.hello = () => 'world';
```
First, create the file `hello.cc`:
```
// hello.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(
isolate, "world").ToLocalChecked());
}
void Initialize(Local<Object> exports) {
NODE_SET_METHOD(exports, "hello", Method);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, Initialize)
} // namespace demo
```
All Node.js addons must export an initialization function following the pattern:
```
void Initialize(Local<Object> exports);
NODE_MODULE(NODE_GYP_MODULE_NAME, Initialize)
```
There is no semi-colon after `NODE_MODULE` as it's not a function (see `node.h`).
The `module_name` must match the filename of the final binary (excluding the `.node` suffix).
In the `hello.cc` example, then, the initialization function is `Initialize` and the addon module name is `addon`.
When building addons with `node-gyp`, using the macro `NODE_GYP_MODULE_NAME` as the first parameter of `NODE_MODULE()` will ensure that the name of the final binary will be passed to `NODE_MODULE()`.
#### Context-aware addons
There are environments in which Node.js addons may need to be loaded multiple times in multiple contexts. For example, the [Electron](https://electronjs.org/) runtime runs multiple instances of Node.js in a single process. Each instance will have its own `require()` cache, and thus each instance will need a native addon to behave correctly when loaded via `require()`. This means that the addon must support multiple initializations.
A context-aware addon can be constructed by using the macro `NODE_MODULE_INITIALIZER`, which expands to the name of a function which Node.js will expect to find when it loads an addon. An addon can thus be initialized as in the following example:
```
using namespace v8;
extern "C" NODE_MODULE_EXPORT void
NODE_MODULE_INITIALIZER(Local<Object> exports,
Local<Value> module,
Local<Context> context) {
/* Perform addon initialization steps here. */
}
```
Another option is to use the macro `NODE_MODULE_INIT()`, which will also construct a context-aware addon. Unlike `NODE_MODULE()`, which is used to construct an addon around a given addon initializer function, `NODE_MODULE_INIT()` serves as the declaration of such an initializer to be followed by a function body.
The following three variables may be used inside the function body following an invocation of `NODE_MODULE_INIT()`:
* `Local<Object> exports`,
* `Local<Value> module`, and
* `Local<Context> context`
The choice to build a context-aware addon carries with it the responsibility of carefully managing global static data. Since the addon may be loaded multiple times, potentially even from different threads, any global static data stored in the addon must be properly protected, and must not contain any persistent references to JavaScript objects. The reason for this is that JavaScript objects are only valid in one context, and will likely cause a crash when accessed from the wrong context or from a different thread than the one on which they were created.
The context-aware addon can be structured to avoid global static data by performing the following steps:
* Define a class which will hold per-addon-instance data and which has a static member of the form
```
static void DeleteInstance(void* data) {
// Cast `data` to an instance of the class and delete it.
}
```
* Heap-allocate an instance of this class in the addon initializer. This can be accomplished using the `new` keyword.
* Call `node::AddEnvironmentCleanupHook()`, passing it the above-created instance and a pointer to `DeleteInstance()`. This will ensure the instance is deleted when the environment is torn down.
* Store the instance of the class in a `v8::External`, and
* Pass the `v8::External` to all methods exposed to JavaScript by passing it to `v8::FunctionTemplate::New()` or `v8::Function::New()` which creates the native-backed JavaScript functions. The third parameter of `v8::FunctionTemplate::New()` or `v8::Function::New()` accepts the `v8::External` and makes it available in the native callback using the `v8::FunctionCallbackInfo::Data()` method.
This will ensure that the per-addon-instance data reaches each binding that can be called from JavaScript. The per-addon-instance data must also be passed into any asynchronous callbacks the addon may create.
The following example illustrates the implementation of a context-aware addon:
```
#include <node.h>
using namespace v8;
class AddonData {
public:
explicit AddonData(Isolate* isolate):
call_count(0) {
// Ensure this per-addon-instance data is deleted at environment cleanup.
node::AddEnvironmentCleanupHook(isolate, DeleteInstance, this);
}
// Per-addon data.
int call_count;
static void DeleteInstance(void* data) {
delete static_cast<AddonData*>(data);
}
};
static void Method(const v8::FunctionCallbackInfo<v8::Value>& info) {
// Retrieve the per-addon-instance data.
AddonData* data =
reinterpret_cast<AddonData*>(info.Data().As<External>()->Value());
data->call_count++;
info.GetReturnValue().Set((double)data->call_count);
}
// Initialize this addon to be context-aware.
NODE_MODULE_INIT(/* exports, module, context */) {
Isolate* isolate = context->GetIsolate();
// Create a new instance of `AddonData` for this instance of the addon and
// tie its life cycle to that of the Node.js environment.
AddonData* data = new AddonData(isolate);
// Wrap the data in a `v8::External` so we can pass it to the method we
// expose.
Local<External> external = External::New(isolate, data);
// Expose the method `Method` to JavaScript, and make sure it receives the
// per-addon-instance data we created above by passing `external` as the
// third parameter to the `FunctionTemplate` constructor.
exports->Set(context,
String::NewFromUtf8(isolate, "method").ToLocalChecked(),
FunctionTemplate::New(isolate, Method, external)
->GetFunction(context).ToLocalChecked()).FromJust();
}
```
##### Worker support
History
| Version | Changes |
| --- | --- |
| v14.8.0, v12.19.0 | Cleanup hooks may now be asynchronous. |
In order to be loaded from multiple Node.js environments, such as a main thread and a Worker thread, an add-on needs to either:
* Be an Node-API addon, or
* Be declared as context-aware using `NODE_MODULE_INIT()` as described above
In order to support [`Worker`](worker_threads#class-worker) threads, addons need to clean up any resources they may have allocated when such a thread exists. This can be achieved through the usage of the `AddEnvironmentCleanupHook()` function:
```
void AddEnvironmentCleanupHook(v8::Isolate* isolate,
void (*fun)(void* arg),
void* arg);
```
This function adds a hook that will run before a given Node.js instance shuts down. If necessary, such hooks can be removed before they are run using `RemoveEnvironmentCleanupHook()`, which has the same signature. Callbacks are run in last-in first-out order.
If necessary, there is an additional pair of `AddEnvironmentCleanupHook()` and `RemoveEnvironmentCleanupHook()` overloads, where the cleanup hook takes a callback function. This can be used for shutting down asynchronous resources, such as any libuv handles registered by the addon.
The following `addon.cc` uses `AddEnvironmentCleanupHook`:
```
// addon.cc
#include <node.h>
#include <assert.h>
#include <stdlib.h>
using node::AddEnvironmentCleanupHook;
using v8::HandleScope;
using v8::Isolate;
using v8::Local;
using v8::Object;
// Note: In a real-world application, do not rely on static/global data.
static char cookie[] = "yum yum";
static int cleanup_cb1_called = 0;
static int cleanup_cb2_called = 0;
static void cleanup_cb1(void* arg) {
Isolate* isolate = static_cast<Isolate*>(arg);
HandleScope scope(isolate);
Local<Object> obj = Object::New(isolate);
assert(!obj.IsEmpty()); // assert VM is still alive
assert(obj->IsObject());
cleanup_cb1_called++;
}
static void cleanup_cb2(void* arg) {
assert(arg == static_cast<void*>(cookie));
cleanup_cb2_called++;
}
static void sanity_check(void*) {
assert(cleanup_cb1_called == 1);
assert(cleanup_cb2_called == 1);
}
// Initialize this addon to be context-aware.
NODE_MODULE_INIT(/* exports, module, context */) {
Isolate* isolate = context->GetIsolate();
AddEnvironmentCleanupHook(isolate, sanity_check, nullptr);
AddEnvironmentCleanupHook(isolate, cleanup_cb2, cookie);
AddEnvironmentCleanupHook(isolate, cleanup_cb1, isolate);
}
```
Test in JavaScript by running:
```
// test.js
require('./build/Release/addon');
```
#### Building
Once the source code has been written, it must be compiled into the binary `addon.node` file. To do so, create a file called `binding.gyp` in the top-level of the project describing the build configuration of the module using a JSON-like format. This file is used by [node-gyp](https://github.com/nodejs/node-gyp), a tool written specifically to compile Node.js addons.
```
{
"targets": [
{
"target_name": "addon",
"sources": [ "hello.cc" ]
}
]
}
```
A version of the `node-gyp` utility is bundled and distributed with Node.js as part of `npm`. This version is not made directly available for developers to use and is intended only to support the ability to use the `npm install` command to compile and install addons. Developers who wish to use `node-gyp` directly can install it using the command `npm install -g node-gyp`. See the `node-gyp` [installation instructions](https://github.com/nodejs/node-gyp#installation) for more information, including platform-specific requirements.
Once the `binding.gyp` file has been created, use `node-gyp configure` to generate the appropriate project build files for the current platform. This will generate either a `Makefile` (on Unix platforms) or a `vcxproj` file (on Windows) in the `build/` directory.
Next, invoke the `node-gyp build` command to generate the compiled `addon.node` file. This will be put into the `build/Release/` directory.
When using `npm install` to install a Node.js addon, npm uses its own bundled version of `node-gyp` to perform this same set of actions, generating a compiled version of the addon for the user's platform on demand.
Once built, the binary addon can be used from within Node.js by pointing [`require()`](modules#requireid) to the built `addon.node` module:
```
// hello.js
const addon = require('./build/Release/addon');
console.log(addon.hello());
// Prints: 'world'
```
Because the exact path to the compiled addon binary can vary depending on how it is compiled (i.e. sometimes it may be in `./build/Debug/`), addons can use the [bindings](https://github.com/TooTallNate/node-bindings) package to load the compiled module.
While the `bindings` package implementation is more sophisticated in how it locates addon modules, it is essentially using a `try…catch` pattern similar to:
```
try {
return require('./build/Release/addon.node');
} catch (err) {
return require('./build/Debug/addon.node');
}
```
#### Linking to libraries included with Node.js
Node.js uses statically linked libraries such as V8, libuv, and OpenSSL. All addons are required to link to V8 and may link to any of the other dependencies as well. Typically, this is as simple as including the appropriate `#include <...>` statements (e.g. `#include <v8.h>`) and `node-gyp` will locate the appropriate headers automatically. However, there are a few caveats to be aware of:
* When `node-gyp` runs, it will detect the specific release version of Node.js and download either the full source tarball or just the headers. If the full source is downloaded, addons will have complete access to the full set of Node.js dependencies. However, if only the Node.js headers are downloaded, then only the symbols exported by Node.js will be available.
* `node-gyp` can be run using the `--nodedir` flag pointing at a local Node.js source image. Using this option, the addon will have access to the full set of dependencies.
#### Loading addons using `require()`
The filename extension of the compiled addon binary is `.node` (as opposed to `.dll` or `.so`). The [`require()`](modules#requireid) function is written to look for files with the `.node` file extension and initialize those as dynamically-linked libraries.
When calling [`require()`](modules#requireid), the `.node` extension can usually be omitted and Node.js will still find and initialize the addon. One caveat, however, is that Node.js will first attempt to locate and load modules or JavaScript files that happen to share the same base name. For instance, if there is a file `addon.js` in the same directory as the binary `addon.node`, then [`require('addon')`](modules#requireid) will give precedence to the `addon.js` file and load it instead.
### Native abstractions for Node.js
Each of the examples illustrated in this document directly use the Node.js and V8 APIs for implementing addons. The V8 API can, and has, changed dramatically from one V8 release to the next (and one major Node.js release to the next). With each change, addons may need to be updated and recompiled in order to continue functioning. The Node.js release schedule is designed to minimize the frequency and impact of such changes but there is little that Node.js can do to ensure stability of the V8 APIs.
The [Native Abstractions for Node.js](https://github.com/nodejs/nan) (or `nan`) provide a set of tools that addon developers are recommended to use to keep compatibility between past and future releases of V8 and Node.js. See the `nan` [examples](https://github.com/nodejs/nan/tree/HEAD/examples/) for an illustration of how it can be used.
### Node-API
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
Node-API is an API for building native addons. It is independent from the underlying JavaScript runtime (e.g. V8) and is maintained as part of Node.js itself. This API will be Application Binary Interface (ABI) stable across versions of Node.js. It is intended to insulate addons from changes in the underlying JavaScript engine and allow modules compiled for one version to run on later versions of Node.js without recompilation. Addons are built/packaged with the same approach/tools outlined in this document (node-gyp, etc.). The only difference is the set of APIs that are used by the native code. Instead of using the V8 or [Native Abstractions for Node.js](https://github.com/nodejs/nan) APIs, the functions available in the Node-API are used.
Creating and maintaining an addon that benefits from the ABI stability provided by Node-API carries with it certain [implementation considerations](n-api#implications-of-abi-stability).
To use Node-API in the above "Hello world" example, replace the content of `hello.cc` with the following. All other instructions remain the same.
```
// hello.cc using Node-API
#include <node_api.h>
namespace demo {
napi_value Method(napi_env env, napi_callback_info args) {
napi_value greeting;
napi_status status;
status = napi_create_string_utf8(env, "world", NAPI_AUTO_LENGTH, &greeting);
if (status != napi_ok) return nullptr;
return greeting;
}
napi_value init(napi_env env, napi_value exports) {
napi_status status;
napi_value fn;
status = napi_create_function(env, nullptr, 0, Method, nullptr, &fn);
if (status != napi_ok) return nullptr;
status = napi_set_named_property(env, exports, "hello", fn);
if (status != napi_ok) return nullptr;
return exports;
}
NAPI_MODULE(NODE_GYP_MODULE_NAME, init)
} // namespace demo
```
The functions available and how to use them are documented in [C/C++ addons with Node-API](n-api).
### Addon examples
Following are some example addons intended to help developers get started. The examples use the V8 APIs. Refer to the online [V8 reference](https://v8docs.nodesource.com/) for help with the various V8 calls, and V8's [Embedder's Guide](https://v8.dev/docs/embed) for an explanation of several concepts used such as handles, scopes, function templates, etc.
Each of these examples using the following `binding.gyp` file:
```
{
"targets": [
{
"target_name": "addon",
"sources": [ "addon.cc" ]
}
]
}
```
In cases where there is more than one `.cc` file, simply add the additional filename to the `sources` array:
```
"sources": ["addon.cc", "myexample.cc"]
```
Once the `binding.gyp` file is ready, the example addons can be configured and built using `node-gyp`:
```
$ node-gyp configure build
```
#### Function arguments
Addons will typically expose objects and functions that can be accessed from JavaScript running within Node.js. When functions are invoked from JavaScript, the input arguments and return value must be mapped to and from the C/C++ code.
The following example illustrates how to read function arguments passed from JavaScript and how to return a result:
```
// addon.cc
#include <node.h>
namespace demo {
using v8::Exception;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
// This is the implementation of the "add" method
// Input arguments are passed using the
// const FunctionCallbackInfo<Value>& args struct
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
// Check the number of arguments passed.
if (args.Length() < 2) {
// Throw an Error that is passed back to JavaScript
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate,
"Wrong number of arguments").ToLocalChecked()));
return;
}
// Check the argument types
if (!args[0]->IsNumber() || !args[1]->IsNumber()) {
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate,
"Wrong arguments").ToLocalChecked()));
return;
}
// Perform the operation
double value =
args[0].As<Number>()->Value() + args[1].As<Number>()->Value();
Local<Number> num = Number::New(isolate, value);
// Set the return value (using the passed in
// FunctionCallbackInfo<Value>&)
args.GetReturnValue().Set(num);
}
void Init(Local<Object> exports) {
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, Init)
} // namespace demo
```
Once compiled, the example addon can be required and used from within Node.js:
```
// test.js
const addon = require('./build/Release/addon');
console.log('This should be eight:', addon.add(3, 5));
```
#### Callbacks
It is common practice within addons to pass JavaScript functions to a C++ function and execute them from there. The following example illustrates how to invoke such callbacks:
```
// addon.cc
#include <node.h>
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Null;
using v8::Object;
using v8::String;
using v8::Value;
void RunCallback(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
Local<Function> cb = Local<Function>::Cast(args[0]);
const unsigned argc = 1;
Local<Value> argv[argc] = {
String::NewFromUtf8(isolate,
"hello world").ToLocalChecked() };
cb->Call(context, Null(isolate), argc, argv).ToLocalChecked();
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", RunCallback);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, Init)
} // namespace demo
```
This example uses a two-argument form of `Init()` that receives the full `module` object as the second argument. This allows the addon to completely overwrite `exports` with a single function instead of adding the function as a property of `exports`.
To test it, run the following JavaScript:
```
// test.js
const addon = require('./build/Release/addon');
addon((msg) => {
console.log(msg);
// Prints: 'hello world'
});
```
In this example, the callback function is invoked synchronously.
#### Object factory
Addons can create and return new objects from within a C++ function as illustrated in the following example. An object is created and returned with a property `msg` that echoes the string passed to `createObject()`:
```
// addon.cc
#include <node.h>
namespace demo {
using v8::Context;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
Local<Object> obj = Object::New(isolate);
obj->Set(context,
String::NewFromUtf8(isolate,
"msg").ToLocalChecked(),
args[0]->ToString(context).ToLocalChecked())
.FromJust();
args.GetReturnValue().Set(obj);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, Init)
} // namespace demo
```
To test it in JavaScript:
```
// test.js
const addon = require('./build/Release/addon');
const obj1 = addon('hello');
const obj2 = addon('world');
console.log(obj1.msg, obj2.msg);
// Prints: 'hello world'
```
#### Function factory
Another common scenario is creating JavaScript functions that wrap C++ functions and returning those back to JavaScript:
```
// addon.cc
#include <node.h>
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void MyFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(
isolate, "hello world").ToLocalChecked());
}
void CreateFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, MyFunction);
Local<Function> fn = tpl->GetFunction(context).ToLocalChecked();
// omit this to make it anonymous
fn->SetName(String::NewFromUtf8(
isolate, "theFunction").ToLocalChecked());
args.GetReturnValue().Set(fn);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateFunction);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, Init)
} // namespace demo
```
To test:
```
// test.js
const addon = require('./build/Release/addon');
const fn = addon();
console.log(fn());
// Prints: 'hello world'
```
#### Wrapping C++ objects
It is also possible to wrap C++ objects/classes in a way that allows new instances to be created using the JavaScript `new` operator:
```
// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Local;
using v8::Object;
void InitAll(Local<Object> exports) {
MyObject::Init(exports);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, InitAll)
} // namespace demo
```
Then, in `myobject.h`, the wrapper class inherits from `node::ObjectWrap`:
```
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Local<v8::Object> exports);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
double value_;
};
} // namespace demo
#endif
```
In `myobject.cc`, implement the various methods that are to be exposed. Below, the method `plusOne()` is exposed by adding it to the constructor's prototype:
```
// myobject.cc
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::ObjectTemplate;
using v8::String;
using v8::Value;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Local<Object> exports) {
Isolate* isolate = exports->GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
Local<ObjectTemplate> addon_data_tpl = ObjectTemplate::New(isolate);
addon_data_tpl->SetInternalFieldCount(1); // 1 field for the MyObject::New()
Local<Object> addon_data =
addon_data_tpl->NewInstance(context).ToLocalChecked();
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New, addon_data);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject").ToLocalChecked());
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
Local<Function> constructor = tpl->GetFunction(context).ToLocalChecked();
addon_data->SetInternalField(0, constructor);
exports->Set(context, String::NewFromUtf8(
isolate, "MyObject").ToLocalChecked(),
constructor).FromJust();
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ?
0 : args[0]->NumberValue(context).FromMaybe(0);
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons =
args.Data().As<Object>()->GetInternalField(0).As<Function>();
Local<Object> result =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(result);
}
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
```
To build this example, the `myobject.cc` file must be added to the `binding.gyp`:
```
{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
```
Test it with:
```
// test.js
const addon = require('./build/Release/addon');
const obj = new addon.MyObject(10);
console.log(obj.plusOne());
// Prints: 11
console.log(obj.plusOne());
// Prints: 12
console.log(obj.plusOne());
// Prints: 13
```
The destructor for a wrapper object will run when the object is garbage-collected. For destructor testing, there are command-line flags that can be used to make it possible to force garbage collection. These flags are provided by the underlying V8 JavaScript engine. They are subject to change or removal at any time. They are not documented by Node.js or V8, and they should never be used outside of testing.
During shutdown of the process or worker threads destructors are not called by the JS engine. Therefore it's the responsibility of the user to track these objects and ensure proper destruction to avoid resource leaks.
#### Factory of wrapped objects
Alternatively, it is possible to use a factory pattern to avoid explicitly creating object instances using the JavaScript `new` operator:
```
const obj = addon.createObject();
// instead of:
// const obj = new addon.Object();
```
First, the `createObject()` method is implemented in `addon.cc`:
```
// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void InitAll(Local<Object> exports, Local<Object> module) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, InitAll)
} // namespace demo
```
In `myobject.h`, the static method `NewInstance()` is added to handle instantiating the object. This method takes the place of using `new` in JavaScript:
```
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Global<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
```
The implementation in `myobject.cc` is similar to the previous example:
```
// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using node::AddEnvironmentCleanupHook;
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Global;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
// Warning! This is not thread-safe, this addon cannot be used for worker
// threads.
Global<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject").ToLocalChecked());
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
Local<Context> context = isolate->GetCurrentContext();
constructor.Reset(isolate, tpl->GetFunction(context).ToLocalChecked());
AddEnvironmentCleanupHook(isolate, [](void*) {
constructor.Reset();
}, nullptr);
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ?
0 : args[0]->NumberValue(context).FromMaybe(0);
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
```
Once again, to build this example, the `myobject.cc` file must be added to the `binding.gyp`:
```
{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
```
Test it with:
```
// test.js
const createObject = require('./build/Release/addon');
const obj = createObject(10);
console.log(obj.plusOne());
// Prints: 11
console.log(obj.plusOne());
// Prints: 12
console.log(obj.plusOne());
// Prints: 13
const obj2 = createObject(20);
console.log(obj2.plusOne());
// Prints: 21
console.log(obj2.plusOne());
// Prints: 22
console.log(obj2.plusOne());
// Prints: 23
```
#### Passing wrapped objects around
In addition to wrapping and returning C++ objects, it is possible to pass wrapped objects around by unwrapping them with the Node.js helper function `node::ObjectWrap::Unwrap`. The following examples shows a function `add()` that can take two `MyObject` objects as input arguments:
```
// addon.cc
#include <node.h>
#include <node_object_wrap.h>
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
MyObject* obj1 = node::ObjectWrap::Unwrap<MyObject>(
args[0]->ToObject(context).ToLocalChecked());
MyObject* obj2 = node::ObjectWrap::Unwrap<MyObject>(
args[1]->ToObject(context).ToLocalChecked());
double sum = obj1->value() + obj2->value();
args.GetReturnValue().Set(Number::New(isolate, sum));
}
void InitAll(Local<Object> exports) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(exports, "createObject", CreateObject);
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, InitAll)
} // namespace demo
```
In `myobject.h`, a new public method is added to allow access to private values after unwrapping the object.
```
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
inline double value() const { return value_; }
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Global<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
```
The implementation of `myobject.cc` is similar to before:
```
// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using node::AddEnvironmentCleanupHook;
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Global;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
// Warning! This is not thread-safe, this addon cannot be used for worker
// threads.
Global<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject").ToLocalChecked());
tpl->InstanceTemplate()->SetInternalFieldCount(1);
Local<Context> context = isolate->GetCurrentContext();
constructor.Reset(isolate, tpl->GetFunction(context).ToLocalChecked());
AddEnvironmentCleanupHook(isolate, [](void*) {
constructor.Reset();
}, nullptr);
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ?
0 : args[0]->NumberValue(context).FromMaybe(0);
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
} // namespace demo
```
Test it with:
```
// test.js
const addon = require('./build/Release/addon');
const obj1 = addon.createObject(10);
const obj2 = addon.createObject(20);
const result = addon.add(obj1, obj2);
console.log(result);
// Prints: 30
```
| programming_docs |
node None Web Crypto API
--------------
History
| Version | Changes |
| --- | --- |
| v19.0.0 | No longer experimental except for the `Ed25519`, `Ed448`, `X25519`, and `X448` algorithms. |
| v18.4.0, v16.17.0 | Removed proprietary `'node.keyObject'` import/export format. |
| v18.4.0, v16.17.0 | Removed proprietary `'NODE-DSA'`, `'NODE-DH'`, and `'NODE-SCRYPT'` algorithms. |
| v18.4.0, v16.17.0 | Added `'Ed25519'`, `'Ed448'`, `'X25519'`, and `'X448'` algorithms. |
| v18.4.0, v16.17.0 | Removed proprietary `'NODE-ED25519'` and `'NODE-ED448'` algorithms. |
| v18.4.0, v16.17.0 | Removed proprietary `'NODE-X25519'` and `'NODE-X448'` named curves from the `'ECDH'` algorithm. |
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
Node.js provides an implementation of the standard [Web Crypto API](https://www.w3.org/TR/WebCryptoAPI/).
Use `globalThis.crypto` or `require('node:crypto').webcrypto` to access this module.
```
const { subtle } = globalThis.crypto;
(async function() {
const key = await subtle.generateKey({
name: 'HMAC',
hash: 'SHA-256',
length: 256
}, true, ['sign', 'verify']);
const enc = new TextEncoder();
const message = enc.encode('I love cupcakes');
const digest = await subtle.sign({
name: 'HMAC'
}, key, message);
})();
```
### Examples
#### Generating keys
The [<SubtleCrypto>](webcrypto#class-subtlecrypto) class can be used to generate symmetric (secret) keys or asymmetric key pairs (public key and private key).
##### AES keys
```
const { subtle } = globalThis.crypto;
async function generateAesKey(length = 256) {
const key = await subtle.generateKey({
name: 'AES-CBC',
length
}, true, ['encrypt', 'decrypt']);
return key;
}
```
##### ECDSA key pairs
```
const { subtle } = globalThis.crypto;
async function generateEcKey(namedCurve = 'P-521') {
const {
publicKey,
privateKey
} = await subtle.generateKey({
name: 'ECDSA',
namedCurve,
}, true, ['sign', 'verify']);
return { publicKey, privateKey };
}
```
##### Ed25519/Ed448/X25519/X448 key pairs
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
```
const { subtle } = globalThis.crypto;
async function generateEd25519Key() {
return subtle.generateKey({
name: 'Ed25519',
}, true, ['sign', 'verify']);
}
async function generateX25519Key() {
return subtle.generateKey({
name: 'X25519',
}, true, ['deriveKey']);
}
```
##### HMAC keys
```
const { subtle } = globalThis.crypto;
async function generateHmacKey(hash = 'SHA-256') {
const key = await subtle.generateKey({
name: 'HMAC',
hash
}, true, ['sign', 'verify']);
return key;
}
```
##### RSA key pairs
```
const { subtle } = globalThis.crypto;
const publicExponent = new Uint8Array([1, 0, 1]);
async function generateRsaKey(modulusLength = 2048, hash = 'SHA-256') {
const {
publicKey,
privateKey
} = await subtle.generateKey({
name: 'RSASSA-PKCS1-v1_5',
modulusLength,
publicExponent,
hash,
}, true, ['sign', 'verify']);
return { publicKey, privateKey };
}
```
#### Encryption and decryption
```
const crypto = globalThis.crypto;
async function aesEncrypt(plaintext) {
const ec = new TextEncoder();
const key = await generateAesKey();
const iv = crypto.getRandomValues(new Uint8Array(16));
const ciphertext = await crypto.subtle.encrypt({
name: 'AES-CBC',
iv,
}, key, ec.encode(plaintext));
return {
key,
iv,
ciphertext
};
}
async function aesDecrypt(ciphertext, key, iv) {
const dec = new TextDecoder();
const plaintext = await crypto.subtle.decrypt({
name: 'AES-CBC',
iv,
}, key, ciphertext);
return dec.decode(plaintext);
}
```
#### Exporting and importing keys
```
const { subtle } = globalThis.crypto;
async function generateAndExportHmacKey(format = 'jwk', hash = 'SHA-512') {
const key = await subtle.generateKey({
name: 'HMAC',
hash
}, true, ['sign', 'verify']);
return subtle.exportKey(format, key);
}
async function importHmacKey(keyData, format = 'jwk', hash = 'SHA-512') {
const key = await subtle.importKey(format, keyData, {
name: 'HMAC',
hash
}, true, ['sign', 'verify']);
return key;
}
```
#### Wrapping and unwrapping keys
```
const { subtle } = globalThis.crypto;
async function generateAndWrapHmacKey(format = 'jwk', hash = 'SHA-512') {
const [
key,
wrappingKey,
] = await Promise.all([
subtle.generateKey({
name: 'HMAC', hash
}, true, ['sign', 'verify']),
subtle.generateKey({
name: 'AES-KW',
length: 256
}, true, ['wrapKey', 'unwrapKey']),
]);
const wrappedKey = await subtle.wrapKey(format, key, wrappingKey, 'AES-KW');
return { wrappedKey, wrappingKey };
}
async function unwrapHmacKey(
wrappedKey,
wrappingKey,
format = 'jwk',
hash = 'SHA-512') {
const key = await subtle.unwrapKey(
format,
wrappedKey,
wrappingKey,
'AES-KW',
{ name: 'HMAC', hash },
true,
['sign', 'verify']);
return key;
}
```
#### Sign and verify
```
const { subtle } = globalThis.crypto;
async function sign(key, data) {
const ec = new TextEncoder();
const signature =
await subtle.sign('RSASSA-PKCS1-v1_5', key, ec.encode(data));
return signature;
}
async function verify(key, signature, data) {
const ec = new TextEncoder();
const verified =
await subtle.verify(
'RSASSA-PKCS1-v1_5',
key,
signature,
ec.encode(data));
return verified;
}
```
#### Deriving bits and keys
```
const { subtle } = globalThis.crypto;
async function pbkdf2(pass, salt, iterations = 1000, length = 256) {
const ec = new TextEncoder();
const key = await subtle.importKey(
'raw',
ec.encode(pass),
'PBKDF2',
false,
['deriveBits']);
const bits = await subtle.deriveBits({
name: 'PBKDF2',
hash: 'SHA-512',
salt: ec.encode(salt),
iterations
}, key, length);
return bits;
}
async function pbkdf2Key(pass, salt, iterations = 1000, length = 256) {
const ec = new TextEncoder();
const keyMaterial = await subtle.importKey(
'raw',
ec.encode(pass),
'PBKDF2',
false,
['deriveKey']);
const key = await subtle.deriveKey({
name: 'PBKDF2',
hash: 'SHA-512',
salt: ec.encode(salt),
iterations
}, keyMaterial, {
name: 'AES-GCM',
length: 256
}, true, ['encrypt', 'decrypt']);
return key;
}
```
#### Digest
```
const { subtle } = globalThis.crypto;
async function digest(data, algorithm = 'SHA-512') {
const ec = new TextEncoder();
const digest = await subtle.digest(algorithm, ec.encode(data));
return digest;
}
```
### Algorithm matrix
The table details the algorithms supported by the Node.js Web Crypto API implementation and the APIs supported for each:
| Algorithm | `generateKey` | `exportKey` | `importKey` | `encrypt` | `decrypt` | `wrapKey` | `unwrapKey` | `deriveBits` | `deriveKey` | `sign` | `verify` | `digest` |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| `'RSASSA-PKCS1-v1_5'` | ✔ | ✔ | ✔ | | | | | | | ✔ | ✔ | |
| `'RSA-PSS'` | ✔ | ✔ | ✔ | | | | | | | ✔ | ✔ | |
| `'RSA-OAEP'` | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | | | | | |
| `'ECDSA'` | ✔ | ✔ | ✔ | | | | | | | ✔ | ✔ | |
| `'Ed25519'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | | | | | | | ✔ | ✔ | |
| `'Ed448'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | | | | | | | ✔ | ✔ | |
| `'ECDH'` | ✔ | ✔ | ✔ | | | | | ✔ | ✔ | | | |
| `'X25519'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | | | | | ✔ | ✔ | | | |
| `'X448'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | | | | | ✔ | ✔ | | | |
| `'AES-CTR'` | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | | | | | |
| `'AES-CBC'` | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | | | | | |
| `'AES-GCM'` | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | | | | | |
| `'AES-KW'` | ✔ | ✔ | ✔ | | | ✔ | ✔ | | | | | |
| `'HMAC'` | ✔ | ✔ | ✔ | | | | | | | ✔ | ✔ | |
| `'HKDF'` | | ✔ | ✔ | | | | | ✔ | ✔ | | | |
| `'PBKDF2'` | | ✔ | ✔ | | | | | ✔ | ✔ | | | |
| `'SHA-1'` | | | | | | | | | | | | ✔ |
| `'SHA-256'` | | | | | | | | | | | | ✔ |
| `'SHA-384'` | | | | | | | | | | | | ✔ |
| `'SHA-512'` | | | | | | | | | | | | ✔ |
### Class: `Crypto`
Added in: v15.0.0 `globalThis.crypto` is an instance of the `Crypto` class. `Crypto` is a singleton that provides access to the remainder of the crypto API.
####
`crypto.subtle`
Added in: v15.0.0 * Type: [<SubtleCrypto>](webcrypto#class-subtlecrypto)
Provides access to the `SubtleCrypto` API.
####
`crypto.getRandomValues(typedArray)`
Added in: v15.0.0 * `typedArray` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray)
* Returns: [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray)
Generates cryptographically strong random values. The given `typedArray` is filled with random values, and a reference to `typedArray` is returned.
The given `typedArray` must be an integer-based instance of [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), i.e. `Float32Array` and `Float64Array` are not accepted.
An error will be thrown if the given `typedArray` is larger than 65,536 bytes.
####
`crypto.randomUUID()`
Added in: v16.7.0 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Generates a random [RFC 4122](https://www.rfc-editor.org/rfc/rfc4122.txt) version 4 UUID. The UUID is generated using a cryptographic pseudorandom number generator.
### Class: `CryptoKey`
Added in: v15.0.0 ####
`cryptoKey.algorithm`
Added in: v15.0.0 * Type: [<AesKeyGenParams>](webcrypto#class-aeskeygenparams) | [<RsaHashedKeyGenParams>](webcrypto#class-rsahashedkeygenparams) | [<EcKeyGenParams>](webcrypto#class-eckeygenparams) | [<HmacKeyGenParams>](webcrypto#class-hmackeygenparams)
An object detailing the algorithm for which the key can be used along with additional algorithm-specific parameters.
Read-only.
####
`cryptoKey.extractable`
Added in: v15.0.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
When `true`, the [<CryptoKey>](webcrypto#class-cryptokey) can be extracted using either `subtleCrypto.exportKey()` or `subtleCrypto.wrapKey()`.
Read-only.
####
`cryptoKey.type`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) One of `'secret'`, `'private'`, or `'public'`.
A string identifying whether the key is a symmetric (`'secret'`) or asymmetric (`'private'` or `'public'`) key.
####
`cryptoKey.usages`
Added in: v15.0.0 * Type: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
An array of strings identifying the operations for which the key may be used.
The possible usages are:
* `'encrypt'` - The key may be used to encrypt data.
* `'decrypt'` - The key may be used to decrypt data.
* `'sign'` - The key may be used to generate digital signatures.
* `'verify'` - The key may be used to verify digital signatures.
* `'deriveKey'` - The key may be used to derive a new key.
* `'deriveBits'` - The key may be used to derive bits.
* `'wrapKey'` - The key may be used to wrap another key.
* `'unwrapKey'` - The key may be used to unwrap another key.
Valid key usages depend on the key algorithm (identified by `cryptokey.algorithm.name`).
| Key Type | `'encrypt'` | `'decrypt'` | `'sign'` | `'verify'` | `'deriveKey'` | `'deriveBits'` | `'wrapKey'` | `'unwrapKey'` |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| `'AES-CBC'` | ✔ | ✔ | | | | | ✔ | ✔ |
| `'AES-CTR'` | ✔ | ✔ | | | | | ✔ | ✔ |
| `'AES-GCM'` | ✔ | ✔ | | | | | ✔ | ✔ |
| `'AES-KW'` | | | | | | | ✔ | ✔ |
| `'ECDH'` | | | | | ✔ | ✔ | | |
| `'X25519'` [1](#user-content-fn-1) | | | | | ✔ | ✔ | | |
| `'X448'` [1](#user-content-fn-1) | | | | | ✔ | ✔ | | |
| `'ECDSA'` | | | ✔ | ✔ | | | | |
| `'Ed25519'` [1](#user-content-fn-1) | | | ✔ | ✔ | | | | |
| `'Ed448'` [1](#user-content-fn-1) | | | ✔ | ✔ | | | | |
| `'HDKF'` | | | | | ✔ | ✔ | | |
| `'HMAC'` | | | ✔ | ✔ | | | | |
| `'PBKDF2'` | | | | | ✔ | ✔ | | |
| `'RSA-OAEP'` | ✔ | ✔ | | | | | ✔ | ✔ |
| `'RSA-PSS'` | | | ✔ | ✔ | | | | |
| `'RSASSA-PKCS1-v1_5'` | | | ✔ | ✔ | | | | |
### Class: `CryptoKeyPair`
Added in: v15.0.0 The `CryptoKeyPair` is a simple dictionary object with `publicKey` and `privateKey` properties, representing an asymmetric key pair.
####
`cryptoKeyPair.privateKey`
Added in: v15.0.0 * Type: [<CryptoKey>](webcrypto#class-cryptokey) A [<CryptoKey>](webcrypto#class-cryptokey) whose `type` will be `'private'`.
####
`cryptoKeyPair.publicKey`
Added in: v15.0.0 * Type: [<CryptoKey>](webcrypto#class-cryptokey) A [<CryptoKey>](webcrypto#class-cryptokey) whose `type` will be `'public'`.
### Class: `SubtleCrypto`
Added in: v15.0.0 ####
`subtle.decrypt(algorithm, key, data)`
Added in: v15.0.0 * `algorithm`: [<RsaOaepParams>](webcrypto#class-rsaoaepparams) | [<AesCtrParams>](webcrypto#class-aesctrparams) | [<AesCbcParams>](webcrypto#class-aescbcparams) | [<AesGcmParams>](webcrypto#class-aesgcmparams)
* `key`: [<CryptoKey>](webcrypto#class-cryptokey)
* `data`: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
Using the method and parameters specified in `algorithm` and the keying material provided by `key`, `subtle.decrypt()` attempts to decipher the provided `data`. If successful, the returned promise will be resolved with an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) containing the plaintext result.
The algorithms currently supported include:
* `'RSA-OAEP'`
* `'AES-CTR'`
* `'AES-CBC'`
* `'AES-GCM`'
####
`subtle.deriveBits(algorithm, baseKey, length)`
History
| Version | Changes |
| --- | --- |
| v18.4.0, v16.17.0 | Added `'X25519'`, and `'X448'` algorithms. |
| v15.0.0 | Added in: v15.0.0 |
* `algorithm`: [<AlgorithmIdentifier>](webcrypto#class-algorithmidentifier) | [<EcdhKeyDeriveParams>](webcrypto#class-ecdhkeyderiveparams) | [<HkdfParams>](webcrypto#class-hkdfparams) | [<Pbkdf2Params>](webcrypto#class-pbkdf2params)
* `baseKey`: [<CryptoKey>](webcrypto#class-cryptokey)
* `length`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
Using the method and parameters specified in `algorithm` and the keying material provided by `baseKey`, `subtle.deriveBits()` attempts to generate `length` bits.
The Node.js implementation requires that when `length` is a number it must be multiple of `8`.
When `length` is `null` the maximum number of bits for a given algorithm is generated. This is allowed for the `'ECDH'`, `'X25519'`, and `'X448'` algorithms.
If successful, the returned promise will be resolved with an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) containing the generated data.
The algorithms currently supported include:
* `'ECDH'`
* `'X25519'` [1](#user-content-fn-1)
* `'X448'` [1](#user-content-fn-1)
* `'HKDF'`
* `'PBKDF2'`
####
`subtle.deriveKey(algorithm, baseKey, derivedKeyAlgorithm, extractable, keyUsages)`
History
| Version | Changes |
| --- | --- |
| v18.4.0, v16.17.0 | Added `'X25519'`, and `'X448'` algorithms. |
| v15.0.0 | Added in: v15.0.0 |
* `algorithm`: [<AlgorithmIdentifier>](webcrypto#class-algorithmidentifier) | [<EcdhKeyDeriveParams>](webcrypto#class-ecdhkeyderiveparams) | [<HkdfParams>](webcrypto#class-hkdfparams) | [<Pbkdf2Params>](webcrypto#class-pbkdf2params)
* `baseKey`: [<CryptoKey>](webcrypto#class-cryptokey)
* `derivedKeyAlgorithm`: [<HmacKeyGenParams>](webcrypto#class-hmackeygenparams) | [<AesKeyGenParams>](webcrypto#class-aeskeygenparams)
* `extractable`: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
* `keyUsages`: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [Key usages](#cryptokeyusages).
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<CryptoKey>](webcrypto#class-cryptokey)
Using the method and parameters specified in `algorithm`, and the keying material provided by `baseKey`, `subtle.deriveKey()` attempts to generate a new [<CryptoKey>](webcrypto#class-cryptokey) based on the method and parameters in `derivedKeyAlgorithm`.
Calling `subtle.deriveKey()` is equivalent to calling `subtle.deriveBits()` to generate raw keying material, then passing the result into the `subtle.importKey()` method using the `deriveKeyAlgorithm`, `extractable`, and `keyUsages` parameters as input.
The algorithms currently supported include:
* `'ECDH'`
* `'X25519'` [1](#user-content-fn-1)
* `'X448'` [1](#user-content-fn-1)
* `'HKDF'`
* `'PBKDF2'`
####
`subtle.digest(algorithm, data)`
Added in: v15.0.0 * `algorithm`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
* `data`: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
Using the method identified by `algorithm`, `subtle.digest()` attempts to generate a digest of `data`. If successful, the returned promise is resolved with an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) containing the computed digest.
If `algorithm` is provided as a [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type), it must be one of:
* `'SHA-1'`
* `'SHA-256'`
* `'SHA-384'`
* `'SHA-512'`
If `algorithm` is provided as an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object), it must have a `name` property whose value is one of the above.
####
`subtle.encrypt(algorithm, key, data)`
Added in: v15.0.0 * `algorithm`: [<RsaOaepParams>](webcrypto#class-rsaoaepparams) | [<AesCtrParams>](webcrypto#class-aesctrparams) | [<AesCbcParams>](webcrypto#class-aescbcparams) | [<AesGcmParams>](webcrypto#class-aesgcmparams)
* `key`: [<CryptoKey>](webcrypto#class-cryptokey)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
Using the method and parameters specified by `algorithm` and the keying material provided by `key`, `subtle.encrypt()` attempts to encipher `data`. If successful, the returned promise is resolved with an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) containing the encrypted result.
The algorithms currently supported include:
* `'RSA-OAEP'`
* `'AES-CTR'`
* `'AES-CBC'`
* `'AES-GCM`'
####
`subtle.exportKey(format, key)`
History
| Version | Changes |
| --- | --- |
| v18.4.0, v16.17.0 | Added `'Ed25519'`, `'Ed448'`, `'X25519'`, and `'X448'` algorithms. |
| v15.9.0 | Removed `'NODE-DSA'` JWK export. |
| v15.0.0 | Added in: v15.0.0 |
* `format`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'raw'`, `'pkcs8'`, `'spki'`, or `'jwk'`.
* `key`: [<CryptoKey>](webcrypto#class-cryptokey)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer).
Exports the given key into the specified format, if supported.
If the [<CryptoKey>](webcrypto#class-cryptokey) is not extractable, the returned promise will reject.
When `format` is either `'pkcs8'` or `'spki'` and the export is successful, the returned promise will be resolved with an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) containing the exported key data.
When `format` is `'jwk'` and the export is successful, the returned promise will be resolved with a JavaScript object conforming to the [JSON Web Key](https://tools.ietf.org/html/rfc7517) specification.
| Key Type | `'spki'` | `'pkcs8'` | `'jwk'` | `'raw'` |
| --- | --- | --- | --- | --- |
| `'AES-CBC'` | | | ✔ | ✔ |
| `'AES-CTR'` | | | ✔ | ✔ |
| `'AES-GCM'` | | | ✔ | ✔ |
| `'AES-KW'` | | | ✔ | ✔ |
| `'ECDH'` | ✔ | ✔ | ✔ | ✔ |
| `'ECDSA'` | ✔ | ✔ | ✔ | ✔ |
| `'Ed25519'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | ✔ |
| `'Ed448'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | ✔ |
| `'HDKF'` | | | | |
| `'HMAC'` | | | ✔ | ✔ |
| `'PBKDF2'` | | | | |
| `'RSA-OAEP'` | ✔ | ✔ | ✔ | |
| `'RSA-PSS'` | ✔ | ✔ | ✔ | |
| `'RSASSA-PKCS1-v1_5'` | ✔ | ✔ | ✔ | |
####
`subtle.generateKey(algorithm, extractable, keyUsages)`
Added in: v15.0.0 * `algorithm`: [<AlgorithmIdentifier>](webcrypto#class-algorithmidentifier) | [<RsaHashedKeyGenParams>](webcrypto#class-rsahashedkeygenparams) | [<EcKeyGenParams>](webcrypto#class-eckeygenparams) | [<HmacKeyGenParams>](webcrypto#class-hmackeygenparams) | [<AesKeyGenParams>](webcrypto#class-aeskeygenparams)
* `extractable`: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
* `keyUsages`: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [Key usages](#cryptokeyusages).
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<CryptoKey>](webcrypto#class-cryptokey) | [<CryptoKeyPair>](webcrypto#class-cryptokeypair)
Using the method and parameters provided in `algorithm`, `subtle.generateKey()` attempts to generate new keying material. Depending the method used, the method may generate either a single [<CryptoKey>](webcrypto#class-cryptokey) or a [<CryptoKeyPair>](webcrypto#class-cryptokeypair).
The [<CryptoKeyPair>](webcrypto#class-cryptokeypair) (public and private key) generating algorithms supported include:
* `'RSASSA-PKCS1-v1_5'`
* `'RSA-PSS'`
* `'RSA-OAEP'`
* `'ECDSA'`
* `'Ed25519'` [1](#user-content-fn-1)
* `'Ed448'` [1](#user-content-fn-1)
* `'ECDH'`
* `'X25519'` [1](#user-content-fn-1)
* `'X448'` [1](#user-content-fn-1)
The [<CryptoKey>](webcrypto#class-cryptokey) (secret key) generating algorithms supported include:
* `'HMAC'`
* `'AES-CTR'`
* `'AES-CBC'`
* `'AES-GCM'`
* `'AES-KW'`
####
`subtle.importKey(format, keyData, algorithm, extractable, keyUsages)`
History
| Version | Changes |
| --- | --- |
| v18.4.0, v16.17.0 | Added `'Ed25519'`, `'Ed448'`, `'X25519'`, and `'X448'` algorithms. |
| v15.9.0 | Removed `'NODE-DSA'` JWK import. |
| v15.0.0 | Added in: v15.0.0 |
* `format`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'raw'`, `'pkcs8'`, `'spki'`, or `'jwk'`.
* `keyData`: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer) | [<KeyObject>](crypto#class-keyobject)
* `algorithm`: [<AlgorithmIdentifier>](webcrypto#class-algorithmidentifier) | [<RsaHashedImportParams>](webcrypto#class-rsahashedimportparams) | [<EcKeyImportParams>](webcrypto#class-eckeyimportparams) | [<HmacImportParams>](webcrypto#class-hmacimportparams)
* `extractable`: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
* `keyUsages`: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [Key usages](#cryptokeyusages).
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<CryptoKey>](webcrypto#class-cryptokey)
The `subtle.importKey()` method attempts to interpret the provided `keyData` as the given `format` to create a [<CryptoKey>](webcrypto#class-cryptokey) instance using the provided `algorithm`, `extractable`, and `keyUsages` arguments. If the import is successful, the returned promise will be resolved with the created [<CryptoKey>](webcrypto#class-cryptokey).
If importing a `'PBKDF2'` key, `extractable` must be `false`.
The algorithms currently supported include:
| Key Type | `'spki'` | `'pkcs8'` | `'jwk'` | `'raw'` |
| --- | --- | --- | --- | --- |
| `'AES-CBC'` | | | ✔ | ✔ |
| `'AES-CTR'` | | | ✔ | ✔ |
| `'AES-GCM'` | | | ✔ | ✔ |
| `'AES-KW'` | | | ✔ | ✔ |
| `'ECDH'` | ✔ | ✔ | ✔ | ✔ |
| `'X25519'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | ✔ |
| `'X448'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | ✔ |
| `'ECDSA'` | ✔ | ✔ | ✔ | ✔ |
| `'Ed25519'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | ✔ |
| `'Ed448'` [1](#user-content-fn-1) | ✔ | ✔ | ✔ | ✔ |
| `'HDKF'` | | | | ✔ |
| `'HMAC'` | | | ✔ | ✔ |
| `'PBKDF2'` | | | | ✔ |
| `'RSA-OAEP'` | ✔ | ✔ | ✔ | |
| `'RSA-PSS'` | ✔ | ✔ | ✔ | |
| `'RSASSA-PKCS1-v1_5'` | ✔ | ✔ | ✔ | |
####
`subtle.sign(algorithm, key, data)`
History
| Version | Changes |
| --- | --- |
| v18.4.0, v16.17.0 | Added `'Ed25519'`, and `'Ed448'` algorithms. |
| v15.0.0 | Added in: v15.0.0 |
* `algorithm`: [<AlgorithmIdentifier>](webcrypto#class-algorithmidentifier) | [<RsaPssParams>](webcrypto#class-rsapssparams) | [<EcdsaParams>](webcrypto#class-ecdsaparams) | [<Ed448Params>](webcrypto#class-ed448params)
* `key`: [<CryptoKey>](webcrypto#class-cryptokey)
* `data`: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
Using the method and parameters given by `algorithm` and the keying material provided by `key`, `subtle.sign()` attempts to generate a cryptographic signature of `data`. If successful, the returned promise is resolved with an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) containing the generated signature.
The algorithms currently supported include:
* `'RSASSA-PKCS1-v1_5'`
* `'RSA-PSS'`
* `'ECDSA'`
* `'Ed25519'` [1](#user-content-fn-1)
* `'Ed448'` [1](#user-content-fn-1)
* `'HMAC'`
####
`subtle.unwrapKey(format, wrappedKey, unwrappingKey, unwrapAlgo, unwrappedKeyAlgo, extractable, keyUsages)`
Added in: v15.0.0 * `format`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'raw'`, `'pkcs8'`, `'spki'`, or `'jwk'`.
* `wrappedKey`: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
* `unwrappingKey`: [<CryptoKey>](webcrypto#class-cryptokey)
* `unwrapAlgo`: [<AlgorithmIdentifier>](webcrypto#class-algorithmidentifier) | [<RsaOaepParams>](webcrypto#class-rsaoaepparams) | [<AesCtrParams>](webcrypto#class-aesctrparams) | [<AesCbcParams>](webcrypto#class-aescbcparams) | [<AesGcmParams>](webcrypto#class-aesgcmparams)
* `unwrappedKeyAlgo`: [<AlgorithmIdentifier>](webcrypto#class-algorithmidentifier) | [<RsaHashedImportParams>](webcrypto#class-rsahashedimportparams) | [<EcKeyImportParams>](webcrypto#class-eckeyimportparams) | [<HmacImportParams>](webcrypto#class-hmacimportparams)
* `extractable`: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
* `keyUsages`: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) See [Key usages](#cryptokeyusages).
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<CryptoKey>](webcrypto#class-cryptokey)
In cryptography, "wrapping a key" refers to exporting and then encrypting the keying material. The `subtle.unwrapKey()` method attempts to decrypt a wrapped key and create a [<CryptoKey>](webcrypto#class-cryptokey) instance. It is equivalent to calling `subtle.decrypt()` first on the encrypted key data (using the `wrappedKey`, `unwrapAlgo`, and `unwrappingKey` arguments as input) then passing the results in to the `subtle.importKey()` method using the `unwrappedKeyAlgo`, `extractable`, and `keyUsages` arguments as inputs. If successful, the returned promise is resolved with a [<CryptoKey>](webcrypto#class-cryptokey) object.
The wrapping algorithms currently supported include:
* `'RSA-OAEP'`
* `'AES-CTR'`
* `'AES-CBC'`
* `'AES-GCM'`
* `'AES-KW'`
The unwrapped key algorithms supported include:
* `'RSASSA-PKCS1-v1_5'`
* `'RSA-PSS'`
* `'RSA-OAEP'`
* `'ECDSA'`
* `'Ed25519'` [1](#user-content-fn-1)
* `'Ed448'` [1](#user-content-fn-1)
* `'ECDH'`
* `'X25519'` [1](#user-content-fn-1)
* `'X448'` [1](#user-content-fn-1)
* `'HMAC'`
* `'AES-CTR'`
* `'AES-CBC'`
* `'AES-GCM'`
* `'AES-KW'`
####
`subtle.verify(algorithm, key, signature, data)`
History
| Version | Changes |
| --- | --- |
| v18.4.0, v16.17.0 | Added `'Ed25519'`, and `'Ed448'` algorithms. |
| v15.0.0 | Added in: v15.0.0 |
* `algorithm`: [<AlgorithmIdentifier>](webcrypto#class-algorithmidentifier) | [<RsaPssParams>](webcrypto#class-rsapssparams) | [<EcdsaParams>](webcrypto#class-ecdsaparams) | [<Ed448Params>](webcrypto#class-ed448params)
* `key`: [<CryptoKey>](webcrypto#class-cryptokey)
* `signature`: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
* `data`: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
Using the method and parameters given in `algorithm` and the keying material provided by `key`, `subtle.verify()` attempts to verify that `signature` is a valid cryptographic signature of `data`. The returned promise is resolved with either `true` or `false`.
The algorithms currently supported include:
* `'RSASSA-PKCS1-v1_5'`
* `'RSA-PSS'`
* `'ECDSA'`
* `'Ed25519'` [1](#user-content-fn-1)
* `'Ed448'` [1](#user-content-fn-1)
* `'HMAC'`
####
`subtle.wrapKey(format, key, wrappingKey, wrapAlgo)`
Added in: v15.0.0 * `format`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'raw'`, `'pkcs8'`, `'spki'`, or `'jwk'`.
* `key`: [<CryptoKey>](webcrypto#class-cryptokey)
* `wrappingKey`: [<CryptoKey>](webcrypto#class-cryptokey)
* `wrapAlgo`: [<AlgorithmIdentifier>](webcrypto#class-algorithmidentifier) | [<RsaOaepParams>](webcrypto#class-rsaoaepparams) | [<AesCtrParams>](webcrypto#class-aesctrparams) | [<AesCbcParams>](webcrypto#class-aescbcparams) | [<AesGcmParams>](webcrypto#class-aesgcmparams)
* Returns: [<Promise>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) containing [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
In cryptography, "wrapping a key" refers to exporting and then encrypting the keying material. The `subtle.wrapKey()` method exports the keying material into the format identified by `format`, then encrypts it using the method and parameters specified by `wrapAlgo` and the keying material provided by `wrappingKey`. It is the equivalent to calling `subtle.exportKey()` using `format` and `key` as the arguments, then passing the result to the `subtle.encrypt()` method using `wrappingKey` and `wrapAlgo` as inputs. If successful, the returned promise will be resolved with an [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) containing the encrypted key data.
The wrapping algorithms currently supported include:
* `'RSA-OAEP'`
* `'AES-CTR'`
* `'AES-CBC'`
* `'AES-GCM'`
* `'AES-KW'`
### Algorithm parameters
The algorithm parameter objects define the methods and parameters used by the various [<SubtleCrypto>](webcrypto#class-subtlecrypto) methods. While described here as "classes", they are simple JavaScript dictionary objects.
#### Class: `AlgorithmIdentifier`
Added in: v18.4.0, v16.17.0 #####
`algorithmIdentifier.name`
Added in: v18.4.0, v16.17.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
#### Class: `AesCbcParams`
Added in: v15.0.0 #####
`aesCbcParams.iv`
Added in: v15.0.0 * Type: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
Provides the initialization vector. It must be exactly 16-bytes in length and should be unpredictable and cryptographically random.
#####
`aesCbcParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'AES-CBC'`.
#### Class: `AesCtrParams`
Added in: v15.0.0 #####
`aesCtrParams.counter`
Added in: v15.0.0 * Type: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
The initial value of the counter block. This must be exactly 16 bytes long.
The `AES-CTR` method uses the rightmost `length` bits of the block as the counter and the remaining bits as the nonce.
#####
`aesCtrParams.length`
Added in: v15.0.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of bits in the `aesCtrParams.counter` that are to be used as the counter.
#####
`aesCtrParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'AES-CTR'`.
#### Class: `AesGcmParams`
Added in: v15.0.0 #####
`aesGcmParams.additionalData`
Added in: v15.0.0 * Type: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
With the AES-GCM method, the `additionalData` is extra input that is not encrypted but is included in the authentication of the data. The use of `additionalData` is optional.
#####
`aesGcmParams.iv`
Added in: v15.0.0 * Type: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
The initialization vector must be unique for every encryption operation using a given key.
Ideally, this is a deterministic 12-byte value that is computed in such a way that it is guaranteed to be unique across all invocations that use the same key. Alternatively, the initialization vector may consist of at least 12 cryptographically random bytes. For more information on constructing initialization vectors for AES-GCM, refer to Section 8 of [NIST SP 800-38D](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf).
#####
`aesGcmParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'AES-GCM'`.
#####
`aesGcmParams.tagLength`
Added in: v15.0.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The size in bits of the generated authentication tag. This values must be one of `32`, `64`, `96`, `104`, `112`, `120`, or `128`. **Default:** `128`.
#### Class: `AesKeyGenParams`
Added in: v15.0.0 #####
`aesKeyGenParams.length`
Added in: v15.0.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The length of the AES key to be generated. This must be either `128`, `192`, or `256`.
#####
`aesKeyGenParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'AES-CBC'`, `'AES-CTR'`, `'AES-GCM'`, or `'AES-KW'`
#### Class: `EcdhKeyDeriveParams`
Added in: v15.0.0 #####
`ecdhKeyDeriveParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'ECDH'`, `'X25519'`, or `'X448'`.
#####
`ecdhKeyDeriveParams.public`
Added in: v15.0.0 * Type: [<CryptoKey>](webcrypto#class-cryptokey)
ECDH key derivation operates by taking as input one parties private key and another parties public key -- using both to generate a common shared secret. The `ecdhKeyDeriveParams.public` property is set to the other parties public key.
#### Class: `EcdsaParams`
Added in: v15.0.0 #####
`ecdsaParams.hash`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
If represented as a [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type), the value must be one of:
* `'SHA-1'`
* `'SHA-256'`
* `'SHA-384'`
* `'SHA-512'`
If represented as an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object), the object must have a `name` property whose value is one of the above listed values.
#####
`ecdsaParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'ECDSA'`.
#### Class: `EcKeyGenParams`
Added in: v15.0.0 #####
`ecKeyGenParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'ECDSA'` or `'ECDH'`.
#####
`ecKeyGenParams.namedCurve`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'P-256'`, `'P-384'`, `'P-521'`.
#### Class: `EcKeyImportParams`
Added in: v15.0.0 #####
`ecKeyImportParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'ECDSA'` or `'ECDH'`.
#####
`ecKeyImportParams.namedCurve`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'P-256'`, `'P-384'`, `'P-521'`.
#### Class: `Ed448Params`
Added in: v15.0.0 #####
`ed448Params.name`
Added in: v18.4.0, v16.17.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'Ed448'`.
#####
`ed448Params.context`
Added in: v18.4.0, v16.17.0 * Type: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
The `context` member represents the optional context data to associate with the message. The Node.js Web Crypto API implementation only supports zero-length context which is equivalent to not providing context at all.
#### Class: `HkdfParams`
Added in: v15.0.0 #####
`hkdfParams.hash`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
If represented as a [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type), the value must be one of:
* `'SHA-1'`
* `'SHA-256'`
* `'SHA-384'`
* `'SHA-512'`
If represented as an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object), the object must have a `name` property whose value is one of the above listed values.
#####
`hkdfParams.info`
Added in: v15.0.0 * Type: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
Provides application-specific contextual input to the HKDF algorithm. This can be zero-length but must be provided.
#####
`hkdfParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'HKDF'`.
#####
`hkdfParams.salt`
Added in: v15.0.0 * Type: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
The salt value significantly improves the strength of the HKDF algorithm. It should be random or pseudorandom and should be the same length as the output of the digest function (for instance, if using `'SHA-256'` as the digest, the salt should be 256-bits of random data).
#### Class: `HmacImportParams`
Added in: v15.0.0 #####
`hmacImportParams.hash`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
If represented as a [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type), the value must be one of:
* `'SHA-1'`
* `'SHA-256'`
* `'SHA-384'`
* `'SHA-512'`
If represented as an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object), the object must have a `name` property whose value is one of the above listed values.
#####
`hmacImportParams.length`
Added in: v15.0.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The optional number of bits in the HMAC key. This is optional and should be omitted for most cases.
#####
`hmacImportParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'HMAC'`.
#### Class: `HmacKeyGenParams`
Added in: v15.0.0 #####
`hmacKeyGenParams.hash`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
If represented as a [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type), the value must be one of:
* `'SHA-1'`
* `'SHA-256'`
* `'SHA-384'`
* `'SHA-512'`
If represented as an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object), the object must have a `name` property whose value is one of the above listed values.
#####
`hmacKeyGenParams.length`
Added in: v15.0.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The number of bits to generate for the HMAC key. If omitted, the length will be determined by the hash algorithm used. This is optional and should be omitted for most cases.
#####
`hmacKeyGenParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'HMAC'`.
#### Class: `Pbkdf2Params`
Added in: v15.0.0 #####
`pbkdb2Params.hash`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
If represented as a [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type), the value must be one of:
* `'SHA-1'`
* `'SHA-256'`
* `'SHA-384'`
* `'SHA-512'`
If represented as an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object), the object must have a `name` property whose value is one of the above listed values.
#####
`pbkdf2Params.iterations`
Added in: v15.0.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The number of iterations the PBKDF2 algorithm should make when deriving bits.
#####
`pbkdf2Params.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'PBKDF2'`.
#####
`pbkdf2Params.salt`
Added in: v15.0.0 * Type: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
Should be at least 16 random or pseudorandom bytes.
#### Class: `RsaHashedImportParams`
Added in: v15.0.0 #####
`rsaHashedImportParams.hash`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
If represented as a [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type), the value must be one of:
* `'SHA-1'`
* `'SHA-256'`
* `'SHA-384'`
* `'SHA-512'`
If represented as an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object), the object must have a `name` property whose value is one of the above listed values.
#####
`rsaHashedImportParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'RSASSA-PKCS1-v1_5'`, `'RSA-PSS'`, or `'RSA-OAEP'`.
#### Class: `RsaHashedKeyGenParams`
Added in: v15.0.0 #####
`rsaHashedKeyGenParams.hash`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
If represented as a [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type), the value must be one of:
* `'SHA-1'`
* `'SHA-256'`
* `'SHA-384'`
* `'SHA-512'`
If represented as an [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object), the object must have a `name` property whose value is one of the above listed values.
#####
`rsaHashedKeyGenParams.modulusLength`
Added in: v15.0.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The length in bits of the RSA modulus. As a best practice, this should be at least `2048`.
#####
`rsaHashedKeyGenParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be one of `'RSASSA-PKCS1-v1_5'`, `'RSA-PSS'`, or `'RSA-OAEP'`.
#####
`rsaHashedKeyGenParams.publicExponent`
Added in: v15.0.0 * Type: [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
The RSA public exponent. This must be a [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) containing a big-endian, unsigned integer that must fit within 32-bits. The [<Uint8Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) may contain an arbitrary number of leading zero-bits. The value must be a prime number. Unless there is reason to use a different value, use `new Uint8Array([1, 0, 1])` (65537) as the public exponent.
#### Class: `RsaOaepParams`
Added in: v15.0.0 ##### rsaOaepParams.label
Added in: v15.0.0 * Type: [<ArrayBuffer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer)
An additional collection of bytes that will not be encrypted, but will be bound to the generated ciphertext.
The `rsaOaepParams.label` parameter is optional.
##### rsaOaepParams.name
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) must be `'RSA-OAEP'`.
#### Class: `RsaPssParams`
Added in: v15.0.0 #####
`rsaPssParams.name`
Added in: v15.0.0 * Type: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Must be `'RSA-PSS'`.
#####
`rsaPssParams.saltLength`
Added in: v15.0.0 * Type: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
The length (in bytes) of the random salt to use.
### Footnotes
1. An experimental implementation of [Secure Curves in the Web Cryptography API](https://wicg.github.io/webcrypto-secure-curves/) as of 05 May 2022 [↩](#user-content-fnref-1) [↩2](#user-content-fnref-1-2) [↩3](#user-content-fnref-1-3) [↩4](#user-content-fnref-1-4) [↩5](#user-content-fnref-1-5) [↩6](#user-content-fnref-1-6) [↩7](#user-content-fnref-1-7) [↩8](#user-content-fnref-1-8) [↩9](#user-content-fnref-1-9) [↩10](#user-content-fnref-1-10) [↩11](#user-content-fnref-1-11) [↩12](#user-content-fnref-1-12) [↩13](#user-content-fnref-1-13) [↩14](#user-content-fnref-1-14) [↩15](#user-content-fnref-1-15) [↩16](#user-content-fnref-1-16) [↩17](#user-content-fnref-1-17) [↩18](#user-content-fnref-1-18) [↩19](#user-content-fnref-1-19) [↩20](#user-content-fnref-1-20) [↩21](#user-content-fnref-1-21) [↩22](#user-content-fnref-1-22) [↩23](#user-content-fnref-1-23) [↩24](#user-content-fnref-1-24) [↩25](#user-content-fnref-1-25) [↩26](#user-content-fnref-1-26) [↩27](#user-content-fnref-1-27) [↩28](#user-content-fnref-1-28) [↩29](#user-content-fnref-1-29) [↩30](#user-content-fnref-1-30)
| programming_docs |
node None TLS (SSL)
---------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/tls.js](https://github.com/nodejs/node/blob/v19.0.1/lib/tls.js)
The `node:tls` module provides an implementation of the Transport Layer Security (TLS) and Secure Socket Layer (SSL) protocols that is built on top of OpenSSL. The module can be accessed using:
```
const tls = require('node:tls');
```
### Determining if crypto support is unavailable
It is possible for Node.js to be built without including support for the `node:crypto` module. In such cases, attempting to `import` from `tls` or calling `require('node:tls')` will result in an error being thrown.
When using CommonJS, the error thrown can be caught using try/catch:
```
let tls;
try {
tls = require('node:tls');
} catch (err) {
console.log('tls support is disabled!');
}
```
When using the lexical ESM `import` keyword, the error can only be caught if a handler for `process.on('uncaughtException')` is registered *before* any attempt to load the module is made (using, for instance, a preload module).
When using ESM, if there is a chance that the code may be run on a build of Node.js where crypto support is not enabled, consider using the [`import()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import) function instead of the lexical `import` keyword:
```
let tls;
try {
tls = await import('node:tls');
} catch (err) {
console.log('tls support is disabled!');
}
```
### TLS/SSL concepts
TLS/SSL is a set of protocols that rely on a public key infrastructure (PKI) to enable secure communication between a client and a server. For most common cases, each server must have a private key.
Private keys can be generated in multiple ways. The example below illustrates use of the OpenSSL command-line interface to generate a 2048-bit RSA private key:
```
openssl genrsa -out ryans-key.pem 2048
```
With TLS/SSL, all servers (and some clients) must have a *certificate*. Certificates are *public keys* that correspond to a private key, and that are digitally signed either by a Certificate Authority or by the owner of the private key (such certificates are referred to as "self-signed"). The first step to obtaining a certificate is to create a *Certificate Signing Request* (CSR) file.
The OpenSSL command-line interface can be used to generate a CSR for a private key:
```
openssl req -new -sha256 -key ryans-key.pem -out ryans-csr.pem
```
Once the CSR file is generated, it can either be sent to a Certificate Authority for signing or used to generate a self-signed certificate.
Creating a self-signed certificate using the OpenSSL command-line interface is illustrated in the example below:
```
openssl x509 -req -in ryans-csr.pem -signkey ryans-key.pem -out ryans-cert.pem
```
Once the certificate is generated, it can be used to generate a `.pfx` or `.p12` file:
```
openssl pkcs12 -export -in ryans-cert.pem -inkey ryans-key.pem \
-certfile ca-cert.pem -out ryans.pfx
```
Where:
* `in`: is the signed certificate
* `inkey`: is the associated private key
* `certfile`: is a concatenation of all Certificate Authority (CA) certs into a single file, e.g. `cat ca1-cert.pem ca2-cert.pem > ca-cert.pem`
#### Perfect forward secrecy
The term *[forward secrecy](https://en.wikipedia.org/wiki/Perfect_forward_secrecy)* or *perfect forward secrecy* describes a feature of key-agreement (i.e., key-exchange) methods. That is, the server and client keys are used to negotiate new temporary keys that are used specifically and only for the current communication session. Practically, this means that even if the server's private key is compromised, communication can only be decrypted by eavesdroppers if the attacker manages to obtain the key-pair specifically generated for the session.
Perfect forward secrecy is achieved by randomly generating a key pair for key-agreement on every TLS/SSL handshake (in contrast to using the same key for all sessions). Methods implementing this technique are called "ephemeral".
Currently two methods are commonly used to achieve perfect forward secrecy (note the character "E" appended to the traditional abbreviations):
* [DHE](https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange): An ephemeral version of the Diffie-Hellman key-agreement protocol.
* [ECDHE](https://en.wikipedia.org/wiki/Elliptic_curve_Diffie%E2%80%93Hellman): An ephemeral version of the Elliptic Curve Diffie-Hellman key-agreement protocol.
To use perfect forward secrecy using `DHE` with the `node:tls` module, it is required to generate Diffie-Hellman parameters and specify them with the `dhparam` option to [`tls.createSecureContext()`](#tlscreatesecurecontextoptions). The following illustrates the use of the OpenSSL command-line interface to generate such parameters:
```
openssl dhparam -outform PEM -out dhparam.pem 2048
```
If using perfect forward secrecy using `ECDHE`, Diffie-Hellman parameters are not required and a default ECDHE curve will be used. The `ecdhCurve` property can be used when creating a TLS Server to specify the list of names of supported curves to use, see [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener) for more info.
Perfect forward secrecy was optional up to TLSv1.2, but it is not optional for TLSv1.3, because all TLSv1.3 cipher suites use ECDHE.
#### ALPN and SNI
ALPN (Application-Layer Protocol Negotiation Extension) and SNI (Server Name Indication) are TLS handshake extensions:
* ALPN: Allows the use of one TLS server for multiple protocols (HTTP, HTTP/2)
* SNI: Allows the use of one TLS server for multiple hostnames with different certificates.
#### Pre-shared keys
TLS-PSK support is available as an alternative to normal certificate-based authentication. It uses a pre-shared key instead of certificates to authenticate a TLS connection, providing mutual authentication. TLS-PSK and public key infrastructure are not mutually exclusive. Clients and servers can accommodate both, choosing either of them during the normal cipher negotiation step.
TLS-PSK is only a good choice where means exist to securely share a key with every connecting machine, so it does not replace the public key infrastructure (PKI) for the majority of TLS uses. The TLS-PSK implementation in OpenSSL has seen many security flaws in recent years, mostly because it is used only by a minority of applications. Please consider all alternative solutions before switching to PSK ciphers. Upon generating PSK it is of critical importance to use sufficient entropy as discussed in [RFC 4086](https://tools.ietf.org/html/rfc4086). Deriving a shared secret from a password or other low-entropy sources is not secure.
PSK ciphers are disabled by default, and using TLS-PSK thus requires explicitly specifying a cipher suite with the `ciphers` option. The list of available ciphers can be retrieved via `openssl ciphers -v 'PSK'`. All TLS 1.3 ciphers are eligible for PSK but currently only those that use SHA256 digest are supported they can be retrieved via `openssl ciphers -v -s -tls1_3 -psk`.
According to the [RFC 4279](https://tools.ietf.org/html/rfc4279), PSK identities up to 128 bytes in length and PSKs up to 64 bytes in length must be supported. As of OpenSSL 1.1.0 maximum identity size is 128 bytes, and maximum PSK length is 256 bytes.
The current implementation doesn't support asynchronous PSK callbacks due to the limitations of the underlying OpenSSL API.
#### Client-initiated renegotiation attack mitigation
The TLS protocol allows clients to renegotiate certain aspects of the TLS session. Unfortunately, session renegotiation requires a disproportionate amount of server-side resources, making it a potential vector for denial-of-service attacks.
To mitigate the risk, renegotiation is limited to three times every ten minutes. An `'error'` event is emitted on the [`tls.TLSSocket`](#class-tlstlssocket) instance when this threshold is exceeded. The limits are configurable:
* `tls.CLIENT_RENEG_LIMIT` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the number of renegotiation requests. **Default:** `3`.
* `tls.CLIENT_RENEG_WINDOW` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Specifies the time renegotiation window in seconds. **Default:** `600` (10 minutes).
The default renegotiation limits should not be modified without a full understanding of the implications and risks.
TLSv1.3 does not support renegotiation.
#### Session resumption
Establishing a TLS session can be relatively slow. The process can be sped up by saving and later reusing the session state. There are several mechanisms to do so, discussed here from oldest to newest (and preferred).
##### Session identifiers
Servers generate a unique ID for new connections and send it to the client. Clients and servers save the session state. When reconnecting, clients send the ID of their saved session state and if the server also has the state for that ID, it can agree to use it. Otherwise, the server will create a new session. See [RFC 2246](https://www.ietf.org/rfc/rfc2246.txt) for more information, page 23 and 30.
Resumption using session identifiers is supported by most web browsers when making HTTPS requests.
For Node.js, clients wait for the [`'session'`](#event-session) event to get the session data, and provide the data to the `session` option of a subsequent [`tls.connect()`](#tlsconnectoptions-callback) to reuse the session. Servers must implement handlers for the [`'newSession'`](#event-newsession) and [`'resumeSession'`](#event-resumesession) events to save and restore the session data using the session ID as the lookup key to reuse sessions. To reuse sessions across load balancers or cluster workers, servers must use a shared session cache (such as Redis) in their session handlers.
##### Session tickets
The servers encrypt the entire session state and send it to the client as a "ticket". When reconnecting, the state is sent to the server in the initial connection. This mechanism avoids the need for a server-side session cache. If the server doesn't use the ticket, for any reason (failure to decrypt it, it's too old, etc.), it will create a new session and send a new ticket. See [RFC 5077](https://tools.ietf.org/html/rfc5077) for more information.
Resumption using session tickets is becoming commonly supported by many web browsers when making HTTPS requests.
For Node.js, clients use the same APIs for resumption with session identifiers as for resumption with session tickets. For debugging, if [`tls.TLSSocket.getTLSTicket()`](#tlssocketgettlsticket) returns a value, the session data contains a ticket, otherwise it contains client-side session state.
With TLSv1.3, be aware that multiple tickets may be sent by the server, resulting in multiple `'session'` events, see [`'session'`](#event-session) for more information.
Single process servers need no specific implementation to use session tickets. To use session tickets across server restarts or load balancers, servers must all have the same ticket keys. There are three 16-byte keys internally, but the tls API exposes them as a single 48-byte buffer for convenience.
It's possible to get the ticket keys by calling [`server.getTicketKeys()`](#servergetticketkeys) on one server instance and then distribute them, but it is more reasonable to securely generate 48 bytes of secure random data and set them with the `ticketKeys` option of [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener). The keys should be regularly regenerated and server's keys can be reset with [`server.setTicketKeys()`](#serversetticketkeyskeys).
Session ticket keys are cryptographic keys, and they ***must be stored securely***. With TLS 1.2 and below, if they are compromised all sessions that used tickets encrypted with them can be decrypted. They should not be stored on disk, and they should be regenerated regularly.
If clients advertise support for tickets, the server will send them. The server can disable tickets by supplying `require('node:constants').SSL_OP_NO_TICKET` in `secureOptions`.
Both session identifiers and session tickets timeout, causing the server to create new sessions. The timeout can be configured with the `sessionTimeout` option of [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener).
For all the mechanisms, when resumption fails, servers will create new sessions. Since failing to resume the session does not cause TLS/HTTPS connection failures, it is easy to not notice unnecessarily poor TLS performance. The OpenSSL CLI can be used to verify that servers are resuming sessions. Use the `-reconnect` option to `openssl s_client`, for example:
```
$ openssl s_client -connect localhost:443 -reconnect
```
Read through the debug output. The first connection should say "New", for example:
```
New, TLSv1.2, Cipher is ECDHE-RSA-AES128-GCM-SHA256
```
Subsequent connections should say "Reused", for example:
```
Reused, TLSv1.2, Cipher is ECDHE-RSA-AES128-GCM-SHA256
```
### Modifying the default TLS cipher suite
Node.js is built with a default suite of enabled and disabled TLS ciphers. This default cipher list can be configured when building Node.js to allow distributions to provide their own default list.
The following command can be used to show the default cipher suite:
```
node -p crypto.constants.defaultCoreCipherList | tr ':' '\n'
TLS_AES_256_GCM_SHA384
TLS_CHACHA20_POLY1305_SHA256
TLS_AES_128_GCM_SHA256
ECDHE-RSA-AES128-GCM-SHA256
ECDHE-ECDSA-AES128-GCM-SHA256
ECDHE-RSA-AES256-GCM-SHA384
ECDHE-ECDSA-AES256-GCM-SHA384
DHE-RSA-AES128-GCM-SHA256
ECDHE-RSA-AES128-SHA256
DHE-RSA-AES128-SHA256
ECDHE-RSA-AES256-SHA384
DHE-RSA-AES256-SHA384
ECDHE-RSA-AES256-SHA256
DHE-RSA-AES256-SHA256
HIGH
!aNULL
!eNULL
!EXPORT
!DES
!RC4
!MD5
!PSK
!SRP
!CAMELLIA
```
This default can be replaced entirely using the [`--tls-cipher-list`](cli#--tls-cipher-listlist) command-line switch (directly, or via the [`NODE_OPTIONS`](cli#node_optionsoptions) environment variable). For instance, the following makes `ECDHE-RSA-AES128-GCM-SHA256:!RC4` the default TLS cipher suite:
```
node --tls-cipher-list='ECDHE-RSA-AES128-GCM-SHA256:!RC4' server.js
export NODE_OPTIONS=--tls-cipher-list='ECDHE-RSA-AES128-GCM-SHA256:!RC4'
node server.js
```
The default can also be replaced on a per client or server basis using the `ciphers` option from [`tls.createSecureContext()`](#tlscreatesecurecontextoptions), which is also available in [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener), [`tls.connect()`](#tlsconnectoptions-callback), and when creating new [`tls.TLSSocket`](#class-tlstlssocket)s.
The ciphers list can contain a mixture of TLSv1.3 cipher suite names, the ones that start with `'TLS_'`, and specifications for TLSv1.2 and below cipher suites. The TLSv1.2 ciphers support a legacy specification format, consult the OpenSSL [cipher list format](https://www.openssl.org/docs/man1.1.1/man1/ciphers.html#CIPHER-LIST-FORMAT) documentation for details, but those specifications do *not* apply to TLSv1.3 ciphers. The TLSv1.3 suites can only be enabled by including their full name in the cipher list. They cannot, for example, be enabled or disabled by using the legacy TLSv1.2 `'EECDH'` or `'!EECDH'` specification.
Despite the relative order of TLSv1.3 and TLSv1.2 cipher suites, the TLSv1.3 protocol is significantly more secure than TLSv1.2, and will always be chosen over TLSv1.2 if the handshake indicates it is supported, and if any TLSv1.3 cipher suites are enabled.
The default cipher suite included within Node.js has been carefully selected to reflect current security best practices and risk mitigation. Changing the default cipher suite can have a significant impact on the security of an application. The `--tls-cipher-list` switch and `ciphers` option should by used only if absolutely necessary.
The default cipher suite prefers GCM ciphers for [Chrome's 'modern cryptography' setting](https://www.chromium.org/Home/chromium-security/education/tls#TOC-Cipher-Suites) and also prefers ECDHE and DHE ciphers for perfect forward secrecy, while offering *some* backward compatibility.
Old clients that rely on insecure and deprecated RC4 or DES-based ciphers (like Internet Explorer 6) cannot complete the handshaking process with the default configuration. If these clients *must* be supported, the [TLS recommendations](https://wiki.mozilla.org/Security/Server_Side_TLS) may offer a compatible cipher suite. For more details on the format, see the OpenSSL [cipher list format](https://www.openssl.org/docs/man1.1.1/man1/ciphers.html#CIPHER-LIST-FORMAT) documentation.
There are only five TLSv1.3 cipher suites:
* `'TLS_AES_256_GCM_SHA384'`
* `'TLS_CHACHA20_POLY1305_SHA256'`
* `'TLS_AES_128_GCM_SHA256'`
* `'TLS_AES_128_CCM_SHA256'`
* `'TLS_AES_128_CCM_8_SHA256'`
The first three are enabled by default. The two `CCM`-based suites are supported by TLSv1.3 because they may be more performant on constrained systems, but they are not enabled by default since they offer less security.
### X509 certificate error codes
Multiple functions can fail due to certificate errors that are reported by OpenSSL. In such a case, the function provides an [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) via its callback that has the property `code` which can take one of the following values:
* `'UNABLE_TO_GET_ISSUER_CERT'`: Unable to get issuer certificate.
* `'UNABLE_TO_GET_CRL'`: Unable to get certificate CRL.
* `'UNABLE_TO_DECRYPT_CERT_SIGNATURE'`: Unable to decrypt certificate's signature.
* `'UNABLE_TO_DECRYPT_CRL_SIGNATURE'`: Unable to decrypt CRL's signature.
* `'UNABLE_TO_DECODE_ISSUER_PUBLIC_KEY'`: Unable to decode issuer public key.
* `'CERT_SIGNATURE_FAILURE'`: Certificate signature failure.
* `'CRL_SIGNATURE_FAILURE'`: CRL signature failure.
* `'CERT_NOT_YET_VALID'`: Certificate is not yet valid.
* `'CERT_HAS_EXPIRED'`: Certificate has expired.
* `'CRL_NOT_YET_VALID'`: CRL is not yet valid.
* `'CRL_HAS_EXPIRED'`: CRL has expired.
* `'ERROR_IN_CERT_NOT_BEFORE_FIELD'`: Format error in certificate's notBefore field.
* `'ERROR_IN_CERT_NOT_AFTER_FIELD'`: Format error in certificate's notAfter field.
* `'ERROR_IN_CRL_LAST_UPDATE_FIELD'`: Format error in CRL's lastUpdate field.
* `'ERROR_IN_CRL_NEXT_UPDATE_FIELD'`: Format error in CRL's nextUpdate field.
* `'OUT_OF_MEM'`: Out of memory.
* `'DEPTH_ZERO_SELF_SIGNED_CERT'`: Self signed certificate.
* `'SELF_SIGNED_CERT_IN_CHAIN'`: Self signed certificate in certificate chain.
* `'UNABLE_TO_GET_ISSUER_CERT_LOCALLY'`: Unable to get local issuer certificate.
* `'UNABLE_TO_VERIFY_LEAF_SIGNATURE'`: Unable to verify the first certificate.
* `'CERT_CHAIN_TOO_LONG'`: Certificate chain too long.
* `'CERT_REVOKED'`: Certificate revoked.
* `'INVALID_CA'`: Invalid CA certificate.
* `'PATH_LENGTH_EXCEEDED'`: Path length constraint exceeded.
* `'INVALID_PURPOSE'`: Unsupported certificate purpose.
* `'CERT_UNTRUSTED'`: Certificate not trusted.
* `'CERT_REJECTED'`: Certificate rejected.
* `'HOSTNAME_MISMATCH'`: Hostname mismatch.
### Class: `tls.CryptoStream`
Added in: v0.3.4Deprecated since: v0.11.3
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`tls.TLSSocket`](#class-tlstlssocket) instead.
The `tls.CryptoStream` class represents a stream of encrypted data. This class is deprecated and should no longer be used.
####
`cryptoStream.bytesWritten`
Added in: v0.3.4Deprecated since: v0.11.3 The `cryptoStream.bytesWritten` property returns the total number of bytes written to the underlying socket *including* the bytes required for the implementation of the TLS protocol.
### Class: `tls.SecurePair`
Added in: v0.3.2Deprecated since: v0.11.3
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`tls.TLSSocket`](#class-tlstlssocket) instead.
Returned by [`tls.createSecurePair()`](#tlscreatesecurepaircontext-isserver-requestcert-rejectunauthorized-options).
#### Event: `'secure'`
Added in: v0.3.2Deprecated since: v0.11.3 The `'secure'` event is emitted by the `SecurePair` object once a secure connection has been established.
As with checking for the server [`'secureConnection'`](#event-secureconnection) event, `pair.cleartext.authorized` should be inspected to confirm whether the certificate used is properly authorized.
### Class: `tls.Server`
Added in: v0.3.2 * Extends: [<net.Server>](net#class-netserver)
Accepts encrypted connections using TLS or SSL.
#### Event: `'connection'`
Added in: v0.3.2 * `socket` [<stream.Duplex>](stream#class-streamduplex)
This event is emitted when a new TCP stream is established, before the TLS handshake begins. `socket` is typically an object of type [`net.Socket`](net#class-netsocket) but will not receive events unlike the socket created from the [`net.Server`](net#class-netserver) `'connection'` event. Usually users will not want to access this event.
This event can also be explicitly emitted by users to inject connections into the TLS server. In that case, any [`Duplex`](stream#class-streamduplex) stream can be passed.
#### Event: `'keylog'`
Added in: v12.3.0, v10.20.0 * `line` [<Buffer>](buffer#class-buffer) Line of ASCII text, in NSS `SSLKEYLOGFILE` format.
* `tlsSocket` [<tls.TLSSocket>](tls#class-tlstlssocket) The `tls.TLSSocket` instance on which it was generated.
The `keylog` event is emitted when key material is generated or received by a connection to this server (typically before handshake has completed, but not necessarily). This keying material can be stored for debugging, as it allows captured TLS traffic to be decrypted. It may be emitted multiple times for each socket.
A typical use case is to append received lines to a common text file, which is later used by software (such as Wireshark) to decrypt the traffic:
```
const logFile = fs.createWriteStream('/tmp/ssl-keys.log', { flags: 'a' });
// ...
server.on('keylog', (line, tlsSocket) => {
if (tlsSocket.remoteAddress !== '...')
return; // Only log keys for a particular IP
logFile.write(line);
});
```
#### Event: `'newSession'`
History
| Version | Changes |
| --- | --- |
| v0.11.12 | The `callback` argument is now supported. |
| v0.9.2 | Added in: v0.9.2 |
The `'newSession'` event is emitted upon creation of a new TLS session. This may be used to store sessions in external storage. The data should be provided to the [`'resumeSession'`](#event-resumesession) callback.
The listener callback is passed three arguments when called:
* `sessionId` [<Buffer>](buffer#class-buffer) The TLS session identifier
* `sessionData` [<Buffer>](buffer#class-buffer) The TLS session data
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function taking no arguments that must be invoked in order for data to be sent or received over the secure connection.
Listening for this event will have an effect only on connections established after the addition of the event listener.
#### Event: `'OCSPRequest'`
Added in: v0.11.13 The `'OCSPRequest'` event is emitted when the client sends a certificate status request. The listener callback is passed three arguments when called:
* `certificate` [<Buffer>](buffer#class-buffer) The server certificate
* `issuer` [<Buffer>](buffer#class-buffer) The issuer's certificate
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function that must be invoked to provide the results of the OCSP request.
The server's current certificate can be parsed to obtain the OCSP URL and certificate ID; after obtaining an OCSP response, `callback(null, resp)` is then invoked, where `resp` is a `Buffer` instance containing the OCSP response. Both `certificate` and `issuer` are `Buffer` DER-representations of the primary and issuer's certificates. These can be used to obtain the OCSP certificate ID and OCSP endpoint URL.
Alternatively, `callback(null, null)` may be called, indicating that there was no OCSP response.
Calling `callback(err)` will result in a `socket.destroy(err)` call.
The typical flow of an OCSP request is as follows:
1. Client connects to the server and sends an `'OCSPRequest'` (via the status info extension in ClientHello).
2. Server receives the request and emits the `'OCSPRequest'` event, calling the listener if registered.
3. Server extracts the OCSP URL from either the `certificate` or `issuer` and performs an [OCSP request](https://en.wikipedia.org/wiki/OCSP_stapling) to the CA.
4. Server receives `'OCSPResponse'` from the CA and sends it back to the client via the `callback` argument
5. Client validates the response and either destroys the socket or performs a handshake.
The `issuer` can be `null` if the certificate is either self-signed or the issuer is not in the root certificates list. (An issuer may be provided via the `ca` option when establishing the TLS connection.)
Listening for this event will have an effect only on connections established after the addition of the event listener.
An npm module like [asn1.js](https://www.npmjs.com/package/asn1.js) may be used to parse the certificates.
#### Event: `'resumeSession'`
Added in: v0.9.2 The `'resumeSession'` event is emitted when the client requests to resume a previous TLS session. The listener callback is passed two arguments when called:
* `sessionId` [<Buffer>](buffer#class-buffer) The TLS session identifier
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function to be called when the prior session has been recovered: `callback([err[, sessionData]])`
+ `err` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)
+ `sessionData` [<Buffer>](buffer#class-buffer)
The event listener should perform a lookup in external storage for the `sessionData` saved by the [`'newSession'`](#event-newsession) event handler using the given `sessionId`. If found, call `callback(null, sessionData)` to resume the session. If not found, the session cannot be resumed. `callback()` must be called without `sessionData` so that the handshake can continue and a new session can be created. It is possible to call `callback(err)` to terminate the incoming connection and destroy the socket.
Listening for this event will have an effect only on connections established after the addition of the event listener.
The following illustrates resuming a TLS session:
```
const tlsSessionStore = {};
server.on('newSession', (id, data, cb) => {
tlsSessionStore[id.toString('hex')] = data;
cb();
});
server.on('resumeSession', (id, cb) => {
cb(null, tlsSessionStore[id.toString('hex')] || null);
});
```
#### Event: `'secureConnection'`
Added in: v0.3.2 The `'secureConnection'` event is emitted after the handshaking process for a new connection has successfully completed. The listener callback is passed a single argument when called:
* `tlsSocket` [<tls.TLSSocket>](tls#class-tlstlssocket) The established TLS socket.
The `tlsSocket.authorized` property is a `boolean` indicating whether the client has been verified by one of the supplied Certificate Authorities for the server. If `tlsSocket.authorized` is `false`, then `socket.authorizationError` is set to describe how authorization failed. Depending on the settings of the TLS server, unauthorized connections may still be accepted.
The `tlsSocket.alpnProtocol` property is a string that contains the selected ALPN protocol. When ALPN has no selected protocol because the client or the server did not send an ALPN extension, `tlsSocket.alpnProtocol` equals `false`.
The `tlsSocket.servername` property is a string containing the server name requested via SNI.
#### Event: `'tlsClientError'`
Added in: v6.0.0 The `'tlsClientError'` event is emitted when an error occurs before a secure connection is established. The listener callback is passed two arguments when called:
* `exception` [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) The `Error` object describing the error
* `tlsSocket` [<tls.TLSSocket>](tls#class-tlstlssocket) The `tls.TLSSocket` instance from which the error originated.
####
`server.addContext(hostname, context)`
Added in: v0.5.3 * `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A SNI host name or wildcard (e.g. `'*'`)
* `context` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object containing any of the possible properties from the [`tls.createSecureContext()`](#tlscreatesecurecontextoptions) `options` arguments (e.g. `key`, `cert`, `ca`, etc).
The `server.addContext()` method adds a secure context that will be used if the client request's SNI name matches the supplied `hostname` (or wildcard).
When there are multiple matching contexts, the most recently added one is used.
####
`server.address()`
Added in: v0.6.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns the bound address, the address family name, and port of the server as reported by the operating system. See [`net.Server.address()`](net#serveraddress) for more information.
####
`server.close([callback])`
Added in: v0.3.2 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A listener callback that will be registered to listen for the server instance's `'close'` event.
* Returns: [<tls.Server>](tls#class-tlsserver)
The `server.close()` method stops the server from accepting new connections.
This function operates asynchronously. The `'close'` event will be emitted when the server has no more open connections.
####
`server.getTicketKeys()`
Added in: v3.0.0 * Returns: [<Buffer>](buffer#class-buffer) A 48-byte buffer containing the session ticket keys.
Returns the session ticket keys.
See [Session Resumption](#session-resumption) for more information.
####
`server.listen()`
Starts the server listening for encrypted connections. This method is identical to [`server.listen()`](net#serverlisten) from [`net.Server`](net#class-netserver).
####
`server.setSecureContext(options)`
Added in: v11.0.0 * `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) An object containing any of the possible properties from the [`tls.createSecureContext()`](#tlscreatesecurecontextoptions) `options` arguments (e.g. `key`, `cert`, `ca`, etc).
The `server.setSecureContext()` method replaces the secure context of an existing server. Existing connections to the server are not interrupted.
####
`server.setTicketKeys(keys)`
Added in: v3.0.0 * `keys` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A 48-byte buffer containing the session ticket keys.
Sets the session ticket keys.
Changes to the ticket keys are effective only for future server connections. Existing or currently pending server connections will use the previous keys.
See [Session Resumption](#session-resumption) for more information.
### Class: `tls.TLSSocket`
Added in: v0.11.4 * Extends: [<net.Socket>](net#class-netsocket)
Performs transparent encryption of written data and all required TLS negotiation.
Instances of `tls.TLSSocket` implement the duplex [Stream](stream#stream) interface.
Methods that return TLS connection metadata (e.g. [`tls.TLSSocket.getPeerCertificate()`](#tlssocketgetpeercertificatedetailed)) will only return data while the connection is open.
####
`new tls.TLSSocket(socket[, options])`
History
| Version | Changes |
| --- | --- |
| v12.2.0 | The `enableTrace` option is now supported. |
| v5.0.0 | ALPN options are supported now. |
| v0.11.4 | Added in: v0.11.4 |
* `socket` [<net.Socket>](net#class-netsocket) | [<stream.Duplex>](stream#class-streamduplex) On the server side, any `Duplex` stream. On the client side, any instance of [`net.Socket`](net#class-netsocket) (for generic `Duplex` stream support on the client side, [`tls.connect()`](#tlsconnectoptions-callback) must be used).
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `enableTrace`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `isServer`: The SSL/TLS protocol is asymmetrical, TLSSockets must know if they are to behave as a server or a client. If `true` the TLS socket will be instantiated as a server. **Default:** `false`.
+ `server` [<net.Server>](net#class-netserver) A [`net.Server`](net#class-netserver) instance.
+ `requestCert`: Whether to authenticate the remote peer by requesting a certificate. Clients always request a server certificate. Servers (`isServer` is true) may set `requestCert` to true to request a client certificate.
+ `rejectUnauthorized`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `ALPNProtocols`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `SNICallback`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `session` [<Buffer>](buffer#class-buffer) A `Buffer` instance containing a TLS session.
+ `requestOCSP` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, specifies that the OCSP status request extension will be added to the client hello and an `'OCSPResponse'` event will be emitted on the socket before establishing a secure communication
+ `secureContext`: TLS context object created with [`tls.createSecureContext()`](#tlscreatesecurecontextoptions). If a `secureContext` is *not* provided, one will be created by passing the entire `options` object to `tls.createSecureContext()`.
+ ...: [`tls.createSecureContext()`](#tlscreatesecurecontextoptions) options that are used if the `secureContext` option is missing. Otherwise, they are ignored.
Construct a new `tls.TLSSocket` object from an existing TCP socket.
#### Event: `'keylog'`
Added in: v12.3.0, v10.20.0 * `line` [<Buffer>](buffer#class-buffer) Line of ASCII text, in NSS `SSLKEYLOGFILE` format.
The `keylog` event is emitted on a `tls.TLSSocket` when key material is generated or received by the socket. This keying material can be stored for debugging, as it allows captured TLS traffic to be decrypted. It may be emitted multiple times, before or after the handshake completes.
A typical use case is to append received lines to a common text file, which is later used by software (such as Wireshark) to decrypt the traffic:
```
const logFile = fs.createWriteStream('/tmp/ssl-keys.log', { flags: 'a' });
// ...
tlsSocket.on('keylog', (line) => logFile.write(line));
```
#### Event: `'OCSPResponse'`
Added in: v0.11.13 The `'OCSPResponse'` event is emitted if the `requestOCSP` option was set when the `tls.TLSSocket` was created and an OCSP response has been received. The listener callback is passed a single argument when called:
* `response` [<Buffer>](buffer#class-buffer) The server's OCSP response
Typically, the `response` is a digitally signed object from the server's CA that contains information about server's certificate revocation status.
#### Event: `'secureConnect'`
Added in: v0.11.4 The `'secureConnect'` event is emitted after the handshaking process for a new connection has successfully completed. The listener callback will be called regardless of whether or not the server's certificate has been authorized. It is the client's responsibility to check the `tlsSocket.authorized` property to determine if the server certificate was signed by one of the specified CAs. If `tlsSocket.authorized === false`, then the error can be found by examining the `tlsSocket.authorizationError` property. If ALPN was used, the `tlsSocket.alpnProtocol` property can be checked to determine the negotiated protocol.
The `'secureConnect'` event is not emitted when a [<tls.TLSSocket>](tls#class-tlstlssocket) is created using the `new tls.TLSSocket()` constructor.
#### Event: `'session'`
Added in: v11.10.0 * `session` [<Buffer>](buffer#class-buffer)
The `'session'` event is emitted on a client `tls.TLSSocket` when a new session or TLS ticket is available. This may or may not be before the handshake is complete, depending on the TLS protocol version that was negotiated. The event is not emitted on the server, or if a new session was not created, for example, when the connection was resumed. For some TLS protocol versions the event may be emitted multiple times, in which case all the sessions can be used for resumption.
On the client, the `session` can be provided to the `session` option of [`tls.connect()`](#tlsconnectoptions-callback) to resume the connection.
See [Session Resumption](#session-resumption) for more information.
For TLSv1.2 and below, [`tls.TLSSocket.getSession()`](#tlssocketgetsession) can be called once the handshake is complete. For TLSv1.3, only ticket-based resumption is allowed by the protocol, multiple tickets are sent, and the tickets aren't sent until after the handshake completes. So it is necessary to wait for the `'session'` event to get a resumable session. Applications should use the `'session'` event instead of `getSession()` to ensure they will work for all TLS versions. Applications that only expect to get or use one session should listen for this event only once:
```
tlsSocket.once('session', (session) => {
// The session can be used immediately or later.
tls.connect({
session: session,
// Other connect options...
});
});
```
####
`tlsSocket.address()`
History
| Version | Changes |
| --- | --- |
| v18.4.0 | The `family` property now returns a string instead of a number. |
| v18.0.0 | The `family` property now returns a number instead of a string. |
| v0.11.4 | Added in: v0.11.4 |
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns the bound `address`, the address `family` name, and `port` of the underlying socket as reported by the operating system: `{ port: 12346, family: 'IPv4', address: '127.0.0.1' }`.
####
`tlsSocket.authorizationError`
Added in: v0.11.4 Returns the reason why the peer's certificate was not been verified. This property is set only when `tlsSocket.authorized === false`.
####
`tlsSocket.authorized`
Added in: v0.11.4 * [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
This property is `true` if the peer certificate was signed by one of the CAs specified when creating the `tls.TLSSocket` instance, otherwise `false`.
####
`tlsSocket.disableRenegotiation()`
Added in: v8.4.0 Disables TLS renegotiation for this `TLSSocket` instance. Once called, attempts to renegotiate will trigger an `'error'` event on the `TLSSocket`.
####
`tlsSocket.enableTrace()`
Added in: v12.2.0 When enabled, TLS packet trace information is written to `stderr`. This can be used to debug TLS connection problems.
The format of the output is identical to the output of `openssl s_client -trace` or `openssl s_server -trace`. While it is produced by OpenSSL's `SSL_trace()` function, the format is undocumented, can change without notice, and should not be relied on.
####
`tlsSocket.encrypted`
Added in: v0.11.4 Always returns `true`. This may be used to distinguish TLS sockets from regular `net.Socket` instances.
####
`tlsSocket.exportKeyingMaterial(length, label[, context])`
Added in: v13.10.0, v12.17.0 * `length` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) number of bytes to retrieve from keying material
* `label` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) an application specific label, typically this will be a value from the [IANA Exporter Label Registry](https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#exporter-labels).
* `context` [<Buffer>](buffer#class-buffer) Optionally provide a context.
* Returns: [<Buffer>](buffer#class-buffer) requested bytes of the keying material
Keying material is used for validations to prevent different kind of attacks in network protocols, for example in the specifications of IEEE 802.1X.
Example
```
const keyingMaterial = tlsSocket.exportKeyingMaterial(
128,
'client finished');
/*
Example return value of keyingMaterial:
<Buffer 76 26 af 99 c5 56 8e 42 09 91 ef 9f 93 cb ad 6c 7b 65 f8 53 f1 d8 d9
12 5a 33 b8 b5 25 df 7b 37 9f e0 e2 4f b8 67 83 a3 2f cd 5d 41 42 4c 91
74 ef 2c ... 78 more bytes>
*/
```
See the OpenSSL [`SSL_export_keying_material`](https://www.openssl.org/docs/man1.1.1/man3/SSL_export_keying_material.html) documentation for more information.
####
`tlsSocket.getCertificate()`
Added in: v11.2.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns an object representing the local certificate. The returned object has some properties corresponding to the fields of the certificate.
See [`tls.TLSSocket.getPeerCertificate()`](#tlssocketgetpeercertificatedetailed) for an example of the certificate structure.
If there is no local certificate, an empty object will be returned. If the socket has been destroyed, `null` will be returned.
####
`tlsSocket.getCipher()`
History
| Version | Changes |
| --- | --- |
| v13.4.0, v12.16.0 | Return the IETF cipher name as `standardName`. |
| v12.0.0 | Return the minimum cipher version, instead of a fixed string (`'TLSv1/SSLv3'`). |
| v0.11.4 | Added in: v0.11.4 |
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) OpenSSL name for the cipher suite.
+ `standardName` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) IETF name for the cipher suite.
+ `version` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The minimum TLS protocol version supported by this cipher suite. For the actual negotiated protocol, see [`tls.TLSSocket.getProtocol()`](#tlssocketgetprotocol).
Returns an object containing information on the negotiated cipher suite.
For example, a TLSv1.2 protocol with AES256-SHA cipher:
```
{
"name": "AES256-SHA",
"standardName": "TLS_RSA_WITH_AES_256_CBC_SHA",
"version": "SSLv3"
}
```
See [SSL\_CIPHER\_get\_name](https://www.openssl.org/docs/man1.1.1/man3/SSL_CIPHER_get_name.html) for more information.
####
`tlsSocket.getEphemeralKeyInfo()`
Added in: v5.0.0 * Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Returns an object representing the type, name, and size of parameter of an ephemeral key exchange in [perfect forward secrecy](#perfect-forward-secrecy) on a client connection. It returns an empty object when the key exchange is not ephemeral. As this is only supported on a client socket; `null` is returned if called on a server socket. The supported types are `'DH'` and `'ECDH'`. The `name` property is available only when type is `'ECDH'`.
For example: `{ type: 'ECDH', name: 'prime256v1', size: 256 }`.
####
`tlsSocket.getFinished()`
Added in: v9.9.0 * Returns: [<Buffer>](buffer#class-buffer) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) The latest `Finished` message that has been sent to the socket as part of a SSL/TLS handshake, or `undefined` if no `Finished` message has been sent yet.
As the `Finished` messages are message digests of the complete handshake (with a total of 192 bits for TLS 1.0 and more for SSL 3.0), they can be used for external authentication procedures when the authentication provided by SSL/TLS is not desired or is not enough.
Corresponds to the `SSL_get_finished` routine in OpenSSL and may be used to implement the `tls-unique` channel binding from [RFC 5929](https://tools.ietf.org/html/rfc5929).
####
`tlsSocket.getPeerCertificate([detailed])`
Added in: v0.11.4 * `detailed` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Include the full certificate chain if `true`, otherwise include just the peer's certificate.
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A certificate object.
Returns an object representing the peer's certificate. If the peer does not provide a certificate, an empty object will be returned. If the socket has been destroyed, `null` will be returned.
If the full certificate chain was requested, each certificate will include an `issuerCertificate` property containing an object representing its issuer's certificate.
##### Certificate object
History
| Version | Changes |
| --- | --- |
| v17.2.0, v16.14.0 | Add fingerprint512. |
| v11.4.0 | Support Elliptic Curve public key info. |
A certificate object has properties corresponding to the fields of the certificate.
* `raw` [<Buffer>](buffer#class-buffer) The DER encoded X.509 certificate data.
* `subject` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The certificate subject, described in terms of Country (`C`), StateOrProvince (`ST`), Locality (`L`), Organization (`O`), OrganizationalUnit (`OU`), and CommonName (`CN`). The CommonName is typically a DNS name with TLS certificates. Example: `{C: 'UK', ST: 'BC', L: 'Metro', O: 'Node Fans', OU: 'Docs', CN: 'example.com'}`.
* `issuer` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The certificate issuer, described in the same terms as the `subject`.
* `valid_from` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The date-time the certificate is valid from.
* `valid_to` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The date-time the certificate is valid to.
* `serialNumber` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The certificate serial number, as a hex string. Example: `'B9B0D332A1AA5635'`.
* `fingerprint` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The SHA-1 digest of the DER encoded certificate. It is returned as a `:` separated hexadecimal string. Example: `'2A:7A:C2:DD:...'`.
* `fingerprint256` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The SHA-256 digest of the DER encoded certificate. It is returned as a `:` separated hexadecimal string. Example: `'2A:7A:C2:DD:...'`.
* `fingerprint512` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The SHA-512 digest of the DER encoded certificate. It is returned as a `:` separated hexadecimal string. Example: `'2A:7A:C2:DD:...'`.
* `ext_key_usage` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) (Optional) The extended key usage, a set of OIDs.
* `subjectaltname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) (Optional) A string containing concatenated names for the subject, an alternative to the `subject` names.
* `infoAccess` [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) (Optional) An array describing the AuthorityInfoAccess, used with OCSP.
* `issuerCertificate` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) (Optional) The issuer certificate object. For self-signed certificates, this may be a circular reference.
The certificate may contain information about the public key, depending on the key type.
For RSA keys, the following properties may be defined:
* `bits` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The RSA bit size. Example: `1024`.
* `exponent` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The RSA exponent, as a string in hexadecimal number notation. Example: `'0x010001'`.
* `modulus` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The RSA modulus, as a hexadecimal string. Example: `'B56CE45CB7...'`.
* `pubkey` [<Buffer>](buffer#class-buffer) The public key.
For EC keys, the following properties may be defined:
* `pubkey` [<Buffer>](buffer#class-buffer) The public key.
* `bits` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The key size in bits. Example: `256`.
* `asn1Curve` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) (Optional) The ASN.1 name of the OID of the elliptic curve. Well-known curves are identified by an OID. While it is unusual, it is possible that the curve is identified by its mathematical properties, in which case it will not have an OID. Example: `'prime256v1'`.
* `nistCurve` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) (Optional) The NIST name for the elliptic curve, if it has one (not all well-known curves have been assigned names by NIST). Example: `'P-256'`.
Example certificate:
```
{ subject:
{ OU: [ 'Domain Control Validated', 'PositiveSSL Wildcard' ],
CN: '*.nodejs.org' },
issuer:
{ C: 'GB',
ST: 'Greater Manchester',
L: 'Salford',
O: 'COMODO CA Limited',
CN: 'COMODO RSA Domain Validation Secure Server CA' },
subjectaltname: 'DNS:*.nodejs.org, DNS:nodejs.org',
infoAccess:
{ 'CA Issuers - URI':
[ 'http://crt.comodoca.com/COMODORSADomainValidationSecureServerCA.crt' ],
'OCSP - URI': [ 'http://ocsp.comodoca.com' ] },
modulus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
exponent: '0x10001',
pubkey: <Buffer ... >,
valid_from: 'Aug 14 00:00:00 2017 GMT',
valid_to: 'Nov 20 23:59:59 2019 GMT',
fingerprint: '01:02:59:D9:C3:D2:0D:08:F7:82:4E:44:A4:B4:53:C5:E2:3A:87:4D',
fingerprint256: '69:AE:1A:6A:D4:3D:C6:C1:1B:EA:C6:23:DE:BA:2A:14:62:62:93:5C:7A:EA:06:41:9B:0B:BC:87:CE:48:4E:02',
fingerprint512: '19:2B:3E:C3:B3:5B:32:E8:AE:BB:78:97:27:E4:BA:6C:39:C9:92:79:4F:31:46:39:E2:70:E5:5F:89:42:17:C9:E8:64:CA:FF:BB:72:56:73:6E:28:8A:92:7E:A3:2A:15:8B:C2:E0:45:CA:C3:BC:EA:40:52:EC:CA:A2:68:CB:32',
ext_key_usage: [ '1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2' ],
serialNumber: '66593D57F20CBC573E433381B5FEC280',
raw: <Buffer ... > }
```
####
`tlsSocket.getPeerFinished()`
Added in: v9.9.0 * Returns: [<Buffer>](buffer#class-buffer) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type) The latest `Finished` message that is expected or has actually been received from the socket as part of a SSL/TLS handshake, or `undefined` if there is no `Finished` message so far.
As the `Finished` messages are message digests of the complete handshake (with a total of 192 bits for TLS 1.0 and more for SSL 3.0), they can be used for external authentication procedures when the authentication provided by SSL/TLS is not desired or is not enough.
Corresponds to the `SSL_get_peer_finished` routine in OpenSSL and may be used to implement the `tls-unique` channel binding from [RFC 5929](https://tools.ietf.org/html/rfc5929).
####
`tlsSocket.getPeerX509Certificate()`
Added in: v15.9.0 * Returns: [<X509Certificate>](crypto#class-x509certificate)
Returns the peer certificate as an [<X509Certificate>](crypto#class-x509certificate) object.
If there is no peer certificate, or the socket has been destroyed, `undefined` will be returned.
####
`tlsSocket.getProtocol()`
Added in: v5.7.0 * Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<null>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type)
Returns a string containing the negotiated SSL/TLS protocol version of the current connection. The value `'unknown'` will be returned for connected sockets that have not completed the handshaking process. The value `null` will be returned for server sockets or disconnected client sockets.
Protocol versions are:
* `'SSLv3'`
* `'TLSv1'`
* `'TLSv1.1'`
* `'TLSv1.2'`
* `'TLSv1.3'`
See the OpenSSL [`SSL_get_version`](https://www.openssl.org/docs/man1.1.1/man3/SSL_get_version.html) documentation for more information.
####
`tlsSocket.getSession()`
Added in: v0.11.4 * [<Buffer>](buffer#class-buffer)
Returns the TLS session data or `undefined` if no session was negotiated. On the client, the data can be provided to the `session` option of [`tls.connect()`](#tlsconnectoptions-callback) to resume the connection. On the server, it may be useful for debugging.
See [Session Resumption](#session-resumption) for more information.
Note: `getSession()` works only for TLSv1.2 and below. For TLSv1.3, applications must use the [`'session'`](#event-session) event (it also works for TLSv1.2 and below).
####
`tlsSocket.getSharedSigalgs()`
Added in: v12.11.0 * Returns: [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) List of signature algorithms shared between the server and the client in the order of decreasing preference.
See [SSL\_get\_shared\_sigalgs](https://www.openssl.org/docs/man1.1.1/man3/SSL_get_shared_sigalgs.html) for more information.
####
`tlsSocket.getTLSTicket()`
Added in: v0.11.4 * [<Buffer>](buffer#class-buffer)
For a client, returns the TLS session ticket if one is available, or `undefined`. For a server, always returns `undefined`.
It may be useful for debugging.
See [Session Resumption](#session-resumption) for more information.
####
`tlsSocket.getX509Certificate()`
Added in: v15.9.0 * Returns: [<X509Certificate>](crypto#class-x509certificate)
Returns the local certificate as an [<X509Certificate>](crypto#class-x509certificate) object.
If there is no local certificate, or the socket has been destroyed, `undefined` will be returned.
####
`tlsSocket.isSessionReused()`
Added in: v0.5.6 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the session was reused, `false` otherwise.
See [Session Resumption](#session-resumption) for more information.
####
`tlsSocket.localAddress`
Added in: v0.11.4 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the string representation of the local IP address.
####
`tlsSocket.localPort`
Added in: v0.11.4 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the numeric representation of the local port.
####
`tlsSocket.remoteAddress`
Added in: v0.11.4 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the string representation of the remote IP address. For example, `'74.125.127.100'` or `'2001:4860:a005::68'`.
####
`tlsSocket.remoteFamily`
Added in: v0.11.4 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns the string representation of the remote IP family. `'IPv4'` or `'IPv6'`.
####
`tlsSocket.remotePort`
Added in: v0.11.4 * [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
Returns the numeric representation of the remote port. For example, `443`.
####
`tlsSocket.renegotiate(options, callback)`
History
| Version | Changes |
| --- | --- |
| v18.0.0 | Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. |
| v0.11.8 | Added in: v0.11.8 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `rejectUnauthorized` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If not `false`, the server certificate is verified against the list of supplied CAs. An `'error'` event is emitted if verification fails; `err.code` contains the OpenSSL error code. **Default:** `true`.
+ `requestCert`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) If `renegotiate()` returned `true`, callback is attached once to the `'secure'` event. If `renegotiate()` returned `false`, `callback` will be called in the next tick with an error, unless the `tlsSocket` has been destroyed, in which case `callback` will not be called at all.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if renegotiation was initiated, `false` otherwise.
The `tlsSocket.renegotiate()` method initiates a TLS renegotiation process. Upon completion, the `callback` function will be passed a single argument that is either an `Error` (if the request failed) or `null`.
This method can be used to request a peer's certificate after the secure connection has been established.
When running as the server, the socket will be destroyed with an error after `handshakeTimeout` timeout.
For TLSv1.3, renegotiation cannot be initiated, it is not supported by the protocol.
####
`tlsSocket.setMaxSendFragment(size)`
Added in: v0.11.11 * `size` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The maximum TLS fragment size. The maximum value is `16384`. **Default:** `16384`.
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `tlsSocket.setMaxSendFragment()` method sets the maximum TLS fragment size. Returns `true` if setting the limit succeeded; `false` otherwise.
Smaller fragment sizes decrease the buffering latency on the client: larger fragments are buffered by the TLS layer until the entire fragment is received and its integrity is verified; large fragments can span multiple roundtrips and their processing can be delayed due to packet loss or reordering. However, smaller fragments add extra TLS framing bytes and CPU overhead, which may decrease overall server throughput.
###
`tls.checkServerIdentity(hostname, cert)`
History
| Version | Changes |
| --- | --- |
| v17.3.1, v16.13.2, v14.18.3, v12.22.9 | Support for `uniformResourceIdentifier` subject alternative names has been disabled in response to CVE-2021-44531. |
| v0.8.4 | Added in: v0.8.4 |
* `hostname` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The host name or IP address to verify the certificate against.
* `cert` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A [certificate object](#certificate-object) representing the peer's certificate.
* Returns: [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) | [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type)
Verifies the certificate `cert` is issued to `hostname`.
Returns [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) object, populating it with `reason`, `host`, and `cert` on failure. On success, returns [<undefined>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type).
This function is intended to be used in combination with the `checkServerIdentity` option that can be passed to [`tls.connect()`](#tlsconnectoptions-callback) and as such operates on a [certificate object](#certificate-object). For other purposes, consider using [`x509.checkHost()`](crypto#x509checkhostname-options) instead.
This function can be overwritten by providing an alternative function as the `options.checkServerIdentity` option that is passed to `tls.connect()`. The overwriting function can call `tls.checkServerIdentity()` of course, to augment the checks done with additional verification.
This function is only called if the certificate passed all other checks, such as being issued by trusted CA (`options.ca`).
Earlier versions of Node.js incorrectly accepted certificates for a given `hostname` if a matching `uniformResourceIdentifier` subject alternative name was present (see [CVE-2021-44531](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-44531)). Applications that wish to accept `uniformResourceIdentifier` subject alternative names can use a custom `options.checkServerIdentity` function that implements the desired behavior.
###
`tls.connect(options[, callback])`
History
| Version | Changes |
| --- | --- |
| v15.1.0, v14.18.0 | Added `onread` option. |
| v14.1.0, v13.14.0 | The `highWaterMark` option is accepted now. |
| v13.6.0, v12.16.0 | The `pskCallback` option is now supported. |
| v12.9.0 | Support the `allowHalfOpen` option. |
| v12.4.0 | The `hints` option is now supported. |
| v12.2.0 | The `enableTrace` option is now supported. |
| v11.8.0, v10.16.0 | The `timeout` option is supported now. |
| v8.0.0 | The `lookup` option is supported now. |
| v8.0.0 | The `ALPNProtocols` option can be a `TypedArray` or `DataView` now. |
| v5.0.0 | ALPN options are supported now. |
| v5.3.0, v4.7.0 | The `secureContext` option is supported now. |
| v0.11.3 | Added in: v0.11.3 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `enableTrace`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Host the client should connect to. **Default:** `'localhost'`.
+ `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Port the client should connect to.
+ `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Creates Unix socket connection to path. If this option is specified, `host` and `port` are ignored.
+ `socket` [<stream.Duplex>](stream#class-streamduplex) Establish secure connection on a given socket rather than creating a new socket. Typically, this is an instance of [`net.Socket`](net#class-netsocket), but any `Duplex` stream is allowed. If this option is specified, `path`, `host`, and `port` are ignored, except for certificate validation. Usually, a socket is already connected when passed to `tls.connect()`, but it can be connected later. Connection/disconnection/destruction of `socket` is the user's responsibility; calling `tls.connect()` will not cause `net.connect()` to be called.
+ `allowHalfOpen` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If set to `false`, then the socket will automatically end the writable side when the readable side ends. If the `socket` option is set, this option has no effect. See the `allowHalfOpen` option of [`net.Socket`](net#class-netsocket) for details. **Default:** `false`.
+ `rejectUnauthorized` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If not `false`, the server certificate is verified against the list of supplied CAs. An `'error'` event is emitted if verification fails; `err.code` contains the OpenSSL error code. **Default:** `true`.
+ `pskCallback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
- hint: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) optional message sent from the server to help client decide which identity to use during negotiation. Always `null` if TLS 1.3 is used.
- Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) in the form `{ psk: <Buffer|TypedArray|DataView>, identity: <string> }` or `null` to stop the negotiation process. `psk` must be compatible with the selected cipher's digest. `identity` must use UTF-8 encoding.When negotiating TLS-PSK (pre-shared keys), this function is called with optional identity `hint` provided by the server or `null` in case of TLS 1.3 where `hint` was removed. It will be necessary to provide a custom `tls.checkServerIdentity()` for the connection as the default one will try to check host name/IP of the server against the certificate but that's not applicable for PSK because there won't be a certificate present. More information can be found in the [RFC 4279](https://tools.ietf.org/html/rfc4279).
+ `ALPNProtocols`: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer[]>](buffer#class-buffer) | [<TypedArray[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) An array of strings, `Buffer`s, `TypedArray`s, or `DataView`s, or a single `Buffer`, `TypedArray`, or `DataView` containing the supported ALPN protocols. `Buffer`s should have the format `[len][name][len][name]...` e.g. `'\x08http/1.1\x08http/1.0'`, where the `len` byte is the length of the next protocol name. Passing an array is usually much simpler, e.g. `['http/1.1', 'http/1.0']`. Protocols earlier in the list have higher preference than those later.
+ `servername`: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Server name for the SNI (Server Name Indication) TLS extension. It is the name of the host being connected to, and must be a host name, and not an IP address. It can be used by a multi-homed server to choose the correct certificate to present to the client, see the `SNICallback` option to [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener).
+ `checkServerIdentity(servername, cert)` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A callback function to be used (instead of the builtin `tls.checkServerIdentity()` function) when checking the server's host name (or the provided `servername` when explicitly set) against the certificate. This should return an [<Error>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) if verification fails. The method should return `undefined` if the `servername` and `cert` are verified.
+ `session` [<Buffer>](buffer#class-buffer) A `Buffer` instance, containing TLS session.
+ `minDHSize` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Minimum size of the DH parameter in bits to accept a TLS connection. When a server offers a DH parameter with a size less than `minDHSize`, the TLS connection is destroyed and an error is thrown. **Default:** `1024`.
+ `highWaterMark`: [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Consistent with the readable stream `highWaterMark` parameter. **Default:** `16 * 1024`.
+ `secureContext`: TLS context object created with [`tls.createSecureContext()`](#tlscreatesecurecontextoptions). If a `secureContext` is *not* provided, one will be created by passing the entire `options` object to `tls.createSecureContext()`.
+ `onread` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) If the `socket` option is missing, incoming data is stored in a single `buffer` and passed to the supplied `callback` when data arrives on the socket, otherwise the option is ignored. See the `onread` option of [`net.Socket`](net#class-netsocket) for details.
+ ...: [`tls.createSecureContext()`](#tlscreatesecurecontextoptions) options that are used if the `secureContext` option is missing, otherwise they are ignored.
+ ...: Any [`socket.connect()`](net#socketconnectoptions-connectlistener) option not already listed.
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<tls.TLSSocket>](tls#class-tlstlssocket)
The `callback` function, if specified, will be added as a listener for the [`'secureConnect'`](#event-secureconnect) event.
`tls.connect()` returns a [`tls.TLSSocket`](#class-tlstlssocket) object.
Unlike the `https` API, `tls.connect()` does not enable the SNI (Server Name Indication) extension by default, which may cause some servers to return an incorrect certificate or reject the connection altogether. To enable SNI, set the `servername` option in addition to `host`.
The following illustrates a client for the echo server example from [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener):
```
// Assumes an echo server that is listening on port 8000.
const tls = require('node:tls');
const fs = require('node:fs');
const options = {
// Necessary only if the server requires client certificate authentication.
key: fs.readFileSync('client-key.pem'),
cert: fs.readFileSync('client-cert.pem'),
// Necessary only if the server uses a self-signed certificate.
ca: [ fs.readFileSync('server-cert.pem') ],
// Necessary only if the server's cert isn't for "localhost".
checkServerIdentity: () => { return null; },
};
const socket = tls.connect(8000, options, () => {
console.log('client connected',
socket.authorized ? 'authorized' : 'unauthorized');
process.stdin.pipe(socket);
process.stdin.resume();
});
socket.setEncoding('utf8');
socket.on('data', (data) => {
console.log(data);
});
socket.on('end', () => {
console.log('server ends connection');
});
```
###
`tls.connect(path[, options][, callback])`
Added in: v0.11.3 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Default value for `options.path`.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) See [`tls.connect()`](#tlsconnectoptions-callback).
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) See [`tls.connect()`](#tlsconnectoptions-callback).
* Returns: [<tls.TLSSocket>](tls#class-tlstlssocket)
Same as [`tls.connect()`](#tlsconnectoptions-callback) except that `path` can be provided as an argument instead of an option.
A path option, if specified, will take precedence over the path argument.
###
`tls.connect(port[, host][, options][, callback])`
Added in: v0.11.3 * `port` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Default value for `options.port`.
* `host` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Default value for `options.host`.
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) See [`tls.connect()`](#tlsconnectoptions-callback).
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) See [`tls.connect()`](#tlsconnectoptions-callback).
* Returns: [<tls.TLSSocket>](tls#class-tlstlssocket)
Same as [`tls.connect()`](#tlsconnectoptions-callback) except that `port` and `host` can be provided as arguments instead of options.
A port or host option, if specified, will take precedence over any port or host argument.
###
`tls.createSecureContext([options])`
History
| Version | Changes |
| --- | --- |
| v12.12.0 | Added `privateKeyIdentifier` and `privateKeyEngine` options to get private key from an OpenSSL engine. |
| v12.11.0 | Added `sigalgs` option to override supported signature algorithms. |
| v12.0.0 | TLSv1.3 support added. |
| v11.5.0 | The `ca:` option now supports `BEGIN TRUSTED CERTIFICATE`. |
| v11.4.0, v10.16.0 | The `minVersion` and `maxVersion` can be used to restrict the allowed TLS protocol versions. |
| v10.0.0 | The `ecdhCurve` cannot be set to `false` anymore due to a change in OpenSSL. |
| v9.3.0 | The `options` parameter can now include `clientCertEngine`. |
| v9.0.0 | The `ecdhCurve` option can now be multiple `':'` separated curve names or `'auto'`. |
| v7.3.0 | If the `key` option is an array, individual entries do not need a `passphrase` property anymore. `Array` entries can also just be `string`s or `Buffer`s now. |
| v5.2.0 | The `ca` option can now be a single string containing multiple CA certificates. |
| v0.11.13 | Added in: v0.11.13 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ca` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Buffer[]>](buffer#class-buffer) Optionally override the trusted CA certificates. Default is to trust the well-known CAs curated by Mozilla. Mozilla's CAs are completely replaced when CAs are explicitly specified using this option. The value can be a string or `Buffer`, or an `Array` of strings and/or `Buffer`s. Any string or `Buffer` can contain multiple PEM CAs concatenated together. The peer's certificate must be chainable to a CA trusted by the server for the connection to be authenticated. When using certificates that are not chainable to a well-known CA, the certificate's CA must be explicitly specified as a trusted or the connection will fail to authenticate. If the peer uses a certificate that doesn't match or chain to one of the default CAs, use the `ca` option to provide a CA certificate that the peer's certificate can match or chain to. For self-signed certificates, the certificate is its own CA, and must be provided. For PEM encoded certificates, supported types are "TRUSTED CERTIFICATE", "X509 CERTIFICATE", and "CERTIFICATE". See also [`tls.rootCertificates`](#tlsrootcertificates).
+ `cert` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Buffer[]>](buffer#class-buffer) Cert chains in PEM format. One cert chain should be provided per private key. Each cert chain should consist of the PEM formatted certificate for a provided private `key`, followed by the PEM formatted intermediate certificates (if any), in order, and not including the root CA (the root CA must be pre-known to the peer, see `ca`). When providing multiple cert chains, they do not have to be in the same order as their private keys in `key`. If the intermediate certificates are not provided, the peer will not be able to validate the certificate, and the handshake will fail.
+ `sigalgs` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Colon-separated list of supported signature algorithms. The list can contain digest algorithms (`SHA256`, `MD5` etc.), public key algorithms (`RSA-PSS`, `ECDSA` etc.), combination of both (e.g 'RSA+SHA384') or TLS v1.3 scheme names (e.g. `rsa_pss_pss_sha512`). See [OpenSSL man pages](https://www.openssl.org/docs/man1.1.1/man3/SSL_CTX_set1_sigalgs_list.html) for more info.
+ `ciphers` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Cipher suite specification, replacing the default. For more information, see [Modifying the default TLS cipher suite](#modifying-the-default-tls-cipher-suite). Permitted ciphers can be obtained via [`tls.getCiphers()`](#tlsgetciphers). Cipher names must be uppercased in order for OpenSSL to accept them.
+ `clientCertEngine` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of an OpenSSL engine which can provide the client certificate.
+ `crl` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Buffer[]>](buffer#class-buffer) PEM formatted CRLs (Certificate Revocation Lists).
+ `dhparam` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) Diffie-Hellman parameters, required for [perfect forward secrecy](#perfect-forward-secrecy). Use `openssl dhparam` to create the parameters. The key length must be greater than or equal to 1024 bits or else an error will be thrown. Although 1024 bits is permissible, use 2048 bits or larger for stronger security. If omitted or invalid, the parameters are silently discarded and DHE ciphers will not be available.
+ `ecdhCurve` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A string describing a named curve or a colon separated list of curve NIDs or names, for example `P-521:P-384:P-256`, to use for ECDH key agreement. Set to `auto` to select the curve automatically. Use [`crypto.getCurves()`](crypto#cryptogetcurves) to obtain a list of available curve names. On recent releases, `openssl ecparam -list_curves` will also display the name and description of each available elliptic curve. **Default:** [`tls.DEFAULT_ECDH_CURVE`](#tlsdefault_ecdh_curve).
+ `honorCipherOrder` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) Attempt to use the server's cipher suite preferences instead of the client's. When `true`, causes `SSL_OP_CIPHER_SERVER_PREFERENCE` to be set in `secureOptions`, see [OpenSSL Options](crypto#openssl-options) for more information.
+ `key` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Buffer[]>](buffer#class-buffer) | [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Private keys in PEM format. PEM allows the option of private keys being encrypted. Encrypted keys will be decrypted with `options.passphrase`. Multiple keys using different algorithms can be provided either as an array of unencrypted key strings or buffers, or an array of objects in the form `{pem: <string|buffer>[, passphrase: <string>]}`. The object form can only occur in an array. `object.passphrase` is optional. Encrypted keys will be decrypted with `object.passphrase` if provided, or `options.passphrase` if it is not.
+ `privateKeyEngine` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of an OpenSSL engine to get private key from. Should be used together with `privateKeyIdentifier`.
+ `privateKeyIdentifier` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Identifier of a private key managed by an OpenSSL engine. Should be used together with `privateKeyEngine`. Should not be set together with `key`, because both options define a private key in different ways.
+ `maxVersion` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Optionally set the maximum TLS version to allow. One of `'TLSv1.3'`, `'TLSv1.2'`, `'TLSv1.1'`, or `'TLSv1'`. Cannot be specified along with the `secureProtocol` option; use one or the other. **Default:** [`tls.DEFAULT_MAX_VERSION`](#tlsdefault_max_version).
+ `minVersion` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Optionally set the minimum TLS version to allow. One of `'TLSv1.3'`, `'TLSv1.2'`, `'TLSv1.1'`, or `'TLSv1'`. Cannot be specified along with the `secureProtocol` option; use one or the other. Avoid setting to less than TLSv1.2, but it may be required for interoperability. **Default:** [`tls.DEFAULT_MIN_VERSION`](#tlsdefault_min_version).
+ `passphrase` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Shared passphrase used for a single private key and/or a PFX.
+ `pfx` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer>](buffer#class-buffer) | [<Buffer[]>](buffer#class-buffer) | [<Object[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) PFX or PKCS12 encoded private key and certificate chain. `pfx` is an alternative to providing `key` and `cert` individually. PFX is usually encrypted, if it is, `passphrase` will be used to decrypt it. Multiple PFX can be provided either as an array of unencrypted PFX buffers, or an array of objects in the form `{buf: <string|buffer>[, passphrase: <string>]}`. The object form can only occur in an array. `object.passphrase` is optional. Encrypted PFX will be decrypted with `object.passphrase` if provided, or `options.passphrase` if it is not.
+ `secureOptions` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Optionally affect the OpenSSL protocol behavior, which is not usually necessary. This should be used carefully if at all! Value is a numeric bitmask of the `SSL_OP_*` options from [OpenSSL Options](crypto#openssl-options).
+ `secureProtocol` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Legacy mechanism to select the TLS protocol version to use, it does not support independent control of the minimum and maximum version, and does not support limiting the protocol to TLSv1.3. Use `minVersion` and `maxVersion` instead. The possible values are listed as [SSL\_METHODS](https://www.openssl.org/docs/man1.1.1/man7/ssl.html#Dealing-with-Protocol-Methods), use the function names as strings. For example, use `'TLSv1_1_method'` to force TLS version 1.1, or `'TLS_method'` to allow any TLS protocol version up to TLSv1.3. It is not recommended to use TLS versions less than 1.2, but it may be required for interoperability. **Default:** none, see `minVersion`.
+ `sessionIdContext` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Opaque identifier used by servers to ensure session state is not shared between applications. Unused by clients.
+ `ticketKeys`: [<Buffer>](buffer#class-buffer) 48-bytes of cryptographically strong pseudorandom data. See [Session Resumption](#session-resumption) for more information.
+ `sessionTimeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of seconds after which a TLS session created by the server will no longer be resumable. See [Session Resumption](#session-resumption) for more information. **Default:** `300`.
[`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener) sets the default value of the `honorCipherOrder` option to `true`, other APIs that create secure contexts leave it unset.
[`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener) uses a 128 bit truncated SHA1 hash value generated from `process.argv` as the default value of the `sessionIdContext` option, other APIs that create secure contexts have no default value.
The `tls.createSecureContext()` method creates a `SecureContext` object. It is usable as an argument to several `tls` APIs, such as [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener) and [`server.addContext()`](#serveraddcontexthostname-context), but has no public methods.
A key is *required* for ciphers that use certificates. Either `key` or `pfx` can be used to provide it.
If the `ca` option is not given, then Node.js will default to using [Mozilla's publicly trusted list of CAs](https://hg.mozilla.org/mozilla-central/raw-file/tip/security/nss/lib/ckfw/builtins/certdata.txt).
###
`tls.createSecurePair([context][, isServer][, requestCert][, rejectUnauthorized][, options])`
History
| Version | Changes |
| --- | --- |
| v5.0.0 | ALPN options are supported now. |
| v0.11.3 | Deprecated since: v0.11.3 |
| v0.3.2 | Added in: v0.3.2 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`tls.TLSSocket`](#class-tlstlssocket) instead.
* `context` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) A secure context object as returned by `tls.createSecureContext()`
* `isServer` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` to specify that this TLS connection should be opened as a server.
* `requestCert` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` to specify whether a server should request a certificate from a connecting client. Only applies when `isServer` is `true`.
* `rejectUnauthorized` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If not `false` a server automatically reject clients with invalid certificates. Only applies when `isServer` is `true`.
* `options`
+ `enableTrace`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `secureContext`: A TLS context object from [`tls.createSecureContext()`](#tlscreatesecurecontextoptions)
+ `isServer`: If `true` the TLS socket will be instantiated in server-mode. **Default:** `false`.
+ `server` [<net.Server>](net#class-netserver) A [`net.Server`](net#class-netserver) instance
+ `requestCert`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `rejectUnauthorized`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `ALPNProtocols`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `SNICallback`: See [`tls.createServer()`](#tlscreateserveroptions-secureconnectionlistener)
+ `session` [<Buffer>](buffer#class-buffer) A `Buffer` instance containing a TLS session.
+ `requestOCSP` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, specifies that the OCSP status request extension will be added to the client hello and an `'OCSPResponse'` event will be emitted on the socket before establishing a secure communication.
Creates a new secure pair object with two streams, one of which reads and writes the encrypted data and the other of which reads and writes the cleartext data. Generally, the encrypted stream is piped to/from an incoming encrypted data stream and the cleartext one is used as a replacement for the initial encrypted stream.
`tls.createSecurePair()` returns a `tls.SecurePair` object with `cleartext` and `encrypted` stream properties.
Using `cleartext` has the same API as [`tls.TLSSocket`](#class-tlstlssocket).
The `tls.createSecurePair()` method is now deprecated in favor of `tls.TLSSocket()`. For example, the code:
```
pair = tls.createSecurePair(/* ... */);
pair.encrypted.pipe(socket);
socket.pipe(pair.encrypted);
```
can be replaced by:
```
secureSocket = tls.TLSSocket(socket, options);
```
where `secureSocket` has the same API as `pair.cleartext`.
###
`tls.createServer([options][, secureConnectionListener])`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | If `ALPNProtocols` is set, incoming connections that send an ALPN extension with no supported protocols are terminated with a fatal `no_application_protocol` alert. |
| v12.3.0 | The `options` parameter now supports `net.createServer()` options. |
| v9.3.0 | The `options` parameter can now include `clientCertEngine`. |
| v8.0.0 | The `ALPNProtocols` option can be a `TypedArray` or `DataView` now. |
| v5.0.0 | ALPN options are supported now. |
| v0.3.2 | Added in: v0.3.2 |
* `options` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
+ `ALPNProtocols`: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<Buffer[]>](buffer#class-buffer) | [<TypedArray[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) | [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) An array of strings, `Buffer`s, `TypedArray`s, or `DataView`s, or a single `Buffer`, `TypedArray`, or `DataView` containing the supported ALPN protocols. `Buffer`s should have the format `[len][name][len][name]...` e.g. `0x05hello0x05world`, where the first byte is the length of the next protocol name. Passing an array is usually much simpler, e.g. `['hello', 'world']`. (Protocols should be ordered by their priority.)
+ `clientCertEngine` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) Name of an OpenSSL engine which can provide the client certificate.
+ `enableTrace` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true`, [`tls.TLSSocket.enableTrace()`](#tlssocketenabletrace) will be called on new connections. Tracing can be enabled after the secure connection is established, but this option must be used to trace the secure connection setup. **Default:** `false`.
+ `handshakeTimeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) Abort the connection if the SSL/TLS handshake does not finish in the specified number of milliseconds. A `'tlsClientError'` is emitted on the `tls.Server` object whenever a handshake times out. **Default:** `120000` (120 seconds).
+ `rejectUnauthorized` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If not `false` the server will reject any connection which is not authorized with the list of supplied CAs. This option only has an effect if `requestCert` is `true`. **Default:** `true`.
+ `requestCert` [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If `true` the server will request a certificate from clients that connect and attempt to verify that certificate. **Default:** `false`.
+ `sessionTimeout` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of seconds after which a TLS session created by the server will no longer be resumable. See [Session Resumption](#session-resumption) for more information. **Default:** `300`.
+ `SNICallback(servername, callback)` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) A function that will be called if the client supports SNI TLS extension. Two arguments will be passed when called: `servername` and `callback`. `callback` is an error-first callback that takes two optional arguments: `error` and `ctx`. `ctx`, if provided, is a `SecureContext` instance. [`tls.createSecureContext()`](#tlscreatesecurecontextoptions) can be used to get a proper `SecureContext`. If `callback` is called with a falsy `ctx` argument, the default secure context of the server will be used. If `SNICallback` wasn't provided the default callback with high-level API will be used (see below).
+ `ticketKeys`: [<Buffer>](buffer#class-buffer) 48-bytes of cryptographically strong pseudorandom data. See [Session Resumption](#session-resumption) for more information.
+ `pskCallback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
- socket: [<tls.TLSSocket>](tls#class-tlstlssocket) the server [`tls.TLSSocket`](#class-tlstlssocket) instance for this connection.
- identity: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) identity parameter sent from the client.
- Returns: [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) pre-shared key that must either be a buffer or `null` to stop the negotiation process. Returned PSK must be compatible with the selected cipher's digest.When negotiating TLS-PSK (pre-shared keys), this function is called with the identity provided by the client. If the return value is `null` the negotiation process will stop and an "unknown\_psk\_identity" alert message will be sent to the other party. If the server wishes to hide the fact that the PSK identity was not known, the callback must provide some random data as `psk` to make the connection fail with "decrypt\_error" before negotiation is finished. PSK ciphers are disabled by default, and using TLS-PSK thus requires explicitly specifying a cipher suite with the `ciphers` option. More information can be found in the [RFC 4279](https://tools.ietf.org/html/rfc4279).
+ `pskIdentityHint` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) optional hint to send to a client to help with selecting the identity during TLS-PSK negotiation. Will be ignored in TLS 1.3. Upon failing to set pskIdentityHint `'tlsClientError'` will be emitted with `'ERR_TLS_PSK_SET_IDENTIY_HINT_FAILED'` code.
+ ...: Any [`tls.createSecureContext()`](#tlscreatesecurecontextoptions) option can be provided. For servers, the identity options (`pfx`, `key`/`cert`, or `pskCallback`) are usually required.
+ ...: Any [`net.createServer()`](net#netcreateserveroptions-connectionlistener) option can be provided.
* `secureConnectionListener` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* Returns: [<tls.Server>](tls#class-tlsserver)
Creates a new [`tls.Server`](#class-tlsserver). The `secureConnectionListener`, if provided, is automatically set as a listener for the [`'secureConnection'`](#event-secureconnection) event.
The `ticketKeys` options is automatically shared between `node:cluster` module workers.
The following illustrates a simple echo server:
```
const tls = require('node:tls');
const fs = require('node:fs');
const options = {
key: fs.readFileSync('server-key.pem'),
cert: fs.readFileSync('server-cert.pem'),
// This is necessary only if using client certificate authentication.
requestCert: true,
// This is necessary only if the client uses a self-signed certificate.
ca: [ fs.readFileSync('client-cert.pem') ]
};
const server = tls.createServer(options, (socket) => {
console.log('server connected',
socket.authorized ? 'authorized' : 'unauthorized');
socket.write('welcome!\n');
socket.setEncoding('utf8');
socket.pipe(socket);
});
server.listen(8000, () => {
console.log('server bound');
});
```
The server can be tested by connecting to it using the example client from [`tls.connect()`](#tlsconnectoptions-callback).
###
`tls.getCiphers()`
Added in: v0.10.2 * Returns: [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns an array with the names of the supported TLS ciphers. The names are lower-case for historical reasons, but must be uppercased to be used in the `ciphers` option of [`tls.createSecureContext()`](#tlscreatesecurecontextoptions).
Not all supported ciphers are enabled by default. See [Modifying the default TLS cipher suite](#modifying-the-default-tls-cipher-suite).
Cipher names that start with `'tls_'` are for TLSv1.3, all the others are for TLSv1.2 and below.
```
console.log(tls.getCiphers()); // ['aes128-gcm-sha256', 'aes128-sha', ...]
```
###
`tls.rootCertificates`
Added in: v12.3.0 * [<string[]>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
An immutable array of strings representing the root certificates (in PEM format) from the bundled Mozilla CA store as supplied by the current Node.js version.
The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms.
###
`tls.DEFAULT_ECDH_CURVE`
History
| Version | Changes |
| --- | --- |
| v10.0.0 | Default value changed to `'auto'`. |
| v0.11.13 | Added in: v0.11.13 |
The default curve name to use for ECDH key agreement in a tls server. The default value is `'auto'`. See [`tls.createSecureContext()`](#tlscreatesecurecontextoptions) for further information.
###
`tls.DEFAULT_MAX_VERSION`
Added in: v11.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The default value of the `maxVersion` option of [`tls.createSecureContext()`](#tlscreatesecurecontextoptions). It can be assigned any of the supported TLS protocol versions, `'TLSv1.3'`, `'TLSv1.2'`, `'TLSv1.1'`, or `'TLSv1'`. **Default:** `'TLSv1.3'`, unless changed using CLI options. Using `--tls-max-v1.2` sets the default to `'TLSv1.2'`. Using `--tls-max-v1.3` sets the default to `'TLSv1.3'`. If multiple of the options are provided, the highest maximum is used.
###
`tls.DEFAULT_MIN_VERSION`
Added in: v11.4.0 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The default value of the `minVersion` option of [`tls.createSecureContext()`](#tlscreatesecurecontextoptions). It can be assigned any of the supported TLS protocol versions, `'TLSv1.3'`, `'TLSv1.2'`, `'TLSv1.1'`, or `'TLSv1'`. **Default:** `'TLSv1.2'`, unless changed using CLI options. Using `--tls-min-v1.0` sets the default to `'TLSv1'`. Using `--tls-min-v1.1` sets the default to `'TLSv1.1'`. Using `--tls-min-v1.3` sets the default to `'TLSv1.3'`. If multiple of the options are provided, the lowest minimum is used.
| programming_docs |
node None Debugger
--------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
Node.js includes a command-line debugging utility. The Node.js debugger client is not a full-featured debugger, but simple stepping and inspection are possible.
To use it, start Node.js with the `inspect` argument followed by the path to the script to debug.
```
$ node inspect myscript.js
< Debugger listening on ws://127.0.0.1:9229/621111f9-ffcb-4e82-b718-48a145fa5db8
< For help, see: https://nodejs.org/en/docs/inspector
<
< Debugger attached.
<
ok
Break on start in myscript.js:2
1 // myscript.js
> 2 global.x = 5;
3 setTimeout(() => {
4 debugger;
debug>
```
The debugger automatically breaks on the first executable line. To instead run until the first breakpoint (specified by a [`debugger`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/debugger) statement), set the `NODE_INSPECT_RESUME_ON_START` environment variable to `1`.
```
$ cat myscript.js
// myscript.js
global.x = 5;
setTimeout(() => {
debugger;
console.log('world');
}, 1000);
console.log('hello');
$ NODE_INSPECT_RESUME_ON_START=1 node inspect myscript.js
< Debugger listening on ws://127.0.0.1:9229/f1ed133e-7876-495b-83ae-c32c6fc319c2
< For help, see: https://nodejs.org/en/docs/inspector
<
connecting to 127.0.0.1:9229 ... ok
< Debugger attached.
<
< hello
<
break in myscript.js:4
2 global.x = 5;
3 setTimeout(() => {
> 4 debugger;
5 console.log('world');
6 }, 1000);
debug> next
break in myscript.js:5
3 setTimeout(() => {
4 debugger;
> 5 console.log('world');
6 }, 1000);
7 console.log('hello');
debug> repl
Press Ctrl+C to leave debug repl
> x
5
> 2 + 2
4
debug> next
< world
<
break in myscript.js:6
4 debugger;
5 console.log('world');
> 6 }, 1000);
7 console.log('hello');
8
debug> .exit
$
```
The `repl` command allows code to be evaluated remotely. The `next` command steps to the next line. Type `help` to see what other commands are available.
Pressing `enter` without typing a command will repeat the previous debugger command.
### Watchers
It is possible to watch expression and variable values while debugging. On every breakpoint, each expression from the watchers list will be evaluated in the current context and displayed immediately before the breakpoint's source code listing.
To begin watching an expression, type `watch('my_expression')`. The command `watchers` will print the active watchers. To remove a watcher, type `unwatch('my_expression')`.
### Command reference
#### Stepping
* `cont`, `c`: Continue execution
* `next`, `n`: Step next
* `step`, `s`: Step in
* `out`, `o`: Step out
* `pause`: Pause running code (like pause button in Developer Tools)
#### Breakpoints
* `setBreakpoint()`, `sb()`: Set breakpoint on current line
* `setBreakpoint(line)`, `sb(line)`: Set breakpoint on specific line
* `setBreakpoint('fn()')`, `sb(...)`: Set breakpoint on a first statement in function's body
* `setBreakpoint('script.js', 1)`, `sb(...)`: Set breakpoint on first line of `script.js`
* `setBreakpoint('script.js', 1, 'num < 4')`, `sb(...)`: Set conditional breakpoint on first line of `script.js` that only breaks when `num < 4` evaluates to `true`
* `clearBreakpoint('script.js', 1)`, `cb(...)`: Clear breakpoint in `script.js` on line 1
It is also possible to set a breakpoint in a file (module) that is not loaded yet:
```
$ node inspect main.js
< Debugger listening on ws://127.0.0.1:9229/48a5b28a-550c-471b-b5e1-d13dd7165df9
< For help, see: https://nodejs.org/en/docs/inspector
<
< Debugger attached.
<
ok
Break on start in main.js:1
> 1 const mod = require('./mod.js');
2 mod.hello();
3 mod.hello();
debug> setBreakpoint('mod.js', 22)
Warning: script 'mod.js' was not loaded yet.
debug> c
break in mod.js:22
20 // USE OR OTHER DEALINGS IN THE SOFTWARE.
21
>22 exports.hello = function() {
23 return 'hello from module';
24 };
debug>
```
It is also possible to set a conditional breakpoint that only breaks when a given expression evaluates to `true`:
```
$ node inspect main.js
< Debugger listening on ws://127.0.0.1:9229/ce24daa8-3816-44d4-b8ab-8273c8a66d35
< For help, see: https://nodejs.org/en/docs/inspector
< Debugger attached.
Break on start in main.js:7
5 }
6
> 7 addOne(10);
8 addOne(-1);
9
debug> setBreakpoint('main.js', 4, 'num < 0')
1 'use strict';
2
3 function addOne(num) {
> 4 return num + 1;
5 }
6
7 addOne(10);
8 addOne(-1);
9
debug> cont
break in main.js:4
2
3 function addOne(num) {
> 4 return num + 1;
5 }
6
debug> exec('num')
-1
debug>
```
#### Information
* `backtrace`, `bt`: Print backtrace of current execution frame
* `list(5)`: List scripts source code with 5 line context (5 lines before and after)
* `watch(expr)`: Add expression to watch list
* `unwatch(expr)`: Remove expression from watch list
* `watchers`: List all watchers and their values (automatically listed on each breakpoint)
* `repl`: Open debugger's repl for evaluation in debugging script's context
* `exec expr`, `p expr`: Execute an expression in debugging script's context and print its value
#### Execution control
* `run`: Run script (automatically runs on debugger's start)
* `restart`: Restart script
* `kill`: Kill script
#### Various
* `scripts`: List all loaded scripts
* `version`: Display V8's version
### Advanced usage
#### V8 inspector integration for Node.js
V8 Inspector integration allows attaching Chrome DevTools to Node.js instances for debugging and profiling. It uses the [Chrome DevTools Protocol](https://chromedevtools.github.io/devtools-protocol/).
V8 Inspector can be enabled by passing the `--inspect` flag when starting a Node.js application. It is also possible to supply a custom port with that flag, e.g. `--inspect=9222` will accept DevTools connections on port 9222.
To break on the first line of the application code, pass the `--inspect-brk` flag instead of `--inspect`.
```
$ node --inspect index.js
Debugger listening on ws://127.0.0.1:9229/dc9010dd-f8b8-4ac5-a510-c1a114ec7d29
For help, see: https://nodejs.org/en/docs/inspector
```
(In the example above, the UUID dc9010dd-f8b8-4ac5-a510-c1a114ec7d29 at the end of the URL is generated on the fly, it varies in different debugging sessions.)
If the Chrome browser is older than 66.0.3345.0, use `inspector.html` instead of `js_app.html` in the above URL.
Chrome DevTools doesn't support debugging [worker threads](worker_threads) yet. [ndb](https://github.com/GoogleChromeLabs/ndb/) can be used to debug them.
node None String decoder
--------------
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/string\_decoder.js](https://github.com/nodejs/node/blob/v19.0.1/lib/string_decoder.js)
The `node:string_decoder` module provides an API for decoding `Buffer` objects into strings in a manner that preserves encoded multi-byte UTF-8 and UTF-16 characters. It can be accessed using:
```
const { StringDecoder } = require('node:string_decoder');
```
The following example shows the basic use of the `StringDecoder` class.
```
const { StringDecoder } = require('node:string_decoder');
const decoder = new StringDecoder('utf8');
const cent = Buffer.from([0xC2, 0xA2]);
console.log(decoder.write(cent));
const euro = Buffer.from([0xE2, 0x82, 0xAC]);
console.log(decoder.write(euro));
```
When a `Buffer` instance is written to the `StringDecoder` instance, an internal buffer is used to ensure that the decoded string does not contain any incomplete multibyte characters. These are held in the buffer until the next call to `stringDecoder.write()` or until `stringDecoder.end()` is called.
In the following example, the three UTF-8 encoded bytes of the European Euro symbol (`€`) are written over three separate operations:
```
const { StringDecoder } = require('node:string_decoder');
const decoder = new StringDecoder('utf8');
decoder.write(Buffer.from([0xE2]));
decoder.write(Buffer.from([0x82]));
console.log(decoder.end(Buffer.from([0xAC])));
```
### Class: `StringDecoder`
####
`new StringDecoder([encoding])`
Added in: v0.1.99 * `encoding` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) The character [encoding](buffer#buffers-and-character-encodings) the `StringDecoder` will use. **Default:** `'utf8'`.
Creates a new `StringDecoder` instance.
####
`stringDecoder.end([buffer])`
Added in: v0.9.3 * `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A `Buffer`, or `TypedArray`, or `DataView` containing the bytes to decode.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns any remaining input stored in the internal buffer as a string. Bytes representing incomplete UTF-8 and UTF-16 characters will be replaced with substitution characters appropriate for the character encoding.
If the `buffer` argument is provided, one final call to `stringDecoder.write()` is performed before returning the remaining input. After `end()` is called, the `stringDecoder` object can be reused for new input.
####
`stringDecoder.write(buffer)`
History
| Version | Changes |
| --- | --- |
| v8.0.0 | Each invalid character is now replaced by a single replacement character instead of one for each individual byte. |
| v0.1.99 | Added in: v0.1.99 |
* `buffer` [<Buffer>](buffer#class-buffer) | [<TypedArray>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) | [<DataView>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) A `Buffer`, or `TypedArray`, or `DataView` containing the bytes to decode.
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Returns a decoded string, ensuring that any incomplete multibyte characters at the end of the `Buffer`, or `TypedArray`, or `DataView` are omitted from the returned string and stored in an internal buffer for the next call to `stringDecoder.write()` or `stringDecoder.end()`.
node None Global objects
--------------
These objects are available in all modules. The following variables may appear to be global but are not. They exist only in the scope of modules, see the [module system documentation](modules):
* [`__dirname`](modules#__dirname)
* [`__filename`](modules#__filename)
* [`exports`](modules#exports)
* [`module`](modules#module)
* [`require()`](modules#requireid)
The objects listed here are specific to Node.js. There are [built-in objects](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects) that are part of the JavaScript language itself, which are also globally accessible.
### Class: `AbortController`
History
| Version | Changes |
| --- | --- |
| v15.4.0 | No longer experimental. |
| v15.0.0, v14.17.0 | Added in: v15.0.0, v14.17.0 |
A utility class used to signal cancelation in selected `Promise`-based APIs. The API is based on the Web API [`AbortController`](https://developer.mozilla.org/en-US/docs/Web/API/AbortController).
```
const ac = new AbortController();
ac.signal.addEventListener('abort', () => console.log('Aborted!'),
{ once: true });
ac.abort();
console.log(ac.signal.aborted); // Prints True
```
####
`abortController.abort([reason])`
History
| Version | Changes |
| --- | --- |
| v17.2.0, v16.14.0 | Added the new optional reason argument. |
| v15.0.0, v14.17.0 | Added in: v15.0.0, v14.17.0 |
* `reason` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) An optional reason, retrievable on the `AbortSignal`'s `reason` property.
Triggers the abort signal, causing the `abortController.signal` to emit the `'abort'` event.
####
`abortController.signal`
Added in: v15.0.0, v14.17.0 * Type: [<AbortSignal>](globals#class-abortsignal)
#### Class: `AbortSignal`
Added in: v15.0.0, v14.17.0 * Extends: [<EventTarget>](events#class-eventtarget)
The `AbortSignal` is used to notify observers when the `abortController.abort()` method is called.
##### Static method: `AbortSignal.abort([reason])`
History
| Version | Changes |
| --- | --- |
| v17.2.0, v16.14.0 | Added the new optional reason argument. |
| v15.12.0, v14.17.0 | Added in: v15.12.0, v14.17.0 |
* `reason`: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
* Returns: [<AbortSignal>](globals#class-abortsignal)
Returns a new already aborted `AbortSignal`.
##### Static method: `AbortSignal.timeout(delay)`
Added in: v17.3.0, v16.14.0 * `delay` [<number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) The number of milliseconds to wait before triggering the AbortSignal.
Returns a new `AbortSignal` which will be aborted in `delay` milliseconds.
##### Event: `'abort'`
Added in: v15.0.0, v14.17.0 The `'abort'` event is emitted when the `abortController.abort()` method is called. The callback is invoked with a single object argument with a single `type` property set to `'abort'`:
```
const ac = new AbortController();
// Use either the onabort property...
ac.signal.onabort = () => console.log('aborted!');
// Or the EventTarget API...
ac.signal.addEventListener('abort', (event) => {
console.log(event.type); // Prints 'abort'
}, { once: true });
ac.abort();
```
The `AbortController` with which the `AbortSignal` is associated will only ever trigger the `'abort'` event once. We recommended that code check that the `abortSignal.aborted` attribute is `false` before adding an `'abort'` event listener.
Any event listeners attached to the `AbortSignal` should use the `{ once: true }` option (or, if using the `EventEmitter` APIs to attach a listener, use the `once()` method) to ensure that the event listener is removed as soon as the `'abort'` event is handled. Failure to do so may result in memory leaks.
#####
`abortSignal.aborted`
Added in: v15.0.0, v14.17.0 * Type: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) True after the `AbortController` has been aborted.
#####
`abortSignal.onabort`
Added in: v15.0.0, v14.17.0 * Type: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
An optional callback function that may be set by user code to be notified when the `abortController.abort()` function has been called.
#####
`abortSignal.reason`
Added in: v17.2.0, v16.14.0 * Type: [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
An optional reason specified when the `AbortSignal` was triggered.
```
const ac = new AbortController();
ac.abort(new Error('boom!'));
console.log(ac.signal.reason); // Error('boom!');
```
#####
`abortSignal.throwIfAborted()`
Added in: v17.3.0, v16.17.0 If `abortSignal.aborted` is `true`, throws `abortSignal.reason`.
### Class: `Blob`
Added in: v18.0.0 See [<Blob>](buffer#class-blob).
### Class: `Buffer`
Added in: v0.1.103 * [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
Used to handle binary data. See the [buffer section](buffer).
### Class: `ByteLengthQueuingStrategy`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`ByteLengthQueuingStrategy`](webstreams#class-bytelengthqueuingstrategy).
###
`__dirname`
This variable may appear to be global but is not. See [`__dirname`](modules#__dirname).
###
`__filename`
This variable may appear to be global but is not. See [`__filename`](modules#__filename).
###
`atob(data)`
Added in: v16.0.0
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy. Use `Buffer.from(data, 'base64')` instead.
Global alias for [`buffer.atob()`](buffer#bufferatobdata).
###
`BroadcastChannel`
Added in: v18.0.0 See [<BroadcastChannel>](worker_threads#class-broadcastchannel-extends-eventtarget).
###
`btoa(data)`
Added in: v16.0.0
[Stability: 3](https://nodejs.org/api/documentation.html#stability-index) - Legacy. Use `buf.toString('base64')` instead.
Global alias for [`buffer.btoa()`](buffer#bufferbtoadata).
###
`clearImmediate(immediateObject)`
Added in: v0.9.1 [`clearImmediate`](timers#clearimmediateimmediate) is described in the <timers> section.
###
`clearInterval(intervalObject)`
Added in: v0.0.1 [`clearInterval`](timers#clearintervaltimeout) is described in the <timers> section.
###
`clearTimeout(timeoutObject)`
Added in: v0.0.1 [`clearTimeout`](timers#cleartimeouttimeout) is described in the <timers> section.
### Class: `CompressionStream`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`CompressionStream`](webstreams#class-compressionstream).
###
`console`
Added in: v0.1.100 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
Used to print to stdout and stderr. See the [`console`](console) section.
### Class: `CountQueuingStrategy`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`CountQueuingStrategy`](webstreams#class-countqueuingstrategy).
###
`Crypto`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | No longer behind `--experimental-global-webcrypto` CLI flag. |
| v17.6.0, v16.15.0 | Added in: v17.6.0, v16.15.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-global-webcrypto`](cli#--no-experimental-global-webcrypto) CLI flag.
A browser-compatible implementation of [<Crypto>](webcrypto#class-crypto). This global is available only if the Node.js binary was compiled with including support for the `node:crypto` module.
###
`crypto`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | No longer behind `--experimental-global-webcrypto` CLI flag. |
| v17.6.0, v16.15.0 | Added in: v17.6.0, v16.15.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-global-webcrypto`](cli#--no-experimental-global-webcrypto) CLI flag.
A browser-compatible implementation of the [Web Crypto API](webcrypto).
###
`CryptoKey`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | No longer behind `--experimental-global-webcrypto` CLI flag. |
| v17.6.0, v16.15.0 | Added in: v17.6.0, v16.15.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-global-webcrypto`](cli#--no-experimental-global-webcrypto) CLI flag.
A browser-compatible implementation of [<CryptoKey>](webcrypto#class-cryptokey). This global is available only if the Node.js binary was compiled with including support for the `node:crypto` module.
###
`CustomEvent`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | No longer behind `--experimental-global-customevent` CLI flag. |
| v18.7.0, v16.17.0 | Added in: v18.7.0, v16.17.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-global-customevent`](cli#--no-experimental-global-customevent) CLI flag.
A browser-compatible implementation of the [`CustomEvent` Web API](https://dom.spec.whatwg.org/#customevent).
### Class: `DecompressionStream`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`DecompressionStream`](webstreams#class-decompressionstream).
###
`Event`
History
| Version | Changes |
| --- | --- |
| v15.4.0 | No longer experimental. |
| v15.0.0 | Added in: v15.0.0 |
A browser-compatible implementation of the `Event` class. See [`EventTarget` and `Event` API](events#eventtarget-and-event-api) for more details.
###
`EventTarget`
History
| Version | Changes |
| --- | --- |
| v15.4.0 | No longer experimental. |
| v15.0.0 | Added in: v15.0.0 |
A browser-compatible implementation of the `EventTarget` class. See [`EventTarget` and `Event` API](events#eventtarget-and-event-api) for more details.
###
`exports`
This variable may appear to be global but is not. See [`exports`](modules#exports).
###
`fetch`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-fetch`](cli#--no-experimental-fetch) CLI flag.
A browser-compatible implementation of the [`fetch()`](https://developer.mozilla.org/en-US/docs/Web/API/fetch) function.
### Class `FormData`
Added in: v17.6.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-fetch`](cli#--no-experimental-fetch) CLI flag.
A browser-compatible implementation of [<FormData>](https://developer.mozilla.org/en-US/docs/Web/API/FormData).
###
`global`
Added in: v0.1.27 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) The global namespace object.
In browsers, the top-level scope is the global scope. This means that within the browser `var something` will define a new global variable. In Node.js this is different. The top-level scope is not the global scope; `var something` inside a Node.js module will be local to that module.
### Class `Headers`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-fetch`](cli#--no-experimental-fetch) CLI flag.
A browser-compatible implementation of [<Headers>](https://developer.mozilla.org/en-US/docs/Web/API/Headers).
###
`MessageChannel`
Added in: v15.0.0 The `MessageChannel` class. See [`MessageChannel`](worker_threads#class-messagechannel) for more details.
###
`MessageEvent`
Added in: v15.0.0 The `MessageEvent` class. See [`MessageEvent`](https://developer.mozilla.org/en-US/docs/Web/API/MessageEvent/MessageEvent) for more details.
###
`MessagePort`
Added in: v15.0.0 The `MessagePort` class. See [`MessagePort`](worker_threads#class-messageport) for more details.
###
`module`
This variable may appear to be global but is not. See [`module`](modules#module).
###
`PerformanceEntry`
Added in: v19.0.0 The `PerformanceEntry` class. See [`PerformanceEntry`](perf_hooks#class-performanceentry) for more details.
###
`PerformanceMark`
Added in: v19.0.0 The `PerformanceMark` class. See [`PerformanceMark`](perf_hooks#class-performancemark) for more details.
###
`PerformanceMeasure`
Added in: v19.0.0 The `PerformanceMeasure` class. See [`PerformanceMeasure`](perf_hooks#class-performancemeasure) for more details.
###
`PerformanceObserver`
Added in: v19.0.0 The `PerformanceObserver` class. See [`PerformanceObserver`](perf_hooks#class-performanceobserver) for more details.
###
`PerformanceObserverEntryList`
Added in: v19.0.0 The `PerformanceObserverEntryList` class. See [`PerformanceObserverEntryList`](perf_hooks#class-performanceobserverentrylist) for more details.
###
`PerformanceResourceTiming`
Added in: v19.0.0 The `PerformanceResourceTiming` class. See [`PerformanceResourceTiming`](perf_hooks#class-performanceresourcetiming) for more details.
###
`performance`
Added in: v16.0.0 The [`perf_hooks.performance`](perf_hooks#perf_hooksperformance) object.
###
`process`
Added in: v0.1.7 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The process object. See the [`process` object](process#process) section.
###
`queueMicrotask(callback)`
Added in: v11.0.0 * `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) Function to be queued.
The `queueMicrotask()` method queues a microtask to invoke `callback`. If `callback` throws an exception, the [`process` object](process#process) `'uncaughtException'` event will be emitted.
The microtask queue is managed by V8 and may be used in a similar manner to the [`process.nextTick()`](process#processnexttickcallback-args) queue, which is managed by Node.js. The `process.nextTick()` queue is always processed before the microtask queue within each turn of the Node.js event loop.
```
// Here, `queueMicrotask()` is used to ensure the 'load' event is always
// emitted asynchronously, and therefore consistently. Using
// `process.nextTick()` here would result in the 'load' event always emitting
// before any other promise jobs.
DataHandler.prototype.load = async function load(key) {
const hit = this._cache.get(key);
if (hit !== undefined) {
queueMicrotask(() => {
this.emit('load', hit);
});
return;
}
const data = await fetchData(key);
this._cache.set(key, data);
this.emit('load', data);
};
```
### Class: `ReadableByteStreamController`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`ReadableByteStreamController`](webstreams#class-readablebytestreamcontroller).
### Class: `ReadableStream`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`ReadableStream`](webstreams#class-readablestream).
### Class: `ReadableStreamBYOBReader`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`ReadableStreamBYOBReader`](webstreams#class-readablestreambyobreader).
### Class: `ReadableStreamBYOBRequest`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`ReadableStreamBYOBRequest`](webstreams#class-readablestreambyobrequest).
### Class: `ReadableStreamDefaultController`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`ReadableStreamDefaultController`](webstreams#class-readablestreamdefaultcontroller).
### Class: `ReadableStreamDefaultReader`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`ReadableStreamDefaultReader`](webstreams#class-readablestreamdefaultreader).
###
`require()`
This variable may appear to be global but is not. See [`require()`](modules#requireid).
###
`Response`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-fetch`](cli#--no-experimental-fetch) CLI flag.
A browser-compatible implementation of [<Response>](https://developer.mozilla.org/en-US/docs/Web/API/Response).
###
`Request`
Added in: v17.5.0, v16.15.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-fetch`](cli#--no-experimental-fetch) CLI flag.
A browser-compatible implementation of [<Request>](https://developer.mozilla.org/en-US/docs/Web/API/Request).
###
`setImmediate(callback[, ...args])`
Added in: v0.9.1 [`setImmediate`](timers#setimmediatecallback-args) is described in the <timers> section.
###
`setInterval(callback, delay[, ...args])`
Added in: v0.0.1 [`setInterval`](timers#setintervalcallback-delay-args) is described in the <timers> section.
###
`setTimeout(callback, delay[, ...args])`
Added in: v0.0.1 [`setTimeout`](timers#settimeoutcallback-delay-args) is described in the <timers> section.
###
`structuredClone(value[, options])`
Added in: v17.0.0 The WHATWG [`structuredClone`](https://developer.mozilla.org/en-US/docs/Web/API/structuredClone) method.
###
`SubtleCrypto`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | No longer behind `--experimental-global-webcrypto` CLI flag. |
| v17.6.0, v16.15.0 | Added in: v17.6.0, v16.15.0 |
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental. Disable this API with the [`--no-experimental-global-webcrypto`](cli#--no-experimental-global-webcrypto) CLI flag.
A browser-compatible implementation of [<SubtleCrypto>](webcrypto#class-subtlecrypto). This global is available only if the Node.js binary was compiled with including support for the `node:crypto` module.
###
`DOMException`
Added in: v17.0.0 The WHATWG `DOMException` class. See [`DOMException`](https://developer.mozilla.org/en-US/docs/Web/API/DOMException) for more details.
###
`TextDecoder`
Added in: v11.0.0 The WHATWG `TextDecoder` class. See the [`TextDecoder`](util#class-utiltextdecoder) section.
### Class: `TextDecoderStream`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`TextDecoderStream`](webstreams#class-textdecoderstream).
###
`TextEncoder`
Added in: v11.0.0 The WHATWG `TextEncoder` class. See the [`TextEncoder`](util#class-utiltextencoder) section.
### Class: `TextEncoderStream`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`TextEncoderStream`](webstreams#class-textencoderstream).
### Class: `TransformStream`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`TransformStream`](webstreams#class-transformstream).
### Class: `TransformStreamDefaultController`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`TransformStreamDefaultController`](webstreams#class-transformstreamdefaultcontroller).
###
`URL`
Added in: v10.0.0 The WHATWG `URL` class. See the [`URL`](url#class-url) section.
###
`URLSearchParams`
Added in: v10.0.0 The WHATWG `URLSearchParams` class. See the [`URLSearchParams`](url#class-urlsearchparams) section.
###
`WebAssembly`
Added in: v8.0.0 * [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The object that acts as the namespace for all W3C [WebAssembly](https://webassembly.org) related functionality. See the [Mozilla Developer Network](https://developer.mozilla.org/en-US/docs/WebAssembly) for usage and compatibility.
### Class: `WritableStream`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`WritableStream`](webstreams#class-writablestream).
### Class: `WritableStreamDefaultController`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`WritableStreamDefaultController`](webstreams#class-writablestreamdefaultcontroller).
### Class: `WritableStreamDefaultWriter`
Added in: v18.0.0
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental.
A browser-compatible implementation of [`WritableStreamDefaultWriter`](webstreams#class-writablestreamdefaultwriter).
| programming_docs |
node None Permissions
-----------
Permissions can be used to control what system resources the Node.js process has access to or what actions the process can take with those resources. Permissions can also control what modules can be accessed by other modules.
* [Module-based permissions](#module-based-permissions) control which files or URLs are available to other modules during application execution. This can be used to control what modules can be accessed by third-party dependencies, for example.
If you find a potential security vulnerability, please refer to our [Security Policy](https://github.com/nodejs/node/blob/main/SECURITY.md).
### Module-based permissions
#### Policies
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
Node.js contains experimental support for creating policies on loading code.
Policies are a security feature intended to allow guarantees about what code Node.js is able to load. The use of policies assumes safe practices for the policy files such as ensuring that policy files cannot be overwritten by the Node.js application by using file permissions.
A best practice would be to ensure that the policy manifest is read-only for the running Node.js application and that the file cannot be changed by the running Node.js application in any way. A typical setup would be to create the policy file as a different user id than the one running Node.js and granting read permissions to the user id running Node.js.
##### Enabling
The `--experimental-policy` flag can be used to enable features for policies when loading modules.
Once this has been set, all modules must conform to a policy manifest file passed to the flag:
```
node --experimental-policy=policy.json app.js
```
The policy manifest will be used to enforce constraints on code loaded by Node.js.
To mitigate tampering with policy files on disk, an integrity for the policy file itself may be provided via `--policy-integrity`. This allows running `node` and asserting the policy file contents even if the file is changed on disk.
```
node --experimental-policy=policy.json --policy-integrity="sha384-SggXRQHwCG8g+DktYYzxkXRIkTiEYWBHqev0xnpCxYlqMBufKZHAHQM3/boDaI/0" app.js
```
##### Features
###### Error behavior
When a policy check fails, Node.js by default will throw an error. It is possible to change the error behavior to one of a few possibilities by defining an "onerror" field in a policy manifest. The following values are available to change the behavior:
* `"exit"`: will exit the process immediately. No cleanup code will be allowed to run.
* `"log"`: will log the error at the site of the failure.
* `"throw"`: will throw a JS error at the site of the failure. This is the default.
```
{
"onerror": "log",
"resources": {
"./app/checked.js": {
"integrity": "sha384-SggXRQHwCG8g+DktYYzxkXRIkTiEYWBHqev0xnpCxYlqMBufKZHAHQM3/boDaI/0"
}
}
}
```
###### Integrity checks
Policy files must use integrity checks with Subresource Integrity strings compatible with the browser [integrity attribute](https://www.w3.org/TR/SRI/#the-integrity-attribute) associated with absolute URLs.
When using `require()` or `import` all resources involved in loading are checked for integrity if a policy manifest has been specified. If a resource does not match the integrity listed in the manifest, an error will be thrown.
An example policy file that would allow loading a file `checked.js`:
```
{
"resources": {
"./app/checked.js": {
"integrity": "sha384-SggXRQHwCG8g+DktYYzxkXRIkTiEYWBHqev0xnpCxYlqMBufKZHAHQM3/boDaI/0"
}
}
}
```
Each resource listed in the policy manifest can be of one the following formats to determine its location:
1. A [relative-URL string](https://url.spec.whatwg.org/#relative-url-with-fragment-string) to a resource from the manifest such as `./resource.js`, `../resource.js`, or `/resource.js`.
2. A complete URL string to a resource such as `file:///resource.js`.
When loading resources the entire URL must match including search parameters and hash fragment. `./a.js?b` will not be used when attempting to load `./a.js` and vice versa.
To generate integrity strings, a script such as `node -e 'process.stdout.write("sha256-");process.stdin.pipe(crypto.createHash("sha256").setEncoding("base64")).pipe(process.stdout)' < FILE` can be used.
Integrity can be specified as the boolean value `true` to accept any body for the resource which can be useful for local development. It is not recommended in production since it would allow unexpected alteration of resources to be considered valid.
###### Dependency redirection
An application may need to ship patched versions of modules or to prevent modules from allowing all modules access to all other modules. Redirection can be used by intercepting attempts to load the modules wishing to be replaced.
```
{
"resources": {
"./app/checked.js": {
"dependencies": {
"fs": true,
"os": "./app/node_modules/alt-os",
"http": { "import": true }
}
}
}
}
```
The dependencies are keyed by the requested specifier string and have values of either `true`, `null`, a string pointing to a module to be resolved, or a conditions object.
The specifier string does not perform any searching and must match exactly what is provided to the `require()` or `import` except for a canonicalization step. Therefore, multiple specifiers may be needed in the policy if it uses multiple different strings to point to the same module (such as excluding the extension).
Specifier strings are canonicalized but not resolved prior to be used for matching in order to have some compatibility with import maps, for example if a resource `file:///C:/app/server.js` was given the following redirection from a policy located at `file:///C:/app/policy.json`:
```
{
"resources": {
"file:///C:/app/utils.js": {
"dependencies": {
"./utils.js": "./utils-v2.js"
}
}
}
}
```
Any specifier used to load `file:///C:/app/utils.js` would then be intercepted and redirected to `file:///C:/app/utils-v2.js` instead regardless of using an absolute or relative specifier. However, if a specifier that is not an absolute or relative URL string is used, it would not be intercepted. So, if an import such as `import('#utils')` was used, it would not be intercepted.
If the value of the redirection is `true`, a "dependencies" field at the top of the policy file will be used. If that field at the top of the policy file is `true` the default node searching algorithms are used to find the module.
If the value of the redirection is a string, it is resolved relative to the manifest and then immediately used without searching.
Any specifier string for which resolution is attempted and that is not listed in the dependencies results in an error according to the policy.
Redirection does not prevent access to APIs through means such as direct access to `require.cache` or through `module.constructor` which allow access to loading modules. Policy redirection only affects specifiers to `require()` and `import`. Other means, such as to prevent undesired access to APIs through variables, are necessary to lock down that path of loading modules.
A boolean value of `true` for the dependencies map can be specified to allow a module to load any specifier without redirection. This can be useful for local development and may have some valid usage in production, but should be used only with care after auditing a module to ensure its behavior is valid.
Similar to `"exports"` in `package.json`, dependencies can also be specified to be objects containing conditions which branch how dependencies are loaded. In the preceding example, `"http"` is allowed when the `"import"` condition is part of loading it.
A value of `null` for the resolved value causes the resolution to fail. This can be used to ensure some kinds of dynamic access are explicitly prevented.
Unknown values for the resolved module location cause failures but are not guaranteed to be forward compatible.
###### Example: Patched dependency
Redirected dependencies can provide attenuated or modified functionality as fits the application. For example, log data about timing of function durations by wrapping the original:
```
const original = require('fn');
module.exports = function fn(...args) {
console.time();
try {
return new.target ?
Reflect.construct(original, args) :
Reflect.apply(original, this, args);
} finally {
console.timeEnd();
}
};
```
##### Scopes
Use the `"scopes"` field of a manifest to set configuration for many resources at once. The `"scopes"` field works by matching resources by their segments. If a scope or resource includes `"cascade": true`, unknown specifiers will be searched for in their containing scope. The containing scope for cascading is found by recursively reducing the resource URL by removing segments for [special schemes](https://url.spec.whatwg.org/#special-scheme), keeping trailing `"/"` suffixes, and removing the query and hash fragment. This leads to the eventual reduction of the URL to its origin. If the URL is non-special the scope will be located by the URL's origin. If no scope is found for the origin or in the case of opaque origins, a protocol string can be used as a scope. If no scope is found for the URL's protocol, a final empty string `""` scope will be used.
Note, `blob:` URLs adopt their origin from the path they contain, and so a scope of `"blob:https://nodejs.org"` will have no effect since no URL can have an origin of `blob:https://nodejs.org`; URLs starting with `blob:https://nodejs.org/` will use `https://nodejs.org` for its origin and thus `https:` for its protocol scope. For opaque origin `blob:` URLs they will have `blob:` for their protocol scope since they do not adopt origins.
###### Example
```
{
"scopes": {
"file:///C:/app/": {},
"file:": {},
"": {}
}
}
```
Given a file located at `file:///C:/app/bin/main.js`, the following scopes would be checked in order:
1. `"file:///C:/app/bin/"`
This determines the policy for all file based resources within `"file:///C:/app/bin/"`. This is not in the `"scopes"` field of the policy and would be skipped. Adding this scope to the policy would cause it to be used prior to the `"file:///C:/app/"` scope.
2. `"file:///C:/app/"`
This determines the policy for all file based resources within `"file:///C:/app/"`. This is in the `"scopes"` field of the policy and it would determine the policy for the resource at `file:///C:/app/bin/main.js`. If the scope has `"cascade": true`, any unsatisfied queries about the resource would delegate to the next relevant scope for `file:///C:/app/bin/main.js`, `"file:"`.
3. `"file:///C:/"`
This determines the policy for all file based resources within `"file:///C:/"`. This is not in the `"scopes"` field of the policy and would be skipped. It would not be used for `file:///C:/app/bin/main.js` unless `"file:///"` is set to cascade or is not in the `"scopes"` of the policy.
4. `"file:///"`
This determines the policy for all file based resources on the `localhost`. This is not in the `"scopes"` field of the policy and would be skipped. It would not be used for `file:///C:/app/bin/main.js` unless `"file:///"` is set to cascade or is not in the `"scopes"` of the policy.
5. `"file:"`
This determines the policy for all file based resources. It would not be used for `file:///C:/app/bin/main.js` unless `"file:///"` is set to cascade or is not in the `"scopes"` of the policy.
6. `""`
This determines the policy for all resources. It would not be used for `file:///C:/app/bin/main.js` unless `"file:"` is set to cascade.
###### Integrity using scopes
Setting an integrity to `true` on a scope will set the integrity for any resource not found in the manifest to `true`.
Setting an integrity to `null` on a scope will set the integrity for any resource not found in the manifest to fail matching.
Not including an integrity is the same as setting the integrity to `null`.
`"cascade"` for integrity checks will be ignored if `"integrity"` is explicitly set.
The following example allows loading any file:
```
{
"scopes": {
"file:": {
"integrity": true
}
}
}
```
###### Dependency redirection using scopes
The following example, would allow access to `fs` for all resources within `./app/`:
```
{
"resources": {
"./app/checked.js": {
"cascade": true,
"integrity": true
}
},
"scopes": {
"./app/": {
"dependencies": {
"fs": true
}
}
}
}
```
The following example, would allow access to `fs` for all `data:` resources:
```
{
"resources": {
"data:text/javascript,import('node:fs');": {
"cascade": true,
"integrity": true
}
},
"scopes": {
"data:": {
"dependencies": {
"fs": true
}
}
}
}
```
###### Example: [import maps](https://url.spec.whatwg.org/#relative-url-with-fragment-string) emulation
Given an import map:
```
{
"imports": {
"react": "./app/node_modules/react/index.js"
},
"scopes": {
"./ssr/": {
"react": "./app/node_modules/server-side-react/index.js"
}
}
}
```
```
{
"dependencies": true,
"scopes": {
"": {
"cascade": true,
"dependencies": {
"react": "./app/node_modules/react/index.js"
}
},
"./ssr/": {
"cascade": true,
"dependencies": {
"react": "./app/node_modules/server-side-react/index.js"
}
}
}
}
```
Import maps assume you can get any resource by default. This means `"dependencies"` at the top level of the policy should be set to `true`. Policies require this to be opt-in since it enables all resources of the application cross linkage which doesn't make sense for many scenarios. They also assume any given scope has access to any scope above its allowed dependencies; all scopes emulating import maps must set `"cascade": true`.
Import maps only have a single top level scope for their "imports". So for emulating `"imports"` use the `""` scope. For emulating `"scopes"` use the `"scopes"` in a similar manner to how `"scopes"` works in import maps.
Caveats: Policies do not use string matching for various finding of scope. They do URL traversals. This means things like `blob:` and `data:` URLs might not be entirely interoperable between the two systems. For example import maps can partially match a `data:` or `blob:` URL by partitioning the URL on a `/` character, policies intentionally cannot. For `blob:` URLs import map scopes do not adopt the origin of the `blob:` URL.
Additionally, import maps only work on `import` so it may be desirable to add a `"import"` condition to all dependency mappings.
node None Diagnostics Channel
-------------------
[Stability: 1](https://nodejs.org/api/documentation.html#stability-index) - Experimental
**Source Code:** [lib/diagnostics\_channel.js](https://github.com/nodejs/node/blob/v19.0.1/lib/diagnostics_channel.js)
The `node:diagnostics_channel` module provides an API to create named channels to report arbitrary message data for diagnostics purposes.
It can be accessed using:
MJS modules
```
import diagnostics_channel from 'node:diagnostics_channel';
```
CJS modules
```
const diagnostics_channel = require('node:diagnostics_channel');
```
It is intended that a module writer wanting to report diagnostics messages will create one or many top-level channels to report messages through. Channels may also be acquired at runtime but it is not encouraged due to the additional overhead of doing so. Channels may be exported for convenience, but as long as the name is known it can be acquired anywhere.
If you intend for your module to produce diagnostics data for others to consume it is recommended that you include documentation of what named channels are used along with the shape of the message data. Channel names should generally include the module name to avoid collisions with data from other modules.
### Public API
#### Overview
Following is a simple overview of the public API.
MJS modules
```
import diagnostics_channel from 'node:diagnostics_channel';
// Get a reusable channel object
const channel = diagnostics_channel.channel('my-channel');
function onMessage(message, name) {
// Received data
}
// Subscribe to the channel
diagnostics_channel.subscribe('my-channel', onMessage);
// Check if the channel has an active subscriber
if (channel.hasSubscribers) {
// Publish data to the channel
channel.publish({
some: 'data'
});
}
// Unsubscribe from the channel
diagnostics_channel.unsubscribe('my-channel', onMessage);
```
CJS modules
```
const diagnostics_channel = require('node:diagnostics_channel');
// Get a reusable channel object
const channel = diagnostics_channel.channel('my-channel');
function onMessage(message, name) {
// Received data
}
// Subscribe to the channel
diagnostics_channel.subscribe('my-channel', onMessage);
// Check if the channel has an active subscriber
if (channel.hasSubscribers) {
// Publish data to the channel
channel.publish({
some: 'data'
});
}
// Unsubscribe from the channel
diagnostics_channel.unsubscribe('my-channel', onMessage);
```
#####
`diagnostics_channel.hasSubscribers(name)`
Added in: v15.1.0, v14.17.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The channel name
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If there are active subscribers
Check if there are active subscribers to the named channel. This is helpful if the message you want to send might be expensive to prepare.
This API is optional but helpful when trying to publish messages from very performance-sensitive code.
MJS modules
```
import diagnostics_channel from 'node:diagnostics_channel';
if (diagnostics_channel.hasSubscribers('my-channel')) {
// There are subscribers, prepare and publish message
}
```
CJS modules
```
const diagnostics_channel = require('node:diagnostics_channel');
if (diagnostics_channel.hasSubscribers('my-channel')) {
// There are subscribers, prepare and publish message
}
```
#####
`diagnostics_channel.channel(name)`
Added in: v15.1.0, v14.17.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The channel name
* Returns: [<Channel>](diagnostics_channel#class-channel) The named channel object
This is the primary entry-point for anyone wanting to publish to a named channel. It produces a channel object which is optimized to reduce overhead at publish time as much as possible.
MJS modules
```
import diagnostics_channel from 'node:diagnostics_channel';
const channel = diagnostics_channel.channel('my-channel');
```
CJS modules
```
const diagnostics_channel = require('node:diagnostics_channel');
const channel = diagnostics_channel.channel('my-channel');
```
#####
`diagnostics_channel.subscribe(name, onMessage)`
Added in: v18.7.0, v16.17.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The channel name
* `onMessage` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The handler to receive channel messages
+ `message` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The message data
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The name of the channel
Register a message handler to subscribe to this channel. This message handler will be run synchronously whenever a message is published to the channel. Any errors thrown in the message handler will trigger an [`'uncaughtException'`](process#event-uncaughtexception).
MJS modules
```
import diagnostics_channel from 'diagnostics_channel';
diagnostics_channel.subscribe('my-channel', (message, name) => {
// Received data
});
```
CJS modules
```
const diagnostics_channel = require('diagnostics_channel');
diagnostics_channel.subscribe('my-channel', (message, name) => {
// Received data
});
```
#####
`diagnostics_channel.unsubscribe(name, onMessage)`
Added in: v18.7.0, v16.17.0 * `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The channel name
* `onMessage` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The previous subscribed handler to remove
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the handler was found, `false` otherwise.
Remove a message handler previously registered to this channel with [`diagnostics_channel.subscribe(name, onMessage)`](#diagnostics_channelsubscribename-onmessage).
MJS modules
```
import diagnostics_channel from 'diagnostics_channel';
function onMessage(message, name) {
// Received data
}
diagnostics_channel.subscribe('my-channel', onMessage);
diagnostics_channel.unsubscribe('my-channel', onMessage);
```
CJS modules
```
const diagnostics_channel = require('diagnostics_channel');
function onMessage(message, name) {
// Received data
}
diagnostics_channel.subscribe('my-channel', onMessage);
diagnostics_channel.unsubscribe('my-channel', onMessage);
```
#### Class: `Channel`
Added in: v15.1.0, v14.17.0 The class `Channel` represents an individual named channel within the data pipeline. It is used to track subscribers and to publish messages when there are subscribers present. It exists as a separate object to avoid channel lookups at publish time, enabling very fast publish speeds and allowing for heavy use while incurring very minimal cost. Channels are created with [`diagnostics_channel.channel(name)`](#diagnostics_channelchannelname), constructing a channel directly with `new Channel(name)` is not supported.
#####
`channel.hasSubscribers`
Added in: v15.1.0, v14.17.0 * Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) If there are active subscribers
Check if there are active subscribers to this channel. This is helpful if the message you want to send might be expensive to prepare.
This API is optional but helpful when trying to publish messages from very performance-sensitive code.
MJS modules
```
import diagnostics_channel from 'node:diagnostics_channel';
const channel = diagnostics_channel.channel('my-channel');
if (channel.hasSubscribers) {
// There are subscribers, prepare and publish message
}
```
CJS modules
```
const diagnostics_channel = require('node:diagnostics_channel');
const channel = diagnostics_channel.channel('my-channel');
if (channel.hasSubscribers) {
// There are subscribers, prepare and publish message
}
```
#####
`channel.publish(message)`
Added in: v15.1.0, v14.17.0 * `message` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The message to send to the channel subscribers
Publish a message to any subscribers to the channel. This will trigger message handlers synchronously so they will execute within the same context.
MJS modules
```
import diagnostics_channel from 'node:diagnostics_channel';
const channel = diagnostics_channel.channel('my-channel');
channel.publish({
some: 'message'
});
```
CJS modules
```
const diagnostics_channel = require('node:diagnostics_channel');
const channel = diagnostics_channel.channel('my-channel');
channel.publish({
some: 'message'
});
```
#####
`channel.subscribe(onMessage)`
Added in: v15.1.0, v14.17.0Deprecated since: v18.7.0, v16.17.0
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`diagnostics_channel.subscribe(name, onMessage)`](#diagnostics_channelsubscribename-onmessage)
* `onMessage` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The handler to receive channel messages
+ `message` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types) The message data
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) | [<symbol>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type) The name of the channel
Register a message handler to subscribe to this channel. This message handler will be run synchronously whenever a message is published to the channel. Any errors thrown in the message handler will trigger an [`'uncaughtException'`](process#event-uncaughtexception).
MJS modules
```
import diagnostics_channel from 'node:diagnostics_channel';
const channel = diagnostics_channel.channel('my-channel');
channel.subscribe((message, name) => {
// Received data
});
```
CJS modules
```
const diagnostics_channel = require('node:diagnostics_channel');
const channel = diagnostics_channel.channel('my-channel');
channel.subscribe((message, name) => {
// Received data
});
```
#####
`channel.unsubscribe(onMessage)`
History
| Version | Changes |
| --- | --- |
| v18.7.0, v16.17.0 | Deprecated since: v18.7.0, v16.17.0 |
| v15.1.0, v14.17.0 | Added in: v15.1.0, v14.17.0 |
| v17.1.0, v16.14.0, v14.19.0 | Added return value. Added to channels without subscribers. |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated: Use [`diagnostics_channel.unsubscribe(name, onMessage)`](#diagnostics_channelunsubscribename-onmessage)
* `onMessage` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The previous subscribed handler to remove
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type) `true` if the handler was found, `false` otherwise.
Remove a message handler previously registered to this channel with [`channel.subscribe(onMessage)`](#channelsubscribeonmessage).
MJS modules
```
import diagnostics_channel from 'node:diagnostics_channel';
const channel = diagnostics_channel.channel('my-channel');
function onMessage(message, name) {
// Received data
}
channel.subscribe(onMessage);
channel.unsubscribe(onMessage);
```
CJS modules
```
const diagnostics_channel = require('node:diagnostics_channel');
const channel = diagnostics_channel.channel('my-channel');
function onMessage(message, name) {
// Received data
}
channel.subscribe(onMessage);
channel.unsubscribe(onMessage);
```
#### Built-in Channels
##### HTTP
`http.client.request.start`
* `request` [<http.ClientRequest>](http#class-httpclientrequest)
Emitted when client starts a request.
`http.client.response.finish`
* `request` [<http.ClientRequest>](http#class-httpclientrequest)
* `response` [<http.IncomingMessage>](http#class-httpincomingmessage)
Emitted when client receives a response.
`http.server.request.start`
* `request` [<http.IncomingMessage>](http#class-httpincomingmessage)
* `response` [<http.ServerResponse>](http#class-httpserverresponse)
* `socket` [<net.Socket>](net#class-netsocket)
* `server` [<http.Server>](http#class-httpserver)
Emitted when server receives a request.
`http.server.response.finish`
* `request` [<http.IncomingMessage>](http#class-httpincomingmessage)
* `response` [<http.ServerResponse>](http#class-httpserverresponse)
* `socket` [<net.Socket>](net#class-netsocket)
* `server` [<http.Server>](http#class-httpserver)
Emitted when server sends a response.
##### NET
`net.client.socket`
* `socket` [<net.Socket>](net#class-netsocket)
Emitted when a new TCP or pipe client socket is created.
`net.server.socket`
* `socket` [<net.Socket>](net#class-netsocket)
Emitted when a new TCP or pipe connection is received.
##### UDP
`udp.socket`
* `socket` [<dgram.Socket>](dgram#class-dgramsocket)
Emitted when a new UDP socket is created.
##### Process
Added in: v16.18.0 `child_process`
* `process` [<ChildProcess>](child_process#class-childprocess)
Emitted when a new process is created.
##### Worker Thread
Added in: v16.18.0 `worker_threads`
* `worker` [`Worker`](worker_threads#class-worker)
Emitted when a new thread is created.
| programming_docs |
node None Domain
------
History
| Version | Changes |
| --- | --- |
| v8.8.0 | Any `Promise`s created in VM contexts no longer have a `.domain` property. Their handlers are still executed in the proper domain, however, and `Promise`s created in the main context still possess a `.domain` property. |
| v8.0.0 | Handlers for `Promise`s are now invoked in the domain in which the first promise of a chain was created. |
| v1.4.2 | Deprecated since: v1.4.2 |
[Stability: 0](https://nodejs.org/api/documentation.html#stability-index) - Deprecated
**Source Code:** [lib/domain.js](https://github.com/nodejs/node/blob/v19.0.1/lib/domain.js)
**This module is pending deprecation.** Once a replacement API has been finalized, this module will be fully deprecated. Most developers should **not** have cause to use this module. Users who absolutely must have the functionality that domains provide may rely on it for the time being but should expect to have to migrate to a different solution in the future.
Domains provide a way to handle multiple different IO operations as a single group. If any of the event emitters or callbacks registered to a domain emit an `'error'` event, or throw an error, then the domain object will be notified, rather than losing the context of the error in the `process.on('uncaughtException')` handler, or causing the program to exit immediately with an error code.
### Warning: Don't ignore errors!
Domain error handlers are not a substitute for closing down a process when an error occurs.
By the very nature of how [`throw`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/throw) works in JavaScript, there is almost never any way to safely "pick up where it left off", without leaking references, or creating some other sort of undefined brittle state.
The safest way to respond to a thrown error is to shut down the process. Of course, in a normal web server, there may be many open connections, and it is not reasonable to abruptly shut those down because an error was triggered by someone else.
The better approach is to send an error response to the request that triggered the error, while letting the others finish in their normal time, and stop listening for new requests in that worker.
In this way, `domain` usage goes hand-in-hand with the cluster module, since the primary process can fork a new worker when a worker encounters an error. For Node.js programs that scale to multiple machines, the terminating proxy or service registry can take note of the failure, and react accordingly.
For example, this is not a good idea:
```
// XXX WARNING! BAD IDEA!
const d = require('node:domain').create();
d.on('error', (er) => {
// The error won't crash the process, but what it does is worse!
// Though we've prevented abrupt process restarting, we are leaking
// a lot of resources if this ever happens.
// This is no better than process.on('uncaughtException')!
console.log(`error, but oh well ${er.message}`);
});
d.run(() => {
require('node:http').createServer((req, res) => {
handleRequest(req, res);
}).listen(PORT);
});
```
By using the context of a domain, and the resilience of separating our program into multiple worker processes, we can react more appropriately, and handle errors with much greater safety.
```
// Much better!
const cluster = require('node:cluster');
const PORT = +process.env.PORT || 1337;
if (cluster.isPrimary) {
// A more realistic scenario would have more than 2 workers,
// and perhaps not put the primary and worker in the same file.
//
// It is also possible to get a bit fancier about logging, and
// implement whatever custom logic is needed to prevent DoS
// attacks and other bad behavior.
//
// See the options in the cluster documentation.
//
// The important thing is that the primary does very little,
// increasing our resilience to unexpected errors.
cluster.fork();
cluster.fork();
cluster.on('disconnect', (worker) => {
console.error('disconnect!');
cluster.fork();
});
} else {
// the worker
//
// This is where we put our bugs!
const domain = require('node:domain');
// See the cluster documentation for more details about using
// worker processes to serve requests. How it works, caveats, etc.
const server = require('node:http').createServer((req, res) => {
const d = domain.create();
d.on('error', (er) => {
console.error(`error ${er.stack}`);
// We're in dangerous territory!
// By definition, something unexpected occurred,
// which we probably didn't want.
// Anything can happen now! Be very careful!
try {
// Make sure we close down within 30 seconds
const killtimer = setTimeout(() => {
process.exit(1);
}, 30000);
// But don't keep the process open just for that!
killtimer.unref();
// Stop taking new requests.
server.close();
// Let the primary know we're dead. This will trigger a
// 'disconnect' in the cluster primary, and then it will fork
// a new worker.
cluster.worker.disconnect();
// Try to send an error to the request that triggered the problem
res.statusCode = 500;
res.setHeader('content-type', 'text/plain');
res.end('Oops, there was a problem!\n');
} catch (er2) {
// Oh well, not much we can do at this point.
console.error(`Error sending 500! ${er2.stack}`);
}
});
// Because req and res were created before this domain existed,
// we need to explicitly add them.
// See the explanation of implicit vs explicit binding below.
d.add(req);
d.add(res);
// Now run the handler function in the domain.
d.run(() => {
handleRequest(req, res);
});
});
server.listen(PORT);
}
// This part is not important. Just an example routing thing.
// Put fancy application logic here.
function handleRequest(req, res) {
switch (req.url) {
case '/error':
// We do some async stuff, and then...
setTimeout(() => {
// Whoops!
flerb.bark();
}, timeout);
break;
default:
res.end('ok');
}
}
```
### Additions to `Error` objects
Any time an `Error` object is routed through a domain, a few extra fields are added to it.
* `error.domain` The domain that first handled the error.
* `error.domainEmitter` The event emitter that emitted an `'error'` event with the error object.
* `error.domainBound` The callback function which was bound to the domain, and passed an error as its first argument.
* `error.domainThrown` A boolean indicating whether the error was thrown, emitted, or passed to a bound callback function.
### Implicit binding
If domains are in use, then all **new** `EventEmitter` objects (including Stream objects, requests, responses, etc.) will be implicitly bound to the active domain at the time of their creation.
Additionally, callbacks passed to lowlevel event loop requests (such as to `fs.open()`, or other callback-taking methods) will automatically be bound to the active domain. If they throw, then the domain will catch the error.
In order to prevent excessive memory usage, `Domain` objects themselves are not implicitly added as children of the active domain. If they were, then it would be too easy to prevent request and response objects from being properly garbage collected.
To nest `Domain` objects as children of a parent `Domain` they must be explicitly added.
Implicit binding routes thrown errors and `'error'` events to the `Domain`'s `'error'` event, but does not register the `EventEmitter` on the `Domain`. Implicit binding only takes care of thrown errors and `'error'` events.
### Explicit binding
Sometimes, the domain in use is not the one that ought to be used for a specific event emitter. Or, the event emitter could have been created in the context of one domain, but ought to instead be bound to some other domain.
For example, there could be one domain in use for an HTTP server, but perhaps we would like to have a separate domain to use for each request.
That is possible via explicit binding.
```
// Create a top-level domain for the server
const domain = require('node:domain');
const http = require('node:http');
const serverDomain = domain.create();
serverDomain.run(() => {
// Server is created in the scope of serverDomain
http.createServer((req, res) => {
// Req and res are also created in the scope of serverDomain
// however, we'd prefer to have a separate domain for each request.
// create it first thing, and add req and res to it.
const reqd = domain.create();
reqd.add(req);
reqd.add(res);
reqd.on('error', (er) => {
console.error('Error', er, req.url);
try {
res.writeHead(500);
res.end('Error occurred, sorry.');
} catch (er2) {
console.error('Error sending 500', er2, req.url);
}
});
}).listen(1337);
});
```
###
`domain.create()`
* Returns: [<Domain>](domain#class-domain)
### Class: `Domain`
* Extends: [<EventEmitter>](events#class-eventemitter)
The `Domain` class encapsulates the functionality of routing errors and uncaught exceptions to the active `Domain` object.
To handle the errors that it catches, listen to its `'error'` event.
####
`domain.members`
* [<Array>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)
An array of timers and event emitters that have been explicitly added to the domain.
####
`domain.add(emitter)`
* `emitter` [<EventEmitter>](events#class-eventemitter) | [<Timer>](timers#timers) emitter or timer to be added to the domain
Explicitly adds an emitter to the domain. If any event handlers called by the emitter throw an error, or if the emitter emits an `'error'` event, it will be routed to the domain's `'error'` event, just like with implicit binding.
This also works with timers that are returned from [`setInterval()`](timers#setintervalcallback-delay-args) and [`setTimeout()`](timers#settimeoutcallback-delay-args). If their callback function throws, it will be caught by the domain `'error'` handler.
If the Timer or `EventEmitter` was already bound to a domain, it is removed from that one, and bound to this one instead.
####
`domain.bind(callback)`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The callback function
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The bound function
The returned function will be a wrapper around the supplied callback function. When the returned function is called, any errors that are thrown will be routed to the domain's `'error'` event.
```
const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.bind((er, data) => {
// If this throws, it will also be passed to the domain.
return cb(er, data ? JSON.parse(data) : null);
}));
}
d.on('error', (er) => {
// An error occurred somewhere. If we throw it now, it will crash the program
// with the normal line number and stack message.
});
```
####
`domain.enter()`
The `enter()` method is plumbing used by the `run()`, `bind()`, and `intercept()` methods to set the active domain. It sets `domain.active` and `process.domain` to the domain, and implicitly pushes the domain onto the domain stack managed by the domain module (see [`domain.exit()`](#domainexit) for details on the domain stack). The call to `enter()` delimits the beginning of a chain of asynchronous calls and I/O operations bound to a domain.
Calling `enter()` changes only the active domain, and does not alter the domain itself. `enter()` and `exit()` can be called an arbitrary number of times on a single domain.
####
`domain.exit()`
The `exit()` method exits the current domain, popping it off the domain stack. Any time execution is going to switch to the context of a different chain of asynchronous calls, it's important to ensure that the current domain is exited. The call to `exit()` delimits either the end of or an interruption to the chain of asynchronous calls and I/O operations bound to a domain.
If there are multiple, nested domains bound to the current execution context, `exit()` will exit any domains nested within this domain.
Calling `exit()` changes only the active domain, and does not alter the domain itself. `enter()` and `exit()` can be called an arbitrary number of times on a single domain.
####
`domain.intercept(callback)`
* `callback` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The callback function
* Returns: [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) The intercepted function
This method is almost identical to [`domain.bind(callback)`](#domainbindcallback). However, in addition to catching thrown errors, it will also intercept [`Error`](errors#class-error) objects sent as the first argument to the function.
In this way, the common `if (err) return callback(err);` pattern can be replaced with a single error handler in a single place.
```
const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.intercept((data) => {
// Note, the first argument is never passed to the
// callback since it is assumed to be the 'Error' argument
// and thus intercepted by the domain.
// If this throws, it will also be passed to the domain
// so the error-handling logic can be moved to the 'error'
// event on the domain instead of being repeated throughout
// the program.
return cb(null, JSON.parse(data));
}));
}
d.on('error', (er) => {
// An error occurred somewhere. If we throw it now, it will crash the program
// with the normal line number and stack message.
});
```
####
`domain.remove(emitter)`
* `emitter` [<EventEmitter>](events#class-eventemitter) | [<Timer>](timers#timers) emitter or timer to be removed from the domain
The opposite of [`domain.add(emitter)`](#domainaddemitter). Removes domain handling from the specified emitter.
####
`domain.run(fn[, ...args])`
* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
* `...args` [<any>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types)
Run the supplied function in the context of the domain, implicitly binding all event emitters, timers, and lowlevel requests that are created in that context. Optionally, arguments can be passed to the function.
This is the most basic way to use a domain.
```
const domain = require('node:domain');
const fs = require('node:fs');
const d = domain.create();
d.on('error', (er) => {
console.error('Caught error!', er);
});
d.run(() => {
process.nextTick(() => {
setTimeout(() => { // Simulating some various async stuff
fs.open('non-existent file', 'r', (er, fd) => {
if (er) throw er;
// proceed...
});
}, 100);
});
});
```
In this example, the `d.on('error')` handler will be triggered, rather than crashing the program.
### Domains and promises
As of Node.js 8.0.0, the handlers of promises are run inside the domain in which the call to `.then()` or `.catch()` itself was made:
```
const d1 = domain.create();
const d2 = domain.create();
let p;
d1.run(() => {
p = Promise.resolve(42);
});
d2.run(() => {
p.then((v) => {
// running in d2
});
});
```
A callback may be bound to a specific domain using [`domain.bind(callback)`](#domainbindcallback):
```
const d1 = domain.create();
const d2 = domain.create();
let p;
d1.run(() => {
p = Promise.resolve(42);
});
d2.run(() => {
p.then(p.domain.bind((v) => {
// running in d1
}));
});
```
Domains will not interfere with the error handling mechanisms for promises. In other words, no `'error'` event will be emitted for unhandled `Promise` rejections.
node None Path
----
[Stability: 2](https://nodejs.org/api/documentation.html#stability-index) - Stable
**Source Code:** [lib/path.js](https://github.com/nodejs/node/blob/v19.0.1/lib/path.js)
The `node:path` module provides utilities for working with file and directory paths. It can be accessed using:
```
const path = require('node:path');
```
### Windows vs. POSIX
The default operation of the `node:path` module varies based on the operating system on which a Node.js application is running. Specifically, when running on a Windows operating system, the `node:path` module will assume that Windows-style paths are being used.
So using `path.basename()` might yield different results on POSIX and Windows:
On POSIX:
```
path.basename('C:\\temp\\myfile.html');
// Returns: 'C:\\temp\\myfile.html'
```
On Windows:
```
path.basename('C:\\temp\\myfile.html');
// Returns: 'myfile.html'
```
To achieve consistent results when working with Windows file paths on any operating system, use [`path.win32`](#pathwin32):
On POSIX and Windows:
```
path.win32.basename('C:\\temp\\myfile.html');
// Returns: 'myfile.html'
```
To achieve consistent results when working with POSIX file paths on any operating system, use [`path.posix`](#pathposix):
On POSIX and Windows:
```
path.posix.basename('/tmp/myfile.html');
// Returns: 'myfile.html'
```
On Windows Node.js follows the concept of per-drive working directory. This behavior can be observed when using a drive path without a backslash. For example, `path.resolve('C:\\')` can potentially return a different result than `path.resolve('C:')`. For more information, see [this MSDN page](https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file#fully-qualified-vs-relative-paths).
###
`path.basename(path[, suffix])`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | Passing a non-string as the `path` argument will throw now. |
| v0.1.25 | Added in: v0.1.25 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `suffix` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) An optional suffix to remove
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `path.basename()` method returns the last portion of a `path`, similar to the Unix `basename` command. Trailing [directory separators](#pathsep) are ignored.
```
path.basename('/foo/bar/baz/asdf/quux.html');
// Returns: 'quux.html'
path.basename('/foo/bar/baz/asdf/quux.html', '.html');
// Returns: 'quux'
```
Although Windows usually treats file names, including file extensions, in a case-insensitive manner, this function does not. For example, `C:\\foo.html` and `C:\\foo.HTML` refer to the same file, but `basename` treats the extension as a case-sensitive string:
```
path.win32.basename('C:\\foo.html', '.html');
// Returns: 'foo'
path.win32.basename('C:\\foo.HTML', '.html');
// Returns: 'foo.HTML'
```
A [`TypeError`](errors#class-typeerror) is thrown if `path` is not a string or if `suffix` is given and is not a string.
###
`path.delimiter`
Added in: v0.9.3 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Provides the platform-specific path delimiter:
* `;` for Windows
* `:` for POSIX
For example, on POSIX:
```
console.log(process.env.PATH);
// Prints: '/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin'
process.env.PATH.split(path.delimiter);
// Returns: ['/usr/bin', '/bin', '/usr/sbin', '/sbin', '/usr/local/bin']
```
On Windows:
```
console.log(process.env.PATH);
// Prints: 'C:\Windows\system32;C:\Windows;C:\Program Files\node\'
process.env.PATH.split(path.delimiter);
// Returns ['C:\\Windows\\system32', 'C:\\Windows', 'C:\\Program Files\\node\\']
```
###
`path.dirname(path)`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | Passing a non-string as the `path` argument will throw now. |
| v0.1.16 | Added in: v0.1.16 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `path.dirname()` method returns the directory name of a `path`, similar to the Unix `dirname` command. Trailing directory separators are ignored, see [`path.sep`](#pathsep).
```
path.dirname('/foo/bar/baz/asdf/quux');
// Returns: '/foo/bar/baz/asdf'
```
A [`TypeError`](errors#class-typeerror) is thrown if `path` is not a string.
###
`path.extname(path)`
History
| Version | Changes |
| --- | --- |
| v6.0.0 | Passing a non-string as the `path` argument will throw now. |
| v0.1.25 | Added in: v0.1.25 |
* `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `path.extname()` method returns the extension of the `path`, from the last occurrence of the `.` (period) character to end of string in the last portion of the `path`. If there is no `.` in the last portion of the `path`, or if there are no `.` characters other than the first character of the basename of `path` (see `path.basename()`) , an empty string is returned.
```
path.extname('index.html');
// Returns: '.html'
path.extname('index.coffee.md');
// Returns: '.md'
path.extname('index.');
// Returns: '.'
path.extname('index');
// Returns: ''
path.extname('.index');
// Returns: ''
path.extname('.index.md');
// Returns: '.md'
```
A [`TypeError`](errors#class-typeerror) is thrown if `path` is not a string.
###
`path.format(pathObject)`
History
| Version | Changes |
| --- | --- |
| v19.0.0 | The dot will be added if it is not specified in `ext`. |
| v0.11.15 | Added in: v0.11.15 |
* `pathObject` [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) Any JavaScript object having the following properties:
+ `dir` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `root` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `base` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
+ `ext` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `path.format()` method returns a path string from an object. This is the opposite of [`path.parse()`](#pathparsepath).
When providing properties to the `pathObject` remember that there are combinations where one property has priority over another:
* `pathObject.root` is ignored if `pathObject.dir` is provided
* `pathObject.ext` and `pathObject.name` are ignored if `pathObject.base` exists
For example, on POSIX:
```
// If `dir`, `root` and `base` are provided,
// `${dir}${path.sep}${base}`
// will be returned. `root` is ignored.
path.format({
root: '/ignored',
dir: '/home/user/dir',
base: 'file.txt'
});
// Returns: '/home/user/dir/file.txt'
// `root` will be used if `dir` is not specified.
// If only `root` is provided or `dir` is equal to `root` then the
// platform separator will not be included. `ext` will be ignored.
path.format({
root: '/',
base: 'file.txt',
ext: 'ignored'
});
// Returns: '/file.txt'
// `name` + `ext` will be used if `base` is not specified.
path.format({
root: '/',
name: 'file',
ext: '.txt'
});
// Returns: '/file.txt'
// The dot will be added if it is not specified in `ext`.
path.format({
root: '/',
name: 'file',
ext: 'txt'
});
// Returns: '/file.txt'
```
On Windows:
```
path.format({
dir: 'C:\\path\\dir',
base: 'file.txt'
});
// Returns: 'C:\\path\\dir\\file.txt'
```
###
`path.isAbsolute(path)`
Added in: v0.11.2 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
The `path.isAbsolute()` method determines if `path` is an absolute path.
If the given `path` is a zero-length string, `false` will be returned.
For example, on POSIX:
```
path.isAbsolute('/foo/bar'); // true
path.isAbsolute('/baz/..'); // true
path.isAbsolute('qux/'); // false
path.isAbsolute('.'); // false
```
On Windows:
```
path.isAbsolute('//server'); // true
path.isAbsolute('\\\\server'); // true
path.isAbsolute('C:/foo/..'); // true
path.isAbsolute('C:\\foo\\..'); // true
path.isAbsolute('bar\\baz'); // false
path.isAbsolute('bar/baz'); // false
path.isAbsolute('.'); // false
```
A [`TypeError`](errors#class-typeerror) is thrown if `path` is not a string.
###
`path.join([...paths])`
Added in: v0.1.16 * `...paths` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A sequence of path segments
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `path.join()` method joins all given `path` segments together using the platform-specific separator as a delimiter, then normalizes the resulting path.
Zero-length `path` segments are ignored. If the joined path string is a zero-length string then `'.'` will be returned, representing the current working directory.
```
path.join('/foo', 'bar', 'baz/asdf', 'quux', '..');
// Returns: '/foo/bar/baz/asdf'
path.join('foo', {}, 'bar');
// Throws 'TypeError: Path must be a string. Received {}'
```
A [`TypeError`](errors#class-typeerror) is thrown if any of the path segments is not a string.
###
`path.normalize(path)`
Added in: v0.1.23 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `path.normalize()` method normalizes the given `path`, resolving `'..'` and `'.'` segments.
When multiple, sequential path segment separation characters are found (e.g. `/` on POSIX and either `\` or `/` on Windows), they are replaced by a single instance of the platform-specific path segment separator (`/` on POSIX and `\` on Windows). Trailing separators are preserved.
If the `path` is a zero-length string, `'.'` is returned, representing the current working directory.
For example, on POSIX:
```
path.normalize('/foo/bar//baz/asdf/quux/..');
// Returns: '/foo/bar/baz/asdf'
```
On Windows:
```
path.normalize('C:\\temp\\\\foo\\bar\\..\\');
// Returns: 'C:\\temp\\foo\\'
```
Since Windows recognizes multiple path separators, both separators will be replaced by instances of the Windows preferred separator (`\`):
```
path.win32.normalize('C:////temp\\\\/\\/\\/foo/bar');
// Returns: 'C:\\temp\\foo\\bar'
```
A [`TypeError`](errors#class-typeerror) is thrown if `path` is not a string.
###
`path.parse(path)`
Added in: v0.11.15 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `path.parse()` method returns an object whose properties represent significant elements of the `path`. Trailing directory separators are ignored, see [`path.sep`](#pathsep).
The returned object will have the following properties:
* `dir` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `root` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `base` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `name` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `ext` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
For example, on POSIX:
```
path.parse('/home/user/dir/file.txt');
// Returns:
// { root: '/',
// dir: '/home/user/dir',
// base: 'file.txt',
// ext: '.txt',
// name: 'file' }
```
```
┌─────────────────────┬────────────┐
│ dir │ base │
├──────┬ ├──────┬─────┤
│ root │ │ name │ ext │
" / home/user/dir / file .txt "
└──────┴──────────────┴──────┴─────┘
(All spaces in the "" line should be ignored. They are purely for formatting.)
```
On Windows:
```
path.parse('C:\\path\\dir\\file.txt');
// Returns:
// { root: 'C:\\',
// dir: 'C:\\path\\dir',
// base: 'file.txt',
// ext: '.txt',
// name: 'file' }
```
```
┌─────────────────────┬────────────┐
│ dir │ base │
├──────┬ ├──────┬─────┤
│ root │ │ name │ ext │
" C:\ path\dir \ file .txt "
└──────┴──────────────┴──────┴─────┘
(All spaces in the "" line should be ignored. They are purely for formatting.)
```
A [`TypeError`](errors#class-typeerror) is thrown if `path` is not a string.
###
`path.posix`
History
| Version | Changes |
| --- | --- |
| v15.3.0 | Exposed as `require('path/posix')`. |
| v0.11.15 | Added in: v0.11.15 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `path.posix` property provides access to POSIX specific implementations of the `path` methods.
The API is accessible via `require('node:path').posix` or `require('node:path/posix')`.
###
`path.relative(from, to)`
History
| Version | Changes |
| --- | --- |
| v6.8.0 | On Windows, the leading slashes for UNC paths are now included in the return value. |
| v0.5.0 | Added in: v0.5.0 |
* `from` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* `to` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `path.relative()` method returns the relative path from `from` to `to` based on the current working directory. If `from` and `to` each resolve to the same path (after calling `path.resolve()` on each), a zero-length string is returned.
If a zero-length string is passed as `from` or `to`, the current working directory will be used instead of the zero-length strings.
For example, on POSIX:
```
path.relative('/data/orandea/test/aaa', '/data/orandea/impl/bbb');
// Returns: '../../impl/bbb'
```
On Windows:
```
path.relative('C:\\orandea\\test\\aaa', 'C:\\orandea\\impl\\bbb');
// Returns: '..\\..\\impl\\bbb'
```
A [`TypeError`](errors#class-typeerror) is thrown if either `from` or `to` is not a string.
###
`path.resolve([...paths])`
Added in: v0.3.4 * `...paths` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) A sequence of paths or path segments
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
The `path.resolve()` method resolves a sequence of paths or path segments into an absolute path.
The given sequence of paths is processed from right to left, with each subsequent `path` prepended until an absolute path is constructed. For instance, given the sequence of path segments: `/foo`, `/bar`, `baz`, calling `path.resolve('/foo', '/bar', 'baz')` would return `/bar/baz` because `'baz'` is not an absolute path but `'/bar' + '/' + 'baz'` is.
If, after processing all given `path` segments, an absolute path has not yet been generated, the current working directory is used.
The resulting path is normalized and trailing slashes are removed unless the path is resolved to the root directory.
Zero-length `path` segments are ignored.
If no `path` segments are passed, `path.resolve()` will return the absolute path of the current working directory.
```
path.resolve('/foo/bar', './baz');
// Returns: '/foo/bar/baz'
path.resolve('/foo/bar', '/tmp/file/');
// Returns: '/tmp/file'
path.resolve('wwwroot', 'static_files/png/', '../gif/image.gif');
// If the current working directory is /home/myself/node,
// this returns '/home/myself/node/wwwroot/static_files/gif/image.gif'
```
A [`TypeError`](errors#class-typeerror) is thrown if any of the arguments is not a string.
###
`path.sep`
Added in: v0.7.9 * [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
Provides the platform-specific path segment separator:
* `\` on Windows
* `/` on POSIX
For example, on POSIX:
```
'foo/bar/baz'.split(path.sep);
// Returns: ['foo', 'bar', 'baz']
```
On Windows:
```
'foo\\bar\\baz'.split(path.sep);
// Returns: ['foo', 'bar', 'baz']
```
On Windows, both the forward slash (`/`) and backward slash (`\`) are accepted as path segment separators; however, the `path` methods only add backward slashes (`\`).
###
`path.toNamespacedPath(path)`
Added in: v9.0.0 * `path` [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
* Returns: [<string>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
On Windows systems only, returns an equivalent [namespace-prefixed path](https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file#namespaces) for the given `path`. If `path` is not a string, `path` will be returned without modifications.
This method is meaningful only on Windows systems. On POSIX systems, the method is non-operational and always returns `path` without modifications.
###
`path.win32`
History
| Version | Changes |
| --- | --- |
| v15.3.0 | Exposed as `require('path/win32')`. |
| v0.11.15 | Added in: v0.11.15 |
* [<Object>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
The `path.win32` property provides access to Windows-specific implementations of the `path` methods.
The API is accessible via `require('node:path').win32` or `require('node:path/win32')`.
| programming_docs |
perl Scalar::Util Scalar::Util
============
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [Core Perl builtin Functions](#Core-Perl-builtin-Functions)
* [FUNCTIONS FOR REFERENCES](#FUNCTIONS-FOR-REFERENCES)
+ [blessed](#blessed)
+ [refaddr](#refaddr)
+ [reftype](#reftype)
+ [weaken](#weaken)
+ [unweaken](#unweaken)
+ [isweak](#isweak)
* [OTHER FUNCTIONS](#OTHER-FUNCTIONS)
+ [dualvar](#dualvar)
+ [isdual](#isdual)
+ [isvstring](#isvstring)
+ [looks\_like\_number](#looks_like_number)
+ [openhandle](#openhandle)
+ [readonly](#readonly)
+ [set\_prototype](#set_prototype)
+ [tainted](#tainted)
* [DIAGNOSTICS](#DIAGNOSTICS)
* [KNOWN BUGS](#KNOWN-BUGS)
* [SEE ALSO](#SEE-ALSO)
* [COPYRIGHT](#COPYRIGHT)
NAME
----
Scalar::Util - A selection of general-utility scalar subroutines
SYNOPSIS
--------
```
use Scalar::Util qw(blessed dualvar isdual readonly refaddr reftype
tainted weaken isweak isvstring looks_like_number
set_prototype);
# and other useful utils appearing below
```
DESCRIPTION
-----------
`Scalar::Util` contains a selection of subroutines that people have expressed would be nice to have in the perl core, but the usage would not really be high enough to warrant the use of a keyword, and the size would be so small that being individual extensions would be wasteful.
By default `Scalar::Util` does not export any subroutines.
###
Core Perl `builtin` Functions
Many functions in this module have served as the inspiration for a new experimental facility in recent versions of Perl. From various development versions, starting at 5.35.7, equivalent functions to many of these utilities are available in the `builtin::` package.
```
use Scalar::Util qw(blessed);
$class = blessed $obj;
$class = builtin::blessed $obj; # equivalent
```
For more information, see the documentation on <builtin>.
FUNCTIONS FOR REFERENCES
-------------------------
The following functions all perform some useful activity on reference values.
### blessed
```
my $pkg = blessed( $ref );
```
If `$ref` is a blessed reference, the name of the package that it is blessed into is returned. Otherwise `undef` is returned.
```
$scalar = "foo";
$class = blessed $scalar; # undef
$ref = [];
$class = blessed $ref; # undef
$obj = bless [], "Foo";
$class = blessed $obj; # "Foo"
```
Take care when using this function simply as a truth test (such as in `if(blessed $ref)...`) because the package name `"0"` is defined yet false.
*Since Perl version 5.35.7* an equivalent function is available as `builtin::blessed`.
### refaddr
```
my $addr = refaddr( $ref );
```
If `$ref` is reference, the internal memory address of the referenced value is returned as a plain integer. Otherwise `undef` is returned.
```
$addr = refaddr "string"; # undef
$addr = refaddr \$var; # eg 12345678
$addr = refaddr []; # eg 23456784
$obj = bless {}, "Foo";
$addr = refaddr $obj; # eg 88123488
```
*Since Perl version 5.35.7* an equivalent function is available as `builtin::refaddr`.
### reftype
```
my $type = reftype( $ref );
```
If `$ref` is a reference, the basic Perl type of the variable referenced is returned as a plain string (such as `ARRAY` or `HASH`). Otherwise `undef` is returned.
```
$type = reftype "string"; # undef
$type = reftype \$var; # SCALAR
$type = reftype []; # ARRAY
$obj = bless {}, "Foo";
$type = reftype $obj; # HASH
```
Note that for internal reasons, all precompiled regexps (`qr/.../`) are blessed references; thus `ref()` returns the package name string `"Regexp"` on these but `reftype()` will return the underlying C structure type of `"REGEXP"` in all capitals.
*Since Perl version 5.35.7* an equivalent function is available as `builtin::refaddr`.
### weaken
```
weaken( $ref );
```
The lvalue `$ref` will be turned into a weak reference. This means that it will not hold a reference count on the object it references. Also, when the reference count on that object reaches zero, the reference will be set to undef. This function mutates the lvalue passed as its argument and returns no value.
This is useful for keeping copies of references, but you don't want to prevent the object being DESTROY-ed at its usual time.
```
{
my $var;
$ref = \$var;
weaken($ref); # Make $ref a weak reference
}
# $ref is now undef
```
Note that if you take a copy of a scalar with a weakened reference, the copy will be a strong reference.
```
my $var;
my $foo = \$var;
weaken($foo); # Make $foo a weak reference
my $bar = $foo; # $bar is now a strong reference
```
This may be less obvious in other situations, such as `grep()`, for instance when grepping through a list of weakened references to objects that may have been destroyed already:
```
@object = grep { defined } @object;
```
This will indeed remove all references to destroyed objects, but the remaining references to objects will be strong, causing the remaining objects to never be destroyed because there is now always a strong reference to them in the @object array.
*Since Perl version 5.35.7* an equivalent function is available as `builtin::weaken`.
### unweaken
```
unweaken( $ref );
```
*Since version 1.36.*
The lvalue `REF` will be turned from a weak reference back into a normal (strong) reference again. This function mutates the lvalue passed as its argument and returns no value. This undoes the action performed by ["weaken"](#weaken).
This function is slightly neater and more convenient than the otherwise-equivalent code
```
my $tmp = $REF;
undef $REF;
$REF = $tmp;
```
(because in particular, simply assigning a weak reference back to itself does not work to unweaken it; `$REF = $REF` does not work).
*Since Perl version 5.35.7* an equivalent function is available as `builtin::unweaken`.
### isweak
```
my $weak = isweak( $ref );
```
Returns true if `$ref` is a weak reference.
```
$ref = \$foo;
$weak = isweak($ref); # false
weaken($ref);
$weak = isweak($ref); # true
```
**NOTE**: Copying a weak reference creates a normal, strong, reference.
```
$copy = $ref;
$weak = isweak($copy); # false
```
*Since Perl version 5.35.7* an equivalent function is available as `builtin::isweak`.
OTHER FUNCTIONS
----------------
### dualvar
```
my $var = dualvar( $num, $string );
```
Returns a scalar that has the value `$num` in a numeric context and the value `$string` in a string context.
```
$foo = dualvar 10, "Hello";
$num = $foo + 2; # 12
$str = $foo . " world"; # Hello world
```
### isdual
```
my $dual = isdual( $var );
```
*Since version 1.26.*
If `$var` is a scalar that has both numeric and string values, the result is true.
```
$foo = dualvar 86, "Nix";
$dual = isdual($foo); # true
```
Note that a scalar can be made to have both string and numeric content through standard operations:
```
$foo = "10";
$dual = isdual($foo); # false
$bar = $foo + 0;
$dual = isdual($foo); # true
```
The `$!` variable is commonly dual-valued, though it is also magical in other ways:
```
$! = 1;
$dual = isdual($!); # true
print("$!\n"); # "Operation not permitted"
```
**CAUTION**: This function is not as useful as it may seem. Dualvars are not a distinct concept in Perl, but a standard internal construct of all scalar values. Almost any value could be considered as a dualvar by this function through the course of normal operations.
### isvstring
```
my $vstring = isvstring( $var );
```
If `$var` is a scalar which was coded as a vstring, the result is true.
```
$vs = v49.46.48;
$fmt = isvstring($vs) ? "%vd" : "%s"; #true
printf($fmt,$vs);
```
### looks\_like\_number
```
my $isnum = looks_like_number( $var );
```
Returns true if perl thinks `$var` is a number. See ["looks\_like\_number" in perlapi](perlapi#looks_like_number).
### openhandle
```
my $fh = openhandle( $fh );
```
Returns `$fh` itself, if `$fh` may be used as a filehandle and is open, or if it is a tied handle. Otherwise `undef` is returned.
```
$fh = openhandle(*STDIN); # \*STDIN
$fh = openhandle(\*STDIN); # \*STDIN
$fh = openhandle(*NOTOPEN); # undef
$fh = openhandle("scalar"); # undef
```
### readonly
```
my $ro = readonly( $var );
```
Returns true if `$var` is readonly.
```
sub foo { readonly($_[0]) }
$readonly = foo($bar); # false
$readonly = foo(0); # true
```
### set\_prototype
```
my $code = set_prototype( $code, $prototype );
```
Sets the prototype of the function given by the `$code` reference, or deletes it if `$prototype` is `undef`. Returns the `$code` reference itself.
```
set_prototype \&foo, '$$';
```
### tainted
```
my $t = tainted( $var );
```
Return true if `$var` is tainted.
```
$taint = tainted("constant"); # false
$taint = tainted($ENV{PWD}); # true if running under -T
```
DIAGNOSTICS
-----------
Module use may give one of the following errors during import.
Vstrings are not implemented in this version of perl The version of perl that you are using does not implement Vstrings, to use ["isvstring"](#isvstring) you will need to use a newer release of perl.
KNOWN BUGS
-----------
There is a bug in perl5.6.0 with UV's that are >= 1<<31. This will show up as tests 8 and 9 of dualvar.t failing
SEE ALSO
---------
<List::Util>
COPYRIGHT
---------
Copyright (c) 1997-2007 Graham Barr <[email protected]>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
Additionally ["weaken"](#weaken) and ["isweak"](#isweak) which are
Copyright (c) 1999 Tuomas J. Lukka <[email protected]>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as perl itself.
Copyright (C) 2004, 2008 Matthijs van Duin. All rights reserved. Copyright (C) 2014 cPanel Inc. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl IO::Compress::Gzip IO::Compress::Gzip
==================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [Functional Interface](#Functional-Interface)
+ [gzip $input\_filename\_or\_reference => $output\_filename\_or\_reference [, OPTS]](#gzip-%24input_filename_or_reference-=%3E-%24output_filename_or_reference-%5B,-OPTS%5D)
- [The $input\_filename\_or\_reference parameter](#The-%24input_filename_or_reference-parameter)
- [The $output\_filename\_or\_reference parameter](#The-%24output_filename_or_reference-parameter)
+ [Notes](#Notes)
+ [Optional Parameters](#Optional-Parameters)
+ [Examples](#Examples)
- [Streaming](#Streaming)
- [Compressing a file from the filesystem](#Compressing-a-file-from-the-filesystem)
- [Reading from a Filehandle and writing to an in-memory buffer](#Reading-from-a-Filehandle-and-writing-to-an-in-memory-buffer)
- [Compressing multiple files](#Compressing-multiple-files)
* [OO Interface](#OO-Interface)
+ [Constructor](#Constructor)
+ [Constructor Options](#Constructor-Options)
+ [Examples](#Examples1)
* [Methods](#Methods)
+ [print](#print)
+ [printf](#printf)
+ [syswrite](#syswrite)
+ [write](#write)
+ [flush](#flush)
+ [tell](#tell)
+ [eof](#eof)
+ [seek](#seek)
+ [binmode](#binmode)
+ [opened](#opened)
+ [autoflush](#autoflush)
+ [input\_line\_number](#input_line_number)
+ [fileno](#fileno)
+ [close](#close)
+ [newStream([OPTS])](#newStream(%5BOPTS%5D))
+ [deflateParams](#deflateParams)
* [Importing](#Importing)
* [EXAMPLES](#EXAMPLES)
+ [Apache::GZip Revisited](#Apache::GZip-Revisited)
+ [Working with Net::FTP](#Working-with-Net::FTP)
* [SUPPORT](#SUPPORT)
* [SEE ALSO](#SEE-ALSO)
* [AUTHOR](#AUTHOR)
* [MODIFICATION HISTORY](#MODIFICATION-HISTORY)
* [COPYRIGHT AND LICENSE](#COPYRIGHT-AND-LICENSE)
NAME
----
IO::Compress::Gzip - Write RFC 1952 files/buffers
SYNOPSIS
--------
```
use IO::Compress::Gzip qw(gzip $GzipError) ;
my $status = gzip $input => $output [,OPTS]
or die "gzip failed: $GzipError\n";
my $z = IO::Compress::Gzip->new( $output [,OPTS] )
or die "gzip failed: $GzipError\n";
$z->print($string);
$z->printf($format, $string);
$z->write($string);
$z->syswrite($string [, $length, $offset]);
$z->flush();
$z->tell();
$z->eof();
$z->seek($position, $whence);
$z->binmode();
$z->fileno();
$z->opened();
$z->autoflush();
$z->input_line_number();
$z->newStream( [OPTS] );
$z->deflateParams();
$z->close() ;
$GzipError ;
# IO::File mode
print $z $string;
printf $z $format, $string;
tell $z
eof $z
seek $z, $position, $whence
binmode $z
fileno $z
close $z ;
```
DESCRIPTION
-----------
This module provides a Perl interface that allows writing compressed data to files or buffer as defined in RFC 1952.
All the gzip headers defined in RFC 1952 can be created using this module.
For reading RFC 1952 files/buffers, see the companion module <IO::Uncompress::Gunzip>.
Functional Interface
---------------------
A top-level function, `gzip`, is provided to carry out "one-shot" compression between buffers and/or files. For finer control over the compression process, see the ["OO Interface"](#OO-Interface) section.
```
use IO::Compress::Gzip qw(gzip $GzipError) ;
gzip $input_filename_or_reference => $output_filename_or_reference [,OPTS]
or die "gzip failed: $GzipError\n";
```
The functional interface needs Perl5.005 or better.
###
gzip $input\_filename\_or\_reference => $output\_filename\_or\_reference [, OPTS]
`gzip` expects at least two parameters, `$input_filename_or_reference` and `$output_filename_or_reference` and zero or more optional parameters (see ["Optional Parameters"](#Optional-Parameters))
####
The `$input_filename_or_reference` parameter
The parameter, `$input_filename_or_reference`, is used to define the source of the uncompressed data.
It can take one of the following forms:
A filename If the `$input_filename_or_reference` parameter is a simple scalar, it is assumed to be a filename. This file will be opened for reading and the input data will be read from it.
A filehandle If the `$input_filename_or_reference` parameter is a filehandle, the input data will be read from it. The string '-' can be used as an alias for standard input.
A scalar reference If `$input_filename_or_reference` is a scalar reference, the input data will be read from `$$input_filename_or_reference`.
An array reference If `$input_filename_or_reference` is an array reference, each element in the array must be a filename.
The input data will be read from each file in turn.
The complete array will be walked to ensure that it only contains valid filenames before any data is compressed.
An Input FileGlob string If `$input_filename_or_reference` is a string that is delimited by the characters "<" and ">" `gzip` will assume that it is an *input fileglob string*. The input is the list of files that match the fileglob.
See <File::GlobMapper> for more details.
If the `$input_filename_or_reference` parameter is any other type, `undef` will be returned.
In addition, if `$input_filename_or_reference` is a simple filename, the default values for the `Name` and `Time` options will be sourced from that file.
If you do not want to use these defaults they can be overridden by explicitly setting the `Name` and `Time` options or by setting the `Minimal` parameter.
####
The `$output_filename_or_reference` parameter
The parameter `$output_filename_or_reference` is used to control the destination of the compressed data. This parameter can take one of these forms.
A filename If the `$output_filename_or_reference` parameter is a simple scalar, it is assumed to be a filename. This file will be opened for writing and the compressed data will be written to it.
A filehandle If the `$output_filename_or_reference` parameter is a filehandle, the compressed data will be written to it. The string '-' can be used as an alias for standard output.
A scalar reference If `$output_filename_or_reference` is a scalar reference, the compressed data will be stored in `$$output_filename_or_reference`.
An Array Reference If `$output_filename_or_reference` is an array reference, the compressed data will be pushed onto the array.
An Output FileGlob If `$output_filename_or_reference` is a string that is delimited by the characters "<" and ">" `gzip` will assume that it is an *output fileglob string*. The output is the list of files that match the fileglob.
When `$output_filename_or_reference` is an fileglob string, `$input_filename_or_reference` must also be a fileglob string. Anything else is an error.
See <File::GlobMapper> for more details.
If the `$output_filename_or_reference` parameter is any other type, `undef` will be returned.
### Notes
When `$input_filename_or_reference` maps to multiple files/buffers and `$output_filename_or_reference` is a single file/buffer the input files/buffers will be stored in `$output_filename_or_reference` as a concatenated series of compressed data streams.
###
Optional Parameters
The optional parameters for the one-shot function `gzip` are (for the most part) identical to those used with the OO interface defined in the ["Constructor Options"](#Constructor-Options) section. The exceptions are listed below
`AutoClose => 0|1`
This option applies to any input or output data streams to `gzip` that are filehandles.
If `AutoClose` is specified, and the value is true, it will result in all input and/or output filehandles being closed once `gzip` has completed.
This parameter defaults to 0.
`BinModeIn => 0|1`
This option is now a no-op. All files will be read in binmode.
`Append => 0|1`
The behaviour of this option is dependent on the type of output data stream.
* A Buffer
If `Append` is enabled, all compressed data will be append to the end of the output buffer. Otherwise the output buffer will be cleared before any compressed data is written to it.
* A Filename
If `Append` is enabled, the file will be opened in append mode. Otherwise the contents of the file, if any, will be truncated before any compressed data is written to it.
* A Filehandle
If `Append` is enabled, the filehandle will be positioned to the end of the file via a call to `seek` before any compressed data is written to it. Otherwise the file pointer will not be moved.
When `Append` is specified, and set to true, it will *append* all compressed data to the output data stream.
So when the output is a filehandle it will carry out a seek to the eof before writing any compressed data. If the output is a filename, it will be opened for appending. If the output is a buffer, all compressed data will be appended to the existing buffer.
Conversely when `Append` is not specified, or it is present and is set to false, it will operate as follows.
When the output is a filename, it will truncate the contents of the file before writing any compressed data. If the output is a filehandle its position will not be changed. If the output is a buffer, it will be wiped before any compressed data is output.
Defaults to 0.
### Examples
Here are a few example that show the capabilities of the module.
#### Streaming
This very simple command line example demonstrates the streaming capabilities of the module. The code reads data from STDIN, compresses it, and writes the compressed data to STDOUT.
```
$ echo hello world | perl -MIO::Compress::Gzip=gzip -e 'gzip \*STDIN => \*STDOUT' >output.gz
```
The special filename "-" can be used as a standin for both `\*STDIN` and `\*STDOUT`, so the above can be rewritten as
```
$ echo hello world | perl -MIO::Compress::Gzip=gzip -e 'gzip "-" => "-"' >output.gz
```
####
Compressing a file from the filesystem
To read the contents of the file `file1.txt` and write the compressed data to the file `file1.txt.gz`.
```
use strict ;
use warnings ;
use IO::Compress::Gzip qw(gzip $GzipError) ;
my $input = "file1.txt";
gzip $input => "$input.gz"
or die "gzip failed: $GzipError\n";
```
####
Reading from a Filehandle and writing to an in-memory buffer
To read from an existing Perl filehandle, `$input`, and write the compressed data to a buffer, `$buffer`.
```
use strict ;
use warnings ;
use IO::Compress::Gzip qw(gzip $GzipError) ;
use IO::File ;
my $input = IO::File->new( "<file1.txt" )
or die "Cannot open 'file1.txt': $!\n" ;
my $buffer ;
gzip $input => \$buffer
or die "gzip failed: $GzipError\n";
```
####
Compressing multiple files
To compress all files in the directory "/my/home" that match "\*.txt" and store the compressed data in the same directory
```
use strict ;
use warnings ;
use IO::Compress::Gzip qw(gzip $GzipError) ;
gzip '</my/home/*.txt>' => '<*.gz>'
or die "gzip failed: $GzipError\n";
```
and if you want to compress each file one at a time, this will do the trick
```
use strict ;
use warnings ;
use IO::Compress::Gzip qw(gzip $GzipError) ;
for my $input ( glob "/my/home/*.txt" )
{
my $output = "$input.gz" ;
gzip $input => $output
or die "Error compressing '$input': $GzipError\n";
}
```
OO Interface
-------------
### Constructor
The format of the constructor for `IO::Compress::Gzip` is shown below
```
my $z = IO::Compress::Gzip->new( $output [,OPTS] )
or die "IO::Compress::Gzip failed: $GzipError\n";
```
It returns an `IO::Compress::Gzip` object on success and undef on failure. The variable `$GzipError` will contain an error message on failure.
If you are running Perl 5.005 or better the object, `$z`, returned from IO::Compress::Gzip can be used exactly like an <IO::File> filehandle. This means that all normal output file operations can be carried out with `$z`. For example, to write to a compressed file/buffer you can use either of these forms
```
$z->print("hello world\n");
print $z "hello world\n";
```
The mandatory parameter `$output` is used to control the destination of the compressed data. This parameter can take one of these forms.
A filename If the `$output` parameter is a simple scalar, it is assumed to be a filename. This file will be opened for writing and the compressed data will be written to it.
A filehandle If the `$output` parameter is a filehandle, the compressed data will be written to it. The string '-' can be used as an alias for standard output.
A scalar reference If `$output` is a scalar reference, the compressed data will be stored in `$$output`.
If the `$output` parameter is any other type, `IO::Compress::Gzip`::new will return undef.
###
Constructor Options
`OPTS` is any combination of zero or more the following options:
`AutoClose => 0|1`
This option is only valid when the `$output` parameter is a filehandle. If specified, and the value is true, it will result in the `$output` being closed once either the `close` method is called or the `IO::Compress::Gzip` object is destroyed.
This parameter defaults to 0.
`Append => 0|1`
Opens `$output` in append mode.
The behaviour of this option is dependent on the type of `$output`.
* A Buffer
If `$output` is a buffer and `Append` is enabled, all compressed data will be append to the end of `$output`. Otherwise `$output` will be cleared before any data is written to it.
* A Filename
If `$output` is a filename and `Append` is enabled, the file will be opened in append mode. Otherwise the contents of the file, if any, will be truncated before any compressed data is written to it.
* A Filehandle
If `$output` is a filehandle, the file pointer will be positioned to the end of the file via a call to `seek` before any compressed data is written to it. Otherwise the file pointer will not be moved.
This parameter defaults to 0.
`Merge => 0|1`
This option is used to compress input data and append it to an existing compressed data stream in `$output`. The end result is a single compressed data stream stored in `$output`.
It is a fatal error to attempt to use this option when `$output` is not an RFC 1952 data stream.
There are a number of other limitations with the `Merge` option:
1. This module needs to have been built with zlib 1.2.1 or better to work. A fatal error will be thrown if `Merge` is used with an older version of zlib.
2. If `$output` is a file or a filehandle, it must be seekable.
This parameter defaults to 0.
-Level Defines the compression level used by zlib. The value should either be a number between 0 and 9 (0 means no compression and 9 is maximum compression), or one of the symbolic constants defined below.
```
Z_NO_COMPRESSION
Z_BEST_SPEED
Z_BEST_COMPRESSION
Z_DEFAULT_COMPRESSION
```
The default is Z\_DEFAULT\_COMPRESSION.
Note, these constants are not imported by `IO::Compress::Gzip` by default.
```
use IO::Compress::Gzip qw(:strategy);
use IO::Compress::Gzip qw(:constants);
use IO::Compress::Gzip qw(:all);
```
-Strategy Defines the strategy used to tune the compression. Use one of the symbolic constants defined below.
```
Z_FILTERED
Z_HUFFMAN_ONLY
Z_RLE
Z_FIXED
Z_DEFAULT_STRATEGY
```
The default is Z\_DEFAULT\_STRATEGY.
`Minimal => 0|1`
If specified, this option will force the creation of the smallest possible compliant gzip header (which is exactly 10 bytes long) as defined in RFC 1952.
See the section titled "Compliance" in RFC 1952 for a definition of the values used for the fields in the gzip header.
All other parameters that control the content of the gzip header will be ignored if this parameter is set to 1.
This parameter defaults to 0.
`Comment => $comment`
Stores the contents of `$comment` in the COMMENT field in the gzip header. By default, no comment field is written to the gzip file.
If the `-Strict` option is enabled, the comment can only consist of ISO 8859-1 characters plus line feed.
If the `-Strict` option is disabled, the comment field can contain any character except NULL. If any null characters are present, the field will be truncated at the first NULL.
`Name => $string`
Stores the contents of `$string` in the gzip NAME header field. If `Name` is not specified, no gzip NAME field will be created.
If the `-Strict` option is enabled, `$string` can only consist of ISO 8859-1 characters.
If `-Strict` is disabled, then `$string` can contain any character except NULL. If any null characters are present, the field will be truncated at the first NULL.
`Time => $number`
Sets the MTIME field in the gzip header to $number.
This field defaults to the time the `IO::Compress::Gzip` object was created if this option is not specified.
`TextFlag => 0|1`
This parameter controls the setting of the FLG.FTEXT bit in the gzip header. It is used to signal that the data stored in the gzip file/buffer is probably text.
The default is 0.
`HeaderCRC => 0|1`
When true this parameter will set the FLG.FHCRC bit to 1 in the gzip header and set the CRC16 header field to the CRC of the complete gzip header except the CRC16 field itself.
**Note** that gzip files created with the `HeaderCRC` flag set to 1 cannot be read by most, if not all, of the standard gunzip utilities, most notably gzip version 1.2.4. You should therefore avoid using this option if you want to maximize the portability of your gzip files.
This parameter defaults to 0.
`OS_Code => $value`
Stores `$value` in the gzip OS header field. A number between 0 and 255 is valid.
If not specified, this parameter defaults to the OS code of the Operating System this module was built on. The value 3 is used as a catch-all for all Unix variants and unknown Operating Systems.
`ExtraField => $data`
This parameter allows additional metadata to be stored in the ExtraField in the gzip header. An RFC 1952 compliant ExtraField consists of zero or more subfields. Each subfield consists of a two byte header followed by the subfield data.
The list of subfields can be supplied in any of the following formats
```
-ExtraField => [$id1, $data1,
$id2, $data2,
...
]
-ExtraField => [ [$id1 => $data1],
[$id2 => $data2],
...
]
-ExtraField => { $id1 => $data1,
$id2 => $data2,
...
}
```
Where `$id1`, `$id2` are two byte subfield ID's. The second byte of the ID cannot be 0, unless the `Strict` option has been disabled.
If you use the hash syntax, you have no control over the order in which the ExtraSubFields are stored, plus you cannot have SubFields with duplicate ID.
Alternatively the list of subfields can by supplied as a scalar, thus
```
-ExtraField => $rawdata
```
If you use the raw format, and the `Strict` option is enabled, `IO::Compress::Gzip` will check that `$rawdata` consists of zero or more conformant sub-fields. When `Strict` is disabled, `$rawdata` can consist of any arbitrary byte stream.
The maximum size of the Extra Field 65535 bytes.
`ExtraFlags => $value`
Sets the XFL byte in the gzip header to `$value`.
If this option is not present, the value stored in XFL field will be determined by the setting of the `Level` option.
If `Level => Z_BEST_SPEED` has been specified then XFL is set to 2. If `Level => Z_BEST_COMPRESSION` has been specified then XFL is set to 4. Otherwise XFL is set to 0.
`Strict => 0|1`
`Strict` will optionally police the values supplied with other options to ensure they are compliant with RFC1952.
This option is enabled by default.
If `Strict` is enabled the following behaviour will be policed:
* The value supplied with the `Name` option can only contain ISO 8859-1 characters.
* The value supplied with the `Comment` option can only contain ISO 8859-1 characters plus line-feed.
* The values supplied with the `-Name` and `-Comment` options cannot contain multiple embedded nulls.
* If an `ExtraField` option is specified and it is a simple scalar, it must conform to the sub-field structure as defined in RFC 1952.
* If an `ExtraField` option is specified the second byte of the ID will be checked in each subfield to ensure that it does not contain the reserved value 0x00.
When `Strict` is disabled the following behaviour will be policed:
* The value supplied with `-Name` option can contain any character except NULL.
* The value supplied with `-Comment` option can contain any character except NULL.
* The values supplied with the `-Name` and `-Comment` options can contain multiple embedded nulls. The string written to the gzip header will consist of the characters up to, but not including, the first embedded NULL.
* If an `ExtraField` option is specified and it is a simple scalar, the structure will not be checked. The only error is if the length is too big.
* The ID header in an `ExtraField` sub-field can consist of any two bytes.
### Examples
TODO
Methods
-------
### print
Usage is
```
$z->print($data)
print $z $data
```
Compresses and outputs the contents of the `$data` parameter. This has the same behaviour as the `print` built-in.
Returns true if successful.
### printf
Usage is
```
$z->printf($format, $data)
printf $z $format, $data
```
Compresses and outputs the contents of the `$data` parameter.
Returns true if successful.
### syswrite
Usage is
```
$z->syswrite $data
$z->syswrite $data, $length
$z->syswrite $data, $length, $offset
```
Compresses and outputs the contents of the `$data` parameter.
Returns the number of uncompressed bytes written, or `undef` if unsuccessful.
### write
Usage is
```
$z->write $data
$z->write $data, $length
$z->write $data, $length, $offset
```
Compresses and outputs the contents of the `$data` parameter.
Returns the number of uncompressed bytes written, or `undef` if unsuccessful.
### flush
Usage is
```
$z->flush;
$z->flush($flush_type);
```
Flushes any pending compressed data to the output file/buffer.
This method takes an optional parameter, `$flush_type`, that controls how the flushing will be carried out. By default the `$flush_type` used is `Z_FINISH`. Other valid values for `$flush_type` are `Z_NO_FLUSH`, `Z_SYNC_FLUSH`, `Z_FULL_FLUSH` and `Z_BLOCK`. It is strongly recommended that you only set the `flush_type` parameter if you fully understand the implications of what it does - overuse of `flush` can seriously degrade the level of compression achieved. See the `zlib` documentation for details.
Returns true on success.
### tell
Usage is
```
$z->tell()
tell $z
```
Returns the uncompressed file offset.
### eof
Usage is
```
$z->eof();
eof($z);
```
Returns true if the `close` method has been called.
### seek
```
$z->seek($position, $whence);
seek($z, $position, $whence);
```
Provides a sub-set of the `seek` functionality, with the restriction that it is only legal to seek forward in the output file/buffer. It is a fatal error to attempt to seek backward.
Empty parts of the file/buffer will have NULL (0x00) bytes written to them.
The `$whence` parameter takes one the usual values, namely SEEK\_SET, SEEK\_CUR or SEEK\_END.
Returns 1 on success, 0 on failure.
### binmode
Usage is
```
$z->binmode
binmode $z ;
```
This is a noop provided for completeness.
### opened
```
$z->opened()
```
Returns true if the object currently refers to a opened file/buffer.
### autoflush
```
my $prev = $z->autoflush()
my $prev = $z->autoflush(EXPR)
```
If the `$z` object is associated with a file or a filehandle, this method returns the current autoflush setting for the underlying filehandle. If `EXPR` is present, and is non-zero, it will enable flushing after every write/print operation.
If `$z` is associated with a buffer, this method has no effect and always returns `undef`.
**Note** that the special variable `$|` **cannot** be used to set or retrieve the autoflush setting.
### input\_line\_number
```
$z->input_line_number()
$z->input_line_number(EXPR)
```
This method always returns `undef` when compressing.
### fileno
```
$z->fileno()
fileno($z)
```
If the `$z` object is associated with a file or a filehandle, `fileno` will return the underlying file descriptor. Once the `close` method is called `fileno` will return `undef`.
If the `$z` object is associated with a buffer, this method will return `undef`.
### close
```
$z->close() ;
close $z ;
```
Flushes any pending compressed data and then closes the output file/buffer.
For most versions of Perl this method will be automatically invoked if the IO::Compress::Gzip object is destroyed (either explicitly or by the variable with the reference to the object going out of scope). The exceptions are Perl versions 5.005 through 5.00504 and 5.8.0. In these cases, the `close` method will be called automatically, but not until global destruction of all live objects when the program is terminating.
Therefore, if you want your scripts to be able to run on all versions of Perl, you should call `close` explicitly and not rely on automatic closing.
Returns true on success, otherwise 0.
If the `AutoClose` option has been enabled when the IO::Compress::Gzip object was created, and the object is associated with a file, the underlying file will also be closed.
###
newStream([OPTS])
Usage is
```
$z->newStream( [OPTS] )
```
Closes the current compressed data stream and starts a new one.
OPTS consists of any of the options that are available when creating the `$z` object.
See the ["Constructor Options"](#Constructor-Options) section for more details.
### deflateParams
Usage is
```
$z->deflateParams
```
TODO
Importing
---------
A number of symbolic constants are required by some methods in `IO::Compress::Gzip`. None are imported by default.
:all Imports `gzip`, `$GzipError` and all symbolic constants that can be used by `IO::Compress::Gzip`. Same as doing this
```
use IO::Compress::Gzip qw(gzip $GzipError :constants) ;
```
:constants Import all symbolic constants. Same as doing this
```
use IO::Compress::Gzip qw(:flush :level :strategy) ;
```
:flush These symbolic constants are used by the `flush` method.
```
Z_NO_FLUSH
Z_PARTIAL_FLUSH
Z_SYNC_FLUSH
Z_FULL_FLUSH
Z_FINISH
Z_BLOCK
```
:level These symbolic constants are used by the `Level` option in the constructor.
```
Z_NO_COMPRESSION
Z_BEST_SPEED
Z_BEST_COMPRESSION
Z_DEFAULT_COMPRESSION
```
:strategy These symbolic constants are used by the `Strategy` option in the constructor.
```
Z_FILTERED
Z_HUFFMAN_ONLY
Z_RLE
Z_FIXED
Z_DEFAULT_STRATEGY
```
EXAMPLES
--------
###
Apache::GZip Revisited
See [IO::Compress::FAQ](IO::Compress::FAQ#Apache%3A%3AGZip-Revisited)
###
Working with Net::FTP
See [IO::Compress::FAQ](IO::Compress::FAQ#Compressed-files-and-Net%3A%3AFTP)
SUPPORT
-------
General feedback/questions/bug reports should be sent to <https://github.com/pmqs/IO-Copress/issues> (preferred) or <https://rt.cpan.org/Public/Dist/Display.html?Name=IO-Copress>.
SEE ALSO
---------
<Compress::Zlib>, <IO::Uncompress::Gunzip>, <IO::Compress::Deflate>, <IO::Uncompress::Inflate>, <IO::Compress::RawDeflate>, <IO::Uncompress::RawInflate>, <IO::Compress::Bzip2>, <IO::Uncompress::Bunzip2>, <IO::Compress::Lzma>, <IO::Uncompress::UnLzma>, <IO::Compress::Xz>, <IO::Uncompress::UnXz>, <IO::Compress::Lzip>, <IO::Uncompress::UnLzip>, <IO::Compress::Lzop>, <IO::Uncompress::UnLzop>, <IO::Compress::Lzf>, <IO::Uncompress::UnLzf>, <IO::Compress::Zstd>, <IO::Uncompress::UnZstd>, <IO::Uncompress::AnyInflate>, <IO::Uncompress::AnyUncompress>
<IO::Compress::FAQ>
<File::GlobMapper>, <Archive::Zip>, <Archive::Tar>, <IO::Zlib>
For RFC 1950, 1951 and 1952 see <https://datatracker.ietf.org/doc/html/rfc1950>, <https://datatracker.ietf.org/doc/html/rfc1951> and <https://datatracker.ietf.org/doc/html/rfc1952>
The *zlib* compression library was written by Jean-loup Gailly `[email protected]` and Mark Adler `[email protected]`.
The primary site for the *zlib* compression library is <http://www.zlib.org>.
The primary site for gzip is <http://www.gzip.org>.
AUTHOR
------
This module was written by Paul Marquess, `[email protected]`.
MODIFICATION HISTORY
---------------------
See the Changes file.
COPYRIGHT AND LICENSE
----------------------
Copyright (c) 2005-2022 Paul Marquess. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
| programming_docs |
perl TAP::Parser::SourceHandler::RawTAP TAP::Parser::SourceHandler::RawTAP
==================================
CONTENTS
--------
* [NAME](#NAME)
* [VERSION](#VERSION)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [METHODS](#METHODS)
+ [Class Methods](#Class-Methods)
- [can\_handle](#can_handle)
- [make\_iterator](#make_iterator)
* [SUBCLASSING](#SUBCLASSING)
* [SEE ALSO](#SEE-ALSO)
NAME
----
TAP::Parser::SourceHandler::RawTAP - Stream output from raw TAP in a scalar/array ref.
VERSION
-------
Version 3.44
SYNOPSIS
--------
```
use TAP::Parser::Source;
use TAP::Parser::SourceHandler::RawTAP;
my $source = TAP::Parser::Source->new->raw( \"1..1\nok 1\n" );
$source->assemble_meta;
my $class = 'TAP::Parser::SourceHandler::RawTAP';
my $vote = $class->can_handle( $source );
my $iter = $class->make_iterator( $source );
```
DESCRIPTION
-----------
This is a *raw TAP output* <TAP::Parser::SourceHandler> - it has 2 jobs:
1. Figure out if the <TAP::Parser::Source> it's given is raw TAP output (["can\_handle"](#can_handle)).
2. Creates an iterator for raw TAP output (["make\_iterator"](#make_iterator)).
Unless you're writing a plugin or subclassing <TAP::Parser>, you probably won't need to use this module directly.
METHODS
-------
###
Class Methods
#### `can_handle`
```
my $vote = $class->can_handle( $source );
```
Only votes if $source is an array, or a scalar with newlines. Casts the following votes:
```
0.9 if it's a scalar with '..' in it
0.7 if it's a scalar with 'ok' in it
0.3 if it's just a scalar with newlines
0.5 if it's an array
```
#### `make_iterator`
```
my $iterator = $class->make_iterator( $source );
```
Returns a new <TAP::Parser::Iterator::Array> for the source. `$source->raw` must be an array ref, or a scalar ref.
`croak`s on error.
SUBCLASSING
-----------
Please see ["SUBCLASSING" in TAP::Parser](TAP::Parser#SUBCLASSING) for a subclassing overview.
SEE ALSO
---------
<TAP::Object>, <TAP::Parser>, <TAP::Parser::IteratorFactory>, <TAP::Parser::SourceHandler>, <TAP::Parser::SourceHandler::Executable>, <TAP::Parser::SourceHandler::Perl>, <TAP::Parser::SourceHandler::File>, <TAP::Parser::SourceHandler::Handle>
perl Filter::Util::Call Filter::Util::Call
==================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [use Filter::Util::Call](#use-Filter::Util::Call)
+ [import()](#import())
+ [filter\_add()](#filter_add())
+ [filter() and anonymous sub](#filter()-and-anonymous-sub)
* [LIMITATIONS](#LIMITATIONS)
* [EXAMPLES](#EXAMPLES)
+ [Example 1: A simple filter.](#Example-1:-A-simple-filter.)
+ [Example 2: Using the context](#Example-2:-Using-the-context)
+ [Example 3: Using the context within the filter](#Example-3:-Using-the-context-within-the-filter)
+ [Example 4: Using filter\_del](#Example-4:-Using-filter_del)
* [Filter::Simple](#Filter::Simple)
* [AUTHOR](#AUTHOR)
* [DATE](#DATE)
* [LICENSE](#LICENSE)
NAME
----
Filter::Util::Call - Perl Source Filter Utility Module
SYNOPSIS
--------
```
use Filter::Util::Call ;
```
DESCRIPTION
-----------
This module provides you with the framework to write *Source Filters* in Perl.
An alternate interface to Filter::Util::Call is now available. See <Filter::Simple> for more details.
A *Perl Source Filter* is implemented as a Perl module. The structure of the module can take one of two broadly similar formats. To distinguish between them, the first will be referred to as *method filter* and the second as *closure filter*.
Here is a skeleton for the *method filter*:
```
package MyFilter ;
use Filter::Util::Call ;
sub import
{
my($type, @arguments) = @_ ;
filter_add([]) ;
}
sub filter
{
my($self) = @_ ;
my($status) ;
$status = filter_read() ;
$status ;
}
1 ;
```
and this is the equivalent skeleton for the *closure filter*:
```
package MyFilter ;
use Filter::Util::Call ;
sub import
{
my($type, @arguments) = @_ ;
filter_add(
sub
{
my($status) ;
$status = filter_read() ;
$status ;
} )
}
1 ;
```
To make use of either of the two filter modules above, place the line below in a Perl source file.
```
use MyFilter;
```
In fact, the skeleton modules shown above are fully functional *Source Filters*, albeit fairly useless ones. All they does is filter the source stream without modifying it at all.
As you can see both modules have a broadly similar structure. They both make use of the `Filter::Util::Call` module and both have an `import` method. The difference between them is that the *method filter* requires a *filter* method, whereas the *closure filter* gets the equivalent of a *filter* method with the anonymous sub passed to *filter\_add*.
To make proper use of the *closure filter* shown above you need to have a good understanding of the concept of a *closure*. See <perlref> for more details on the mechanics of *closures*.
###
**use Filter::Util::Call**
The following functions are exported by `Filter::Util::Call`:
```
filter_add()
filter_read()
filter_read_exact()
filter_del()
```
###
**import()**
The `import` method is used to create an instance of the filter. It is called indirectly by Perl when it encounters the `use MyFilter` line in a source file (See ["import" in perlfunc](perlfunc#import) for more details on `import`).
It will always have at least one parameter automatically passed by Perl - this corresponds to the name of the package. In the example above it will be `"MyFilter"`.
Apart from the first parameter, import can accept an optional list of parameters. These can be used to pass parameters to the filter. For example:
```
use MyFilter qw(a b c) ;
```
will result in the `@_` array having the following values:
```
@_ [0] => "MyFilter"
@_ [1] => "a"
@_ [2] => "b"
@_ [3] => "c"
```
Before terminating, the `import` function must explicitly install the filter by calling `filter_add`.
###
**filter\_add()**
The function, `filter_add`, actually installs the filter. It takes one parameter which should be a reference. The kind of reference used will dictate which of the two filter types will be used.
If a CODE reference is used then a *closure filter* will be assumed.
If a CODE reference is not used, a *method filter* will be assumed. In a *method filter*, the reference can be used to store context information. The reference will be *blessed* into the package by `filter_add`, unless the reference was already blessed.
See the filters at the end of this documents for examples of using context information using both *method filters* and *closure filters*.
###
**filter() and anonymous sub**
Both the `filter` method used with a *method filter* and the anonymous sub used with a *closure filter* is where the main processing for the filter is done.
The big difference between the two types of filter is that the *method filter* uses the object passed to the method to store any context data, whereas the *closure filter* uses the lexical variables that are maintained by the closure.
Note that the single parameter passed to the *method filter*, `$self`, is the same reference that was passed to `filter_add` blessed into the filter's package. See the example filters later on for details of using `$self`.
Here is a list of the common features of the anonymous sub and the `filter()` method.
**$\_**
Although `$_` doesn't actually appear explicitly in the sample filters above, it is implicitly used in a number of places.
Firstly, when either `filter` or the anonymous sub are called, a local copy of `$_` will automatically be created. It will always contain the empty string at this point.
Next, both `filter_read` and `filter_read_exact` will append any source data that is read to the end of `$_`.
Finally, when `filter` or the anonymous sub are finished processing, they are expected to return the filtered source using `$_`.
This implicit use of `$_` greatly simplifies the filter.
**$status**
The status value that is returned by the user's `filter` method or anonymous sub and the `filter_read` and `read_exact` functions take the same set of values, namely:
```
< 0 Error
= 0 EOF
> 0 OK
```
**filter\_read** and **filter\_read\_exact**
These functions are used by the filter to obtain either a line or block from the next filter in the chain or the actual source file if there aren't any other filters.
The function `filter_read` takes two forms:
```
$status = filter_read() ;
$status = filter_read($size) ;
```
The first form is used to request a *line*, the second requests a *block*.
In line mode, `filter_read` will append the next source line to the end of the `$_` scalar.
In block mode, `filter_read` will append a block of data which is <= `$size` to the end of the `$_` scalar. It is important to emphasise the that `filter_read` will not necessarily read a block which is *precisely* `$size` bytes.
If you need to be able to read a block which has an exact size, you can use the function `filter_read_exact`. It works identically to `filter_read` in block mode, except it will try to read a block which is exactly `$size` bytes in length. The only circumstances when it will not return a block which is `$size` bytes long is on EOF or error.
It is *very* important to check the value of `$status` after *every* call to `filter_read` or `filter_read_exact`.
**filter\_del** The function, `filter_del`, is used to disable the current filter. It does not affect the running of the filter. All it does is tell Perl not to call filter any more.
See ["Example 4: Using filter\_del"](#Example-4%3A-Using-filter_del) for details.
*real\_import* Internal function which adds the filter, based on the <filter_add> argument type.
*unimport()*
May be used to disable a filter, but is rarely needed. See <filter_del>.
LIMITATIONS
-----------
See ["LIMITATIONS" in perlfilter](perlfilter#LIMITATIONS) for an overview of the general problems filtering code in a textual line-level only.
\_\_DATA\_\_ is ignored The content from the \_\_DATA\_\_ block is not filtered. This is a serious limitation, e.g. for the [Switch](switch) module. See <http://search.cpan.org/perldoc?Switch#LIMITATIONS> for more.
Max. codesize limited to 32-bit Currently internal buffer lengths are limited to 32-bit only.
EXAMPLES
--------
Here are a few examples which illustrate the key concepts - as such most of them are of little practical use.
The `examples` sub-directory has copies of all these filters implemented both as *method filters* and as *closure filters*.
###
Example 1: A simple filter.
Below is a *method filter* which is hard-wired to replace all occurrences of the string `"Joe"` to `"Jim"`. Not particularly Useful, but it is the first example and I wanted to keep it simple.
```
package Joe2Jim ;
use Filter::Util::Call ;
sub import
{
my($type) = @_ ;
filter_add(bless []) ;
}
sub filter
{
my($self) = @_ ;
my($status) ;
s/Joe/Jim/g
if ($status = filter_read()) > 0 ;
$status ;
}
1 ;
```
Here is an example of using the filter:
```
use Joe2Jim ;
print "Where is Joe?\n" ;
```
And this is what the script above will print:
```
Where is Jim?
```
###
Example 2: Using the context
The previous example was not particularly useful. To make it more general purpose we will make use of the context data and allow any arbitrary *from* and *to* strings to be used. This time we will use a *closure filter*. To reflect its enhanced role, the filter is called `Subst`.
```
package Subst ;
use Filter::Util::Call ;
use Carp ;
sub import
{
croak("usage: use Subst qw(from to)")
unless @_ == 3 ;
my ($self, $from, $to) = @_ ;
filter_add(
sub
{
my ($status) ;
s/$from/$to/
if ($status = filter_read()) > 0 ;
$status ;
})
}
1 ;
```
and is used like this:
```
use Subst qw(Joe Jim) ;
print "Where is Joe?\n" ;
```
###
Example 3: Using the context within the filter
Here is a filter which a variation of the `Joe2Jim` filter. As well as substituting all occurrences of `"Joe"` to `"Jim"` it keeps a count of the number of substitutions made in the context object.
Once EOF is detected (`$status` is zero) the filter will insert an extra line into the source stream. When this extra line is executed it will print a count of the number of substitutions actually made. Note that `$status` is set to `1` in this case.
```
package Count ;
use Filter::Util::Call ;
sub filter
{
my ($self) = @_ ;
my ($status) ;
if (($status = filter_read()) > 0 ) {
s/Joe/Jim/g ;
++ $$self ;
}
elsif ($$self >= 0) { # EOF
$_ = "print q[Made ${$self} substitutions\n]" ;
$status = 1 ;
$$self = -1 ;
}
$status ;
}
sub import
{
my ($self) = @_ ;
my ($count) = 0 ;
filter_add(\$count) ;
}
1 ;
```
Here is a script which uses it:
```
use Count ;
print "Hello Joe\n" ;
print "Where is Joe\n" ;
```
Outputs:
```
Hello Jim
Where is Jim
Made 2 substitutions
```
###
Example 4: Using filter\_del
Another variation on a theme. This time we will modify the `Subst` filter to allow a starting and stopping pattern to be specified as well as the *from* and *to* patterns. If you know the *vi* editor, it is the equivalent of this command:
```
:/start/,/stop/s/from/to/
```
When used as a filter we want to invoke it like this:
```
use NewSubst qw(start stop from to) ;
```
Here is the module.
```
package NewSubst ;
use Filter::Util::Call ;
use Carp ;
sub import
{
my ($self, $start, $stop, $from, $to) = @_ ;
my ($found) = 0 ;
croak("usage: use Subst qw(start stop from to)")
unless @_ == 5 ;
filter_add(
sub
{
my ($status) ;
if (($status = filter_read()) > 0) {
$found = 1
if $found == 0 and /$start/ ;
if ($found) {
s/$from/$to/ ;
filter_del() if /$stop/ ;
}
}
$status ;
} )
}
1 ;
```
Filter::Simple
---------------
If you intend using the Filter::Call functionality, I would strongly recommend that you check out Damian Conway's excellent Filter::Simple module. Damian's module provides a much cleaner interface than Filter::Util::Call. Although it doesn't allow the fine control that Filter::Util::Call does, it should be adequate for the majority of applications. It's available at
```
http://search.cpan.org/dist/Filter-Simple/
```
AUTHOR
------
Paul Marquess
DATE
----
26th January 1996
LICENSE
-------
Copyright (c) 1995-2011 Paul Marquess. All rights reserved. Copyright (c) 2011-2014 Reini Urban. All rights reserved. Copyright (c) 2014-2017 cPanel Inc. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl perlglossary perlglossary
============
CONTENTS
--------
* [NAME](#NAME)
* [VERSION](#VERSION)
* [DESCRIPTION](#DESCRIPTION)
+ [A](#A)
+ [B](#B)
+ [C](#C)
+ [D](#D)
+ [E](#E)
+ [F](#F)
+ [G](#G)
+ [H](#H)
+ [I](#I)
+ [J](#J)
+ [K](#K)
+ [L](#L)
+ [M](#M)
+ [N](#N)
+ [O](#O)
+ [P](#P)
+ [Q](#Q)
+ [R](#R)
+ [S](#S)
+ [T](#T)
+ [U](#U)
+ [V](#V)
+ [W](#W)
+ [X](#X)
+ [Y](#Y)
+ [Z](#Z)
* [AUTHOR AND COPYRIGHT](#AUTHOR-AND-COPYRIGHT)
NAME
----
perlglossary - Perl Glossary
VERSION
-------
version 5.20210520
DESCRIPTION
-----------
A glossary of terms (technical and otherwise) used in the Perl documentation, derived from the Glossary of *Programming Perl*, Fourth Edition. Words or phrases in bold are defined elsewhere in this glossary.
Other useful sources include the Unicode Glossary <http://unicode.org/glossary/>, the Free On-Line Dictionary of Computing <http://foldoc.org/>, the Jargon File <http://catb.org/~esr/jargon/>, and Wikipedia <http://www.wikipedia.org/>.
### A
accessor methods A [**method**](#method) used to indirectly inspect or update an [**object**](#object)’s state (its [**instance variables**](#instance-variable)).
actual arguments The [**scalar values**](#scalar-value) that you supply to a [**function**](#function) or [**subroutine**](#subroutine) when you call it. For instance, when you call `power("puff")`, the string `"puff"` is the actual argument. See also [**argument**](#argument) and [**formal arguments**](#formal-arguments).
address operator Some languages work directly with the memory addresses of values, but this can be like playing with fire. Perl provides a set of asbestos gloves for handling all memory management. The closest to an address operator in Perl is the backslash operator, but it gives you a [**hard reference**](#hard-reference), which is much safer than a memory address.
algorithm A well-defined sequence of steps, explained clearly enough that even a computer could do them.
alias A nickname for something, which behaves in all ways as though you’d used the original name instead of the nickname. Temporary aliases are implicitly created in the loop variable for `foreach` loops, in the `$_` variable for `map` or `grep` operators, in `$a` and `$b` during `sort`’s comparison function, and in each element of `@_` for the [**actual arguments**](#actual-arguments) of a subroutine call. Permanent aliases are explicitly created in [**packages**](#package) by [**importing**](#import) symbols or by assignment to [**typeglobs**](#typeglob). Lexically scoped aliases for package variables are explicitly created by the `our` declaration.
alphabetic The sort of characters we put into words. In Unicode, this is all letters including all ideographs and certain diacritics, letter numbers like Roman numerals, and various combining marks.
alternatives A list of possible choices from which you may select only one, as in, “Would you like door A, B, or C?” Alternatives in regular expressions are separated with a single vertical bar: `|`. Alternatives in normal Perl expressions are separated with a double vertical bar: `||`. Logical alternatives in [**Boolean**](#Boolean) expressions are separated with either `||` or `or`.
anonymous Used to describe a [**referent**](#referent) that is not directly accessible through a named [**variable**](#variable). Such a referent must be indirectly accessible through at least one [**hard reference**](#hard-reference). When the last hard reference goes away, the anonymous referent is destroyed without pity.
application A bigger, fancier sort of [**program**](#program) with a fancier name so people don’t realize they are using a program.
architecture The kind of computer you’re working on, where one “kind of computer” means all those computers sharing a compatible machine language. Since Perl programs are (typically) simple text files, not executable images, a Perl program is much less sensitive to the architecture it’s running on than programs in other languages, such as C, that are [**compiled**](#compile) into machine code. See also [**platform**](#platform) and [**operating system**](#operating-system).
argument A piece of data supplied to a [**program**](#program), [**subroutine**](#subroutine), [**function**](#function), or [**method**](#method) to tell it what it’s supposed to do. Also called a “parameter”.
ARGV The name of the array containing the [**argument**](#argument) [**vector**](#vector) from the command line. If you use the empty `<>` operator, `ARGV` is the name of both the [**filehandle**](#filehandle) used to traverse the arguments and the [**scalar**](#scalar) containing the name of the current input file.
arithmetical operator A [**symbol**](#symbol) such as `+` or `/` that tells Perl to do the arithmetic you were supposed to learn in grade school.
array An ordered sequence of [**values**](#value), stored such that you can easily access any of the values using an *integer subscript* that specifies the value’s [**offset**](#offset) in the sequence.
array context An archaic expression for what is more correctly referred to as [**list context**](#list-context).
Artistic License The open source license that Larry Wall created for Perl, maximizing Perl’s usefulness, availability, and modifiability. The current version is 2. (<http://www.opensource.org/licenses/artistic-license.php>).
ASCII The American Standard Code for Information Interchange (a 7-bit character set adequate only for poorly representing English text). Often used loosely to describe the lowest 128 values of the various ISO-8859-X character sets, a bunch of mutually incompatible 8-bit codes best described as half ASCII. See also [**Unicode**](#Unicode).
assertion A component of a [**regular expression**](#regular-expression) that must be true for the pattern to match but does not necessarily match any characters itself. Often used specifically to mean a [**zero-width**](#zero-width) assertion.
assignment An [**operator**](#operator) whose assigned mission in life is to change the value of a [**variable**](#variable).
assignment operator Either a regular [**assignment**](#assignment) or a compound [**operator**](#operator) composed of an ordinary assignment and some other operator, that changes the value of a variable in place; that is, relative to its old value. For example, `$a += 2` adds `2` to `$a`.
associative array See [**hash**](#hash). Please. The term associative array is the old Perl 4 term for a [**hash**](#hash). Some languages call it a dictionary.
associativity Determines whether you do the left [**operator**](#operator) first or the right [**operator**](#operator) first when you have “A [**operator**](#operator) B [**operator**](#operator) C”, and the two operators are of the same precedence. Operators like `+` are left associative, while operators like `**` are right associative. See Camel chapter 3, “Unary and Binary Operators” for a list of operators and their associativity.
asynchronous Said of events or activities whose relative temporal ordering is indeterminate because too many things are going on at once. Hence, an asynchronous event is one you didn’t know when to expect.
atom A [**regular expression**](#regular-expression) component potentially matching a [**substring**](#substring) containing one or more characters and treated as an indivisible syntactic unit by any following [**quantifier**](#quantifier). (Contrast with an [**assertion**](#assertion) that matches something of [**zero width**](#zero-width) and may not be quantified.)
atomic operation When Democritus gave the word “atom” to the indivisible bits of matter, he meant literally something that could not be cut: *ἀ-* (not) + *-τομος* (cuttable). An atomic operation is an action that can’t be interrupted, not one forbidden in a nuclear-free zone.
attribute A new feature that allows the declaration of [**variables**](#variable) and [**subroutines**](#subroutine) with modifiers, as in `sub foo : locked method`. Also another name for an [**instance variable**](#instance-variable) of an [**object**](#object).
autogeneration A feature of [**operator overloading**](#operator-overloading) of [**objects**](#object), whereby the behavior of certain [**operators**](#operator) can be reasonably deduced using more fundamental operators. This assumes that the overloaded operators will often have the same relationships as the regular operators. See Camel chapter 13, “Overloading”.
autoincrement To add one to something automatically, hence the name of the `++` operator. To instead subtract one from something automatically is known as an “autodecrement”.
autoload To load on demand. (Also called “lazy” loading.) Specifically, to call an `AUTOLOAD` subroutine on behalf of an undefined subroutine.
autosplit To split a string automatically, as the *–a* [**switch**](#switch) does when running under *–p* or *–n* in order to emulate [**awk**](#awk). (See also the `AutoSplit` module, which has nothing to do with the `–a` switch but a lot to do with autoloading.)
autovivification A Graeco-Roman word meaning “to bring oneself to life”. In Perl, storage locations ([**lvalues**](#lvalue)) spontaneously generate themselves as needed, including the creation of any [**hard reference**](#hard-reference) values to point to the next level of storage. The assignment `$a[5][5][5][5][5] = "quintet"` potentially creates five scalar storage locations, plus four references (in the first four scalar locations) pointing to four new anonymous arrays (to hold the last four scalar locations). But the point of autovivification is that you don’t have to worry about it.
AV Short for “array value”, which refers to one of Perl’s internal data types that holds an [**array**](#array). The `AV` type is a subclass of [**SV**](#SV).
awk Descriptive editing term—short for “awkward”. Also coincidentally refers to a venerable text-processing language from which Perl derived some of its high-level ideas.
### B
backreference A substring [**captured**](#capturing) by a subpattern within unadorned parentheses in a [**regex**](#regex). Backslashed decimal numbers (`\1`, `\2`, etc.) later in the same pattern refer back to the corresponding subpattern in the current match. Outside the pattern, the numbered variables (`$1`, `$2`, etc.) continue to refer to these same values, as long as the pattern was the last successful match of the current [**dynamic scope**](#dynamic-scoping).
backtracking The practice of saying, “If I had to do it all over, I’d do it differently,” and then actually going back and doing it all over differently. Mathematically speaking, it’s returning from an unsuccessful recursion on a tree of possibilities. Perl backtracks when it attempts to match patterns with a [**regular expression**](#regular-expression), and its earlier attempts don’t pan out. See the section “The Little Engine That /Couldn(n’t)” in Camel chapter 5, “Pattern Matching”.
backward compatibility Means you can still run your old program because we didn’t break any of the features or bugs it was relying on.
bareword A word sufficiently ambiguous to be deemed illegal under `use strict 'subs'`. In the absence of that stricture, a bareword is treated as if quotes were around it.
base class A generic [**object**](#object) type; that is, a [**class**](#class) from which other, more specific classes are derived genetically by [**inheritance**](#inheritance). Also called a “superclass” by people who respect their ancestors.
big-endian From Swift: someone who eats eggs big end first. Also used of computers that store the most significant [**byte**](#byte) of a word at a lower byte address than the least significant byte. Often considered superior to little-endian machines. See also [**little-endian**](#little-endian).
binary Having to do with numbers represented in base 2. That means there’s basically two numbers: 0 and 1. Also used to describe a file of “nontext”, presumably because such a file makes full use of all the binary bits in its bytes. With the advent of [**Unicode**](#Unicode), this distinction, already suspect, loses even more of its meaning.
binary operator An [**operator**](#operator) that takes two [**operands**](#operand).
bind To assign a specific [**network address**](#network-address) to a [**socket**](#socket).
bit An integer in the range from 0 to 1, inclusive. The smallest possible unit of information storage. An eighth of a [**byte**](#byte) or of a dollar. (The term “Pieces of Eight” comes from being able to split the old Spanish dollar into 8 bits, each of which still counted for money. That’s why a 25- cent piece today is still “two bits”.)
bit shift The movement of bits left or right in a computer word, which has the effect of multiplying or dividing by a power of 2.
bit string A sequence of [**bits**](#bit) that is actually being thought of as a sequence of bits, for once.
bless In corporate life, to grant official approval to a thing, as in, “The VP of Engineering has blessed our WebCruncher project.” Similarly, in Perl, to grant official approval to a [**referent**](#referent) so that it can function as an [**object**](#object), such as a WebCruncher object. See the `bless` function in Camel chapter 27, “Functions”.
block What a [**process**](#process) does when it has to wait for something: “My process blocked waiting for the disk.” As an unrelated noun, it refers to a large chunk of data, of a size that the [**operating system**](#operating-system) likes to deal with (normally a power of 2 such as 512 or 8192). Typically refers to a chunk of data that’s coming from or going to a disk file.
BLOCK A syntactic construct consisting of a sequence of Perl [**statements**](#statement) that is delimited by braces. The `if` and `while` statements are defined in terms of *`BLOCK`*s, for instance. Sometimes we also say “block” to mean a lexical scope; that is, a sequence of statements that acts like a *`BLOCK`*, such as within an `eval` or a file, even though the statements aren’t delimited by braces.
block buffering A method of making input and output efficient by passing one [**block**](#BLOCK) at a time. By default, Perl does block buffering to disk files. See [**buffer**](#buffer) and [**command buffering**](#command-buffering).
Boolean A value that is either [**true**](#true) or [**false**](#false).
Boolean context A special kind of [**scalar context**](#scalar-context) used in conditionals to decide whether the [**scalar value**](#scalar-value) returned by an expression is [**true**](#true) or [**false**](#false). Does not evaluate as either a string or a number. See [**context**](#context).
breakpoint A spot in your program where you’ve told the debugger to stop [**execution**](#execute) so you can poke around and see whether anything is wrong yet.
broadcast To send a [**datagram**](#datagram) to multiple destinations simultaneously.
BSD A psychoactive drug, popular in the ’80s, probably developed at UC Berkeley or thereabouts. Similar in many ways to the prescription-only medication called “System V”, but infinitely more useful. (Or, at least, more fun.) The full chemical name is “Berkeley Standard Distribution”.
bucket A location in a [**hash table**](#hash-table) containing (potentially) multiple entries whose keys “hash” to the same hash value according to its hash function. (As internal policy, you don’t have to worry about it unless you’re into internals, or policy.)
buffer A temporary holding location for data. Data that are [**Block buffering**](#block-buffering) means that the data is passed on to its destination whenever the buffer is full. [**Line buffering**](#line-buffering) means that it’s passed on whenever a complete line is received. [**Command buffering**](#command-buffering) means that it’s passed every time you do a `print` command (or equivalent). If your output is unbuffered, the system processes it one byte at a time without the use of a holding area. This can be rather inefficient.
built-in A [**function**](#function) that is predefined in the language. Even when hidden by [**overriding**](#overriding), you can always get at a built- in function by [**qualifying**](#qualified) its name with the `CORE::` pseudopackage.
bundle A group of related modules on [**CPAN**](#CPAN). (Also sometimes refers to a group of command-line switches grouped into one [**switch cluster**](#switch-cluster).)
byte A piece of data worth eight [**bits**](#bit) in most places.
bytecode A pidgin-like lingo spoken among ’droids when they don’t wish to reveal their orientation (see [**endian**](#endian)). Named after some similar languages spoken (for similar reasons) between compilers and interpreters in the late 20ᵗʰ century. These languages are characterized by representing everything as a nonarchitecture-dependent sequence of bytes.
### C
C A language beloved by many for its inside-out [**type**](#type) definitions, inscrutable [**precedence**](#precedence) rules, and heavy [**overloading**](#overloading) of the function-call mechanism. (Well, actually, people first switched to C because they found lowercase identifiers easier to read than upper.) Perl is written in C, so it’s not surprising that Perl borrowed a few ideas from it.
cache A data repository. Instead of computing expensive answers several times, compute it once and save the result.
callback A [**handler**](#handler) that you register with some other part of your program in the hope that the other part of your program will [**trigger**](#trigger) your handler when some event of interest transpires.
call by reference An [**argument**](#argument)-passing mechanism in which the [**formal arguments**](#formal-arguments) refer directly to the [**actual arguments**](#actual-arguments), and the [**subroutine**](#subroutine) can change the actual arguments by changing the formal arguments. That is, the formal argument is an [**alias**](#alias) for the actual argument. See also [**call by value**](#call-by-value).
call by value An [**argument**](#argument)-passing mechanism in which the [**formal arguments**](#formal-arguments) refer to a copy of the [**actual arguments**](#actual-arguments), and the [**subroutine**](#subroutine) cannot change the actual arguments by changing the formal arguments. See also [**call by reference**](#call-by-reference).
canonical Reduced to a standard form to facilitate comparison.
capture variables The variables—such as `$1` and `$2`, and `%+` and `%–` —that hold the text remembered in a pattern match. See Camel chapter 5, “Pattern Matching”.
capturing The use of parentheses around a [**subpattern**](#subpattern) in a [**regular expression**](#regular-expression) to store the matched [**substring**](#substring) as a [**backreference**](#backreference). (Captured strings are also returned as a list in [**list context**](#list-context).) See Camel chapter 5, “Pattern Matching”.
cargo cult Copying and pasting code without understanding it, while superstitiously believing in its value. This term originated from preindustrial cultures dealing with the detritus of explorers and colonizers of technologically advanced cultures. See *The Gods Must Be Crazy*.
case A property of certain characters. Originally, typesetter stored capital letters in the upper of two cases and small letters in the lower one. Unicode recognizes three cases: [**lowercase**](#lowercase) ([**character property**](#character-property) `\p{lower}`), [**titlecase**](#titlecase) (`\p{title}`), and [**uppercase**](#uppercase) (`\p{upper}`). A fourth casemapping called [**foldcase**](#foldcase) is not itself a distinct case, but it is used internally to implement [**casefolding**](#casefolding). Not all letters have case, and some nonletters have case.
casefolding Comparing or matching a string case-insensitively. In Perl, it is implemented with the `/i` pattern modifier, the `fc` function, and the `\F` double-quote translation escape.
casemapping The process of converting a string to one of the four Unicode [**casemaps**](#case); in Perl, it is implemented with the `fc`, `lc`, `ucfirst`, and `uc` functions.
character The smallest individual element of a string. Computers store characters as integers, but Perl lets you operate on them as text. The integer used to represent a particular character is called that character’s [**codepoint**](#codepoint).
character class A square-bracketed list of characters used in a [**regular expression**](#regular-expression) to indicate that any character of the set may occur at a given point. Loosely, any predefined set of characters so used.
character property A predefined [**character class**](#character-class) matchable by the `\p` or `\P` [**metasymbol**](#metasymbol). [**Unicode**](#Unicode) defines hundreds of standard properties for every possible codepoint, and Perl defines a few of its own, too.
circumfix operator An [**operator**](#operator) that surrounds its [**operand**](#operand), like the angle operator, or parentheses, or a hug.
class A user-defined [**type**](#type), implemented in Perl via a [**package**](#package) that provides (either directly or by inheritance) [**methods**](#method) (that is, [**subroutines**](#subroutine)) to handle [**instances**](#instance) of the class (its [**objects**](#object)). See also [**inheritance**](#inheritance).
class method A [**method**](#method) whose [**invocant**](#invocant) is a [**package**](#package) name, not an [**object**](#object) reference. A method associated with the class as a whole. Also see [**instance method**](#instance-method).
client In networking, a [**process**](#process) that initiates contact with a [**server**](#server) process in order to exchange data and perhaps receive a service.
closure An [**anonymous**](#anonymous) subroutine that, when a reference to it is generated at runtime, keeps track of the identities of externally visible [**lexical variables**](#lexical-variable), even after those lexical variables have supposedly gone out of [**scope**](#scope). They’re called “closures” because this sort of behavior gives mathematicians a sense of closure.
cluster A parenthesized [**subpattern**](#subpattern) used to group parts of a [**regular expression**](#regular-expression) into a single [**atom**](#atom).
CODE The word returned by the `ref` function when you apply it to a reference to a subroutine. See also [**CV**](#CV).
code generator A system that writes code for you in a low-level language, such as code to implement the backend of a compiler. See [**program generator**](#program-generator).
codepoint The integer a computer uses to represent a given character. ASCII codepoints are in the range 0 to 127; Unicode codepoints are in the range 0 to 0x1F\_FFFF; and Perl codepoints are in the range 0 to 2³²−1 or 0 to 2⁶⁴−1, depending on your native integer size. In Perl Culture, sometimes called [**ordinals**](#ordinal).
code subpattern A [**regular expression**](#regular-expression) subpattern whose real purpose is to execute some Perl code—for example, the `(?{...})` and `(??{...})` subpatterns.
collating sequence The order into which [**characters**](#character) sort. This is used by [**string**](#string) comparison routines to decide, for example, where in this glossary to put “collating sequence”.
co-maintainer A person with permissions to index a [**namespace**](#namespace) in [**PAUSE**](#PAUSE). Anyone can upload any namespace, but only primary and co-maintainers get their contributions indexed.
combining character Any character with the General Category of Combining Mark (`\p{GC=M}`), which may be spacing or nonspacing. Some are even invisible. A sequence of combining characters following a grapheme base character together make up a single user-visible character called a [**grapheme**](#grapheme). Most but not all diacritics are combining characters, and vice versa.
command In [**shell**](#shell) programming, the syntactic combination of a program name and its arguments. More loosely, anything you type to a shell (a command interpreter) that starts it doing something. Even more loosely, a Perl [**statement**](#statement), which might start with a [**label**](#label) and typically ends with a semicolon.
command buffering A mechanism in Perl that lets you store up the output of each Perl [**command**](#command) and then flush it out as a single request to the [**operating system**](#operating-system). It’s enabled by setting the `$|` (`$AUTOFLUSH`) variable to a true value. It’s used when you don’t want data sitting around, not going where it’s supposed to, which may happen because the default on a [**file**](#file) or [**pipe**](#pipe) is to use [**block buffering**](#block-buffering).
command-line arguments The [**values**](#value) you supply along with a program name when you tell a [**shell**](#shell) to execute a [**command**](#command). These values are passed to a Perl program through `@ARGV`.
command name The name of the program currently executing, as typed on the command line. In C, the [**command**](#command) name is passed to the program as the first command-line argument. In Perl, it comes in separately as `$0`.
comment A remark that doesn’t affect the meaning of the program. In Perl, a comment is introduced by a `#` character and continues to the end of the line.
compilation unit The [**file**](#file) (or [**string**](#string), in the case of `eval`) that is currently being [**compiled**](#compile).
compile The process of turning source code into a machine-usable form. See [**compile phase**](#compile-phase).
compile phase Any time before Perl starts running your main program. See also [**run phase**](#run-phase). Compile phase is mostly spent in [**compile time**](#compile-time), but may also be spent in [**runtime**](#runtime) when `BEGIN` blocks, `use` or `no` declarations, or constant subexpressions are being evaluated. The startup and import code of any `use` declaration is also run during compile phase.
compiler Strictly speaking, a program that munches up another program and spits out yet another file containing the program in a “more executable” form, typically containing native machine instructions. The *perl* program is not a compiler by this definition, but it does contain a kind of compiler that takes a program and turns it into a more executable form ([**syntax trees**](#syntax-tree)) within the *perl* process itself, which the [**interpreter**](#interpreter) then interprets. There are, however, extension [**modules**](#module) to get Perl to act more like a “real” compiler. See Camel chapter 16, “Compiling”.
compile time The time when Perl is trying to make sense of your code, as opposed to when it thinks it knows what your code means and is merely trying to do what it thinks your code says to do, which is [**runtime**](#runtime).
composer A “constructor” for a [**referent**](#referent) that isn’t really an [**object**](#object), like an anonymous array or a hash (or a sonata, for that matter). For example, a pair of braces acts as a composer for a hash, and a pair of brackets acts as a composer for an array. See the section “Creating References” in Camel chapter 8, “References”.
concatenation The process of gluing one cat’s nose to another cat’s tail. Also a similar operation on two [**strings**](#string).
conditional Something “iffy”. See [**Boolean context**](#Boolean-context).
connection In telephony, the temporary electrical circuit between the caller’s and the callee’s phone. In networking, the same kind of temporary circuit between a [**client**](#client) and a [**server**](#server).
construct As a noun, a piece of syntax made up of smaller pieces. As a transitive verb, to create an [**object**](#object) using a [**constructor**](#constructor).
constructor Any [**class method**](#class-method), [**instance**](#instance), or [**subroutine**](#subroutine) that composes, initializes, blesses, and returns an [**object**](#object). Sometimes we use the term loosely to mean a [**composer**](#composer).
context The surroundings or environment. The context given by the surrounding code determines what kind of data a particular [**expression**](#expression) is expected to return. The three primary contexts are [**list context**](#list-context), [**scalar**](#scalar), and [**void context**](#void-context). Scalar context is sometimes subdivided into [**Boolean context**](#Boolean-context), [**numeric context**](#numeric-context), [**string context**](#string-context), and [**void context**](#void-context). There’s also a “don’t care” context (which is dealt with in Camel chapter 2, “Bits and Pieces”, if you care).
continuation The treatment of more than one physical [**line**](#line) as a single logical line. [**Makefile**](#Makefile) lines are continued by putting a backslash before the [**newline**](#newline). Mail headers, as defined by RFC 822, are continued by putting a space or tab *after* the newline. In general, lines in Perl do not need any form of continuation mark, because [**whitespace**](#whitespace) (including newlines) is gleefully ignored. Usually.
core dump The corpse of a [**process**](#process), in the form of a file left in the [**working directory**](#working-directory) of the process, usually as a result of certain kinds of fatal errors.
CPAN The Comprehensive Perl Archive Network. (See the Camel Preface and Camel chapter 19, “CPAN” for details.)
C preprocessor The typical C compiler’s first pass, which processes lines beginning with `#` for conditional compilation and macro definition, and does various manipulations of the program text based on the current definitions. Also known as *cpp*(1).
cracker Someone who breaks security on computer systems. A cracker may be a true [**hacker**](#hacker) or only a [**script kiddie**](#script-kiddie).
currently selected output channel The last [**filehandle**](#filehandle) that was designated with `select(FILEHANDLE)`; `STDOUT`, if no filehandle has been selected.
current package The [**package**](#package) in which the current statement is [**compiled**](#compile). Scan backward in the text of your program through the current [**lexical scope**](#lexical-scoping) or any enclosing lexical scopes until you find a package declaration. That’s your current package name.
current working directory See [**working directory**](#working-directory).
CV In academia, a curriculum vitæ, a fancy kind of résumé. In Perl, an internal “code value” typedef holding a [**subroutine**](#subroutine). The `CV` type is a subclass of [**SV**](#SV).
### D
dangling statement A bare, single [**statement**](#statement), without any braces, hanging off an `if` or `while` conditional. C allows them. Perl doesn’t.
datagram A packet of data, such as a [**UDP**](#UDP) message, that (from the viewpoint of the programs involved) can be sent independently over the network. (In fact, all packets are sent independently at the [**IP**](#IP) level, but [**stream**](#stream) protocols such as [**TCP**](#TCP) hide this from your program.)
data structure How your various pieces of data relate to each other and what shape they make when you put them all together, as in a rectangular table or a triangular tree.
data type A set of possible values, together with all the operations that know how to deal with those values. For example, a numeric data type has a certain set of numbers that you can work with, as well as various mathematical operations that you can do on the numbers, but would make little sense on, say, a string such as `"Kilroy"`. Strings have their own operations, such as [**concatenation**](#concatenation). Compound types made of a number of smaller pieces generally have operations to compose and decompose them, and perhaps to rearrange them. [**Objects**](#object) that model things in the real world often have operations that correspond to real activities. For instance, if you model an elevator, your elevator object might have an `open_door` [**method**](#method).
DBM Stands for “Database Management” routines, a set of routines that emulate an [**associative array**](#associative-array) using disk files. The routines use a dynamic hashing scheme to locate any entry with only two disk accesses. DBM files allow a Perl program to keep a persistent [**hash**](#hash) across multiple invocations. You can `tie` your hash variables to various DBM implementations.
declaration An [**assertion**](#assertion) that states something exists and perhaps describes what it’s like, without giving any commitment as to how or where you’ll use it. A declaration is like the part of your recipe that says, “two cups flour, one large egg, four or five tadpoles…” See [**statement**](#statement) for its opposite. Note that some declarations also function as statements. Subroutine declarations also act as definitions if a body is supplied.
declarator Something that tells your program what sort of variable you’d like. Perl doesn’t require you to declare variables, but you can use `my`, `our`, or `state` to denote that you want something other than the default.
decrement To subtract a value from a variable, as in “decrement `$x`” (meaning to remove 1 from its value) or “decrement `$x` by 3”.
default A [**value**](#value) chosen for you if you don’t supply a value of your own.
defined Having a meaning. Perl thinks that some of the things people try to do are devoid of meaning; in particular, making use of variables that have never been given a [**value**](#value) and performing certain operations on data that isn’t there. For example, if you try to read data past the end of a file, Perl will hand you back an undefined value. See also [**false**](#false) and the `defined` entry in Camel chapter 27, “Functions”.
delimiter A [**character**](#character) or [**string**](#string) that sets bounds to an arbitrarily sized textual object, not to be confused with a [**separator**](#separator) or [**terminator**](#terminator). “To delimit” really just means “to surround” or “to enclose” (like these parentheses are doing).
dereference A fancy computer science term meaning “to follow a [**reference**](#reference) to what it points to”. The “de” part of it refers to the fact that you’re taking away one level of [**indirection**](#indirection).
derived class A [**class**](#class) that defines some of its [**methods**](#method) in terms of a more generic class, called a [**base class**](#base-class). Note that classes aren’t classified exclusively into base classes or derived classes: a class can function as both a derived class and a base class simultaneously, which is kind of classy.
descriptor See [**file descriptor**](#file-descriptor).
destroy To deallocate the memory of a [**referent**](#referent) (first triggering its `DESTROY` method, if it has one).
destructor A special [**method**](#method) that is called when an [**object**](#object) is thinking about [**destroying**](#destroy) itself. A Perl program’s `DESTROY` method doesn’t do the actual destruction; Perl just [**triggers**](#trigger) the method in case the [**class**](#class) wants to do any associated cleanup.
device A whiz-bang hardware gizmo (like a disk or tape drive or a modem or a joystick or a mouse) attached to your computer, which the [**operating system**](#operating-system) tries to make look like a [**file**](#file) (or a bunch of files). Under Unix, these fake files tend to live in the */dev* directory.
directive A [**pod**](#pod) directive. See Camel chapter 23, “Plain Old Documentation”.
directory A special file that contains other files. Some [**operating systems**](#operating-system) call these “folders”, “drawers”, “catalogues”, or “catalogs”.
directory handle A name that represents a particular instance of opening a directory to read it, until you close it. See the `opendir` function.
discipline Some people need this and some people avoid it. For Perl, it’s an old way to say [**I/O layer**](#I/O-layer).
dispatch To send something to its correct destination. Often used metaphorically to indicate a transfer of programmatic control to a destination selected algorithmically, often by lookup in a table of function [**references**](#reference) or, in the case of object [**methods**](#method), by traversing the inheritance tree looking for the most specific definition for the method.
distribution A standard, bundled release of a system of software. The default usage implies source code is included. If that is not the case, it will be called a “binary-only” distribution.
dual-lived Some modules live both in the [**Standard Library**](#Standard-Library) and on [**CPAN**](#CPAN). These modules might be developed on two tracks as people modify either version. The trend currently is to untangle these situations.
dweomer An enchantment, illusion, phantasm, or jugglery. Said when Perl’s magical [**dwimmer**](#dwimmer) effects don’t do what you expect, but rather seem to be the product of arcane *dweomercraft*, sorcery, or wonder working. [From Middle English.]
dwimmer DWIM is an acronym for “Do What I Mean”, the principle that something should just do what you want it to do without an undue amount of fuss. A bit of code that does “dwimming” is a “dwimmer”. Dwimming can require a great deal of behind-the-scenes magic, which (if it doesn’t stay properly behind the scenes) is called a [**dweomer**](#dweomer) instead.
dynamic scoping Dynamic scoping works over a [**dynamic scope**](#dynamic-scoping), making variables visible throughout the rest of the [**block**](#BLOCK) in which they are first used and in any [**subroutines**](#subroutine) that are called by the rest of the block. Dynamically scoped variables can have their values temporarily changed (and implicitly restored later) by a `local` operator. (Compare [**lexical scoping**](#lexical-scoping).) Used more loosely to mean how a subroutine that is in the middle of calling another subroutine “contains” that subroutine at [**runtime**](#runtime).
### E
eclectic Derived from many sources. Some would say *too* many.
element A basic building block. When you’re talking about an [**array**](#array), it’s one of the items that make up the array.
embedding When something is contained in something else, particularly when that might be considered surprising: “I’ve embedded a complete Perl interpreter in my editor!”
empty subclass test The notion that an empty [**derived class**](#derived-class) should behave exactly like its [**base class**](#base-class).
encapsulation The veil of abstraction separating the [**interface**](#interface) from the [**implementation**](#implementation) (whether enforced or not), which mandates that all access to an [**object**](#object)’s state be through [**methods**](#method) alone.
endian See [**little-endian**](#little-endian) and [**big-endian**](#big-endian).
en passant When you change a [**value**](#value) as it is being copied. [From French “in passing”, as in the exotic pawn-capturing maneuver in chess.]
environment The collective set of [**environment variables**](#environment-variable) your [**process**](#process) inherits from its parent. Accessed via `%ENV`.
environment variable A mechanism by which some high-level agent such as a user can pass its preferences down to its future offspring (child [**processes**](#process), grandchild processes, great-grandchild processes, and so on). Each environment variable is a [**key**](#key)/[**value**](#value) pair, like one entry in a [**hash**](#hash).
EOF End of File. Sometimes used metaphorically as the terminating string of a [**here document**](#here-document).
errno The error number returned by a [**syscall**](#syscall) when it fails. Perl refers to the error by the name `$!` (or `$OS_ERROR` if you use the English module).
error See [**exception**](#exception) or [**fatal error**](#fatal-error).
escape sequence See [**metasymbol**](#metasymbol).
exception A fancy term for an error. See [**fatal error**](#fatal-error).
exception handling The way a program responds to an error. The exception-handling mechanism in Perl is the `eval` operator.
exec To throw away the current [**process**](#process)’s program and replace it with another, without exiting the process or relinquishing any resources held (apart from the old memory image).
executable file A [**file**](#file) that is specially marked to tell the [**operating system**](#operating-system) that it’s okay to run this file as a program. Usually shortened to “executable”.
execute To run a [**program**](#program) or [**subroutine**](#subroutine). (Has nothing to do with the `kill` built-in, unless you’re trying to run a [**signal handler**](#signal-handler).)
execute bit The special mark that tells the operating system it can run this program. There are actually three execute bits under Unix, and which bit gets used depends on whether you own the file singularly, collectively, or not at all.
exit status See [**status**](#status).
exploit Used as a noun in this case, this refers to a known way to compromise a program to get it to do something the author didn’t intend. Your task is to write unexploitable programs.
export To make symbols from a [**module**](#module) available for [**import**](#import) by other modules.
expression Anything you can legally say in a spot where a [**value**](#value) is required. Typically composed of [**literals**](#literal), [**variables**](#variable), [**operators**](#operator), [**functions**](#function), and [**subroutine**](#subroutine) calls, not necessarily in that order.
extension A Perl module that also pulls in [**compiled**](#compile) C or C++ code. More generally, any experimental option that can be [**compiled**](#compile) into Perl, such as multithreading.
### F
false In Perl, any value that would look like `""` or `"0"` if evaluated in a string context. Since undefined values evaluate to `""`, all undefined values are false, but not all false values are undefined.
FAQ Frequently Asked Question (although not necessarily frequently answered, especially if the answer appears in the Perl FAQ shipped standard with Perl).
fatal error An uncaught [**exception**](#exception), which causes termination of the [**process**](#process) after printing a message on your [**standard error**](#standard-error) stream. Errors that happen inside an `eval` are not fatal. Instead, the `eval` terminates after placing the exception message in the `$@` (`$EVAL_ERROR`) variable. You can try to provoke a fatal error with the `die` operator (known as throwing or raising an exception), but this may be caught by a dynamically enclosing `eval`. If not caught, the `die` becomes a fatal error.
feeping creaturism A spoonerism of “creeping featurism”, noting the biological urge to add just one more feature to a program.
field A single piece of numeric or string data that is part of a longer [**string**](#string), [**record**](#record), or [**line**](#line). Variable-width fields are usually split up by [**separators**](#separator) (so use `split` to extract the fields), while fixed-width fields are usually at fixed positions (so use `unpack`). [**Instance variables**](#instance-variable) are also known as “fields”.
FIFO First In, First Out. See also [**LIFO**](#LIFO). Also a nickname for a [**named pipe**](#named-pipe).
file A named collection of data, usually stored on disk in a [**directory**](#directory) in a [**filesystem**](#filesystem). Roughly like a document, if you’re into office metaphors. In modern filesystems, you can actually give a file more than one name. Some files have special properties, like directories and devices.
file descriptor The little number the [**operating system**](#operating-system) uses to keep track of which opened [**file**](#file) you’re talking about. Perl hides the file descriptor inside a [**standard I/O**](#standard-I/O) stream and then attaches the stream to a [**filehandle**](#filehandle).
fileglob A “wildcard” match on [**filenames**](#filename). See the `glob` function.
filehandle An identifier (not necessarily related to the real name of a file) that represents a particular instance of opening a file, until you close it. If you’re going to open and close several different files in succession, it’s fine to open each of them with the same filehandle, so you don’t have to write out separate code to process each file.
filename One name for a file. This name is listed in a [**directory**](#directory). You can use it in an `open` to tell the [**operating system**](#operating-system) exactly which file you want to open, and associate the file with a [**filehandle**](#filehandle), which will carry the subsequent identity of that file in your program, until you close it.
filesystem A set of [**directories**](#directory) and [**files**](#file) residing on a partition of the disk. Sometimes known as a “partition”. You can change the file’s name or even move a file around from directory to directory within a filesystem without actually moving the file itself, at least under Unix.
file test operator A built-in unary operator that you use to determine whether something is [**true**](#true) about a file, such as `–o $filename` to test whether you’re the owner of the file.
filter A program designed to take a [**stream**](#stream) of input and transform it into a stream of output.
first-come The first [**PAUSE**](#PAUSE) author to upload a [**namespace**](#namespace) automatically becomes the [**primary maintainer**](#primary-maintainer) for that namespace. The “first come” permissions distinguish a [**primary maintainer**](#primary-maintainer) who was assigned that role from one who received it automatically.
flag We tend to avoid this term because it means so many things. It may mean a command-line [**switch**](#switch) that takes no argument itself (such as Perl’s `–n` and `–p` flags) or, less frequently, a single-bit indicator (such as the `O_CREAT` and `O_EXCL` flags used in `sysopen`). Sometimes informally used to refer to certain regex modifiers.
floating point A method of storing numbers in “scientific notation”, such that the precision of the number is independent of its magnitude (the decimal point “floats”). Perl does its numeric work with floating-point numbers (sometimes called “floats”) when it can’t get away with using [**integers**](#integer). Floating-point numbers are mere approximations of real numbers.
flush The act of emptying a [**buffer**](#buffer), often before it’s full.
FMTEYEWTK Far More Than Everything You Ever Wanted To Know. An exhaustive treatise on one narrow topic, something of a super-[**FAQ**](#FAQ). See Tom for far more.
foldcase The casemap used in Unicode when comparing or matching without regard to case. Comparing lower-, title-, or uppercase are all unreliable due to Unicode’s complex, one-to-many case mappings. Foldcase is a [**lowercase**](#lowercase) variant (using a partially decomposed [**normalization**](#normalization) form for certain codepoints) created specifically to resolve this.
fork To create a child [**process**](#process) identical to the parent process at its moment of conception, at least until it gets ideas of its own. A thread with protected memory.
formal arguments The generic names by which a [**subroutine**](#subroutine) knows its [**arguments**](#argument). In many languages, formal arguments are always given individual names; in Perl, the formal arguments are just the elements of an array. The formal arguments to a Perl program are `$ARGV[0]`, `$ARGV[1]`, and so on. Similarly, the formal arguments to a Perl subroutine are `$_[0]`, `$_[1]`, and so on. You may give the arguments individual names by assigning the values to a `my` list. See also [**actual arguments**](#actual-arguments).
format A specification of how many spaces and digits and things to put somewhere so that whatever you’re printing comes out nice and pretty.
freely available Means you don’t have to pay money to get it, but the copyright on it may still belong to someone else (like Larry).
freely redistributable Means you’re not in legal trouble if you give a bootleg copy of it to your friends and we find out about it. In fact, we’d rather you gave a copy to all your friends.
freeware Historically, any software that you give away, particularly if you make the source code available as well. Now often called [**open source software**](#open-source-software). Recently there has been a trend to use the term in contradistinction to [**open source software**](#open-source-software), to refer only to free software released under the Free Software Foundation’s GPL (General Public License), but this is difficult to justify etymologically.
function Mathematically, a mapping of each of a set of input values to a particular output value. In computers, refers to a [**subroutine**](#subroutine) or [**operator**](#operator) that returns a [**value**](#value). It may or may not have input values (called [**arguments**](#argument)).
funny character Someone like Larry, or one of his peculiar friends. Also refers to the strange prefixes that Perl requires as noun markers on its variables.
### G
garbage collection A misnamed feature—it should be called, “expecting your mother to pick up after you”. Strictly speaking, Perl doesn’t do this, but it relies on a reference-counting mechanism to keep things tidy. However, we rarely speak strictly and will often refer to the reference-counting scheme as a form of garbage collection. (If it’s any comfort, when your interpreter exits, a “real” garbage collector runs to make sure everything is cleaned up if you’ve been messy with circular references and such.)
GID Group ID—in Unix, the numeric group ID that the [**operating system**](#operating-system) uses to identify you and members of your [**group**](#group).
glob Strictly, the shell’s `*` character, which will match a “glob” of characters when you’re trying to generate a list of filenames. Loosely, the act of using globs and similar symbols to do pattern matching. See also [**fileglob**](#fileglob) and [**typeglob**](#typeglob).
global Something you can see from anywhere, usually used of [**variables**](#variable) and [**subroutines**](#subroutine) that are visible everywhere in your program. In Perl, only certain special variables are truly global—most variables (and all subroutines) exist only in the current [**package**](#package). Global variables can be declared with `our`. See “Global Declarations” in Camel chapter 4, “Statements and Declarations”.
global destruction The [**garbage collection**](#garbage-collection) of globals (and the running of any associated object destructors) that takes place when a Perl [**interpreter**](#interpreter) is being shut down. Global destruction should not be confused with the Apocalypse, except perhaps when it should.
glue language A language such as Perl that is good at hooking things together that weren’t intended to be hooked together.
granularity The size of the pieces you’re dealing with, mentally speaking.
grapheme A graphene is an allotrope of carbon arranged in a hexagonal crystal lattice one atom thick. A [**grapheme**](#grapheme), or more fully, a *grapheme cluster string* is a single user-visible [**character**](#character), which may in turn be several characters ([**codepoints**](#codepoint)) long. For example, a carriage return plus a line feed is a single grapheme but two characters, while a “ȫ” is a single grapheme but one, two, or even three characters, depending on [**normalization**](#normalization).
greedy A [**subpattern**](#subpattern) whose [**quantifier**](#quantifier) wants to match as many things as possible.
grep Originally from the old Unix editor command for “Globally search for a Regular Expression and Print it”, now used in the general sense of any kind of search, especially text searches. Perl has a built-in `grep` function that searches a list for elements matching any given criterion, whereas the [**grep**](#grep)(1) program searches for lines matching a [**regular expression**](#regular-expression) in one or more files.
group A set of users of which you are a member. In some operating systems (like Unix), you can give certain file access permissions to other members of your group.
GV An internal “glob value” typedef, holding a [**typeglob**](#typeglob). The `GV` type is a subclass of [**SV**](#SV).
### H
hacker Someone who is brilliantly persistent in solving technical problems, whether these involve golfing, fighting orcs, or programming. Hacker is a neutral term, morally speaking. Good hackers are not to be confused with evil [**crackers**](#cracker) or clueless [**script kiddies**](#script-kiddie). If you confuse them, we will presume that you are either evil or clueless.
handler A [**subroutine**](#subroutine) or [**method**](#method) that Perl calls when your program needs to respond to some internal event, such as a [**signal**](#signal), or an encounter with an operator subject to [**operator overloading**](#operator-overloading). See also [**callback**](#callback).
hard reference A [**scalar**](#scalar) [**value**](#value) containing the actual address of a [**referent**](#referent), such that the referent’s [**reference**](#reference) count accounts for it. (Some hard references are held internally, such as the implicit reference from one of a [**typeglob**](#typeglob)’s variable slots to its corresponding referent.) A hard reference is different from a [**symbolic reference**](#symbolic-reference).
hash An unordered association of [**key**](#key)/[**value**](#value) pairs, stored such that you can easily use a string [**key**](#key) to look up its associated data [**value**](#value). This glossary is like a hash, where the word to be defined is the key and the definition is the value. A hash is also sometimes septisyllabically called an “associative array”, which is a pretty good reason for simply calling it a “hash” instead.
hash table A data structure used internally by Perl for implementing associative arrays (hashes) efficiently. See also [**bucket**](#bucket).
header file A file containing certain required definitions that you must include “ahead” of the rest of your program to do certain obscure operations. A C header file has a *.h* extension. Perl doesn’t really have header files, though historically Perl has sometimes used translated *.h* files with a *.ph* extension. See `require` in Camel chapter 27, “Functions”. (Header files have been superseded by the [**module**](#module) mechanism.)
here document So called because of a similar construct in [**shells**](#shell) that pretends that the [**lines**](#line) following the [**command**](#command) are a separate [**file**](#file) to be fed to the command, up to some terminating string. In Perl, however, it’s just a fancy form of quoting.
hexadecimal A number in base 16, “hex” for short. The digits for 10 through 15 are customarily represented by the letters `a` through `f`. Hexadecimal constants in Perl start with `0x`. See also the `hex` function in Camel chapter 27, “Functions”.
home directory The directory you are put into when you log in. On a Unix system, the name is often placed into `$ENV{HOME}` or `$ENV{LOGDIR}` by *login*, but you can also find it with `(get``pwuid($<))[7]`. (Some platforms do not have a concept of a home directory.)
host The computer on which a program or other data resides.
hubris Excessive pride, the sort of thing for which Zeus zaps you. Also the quality that makes you write (and maintain) programs that other people won’t want to say bad things about. Hence, the third great virtue of a programmer. See also [**laziness**](#laziness) and [**impatience**](#impatience).
HV Short for a “hash value” typedef, which holds Perl’s internal representation of a hash. The `HV` type is a subclass of [**SV**](#SV).
### I
identifier A legally formed name for most anything in which a computer program might be interested. Many languages (including Perl) allow identifiers to start with an alphabetic character, and then contain alphabetics and digits. Perl also allows connector punctuation like the underscore character wherever it allows alphabetics. (Perl also has more complicated names, like [**qualified**](#qualified) names.)
impatience The anger you feel when the computer is being lazy. This makes you write programs that don’t just react to your needs, but actually anticipate them. Or at least that pretend to. Hence, the second great virtue of a programmer. See also [**laziness**](#laziness) and [**hubris**](#hubris).
implementation How a piece of code actually goes about doing its job. Users of the code should not count on implementation details staying the same unless they are part of the published [**interface**](#interface).
import To gain access to symbols that are exported from another module. See `use` in Camel chapter 27, “Functions”.
increment To increase the value of something by 1 (or by some other number, if so specified).
indexing In olden days, the act of looking up a [**key**](#key) in an actual index (such as a phone book). But now it's merely the act of using any kind of key or position to find the corresponding [**value**](#value), even if no index is involved. Things have degenerated to the point that Perl’s `index` function merely locates the position (index) of one string in another.
indirect filehandle An [**expression**](#expression) that evaluates to something that can be used as a [**filehandle**](#filehandle): a [**string**](#string) (filehandle name), a [**typeglob**](#typeglob), a typeglob [**reference**](#reference), or a low-level [**IO**](#IO) object.
indirection If something in a program isn’t the value you’re looking for but indicates where the value is, that’s indirection. This can be done with either [**symbolic references**](#symbolic-reference) or [**hard**](#hard-reference).
indirect object In English grammar, a short noun phrase between a verb and its direct object indicating the beneficiary or recipient of the action. In Perl, `print STDOUT "$foo\n";` can be understood as “verb indirect-object object”, where `STDOUT` is the recipient of the `print` action, and `"$foo"` is the object being printed. Similarly, when invoking a [**method**](#method), you might place the invocant in the dative slot between the method and its arguments:
```
$gollum = new Pathetic::Creature "Sméagol";
give $gollum "Fisssssh!";
give $gollum "Precious!";
```
indirect object slot The syntactic position falling between a method call and its arguments when using the indirect object invocation syntax. (The slot is distinguished by the absence of a comma between it and the next argument.) `STDERR` is in the indirect object slot here:
```
print STDERR "Awake! Awake! Fear, Fire, Foes! Awake!\n";
```
infix An [**operator**](#operator) that comes in between its [**operands**](#operand), such as multiplication in `24 * 7`.
inheritance What you get from your ancestors, genetically or otherwise. If you happen to be a [**class**](#class), your ancestors are called [**base classes**](#base-class) and your descendants are called [**derived classes**](#derived-class). See [**single inheritance**](#single-inheritance) and [**multiple inheritance**](#multiple-inheritance).
instance Short for “an instance of a class”, meaning an [**object**](#object) of that [**class**](#class).
instance data See [**instance variable**](#instance-variable).
instance method A [**method**](#method) of an [**object**](#object), as opposed to a [**class method**](#class-method).
A [**method**](#method) whose [**invocant**](#invocant) is an [**object**](#object), not a [**package**](#package) name. Every object of a class shares all the methods of that class, so an instance method applies to all instances of the class, rather than applying to a particular instance. Also see [**class method**](#class-method).
instance variable An [**attribute**](#attribute) of an [**object**](#object); data stored with the particular object rather than with the class as a whole.
integer A number with no fractional (decimal) part. A counting number, like 1, 2, 3, and so on, but including 0 and the negatives.
interface The services a piece of code promises to provide forever, in contrast to its [**implementation**](#implementation), which it should feel free to change whenever it likes.
interpolation The insertion of a scalar or list value somewhere in the middle of another value, such that it appears to have been there all along. In Perl, variable interpolation happens in double-quoted strings and patterns, and list interpolation occurs when constructing the list of values to pass to a list operator or other such construct that takes a *`LIST`*.
interpreter Strictly speaking, a program that reads a second program and does what the second program says directly without turning the program into a different form first, which is what [**compilers**](#compiler) do. Perl is not an interpreter by this definition, because it contains a kind of compiler that takes a program and turns it into a more executable form ([**syntax trees**](#syntax-tree)) within the *perl* process itself, which the Perl [**runtime**](#runtime) system then interprets.
invocant The agent on whose behalf a [**method**](#method) is invoked. In a [**class**](#class) method, the invocant is a package name. In an [**instance**](#instance) method, the invocant is an object reference.
invocation The act of calling up a deity, daemon, program, method, subroutine, or function to get it to do what you think it’s supposed to do. We usually “call” subroutines but “invoke” methods, since it sounds cooler.
I/O Input from, or output to, a [**file**](#file) or [**device**](#device).
IO An internal I/O object. Can also mean [**indirect object**](#indirect-object).
I/O layer One of the filters between the data and what you get as input or what you end up with as output.
IPA India Pale Ale. Also the International Phonetic Alphabet, the standard alphabet used for phonetic notation worldwide. Draws heavily on Unicode, including many combining characters.
IP Internet Protocol, or Intellectual Property.
IPC Interprocess Communication.
is-a A relationship between two [**objects**](#object) in which one object is considered to be a more specific version of the other, generic object: “A camel is a mammal.” Since the generic object really only exists in a Platonic sense, we usually add a little abstraction to the notion of objects and think of the relationship as being between a generic [**base class**](#base-class) and a specific [**derived class**](#derived-class). Oddly enough, Platonic classes don’t always have Platonic relationships—see [**inheritance**](#inheritance).
iteration Doing something repeatedly.
iterator A special programming gizmo that keeps track of where you are in something that you’re trying to iterate over. The `foreach` loop in Perl contains an iterator; so does a hash, allowing you to `each` through it.
IV The integer four, not to be confused with six, Tom’s favorite editor. IV also means an internal Integer Value of the type a [**scalar**](#scalar) can hold, not to be confused with an [**NV**](#NV).
### J
JAPH “Just Another Perl Hacker”, a clever but cryptic bit of Perl code that, when executed, evaluates to that string. Often used to illustrate a particular Perl feature, and something of an ongoing Obfuscated Perl Contest seen in USENET signatures.
### K
key The string index to a [**hash**](#hash), used to look up the [**value**](#value) associated with that key.
keyword See [**reserved words**](#reserved-words).
### L
label A name you give to a [**statement**](#statement) so that you can talk about that statement elsewhere in the program.
laziness The quality that makes you go to great effort to reduce overall energy expenditure. It makes you write labor-saving programs that other people will find useful, and then document what you wrote so you don’t have to answer so many questions about it. Hence, the first great virtue of a programmer. Also hence, this book. See also [**impatience**](#impatience) and [**hubris**](#hubris).
leftmost longest The preference of the [**regular expression**](#regular-expression) engine to match the leftmost occurrence of a [**pattern**](#pattern), then given a position at which a match will occur, the preference for the longest match (presuming the use of a [**greedy**](#greedy) quantifier). See Camel chapter 5, “Pattern Matching” for *much* more on this subject.
left shift A [**bit shift**](#bit-shift) that multiplies the number by some power of 2.
lexeme Fancy term for a [**token**](#token).
lexer Fancy term for a [**tokener**](#tokener).
lexical analysis Fancy term for [**tokenizing**](#tokenizing).
lexical scoping Looking at your *Oxford English Dictionary* through a microscope. (Also known as [**static scoping**](#static-scoping), because dictionaries don’t change very fast.) Similarly, looking at variables stored in a private dictionary (namespace) for each scope, which are visible only from their point of declaration down to the end of the lexical scope in which they are declared. —Syn. [**static scoping**](#static-scoping). —Ant. [**dynamic scoping**](#dynamic-scoping).
lexical variable A [**variable**](#variable) subject to [**lexical scoping**](#lexical-scoping), declared by `my`. Often just called a “lexical”. (The `our` declaration declares a lexically scoped name for a global variable, which is not itself a lexical variable.)
library Generally, a collection of procedures. In ancient days, referred to a collection of subroutines in a *.pl* file. In modern times, refers more often to the entire collection of Perl [**modules**](#module) on your system.
LIFO Last In, First Out. See also [**FIFO**](#FIFO). A LIFO is usually called a [**stack**](#stack).
line In Unix, a sequence of zero or more nonnewline characters terminated with a [**newline**](#newline) character. On non-Unix machines, this is emulated by the C library even if the underlying [**operating system**](#operating-system) has different ideas.
linebreak A [**grapheme**](#grapheme) consisting of either a carriage return followed by a line feed or any character with the Unicode Vertical Space [**character property**](#character-property).
line buffering Used by a [**standard I/O**](#standard-I/O) output stream that flushes its [**buffer**](#buffer) after every [**newline**](#newline). Many standard I/O libraries automatically set up line buffering on output that is going to the terminal.
line number The number of lines read previous to this one, plus 1. Perl keeps a separate line number for each source or input file it opens. The current source file’s line number is represented by `__LINE__`. The current input line number (for the file that was most recently read via `<FH>`) is represented by the `$.` (`$INPUT_LINE_NUMBER`) variable. Many error messages report both values, if available.
link Used as a noun, a name in a [**directory**](#directory) that represents a [**file**](#file). A given file can have multiple links to it. It’s like having the same phone number listed in the phone directory under different names. As a verb, to resolve a partially [**compiled**](#compile) file’s unresolved symbols into a (nearly) executable image. Linking can generally be static or dynamic, which has nothing to do with static or dynamic scoping.
LIST A syntactic construct representing a comma- separated list of expressions, evaluated to produce a [**list value**](#list-value). Each [**expression**](#expression) in a *`LIST`* is evaluated in [**list context**](#list-context) and interpolated into the list value.
list An ordered set of scalar values.
list context The situation in which an [**expression**](#expression) is expected by its surroundings (the code calling it) to return a list of values rather than a single value. Functions that want a *`LIST`* of arguments tell those arguments that they should produce a list value. See also [**context**](#context).
list operator An [**operator**](#operator) that does something with a list of values, such as `join` or `grep`. Usually used for named built-in operators (such as `print`, `unlink`, and `system`) that do not require parentheses around their [**argument**](#argument) list.
list value An unnamed list of temporary scalar values that may be passed around within a program from any list-generating function to any function or construct that provides a [**list context**](#list-context).
literal A token in a programming language, such as a number or [**string**](#string), that gives you an actual [**value**](#value) instead of merely representing possible values as a [**variable**](#variable) does.
little-endian From Swift: someone who eats eggs little end first. Also used of computers that store the least significant [**byte**](#byte) of a word at a lower byte address than the most significant byte. Often considered superior to big-endian machines. See also [**big-endian**](#big-endian).
local Not meaning the same thing everywhere. A global variable in Perl can be localized inside a [**dynamic scope**](#dynamic-scoping) via the `local` operator.
logical operator Symbols representing the concepts “and”, “or”, “xor”, and “not”.
lookahead An [**assertion**](#assertion) that peeks at the string to the right of the current match location.
lookbehind An [**assertion**](#assertion) that peeks at the string to the left of the current match location.
loop A construct that performs something repeatedly, like a roller coaster.
loop control statement Any statement within the body of a loop that can make a loop prematurely stop looping or skip an [**iteration**](#iteration). Generally, you shouldn’t try this on roller coasters.
loop label A kind of key or name attached to a loop (or roller coaster) so that loop control statements can talk about which loop they want to control.
lowercase In Unicode, not just characters with the General Category of Lowercase Letter, but any character with the Lowercase property, including Modifier Letters, Letter Numbers, some Other Symbols, and one Combining Mark.
lvaluable Able to serve as an [**lvalue**](#lvalue).
lvalue Term used by language lawyers for a storage location you can assign a new [**value**](#value) to, such as a [**variable**](#variable) or an element of an [**array**](#array). The “l” is short for “left”, as in the left side of an assignment, a typical place for lvalues. An [**lvaluable**](#lvaluable) function or expression is one to which a value may be assigned, as in `pos($x) = 10`.
lvalue modifier An adjectival pseudofunction that warps the meaning of an [**lvalue**](#lvalue) in some declarative fashion. Currently there are three lvalue modifiers: `my`, `our`, and `local`.
### M
magic Technically speaking, any extra semantics attached to a variable such as `$!`, `$0`, `%ENV`, or `%SIG`, or to any tied variable. Magical things happen when you diddle those variables.
magical increment An [**increment**](#increment) operator that knows how to bump up ASCII alphabetics as well as numbers.
magical variables Special variables that have side effects when you access them or assign to them. For example, in Perl, changing elements of the `%ENV` array also changes the corresponding environment variables that subprocesses will use. Reading the `$!` variable gives you the current system error number or message.
Makefile A file that controls the compilation of a program. Perl programs don’t usually need a [**Makefile**](#Makefile) because the Perl compiler has plenty of self-control.
man The Unix program that displays online documentation (manual pages) for you.
manpage A “page” from the manuals, typically accessed via the *man*(1) command. A manpage contains a SYNOPSIS, a DESCRIPTION, a list of BUGS, and so on, and is typically longer than a page. There are manpages documenting [**commands**](#command), [**syscalls**](#syscall), [**library**](#library) [**functions**](#function), [**devices**](#device), [**protocols**](#protocol), [**files**](#file), and such. In this book, we call any piece of standard Perl documentation (like <perlop> or [perldelta](https://perldoc.perl.org/5.36.0/perldelta)) a manpage, no matter what format it’s installed in on your system.
matching See [**pattern matching**](#pattern-matching).
member data See [**instance variable**](#instance-variable).
memory This always means your main memory, not your disk. Clouding the issue is the fact that your machine may implement [**virtual**](#virtual) memory; that is, it will pretend that it has more memory than it really does, and it’ll use disk space to hold inactive bits. This can make it seem like you have a little more memory than you really do, but it’s not a substitute for real memory. The best thing that can be said about virtual memory is that it lets your performance degrade gradually rather than suddenly when you run out of real memory. But your program can die when you run out of virtual memory, too—if you haven’t thrashed your disk to death first.
metacharacter A [**character**](#character) that is *not* supposed to be treated normally. Which characters are to be treated specially as metacharacters varies greatly from context to context. Your [**shell**](#shell) will have certain metacharacters, double-quoted Perl [**strings**](#string) have other metacharacters, and [**regular expression**](#regular-expression) patterns have all the double-quote metacharacters plus some extra ones of their own.
metasymbol Something we’d call a [**metacharacter**](#metacharacter) except that it’s a sequence of more than one character. Generally, the first character in the sequence must be a true metacharacter to get the other characters in the metasymbol to misbehave along with it.
method A kind of action that an [**object**](#object) can take if you tell it to. See Camel chapter 12, “Objects”.
method resolution order The path Perl takes through `@INC`. By default, this is a double depth first search, once looking for defined methods and once for `AUTOLOAD`. However, Perl lets you configure this with `mro`.
minicpan A CPAN mirror that includes just the latest versions for each distribution, probably created with `CPAN::Mini`. See Camel chapter 19, “CPAN”.
minimalism The belief that “small is beautiful”. Paradoxically, if you say something in a small language, it turns out big, and if you say it in a big language, it turns out small. Go figure.
mode In the context of the *stat*(2) syscall, refers to the field holding the [**permission bits**](#permission-bits) and the type of the [**file**](#file).
modifier See [**statement modifier**](#statement-modifier), [**regular expression**](#regular-expression), and [**lvalue**](#lvalue), not necessarily in that order.
module A [**file**](#file) that defines a [**package**](#package) of (almost) the same name, which can either [**export**](#export) symbols or function as an [**object**](#object) class. (A module’s main *.pm* file may also load in other files in support of the module.) See the `use` built-in.
modulus An integer divisor when you’re interested in the remainder instead of the quotient.
mojibake When you speak one language and the computer thinks you’re speaking another. You’ll see odd translations when you send UTF‑8, for instance, but the computer thinks you sent Latin-1, showing all sorts of weird characters instead. The term is written 「文字化け」in Japanese and means “character rot”, an apt description. Pronounced [`modʑibake`] in standard [**IPA**](#IPA) phonetics, or approximately “moh-jee-bah-keh”.
monger Short for one member of [**Perl mongers**](#Perl-mongers), a purveyor of Perl.
mortal A temporary value scheduled to die when the current statement finishes.
mro See [**method resolution order**](#method-resolution-order).
multidimensional array An array with multiple subscripts for finding a single element. Perl implements these using [**references**](#reference)—see Camel chapter 9, “Data Structures”.
multiple inheritance The features you got from your mother and father, mixed together unpredictably. (See also [**inheritance**](#inheritance) and [**single inheritance**](#single-inheritance).) In computer languages (including Perl), it is the notion that a given class may have multiple direct ancestors or [**base classes**](#base-class).
### N
named pipe A [**pipe**](#pipe) with a name embedded in the [**filesystem**](#filesystem) so that it can be accessed by two unrelated [**processes**](#process).
namespace A domain of names. You needn’t worry about whether the names in one such domain have been used in another. See [**package**](#package).
NaN Not a number. The value Perl uses for certain invalid or inexpressible floating-point operations.
network address The most important attribute of a socket, like your telephone’s telephone number. Typically an IP address. See also [**port**](#port).
newline A single character that represents the end of a line, with the ASCII value of 012 octal under Unix (but 015 on a Mac), and represented by `\n` in Perl strings. For Windows machines writing text files, and for certain physical devices like terminals, the single newline gets automatically translated by your C library into a line feed and a carriage return, but normally, no translation is done.
NFS Network File System, which allows you to mount a remote filesystem as if it were local.
normalization Converting a text string into an alternate but equivalent [**canonical**](#canonical) (or compatible) representation that can then be compared for equivalence. Unicode recognizes four different normalization forms: NFD, NFC, NFKD, and NFKC.
null character A character with the numeric value of zero. It’s used by C to terminate strings, but Perl allows strings to contain a null.
null list A [**list value**](#list-value) with zero elements, represented in Perl by `()`.
null string A [**string**](#string) containing no characters, not to be confused with a string containing a [**null character**](#null-character), which has a positive length and is [**true**](#true).
numeric context The situation in which an expression is expected by its surroundings (the code calling it) to return a number. See also [**context**](#context) and [**string context**](#string-context).
numification (Sometimes spelled *nummification* and *nummify*.) Perl lingo for implicit conversion into a number; the related verb is *numify*. *Numification* is intended to rhyme with *mummification*, and *numify* with *mummify*. It is unrelated to English *numen*, *numina*, *numinous*. We originally forgot the extra *m* a long time ago, and some people got used to our funny spelling, and so just as with `HTTP_REFERER`’s own missing letter, our weird spelling has stuck around.
NV Short for Nevada, no part of which will ever be confused with civilization. NV also means an internal floating- point Numeric Value of the type a [**scalar**](#scalar) can hold, not to be confused with an [**IV**](#IV).
nybble Half a [**byte**](#byte), equivalent to one [**hexadecimal**](#hexadecimal) digit, and worth four [**bits**](#bit).
### O
object An [**instance**](#instance) of a [**class**](#class). Something that “knows” what user-defined type (class) it is, and what it can do because of what class it is. Your program can request an object to do things, but the object gets to decide whether it wants to do them or not. Some objects are more accommodating than others.
octal A number in base 8. Only the digits 0 through 7 are allowed. Octal constants in Perl start with 0, as in 013. See also the `oct` function.
offset How many things you have to skip over when moving from the beginning of a string or array to a specific position within it. Thus, the minimum offset is zero, not one, because you don’t skip anything to get to the first item.
one-liner An entire computer program crammed into one line of text.
open source software Programs for which the source code is freely available and freely redistributable, with no commercial strings attached. For a more detailed definition, see <http://www.opensource.org/osd.html>.
operand An [**expression**](#expression) that yields a [**value**](#value) that an [**operator**](#operator) operates on. See also [**precedence**](#precedence).
operating system A special program that runs on the bare machine and hides the gory details of managing [**processes**](#process) and [**devices**](#device). Usually used in a looser sense to indicate a particular culture of programming. The loose sense can be used at varying levels of specificity. At one extreme, you might say that all versions of Unix and Unix-lookalikes are the same operating system (upsetting many people, especially lawyers and other advocates). At the other extreme, you could say this particular version of this particular vendor’s operating system is different from any other version of this or any other vendor’s operating system. Perl is much more portable across operating systems than many other languages. See also [**architecture**](#architecture) and [**platform**](#platform).
operator A gizmo that transforms some number of input values to some number of output values, often built into a language with a special syntax or symbol. A given operator may have specific expectations about what [**types**](#type) of data you give as its arguments ([**operands**](#operand)) and what type of data you want back from it.
operator overloading A kind of [**overloading**](#overloading) that you can do on built-in [**operators**](#operator) to make them work on [**objects**](#object) as if the objects were ordinary scalar values, but with the actual semantics supplied by the object class. This is set up with the overload [**pragma**](#pragma)—see Camel chapter 13, “Overloading”.
options See either [**switches**](#switch) or [**regular expression modifiers**](#regular-expression-modifier).
ordinal An abstract character’s integer value. Same thing as [**codepoint**](#codepoint).
overloading Giving additional meanings to a symbol or construct. Actually, all languages do overloading to one extent or another, since people are good at figuring out things from [**context**](#context).
overriding Hiding or invalidating some other definition of the same name. (Not to be confused with [**overloading**](#overloading), which adds definitions that must be disambiguated some other way.) To confuse the issue further, we use the word with two overloaded definitions: to describe how you can define your own [**subroutine**](#subroutine) to hide a built-in [**function**](#function) of the same name (see the section “Overriding Built-in Functions” in Camel chapter 11, “Modules”), and to describe how you can define a replacement [**method**](#method) in a [**derived class**](#derived-class) to hide a [**base class**](#base-class)’s method of the same name (see Camel chapter 12, “Objects”).
owner The one user (apart from the superuser) who has absolute control over a [**file**](#file). A file may also have a [**group**](#group) of users who may exercise joint ownership if the real owner permits it. See [**permission bits**](#permission-bits).
### P
package A [**namespace**](#namespace) for global [**variables**](#variable), [**subroutines**](#subroutine), and the like, such that they can be kept separate from like-named [**symbols**](#symbol) in other namespaces. In a sense, only the package is global, since the symbols in the package’s symbol table are only accessible from code [**compiled**](#compile) outside the package by naming the package. But in another sense, all package symbols are also globals—they’re just well-organized globals.
pad Short for [**scratchpad**](#scratchpad).
parameter See [**argument**](#argument).
parent class See [**base class**](#base-class).
parse tree See [**syntax tree**](#syntax-tree).
parsing The subtle but sometimes brutal art of attempting to turn your possibly malformed program into a valid [**syntax tree**](#syntax-tree).
patch To fix by applying one, as it were. In the realm of hackerdom, a listing of the differences between two versions of a program as might be applied by the [**patch**](#patch)(1) program when you want to fix a bug or upgrade your old version.
PATH The list of [**directories**](#directory) the system searches to find a program you want to [**execute**](#execute). The list is stored as one of your [**environment variables**](#environment-variable), accessible in Perl as `$ENV{PATH}`.
pathname A fully qualified filename such as */usr/bin/perl*. Sometimes confused with `PATH`.
pattern A template used in [**pattern matching**](#pattern-matching).
pattern matching Taking a pattern, usually a [**regular expression**](#regular-expression), and trying the pattern various ways on a string to see whether there’s any way to make it fit. Often used to pick interesting tidbits out of a file.
PAUSE The Perl Authors Upload SErver (<http://pause.perl.org>), the gateway for [**modules**](#module) on their way to [**CPAN**](#CPAN).
Perl mongers A Perl user group, taking the form of its name from the New York Perl mongers, the first Perl user group. Find one near you at <http://www.pm.org>.
permission bits Bits that the [**owner**](#owner) of a file sets or unsets to allow or disallow access to other people. These flag bits are part of the [**mode**](#mode) word returned by the `stat` built-in when you ask about a file. On Unix systems, you can check the *ls*(1) manpage for more information.
Pern What you get when you do `Perl++` twice. Doing it only once will curl your hair. You have to increment it eight times to shampoo your hair. Lather, rinse, iterate.
pipe A direct [**connection**](#connection) that carries the output of one [**process**](#process) to the input of another without an intermediate temporary file. Once the pipe is set up, the two processes in question can read and write as if they were talking to a normal file, with some caveats.
pipeline A series of [**processes**](#process) all in a row, linked by [**pipes**](#pipe), where each passes its output stream to the next.
platform The entire hardware and software context in which a program runs. A program written in a platform-dependent language might break if you change any of the following: machine, operating system, libraries, compiler, or system configuration. The *perl* interpreter has to be [**compiled**](#compile) differently for each platform because it is implemented in C, but programs written in the Perl language are largely platform independent.
pod The markup used to embed documentation into your Perl code. Pod stands for “Plain old documentation”. See Camel chapter 23, “Plain Old Documentation”.
pod command A sequence, such as `=head1`, that denotes the start of a [**pod**](#pod) section.
pointer A [**variable**](#variable) in a language like C that contains the exact memory location of some other item. Perl handles pointers internally so you don’t have to worry about them. Instead, you just use symbolic pointers in the form of [**keys**](#key) and [**variable**](#variable) names, or [**hard references**](#hard-reference), which aren’t pointers (but act like pointers and do in fact contain pointers).
polymorphism The notion that you can tell an [**object**](#object) to do something generic, and the object will interpret the command in different ways depending on its type. [< Greek πολυ- + μορϕή, many forms.]
port The part of the address of a TCP or UDP socket that directs packets to the correct process after finding the right machine, something like the phone extension you give when you reach the company operator. Also the result of converting code to run on a different platform than originally intended, or the verb denoting this conversion.
portable Once upon a time, C code compilable under both BSD and SysV. In general, code that can be easily converted to run on another [**platform**](#platform), where “easily” can be defined however you like, and usually is. Anything may be considered portable if you try hard enough, such as a mobile home or London Bridge.
porter Someone who “carries” software from one [**platform**](#platform) to another. Porting programs written in platform-dependent languages such as C can be difficult work, but porting programs like Perl is very much worth the agony.
possessive Said of quantifiers and groups in patterns that refuse to give up anything once they’ve gotten their mitts on it. Catchier and easier to say than the even more formal *nonbacktrackable*.
POSIX The Portable Operating System Interface specification.
postfix An [**operator**](#operator) that follows its [**operand**](#operand), as in `$x++`.
pp An internal shorthand for a “push- pop” code; that is, C code implementing Perl’s stack machine.
pragma A standard module whose practical hints and suggestions are received (and possibly ignored) at compile time. Pragmas are named in all lowercase.
precedence The rules of conduct that, in the absence of other guidance, determine what should happen first. For example, in the absence of parentheses, you always do multiplication before addition.
prefix An [**operator**](#operator) that precedes its [**operand**](#operand), as in `++$x`.
preprocessing What some helper [**process**](#process) did to transform the incoming data into a form more suitable for the current process. Often done with an incoming [**pipe**](#pipe). See also [**C preprocessor**](#C-preprocessor).
primary maintainer The author that PAUSE allows to assign [**co-maintainer**](#co-maintainer) permissions to a [**namespace**](#namespace). A primary maintainer can give up this distinction by assigning it to another PAUSE author. See Camel chapter 19, “CPAN”.
procedure A [**subroutine**](#subroutine).
process An instance of a running program. Under multitasking systems like Unix, two or more separate processes could be running the same program independently at the same time—in fact, the `fork` function is designed to bring about this happy state of affairs. Under other operating systems, processes are sometimes called “threads”, “tasks”, or “jobs”, often with slight nuances in meaning.
program See [**script**](#script).
program generator A system that algorithmically writes code for you in a high-level language. See also [**code generator**](#code-generator).
progressive matching [**Pattern matching**](#pattern-matching) matching>that picks up where it left off before.
property See either [**instance variable**](#instance-variable) or [**character property**](#character-property).
protocol In networking, an agreed-upon way of sending messages back and forth so that neither correspondent will get too confused.
prototype An optional part of a [**subroutine**](#subroutine) declaration telling the Perl compiler how many and what flavor of arguments may be passed as [**actual arguments**](#actual-arguments), so you can write subroutine calls that parse much like built-in functions. (Or don’t parse, as the case may be.)
pseudofunction A construct that sometimes looks like a function but really isn’t. Usually reserved for [**lvalue**](#lvalue) modifiers like `my`, for [**context**](#context) modifiers like `scalar`, and for the pick-your-own-quotes constructs, `q//`, `qq//`, `qx//`, `qw//`, `qr//`, `m//`, `s///`, `y///`, and `tr///`.
pseudohash Formerly, a reference to an array whose initial element happens to hold a reference to a hash. You used to be able to treat a pseudohash reference as either an array reference or a hash reference. Pseudohashes are no longer supported.
pseudoliteral An [**operator**](#operator) X`that looks something like a [**literal**](#literal), such as the output-grabbing operator, <literal moreinfo="none"``>*`command`*```.
public domain Something not owned by anybody. Perl is copyrighted and is thus *not* in the public domain—it’s just [**freely available**](#freely-available) and [**freely redistributable**](#freely-redistributable).
pumpkin A notional “baton” handed around the Perl community indicating who is the lead integrator in some arena of development.
pumpking A [**pumpkin**](#pumpkin) holder, the person in charge of pumping the pump, or at least priming it. Must be willing to play the part of the Great Pumpkin now and then.
PV A “pointer value”, which is Perl Internals Talk for a `char*`.
### Q
qualified Possessing a complete name. The symbol `$Ent::moot` is qualified; `$moot` is unqualified. A fully qualified filename is specified from the top-level directory.
quantifier A component of a [**regular expression**](#regular-expression) specifying how many times the foregoing [**atom**](#atom) may occur.
### R
race condition A race condition exists when the result of several interrelated events depends on the ordering of those events, but that order cannot be guaranteed due to nondeterministic timing effects. If two or more programs, or parts of the same program, try to go through the same series of events, one might interrupt the work of the other. This is a good way to find an [**exploit**](#exploit).
readable With respect to files, one that has the proper permission bit set to let you access the file. With respect to computer programs, one that’s written well enough that someone has a chance of figuring out what it’s trying to do.
reaping The last rites performed by a parent [**process**](#process) on behalf of a deceased child process so that it doesn’t remain a [**zombie**](#zombie). See the `wait` and `waitpid` function calls.
record A set of related data values in a [**file**](#file) or [**stream**](#stream), often associated with a unique [**key**](#key) field. In Unix, often commensurate with a [**line**](#line), or a blank-line–terminated set of lines (a “paragraph”). Each line of the */etc/passwd* file is a record, keyed on login name, containing information about that user.
recursion The art of defining something (at least partly) in terms of itself, which is a naughty no-no in dictionaries but often works out okay in computer programs if you’re careful not to recurse forever (which is like an infinite loop with more spectacular failure modes).
reference Where you look to find a pointer to information somewhere else. (See [**indirection**](#indirection).) References come in two flavors: [**symbolic references**](#symbolic-reference) and [**hard references**](#hard-reference).
referent Whatever a reference refers to, which may or may not have a name. Common types of referents include scalars, arrays, hashes, and subroutines.
regex See [**regular expression**](#regular-expression).
regular expression A single entity with various interpretations, like an elephant. To a computer scientist, it’s a grammar for a little language in which some strings are legal and others aren’t. To normal people, it’s a pattern you can use to find what you’re looking for when it varies from case to case. Perl’s regular expressions are far from regular in the theoretical sense, but in regular use they work quite well. Here’s a regular expression: `/Oh s.*t./`. This will match strings like “`Oh say can you see by the dawn's early light`” and “`Oh sit!`”. See Camel chapter 5, “Pattern Matching”.
regular expression modifier An option on a pattern or substitution, such as `/i` to render the pattern case- insensitive.
regular file A [**file**](#file) that’s not a [**directory**](#directory), a [**device**](#device), a named [**pipe**](#pipe) or [**socket**](#socket), or a [**symbolic link**](#symbolic-link). Perl uses the `–f` file test operator to identify regular files. Sometimes called a “plain” file.
relational operator An [**operator**](#operator) that says whether a particular ordering relationship is [**true**](#true) about a pair of [**operands**](#operand). Perl has both numeric and string relational operators. See [**collating sequence**](#collating-sequence).
reserved words A word with a specific, built-in meaning to a [**compiler**](#compiler), such as `if` or `delete`. In many languages (not Perl), it’s illegal to use reserved words to name anything else. (Which is why they’re reserved, after all.) In Perl, you just can’t use them to name [**labels**](#label) or [**filehandles**](#filehandle). Also called “keywords”.
return value The [**value**](#value) produced by a [**subroutine**](#subroutine) or [**expression**](#expression) when evaluated. In Perl, a return value may be either a [**list**](#list) or a [**scalar**](#scalar).
RFC Request For Comment, which despite the timid connotations is the name of a series of important standards documents.
right shift A [**bit shift**](#bit-shift) that divides a number by some power of 2.
role A name for a concrete set of behaviors. A role is a way to add behavior to a class without inheritance.
root The superuser (`UID` == 0). Also the top-level directory of the filesystem.
RTFM What you are told when someone thinks you should Read The Fine Manual.
run phase Any time after Perl starts running your main program. See also [**compile phase**](#compile-phase). Run phase is mostly spent in [**runtime**](#runtime) but may also be spent in [**compile time**](#compile-time) when `require`, `do` *`FILE`*, or `eval` *`STRING`* operators are executed, or when a substitution uses the `/ee` modifier.
runtime The time when Perl is actually doing what your code says to do, as opposed to the earlier period of time when it was trying to figure out whether what you said made any sense whatsoever, which is [**compile time**](#compile-time).
runtime pattern A pattern that contains one or more variables to be interpolated before parsing the pattern as a [**regular expression**](#regular-expression), and that therefore cannot be analyzed at compile time, but must be reanalyzed each time the pattern match operator is evaluated. Runtime patterns are useful but expensive.
RV A recreational vehicle, not to be confused with vehicular recreation. RV also means an internal Reference Value of the type a [**scalar**](#scalar) can hold. See also [**IV**](#IV) and [**NV**](#NV) if you’re not confused yet.
rvalue A [**value**](#value) that you might find on the right side of an [**assignment**](#assignment). See also [**lvalue**](#lvalue).
### S
sandbox A walled off area that’s not supposed to affect beyond its walls. You let kids play in the sandbox instead of running in the road. See Camel chapter 20, “Security”.
scalar A simple, singular value; a number, [**string**](#string), or [**reference**](#reference).
scalar context The situation in which an [**expression**](#expression) is expected by its surroundings (the code calling it) to return a single [**value**](#value) rather than a [**list**](#list) of values. See also [**context**](#context) and [**list context**](#list-context). A scalar context sometimes imposes additional constraints on the return value—see [**string context**](#string-context) and [**numeric context**](#numeric-context). Sometimes we talk about a [**Boolean context**](#Boolean-context) inside conditionals, but this imposes no additional constraints, since any scalar value, whether numeric or [**string**](#string), is already true or false.
scalar literal A number or quoted [**string**](#string)—an actual [**value**](#value) in the text of your program, as opposed to a [**variable**](#variable).
scalar value A value that happens to be a [**scalar**](#scalar) as opposed to a [**list**](#list).
scalar variable A [**variable**](#variable) prefixed with `$` that holds a single value.
scope From how far away you can see a variable, looking through one. Perl has two visibility mechanisms. It does [**dynamic scoping**](#dynamic-scoping) of `local` [**variables**](#variable), meaning that the rest of the [**block**](#BLOCK), and any [**subroutines**](#subroutine) that are called by the rest of the block, can see the variables that are local to the block. Perl does [**lexical scoping**](#lexical-scoping) of `my` variables, meaning that the rest of the block can see the variable, but other subroutines called by the block *cannot* see the variable.
scratchpad The area in which a particular invocation of a particular file or subroutine keeps some of its temporary values, including any lexically scoped variables.
script A text [**file**](#file) that is a program intended to be [**executed**](#execute) directly rather than [**compiled**](#compile) to another form of file before [**execution**](#execute).
Also, in the context of [**Unicode**](#Unicode), a writing system for a particular language or group of languages, such as Greek, Bengali, or Tengwar.
script kiddie A [**cracker**](#cracker) who is not a [**hacker**](#hacker) but knows just enough to run canned scripts. A [**cargo-cult**](#cargo-cult) programmer.
sed A venerable Stream EDitor from which Perl derives some of its ideas.
semaphore A fancy kind of interlock that prevents multiple [**threads**](#thread) or [**processes**](#process) from using up the same resources simultaneously.
separator A [**character**](#character) or [**string**](#string) that keeps two surrounding strings from being confused with each other. The `split` function works on separators. Not to be confused with [**delimiters**](#delimiter) or [**terminators**](#terminator). The “or” in the previous sentence separated the two alternatives.
serialization Putting a fancy [**data structure**](#data-structure) into linear order so that it can be stored as a [**string**](#string) in a disk file or database, or sent through a [**pipe**](#pipe). Also called marshalling.
server In networking, a [**process**](#process) that either advertises a [**service**](#service) or just hangs around at a known location and waits for [**clients**](#client) who need service to get in touch with it.
service Something you do for someone else to make them happy, like giving them the time of day (or of their life). On some machines, well-known services are listed by the `getservent` function.
setgid Same as [**setuid**](#setuid), only having to do with giving away [**group**](#group) privileges.
setuid Said of a program that runs with the privileges of its [**owner**](#owner) rather than (as is usually the case) the privileges of whoever is running it. Also describes the bit in the mode word ([**permission bits**](#permission-bits)) that controls the feature. This bit must be explicitly set by the owner to enable this feature, and the program must be carefully written not to give away more privileges than it ought to.
shared memory A piece of [**memory**](#memory) accessible by two different [**processes**](#process) who otherwise would not see each other’s memory.
shebang Irish for the whole McGillicuddy. In Perl culture, a portmanteau of “sharp” and “bang”, meaning the `#!` sequence that tells the system where to find the interpreter.
shell A [**command**](#command)-line [**interpreter**](#interpreter). The program that interactively gives you a prompt, accepts one or more [**lines**](#line) of input, and executes the programs you mentioned, feeding each of them their proper [**arguments**](#argument) and input data. Shells can also execute scripts containing such commands. Under Unix, typical shells include the Bourne shell (*/bin/sh*), the C shell (*/bin/csh*), and the Korn shell (*/bin/ksh*). Perl is not strictly a shell because it’s not interactive (although Perl programs can be interactive).
side effects Something extra that happens when you evaluate an [**expression**](#expression). Nowadays it can refer to almost anything. For example, evaluating a simple assignment statement typically has the “side effect” of assigning a value to a variable. (And you thought assigning the value was your primary intent in the first place!) Likewise, assigning a value to the special variable `$|` (`$AUTOFLUSH`) has the side effect of forcing a flush after every `write` or `print` on the currently selected filehandle.
sigil A glyph used in magic. Or, for Perl, the symbol in front of a variable name, such as `$`, `@`, and `%`.
signal A bolt out of the blue; that is, an event triggered by the [**operating system**](#operating-system), probably when you’re least expecting it.
signal handler A [**subroutine**](#subroutine) that, instead of being content to be called in the normal fashion, sits around waiting for a bolt out of the blue before it will deign to [**execute**](#execute). Under Perl, bolts out of the blue are called signals, and you send them with the `kill` built-in. See the `%SIG` hash in Camel chapter 25, “Special Names” and the section “Signals” in Camel chapter 15, “Interprocess Communication”.
single inheritance The features you got from your mother, if she told you that you don’t have a father. (See also [**inheritance**](#inheritance) and [**multiple inheritance**](#multiple-inheritance).) In computer languages, the idea that [**classes**](#class) reproduce asexually so that a given class can only have one direct ancestor or [**base class**](#base-class). Perl supplies no such restriction, though you may certainly program Perl that way if you like.
slice A selection of any number of [**elements**](#element) from a [**list**](#list), [**array**](#array), or [**hash**](#hash).
slurp To read an entire [**file**](#file) into a [**string**](#string) in one operation.
socket An endpoint for network communication among multiple [**processes**](#process) that works much like a telephone or a post office box. The most important thing about a socket is its [**network address**](#network-address) (like a phone number). Different kinds of sockets have different kinds of addresses—some look like filenames, and some don’t.
soft reference See [**symbolic reference**](#symbolic-reference).
source filter A special kind of [**module**](#module) that does [**preprocessing**](#preprocessing) on your script just before it gets to the [**tokener**](#tokener).
stack A device you can put things on the top of, and later take them back off in the opposite order in which you put them on. See [**LIFO**](#LIFO).
standard Included in the official Perl distribution, as in a standard module, a standard tool, or a standard Perl [**manpage**](#manpage).
standard error The default output [**stream**](#stream) for nasty remarks that don’t belong in [**standard output**](#standard-output). Represented within a Perl program by the output> [**filehandle**](#filehandle) `STDERR`. You can use this stream explicitly, but the `die` and `warn` built-ins write to your standard error stream automatically (unless trapped or otherwise intercepted).
standard input The default input [**stream**](#stream) for your program, which if possible shouldn’t care where its data is coming from. Represented within a Perl program by the [**filehandle**](#filehandle) `STDIN`.
standard I/O A standard C library for doing [**buffered**](#buffer) input and output to the [**operating system**](#operating-system). (The “standard” of standard I/O is at most marginally related to the “standard” of standard input and output.) In general, Perl relies on whatever implementation of standard I/O a given operating system supplies, so the buffering characteristics of a Perl program on one machine may not exactly match those on another machine. Normally this only influences efficiency, not semantics. If your standard I/O package is doing block buffering and you want it to [**flush**](#flush) the buffer more often, just set the `$|` variable to a true value.
Standard Library Everything that comes with the official *perl* distribution. Some vendor versions of *perl* change their distributions, leaving out some parts or including extras. See also [**dual-lived**](#dual-lived).
standard output The default output [**stream**](#stream) for your program, which if possible shouldn’t care where its data is going. Represented within a Perl program by the [**filehandle**](#filehandle) `STDOUT`.
statement A [**command**](#command) to the computer about what to do next, like a step in a recipe: “Add marmalade to batter and mix until mixed.” A statement is distinguished from a [**declaration**](#declaration), which doesn’t tell the computer to do anything, but just to learn something.
statement modifier A [**conditional**](#conditional) or [**loop**](#loop) that you put after the [**statement**](#statement) instead of before, if you know what we mean.
static Varying slowly compared to something else. (Unfortunately, everything is relatively stable compared to something else, except for certain elementary particles, and we’re not so sure about them.) In computers, where things are supposed to vary rapidly, “static” has a derogatory connotation, indicating a slightly dysfunctional [**variable**](#variable), [**subroutine**](#subroutine), or [**method**](#method). In Perl culture, the word is politely avoided.
If you’re a C or C++ programmer, you might be looking for Perl’s `state` keyword.
static method No such thing. See [**class method**](#class-method).
static scoping No such thing. See [**lexical scoping**](#lexical-scoping).
static variable No such thing. Just use a [**lexical variable**](#lexical-variable) in a scope larger than your [**subroutine**](#subroutine), or declare it with `state` instead of with `my`.
stat structure A special internal spot in which Perl keeps the information about the last [**file**](#file) on which you requested information.
status The [**value**](#value) returned to the parent [**process**](#process) when one of its child processes dies. This value is placed in the special variable `$?`. Its upper eight [**bits**](#bit) are the exit status of the defunct process, and its lower eight bits identify the signal (if any) that the process died from. On Unix systems, this status value is the same as the status word returned by *wait*(2). See `system` in Camel chapter 27, “Functions”.
STDERR See [**standard error**](#standard-error).
STDIN See [**standard input**](#standard-input).
STDIO See [**standard I/O**](#standard-I/O).
STDOUT See [**standard output**](#standard-output).
stream A flow of data into or out of a process as a steady sequence of bytes or characters, without the appearance of being broken up into packets. This is a kind of [**interface**](#interface)—the underlying [**implementation**](#implementation) may well break your data up into separate packets for delivery, but this is hidden from you.
string A sequence of characters such as “He said !@#\*&%@#\*?!”. A string does not have to be entirely printable.
string context The situation in which an expression is expected by its surroundings (the code calling it) to return a [**string**](#string). See also [**context**](#context) and [**numeric context**](#numeric-context).
stringification The process of producing a [**string**](#string) representation of an abstract object.
struct C keyword introducing a structure definition or name.
structure See [**data structure**](#data-structure).
subclass See [**derived class**](#derived-class).
subpattern A component of a [**regular expression**](#regular-expression) pattern.
subroutine A named or otherwise accessible piece of program that can be invoked from elsewhere in the program in order to accomplish some subgoal of the program. A subroutine is often parameterized to accomplish different but related things depending on its input [**arguments**](#argument). If the subroutine returns a meaningful [**value**](#value), it is also called a [**function**](#function).
subscript A [**value**](#value) that indicates the position of a particular [**array**](#array) [**element**](#element) in an array.
substitution Changing parts of a string via the `s///` operator. (We avoid use of this term to mean [**variable interpolation**](#variable-interpolation).)
substring A portion of a [**string**](#string), starting at a certain [**character**](#character) position ([**offset**](#offset)) and proceeding for a certain number of characters.
superclass See [**base class**](#base-class).
superuser The person whom the [**operating system**](#operating-system) will let do almost anything. Typically your system administrator or someone pretending to be your system administrator. On Unix systems, the [**root**](#root) user. On Windows systems, usually the Administrator user.
SV Short for “scalar value”. But within the Perl interpreter, every [**referent**](#referent) is treated as a member of a class derived from SV, in an object-oriented sort of way. Every [**value**](#value) inside Perl is passed around as a C language `SV*` pointer. The SV [**struct**](#struct) knows its own “referent type”, and the code is smart enough (we hope) not to try to call a [**hash**](#hash) function on a [**subroutine**](#subroutine).
switch An option you give on a command line to influence the way your program works, usually introduced with a minus sign. The word is also used as a nickname for a [**switch statement**](#switch-statement).
switch cluster The combination of multiple command- line switches (*e.g.*, `–a –b –c`) into one switch (*e.g.*, `–abc`). Any switch with an additional [**argument**](#argument) must be the last switch in a cluster.
switch statement A program technique that lets you evaluate an [**expression**](#expression) and then, based on the value of the expression, do a multiway branch to the appropriate piece of code for that value. Also called a “case structure”, named after the similar Pascal construct. Most switch statements in Perl are spelled `given`. See “The `given` statement” in Camel chapter 4, “Statements and Declarations”.
symbol Generally, any [**token**](#token) or [**metasymbol**](#metasymbol). Often used more specifically to mean the sort of name you might find in a [**symbol table**](#symbol-table).
symbolic debugger A program that lets you step through the [**execution**](#execute) of your program, stopping or printing things out here and there to see whether anything has gone wrong, and, if so, what. The “symbolic” part just means that you can talk to the debugger using the same symbols with which your program is written.
symbolic link An alternate filename that points to the real [**filename**](#filename), which in turn points to the real [**file**](#file). Whenever the [**operating system**](#operating-system) is trying to parse a [**pathname**](#pathname) containing a symbolic link, it merely substitutes the new name and continues parsing.
symbolic reference A variable whose value is the name of another variable or subroutine. By [**dereferencing**](#dereference) the first variable, you can get at the second one. Symbolic references are illegal under `use strict "refs"`.
symbol table Where a [**compiler**](#compiler) remembers symbols. A program like Perl must somehow remember all the names of all the [**variables**](#variable), [**filehandles**](#filehandle), and [**subroutines**](#subroutine) you’ve used. It does this by placing the names in a symbol table, which is implemented in Perl using a [**hash table**](#hash-table). There is a separate symbol table for each [**package**](#package) to give each package its own [**namespace**](#namespace).
synchronous Programming in which the orderly sequence of events can be determined; that is, when things happen one after the other, not at the same time.
syntactic sugar An alternative way of writing something more easily; a shortcut.
syntax From Greek σύνταξις, “with-arrangement”. How things (particularly symbols) are put together with each other.
syntax tree An internal representation of your program wherein lower-level [**constructs**](#construct) dangle off the higher-level constructs enclosing them.
syscall A [**function**](#function) call directly to the [**operating system**](#operating-system). Many of the important subroutines and functions you use aren’t direct system calls, but are built up in one or more layers above the system call level. In general, Perl programmers don’t need to worry about the distinction. However, if you do happen to know which Perl functions are really syscalls, you can predict which of these will set the `$!` (`$ERRNO`) variable on failure. Unfortunately, beginning programmers often confusingly employ the term “system call” to mean what happens when you call the Perl `system` function, which actually involves many syscalls. To avoid any confusion, we nearly always say “syscall” for something you could call indirectly via Perl’s `syscall` function, and never for something you would call with Perl’s `system` function.
### T
taint checks The special bookkeeping Perl does to track the flow of external data through your program and disallow their use in system commands.
tainted Said of data derived from the grubby hands of a user, and thus unsafe for a secure program to rely on. Perl does taint checks if you run a [**setuid**](#setuid) (or [**setgid**](#setgid)) program, or if you use the `–T` switch.
taint mode Running under the `–T` switch, marking all external data as suspect and refusing to use it with system commands. See Camel chapter 20, “Security”.
TCP Short for Transmission Control Protocol. A protocol wrapped around the Internet Protocol to make an unreliable packet transmission mechanism appear to the application program to be a reliable [**stream**](#stream) of bytes. (Usually.)
term Short for a “terminal”—that is, a leaf node of a [**syntax tree**](#syntax-tree). A thing that functions grammatically as an [**operand**](#operand) for the operators in an expression.
terminator A [**character**](#character) or [**string**](#string) that marks the end of another string. The `$/` variable contains the string that terminates a `readline` operation, which `chomp` deletes from the end. Not to be confused with [**delimiters**](#delimiter) or [**separators**](#separator). The period at the end of this sentence is a terminator.
ternary An [**operator**](#operator) taking three [**operands**](#operand). Sometimes pronounced [**trinary**](#trinary).
text A [**string**](#string) or [**file**](#file) containing primarily printable characters.
thread Like a forked process, but without [**fork**](#fork)’s inherent memory protection. A thread is lighter weight than a full process, in that a process could have multiple threads running around in it, all fighting over the same process’s memory space unless steps are taken to protect threads from one another.
tie The bond between a magical variable and its implementation class. See the `tie` function in Camel chapter 27, “Functions” and Camel chapter 14, “Tied Variables”.
titlecase The case used for capitals that are followed by lowercase characters instead of by more capitals. Sometimes called sentence case or headline case. English doesn’t use Unicode titlecase, but casing rules for English titles are more complicated than simply capitalizing each word’s first character.
TMTOWTDI There’s More Than One Way To Do It, the Perl Motto. The notion that there can be more than one valid path to solving a programming problem in context. (This doesn’t mean that more ways are always better or that all possible paths are equally desirable—just that there need not be One True Way.)
token A morpheme in a programming language, the smallest unit of text with semantic significance.
tokener A module that breaks a program text into a sequence of [**tokens**](#token) for later analysis by a parser.
tokenizing Splitting up a program text into [**tokens**](#token). Also known as “lexing”, in which case you get “lexemes” instead of tokens.
toolbox approach The notion that, with a complete set of simple tools that work well together, you can build almost anything you want. Which is fine if you’re assembling a tricycle, but if you’re building a defranishizing comboflux regurgalator, you really want your own machine shop in which to build special tools. Perl is sort of a machine shop.
topic The thing you’re working on. Structures like `while(<>)`, `for`, `foreach`, and `given` set the topic for you by assigning to `$_`, the default (*topic*) variable.
transliterate To turn one string representation into another by mapping each character of the source string to its corresponding character in the result string. Not to be confused with translation: for example, Greek *πολύχρωμος* transliterates into *polychromos* but translates into *many-colored*. See the `tr///` operator in Camel chapter 5, “Pattern Matching”.
trigger An event that causes a [**handler**](#handler) to be run.
trinary Not a stellar system with three stars, but an [**operator**](#operator) taking three [**operands**](#operand). Sometimes pronounced [**ternary**](#ternary).
troff A venerable typesetting language from which Perl derives the name of its `$%` variable and which is secretly used in the production of Camel books.
true Any scalar value that doesn’t evaluate to 0 or `""`.
truncating Emptying a file of existing contents, either automatically when opening a file for writing or explicitly via the `truncate` function.
type See [**data type**](#data-type) and [**class**](#class).
type casting Converting data from one type to another. C permits this. Perl does not need it. Nor want it.
typedef A type definition in the C and C++ languages.
typed lexical A [**lexical variable**](#lexical-variable) lexical>that is declared with a [**class**](#class) type: `my Pony $bill`.
typeglob Use of a single identifier, prefixed with `*`. For example, `*name` stands for any or all of `$name`, `@name`, `%name`, `&name`, or just `name`. How you use it determines whether it is interpreted as all or only one of them. See “Typeglobs and Filehandles” in Camel chapter 2, “Bits and Pieces”.
typemap A description of how C types may be transformed to and from Perl types within an [**extension**](#extension) module written in [**XS**](#XS).
### U
UDP User Datagram Protocol, the typical way to send [**datagrams**](#datagram) over the Internet.
UID A user ID. Often used in the context of [**file**](#file) or [**process**](#process) ownership.
umask A mask of those [**permission bits**](#permission-bits) that should be forced off when creating files or directories, in order to establish a policy of whom you’ll ordinarily deny access to. See the `umask` function.
unary operator An operator with only one [**operand**](#operand), like `!` or `chdir`. Unary operators are usually prefix operators; that is, they precede their operand. The `++` and `––` operators can be either prefix or postfix. (Their position *does* change their meanings.)
Unicode A character set comprising all the major character sets of the world, more or less. See <http://www.unicode.org>.
Unix A very large and constantly evolving language with several alternative and largely incompatible syntaxes, in which anyone can define anything any way they choose, and usually do. Speakers of this language think it’s easy to learn because it’s so easily twisted to one’s own ends, but dialectical differences make tribal intercommunication nearly impossible, and travelers are often reduced to a pidgin-like subset of the language. To be universally understood, a Unix shell programmer must spend years of study in the art. Many have abandoned this discipline and now communicate via an Esperanto-like language called Perl.
In ancient times, Unix was also used to refer to some code that a couple of people at Bell Labs wrote to make use of a PDP-7 computer that wasn’t doing much of anything else at the time.
uppercase In Unicode, not just characters with the General Category of Uppercase Letter, but any character with the Uppercase property, including some Letter Numbers and Symbols. Not to be confused with [**titlecase**](#titlecase).
### V
value An actual piece of data, in contrast to all the variables, references, keys, indices, operators, and whatnot that you need to access the value.
variable A named storage location that can hold any of various kinds of [**value**](#value), as your program sees fit.
variable interpolation The [**interpolation**](#interpolation) of a scalar or array variable into a string.
variadic Said of a [**function**](#function) that happily receives an indeterminate number of [**actual arguments**](#actual-arguments).
vector Mathematical jargon for a list of [**scalar values**](#scalar-value).
virtual Providing the appearance of something without the reality, as in: virtual memory is not real memory. (See also [**memory**](#memory).) The opposite of “virtual” is “transparent”, which means providing the reality of something without the appearance, as in: Perl handles the variable-length UTF‑8 character encoding transparently.
void context A form of [**scalar context**](#scalar-context) in which an [**expression**](#expression) is not expected to return any [**value**](#value) at all and is evaluated for its [**side effects**](#side-effects) alone.
v-string A “version” or “vector” [**string**](#string) specified with a `v` followed by a series of decimal integers in dot notation, for instance, `v1.20.300.4000`. Each number turns into a [**character**](#character) with the specified ordinal value. (The `v` is optional when there are at least three integers.)
### W
warning A message printed to the `STDERR` stream to the effect that something might be wrong but isn’t worth blowing up over. See `warn` in Camel chapter 27, “Functions” and the `warnings` pragma in Camel chapter 28, “Pragmantic Modules”.
watch expression An expression which, when its value changes, causes a breakpoint in the Perl debugger.
weak reference A reference that doesn’t get counted normally. When all the normal references to data disappear, the data disappears. These are useful for circular references that would never disappear otherwise.
whitespace A [**character**](#character) that moves your cursor but doesn’t otherwise put anything on your screen. Typically refers to any of: space, tab, line feed, carriage return, or form feed. In Unicode, matches many other characters that Unicode considers whitespace, including the ɴ-ʙʀ .
word In normal “computerese”, the piece of data of the size most efficiently handled by your computer, typically 32 bits or so, give or take a few powers of 2. In Perl culture, it more often refers to an alphanumeric [**identifier**](#identifier) (including underscores), or to a string of nonwhitespace [**characters**](#character) bounded by whitespace or string boundaries.
working directory Your current [**directory**](#directory), from which relative pathnames are interpreted by the [**operating system**](#operating-system). The operating system knows your current directory because you told it with a `chdir`, or because you started out in the place where your parent [**process**](#process) was when you were born.
wrapper A program or subroutine that runs some other program or subroutine for you, modifying some of its input or output to better suit your purposes.
WYSIWYG What You See Is What You Get. Usually used when something that appears on the screen matches how it will eventually look, like Perl’s `format` declarations. Also used to mean the opposite of magic because everything works exactly as it appears, as in the three- argument form of `open`.
### X
XS An extraordinarily exported, expeditiously excellent, expressly eXternal Subroutine, executed in existing C or C++ or in an exciting extension language called (exasperatingly) XS.
XSUB An external [**subroutine**](#subroutine) defined in [**XS**](#XS).
### Y
yacc Yet Another Compiler Compiler. A parser generator without which Perl probably would not have existed. See the file *perly.y* in the Perl source distribution.
### Z
zero width A subpattern [**assertion**](#assertion) matching the [**null string**](#null-string) between [**characters**](#character).
zombie A process that has died (exited) but whose parent has not yet received proper notification of its demise by virtue of having called `wait` or `waitpid`. If you `fork`, you must clean up after your child processes when they exit; otherwise, the process table will fill up and your system administrator will Not Be Happy with you.
AUTHOR AND COPYRIGHT
---------------------
Based on the Glossary of *Programming Perl*, Fourth Edition, by Tom Christiansen, brian d foy, Larry Wall, & Jon Orwant. Copyright (c) 2000, 1996, 1991, 2012 O'Reilly Media, Inc. This document may be distributed under the same terms as Perl itself.
| programming_docs |
perl IO::Compress::Base IO::Compress::Base
==================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [SUPPORT](#SUPPORT)
* [SEE ALSO](#SEE-ALSO)
* [AUTHOR](#AUTHOR)
* [MODIFICATION HISTORY](#MODIFICATION-HISTORY)
* [COPYRIGHT AND LICENSE](#COPYRIGHT-AND-LICENSE)
NAME
----
IO::Compress::Base - Base Class for IO::Compress modules
SYNOPSIS
--------
```
use IO::Compress::Base ;
```
DESCRIPTION
-----------
This module is not intended for direct use in application code. Its sole purpose is to be sub-classed by IO::Compress modules.
SUPPORT
-------
General feedback/questions/bug reports should be sent to <https://github.com/pmqs/IO-Compress/issues> (preferred) or <https://rt.cpan.org/Public/Dist/Display.html?Name=IO-Compress>.
SEE ALSO
---------
<Compress::Zlib>, <IO::Compress::Gzip>, <IO::Uncompress::Gunzip>, <IO::Compress::Deflate>, <IO::Uncompress::Inflate>, <IO::Compress::RawDeflate>, <IO::Uncompress::RawInflate>, <IO::Compress::Bzip2>, <IO::Uncompress::Bunzip2>, <IO::Compress::Lzma>, <IO::Uncompress::UnLzma>, <IO::Compress::Xz>, <IO::Uncompress::UnXz>, <IO::Compress::Lzip>, <IO::Uncompress::UnLzip>, <IO::Compress::Lzop>, <IO::Uncompress::UnLzop>, <IO::Compress::Lzf>, <IO::Uncompress::UnLzf>, <IO::Compress::Zstd>, <IO::Uncompress::UnZstd>, <IO::Uncompress::AnyInflate>, <IO::Uncompress::AnyUncompress>
<IO::Compress::FAQ>
<File::GlobMapper>, <Archive::Zip>, <Archive::Tar>, <IO::Zlib>
AUTHOR
------
This module was written by Paul Marquess, `[email protected]`.
MODIFICATION HISTORY
---------------------
See the Changes file.
COPYRIGHT AND LICENSE
----------------------
Copyright (c) 2005-2022 Paul Marquess. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl Net::hostent Net::hostent
============
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [EXAMPLES](#EXAMPLES)
* [NOTE](#NOTE)
* [AUTHOR](#AUTHOR)
NAME
----
Net::hostent - by-name interface to Perl's built-in gethost\*() functions
SYNOPSIS
--------
```
use Net::hostent;
```
DESCRIPTION
-----------
This module's default exports override the core gethostbyname() and gethostbyaddr() functions, replacing them with versions that return "Net::hostent" objects. This object has methods that return the similarly named structure field name from the C's hostent structure from *netdb.h*; namely name, aliases, addrtype, length, and addr\_list. The aliases and addr\_list methods return array reference, the rest scalars. The addr method is equivalent to the zeroth element in the addr\_list array reference.
You may also import all the structure fields directly into your namespace as regular variables using the :FIELDS import tag. (Note that this still overrides your core functions.) Access these fields as variables named with a preceding `h_`. Thus, `$host_obj->name()` corresponds to $h\_name if you import the fields. Array references are available as regular array variables, so for example `@{ $host_obj->aliases() }` would be simply @h\_aliases.
The gethost() function is a simple front-end that forwards a numeric argument to gethostbyaddr() by way of Socket::inet\_aton, and the rest to gethostbyname().
To access this functionality without the core overrides, pass the `use` an empty import list, and then access function functions with their full qualified names. On the other hand, the built-ins are still available via the `CORE::` pseudo-package.
EXAMPLES
--------
```
use Net::hostent;
use Socket;
@ARGV = ('netscape.com') unless @ARGV;
for $host ( @ARGV ) {
unless ($h = gethost($host)) {
warn "$0: no such host: $host\n";
next;
}
printf "\n%s is %s%s\n",
$host,
lc($h->name) eq lc($host) ? "" : "*really* ",
$h->name;
print "\taliases are ", join(", ", @{$h->aliases}), "\n"
if @{$h->aliases};
if ( @{$h->addr_list} > 1 ) {
my $i;
for $addr ( @{$h->addr_list} ) {
printf "\taddr #%d is [%s]\n", $i++, inet_ntoa($addr);
}
} else {
printf "\taddress is [%s]\n", inet_ntoa($h->addr);
}
if ($h = gethostbyaddr($h->addr)) {
if (lc($h->name) ne lc($host)) {
printf "\tThat addr reverses to host %s!\n", $h->name;
$host = $h->name;
redo;
}
}
}
```
NOTE
----
While this class is currently implemented using the Class::Struct module to build a struct-like class, you shouldn't rely upon this.
AUTHOR
------
Tom Christiansen
perl Test2::EventFacet::Parent Test2::EventFacet::Parent
=========================
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
* [FIELDS](#FIELDS)
* [SOURCE](#SOURCE)
* [MAINTAINERS](#MAINTAINERS)
* [AUTHORS](#AUTHORS)
* [COPYRIGHT](#COPYRIGHT)
NAME
----
Test2::EventFacet::Parent - Facet for events contains other events
DESCRIPTION
-----------
This facet is used when an event contains other events, such as a subtest.
FIELDS
------
$string = $parent->{details}
$string = $parent->details() Human readable description of the event.
$hid = $parent->{hid}
$hid = $parent->hid() Hub ID of the hub that is represented in the parent-child relationship.
$arrayref = $parent->{children}
$arrayref = $parent->children() Arrayref containing the facet-data hashes of events nested under this one.
*To get the actual events you need to get them from the parent event directly*
$bool = $parent->{buffered}
$bool = $parent->buffered() True if the subtest is buffered (meaning the formatter has probably not seen them yet).
SOURCE
------
The source code repository for Test2 can be found at *http://github.com/Test-More/test-more/*.
MAINTAINERS
-----------
Chad Granum <[email protected]> AUTHORS
-------
Chad Granum <[email protected]> COPYRIGHT
---------
Copyright 2020 Chad Granum <[email protected]>.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
See *http://dev.perl.org/licenses/*
perl IO::Compress::Deflate IO::Compress::Deflate
=====================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [Functional Interface](#Functional-Interface)
+ [deflate $input\_filename\_or\_reference => $output\_filename\_or\_reference [, OPTS]](#deflate-%24input_filename_or_reference-=%3E-%24output_filename_or_reference-%5B,-OPTS%5D)
- [The $input\_filename\_or\_reference parameter](#The-%24input_filename_or_reference-parameter)
- [The $output\_filename\_or\_reference parameter](#The-%24output_filename_or_reference-parameter)
+ [Notes](#Notes)
+ [Optional Parameters](#Optional-Parameters)
+ [Examples](#Examples)
- [Streaming](#Streaming)
- [Compressing a file from the filesystem](#Compressing-a-file-from-the-filesystem)
- [Reading from a Filehandle and writing to an in-memory buffer](#Reading-from-a-Filehandle-and-writing-to-an-in-memory-buffer)
- [Compressing multiple files](#Compressing-multiple-files)
* [OO Interface](#OO-Interface)
+ [Constructor](#Constructor)
+ [Constructor Options](#Constructor-Options)
+ [Examples](#Examples1)
* [Methods](#Methods)
+ [print](#print)
+ [printf](#printf)
+ [syswrite](#syswrite)
+ [write](#write)
+ [flush](#flush)
+ [tell](#tell)
+ [eof](#eof)
+ [seek](#seek)
+ [binmode](#binmode)
+ [opened](#opened)
+ [autoflush](#autoflush)
+ [input\_line\_number](#input_line_number)
+ [fileno](#fileno)
+ [close](#close)
+ [newStream([OPTS])](#newStream(%5BOPTS%5D))
+ [deflateParams](#deflateParams)
* [Importing](#Importing)
* [EXAMPLES](#EXAMPLES)
+ [Apache::GZip Revisited](#Apache::GZip-Revisited)
+ [Working with Net::FTP](#Working-with-Net::FTP)
* [SUPPORT](#SUPPORT)
* [SEE ALSO](#SEE-ALSO)
* [AUTHOR](#AUTHOR)
* [MODIFICATION HISTORY](#MODIFICATION-HISTORY)
* [COPYRIGHT AND LICENSE](#COPYRIGHT-AND-LICENSE)
NAME
----
IO::Compress::Deflate - Write RFC 1950 files/buffers
SYNOPSIS
--------
```
use IO::Compress::Deflate qw(deflate $DeflateError) ;
my $status = deflate $input => $output [,OPTS]
or die "deflate failed: $DeflateError\n";
my $z = IO::Compress::Deflate->new( $output [,OPTS] )
or die "deflate failed: $DeflateError\n";
$z->print($string);
$z->printf($format, $string);
$z->write($string);
$z->syswrite($string [, $length, $offset]);
$z->flush();
$z->tell();
$z->eof();
$z->seek($position, $whence);
$z->binmode();
$z->fileno();
$z->opened();
$z->autoflush();
$z->input_line_number();
$z->newStream( [OPTS] );
$z->deflateParams();
$z->close() ;
$DeflateError ;
# IO::File mode
print $z $string;
printf $z $format, $string;
tell $z
eof $z
seek $z, $position, $whence
binmode $z
fileno $z
close $z ;
```
DESCRIPTION
-----------
This module provides a Perl interface that allows writing compressed data to files or buffer as defined in RFC 1950.
For reading RFC 1950 files/buffers, see the companion module <IO::Uncompress::Inflate>.
Functional Interface
---------------------
A top-level function, `deflate`, is provided to carry out "one-shot" compression between buffers and/or files. For finer control over the compression process, see the ["OO Interface"](#OO-Interface) section.
```
use IO::Compress::Deflate qw(deflate $DeflateError) ;
deflate $input_filename_or_reference => $output_filename_or_reference [,OPTS]
or die "deflate failed: $DeflateError\n";
```
The functional interface needs Perl5.005 or better.
###
deflate $input\_filename\_or\_reference => $output\_filename\_or\_reference [, OPTS]
`deflate` expects at least two parameters, `$input_filename_or_reference` and `$output_filename_or_reference` and zero or more optional parameters (see ["Optional Parameters"](#Optional-Parameters))
####
The `$input_filename_or_reference` parameter
The parameter, `$input_filename_or_reference`, is used to define the source of the uncompressed data.
It can take one of the following forms:
A filename If the `$input_filename_or_reference` parameter is a simple scalar, it is assumed to be a filename. This file will be opened for reading and the input data will be read from it.
A filehandle If the `$input_filename_or_reference` parameter is a filehandle, the input data will be read from it. The string '-' can be used as an alias for standard input.
A scalar reference If `$input_filename_or_reference` is a scalar reference, the input data will be read from `$$input_filename_or_reference`.
An array reference If `$input_filename_or_reference` is an array reference, each element in the array must be a filename.
The input data will be read from each file in turn.
The complete array will be walked to ensure that it only contains valid filenames before any data is compressed.
An Input FileGlob string If `$input_filename_or_reference` is a string that is delimited by the characters "<" and ">" `deflate` will assume that it is an *input fileglob string*. The input is the list of files that match the fileglob.
See <File::GlobMapper> for more details.
If the `$input_filename_or_reference` parameter is any other type, `undef` will be returned.
####
The `$output_filename_or_reference` parameter
The parameter `$output_filename_or_reference` is used to control the destination of the compressed data. This parameter can take one of these forms.
A filename If the `$output_filename_or_reference` parameter is a simple scalar, it is assumed to be a filename. This file will be opened for writing and the compressed data will be written to it.
A filehandle If the `$output_filename_or_reference` parameter is a filehandle, the compressed data will be written to it. The string '-' can be used as an alias for standard output.
A scalar reference If `$output_filename_or_reference` is a scalar reference, the compressed data will be stored in `$$output_filename_or_reference`.
An Array Reference If `$output_filename_or_reference` is an array reference, the compressed data will be pushed onto the array.
An Output FileGlob If `$output_filename_or_reference` is a string that is delimited by the characters "<" and ">" `deflate` will assume that it is an *output fileglob string*. The output is the list of files that match the fileglob.
When `$output_filename_or_reference` is an fileglob string, `$input_filename_or_reference` must also be a fileglob string. Anything else is an error.
See <File::GlobMapper> for more details.
If the `$output_filename_or_reference` parameter is any other type, `undef` will be returned.
### Notes
When `$input_filename_or_reference` maps to multiple files/buffers and `$output_filename_or_reference` is a single file/buffer the input files/buffers will be stored in `$output_filename_or_reference` as a concatenated series of compressed data streams.
###
Optional Parameters
The optional parameters for the one-shot function `deflate` are (for the most part) identical to those used with the OO interface defined in the ["Constructor Options"](#Constructor-Options) section. The exceptions are listed below
`AutoClose => 0|1`
This option applies to any input or output data streams to `deflate` that are filehandles.
If `AutoClose` is specified, and the value is true, it will result in all input and/or output filehandles being closed once `deflate` has completed.
This parameter defaults to 0.
`BinModeIn => 0|1`
This option is now a no-op. All files will be read in binmode.
`Append => 0|1`
The behaviour of this option is dependent on the type of output data stream.
* A Buffer
If `Append` is enabled, all compressed data will be append to the end of the output buffer. Otherwise the output buffer will be cleared before any compressed data is written to it.
* A Filename
If `Append` is enabled, the file will be opened in append mode. Otherwise the contents of the file, if any, will be truncated before any compressed data is written to it.
* A Filehandle
If `Append` is enabled, the filehandle will be positioned to the end of the file via a call to `seek` before any compressed data is written to it. Otherwise the file pointer will not be moved.
When `Append` is specified, and set to true, it will *append* all compressed data to the output data stream.
So when the output is a filehandle it will carry out a seek to the eof before writing any compressed data. If the output is a filename, it will be opened for appending. If the output is a buffer, all compressed data will be appended to the existing buffer.
Conversely when `Append` is not specified, or it is present and is set to false, it will operate as follows.
When the output is a filename, it will truncate the contents of the file before writing any compressed data. If the output is a filehandle its position will not be changed. If the output is a buffer, it will be wiped before any compressed data is output.
Defaults to 0.
### Examples
Here are a few example that show the capabilities of the module.
#### Streaming
This very simple command line example demonstrates the streaming capabilities of the module. The code reads data from STDIN, compresses it, and writes the compressed data to STDOUT.
```
$ echo hello world | perl -MIO::Compress::Deflate=deflate -e 'deflate \*STDIN => \*STDOUT' >output.1950
```
The special filename "-" can be used as a standin for both `\*STDIN` and `\*STDOUT`, so the above can be rewritten as
```
$ echo hello world | perl -MIO::Compress::Deflate=deflate -e 'deflate "-" => "-"' >output.1950
```
####
Compressing a file from the filesystem
To read the contents of the file `file1.txt` and write the compressed data to the file `file1.txt.1950`.
```
use strict ;
use warnings ;
use IO::Compress::Deflate qw(deflate $DeflateError) ;
my $input = "file1.txt";
deflate $input => "$input.1950"
or die "deflate failed: $DeflateError\n";
```
####
Reading from a Filehandle and writing to an in-memory buffer
To read from an existing Perl filehandle, `$input`, and write the compressed data to a buffer, `$buffer`.
```
use strict ;
use warnings ;
use IO::Compress::Deflate qw(deflate $DeflateError) ;
use IO::File ;
my $input = IO::File->new( "<file1.txt" )
or die "Cannot open 'file1.txt': $!\n" ;
my $buffer ;
deflate $input => \$buffer
or die "deflate failed: $DeflateError\n";
```
####
Compressing multiple files
To compress all files in the directory "/my/home" that match "\*.txt" and store the compressed data in the same directory
```
use strict ;
use warnings ;
use IO::Compress::Deflate qw(deflate $DeflateError) ;
deflate '</my/home/*.txt>' => '<*.1950>'
or die "deflate failed: $DeflateError\n";
```
and if you want to compress each file one at a time, this will do the trick
```
use strict ;
use warnings ;
use IO::Compress::Deflate qw(deflate $DeflateError) ;
for my $input ( glob "/my/home/*.txt" )
{
my $output = "$input.1950" ;
deflate $input => $output
or die "Error compressing '$input': $DeflateError\n";
}
```
OO Interface
-------------
### Constructor
The format of the constructor for `IO::Compress::Deflate` is shown below
```
my $z = IO::Compress::Deflate->new( $output [,OPTS] )
or die "IO::Compress::Deflate failed: $DeflateError\n";
```
It returns an `IO::Compress::Deflate` object on success and undef on failure. The variable `$DeflateError` will contain an error message on failure.
If you are running Perl 5.005 or better the object, `$z`, returned from IO::Compress::Deflate can be used exactly like an <IO::File> filehandle. This means that all normal output file operations can be carried out with `$z`. For example, to write to a compressed file/buffer you can use either of these forms
```
$z->print("hello world\n");
print $z "hello world\n";
```
The mandatory parameter `$output` is used to control the destination of the compressed data. This parameter can take one of these forms.
A filename If the `$output` parameter is a simple scalar, it is assumed to be a filename. This file will be opened for writing and the compressed data will be written to it.
A filehandle If the `$output` parameter is a filehandle, the compressed data will be written to it. The string '-' can be used as an alias for standard output.
A scalar reference If `$output` is a scalar reference, the compressed data will be stored in `$$output`.
If the `$output` parameter is any other type, `IO::Compress::Deflate`::new will return undef.
###
Constructor Options
`OPTS` is any combination of zero or more the following options:
`AutoClose => 0|1`
This option is only valid when the `$output` parameter is a filehandle. If specified, and the value is true, it will result in the `$output` being closed once either the `close` method is called or the `IO::Compress::Deflate` object is destroyed.
This parameter defaults to 0.
`Append => 0|1`
Opens `$output` in append mode.
The behaviour of this option is dependent on the type of `$output`.
* A Buffer
If `$output` is a buffer and `Append` is enabled, all compressed data will be append to the end of `$output`. Otherwise `$output` will be cleared before any data is written to it.
* A Filename
If `$output` is a filename and `Append` is enabled, the file will be opened in append mode. Otherwise the contents of the file, if any, will be truncated before any compressed data is written to it.
* A Filehandle
If `$output` is a filehandle, the file pointer will be positioned to the end of the file via a call to `seek` before any compressed data is written to it. Otherwise the file pointer will not be moved.
This parameter defaults to 0.
`Merge => 0|1`
This option is used to compress input data and append it to an existing compressed data stream in `$output`. The end result is a single compressed data stream stored in `$output`.
It is a fatal error to attempt to use this option when `$output` is not an RFC 1950 data stream.
There are a number of other limitations with the `Merge` option:
1. This module needs to have been built with zlib 1.2.1 or better to work. A fatal error will be thrown if `Merge` is used with an older version of zlib.
2. If `$output` is a file or a filehandle, it must be seekable.
This parameter defaults to 0.
-Level Defines the compression level used by zlib. The value should either be a number between 0 and 9 (0 means no compression and 9 is maximum compression), or one of the symbolic constants defined below.
```
Z_NO_COMPRESSION
Z_BEST_SPEED
Z_BEST_COMPRESSION
Z_DEFAULT_COMPRESSION
```
The default is Z\_DEFAULT\_COMPRESSION.
Note, these constants are not imported by `IO::Compress::Deflate` by default.
```
use IO::Compress::Deflate qw(:strategy);
use IO::Compress::Deflate qw(:constants);
use IO::Compress::Deflate qw(:all);
```
-Strategy Defines the strategy used to tune the compression. Use one of the symbolic constants defined below.
```
Z_FILTERED
Z_HUFFMAN_ONLY
Z_RLE
Z_FIXED
Z_DEFAULT_STRATEGY
```
The default is Z\_DEFAULT\_STRATEGY.
`Strict => 0|1`
This is a placeholder option.
### Examples
TODO
Methods
-------
### print
Usage is
```
$z->print($data)
print $z $data
```
Compresses and outputs the contents of the `$data` parameter. This has the same behaviour as the `print` built-in.
Returns true if successful.
### printf
Usage is
```
$z->printf($format, $data)
printf $z $format, $data
```
Compresses and outputs the contents of the `$data` parameter.
Returns true if successful.
### syswrite
Usage is
```
$z->syswrite $data
$z->syswrite $data, $length
$z->syswrite $data, $length, $offset
```
Compresses and outputs the contents of the `$data` parameter.
Returns the number of uncompressed bytes written, or `undef` if unsuccessful.
### write
Usage is
```
$z->write $data
$z->write $data, $length
$z->write $data, $length, $offset
```
Compresses and outputs the contents of the `$data` parameter.
Returns the number of uncompressed bytes written, or `undef` if unsuccessful.
### flush
Usage is
```
$z->flush;
$z->flush($flush_type);
```
Flushes any pending compressed data to the output file/buffer.
This method takes an optional parameter, `$flush_type`, that controls how the flushing will be carried out. By default the `$flush_type` used is `Z_FINISH`. Other valid values for `$flush_type` are `Z_NO_FLUSH`, `Z_SYNC_FLUSH`, `Z_FULL_FLUSH` and `Z_BLOCK`. It is strongly recommended that you only set the `flush_type` parameter if you fully understand the implications of what it does - overuse of `flush` can seriously degrade the level of compression achieved. See the `zlib` documentation for details.
Returns true on success.
### tell
Usage is
```
$z->tell()
tell $z
```
Returns the uncompressed file offset.
### eof
Usage is
```
$z->eof();
eof($z);
```
Returns true if the `close` method has been called.
### seek
```
$z->seek($position, $whence);
seek($z, $position, $whence);
```
Provides a sub-set of the `seek` functionality, with the restriction that it is only legal to seek forward in the output file/buffer. It is a fatal error to attempt to seek backward.
Empty parts of the file/buffer will have NULL (0x00) bytes written to them.
The `$whence` parameter takes one the usual values, namely SEEK\_SET, SEEK\_CUR or SEEK\_END.
Returns 1 on success, 0 on failure.
### binmode
Usage is
```
$z->binmode
binmode $z ;
```
This is a noop provided for completeness.
### opened
```
$z->opened()
```
Returns true if the object currently refers to a opened file/buffer.
### autoflush
```
my $prev = $z->autoflush()
my $prev = $z->autoflush(EXPR)
```
If the `$z` object is associated with a file or a filehandle, this method returns the current autoflush setting for the underlying filehandle. If `EXPR` is present, and is non-zero, it will enable flushing after every write/print operation.
If `$z` is associated with a buffer, this method has no effect and always returns `undef`.
**Note** that the special variable `$|` **cannot** be used to set or retrieve the autoflush setting.
### input\_line\_number
```
$z->input_line_number()
$z->input_line_number(EXPR)
```
This method always returns `undef` when compressing.
### fileno
```
$z->fileno()
fileno($z)
```
If the `$z` object is associated with a file or a filehandle, `fileno` will return the underlying file descriptor. Once the `close` method is called `fileno` will return `undef`.
If the `$z` object is associated with a buffer, this method will return `undef`.
### close
```
$z->close() ;
close $z ;
```
Flushes any pending compressed data and then closes the output file/buffer.
For most versions of Perl this method will be automatically invoked if the IO::Compress::Deflate object is destroyed (either explicitly or by the variable with the reference to the object going out of scope). The exceptions are Perl versions 5.005 through 5.00504 and 5.8.0. In these cases, the `close` method will be called automatically, but not until global destruction of all live objects when the program is terminating.
Therefore, if you want your scripts to be able to run on all versions of Perl, you should call `close` explicitly and not rely on automatic closing.
Returns true on success, otherwise 0.
If the `AutoClose` option has been enabled when the IO::Compress::Deflate object was created, and the object is associated with a file, the underlying file will also be closed.
###
newStream([OPTS])
Usage is
```
$z->newStream( [OPTS] )
```
Closes the current compressed data stream and starts a new one.
OPTS consists of any of the options that are available when creating the `$z` object.
See the ["Constructor Options"](#Constructor-Options) section for more details.
### deflateParams
Usage is
```
$z->deflateParams
```
TODO
Importing
---------
A number of symbolic constants are required by some methods in `IO::Compress::Deflate`. None are imported by default.
:all Imports `deflate`, `$DeflateError` and all symbolic constants that can be used by `IO::Compress::Deflate`. Same as doing this
```
use IO::Compress::Deflate qw(deflate $DeflateError :constants) ;
```
:constants Import all symbolic constants. Same as doing this
```
use IO::Compress::Deflate qw(:flush :level :strategy) ;
```
:flush These symbolic constants are used by the `flush` method.
```
Z_NO_FLUSH
Z_PARTIAL_FLUSH
Z_SYNC_FLUSH
Z_FULL_FLUSH
Z_FINISH
Z_BLOCK
```
:level These symbolic constants are used by the `Level` option in the constructor.
```
Z_NO_COMPRESSION
Z_BEST_SPEED
Z_BEST_COMPRESSION
Z_DEFAULT_COMPRESSION
```
:strategy These symbolic constants are used by the `Strategy` option in the constructor.
```
Z_FILTERED
Z_HUFFMAN_ONLY
Z_RLE
Z_FIXED
Z_DEFAULT_STRATEGY
```
EXAMPLES
--------
###
Apache::GZip Revisited
See [IO::Compress::FAQ](IO::Compress::FAQ#Apache%3A%3AGZip-Revisited)
###
Working with Net::FTP
See [IO::Compress::FAQ](IO::Compress::FAQ#Compressed-files-and-Net%3A%3AFTP)
SUPPORT
-------
General feedback/questions/bug reports should be sent to <https://github.com/pmqs/IO-Compress/issues> (preferred) or <https://rt.cpan.org/Public/Dist/Display.html?Name=IO-Compress>.
SEE ALSO
---------
<Compress::Zlib>, <IO::Compress::Gzip>, <IO::Uncompress::Gunzip>, <IO::Uncompress::Inflate>, <IO::Compress::RawDeflate>, <IO::Uncompress::RawInflate>, <IO::Compress::Bzip2>, <IO::Uncompress::Bunzip2>, <IO::Compress::Lzma>, <IO::Uncompress::UnLzma>, <IO::Compress::Xz>, <IO::Uncompress::UnXz>, <IO::Compress::Lzip>, <IO::Uncompress::UnLzip>, <IO::Compress::Lzop>, <IO::Uncompress::UnLzop>, <IO::Compress::Lzf>, <IO::Uncompress::UnLzf>, <IO::Compress::Zstd>, <IO::Uncompress::UnZstd>, <IO::Uncompress::AnyInflate>, <IO::Uncompress::AnyUncompress>
<IO::Compress::FAQ>
<File::GlobMapper>, <Archive::Zip>, <Archive::Tar>, <IO::Zlib>
For RFC 1950, 1951 and 1952 see <https://datatracker.ietf.org/doc/html/rfc1950>, <https://datatracker.ietf.org/doc/html/rfc1951> and <https://datatracker.ietf.org/doc/html/rfc1952>
The *zlib* compression library was written by Jean-loup Gailly `[email protected]` and Mark Adler `[email protected]`.
The primary site for the *zlib* compression library is <http://www.zlib.org>.
The primary site for gzip is <http://www.gzip.org>.
AUTHOR
------
This module was written by Paul Marquess, `[email protected]`.
MODIFICATION HISTORY
---------------------
See the Changes file.
COPYRIGHT AND LICENSE
----------------------
Copyright (c) 2005-2022 Paul Marquess. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
| programming_docs |
perl ExtUtils::XSSymSet ExtUtils::XSSymSet
==================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [AUTHOR](#AUTHOR)
* [REVISION](#REVISION)
NAME
----
ExtUtils::XSSymSet - keep sets of symbol names palatable to the VMS linker
SYNOPSIS
--------
```
use ExtUtils::XSSymSet;
$set = new ExtUtils::XSSymSet;
while ($sym = make_symbol()) { $set->addsym($sym); }
foreach $safesym ($set->all_trimmed) {
print "Processing $safesym (derived from ",
$self->get_orig($safesym), ")\n";
do_stuff($safesym);
}
$safesym = ExtUtils::XSSymSet->trimsym($onesym);
```
DESCRIPTION
-----------
Since the VMS linker distinguishes symbols based only on the first 31 characters of their names, it is occasionally necessary to shorten symbol names in order to avoid collisions. (This is especially true of names generated by xsubpp, since prefixes generated by nested package names can become quite long.) `ExtUtils::XSSymSet` provides functions to shorten names in a consistent fashion, and to track a set of names to insure that each is unique. While designed with *xsubpp* in mind, it may be used with any set of strings.
This package supplies the following functions, all of which should be called as methods.
new([$maxlen[,$silent]]) Creates an empty `ExtUtils::XSSymset` set of symbols. This function may be called as a static method or via an existing object. If `$maxlen` or `$silent` are specified, they are used as the defaults for maximum name length and warning behavior in future calls to addsym() or trimsym() via this object. If the compiler has been instructed to do its own symbol shortening via `$Config{'useshortenedsymbols'}`, a value of 2048 is assumed for `$maxlen` as a way of bypassing the shortening done by this module.
addsym($name[,$maxlen[,$silent]]) Creates a symbol name from `$name`, using the methods described under trimsym(), which is unique in this set of symbols, and returns the new name. `$name` and its resultant are added to the set, and any future calls to addsym() specifying the same `$name` will return the same result, regardless of the value of `$maxlen` specified. Unless `$silent` is true, warnings are output if `$name` had to be trimmed or changed in order to avoid collision with an existing symbol name. `$maxlen` and `$silent` default to the values specified when this set of symbols was created. This method must be called via an existing object.
trimsym($name[,$maxlen[,$silent]]) Creates a symbol name `$maxlen` or fewer characters long from `$name` and returns it. If `$name` is too long, it first tries to shorten it by removing duplicate characters, then by periodically removing non-underscore characters, and finally, if necessary, by periodically removing characters of any type. `$maxlen` defaults to 31. Unless `$silent` is true, a warning is output if `$name` is altered in any way. This function may be called either as a static method or via an existing object, but in the latter case no check is made to insure that the resulting name is unique in the set of symbols. If the compiler has been instructed to do its own symbol shortening via `$Config{'useshortenedsymbols'}`, a value of 2048 is assumed for `$maxlen` as a way of bypassing the shortening done by this module.
delsym($name) Removes `$name` from the set of symbols, where `$name` is the original symbol name passed previously to addsym(). If `$name` existed in the set of symbols, returns its "trimmed" equivalent, otherwise returns `undef`. This method must be called via an existing object.
get\_orig($trimmed) Returns the original name which was trimmed to `$trimmed` by a previous call to addsym(), or `undef` if `$trimmed` does not correspond to a member of this set of symbols. This method must be called via an existing object.
get\_trimmed($name) Returns the trimmed name which was generated from `$name` by a previous call to addsym(), or `undef` if `$name` is not a member of this set of symbols. This method must be called via an existing object.
all\_orig() Returns a list containing all of the original symbol names from this set.
all\_trimmed() Returns a list containing all of the trimmed symbol names from this set.
AUTHOR
------
Charles Bailey <*[email protected]*>
REVISION
--------
Last revised 8-Oct-2010, for Perl 5.13.6.
perl sort sort
====
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [CAVEATS](#CAVEATS)
NAME
----
sort - perl pragma to control sort() behaviour
SYNOPSIS
--------
The sort pragma is now a no-op, and its use is discouraged. These three operations are valid, but have no effect:
```
use sort 'stable'; # guarantee stability
use sort 'defaults'; # revert to default behavior
no sort 'stable'; # stability not important
```
DESCRIPTION
-----------
Historically the `sort` pragma you can control the behaviour of the builtin `sort()` function.
Prior to v5.28.0 there were two other options:
```
use sort '_mergesort';
use sort '_qsort'; # or '_quicksort'
```
If you try and specify either of these in v5.28+ it will croak.
The default sort has been stable since v5.8.0, and given this consistent behaviour for almost two decades, everyone has come to assume stability.
Stability will remain the default - hence there is no need for a pragma for code to opt into stability "just in case" this changes - it won't.
We do not foresee going back to offering multiple implementations of general purpose sorting - hence there is no future need to offer a pragma to choose between them.
If you know that you care that much about performance of your sorting, and that for your use case and your data, it was worth investigating alternatives, possible to identify an alternative from our default that was better, and the cost of switching was worth it, then you know more than we do. Likely whatever choices we can give are not as good as implementing your own. (For example, a Radix sort can be faster than O(n log n), but can't be used for all keys and has larger overheads.)
We are not averse to **changing** the sort algorithm, but we don't see the benefit in offering the choice of two general purpose implementations.
CAVEATS
-------
The function `sort::current()` was provided to report the current state of the sort pragmata. This function was not exported, and there is no code to call it on CPAN. It is now deprecated, and will warn by default.
As we no longer store any sort "state", it can no longer return the correct value, so it will always return the string `stable`, as this is consistent with what we actually have implemented.
perl perlpragma perlpragma
==========
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
* [A basic example](#A-basic-example)
* [Key naming](#Key-naming)
* [Implementation details](#Implementation-details)
NAME
----
perlpragma - how to write a user pragma
DESCRIPTION
-----------
A pragma is a module which influences some aspect of the compile time or run time behaviour of Perl, such as `strict` or `warnings`. With Perl 5.10 you are no longer limited to the built in pragmata; you can now create user pragmata that modify the behaviour of user functions within a lexical scope.
A basic example
----------------
For example, say you need to create a class implementing overloaded mathematical operators, and would like to provide your own pragma that functions much like `use integer;` You'd like this code
```
use MyMaths;
my $l = MyMaths->new(1.2);
my $r = MyMaths->new(3.4);
print "A: ", $l + $r, "\n";
use myint;
print "B: ", $l + $r, "\n";
{
no myint;
print "C: ", $l + $r, "\n";
}
print "D: ", $l + $r, "\n";
no myint;
print "E: ", $l + $r, "\n";
```
to give the output
```
A: 4.6
B: 4
C: 4.6
D: 4
E: 4.6
```
*i.e.*, where `use myint;` is in effect, addition operations are forced to integer, whereas by default they are not, with the default behaviour being restored via `no myint;`
The minimal implementation of the package `MyMaths` would be something like this:
```
package MyMaths;
use v5.36;
use myint();
use overload '+' => sub {
my ($l, $r) = @_;
# Pass 1 to check up one call level from here
if (myint::in_effect(1)) {
int($$l) + int($$r);
} else {
$$l + $$r;
}
};
sub new {
my ($class, $value) = @_;
bless \$value, $class;
}
1;
```
Note how we load the user pragma `myint` with an empty list `()` to prevent its `import` being called.
The interaction with the Perl compilation happens inside package `myint`:
```
package myint;
use v5.36;
sub import {
$^H{"myint/in_effect"} = 1;
}
sub unimport {
$^H{"myint/in_effect"} = 0;
}
sub in_effect {
my $level = shift // 0;
my $hinthash = (caller($level))[10];
return $hinthash->{"myint/in_effect"};
}
1;
```
As pragmata are implemented as modules, like any other module, `use myint;` becomes
```
BEGIN {
require myint;
myint->import();
}
```
and `no myint;` is
```
BEGIN {
require myint;
myint->unimport();
}
```
Hence the `import` and `unimport` routines are called at **compile time** for the user's code.
User pragmata store their state by writing to the magical hash `%^H`, hence these two routines manipulate it. The state information in `%^H` is stored in the optree, and can be retrieved read-only at runtime with `caller()`, at index 10 of the list of returned results. In the example pragma, retrieval is encapsulated into the routine `in_effect()`, which takes as parameter the number of call frames to go up to find the value of the pragma in the user's script. This uses `caller()` to determine the value of `$^H{"myint/in_effect"}` when each line of the user's script was called, and therefore provide the correct semantics in the subroutine implementing the overloaded addition.
Key naming
-----------
There is only a single `%^H`, but arbitrarily many modules that want to use its scoping semantics. To avoid stepping on each other's toes, they need to be sure to use different keys in the hash. It is therefore conventional for a module to use only keys that begin with the module's name (the name of its main package) and a "/" character. After this module-identifying prefix, the rest of the key is entirely up to the module: it may include any characters whatsoever. For example, a module `Foo::Bar` should use keys such as `Foo::Bar/baz` and `Foo::Bar/$%/_!`. Modules following this convention all play nicely with each other.
The Perl core uses a handful of keys in `%^H` which do not follow this convention, because they predate it. Keys that follow the convention won't conflict with the core's historical keys.
Implementation details
-----------------------
The optree is shared between threads. This means there is a possibility that the optree will outlive the particular thread (and therefore the interpreter instance) that created it, so true Perl scalars cannot be stored in the optree. Instead a compact form is used, which can only store values that are integers (signed and unsigned), strings or `undef` - references and floating point values are stringified. If you need to store multiple values or complex structures, you should serialise them, for example with `pack`. The deletion of a hash key from `%^H` is recorded, and as ever can be distinguished from the existence of a key with value `undef` with `exists`.
**Don't** attempt to store references to data structures as integers which are retrieved via `caller` and converted back, as this will not be threadsafe. Accesses would be to the structure without locking (which is not safe for Perl's scalars), and either the structure has to leak, or it has to be freed when its creating thread terminates, which may be before the optree referencing it is deleted, if other threads outlive it.
perl IO::File IO::File
========
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [CONSTRUCTOR](#CONSTRUCTOR)
* [METHODS](#METHODS)
* [NOTE](#NOTE)
* [SEE ALSO](#SEE-ALSO)
* [HISTORY](#HISTORY)
NAME
----
IO::File - supply object methods for filehandles
SYNOPSIS
--------
```
use IO::File;
$fh = IO::File->new();
if ($fh->open("< file")) {
print <$fh>;
$fh->close;
}
$fh = IO::File->new("> file");
if (defined $fh) {
print $fh "bar\n";
$fh->close;
}
$fh = IO::File->new("file", "r");
if (defined $fh) {
print <$fh>;
undef $fh; # automatically closes the file
}
$fh = IO::File->new("file", O_WRONLY|O_APPEND);
if (defined $fh) {
print $fh "corge\n";
$pos = $fh->getpos;
$fh->setpos($pos);
undef $fh; # automatically closes the file
}
autoflush STDOUT 1;
```
DESCRIPTION
-----------
`IO::File` inherits from `IO::Handle` and `IO::Seekable`. It extends these classes with methods that are specific to file handles.
CONSTRUCTOR
-----------
new ( FILENAME [,MODE [,PERMS]] ) Creates an `IO::File`. If it receives any parameters, they are passed to the method `open`; if the open fails, the object is destroyed. Otherwise, it is returned to the caller.
new\_tmpfile Creates an `IO::File` opened for read/write on a newly created temporary file. On systems where this is possible, the temporary file is anonymous (i.e. it is unlinked after creation, but held open). If the temporary file cannot be created or opened, the `IO::File` object is destroyed. Otherwise, it is returned to the caller.
METHODS
-------
open( FILENAME [,MODE [,PERMS]] )
open( FILENAME, IOLAYERS ) `open` accepts one, two or three parameters. With one parameter, it is just a front end for the built-in `open` function. With two or three parameters, the first parameter is a filename that may include whitespace or other special characters, and the second parameter is the open mode, optionally followed by a file permission value.
If `IO::File::open` receives a Perl mode string (">", "+<", etc.) or an ANSI C fopen() mode string ("w", "r+", etc.), it uses the basic Perl `open` operator (but protects any special characters).
If `IO::File::open` is given a numeric mode, it passes that mode and the optional permissions value to the Perl `sysopen` operator. The permissions default to 0666.
If `IO::File::open` is given a mode that includes the `:` character, it passes all the three arguments to the three-argument `open` operator.
For convenience, `IO::File` exports the O\_XXX constants from the Fcntl module, if this module is available.
binmode( [LAYER] ) `binmode` sets `binmode` on the underlying `IO` object, as documented in `perldoc -f binmode`.
`binmode` accepts one optional parameter, which is the layer to be passed on to the `binmode` call.
NOTE
----
Some operating systems may perform `IO::File::new()` or `IO::File::open()` on a directory without errors. This behavior is not portable and not suggested for use. Using `opendir()` and `readdir()` or `IO::Dir` are suggested instead.
SEE ALSO
---------
<perlfunc>, ["I/O Operators" in perlop](perlop#I%2FO-Operators), <IO::Handle>, <IO::Seekable>, <IO::Dir>
HISTORY
-------
Derived from FileHandle.pm by Graham Barr <*[email protected]*>.
perl Text::Balanced Text::Balanced
==============
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [General Behaviour in List Contexts](#General-Behaviour-in-List-Contexts)
+ [General Behaviour in Scalar and Void Contexts](#General-Behaviour-in-Scalar-and-Void-Contexts)
+ [A Note About Prefixes](#A-Note-About-Prefixes)
+ [Functions](#Functions)
* [DIAGNOSTICS](#DIAGNOSTICS)
* [EXPORTS](#EXPORTS)
* [KNOWN BUGS](#KNOWN-BUGS)
* [FEEDBACK](#FEEDBACK)
* [AVAILABILITY](#AVAILABILITY)
* [INSTALLATION](#INSTALLATION)
* [AUTHOR](#AUTHOR)
* [COPYRIGHT](#COPYRIGHT)
* [LICENCE](#LICENCE)
* [VERSION](#VERSION)
* [DATE](#DATE)
* [HISTORY](#HISTORY)
NAME
----
Text::Balanced - Extract delimited text sequences from strings.
SYNOPSIS
--------
```
use Text::Balanced qw (
extract_delimited
extract_bracketed
extract_quotelike
extract_codeblock
extract_variable
extract_tagged
extract_multiple
gen_delimited_pat
gen_extract_tagged
);
# Extract the initial substring of $text that is delimited by
# two (unescaped) instances of the first character in $delim.
($extracted, $remainder) = extract_delimited($text,$delim);
# Extract the initial substring of $text that is bracketed
# with a delimiter(s) specified by $delim (where the string
# in $delim contains one or more of '(){}[]<>').
($extracted, $remainder) = extract_bracketed($text,$delim);
# Extract the initial substring of $text that is bounded by
# an XML tag.
($extracted, $remainder) = extract_tagged($text);
# Extract the initial substring of $text that is bounded by
# a C<BEGIN>...C<END> pair. Don't allow nested C<BEGIN> tags
($extracted, $remainder) =
extract_tagged($text,"BEGIN","END",undef,{bad=>["BEGIN"]});
# Extract the initial substring of $text that represents a
# Perl "quote or quote-like operation"
($extracted, $remainder) = extract_quotelike($text);
# Extract the initial substring of $text that represents a block
# of Perl code, bracketed by any of character(s) specified by $delim
# (where the string $delim contains one or more of '(){}[]<>').
($extracted, $remainder) = extract_codeblock($text,$delim);
# Extract the initial substrings of $text that would be extracted by
# one or more sequential applications of the specified functions
# or regular expressions
@extracted = extract_multiple($text,
[ \&extract_bracketed,
\&extract_quotelike,
\&some_other_extractor_sub,
qr/[xyz]*/,
'literal',
]);
# Create a string representing an optimized pattern (a la Friedl)
# that matches a substring delimited by any of the specified characters
# (in this case: any type of quote or a slash)
$patstring = gen_delimited_pat(q{'"`/});
# Generate a reference to an anonymous sub that is just like extract_tagged
# but pre-compiled and optimized for a specific pair of tags, and
# consequently much faster (i.e. 3 times faster). It uses qr// for better
# performance on repeated calls.
$extract_head = gen_extract_tagged('<HEAD>','</HEAD>');
($extracted, $remainder) = $extract_head->($text);
```
DESCRIPTION
-----------
The various `extract_...` subroutines may be used to extract a delimited substring, possibly after skipping a specified prefix string. By default, that prefix is optional whitespace (`/\s*/`), but you can change it to whatever you wish (see below).
The substring to be extracted must appear at the current `pos` location of the string's variable (or at index zero, if no `pos` position is defined). In other words, the `extract_...` subroutines *don't* extract the first occurrence of a substring anywhere in a string (like an unanchored regex would). Rather, they extract an occurrence of the substring appearing immediately at the current matching position in the string (like a `\G`-anchored regex would).
###
General Behaviour in List Contexts
In a list context, all the subroutines return a list, the first three elements of which are always:
[0] The extracted string, including the specified delimiters. If the extraction fails `undef` is returned.
[1] The remainder of the input string (i.e. the characters after the extracted string). On failure, the entire string is returned.
[2] The skipped prefix (i.e. the characters before the extracted string). On failure, `undef` is returned.
Note that in a list context, the contents of the original input text (the first argument) are not modified in any way.
However, if the input text was passed in a variable, that variable's `pos` value is updated to point at the first character after the extracted text. That means that in a list context the various subroutines can be used much like regular expressions. For example:
```
while ( $next = (extract_quotelike($text))[0] )
{
# process next quote-like (in $next)
}
```
###
General Behaviour in Scalar and Void Contexts
In a scalar context, the extracted string is returned, having first been removed from the input text. Thus, the following code also processes each quote-like operation, but actually removes them from $text:
```
while ( $next = extract_quotelike($text) )
{
# process next quote-like (in $next)
}
```
Note that if the input text is a read-only string (i.e. a literal), no attempt is made to remove the extracted text.
In a void context the behaviour of the extraction subroutines is exactly the same as in a scalar context, except (of course) that the extracted substring is not returned.
###
A Note About Prefixes
Prefix patterns are matched without any trailing modifiers (`/gimsox` etc.) This can bite you if you're expecting a prefix specification like '.\*?(?=<H1>)' to skip everything up to the first <H1> tag. Such a prefix pattern will only succeed if the <H1> tag is on the current line, since . normally doesn't match newlines.
To overcome this limitation, you need to turn on /s matching within the prefix pattern, using the `(?s)` directive: '(?s).\*?(?=<H1>)'
### Functions
`extract_delimited` The `extract_delimited` function formalizes the common idiom of extracting a single-character-delimited substring from the start of a string. For example, to extract a single-quote delimited string, the following code is typically used:
```
($remainder = $text) =~ s/\A('(\\.|[^'])*')//s;
$extracted = $1;
```
but with `extract_delimited` it can be simplified to:
```
($extracted,$remainder) = extract_delimited($text, "'");
```
`extract_delimited` takes up to four scalars (the input text, the delimiters, a prefix pattern to be skipped, and any escape characters) and extracts the initial substring of the text that is appropriately delimited. If the delimiter string has multiple characters, the first one encountered in the text is taken to delimit the substring. The third argument specifies a prefix pattern that is to be skipped (but must be present!) before the substring is extracted. The final argument specifies the escape character to be used for each delimiter.
All arguments are optional. If the escape characters are not specified, every delimiter is escaped with a backslash (`\`). If the prefix is not specified, the pattern `'\s*'` - optional whitespace - is used. If the delimiter set is also not specified, the set `/["'`]/` is used. If the text to be processed is not specified either, `$_` is used.
In list context, `extract_delimited` returns a array of three elements, the extracted substring (*including the surrounding delimiters*), the remainder of the text, and the skipped prefix (if any). If a suitable delimited substring is not found, the first element of the array is the empty string, the second is the complete original text, and the prefix returned in the third element is an empty string.
In a scalar context, just the extracted substring is returned. In a void context, the extracted substring (and any prefix) are simply removed from the beginning of the first argument.
Examples:
```
# Remove a single-quoted substring from the very beginning of $text:
$substring = extract_delimited($text, "'", '');
# Remove a single-quoted Pascalish substring (i.e. one in which
# doubling the quote character escapes it) from the very
# beginning of $text:
$substring = extract_delimited($text, "'", '', "'");
# Extract a single- or double- quoted substring from the
# beginning of $text, optionally after some whitespace
# (note the list context to protect $text from modification):
($substring) = extract_delimited $text, q{"'};
# Delete the substring delimited by the first '/' in $text:
$text = join '', (extract_delimited($text,'/','[^/]*')[2,1];
```
Note that this last example is *not* the same as deleting the first quote-like pattern. For instance, if `$text` contained the string:
```
"if ('./cmd' =~ m/$UNIXCMD/s) { $cmd = $1; }"
```
then after the deletion it would contain:
```
"if ('.$UNIXCMD/s) { $cmd = $1; }"
```
not:
```
"if ('./cmd' =~ ms) { $cmd = $1; }"
```
See ["extract\_quotelike"](#extract_quotelike) for a (partial) solution to this problem.
`extract_bracketed` Like `"extract_delimited"`, the `extract_bracketed` function takes up to three optional scalar arguments: a string to extract from, a delimiter specifier, and a prefix pattern. As before, a missing prefix defaults to optional whitespace and a missing text defaults to `$_`. However, a missing delimiter specifier defaults to `'{}()[]<>'` (see below).
`extract_bracketed` extracts a balanced-bracket-delimited substring (using any one (or more) of the user-specified delimiter brackets: '(..)', '{..}', '[..]', or '<..>'). Optionally it will also respect quoted unbalanced brackets (see below).
A "delimiter bracket" is a bracket in list of delimiters passed as `extract_bracketed`'s second argument. Delimiter brackets are specified by giving either the left or right (or both!) versions of the required bracket(s). Note that the order in which two or more delimiter brackets are specified is not significant.
A "balanced-bracket-delimited substring" is a substring bounded by matched brackets, such that any other (left or right) delimiter bracket *within* the substring is also matched by an opposite (right or left) delimiter bracket *at the same level of nesting*. Any type of bracket not in the delimiter list is treated as an ordinary character.
In other words, each type of bracket specified as a delimiter must be balanced and correctly nested within the substring, and any other kind of ("non-delimiter") bracket in the substring is ignored.
For example, given the string:
```
$text = "{ an '[irregularly :-(] {} parenthesized >:-)' string }";
```
then a call to `extract_bracketed` in a list context:
```
@result = extract_bracketed( $text, '{}' );
```
would return:
```
( "{ an '[irregularly :-(] {} parenthesized >:-)' string }" , "" , "" )
```
since both sets of `'{..}'` brackets are properly nested and evenly balanced. (In a scalar context just the first element of the array would be returned. In a void context, `$text` would be replaced by an empty string.)
Likewise the call in:
```
@result = extract_bracketed( $text, '{[' );
```
would return the same result, since all sets of both types of specified delimiter brackets are correctly nested and balanced.
However, the call in:
```
@result = extract_bracketed( $text, '{([<' );
```
would fail, returning:
```
( undef , "{ an '[irregularly :-(] {} parenthesized >:-)' string }" );
```
because the embedded pairs of `'(..)'`s and `'[..]'`s are "cross-nested" and the embedded `'>'` is unbalanced. (In a scalar context, this call would return an empty string. In a void context, `$text` would be unchanged.)
Note that the embedded single-quotes in the string don't help in this case, since they have not been specified as acceptable delimiters and are therefore treated as non-delimiter characters (and ignored).
However, if a particular species of quote character is included in the delimiter specification, then that type of quote will be correctly handled. for example, if `$text` is:
```
$text = '<A HREF=">>>>">link</A>';
```
then
```
@result = extract_bracketed( $text, '<">' );
```
returns:
```
( '<A HREF=">>>>">', 'link</A>', "" )
```
as expected. Without the specification of `"` as an embedded quoter:
```
@result = extract_bracketed( $text, '<>' );
```
the result would be:
```
( '<A HREF=">', '>>>">link</A>', "" )
```
In addition to the quote delimiters `'`, `"`, and ```, full Perl quote-like quoting (i.e. q{string}, qq{string}, etc) can be specified by including the letter 'q' as a delimiter. Hence:
```
@result = extract_bracketed( $text, '<q>' );
```
would correctly match something like this:
```
$text = '<leftop: conj /and/ conj>';
```
See also: `"extract_quotelike"` and `"extract_codeblock"`.
`extract_variable` `extract_variable` extracts any valid Perl variable or variable-involved expression, including scalars, arrays, hashes, array accesses, hash look-ups, method calls through objects, subroutine calls through subroutine references, etc.
The subroutine takes up to two optional arguments:
1. A string to be processed (`$_` if the string is omitted or `undef`)
2. A string specifying a pattern to be matched as a prefix (which is to be skipped). If omitted, optional whitespace is skipped.
On success in a list context, an array of 3 elements is returned. The elements are:
[0] the extracted variable, or variablish expression
[1] the remainder of the input text,
[2] the prefix substring (if any),
On failure, all of these values (except the remaining text) are `undef`.
In a scalar context, `extract_variable` returns just the complete substring that matched a variablish expression. `undef` is returned on failure. In addition, the original input text has the returned substring (and any prefix) removed from it.
In a void context, the input text just has the matched substring (and any specified prefix) removed.
`extract_tagged` `extract_tagged` extracts and segments text between (balanced) specified tags.
The subroutine takes up to five optional arguments:
1. A string to be processed (`$_` if the string is omitted or `undef`)
2. A string specifying a pattern to be matched as the opening tag. If the pattern string is omitted (or `undef`) then a pattern that matches any standard XML tag is used.
3. A string specifying a pattern to be matched at the closing tag. If the pattern string is omitted (or `undef`) then the closing tag is constructed by inserting a `/` after any leading bracket characters in the actual opening tag that was matched (*not* the pattern that matched the tag). For example, if the opening tag pattern is specified as `'{{\w+}}'` and actually matched the opening tag `"{{DATA}}"`, then the constructed closing tag would be `"{{/DATA}}"`.
4. A string specifying a pattern to be matched as a prefix (which is to be skipped). If omitted, optional whitespace is skipped.
5. A hash reference containing various parsing options (see below)
The various options that can be specified are:
`reject => $listref`
The list reference contains one or more strings specifying patterns that must *not* appear within the tagged text.
For example, to extract an HTML link (which should not contain nested links) use:
```
extract_tagged($text, '<A>', '</A>', undef, {reject => ['<A>']} );
```
`ignore => $listref`
The list reference contains one or more strings specifying patterns that are *not* to be treated as nested tags within the tagged text (even if they would match the start tag pattern).
For example, to extract an arbitrary XML tag, but ignore "empty" elements:
```
extract_tagged($text, undef, undef, undef, {ignore => ['<[^>]*/>']} );
```
(also see ["gen\_delimited\_pat"](#gen_delimited_pat) below).
`fail => $str`
The `fail` option indicates the action to be taken if a matching end tag is not encountered (i.e. before the end of the string or some `reject` pattern matches). By default, a failure to match a closing tag causes `extract_tagged` to immediately fail.
However, if the string value associated with <reject> is "MAX", then `extract_tagged` returns the complete text up to the point of failure. If the string is "PARA", `extract_tagged` returns only the first paragraph after the tag (up to the first line that is either empty or contains only whitespace characters). If the string is "", the default behaviour (i.e. failure) is reinstated.
For example, suppose the start tag "/para" introduces a paragraph, which then continues until the next "/endpara" tag or until another "/para" tag is encountered:
```
$text = "/para line 1\n\nline 3\n/para line 4";
extract_tagged($text, '/para', '/endpara', undef,
{reject => '/para', fail => MAX );
# EXTRACTED: "/para line 1\n\nline 3\n"
```
Suppose instead, that if no matching "/endpara" tag is found, the "/para" tag refers only to the immediately following paragraph:
```
$text = "/para line 1\n\nline 3\n/para line 4";
extract_tagged($text, '/para', '/endpara', undef,
{reject => '/para', fail => MAX );
# EXTRACTED: "/para line 1\n"
```
Note that the specified `fail` behaviour applies to nested tags as well.
On success in a list context, an array of 6 elements is returned. The elements are:
[0] the extracted tagged substring (including the outermost tags),
[1] the remainder of the input text,
[2] the prefix substring (if any),
[3] the opening tag
[4] the text between the opening and closing tags
[5] the closing tag (or "" if no closing tag was found)
On failure, all of these values (except the remaining text) are `undef`.
In a scalar context, `extract_tagged` returns just the complete substring that matched a tagged text (including the start and end tags). `undef` is returned on failure. In addition, the original input text has the returned substring (and any prefix) removed from it.
In a void context, the input text just has the matched substring (and any specified prefix) removed.
`gen_extract_tagged` `gen_extract_tagged` generates a new anonymous subroutine which extracts text between (balanced) specified tags. In other words, it generates a function identical in function to `extract_tagged`.
The difference between `extract_tagged` and the anonymous subroutines generated by `gen_extract_tagged`, is that those generated subroutines:
* do not have to reparse tag specification or parsing options every time they are called (whereas `extract_tagged` has to effectively rebuild its tag parser on every call);
* make use of the new qr// construct to pre-compile the regexes they use (whereas `extract_tagged` uses standard string variable interpolation to create tag-matching patterns).
The subroutine takes up to four optional arguments (the same set as `extract_tagged` except for the string to be processed). It returns a reference to a subroutine which in turn takes a single argument (the text to be extracted from).
In other words, the implementation of `extract_tagged` is exactly equivalent to:
```
sub extract_tagged
{
my $text = shift;
$extractor = gen_extract_tagged(@_);
return $extractor->($text);
}
```
(although `extract_tagged` is not currently implemented that way).
Using `gen_extract_tagged` to create extraction functions for specific tags is a good idea if those functions are going to be called more than once, since their performance is typically twice as good as the more general-purpose `extract_tagged`.
`extract_quotelike` `extract_quotelike` attempts to recognize, extract, and segment any one of the various Perl quotes and quotelike operators (see [perlop(3)](http://man.he.net/man3/perlop)) Nested backslashed delimiters, embedded balanced bracket delimiters (for the quotelike operators), and trailing modifiers are all caught. For example, in:
```
extract_quotelike 'q # an octothorpe: \# (not the end of the q!) #'
extract_quotelike ' "You said, \"Use sed\"." '
extract_quotelike ' s{([A-Z]{1,8}\.[A-Z]{3})} /\L$1\E/; '
extract_quotelike ' tr/\\\/\\\\/\\\//ds; '
```
the full Perl quotelike operations are all extracted correctly.
Note too that, when using the /x modifier on a regex, any comment containing the current pattern delimiter will cause the regex to be immediately terminated. In other words:
```
'm /
(?i) # CASE INSENSITIVE
[a-z_] # LEADING ALPHABETIC/UNDERSCORE
[a-z0-9]* # FOLLOWED BY ANY NUMBER OF ALPHANUMERICS
/x'
```
will be extracted as if it were:
```
'm /
(?i) # CASE INSENSITIVE
[a-z_] # LEADING ALPHABETIC/'
```
This behaviour is identical to that of the actual compiler.
`extract_quotelike` takes two arguments: the text to be processed and a prefix to be matched at the very beginning of the text. If no prefix is specified, optional whitespace is the default. If no text is given, `$_` is used.
In a list context, an array of 11 elements is returned. The elements are:
[0] the extracted quotelike substring (including trailing modifiers),
[1] the remainder of the input text,
[2] the prefix substring (if any),
[3] the name of the quotelike operator (if any),
[4] the left delimiter of the first block of the operation,
[5] the text of the first block of the operation (that is, the contents of a quote, the regex of a match or substitution or the target list of a translation),
[6] the right delimiter of the first block of the operation,
[7] the left delimiter of the second block of the operation (that is, if it is a `s`, `tr`, or `y`),
[8] the text of the second block of the operation (that is, the replacement of a substitution or the translation list of a translation),
[9] the right delimiter of the second block of the operation (if any),
[10] the trailing modifiers on the operation (if any).
For each of the fields marked "(if any)" the default value on success is an empty string. On failure, all of these values (except the remaining text) are `undef`.
In a scalar context, `extract_quotelike` returns just the complete substring that matched a quotelike operation (or `undef` on failure). In a scalar or void context, the input text has the same substring (and any specified prefix) removed.
Examples:
```
# Remove the first quotelike literal that appears in text
$quotelike = extract_quotelike($text,'.*?');
# Replace one or more leading whitespace-separated quotelike
# literals in $_ with "<QLL>"
do { $_ = join '<QLL>', (extract_quotelike)[2,1] } until $@;
# Isolate the search pattern in a quotelike operation from $text
($op,$pat) = (extract_quotelike $text)[3,5];
if ($op =~ /[ms]/)
{
print "search pattern: $pat\n";
}
else
{
print "$op is not a pattern matching operation\n";
}
```
`extract_quotelike` `extract_quotelike` can successfully extract "here documents" from an input string, but with an important caveat in list contexts.
Unlike other types of quote-like literals, a here document is rarely a contiguous substring. For example, a typical piece of code using here document might look like this:
```
<<'EOMSG' || die;
This is the message.
EOMSG
exit;
```
Given this as an input string in a scalar context, `extract_quotelike` would correctly return the string "<<'EOMSG'\nThis is the message.\nEOMSG", leaving the string " || die;\nexit;" in the original variable. In other words, the two separate pieces of the here document are successfully extracted and concatenated.
In a list context, `extract_quotelike` would return the list
[0] "<<'EOMSG'\nThis is the message.\nEOMSG\n" (i.e. the full extracted here document, including fore and aft delimiters),
[1] " || die;\nexit;" (i.e. the remainder of the input text, concatenated),
[2] "" (i.e. the prefix substring -- trivial in this case),
[3] "<<" (i.e. the "name" of the quotelike operator)
[4] "'EOMSG'" (i.e. the left delimiter of the here document, including any quotes),
[5] "This is the message.\n" (i.e. the text of the here document),
[6] "EOMSG" (i.e. the right delimiter of the here document),
[7..10] "" (a here document has no second left delimiter, second text, second right delimiter, or trailing modifiers).
However, the matching position of the input variable would be set to "exit;" (i.e. *after* the closing delimiter of the here document), which would cause the earlier " || die;\nexit;" to be skipped in any sequence of code fragment extractions.
To avoid this problem, when it encounters a here document whilst extracting from a modifiable string, `extract_quotelike` silently rearranges the string to an equivalent piece of Perl:
```
<<'EOMSG'
This is the message.
EOMSG
|| die;
exit;
```
in which the here document *is* contiguous. It still leaves the matching position after the here document, but now the rest of the line on which the here document starts is not skipped.
To prevent <extract\_quotelike> from mucking about with the input in this way (this is the only case where a list-context `extract_quotelike` does so), you can pass the input variable as an interpolated literal:
```
$quotelike = extract_quotelike("$var");
```
`extract_codeblock` `extract_codeblock` attempts to recognize and extract a balanced bracket delimited substring that may contain unbalanced brackets inside Perl quotes or quotelike operations. That is, `extract_codeblock` is like a combination of `"extract_bracketed"` and `"extract_quotelike"`.
`extract_codeblock` takes the same initial three parameters as `extract_bracketed`: a text to process, a set of delimiter brackets to look for, and a prefix to match first. It also takes an optional fourth parameter, which allows the outermost delimiter brackets to be specified separately (see below).
Omitting the first argument (input text) means process `$_` instead. Omitting the second argument (delimiter brackets) indicates that only `'{'` is to be used. Omitting the third argument (prefix argument) implies optional whitespace at the start. Omitting the fourth argument (outermost delimiter brackets) indicates that the value of the second argument is to be used for the outermost delimiters.
Once the prefix and the outermost opening delimiter bracket have been recognized, code blocks are extracted by stepping through the input text and trying the following alternatives in sequence:
1. Try and match a closing delimiter bracket. If the bracket was the same species as the last opening bracket, return the substring to that point. If the bracket was mismatched, return an error.
2. Try to match a quote or quotelike operator. If found, call `extract_quotelike` to eat it. If `extract_quotelike` fails, return the error it returned. Otherwise go back to step 1.
3. Try to match an opening delimiter bracket. If found, call `extract_codeblock` recursively to eat the embedded block. If the recursive call fails, return an error. Otherwise, go back to step 1.
4. Unconditionally match a bareword or any other single character, and then go back to step 1.
Examples:
```
# Find a while loop in the text
if ($text =~ s/.*?while\s*\{/{/)
{
$loop = "while " . extract_codeblock($text);
}
# Remove the first round-bracketed list (which may include
# round- or curly-bracketed code blocks or quotelike operators)
extract_codeblock $text, "(){}", '[^(]*';
```
The ability to specify a different outermost delimiter bracket is useful in some circumstances. For example, in the Parse::RecDescent module, parser actions which are to be performed only on a successful parse are specified using a `<defer:...>` directive. For example:
```
sentence: subject verb object
<defer: {$::theVerb = $item{verb}} >
```
Parse::RecDescent uses `extract_codeblock($text, '{}<>')` to extract the code within the `<defer:...>` directive, but there's a problem.
A deferred action like this:
```
<defer: {if ($count>10) {$count--}} >
```
will be incorrectly parsed as:
```
<defer: {if ($count>
```
because the "less than" operator is interpreted as a closing delimiter.
But, by extracting the directive using `extract_codeblock($text, '{}', undef, '<>')` the '>' character is only treated as a delimited at the outermost level of the code block, so the directive is parsed correctly.
`extract_multiple` The `extract_multiple` subroutine takes a string to be processed and a list of extractors (subroutines or regular expressions) to apply to that string.
In an array context `extract_multiple` returns an array of substrings of the original string, as extracted by the specified extractors. In a scalar context, `extract_multiple` returns the first substring successfully extracted from the original string. In both scalar and void contexts the original string has the first successfully extracted substring removed from it. In all contexts `extract_multiple` starts at the current `pos` of the string, and sets that `pos` appropriately after it matches.
Hence, the aim of a call to `extract_multiple` in a list context is to split the processed string into as many non-overlapping fields as possible, by repeatedly applying each of the specified extractors to the remainder of the string. Thus `extract_multiple` is a generalized form of Perl's `split` subroutine.
The subroutine takes up to four optional arguments:
1. A string to be processed (`$_` if the string is omitted or `undef`)
2. A reference to a list of subroutine references and/or qr// objects and/or literal strings and/or hash references, specifying the extractors to be used to split the string. If this argument is omitted (or `undef`) the list:
```
[
sub { extract_variable($_[0], '') },
sub { extract_quotelike($_[0],'') },
sub { extract_codeblock($_[0],'{}','') },
]
```
is used.
3. An number specifying the maximum number of fields to return. If this argument is omitted (or `undef`), split continues as long as possible.
If the third argument is *N*, then extraction continues until *N* fields have been successfully extracted, or until the string has been completely processed.
Note that in scalar and void contexts the value of this argument is automatically reset to 1 (under `-w`, a warning is issued if the argument has to be reset).
4. A value indicating whether unmatched substrings (see below) within the text should be skipped or returned as fields. If the value is true, such substrings are skipped. Otherwise, they are returned.
The extraction process works by applying each extractor in sequence to the text string.
If the extractor is a subroutine it is called in a list context and is expected to return a list of a single element, namely the extracted text. It may optionally also return two further arguments: a string representing the text left after extraction (like $' for a pattern match), and a string representing any prefix skipped before the extraction (like $` in a pattern match). Note that this is designed to facilitate the use of other Text::Balanced subroutines with `extract_multiple`. Note too that the value returned by an extractor subroutine need not bear any relationship to the corresponding substring of the original text (see examples below).
If the extractor is a precompiled regular expression or a string, it is matched against the text in a scalar context with a leading '\G' and the gc modifiers enabled. The extracted value is either $1 if that variable is defined after the match, or else the complete match (i.e. $&).
If the extractor is a hash reference, it must contain exactly one element. The value of that element is one of the above extractor types (subroutine reference, regular expression, or string). The key of that element is the name of a class into which the successful return value of the extractor will be blessed.
If an extractor returns a defined value, that value is immediately treated as the next extracted field and pushed onto the list of fields. If the extractor was specified in a hash reference, the field is also blessed into the appropriate class,
If the extractor fails to match (in the case of a regex extractor), or returns an empty list or an undefined value (in the case of a subroutine extractor), it is assumed to have failed to extract. If none of the extractor subroutines succeeds, then one character is extracted from the start of the text and the extraction subroutines reapplied. Characters which are thus removed are accumulated and eventually become the next field (unless the fourth argument is true, in which case they are discarded).
For example, the following extracts substrings that are valid Perl variables:
```
@fields = extract_multiple($text,
[ sub { extract_variable($_[0]) } ],
undef, 1);
```
This example separates a text into fields which are quote delimited, curly bracketed, and anything else. The delimited and bracketed parts are also blessed to identify them (the "anything else" is unblessed):
```
@fields = extract_multiple($text,
[
{ Delim => sub { extract_delimited($_[0],q{'"}) } },
{ Brack => sub { extract_bracketed($_[0],'{}') } },
]);
```
This call extracts the next single substring that is a valid Perl quotelike operator (and removes it from $text):
```
$quotelike = extract_multiple($text,
[
sub { extract_quotelike($_[0]) },
], undef, 1);
```
Finally, here is yet another way to do comma-separated value parsing:
```
@fields = extract_multiple($csv_text,
[
sub { extract_delimited($_[0],q{'"}) },
qr/([^,]+)(.*)/,
],
undef,1);
```
The list in the second argument means: *"Try and extract a ' or " delimited string, otherwise extract anything up to a comma..."*. The undef third argument means: *"...as many times as possible..."*, and the true value in the fourth argument means *"...discarding anything else that appears (i.e. the commas)"*.
If you wanted the commas preserved as separate fields (i.e. like split does if your split pattern has capturing parentheses), you would just make the last parameter undefined (or remove it).
`gen_delimited_pat` The `gen_delimited_pat` subroutine takes a single (string) argument and > builds a Friedl-style optimized regex that matches a string delimited by any one of the characters in the single argument. For example:
```
gen_delimited_pat(q{'"})
```
returns the regex:
```
(?:\"(?:\\\"|(?!\").)*\"|\'(?:\\\'|(?!\').)*\')
```
Note that the specified delimiters are automatically quotemeta'd.
A typical use of `gen_delimited_pat` would be to build special purpose tags for `extract_tagged`. For example, to properly ignore "empty" XML elements (which might contain quoted strings):
```
my $empty_tag = '<(' . gen_delimited_pat(q{'"}) . '|.)+/>';
extract_tagged($text, undef, undef, undef, {ignore => [$empty_tag]} );
```
`gen_delimited_pat` may also be called with an optional second argument, which specifies the "escape" character(s) to be used for each delimiter. For example to match a Pascal-style string (where ' is the delimiter and '' is a literal ' within the string):
```
gen_delimited_pat(q{'},q{'});
```
Different escape characters can be specified for different delimiters. For example, to specify that '/' is the escape for single quotes and '%' is the escape for double quotes:
```
gen_delimited_pat(q{'"},q{/%});
```
If more delimiters than escape chars are specified, the last escape char is used for the remaining delimiters. If no escape char is specified for a given specified delimiter, '\' is used.
`delimited_pat` Note that `gen_delimited_pat` was previously called `delimited_pat`. That name may still be used, but is now deprecated.
DIAGNOSTICS
-----------
In a list context, all the functions return `(undef,$original_text)` on failure. In a scalar context, failure is indicated by returning `undef` (in this case the input text is not modified in any way).
In addition, on failure in *any* context, the `$@` variable is set. Accessing `$@->{error}` returns one of the error diagnostics listed below. Accessing `$@->{pos}` returns the offset into the original string at which the error was detected (although not necessarily where it occurred!) Printing `$@` directly produces the error message, with the offset appended. On success, the `$@` variable is guaranteed to be `undef`.
The available diagnostics are:
`Did not find a suitable bracket: "%s"`
The delimiter provided to `extract_bracketed` was not one of `'()[]<>{}'`.
`Did not find prefix: /%s/`
A non-optional prefix was specified but wasn't found at the start of the text.
`Did not find opening bracket after prefix: "%s"`
`extract_bracketed` or `extract_codeblock` was expecting a particular kind of bracket at the start of the text, and didn't find it.
`No quotelike operator found after prefix: "%s"`
`extract_quotelike` didn't find one of the quotelike operators `q`, `qq`, `qw`, `qx`, `s`, `tr` or `y` at the start of the substring it was extracting.
`Unmatched closing bracket: "%c"`
`extract_bracketed`, `extract_quotelike` or `extract_codeblock` encountered a closing bracket where none was expected.
`Unmatched opening bracket(s): "%s"`
`extract_bracketed`, `extract_quotelike` or `extract_codeblock` ran out of characters in the text before closing one or more levels of nested brackets.
`Unmatched embedded quote (%s)`
`extract_bracketed` attempted to match an embedded quoted substring, but failed to find a closing quote to match it.
`Did not find closing delimiter to match '%s'`
`extract_quotelike` was unable to find a closing delimiter to match the one that opened the quote-like operation.
`Mismatched closing bracket: expected "%c" but found "%s"`
`extract_bracketed`, `extract_quotelike` or `extract_codeblock` found a valid bracket delimiter, but it was the wrong species. This usually indicates a nesting error, but may indicate incorrect quoting or escaping.
`No block delimiter found after quotelike "%s"`
`extract_quotelike` or `extract_codeblock` found one of the quotelike operators `q`, `qq`, `qw`, `qx`, `s`, `tr` or `y` without a suitable block after it.
`Did not find leading dereferencer`
`extract_variable` was expecting one of '$', '@', or '%' at the start of a variable, but didn't find any of them.
`Bad identifier after dereferencer`
`extract_variable` found a '$', '@', or '%' indicating a variable, but that character was not followed by a legal Perl identifier.
`Did not find expected opening bracket at %s`
`extract_codeblock` failed to find any of the outermost opening brackets that were specified.
`Improperly nested codeblock at %s`
A nested code block was found that started with a delimiter that was specified as being only to be used as an outermost bracket.
`Missing second block for quotelike "%s"`
`extract_codeblock` or `extract_quotelike` found one of the quotelike operators `s`, `tr` or `y` followed by only one block.
`No match found for opening bracket`
`extract_codeblock` failed to find a closing bracket to match the outermost opening bracket.
`Did not find opening tag: /%s/`
`extract_tagged` did not find a suitable opening tag (after any specified prefix was removed).
`Unable to construct closing tag to match: /%s/`
`extract_tagged` matched the specified opening tag and tried to modify the matched text to produce a matching closing tag (because none was specified). It failed to generate the closing tag, almost certainly because the opening tag did not start with a bracket of some kind.
`Found invalid nested tag: %s`
`extract_tagged` found a nested tag that appeared in the "reject" list (and the failure mode was not "MAX" or "PARA").
`Found unbalanced nested tag: %s`
`extract_tagged` found a nested opening tag that was not matched by a corresponding nested closing tag (and the failure mode was not "MAX" or "PARA").
`Did not find closing tag`
`extract_tagged` reached the end of the text without finding a closing tag to match the original opening tag (and the failure mode was not "MAX" or "PARA").
EXPORTS
-------
The following symbols are, or can be, exported by this module:
Default Exports *None*.
Optional Exports `extract_delimited`, `extract_bracketed`, `extract_quotelike`, `extract_codeblock`, `extract_variable`, `extract_tagged`, `extract_multiple`, `gen_delimited_pat`, `gen_extract_tagged`, `delimited_pat`.
Export Tags
`:ALL`
`extract_delimited`, `extract_bracketed`, `extract_quotelike`, `extract_codeblock`, `extract_variable`, `extract_tagged`, `extract_multiple`, `gen_delimited_pat`, `gen_extract_tagged`, `delimited_pat`.
KNOWN BUGS
-----------
See <https://rt.cpan.org/Dist/Display.html?Status=Active&Queue=Text-Balanced>.
FEEDBACK
--------
Patches, bug reports, suggestions or any other feedback is welcome.
Patches can be sent as GitHub pull requests at <https://github.com/steve-m-hay/Text-Balanced/pulls>.
Bug reports and suggestions can be made on the CPAN Request Tracker at <https://rt.cpan.org/Public/Bug/Report.html?Queue=Text-Balanced>.
Currently active requests on the CPAN Request Tracker can be viewed at <https://rt.cpan.org/Public/Dist/Display.html?Status=Active;Queue=Text-Balanced>.
Please test this distribution. See CPAN Testers Reports at <https://www.cpantesters.org/> for details of how to get involved.
Previous test results on CPAN Testers Reports can be viewed at <https://www.cpantesters.org/distro/T/Text-Balanced.html>.
Please rate this distribution on CPAN Ratings at <https://cpanratings.perl.org/rate/?distribution=Text-Balanced>.
AVAILABILITY
------------
The latest version of this module is available from CPAN (see ["CPAN" in perlmodlib](perlmodlib#CPAN) for details) at
<https://metacpan.org/release/Text-Balanced> or
<https://www.cpan.org/authors/id/S/SH/SHAY/> or
<https://www.cpan.org/modules/by-module/Text/>.
The latest source code is available from GitHub at <https://github.com/steve-m-hay/Text-Balanced>.
INSTALLATION
------------
See the *INSTALL* file.
AUTHOR
------
Damian Conway <[[email protected]](mailto:[email protected])>.
Steve Hay <[[email protected]](mailto:[email protected])> is now maintaining Text::Balanced as of version 2.03.
COPYRIGHT
---------
Copyright (C) 1997-2001 Damian Conway. All rights reserved.
Copyright (C) 2009 Adam Kennedy.
Copyright (C) 2015, 2020 Steve Hay. All rights reserved.
LICENCE
-------
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself, i.e. under the terms of either the GNU General Public License or the Artistic License, as specified in the *LICENCE* file.
VERSION
-------
Version 2.04
DATE
----
11 Dec 2020
HISTORY
-------
See the *Changes* file.
| programming_docs |
perl TAP::Parser::Result::Test TAP::Parser::Result::Test
=========================
CONTENTS
--------
* [NAME](#NAME)
* [VERSION](#VERSION)
* [DESCRIPTION](#DESCRIPTION)
* [OVERRIDDEN METHODS](#OVERRIDDEN-METHODS)
+ [Instance Methods](#Instance-Methods)
- [ok](#ok)
- [number](#number)
- [description](#description)
- [directive](#directive)
- [explanation](#explanation)
- [is\_ok](#is_ok)
- [is\_actual\_ok](#is_actual_ok)
- [actual\_passed](#actual_passed)
- [todo\_passed](#todo_passed)
- [todo\_failed](#todo_failed)
- [has\_skip](#has_skip)
- [has\_todo](#has_todo)
- [as\_string](#as_string)
- [is\_unplanned](#is_unplanned)
NAME
----
TAP::Parser::Result::Test - Test result token.
VERSION
-------
Version 3.44
DESCRIPTION
-----------
This is a subclass of <TAP::Parser::Result>. A token of this class will be returned if a test line is encountered.
```
1..1
ok 1 - woo hooo!
```
OVERRIDDEN METHODS
-------------------
This class is the workhorse of the <TAP::Parser> system. Most TAP lines will be test lines and if `$result->is_test`, then you have a bunch of methods at your disposal.
###
Instance Methods
#### `ok`
```
my $ok = $result->ok;
```
Returns the literal text of the `ok` or `not ok` status.
#### `number`
```
my $test_number = $result->number;
```
Returns the number of the test, even if the original TAP output did not supply that number.
#### `description`
```
my $description = $result->description;
```
Returns the description of the test, if any. This is the portion after the test number but before the directive.
#### `directive`
```
my $directive = $result->directive;
```
Returns either `TODO` or `SKIP` if either directive was present for a test line.
#### `explanation`
```
my $explanation = $result->explanation;
```
If a test had either a `TODO` or `SKIP` directive, this method will return the accompanying explanation, if present.
```
not ok 17 - 'Pigs can fly' # TODO not enough acid
```
For the above line, the explanation is *not enough acid*.
#### `is_ok`
```
if ( $result->is_ok ) { ... }
```
Returns a boolean value indicating whether or not the test passed. Remember that for TODO tests, the test always passes.
If the test is unplanned, this method will always return false. See `is_unplanned`.
#### `is_actual_ok`
```
if ( $result->is_actual_ok ) { ... }
```
Returns a boolean value indicating whether or not the test passed, regardless of its TODO status.
#### `actual_passed`
Deprecated. Please use `is_actual_ok` instead.
#### `todo_passed`
```
if ( $test->todo_passed ) {
# test unexpectedly succeeded
}
```
If this is a TODO test and an 'ok' line, this method returns true. Otherwise, it will always return false (regardless of passing status on non-todo tests).
This is used to track which tests unexpectedly succeeded.
#### `todo_failed`
```
# deprecated in favor of 'todo_passed'. This method was horribly misnamed.
```
This was a badly misnamed method. It indicates which TODO tests unexpectedly succeeded. Will now issue a warning and call `todo_passed`.
#### `has_skip`
```
if ( $result->has_skip ) { ... }
```
Returns a boolean value indicating whether or not this test has a SKIP directive.
#### `has_todo`
```
if ( $result->has_todo ) { ... }
```
Returns a boolean value indicating whether or not this test has a TODO directive.
#### `as_string`
```
print $result->as_string;
```
This method prints the test as a string. It will probably be similar, but not necessarily identical, to the original test line. Directives are capitalized, some whitespace may be trimmed and a test number will be added if it was not present in the original line. If you need the original text of the test line, use the `raw` method.
#### `is_unplanned`
```
if ( $test->is_unplanned ) { ... }
$test->is_unplanned(1);
```
If a test number is greater than the number of planned tests, this method will return true. Unplanned tests will *always* return false for `is_ok`, regardless of whether or not the test `has_todo`.
Note that if tests have a trailing plan, it is not possible to set this property for unplanned tests as we do not know it's unplanned until the plan is reached:
```
print <<'END';
ok 1
ok 2
1..1
END
```
perl perlre perlre
======
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
+ [The Basics](#The-Basics)
- [Metacharacters](#Metacharacters)
+ [Modifiers](#Modifiers)
- [Overview](#Overview)
- [Details on some modifiers](#Details-on-some-modifiers)
* [/x and /xx](#/x-and-/xx)
* [Character set modifiers](#Character-set-modifiers)
* [/l](#/l)
* [/u](#/u)
* [/d](#/d)
* [/a (and /aa)](#/a-(and-/aa))
* [Which character set modifier is in effect?](#Which-character-set-modifier-is-in-effect?)
* [Character set modifier behavior prior to Perl 5.14](#Character-set-modifier-behavior-prior-to-Perl-5.14)
+ [Regular Expressions](#Regular-Expressions)
- [Quantifiers](#Quantifiers)
- [Escape sequences](#Escape-sequences)
- [Character Classes and other Special Escapes](#Character-Classes-and-other-Special-Escapes)
- [Assertions](#Assertions)
- [Capture groups](#Capture-groups)
+ [Quoting metacharacters](#Quoting-metacharacters)
+ [Extended Patterns](#Extended-Patterns)
+ [Backtracking](#Backtracking)
+ [Script Runs](#Script-Runs)
+ [Special Backtracking Control Verbs](#Special-Backtracking-Control-Verbs)
+ [Warning on \1 Instead of $1](#Warning-on-%5C1-Instead-of-%241)
+ [Repeated Patterns Matching a Zero-length Substring](#Repeated-Patterns-Matching-a-Zero-length-Substring)
+ [Combining RE Pieces](#Combining-RE-Pieces)
+ [Creating Custom RE Engines](#Creating-Custom-RE-Engines)
+ [Embedded Code Execution Frequency](#Embedded-Code-Execution-Frequency)
+ [PCRE/Python Support](#PCRE/Python-Support)
* [BUGS](#BUGS)
* [SEE ALSO](#SEE-ALSO)
NAME
----
perlre - Perl regular expressions
DESCRIPTION
-----------
This page describes the syntax of regular expressions in Perl.
If you haven't used regular expressions before, a tutorial introduction is available in <perlretut>. If you know just a little about them, a quick-start introduction is available in <perlrequick>.
Except for ["The Basics"](#The-Basics) section, this page assumes you are familiar with regular expression basics, like what is a "pattern", what does it look like, and how it is basically used. For a reference on how they are used, plus various examples of the same, see discussions of `m//`, `s///`, `qr//` and `"??"` in ["Regexp Quote-Like Operators" in perlop](perlop#Regexp-Quote-Like-Operators).
New in v5.22, [`use re 'strict'`](re#%27strict%27-mode) applies stricter rules than otherwise when compiling regular expression patterns. It can find things that, while legal, may not be what you intended.
###
The Basics
Regular expressions are strings with the very particular syntax and meaning described in this document and auxiliary documents referred to by this one. The strings are called "patterns". Patterns are used to determine if some other string, called the "target", has (or doesn't have) the characteristics specified by the pattern. We call this "matching" the target string against the pattern. Usually the match is done by having the target be the first operand, and the pattern be the second operand, of one of the two binary operators `=~` and `!~`, listed in ["Binding Operators" in perlop](perlop#Binding-Operators); and the pattern will have been converted from an ordinary string by one of the operators in ["Regexp Quote-Like Operators" in perlop](perlop#Regexp-Quote-Like-Operators), like so:
```
$foo =~ m/abc/
```
This evaluates to true if and only if the string in the variable `$foo` contains somewhere in it, the sequence of characters "a", "b", then "c". (The `=~ m`, or match operator, is described in ["m/PATTERN/msixpodualngc" in perlop](perlop#m%2FPATTERN%2Fmsixpodualngc).)
Patterns that aren't already stored in some variable must be delimited, at both ends, by delimiter characters. These are often, as in the example above, forward slashes, and the typical way a pattern is written in documentation is with those slashes. In most cases, the delimiter is the same character, fore and aft, but there are a few cases where a character looks like it has a mirror-image mate, where the opening version is the beginning delimiter, and the closing one is the ending delimiter, like
```
$foo =~ m<abc>
```
Most times, the pattern is evaluated in double-quotish context, but it is possible to choose delimiters to force single-quotish, like
```
$foo =~ m'abc'
```
If the pattern contains its delimiter within it, that delimiter must be escaped. Prefixing it with a backslash (*e.g.*, `"/foo\/bar/"`) serves this purpose.
Any single character in a pattern matches that same character in the target string, unless the character is a *metacharacter* with a special meaning described in this document. A sequence of non-metacharacters matches the same sequence in the target string, as we saw above with `m/abc/`.
Only a few characters (all of them being ASCII punctuation characters) are metacharacters. The most commonly used one is a dot `"."`, which normally matches almost any character (including a dot itself).
You can cause characters that normally function as metacharacters to be interpreted literally by prefixing them with a `"\"`, just like the pattern's delimiter must be escaped if it also occurs within the pattern. Thus, `"\."` matches just a literal dot, `"."` instead of its normal meaning. This means that the backslash is also a metacharacter, so `"\\"` matches a single `"\"`. And a sequence that contains an escaped metacharacter matches the same sequence (but without the escape) in the target string. So, the pattern `/blur\\fl/` would match any target string that contains the sequence `"blur\fl"`.
The metacharacter `"|"` is used to match one thing or another. Thus
```
$foo =~ m/this|that/
```
is TRUE if and only if `$foo` contains either the sequence `"this"` or the sequence `"that"`. Like all metacharacters, prefixing the `"|"` with a backslash makes it match the plain punctuation character; in its case, the VERTICAL LINE.
```
$foo =~ m/this\|that/
```
is TRUE if and only if `$foo` contains the sequence `"this|that"`.
You aren't limited to just a single `"|"`.
```
$foo =~ m/fee|fie|foe|fum/
```
is TRUE if and only if `$foo` contains any of those 4 sequences from the children's story "Jack and the Beanstalk".
As you can see, the `"|"` binds less tightly than a sequence of ordinary characters. We can override this by using the grouping metacharacters, the parentheses `"("` and `")"`.
```
$foo =~ m/th(is|at) thing/
```
is TRUE if and only if `$foo` contains either the sequence `"this thing"` or the sequence `"that thing"`. The portions of the string that match the portions of the pattern enclosed in parentheses are normally made available separately for use later in the pattern, substitution, or program. This is called "capturing", and it can get complicated. See ["Capture groups"](#Capture-groups).
The first alternative includes everything from the last pattern delimiter (`"("`, `"(?:"` (described later), *etc*. or the beginning of the pattern) up to the first `"|"`, and the last alternative contains everything from the last `"|"` to the next closing pattern delimiter. That's why it's common practice to include alternatives in parentheses: to minimize confusion about where they start and end.
Alternatives are tried from left to right, so the first alternative found for which the entire expression matches, is the one that is chosen. This means that alternatives are not necessarily greedy. For example: when matching `foo|foot` against `"barefoot"`, only the `"foo"` part will match, as that is the first alternative tried, and it successfully matches the target string. (This might not seem important, but it is important when you are capturing matched text using parentheses.)
Besides taking away the special meaning of a metacharacter, a prefixed backslash changes some letter and digit characters away from matching just themselves to instead have special meaning. These are called "escape sequences", and all such are described in <perlrebackslash>. A backslash sequence (of a letter or digit) that doesn't currently have special meaning to Perl will raise a warning if warnings are enabled, as those are reserved for potential future use.
One such sequence is `\b`, which matches a boundary of some sort. `\b{wb}` and a few others give specialized types of boundaries. (They are all described in detail starting at ["\b{}, \b, \B{}, \B" in perlrebackslash](perlrebackslash#%5Cb%7B%7D%2C-%5Cb%2C-%5CB%7B%7D%2C-%5CB).) Note that these don't match characters, but the zero-width spaces between characters. They are an example of a [zero-width assertion](#Assertions). Consider again,
```
$foo =~ m/fee|fie|foe|fum/
```
It evaluates to TRUE if, besides those 4 words, any of the sequences "feed", "field", "Defoe", "fume", and many others are in `$foo`. By judicious use of `\b` (or better (because it is designed to handle natural language) `\b{wb}`), we can make sure that only the Giant's words are matched:
```
$foo =~ m/\b(fee|fie|foe|fum)\b/
$foo =~ m/\b{wb}(fee|fie|foe|fum)\b{wb}/
```
The final example shows that the characters `"{"` and `"}"` are metacharacters.
Another use for escape sequences is to specify characters that cannot (or which you prefer not to) be written literally. These are described in detail in ["Character Escapes" in perlrebackslash](perlrebackslash#Character-Escapes), but the next three paragraphs briefly describe some of them.
Various control characters can be written in C language style: `"\n"` matches a newline, `"\t"` a tab, `"\r"` a carriage return, `"\f"` a form feed, *etc*.
More generally, `\*nnn*`, where *nnn* is a string of three octal digits, matches the character whose native code point is *nnn*. You can easily run into trouble if you don't have exactly three digits. So always use three, or since Perl 5.14, you can use `\o{...}` to specify any number of octal digits.
Similarly, `\x*nn*`, where *nn* are hexadecimal digits, matches the character whose native ordinal is *nn*. Again, not using exactly two digits is a recipe for disaster, but you can use `\x{...}` to specify any number of hex digits.
Besides being a metacharacter, the `"."` is an example of a "character class", something that can match any single character of a given set of them. In its case, the set is just about all possible characters. Perl predefines several character classes besides the `"."`; there is a separate reference page about just these, <perlrecharclass>.
You can define your own custom character classes, by putting into your pattern in the appropriate place(s), a list of all the characters you want in the set. You do this by enclosing the list within `[]` bracket characters. These are called "bracketed character classes" when we are being precise, but often the word "bracketed" is dropped. (Dropping it usually doesn't cause confusion.) This means that the `"["` character is another metacharacter. It doesn't match anything just by itself; it is used only to tell Perl that what follows it is a bracketed character class. If you want to match a literal left square bracket, you must escape it, like `"\["`. The matching `"]"` is also a metacharacter; again it doesn't match anything by itself, but just marks the end of your custom class to Perl. It is an example of a "sometimes metacharacter". It isn't a metacharacter if there is no corresponding `"["`, and matches its literal self:
```
print "]" =~ /]/; # prints 1
```
The list of characters within the character class gives the set of characters matched by the class. `"[abc]"` matches a single "a" or "b" or "c". But if the first character after the `"["` is `"^"`, the class instead matches any character not in the list. Within a list, the `"-"` character specifies a range of characters, so that `a-z` represents all characters between "a" and "z", inclusive. If you want either `"-"` or `"]"` itself to be a member of a class, put it at the start of the list (possibly after a `"^"`), or escape it with a backslash. `"-"` is also taken literally when it is at the end of the list, just before the closing `"]"`. (The following all specify the same class of three characters: `[-az]`, `[az-]`, and `[a\-z]`. All are different from `[a-z]`, which specifies a class containing twenty-six characters, even on EBCDIC-based character sets.)
There is lots more to bracketed character classes; full details are in ["Bracketed Character Classes" in perlrecharclass](perlrecharclass#Bracketed-Character-Classes).
#### Metacharacters
["The Basics"](#The-Basics) introduced some of the metacharacters. This section gives them all. Most of them have the same meaning as in the *egrep* command.
Only the `"\"` is always a metacharacter. The others are metacharacters just sometimes. The following tables lists all of them, summarizes their use, and gives the contexts where they are metacharacters. Outside those contexts or if prefixed by a `"\"`, they match their corresponding punctuation character. In some cases, their meaning varies depending on various pattern modifiers that alter the default behaviors. See ["Modifiers"](#Modifiers).
```
PURPOSE WHERE
\ Escape the next character Always, except when
escaped by another \
^ Match the beginning of the string Not in []
(or line, if /m is used)
^ Complement the [] class At the beginning of []
. Match any single character except newline Not in []
(under /s, includes newline)
$ Match the end of the string Not in [], but can
(or before newline at the end of the mean interpolate a
string; or before any newline if /m is scalar
used)
| Alternation Not in []
() Grouping Not in []
[ Start Bracketed Character class Not in []
] End Bracketed Character class Only in [], and
not first
* Matches the preceding element 0 or more Not in []
times
+ Matches the preceding element 1 or more Not in []
times
? Matches the preceding element 0 or 1 Not in []
times
{ Starts a sequence that gives number(s) Not in []
of times the preceding element can be
matched
{ when following certain escape sequences
starts a modifier to the meaning of the
sequence
} End sequence started by {
- Indicates a range Only in [] interior
# Beginning of comment, extends to line end Only with /x modifier
```
Notice that most of the metacharacters lose their special meaning when they occur in a bracketed character class, except `"^"` has a different meaning when it is at the beginning of such a class. And `"-"` and `"]"` are metacharacters only at restricted positions within bracketed character classes; while `"}"` is a metacharacter only when closing a special construct started by `"{"`.
In double-quotish context, as is usually the case, you need to be careful about `"$"` and the non-metacharacter `"@"`. Those could interpolate variables, which may or may not be what you intended.
These rules were designed for compactness of expression, rather than legibility and maintainability. The ["/x and /xx"](#%2Fx-and-%2Fxx) pattern modifiers allow you to insert white space to improve readability. And use of `[re 'strict'](re#%27strict%27-mode)` adds extra checking to catch some typos that might silently compile into something unintended.
By default, the `"^"` character is guaranteed to match only the beginning of the string, the `"$"` character only the end (or before the newline at the end), and Perl does certain optimizations with the assumption that the string contains only one line. Embedded newlines will not be matched by `"^"` or `"$"`. You may, however, wish to treat a string as a multi-line buffer, such that the `"^"` will match after any newline within the string (except if the newline is the last character in the string), and `"$"` will match before any newline. At the cost of a little more overhead, you can do this by using the `["/m"](#%2Fm)` modifier on the pattern match operator. (Older programs did this by setting `$*`, but this option was removed in perl 5.10.)
To simplify multi-line substitutions, the `"."` character never matches a newline unless you use the [`/s`](#s) modifier, which in effect tells Perl to pretend the string is a single line--even if it isn't.
### Modifiers
#### Overview
The default behavior for matching can be changed, using various modifiers. Modifiers that relate to the interpretation of the pattern are listed just below. Modifiers that alter the way a pattern is used by Perl are detailed in ["Regexp Quote-Like Operators" in perlop](perlop#Regexp-Quote-Like-Operators) and ["Gory details of parsing quoted constructs" in perlop](perlop#Gory-details-of-parsing-quoted-constructs). Modifiers can be added dynamically; see ["Extended Patterns"](#Extended-Patterns) below.
**`m`** Treat the string being matched against as multiple lines. That is, change `"^"` and `"$"` from matching the start of the string's first line and the end of its last line to matching the start and end of each line within the string.
**`s`** Treat the string as single line. That is, change `"."` to match any character whatsoever, even a newline, which normally it would not match.
Used together, as `/ms`, they let the `"."` match any character whatsoever, while still allowing `"^"` and `"$"` to match, respectively, just after and just before newlines within the string.
**`i`** Do case-insensitive pattern matching. For example, "A" will match "a" under `/i`.
If locale matching rules are in effect, the case map is taken from the current locale for code points less than 255, and from Unicode rules for larger code points. However, matches that would cross the Unicode rules/non-Unicode rules boundary (ords 255/256) will not succeed, unless the locale is a UTF-8 one. See <perllocale>.
There are a number of Unicode characters that match a sequence of multiple characters under `/i`. For example, `LATIN SMALL LIGATURE FI` should match the sequence `fi`. Perl is not currently able to do this when the multiple characters are in the pattern and are split between groupings, or when one or more are quantified. Thus
```
"\N{LATIN SMALL LIGATURE FI}" =~ /fi/i; # Matches
"\N{LATIN SMALL LIGATURE FI}" =~ /[fi][fi]/i; # Doesn't match!
"\N{LATIN SMALL LIGATURE FI}" =~ /fi*/i; # Doesn't match!
# The below doesn't match, and it isn't clear what $1 and $2 would
# be even if it did!!
"\N{LATIN SMALL LIGATURE FI}" =~ /(f)(i)/i; # Doesn't match!
```
Perl doesn't match multiple characters in a bracketed character class unless the character that maps to them is explicitly mentioned, and it doesn't match them at all if the character class is inverted, which otherwise could be highly confusing. See ["Bracketed Character Classes" in perlrecharclass](perlrecharclass#Bracketed-Character-Classes), and ["Negation" in perlrecharclass](perlrecharclass#Negation).
**`x`** and **`xx`** Extend your pattern's legibility by permitting whitespace and comments. Details in ["/x and /xx"](#%2Fx-and-%2Fxx)
**`p`** Preserve the string matched such that `${^PREMATCH}`, `${^MATCH}`, and `${^POSTMATCH}` are available for use after matching.
In Perl 5.20 and higher this is ignored. Due to a new copy-on-write mechanism, `${^PREMATCH}`, `${^MATCH}`, and `${^POSTMATCH}` will be available after the match regardless of the modifier.
**`a`**, **`d`**, **`l`**, and **`u`** These modifiers, all new in 5.14, affect which character-set rules (Unicode, *etc*.) are used, as described below in ["Character set modifiers"](#Character-set-modifiers).
**`n`** Prevent the grouping metacharacters `()` from capturing. This modifier, new in 5.22, will stop `$1`, `$2`, *etc*... from being filled in.
```
"hello" =~ /(hi|hello)/; # $1 is "hello"
"hello" =~ /(hi|hello)/n; # $1 is undef
```
This is equivalent to putting `?:` at the beginning of every capturing group:
```
"hello" =~ /(?:hi|hello)/; # $1 is undef
```
`/n` can be negated on a per-group basis. Alternatively, named captures may still be used.
```
"hello" =~ /(?-n:(hi|hello))/n; # $1 is "hello"
"hello" =~ /(?<greet>hi|hello)/n; # $1 is "hello", $+{greet} is
# "hello"
```
Other Modifiers There are a number of flags that can be found at the end of regular expression constructs that are *not* generic regular expression flags, but apply to the operation being performed, like matching or substitution (`m//` or `s///` respectively).
Flags described further in ["Using regular expressions in Perl" in perlretut](perlretut#Using-regular-expressions-in-Perl) are:
```
c - keep the current position during repeated matching
g - globally match the pattern repeatedly in the string
```
Substitution-specific modifiers described in ["s/PATTERN/REPLACEMENT/msixpodualngcer" in perlop](perlop#s%2FPATTERN%2FREPLACEMENT%2Fmsixpodualngcer) are:
```
e - evaluate the right-hand side as an expression
ee - evaluate the right side as a string then eval the result
o - pretend to optimize your code, but actually introduce bugs
r - perform non-destructive substitution and return the new value
```
Regular expression modifiers are usually written in documentation as *e.g.*, "the `/x` modifier", even though the delimiter in question might not really be a slash. The modifiers `/imnsxadlup` may also be embedded within the regular expression itself using the `(?...)` construct, see ["Extended Patterns"](#Extended-Patterns) below.
####
Details on some modifiers
Some of the modifiers require more explanation than given in the ["Overview"](#Overview) above.
#####
`/x` and `/xx`
A single `/x` tells the regular expression parser to ignore most whitespace that is neither backslashed nor within a bracketed character class. You can use this to break up your regular expression into more readable parts. Also, the `"#"` character is treated as a metacharacter introducing a comment that runs up to the pattern's closing delimiter, or to the end of the current line if the pattern extends onto the next line. Hence, this is very much like an ordinary Perl code comment. (You can include the closing delimiter within the comment only if you precede it with a backslash, so be careful!)
Use of `/x` means that if you want real whitespace or `"#"` characters in the pattern (outside a bracketed character class, which is unaffected by `/x`), then you'll either have to escape them (using backslashes or `\Q...\E`) or encode them using octal, hex, or `\N{}` or `\p{name=...}` escapes. It is ineffective to try to continue a comment onto the next line by escaping the `\n` with a backslash or `\Q`.
You can use ["(?#text)"](#%28%3F%23text%29) to create a comment that ends earlier than the end of the current line, but `text` also can't contain the closing delimiter unless escaped with a backslash.
A common pitfall is to forget that `"#"` characters (outside a bracketed character class) begin a comment under `/x` and are not matched literally. Just keep that in mind when trying to puzzle out why a particular `/x` pattern isn't working as expected. Inside a bracketed character class, `"#"` retains its non-special, literal meaning.
Starting in Perl v5.26, if the modifier has a second `"x"` within it, the effect of a single `/x` is increased. The only difference is that inside bracketed character classes, non-escaped (by a backslash) SPACE and TAB characters are not added to the class, and hence can be inserted to make the classes more readable:
```
/ [d-e g-i 3-7]/xx
/[ ! @ " # $ % ^ & * () = ? <> ' ]/xx
```
may be easier to grasp than the squashed equivalents
```
/[d-eg-i3-7]/
/[!@"#$%^&*()=?<>']/
```
Note that this unfortunately doesn't mean that your bracketed classes can contain comments or extend over multiple lines. A `#` inside a character class is still just a literal `#`, and doesn't introduce a comment. And, unless the closing bracket is on the same line as the opening one, the newline character (and everything on the next line(s) until terminated by a `]` will be part of the class, just as if you'd written `\n`.
Taken together, these features go a long way towards making Perl's regular expressions more readable. Here's an example:
```
# Delete (most) C comments.
$program =~ s {
/\* # Match the opening delimiter.
.*? # Match a minimal number of characters.
\*/ # Match the closing delimiter.
} []gsx;
```
Note that anything inside a `\Q...\E` stays unaffected by `/x`. And note that `/x` doesn't affect space interpretation within a single multi-character construct. For example `(?:...)` can't have a space between the `"("`, `"?"`, and `":"`. Within any delimiters for such a construct, allowed spaces are not affected by `/x`, and depend on the construct. For example, all constructs using curly braces as delimiters, such as `\x{...}` can have blanks within but adjacent to the braces, but not elsewhere, and no non-blank space characters. An exception are Unicode properties which follow Unicode rules, for which see ["Properties accessible through \p{} and \P{}" in perluniprops](perluniprops#Properties-accessible-through-%5Cp%7B%7D-and-%5CP%7B%7D).
The set of characters that are deemed whitespace are those that Unicode calls "Pattern White Space", namely:
```
U+0009 CHARACTER TABULATION
U+000A LINE FEED
U+000B LINE TABULATION
U+000C FORM FEED
U+000D CARRIAGE RETURN
U+0020 SPACE
U+0085 NEXT LINE
U+200E LEFT-TO-RIGHT MARK
U+200F RIGHT-TO-LEFT MARK
U+2028 LINE SEPARATOR
U+2029 PARAGRAPH SEPARATOR
```
#####
Character set modifiers
`/d`, `/u`, `/a`, and `/l`, available starting in 5.14, are called the character set modifiers; they affect the character set rules used for the regular expression.
The `/d`, `/u`, and `/l` modifiers are not likely to be of much use to you, and so you need not worry about them very much. They exist for Perl's internal use, so that complex regular expression data structures can be automatically serialized and later exactly reconstituted, including all their nuances. But, since Perl can't keep a secret, and there may be rare instances where they are useful, they are documented here.
The `/a` modifier, on the other hand, may be useful. Its purpose is to allow code that is to work mostly on ASCII data to not have to concern itself with Unicode.
Briefly, `/l` sets the character set to that of whatever **L**ocale is in effect at the time of the execution of the pattern match.
`/u` sets the character set to **U**nicode.
`/a` also sets the character set to Unicode, BUT adds several restrictions for **A**SCII-safe matching.
`/d` is the old, problematic, pre-5.14 **D**efault character set behavior. Its only use is to force that old behavior.
At any given time, exactly one of these modifiers is in effect. Their existence allows Perl to keep the originally compiled behavior of a regular expression, regardless of what rules are in effect when it is actually executed. And if it is interpolated into a larger regex, the original's rules continue to apply to it, and don't affect the other parts.
The `/l` and `/u` modifiers are automatically selected for regular expressions compiled within the scope of various pragmas, and we recommend that in general, you use those pragmas instead of specifying these modifiers explicitly. For one thing, the modifiers affect only pattern matching, and do not extend to even any replacement done, whereas using the pragmas gives consistent results for all appropriate operations within their scopes. For example,
```
s/foo/\Ubar/il
```
will match "foo" using the locale's rules for case-insensitive matching, but the `/l` does not affect how the `\U` operates. Most likely you want both of them to use locale rules. To do this, instead compile the regular expression within the scope of `use locale`. This both implicitly adds the `/l`, and applies locale rules to the `\U`. The lesson is to `use locale`, and not `/l` explicitly.
Similarly, it would be better to use `use feature 'unicode_strings'` instead of,
```
s/foo/\Lbar/iu
```
to get Unicode rules, as the `\L` in the former (but not necessarily the latter) would also use Unicode rules.
More detail on each of the modifiers follows. Most likely you don't need to know this detail for `/l`, `/u`, and `/d`, and can skip ahead to [/a](#%2Fa-%28and-%2Faa%29).
#####
/l
means to use the current locale's rules (see <perllocale>) when pattern matching. For example, `\w` will match the "word" characters of that locale, and `"/i"` case-insensitive matching will match according to the locale's case folding rules. The locale used will be the one in effect at the time of execution of the pattern match. This may not be the same as the compilation-time locale, and can differ from one match to another if there is an intervening call of the [setlocale() function](perllocale#The-setlocale-function).
Prior to v5.20, Perl did not support multi-byte locales. Starting then, UTF-8 locales are supported. No other multi byte locales are ever likely to be supported. However, in all locales, one can have code points above 255 and these will always be treated as Unicode no matter what locale is in effect.
Under Unicode rules, there are a few case-insensitive matches that cross the 255/256 boundary. Except for UTF-8 locales in Perls v5.20 and later, these are disallowed under `/l`. For example, 0xFF (on ASCII platforms) does not caselessly match the character at 0x178, `LATIN CAPITAL LETTER Y WITH DIAERESIS`, because 0xFF may not be `LATIN SMALL LETTER Y WITH DIAERESIS` in the current locale, and Perl has no way of knowing if that character even exists in the locale, much less what code point it is.
In a UTF-8 locale in v5.20 and later, the only visible difference between locale and non-locale in regular expressions should be tainting, if your perl supports taint checking (see <perlsec>).
This modifier may be specified to be the default by `use locale`, but see ["Which character set modifier is in effect?"](#Which-character-set-modifier-is-in-effect%3F).
#####
/u
means to use Unicode rules when pattern matching. On ASCII platforms, this means that the code points between 128 and 255 take on their Latin-1 (ISO-8859-1) meanings (which are the same as Unicode's). (Otherwise Perl considers their meanings to be undefined.) Thus, under this modifier, the ASCII platform effectively becomes a Unicode platform; and hence, for example, `\w` will match any of the more than 100\_000 word characters in Unicode.
Unlike most locales, which are specific to a language and country pair, Unicode classifies all the characters that are letters *somewhere* in the world as `\w`. For example, your locale might not think that `LATIN SMALL LETTER ETH` is a letter (unless you happen to speak Icelandic), but Unicode does. Similarly, all the characters that are decimal digits somewhere in the world will match `\d`; this is hundreds, not 10, possible matches. And some of those digits look like some of the 10 ASCII digits, but mean a different number, so a human could easily think a number is a different quantity than it really is. For example, `BENGALI DIGIT FOUR` (U+09EA) looks very much like an `ASCII DIGIT EIGHT` (U+0038), and `LEPCHA DIGIT SIX` (U+1C46) looks very much like an `ASCII DIGIT FIVE` (U+0035). And, `\d+`, may match strings of digits that are a mixture from different writing systems, creating a security issue. A fraudulent website, for example, could display the price of something using U+1C46, and it would appear to the user that something cost 500 units, but it really costs 600. A browser that enforced script runs (["Script Runs"](#Script-Runs)) would prevent that fraudulent display. ["num()" in Unicode::UCD](Unicode::UCD#num%28%29) can also be used to sort this out. Or the `/a` modifier can be used to force `\d` to match just the ASCII 0 through 9.
Also, under this modifier, case-insensitive matching works on the full set of Unicode characters. The `KELVIN SIGN`, for example matches the letters "k" and "K"; and `LATIN SMALL LIGATURE FF` matches the sequence "ff", which, if you're not prepared, might make it look like a hexadecimal constant, presenting another potential security issue. See <https://unicode.org/reports/tr36> for a detailed discussion of Unicode security issues.
This modifier may be specified to be the default by `use feature 'unicode_strings`, `use locale ':not_characters'`, or `[use v5.12](perlfunc#use-VERSION)` (or higher), but see ["Which character set modifier is in effect?"](#Which-character-set-modifier-is-in-effect%3F).
#####
/d
**IMPORTANT:** Because of the unpredictable behaviors this modifier causes, only use it to maintain weird backward compatibilities. Use the [`unicode_strings`](feature#The-%27unicode_strings%27-feature) feature in new code to avoid inadvertently enabling this modifier by default.
What does this modifier do? It "Depends"!
This modifier means to use platform-native matching rules except when there is cause to use Unicode rules instead, as follows:
1. the target string's [UTF8 flag](perlunifaq#What-is-%22the-UTF8-flag%22%3F) (see below) is set; or
2. the pattern's [UTF8 flag](perlunifaq#What-is-%22the-UTF8-flag%22%3F) (see below) is set; or
3. the pattern explicitly mentions a code point that is above 255 (say by `\x{100}`); or
4. the pattern uses a Unicode name (`\N{...}`); or
5. the pattern uses a Unicode property (`\p{...}` or `\P{...}`); or
6. the pattern uses a Unicode break (`\b{...}` or `\B{...}`); or
7. the pattern uses `["(?[ ])"](#%28%3F%5B-%5D%29)`
8. the pattern uses [`(*script_run: ...)`](#Script-Runs)
Regarding the "UTF8 flag" references above: normally Perl applications shouldn't think about that flag. It's part of Perl's internals, so it can change whenever Perl wants. `/d` may thus cause unpredictable results. See ["The "Unicode Bug"" in perlunicode](perlunicode#The-%22Unicode-Bug%22). This bug has become rather infamous, leading to yet other (without swearing) names for this modifier like "Dicey" and "Dodgy".
Here are some examples of how that works on an ASCII platform:
```
$str = "\xDF"; #
utf8::downgrade($str); # $str is not UTF8-flagged.
$str =~ /^\w/; # No match, since no UTF8 flag.
$str .= "\x{0e0b}"; # Now $str is UTF8-flagged.
$str =~ /^\w/; # Match! $str is now UTF8-flagged.
chop $str;
$str =~ /^\w/; # Still a match! $str retains its UTF8 flag.
```
Under Perl's default configuration this modifier is automatically selected by default when none of the others are, so yet another name for it (unfortunately) is "Default".
Whenever you can, use the [`unicode_strings`](feature#The-%27unicode_strings%27-feature) to cause to be the default instead.
#####
/a (and /aa)
This modifier stands for ASCII-restrict (or ASCII-safe). This modifier may be doubled-up to increase its effect.
When it appears singly, it causes the sequences `\d`, `\s`, `\w`, and the Posix character classes to match only in the ASCII range. They thus revert to their pre-5.6, pre-Unicode meanings. Under `/a`, `\d` always means precisely the digits `"0"` to `"9"`; `\s` means the five characters `[ \f\n\r\t]`, and starting in Perl v5.18, the vertical tab; `\w` means the 63 characters `[A-Za-z0-9_]`; and likewise, all the Posix classes such as `[[:print:]]` match only the appropriate ASCII-range characters.
This modifier is useful for people who only incidentally use Unicode, and who do not wish to be burdened with its complexities and security concerns.
With `/a`, one can write `\d` with confidence that it will only match ASCII characters, and should the need arise to match beyond ASCII, you can instead use `\p{Digit}` (or `\p{Word}` for `\w`). There are similar `\p{...}` constructs that can match beyond ASCII both white space (see ["Whitespace" in perlrecharclass](perlrecharclass#Whitespace)), and Posix classes (see ["POSIX Character Classes" in perlrecharclass](perlrecharclass#POSIX-Character-Classes)). Thus, this modifier doesn't mean you can't use Unicode, it means that to get Unicode matching you must explicitly use a construct (`\p{}`, `\P{}`) that signals Unicode.
As you would expect, this modifier causes, for example, `\D` to mean the same thing as `[^0-9]`; in fact, all non-ASCII characters match `\D`, `\S`, and `\W`. `\b` still means to match at the boundary between `\w` and `\W`, using the `/a` definitions of them (similarly for `\B`).
Otherwise, `/a` behaves like the `/u` modifier, in that case-insensitive matching uses Unicode rules; for example, "k" will match the Unicode `\N{KELVIN SIGN}` under `/i` matching, and code points in the Latin1 range, above ASCII will have Unicode rules when it comes to case-insensitive matching.
To forbid ASCII/non-ASCII matches (like "k" with `\N{KELVIN SIGN}`), specify the `"a"` twice, for example `/aai` or `/aia`. (The first occurrence of `"a"` restricts the `\d`, *etc*., and the second occurrence adds the `/i` restrictions.) But, note that code points outside the ASCII range will use Unicode rules for `/i` matching, so the modifier doesn't really restrict things to just ASCII; it just forbids the intermixing of ASCII and non-ASCII.
To summarize, this modifier provides protection for applications that don't wish to be exposed to all of Unicode. Specifying it twice gives added protection.
This modifier may be specified to be the default by `use re '/a'` or `use re '/aa'`. If you do so, you may actually have occasion to use the `/u` modifier explicitly if there are a few regular expressions where you do want full Unicode rules (but even here, it's best if everything were under feature `"unicode_strings"`, along with the `use re '/aa'`). Also see ["Which character set modifier is in effect?"](#Which-character-set-modifier-is-in-effect%3F).
#####
Which character set modifier is in effect?
Which of these modifiers is in effect at any given point in a regular expression depends on a fairly complex set of interactions. These have been designed so that in general you don't have to worry about it, but this section gives the gory details. As explained below in ["Extended Patterns"](#Extended-Patterns) it is possible to explicitly specify modifiers that apply only to portions of a regular expression. The innermost always has priority over any outer ones, and one applying to the whole expression has priority over any of the default settings that are described in the remainder of this section.
The `[use re '/foo'](re#%27%2Fflags%27-mode)` pragma can be used to set default modifiers (including these) for regular expressions compiled within its scope. This pragma has precedence over the other pragmas listed below that also change the defaults.
Otherwise, `[use locale](perllocale)` sets the default modifier to `/l`; and `[use feature 'unicode\_strings](feature)`, or `[use v5.12](perlfunc#use-VERSION)` (or higher) set the default to `/u` when not in the same scope as either `[use locale](perllocale)` or `[use bytes](bytes)`. (`[use locale ':not\_characters'](perllocale#Unicode-and-UTF-8)` also sets the default to `/u`, overriding any plain `use locale`.) Unlike the mechanisms mentioned above, these affect operations besides regular expressions pattern matching, and so give more consistent results with other operators, including using `\U`, `\l`, *etc*. in substitution replacements.
If none of the above apply, for backwards compatibility reasons, the `/d` modifier is the one in effect by default. As this can lead to unexpected results, it is best to specify which other rule set should be used.
#####
Character set modifier behavior prior to Perl 5.14
Prior to 5.14, there were no explicit modifiers, but `/l` was implied for regexes compiled within the scope of `use locale`, and `/d` was implied otherwise. However, interpolating a regex into a larger regex would ignore the original compilation in favor of whatever was in effect at the time of the second compilation. There were a number of inconsistencies (bugs) with the `/d` modifier, where Unicode rules would be used when inappropriate, and vice versa. `\p{}` did not imply Unicode rules, and neither did all occurrences of `\N{}`, until 5.12.
###
Regular Expressions
#### Quantifiers
Quantifiers are used when a particular portion of a pattern needs to match a certain number (or numbers) of times. If there isn't a quantifier the number of times to match is exactly one. The following standard quantifiers are recognized:
```
* Match 0 or more times
+ Match 1 or more times
? Match 1 or 0 times
{n} Match exactly n times
{n,} Match at least n times
{,n} Match at most n times
{n,m} Match at least n but not more than m times
```
(If a non-escaped curly bracket occurs in a context other than one of the quantifiers listed above, where it does not form part of a backslashed sequence like `\x{...}`, it is either a fatal syntax error, or treated as a regular character, generally with a deprecation warning raised. To escape it, you can precede it with a backslash (`"\{"`) or enclose it within square brackets (`"[{]"`). This change will allow for future syntax extensions (like making the lower bound of a quantifier optional), and better error checking of quantifiers).
The `"*"` quantifier is equivalent to `{0,}`, the `"+"` quantifier to `{1,}`, and the `"?"` quantifier to `{0,1}`. *n* and *m* are limited to non-negative integral values less than a preset limit defined when perl is built. This is usually 65534 on the most common platforms. The actual limit can be seen in the error message generated by code such as this:
```
$_ **= $_ , / {$_} / for 2 .. 42;
```
By default, a quantified subpattern is "greedy", that is, it will match as many times as possible (given a particular starting location) while still allowing the rest of the pattern to match. If you want it to match the minimum number of times possible, follow the quantifier with a `"?"`. Note that the meanings don't change, just the "greediness":
```
*? Match 0 or more times, not greedily
+? Match 1 or more times, not greedily
?? Match 0 or 1 time, not greedily
{n}? Match exactly n times, not greedily (redundant)
{n,}? Match at least n times, not greedily
{,n}? Match at most n times, not greedily
{n,m}? Match at least n but not more than m times, not greedily
```
Normally when a quantified subpattern does not allow the rest of the overall pattern to match, Perl will backtrack. However, this behaviour is sometimes undesirable. Thus Perl provides the "possessive" quantifier form as well.
```
*+ Match 0 or more times and give nothing back
++ Match 1 or more times and give nothing back
?+ Match 0 or 1 time and give nothing back
{n}+ Match exactly n times and give nothing back (redundant)
{n,}+ Match at least n times and give nothing back
{,n}+ Match at most n times and give nothing back
{n,m}+ Match at least n but not more than m times and give nothing back
```
For instance,
```
'aaaa' =~ /a++a/
```
will never match, as the `a++` will gobble up all the `"a"`'s in the string and won't leave any for the remaining part of the pattern. This feature can be extremely useful to give perl hints about where it shouldn't backtrack. For instance, the typical "match a double-quoted string" problem can be most efficiently performed when written as:
```
/"(?:[^"\\]++|\\.)*+"/
```
as we know that if the final quote does not match, backtracking will not help. See the independent subexpression `["(?>*pattern*)"](#%28%3F%3Epattern%29)` for more details; possessive quantifiers are just syntactic sugar for that construct. For instance the above example could also be written as follows:
```
/"(?>(?:(?>[^"\\]+)|\\.)*)"/
```
Note that the possessive quantifier modifier can not be combined with the non-greedy modifier. This is because it would make no sense. Consider the follow equivalency table:
```
Illegal Legal
------------ ------
X??+ X{0}
X+?+ X{1}
X{min,max}?+ X{min}
```
####
Escape sequences
Because patterns are processed as double-quoted strings, the following also work:
```
\t tab (HT, TAB)
\n newline (LF, NL)
\r return (CR)
\f form feed (FF)
\a alarm (bell) (BEL)
\e escape (think troff) (ESC)
\cK control char (example: VT)
\x{}, \x00 character whose ordinal is the given hexadecimal number
\N{name} named Unicode character or character sequence
\N{U+263D} Unicode character (example: FIRST QUARTER MOON)
\o{}, \000 character whose ordinal is the given octal number
\l lowercase next char (think vi)
\u uppercase next char (think vi)
\L lowercase until \E (think vi)
\U uppercase until \E (think vi)
\Q quote (disable) pattern metacharacters until \E
\E end either case modification or quoted section, think vi
```
Details are in ["Quote and Quote-like Operators" in perlop](perlop#Quote-and-Quote-like-Operators).
####
Character Classes and other Special Escapes
In addition, Perl defines the following:
```
Sequence Note Description
[...] [1] Match a character according to the rules of the
bracketed character class defined by the "...".
Example: [a-z] matches "a" or "b" or "c" ... or "z"
[[:...:]] [2] Match a character according to the rules of the POSIX
character class "..." within the outer bracketed
character class. Example: [[:upper:]] matches any
uppercase character.
(?[...]) [8] Extended bracketed character class
\w [3] Match a "word" character (alphanumeric plus "_", plus
other connector punctuation chars plus Unicode
marks)
\W [3] Match a non-"word" character
\s [3] Match a whitespace character
\S [3] Match a non-whitespace character
\d [3] Match a decimal digit character
\D [3] Match a non-digit character
\pP [3] Match P, named property. Use \p{Prop} for longer names
\PP [3] Match non-P
\X [4] Match Unicode "eXtended grapheme cluster"
\1 [5] Backreference to a specific capture group or buffer.
'1' may actually be any positive integer.
\g1 [5] Backreference to a specific or previous group,
\g{-1} [5] The number may be negative indicating a relative
previous group and may optionally be wrapped in
curly brackets for safer parsing.
\g{name} [5] Named backreference
\k<name> [5] Named backreference
\k'name' [5] Named backreference
\k{name} [5] Named backreference
\K [6] Keep the stuff left of the \K, don't include it in $&
\N [7] Any character but \n. Not affected by /s modifier
\v [3] Vertical whitespace
\V [3] Not vertical whitespace
\h [3] Horizontal whitespace
\H [3] Not horizontal whitespace
\R [4] Linebreak
```
[1] See ["Bracketed Character Classes" in perlrecharclass](perlrecharclass#Bracketed-Character-Classes) for details.
[2] See ["POSIX Character Classes" in perlrecharclass](perlrecharclass#POSIX-Character-Classes) for details.
[3] See ["Unicode Character Properties" in perlunicode](perlunicode#Unicode-Character-Properties) for details
[4] See ["Misc" in perlrebackslash](perlrebackslash#Misc) for details.
[5] See ["Capture groups"](#Capture-groups) below for details.
[6] See ["Extended Patterns"](#Extended-Patterns) below for details.
[7] Note that `\N` has two meanings. When of the form `\N{*NAME*}`, it matches the character or character sequence whose name is *NAME*; and similarly when of the form `\N{U+*hex*}`, it matches the character whose Unicode code point is *hex*. Otherwise it matches any character but `\n`.
[8] See ["Extended Bracketed Character Classes" in perlrecharclass](perlrecharclass#Extended-Bracketed-Character-Classes) for details.
#### Assertions
Besides [`"^"` and `"$"`](#Metacharacters), Perl defines the following zero-width assertions:
```
\b{} Match at Unicode boundary of specified type
\B{} Match where corresponding \b{} doesn't match
\b Match a \w\W or \W\w boundary
\B Match except at a \w\W or \W\w boundary
\A Match only at beginning of string
\Z Match only at end of string, or before newline at the end
\z Match only at end of string
\G Match only at pos() (e.g. at the end-of-match position
of prior m//g)
```
A Unicode boundary (`\b{}`), available starting in v5.22, is a spot between two characters, or before the first character in the string, or after the final character in the string where certain criteria defined by Unicode are met. See ["\b{}, \b, \B{}, \B" in perlrebackslash](perlrebackslash#%5Cb%7B%7D%2C-%5Cb%2C-%5CB%7B%7D%2C-%5CB) for details.
A word boundary (`\b`) is a spot between two characters that has a `\w` on one side of it and a `\W` on the other side of it (in either order), counting the imaginary characters off the beginning and end of the string as matching a `\W`. (Within character classes `\b` represents backspace rather than a word boundary, just as it normally does in any double-quoted string.) The `\A` and `\Z` are just like `"^"` and `"$"`, except that they won't match multiple times when the `/m` modifier is used, while `"^"` and `"$"` will match at every internal line boundary. To match the actual end of the string and not ignore an optional trailing newline, use `\z`.
The `\G` assertion can be used to chain global matches (using `m//g`), as described in ["Regexp Quote-Like Operators" in perlop](perlop#Regexp-Quote-Like-Operators). It is also useful when writing `lex`-like scanners, when you have several patterns that you want to match against consequent substrings of your string; see the previous reference. The actual location where `\G` will match can also be influenced by using `pos()` as an lvalue: see ["pos" in perlfunc](perlfunc#pos). Note that the rule for zero-length matches (see ["Repeated Patterns Matching a Zero-length Substring"](#Repeated-Patterns-Matching-a-Zero-length-Substring)) is modified somewhat, in that contents to the left of `\G` are not counted when determining the length of the match. Thus the following will not match forever:
```
my $string = 'ABC';
pos($string) = 1;
while ($string =~ /(.\G)/g) {
print $1;
}
```
It will print 'A' and then terminate, as it considers the match to be zero-width, and thus will not match at the same position twice in a row.
It is worth noting that `\G` improperly used can result in an infinite loop. Take care when using patterns that include `\G` in an alternation.
Note also that `s///` will refuse to overwrite part of a substitution that has already been replaced; so for example this will stop after the first iteration, rather than iterating its way backwards through the string:
```
$_ = "123456789";
pos = 6;
s/.(?=.\G)/X/g;
print; # prints 1234X6789, not XXXXX6789
```
####
Capture groups
The grouping construct `( ... )` creates capture groups (also referred to as capture buffers). To refer to the current contents of a group later on, within the same pattern, use `\g1` (or `\g{1}`) for the first, `\g2` (or `\g{2}`) for the second, and so on. This is called a *backreference*. There is no limit to the number of captured substrings that you may use. Groups are numbered with the leftmost open parenthesis being number 1, *etc*. If a group did not match, the associated backreference won't match either. (This can happen if the group is optional, or in a different branch of an alternation.) You can omit the `"g"`, and write `"\1"`, *etc*, but there are some issues with this form, described below.
You can also refer to capture groups relatively, by using a negative number, so that `\g-1` and `\g{-1}` both refer to the immediately preceding capture group, and `\g-2` and `\g{-2}` both refer to the group before it. For example:
```
/
(Y) # group 1
( # group 2
(X) # group 3
\g{-1} # backref to group 3
\g{-3} # backref to group 1
)
/x
```
would match the same as `/(Y) ( (X) \g3 \g1 )/x`. This allows you to interpolate regexes into larger regexes and not have to worry about the capture groups being renumbered.
You can dispense with numbers altogether and create named capture groups. The notation is `(?<*name*>...)` to declare and `\g{*name*}` to reference. (To be compatible with .Net regular expressions, `\g{*name*}` may also be written as `\k{*name*}`, `\k<*name*>` or `\k'*name*'`.) *name* must not begin with a number, nor contain hyphens. When different groups within the same pattern have the same name, any reference to that name assumes the leftmost defined group. Named groups count in absolute and relative numbering, and so can also be referred to by those numbers. (It's possible to do things with named capture groups that would otherwise require `(??{})`.)
Capture group contents are dynamically scoped and available to you outside the pattern until the end of the enclosing block or until the next successful match, whichever comes first. (See ["Compound Statements" in perlsyn](perlsyn#Compound-Statements).) You can refer to them by absolute number (using `"$1"` instead of `"\g1"`, *etc*); or by name via the `%+` hash, using `"$+{*name*}"`.
Braces are required in referring to named capture groups, but are optional for absolute or relative numbered ones. Braces are safer when creating a regex by concatenating smaller strings. For example if you have `qr/$a$b/`, and `$a` contained `"\g1"`, and `$b` contained `"37"`, you would get `/\g137/` which is probably not what you intended.
If you use braces, you may also optionally add any number of blank (space or tab) characters within but adjacent to the braces, like `\g{ -1 }`, or `\k{ *name* }`.
The `\g` and `\k` notations were introduced in Perl 5.10.0. Prior to that there were no named nor relative numbered capture groups. Absolute numbered groups were referred to using `\1`, `\2`, *etc*., and this notation is still accepted (and likely always will be). But it leads to some ambiguities if there are more than 9 capture groups, as `\10` could mean either the tenth capture group, or the character whose ordinal in octal is 010 (a backspace in ASCII). Perl resolves this ambiguity by interpreting `\10` as a backreference only if at least 10 left parentheses have opened before it. Likewise `\11` is a backreference only if at least 11 left parentheses have opened before it. And so on. `\1` through `\9` are always interpreted as backreferences. There are several examples below that illustrate these perils. You can avoid the ambiguity by always using `\g{}` or `\g` if you mean capturing groups; and for octal constants always using `\o{}`, or for `\077` and below, using 3 digits padded with leading zeros, since a leading zero implies an octal constant.
The `\*digit*` notation also works in certain circumstances outside the pattern. See ["Warning on \1 Instead of $1"](#Warning-on-%5C1-Instead-of-%241) below for details.
Examples:
```
s/^([^ ]*) *([^ ]*)/$2 $1/; # swap first two words
/(.)\g1/ # find first doubled char
and print "'$1' is the first doubled character\n";
/(?<char>.)\k<char>/ # ... a different way
and print "'$+{char}' is the first doubled character\n";
/(?'char'.)\g1/ # ... mix and match
and print "'$1' is the first doubled character\n";
if (/Time: (..):(..):(..)/) { # parse out values
$hours = $1;
$minutes = $2;
$seconds = $3;
}
/(.)(.)(.)(.)(.)(.)(.)(.)(.)\g10/ # \g10 is a backreference
/(.)(.)(.)(.)(.)(.)(.)(.)(.)\10/ # \10 is octal
/((.)(.)(.)(.)(.)(.)(.)(.)(.))\10/ # \10 is a backreference
/((.)(.)(.)(.)(.)(.)(.)(.)(.))\010/ # \010 is octal
$a = '(.)\1'; # Creates problems when concatenated.
$b = '(.)\g{1}'; # Avoids the problems.
"aa" =~ /${a}/; # True
"aa" =~ /${b}/; # True
"aa0" =~ /${a}0/; # False!
"aa0" =~ /${b}0/; # True
"aa\x08" =~ /${a}0/; # True!
"aa\x08" =~ /${b}0/; # False
```
Several special variables also refer back to portions of the previous match. `$+` returns whatever the last bracket match matched. `$&` returns the entire matched string. (At one point `$0` did also, but now it returns the name of the program.) `$`` returns everything before the matched string. `$'` returns everything after the matched string. And `$^N` contains whatever was matched by the most-recently closed group (submatch). `$^N` can be used in extended patterns (see below), for example to assign a submatch to a variable.
These special variables, like the `%+` hash and the numbered match variables (`$1`, `$2`, `$3`, *etc*.) are dynamically scoped until the end of the enclosing block or until the next successful match, whichever comes first. (See ["Compound Statements" in perlsyn](perlsyn#Compound-Statements).)
The `@{^CAPTURE}` array may be used to access ALL of the capture buffers as an array without needing to know how many there are. For instance
```
$string=~/$pattern/ and @captured = @{^CAPTURE};
```
will place a copy of each capture variable, `$1`, `$2` etc, into the `@captured` array.
Be aware that when interpolating a subscript of the `@{^CAPTURE}` array you must use demarcated curly brace notation:
```
print "@{^CAPTURE[0]}";
```
See ["Demarcated variable names using braces" in perldata](perldata#Demarcated-variable-names-using-braces) for more on this notation.
**NOTE**: Failed matches in Perl do not reset the match variables, which makes it easier to write code that tests for a series of more specific cases and remembers the best match.
**WARNING**: If your code is to run on Perl 5.16 or earlier, beware that once Perl sees that you need one of `$&`, `$``, or `$'` anywhere in the program, it has to provide them for every pattern match. This may substantially slow your program.
Perl uses the same mechanism to produce `$1`, `$2`, *etc*, so you also pay a price for each pattern that contains capturing parentheses. (To avoid this cost while retaining the grouping behaviour, use the extended regular expression `(?: ... )` instead.) But if you never use `$&`, `$`` or `$'`, then patterns *without* capturing parentheses will not be penalized. So avoid `$&`, `$'`, and `$`` if you can, but if you can't (and some algorithms really appreciate them), once you've used them once, use them at will, because you've already paid the price.
Perl 5.16 introduced a slightly more efficient mechanism that notes separately whether each of `$``, `$&`, and `$'` have been seen, and thus may only need to copy part of the string. Perl 5.20 introduced a much more efficient copy-on-write mechanism which eliminates any slowdown.
As another workaround for this problem, Perl 5.10.0 introduced `${^PREMATCH}`, `${^MATCH}` and `${^POSTMATCH}`, which are equivalent to `$``, `$&` and `$'`, **except** that they are only guaranteed to be defined after a successful match that was executed with the `/p` (preserve) modifier. The use of these variables incurs no global performance penalty, unlike their punctuation character equivalents, however at the trade-off that you have to tell perl when you want to use them. As of Perl 5.20, these three variables are equivalent to `$``, `$&` and `$'`, and `/p` is ignored.
###
Quoting metacharacters
Backslashed metacharacters in Perl are alphanumeric, such as `\b`, `\w`, `\n`. Unlike some other regular expression languages, there are no backslashed symbols that aren't alphanumeric. So anything that looks like `\\`, `\(`, `\)`, `\[`, `\]`, `\{`, or `\}` is always interpreted as a literal character, not a metacharacter. This was once used in a common idiom to disable or quote the special meanings of regular expression metacharacters in a string that you want to use for a pattern. Simply quote all non-"word" characters:
```
$pattern =~ s/(\W)/\\$1/g;
```
(If `use locale` is set, then this depends on the current locale.) Today it is more common to use the `[quotemeta()](perlfunc#quotemeta)` function or the `\Q` metaquoting escape sequence to disable all metacharacters' special meanings like this:
```
/$unquoted\Q$quoted\E$unquoted/
```
Beware that if you put literal backslashes (those not inside interpolated variables) between `\Q` and `\E`, double-quotish backslash interpolation may lead to confusing results. If you *need* to use literal backslashes within `\Q...\E`, consult ["Gory details of parsing quoted constructs" in perlop](perlop#Gory-details-of-parsing-quoted-constructs).
`quotemeta()` and `\Q` are fully described in ["quotemeta" in perlfunc](perlfunc#quotemeta).
###
Extended Patterns
Perl also defines a consistent extension syntax for features not found in standard tools like **awk** and **lex**. The syntax for most of these is a pair of parentheses with a question mark as the first thing within the parentheses. The character after the question mark indicates the extension.
A question mark was chosen for this and for the minimal-matching construct because 1) question marks are rare in older regular expressions, and 2) whenever you see one, you should stop and "question" exactly what is going on. That's psychology....
`(?#*text*)` A comment. The *text* is ignored. Note that Perl closes the comment as soon as it sees a `")"`, so there is no way to put a literal `")"` in the comment. The pattern's closing delimiter must be escaped by a backslash if it appears in the comment.
See ["/x"](#%2Fx) for another way to have comments in patterns.
Note that a comment can go just about anywhere, except in the middle of an escape sequence. Examples:
```
qr/foo(?#comment)bar/' # Matches 'foobar'
# The pattern below matches 'abcd', 'abccd', or 'abcccd'
qr/abc(?#comment between literal and its quantifier){1,3}d/
# The pattern below generates a syntax error, because the '\p' must
# be followed immediately by a '{'.
qr/\p(?#comment between \p and its property name){Any}/
# The pattern below generates a syntax error, because the initial
# '\(' is a literal opening parenthesis, and so there is nothing
# for the closing ')' to match
qr/\(?#the backslash means this isn't a comment)p{Any}/
# Comments can be used to fold long patterns into multiple lines
qr/First part of a long regex(?#
)remaining part/
```
`(?adlupimnsx-imnsx)`
`(?^alupimnsx)` Zero or more embedded pattern-match modifiers, to be turned on (or turned off if preceded by `"-"`) for the remainder of the pattern or the remainder of the enclosing pattern group (if any).
This is particularly useful for dynamically-generated patterns, such as those read in from a configuration file, taken from an argument, or specified in a table somewhere. Consider the case where some patterns want to be case-sensitive and some do not: The case-insensitive ones merely need to include `(?i)` at the front of the pattern. For example:
```
$pattern = "foobar";
if ( /$pattern/i ) { }
# more flexible:
$pattern = "(?i)foobar";
if ( /$pattern/ ) { }
```
These modifiers are restored at the end of the enclosing group. For example,
```
( (?i) blah ) \s+ \g1
```
will match `blah` in any case, some spaces, and an exact (*including the case*!) repetition of the previous word, assuming the `/x` modifier, and no `/i` modifier outside this group.
These modifiers do not carry over into named subpatterns called in the enclosing group. In other words, a pattern such as `((?i)(?&*NAME*))` does not change the case-sensitivity of the *NAME* pattern.
A modifier is overridden by later occurrences of this construct in the same scope containing the same modifier, so that
```
/((?im)foo(?-m)bar)/
```
matches all of `foobar` case insensitively, but uses `/m` rules for only the `foo` portion. The `"a"` flag overrides `aa` as well; likewise `aa` overrides `"a"`. The same goes for `"x"` and `xx`. Hence, in
```
/(?-x)foo/xx
```
both `/x` and `/xx` are turned off during matching `foo`. And in
```
/(?x)foo/x
```
`/x` but NOT `/xx` is turned on for matching `foo`. (One might mistakenly think that since the inner `(?x)` is already in the scope of `/x`, that the result would effectively be the sum of them, yielding `/xx`. It doesn't work that way.) Similarly, doing something like `(?xx-x)foo` turns off all `"x"` behavior for matching `foo`, it is not that you subtract 1 `"x"` from 2 to get 1 `"x"` remaining.
Any of these modifiers can be set to apply globally to all regular expressions compiled within the scope of a `use re`. See ["'/flags' mode" in re](re#%27%2Fflags%27-mode).
Starting in Perl 5.14, a `"^"` (caret or circumflex accent) immediately after the `"?"` is a shorthand equivalent to `d-imnsx`. Flags (except `"d"`) may follow the caret to override it. But a minus sign is not legal with it.
Note that the `"a"`, `"d"`, `"l"`, `"p"`, and `"u"` modifiers are special in that they can only be enabled, not disabled, and the `"a"`, `"d"`, `"l"`, and `"u"` modifiers are mutually exclusive: specifying one de-specifies the others, and a maximum of one (or two `"a"`'s) may appear in the construct. Thus, for example, `(?-p)` will warn when compiled under `use warnings`; `(?-d:...)` and `(?dl:...)` are fatal errors.
Note also that the `"p"` modifier is special in that its presence anywhere in a pattern has a global effect.
Having zero modifiers makes this a no-op (so why did you specify it, unless it's generated code), and starting in v5.30, warns under [`use re 'strict'`](re#%27strict%27-mode).
`(?:*pattern*)`
`(?adluimnsx-imnsx:*pattern*)`
`(?^aluimnsx:*pattern*)` This is for clustering, not capturing; it groups subexpressions like `"()"`, but doesn't make backreferences as `"()"` does. So
```
@fields = split(/\b(?:a|b|c)\b/)
```
matches the same field delimiters as
```
@fields = split(/\b(a|b|c)\b/)
```
but doesn't spit out the delimiters themselves as extra fields (even though that's the behaviour of ["split" in perlfunc](perlfunc#split) when its pattern contains capturing groups). It's also cheaper not to capture characters if you don't need to.
Any letters between `"?"` and `":"` act as flags modifiers as with `(?adluimnsx-imnsx)`. For example,
```
/(?s-i:more.*than).*million/i
```
is equivalent to the more verbose
```
/(?:(?s-i)more.*than).*million/i
```
Note that any `()` constructs enclosed within this one will still capture unless the `/n` modifier is in effect.
Like the ["(?adlupimnsx-imnsx)"](#%28%3Fadlupimnsx-imnsx%29) construct, `aa` and `"a"` override each other, as do `xx` and `"x"`. They are not additive. So, doing something like `(?xx-x:foo)` turns off all `"x"` behavior for matching `foo`.
Starting in Perl 5.14, a `"^"` (caret or circumflex accent) immediately after the `"?"` is a shorthand equivalent to `d-imnsx`. Any positive flags (except `"d"`) may follow the caret, so
```
(?^x:foo)
```
is equivalent to
```
(?x-imns:foo)
```
The caret tells Perl that this cluster doesn't inherit the flags of any surrounding pattern, but uses the system defaults (`d-imnsx`), modified by any flags specified.
The caret allows for simpler stringification of compiled regular expressions. These look like
```
(?^:pattern)
```
with any non-default flags appearing between the caret and the colon. A test that looks at such stringification thus doesn't need to have the system default flags hard-coded in it, just the caret. If new flags are added to Perl, the meaning of the caret's expansion will change to include the default for those flags, so the test will still work, unchanged.
Specifying a negative flag after the caret is an error, as the flag is redundant.
Mnemonic for `(?^...)`: A fresh beginning since the usual use of a caret is to match at the beginning.
`(?|*pattern*)` This is the "branch reset" pattern, which has the special property that the capture groups are numbered from the same starting point in each alternation branch. It is available starting from perl 5.10.0.
Capture groups are numbered from left to right, but inside this construct the numbering is restarted for each branch.
The numbering within each branch will be as normal, and any groups following this construct will be numbered as though the construct contained only one branch, that being the one with the most capture groups in it.
This construct is useful when you want to capture one of a number of alternative matches.
Consider the following pattern. The numbers underneath show in which group the captured content will be stored.
```
# before ---------------branch-reset----------- after
/ ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
# 1 2 2 3 2 3 4
```
Be careful when using the branch reset pattern in combination with named captures. Named captures are implemented as being aliases to numbered groups holding the captures, and that interferes with the implementation of the branch reset pattern. If you are using named captures in a branch reset pattern, it's best to use the same names, in the same order, in each of the alternations:
```
/(?| (?<a> x ) (?<b> y )
| (?<a> z ) (?<b> w )) /x
```
Not doing so may lead to surprises:
```
"12" =~ /(?| (?<a> \d+ ) | (?<b> \D+))/x;
say $+{a}; # Prints '12'
say $+{b}; # *Also* prints '12'.
```
The problem here is that both the group named `a` and the group named `b` are aliases for the group belonging to `$1`.
Lookaround Assertions Lookaround assertions are zero-width patterns which match a specific pattern without including it in `$&`. Positive assertions match when their subpattern matches, negative assertions match when their subpattern fails. Lookbehind matches text up to the current match position, lookahead matches text following the current match position.
`(?=*pattern*)`
`(*pla:*pattern*)`
`(*positive_lookahead:*pattern*)` A zero-width positive lookahead assertion. For example, `/\w+(?=\t)/` matches a word followed by a tab, without including the tab in `$&`.
`(?!*pattern*)`
`(*nla:*pattern*)`
`(*negative_lookahead:*pattern*)` A zero-width negative lookahead assertion. For example `/foo(?!bar)/` matches any occurrence of "foo" that isn't followed by "bar". Note however that lookahead and lookbehind are NOT the same thing. You cannot use this for lookbehind.
If you are looking for a "bar" that isn't preceded by a "foo", `/(?!foo)bar/` will not do what you want. That's because the `(?!foo)` is just saying that the next thing cannot be "foo"--and it's not, it's a "bar", so "foobar" will match. Use lookbehind instead (see below).
`(?<=*pattern*)`
`\K`
`(*plb:*pattern*)`
`(*positive_lookbehind:*pattern*)` A zero-width positive lookbehind assertion. For example, `/(?<=\t)\w+/` matches a word that follows a tab, without including the tab in `$&`.
Prior to Perl 5.30, it worked only for fixed-width lookbehind, but starting in that release, it can handle variable lengths from 1 to 255 characters as an experimental feature. The feature is enabled automatically if you use a variable length positive lookbehind assertion.
In Perl 5.35.10 the scope of the experimental nature of this construct has been reduced, and experimental warnings will only be produced when the construct contains capturing parenthesis. The warnings will be raised at pattern compilation time, unless turned off, in the `experimental::vlb` category. This is to warn you that the exact contents of capturing buffers in a variable length positive lookbehind is not well defined and is subject to change in a future release of perl.
Currently if you use capture buffers inside of a positive variable length lookbehind the result will be the longest and thus leftmost match possible. This means that
```
"aax" =~ /(?=x)(?<=(a|aa))/
"aax" =~ /(?=x)(?<=(aa|a))/
"aax" =~ /(?=x)(?<=(a{1,2}?)/
"aax" =~ /(?=x)(?<=(a{1,2})/
```
will all result in `$1` containing `"aa"`. It is possible in a future release of perl we will change this behavior.
There is a special form of this construct, called `\K` (available since Perl 5.10.0), which causes the regex engine to "keep" everything it had matched prior to the `\K` and not include it in `$&`. This effectively provides non-experimental variable-length lookbehind of any length.
And, there is a technique that can be used to handle variable length lookbehinds on earlier releases, and longer than 255 characters. It is described in <http://www.drregex.com/2019/02/variable-length-lookbehinds-actually.html>.
Note that under `/i`, a few single characters match two or three other characters. This makes them variable length, and the 255 length applies to the maximum number of characters in the match. For example `qr/\N{LATIN SMALL LETTER SHARP S}/i` matches the sequence `"ss"`. Your lookbehind assertion could contain 127 Sharp S characters under `/i`, but adding a 128th would generate a compilation error, as that could match 256 `"s"` characters in a row.
The use of `\K` inside of another lookaround assertion is allowed, but the behaviour is currently not well defined.
For various reasons `\K` may be significantly more efficient than the equivalent `(?<=...)` construct, and it is especially useful in situations where you want to efficiently remove something following something else in a string. For instance
```
s/(foo)bar/$1/g;
```
can be rewritten as the much more efficient
```
s/foo\Kbar//g;
```
Use of the non-greedy modifier `"?"` may not give you the expected results if it is within a capturing group within the construct.
`(?<!*pattern*)`
`(*nlb:*pattern*)`
`(*negative_lookbehind:*pattern*)` A zero-width negative lookbehind assertion. For example `/(?<!bar)foo/` matches any occurrence of "foo" that does not follow "bar".
Prior to Perl 5.30, it worked only for fixed-width lookbehind, but starting in that release, it can handle variable lengths from 1 to 255 characters as an experimental feature. The feature is enabled automatically if you use a variable length negative lookbehind assertion.
In Perl 5.35.10 the scope of the experimental nature of this construct has been reduced, and experimental warnings will only be produced when the construct contains capturing parentheses. The warnings will be raised at pattern compilation time, unless turned off, in the `experimental::vlb` category. This is to warn you that the exact contents of capturing buffers in a variable length negative lookbehind is not well defined and is subject to change in a future release of perl.
Currently if you use capture buffers inside of a negative variable length lookbehind the result may not be what you expect, for instance:
```
say "axfoo"=~/(?=foo)(?<!(a|ax)(?{ say $1 }))/ ? "y" : "n";
```
will output the following:
```
a
no
```
which does not make sense as this should print out "ax" as the "a" does not line up at the correct place. Another example would be:
```
say "yes: '$1-$2'" if "aayfoo"=~/(?=foo)(?<!(a|aa)(a|aa)x)/;
```
will output the following:
```
yes: 'aa-a'
```
It is possible in a future release of perl we will change this behavior so both of these examples produced more reasonable output.
Note that we are confident that the construct will match and reject patterns appropriately, the undefined behavior strictly relates to the value of the capture buffer during or after matching.
There is a technique that can be used to handle variable length lookbehind on earlier releases, and longer than 255 characters. It is described in <http://www.drregex.com/2019/02/variable-length-lookbehinds-actually.html>.
Note that under `/i`, a few single characters match two or three other characters. This makes them variable length, and the 255 length applies to the maximum number of characters in the match. For example `qr/\N{LATIN SMALL LETTER SHARP S}/i` matches the sequence `"ss"`. Your lookbehind assertion could contain 127 Sharp S characters under `/i`, but adding a 128th would generate a compilation error, as that could match 256 `"s"` characters in a row.
Use of the non-greedy modifier `"?"` may not give you the expected results if it is within a capturing group within the construct.
`(?<*NAME*>*pattern*)`
`(?'*NAME*'*pattern*)` A named capture group. Identical in every respect to normal capturing parentheses `()` but for the additional fact that the group can be referred to by name in various regular expression constructs (like `\g{*NAME*}`) and can be accessed by name after a successful match via `%+` or `%-`. See <perlvar> for more details on the `%+` and `%-` hashes.
If multiple distinct capture groups have the same name, then `$+{*NAME*}` will refer to the leftmost defined group in the match.
The forms `(?'*NAME*'*pattern*)` and `(?<*NAME*>*pattern*)` are equivalent.
**NOTE:** While the notation of this construct is the same as the similar function in .NET regexes, the behavior is not. In Perl the groups are numbered sequentially regardless of being named or not. Thus in the pattern
```
/(x)(?<foo>y)(z)/
```
`$+{foo}` will be the same as `$2`, and `$3` will contain 'z' instead of the opposite which is what a .NET regex hacker might expect.
Currently *NAME* is restricted to simple identifiers only. In other words, it must match `/^[_A-Za-z][_A-Za-z0-9]*\z/` or its Unicode extension (see <utf8>), though it isn't extended by the locale (see <perllocale>).
**NOTE:** In order to make things easier for programmers with experience with the Python or PCRE regex engines, the pattern `(?P<*NAME*>*pattern*)` may be used instead of `(?<*NAME*>*pattern*)`; however this form does not support the use of single quotes as a delimiter for the name.
`\k<*NAME*>`
`\k'*NAME*'`
`\k{*NAME*}`
Named backreference. Similar to numeric backreferences, except that the group is designated by name and not number. If multiple groups have the same name then it refers to the leftmost defined group in the current match.
It is an error to refer to a name not defined by a `(?<*NAME*>)` earlier in the pattern.
All three forms are equivalent, although with `\k{ *NAME* }`, you may optionally have blanks within but adjacent to the braces, as shown.
**NOTE:** In order to make things easier for programmers with experience with the Python or PCRE regex engines, the pattern `(?P=*NAME*)` may be used instead of `\k<*NAME*>`.
`(?{ *code* })` **WARNING**: Using this feature safely requires that you understand its limitations. Code executed that has side effects may not perform identically from version to version due to the effect of future optimisations in the regex engine. For more information on this, see ["Embedded Code Execution Frequency"](#Embedded-Code-Execution-Frequency).
This zero-width assertion executes any embedded Perl code. It always succeeds, and its return value is set as `$^R`.
In literal patterns, the code is parsed at the same time as the surrounding code. While within the pattern, control is passed temporarily back to the perl parser, until the logically-balancing closing brace is encountered. This is similar to the way that an array index expression in a literal string is handled, for example
```
"abc$array[ 1 + f('[') + g()]def"
```
In particular, braces do not need to be balanced:
```
s/abc(?{ f('{'); })/def/
```
Even in a pattern that is interpolated and compiled at run-time, literal code blocks will be compiled once, at perl compile time; the following prints "ABCD":
```
print "D";
my $qr = qr/(?{ BEGIN { print "A" } })/;
my $foo = "foo";
/$foo$qr(?{ BEGIN { print "B" } })/;
BEGIN { print "C" }
```
In patterns where the text of the code is derived from run-time information rather than appearing literally in a source code /pattern/, the code is compiled at the same time that the pattern is compiled, and for reasons of security, `use re 'eval'` must be in scope. This is to stop user-supplied patterns containing code snippets from being executable.
In situations where you need to enable this with `use re 'eval'`, you should also have taint checking enabled, if your perl supports it. Better yet, use the carefully constrained evaluation within a Safe compartment. See <perlsec> for details about both these mechanisms.
From the viewpoint of parsing, lexical variable scope and closures,
```
/AAA(?{ BBB })CCC/
```
behaves approximately like
```
/AAA/ && do { BBB } && /CCC/
```
Similarly,
```
qr/AAA(?{ BBB })CCC/
```
behaves approximately like
```
sub { /AAA/ && do { BBB } && /CCC/ }
```
In particular:
```
{ my $i = 1; $r = qr/(?{ print $i })/ }
my $i = 2;
/$r/; # prints "1"
```
Inside a `(?{...})` block, `$_` refers to the string the regular expression is matching against. You can also use `pos()` to know what is the current position of matching within this string.
The code block introduces a new scope from the perspective of lexical variable declarations, but **not** from the perspective of `local` and similar localizing behaviours. So later code blocks within the same pattern will still see the values which were localized in earlier blocks. These accumulated localizations are undone either at the end of a successful match, or if the assertion is backtracked (compare ["Backtracking"](#Backtracking)). For example,
```
$_ = 'a' x 8;
m<
(?{ $cnt = 0 }) # Initialize $cnt.
(
a
(?{
local $cnt = $cnt + 1; # Update $cnt,
# backtracking-safe.
})
)*
aaaa
(?{ $res = $cnt }) # On success copy to
# non-localized location.
>x;
```
will initially increment `$cnt` up to 8; then during backtracking, its value will be unwound back to 4, which is the value assigned to `$res`. At the end of the regex execution, `$cnt` will be wound back to its initial value of 0.
This assertion may be used as the condition in a
```
(?(condition)yes-pattern|no-pattern)
```
switch. If *not* used in this way, the result of evaluation of *code* is put into the special variable `$^R`. This happens immediately, so `$^R` can be used from other `(?{ *code* })` assertions inside the same regular expression.
The assignment to `$^R` above is properly localized, so the old value of `$^R` is restored if the assertion is backtracked; compare ["Backtracking"](#Backtracking).
Note that the special variable `$^N` is particularly useful with code blocks to capture the results of submatches in variables without having to keep track of the number of nested parentheses. For example:
```
$_ = "The brown fox jumps over the lazy dog";
/the (\S+)(?{ $color = $^N }) (\S+)(?{ $animal = $^N })/i;
print "color = $color, animal = $animal\n";
```
`(??{ *code* })` **WARNING**: Using this feature safely requires that you understand its limitations. Code executed that has side effects may not perform identically from version to version due to the effect of future optimisations in the regex engine. For more information on this, see ["Embedded Code Execution Frequency"](#Embedded-Code-Execution-Frequency).
This is a "postponed" regular subexpression. It behaves in *exactly* the same way as a `(?{ *code* })` code block as described above, except that its return value, rather than being assigned to `$^R`, is treated as a pattern, compiled if it's a string (or used as-is if its a qr// object), then matched as if it were inserted instead of this construct.
During the matching of this sub-pattern, it has its own set of captures which are valid during the sub-match, but are discarded once control returns to the main pattern. For example, the following matches, with the inner pattern capturing "B" and matching "BB", while the outer pattern captures "A";
```
my $inner = '(.)\1';
"ABBA" =~ /^(.)(??{ $inner })\1/;
print $1; # prints "A";
```
Note that this means that there is no way for the inner pattern to refer to a capture group defined outside. (The code block itself can use `$1`, *etc*., to refer to the enclosing pattern's capture groups.) Thus, although
```
('a' x 100)=~/(??{'(.)' x 100})/
```
*will* match, it will *not* set `$1` on exit.
The following pattern matches a parenthesized group:
```
$re = qr{
\(
(?:
(?> [^()]+ ) # Non-parens without backtracking
|
(??{ $re }) # Group with matching parens
)*
\)
}x;
```
See also [`(?*PARNO*)`](#%28%3FPARNO%29-%28%3F-PARNO%29-%28%3F%2BPARNO%29-%28%3FR%29-%28%3F0%29) for a different, more efficient way to accomplish the same task.
Executing a postponed regular expression too many times without consuming any input string will also result in a fatal error. The depth at which that happens is compiled into perl, so it can be changed with a custom build.
`(?*PARNO*)` `(?-*PARNO*)` `(?+*PARNO*)` `(?R)` `(?0)` Recursive subpattern. Treat the contents of a given capture buffer in the current pattern as an independent subpattern and attempt to match it at the current position in the string. Information about capture state from the caller for things like backreferences is available to the subpattern, but capture buffers set by the subpattern are not visible to the caller.
Similar to `(??{ *code* })` except that it does not involve executing any code or potentially compiling a returned pattern string; instead it treats the part of the current pattern contained within a specified capture group as an independent pattern that must match at the current position. Also different is the treatment of capture buffers, unlike `(??{ *code* })` recursive patterns have access to their caller's match state, so one can use backreferences safely.
*PARNO* is a sequence of digits (not starting with 0) whose value reflects the paren-number of the capture group to recurse to. `(?R)` recurses to the beginning of the whole pattern. `(?0)` is an alternate syntax for `(?R)`. If *PARNO* is preceded by a plus or minus sign then it is assumed to be relative, with negative numbers indicating preceding capture groups and positive ones following. Thus `(?-1)` refers to the most recently declared group, and `(?+1)` indicates the next group to be declared. Note that the counting for relative recursion differs from that of relative backreferences, in that with recursion unclosed groups **are** included.
The following pattern matches a function `foo()` which may contain balanced parentheses as the argument.
```
$re = qr{ ( # paren group 1 (full function)
foo
( # paren group 2 (parens)
\(
( # paren group 3 (contents of parens)
(?:
(?> [^()]+ ) # Non-parens without backtracking
|
(?2) # Recurse to start of paren group 2
)*
)
\)
)
)
}x;
```
If the pattern was used as follows
```
'foo(bar(baz)+baz(bop))'=~/$re/
and print "\$1 = $1\n",
"\$2 = $2\n",
"\$3 = $3\n";
```
the output produced should be the following:
```
$1 = foo(bar(baz)+baz(bop))
$2 = (bar(baz)+baz(bop))
$3 = bar(baz)+baz(bop)
```
If there is no corresponding capture group defined, then it is a fatal error. Recursing deeply without consuming any input string will also result in a fatal error. The depth at which that happens is compiled into perl, so it can be changed with a custom build.
The following shows how using negative indexing can make it easier to embed recursive patterns inside of a `qr//` construct for later use:
```
my $parens = qr/(\((?:[^()]++|(?-1))*+\))/;
if (/foo $parens \s+ \+ \s+ bar $parens/x) {
# do something here...
}
```
**Note** that this pattern does not behave the same way as the equivalent PCRE or Python construct of the same form. In Perl you can backtrack into a recursed group, in PCRE and Python the recursed into group is treated as atomic. Also, modifiers are resolved at compile time, so constructs like `(?i:(?1))` or `(?:(?i)(?1))` do not affect how the sub-pattern will be processed.
`(?&*NAME*)` Recurse to a named subpattern. Identical to `(?*PARNO*)` except that the parenthesis to recurse to is determined by name. If multiple parentheses have the same name, then it recurses to the leftmost.
It is an error to refer to a name that is not declared somewhere in the pattern.
**NOTE:** In order to make things easier for programmers with experience with the Python or PCRE regex engines the pattern `(?P>*NAME*)` may be used instead of `(?&*NAME*)`.
`(?(*condition*)*yes-pattern*|*no-pattern*)`
`(?(*condition*)*yes-pattern*)`
Conditional expression. Matches *yes-pattern* if *condition* yields a true value, matches *no-pattern* otherwise. A missing pattern always matches.
`(*condition*)` should be one of:
an integer in parentheses (which is valid if the corresponding pair of parentheses matched);
a lookahead/lookbehind/evaluate zero-width assertion;
a name in angle brackets or single quotes (which is valid if a group with the given name matched);
the special symbol `(R)`
(true when evaluated inside of recursion or eval). Additionally the `"R"` may be followed by a number, (which will be true when evaluated when recursing inside of the appropriate group), or by `&*NAME*`, in which case it will be true only when evaluated during recursion in the named group.
Here's a summary of the possible predicates:
`(1)` `(2)` ... Checks if the numbered capturing group has matched something. Full syntax: `(?(1)then|else)`
`(<*NAME*>)` `('*NAME*')`
Checks if a group with the given name has matched something. Full syntax: `(?(<name>)then|else)`
`(?=...)` `(?!...)` `(?<=...)` `(?<!...)`
Checks whether the pattern matches (or does not match, for the `"!"` variants). Full syntax: `(?(?=*lookahead*)*then*|*else*)`
`(?{ *CODE* })`
Treats the return value of the code block as the condition. Full syntax: `(?(?{ *code* })*then*|*else*)`
`(R)`
Checks if the expression has been evaluated inside of recursion. Full syntax: `(?(R)*then*|*else*)`
`(R1)` `(R2)` ... Checks if the expression has been evaluated while executing directly inside of the n-th capture group. This check is the regex equivalent of
```
if ((caller(0))[3] eq 'subname') { ... }
```
In other words, it does not check the full recursion stack.
Full syntax: `(?(R1)*then*|*else*)`
`(R&*NAME*)`
Similar to `(R1)`, this predicate checks to see if we're executing directly inside of the leftmost group with a given name (this is the same logic used by `(?&*NAME*)` to disambiguate). It does not check the full stack, but only the name of the innermost active recursion. Full syntax: `(?(R&*name*)*then*|*else*)`
`(DEFINE)`
In this case, the yes-pattern is never directly executed, and no no-pattern is allowed. Similar in spirit to `(?{0})` but more efficient. See below for details. Full syntax: `(?(DEFINE)*definitions*...)`
For example:
```
m{ ( \( )?
[^()]+
(?(1) \) )
}x
```
matches a chunk of non-parentheses, possibly included in parentheses themselves.
A special form is the `(DEFINE)` predicate, which never executes its yes-pattern directly, and does not allow a no-pattern. This allows one to define subpatterns which will be executed only by the recursion mechanism. This way, you can define a set of regular expression rules that can be bundled into any pattern you choose.
It is recommended that for this usage you put the DEFINE block at the end of the pattern, and that you name any subpatterns defined within it.
Also, it's worth noting that patterns defined this way probably will not be as efficient, as the optimizer is not very clever about handling them.
An example of how this might be used is as follows:
```
/(?<NAME>(?&NAME_PAT))(?<ADDR>(?&ADDRESS_PAT))
(?(DEFINE)
(?<NAME_PAT>....)
(?<ADDRESS_PAT>....)
)/x
```
Note that capture groups matched inside of recursion are not accessible after the recursion returns, so the extra layer of capturing groups is necessary. Thus `$+{NAME_PAT}` would not be defined even though `$+{NAME}` would be.
Finally, keep in mind that subpatterns created inside a DEFINE block count towards the absolute and relative number of captures, so this:
```
my @captures = "a" =~ /(.) # First capture
(?(DEFINE)
(?<EXAMPLE> 1 ) # Second capture
)/x;
say scalar @captures;
```
Will output 2, not 1. This is particularly important if you intend to compile the definitions with the `qr//` operator, and later interpolate them in another pattern.
`(?>*pattern*)`
`(*atomic:*pattern*)` An "independent" subexpression, one which matches the substring that a standalone *pattern* would match if anchored at the given position, and it matches *nothing other than this substring*. This construct is useful for optimizations of what would otherwise be "eternal" matches, because it will not backtrack (see ["Backtracking"](#Backtracking)). It may also be useful in places where the "grab all you can, and do not give anything back" semantic is desirable.
For example: `^(?>a*)ab` will never match, since `(?>a*)` (anchored at the beginning of string, as above) will match *all* characters `"a"` at the beginning of string, leaving no `"a"` for `ab` to match. In contrast, `a*ab` will match the same as `a+b`, since the match of the subgroup `a*` is influenced by the following group `ab` (see ["Backtracking"](#Backtracking)). In particular, `a*` inside `a*ab` will match fewer characters than a standalone `a*`, since this makes the tail match.
`(?>*pattern*)` does not disable backtracking altogether once it has matched. It is still possible to backtrack past the construct, but not into it. So `((?>a*)|(?>b*))ar` will still match "bar".
An effect similar to `(?>*pattern*)` may be achieved by writing `(?=(*pattern*))\g{-1}`. This matches the same substring as a standalone `a+`, and the following `\g{-1}` eats the matched string; it therefore makes a zero-length assertion into an analogue of `(?>...)`. (The difference between these two constructs is that the second one uses a capturing group, thus shifting ordinals of backreferences in the rest of a regular expression.)
Consider this pattern:
```
m{ \(
(
[^()]+ # x+
|
\( [^()]* \)
)+
\)
}x
```
That will efficiently match a nonempty group with matching parentheses two levels deep or less. However, if there is no such group, it will take virtually forever on a long string. That's because there are so many different ways to split a long string into several substrings. This is what `(.+)+` is doing, and `(.+)+` is similar to a subpattern of the above pattern. Consider how the pattern above detects no-match on `((()aaaaaaaaaaaaaaaaaa` in several seconds, but that each extra letter doubles this time. This exponential performance will make it appear that your program has hung. However, a tiny change to this pattern
```
m{ \(
(
(?> [^()]+ ) # change x+ above to (?> x+ )
|
\( [^()]* \)
)+
\)
}x
```
which uses `(?>...)` matches exactly when the one above does (verifying this yourself would be a productive exercise), but finishes in a fourth the time when used on a similar string with 1000000 `"a"`s. Be aware, however, that, when this construct is followed by a quantifier, it currently triggers a warning message under the `use warnings` pragma or **-w** switch saying it `"matches null string many times in regex"`.
On simple groups, such as the pattern `(?> [^()]+ )`, a comparable effect may be achieved by negative lookahead, as in `[^()]+ (?! [^()] )`. This was only 4 times slower on a string with 1000000 `"a"`s.
The "grab all you can, and do not give anything back" semantic is desirable in many situations where on the first sight a simple `()*` looks like the correct solution. Suppose we parse text with comments being delimited by `"#"` followed by some optional (horizontal) whitespace. Contrary to its appearance, `#[ \t]*` *is not* the correct subexpression to match the comment delimiter, because it may "give up" some whitespace if the remainder of the pattern can be made to match that way. The correct answer is either one of these:
```
(?>#[ \t]*)
#[ \t]*(?![ \t])
```
For example, to grab non-empty comments into `$1`, one should use either one of these:
```
/ (?> \# [ \t]* ) ( .+ ) /x;
/ \# [ \t]* ( [^ \t] .* ) /x;
```
Which one you pick depends on which of these expressions better reflects the above specification of comments.
In some literature this construct is called "atomic matching" or "possessive matching".
Possessive quantifiers are equivalent to putting the item they are applied to inside of one of these constructs. The following equivalences apply:
```
Quantifier Form Bracketing Form
--------------- ---------------
PAT*+ (?>PAT*)
PAT++ (?>PAT+)
PAT?+ (?>PAT?)
PAT{min,max}+ (?>PAT{min,max})
```
Nested `(?>...)` constructs are not no-ops, even if at first glance they might seem to be. This is because the nested `(?>...)` can restrict internal backtracking that otherwise might occur. For example,
```
"abc" =~ /(?>a[bc]*c)/
```
matches, but
```
"abc" =~ /(?>a(?>[bc]*)c)/
```
does not.
`(?[ ])`
See ["Extended Bracketed Character Classes" in perlrecharclass](perlrecharclass#Extended-Bracketed-Character-Classes).
### Backtracking
NOTE: This section presents an abstract approximation of regular expression behavior. For a more rigorous (and complicated) view of the rules involved in selecting a match among possible alternatives, see ["Combining RE Pieces"](#Combining-RE-Pieces).
A fundamental feature of regular expression matching involves the notion called *backtracking*, which is currently used (when needed) by all regular non-possessive expression quantifiers, namely `"*"`, `*?`, `"+"`, `+?`, `{n,m}`, and `{n,m}?`. Backtracking is often optimized internally, but the general principle outlined here is valid.
For a regular expression to match, the *entire* regular expression must match, not just part of it. So if the beginning of a pattern containing a quantifier succeeds in a way that causes later parts in the pattern to fail, the matching engine backs up and recalculates the beginning part--that's why it's called backtracking.
Here is an example of backtracking: Let's say you want to find the word following "foo" in the string "Food is on the foo table.":
```
$_ = "Food is on the foo table.";
if ( /\b(foo)\s+(\w+)/i ) {
print "$2 follows $1.\n";
}
```
When the match runs, the first part of the regular expression (`\b(foo)`) finds a possible match right at the beginning of the string, and loads up `$1` with "Foo". However, as soon as the matching engine sees that there's no whitespace following the "Foo" that it had saved in `$1`, it realizes its mistake and starts over again one character after where it had the tentative match. This time it goes all the way until the next occurrence of "foo". The complete regular expression matches this time, and you get the expected output of "table follows foo."
Sometimes minimal matching can help a lot. Imagine you'd like to match everything between "foo" and "bar". Initially, you write something like this:
```
$_ = "The food is under the bar in the barn.";
if ( /foo(.*)bar/ ) {
print "got <$1>\n";
}
```
Which perhaps unexpectedly yields:
```
got <d is under the bar in the >
```
That's because `.*` was greedy, so you get everything between the *first* "foo" and the *last* "bar". Here it's more effective to use minimal matching to make sure you get the text between a "foo" and the first "bar" thereafter.
```
if ( /foo(.*?)bar/ ) { print "got <$1>\n" }
got <d is under the >
```
Here's another example. Let's say you'd like to match a number at the end of a string, and you also want to keep the preceding part of the match. So you write this:
```
$_ = "I have 2 numbers: 53147";
if ( /(.*)(\d*)/ ) { # Wrong!
print "Beginning is <$1>, number is <$2>.\n";
}
```
That won't work at all, because `.*` was greedy and gobbled up the whole string. As `\d*` can match on an empty string the complete regular expression matched successfully.
```
Beginning is <I have 2 numbers: 53147>, number is <>.
```
Here are some variants, most of which don't work:
```
$_ = "I have 2 numbers: 53147";
@pats = qw{
(.*)(\d*)
(.*)(\d+)
(.*?)(\d*)
(.*?)(\d+)
(.*)(\d+)$
(.*?)(\d+)$
(.*)\b(\d+)$
(.*\D)(\d+)$
};
for $pat (@pats) {
printf "%-12s ", $pat;
if ( /$pat/ ) {
print "<$1> <$2>\n";
} else {
print "FAIL\n";
}
}
```
That will print out:
```
(.*)(\d*) <I have 2 numbers: 53147> <>
(.*)(\d+) <I have 2 numbers: 5314> <7>
(.*?)(\d*) <> <>
(.*?)(\d+) <I have > <2>
(.*)(\d+)$ <I have 2 numbers: 5314> <7>
(.*?)(\d+)$ <I have 2 numbers: > <53147>
(.*)\b(\d+)$ <I have 2 numbers: > <53147>
(.*\D)(\d+)$ <I have 2 numbers: > <53147>
```
As you see, this can be a bit tricky. It's important to realize that a regular expression is merely a set of assertions that gives a definition of success. There may be 0, 1, or several different ways that the definition might succeed against a particular string. And if there are multiple ways it might succeed, you need to understand backtracking to know which variety of success you will achieve.
When using lookahead assertions and negations, this can all get even trickier. Imagine you'd like to find a sequence of non-digits not followed by "123". You might try to write that as
```
$_ = "ABC123";
if ( /^\D*(?!123)/ ) { # Wrong!
print "Yup, no 123 in $_\n";
}
```
But that isn't going to match; at least, not the way you're hoping. It claims that there is no 123 in the string. Here's a clearer picture of why that pattern matches, contrary to popular expectations:
```
$x = 'ABC123';
$y = 'ABC445';
print "1: got $1\n" if $x =~ /^(ABC)(?!123)/;
print "2: got $1\n" if $y =~ /^(ABC)(?!123)/;
print "3: got $1\n" if $x =~ /^(\D*)(?!123)/;
print "4: got $1\n" if $y =~ /^(\D*)(?!123)/;
```
This prints
```
2: got ABC
3: got AB
4: got ABC
```
You might have expected test 3 to fail because it seems to a more general purpose version of test 1. The important difference between them is that test 3 contains a quantifier (`\D*`) and so can use backtracking, whereas test 1 will not. What's happening is that you've asked "Is it true that at the start of `$x`, following 0 or more non-digits, you have something that's not 123?" If the pattern matcher had let `\D*` expand to "ABC", this would have caused the whole pattern to fail.
The search engine will initially match `\D*` with "ABC". Then it will try to match `(?!123)` with "123", which fails. But because a quantifier (`\D*`) has been used in the regular expression, the search engine can backtrack and retry the match differently in the hope of matching the complete regular expression.
The pattern really, *really* wants to succeed, so it uses the standard pattern back-off-and-retry and lets `\D*` expand to just "AB" this time. Now there's indeed something following "AB" that is not "123". It's "C123", which suffices.
We can deal with this by using both an assertion and a negation. We'll say that the first part in `$1` must be followed both by a digit and by something that's not "123". Remember that the lookaheads are zero-width expressions--they only look, but don't consume any of the string in their match. So rewriting this way produces what you'd expect; that is, case 5 will fail, but case 6 succeeds:
```
print "5: got $1\n" if $x =~ /^(\D*)(?=\d)(?!123)/;
print "6: got $1\n" if $y =~ /^(\D*)(?=\d)(?!123)/;
6: got ABC
```
In other words, the two zero-width assertions next to each other work as though they're ANDed together, just as you'd use any built-in assertions: `/^$/` matches only if you're at the beginning of the line AND the end of the line simultaneously. The deeper underlying truth is that juxtaposition in regular expressions always means AND, except when you write an explicit OR using the vertical bar. `/ab/` means match "a" AND (then) match "b", although the attempted matches are made at different positions because "a" is not a zero-width assertion, but a one-width assertion.
**WARNING**: Particularly complicated regular expressions can take exponential time to solve because of the immense number of possible ways they can use backtracking to try for a match. For example, without internal optimizations done by the regular expression engine, this will take a painfully long time to run:
```
'aaaaaaaaaaaa' =~ /((a{0,5}){0,5})*[c]/
```
And if you used `"*"`'s in the internal groups instead of limiting them to 0 through 5 matches, then it would take forever--or until you ran out of stack space. Moreover, these internal optimizations are not always applicable. For example, if you put `{0,5}` instead of `"*"` on the external group, no current optimization is applicable, and the match takes a long time to finish.
A powerful tool for optimizing such beasts is what is known as an "independent group", which does not backtrack (see `["(?>pattern)"](#%28%3F%3Epattern%29)`). Note also that zero-length lookahead/lookbehind assertions will not backtrack to make the tail match, since they are in "logical" context: only whether they match is considered relevant. For an example where side-effects of lookahead *might* have influenced the following match, see `["(?>pattern)"](#%28%3F%3Epattern%29)`.
###
Script Runs
A script run is basically a sequence of characters, all from the same Unicode script (see ["Scripts" in perlunicode](perlunicode#Scripts)), such as Latin or Greek. In most places a single word would never be written in multiple scripts, unless it is a spoofing attack. An infamous example, is
```
paypal.com
```
Those letters could all be Latin (as in the example just above), or they could be all Cyrillic (except for the dot), or they could be a mixture of the two. In the case of an internet address the `.com` would be in Latin, And any Cyrillic ones would cause it to be a mixture, not a script run. Someone clicking on such a link would not be directed to the real Paypal website, but an attacker would craft a look-alike one to attempt to gather sensitive information from the person.
Starting in Perl 5.28, it is now easy to detect strings that aren't script runs. Simply enclose just about any pattern like either of these:
```
(*script_run:pattern)
(*sr:pattern)
```
What happens is that after *pattern* succeeds in matching, it is subjected to the additional criterion that every character in it must be from the same script (see exceptions below). If this isn't true, backtracking occurs until something all in the same script is found that matches, or all possibilities are exhausted. This can cause a lot of backtracking, but generally, only malicious input will result in this, though the slow down could cause a denial of service attack. If your needs permit, it is best to make the pattern atomic to cut down on the amount of backtracking. This is so likely to be what you want, that instead of writing this:
```
(*script_run:(?>pattern))
```
you can write either of these:
```
(*atomic_script_run:pattern)
(*asr:pattern)
```
(See `["(?>*pattern*)"](#%28%3F%3Epattern%29)`.)
In Taiwan, Japan, and Korea, it is common for text to have a mixture of characters from their native scripts and base Chinese. Perl follows Unicode's UTS 39 (<https://unicode.org/reports/tr39/>) Unicode Security Mechanisms in allowing such mixtures. For example, the Japanese scripts Katakana and Hiragana are commonly mixed together in practice, along with some Chinese characters, and hence are treated as being in a single script run by Perl.
The rules used for matching decimal digits are slightly stricter. Many scripts have their own sets of digits equivalent to the Western `0` through `9` ones. A few, such as Arabic, have more than one set. For a string to be considered a script run, all digits in it must come from the same set of ten, as determined by the first digit encountered. As an example,
```
qr/(*script_run: \d+ \b )/x
```
guarantees that the digits matched will all be from the same set of 10. You won't get a look-alike digit from a different script that has a different value than what it appears to be.
Unicode has three pseudo scripts that are handled specially.
"Unknown" is applied to code points whose meaning has yet to be determined. Perl currently will match as a script run, any single character string consisting of one of these code points. But any string longer than one code point containing one of these will not be considered a script run.
"Inherited" is applied to characters that modify another, such as an accent of some type. These are considered to be in the script of the master character, and so never cause a script run to not match.
The other one is "Common". This consists of mostly punctuation, emoji, and characters used in mathematics and music, the ASCII digits `0` through `9`, and full-width forms of these digits. These characters can appear intermixed in text in many of the world's scripts. These also don't cause a script run to not match. But like other scripts, all digits in a run must come from the same set of 10.
This construct is non-capturing. You can add parentheses to *pattern* to capture, if desired. You will have to do this if you plan to use ["(\*ACCEPT) (\*ACCEPT:arg)"](#%28%2AACCEPT%29-%28%2AACCEPT%3Aarg%29) and not have it bypass the script run checking.
The `Script_Extensions` property as modified by UTS 39 (<https://unicode.org/reports/tr39/>) is used as the basis for this feature.
To summarize,
* All length 0 or length 1 sequences are script runs.
* A longer sequence is a script run if and only if **all** of the following conditions are met:
1. No code point in the sequence has the `Script_Extension` property of `Unknown`.
This currently means that all code points in the sequence have been assigned by Unicode to be characters that aren't private use nor surrogate code points.
2. All characters in the sequence come from the Common script and/or the Inherited script and/or a single other script.
The script of a character is determined by the `Script_Extensions` property as modified by UTS 39 (<https://unicode.org/reports/tr39/>), as described above.
3. All decimal digits in the sequence come from the same block of 10 consecutive digits.
###
Special Backtracking Control Verbs
These special patterns are generally of the form `(**VERB*:*arg*)`. Unless otherwise stated the *arg* argument is optional; in some cases, it is mandatory.
Any pattern containing a special backtracking verb that allows an argument has the special behaviour that when executed it sets the current package's `$REGERROR` and `$REGMARK` variables. When doing so the following rules apply:
On failure, the `$REGERROR` variable will be set to the *arg* value of the verb pattern, if the verb was involved in the failure of the match. If the *arg* part of the pattern was omitted, then `$REGERROR` will be set to the name of the last `(*MARK:*NAME*)` pattern executed, or to TRUE if there was none. Also, the `$REGMARK` variable will be set to FALSE.
On a successful match, the `$REGERROR` variable will be set to FALSE, and the `$REGMARK` variable will be set to the name of the last `(*MARK:*NAME*)` pattern executed. See the explanation for the `(*MARK:*NAME*)` verb below for more details.
**NOTE:** `$REGERROR` and `$REGMARK` are not magic variables like `$1` and most other regex-related variables. They are not local to a scope, nor readonly, but instead are volatile package variables similar to `$AUTOLOAD`. They are set in the package containing the code that *executed* the regex (rather than the one that compiled it, where those differ). If necessary, you can use `local` to localize changes to these variables to a specific scope before executing a regex.
If a pattern does not contain a special backtracking verb that allows an argument, then `$REGERROR` and `$REGMARK` are not touched at all.
Verbs
`(*PRUNE)` `(*PRUNE:*NAME*)` This zero-width pattern prunes the backtracking tree at the current point when backtracked into on failure. Consider the pattern `/*A* (*PRUNE) *B*/`, where *A* and *B* are complex patterns. Until the `(*PRUNE)` verb is reached, *A* may backtrack as necessary to match. Once it is reached, matching continues in *B*, which may also backtrack as necessary; however, should B not match, then no further backtracking will take place, and the pattern will fail outright at the current starting position.
The following example counts all the possible matching strings in a pattern (without actually matching any of them).
```
'aaab' =~ /a+b?(?{print "$&\n"; $count++})(*FAIL)/;
print "Count=$count\n";
```
which produces:
```
aaab
aaa
aa
a
aab
aa
a
ab
a
Count=9
```
If we add a `(*PRUNE)` before the count like the following
```
'aaab' =~ /a+b?(*PRUNE)(?{print "$&\n"; $count++})(*FAIL)/;
print "Count=$count\n";
```
we prevent backtracking and find the count of the longest matching string at each matching starting point like so:
```
aaab
aab
ab
Count=3
```
Any number of `(*PRUNE)` assertions may be used in a pattern.
See also `["(?>*pattern*)"](#%28%3F%3Epattern%29)` and possessive quantifiers for other ways to control backtracking. In some cases, the use of `(*PRUNE)` can be replaced with a `(?>pattern)` with no functional difference; however, `(*PRUNE)` can be used to handle cases that cannot be expressed using a `(?>pattern)` alone.
`(*SKIP)` `(*SKIP:*NAME*)` This zero-width pattern is similar to `(*PRUNE)`, except that on failure it also signifies that whatever text that was matched leading up to the `(*SKIP)` pattern being executed cannot be part of *any* match of this pattern. This effectively means that the regex engine "skips" forward to this position on failure and tries to match again, (assuming that there is sufficient room to match).
The name of the `(*SKIP:*NAME*)` pattern has special significance. If a `(*MARK:*NAME*)` was encountered while matching, then it is that position which is used as the "skip point". If no `(*MARK)` of that name was encountered, then the `(*SKIP)` operator has no effect. When used without a name the "skip point" is where the match point was when executing the `(*SKIP)` pattern.
Compare the following to the examples in `(*PRUNE)`; note the string is twice as long:
```
'aaabaaab' =~ /a+b?(*SKIP)(?{print "$&\n"; $count++})(*FAIL)/;
print "Count=$count\n";
```
outputs
```
aaab
aaab
Count=2
```
Once the 'aaab' at the start of the string has matched, and the `(*SKIP)` executed, the next starting point will be where the cursor was when the `(*SKIP)` was executed.
`(*MARK:*NAME*)` `(*:*NAME*)` This zero-width pattern can be used to mark the point reached in a string when a certain part of the pattern has been successfully matched. This mark may be given a name. A later `(*SKIP)` pattern will then skip forward to that point if backtracked into on failure. Any number of `(*MARK)` patterns are allowed, and the *NAME* portion may be duplicated.
In addition to interacting with the `(*SKIP)` pattern, `(*MARK:*NAME*)` can be used to "label" a pattern branch, so that after matching, the program can determine which branches of the pattern were involved in the match.
When a match is successful, the `$REGMARK` variable will be set to the name of the most recently executed `(*MARK:*NAME*)` that was involved in the match.
This can be used to determine which branch of a pattern was matched without using a separate capture group for each branch, which in turn can result in a performance improvement, as perl cannot optimize `/(?:(x)|(y)|(z))/` as efficiently as something like `/(?:x(*MARK:x)|y(*MARK:y)|z(*MARK:z))/`.
When a match has failed, and unless another verb has been involved in failing the match and has provided its own name to use, the `$REGERROR` variable will be set to the name of the most recently executed `(*MARK:*NAME*)`.
See ["(\*SKIP)"](#%28%2ASKIP%29) for more details.
As a shortcut `(*MARK:*NAME*)` can be written `(*:*NAME*)`.
`(*THEN)` `(*THEN:*NAME*)`
This is similar to the "cut group" operator `::` from Raku. Like `(*PRUNE)`, this verb always matches, and when backtracked into on failure, it causes the regex engine to try the next alternation in the innermost enclosing group (capturing or otherwise) that has alternations. The two branches of a `(?(*condition*)*yes-pattern*|*no-pattern*)` do not count as an alternation, as far as `(*THEN)` is concerned.
Its name comes from the observation that this operation combined with the alternation operator (`"|"`) can be used to create what is essentially a pattern-based if/then/else block:
```
( COND (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ )
```
Note that if this operator is used and NOT inside of an alternation then it acts exactly like the `(*PRUNE)` operator.
```
/ A (*PRUNE) B /
```
is the same as
```
/ A (*THEN) B /
```
but
```
/ ( A (*THEN) B | C ) /
```
is not the same as
```
/ ( A (*PRUNE) B | C ) /
```
as after matching the *A* but failing on the *B* the `(*THEN)` verb will backtrack and try *C*; but the `(*PRUNE)` verb will simply fail.
`(*COMMIT)` `(*COMMIT:*arg*)` This is the Raku "commit pattern" `<commit>` or `:::`. It's a zero-width pattern similar to `(*SKIP)`, except that when backtracked into on failure it causes the match to fail outright. No further attempts to find a valid match by advancing the start pointer will occur again. For example,
```
'aaabaaab' =~ /a+b?(*COMMIT)(?{print "$&\n"; $count++})(*FAIL)/;
print "Count=$count\n";
```
outputs
```
aaab
Count=1
```
In other words, once the `(*COMMIT)` has been entered, and if the pattern does not match, the regex engine will not try any further matching on the rest of the string.
`(*FAIL)` `(*F)` `(*FAIL:*arg*)` This pattern matches nothing and always fails. It can be used to force the engine to backtrack. It is equivalent to `(?!)`, but easier to read. In fact, `(?!)` gets optimised into `(*FAIL)` internally. You can provide an argument so that if the match fails because of this `FAIL` directive the argument can be obtained from `$REGERROR`.
It is probably useful only when combined with `(?{})` or `(??{})`.
`(*ACCEPT)` `(*ACCEPT:*arg*)` This pattern matches nothing and causes the end of successful matching at the point at which the `(*ACCEPT)` pattern was encountered, regardless of whether there is actually more to match in the string. When inside of a nested pattern, such as recursion, or in a subpattern dynamically generated via `(??{})`, only the innermost pattern is ended immediately.
If the `(*ACCEPT)` is inside of capturing groups then the groups are marked as ended at the point at which the `(*ACCEPT)` was encountered. For instance:
```
'AB' =~ /(A (A|B(*ACCEPT)|C) D)(E)/x;
```
will match, and `$1` will be `AB` and `$2` will be `"B"`, `$3` will not be set. If another branch in the inner parentheses was matched, such as in the string 'ACDE', then the `"D"` and `"E"` would have to be matched as well.
You can provide an argument, which will be available in the var `$REGMARK` after the match completes.
###
Warning on `\1` Instead of `$1`
Some people get too used to writing things like:
```
$pattern =~ s/(\W)/\\\1/g;
```
This is grandfathered (for \1 to \9) for the RHS of a substitute to avoid shocking the **sed** addicts, but it's a dirty habit to get into. That's because in PerlThink, the righthand side of an `s///` is a double-quoted string. `\1` in the usual double-quoted string means a control-A. The customary Unix meaning of `\1` is kludged in for `s///`. However, if you get into the habit of doing that, you get yourself into trouble if you then add an `/e` modifier.
```
s/(\d+)/ \1 + 1 /eg; # causes warning under -w
```
Or if you try to do
```
s/(\d+)/\1000/;
```
You can't disambiguate that by saying `\{1}000`, whereas you can fix it with `${1}000`. The operation of interpolation should not be confused with the operation of matching a backreference. Certainly they mean two different things on the *left* side of the `s///`.
###
Repeated Patterns Matching a Zero-length Substring
**WARNING**: Difficult material (and prose) ahead. This section needs a rewrite.
Regular expressions provide a terse and powerful programming language. As with most other power tools, power comes together with the ability to wreak havoc.
A common abuse of this power stems from the ability to make infinite loops using regular expressions, with something as innocuous as:
```
'foo' =~ m{ ( o? )* }x;
```
The `o?` matches at the beginning of "`foo`", and since the position in the string is not moved by the match, `o?` would match again and again because of the `"*"` quantifier. Another common way to create a similar cycle is with the looping modifier `/g`:
```
@matches = ( 'foo' =~ m{ o? }xg );
```
or
```
print "match: <$&>\n" while 'foo' =~ m{ o? }xg;
```
or the loop implied by `split()`.
However, long experience has shown that many programming tasks may be significantly simplified by using repeated subexpressions that may match zero-length substrings. Here's a simple example being:
```
@chars = split //, $string; # // is not magic in split
($whitewashed = $string) =~ s/()/ /g; # parens avoid magic s// /
```
Thus Perl allows such constructs, by *forcefully breaking the infinite loop*. The rules for this are different for lower-level loops given by the greedy quantifiers `*+{}`, and for higher-level ones like the `/g` modifier or `split()` operator.
The lower-level loops are *interrupted* (that is, the loop is broken) when Perl detects that a repeated expression matched a zero-length substring. Thus
```
m{ (?: NON_ZERO_LENGTH | ZERO_LENGTH )* }x;
```
is made equivalent to
```
m{ (?: NON_ZERO_LENGTH )* (?: ZERO_LENGTH )? }x;
```
For example, this program
```
#!perl -l
"aaaaab" =~ /
(?:
a # non-zero
| # or
(?{print "hello"}) # print hello whenever this
# branch is tried
(?=(b)) # zero-width assertion
)* # any number of times
/x;
print $&;
print $1;
```
prints
```
hello
aaaaa
b
```
Notice that "hello" is only printed once, as when Perl sees that the sixth iteration of the outermost `(?:)*` matches a zero-length string, it stops the `"*"`.
The higher-level loops preserve an additional state between iterations: whether the last match was zero-length. To break the loop, the following match after a zero-length match is prohibited to have a length of zero. This prohibition interacts with backtracking (see ["Backtracking"](#Backtracking)), and so the *second best* match is chosen if the *best* match is of zero length.
For example:
```
$_ = 'bar';
s/\w??/<$&>/g;
```
results in `<><b><><a><><r><>`. At each position of the string the best match given by non-greedy `??` is the zero-length match, and the *second best* match is what is matched by `\w`. Thus zero-length matches alternate with one-character-long matches.
Similarly, for repeated `m/()/g` the second-best match is the match at the position one notch further in the string.
The additional state of being *matched with zero-length* is associated with the matched string, and is reset by each assignment to `pos()`. Zero-length matches at the end of the previous match are ignored during `split`.
###
Combining RE Pieces
Each of the elementary pieces of regular expressions which were described before (such as `ab` or `\Z`) could match at most one substring at the given position of the input string. However, in a typical regular expression these elementary pieces are combined into more complicated patterns using combining operators `ST`, `S|T`, `S*` *etc*. (in these examples `"S"` and `"T"` are regular subexpressions).
Such combinations can include alternatives, leading to a problem of choice: if we match a regular expression `a|ab` against `"abc"`, will it match substring `"a"` or `"ab"`? One way to describe which substring is actually matched is the concept of backtracking (see ["Backtracking"](#Backtracking)). However, this description is too low-level and makes you think in terms of a particular implementation.
Another description starts with notions of "better"/"worse". All the substrings which may be matched by the given regular expression can be sorted from the "best" match to the "worst" match, and it is the "best" match which is chosen. This substitutes the question of "what is chosen?" by the question of "which matches are better, and which are worse?".
Again, for elementary pieces there is no such question, since at most one match at a given position is possible. This section describes the notion of better/worse for combining operators. In the description below `"S"` and `"T"` are regular subexpressions.
`ST` Consider two possible matches, `AB` and `A'B'`, `"A"` and `A'` are substrings which can be matched by `"S"`, `"B"` and `B'` are substrings which can be matched by `"T"`.
If `"A"` is a better match for `"S"` than `A'`, `AB` is a better match than `A'B'`.
If `"A"` and `A'` coincide: `AB` is a better match than `AB'` if `"B"` is a better match for `"T"` than `B'`.
`S|T`
When `"S"` can match, it is a better match than when only `"T"` can match.
Ordering of two matches for `"S"` is the same as for `"S"`. Similar for two matches for `"T"`.
`S{REPEAT_COUNT}`
Matches as `SSS...S` (repeated as many times as necessary).
`S{min,max}`
Matches as `S{max}|S{max-1}|...|S{min+1}|S{min}`.
`S{min,max}?`
Matches as `S{min}|S{min+1}|...|S{max-1}|S{max}`.
`S?`, `S*`, `S+`
Same as `S{0,1}`, `S{0,BIG_NUMBER}`, `S{1,BIG_NUMBER}` respectively.
`S??`, `S*?`, `S+?`
Same as `S{0,1}?`, `S{0,BIG_NUMBER}?`, `S{1,BIG_NUMBER}?` respectively.
`(?>S)`
Matches the best match for `"S"` and only that.
`(?=S)`, `(?<=S)`
Only the best match for `"S"` is considered. (This is important only if `"S"` has capturing parentheses, and backreferences are used somewhere else in the whole regular expression.)
`(?!S)`, `(?<!S)`
For this grouping operator there is no need to describe the ordering, since only whether or not `"S"` can match is important.
`(??{ *EXPR* })`, `(?*PARNO*)`
The ordering is the same as for the regular expression which is the result of *EXPR*, or the pattern contained by capture group *PARNO*.
`(?(*condition*)*yes-pattern*|*no-pattern*)`
Recall that which of *yes-pattern* or *no-pattern* actually matches is already determined. The ordering of the matches is the same as for the chosen subexpression.
The above recipes describe the ordering of matches *at a given position*. One more rule is needed to understand how a match is determined for the whole regular expression: a match at an earlier position is always better than a match at a later position.
###
Creating Custom RE Engines
As of Perl 5.10.0, one can create custom regular expression engines. This is not for the faint of heart, as they have to plug in at the C level. See <perlreapi> for more details.
As an alternative, overloaded constants (see <overload>) provide a simple way to extend the functionality of the RE engine, by substituting one pattern for another.
Suppose that we want to enable a new RE escape-sequence `\Y|` which matches at a boundary between whitespace characters and non-whitespace characters. Note that `(?=\S)(?<!\S)|(?!\S)(?<=\S)` matches exactly at these positions, so we want to have each `\Y|` in the place of the more complicated version. We can create a module `customre` to do this:
```
package customre;
use overload;
sub import {
shift;
die "No argument to customre::import allowed" if @_;
overload::constant 'qr' => \&convert;
}
sub invalid { die "/$_[0]/: invalid escape '\\$_[1]'"}
# We must also take care of not escaping the legitimate \\Y|
# sequence, hence the presence of '\\' in the conversion rules.
my %rules = ( '\\' => '\\\\',
'Y|' => qr/(?=\S)(?<!\S)|(?!\S)(?<=\S)/ );
sub convert {
my $re = shift;
$re =~ s{
\\ ( \\ | Y . )
}
{ $rules{$1} or invalid($re,$1) }sgex;
return $re;
}
```
Now `use customre` enables the new escape in constant regular expressions, *i.e.*, those without any runtime variable interpolations. As documented in <overload>, this conversion will work only over literal parts of regular expressions. For `\Y|$re\Y|` the variable part of this regular expression needs to be converted explicitly (but only if the special meaning of `\Y|` should be enabled inside `$re`):
```
use customre;
$re = <>;
chomp $re;
$re = customre::convert $re;
/\Y|$re\Y|/;
```
###
Embedded Code Execution Frequency
The exact rules for how often `(??{})` and `(?{})` are executed in a pattern are unspecified. In the case of a successful match you can assume that they DWIM and will be executed in left to right order the appropriate number of times in the accepting path of the pattern as would any other meta-pattern. How non-accepting pathways and match failures affect the number of times a pattern is executed is specifically unspecified and may vary depending on what optimizations can be applied to the pattern and is likely to change from version to version.
For instance in
```
"aaabcdeeeee"=~/a(?{print "a"})b(?{print "b"})cde/;
```
the exact number of times "a" or "b" are printed out is unspecified for failure, but you may assume they will be printed at least once during a successful match, additionally you may assume that if "b" is printed, it will be preceded by at least one "a".
In the case of branching constructs like the following:
```
/a(b|(?{ print "a" }))c(?{ print "c" })/;
```
you can assume that the input "ac" will output "ac", and that "abc" will output only "c".
When embedded code is quantified, successful matches will call the code once for each matched iteration of the quantifier. For example:
```
"good" =~ /g(?:o(?{print "o"}))*d/;
```
will output "o" twice.
###
PCRE/Python Support
As of Perl 5.10.0, Perl supports several Python/PCRE-specific extensions to the regex syntax. While Perl programmers are encouraged to use the Perl-specific syntax, the following are also accepted:
`(?P<*NAME*>*pattern*)`
Define a named capture group. Equivalent to `(?<*NAME*>*pattern*)`.
`(?P=*NAME*)`
Backreference to a named capture group. Equivalent to `\g{*NAME*}`.
`(?P>*NAME*)`
Subroutine call to a named capture group. Equivalent to `(?&*NAME*)`.
BUGS
----
There are a number of issues with regard to case-insensitive matching in Unicode rules. See `"i"` under ["Modifiers"](#Modifiers) above.
This document varies from difficult to understand to completely and utterly opaque. The wandering prose riddled with jargon is hard to fathom in several places.
This document needs a rewrite that separates the tutorial content from the reference content.
SEE ALSO
---------
The syntax of patterns used in Perl pattern matching evolved from those supplied in the Bell Labs Research Unix 8th Edition (Version 8) regex routines. (The code is actually derived (distantly) from Henry Spencer's freely redistributable reimplementation of those V8 routines.)
<perlrequick>.
<perlretut>.
["Regexp Quote-Like Operators" in perlop](perlop#Regexp-Quote-Like-Operators).
["Gory details of parsing quoted constructs" in perlop](perlop#Gory-details-of-parsing-quoted-constructs).
<perlfaq6>.
["pos" in perlfunc](perlfunc#pos).
<perllocale>.
<perlebcdic>.
*Mastering Regular Expressions* by Jeffrey Friedl, published by O'Reilly and Associates.
| programming_docs |
perl ExtUtils::ParseXS::Utilities ExtUtils::ParseXS::Utilities
============================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [SUBROUTINES](#SUBROUTINES)
+ [standard\_typemap\_locations()](#standard_typemap_locations())
+ [trim\_whitespace()](#trim_whitespace())
+ [C\_string()](#C_string())
+ [valid\_proto\_string()](#valid_proto_string())
+ [process\_typemaps()](#process_typemaps())
+ [map\_type()](#map_type())
+ [standard\_XS\_defs()](#standard_XS_defs())
+ [assign\_func\_args()](#assign_func_args())
+ [analyze\_preprocessor\_statements()](#analyze_preprocessor_statements())
+ [set\_cond()](#set_cond())
+ [current\_line\_number()](#current_line_number())
+ [Warn()](#Warn())
+ [blurt()](#blurt())
+ [death()](#death())
+ [check\_conditional\_preprocessor\_statements()](#check_conditional_preprocessor_statements())
+ [escape\_file\_for\_line\_directive()](#escape_file_for_line_directive())
+ [report\_typemap\_failure](#report_typemap_failure)
NAME
----
ExtUtils::ParseXS::Utilities - Subroutines used with ExtUtils::ParseXS
SYNOPSIS
--------
```
use ExtUtils::ParseXS::Utilities qw(
standard_typemap_locations
trim_whitespace
C_string
valid_proto_string
process_typemaps
map_type
standard_XS_defs
assign_func_args
analyze_preprocessor_statements
set_cond
Warn
blurt
death
check_conditional_preprocessor_statements
escape_file_for_line_directive
report_typemap_failure
);
```
SUBROUTINES
-----------
The following functions are not considered to be part of the public interface. They are documented here for the benefit of future maintainers of this module.
###
`standard_typemap_locations()`
* Purpose
Provide a list of filepaths where *typemap* files may be found. The filepaths -- relative paths to files (not just directory paths) -- appear in this list in lowest-to-highest priority.
The highest priority is to look in the current directory.
```
'typemap'
```
The second and third highest priorities are to look in the parent of the current directory and a directory called *lib/ExtUtils* underneath the parent directory.
```
'../typemap',
'../lib/ExtUtils/typemap',
```
The fourth through ninth highest priorities are to look in the corresponding grandparent, great-grandparent and great-great-grandparent directories.
```
'../../typemap',
'../../lib/ExtUtils/typemap',
'../../../typemap',
'../../../lib/ExtUtils/typemap',
'../../../../typemap',
'../../../../lib/ExtUtils/typemap',
```
The tenth and subsequent priorities are to look in directories named *ExtUtils* which are subdirectories of directories found in `@INC` -- *provided* a file named *typemap* actually exists in such a directory. Example:
```
'/usr/local/lib/perl5/5.10.1/ExtUtils/typemap',
```
However, these filepaths appear in the list returned by `standard_typemap_locations()` in reverse order, *i.e.*, lowest-to-highest.
```
'/usr/local/lib/perl5/5.10.1/ExtUtils/typemap',
'../../../../lib/ExtUtils/typemap',
'../../../../typemap',
'../../../lib/ExtUtils/typemap',
'../../../typemap',
'../../lib/ExtUtils/typemap',
'../../typemap',
'../lib/ExtUtils/typemap',
'../typemap',
'typemap'
```
* Arguments
```
my @stl = standard_typemap_locations( \@INC );
```
Reference to `@INC`.
* Return Value
Array holding list of directories to be searched for *typemap* files.
###
`trim_whitespace()`
* Purpose
Perform an in-place trimming of leading and trailing whitespace from the first argument provided to the function.
* Argument
```
trim_whitespace($arg);
```
* Return Value
None. Remember: this is an *in-place* modification of the argument.
###
`C_string()`
* Purpose
Escape backslashes (`\`) in prototype strings.
* Arguments
```
$ProtoThisXSUB = C_string($_);
```
String needing escaping.
* Return Value
Properly escaped string.
###
`valid_proto_string()`
* Purpose
Validate prototype string.
* Arguments
String needing checking.
* Return Value
Upon success, returns the same string passed as argument.
Upon failure, returns `0`.
###
`process_typemaps()`
* Purpose
Process all typemap files.
* Arguments
```
my $typemaps_object = process_typemaps( $args{typemap}, $pwd );
```
List of two elements: `typemap` element from `%args`; current working directory.
* Return Value
Upon success, returns an <ExtUtils::Typemaps> object.
###
`map_type()`
* Purpose
Performs a mapping at several places inside `PARAGRAPH` loop.
* Arguments
```
$type = map_type($self, $type, $varname);
```
List of three arguments.
* Return Value
String holding augmented version of second argument.
###
`standard_XS_defs()`
* Purpose
Writes to the `.c` output file certain preprocessor directives and function headers needed in all such files.
* Arguments
None.
* Return Value
Returns true.
###
`assign_func_args()`
* Purpose
Perform assignment to the `func_args` attribute.
* Arguments
```
$string = assign_func_args($self, $argsref, $class);
```
List of three elements. Second is an array reference; third is a string.
* Return Value
String.
###
`analyze_preprocessor_statements()`
* Purpose
Within each function inside each Xsub, print to the *.c* output file certain preprocessor statements.
* Arguments
```
( $self, $XSS_work_idx, $BootCode_ref ) =
analyze_preprocessor_statements(
$self, $statement, $XSS_work_idx, $BootCode_ref
);
```
List of four elements.
* Return Value
Modifed values of three of the arguments passed to the function. In particular, the `XSStack` and `InitFileCode` attributes are modified.
###
`set_cond()`
* Purpose
* Arguments
* Return Value
###
`current_line_number()`
* Purpose
Figures out the current line number in the XS file.
* Arguments
`$self`
* Return Value
The current line number.
###
`Warn()`
* Purpose
* Arguments
* Return Value
###
`blurt()`
* Purpose
* Arguments
* Return Value
###
`death()`
* Purpose
* Arguments
* Return Value
###
`check_conditional_preprocessor_statements()`
* Purpose
* Arguments
* Return Value
###
`escape_file_for_line_directive()`
* Purpose
Escapes a given code source name (typically a file name but can also be a command that was read from) so that double-quotes and backslashes are escaped.
* Arguments
A string.
* Return Value
A string with escapes for double-quotes and backslashes.
### `report_typemap_failure`
* Purpose
Do error reporting for missing typemaps.
* Arguments
The `ExtUtils::ParseXS` object.
An `ExtUtils::Typemaps` object.
The string that represents the C type that was not found in the typemap.
Optionally, the string `death` or `blurt` to choose whether the error is immediately fatal or not. Default: `blurt`
* Return Value
Returns nothing. Depending on the arguments, this may call `death` or `blurt`, the former of which is fatal.
perl ExtUtils::CBuilder::Platform::Windows ExtUtils::CBuilder::Platform::Windows
=====================================
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
* [AUTHOR](#AUTHOR)
* [SEE ALSO](#SEE-ALSO)
NAME
----
ExtUtils::CBuilder::Platform::Windows - Builder class for Windows platforms
DESCRIPTION
-----------
This module implements the Windows-specific parts of ExtUtils::CBuilder. Most of the Windows-specific stuff has to do with compiling and linking C code. Currently we support the 3 compilers perl itself supports: MSVC, BCC, and GCC.
This module inherits from `ExtUtils::CBuilder::Base`, so any functionality not implemented here will be implemented there. The interfaces are defined by the <ExtUtils::CBuilder> documentation.
AUTHOR
------
Ken Williams <[email protected]>
Most of the code here was written by Randy W. Sims <[email protected]>.
SEE ALSO
---------
perl(1), ExtUtils::CBuilder(3), ExtUtils::MakeMaker(3)
perl Attribute::Handlers Attribute::Handlers
===================
CONTENTS
--------
* [NAME](#NAME)
* [VERSION](#VERSION)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [Typed lexicals](#Typed-lexicals)
+ [Type-specific attribute handlers](#Type-specific-attribute-handlers)
+ [Non-interpretive attribute handlers](#Non-interpretive-attribute-handlers)
+ [Phase-specific attribute handlers](#Phase-specific-attribute-handlers)
+ [Attributes as tie interfaces](#Attributes-as-tie-interfaces)
- [Passing the tied object to tie](#Passing-the-tied-object-to-tie)
* [EXAMPLES](#EXAMPLES)
* [UTILITY FUNCTIONS](#UTILITY-FUNCTIONS)
* [DIAGNOSTICS](#DIAGNOSTICS)
* [AUTHOR](#AUTHOR)
* [BUGS](#BUGS)
* [COPYRIGHT AND LICENSE](#COPYRIGHT-AND-LICENSE)
NAME
----
Attribute::Handlers - Simpler definition of attribute handlers
VERSION
-------
This document describes version 1.02 of Attribute::Handlers.
SYNOPSIS
--------
```
package MyClass;
require 5.006;
use Attribute::Handlers;
no warnings 'redefine';
sub Good : ATTR(SCALAR) {
my ($package, $symbol, $referent, $attr, $data) = @_;
# Invoked for any scalar variable with a :Good attribute,
# provided the variable was declared in MyClass (or
# a derived class) or typed to MyClass.
# Do whatever to $referent here (executed in CHECK phase).
...
}
sub Bad : ATTR(SCALAR) {
# Invoked for any scalar variable with a :Bad attribute,
# provided the variable was declared in MyClass (or
# a derived class) or typed to MyClass.
...
}
sub Good : ATTR(ARRAY) {
# Invoked for any array variable with a :Good attribute,
# provided the variable was declared in MyClass (or
# a derived class) or typed to MyClass.
...
}
sub Good : ATTR(HASH) {
# Invoked for any hash variable with a :Good attribute,
# provided the variable was declared in MyClass (or
# a derived class) or typed to MyClass.
...
}
sub Ugly : ATTR(CODE) {
# Invoked for any subroutine declared in MyClass (or a
# derived class) with an :Ugly attribute.
...
}
sub Omni : ATTR {
# Invoked for any scalar, array, hash, or subroutine
# with an :Omni attribute, provided the variable or
# subroutine was declared in MyClass (or a derived class)
# or the variable was typed to MyClass.
# Use ref($_[2]) to determine what kind of referent it was.
...
}
use Attribute::Handlers autotie => { Cycle => Tie::Cycle };
my $next : Cycle(['A'..'Z']);
```
DESCRIPTION
-----------
This module, when inherited by a package, allows that package's class to define attribute handler subroutines for specific attributes. Variables and subroutines subsequently defined in that package, or in packages derived from that package may be given attributes with the same names as the attribute handler subroutines, which will then be called in one of the compilation phases (i.e. in a `BEGIN`, `CHECK`, `INIT`, or `END` block). (`UNITCHECK` blocks don't correspond to a global compilation phase, so they can't be specified here.)
To create a handler, define it as a subroutine with the same name as the desired attribute, and declare the subroutine itself with the attribute `:ATTR`. For example:
```
package LoudDecl;
use Attribute::Handlers;
sub Loud :ATTR {
my ($package, $symbol, $referent, $attr, $data, $phase,
$filename, $linenum) = @_;
print STDERR
ref($referent), " ",
*{$symbol}{NAME}, " ",
"($referent) ", "was just declared ",
"and ascribed the ${attr} attribute ",
"with data ($data)\n",
"in phase $phase\n",
"in file $filename at line $linenum\n";
}
```
This creates a handler for the attribute `:Loud` in the class LoudDecl. Thereafter, any subroutine declared with a `:Loud` attribute in the class LoudDecl:
```
package LoudDecl;
sub foo: Loud {...}
```
causes the above handler to be invoked, and passed:
[0] the name of the package into which it was declared;
[1] a reference to the symbol table entry (typeglob) containing the subroutine;
[2] a reference to the subroutine;
[3] the name of the attribute;
[4] any data associated with that attribute;
[5] the name of the phase in which the handler is being invoked;
[6] the filename in which the handler is being invoked;
[7] the line number in this file.
Likewise, declaring any variables with the `:Loud` attribute within the package:
```
package LoudDecl;
my $foo :Loud;
my @foo :Loud;
my %foo :Loud;
```
will cause the handler to be called with a similar argument list (except, of course, that `$_[2]` will be a reference to the variable).
The package name argument will typically be the name of the class into which the subroutine was declared, but it may also be the name of a derived class (since handlers are inherited).
If a lexical variable is given an attribute, there is no symbol table to which it belongs, so the symbol table argument (`$_[1]`) is set to the string `'LEXICAL'` in that case. Likewise, ascribing an attribute to an anonymous subroutine results in a symbol table argument of `'ANON'`.
The data argument passes in the value (if any) associated with the attribute. For example, if `&foo` had been declared:
```
sub foo :Loud("turn it up to 11, man!") {...}
```
then a reference to an array containing the string `"turn it up to 11, man!"` would be passed as the last argument.
Attribute::Handlers makes strenuous efforts to convert the data argument (`$_[4]`) to a usable form before passing it to the handler (but see ["Non-interpretive attribute handlers"](#Non-interpretive-attribute-handlers)). If those efforts succeed, the interpreted data is passed in an array reference; if they fail, the raw data is passed as a string. For example, all of these:
```
sub foo :Loud(till=>ears=>are=>bleeding) {...}
sub foo :Loud(qw/till ears are bleeding/) {...}
sub foo :Loud(qw/till, ears, are, bleeding/) {...}
sub foo :Loud(till,ears,are,bleeding) {...}
```
causes it to pass `['till','ears','are','bleeding']` as the handler's data argument. While:
```
sub foo :Loud(['till','ears','are','bleeding']) {...}
```
causes it to pass `[ ['till','ears','are','bleeding'] ]`; the array reference specified in the data being passed inside the standard array reference indicating successful interpretation.
However, if the data can't be parsed as valid Perl, then it is passed as an uninterpreted string. For example:
```
sub foo :Loud(my,ears,are,bleeding) {...}
sub foo :Loud(qw/my ears are bleeding) {...}
```
cause the strings `'my,ears,are,bleeding'` and `'qw/my ears are bleeding'` respectively to be passed as the data argument.
If no value is associated with the attribute, `undef` is passed.
###
Typed lexicals
Regardless of the package in which it is declared, if a lexical variable is ascribed an attribute, the handler that is invoked is the one belonging to the package to which it is typed. For example, the following declarations:
```
package OtherClass;
my LoudDecl $loudobj : Loud;
my LoudDecl @loudobjs : Loud;
my LoudDecl %loudobjex : Loud;
```
causes the LoudDecl::Loud handler to be invoked (even if OtherClass also defines a handler for `:Loud` attributes).
###
Type-specific attribute handlers
If an attribute handler is declared and the `:ATTR` specifier is given the name of a built-in type (`SCALAR`, `ARRAY`, `HASH`, or `CODE`), the handler is only applied to declarations of that type. For example, the following definition:
```
package LoudDecl;
sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
```
creates an attribute handler that applies only to scalars:
```
package Painful;
use base LoudDecl;
my $metal : RealLoud; # invokes &LoudDecl::RealLoud
my @metal : RealLoud; # error: unknown attribute
my %metal : RealLoud; # error: unknown attribute
sub metal : RealLoud {...} # error: unknown attribute
```
You can, of course, declare separate handlers for these types as well (but you'll need to specify `no warnings 'redefine'` to do it quietly):
```
package LoudDecl;
use Attribute::Handlers;
no warnings 'redefine';
sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" }
sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" }
sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" }
```
You can also explicitly indicate that a single handler is meant to be used for all types of referents like so:
```
package LoudDecl;
use Attribute::Handlers;
sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" }
```
(I.e. `ATTR(ANY)` is a synonym for `:ATTR`).
###
Non-interpretive attribute handlers
Occasionally the strenuous efforts Attribute::Handlers makes to convert the data argument (`$_[4]`) to a usable form before passing it to the handler get in the way.
You can turn off that eagerness-to-help by declaring an attribute handler with the keyword `RAWDATA`. For example:
```
sub Raw : ATTR(RAWDATA) {...}
sub Nekkid : ATTR(SCALAR,RAWDATA) {...}
sub Au::Naturale : ATTR(RAWDATA,ANY) {...}
```
Then the handler makes absolutely no attempt to interpret the data it receives and simply passes it as a string:
```
my $power : Raw(1..100); # handlers receives "1..100"
```
###
Phase-specific attribute handlers
By default, attribute handlers are called at the end of the compilation phase (in a `CHECK` block). This seems to be optimal in most cases because most things that can be defined are defined by that point but nothing has been executed.
However, it is possible to set up attribute handlers that are called at other points in the program's compilation or execution, by explicitly stating the phase (or phases) in which you wish the attribute handler to be called. For example:
```
sub Early :ATTR(SCALAR,BEGIN) {...}
sub Normal :ATTR(SCALAR,CHECK) {...}
sub Late :ATTR(SCALAR,INIT) {...}
sub Final :ATTR(SCALAR,END) {...}
sub Bookends :ATTR(SCALAR,BEGIN,END) {...}
```
As the last example indicates, a handler may be set up to be (re)called in two or more phases. The phase name is passed as the handler's final argument.
Note that attribute handlers that are scheduled for the `BEGIN` phase are handled as soon as the attribute is detected (i.e. before any subsequently defined `BEGIN` blocks are executed).
###
Attributes as `tie` interfaces
Attributes make an excellent and intuitive interface through which to tie variables. For example:
```
use Attribute::Handlers;
use Tie::Cycle;
sub UNIVERSAL::Cycle : ATTR(SCALAR) {
my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
$data = [ $data ] unless ref $data eq 'ARRAY';
tie $$referent, 'Tie::Cycle', $data;
}
# and thereafter...
package main;
my $next : Cycle('A'..'Z'); # $next is now a tied variable
while (<>) {
print $next;
}
```
Note that, because the `Cycle` attribute receives its arguments in the `$data` variable, if the attribute is given a list of arguments, `$data` will consist of a single array reference; otherwise, it will consist of the single argument directly. Since Tie::Cycle requires its cycling values to be passed as an array reference, this means that we need to wrap non-array-reference arguments in an array constructor:
```
$data = [ $data ] unless ref $data eq 'ARRAY';
```
Typically, however, things are the other way around: the tieable class expects its arguments as a flattened list, so the attribute looks like:
```
sub UNIVERSAL::Cycle : ATTR(SCALAR) {
my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
my @data = ref $data eq 'ARRAY' ? @$data : $data;
tie $$referent, 'Tie::Whatever', @data;
}
```
This software pattern is so widely applicable that Attribute::Handlers provides a way to automate it: specifying `'autotie'` in the `use Attribute::Handlers` statement. So, the cycling example, could also be written:
```
use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' };
# and thereafter...
package main;
my $next : Cycle(['A'..'Z']); # $next is now a tied variable
while (<>) {
print $next;
}
```
Note that we now have to pass the cycling values as an array reference, since the `autotie` mechanism passes `tie` a list of arguments as a list (as in the Tie::Whatever example), *not* as an array reference (as in the original Tie::Cycle example at the start of this section).
The argument after `'autotie'` is a reference to a hash in which each key is the name of an attribute to be created, and each value is the class to which variables ascribed that attribute should be tied.
Note that there is no longer any need to import the Tie::Cycle module -- Attribute::Handlers takes care of that automagically. You can even pass arguments to the module's `import` subroutine, by appending them to the class name. For example:
```
use Attribute::Handlers
autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' };
```
If the attribute name is unqualified, the attribute is installed in the current package. Otherwise it is installed in the qualifier's package:
```
package Here;
use Attribute::Handlers autotie => {
Other::Good => Tie::SecureHash, # tie attr installed in Other::
Bad => Tie::Taxes, # tie attr installed in Here::
UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere
};
```
Autoties are most commonly used in the module to which they actually tie, and need to export their attributes to any module that calls them. To facilitate this, Attribute::Handlers recognizes a special "pseudo-class" -- `__CALLER__`, which may be specified as the qualifier of an attribute:
```
package Tie::Me::Kangaroo::Down::Sport;
use Attribute::Handlers autotie =>
{ '__CALLER__::Roo' => __PACKAGE__ };
```
This causes Attribute::Handlers to define the `Roo` attribute in the package that imports the Tie::Me::Kangaroo::Down::Sport module.
Note that it is important to quote the \_\_CALLER\_\_::Roo identifier because a bug in perl 5.8 will refuse to parse it and cause an unknown error.
####
Passing the tied object to `tie`
Occasionally it is important to pass a reference to the object being tied to the TIESCALAR, TIEHASH, etc. that ties it.
The `autotie` mechanism supports this too. The following code:
```
use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
my $var : Selfish(@args);
```
has the same effect as:
```
tie my $var, 'Tie::Selfish', @args;
```
But when `"autotieref"` is used instead of `"autotie"`:
```
use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
my $var : Selfish(@args);
```
the effect is to pass the `tie` call an extra reference to the variable being tied:
```
tie my $var, 'Tie::Selfish', \$var, @args;
```
EXAMPLES
--------
If the class shown in ["SYNOPSIS"](#SYNOPSIS) were placed in the MyClass.pm module, then the following code:
```
package main;
use MyClass;
my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
package SomeOtherClass;
use base MyClass;
sub tent { 'acle' }
sub fn :Ugly(sister) :Omni('po',tent()) {...}
my @arr :Good :Omni(s/cie/nt/);
my %hsh :Good(q/bye/) :Omni(q/bus/);
```
would cause the following handlers to be invoked:
```
# my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
MyClass::Good:ATTR(SCALAR)( 'MyClass', # class
'LEXICAL', # no typeglob
\$slr, # referent
'Good', # attr name
undef # no attr data
'CHECK', # compiler phase
);
MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class
'LEXICAL', # no typeglob
\$slr, # referent
'Bad', # attr name
0 # eval'd attr data
'CHECK', # compiler phase
);
MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class
'LEXICAL', # no typeglob
\$slr, # referent
'Omni', # attr name
'-vorous' # eval'd attr data
'CHECK', # compiler phase
);
# sub fn :Ugly(sister) :Omni('po',tent()) {...}
MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class
\*SomeOtherClass::fn, # typeglob
\&SomeOtherClass::fn, # referent
'Ugly', # attr name
'sister' # eval'd attr data
'CHECK', # compiler phase
);
MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class
\*SomeOtherClass::fn, # typeglob
\&SomeOtherClass::fn, # referent
'Omni', # attr name
['po','acle'] # eval'd attr data
'CHECK', # compiler phase
);
# my @arr :Good :Omni(s/cie/nt/);
MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class
'LEXICAL', # no typeglob
\@arr, # referent
'Good', # attr name
undef # no attr data
'CHECK', # compiler phase
);
MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class
'LEXICAL', # no typeglob
\@arr, # referent
'Omni', # attr name
"" # eval'd attr data
'CHECK', # compiler phase
);
# my %hsh :Good(q/bye) :Omni(q/bus/);
MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class
'LEXICAL', # no typeglob
\%hsh, # referent
'Good', # attr name
'q/bye' # raw attr data
'CHECK', # compiler phase
);
MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class
'LEXICAL', # no typeglob
\%hsh, # referent
'Omni', # attr name
'bus' # eval'd attr data
'CHECK', # compiler phase
);
```
Installing handlers into UNIVERSAL, makes them...err..universal. For example:
```
package Descriptions;
use Attribute::Handlers;
my %name;
sub name { return $name{$_[2]}||*{$_[1]}{NAME} }
sub UNIVERSAL::Name :ATTR {
$name{$_[2]} = $_[4];
}
sub UNIVERSAL::Purpose :ATTR {
print STDERR "Purpose of ", &name, " is $_[4]\n";
}
sub UNIVERSAL::Unit :ATTR {
print STDERR &name, " measured in $_[4]\n";
}
```
Let's you write:
```
use Descriptions;
my $capacity : Name(capacity)
: Purpose(to store max storage capacity for files)
: Unit(Gb);
package Other;
sub foo : Purpose(to foo all data before barring it) { }
# etc.
```
UTILITY FUNCTIONS
------------------
This module offers a single utility function, `findsym()`.
findsym
```
my $symbol = Attribute::Handlers::findsym($package, $referent);
```
The function looks in the symbol table of `$package` for the typeglob for `$referent`, which is a reference to a variable or subroutine (SCALAR, ARRAY, HASH, or CODE). If it finds the typeglob, it returns it. Otherwise, it returns undef. Note that `findsym` memoizes the typeglobs it has previously successfully found, so subsequent calls with the same arguments should be much faster.
DIAGNOSTICS
-----------
`Bad attribute type: ATTR(%s)`
An attribute handler was specified with an `:ATTR(*ref\_type*)`, but the type of referent it was defined to handle wasn't one of the five permitted: `SCALAR`, `ARRAY`, `HASH`, `CODE`, or `ANY`.
`Attribute handler %s doesn't handle %s attributes`
A handler for attributes of the specified name *was* defined, but not for the specified type of declaration. Typically encountered when trying to apply a `VAR` attribute handler to a subroutine, or a `SCALAR` attribute handler to some other type of variable.
`Declaration of %s attribute in package %s may clash with future reserved word`
A handler for an attributes with an all-lowercase name was declared. An attribute with an all-lowercase name might have a meaning to Perl itself some day, even though most don't yet. Use a mixed-case attribute name, instead.
`Can't have two ATTR specifiers on one subroutine`
You just can't, okay? Instead, put all the specifications together with commas between them in a single `ATTR(*specification*)`.
`Can't autotie a %s`
You can only declare autoties for types `"SCALAR"`, `"ARRAY"`, and `"HASH"`. They're the only things (apart from typeglobs -- which are not declarable) that Perl can tie.
`Internal error: %s symbol went missing`
Something is rotten in the state of the program. An attributed subroutine ceased to exist between the point it was declared and the point at which its attribute handler(s) would have been called.
`Won't be able to apply END handler`
You have defined an END handler for an attribute that is being applied to a lexical variable. Since the variable may not be available during END this won't happen.
AUTHOR
------
Damian Conway ([email protected]). The maintainer of this module is now Rafael Garcia-Suarez ([email protected]).
Maintainer of the CPAN release is Steffen Mueller ([email protected]). Contact him with technical difficulties with respect to the packaging of the CPAN module.
BUGS
----
There are undoubtedly serious bugs lurking somewhere in code this funky :-) Bug reports and other feedback are most welcome.
COPYRIGHT AND LICENSE
----------------------
```
Copyright (c) 2001-2014, Damian Conway. All Rights Reserved.
This module is free software. It may be used, redistributed
and/or modified under the same terms as Perl itself.
```
| programming_docs |
perl ExtUtils::Command ExtUtils::Command
=================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [FUNCTIONS](#FUNCTIONS)
* [SEE ALSO](#SEE-ALSO)
* [AUTHOR](#AUTHOR)
NAME
----
ExtUtils::Command - utilities to replace common UNIX commands in Makefiles etc.
SYNOPSIS
--------
```
perl -MExtUtils::Command -e cat files... > destination
perl -MExtUtils::Command -e mv source... destination
perl -MExtUtils::Command -e cp source... destination
perl -MExtUtils::Command -e touch files...
perl -MExtUtils::Command -e rm_f files...
perl -MExtUtils::Command -e rm_rf directories...
perl -MExtUtils::Command -e mkpath directories...
perl -MExtUtils::Command -e eqtime source destination
perl -MExtUtils::Command -e test_f file
perl -MExtUtils::Command -e test_d directory
perl -MExtUtils::Command -e chmod mode files...
...
```
DESCRIPTION
-----------
The module is used to replace common UNIX commands. In all cases the functions work from @ARGV rather than taking arguments. This makes them easier to deal with in Makefiles. Call them like this:
```
perl -MExtUtils::Command -e some_command some files to work on
```
and *NOT* like this:
```
perl -MExtUtils::Command -e 'some_command qw(some files to work on)'
```
For that use <Shell::Command>.
Filenames with \* and ? will be glob expanded.
### FUNCTIONS
cat
```
cat file ...
```
Concatenates all files mentioned on command line to STDOUT.
eqtime
```
eqtime source destination
```
Sets modified time of destination to that of source.
rm\_rf
```
rm_rf files or directories ...
```
Removes files and directories - recursively (even if readonly)
rm\_f
```
rm_f file ...
```
Removes files (even if readonly)
touch
```
touch file ...
```
Makes files exist, with current timestamp
mv
```
mv source_file destination_file
mv source_file source_file destination_dir
```
Moves source to destination. Multiple sources are allowed if destination is an existing directory.
Returns true if all moves succeeded, false otherwise.
cp
```
cp source_file destination_file
cp source_file source_file destination_dir
```
Copies sources to the destination. Multiple sources are allowed if destination is an existing directory.
Returns true if all copies succeeded, false otherwise.
chmod
```
chmod mode files ...
```
Sets UNIX like permissions 'mode' on all the files. e.g. 0666
mkpath
```
mkpath directory ...
```
Creates directories, including any parent directories.
test\_f
```
test_f file
```
Tests if a file exists. *Exits* with 0 if it does, 1 if it does not (ie. shell's idea of true and false).
test\_d
```
test_d directory
```
Tests if a directory exists. *Exits* with 0 if it does, 1 if it does not (ie. shell's idea of true and false).
dos2unix
```
dos2unix files or dirs ...
```
Converts DOS and OS/2 linefeeds to Unix style recursively.
SEE ALSO
---------
Shell::Command which is these same functions but take arguments normally.
AUTHOR
------
Nick Ing-Simmons `[email protected]`
Maintained by Michael G Schwern `[email protected]` within the ExtUtils-MakeMaker package and, as a separate CPAN package, by Randy Kobes `[email protected]`.
perl bigint bigint
======
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [use integer vs. use bigint](#use-integer-vs.-use-bigint)
+ [Options](#Options)
+ [Math Library](#Math-Library)
+ [Method calls](#Method-calls)
+ [Methods](#Methods)
* [CAVEATS](#CAVEATS)
* [EXAMPLES](#EXAMPLES)
* [BUGS](#BUGS)
* [SUPPORT](#SUPPORT)
* [LICENSE](#LICENSE)
* [SEE ALSO](#SEE-ALSO)
* [AUTHORS](#AUTHORS)
NAME
----
bigint - transparent big integer support for Perl
SYNOPSIS
--------
```
use bigint;
$x = 2 + 4.5; # Math::BigInt 6
print 2 ** 512; # Math::BigInt 134...096
print inf + 42; # Math::BigInt inf
print NaN * 7; # Math::BigInt NaN
print hex("0x1234567890123490"); # Perl v5.10.0 or later
{
no bigint;
print 2 ** 256; # a normal Perl scalar now
}
# for older Perls, import into current package:
use bigint qw/hex oct/;
print hex("0x1234567890123490");
print oct("01234567890123490");
```
DESCRIPTION
-----------
All numeric literal in the given scope are converted to Math::BigInt objects. Numeric literal that represent non-integers are truncated to an integer. All results of expressions are also truncated to integer.
All operators (including basic math operations) except the range operator `..` are overloaded.
Unlike the <integer> pragma, the `bigint` pragma creates integers that are only limited in their size by the available memory.
So, the following:
```
use bigint;
$x = 1234;
```
creates a Math::BigInt and stores a reference to in $x. This happens transparently and behind your back, so to speak.
You can see this with the following:
```
perl -Mbigint -le 'print ref(1234)'
```
Since numbers are actually objects, you can call all the usual methods from Math::BigFloat on them. This even works to some extent on expressions:
```
perl -Mbigint -le '$x = 1234; print $x->bdec()'
perl -Mbigint -le 'print 1234->copy()->binc();'
perl -Mbigint -le 'print 1234->copy()->binc->badd(6);'
perl -Mbigint -le 'print +(1234)->copy()->binc()'
```
(Note that print doesn't do what you expect if the expression starts with '(' hence the `+`)
You can even chain the operations together as usual:
```
perl -Mbigint -le 'print 1234->copy()->binc->badd(6);'
1241
```
Please note the following does not work as expected (prints nothing), since overloading of '..' is not yet possible in Perl (as of v5.8.0):
```
perl -Mbigint -le 'for (1..2) { print ref($_); }'
```
###
use integer vs. use bigint
There are some difference between `use integer` and `use bigint`.
Whereas `use integer` is limited to what can be handled as a Perl scalar, `use bigint` can handle arbitrarily large integers.
Also, `use integer` does affect assignments to variables and the return value of some functions. `use bigint` truncates these results to integer:
```
# perl -Minteger -wle 'print 3.2'
3.2
# perl -Minteger -wle 'print 3.2 + 0'
3
# perl -Mbigint -wle 'print 3.2'
3
# perl -Mbigint -wle 'print 3.2 + 0'
3
# perl -Mbigint -wle 'print exp(1) + 0'
2
# perl -Mbigint -wle 'print exp(1)'
2
# perl -Minteger -wle 'print exp(1)'
2.71828182845905
# perl -Minteger -wle 'print exp(1) + 0'
2
```
In practice this seldom makes a difference for small integers as **parts and results** of expressions are truncated anyway, but this can, for instance, affect the return value of subroutines:
```
sub three_integer { use integer; return 3.2; }
sub three_bigint { use bigint; return 3.2; }
print three_integer(), " ", three_bigint(),"\n"; # prints "3.2 3"
```
### Options
`bigint` recognizes some options that can be passed while loading it via `use`. The following options exist:
a or accuracy This sets the accuracy for all math operations. The argument must be greater than or equal to zero. See Math::BigInt's bround() method for details.
```
perl -Mbigint=a,2 -le 'print 12345+1'
```
Note that setting precision and accuracy at the same time is not possible.
p or precision This sets the precision for all math operations. The argument can be any integer. Negative values mean a fixed number of digits after the dot, and are ignored since all operations happen in integer space. A positive value rounds to this digit left from the dot. 0 means round to integer. See Math::BigInt's bfround() method for details.
```
perl -mbigint=p,5 -le 'print 123456789+123'
```
Note that setting precision and accuracy at the same time is not possible.
t or trace This enables a trace mode and is primarily for debugging.
l, lib, try, or only Load a different math lib, see ["Math Library"](#Math-Library).
```
perl -Mbigint=l,GMP -e 'print 2 ** 512'
perl -Mbigint=lib,GMP -e 'print 2 ** 512'
perl -Mbigint=try,GMP -e 'print 2 ** 512'
perl -Mbigint=only,GMP -e 'print 2 ** 512'
```
hex Override the built-in hex() method with a version that can handle big numbers. This overrides it by exporting it to the current package. Under Perl v5.10.0 and higher, this is not so necessary, as hex() is lexically overridden in the current scope whenever the `bigint` pragma is active.
oct Override the built-in oct() method with a version that can handle big numbers. This overrides it by exporting it to the current package. Under Perl v5.10.0 and higher, this is not so necessary, as oct() is lexically overridden in the current scope whenever the `bigint` pragma is active.
v or version this prints out the name and version of the modules and then exits.
```
perl -Mbigint=v
```
###
Math Library
Math with the numbers is done (by default) by a backend library module called Math::BigInt::Calc. The default is equivalent to saying:
```
use bigint lib => 'Calc';
```
you can change this by using:
```
use bigint lib => 'GMP';
```
The following would first try to find Math::BigInt::Foo, then Math::BigInt::Bar, and if this also fails, revert to Math::BigInt::Calc:
```
use bigint lib => 'Foo,Math::BigInt::Bar';
```
Using c<lib> warns if none of the specified libraries can be found and <Math::BigInt> fell back to one of the default libraries. To suppress this warning, use c<try> instead:
```
use bigint try => 'GMP';
```
If you want the code to die instead of falling back, use `only` instead:
```
use bigint only => 'GMP';
```
Please see the respective module documentation for further details.
###
Method calls
Since all numbers are now objects, you can use all methods that are part of the Math::BigInt API.
But a warning is in order. When using the following to make a copy of a number, only a shallow copy will be made.
```
$x = 9; $y = $x;
$x = $y = 7;
```
Using the copy or the original with overloaded math is okay, e.g., the following work:
```
$x = 9; $y = $x;
print $x + 1, " ", $y,"\n"; # prints 10 9
```
but calling any method that modifies the number directly will result in **both** the original and the copy being destroyed:
```
$x = 9; $y = $x;
print $x->badd(1), " ", $y,"\n"; # prints 10 10
$x = 9; $y = $x;
print $x->binc(1), " ", $y,"\n"; # prints 10 10
$x = 9; $y = $x;
print $x->bmul(2), " ", $y,"\n"; # prints 18 18
```
Using methods that do not modify, but test that the contents works:
```
$x = 9; $y = $x;
$z = 9 if $x->is_zero(); # works fine
```
See the documentation about the copy constructor and `=` in overload, as well as the documentation in Math::BigInt for further details.
### Methods
inf() A shortcut to return Math::BigInt->binf(). Useful because Perl does not always handle bareword `inf` properly.
NaN() A shortcut to return Math::BigInt->bnan(). Useful because Perl does not always handle bareword `NaN` properly.
e
```
# perl -Mbigint=e -wle 'print e'
```
Returns Euler's number `e`, aka exp(1). Note that under `bigint`, this is truncated to an integer, i.e., 2.
PI
```
# perl -Mbigint=PI -wle 'print PI'
```
Returns PI. Note that under `bigint`, this is truncated to an integer, i.e., 3.
bexp()
```
bexp($power, $accuracy);
```
Returns Euler's number `e` raised to the appropriate power, to the wanted accuracy.
Note that under `bigint`, the result is truncated to an integer.
Example:
```
# perl -Mbigint=bexp -wle 'print bexp(1,80)'
```
bpi()
```
bpi($accuracy);
```
Returns PI to the wanted accuracy. Note that under `bigint`, this is truncated to an integer, i.e., 3.
Example:
```
# perl -Mbigint=bpi -wle 'print bpi(80)'
```
accuracy() Set or get the accuracy.
precision() Set or get the precision.
round\_mode() Set or get the rounding mode.
div\_scale() Set or get the division scale.
in\_effect()
```
use bigint;
print "in effect\n" if bigint::in_effect; # true
{
no bigint;
print "in effect\n" if bigint::in_effect; # false
}
```
Returns true or false if `bigint` is in effect in the current scope.
This method only works on Perl v5.9.4 or later.
CAVEATS
-------
Hexadecimal, octal, and binary floating point literals Perl (and this module) accepts hexadecimal, octal, and binary floating point literals, but use them with care with Perl versions before v5.32.0, because some versions of Perl silently give the wrong result.
Operator vs literal overloading `bigint` works by overloading handling of integer and floating point literals, converting them to <Math::BigInt> objects.
This means that arithmetic involving only string values or string literals are performed using Perl's built-in operators.
For example:
```
use bigint;
my $x = "900000000000000009";
my $y = "900000000000000007";
print $x - $y;
```
outputs `0` on default 32-bit builds, since `bigint` never sees the string literals. To ensure the expression is all treated as `Math::BigInt` objects, use a literal number in the expression:
```
print +(0+$x) - $y;
```
Ranges Perl does not allow overloading of ranges, so you can neither safely use ranges with `bigint` endpoints, nor is the iterator variable a `Math::BigInt`.
```
use 5.010;
for my $i (12..13) {
for my $j (20..21) {
say $i ** $j; # produces a floating-point number,
# not an object
}
}
```
in\_effect() This method only works on Perl v5.9.4 or later.
hex()/oct() `bigint` overrides these routines with versions that can also handle big integer values. Under Perl prior to version v5.9.4, however, this will not happen unless you specifically ask for it with the two import tags "hex" and "oct" - and then it will be global and cannot be disabled inside a scope with `no bigint`:
```
use bigint qw/hex oct/;
print hex("0x1234567890123456");
{
no bigint;
print hex("0x1234567890123456");
}
```
The second call to hex() will warn about a non-portable constant.
Compare this to:
```
use bigint;
# will warn only under Perl older than v5.9.4
print hex("0x1234567890123456");
```
EXAMPLES
--------
Some cool command line examples to impress the Python crowd ;) You might want to compare them to the results under -Mbigfloat or -Mbigrat:
```
perl -Mbigint -le 'print sqrt(33)'
perl -Mbigint -le 'print 2*255'
perl -Mbigint -le 'print 4.5+2*255'
perl -Mbigint -le 'print 123->is_odd()'
perl -Mbigint=l,GMP -le 'print 7 ** 7777'
```
BUGS
----
Please report any bugs or feature requests to `bug-bignum at rt.cpan.org`, or through the web interface at <https://rt.cpan.org/Ticket/Create.html?Queue=bignum> (requires login). We will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
SUPPORT
-------
You can find documentation for this module with the perldoc command.
```
perldoc bigint
```
You can also look for information at:
* GitHub
<https://github.com/pjacklam/p5-bignum>
* RT: CPAN's request tracker
<https://rt.cpan.org/Dist/Display.html?Name=bignum>
* MetaCPAN
<https://metacpan.org/release/bignum>
* CPAN Testers Matrix
<http://matrix.cpantesters.org/?dist=bignum>
* CPAN Ratings
<https://cpanratings.perl.org/dist/bignum>
LICENSE
-------
This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself.
SEE ALSO
---------
<bignum> and <bigrat>.
<Math::BigInt>, <Math::BigFloat>, <Math::BigRat> and <Math::Big> as well as <Math::BigInt::FastCalc>, <Math::BigInt::Pari> and <Math::BigInt::GMP>.
AUTHORS
-------
* (C) by Tels <http://bloodgate.com/> in early 2002 - 2007.
* Maintained by Peter John Acklam <[email protected]>, 2014-.
perl B B
=
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [OVERVIEW](#OVERVIEW)
* [Utility Functions](#Utility-Functions)
+ [Functions Returning B::SV, B::AV, B::HV, and B::CV objects](#Functions-Returning-B::SV,-B::AV,-B::HV,-and-B::CV-objects)
+ [Functions for Examining the Symbol Table](#Functions-for-Examining-the-Symbol-Table)
+ [Functions Returning B::OP objects or for walking op trees](#Functions-Returning-B::OP-objects-or-for-walking-op-trees)
+ [Miscellaneous Utility Functions](#Miscellaneous-Utility-Functions)
+ [Exported utility variables](#Exported-utility-variables)
* [OVERVIEW OF CLASSES](#OVERVIEW-OF-CLASSES)
+ [SV-RELATED CLASSES](#SV-RELATED-CLASSES)
+ [B::SV Methods](#B::SV-Methods)
+ [B::IV Methods](#B::IV-Methods)
+ [B::NV Methods](#B::NV-Methods)
+ [B::RV Methods](#B::RV-Methods)
+ [B::PV Methods](#B::PV-Methods)
+ [B::PVMG Methods](#B::PVMG-Methods)
+ [B::MAGIC Methods](#B::MAGIC-Methods)
+ [B::INVLIST Methods](#B::INVLIST-Methods)
+ [B::PVLV Methods](#B::PVLV-Methods)
+ [B::BM Methods](#B::BM-Methods)
+ [B::REGEXP Methods](#B::REGEXP-Methods)
+ [B::GV Methods](#B::GV-Methods)
+ [B::IO Methods](#B::IO-Methods)
+ [B::AV Methods](#B::AV-Methods)
+ [B::CV Methods](#B::CV-Methods)
+ [B::HV Methods](#B::HV-Methods)
+ [OP-RELATED CLASSES](#OP-RELATED-CLASSES)
+ [B::OP Methods](#B::OP-Methods)
+ [B::UNOP Method](#B::UNOP-Method)
+ [B::UNOP\_AUX Methods (since 5.22)](#B::UNOP_AUX-Methods-(since-5.22))
+ [B::BINOP Method](#B::BINOP-Method)
+ [B::LOGOP Method](#B::LOGOP-Method)
+ [B::LISTOP Method](#B::LISTOP-Method)
+ [B::PMOP Methods](#B::PMOP-Methods)
+ [B::SVOP Methods](#B::SVOP-Methods)
+ [B::PADOP Method](#B::PADOP-Method)
+ [B::PVOP Method](#B::PVOP-Method)
+ [B::LOOP Methods](#B::LOOP-Methods)
+ [B::COP Methods](#B::COP-Methods)
+ [B::METHOP Methods (Since Perl 5.22)](#B::METHOP-Methods-(Since-Perl-5.22))
+ [PAD-RELATED CLASSES](#PAD-RELATED-CLASSES)
+ [B::PADLIST Methods](#B::PADLIST-Methods)
+ [B::PADNAMELIST Methods](#B::PADNAMELIST-Methods)
+ [B::PADNAME Methods](#B::PADNAME-Methods)
+ [$B::overlay](#%24B::overlay)
* [AUTHOR](#AUTHOR)
NAME
----
B - The Perl Compiler Backend
SYNOPSIS
--------
```
use B;
```
DESCRIPTION
-----------
The `B` module supplies classes which allow a Perl program to delve into its own innards. It is the module used to implement the "backends" of the Perl compiler. Usage of the compiler does not require knowledge of this module: see the *O* module for the user-visible part. The `B` module is of use to those who want to write new compiler backends. This documentation assumes that the reader knows a fair amount about perl's internals including such things as SVs, OPs and the internal symbol table and syntax tree of a program.
OVERVIEW
--------
The `B` module contains a set of utility functions for querying the current state of the Perl interpreter; typically these functions return objects from the B::SV and B::OP classes, or their derived classes. These classes in turn define methods for querying the resulting objects about their own internal state.
Utility Functions
------------------
The `B` module exports a variety of functions: some are simple utility functions, others provide a Perl program with a way to get an initial "handle" on an internal object.
###
Functions Returning `B::SV`, `B::AV`, `B::HV`, and `B::CV` objects
For descriptions of the class hierarchy of these objects and the methods that can be called on them, see below, ["OVERVIEW OF CLASSES"](#OVERVIEW-OF-CLASSES) and ["SV-RELATED CLASSES"](#SV-RELATED-CLASSES).
sv\_undef Returns the SV object corresponding to the C variable `sv_undef`.
sv\_yes Returns the SV object corresponding to the C variable `sv_yes`.
sv\_no Returns the SV object corresponding to the C variable `sv_no`.
svref\_2object(SVREF) Takes a reference to any Perl value, and turns the referred-to value into an object in the appropriate B::OP-derived or B::SV-derived class. Apart from functions such as `main_root`, this is the primary way to get an initial "handle" on an internal perl data structure which can then be followed with the other access methods.
The returned object will only be valid as long as the underlying OPs and SVs continue to exist. Do not attempt to use the object after the underlying structures are freed.
amagic\_generation Returns the SV object corresponding to the C variable `amagic_generation`. As of Perl 5.18, this is just an alias to `PL_na`, so its value is meaningless.
init\_av Returns the AV object (i.e. in class B::AV) representing INIT blocks.
check\_av Returns the AV object (i.e. in class B::AV) representing CHECK blocks.
unitcheck\_av Returns the AV object (i.e. in class B::AV) representing UNITCHECK blocks.
begin\_av Returns the AV object (i.e. in class B::AV) representing BEGIN blocks.
end\_av Returns the AV object (i.e. in class B::AV) representing END blocks.
comppadlist Returns the PADLIST object (i.e. in class B::PADLIST) of the global comppadlist. In Perl 5.16 and earlier it returns an AV object (class B::AV).
regex\_padav Only when perl was compiled with ithreads.
main\_cv Return the (faked) CV corresponding to the main part of the Perl program.
###
Functions for Examining the Symbol Table
walksymtable(SYMREF, METHOD, RECURSE, PREFIX) Walk the symbol table starting at SYMREF and call METHOD on each symbol (a B::GV object) visited. When the walk reaches package symbols (such as "Foo::") it invokes RECURSE, passing in the symbol name, and only recurses into the package if that sub returns true.
PREFIX is the name of the SYMREF you're walking.
For example:
```
# Walk CGI's symbol table calling print_subs on each symbol.
# Recurse only into CGI::Util::
walksymtable(\%CGI::, 'print_subs',
sub { $_[0] eq 'CGI::Util::' }, 'CGI::');
```
print\_subs() is a B::GV method you have declared. Also see ["B::GV Methods"](#B%3A%3AGV-Methods), below.
###
Functions Returning `B::OP` objects or for walking op trees
For descriptions of the class hierarchy of these objects and the methods that can be called on them, see below, ["OVERVIEW OF CLASSES"](#OVERVIEW-OF-CLASSES) and ["OP-RELATED CLASSES"](#OP-RELATED-CLASSES).
main\_root Returns the root op (i.e. an object in the appropriate B::OP-derived class) of the main part of the Perl program.
main\_start Returns the starting op of the main part of the Perl program.
walkoptree(OP, METHOD) Does a tree-walk of the syntax tree based at OP and calls METHOD on each op it visits. Each node is visited before its children. If `walkoptree_debug` (see below) has been called to turn debugging on then the method `walkoptree_debug` is called on each op before METHOD is called.
walkoptree\_debug(DEBUG) Returns the current debugging flag for `walkoptree`. If the optional DEBUG argument is non-zero, it sets the debugging flag to that. See the description of `walkoptree` above for what the debugging flag does.
###
Miscellaneous Utility Functions
ppname(OPNUM) Return the PP function name (e.g. "pp\_add") of op number OPNUM.
hash(STR) Returns a string in the form "0x..." representing the value of the internal hash function used by perl on string STR.
cast\_I32(I) Casts I to the internal I32 type used by that perl.
minus\_c Does the equivalent of the `-c` command-line option. Obviously, this is only useful in a BEGIN block or else the flag is set too late.
cstring(STR) Returns a double-quote-surrounded escaped version of STR which can be used as a string in C source code.
perlstring(STR) Returns a double-quote-surrounded escaped version of STR which can be used as a string in Perl source code.
safename(STR) This function returns the string with the first character modified if it is a control character. It converts it to ^X format first, so that "\cG" becomes "^G". This is used internally by [B::GV::SAFENAME](#SAFENAME), but you can call it directly.
class(OBJ) Returns the class of an object without the part of the classname preceding the first `"::"`. This is used to turn `"B::UNOP"` into `"UNOP"` for example.
threadsv\_names This used to provide support for the old 5.005 threading module. It now does nothing.
###
Exported utility variables
@optype
```
my $op_type = $optype[$op_type_num];
```
A simple mapping of the op type number to its type (like 'COP' or 'BINOP').
@specialsv\_name
```
my $sv_name = $specialsv_name[$sv_index];
```
Certain SV types are considered 'special'. They're represented by B::SPECIAL and are referred to by a number from the specialsv\_list. This array maps that number back to the name of the SV (like 'Nullsv' or '&PL\_sv\_undef').
OVERVIEW OF CLASSES
--------------------
The C structures used by Perl's internals to hold SV and OP information (PVIV, AV, HV, ..., OP, SVOP, UNOP, ...) are modelled on a class hierarchy and the `B` module gives access to them via a true object hierarchy. Structure fields which point to other objects (whether types of SV or types of OP) are represented by the `B` module as Perl objects of the appropriate class.
The bulk of the `B` module is the methods for accessing fields of these structures.
Note that all access is read-only. You cannot modify the internals by using this module. Also, note that the B::OP and B::SV objects created by this module are only valid for as long as the underlying objects exist; their creation doesn't increase the reference counts of the underlying objects. Trying to access the fields of a freed object will give incomprehensible results, or worse.
###
SV-RELATED CLASSES
B::IV, B::NV, B::PV, B::PVIV, B::PVNV, B::PVMG, B::PVLV, B::AV, B::HV, B::CV, B::GV, B::FM, B::IO. These classes correspond in the obvious way to the underlying C structures of similar names. The inheritance hierarchy mimics the underlying C "inheritance":
```
B::SV
|
+------------+------------+
| | |
B::PV B::IV B::NV
/ \ / /
/ \ / /
B::INVLIST B::PVIV /
\ /
\ /
\ /
B::PVNV
|
|
B::PVMG
|
+-------+-------+---+---+-------+-------+
| | | | | |
B::AV B::GV B::HV B::CV B::IO B::REGEXP
| |
| |
B::PVLV B::FM
```
Access methods correspond to the underlying C macros for field access, usually with the leading "class indication" prefix removed (Sv, Av, Hv, ...). The leading prefix is only left in cases where its removal would cause a clash in method name. For example, `GvREFCNT` stays as-is since its abbreviation would clash with the "superclass" method `REFCNT` (corresponding to the C function `SvREFCNT`).
###
B::SV Methods
REFCNT FLAGS object\_2svref Returns a reference to the regular scalar corresponding to this B::SV object. In other words, this method is the inverse operation to the svref\_2object() subroutine. This scalar and other data it points at should be considered read-only: modifying them is neither safe nor guaranteed to have a sensible effect.
###
B::IV Methods
IV Returns the value of the IV, *interpreted as a signed integer*. This will be misleading if `FLAGS & SVf_IVisUV`. Perhaps you want the `int_value` method instead?
IVX UVX int\_value This method returns the value of the IV as an integer. It differs from `IV` in that it returns the correct value regardless of whether it's stored signed or unsigned.
needs64bits packiv ###
B::NV Methods
NV NVX COP\_SEQ\_RANGE\_LOW COP\_SEQ\_RANGE\_HIGH These last two are only valid for pad name SVs. They only existed in the B::NV class before Perl 5.22. In 5.22 they were moved to the B::PADNAME class.
###
B::RV Methods
RV ###
B::PV Methods
PV This method is the one you usually want. It constructs a string using the length and offset information in the struct: for ordinary scalars it will return the string that you'd see from Perl, even if it contains null characters.
RV Same as B::RV::RV, except that it will die() if the PV isn't a reference.
PVX This method is less often useful. It assumes that the string stored in the struct is null-terminated, and disregards the length information.
It is the appropriate method to use if you need to get the name of a lexical variable from a padname array. Lexical variable names are always stored with a null terminator, and the length field (CUR) is overloaded for other purposes and can't be relied on here.
CUR This method returns the internal length field, which consists of the number of internal bytes, not necessarily the number of logical characters.
LEN This method returns the number of bytes allocated (via malloc) for storing the string. This is 0 if the scalar does not "own" the string.
###
B::PVMG Methods
MAGIC SvSTASH ###
B::MAGIC Methods
MOREMAGIC precomp Only valid on r-magic, returns the string that generated the regexp.
PRIVATE TYPE FLAGS OBJ Will die() if called on r-magic.
PTR REGEX Only valid on r-magic, returns the integer value of the REGEX stored in the MAGIC.
###
B::INVLIST Methods
prev\_index Returns the cache result of previous invlist\_search() (internal usage)
is\_offset Returns a boolean value (0 or 1) to know if the invlist is using an offset. When false the list begins with the code point U+0000. When true the list begins with the following elements.
array\_len Returns an integer with the size of the array used to define the invlist.
get\_invlist\_array This method returns a list of integers representing the array used by the invlist. Note: this cannot be used while in middle of iterating on an invlist and croaks.
###
B::PVLV Methods
TARGOFF TARGLEN TYPE TARG ###
B::BM Methods
USEFUL PREVIOUS RARE TABLE ###
B::REGEXP Methods
REGEX precomp qr\_anoncv compflags The last two were added in Perl 5.22.
###
B::GV Methods
is\_empty This method returns TRUE if the GP field of the GV is NULL.
NAME SAFENAME This method returns the name of the glob, but if the first character of the name is a control character, then it converts it to ^X first, so that \*^G would return "^G" rather than "\cG".
It's useful if you want to print out the name of a variable. If you restrict yourself to globs which exist at compile-time then the result ought to be unambiguous, because code like `${"^G"} = 1` is compiled as two ops - a constant string and a dereference (rv2gv) - so that the glob is created at runtime.
If you're working with globs at runtime, and need to disambiguate \*^G from \*{"^G"}, then you should use the raw NAME method.
STASH SV IO FORM AV HV EGV CV CVGEN LINE FILE FILEGV GvREFCNT FLAGS GPFLAGS This last one is present only in perl 5.22.0 and higher.
###
B::IO Methods
B::IO objects derive from IO objects and you will get more information from the IO object itself.
For example:
```
$gvio = B::svref_2object(\*main::stdin)->IO;
$IO = $gvio->object_2svref();
$fd = $IO->fileno();
```
LINES PAGE PAGE\_LEN LINES\_LEFT TOP\_NAME TOP\_GV FMT\_NAME FMT\_GV BOTTOM\_NAME BOTTOM\_GV SUBPROCESS IoTYPE A character symbolizing the type of IO Handle.
```
- STDIN/OUT
I STDIN/OUT/ERR
< read-only
> write-only
a append
+ read and write
s socket
| pipe
I IMPLICIT
# NUMERIC
space closed handle
\0 closed internal handle
```
IoFLAGS IsSTD Takes one argument ( 'stdin' | 'stdout' | 'stderr' ) and returns true if the IoIFP of the object is equal to the handle whose name was passed as argument; i.e., $io->IsSTD('stderr') is true if IoIFP($io) == PerlIO\_stderr().
###
B::AV Methods
FILL MAX ARRAY ARRAYelt Like `ARRAY`, but takes an index as an argument to get only one element, rather than a list of all of them.
###
B::CV Methods
STASH START ROOT GV FILE DEPTH PADLIST Returns a B::PADLIST object.
OUTSIDE OUTSIDE\_SEQ XSUB XSUBANY For constant subroutines, returns the constant SV returned by the subroutine.
CvFLAGS const\_sv NAME\_HEK Returns the name of a lexical sub, otherwise `undef`.
###
B::HV Methods
FILL MAX KEYS RITER NAME ARRAY ###
OP-RELATED CLASSES
`B::OP`, `B::UNOP`, `B::UNOP_AUX`, `B::BINOP`, `B::LOGOP`, `B::LISTOP`, `B::PMOP`, `B::SVOP`, `B::PADOP`, `B::PVOP`, `B::LOOP`, `B::COP`, `B::METHOP`.
These classes correspond in the obvious way to the underlying C structures of similar names. The inheritance hierarchy mimics the underlying C "inheritance":
```
B::OP
|
+----------+---------+--------+-------+---------+
| | | | | |
B::UNOP B::SVOP B::PADOP B::COP B::PVOP B::METHOP
|
+---+---+---------+
| | |
B::BINOP B::LOGOP B::UNOP_AUX
|
|
B::LISTOP
|
+---+---+
| |
B::LOOP B::PMOP
```
Access methods correspond to the underlying C structure field names, with the leading "class indication" prefix (`"op_"`) removed.
###
B::OP Methods
These methods get the values of similarly named fields within the OP data structure. See top of `op.h` for more info.
next sibling parent Returns the OP's parent. If it has no parent, or if your perl wasn't built with `-DPERL_OP_PARENT`, returns NULL.
Note that the global variable `$B::OP::does_parent` is undefined on older perls that don't support the `parent` method, is defined but false on perls that support the method but were built without `-DPERL_OP_PARENT`, and is true otherwise.
name This returns the op name as a string (e.g. "add", "rv2av").
ppaddr This returns the function name as a string (e.g. "PL\_ppaddr[OP\_ADD]", "PL\_ppaddr[OP\_RV2AV]").
desc This returns the op description from the global C PL\_op\_desc array (e.g. "addition" "array deref").
targ type opt flags private spare ###
B::UNOP Method
first ###
B::UNOP\_AUX Methods (since 5.22)
aux\_list(cv) This returns a list of the elements of the op's aux data structure, or a null list if there is no aux. What will be returned depends on the object's type, but will typically be a collection of `B::IV`, `B::GV`, etc. objects. `cv` is the `B::CV` object representing the sub that the op is contained within.
string(cv) This returns a textual representation of the object (likely to b useful for deparsing and debugging), or an empty string if the op type doesn't support this. `cv` is the `B::CV` object representing the sub that the op is contained within.
###
B::BINOP Method
last ###
B::LOGOP Method
other ###
B::LISTOP Method
children ###
B::PMOP Methods
pmreplroot pmreplstart pmflags precomp pmoffset Only when perl was compiled with ithreads.
code\_list Since perl 5.17.1
pmregexp Added in perl 5.22, this method returns the B::REGEXP associated with the op. While PMOPs do not actually have `pmregexp` fields under threaded builds, this method returns the regexp under threads nonetheless, for convenience.
###
B::SVOP Methods
sv gv ###
B::PADOP Method
padix ###
B::PVOP Method
pv ###
B::LOOP Methods
redoop nextop lastop ###
B::COP Methods
The `B::COP` class is used for "nextstate" and "dbstate" ops. As of Perl 5.22, it is also used for "null" ops that started out as COPs.
label stash stashpv
stashoff (threaded only) file cop\_seq line warnings io hints hints\_hash ###
B::METHOP Methods (Since Perl 5.22)
first meth\_sv ###
PAD-RELATED CLASSES
Perl 5.18 introduced a new class, B::PADLIST, returned by B::CV's `PADLIST` method.
Perl 5.22 introduced the B::PADNAMELIST and B::PADNAME classes.
###
B::PADLIST Methods
MAX ARRAY A list of pads. The first one is a B::PADNAMELIST containing the names. The rest are currently B::AV objects, but that could change in future versions.
ARRAYelt Like `ARRAY`, but takes an index as an argument to get only one element, rather than a list of all of them.
NAMES This method, introduced in 5.22, returns the B::PADNAMELIST. It is equivalent to `ARRAYelt` with a 0 argument.
REFCNT id This method, introduced in 5.22, returns an ID shared by clones of the same padlist.
outid This method, also added in 5.22, returns the ID of the outer padlist.
###
B::PADNAMELIST Methods
MAX ARRAY ARRAYelt These two methods return the pad names, using B::SPECIAL objects for null pointers and B::PADNAME objects otherwise.
REFCNT ###
B::PADNAME Methods
PV PVX LEN REFCNT FLAGS For backward-compatibility, if the PADNAMEt\_OUTER flag is set, the FLAGS method adds the SVf\_FAKE flag, too.
TYPE A B::HV object representing the stash for a typed lexical.
SvSTASH A backward-compatibility alias for TYPE.
OURSTASH A B::HV object representing the stash for 'our' variables.
PROTOCV The prototype CV for a 'my' sub.
COP\_SEQ\_RANGE\_LOW COP\_SEQ\_RANGE\_HIGH Sequence numbers representing the scope within which a lexical is visible. Meaningless if PADNAMEt\_OUTER is set.
PARENT\_PAD\_INDEX Only meaningful if PADNAMEt\_OUTER is set.
PARENT\_FAKELEX\_FLAGS Only meaningful if PADNAMEt\_OUTER is set.
###
$B::overlay
Although the optree is read-only, there is an overlay facility that allows you to override what values the various B::\*OP methods return for a particular op. `$B::overlay` should be set to reference a two-deep hash: indexed by OP address, then method name. Whenever a an op method is called, the value in the hash is returned if it exists. This facility is used by B::Deparse to "undo" some optimisations. For example:
```
local $B::overlay = {};
...
if ($op->name eq "foo") {
$B::overlay->{$$op} = {
name => 'bar',
next => $op->next->next,
};
}
...
$op->name # returns "bar"
$op->next # returns the next op but one
```
AUTHOR
------
Malcolm Beattie, `[email protected]`
| programming_docs |
perl perlreftut perlreftut
==========
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
* [Who Needs Complicated Data Structures?](#Who-Needs-Complicated-Data-Structures?)
* [The Solution](#The-Solution)
* [Syntax](#Syntax)
+ [Making References](#Making-References)
- [Make Rule 1](#Make-Rule-1)
- [Make Rule 2](#Make-Rule-2)
+ [Using References](#Using-References)
- [Use Rule 1](#Use-Rule-1)
- [Use Rule 2](#Use-Rule-2)
+ [An Example](#An-Example)
+ [Arrow Rule](#Arrow-Rule)
* [Solution](#Solution)
* [The Rest](#The-Rest)
* [Summary](#Summary)
* [Credits](#Credits)
+ [Distribution Conditions](#Distribution-Conditions)
NAME
----
perlreftut - Mark's very short tutorial about references
DESCRIPTION
-----------
One of the most important new features in Perl 5 was the capability to manage complicated data structures like multidimensional arrays and nested hashes. To enable these, Perl 5 introduced a feature called *references*, and using references is the key to managing complicated, structured data in Perl. Unfortunately, there's a lot of funny syntax to learn, and the main manual page can be hard to follow. The manual is quite complete, and sometimes people find that a problem, because it can be hard to tell what is important and what isn't.
Fortunately, you only need to know 10% of what's in the main page to get 90% of the benefit. This page will show you that 10%.
Who Needs Complicated Data Structures?
---------------------------------------
One problem that comes up all the time is needing a hash whose values are lists. Perl has hashes, of course, but the values have to be scalars; they can't be lists.
Why would you want a hash of lists? Let's take a simple example: You have a file of city and country names, like this:
```
Chicago, USA
Frankfurt, Germany
Berlin, Germany
Washington, USA
Helsinki, Finland
New York, USA
```
and you want to produce an output like this, with each country mentioned once, and then an alphabetical list of the cities in that country:
```
Finland: Helsinki.
Germany: Berlin, Frankfurt.
USA: Chicago, New York, Washington.
```
The natural way to do this is to have a hash whose keys are country names. Associated with each country name key is a list of the cities in that country. Each time you read a line of input, split it into a country and a city, look up the list of cities already known to be in that country, and append the new city to the list. When you're done reading the input, iterate over the hash as usual, sorting each list of cities before you print it out.
If hash values couldn't be lists, you lose. You'd probably have to combine all the cities into a single string somehow, and then when time came to write the output, you'd have to break the string into a list, sort the list, and turn it back into a string. This is messy and error-prone. And it's frustrating, because Perl already has perfectly good lists that would solve the problem if only you could use them.
The Solution
-------------
By the time Perl 5 rolled around, we were already stuck with this design: Hash values must be scalars. The solution to this is references.
A reference is a scalar value that *refers to* an entire array or an entire hash (or to just about anything else). Names are one kind of reference that you're already familiar with. Each human being is a messy, inconvenient collection of cells. But to refer to a particular human, for instance the first computer programmer, it isn't necessary to describe each of their cells; all you need is the easy, convenient scalar string "Ada Lovelace".
References in Perl are like names for arrays and hashes. They're Perl's private, internal names, so you can be sure they're unambiguous. Unlike a human name, a reference only refers to one thing, and you always know what it refers to. If you have a reference to an array, you can recover the entire array from it. If you have a reference to a hash, you can recover the entire hash. But the reference is still an easy, compact scalar value.
You can't have a hash whose values are arrays; hash values can only be scalars. We're stuck with that. But a single reference can refer to an entire array, and references are scalars, so you can have a hash of references to arrays, and it'll act a lot like a hash of arrays, and it'll be just as useful as a hash of arrays.
We'll come back to this city-country problem later, after we've seen some syntax for managing references.
Syntax
------
There are just two ways to make a reference, and just two ways to use it once you have it.
###
Making References
####
**Make Rule 1**
If you put a `\` in front of a variable, you get a reference to that variable.
```
$aref = \@array; # $aref now holds a reference to @array
$href = \%hash; # $href now holds a reference to %hash
$sref = \$scalar; # $sref now holds a reference to $scalar
```
Once the reference is stored in a variable like $aref or $href, you can copy it or store it just the same as any other scalar value:
```
$xy = $aref; # $xy now holds a reference to @array
$p[3] = $href; # $p[3] now holds a reference to %hash
$z = $p[3]; # $z now holds a reference to %hash
```
These examples show how to make references to variables with names. Sometimes you want to make an array or a hash that doesn't have a name. This is analogous to the way you like to be able to use the string `"\n"` or the number 80 without having to store it in a named variable first.
####
**Make Rule 2**
`[ ITEMS ]` makes a new, anonymous array, and returns a reference to that array. `{ ITEMS }` makes a new, anonymous hash, and returns a reference to that hash.
```
$aref = [ 1, "foo", undef, 13 ];
# $aref now holds a reference to an array
$href = { APR => 4, AUG => 8 };
# $href now holds a reference to a hash
```
The references you get from rule 2 are the same kind of references that you get from rule 1:
```
# This:
$aref = [ 1, 2, 3 ];
# Does the same as this:
@array = (1, 2, 3);
$aref = \@array;
```
The first line is an abbreviation for the following two lines, except that it doesn't create the superfluous array variable `@array`.
If you write just `[]`, you get a new, empty anonymous array. If you write just `{}`, you get a new, empty anonymous hash.
###
Using References
What can you do with a reference once you have it? It's a scalar value, and we've seen that you can store it as a scalar and get it back again just like any scalar. There are just two more ways to use it:
####
**Use Rule 1**
You can always use an array reference, in curly braces, in place of the name of an array. For example, `@{$aref}` instead of `@array`.
Here are some examples of that:
Arrays:
```
@a @{$aref} An array
reverse @a reverse @{$aref} Reverse the array
$a[3] ${$aref}[3] An element of the array
$a[3] = 17; ${$aref}[3] = 17 Assigning an element
```
On each line are two expressions that do the same thing. The left-hand versions operate on the array `@a`. The right-hand versions operate on the array that is referred to by `$aref`. Once they find the array they're operating on, both versions do the same things to the arrays.
Using a hash reference is *exactly* the same:
```
%h %{$href} A hash
keys %h keys %{$href} Get the keys from the hash
$h{'red'} ${$href}{'red'} An element of the hash
$h{'red'} = 17 ${$href}{'red'} = 17 Assigning an element
```
Whatever you want to do with a reference, **Use Rule 1** tells you how to do it. You just write the Perl code that you would have written for doing the same thing to a regular array or hash, and then replace the array or hash name with `{$reference}`. "How do I loop over an array when all I have is a reference?" Well, to loop over an array, you would write
```
for my $element (@array) {
...
}
```
so replace the array name, `@array`, with the reference:
```
for my $element (@{$aref}) {
...
}
```
"How do I print out the contents of a hash when all I have is a reference?" First write the code for printing out a hash:
```
for my $key (keys %hash) {
print "$key => $hash{$key}\n";
}
```
And then replace the hash name with the reference:
```
for my $key (keys %{$href}) {
print "$key => ${$href}{$key}\n";
}
```
####
**Use Rule 2**
[**Use Rule 1**](#Use-Rule-1) is all you really need, because it tells you how to do absolutely everything you ever need to do with references. But the most common thing to do with an array or a hash is to extract a single element, and the [**Use Rule 1**](#Use-Rule-1) notation is cumbersome. So there is an abbreviation.
`${$aref}[3]` is too hard to read, so you can write `$aref->[3]` instead.
`${$href}{red}` is too hard to read, so you can write `$href->{red}` instead.
If `$aref` holds a reference to an array, then `$aref->[3]` is the fourth element of the array. Don't confuse this with `$aref[3]`, which is the fourth element of a totally different array, one deceptively named `@aref`. `$aref` and `@aref` are unrelated the same way that `$item` and `@item` are.
Similarly, `$href->{'red'}` is part of the hash referred to by the scalar variable `$href`, perhaps even one with no name. `$href{'red'}` is part of the deceptively named `%href` hash. It's easy to forget to leave out the `->`, and if you do, you'll get bizarre results when your program gets array and hash elements out of totally unexpected hashes and arrays that weren't the ones you wanted to use.
###
An Example
Let's see a quick example of how all this is useful.
First, remember that `[1, 2, 3]` makes an anonymous array containing `(1, 2, 3)`, and gives you a reference to that array.
Now think about
```
@a = ( [1, 2, 3],
[4, 5, 6],
[7, 8, 9]
);
```
`@a` is an array with three elements, and each one is a reference to another array.
`$a[1]` is one of these references. It refers to an array, the array containing `(4, 5, 6)`, and because it is a reference to an array, [**Use Rule 2**](#Use-Rule-2) says that we can write `$a[1]->[2]` to get the third element from that array. `$a[1]->[2]` is the 6. Similarly, `$a[0]->[1]` is the 2. What we have here is like a two-dimensional array; you can write `$a[ROW]->[COLUMN]` to get or set the element in any row and any column of the array.
The notation still looks a little cumbersome, so there's one more abbreviation:
###
Arrow Rule
In between two **subscripts**, the arrow is optional.
Instead of `$a[1]->[2]`, we can write `$a[1][2]`; it means the same thing. Instead of `$a[0]->[1] = 23`, we can write `$a[0][1] = 23`; it means the same thing.
Now it really looks like two-dimensional arrays!
You can see why the arrows are important. Without them, we would have had to write `${$a[1]}[2]` instead of `$a[1][2]`. For three-dimensional arrays, they let us write `$x[2][3][5]` instead of the unreadable `${${$x[2]}[3]}[5]`.
Solution
--------
Here's the answer to the problem I posed earlier, of reformatting a file of city and country names.
```
1 my %table;
2 while (<>) {
3 chomp;
4 my ($city, $country) = split /, /;
5 $table{$country} = [] unless exists $table{$country};
6 push @{$table{$country}}, $city;
7 }
8 for my $country (sort keys %table) {
9 print "$country: ";
10 my @cities = @{$table{$country}};
11 print join ', ', sort @cities;
12 print ".\n";
13 }
```
The program has two pieces: Lines 2-7 read the input and build a data structure, and lines 8-13 analyze the data and print out the report. We're going to have a hash, `%table`, whose keys are country names, and whose values are references to arrays of city names. The data structure will look like this:
```
%table
+-------+---+
| | | +-----------+--------+
|Germany| *---->| Frankfurt | Berlin |
| | | +-----------+--------+
+-------+---+
| | | +----------+
|Finland| *---->| Helsinki |
| | | +----------+
+-------+---+
| | | +---------+------------+----------+
| USA | *---->| Chicago | Washington | New York |
| | | +---------+------------+----------+
+-------+---+
```
We'll look at output first. Supposing we already have this structure, how do we print it out?
```
8 for my $country (sort keys %table) {
9 print "$country: ";
10 my @cities = @{$table{$country}};
11 print join ', ', sort @cities;
12 print ".\n";
13 }
```
`%table` is an ordinary hash, and we get a list of keys from it, sort the keys, and loop over the keys as usual. The only use of references is in line 10. `$table{$country}` looks up the key `$country` in the hash and gets the value, which is a reference to an array of cities in that country. [**Use Rule 1**](#Use-Rule-1) says that we can recover the array by saying `@{$table{$country}}`. Line 10 is just like
```
@cities = @array;
```
except that the name `array` has been replaced by the reference `{$table{$country}}`. The `@` tells Perl to get the entire array. Having gotten the list of cities, we sort it, join it, and print it out as usual.
Lines 2-7 are responsible for building the structure in the first place. Here they are again:
```
2 while (<>) {
3 chomp;
4 my ($city, $country) = split /, /;
5 $table{$country} = [] unless exists $table{$country};
6 push @{$table{$country}}, $city;
7 }
```
Lines 2-4 acquire a city and country name. Line 5 looks to see if the country is already present as a key in the hash. If it's not, the program uses the `[]` notation ([**Make Rule 2**](#Make-Rule-2)) to manufacture a new, empty anonymous array of cities, and installs a reference to it into the hash under the appropriate key.
Line 6 installs the city name into the appropriate array. `$table{$country}` now holds a reference to the array of cities seen in that country so far. Line 6 is exactly like
```
push @array, $city;
```
except that the name `array` has been replaced by the reference `{$table{$country}}`. The [`push`](perlfunc#push-ARRAY%2CLIST) adds a city name to the end of the referred-to array.
There's one fine point I skipped. Line 5 is unnecessary, and we can get rid of it.
```
2 while (<>) {
3 chomp;
4 my ($city, $country) = split /, /;
5 #### $table{$country} = [] unless exists $table{$country};
6 push @{$table{$country}}, $city;
7 }
```
If there's already an entry in `%table` for the current `$country`, then nothing is different. Line 6 will locate the value in `$table{$country}`, which is a reference to an array, and push `$city` into the array. But what does it do when `$country` holds a key, say `Greece`, that is not yet in `%table`?
This is Perl, so it does the exact right thing. It sees that you want to push `Athens` onto an array that doesn't exist, so it helpfully makes a new, empty, anonymous array for you, installs it into `%table`, and then pushes `Athens` onto it. This is called *autovivification*--bringing things to life automatically. Perl saw that the key wasn't in the hash, so it created a new hash entry automatically. Perl saw that you wanted to use the hash value as an array, so it created a new empty array and installed a reference to it in the hash automatically. And as usual, Perl made the array one element longer to hold the new city name.
The Rest
---------
I promised to give you 90% of the benefit with 10% of the details, and that means I left out 90% of the details. Now that you have an overview of the important parts, it should be easier to read the <perlref> manual page, which discusses 100% of the details.
Some of the highlights of <perlref>:
* You can make references to anything, including scalars, functions, and other references.
* In [**Use Rule 1**](#Use-Rule-1), you can omit the curly brackets whenever the thing inside them is an atomic scalar variable like `$aref`. For example, `@$aref` is the same as `@{$aref}`, and `$$aref[1]` is the same as `${$aref}[1]`. If you're just starting out, you may want to adopt the habit of always including the curly brackets.
* This doesn't copy the underlying array:
```
$aref2 = $aref1;
```
You get two references to the same array. If you modify `$aref1->[23]` and then look at `$aref2->[23]` you'll see the change.
To copy the array, use
```
$aref2 = [@{$aref1}];
```
This uses `[...]` notation to create a new anonymous array, and `$aref2` is assigned a reference to the new array. The new array is initialized with the contents of the array referred to by `$aref1`.
Similarly, to copy an anonymous hash, you can use
```
$href2 = {%{$href1}};
```
* To see if a variable contains a reference, use the [`ref`](perlfunc#ref-EXPR) function. It returns true if its argument is a reference. Actually it's a little better than that: It returns `HASH` for hash references and `ARRAY` for array references.
* If you try to use a reference like a string, you get strings like
```
ARRAY(0x80f5dec) or HASH(0x826afc0)
```
If you ever see a string that looks like this, you'll know you printed out a reference by mistake.
A side effect of this representation is that you can use [`eq`](perlop#Equality-Operators) to see if two references refer to the same thing. (But you should usually use [`==`](perlop#Equality-Operators) instead because it's much faster.)
* You can use a string as if it were a reference. If you use the string `"foo"` as an array reference, it's taken to be a reference to the array `@foo`. This is called a *symbolic reference*. The declaration [`use strict 'refs'`](strict) disables this feature, which can cause all sorts of trouble if you use it by accident.
You might prefer to go on to <perllol> instead of <perlref>; it discusses lists of lists and multidimensional arrays in detail. After that, you should move on to <perldsc>; it's a Data Structure Cookbook that shows recipes for using and printing out arrays of hashes, hashes of arrays, and other kinds of data.
Summary
-------
Everyone needs compound data structures, and in Perl the way you get them is with references. There are four important rules for managing references: Two for making references and two for using them. Once you know these rules you can do most of the important things you need to do with references.
Credits
-------
Author: Mark Jason Dominus, Plover Systems (`[email protected]`)
This article originally appeared in *The Perl Journal* ( <http://www.tpj.com/> ) volume 3, #2. Reprinted with permission.
The original title was *Understand References Today*.
###
Distribution Conditions
Copyright 1998 The Perl Journal.
This documentation is free; you can redistribute it and/or modify it under the same terms as Perl itself.
Irrespective of its distribution, all code examples in these files are hereby placed into the public domain. You are permitted and encouraged to use this code in your own programs for fun or for profit as you see fit. A simple comment in the code giving credit would be courteous but is not required.
perl List::Util::XS List::Util::XS
==============
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [SEE ALSO](#SEE-ALSO)
* [COPYRIGHT](#COPYRIGHT)
NAME
----
List::Util::XS - Indicate if List::Util was compiled with a C compiler
SYNOPSIS
--------
```
use List::Util::XS 1.20;
```
DESCRIPTION
-----------
`List::Util::XS` can be used as a dependency to ensure List::Util was installed using a C compiler and that the XS version is installed.
During installation `$List::Util::XS::VERSION` will be set to `undef` if the XS was not compiled.
Starting with release 1.23\_03, Scalar-List-Util is **always** using the XS implementation, but for backwards compatibility, we still ship the `List::Util::XS` module which just loads `List::Util`.
SEE ALSO
---------
<Scalar::Util>, <List::Util>, <List::MoreUtils>
COPYRIGHT
---------
Copyright (c) 2008 Graham Barr <[email protected]>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
| programming_docs |
perl ExtUtils::MM_Win32 ExtUtils::MM\_Win32
===================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [Overridden methods](#Overridden-methods)
NAME
----
ExtUtils::MM\_Win32 - methods to override UN\*X behaviour in ExtUtils::MakeMaker
SYNOPSIS
--------
```
use ExtUtils::MM_Win32; # Done internally by ExtUtils::MakeMaker if needed
```
DESCRIPTION
-----------
See <ExtUtils::MM_Unix> for a documentation of the methods provided there. This package overrides the implementation of these methods, not the semantics.
###
Overridden methods
**dlsyms** xs\_dlsyms\_ext On Win32, is `.def`.
replace\_manpage\_separator Changes the path separator with .
**maybe\_command** Since Windows has nothing as simple as an executable bit, we check the file extension.
The PATHEXT env variable will be used to get a list of extensions that might indicate a command, otherwise .com, .exe, .bat and .cmd will be used by default.
**init\_DIRFILESEP** Using \ for Windows, except for "gmake" where it is /.
init\_tools Override some of the slower, portable commands with Windows specific ones.
init\_others Override the default link and compile tools.
LDLOADLIBS's default is changed to $Config{libs}.
Adjustments are made for Borland's quirks needing -L to come first.
init\_platform Add MM\_Win32\_VERSION.
platform\_constants specify\_shell Set SHELL to $ENV{COMSPEC} only if make is type 'gmake'.
constants Add MAXLINELENGTH for dmake before all the constants are output.
special\_targets Add .USESHELL target for dmake.
static\_lib\_pure\_cmd Defines how to run the archive utility
dynamic\_lib Methods are overridden here: not dynamic\_lib itself, but the utility ones that do the OS-specific work.
extra\_clean\_files Clean out some extra dll.{base,exp} files which might be generated by gcc. Otherwise, take out all \*.pdb files.
init\_linker perl\_script Checks for the perl program under several common perl extensions.
quote\_dep xs\_obj\_opt Override to fixup -o flags for MSVC.
pasthru All we send is -nologo to nmake to prevent it from printing its damned banner.
arch\_check (override) Normalize all arguments for consistency of comparison.
oneliner These are based on what command.com does on Win98. They may be wrong for other Windows shells, I don't know.
cd dmake can handle Unix style cd'ing but nmake (at least 1.5) cannot. It wants:
```
cd dir1\dir2
command
another_command
cd ..\..
```
max\_exec\_len nmake 1.50 limits command length to 2048 characters.
os\_flavor Windows is Win32.
dbgoutflag Returns a CC flag that tells the CC to emit a separate debugging symbol file when compiling an object file.
cflags Defines the PERLDLL symbol if we are configured for static building since all code destined for the perl5xx.dll must be compiled with the PERLDLL symbol defined.
make\_type Returns a suitable string describing the type of makefile being written.
perl Pod::Simple::PullParserToken Pod::Simple::PullParserToken
============================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [SEE ALSO](#SEE-ALSO)
* [SUPPORT](#SUPPORT)
* [COPYRIGHT AND DISCLAIMERS](#COPYRIGHT-AND-DISCLAIMERS)
* [AUTHOR](#AUTHOR)
NAME
----
Pod::Simple::PullParserToken -- tokens from Pod::Simple::PullParser
SYNOPSIS
--------
Given a $parser that's an object of class Pod::Simple::PullParser (or a subclass)...
```
while(my $token = $parser->get_token) {
$DEBUG and print STDERR "Token: ", $token->dump, "\n";
if($token->is_start) {
...access $token->tagname, $token->attr, etc...
} elsif($token->is_text) {
...access $token->text, $token->text_r, etc...
} elsif($token->is_end) {
...access $token->tagname...
}
}
```
(Also see <Pod::Simple::PullParser>)
DESCRIPTION
-----------
When you do $parser->get\_token on a <Pod::Simple::PullParser>, you should get an object of a subclass of Pod::Simple::PullParserToken.
Subclasses will add methods, and will also inherit these methods:
$token->type This returns the type of the token. This will be either the string "start", the string "text", or the string "end".
Once you know what the type of an object is, you then know what subclass it belongs to, and therefore what methods it supports.
Yes, you could probably do the same thing with code like $token->isa('Pod::Simple::PullParserEndToken'), but that's not so pretty as using just $token->type, or even the following shortcuts:
$token->is\_start This is a shortcut for `$token->type() eq "start"`
$token->is\_text This is a shortcut for `$token->type() eq "text"`
$token->is\_end This is a shortcut for `$token->type() eq "end"`
$token->dump This returns a handy stringified value of this object. This is useful for debugging, as in:
```
while(my $token = $parser->get_token) {
$DEBUG and print STDERR "Token: ", $token->dump, "\n";
...
}
```
SEE ALSO
---------
My subclasses: <Pod::Simple::PullParserStartToken>, <Pod::Simple::PullParserTextToken>, and <Pod::Simple::PullParserEndToken>.
<Pod::Simple::PullParser> and <Pod::Simple>
SUPPORT
-------
Questions or discussion about POD and Pod::Simple should be sent to the [email protected] mail list. Send an empty email to [email protected] to subscribe.
This module is managed in an open GitHub repository, <https://github.com/perl-pod/pod-simple/>. Feel free to fork and contribute, or to clone <git://github.com/perl-pod/pod-simple.git> and send patches!
Patches against Pod::Simple are welcome. Please send bug reports to <[email protected]>.
COPYRIGHT AND DISCLAIMERS
--------------------------
Copyright (c) 2002 Sean M. Burke.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.
AUTHOR
------
Pod::Simple was created by Sean M. Burke <[email protected]>. But don't bother him, he's retired.
Pod::Simple is maintained by:
* Allison Randal `[email protected]`
* Hans Dieter Pearcey `[email protected]`
* David E. Wheeler `[email protected]`
perl warnings warnings
========
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [Default Warnings and Optional Warnings](#Default-Warnings-and-Optional-Warnings)
+ ["Negative warnings"](#%22Negative-warnings%22)
+ [What's wrong with -w and $^W](#What's-wrong-with-w-and-%24%5EW)
+ [Controlling Warnings from the Command Line](#Controlling-Warnings-from-the-Command-Line)
+ [Backward Compatibility](#Backward-Compatibility)
+ [Category Hierarchy](#Category-Hierarchy)
+ [Fatal Warnings](#Fatal-Warnings)
+ [Reporting Warnings from a Module](#Reporting-Warnings-from-a-Module)
* [FUNCTIONS](#FUNCTIONS)
NAME
----
warnings - Perl pragma to control optional warnings
SYNOPSIS
--------
```
use warnings;
no warnings;
# Standard warnings are enabled by use v5.35 or above
use v5.35;
use warnings "all";
no warnings "uninitialized";
# or equivalent to those last two ...
use warnings qw(all -uninitialized);
use warnings::register;
if (warnings::enabled()) {
warnings::warn("some warning");
}
if (warnings::enabled("void")) {
warnings::warn("void", "some warning");
}
if (warnings::enabled($object)) {
warnings::warn($object, "some warning");
}
warnings::warnif("some warning");
warnings::warnif("void", "some warning");
warnings::warnif($object, "some warning");
```
DESCRIPTION
-----------
The `warnings` pragma gives control over which warnings are enabled in which parts of a Perl program. It's a more flexible alternative for both the command line flag **-w** and the equivalent Perl variable, `$^W`.
This pragma works just like the `strict` pragma. This means that the scope of the warning pragma is limited to the enclosing block. It also means that the pragma setting will not leak across files (via `use`, `require` or `do`). This allows authors to independently define the degree of warning checks that will be applied to their module.
By default, optional warnings are disabled, so any legacy code that doesn't attempt to control the warnings will work unchanged.
All warnings are enabled in a block by either of these:
```
use warnings;
use warnings 'all';
```
Similarly all warnings are disabled in a block by either of these:
```
no warnings;
no warnings 'all';
```
For example, consider the code below:
```
use warnings;
my @x;
{
no warnings;
my $y = @x[0];
}
my $z = @x[0];
```
The code in the enclosing block has warnings enabled, but the inner block has them disabled. In this case that means the assignment to the scalar `$z` will trip the `"Scalar value @x[0] better written as $x[0]"` warning, but the assignment to the scalar `$y` will not.
All warnings are enabled automatically within the scope of a `[use v5.35](perlfunc#use-VERSION)` (or higher) declaration.
###
Default Warnings and Optional Warnings
Before the introduction of lexical warnings, Perl had two classes of warnings: mandatory and optional.
As its name suggests, if your code tripped a mandatory warning, you would get a warning whether you wanted it or not. For example, the code below would always produce an `"isn't numeric"` warning about the "2:".
```
my $x = "2:" + 3;
```
With the introduction of lexical warnings, mandatory warnings now become *default* warnings. The difference is that although the previously mandatory warnings are still enabled by default, they can then be subsequently enabled or disabled with the lexical warning pragma. For example, in the code below, an `"isn't numeric"` warning will only be reported for the `$x` variable.
```
my $x = "2:" + 3;
no warnings;
my $y = "2:" + 3;
```
Note that neither the **-w** flag or the `$^W` can be used to disable/enable default warnings. They are still mandatory in this case.
###
"Negative warnings"
As a convenience, you can (as of Perl 5.34) pass arguments to the `import()` method both positively and negatively. Negative warnings are those with a `-` sign prepended to their names; positive warnings are anything else. This lets you turn on some warnings and turn off others in one command. So, assuming that you've already turned on a bunch of warnings but want to tweak them a bit in some block, you can do this:
```
{
use warnings qw(uninitialized -redefine);
...
}
```
which is equivalent to:
```
{
use warnings qw(uninitialized);
no warnings qw(redefine);
...
}
```
The argument list is processed in the order you specify. So, for example, if you don't want to be warned about use of experimental features, except for `somefeature` that you really dislike, you can say this:
```
use warnings qw(all -experimental experimental::somefeature);
```
which is equivalent to:
```
use warnings 'all';
no warnings 'experimental';
use warnings 'experimental::somefeature';
```
###
What's wrong with **-w** and `$^W`
Although very useful, the big problem with using **-w** on the command line to enable warnings is that it is all or nothing. Take the typical scenario when you are writing a Perl program. Parts of the code you will write yourself, but it's very likely that you will make use of pre-written Perl modules. If you use the **-w** flag in this case, you end up enabling warnings in pieces of code that you haven't written.
Similarly, using `$^W` to either disable or enable blocks of code is fundamentally flawed. For a start, say you want to disable warnings in a block of code. You might expect this to be enough to do the trick:
```
{
local ($^W) = 0;
my $x =+ 2;
my $y; chop $y;
}
```
When this code is run with the **-w** flag, a warning will be produced for the `$x` line: `"Reversed += operator"`.
The problem is that Perl has both compile-time and run-time warnings. To disable compile-time warnings you need to rewrite the code like this:
```
{
BEGIN { $^W = 0 }
my $x =+ 2;
my $y; chop $y;
}
```
And note that unlike the first example, this will permanently set `$^W` since it cannot both run during compile-time and be localized to a run-time block.
The other big problem with `$^W` is the way you can inadvertently change the warning setting in unexpected places in your code. For example, when the code below is run (without the **-w** flag), the second call to `doit` will trip a `"Use of uninitialized value"` warning, whereas the first will not.
```
sub doit
{
my $y; chop $y;
}
doit();
{
local ($^W) = 1;
doit()
}
```
This is a side-effect of `$^W` being dynamically scoped.
Lexical warnings get around these limitations by allowing finer control over where warnings can or can't be tripped.
###
Controlling Warnings from the Command Line
There are three Command Line flags that can be used to control when warnings are (or aren't) produced:
**-w** This is the existing flag. If the lexical warnings pragma is **not** used in any of your code, or any of the modules that you use, this flag will enable warnings everywhere. See ["Backward Compatibility"](#Backward-Compatibility) for details of how this flag interacts with lexical warnings.
**-W** If the **-W** flag is used on the command line, it will enable all warnings throughout the program regardless of whether warnings were disabled locally using `no warnings` or `$^W =0`. This includes all files that get included via `use`, `require` or `do`. Think of it as the Perl equivalent of the "lint" command.
**-X** Does the exact opposite to the **-W** flag, i.e. it disables all warnings.
###
Backward Compatibility
If you are used to working with a version of Perl prior to the introduction of lexically scoped warnings, or have code that uses both lexical warnings and `$^W`, this section will describe how they interact.
How Lexical Warnings interact with **-w**/`$^W`:
1. If none of the three command line flags (**-w**, **-W** or **-X**) that control warnings is used and neither `$^W` nor the `warnings` pragma are used, then default warnings will be enabled and optional warnings disabled. This means that legacy code that doesn't attempt to control the warnings will work unchanged.
2. The **-w** flag just sets the global `$^W` variable as in 5.005. This means that any legacy code that currently relies on manipulating `$^W` to control warning behavior will still work as is.
3. Apart from now being a boolean, the `$^W` variable operates in exactly the same horrible uncontrolled global way, except that it cannot disable/enable default warnings.
4. If a piece of code is under the control of the `warnings` pragma, both the `$^W` variable and the **-w** flag will be ignored for the scope of the lexical warning.
5. The only way to override a lexical warnings setting is with the **-W** or **-X** command line flags.
The combined effect of 3 & 4 is that it will allow code which uses the `warnings` pragma to control the warning behavior of $^W-type code (using a `local $^W=0`) if it really wants to, but not vice-versa.
###
Category Hierarchy
A hierarchy of "categories" have been defined to allow groups of warnings to be enabled/disabled in isolation.
The current hierarchy is:
```
all -+
|
+- closure
|
+- deprecated
|
+- exiting
|
+- experimental --+
| |
| +- experimental::alpha_assertions
| |
| +- experimental::args_array_with_signatures
| |
| +- experimental::bitwise
| |
| +- experimental::builtin
| |
| +- experimental::const_attr
| |
| +- experimental::declared_refs
| |
| +- experimental::defer
| |
| +- experimental::extra_paired_delimiters
| |
| +- experimental::for_list
| |
| +- experimental::isa
| |
| +- experimental::lexical_subs
| |
| +- experimental::postderef
| |
| +- experimental::private_use
| |
| +- experimental::re_strict
| |
| +- experimental::refaliasing
| |
| +- experimental::regex_sets
| |
| +- experimental::script_run
| |
| +- experimental::signatures
| |
| +- experimental::smartmatch
| |
| +- experimental::try
| |
| +- experimental::uniprop_wildcards
| |
| +- experimental::vlb
|
+- glob
|
+- imprecision
|
+- io ------------+
| |
| +- closed
| |
| +- exec
| |
| +- layer
| |
| +- newline
| |
| +- pipe
| |
| +- syscalls
| |
| +- unopened
|
+- locale
|
+- misc
|
+- missing
|
+- numeric
|
+- once
|
+- overflow
|
+- pack
|
+- portable
|
+- recursion
|
+- redefine
|
+- redundant
|
+- regexp
|
+- scalar
|
+- severe --------+
| |
| +- debugging
| |
| +- inplace
| |
| +- internal
| |
| +- malloc
|
+- shadow
|
+- signal
|
+- substr
|
+- syntax --------+
| |
| +- ambiguous
| |
| +- bareword
| |
| +- digit
| |
| +- illegalproto
| |
| +- parenthesis
| |
| +- precedence
| |
| +- printf
| |
| +- prototype
| |
| +- qw
| |
| +- reserved
| |
| +- semicolon
|
+- taint
|
+- threads
|
+- uninitialized
|
+- unpack
|
+- untie
|
+- utf8 ----------+
| |
| +- non_unicode
| |
| +- nonchar
| |
| +- surrogate
|
+- void
```
Just like the "strict" pragma any of these categories can be combined
```
use warnings qw(void redefine);
no warnings qw(io syntax untie);
```
Also like the "strict" pragma, if there is more than one instance of the `warnings` pragma in a given scope the cumulative effect is additive.
```
use warnings qw(void); # only "void" warnings enabled
...
use warnings qw(io); # only "void" & "io" warnings enabled
...
no warnings qw(void); # only "io" warnings enabled
```
To determine which category a specific warning has been assigned to see <perldiag>.
Note: Before Perl 5.8.0, the lexical warnings category "deprecated" was a sub-category of the "syntax" category. It is now a top-level category in its own right.
Note: Before 5.21.0, the "missing" lexical warnings category was internally defined to be the same as the "uninitialized" category. It is now a top-level category in its own right.
###
Fatal Warnings
The presence of the word "FATAL" in the category list will escalate warnings in those categories into fatal errors in that lexical scope.
**NOTE:** FATAL warnings should be used with care, particularly `FATAL => 'all'`.
Libraries using [warnings::warn](#FUNCTIONS) for custom warning categories generally don't expect [warnings::warn](#FUNCTIONS) to be fatal and can wind up in an unexpected state as a result. For XS modules issuing categorized warnings, such unanticipated exceptions could also expose memory leak bugs.
Moreover, the Perl interpreter itself has had serious bugs involving fatalized warnings. For a summary of resolved and unresolved problems as of January 2015, please see [this perl5-porters post](http://www.nntp.perl.org/group/perl.perl5.porters/2015/01/msg225235.html).
While some developers find fatalizing some warnings to be a useful defensive programming technique, using `FATAL => 'all'` to fatalize all possible warning categories -- including custom ones -- is particularly risky. Therefore, the use of `FATAL => 'all'` is [discouraged](perlpolicy#discouraged).
The [strictures](strictures#VERSION-2) module on CPAN offers one example of a warnings subset that the module's authors believe is relatively safe to fatalize.
**NOTE:** Users of FATAL warnings, especially those using `FATAL => 'all'`, should be fully aware that they are risking future portability of their programs by doing so. Perl makes absolutely no commitments to not introduce new warnings or warnings categories in the future; indeed, we explicitly reserve the right to do so. Code that may not warn now may warn in a future release of Perl if the Perl5 development team deems it in the best interests of the community to do so. Should code using FATAL warnings break due to the introduction of a new warning we will NOT consider it an incompatible change. Users of FATAL warnings should take special caution during upgrades to check to see if their code triggers any new warnings and should pay particular attention to the fine print of the documentation of the features they use to ensure they do not exploit features that are documented as risky, deprecated, or unspecified, or where the documentation says "so don't do that", or anything with the same sense and spirit. Use of such features in combination with FATAL warnings is ENTIRELY AT THE USER'S RISK.
The following documentation describes how to use FATAL warnings but the perl5 porters strongly recommend that you understand the risks before doing so, especially for library code intended for use by others, as there is no way for downstream users to change the choice of fatal categories.
In the code below, the use of `time`, `length` and `join` can all produce a `"Useless use of xxx in void context"` warning.
```
use warnings;
time;
{
use warnings FATAL => qw(void);
length "abc";
}
join "", 1,2,3;
print "done\n";
```
When run it produces this output
```
Useless use of time in void context at fatal line 3.
Useless use of length in void context at fatal line 7.
```
The scope where `length` is used has escalated the `void` warnings category into a fatal error, so the program terminates immediately when it encounters the warning.
To explicitly turn off a "FATAL" warning you just disable the warning it is associated with. So, for example, to disable the "void" warning in the example above, either of these will do the trick:
```
no warnings qw(void);
no warnings FATAL => qw(void);
```
If you want to downgrade a warning that has been escalated into a fatal error back to a normal warning, you can use the "NONFATAL" keyword. For example, the code below will promote all warnings into fatal errors, except for those in the "syntax" category.
```
use warnings FATAL => 'all', NONFATAL => 'syntax';
```
As of Perl 5.20, instead of `use warnings FATAL => 'all';` you can use:
```
use v5.20; # Perl 5.20 or greater is required for the following
use warnings 'FATAL'; # short form of "use warnings FATAL => 'all';"
```
However, you should still heed the guidance earlier in this section against using `use warnings FATAL => 'all';`.
If you want your program to be compatible with versions of Perl before 5.20, you must use `use warnings FATAL => 'all';` instead. (In previous versions of Perl, the behavior of the statements `use warnings 'FATAL';`, `use warnings 'NONFATAL';` and `no warnings 'FATAL';` was unspecified; they did not behave as if they included the `=> 'all'` portion. As of 5.20, they do.)
###
Reporting Warnings from a Module
The `warnings` pragma provides a number of functions that are useful for module authors. These are used when you want to report a module-specific warning to a calling module has enabled warnings via the `warnings` pragma.
Consider the module `MyMod::Abc` below.
```
package MyMod::Abc;
use warnings::register;
sub open {
my $path = shift;
if ($path !~ m#^/#) {
warnings::warn("changing relative path to /var/abc")
if warnings::enabled();
$path = "/var/abc/$path";
}
}
1;
```
The call to `warnings::register` will create a new warnings category called "MyMod::Abc", i.e. the new category name matches the current package name. The `open` function in the module will display a warning message if it gets given a relative path as a parameter. This warnings will only be displayed if the code that uses `MyMod::Abc` has actually enabled them with the `warnings` pragma like below.
```
use MyMod::Abc;
use warnings 'MyMod::Abc';
...
abc::open("../fred.txt");
```
It is also possible to test whether the pre-defined warnings categories are set in the calling module with the `warnings::enabled` function. Consider this snippet of code:
```
package MyMod::Abc;
sub open {
if (warnings::enabled("deprecated")) {
warnings::warn("deprecated",
"open is deprecated, use new instead");
}
new(@_);
}
sub new
...
1;
```
The function `open` has been deprecated, so code has been included to display a warning message whenever the calling module has (at least) the "deprecated" warnings category enabled. Something like this, say.
```
use warnings 'deprecated';
use MyMod::Abc;
...
MyMod::Abc::open($filename);
```
Either the `warnings::warn` or `warnings::warnif` function should be used to actually display the warnings message. This is because they can make use of the feature that allows warnings to be escalated into fatal errors. So in this case
```
use MyMod::Abc;
use warnings FATAL => 'MyMod::Abc';
...
MyMod::Abc::open('../fred.txt');
```
the `warnings::warnif` function will detect this and die after displaying the warning message.
The three warnings functions, `warnings::warn`, `warnings::warnif` and `warnings::enabled` can optionally take an object reference in place of a category name. In this case the functions will use the class name of the object as the warnings category.
Consider this example:
```
package Original;
no warnings;
use warnings::register;
sub new
{
my $class = shift;
bless [], $class;
}
sub check
{
my $self = shift;
my $value = shift;
if ($value % 2 && warnings::enabled($self))
{ warnings::warn($self, "Odd numbers are unsafe") }
}
sub doit
{
my $self = shift;
my $value = shift;
$self->check($value);
# ...
}
1;
package Derived;
use warnings::register;
use Original;
our @ISA = qw( Original );
sub new
{
my $class = shift;
bless [], $class;
}
1;
```
The code below makes use of both modules, but it only enables warnings from `Derived`.
```
use Original;
use Derived;
use warnings 'Derived';
my $x = Original->new();
$x->doit(1);
my $y = Derived->new();
$x->doit(1);
```
When this code is run only the `Derived` object, `$y`, will generate a warning.
```
Odd numbers are unsafe at main.pl line 7
```
Notice also that the warning is reported at the line where the object is first used.
When registering new categories of warning, you can supply more names to warnings::register like this:
```
package MyModule;
use warnings::register qw(format precision);
...
warnings::warnif('MyModule::format', '...');
```
FUNCTIONS
---------
Note: The functions with names ending in `_at_level` were added in Perl 5.28.
use warnings::register Creates a new warnings category with the same name as the package where the call to the pragma is used.
warnings::enabled() Use the warnings category with the same name as the current package.
Return TRUE if that warnings category is enabled in the calling module. Otherwise returns FALSE.
warnings::enabled($category) Return TRUE if the warnings category, `$category`, is enabled in the calling module. Otherwise returns FALSE.
warnings::enabled($object) Use the name of the class for the object reference, `$object`, as the warnings category.
Return TRUE if that warnings category is enabled in the first scope where the object is used. Otherwise returns FALSE.
warnings::enabled\_at\_level($category, $level) Like `warnings::enabled`, but $level specifies the exact call frame, 0 being the immediate caller.
warnings::fatal\_enabled() Return TRUE if the warnings category with the same name as the current package has been set to FATAL in the calling module. Otherwise returns FALSE.
warnings::fatal\_enabled($category) Return TRUE if the warnings category `$category` has been set to FATAL in the calling module. Otherwise returns FALSE.
warnings::fatal\_enabled($object) Use the name of the class for the object reference, `$object`, as the warnings category.
Return TRUE if that warnings category has been set to FATAL in the first scope where the object is used. Otherwise returns FALSE.
warnings::fatal\_enabled\_at\_level($category, $level) Like `warnings::fatal_enabled`, but $level specifies the exact call frame, 0 being the immediate caller.
warnings::warn($message) Print `$message` to STDERR.
Use the warnings category with the same name as the current package.
If that warnings category has been set to "FATAL" in the calling module then die. Otherwise return.
warnings::warn($category, $message) Print `$message` to STDERR.
If the warnings category, `$category`, has been set to "FATAL" in the calling module then die. Otherwise return.
warnings::warn($object, $message) Print `$message` to STDERR.
Use the name of the class for the object reference, `$object`, as the warnings category.
If that warnings category has been set to "FATAL" in the scope where `$object` is first used then die. Otherwise return.
warnings::warn\_at\_level($category, $level, $message) Like `warnings::warn`, but $level specifies the exact call frame, 0 being the immediate caller.
warnings::warnif($message) Equivalent to:
```
if (warnings::enabled())
{ warnings::warn($message) }
```
warnings::warnif($category, $message) Equivalent to:
```
if (warnings::enabled($category))
{ warnings::warn($category, $message) }
```
warnings::warnif($object, $message) Equivalent to:
```
if (warnings::enabled($object))
{ warnings::warn($object, $message) }
```
warnings::warnif\_at\_level($category, $level, $message) Like `warnings::warnif`, but $level specifies the exact call frame, 0 being the immediate caller.
warnings::register\_categories(@names) This registers warning categories for the given names and is primarily for use by the warnings::register pragma.
See also ["Pragmatic Modules" in perlmodlib](perlmodlib#Pragmatic-Modules) and <perldiag>.
| programming_docs |
perl ExtUtils::MM_DOS ExtUtils::MM\_DOS
=================
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [Overridden methods](#Overridden-methods)
* [AUTHOR](#AUTHOR)
* [SEE ALSO](#SEE-ALSO)
NAME
----
ExtUtils::MM\_DOS - DOS specific subclass of ExtUtils::MM\_Unix
SYNOPSIS
--------
```
Don't use this module directly.
Use ExtUtils::MM and let it choose.
```
DESCRIPTION
-----------
This is a subclass of <ExtUtils::MM_Unix> which contains functionality for DOS.
Unless otherwise stated, it works just like ExtUtils::MM\_Unix.
###
Overridden methods
os\_flavor **replace\_manpage\_separator** Generates Foo\_\_Bar.3 style man page names
xs\_static\_lib\_is\_xs AUTHOR
------
Michael G Schwern <[email protected]> with code from ExtUtils::MM\_Unix
SEE ALSO
---------
<ExtUtils::MM_Unix>, <ExtUtils::MakeMaker>
perl sigtrap sigtrap
=======
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [OPTIONS](#OPTIONS)
+ [SIGNAL HANDLERS](#SIGNAL-HANDLERS)
+ [SIGNAL LISTS](#SIGNAL-LISTS)
+ [OTHER](#OTHER)
* [EXAMPLES](#EXAMPLES)
NAME
----
sigtrap - Perl pragma to enable simple signal handling
SYNOPSIS
--------
```
use sigtrap;
use sigtrap qw(stack-trace old-interface-signals); # equivalent
use sigtrap qw(BUS SEGV PIPE ABRT);
use sigtrap qw(die INT QUIT);
use sigtrap qw(die normal-signals);
use sigtrap qw(die untrapped normal-signals);
use sigtrap qw(die untrapped normal-signals
stack-trace any error-signals);
use sigtrap 'handler' => \&my_handler, 'normal-signals';
use sigtrap qw(handler my_handler normal-signals
stack-trace error-signals);
```
DESCRIPTION
-----------
The **sigtrap** pragma is a simple interface to installing signal handlers. You can have it install one of two handlers supplied by **sigtrap** itself (one which provides a Perl stack trace and one which simply `die()`s), or alternately you can supply your own handler for it to install. It can be told only to install a handler for signals which are either untrapped or ignored. It has three lists of signals to trap, plus you can supply your own list of signals.
The arguments passed to the `use` statement which invokes **sigtrap** are processed in order. When a signal name or the name of one of **sigtrap**'s signal lists is encountered a handler is immediately installed, when an option is encountered it affects subsequently installed handlers.
OPTIONS
-------
###
SIGNAL HANDLERS
These options affect which handler will be used for subsequently installed signals.
**stack-trace**
The handler used for subsequently installed signals outputs a Perl stack trace to STDERR and then tries to dump core. This is the default signal handler.
**die** The handler used for subsequently installed signals calls `die` (actually `croak`) with a message indicating which signal was caught.
**handler** *your-handler*
*your-handler* will be used as the handler for subsequently installed signals. *your-handler* can be any value which is valid as an assignment to an element of `%SIG`. See <perlvar> for examples of handler functions.
###
SIGNAL LISTS
**sigtrap** has a few built-in lists of signals to trap. They are:
**normal-signals**
These are the signals which a program might normally expect to encounter and which by default cause it to terminate. They are HUP, INT, PIPE and TERM.
**error-signals**
These signals usually indicate a serious problem with the Perl interpreter or with your script. They are ABRT, BUS, EMT, FPE, ILL, QUIT, SEGV, SYS and TRAP.
**old-interface-signals**
These are the signals which were trapped by default by the old **sigtrap** interface, they are ABRT, BUS, EMT, FPE, ILL, PIPE, QUIT, SEGV, SYS, TERM, and TRAP. If no signals or signals lists are passed to **sigtrap**, this list is used.
For each of these three lists, the collection of signals set to be trapped is checked before trapping; if your architecture does not implement a particular signal, it will not be trapped but rather silently ignored.
### OTHER
**untrapped** This token tells **sigtrap** to install handlers only for subsequently listed signals which aren't already trapped or ignored.
**any** This token tells **sigtrap** to install handlers for all subsequently listed signals. This is the default behavior.
*signal* Any argument which looks like a signal name (that is, `/^[A-Z][A-Z0-9]*$/`) indicates that **sigtrap** should install a handler for that name.
*number* Require that at least version *number* of **sigtrap** is being used.
EXAMPLES
--------
Provide a stack trace for the old-interface-signals:
```
use sigtrap;
```
Ditto:
```
use sigtrap qw(stack-trace old-interface-signals);
```
Provide a stack trace on the 4 listed signals only:
```
use sigtrap qw(BUS SEGV PIPE ABRT);
```
Die on INT or QUIT:
```
use sigtrap qw(die INT QUIT);
```
Die on HUP, INT, PIPE or TERM:
```
use sigtrap qw(die normal-signals);
```
Die on HUP, INT, PIPE or TERM, except don't change the behavior for signals which are already trapped or ignored:
```
use sigtrap qw(die untrapped normal-signals);
```
Die on receipt one of any of the **normal-signals** which is currently **untrapped**, provide a stack trace on receipt of **any** of the **error-signals**:
```
use sigtrap qw(die untrapped normal-signals
stack-trace any error-signals);
```
Install my\_handler() as the handler for the **normal-signals**:
```
use sigtrap 'handler', \&my_handler, 'normal-signals';
```
Install my\_handler() as the handler for the normal-signals, provide a Perl stack trace on receipt of one of the error-signals:
```
use sigtrap qw(handler my_handler normal-signals
stack-trace error-signals);
```
perl perlpacktut perlpacktut
===========
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
* [The Basic Principle](#The-Basic-Principle)
* [Packing Text](#Packing-Text)
* [Packing Numbers](#Packing-Numbers)
+ [Integers](#Integers)
+ [Unpacking a Stack Frame](#Unpacking-a-Stack-Frame)
+ [How to Eat an Egg on a Net](#How-to-Eat-an-Egg-on-a-Net)
+ [Byte-order modifiers](#Byte-order-modifiers)
+ [Floating point Numbers](#Floating-point-Numbers)
* [Exotic Templates](#Exotic-Templates)
+ [Bit Strings](#Bit-Strings)
+ [Uuencoding](#Uuencoding)
+ [Doing Sums](#Doing-Sums)
+ [Unicode](#Unicode)
+ [Another Portable Binary Encoding](#Another-Portable-Binary-Encoding)
* [Template Grouping](#Template-Grouping)
* [Lengths and Widths](#Lengths-and-Widths)
+ [String Lengths](#String-Lengths)
+ [Dynamic Templates](#Dynamic-Templates)
+ [Counting Repetitions](#Counting-Repetitions)
+ [Intel HEX](#Intel-HEX)
* [Packing and Unpacking C Structures](#Packing-and-Unpacking-C-Structures)
+ [The Alignment Pit](#The-Alignment-Pit)
+ [Dealing with Endian-ness](#Dealing-with-Endian-ness)
+ [Alignment, Take 2](#Alignment,-Take-2)
+ [Alignment, Take 3](#Alignment,-Take-3)
+ [Pointers for How to Use Them](#Pointers-for-How-to-Use-Them)
* [Pack Recipes](#Pack-Recipes)
* [Funnies Section](#Funnies-Section)
* [Authors](#Authors)
NAME
----
perlpacktut - tutorial on `pack` and `unpack`
DESCRIPTION
-----------
`pack` and `unpack` are two functions for transforming data according to a user-defined template, between the guarded way Perl stores values and some well-defined representation as might be required in the environment of a Perl program. Unfortunately, they're also two of the most misunderstood and most often overlooked functions that Perl provides. This tutorial will demystify them for you.
The Basic Principle
--------------------
Most programming languages don't shelter the memory where variables are stored. In C, for instance, you can take the address of some variable, and the `sizeof` operator tells you how many bytes are allocated to the variable. Using the address and the size, you may access the storage to your heart's content.
In Perl, you just can't access memory at random, but the structural and representational conversion provided by `pack` and `unpack` is an excellent alternative. The `pack` function converts values to a byte sequence containing representations according to a given specification, the so-called "template" argument. `unpack` is the reverse process, deriving some values from the contents of a string of bytes. (Be cautioned, however, that not all that has been packed together can be neatly unpacked - a very common experience as seasoned travellers are likely to confirm.)
Why, you may ask, would you need a chunk of memory containing some values in binary representation? One good reason is input and output accessing some file, a device, or a network connection, whereby this binary representation is either forced on you or will give you some benefit in processing. Another cause is passing data to some system call that is not available as a Perl function: `syscall` requires you to provide parameters stored in the way it happens in a C program. Even text processing (as shown in the next section) may be simplified with judicious usage of these two functions.
To see how (un)packing works, we'll start with a simple template code where the conversion is in low gear: between the contents of a byte sequence and a string of hexadecimal digits. Let's use `unpack`, since this is likely to remind you of a dump program, or some desperate last message unfortunate programs are wont to throw at you before they expire into the wild blue yonder. Assuming that the variable `$mem` holds a sequence of bytes that we'd like to inspect without assuming anything about its meaning, we can write
```
my( $hex ) = unpack( 'H*', $mem );
print "$hex\n";
```
whereupon we might see something like this, with each pair of hex digits corresponding to a byte:
```
41204d414e204120504c414e20412043414e414c2050414e414d41
```
What was in this chunk of memory? Numbers, characters, or a mixture of both? Assuming that we're on a computer where ASCII (or some similar) encoding is used: hexadecimal values in the range `0x40` - `0x5A` indicate an uppercase letter, and `0x20` encodes a space. So we might assume it is a piece of text, which some are able to read like a tabloid; but others will have to get hold of an ASCII table and relive that firstgrader feeling. Not caring too much about which way to read this, we note that `unpack` with the template code `H` converts the contents of a sequence of bytes into the customary hexadecimal notation. Since "a sequence of" is a pretty vague indication of quantity, `H` has been defined to convert just a single hexadecimal digit unless it is followed by a repeat count. An asterisk for the repeat count means to use whatever remains.
The inverse operation - packing byte contents from a string of hexadecimal digits - is just as easily written. For instance:
```
my $s = pack( 'H2' x 10, 30..39 );
print "$s\n";
```
Since we feed a list of ten 2-digit hexadecimal strings to `pack`, the pack template should contain ten pack codes. If this is run on a computer with ASCII character coding, it will print `0123456789`.
Packing Text
-------------
Let's suppose you've got to read in a data file like this:
```
Date |Description | Income|Expenditure
01/24/2001 Zed's Camel Emporium 1147.99
01/28/2001 Flea spray 24.99
01/29/2001 Camel rides to tourists 235.00
```
How do we do it? You might think first to use `split`; however, since `split` collapses blank fields, you'll never know whether a record was income or expenditure. Oops. Well, you could always use `substr`:
```
while (<>) {
my $date = substr($_, 0, 11);
my $desc = substr($_, 12, 27);
my $income = substr($_, 40, 7);
my $expend = substr($_, 52, 7);
...
}
```
It's not really a barrel of laughs, is it? In fact, it's worse than it may seem; the eagle-eyed may notice that the first field should only be 10 characters wide, and the error has propagated right through the other numbers - which we've had to count by hand. So it's error-prone as well as horribly unfriendly.
Or maybe we could use regular expressions:
```
while (<>) {
my($date, $desc, $income, $expend) =
m|(\d\d/\d\d/\d{4}) (.{27}) (.{7})(.*)|;
...
}
```
Urgh. Well, it's a bit better, but - well, would you want to maintain that?
Hey, isn't Perl supposed to make this sort of thing easy? Well, it does, if you use the right tools. `pack` and `unpack` are designed to help you out when dealing with fixed-width data like the above. Let's have a look at a solution with `unpack`:
```
while (<>) {
my($date, $desc, $income, $expend) = unpack("A10xA27xA7A*", $_);
...
}
```
That looks a bit nicer; but we've got to take apart that weird template. Where did I pull that out of?
OK, let's have a look at some of our data again; in fact, we'll include the headers, and a handy ruler so we can keep track of where we are.
```
1 2 3 4 5
1234567890123456789012345678901234567890123456789012345678
Date |Description | Income|Expenditure
01/28/2001 Flea spray 24.99
01/29/2001 Camel rides to tourists 235.00
```
From this, we can see that the date column stretches from column 1 to column 10 - ten characters wide. The `pack`-ese for "character" is `A`, and ten of them are `A10`. So if we just wanted to extract the dates, we could say this:
```
my($date) = unpack("A10", $_);
```
OK, what's next? Between the date and the description is a blank column; we want to skip over that. The `x` template means "skip forward", so we want one of those. Next, we have another batch of characters, from 12 to 38. That's 27 more characters, hence `A27`. (Don't make the fencepost error - there are 27 characters between 12 and 38, not 26. Count 'em!)
Now we skip another character and pick up the next 7 characters:
```
my($date,$description,$income) = unpack("A10xA27xA7", $_);
```
Now comes the clever bit. Lines in our ledger which are just income and not expenditure might end at column 46. Hence, we don't want to tell our `unpack` pattern that we **need** to find another 12 characters; we'll just say "if there's anything left, take it". As you might guess from regular expressions, that's what the `*` means: "use everything remaining".
* Be warned, though, that unlike regular expressions, if the `unpack` template doesn't match the incoming data, Perl will scream and die.
Hence, putting it all together:
```
my ($date, $description, $income, $expend) =
unpack("A10xA27xA7xA*", $_);
```
Now, that's our data parsed. I suppose what we might want to do now is total up our income and expenditure, and add another line to the end of our ledger - in the same format - saying how much we've brought in and how much we've spent:
```
while (<>) {
my ($date, $desc, $income, $expend) =
unpack("A10xA27xA7xA*", $_);
$tot_income += $income;
$tot_expend += $expend;
}
$tot_income = sprintf("%.2f", $tot_income); # Get them into
$tot_expend = sprintf("%.2f", $tot_expend); # "financial" format
$date = POSIX::strftime("%m/%d/%Y", localtime);
# OK, let's go:
print pack("A10xA27xA7xA*", $date, "Totals",
$tot_income, $tot_expend);
```
Oh, hmm. That didn't quite work. Let's see what happened:
```
01/24/2001 Zed's Camel Emporium 1147.99
01/28/2001 Flea spray 24.99
01/29/2001 Camel rides to tourists 1235.00
03/23/2001Totals 1235.001172.98
```
OK, it's a start, but what happened to the spaces? We put `x`, didn't we? Shouldn't it skip forward? Let's look at what ["pack" in perlfunc](perlfunc#pack) says:
```
x A null byte.
```
Urgh. No wonder. There's a big difference between "a null byte", character zero, and "a space", character 32. Perl's put something between the date and the description - but unfortunately, we can't see it!
What we actually need to do is expand the width of the fields. The `A` format pads any non-existent characters with spaces, so we can use the additional spaces to line up our fields, like this:
```
print pack("A11 A28 A8 A*", $date, "Totals",
$tot_income, $tot_expend);
```
(Note that you can put spaces in the template to make it more readable, but they don't translate to spaces in the output.) Here's what we got this time:
```
01/24/2001 Zed's Camel Emporium 1147.99
01/28/2001 Flea spray 24.99
01/29/2001 Camel rides to tourists 1235.00
03/23/2001 Totals 1235.00 1172.98
```
That's a bit better, but we still have that last column which needs to be moved further over. There's an easy way to fix this up: unfortunately, we can't get `pack` to right-justify our fields, but we can get `sprintf` to do it:
```
$tot_income = sprintf("%.2f", $tot_income);
$tot_expend = sprintf("%12.2f", $tot_expend);
$date = POSIX::strftime("%m/%d/%Y", localtime);
print pack("A11 A28 A8 A*", $date, "Totals",
$tot_income, $tot_expend);
```
This time we get the right answer:
```
01/28/2001 Flea spray 24.99
01/29/2001 Camel rides to tourists 1235.00
03/23/2001 Totals 1235.00 1172.98
```
So that's how we consume and produce fixed-width data. Let's recap what we've seen of `pack` and `unpack` so far:
* Use `pack` to go from several pieces of data to one fixed-width version; use `unpack` to turn a fixed-width-format string into several pieces of data.
* The pack format `A` means "any character"; if you're `pack`ing and you've run out of things to pack, `pack` will fill the rest up with spaces.
* `x` means "skip a byte" when `unpack`ing; when `pack`ing, it means "introduce a null byte" - that's probably not what you mean if you're dealing with plain text.
* You can follow the formats with numbers to say how many characters should be affected by that format: `A12` means "take 12 characters"; `x6` means "skip 6 bytes" or "character 0, 6 times".
* Instead of a number, you can use `*` to mean "consume everything else left".
**Warning**: when packing multiple pieces of data, `*` only means "consume all of the current piece of data". That's to say
```
pack("A*A*", $one, $two)
```
packs all of `$one` into the first `A*` and then all of `$two` into the second. This is a general principle: each format character corresponds to one piece of data to be `pack`ed.
Packing Numbers
----------------
So much for textual data. Let's get onto the meaty stuff that `pack` and `unpack` are best at: handling binary formats for numbers. There is, of course, not just one binary format - life would be too simple - but Perl will do all the finicky labor for you.
### Integers
Packing and unpacking numbers implies conversion to and from some *specific* binary representation. Leaving floating point numbers aside for the moment, the salient properties of any such representation are:
* the number of bytes used for storing the integer,
* whether the contents are interpreted as a signed or unsigned number,
* the byte ordering: whether the first byte is the least or most significant byte (or: little-endian or big-endian, respectively).
So, for instance, to pack 20302 to a signed 16 bit integer in your computer's representation you write
```
my $ps = pack( 's', 20302 );
```
Again, the result is a string, now containing 2 bytes. If you print this string (which is, generally, not recommended) you might see `ON` or `NO` (depending on your system's byte ordering) - or something entirely different if your computer doesn't use ASCII character encoding. Unpacking `$ps` with the same template returns the original integer value:
```
my( $s ) = unpack( 's', $ps );
```
This is true for all numeric template codes. But don't expect miracles: if the packed value exceeds the allotted byte capacity, high order bits are silently discarded, and unpack certainly won't be able to pull them back out of some magic hat. And, when you pack using a signed template code such as `s`, an excess value may result in the sign bit getting set, and unpacking this will smartly return a negative value.
16 bits won't get you too far with integers, but there is `l` and `L` for signed and unsigned 32-bit integers. And if this is not enough and your system supports 64 bit integers you can push the limits much closer to infinity with pack codes `q` and `Q`. A notable exception is provided by pack codes `i` and `I` for signed and unsigned integers of the "local custom" variety: Such an integer will take up as many bytes as a local C compiler returns for `sizeof(int)`, but it'll use *at least* 32 bits.
Each of the integer pack codes `sSlLqQ` results in a fixed number of bytes, no matter where you execute your program. This may be useful for some applications, but it does not provide for a portable way to pass data structures between Perl and C programs (bound to happen when you call XS extensions or the Perl function `syscall`), or when you read or write binary files. What you'll need in this case are template codes that depend on what your local C compiler compiles when you code `short` or `unsigned long`, for instance. These codes and their corresponding byte lengths are shown in the table below. Since the C standard leaves much leeway with respect to the relative sizes of these data types, actual values may vary, and that's why the values are given as expressions in C and Perl. (If you'd like to use values from `%Config` in your program you have to import it with `use Config`.)
```
signed unsigned byte length in C byte length in Perl
s! S! sizeof(short) $Config{shortsize}
i! I! sizeof(int) $Config{intsize}
l! L! sizeof(long) $Config{longsize}
q! Q! sizeof(long long) $Config{longlongsize}
```
The `i!` and `I!` codes aren't different from `i` and `I`; they are tolerated for completeness' sake.
###
Unpacking a Stack Frame
Requesting a particular byte ordering may be necessary when you work with binary data coming from some specific architecture whereas your program could run on a totally different system. As an example, assume you have 24 bytes containing a stack frame as it happens on an Intel 8086:
```
+---------+ +----+----+ +---------+
TOS: | IP | TOS+4:| FL | FH | FLAGS TOS+14:| SI |
+---------+ +----+----+ +---------+
| CS | | AL | AH | AX | DI |
+---------+ +----+----+ +---------+
| BL | BH | BX | BP |
+----+----+ +---------+
| CL | CH | CX | DS |
+----+----+ +---------+
| DL | DH | DX | ES |
+----+----+ +---------+
```
First, we note that this time-honored 16-bit CPU uses little-endian order, and that's why the low order byte is stored at the lower address. To unpack such a (unsigned) short we'll have to use code `v`. A repeat count unpacks all 12 shorts:
```
my( $ip, $cs, $flags, $ax, $bx, $cx, $dx, $si, $di, $bp, $ds, $es ) =
unpack( 'v12', $frame );
```
Alternatively, we could have used `C` to unpack the individually accessible byte registers FL, FH, AL, AH, etc.:
```
my( $fl, $fh, $al, $ah, $bl, $bh, $cl, $ch, $dl, $dh ) =
unpack( 'C10', substr( $frame, 4, 10 ) );
```
It would be nice if we could do this in one fell swoop: unpack a short, back up a little, and then unpack 2 bytes. Since Perl *is* nice, it proffers the template code `X` to back up one byte. Putting this all together, we may now write:
```
my( $ip, $cs,
$flags,$fl,$fh,
$ax,$al,$ah, $bx,$bl,$bh, $cx,$cl,$ch, $dx,$dl,$dh,
$si, $di, $bp, $ds, $es ) =
unpack( 'v2' . ('vXXCC' x 5) . 'v5', $frame );
```
(The clumsy construction of the template can be avoided - just read on!)
We've taken some pains to construct the template so that it matches the contents of our frame buffer. Otherwise we'd either get undefined values, or `unpack` could not unpack all. If `pack` runs out of items, it will supply null strings (which are coerced into zeroes whenever the pack code says so).
###
How to Eat an Egg on a Net
The pack code for big-endian (high order byte at the lowest address) is `n` for 16 bit and `N` for 32 bit integers. You use these codes if you know that your data comes from a compliant architecture, but, surprisingly enough, you should also use these pack codes if you exchange binary data, across the network, with some system that you know next to nothing about. The simple reason is that this order has been chosen as the *network order*, and all standard-fearing programs ought to follow this convention. (This is, of course, a stern backing for one of the Lilliputian parties and may well influence the political development there.) So, if the protocol expects you to send a message by sending the length first, followed by just so many bytes, you could write:
```
my $buf = pack( 'N', length( $msg ) ) . $msg;
```
or even:
```
my $buf = pack( 'NA*', length( $msg ), $msg );
```
and pass `$buf` to your send routine. Some protocols demand that the count should include the length of the count itself: then just add 4 to the data length. (But make sure to read ["Lengths and Widths"](#Lengths-and-Widths) before you really code this!)
###
Byte-order modifiers
In the previous sections we've learned how to use `n`, `N`, `v` and `V` to pack and unpack integers with big- or little-endian byte-order. While this is nice, it's still rather limited because it leaves out all kinds of signed integers as well as 64-bit integers. For example, if you wanted to unpack a sequence of signed big-endian 16-bit integers in a platform-independent way, you would have to write:
```
my @data = unpack 's*', pack 'S*', unpack 'n*', $buf;
```
This is ugly. As of Perl 5.9.2, there's a much nicer way to express your desire for a certain byte-order: the `>` and `<` modifiers. `>` is the big-endian modifier, while `<` is the little-endian modifier. Using them, we could rewrite the above code as:
```
my @data = unpack 's>*', $buf;
```
As you can see, the "big end" of the arrow touches the `s`, which is a nice way to remember that `>` is the big-endian modifier. The same obviously works for `<`, where the "little end" touches the code.
You will probably find these modifiers even more useful if you have to deal with big- or little-endian C structures. Be sure to read ["Packing and Unpacking C Structures"](#Packing-and-Unpacking-C-Structures) for more on that.
###
Floating point Numbers
For packing floating point numbers you have the choice between the pack codes `f`, `d`, `F` and `D`. `f` and `d` pack into (or unpack from) single-precision or double-precision representation as it is provided by your system. If your systems supports it, `D` can be used to pack and unpack (`long double`) values, which can offer even more resolution than `f` or `d`. **Note that there are different long double formats.**
`F` packs an `NV`, which is the floating point type used by Perl internally.
There is no such thing as a network representation for reals, so if you want to send your real numbers across computer boundaries, you'd better stick to text representation, possibly using the hexadecimal float format (avoiding the decimal conversion loss), unless you're absolutely sure what's on the other end of the line. For the even more adventuresome, you can use the byte-order modifiers from the previous section also on floating point codes.
Exotic Templates
-----------------
###
Bit Strings
Bits are the atoms in the memory world. Access to individual bits may have to be used either as a last resort or because it is the most convenient way to handle your data. Bit string (un)packing converts between strings containing a series of `0` and `1` characters and a sequence of bytes each containing a group of 8 bits. This is almost as simple as it sounds, except that there are two ways the contents of a byte may be written as a bit string. Let's have a look at an annotated byte:
```
7 6 5 4 3 2 1 0
+-----------------+
| 1 0 0 0 1 1 0 0 |
+-----------------+
MSB LSB
```
It's egg-eating all over again: Some think that as a bit string this should be written "10001100" i.e. beginning with the most significant bit, others insist on "00110001". Well, Perl isn't biased, so that's why we have two bit string codes:
```
$byte = pack( 'B8', '10001100' ); # start with MSB
$byte = pack( 'b8', '00110001' ); # start with LSB
```
It is not possible to pack or unpack bit fields - just integral bytes. `pack` always starts at the next byte boundary and "rounds up" to the next multiple of 8 by adding zero bits as required. (If you do want bit fields, there is ["vec" in perlfunc](perlfunc#vec). Or you could implement bit field handling at the character string level, using split, substr, and concatenation on unpacked bit strings.)
To illustrate unpacking for bit strings, we'll decompose a simple status register (a "-" stands for a "reserved" bit):
```
+-----------------+-----------------+
| S Z - A - P - C | - - - - O D I T |
+-----------------+-----------------+
MSB LSB MSB LSB
```
Converting these two bytes to a string can be done with the unpack template `'b16'`. To obtain the individual bit values from the bit string we use `split` with the "empty" separator pattern which dissects into individual characters. Bit values from the "reserved" positions are simply assigned to `undef`, a convenient notation for "I don't care where this goes".
```
($carry, undef, $parity, undef, $auxcarry, undef, $zero, $sign,
$trace, $interrupt, $direction, $overflow) =
split( //, unpack( 'b16', $status ) );
```
We could have used an unpack template `'b12'` just as well, since the last 4 bits can be ignored anyway.
### Uuencoding
Another odd-man-out in the template alphabet is `u`, which packs a "uuencoded string". ("uu" is short for Unix-to-Unix.) Chances are that you won't ever need this encoding technique which was invented to overcome the shortcomings of old-fashioned transmission mediums that do not support other than simple ASCII data. The essential recipe is simple: Take three bytes, or 24 bits. Split them into 4 six-packs, adding a space (0x20) to each. Repeat until all of the data is blended. Fold groups of 4 bytes into lines no longer than 60 and garnish them in front with the original byte count (incremented by 0x20) and a `"\n"` at the end. - The `pack` chef will prepare this for you, a la minute, when you select pack code `u` on the menu:
```
my $uubuf = pack( 'u', $bindat );
```
A repeat count after `u` sets the number of bytes to put into an uuencoded line, which is the maximum of 45 by default, but could be set to some (smaller) integer multiple of three. `unpack` simply ignores the repeat count.
###
Doing Sums
An even stranger template code is `%`<*number*>. First, because it's used as a prefix to some other template code. Second, because it cannot be used in `pack` at all, and third, in `unpack`, doesn't return the data as defined by the template code it precedes. Instead it'll give you an integer of *number* bits that is computed from the data value by doing sums. For numeric unpack codes, no big feat is achieved:
```
my $buf = pack( 'iii', 100, 20, 3 );
print unpack( '%32i3', $buf ), "\n"; # prints 123
```
For string values, `%` returns the sum of the byte values saving you the trouble of a sum loop with `substr` and `ord`:
```
print unpack( '%32A*', "\x01\x10" ), "\n"; # prints 17
```
Although the `%` code is documented as returning a "checksum": don't put your trust in such values! Even when applied to a small number of bytes, they won't guarantee a noticeable Hamming distance.
In connection with `b` or `B`, `%` simply adds bits, and this can be put to good use to count set bits efficiently:
```
my $bitcount = unpack( '%32b*', $mask );
```
And an even parity bit can be determined like this:
```
my $evenparity = unpack( '%1b*', $mask );
```
### Unicode
Unicode is a character set that can represent most characters in most of the world's languages, providing room for over one million different characters. Unicode 3.1 specifies 94,140 characters: The Basic Latin characters are assigned to the numbers 0 - 127. The Latin-1 Supplement with characters that are used in several European languages is in the next range, up to 255. After some more Latin extensions we find the character sets from languages using non-Roman alphabets, interspersed with a variety of symbol sets such as currency symbols, Zapf Dingbats or Braille. (You might want to visit <https://www.unicode.org/> for a look at some of them - my personal favourites are Telugu and Kannada.)
The Unicode character sets associates characters with integers. Encoding these numbers in an equal number of bytes would more than double the requirements for storing texts written in Latin alphabets. The UTF-8 encoding avoids this by storing the most common (from a western point of view) characters in a single byte while encoding the rarer ones in three or more bytes.
Perl uses UTF-8, internally, for most Unicode strings.
So what has this got to do with `pack`? Well, if you want to compose a Unicode string (that is internally encoded as UTF-8), you can do so by using template code `U`. As an example, let's produce the Euro currency symbol (code number 0x20AC):
```
$UTF8{Euro} = pack( 'U', 0x20AC );
# Equivalent to: $UTF8{Euro} = "\x{20ac}";
```
Inspecting `$UTF8{Euro}` shows that it contains 3 bytes: "\xe2\x82\xac". However, it contains only 1 character, number 0x20AC. The round trip can be completed with `unpack`:
```
$Unicode{Euro} = unpack( 'U', $UTF8{Euro} );
```
Unpacking using the `U` template code also works on UTF-8 encoded byte strings.
Usually you'll want to pack or unpack UTF-8 strings:
```
# pack and unpack the Hebrew alphabet
my $alefbet = pack( 'U*', 0x05d0..0x05ea );
my @hebrew = unpack( 'U*', $utf );
```
Please note: in the general case, you're better off using [`Encode::decode('UTF-8', $utf)`](encode#decode) to decode a UTF-8 encoded byte string to a Perl Unicode string, and [`Encode::encode('UTF-8', $str)`](encode#encode) to encode a Perl Unicode string to UTF-8 bytes. These functions provide means of handling invalid byte sequences and generally have a friendlier interface.
###
Another Portable Binary Encoding
The pack code `w` has been added to support a portable binary data encoding scheme that goes way beyond simple integers. (Details can be found at <https://github.com/mworks-project/mw_scarab/blob/master/Scarab-0.1.00d19/doc/binary-serialization.txt>, the Scarab project.) A BER (Binary Encoded Representation) compressed unsigned integer stores base 128 digits, most significant digit first, with as few digits as possible. Bit eight (the high bit) is set on each byte except the last. There is no size limit to BER encoding, but Perl won't go to extremes.
```
my $berbuf = pack( 'w*', 1, 128, 128+1, 128*128+127 );
```
A hex dump of `$berbuf`, with spaces inserted at the right places, shows 01 8100 8101 81807F. Since the last byte is always less than 128, `unpack` knows where to stop.
Template Grouping
------------------
Prior to Perl 5.8, repetitions of templates had to be made by `x`-multiplication of template strings. Now there is a better way as we may use the pack codes `(` and `)` combined with a repeat count. The `unpack` template from the Stack Frame example can simply be written like this:
```
unpack( 'v2 (vXXCC)5 v5', $frame )
```
Let's explore this feature a little more. We'll begin with the equivalent of
```
join( '', map( substr( $_, 0, 1 ), @str ) )
```
which returns a string consisting of the first character from each string. Using pack, we can write
```
pack( '(A)'.@str, @str )
```
or, because a repeat count `*` means "repeat as often as required", simply
```
pack( '(A)*', @str )
```
(Note that the template `A*` would only have packed `$str[0]` in full length.)
To pack dates stored as triplets ( day, month, year ) in an array `@dates` into a sequence of byte, byte, short integer we can write
```
$pd = pack( '(CCS)*', map( @$_, @dates ) );
```
To swap pairs of characters in a string (with even length) one could use several techniques. First, let's use `x` and `X` to skip forward and back:
```
$s = pack( '(A)*', unpack( '(xAXXAx)*', $s ) );
```
We can also use `@` to jump to an offset, with 0 being the position where we were when the last `(` was encountered:
```
$s = pack( '(A)*', unpack( '(@1A @0A @2)*', $s ) );
```
Finally, there is also an entirely different approach by unpacking big endian shorts and packing them in the reverse byte order:
```
$s = pack( '(v)*', unpack( '(n)*', $s );
```
Lengths and Widths
-------------------
###
String Lengths
In the previous section we've seen a network message that was constructed by prefixing the binary message length to the actual message. You'll find that packing a length followed by so many bytes of data is a frequently used recipe since appending a null byte won't work if a null byte may be part of the data. Here is an example where both techniques are used: after two null terminated strings with source and destination address, a Short Message (to a mobile phone) is sent after a length byte:
```
my $msg = pack( 'Z*Z*CA*', $src, $dst, length( $sm ), $sm );
```
Unpacking this message can be done with the same template:
```
( $src, $dst, $len, $sm ) = unpack( 'Z*Z*CA*', $msg );
```
There's a subtle trap lurking in the offing: Adding another field after the Short Message (in variable `$sm`) is all right when packing, but this cannot be unpacked naively:
```
# pack a message
my $msg = pack( 'Z*Z*CA*C', $src, $dst, length( $sm ), $sm, $prio );
# unpack fails - $prio remains undefined!
( $src, $dst, $len, $sm, $prio ) = unpack( 'Z*Z*CA*C', $msg );
```
The pack code `A*` gobbles up all remaining bytes, and `$prio` remains undefined! Before we let disappointment dampen the morale: Perl's got the trump card to make this trick too, just a little further up the sleeve. Watch this:
```
# pack a message: ASCIIZ, ASCIIZ, length/string, byte
my $msg = pack( 'Z* Z* C/A* C', $src, $dst, $sm, $prio );
# unpack
( $src, $dst, $sm, $prio ) = unpack( 'Z* Z* C/A* C', $msg );
```
Combining two pack codes with a slash (`/`) associates them with a single value from the argument list. In `pack`, the length of the argument is taken and packed according to the first code while the argument itself is added after being converted with the template code after the slash. This saves us the trouble of inserting the `length` call, but it is in `unpack` where we really score: The value of the length byte marks the end of the string to be taken from the buffer. Since this combination doesn't make sense except when the second pack code isn't `a*`, `A*` or `Z*`, Perl won't let you.
The pack code preceding `/` may be anything that's fit to represent a number: All the numeric binary pack codes, and even text codes such as `A4` or `Z*`:
```
# pack/unpack a string preceded by its length in ASCII
my $buf = pack( 'A4/A*', "Humpty-Dumpty" );
# unpack $buf: '13 Humpty-Dumpty'
my $txt = unpack( 'A4/A*', $buf );
```
`/` is not implemented in Perls before 5.6, so if your code is required to work on ancient Perls you'll need to `unpack( 'Z* Z* C')` to get the length, then use it to make a new unpack string. For example
```
# pack a message: ASCIIZ, ASCIIZ, length, string, byte
# (5.005 compatible)
my $msg = pack( 'Z* Z* C A* C', $src, $dst, length $sm, $sm, $prio );
# unpack
( undef, undef, $len) = unpack( 'Z* Z* C', $msg );
($src, $dst, $sm, $prio) = unpack ( "Z* Z* x A$len C", $msg );
```
But that second `unpack` is rushing ahead. It isn't using a simple literal string for the template. So maybe we should introduce...
###
Dynamic Templates
So far, we've seen literals used as templates. If the list of pack items doesn't have fixed length, an expression constructing the template is required (whenever, for some reason, `()*` cannot be used). Here's an example: To store named string values in a way that can be conveniently parsed by a C program, we create a sequence of names and null terminated ASCII strings, with `=` between the name and the value, followed by an additional delimiting null byte. Here's how:
```
my $env = pack( '(A*A*Z*)' . keys( %Env ) . 'C',
map( { ( $_, '=', $Env{$_} ) } keys( %Env ) ), 0 );
```
Let's examine the cogs of this byte mill, one by one. There's the `map` call, creating the items we intend to stuff into the `$env` buffer: to each key (in `$_`) it adds the `=` separator and the hash entry value. Each triplet is packed with the template code sequence `A*A*Z*` that is repeated according to the number of keys. (Yes, that's what the `keys` function returns in scalar context.) To get the very last null byte, we add a `0` at the end of the `pack` list, to be packed with `C`. (Attentive readers may have noticed that we could have omitted the 0.)
For the reverse operation, we'll have to determine the number of items in the buffer before we can let `unpack` rip it apart:
```
my $n = $env =~ tr/\0// - 1;
my %env = map( split( /=/, $_ ), unpack( "(Z*)$n", $env ) );
```
The `tr` counts the null bytes. The `unpack` call returns a list of name-value pairs each of which is taken apart in the `map` block.
###
Counting Repetitions
Rather than storing a sentinel at the end of a data item (or a list of items), we could precede the data with a count. Again, we pack keys and values of a hash, preceding each with an unsigned short length count, and up front we store the number of pairs:
```
my $env = pack( 'S(S/A* S/A*)*', scalar keys( %Env ), %Env );
```
This simplifies the reverse operation as the number of repetitions can be unpacked with the `/` code:
```
my %env = unpack( 'S/(S/A* S/A*)', $env );
```
Note that this is one of the rare cases where you cannot use the same template for `pack` and `unpack` because `pack` can't determine a repeat count for a `()`-group.
###
Intel HEX
Intel HEX is a file format for representing binary data, mostly for programming various chips, as a text file. (See <https://en.wikipedia.org/wiki/.hex> for a detailed description, and <https://en.wikipedia.org/wiki/SREC_(file_format)> for the Motorola S-record format, which can be unravelled using the same technique.) Each line begins with a colon (':') and is followed by a sequence of hexadecimal characters, specifying a byte count *n* (8 bit), an address (16 bit, big endian), a record type (8 bit), *n* data bytes and a checksum (8 bit) computed as the least significant byte of the two's complement sum of the preceding bytes. Example: `:0300300002337A1E`.
The first step of processing such a line is the conversion, to binary, of the hexadecimal data, to obtain the four fields, while checking the checksum. No surprise here: we'll start with a simple `pack` call to convert everything to binary:
```
my $binrec = pack( 'H*', substr( $hexrec, 1 ) );
```
The resulting byte sequence is most convenient for checking the checksum. Don't slow your program down with a for loop adding the `ord` values of this string's bytes - the `unpack` code `%` is the thing to use for computing the 8-bit sum of all bytes, which must be equal to zero:
```
die unless unpack( "%8C*", $binrec ) == 0;
```
Finally, let's get those four fields. By now, you shouldn't have any problems with the first three fields - but how can we use the byte count of the data in the first field as a length for the data field? Here the codes `x` and `X` come to the rescue, as they permit jumping back and forth in the string to unpack.
```
my( $addr, $type, $data ) = unpack( "x n C X4 C x3 /a", $bin );
```
Code `x` skips a byte, since we don't need the count yet. Code `n` takes care of the 16-bit big-endian integer address, and `C` unpacks the record type. Being at offset 4, where the data begins, we need the count. `X4` brings us back to square one, which is the byte at offset 0. Now we pick up the count, and zoom forth to offset 4, where we are now fully furnished to extract the exact number of data bytes, leaving the trailing checksum byte alone.
Packing and Unpacking C Structures
-----------------------------------
In previous sections we have seen how to pack numbers and character strings. If it were not for a couple of snags we could conclude this section right away with the terse remark that C structures don't contain anything else, and therefore you already know all there is to it. Sorry, no: read on, please.
If you have to deal with a lot of C structures, and don't want to hack all your template strings manually, you'll probably want to have a look at the CPAN module `Convert::Binary::C`. Not only can it parse your C source directly, but it also has built-in support for all the odds and ends described further on in this section.
###
The Alignment Pit
In the consideration of speed against memory requirements the balance has been tilted in favor of faster execution. This has influenced the way C compilers allocate memory for structures: On architectures where a 16-bit or 32-bit operand can be moved faster between places in memory, or to or from a CPU register, if it is aligned at an even or multiple-of-four or even at a multiple-of eight address, a C compiler will give you this speed benefit by stuffing extra bytes into structures. If you don't cross the C shoreline this is not likely to cause you any grief (although you should care when you design large data structures, or you want your code to be portable between architectures (you do want that, don't you?)).
To see how this affects `pack` and `unpack`, we'll compare these two C structures:
```
typedef struct {
char c1;
short s;
char c2;
long l;
} gappy_t;
typedef struct {
long l;
short s;
char c1;
char c2;
} dense_t;
```
Typically, a C compiler allocates 12 bytes to a `gappy_t` variable, but requires only 8 bytes for a `dense_t`. After investigating this further, we can draw memory maps, showing where the extra 4 bytes are hidden:
```
0 +4 +8 +12
+--+--+--+--+--+--+--+--+--+--+--+--+
|c1|xx| s |c2|xx|xx|xx| l | xx = fill byte
+--+--+--+--+--+--+--+--+--+--+--+--+
gappy_t
0 +4 +8
+--+--+--+--+--+--+--+--+
| l | h |c1|c2|
+--+--+--+--+--+--+--+--+
dense_t
```
And that's where the first quirk strikes: `pack` and `unpack` templates have to be stuffed with `x` codes to get those extra fill bytes.
The natural question: "Why can't Perl compensate for the gaps?" warrants an answer. One good reason is that C compilers might provide (non-ANSI) extensions permitting all sorts of fancy control over the way structures are aligned, even at the level of an individual structure field. And, if this were not enough, there is an insidious thing called `union` where the amount of fill bytes cannot be derived from the alignment of the next item alone.
OK, so let's bite the bullet. Here's one way to get the alignment right by inserting template codes `x`, which don't take a corresponding item from the list:
```
my $gappy = pack( 'cxs cxxx l!', $c1, $s, $c2, $l );
```
Note the `!` after `l`: We want to make sure that we pack a long integer as it is compiled by our C compiler. And even now, it will only work for the platforms where the compiler aligns things as above. And somebody somewhere has a platform where it doesn't. [Probably a Cray, where `short`s, `int`s and `long`s are all 8 bytes. :-)]
Counting bytes and watching alignments in lengthy structures is bound to be a drag. Isn't there a way we can create the template with a simple program? Here's a C program that does the trick:
```
#include <stdio.h>
#include <stddef.h>
typedef struct {
char fc1;
short fs;
char fc2;
long fl;
} gappy_t;
#define Pt(struct,field,tchar) \
printf( "@%d%s ", offsetof(struct,field), # tchar );
int main() {
Pt( gappy_t, fc1, c );
Pt( gappy_t, fs, s! );
Pt( gappy_t, fc2, c );
Pt( gappy_t, fl, l! );
printf( "\n" );
}
```
The output line can be used as a template in a `pack` or `unpack` call:
```
my $gappy = pack( '@0c @2s! @4c @8l!', $c1, $s, $c2, $l );
```
Gee, yet another template code - as if we hadn't plenty. But `@` saves our day by enabling us to specify the offset from the beginning of the pack buffer to the next item: This is just the value the `offsetof` macro (defined in `<stddef.h>`) returns when given a `struct` type and one of its field names ("member-designator" in C standardese).
Neither using offsets nor adding `x`'s to bridge the gaps is satisfactory. (Just imagine what happens if the structure changes.) What we really need is a way of saying "skip as many bytes as required to the next multiple of N". In fluent templates, you say this with `x!N` where N is replaced by the appropriate value. Here's the next version of our struct packaging:
```
my $gappy = pack( 'c x!2 s c x!4 l!', $c1, $s, $c2, $l );
```
That's certainly better, but we still have to know how long all the integers are, and portability is far away. Rather than `2`, for instance, we want to say "however long a short is". But this can be done by enclosing the appropriate pack code in brackets: `[s]`. So, here's the very best we can do:
```
my $gappy = pack( 'c x![s] s c x![l!] l!', $c1, $s, $c2, $l );
```
###
Dealing with Endian-ness
Now, imagine that we want to pack the data for a machine with a different byte-order. First, we'll have to figure out how big the data types on the target machine really are. Let's assume that the longs are 32 bits wide and the shorts are 16 bits wide. You can then rewrite the template as:
```
my $gappy = pack( 'c x![s] s c x![l] l', $c1, $s, $c2, $l );
```
If the target machine is little-endian, we could write:
```
my $gappy = pack( 'c x![s] s< c x![l] l<', $c1, $s, $c2, $l );
```
This forces the short and the long members to be little-endian, and is just fine if you don't have too many struct members. But we could also use the byte-order modifier on a group and write the following:
```
my $gappy = pack( '( c x![s] s c x![l] l )<', $c1, $s, $c2, $l );
```
This is not as short as before, but it makes it more obvious that we intend to have little-endian byte-order for a whole group, not only for individual template codes. It can also be more readable and easier to maintain.
###
Alignment, Take 2
I'm afraid that we're not quite through with the alignment catch yet. The hydra raises another ugly head when you pack arrays of structures:
```
typedef struct {
short count;
char glyph;
} cell_t;
typedef cell_t buffer_t[BUFLEN];
```
Where's the catch? Padding is neither required before the first field `count`, nor between this and the next field `glyph`, so why can't we simply pack like this:
```
# something goes wrong here:
pack( 's!a' x @buffer,
map{ ( $_->{count}, $_->{glyph} ) } @buffer );
```
This packs `3*@buffer` bytes, but it turns out that the size of `buffer_t` is four times `BUFLEN`! The moral of the story is that the required alignment of a structure or array is propagated to the next higher level where we have to consider padding *at the end* of each component as well. Thus the correct template is:
```
pack( 's!ax' x @buffer,
map{ ( $_->{count}, $_->{glyph} ) } @buffer );
```
###
Alignment, Take 3
And even if you take all the above into account, ANSI still lets this:
```
typedef struct {
char foo[2];
} foo_t;
```
vary in size. The alignment constraint of the structure can be greater than any of its elements. [And if you think that this doesn't affect anything common, dismember the next cellphone that you see. Many have ARM cores, and the ARM structure rules make `sizeof (foo_t)` == 4]
###
Pointers for How to Use Them
The title of this section indicates the second problem you may run into sooner or later when you pack C structures. If the function you intend to call expects a, say, `void *` value, you *cannot* simply take a reference to a Perl variable. (Although that value certainly is a memory address, it's not the address where the variable's contents are stored.)
Template code `P` promises to pack a "pointer to a fixed length string". Isn't this what we want? Let's try:
```
# allocate some storage and pack a pointer to it
my $memory = "\x00" x $size;
my $memptr = pack( 'P', $memory );
```
But wait: doesn't `pack` just return a sequence of bytes? How can we pass this string of bytes to some C code expecting a pointer which is, after all, nothing but a number? The answer is simple: We have to obtain the numeric address from the bytes returned by `pack`.
```
my $ptr = unpack( 'L!', $memptr );
```
Obviously this assumes that it is possible to typecast a pointer to an unsigned long and vice versa, which frequently works but should not be taken as a universal law. - Now that we have this pointer the next question is: How can we put it to good use? We need a call to some C function where a pointer is expected. The read(2) system call comes to mind:
```
ssize_t read(int fd, void *buf, size_t count);
```
After reading <perlfunc> explaining how to use `syscall` we can write this Perl function copying a file to standard output:
```
require 'syscall.ph'; # run h2ph to generate this file
sub cat($){
my $path = shift();
my $size = -s $path;
my $memory = "\x00" x $size; # allocate some memory
my $ptr = unpack( 'L', pack( 'P', $memory ) );
open( F, $path ) || die( "$path: cannot open ($!)\n" );
my $fd = fileno(F);
my $res = syscall( &SYS_read, fileno(F), $ptr, $size );
print $memory;
close( F );
}
```
This is neither a specimen of simplicity nor a paragon of portability but it illustrates the point: We are able to sneak behind the scenes and access Perl's otherwise well-guarded memory! (Important note: Perl's `syscall` does *not* require you to construct pointers in this roundabout way. You simply pass a string variable, and Perl forwards the address.)
How does `unpack` with `P` work? Imagine some pointer in the buffer about to be unpacked: If it isn't the null pointer (which will smartly produce the `undef` value) we have a start address - but then what? Perl has no way of knowing how long this "fixed length string" is, so it's up to you to specify the actual size as an explicit length after `P`.
```
my $mem = "abcdefghijklmn";
print unpack( 'P5', pack( 'P', $mem ) ); # prints "abcde"
```
As a consequence, `pack` ignores any number or `*` after `P`.
Now that we have seen `P` at work, we might as well give `p` a whirl. Why do we need a second template code for packing pointers at all? The answer lies behind the simple fact that an `unpack` with `p` promises a null-terminated string starting at the address taken from the buffer, and that implies a length for the data item to be returned:
```
my $buf = pack( 'p', "abc\x00efhijklmn" );
print unpack( 'p', $buf ); # prints "abc"
```
Albeit this is apt to be confusing: As a consequence of the length being implied by the string's length, a number after pack code `p` is a repeat count, not a length as after `P`.
Using `pack(..., $x)` with `P` or `p` to get the address where `$x` is actually stored must be used with circumspection. Perl's internal machinery considers the relation between a variable and that address as its very own private matter and doesn't really care that we have obtained a copy. Therefore:
* Do not use `pack` with `p` or `P` to obtain the address of variable that's bound to go out of scope (and thereby freeing its memory) before you are done with using the memory at that address.
* Be very careful with Perl operations that change the value of the variable. Appending something to the variable, for instance, might require reallocation of its storage, leaving you with a pointer into no-man's land.
* Don't think that you can get the address of a Perl variable when it is stored as an integer or double number! `pack('P', $x)` will force the variable's internal representation to string, just as if you had written something like `$x .= ''`.
It's safe, however, to P- or p-pack a string literal, because Perl simply allocates an anonymous variable.
Pack Recipes
-------------
Here are a collection of (possibly) useful canned recipes for `pack` and `unpack`:
```
# Convert IP address for socket functions
pack( "C4", split /\./, "123.4.5.6" );
# Count the bits in a chunk of memory (e.g. a select vector)
unpack( '%32b*', $mask );
# Determine the endianness of your system
$is_little_endian = unpack( 'c', pack( 's', 1 ) );
$is_big_endian = unpack( 'xc', pack( 's', 1 ) );
# Determine the number of bits in a native integer
$bits = unpack( '%32I!', ~0 );
# Prepare argument for the nanosleep system call
my $timespec = pack( 'L!L!', $secs, $nanosecs );
```
For a simple memory dump we unpack some bytes into just as many pairs of hex digits, and use `map` to handle the traditional spacing - 16 bytes to a line:
```
my $i;
print map( ++$i % 16 ? "$_ " : "$_\n",
unpack( 'H2' x length( $mem ), $mem ) ),
length( $mem ) % 16 ? "\n" : '';
```
Funnies Section
----------------
```
# Pulling digits out of nowhere...
print unpack( 'C', pack( 'x' ) ),
unpack( '%B*', pack( 'A' ) ),
unpack( 'H', pack( 'A' ) ),
unpack( 'A', unpack( 'C', pack( 'A' ) ) ), "\n";
# One for the road ;-)
my $advice = pack( 'all u can in a van' );
```
Authors
-------
Simon Cozens and Wolfgang Laun.
| programming_docs |
perl perlsub perlsub
=======
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
+ [Signatures](#Signatures)
+ [Private Variables via my()](#Private-Variables-via-my())
+ [Persistent Private Variables](#Persistent-Private-Variables)
- [Persistent variables via state()](#Persistent-variables-via-state())
- [Persistent variables with closures](#Persistent-variables-with-closures)
+ [Temporary Values via local()](#Temporary-Values-via-local())
- [Grammatical note on local()](#Grammatical-note-on-local())
- [Localization of special variables](#Localization-of-special-variables)
- [Localization of globs](#Localization-of-globs)
- [Localization of elements of composite types](#Localization-of-elements-of-composite-types)
- [Localized deletion of elements of composite types](#Localized-deletion-of-elements-of-composite-types)
+ [Lvalue subroutines](#Lvalue-subroutines)
+ [Lexical Subroutines](#Lexical-Subroutines)
- [state sub vs my sub](#state-sub-vs-my-sub)
- [our subroutines](#our-subroutines)
+ [Passing Symbol Table Entries (typeglobs)](#Passing-Symbol-Table-Entries-(typeglobs))
+ [When to Still Use local()](#When-to-Still-Use-local())
+ [Pass by Reference](#Pass-by-Reference)
+ [Prototypes](#Prototypes)
+ [Constant Functions](#Constant-Functions)
+ [Overriding Built-in Functions](#Overriding-Built-in-Functions)
+ [Autoloading](#Autoloading)
+ [Subroutine Attributes](#Subroutine-Attributes)
* [SEE ALSO](#SEE-ALSO)
NAME
----
perlsub - Perl subroutines
SYNOPSIS
--------
To declare subroutines:
```
sub NAME; # A "forward" declaration.
sub NAME(PROTO); # ditto, but with prototypes
sub NAME : ATTRS; # with attributes
sub NAME(PROTO) : ATTRS; # with attributes and prototypes
sub NAME BLOCK # A declaration and a definition.
sub NAME(PROTO) BLOCK # ditto, but with prototypes
sub NAME : ATTRS BLOCK # with attributes
sub NAME(PROTO) : ATTRS BLOCK # with prototypes and attributes
use feature 'signatures';
sub NAME(SIG) BLOCK # with signature
sub NAME :ATTRS (SIG) BLOCK # with signature, attributes
sub NAME :prototype(PROTO) (SIG) BLOCK # with signature, prototype
```
To define an anonymous subroutine at runtime:
```
$subref = sub BLOCK; # no proto
$subref = sub (PROTO) BLOCK; # with proto
$subref = sub : ATTRS BLOCK; # with attributes
$subref = sub (PROTO) : ATTRS BLOCK; # with proto and attributes
use feature 'signatures';
$subref = sub (SIG) BLOCK; # with signature
$subref = sub : ATTRS(SIG) BLOCK; # with signature, attributes
```
To import subroutines:
```
use MODULE qw(NAME1 NAME2 NAME3);
```
To call subroutines:
```
NAME(LIST); # & is optional with parentheses.
NAME LIST; # Parentheses optional if predeclared/imported.
&NAME(LIST); # Circumvent prototypes.
&NAME; # Makes current @_ visible to called subroutine.
```
DESCRIPTION
-----------
Like many languages, Perl provides for user-defined subroutines. These may be located anywhere in the main program, loaded in from other files via the `do`, `require`, or `use` keywords, or generated on the fly using `eval` or anonymous subroutines. You can even call a function indirectly using a variable containing its name or a CODE reference.
The Perl model for function call and return values is simple: all functions are passed as parameters one single flat list of scalars, and all functions likewise return to their caller one single flat list of scalars. Any arrays or hashes in these call and return lists will collapse, losing their identities--but you may always use pass-by-reference instead to avoid this. Both call and return lists may contain as many or as few scalar elements as you'd like. (Often a function without an explicit return statement is called a subroutine, but there's really no difference from Perl's perspective.)
In a subroutine that uses signatures (see ["Signatures"](#Signatures) below), arguments are assigned into lexical variables introduced by the signature. In the current implementation of perl they are also accessible in the `@_` array in the same way as for non-signature subroutines, but accessing them in this manner is now discouraged inside such a signature-using subroutine.
In a subroutine that does not use signatures, any arguments passed in show up in the array `@_`. Therefore, if you called a function with two arguments, those would be stored in `$_[0]` and `$_[1]`. The array `@_` is a local array, but its elements are aliases for the actual scalar parameters. In particular, if an element `$_[0]` is updated, the corresponding argument is updated (or an error occurs if it is not updatable). If an argument is an array or hash element which did not exist when the function was called, that element is created only when (and if) it is modified or a reference to it is taken. (Some earlier versions of Perl created the element whether or not the element was assigned to.) Assigning to the whole array `@_` removes that aliasing, and does not update any arguments.
When not using signatures, Perl does not otherwise provide a means to create named formal parameters. In practice all you do is assign to a `my()` list of these. Variables that aren't declared to be private are global variables. For gory details on creating private variables, see ["Private Variables via my()"](#Private-Variables-via-my%28%29) and ["Temporary Values via local()"](#Temporary-Values-via-local%28%29). To create protected environments for a set of functions in a separate package (and probably a separate file), see ["Packages" in perlmod](perlmod#Packages).
A `return` statement may be used to exit a subroutine, optionally specifying the returned value, which will be evaluated in the appropriate context (list, scalar, or void) depending on the context of the subroutine call. If you specify no return value, the subroutine returns an empty list in list context, the undefined value in scalar context, or nothing in void context. If you return one or more aggregates (arrays and hashes), these will be flattened together into one large indistinguishable list.
If no `return` is found and if the last statement is an expression, its value is returned. If the last statement is a loop control structure like a `foreach` or a `while`, the returned value is unspecified. The empty sub returns the empty list.
Example:
```
sub max {
my $max = shift(@_);
foreach $foo (@_) {
$max = $foo if $max < $foo;
}
return $max;
}
$bestday = max($mon,$tue,$wed,$thu,$fri);
```
Example:
```
# get a line, combining continuation lines
# that start with whitespace
sub get_line {
$thisline = $lookahead; # global variables!
LINE: while (defined($lookahead = <STDIN>)) {
if ($lookahead =~ /^[ \t]/) {
$thisline .= $lookahead;
}
else {
last LINE;
}
}
return $thisline;
}
$lookahead = <STDIN>; # get first line
while (defined($line = get_line())) {
...
}
```
Assigning to a list of private variables to name your arguments:
```
sub maybeset {
my($key, $value) = @_;
$Foo{$key} = $value unless $Foo{$key};
}
```
Because the assignment copies the values, this also has the effect of turning call-by-reference into call-by-value. Otherwise a function is free to do in-place modifications of `@_` and change its caller's values.
```
upcase_in($v1, $v2); # this changes $v1 and $v2
sub upcase_in {
for (@_) { tr/a-z/A-Z/ }
}
```
You aren't allowed to modify constants in this way, of course. If an argument were actually literal and you tried to change it, you'd take a (presumably fatal) exception. For example, this won't work:
```
upcase_in("frederick");
```
It would be much safer if the `upcase_in()` function were written to return a copy of its parameters instead of changing them in place:
```
($v3, $v4) = upcase($v1, $v2); # this doesn't change $v1 and $v2
sub upcase {
return unless defined wantarray; # void context, do nothing
my @parms = @_;
for (@parms) { tr/a-z/A-Z/ }
return wantarray ? @parms : $parms[0];
}
```
Notice how this (unprototyped) function doesn't care whether it was passed real scalars or arrays. Perl sees all arguments as one big, long, flat parameter list in `@_`. This is one area where Perl's simple argument-passing style shines. The `upcase()` function would work perfectly well without changing the `upcase()` definition even if we fed it things like this:
```
@newlist = upcase(@list1, @list2);
@newlist = upcase( split /:/, $var );
```
Do not, however, be tempted to do this:
```
(@a, @b) = upcase(@list1, @list2);
```
Like the flattened incoming parameter list, the return list is also flattened on return. So all you have managed to do here is stored everything in `@a` and made `@b` empty. See ["Pass by Reference"](#Pass-by-Reference) for alternatives.
A subroutine may be called using an explicit `&` prefix. The `&` is optional in modern Perl, as are parentheses if the subroutine has been predeclared. The `&` is *not* optional when just naming the subroutine, such as when it's used as an argument to defined() or undef(). Nor is it optional when you want to do an indirect subroutine call with a subroutine name or reference using the `&$subref()` or `&{$subref}()` constructs, although the `$subref->()` notation solves that problem. See <perlref> for more about all that.
Subroutines may be called recursively. If a subroutine is called using the `&` form, the argument list is optional, and if omitted, no `@_` array is set up for the subroutine: the `@_` array at the time of the call is visible to subroutine instead. This is an efficiency mechanism that new users may wish to avoid.
```
&foo(1,2,3); # pass three arguments
foo(1,2,3); # the same
foo(); # pass a null list
&foo(); # the same
&foo; # foo() get current args, like foo(@_) !!
use strict 'subs';
foo; # like foo() iff sub foo predeclared, else
# a compile-time error
no strict 'subs';
foo; # like foo() iff sub foo predeclared, else
# a literal string "foo"
```
Not only does the `&` form make the argument list optional, it also disables any prototype checking on arguments you do provide. This is partly for historical reasons, and partly for having a convenient way to cheat if you know what you're doing. See ["Prototypes"](#Prototypes) below.
Since Perl 5.16.0, the `__SUB__` token is available under `use feature 'current_sub'` and `use v5.16`. It will evaluate to a reference to the currently-running sub, which allows for recursive calls without knowing your subroutine's name.
```
use v5.16;
my $factorial = sub {
my ($x) = @_;
return 1 if $x == 1;
return($x * __SUB__->( $x - 1 ) );
};
```
The behavior of `__SUB__` within a regex code block (such as `/(?{...})/`) is subject to change.
Subroutines whose names are in all upper case are reserved to the Perl core, as are modules whose names are in all lower case. A subroutine in all capitals is a loosely-held convention meaning it will be called indirectly by the run-time system itself, usually due to a triggered event. Subroutines whose name start with a left parenthesis are also reserved the same way. The following is a list of some subroutines that currently do special, pre-defined things.
documented later in this document `AUTOLOAD`
documented in <perlmod>
`CLONE`, `CLONE_SKIP`
documented in <perlobj>
`DESTROY`, `DOES`
documented in <perltie>
`BINMODE`, `CLEAR`, `CLOSE`, `DELETE`, `DESTROY`, `EOF`, `EXISTS`, `EXTEND`, `FETCH`, `FETCHSIZE`, `FILENO`, `FIRSTKEY`, `GETC`, `NEXTKEY`, `OPEN`, `POP`, `PRINT`, `PRINTF`, `PUSH`, `READ`, `READLINE`, `SCALAR`, `SEEK`, `SHIFT`, `SPLICE`, `STORE`, `STORESIZE`, `TELL`, `TIEARRAY`, `TIEHANDLE`, `TIEHASH`, `TIESCALAR`, `UNSHIFT`, `UNTIE`, `WRITE`
documented in <PerlIO::via>
`BINMODE`, `CLEARERR`, `CLOSE`, `EOF`, `ERROR`, `FDOPEN`, `FILENO`, `FILL`, `FLUSH`, `OPEN`, `POPPED`, `PUSHED`, `READ`, `SEEK`, `SETLINEBUF`, `SYSOPEN`, `TELL`, `UNREAD`, `UTF8`, `WRITE`
documented in <perlfunc>
[`import`](%20perlfunc#use) , [`unimport`](%20perlfunc#use) , [`INC`](%20perlfunc#require)
documented in [UNIVERSAL](universal)
`VERSION`
documented in <perldebguts>
`DB::DB`, `DB::sub`, `DB::lsub`, `DB::goto`, `DB::postponed`
undocumented, used internally by the <overload> feature any starting with `(`
The `BEGIN`, `UNITCHECK`, `CHECK`, `INIT` and `END` subroutines are not so much subroutines as named special code blocks, of which you can have more than one in a package, and which you can **not** call explicitly. See ["BEGIN, UNITCHECK, CHECK, INIT and END" in perlmod](perlmod#BEGIN%2C-UNITCHECK%2C-CHECK%2C-INIT-and-END)
### Signatures
Perl has a facility to allow a subroutine's formal parameters to be declared by special syntax, separate from the procedural code of the subroutine body. The formal parameter list is known as a *signature*.
This facility must be enabled before it can be used. It is enabled automatically by a `use v5.36` (or higher) declaration, or more directly by `use feature 'signatures'`, in the current scope.
The signature is part of a subroutine's body. Normally the body of a subroutine is simply a braced block of code, but when using a signature, the signature is a parenthesised list that goes immediately before the block, after any name or attributes.
For example,
```
sub foo :lvalue ($a, $b = 1, @c) { .... }
```
The signature declares lexical variables that are in scope for the block. When the subroutine is called, the signature takes control first. It populates the signature variables from the list of arguments that were passed. If the argument list doesn't meet the requirements of the signature, then it will throw an exception. When the signature processing is complete, control passes to the block.
Positional parameters are handled by simply naming scalar variables in the signature. For example,
```
sub foo ($left, $right) {
return $left + $right;
}
```
takes two positional parameters, which must be filled at runtime by two arguments. By default the parameters are mandatory, and it is not permitted to pass more arguments than expected. So the above is equivalent to
```
sub foo {
die "Too many arguments for subroutine" unless @_ <= 2;
die "Too few arguments for subroutine" unless @_ >= 2;
my $left = $_[0];
my $right = $_[1];
return $left + $right;
}
```
An argument can be ignored by omitting the main part of the name from a parameter declaration, leaving just a bare `$` sigil. For example,
```
sub foo ($first, $, $third) {
return "first=$first, third=$third";
}
```
Although the ignored argument doesn't go into a variable, it is still mandatory for the caller to pass it.
A positional parameter is made optional by giving a default value, separated from the parameter name by `=`:
```
sub foo ($left, $right = 0) {
return $left + $right;
}
```
The above subroutine may be called with either one or two arguments. The default value expression is evaluated when the subroutine is called, so it may provide different default values for different calls. It is only evaluated if the argument was actually omitted from the call. For example,
```
my $auto_id = 0;
sub foo ($thing, $id = $auto_id++) {
print "$thing has ID $id";
}
```
automatically assigns distinct sequential IDs to things for which no ID was supplied by the caller. A default value expression may also refer to parameters earlier in the signature, making the default for one parameter vary according to the earlier parameters. For example,
```
sub foo ($first_name, $surname, $nickname = $first_name) {
print "$first_name $surname is known as \"$nickname\"";
}
```
An optional parameter can be nameless just like a mandatory parameter. For example,
```
sub foo ($thing, $ = 1) {
print $thing;
}
```
The parameter's default value will still be evaluated if the corresponding argument isn't supplied, even though the value won't be stored anywhere. This is in case evaluating it has important side effects. However, it will be evaluated in void context, so if it doesn't have side effects and is not trivial it will generate a warning if the "void" warning category is enabled. If a nameless optional parameter's default value is not important, it may be omitted just as the parameter's name was:
```
sub foo ($thing, $=) {
print $thing;
}
```
Optional positional parameters must come after all mandatory positional parameters. (If there are no mandatory positional parameters then an optional positional parameters can be the first thing in the signature.) If there are multiple optional positional parameters and not enough arguments are supplied to fill them all, they will be filled from left to right.
After positional parameters, additional arguments may be captured in a slurpy parameter. The simplest form of this is just an array variable:
```
sub foo ($filter, @inputs) {
print $filter->($_) foreach @inputs;
}
```
With a slurpy parameter in the signature, there is no upper limit on how many arguments may be passed. A slurpy array parameter may be nameless just like a positional parameter, in which case its only effect is to turn off the argument limit that would otherwise apply:
```
sub foo ($thing, @) {
print $thing;
}
```
A slurpy parameter may instead be a hash, in which case the arguments available to it are interpreted as alternating keys and values. There must be as many keys as values: if there is an odd argument then an exception will be thrown. Keys will be stringified, and if there are duplicates then the later instance takes precedence over the earlier, as with standard hash construction.
```
sub foo ($filter, %inputs) {
print $filter->($_, $inputs{$_}) foreach sort keys %inputs;
}
```
A slurpy hash parameter may be nameless just like other kinds of parameter. It still insists that the number of arguments available to it be even, even though they're not being put into a variable.
```
sub foo ($thing, %) {
print $thing;
}
```
A slurpy parameter, either array or hash, must be the last thing in the signature. It may follow mandatory and optional positional parameters; it may also be the only thing in the signature. Slurpy parameters cannot have default values: if no arguments are supplied for them then you get an empty array or empty hash.
A signature may be entirely empty, in which case all it does is check that the caller passed no arguments:
```
sub foo () {
return 123;
}
```
Prior to Perl 5.36 these were considered experimental, and emitted a warning in the `experimental::signatures` category. From Perl 5.36 onwards this no longer happens, though the warning category still exists for back-compatibility with code that attempts to disable it with a statement such as:
```
no warnings 'experimental::signatures';
```
In the current perl implementation, when using a signature the arguments are still also available in the special array variable `@_`. However, accessing them via this array is now discouraged, and should not be relied upon in newly-written code as this ability may change in a future version. Code that attempts to access the `@_` array will produce warnings in the `experimental::args_array_with_signatures` category when compiled:
```
sub f ($x) {
# This line emits the warning seen below
print "Arguments are @_";
}
```
```
Use of @_ in join or string with signatured subroutine is
experimental at ...
```
There is a difference between the two ways of accessing the arguments: `@_` *aliases* the arguments, but the signature variables get *copies* of the arguments. So writing to a signature variable only changes that variable, and has no effect on the caller's variables, but writing to an element of `@_` modifies whatever the caller used to supply that argument.
There is a potential syntactic ambiguity between signatures and prototypes (see ["Prototypes"](#Prototypes)), because both start with an opening parenthesis and both can appear in some of the same places, such as just after the name in a subroutine declaration. For historical reasons, when signatures are not enabled, any opening parenthesis in such a context will trigger very forgiving prototype parsing. Most signatures will be interpreted as prototypes in those circumstances, but won't be valid prototypes. (A valid prototype cannot contain any alphabetic character.) This will lead to somewhat confusing error messages.
To avoid ambiguity, when signatures are enabled the special syntax for prototypes is disabled. There is no attempt to guess whether a parenthesised group was intended to be a prototype or a signature. To give a subroutine a prototype under these circumstances, use a [prototype attribute](attributes#Built-in-Attributes). For example,
```
sub foo :prototype($) { $_[0] }
```
It is entirely possible for a subroutine to have both a prototype and a signature. They do different jobs: the prototype affects compilation of calls to the subroutine, and the signature puts argument values into lexical variables at runtime. You can therefore write
```
sub foo :prototype($$) ($left, $right) {
return $left + $right;
}
```
The prototype attribute, and any other attributes, must come before the signature. The signature always immediately precedes the block of the subroutine's body.
###
Private Variables via my()
Synopsis:
```
my $foo; # declare $foo lexically local
my (@wid, %get); # declare list of variables local
my $foo = "flurp"; # declare $foo lexical, and init it
my @oof = @bar; # declare @oof lexical, and init it
my $x : Foo = $y; # similar, with an attribute applied
```
**WARNING**: The use of attribute lists on `my` declarations is still evolving. The current semantics and interface are subject to change. See <attributes> and <Attribute::Handlers>.
The `my` operator declares the listed variables to be lexically confined to the enclosing block, conditional (`if`/`unless`/`elsif`/`else`), loop (`for`/`foreach`/`while`/`until`/`continue`), subroutine, `eval`, or `do`/`require`/`use`'d file. If more than one value is listed, the list must be placed in parentheses. All listed elements must be legal lvalues. Only alphanumeric identifiers may be lexically scoped--magical built-ins like `$/` must currently be `local`ized with `local` instead.
Unlike dynamic variables created by the `local` operator, lexical variables declared with `my` are totally hidden from the outside world, including any called subroutines. This is true if it's the same subroutine called from itself or elsewhere--every call gets its own copy.
This doesn't mean that a `my` variable declared in a statically enclosing lexical scope would be invisible. Only dynamic scopes are cut off. For example, the `bumpx()` function below has access to the lexical $x variable because both the `my` and the `sub` occurred at the same scope, presumably file scope.
```
my $x = 10;
sub bumpx { $x++ }
```
An `eval()`, however, can see lexical variables of the scope it is being evaluated in, so long as the names aren't hidden by declarations within the `eval()` itself. See <perlref>.
The parameter list to my() may be assigned to if desired, which allows you to initialize your variables. (If no initializer is given for a particular variable, it is created with the undefined value.) Commonly this is used to name input parameters to a subroutine. Examples:
```
$arg = "fred"; # "global" variable
$n = cube_root(27);
print "$arg thinks the root is $n\n";
fred thinks the root is 3
sub cube_root {
my $arg = shift; # name doesn't matter
$arg **= 1/3;
return $arg;
}
```
The `my` is simply a modifier on something you might assign to. So when you do assign to variables in its argument list, `my` doesn't change whether those variables are viewed as a scalar or an array. So
```
my ($foo) = <STDIN>; # WRONG?
my @FOO = <STDIN>;
```
both supply a list context to the right-hand side, while
```
my $foo = <STDIN>;
```
supplies a scalar context. But the following declares only one variable:
```
my $foo, $bar = 1; # WRONG
```
That has the same effect as
```
my $foo;
$bar = 1;
```
The declared variable is not introduced (is not visible) until after the current statement. Thus,
```
my $x = $x;
```
can be used to initialize a new $x with the value of the old $x, and the expression
```
my $x = 123 and $x == 123
```
is false unless the old $x happened to have the value `123`.
Lexical scopes of control structures are not bounded precisely by the braces that delimit their controlled blocks; control expressions are part of that scope, too. Thus in the loop
```
while (my $line = <>) {
$line = lc $line;
} continue {
print $line;
}
```
the scope of $line extends from its declaration throughout the rest of the loop construct (including the `continue` clause), but not beyond it. Similarly, in the conditional
```
if ((my $answer = <STDIN>) =~ /^yes$/i) {
user_agrees();
} elsif ($answer =~ /^no$/i) {
user_disagrees();
} else {
chomp $answer;
die "'$answer' is neither 'yes' nor 'no'";
}
```
the scope of $answer extends from its declaration through the rest of that conditional, including any `elsif` and `else` clauses, but not beyond it. See ["Simple Statements" in perlsyn](perlsyn#Simple-Statements) for information on the scope of variables in statements with modifiers.
The `foreach` loop defaults to scoping its index variable dynamically in the manner of `local`. However, if the index variable is prefixed with the keyword `my`, or if there is already a lexical by that name in scope, then a new lexical is created instead. Thus in the loop
```
for my $i (1, 2, 3) {
some_function();
}
```
the scope of $i extends to the end of the loop, but not beyond it, rendering the value of $i inaccessible within `some_function()`.
Some users may wish to encourage the use of lexically scoped variables. As an aid to catching implicit uses to package variables, which are always global, if you say
```
use strict 'vars';
```
then any variable mentioned from there to the end of the enclosing block must either refer to a lexical variable, be predeclared via `our` or `use vars`, or else must be fully qualified with the package name. A compilation error results otherwise. An inner block may countermand this with `no strict 'vars'`.
A `my` has both a compile-time and a run-time effect. At compile time, the compiler takes notice of it. The principal usefulness of this is to quiet `use strict 'vars'`, but it is also essential for generation of closures as detailed in <perlref>. Actual initialization is delayed until run time, though, so it gets executed at the appropriate time, such as each time through a loop, for example.
Variables declared with `my` are not part of any package and are therefore never fully qualified with the package name. In particular, you're not allowed to try to make a package variable (or other global) lexical:
```
my $pack::var; # ERROR! Illegal syntax
```
In fact, a dynamic variable (also known as package or global variables) are still accessible using the fully qualified `::` notation even while a lexical of the same name is also visible:
```
package main;
local $x = 10;
my $x = 20;
print "$x and $::x\n";
```
That will print out `20` and `10`.
You may declare `my` variables at the outermost scope of a file to hide any such identifiers from the world outside that file. This is similar in spirit to C's static variables when they are used at the file level. To do this with a subroutine requires the use of a closure (an anonymous function that accesses enclosing lexicals). If you want to create a private subroutine that cannot be called from outside that block, it can declare a lexical variable containing an anonymous sub reference:
```
my $secret_version = '1.001-beta';
my $secret_sub = sub { print $secret_version };
&$secret_sub();
```
As long as the reference is never returned by any function within the module, no outside module can see the subroutine, because its name is not in any package's symbol table. Remember that it's not *REALLY* called `$some_pack::secret_version` or anything; it's just $secret\_version, unqualified and unqualifiable.
This does not work with object methods, however; all object methods have to be in the symbol table of some package to be found. See ["Function Templates" in perlref](perlref#Function-Templates) for something of a work-around to this.
###
Persistent Private Variables
There are two ways to build persistent private variables in Perl 5.10. First, you can simply use the `state` feature. Or, you can use closures, if you want to stay compatible with releases older than 5.10.
####
Persistent variables via state()
Beginning with Perl 5.10.0, you can declare variables with the `state` keyword in place of `my`. For that to work, though, you must have enabled that feature beforehand, either by using the `feature` pragma, or by using `-E` on one-liners (see <feature>). Beginning with Perl 5.16, the `CORE::state` form does not require the `feature` pragma.
The `state` keyword creates a lexical variable (following the same scoping rules as `my`) that persists from one subroutine call to the next. If a state variable resides inside an anonymous subroutine, then each copy of the subroutine has its own copy of the state variable. However, the value of the state variable will still persist between calls to the same copy of the anonymous subroutine. (Don't forget that `sub { ... }` creates a new subroutine each time it is executed.)
For example, the following code maintains a private counter, incremented each time the gimme\_another() function is called:
```
use feature 'state';
sub gimme_another { state $x; return ++$x }
```
And this example uses anonymous subroutines to create separate counters:
```
use feature 'state';
sub create_counter {
return sub { state $x; return ++$x }
}
```
Also, since `$x` is lexical, it can't be reached or modified by any Perl code outside.
When combined with variable declaration, simple assignment to `state` variables (as in `state $x = 42`) is executed only the first time. When such statements are evaluated subsequent times, the assignment is ignored. The behavior of assignment to `state` declarations where the left hand side of the assignment involves any parentheses is currently undefined.
####
Persistent variables with closures
Just because a lexical variable is lexically (also called statically) scoped to its enclosing block, `eval`, or `do` FILE, this doesn't mean that within a function it works like a C static. It normally works more like a C auto, but with implicit garbage collection.
Unlike local variables in C or C++, Perl's lexical variables don't necessarily get recycled just because their scope has exited. If something more permanent is still aware of the lexical, it will stick around. So long as something else references a lexical, that lexical won't be freed--which is as it should be. You wouldn't want memory being free until you were done using it, or kept around once you were done. Automatic garbage collection takes care of this for you.
This means that you can pass back or save away references to lexical variables, whereas to return a pointer to a C auto is a grave error. It also gives us a way to simulate C's function statics. Here's a mechanism for giving a function private variables with both lexical scoping and a static lifetime. If you do want to create something like C's static variables, just enclose the whole function in an extra block, and put the static variable outside the function but in the block.
```
{
my $secret_val = 0;
sub gimme_another {
return ++$secret_val;
}
}
# $secret_val now becomes unreachable by the outside
# world, but retains its value between calls to gimme_another
```
If this function is being sourced in from a separate file via `require` or `use`, then this is probably just fine. If it's all in the main program, you'll need to arrange for the `my` to be executed early, either by putting the whole block above your main program, or more likely, placing merely a `BEGIN` code block around it to make sure it gets executed before your program starts to run:
```
BEGIN {
my $secret_val = 0;
sub gimme_another {
return ++$secret_val;
}
}
```
See ["BEGIN, UNITCHECK, CHECK, INIT and END" in perlmod](perlmod#BEGIN%2C-UNITCHECK%2C-CHECK%2C-INIT-and-END) about the special triggered code blocks, `BEGIN`, `UNITCHECK`, `CHECK`, `INIT` and `END`.
If declared at the outermost scope (the file scope), then lexicals work somewhat like C's file statics. They are available to all functions in that same file declared below them, but are inaccessible from outside that file. This strategy is sometimes used in modules to create private variables that the whole module can see.
###
Temporary Values via local()
**WARNING**: In general, you should be using `my` instead of `local`, because it's faster and safer. Exceptions to this include the global punctuation variables, global filehandles and formats, and direct manipulation of the Perl symbol table itself. `local` is mostly used when the current value of a variable must be visible to called subroutines.
Synopsis:
```
# localization of values
local $foo; # make $foo dynamically local
local (@wid, %get); # make list of variables local
local $foo = "flurp"; # make $foo dynamic, and init it
local @oof = @bar; # make @oof dynamic, and init it
local $hash{key} = "val"; # sets a local value for this hash entry
delete local $hash{key}; # delete this entry for the current block
local ($cond ? $v1 : $v2); # several types of lvalues support
# localization
# localization of symbols
local *FH; # localize $FH, @FH, %FH, &FH ...
local *merlyn = *randal; # now $merlyn is really $randal, plus
# @merlyn is really @randal, etc
local *merlyn = 'randal'; # SAME THING: promote 'randal' to *randal
local *merlyn = \$randal; # just alias $merlyn, not @merlyn etc
```
A `local` modifies its listed variables to be "local" to the enclosing block, `eval`, or `do FILE`--and to *any subroutine called from within that block*. A `local` just gives temporary values to global (meaning package) variables. It does *not* create a local variable. This is known as dynamic scoping. Lexical scoping is done with `my`, which works more like C's auto declarations.
Some types of lvalues can be localized as well: hash and array elements and slices, conditionals (provided that their result is always localizable), and symbolic references. As for simple variables, this creates new, dynamically scoped values.
If more than one variable or expression is given to `local`, they must be placed in parentheses. This operator works by saving the current values of those variables in its argument list on a hidden stack and restoring them upon exiting the block, subroutine, or eval. This means that called subroutines can also reference the local variable, but not the global one. The argument list may be assigned to if desired, which allows you to initialize your local variables. (If no initializer is given for a particular variable, it is created with an undefined value.)
Because `local` is a run-time operator, it gets executed each time through a loop. Consequently, it's more efficient to localize your variables outside the loop.
####
Grammatical note on local()
A `local` is simply a modifier on an lvalue expression. When you assign to a `local`ized variable, the `local` doesn't change whether its list is viewed as a scalar or an array. So
```
local($foo) = <STDIN>;
local @FOO = <STDIN>;
```
both supply a list context to the right-hand side, while
```
local $foo = <STDIN>;
```
supplies a scalar context.
####
Localization of special variables
If you localize a special variable, you'll be giving a new value to it, but its magic won't go away. That means that all side-effects related to this magic still work with the localized value.
This feature allows code like this to work :
```
# Read the whole contents of FILE in $slurp
{ local $/ = undef; $slurp = <FILE>; }
```
Note, however, that this restricts localization of some values ; for example, the following statement dies, as of perl 5.10.0, with an error *Modification of a read-only value attempted*, because the $1 variable is magical and read-only :
```
local $1 = 2;
```
One exception is the default scalar variable: starting with perl 5.14 `local($_)` will always strip all magic from $\_, to make it possible to safely reuse $\_ in a subroutine.
**WARNING**: Localization of tied arrays and hashes does not currently work as described. This will be fixed in a future release of Perl; in the meantime, avoid code that relies on any particular behavior of localising tied arrays or hashes (localising individual elements is still okay). See ["Localising Tied Arrays and Hashes Is Broken" in perl58delta](https://perldoc.perl.org/5.36.0/perl58delta#Localising-Tied-Arrays-and-Hashes-Is-Broken) for more details.
####
Localization of globs
The construct
```
local *name;
```
creates a whole new symbol table entry for the glob `name` in the current package. That means that all variables in its glob slot ($name, @name, %name, &name, and the `name` filehandle) are dynamically reset.
This implies, among other things, that any magic eventually carried by those variables is locally lost. In other words, saying `local */` will not have any effect on the internal value of the input record separator.
####
Localization of elements of composite types
It's also worth taking a moment to explain what happens when you `local`ize a member of a composite type (i.e. an array or hash element). In this case, the element is `local`ized *by name*. This means that when the scope of the `local()` ends, the saved value will be restored to the hash element whose key was named in the `local()`, or the array element whose index was named in the `local()`. If that element was deleted while the `local()` was in effect (e.g. by a `delete()` from a hash or a `shift()` of an array), it will spring back into existence, possibly extending an array and filling in the skipped elements with `undef`. For instance, if you say
```
%hash = ( 'This' => 'is', 'a' => 'test' );
@ary = ( 0..5 );
{
local($ary[5]) = 6;
local($hash{'a'}) = 'drill';
while (my $e = pop(@ary)) {
print "$e . . .\n";
last unless $e > 3;
}
if (@ary) {
$hash{'only a'} = 'test';
delete $hash{'a'};
}
}
print join(' ', map { "$_ $hash{$_}" } sort keys %hash),".\n";
print "The array has ",scalar(@ary)," elements: ",
join(', ', map { defined $_ ? $_ : 'undef' } @ary),"\n";
```
Perl will print
```
6 . . .
4 . . .
3 . . .
This is a test only a test.
The array has 6 elements: 0, 1, 2, undef, undef, 5
```
The behavior of local() on non-existent members of composite types is subject to change in future. The behavior of local() on array elements specified using negative indexes is particularly surprising, and is very likely to change.
####
Localized deletion of elements of composite types
You can use the `delete local $array[$idx]` and `delete local $hash{key}` constructs to delete a composite type entry for the current block and restore it when it ends. They return the array/hash value before the localization, which means that they are respectively equivalent to
```
do {
my $val = $array[$idx];
local $array[$idx];
delete $array[$idx];
$val
}
```
and
```
do {
my $val = $hash{key};
local $hash{key};
delete $hash{key};
$val
}
```
except that for those the `local` is scoped to the `do` block. Slices are also accepted.
```
my %hash = (
a => [ 7, 8, 9 ],
b => 1,
)
{
my $a = delete local $hash{a};
# $a is [ 7, 8, 9 ]
# %hash is (b => 1)
{
my @nums = delete local @$a[0, 2]
# @nums is (7, 9)
# $a is [ undef, 8 ]
$a[0] = 999; # will be erased when the scope ends
}
# $a is back to [ 7, 8, 9 ]
}
# %hash is back to its original state
```
This construct is supported since Perl v5.12.
###
Lvalue subroutines
It is possible to return a modifiable value from a subroutine. To do this, you have to declare the subroutine to return an lvalue.
```
my $val;
sub canmod : lvalue {
$val; # or: return $val;
}
sub nomod {
$val;
}
canmod() = 5; # assigns to $val
nomod() = 5; # ERROR
```
The scalar/list context for the subroutine and for the right-hand side of assignment is determined as if the subroutine call is replaced by a scalar. For example, consider:
```
data(2,3) = get_data(3,4);
```
Both subroutines here are called in a scalar context, while in:
```
(data(2,3)) = get_data(3,4);
```
and in:
```
(data(2),data(3)) = get_data(3,4);
```
all the subroutines are called in a list context.
Lvalue subroutines are convenient, but you have to keep in mind that, when used with objects, they may violate encapsulation. A normal mutator can check the supplied argument before setting the attribute it is protecting, an lvalue subroutine cannot. If you require any special processing when storing and retrieving the values, consider using the CPAN module Sentinel or something similar.
###
Lexical Subroutines
Beginning with Perl 5.18, you can declare a private subroutine with `my` or `state`. As with state variables, the `state` keyword is only available under `use feature 'state'` or `use v5.10` or higher.
Prior to Perl 5.26, lexical subroutines were deemed experimental and were available only under the `use feature 'lexical_subs'` pragma. They also produced a warning unless the "experimental::lexical\_subs" warnings category was disabled.
These subroutines are only visible within the block in which they are declared, and only after that declaration:
```
# Include these two lines if your code is intended to run under Perl
# versions earlier than 5.26.
no warnings "experimental::lexical_subs";
use feature 'lexical_subs';
foo(); # calls the package/global subroutine
state sub foo {
foo(); # also calls the package subroutine
}
foo(); # calls "state" sub
my $ref = \&foo; # take a reference to "state" sub
my sub bar { ... }
bar(); # calls "my" sub
```
You can't (directly) write a recursive lexical subroutine:
```
# WRONG
my sub baz {
baz();
}
```
This example fails because `baz()` refers to the package/global subroutine `baz`, not the lexical subroutine currently being defined.
The solution is to use [`__SUB__`](perlfunc#__SUB__):
```
my sub baz {
__SUB__->(); # calls itself
}
```
It is possible to predeclare a lexical subroutine. The `sub foo {...}` subroutine definition syntax respects any previous `my sub;` or `state sub;` declaration. Using this to define recursive subroutines is a bad idea, however:
```
my sub baz; # predeclaration
sub baz { # define the "my" sub
baz(); # WRONG: calls itself, but leaks memory
}
```
Just like `my $f; $f = sub { $f->() }`, this example leaks memory. The name `baz` is a reference to the subroutine, and the subroutine uses the name `baz`; they keep each other alive (see ["Circular References" in perlref](perlref#Circular-References)).
####
`state sub` vs `my sub`
What is the difference between "state" subs and "my" subs? Each time that execution enters a block when "my" subs are declared, a new copy of each sub is created. "State" subroutines persist from one execution of the containing block to the next.
So, in general, "state" subroutines are faster. But "my" subs are necessary if you want to create closures:
```
sub whatever {
my $x = shift;
my sub inner {
... do something with $x ...
}
inner();
}
```
In this example, a new `$x` is created when `whatever` is called, and also a new `inner`, which can see the new `$x`. A "state" sub will only see the `$x` from the first call to `whatever`.
####
`our` subroutines
Like `our $variable`, `our sub` creates a lexical alias to the package subroutine of the same name.
The two main uses for this are to switch back to using the package sub inside an inner scope:
```
sub foo { ... }
sub bar {
my sub foo { ... }
{
# need to use the outer foo here
our sub foo;
foo();
}
}
```
and to make a subroutine visible to other packages in the same scope:
```
package MySneakyModule;
our sub do_something { ... }
sub do_something_with_caller {
package DB;
() = caller 1; # sets @DB::args
do_something(@args); # uses MySneakyModule::do_something
}
```
###
Passing Symbol Table Entries (typeglobs)
**WARNING**: The mechanism described in this section was originally the only way to simulate pass-by-reference in older versions of Perl. While it still works fine in modern versions, the new reference mechanism is generally easier to work with. See below.
Sometimes you don't want to pass the value of an array to a subroutine but rather the name of it, so that the subroutine can modify the global copy of it rather than working with a local copy. In perl you can refer to all objects of a particular name by prefixing the name with a star: `*foo`. This is often known as a "typeglob", because the star on the front can be thought of as a wildcard match for all the funny prefix characters on variables and subroutines and such.
When evaluated, the typeglob produces a scalar value that represents all the objects of that name, including any filehandle, format, or subroutine. When assigned to, it causes the name mentioned to refer to whatever `*` value was assigned to it. Example:
```
sub doubleary {
local(*someary) = @_;
foreach $elem (@someary) {
$elem *= 2;
}
}
doubleary(*foo);
doubleary(*bar);
```
Scalars are already passed by reference, so you can modify scalar arguments without using this mechanism by referring explicitly to `$_[0]` etc. You can modify all the elements of an array by passing all the elements as scalars, but you have to use the `*` mechanism (or the equivalent reference mechanism) to `push`, `pop`, or change the size of an array. It will certainly be faster to pass the typeglob (or reference).
Even if you don't want to modify an array, this mechanism is useful for passing multiple arrays in a single LIST, because normally the LIST mechanism will merge all the array values so that you can't extract out the individual arrays. For more on typeglobs, see ["Typeglobs and Filehandles" in perldata](perldata#Typeglobs-and-Filehandles).
###
When to Still Use local()
Despite the existence of `my`, there are still three places where the `local` operator still shines. In fact, in these three places, you *must* use `local` instead of `my`.
1. You need to give a global variable a temporary value, especially $\_.
The global variables, like `@ARGV` or the punctuation variables, must be `local`ized with `local()`. This block reads in */etc/motd*, and splits it up into chunks separated by lines of equal signs, which are placed in `@Fields`.
```
{
local @ARGV = ("/etc/motd");
local $/ = undef;
local $_ = <>;
@Fields = split /^\s*=+\s*$/;
}
```
It particular, it's important to `local`ize $\_ in any routine that assigns to it. Look out for implicit assignments in `while` conditionals.
2. You need to create a local file or directory handle or a local function.
A function that needs a filehandle of its own must use `local()` on a complete typeglob. This can be used to create new symbol table entries:
```
sub ioqueue {
local (*READER, *WRITER); # not my!
pipe (READER, WRITER) or die "pipe: $!";
return (*READER, *WRITER);
}
($head, $tail) = ioqueue();
```
See the Symbol module for a way to create anonymous symbol table entries.
Because assignment of a reference to a typeglob creates an alias, this can be used to create what is effectively a local function, or at least, a local alias.
```
{
local *grow = \&shrink; # only until this block exits
grow(); # really calls shrink()
move(); # if move() grow()s, it shrink()s too
}
grow(); # get the real grow() again
```
See ["Function Templates" in perlref](perlref#Function-Templates) for more about manipulating functions by name in this way.
3. You want to temporarily change just one element of an array or hash.
You can `local`ize just one element of an aggregate. Usually this is done on dynamics:
```
{
local $SIG{INT} = 'IGNORE';
funct(); # uninterruptible
}
# interruptibility automatically restored here
```
But it also works on lexically declared aggregates.
###
Pass by Reference
If you want to pass more than one array or hash into a function--or return them from it--and have them maintain their integrity, then you're going to have to use an explicit pass-by-reference. Before you do that, you need to understand references as detailed in <perlref>. This section may not make much sense to you otherwise.
Here are a few simple examples. First, let's pass in several arrays to a function and have it `pop` all of then, returning a new list of all their former last elements:
```
@tailings = popmany ( \@a, \@b, \@c, \@d );
sub popmany {
my $aref;
my @retlist;
foreach $aref ( @_ ) {
push @retlist, pop @$aref;
}
return @retlist;
}
```
Here's how you might write a function that returns a list of keys occurring in all the hashes passed to it:
```
@common = inter( \%foo, \%bar, \%joe );
sub inter {
my ($k, $href, %seen); # locals
foreach $href (@_) {
while ( $k = each %$href ) {
$seen{$k}++;
}
}
return grep { $seen{$_} == @_ } keys %seen;
}
```
So far, we're using just the normal list return mechanism. What happens if you want to pass or return a hash? Well, if you're using only one of them, or you don't mind them concatenating, then the normal calling convention is ok, although a little expensive.
Where people get into trouble is here:
```
(@a, @b) = func(@c, @d);
or
(%a, %b) = func(%c, %d);
```
That syntax simply won't work. It sets just `@a` or `%a` and clears the `@b` or `%b`. Plus the function didn't get passed into two separate arrays or hashes: it got one long list in `@_`, as always.
If you can arrange for everyone to deal with this through references, it's cleaner code, although not so nice to look at. Here's a function that takes two array references as arguments, returning the two array elements in order of how many elements they have in them:
```
($aref, $bref) = func(\@c, \@d);
print "@$aref has more than @$bref\n";
sub func {
my ($cref, $dref) = @_;
if (@$cref > @$dref) {
return ($cref, $dref);
} else {
return ($dref, $cref);
}
}
```
It turns out that you can actually do this also:
```
(*a, *b) = func(\@c, \@d);
print "@a has more than @b\n";
sub func {
local (*c, *d) = @_;
if (@c > @d) {
return (\@c, \@d);
} else {
return (\@d, \@c);
}
}
```
Here we're using the typeglobs to do symbol table aliasing. It's a tad subtle, though, and also won't work if you're using `my` variables, because only globals (even in disguise as `local`s) are in the symbol table.
If you're passing around filehandles, you could usually just use the bare typeglob, like `*STDOUT`, but typeglobs references work, too. For example:
```
splutter(\*STDOUT);
sub splutter {
my $fh = shift;
print $fh "her um well a hmmm\n";
}
$rec = get_rec(\*STDIN);
sub get_rec {
my $fh = shift;
return scalar <$fh>;
}
```
If you're planning on generating new filehandles, you could do this. Notice to pass back just the bare \*FH, not its reference.
```
sub openit {
my $path = shift;
local *FH;
return open (FH, $path) ? *FH : undef;
}
```
### Prototypes
Perl supports a very limited kind of compile-time argument checking using function prototyping. This can be declared in either the PROTO section or with a [prototype attribute](attributes#Built-in-Attributes). If you declare either of
```
sub mypush (\@@)
sub mypush :prototype(\@@)
```
then `mypush()` takes arguments exactly like `push()` does.
If subroutine signatures are enabled (see ["Signatures"](#Signatures)), then the shorter PROTO syntax is unavailable, because it would clash with signatures. In that case, a prototype can only be declared in the form of an attribute.
The function declaration must be visible at compile time. The prototype affects only interpretation of new-style calls to the function, where new-style is defined as not using the `&` character. In other words, if you call it like a built-in function, then it behaves like a built-in function. If you call it like an old-fashioned subroutine, then it behaves like an old-fashioned subroutine. It naturally falls out from this rule that prototypes have no influence on subroutine references like `\&foo` or on indirect subroutine calls like `&{$subref}` or `$subref->()`.
Method calls are not influenced by prototypes either, because the function to be called is indeterminate at compile time, since the exact code called depends on inheritance.
Because the intent of this feature is primarily to let you define subroutines that work like built-in functions, here are prototypes for some other functions that parse almost exactly like the corresponding built-in.
```
Declared as Called as
sub mylink ($$) mylink $old, $new
sub myvec ($$$) myvec $var, $offset, 1
sub myindex ($$;$) myindex &getstring, "substr"
sub mysyswrite ($$$;$) mysyswrite $buf, 0, length($buf) - $off, $off
sub myreverse (@) myreverse $a, $b, $c
sub myjoin ($@) myjoin ":", $a, $b, $c
sub mypop (\@) mypop @array
sub mysplice (\@$$@) mysplice @array, 0, 2, @pushme
sub mykeys (\[%@]) mykeys $hashref->%*
sub myopen (*;$) myopen HANDLE, $name
sub mypipe (**) mypipe READHANDLE, WRITEHANDLE
sub mygrep (&@) mygrep { /foo/ } $a, $b, $c
sub myrand (;$) myrand 42
sub mytime () mytime
```
Any backslashed prototype character represents an actual argument that must start with that character (optionally preceded by `my`, `our` or `local`), with the exception of `$`, which will accept any scalar lvalue expression, such as `$foo = 7` or `my_function()->[0]`. The value passed as part of `@_` will be a reference to the actual argument given in the subroutine call, obtained by applying `\` to that argument.
You can use the `\[]` backslash group notation to specify more than one allowed argument type. For example:
```
sub myref (\[$@%&*])
```
will allow calling myref() as
```
myref $var
myref @array
myref %hash
myref &sub
myref *glob
```
and the first argument of myref() will be a reference to a scalar, an array, a hash, a code, or a glob.
Unbackslashed prototype characters have special meanings. Any unbackslashed `@` or `%` eats all remaining arguments, and forces list context. An argument represented by `$` forces scalar context. An `&` requires an anonymous subroutine, which, if passed as the first argument, does not require the `sub` keyword or a subsequent comma.
A `*` allows the subroutine to accept a bareword, constant, scalar expression, typeglob, or a reference to a typeglob in that slot. The value will be available to the subroutine either as a simple scalar, or (in the latter two cases) as a reference to the typeglob. If you wish to always convert such arguments to a typeglob reference, use Symbol::qualify\_to\_ref() as follows:
```
use Symbol 'qualify_to_ref';
sub foo (*) {
my $fh = qualify_to_ref(shift, caller);
...
}
```
The `+` prototype is a special alternative to `$` that will act like `\[@%]` when given a literal array or hash variable, but will otherwise force scalar context on the argument. This is useful for functions which should accept either a literal array or an array reference as the argument:
```
sub mypush (+@) {
my $aref = shift;
die "Not an array or arrayref" unless ref $aref eq 'ARRAY';
push @$aref, @_;
}
```
When using the `+` prototype, your function must check that the argument is of an acceptable type.
A semicolon (`;`) separates mandatory arguments from optional arguments. It is redundant before `@` or `%`, which gobble up everything else.
As the last character of a prototype, or just before a semicolon, a `@` or a `%`, you can use `_` in place of `$`: if this argument is not provided, `$_` will be used instead.
Note how the last three examples in the table above are treated specially by the parser. `mygrep()` is parsed as a true list operator, `myrand()` is parsed as a true unary operator with unary precedence the same as `rand()`, and `mytime()` is truly without arguments, just like `time()`. That is, if you say
```
mytime +2;
```
you'll get `mytime() + 2`, not `mytime(2)`, which is how it would be parsed without a prototype. If you want to force a unary function to have the same precedence as a list operator, add `;` to the end of the prototype:
```
sub mygetprotobynumber($;);
mygetprotobynumber $a > $b; # parsed as mygetprotobynumber($a > $b)
```
The interesting thing about `&` is that you can generate new syntax with it, provided it's in the initial position:
```
sub try (&@) {
my($try,$catch) = @_;
eval { &$try };
if ($@) {
local $_ = $@;
&$catch;
}
}
sub catch (&) { $_[0] }
try {
die "phooey";
} catch {
/phooey/ and print "unphooey\n";
};
```
That prints `"unphooey"`. (Yes, there are still unresolved issues having to do with visibility of `@_`. I'm ignoring that question for the moment. (But note that if we make `@_` lexically scoped, those anonymous subroutines can act like closures... (Gee, is this sounding a little Lispish? (Never mind.))))
And here's a reimplementation of the Perl `grep` operator:
```
sub mygrep (&@) {
my $code = shift;
my @result;
foreach $_ (@_) {
push(@result, $_) if &$code;
}
@result;
}
```
Some folks would prefer full alphanumeric prototypes. Alphanumerics have been intentionally left out of prototypes for the express purpose of someday in the future adding named, formal parameters. The current mechanism's main goal is to let module writers provide better diagnostics for module users. Larry feels the notation quite understandable to Perl programmers, and that it will not intrude greatly upon the meat of the module, nor make it harder to read. The line noise is visually encapsulated into a small pill that's easy to swallow.
If you try to use an alphanumeric sequence in a prototype you will generate an optional warning - "Illegal character in prototype...". Unfortunately earlier versions of Perl allowed the prototype to be used as long as its prefix was a valid prototype. The warning may be upgraded to a fatal error in a future version of Perl once the majority of offending code is fixed.
It's probably best to prototype new functions, not retrofit prototyping into older ones. That's because you must be especially careful about silent impositions of differing list versus scalar contexts. For example, if you decide that a function should take just one parameter, like this:
```
sub func ($) {
my $n = shift;
print "you gave me $n\n";
}
```
and someone has been calling it with an array or expression returning a list:
```
func(@foo);
func( $text =~ /\w+/g );
```
Then you've just supplied an automatic `scalar` in front of their argument, which can be more than a bit surprising. The old `@foo` which used to hold one thing doesn't get passed in. Instead, `func()` now gets passed in a `1`; that is, the number of elements in `@foo`. And the `m//g` gets called in scalar context so instead of a list of words it returns a boolean result and advances `pos($text)`. Ouch!
If a sub has both a PROTO and a BLOCK, the prototype is not applied until after the BLOCK is completely defined. This means that a recursive function with a prototype has to be predeclared for the prototype to take effect, like so:
```
sub foo($$);
sub foo($$) {
foo 1, 2;
}
```
This is all very powerful, of course, and should be used only in moderation to make the world a better place.
###
Constant Functions
Functions with a prototype of `()` are potential candidates for inlining. If the result after optimization and constant folding is either a constant or a lexically-scoped scalar which has no other references, then it will be used in place of function calls made without `&`. Calls made using `&` are never inlined. (See <constant> for an easy way to declare most constants.)
The following functions would all be inlined:
```
sub pi () { 3.14159 } # Not exact, but close.
sub PI () { 4 * atan2 1, 1 } # As good as it gets,
# and it's inlined, too!
sub ST_DEV () { 0 }
sub ST_INO () { 1 }
sub FLAG_FOO () { 1 << 8 }
sub FLAG_BAR () { 1 << 9 }
sub FLAG_MASK () { FLAG_FOO | FLAG_BAR }
sub OPT_BAZ () { not (0x1B58 & FLAG_MASK) }
sub N () { int(OPT_BAZ) / 3 }
sub FOO_SET () { 1 if FLAG_MASK & FLAG_FOO }
sub FOO_SET2 () { if (FLAG_MASK & FLAG_FOO) { 1 } }
```
(Be aware that the last example was not always inlined in Perl 5.20 and earlier, which did not behave consistently with subroutines containing inner scopes.) You can countermand inlining by using an explicit `return`:
```
sub baz_val () {
if (OPT_BAZ) {
return 23;
}
else {
return 42;
}
}
sub bonk_val () { return 12345 }
```
As alluded to earlier you can also declare inlined subs dynamically at BEGIN time if their body consists of a lexically-scoped scalar which has no other references. Only the first example here will be inlined:
```
BEGIN {
my $var = 1;
no strict 'refs';
*INLINED = sub () { $var };
}
BEGIN {
my $var = 1;
my $ref = \$var;
no strict 'refs';
*NOT_INLINED = sub () { $var };
}
```
A not so obvious caveat with this (see [RT #79908]) is what happens if the variable is potentially modifiable. For example:
```
BEGIN {
my $x = 10;
*FOO = sub () { $x };
$x++;
}
print FOO(); # printed 10 prior to 5.32.0
```
From Perl 5.22 onwards this gave a deprecation warning, and from Perl 5.32 onwards it became a run-time error. Previously the variable was immediately inlined, and stopped behaving like a normal lexical variable; so it printed `10`, not `11`.
If you still want such a subroutine to be inlined (with no warning), make sure the variable is not used in a context where it could be modified aside from where it is declared.
```
# Fine, no warning
BEGIN {
my $x = 54321;
*INLINED = sub () { $x };
}
# Error
BEGIN {
my $x;
$x = 54321;
*ALSO_INLINED = sub () { $x };
}
```
Perl 5.22 also introduces the experimental "const" attribute as an alternative. (Disable the "experimental::const\_attr" warnings if you want to use it.) When applied to an anonymous subroutine, it forces the sub to be called when the `sub` expression is evaluated. The return value is captured and turned into a constant subroutine:
```
my $x = 54321;
*INLINED = sub : const { $x };
$x++;
```
The return value of `INLINED` in this example will always be 54321, regardless of later modifications to $x. You can also put any arbitrary code inside the sub, at it will be executed immediately and its return value captured the same way.
If you really want a subroutine with a `()` prototype that returns a lexical variable you can easily force it to not be inlined by adding an explicit `return`:
```
BEGIN {
my $x = 10;
*FOO = sub () { return $x };
$x++;
}
print FOO(); # prints 11
```
The easiest way to tell if a subroutine was inlined is by using <B::Deparse>. Consider this example of two subroutines returning `1`, one with a `()` prototype causing it to be inlined, and one without (with deparse output truncated for clarity):
```
$ perl -MO=Deparse -le 'sub ONE { 1 } if (ONE) { print ONE if ONE }'
sub ONE {
1;
}
if (ONE ) {
print ONE() if ONE ;
}
$ perl -MO=Deparse -le 'sub ONE () { 1 } if (ONE) { print ONE if ONE }'
sub ONE () { 1 }
do {
print 1
};
```
If you redefine a subroutine that was eligible for inlining, you'll get a warning by default. You can use this warning to tell whether or not a particular subroutine is considered inlinable, since it's different than the warning for overriding non-inlined subroutines:
```
$ perl -e 'sub one () {1} sub one () {2}'
Constant subroutine one redefined at -e line 1.
$ perl -we 'sub one {1} sub one {2}'
Subroutine one redefined at -e line 1.
```
The warning is considered severe enough not to be affected by the **-w** switch (or its absence) because previously compiled invocations of the function will still be using the old value of the function. If you need to be able to redefine the subroutine, you need to ensure that it isn't inlined, either by dropping the `()` prototype (which changes calling semantics, so beware) or by thwarting the inlining mechanism in some other way, e.g. by adding an explicit `return`, as mentioned above:
```
sub not_inlined () { return 23 }
```
###
Overriding Built-in Functions
Many built-in functions may be overridden, though this should be tried only occasionally and for good reason. Typically this might be done by a package attempting to emulate missing built-in functionality on a non-Unix system.
Overriding may be done only by importing the name from a module at compile time--ordinary predeclaration isn't good enough. However, the `use subs` pragma lets you, in effect, predeclare subs via the import syntax, and these names may then override built-in ones:
```
use subs 'chdir', 'chroot', 'chmod', 'chown';
chdir $somewhere;
sub chdir { ... }
```
To unambiguously refer to the built-in form, precede the built-in name with the special package qualifier `CORE::`. For example, saying `CORE::open()` always refers to the built-in `open()`, even if the current package has imported some other subroutine called `&open()` from elsewhere. Even though it looks like a regular function call, it isn't: the CORE:: prefix in that case is part of Perl's syntax, and works for any keyword, regardless of what is in the CORE package. Taking a reference to it, that is, `\&CORE::open`, only works for some keywords. See [CORE](core).
Library modules should not in general export built-in names like `open` or `chdir` as part of their default `@EXPORT` list, because these may sneak into someone else's namespace and change the semantics unexpectedly. Instead, if the module adds that name to `@EXPORT_OK`, then it's possible for a user to import the name explicitly, but not implicitly. That is, they could say
```
use Module 'open';
```
and it would import the `open` override. But if they said
```
use Module;
```
they would get the default imports without overrides.
The foregoing mechanism for overriding built-in is restricted, quite deliberately, to the package that requests the import. There is a second method that is sometimes applicable when you wish to override a built-in everywhere, without regard to namespace boundaries. This is achieved by importing a sub into the special namespace `CORE::GLOBAL::`. Here is an example that quite brazenly replaces the `glob` operator with something that understands regular expressions.
```
package REGlob;
require Exporter;
@ISA = 'Exporter';
@EXPORT_OK = 'glob';
sub import {
my $pkg = shift;
return unless @_;
my $sym = shift;
my $where = ($sym =~ s/^GLOBAL_// ? 'CORE::GLOBAL' : caller(0));
$pkg->export($where, $sym, @_);
}
sub glob {
my $pat = shift;
my @got;
if (opendir my $d, '.') {
@got = grep /$pat/, readdir $d;
closedir $d;
}
return @got;
}
1;
```
And here's how it could be (ab)used:
```
#use REGlob 'GLOBAL_glob'; # override glob() in ALL namespaces
package Foo;
use REGlob 'glob'; # override glob() in Foo:: only
print for <^[a-z_]+\.pm\$>; # show all pragmatic modules
```
The initial comment shows a contrived, even dangerous example. By overriding `glob` globally, you would be forcing the new (and subversive) behavior for the `glob` operator for *every* namespace, without the complete cognizance or cooperation of the modules that own those namespaces. Naturally, this should be done with extreme caution--if it must be done at all.
The `REGlob` example above does not implement all the support needed to cleanly override perl's `glob` operator. The built-in `glob` has different behaviors depending on whether it appears in a scalar or list context, but our `REGlob` doesn't. Indeed, many perl built-in have such context sensitive behaviors, and these must be adequately supported by a properly written override. For a fully functional example of overriding `glob`, study the implementation of `File::DosGlob` in the standard library.
When you override a built-in, your replacement should be consistent (if possible) with the built-in native syntax. You can achieve this by using a suitable prototype. To get the prototype of an overridable built-in, use the `prototype` function with an argument of `"CORE::builtin_name"` (see ["prototype" in perlfunc](perlfunc#prototype)).
Note however that some built-ins can't have their syntax expressed by a prototype (such as `system` or `chomp`). If you override them you won't be able to fully mimic their original syntax.
The built-ins `do`, `require` and `glob` can also be overridden, but due to special magic, their original syntax is preserved, and you don't have to define a prototype for their replacements. (You can't override the `do BLOCK` syntax, though).
`require` has special additional dark magic: if you invoke your `require` replacement as `require Foo::Bar`, it will actually receive the argument `"Foo/Bar.pm"` in @\_. See ["require" in perlfunc](perlfunc#require).
And, as you'll have noticed from the previous example, if you override `glob`, the `<*>` glob operator is overridden as well.
In a similar fashion, overriding the `readline` function also overrides the equivalent I/O operator `<FILEHANDLE>`. Also, overriding `readpipe` also overrides the operators ```` and `qx//`.
Finally, some built-ins (e.g. `exists` or `grep`) can't be overridden.
### Autoloading
If you call a subroutine that is undefined, you would ordinarily get an immediate, fatal error complaining that the subroutine doesn't exist. (Likewise for subroutines being used as methods, when the method doesn't exist in any base class of the class's package.) However, if an `AUTOLOAD` subroutine is defined in the package or packages used to locate the original subroutine, then that `AUTOLOAD` subroutine is called with the arguments that would have been passed to the original subroutine. The fully qualified name of the original subroutine magically appears in the global $AUTOLOAD variable of the same package as the `AUTOLOAD` routine. The name is not passed as an ordinary argument because, er, well, just because, that's why. (As an exception, a method call to a nonexistent `import` or `unimport` method is just skipped instead. Also, if the AUTOLOAD subroutine is an XSUB, there are other ways to retrieve the subroutine name. See ["Autoloading with XSUBs" in perlguts](perlguts#Autoloading-with-XSUBs) for details.)
Many `AUTOLOAD` routines load in a definition for the requested subroutine using eval(), then execute that subroutine using a special form of goto() that erases the stack frame of the `AUTOLOAD` routine without a trace. (See the source to the standard module documented in [AutoLoader](autoloader), for example.) But an `AUTOLOAD` routine can also just emulate the routine and never define it. For example, let's pretend that a function that wasn't defined should just invoke `system` with those arguments. All you'd do is:
```
sub AUTOLOAD {
our $AUTOLOAD; # keep 'use strict' happy
my $program = $AUTOLOAD;
$program =~ s/.*:://;
system($program, @_);
}
date();
who();
ls('-l');
```
In fact, if you predeclare functions you want to call that way, you don't even need parentheses:
```
use subs qw(date who ls);
date;
who;
ls '-l';
```
A more complete example of this is the Shell module on CPAN, which can treat undefined subroutine calls as calls to external programs.
Mechanisms are available to help modules writers split their modules into autoloadable files. See the standard AutoLoader module described in [AutoLoader](autoloader) and in [AutoSplit](autosplit), the standard SelfLoader modules in [SelfLoader](selfloader), and the document on adding C functions to Perl code in <perlxs>.
###
Subroutine Attributes
A subroutine declaration or definition may have a list of attributes associated with it. If such an attribute list is present, it is broken up at space or colon boundaries and treated as though a `use attributes` had been seen. See <attributes> for details about what attributes are currently supported. Unlike the limitation with the obsolescent `use attrs`, the `sub : ATTRLIST` syntax works to associate the attributes with a pre-declaration, and not just with a subroutine definition.
The attributes must be valid as simple identifier names (without any punctuation other than the '\_' character). They may have a parameter list appended, which is only checked for whether its parentheses ('(',')') nest properly.
Examples of valid syntax (even though the attributes are unknown):
```
sub fnord (&\%) : switch(10,foo(7,3)) : expensive;
sub plugh () : Ugly('\(") :Bad;
sub xyzzy : _5x5 { ... }
```
Examples of invalid syntax:
```
sub fnord : switch(10,foo(); # ()-string not balanced
sub snoid : Ugly('('); # ()-string not balanced
sub xyzzy : 5x5; # "5x5" not a valid identifier
sub plugh : Y2::north; # "Y2::north" not a simple identifier
sub snurt : foo + bar; # "+" not a colon or space
```
The attribute list is passed as a list of constant strings to the code which associates them with the subroutine. In particular, the second example of valid syntax above currently looks like this in terms of how it's parsed and invoked:
```
use attributes __PACKAGE__, \&plugh, q[Ugly('\(")], 'Bad';
```
For further details on attribute lists and their manipulation, see <attributes> and <Attribute::Handlers>.
SEE ALSO
---------
See ["Function Templates" in perlref](perlref#Function-Templates) for more about references and closures. See <perlxs> if you'd like to learn about calling C subroutines from Perl. See <perlembed> if you'd like to learn about calling Perl subroutines from C. See <perlmod> to learn about bundling up your functions in separate files. See <perlmodlib> to learn what library modules come standard on your system. See <perlootut> to learn how to make object method calls.
| programming_docs |
perl perldebtut perldebtut
==========
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
* [use strict](#use-strict)
* [Looking at data and -w and v](#Looking-at-data-and-w-and-v)
* [help](#help)
* [Stepping through code](#Stepping-through-code)
* [Placeholder for a, w, t, T](#Placeholder-for-a,-w,-t,-T)
* [REGULAR EXPRESSIONS](#REGULAR-EXPRESSIONS)
* [OUTPUT TIPS](#OUTPUT-TIPS)
* [CGI](#CGI)
* [GUIs](#GUIs)
* [SUMMARY](#SUMMARY)
* [SEE ALSO](#SEE-ALSO)
* [AUTHOR](#AUTHOR)
* [CONTRIBUTORS](#CONTRIBUTORS)
NAME
----
perldebtut - Perl debugging tutorial
DESCRIPTION
-----------
A (very) lightweight introduction in the use of the perl debugger, and a pointer to existing, deeper sources of information on the subject of debugging perl programs.
There's an extraordinary number of people out there who don't appear to know anything about using the perl debugger, though they use the language every day. This is for them.
use strict
-----------
First of all, there's a few things you can do to make your life a lot more straightforward when it comes to debugging perl programs, without using the debugger at all. To demonstrate, here's a simple script, named "hello", with a problem:
```
#!/usr/bin/perl
$var1 = 'Hello World'; # always wanted to do that :-)
$var2 = "$varl\n";
print $var2;
exit;
```
While this compiles and runs happily, it probably won't do what's expected, namely it doesn't print "Hello World\n" at all; It will on the other hand do exactly what it was told to do, computers being a bit that way inclined. That is, it will print out a newline character, and you'll get what looks like a blank line. It looks like there's 2 variables when (because of the typo) there's really 3:
```
$var1 = 'Hello World';
$varl = undef;
$var2 = "\n";
```
To catch this kind of problem, we can force each variable to be declared before use by pulling in the strict module, by putting 'use strict;' after the first line of the script.
Now when you run it, perl complains about the 3 undeclared variables and we get four error messages because one variable is referenced twice:
```
Global symbol "$var1" requires explicit package name at ./t1 line 4.
Global symbol "$var2" requires explicit package name at ./t1 line 5.
Global symbol "$varl" requires explicit package name at ./t1 line 5.
Global symbol "$var2" requires explicit package name at ./t1 line 7.
Execution of ./hello aborted due to compilation errors.
```
Luvverly! and to fix this we declare all variables explicitly and now our script looks like this:
```
#!/usr/bin/perl
use strict;
my $var1 = 'Hello World';
my $varl = undef;
my $var2 = "$varl\n";
print $var2;
exit;
```
We then do (always a good idea) a syntax check before we try to run it again:
```
> perl -c hello
hello syntax OK
```
And now when we run it, we get "\n" still, but at least we know why. Just getting this script to compile has exposed the '$varl' (with the letter 'l') variable, and simply changing $varl to $var1 solves the problem.
Looking at data and -w and v
-----------------------------
Ok, but how about when you want to really see your data, what's in that dynamic variable, just before using it?
```
#!/usr/bin/perl
use strict;
my $key = 'welcome';
my %data = (
'this' => qw(that),
'tom' => qw(and jerry),
'welcome' => q(Hello World),
'zip' => q(welcome),
);
my @data = keys %data;
print "$data{$key}\n";
exit;
```
Looks OK, after it's been through the syntax check (perl -c scriptname), we run it and all we get is a blank line again! Hmmmm.
One common debugging approach here, would be to liberally sprinkle a few print statements, to add a check just before we print out our data, and another just after:
```
print "All OK\n" if grep($key, keys %data);
print "$data{$key}\n";
print "done: '$data{$key}'\n";
```
And try again:
```
> perl data
All OK
done: ''
```
After much staring at the same piece of code and not seeing the wood for the trees for some time, we get a cup of coffee and try another approach. That is, we bring in the cavalry by giving perl the '**-d**' switch on the command line:
```
> perl -d data
Default die handler restored.
Loading DB routines from perl5db.pl version 1.07
Editor support available.
Enter h or `h h' for help, or `man perldebug' for more help.
main::(./data:4): my $key = 'welcome';
```
Now, what we've done here is to launch the built-in perl debugger on our script. It's stopped at the first line of executable code and is waiting for input.
Before we go any further, you'll want to know how to quit the debugger: use just the letter '**q**', not the words 'quit' or 'exit':
```
DB<1> q
>
```
That's it, you're back on home turf again.
help
----
Fire the debugger up again on your script and we'll look at the help menu. There's a couple of ways of calling help: a simple '**h**' will get the summary help list, '**|h**' (pipe-h) will pipe the help through your pager (which is (probably 'more' or 'less'), and finally, '**h h**' (h-space-h) will give you the entire help screen. Here is the summary page:
D**1**h
```
List/search source lines: Control script execution:
l [ln|sub] List source code T Stack trace
- or . List previous/current line s [expr] Single step
[in expr]
v [line] View around line n [expr] Next, steps over
subs
f filename View source in file <CR/Enter> Repeat last n or s
/pattern/ ?patt? Search forw/backw r Return from
subroutine
M Show module versions c [ln|sub] Continue until
position
Debugger controls: L List break/watch/
actions
o [...] Set debugger options t [expr] Toggle trace
[trace expr]
<[<]|{[{]|>[>] [cmd] Do pre/post-prompt b [ln|event|sub] [cnd] Set
breakpoint
! [N|pat] Redo a previous command B ln|* Delete a/all
breakpoints
H [-num] Display last num commands a [ln] cmd Do cmd before line
= [a val] Define/list an alias A ln|* Delete a/all
actions
h [db_cmd] Get help on command w expr Add a watch
expression
h h Complete help page W expr|* Delete a/all watch
exprs
|[|]db_cmd Send output to pager ![!] syscmd Run cmd in a
subprocess
q or ^D Quit R Attempt a restart
Data Examination: expr Execute perl code, also see: s,n,t expr
x|m expr Evals expr in list context, dumps the result or lists
methods.
p expr Print expression (uses script's current package).
S [[!]pat] List subroutine names [not] matching pattern
V [Pk [Vars]] List Variables in Package. Vars can be ~pattern or
!pattern.
X [Vars] Same as "V current_package [Vars]".
y [n [Vars]] List lexicals in higher scope <n>. Vars same as V.
For more help, type h cmd_letter, or run man perldebug for all docs.
```
More confusing options than you can shake a big stick at! It's not as bad as it looks and it's very useful to know more about all of it, and fun too!
There's a couple of useful ones to know about straight away. You wouldn't think we're using any libraries at all at the moment, but '**M**' will show which modules are currently loaded, and their version number, while '**m**' will show the methods, and '**S**' shows all subroutines (by pattern) as shown below. '**V**' and '**X**' show variables in the program by package scope and can be constrained by pattern.
```
DB<2>S str
dumpvar::stringify
strict::bits
strict::import
strict::unimport
```
Using 'X' and cousins requires you not to use the type identifiers ($@%), just the 'name':
```
DM<3>X ~err
FileHandle(stderr) => fileno(2)
```
Remember we're in our tiny program with a problem, we should have a look at where we are, and what our data looks like. First of all let's view some code at our present position (the first line of code in this case), via '**v**':
```
DB<4> v
1 #!/usr/bin/perl
2: use strict;
3
4==> my $key = 'welcome';
5: my %data = (
6 'this' => qw(that),
7 'tom' => qw(and jerry),
8 'welcome' => q(Hello World),
9 'zip' => q(welcome),
10 );
```
At line number 4 is a helpful pointer, that tells you where you are now. To see more code, type 'v' again:
```
DB<4> v
8 'welcome' => q(Hello World),
9 'zip' => q(welcome),
10 );
11: my @data = keys %data;
12: print "All OK\n" if grep($key, keys %data);
13: print "$data{$key}\n";
14: print "done: '$data{$key}'\n";
15: exit;
```
And if you wanted to list line 5 again, type 'l 5', (note the space):
```
DB<4> l 5
5: my %data = (
```
In this case, there's not much to see, but of course normally there's pages of stuff to wade through, and 'l' can be very useful. To reset your view to the line we're about to execute, type a lone period '.':
```
DB<5> .
main::(./data_a:4): my $key = 'welcome';
```
The line shown is the one that is about to be executed **next**, it hasn't happened yet. So while we can print a variable with the letter '**p**', at this point all we'd get is an empty (undefined) value back. What we need to do is to step through the next executable statement with an '**s**':
```
DB<6> s
main::(./data_a:5): my %data = (
main::(./data_a:6): 'this' => qw(that),
main::(./data_a:7): 'tom' => qw(and jerry),
main::(./data_a:8): 'welcome' => q(Hello World),
main::(./data_a:9): 'zip' => q(welcome),
main::(./data_a:10): );
```
Now we can have a look at that first ($key) variable:
```
DB<7> p $key
welcome
```
line 13 is where the action is, so let's continue down to there via the letter '**c**', which by the way, inserts a 'one-time-only' breakpoint at the given line or sub routine:
```
DB<8> c 13
All OK
main::(./data_a:13): print "$data{$key}\n";
```
We've gone past our check (where 'All OK' was printed) and have stopped just before the meat of our task. We could try to print out a couple of variables to see what is happening:
```
DB<9> p $data{$key}
```
Not much in there, lets have a look at our hash:
```
DB<10> p %data
Hello Worldziptomandwelcomejerrywelcomethisthat
DB<11> p keys %data
Hello Worldtomwelcomejerrythis
```
Well, this isn't very easy to read, and using the helpful manual (**h h**), the '**x**' command looks promising:
```
DB<12> x %data
0 'Hello World'
1 'zip'
2 'tom'
3 'and'
4 'welcome'
5 undef
6 'jerry'
7 'welcome'
8 'this'
9 'that'
```
That's not much help, a couple of welcomes in there, but no indication of which are keys, and which are values, it's just a listed array dump and, in this case, not particularly helpful. The trick here, is to use a **reference** to the data structure:
```
DB<13> x \%data
0 HASH(0x8194bc4)
'Hello World' => 'zip'
'jerry' => 'welcome'
'this' => 'that'
'tom' => 'and'
'welcome' => undef
```
The reference is truly dumped and we can finally see what we're dealing with. Our quoting was perfectly valid but wrong for our purposes, with 'and jerry' being treated as 2 separate words rather than a phrase, thus throwing the evenly paired hash structure out of alignment.
The '**-w**' switch would have told us about this, had we used it at the start, and saved us a lot of trouble:
```
> perl -w data
Odd number of elements in hash assignment at ./data line 5.
```
We fix our quoting: 'tom' => q(and jerry), and run it again, this time we get our expected output:
```
> perl -w data
Hello World
```
While we're here, take a closer look at the '**x**' command, it's really useful and will merrily dump out nested references, complete objects, partial objects - just about whatever you throw at it:
Let's make a quick object and x-plode it, first we'll start the debugger: it wants some form of input from STDIN, so we give it something non-committal, a zero:
```
> perl -de 0
Default die handler restored.
Loading DB routines from perl5db.pl version 1.07
Editor support available.
Enter h or `h h' for help, or `man perldebug' for more help.
main::(-e:1): 0
```
Now build an on-the-fly object over a couple of lines (note the backslash):
```
DB<1> $obj = bless({'unique_id'=>'123', 'attr'=> \
cont: {'col' => 'black', 'things' => [qw(this that etc)]}}, 'MY_class')
```
And let's have a look at it:
```
DB<2> x $obj
0 MY_class=HASH(0x828ad98)
'attr' => HASH(0x828ad68)
'col' => 'black'
'things' => ARRAY(0x828abb8)
0 'this'
1 'that'
2 'etc'
'unique_id' => 123
DB<3>
```
Useful, huh? You can eval nearly anything in there, and experiment with bits of code or regexes until the cows come home:
```
DB<3> @data = qw(this that the other atheism leather theory scythe)
DB<4> p 'saw -> '.($cnt += map { print "\t:\t$_\n" } grep(/the/, sort @data))
atheism
leather
other
scythe
the
theory
saw -> 6
```
If you want to see the command History, type an '**H**':
```
DB<5> H
4: p 'saw -> '.($cnt += map { print "\t:\t$_\n" } grep(/the/, sort @data))
3: @data = qw(this that the other atheism leather theory scythe)
2: x $obj
1: $obj = bless({'unique_id'=>'123', 'attr'=>
{'col' => 'black', 'things' => [qw(this that etc)]}}, 'MY_class')
DB<5>
```
And if you want to repeat any previous command, use the exclamation: '**!**':
```
DB<5> !4
p 'saw -> '.($cnt += map { print "$_\n" } grep(/the/, sort @data))
atheism
leather
other
scythe
the
theory
saw -> 12
```
For more on references see <perlref> and <perlreftut>
Stepping through code
----------------------
Here's a simple program which converts between Celsius and Fahrenheit, it too has a problem:
```
#!/usr/bin/perl
use v5.36;
my $arg = $ARGV[0] || '-c20';
if ($arg =~ /^\-(c|f)((\-|\+)*\d+(\.\d+)*)$/) {
my ($deg, $num) = ($1, $2);
my ($in, $out) = ($num, $num);
if ($deg eq 'c') {
$deg = 'f';
$out = &c2f($num);
} else {
$deg = 'c';
$out = &f2c($num);
}
$out = sprintf('%0.2f', $out);
$out =~ s/^((\-|\+)*\d+)\.0+$/$1/;
print "$out $deg\n";
} else {
print "Usage: $0 -[c|f] num\n";
}
exit;
sub f2c {
my $f = shift;
my $c = 5 * $f - 32 / 9;
return $c;
}
sub c2f {
my $c = shift;
my $f = 9 * $c / 5 + 32;
return $f;
}
```
For some reason, the Fahrenheit to Celsius conversion fails to return the expected output. This is what it does:
```
> temp -c0.72
33.30 f
> temp -f33.3
162.94 c
```
Not very consistent! We'll set a breakpoint in the code manually and run it under the debugger to see what's going on. A breakpoint is a flag, to which the debugger will run without interruption, when it reaches the breakpoint, it will stop execution and offer a prompt for further interaction. In normal use, these debugger commands are completely ignored, and they are safe - if a little messy, to leave in production code.
```
my ($in, $out) = ($num, $num);
$DB::single=2; # insert at line 9!
if ($deg eq 'c')
...
> perl -d temp -f33.3
Default die handler restored.
Loading DB routines from perl5db.pl version 1.07
Editor support available.
Enter h or `h h' for help, or `man perldebug' for more help.
main::(temp:4): my $arg = $ARGV[0] || '-c100';
```
We'll simply continue down to our pre-set breakpoint with a '**c**':
```
DB<1> c
main::(temp:10): if ($deg eq 'c') {
```
Followed by a view command to see where we are:
```
DB<1> v
7: my ($deg, $num) = ($1, $2);
8: my ($in, $out) = ($num, $num);
9: $DB::single=2;
10==> if ($deg eq 'c') {
11: $deg = 'f';
12: $out = &c2f($num);
13 } else {
14: $deg = 'c';
15: $out = &f2c($num);
16 }
```
And a print to show what values we're currently using:
```
DB<1> p $deg, $num
f33.3
```
We can put another break point on any line beginning with a colon, we'll use line 17 as that's just as we come out of the subroutine, and we'd like to pause there later on:
```
DB<2> b 17
```
There's no feedback from this, but you can see what breakpoints are set by using the list 'L' command:
```
DB<3> L
temp:
17: print "$out $deg\n";
break if (1)
```
Note that to delete a breakpoint you use 'B'.
Now we'll continue down into our subroutine, this time rather than by line number, we'll use the subroutine name, followed by the now familiar 'v':
```
DB<3> c f2c
main::f2c(temp:30): my $f = shift;
DB<4> v
24: exit;
25
26 sub f2c {
27==> my $f = shift;
28: my $c = 5 * $f - 32 / 9;
29: return $c;
30 }
31
32 sub c2f {
33: my $c = shift;
```
Note that if there was a subroutine call between us and line 29, and we wanted to **single-step** through it, we could use the '**s**' command, and to step over it we would use '**n**' which would execute the sub, but not descend into it for inspection. In this case though, we simply continue down to line 29:
```
DB<4> c 29
main::f2c(temp:29): return $c;
```
And have a look at the return value:
```
DB<5> p $c
162.944444444444
```
This is not the right answer at all, but the sum looks correct. I wonder if it's anything to do with operator precedence? We'll try a couple of other possibilities with our sum:
```
DB<6> p (5 * $f - 32 / 9)
162.944444444444
DB<7> p 5 * $f - (32 / 9)
162.944444444444
DB<8> p (5 * $f) - 32 / 9
162.944444444444
DB<9> p 5 * ($f - 32) / 9
0.722222222222221
```
:-) that's more like it! Ok, now we can set our return variable and we'll return out of the sub with an 'r':
```
DB<10> $c = 5 * ($f - 32) / 9
DB<11> r
scalar context return from main::f2c: 0.722222222222221
```
Looks good, let's just continue off the end of the script:
```
DB<12> c
0.72 c
Debugged program terminated. Use q to quit or R to restart,
use O inhibit_exit to avoid stopping after program termination,
h q, h R or h O to get additional info.
```
A quick fix to the offending line (insert the missing parentheses) in the actual program and we're finished.
Placeholder for a, w, t, T
---------------------------
Actions, watch variables, stack traces etc.: on the TODO list.
```
a
w
t
T
```
REGULAR EXPRESSIONS
--------------------
Ever wanted to know what a regex looked like? You'll need perl compiled with the DEBUGGING flag for this one:
```
> perl -Dr -e '/^pe(a)*rl$/i'
Compiling REx `^pe(a)*rl$'
size 17 first at 2
rarest char
at 0
1: BOL(2)
2: EXACTF <pe>(4)
4: CURLYN[1] {0,32767}(14)
6: NOTHING(8)
8: EXACTF <a>(0)
12: WHILEM(0)
13: NOTHING(14)
14: EXACTF <rl>(16)
16: EOL(17)
17: END(0)
floating `'$ at 4..2147483647 (checking floating) stclass
`EXACTF <pe>' anchored(BOL) minlen 4
Omitting $` $& $' support.
EXECUTING...
Freeing REx: `^pe(a)*rl$'
```
Did you really want to know? :-) For more gory details on getting regular expressions to work, have a look at <perlre>, <perlretut>, and to decode the mysterious labels (BOL and CURLYN, etc. above), see <perldebguts>.
OUTPUT TIPS
------------
To get all the output from your error log, and not miss any messages via helpful operating system buffering, insert a line like this, at the start of your script:
```
$|=1;
```
To watch the tail of a dynamically growing logfile, (from the command line):
```
tail -f $error_log
```
Wrapping all die calls in a handler routine can be useful to see how, and from where, they're being called, <perlvar> has more information:
```
BEGIN { $SIG{__DIE__} = sub { require Carp; Carp::confess(@_) } }
```
Various useful techniques for the redirection of STDOUT and STDERR filehandles are explained in <perlopentut> and <perlfaq8>.
CGI
---
Just a quick hint here for all those CGI programmers who can't figure out how on earth to get past that 'waiting for input' prompt, when running their CGI script from the command-line, try something like this:
```
> perl -d my_cgi.pl -nodebug
```
Of course [CGI](cgi) and <perlfaq9> will tell you more.
GUIs
----
The command line interface is tightly integrated with an **emacs** extension and there's a **vi** interface too.
You don't have to do this all on the command line, though, there are a few GUI options out there. The nice thing about these is you can wave a mouse over a variable and a dump of its data will appear in an appropriate window, or in a popup balloon, no more tiresome typing of 'x $varname' :-)
In particular have a hunt around for the following:
**ptkdb** perlTK based wrapper for the built-in debugger
**ddd** data display debugger
**PerlDevKit** and **PerlBuilder** are NT specific
NB. (more info on these and others would be appreciated).
SUMMARY
-------
We've seen how to encourage good coding practices with **use strict** and **-w**. We can run the perl debugger **perl -d scriptname** to inspect your data from within the perl debugger with the **p** and **x** commands. You can walk through your code, set breakpoints with **b** and step through that code with **s** or **n**, continue with **c** and return from a sub with **r**. Fairly intuitive stuff when you get down to it.
There is of course lots more to find out about, this has just scratched the surface. The best way to learn more is to use perldoc to find out more about the language, to read the on-line help (<perldebug> is probably the next place to go), and of course, experiment.
SEE ALSO
---------
<perldebug>, <perldebguts>, <perl5db.pl>, <perldiag>, <perlrun>
AUTHOR
------
Richard Foley <[email protected]> Copyright (c) 2000
CONTRIBUTORS
------------
Various people have made helpful suggestions and contributions, in particular:
Ronald J Kimball <[email protected]>
Hugo van der Sanden <[email protected]>
Peter Scott <[email protected]>
| programming_docs |
perl perldata perldata
========
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
+ [Variable names](#Variable-names)
+ [Identifier parsing](#Identifier-parsing)
+ [Context](#Context)
+ [Scalar values](#Scalar-values)
+ [Scalar value constructors](#Scalar-value-constructors)
- [Demarcated variable names using braces](#Demarcated-variable-names-using-braces)
- [Special floating point: infinity (Inf) and not-a-number (NaN)](#Special-floating-point:-infinity-(Inf)-and-not-a-number-(NaN))
- [Version Strings](#Version-Strings)
- [Special Literals](#Special-Literals)
- [Barewords](#Barewords)
- [Array Interpolation](#Array-Interpolation)
+ [List value constructors](#List-value-constructors)
+ [Subscripts](#Subscripts)
+ [Multi-dimensional array emulation](#Multi-dimensional-array-emulation)
+ [Slices](#Slices)
- [Key/Value Hash Slices](#Key/Value-Hash-Slices)
- [Index/Value Array Slices](#Index/Value-Array-Slices)
+ [Typeglobs and Filehandles](#Typeglobs-and-Filehandles)
* [SEE ALSO](#SEE-ALSO)
NAME
----
perldata - Perl data types
DESCRIPTION
-----------
###
Variable names
Perl has three built-in data types: scalars, arrays of scalars, and associative arrays of scalars, known as "hashes". A scalar is a single string (of any size, limited only by the available memory), number, or a reference to something (which will be discussed in <perlref>). Normal arrays are ordered lists of scalars indexed by number, starting with 0. Hashes are unordered collections of scalar values indexed by their associated string key.
Values are usually referred to by name, or through a named reference. The first character of the name tells you to what sort of data structure it refers. The rest of the name tells you the particular value to which it refers. Usually this name is a single *identifier*, that is, a string beginning with a letter or underscore, and containing letters, underscores, and digits. In some cases, it may be a chain of identifiers, separated by `::` (or by the slightly archaic `'`); all but the last are interpreted as names of packages, to locate the namespace in which to look up the final identifier (see ["Packages" in perlmod](perlmod#Packages) for details). For a more in-depth discussion on identifiers, see ["Identifier parsing"](#Identifier-parsing). It's possible to substitute for a simple identifier, an expression that produces a reference to the value at runtime. This is described in more detail below and in <perlref>.
Perl also has its own built-in variables whose names don't follow these rules. They have strange names so they don't accidentally collide with one of your normal variables. Strings that match parenthesized parts of a regular expression are saved under names containing only digits after the `$` (see <perlop> and <perlre>). In addition, several special variables that provide windows into the inner working of Perl have names containing punctuation characters. These are documented in <perlvar>.
Scalar values are always named with '$', even when referring to a scalar that is part of an array or a hash. The '$' symbol works semantically like the English word "the" in that it indicates a single value is expected.
```
$days # the simple scalar value "days"
$days[28] # the 29th element of array @days
$days{'Feb'} # the 'Feb' value from hash %days
$#days # the last index of array @days
```
Entire arrays (and slices of arrays and hashes) are denoted by '@', which works much as the word "these" or "those" does in English, in that it indicates multiple values are expected.
```
@days # ($days[0], $days[1],... $days[n])
@days[3,4,5] # same as ($days[3],$days[4],$days[5])
@days{'a','c'} # same as ($days{'a'},$days{'c'})
```
Entire hashes are denoted by '%':
```
%days # (key1, val1, key2, val2 ...)
```
In addition, subroutines are named with an initial '&', though this is optional when unambiguous, just as the word "do" is often redundant in English. Symbol table entries can be named with an initial '\*', but you don't really care about that yet (if ever :-).
Every variable type has its own namespace, as do several non-variable identifiers. This means that you can, without fear of conflict, use the same name for a scalar variable, an array, or a hash--or, for that matter, for a filehandle, a directory handle, a subroutine name, a format name, or a label. This means that $foo and @foo are two different variables. It also means that `$foo[1]` is a part of @foo, not a part of $foo. This may seem a bit weird, but that's okay, because it is weird.
Because variable references always start with '$', '@', or '%', the "reserved" words aren't in fact reserved with respect to variable names. They *are* reserved with respect to labels and filehandles, however, which don't have an initial special character. You can't have a filehandle named "log", for instance. Hint: you could say `open(LOG,'logfile')` rather than `open(log,'logfile')`. Using uppercase filehandles also improves readability and protects you from conflict with future reserved words. Case *is* significant--"FOO", "Foo", and "foo" are all different names. Names that start with a letter or underscore may also contain digits and underscores.
It is possible to replace such an alphanumeric name with an expression that returns a reference to the appropriate type. For a description of this, see <perlref>.
Names that start with a digit may contain only more digits. Names that do not start with a letter, underscore, digit or a caret are limited to one character, e.g., `$%` or `$$`. (Most of these one character names have a predefined significance to Perl. For instance, `$$` is the current process id. And all such names are reserved for Perl's possible use.)
###
Identifier parsing
Up until Perl 5.18, the actual rules of what a valid identifier was were a bit fuzzy. However, in general, anything defined here should work on previous versions of Perl, while the opposite -- edge cases that work in previous versions, but aren't defined here -- probably won't work on newer versions. As an important side note, please note that the following only applies to bareword identifiers as found in Perl source code, not identifiers introduced through symbolic references, which have much fewer restrictions. If working under the effect of the `use utf8;` pragma, the following rules apply:
```
/ (?[ ( \p{Word} & \p{XID_Start} ) + [_] ])
(?[ ( \p{Word} & \p{XID_Continue} ) ]) * /x
```
That is, a "start" character followed by any number of "continue" characters. Perl requires every character in an identifier to also match `\w` (this prevents some problematic cases); and Perl additionally accepts identifier names beginning with an underscore.
If not under `use utf8`, the source is treated as ASCII + 128 extra generic characters, and identifiers should match
```
/ (?aa) (?!\d) \w+ /x
```
That is, any word character in the ASCII range, as long as the first character is not a digit.
There are two package separators in Perl: A double colon (`::`) and a single quote (`'`). Normal identifiers can start or end with a double colon, and can contain several parts delimited by double colons. Single quotes have similar rules, but with the exception that they are not legal at the end of an identifier: That is, `$'foo` and `$foo'bar` are legal, but `$foo'bar'` is not.
Additionally, if the identifier is preceded by a sigil -- that is, if the identifier is part of a variable name -- it may optionally be enclosed in braces.
While you can mix double colons with singles quotes, the quotes must come after the colons: `$::::'foo` and `$foo::'bar` are legal, but `$::'::foo` and `$foo'::bar` are not.
Put together, a grammar to match a basic identifier becomes
```
/
(?(DEFINE)
(?<variable>
(?&sigil)
(?:
(?&normal_identifier)
| \{ \s* (?&normal_identifier) \s* \}
)
)
(?<normal_identifier>
(?: :: )* '?
(?&basic_identifier)
(?: (?= (?: :: )+ '? | (?: :: )* ' ) (?&normal_identifier) )?
(?: :: )*
)
(?<basic_identifier>
# is use utf8 on?
(?(?{ (caller(0))[8] & $utf8::hint_bits })
(?&Perl_XIDS) (?&Perl_XIDC)*
| (?aa) (?!\d) \w+
)
)
(?<sigil> [&*\$\@\%])
(?<Perl_XIDS> (?[ ( \p{Word} & \p{XID_Start} ) + [_] ]) )
(?<Perl_XIDC> (?[ \p{Word} & \p{XID_Continue} ]) )
)
/x
```
Meanwhile, special identifiers don't follow the above rules; For the most part, all of the identifiers in this category have a special meaning given by Perl. Because they have special parsing rules, these generally can't be fully-qualified. They come in six forms (but don't use forms 5 and 6):
1. A sigil, followed solely by digits matching `\p{POSIX_Digit}`, like `$0`, `$1`, or `$10000`.
2. A sigil followed by a single character matching the `\p{POSIX_Punct}` property, like `$!` or `%+`, except the character `"{"` doesn't work.
3. A sigil, followed by a caret and any one of the characters `[][A-Z^_?\]`, like `$^V` or `$^]`.
4. Similar to the above, a sigil, followed by bareword text in braces, where the first character is a caret. The next character is any one of the characters `[][A-Z^_?\]`, followed by ASCII word characters. An example is `${^GLOBAL_PHASE}`.
5. A sigil, followed by any single character in the range `[\xA1-\xAC\xAE-\xFF]` when not under `"use utf8"`. (Under `"use utf8"`, the normal identifier rules given earlier in this section apply.) Use of non-graphic characters (the C1 controls, the NO-BREAK SPACE, and the SOFT HYPHEN) has been disallowed since v5.26.0. The use of the other characters is unwise, as these are all reserved to have special meaning to Perl, and none of them currently do have special meaning, though this could change without notice.
Note that an implication of this form is that there are identifiers only legal under `"use utf8"`, and vice-versa, for example the identifier `$état` is legal under `"use utf8"`, but is otherwise considered to be the single character variable `$é` followed by the bareword `"tat"`, the combination of which is a syntax error.
6. This is a combination of the previous two forms. It is valid only when not under `"use utf8"` (normal identifier rules apply when under `"use utf8"`). The form is a sigil, followed by text in braces, where the first character is any one of the characters in the range `[\x80-\xFF]` followed by ASCII word characters up to the trailing brace.
The same caveats as the previous form apply: The non-graphic characters are no longer allowed with "use utf8", it is unwise to use this form at all, and utf8ness makes a big difference.
Prior to Perl v5.24, non-graphical ASCII control characters were also allowed in some situations; this had been deprecated since v5.20.
### Context
The interpretation of operations and values in Perl sometimes depends on the requirements of the context around the operation or value. There are two major contexts: list and scalar. Certain operations return list values in contexts wanting a list, and scalar values otherwise. If this is true of an operation it will be mentioned in the documentation for that operation. In other words, Perl overloads certain operations based on whether the expected return value is singular or plural. Some words in English work this way, like "fish" and "sheep".
In a reciprocal fashion, an operation provides either a scalar or a list context to each of its arguments. For example, if you say
```
int( <STDIN> )
```
the integer operation provides scalar context for the <> operator, which responds by reading one line from STDIN and passing it back to the integer operation, which will then find the integer value of that line and return that. If, on the other hand, you say
```
sort( <STDIN> )
```
then the sort operation provides list context for <>, which will proceed to read every line available up to the end of file, and pass that list of lines back to the sort routine, which will then sort those lines and return them as a list to whatever the context of the sort was.
Assignment is a little bit special in that it uses its left argument to determine the context for the right argument. Assignment to a scalar evaluates the right-hand side in scalar context, while assignment to an array or hash evaluates the righthand side in list context. Assignment to a list (or slice, which is just a list anyway) also evaluates the right-hand side in list context.
When you use the `use warnings` pragma or Perl's **-w** command-line option, you may see warnings about useless uses of constants or functions in "void context". Void context just means the value has been discarded, such as a statement containing only `"fred";` or `getpwuid(0);`. It still counts as scalar context for functions that care whether or not they're being called in list context.
User-defined subroutines may choose to care whether they are being called in a void, scalar, or list context. Most subroutines do not need to bother, though. That's because both scalars and lists are automatically interpolated into lists. See ["wantarray" in perlfunc](perlfunc#wantarray) for how you would dynamically discern your function's calling context.
###
Scalar values
All data in Perl is a scalar, an array of scalars, or a hash of scalars. A scalar may contain one single value in any of three different flavors: a number, a string, or a reference. In general, conversion from one form to another is transparent. Although a scalar may not directly hold multiple values, it may contain a reference to an array or hash which in turn contains multiple values.
Scalars aren't necessarily one thing or another. There's no place to declare a scalar variable to be of type "string", type "number", type "reference", or anything else. Because of the automatic conversion of scalars, operations that return scalars don't need to care (and in fact, cannot care) whether their caller is looking for a string, a number, or a reference. Perl is a contextually polymorphic language whose scalars can be strings, numbers, or references (which includes objects). Although strings and numbers are considered pretty much the same thing for nearly all purposes, references are strongly-typed, uncastable pointers with builtin reference-counting and destructor invocation.
A scalar value is interpreted as FALSE in the Boolean sense if it is undefined, the null string or the number 0 (or its string equivalent, "0"), and TRUE if it is anything else. The Boolean context is just a special kind of scalar context where no conversion to a string or a number is ever performed. Negation of a true value by `!` or `not` returns a special false value. When evaluated as a string it is treated as `""`, but as a number, it is treated as 0. Most Perl operators that return true or false behave this way.
There are actually two varieties of null strings (sometimes referred to as "empty" strings), a defined one and an undefined one. The defined version is just a string of length zero, such as `""`. The undefined version is the value that indicates that there is no real value for something, such as when there was an error, or at end of file, or when you refer to an uninitialized variable or element of an array or hash. Although in early versions of Perl, an undefined scalar could become defined when first used in a place expecting a defined value, this no longer happens except for rare cases of autovivification as explained in <perlref>. You can use the defined() operator to determine whether a scalar value is defined (this has no meaning on arrays or hashes), and the undef() operator to produce an undefined value.
To find out whether a given string is a valid non-zero number, it's sometimes enough to test it against both numeric 0 and also lexical "0" (although this will cause noises if warnings are on). That's because strings that aren't numbers count as 0, just as they do in **awk**:
```
if ($str == 0 && $str ne "0") {
warn "That doesn't look like a number";
}
```
That method may be best because otherwise you won't treat IEEE notations like `NaN` or `Infinity` properly. At other times, you might prefer to determine whether string data can be used numerically by calling the POSIX::strtod() function or by inspecting your string with a regular expression (as documented in <perlre>).
```
warn "has nondigits" if /\D/;
warn "not a natural number" unless /^\d+$/; # rejects -3
warn "not an integer" unless /^-?\d+$/; # rejects +3
warn "not an integer" unless /^[+-]?\d+$/;
warn "not a decimal number" unless /^-?\d+\.?\d*$/; # rejects .2
warn "not a decimal number" unless /^-?(?:\d+(?:\.\d*)?|\.\d+)$/;
warn "not a C float"
unless /^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/;
```
The length of an array is a scalar value. You may find the length of array @days by evaluating `$#days`, as in **csh**. However, this isn't the length of the array; it's the subscript of the last element, which is a different value since there is ordinarily a 0th element. Assigning to `$#days` actually changes the length of the array. Shortening an array this way destroys intervening values. Lengthening an array that was previously shortened does not recover values that were in those elements.
You can also gain some minuscule measure of efficiency by pre-extending an array that is going to get big. You can also extend an array by assigning to an element that is off the end of the array. You can truncate an array down to nothing by assigning the null list () to it. The following are equivalent:
```
@whatever = ();
$#whatever = -1;
```
If you evaluate an array in scalar context, it returns the length of the array. (Note that this is not true of lists, which return the last value, like the C comma operator, nor of built-in functions, which return whatever they feel like returning.) The following is always true:
```
scalar(@whatever) == $#whatever + 1;
```
Some programmers choose to use an explicit conversion so as to leave nothing to doubt:
```
$element_count = scalar(@whatever);
```
If you evaluate a hash in scalar context, it returns a false value if the hash is empty. If there are any key/value pairs, it returns a true value. A more precise definition is version dependent.
Prior to Perl 5.25 the value returned was a string consisting of the number of used buckets and the number of allocated buckets, separated by a slash. This is pretty much useful only to find out whether Perl's internal hashing algorithm is performing poorly on your data set. For example, you stick 10,000 things in a hash, but evaluating %HASH in scalar context reveals `"1/16"`, which means only one out of sixteen buckets has been touched, and presumably contains all 10,000 of your items. This isn't supposed to happen.
As of Perl 5.25 the return was changed to be the count of keys in the hash. If you need access to the old behavior you can use `Hash::Util::bucket_ratio()` instead.
If a tied hash is evaluated in scalar context, the `SCALAR` method is called (with a fallback to `FIRSTKEY`).
You can preallocate space for a hash by assigning to the keys() function. This rounds up the allocated buckets to the next power of two:
```
keys(%users) = 1000; # allocate 1024 buckets
```
###
Scalar value constructors
Numeric literals are specified in any of the following floating point or integer formats:
```
12345
12345.67
.23E-10 # a very small number
3.14_15_92 # a very important number
4_294_967_296 # underscore for legibility
0xff # hex
0xdead_beef # more hex
0377 # octal (only numbers, begins with 0)
0o12_345 # alternative octal (introduced in Perl 5.33.5)
0b011011 # binary
0x1.999ap-4 # hexadecimal floating point (the 'p' is required)
```
You are allowed to use underscores (underbars) in numeric literals between digits for legibility (but not multiple underscores in a row: `23__500` is not legal; `23_500` is). You could, for example, group binary digits by threes (as for a Unix-style mode argument such as 0b110\_100\_100) or by fours (to represent nibbles, as in 0b1010\_0110) or in other groups.
String literals are usually delimited by either single or double quotes. They work much like quotes in the standard Unix shells: double-quoted string literals are subject to backslash and variable substitution; single-quoted strings are not (except for `\'` and `\\`). The usual C-style backslash rules apply for making characters such as newline, tab, etc., as well as some more exotic forms. See ["Quote and Quote-like Operators" in perlop](perlop#Quote-and-Quote-like-Operators) for a list.
Hexadecimal, octal, or binary, representations in string literals (e.g. '0xff') are not automatically converted to their integer representation. The hex() and oct() functions make these conversions for you. See ["hex" in perlfunc](perlfunc#hex) and ["oct" in perlfunc](perlfunc#oct) for more details.
Hexadecimal floating point can start just like a hexadecimal literal, and it can be followed by an optional fractional hexadecimal part, but it must be followed by `p`, an optional sign, and a power of two. The format is useful for accurately presenting floating point values, avoiding conversions to or from decimal floating point, and therefore avoiding possible loss in precision. Notice that while most current platforms use the 64-bit IEEE 754 floating point, not all do. Another potential source of (low-order) differences are the floating point rounding modes, which can differ between CPUs, operating systems, and compilers, and which Perl doesn't control.
You can also embed newlines directly in your strings, i.e., they can end on a different line than they begin. This is nice, but if you forget your trailing quote, the error will not be reported until Perl finds another line containing the quote character, which may be much further on in the script. Variable substitution inside strings is limited to scalar variables, arrays, and array or hash slices. (In other words, names beginning with $ or @, followed by an optional bracketed expression as a subscript.) The following code segment prints out "The price is $100."
```
$Price = '$100'; # not interpolated
print "The price is $Price.\n"; # interpolated
```
There is no double interpolation in Perl, so the `$100` is left as is.
By default floating point numbers substituted inside strings use the dot (".") as the decimal separator. If `use locale` is in effect, and POSIX::setlocale() has been called, the character used for the decimal separator is affected by the LC\_NUMERIC locale. See <perllocale> and [POSIX](posix).
####
Demarcated variable names using braces
As in some shells, you can enclose the variable name in braces as a demarcator to disambiguate it from following alphanumerics and underscores or other text. You must also do this when interpolating a variable into a string to separate the variable name from a following double-colon or an apostrophe since these would be otherwise treated as a package separator:
```
$who = "Larry";
print PASSWD "${who}::0:0:Superuser:/:/bin/perl\n";
print "We use ${who}speak when ${who}'s here.\n";
```
Without the braces, Perl would have looked for a $whospeak, a `$who::0`, and a `$who's` variable. The last two would be the $0 and the $s variables in the (presumably) non-existent package `who`.
In fact, a simple identifier within such curly braces is forced to be a string, and likewise within a hash subscript. Neither need quoting. Our earlier example, `$days{'Feb'}` can be written as `$days{Feb}` and the quotes will be assumed automatically. But anything more complicated in the subscript will be interpreted as an expression. This means for example that `$version{2.0}++` is equivalent to `$version{2}++`, not to `$version{'2.0'}++`.
There is a similar problem with interpolation with text that looks like array or hash access notation. Placing a simple variable like `$who` immediately in front of text like `"[1]"` or `"{foo}"` would cause the variable to be interpolated as accessing an element of `@who` or a value stored in `%who`:
```
$who = "Larry Wall";
print "$who[1] is the father of Perl.\n";
```
would attempt to access index 1 of an array named `@who`. Again, using braces will prevent this from happening:
```
$who = "Larry Wall";
print "${who}[1] is the father of Perl.\n";
```
will be treated the same as
```
$who = "Larry Wall";
print $who . "[1] is the father of Perl.\n";
```
This notation also applies to more complex variable descriptions, such as array or hash access with subscripts. For instance
```
@name = qw(Larry Curly Moe);
print "Also ${name[0]}[1] was a member\n";
```
Without the braces the above example would be parsed as a two level array subscript in the `@name` array, and under `use strict` would likely produce a fatal exception, as it would be parsed like this:
```
print "Also " . $name[0][1] . " was a member\n";
```
and not as the intended:
```
print "Also " . $name[0] . "[1] was a member\n";
```
A similar result may be derived by using a backslash on the first character of the subscript or package notation that is not part of the variable you want to access. Thus the above example could also be written:
```
@name = qw(Larry Curly Moe);
print "Also $name[0]\[1] was a member\n";
```
however for some special variables (multi character caret variables) the demarcated form using curly braces is the **only** way you can reference the variable at all, and the only way you can access a subscript of the variable via interpolation.
Consider the magic array `@{^CAPTURE}` which is populated by the regex engine with the contents of all of the capture buffers in a pattern (see <perlvar> and <perlre>). The **only** way you can access one of these members inside of a string is via the braced (demarcated) form:
```
"abc"=~/(.)(.)(.)/
and print "Second buffer is ${^CAPTURE[1]}";
```
is equivalent to
```
"abc"=~/(.)(.)(.)/
and print "Second buffer is " . ${^CAPTURE}[1];
```
Saying `@^CAPTURE` is a syntax error, so it **must** be referenced as `@{^CAPTURE}`, and to access one of its elements in normal code you would write `${^CAPTURE}[1]` . However when interpolating in a string `"${^CAPTURE}[1]"` would be equivalent to `${^CAPTURE} . "[1]"`, which does not even refer to the same variable! Thus the subscripts must **also** be placed **inside** of the braces: `"${^CAPTURE[1]}"`.
The demarcated form using curly braces can be used with all the different types of variable access, including array and hash slices. For instance code like the following:
```
@name = qw(Larry Curly Moe);
local $" = " and ";
print "My favorites were @{name[1,2]}.\n";
```
would output
```
My favorites were Curly and Moe.
```
####
Special floating point: infinity (Inf) and not-a-number (NaN)
Floating point values include the special values `Inf` and `NaN`, for infinity and not-a-number. The infinity can be also negative.
The infinity is the result of certain math operations that overflow the floating point range, like 9\*\*9\*\*9. The not-a-number is the result when the result is undefined or unrepresentable. Though note that you cannot get `NaN` from some common "undefined" or "out-of-range" operations like dividing by zero, or square root of a negative number, since Perl generates fatal errors for those.
The infinity and not-a-number have their own special arithmetic rules. The general rule is that they are "contagious": `Inf` plus one is `Inf`, and `NaN` plus one is `NaN`. Where things get interesting is when you combine infinities and not-a-numbers: `Inf` minus `Inf` and `Inf` divided by `Inf` are `NaN` (while `Inf` plus `Inf` is `Inf` and `Inf` times `Inf` is `Inf`). `NaN` is also curious in that it does not equal any number, *including* itself: `NaN` != `NaN`.
Perl doesn't understand `Inf` and `NaN` as numeric literals, but you can have them as strings, and Perl will convert them as needed: "Inf" + 1. (You can, however, import them from the POSIX extension; `use POSIX qw(Inf NaN);` and then use them as literals.)
Note that on input (string to number) Perl accepts `Inf` and `NaN` in many forms. Case is ignored, and the Win32-specific forms like `1.#INF` are understood, but on output the values are normalized to `Inf` and `NaN`.
####
Version Strings
A literal of the form `v1.20.300.4000` is parsed as a string composed of characters with the specified ordinals. This form, known as v-strings, provides an alternative, more readable way to construct strings, rather than use the somewhat less readable interpolation form `"\x{1}\x{14}\x{12c}\x{fa0}"`. This is useful for representing Unicode strings, and for comparing version "numbers" using the string comparison operators, `cmp`, `gt`, `lt` etc. If there are two or more dots in the literal, the leading `v` may be omitted.
```
print v9786; # prints SMILEY, "\x{263a}"
print v102.111.111; # prints "foo"
print 102.111.111; # same
```
Such literals are accepted by both `require` and `use` for doing a version check. Note that using the v-strings for IPv4 addresses is not portable unless you also use the inet\_aton()/inet\_ntoa() routines of the Socket package.
Note that since Perl 5.8.1 the single-number v-strings (like `v65`) are not v-strings before the `=>` operator (which is usually used to separate a hash key from a hash value); instead they are interpreted as literal strings ('v65'). They were v-strings from Perl 5.6.0 to Perl 5.8.0, but that caused more confusion and breakage than good. Multi-number v-strings like `v65.66` and `65.66.67` continue to be v-strings always.
####
Special Literals
The special literals \_\_FILE\_\_, \_\_LINE\_\_, and \_\_PACKAGE\_\_ represent the current filename, line number, and package name at that point in your program. \_\_SUB\_\_ gives a reference to the current subroutine. They may be used only as separate tokens; they will not be interpolated into strings. If there is no current package (due to an empty `package;` directive), \_\_PACKAGE\_\_ is the undefined value. (But the empty `package;` is no longer supported, as of version 5.10.) Outside of a subroutine, \_\_SUB\_\_ is the undefined value. \_\_SUB\_\_ is only available in 5.16 or higher, and only with a `use v5.16` or `use feature "current_sub"` declaration.
The two control characters ^D and ^Z, and the tokens \_\_END\_\_ and \_\_DATA\_\_ may be used to indicate the logical end of the script before the actual end of file. Any following text is ignored by the interpreter unless read by the program as described below.
Text after \_\_DATA\_\_ may be read via the filehandle `PACKNAME::DATA`, where `PACKNAME` is the package that was current when the \_\_DATA\_\_ token was encountered. The filehandle is left open pointing to the line after \_\_DATA\_\_. The program should `close DATA` when it is done reading from it. (Leaving it open leaks filehandles if the module is reloaded for any reason, so it's a safer practice to close it.) For compatibility with older scripts written before \_\_DATA\_\_ was introduced, \_\_END\_\_ behaves like \_\_DATA\_\_ in the top level script (but not in files loaded with `require` or `do`) and leaves the remaining contents of the file accessible via `main::DATA`.
```
while (my $line = <DATA>) { print $line; }
close DATA;
__DATA__
Hello world.
```
The `DATA` file handle by default has whatever PerlIO layers were in place when Perl read the file to parse the source. Normally that means that the file is being read bytewise, as if it were encoded in Latin-1, but there are two major ways for it to be otherwise. Firstly, if the `__END__`/`__DATA__` token is in the scope of a `use utf8` pragma then the `DATA` handle will be in UTF-8 mode. And secondly, if the source is being read from perl's standard input then the `DATA` file handle is actually aliased to the `STDIN` file handle, and may be in UTF-8 mode because of the `PERL_UNICODE` environment variable or perl's command-line switches.
See [SelfLoader](selfloader) for more description of \_\_DATA\_\_, and an example of its use. Note that you cannot read from the DATA filehandle in a BEGIN block: the BEGIN block is executed as soon as it is seen (during compilation), at which point the corresponding \_\_DATA\_\_ (or \_\_END\_\_) token has not yet been seen.
#### Barewords
A word that has no other interpretation in the grammar will be treated as if it were a quoted string. These are known as "barewords". As with filehandles and labels, a bareword that consists entirely of lowercase letters risks conflict with future reserved words, and if you use the `use warnings` pragma or the **-w** switch, Perl will warn you about any such words. Perl limits barewords (like identifiers) to about 250 characters. Future versions of Perl are likely to eliminate these arbitrary limitations.
Some people may wish to outlaw barewords entirely. If you say
```
use strict 'subs';
```
then any bareword that would NOT be interpreted as a subroutine call produces a compile-time error instead. The restriction lasts to the end of the enclosing block. An inner block may countermand this by saying `no strict 'subs'`.
####
Array Interpolation
Arrays and slices are interpolated into double-quoted strings by joining the elements with the delimiter specified in the `$"` variable (`$LIST_SEPARATOR` if "use English;" is specified), space by default. The following are equivalent:
```
$temp = join($", @ARGV);
system "echo $temp";
system "echo @ARGV";
```
Within search patterns (which also undergo double-quotish substitution) there is an unfortunate ambiguity: Is `/$foo[bar]/` to be interpreted as `/${foo}[bar]/` (where `[bar]` is a character class for the regular expression) or as `/${foo[bar]}/` (where `[bar]` is the subscript to array @foo)? If @foo doesn't otherwise exist, then it's obviously a character class. If @foo exists, Perl takes a good guess about `[bar]`, and is almost always right. If it does guess wrong, or if you're just plain paranoid, you can force the correct interpretation with curly braces as above.
If you're looking for the information on how to use here-documents, which used to be here, that's been moved to ["Quote and Quote-like Operators" in perlop](perlop#Quote-and-Quote-like-Operators).
###
List value constructors
List values are denoted by separating individual values by commas (and enclosing the list in parentheses where precedence requires it):
```
(LIST)
```
In a context not requiring a list value, the value of what appears to be a list literal is simply the value of the final element, as with the C comma operator. For example,
```
@foo = ('cc', '-E', $bar);
```
assigns the entire list value to array @foo, but
```
$foo = ('cc', '-E', $bar);
```
assigns the value of variable $bar to the scalar variable $foo. Note that the value of an actual array in scalar context is the length of the array; the following assigns the value 3 to $foo:
```
@foo = ('cc', '-E', $bar);
$foo = @foo; # $foo gets 3
```
You may have an optional comma before the closing parenthesis of a list literal, so that you can say:
```
@foo = (
1,
2,
3,
);
```
To use a here-document to assign an array, one line per element, you might use an approach like this:
```
@sauces = <<End_Lines =~ m/(\S.*\S)/g;
normal tomato
spicy tomato
green chile
pesto
white wine
End_Lines
```
LISTs do automatic interpolation of sublists. That is, when a LIST is evaluated, each element of the list is evaluated in list context, and the resulting list value is interpolated into LIST just as if each individual element were a member of LIST. Thus arrays and hashes lose their identity in a LIST--the list
```
(@foo,@bar,&SomeSub,%glarch)
```
contains all the elements of @foo followed by all the elements of @bar, followed by all the elements returned by the subroutine named SomeSub called in list context, followed by the key/value pairs of %glarch. To make a list reference that does *NOT* interpolate, see <perlref>.
The null list is represented by (). Interpolating it in a list has no effect. Thus ((),(),()) is equivalent to (). Similarly, interpolating an array with no elements is the same as if no array had been interpolated at that point.
This interpolation combines with the facts that the opening and closing parentheses are optional (except when necessary for precedence) and lists may end with an optional comma to mean that multiple commas within lists are legal syntax. The list `1,,3` is a concatenation of two lists, `1,` and `3`, the first of which ends with that optional comma. `1,,3` is `(1,),(3)` is `1,3` (And similarly for `1,,,3` is `(1,),(,),3` is `1,3` and so on.) Not that we'd advise you to use this obfuscation.
A list value may also be subscripted like a normal array. You must put the list in parentheses to avoid ambiguity. For example:
```
# Stat returns list value.
$time = (stat($file))[8];
# SYNTAX ERROR HERE.
$time = stat($file)[8]; # OOPS, FORGOT PARENTHESES
# Find a hex digit.
$hexdigit = ('a','b','c','d','e','f')[$digit-10];
# A "reverse comma operator".
return (pop(@foo),pop(@foo))[0];
```
Lists may be assigned to only when each element of the list is itself legal to assign to:
```
($x, $y, $z) = (1, 2, 3);
($map{'red'}, $map{'blue'}, $map{'green'}) = (0x00f, 0x0f0, 0xf00);
```
An exception to this is that you may assign to `undef` in a list. This is useful for throwing away some of the return values of a function:
```
($dev, $ino, undef, undef, $uid, $gid) = stat($file);
```
As of Perl 5.22, you can also use `(undef)x2` instead of `undef, undef`. (You can also do `($x) x 2`, which is less useful, because it assigns to the same variable twice, clobbering the first value assigned.)
When you assign a list of scalars to an array, all previous values in that array are wiped out and the number of elements in the array will now be equal to the number of elements in the right-hand list -- the list from which assignment was made. The array will automatically resize itself to precisely accommodate each element in the right-hand list.
```
use warnings;
my (@xyz, $x, $y, $z);
@xyz = (1, 2, 3);
print "@xyz\n"; # 1 2 3
@xyz = ('al', 'be', 'ga', 'de');
print "@xyz\n"; # al be ga de
@xyz = (101, 102);
print "@xyz\n"; # 101 102
```
When, however, you assign a list of scalars to another list of scalars, the results differ according to whether the left-hand list -- the list being assigned to -- has the same, more or fewer elements than the right-hand list.
```
($x, $y, $z) = (1, 2, 3);
print "$x $y $z\n"; # 1 2 3
($x, $y, $z) = ('al', 'be', 'ga', 'de');
print "$x $y $z\n"; # al be ga
($x, $y, $z) = (101, 102);
print "$x $y $z\n"; # 101 102
# Use of uninitialized value $z in concatenation (.)
# or string at [program] line [line number].
```
If the number of scalars in the left-hand list is less than that in the right-hand list, the "extra" scalars in the right-hand list will simply not be assigned.
If the number of scalars in the left-hand list is greater than that in the left-hand list, the "missing" scalars will become undefined.
```
($x, $y, $z) = (101, 102);
for my $el ($x, $y, $z) {
(defined $el) ? print "$el " : print "<undef>";
}
print "\n";
# 101 102 <undef>
```
List assignment in scalar context returns the number of elements produced by the expression on the right side of the assignment:
```
$x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2
$x = (($foo,$bar) = f()); # set $x to f()'s return count
```
This is handy when you want to do a list assignment in a Boolean context, because most list functions return a null list when finished, which when assigned produces a 0, which is interpreted as FALSE.
It's also the source of a useful idiom for executing a function or performing an operation in list context and then counting the number of return values, by assigning to an empty list and then using that assignment in scalar context. For example, this code:
```
$count = () = $string =~ /\d+/g;
```
will place into $count the number of digit groups found in $string. This happens because the pattern match is in list context (since it is being assigned to the empty list), and will therefore return a list of all matching parts of the string. The list assignment in scalar context will translate that into the number of elements (here, the number of times the pattern matched) and assign that to $count. Note that simply using
```
$count = $string =~ /\d+/g;
```
would not have worked, since a pattern match in scalar context will only return true or false, rather than a count of matches.
The final element of a list assignment may be an array or a hash:
```
($x, $y, @rest) = split;
my($x, $y, %rest) = @_;
```
You can actually put an array or hash anywhere in the list, but the first one in the list will soak up all the values, and anything after it will become undefined. This may be useful in a my() or local().
A hash can be initialized using a literal list holding pairs of items to be interpreted as a key and a value:
```
# same as map assignment above
%map = ('red',0x00f,'blue',0x0f0,'green',0xf00);
```
While literal lists and named arrays are often interchangeable, that's not the case for hashes. Just because you can subscript a list value like a normal array does not mean that you can subscript a list value as a hash. Likewise, hashes included as parts of other lists (including parameters lists and return lists from functions) always flatten out into key/value pairs. That's why it's good to use references sometimes.
It is often more readable to use the `=>` operator between key/value pairs. The `=>` operator is mostly just a more visually distinctive synonym for a comma, but it also arranges for its left-hand operand to be interpreted as a string if it's a bareword that would be a legal simple identifier. `=>` doesn't quote compound identifiers, that contain double colons. This makes it nice for initializing hashes:
```
%map = (
red => 0x00f,
blue => 0x0f0,
green => 0xf00,
);
```
or for initializing hash references to be used as records:
```
$rec = {
witch => 'Mable the Merciless',
cat => 'Fluffy the Ferocious',
date => '10/31/1776',
};
```
or for using call-by-named-parameter to complicated functions:
```
$field = $query->radio_group(
name => 'group_name',
values => ['eenie','meenie','minie'],
default => 'meenie',
linebreak => 'true',
labels => \%labels
);
```
Note that just because a hash is initialized in that order doesn't mean that it comes out in that order. See ["sort" in perlfunc](perlfunc#sort) for examples of how to arrange for an output ordering.
If a key appears more than once in the initializer list of a hash, the last occurrence wins:
```
%circle = (
center => [5, 10],
center => [27, 9],
radius => 100,
color => [0xDF, 0xFF, 0x00],
radius => 54,
);
# same as
%circle = (
center => [27, 9],
color => [0xDF, 0xFF, 0x00],
radius => 54,
);
```
This can be used to provide overridable configuration defaults:
```
# values in %args take priority over %config_defaults
%config = (%config_defaults, %args);
```
### Subscripts
An array can be accessed one scalar at a time by specifying a dollar sign (`$`), then the name of the array (without the leading `@`), then the subscript inside square brackets. For example:
```
@myarray = (5, 50, 500, 5000);
print "The Third Element is", $myarray[2], "\n";
```
The array indices start with 0. A negative subscript retrieves its value from the end. In our example, `$myarray[-1]` would have been 5000, and `$myarray[-2]` would have been 500.
Hash subscripts are similar, only instead of square brackets curly brackets are used. For example:
```
%scientists =
(
"Newton" => "Isaac",
"Einstein" => "Albert",
"Darwin" => "Charles",
"Feynman" => "Richard",
);
print "Darwin's First Name is ", $scientists{"Darwin"}, "\n";
```
You can also subscript a list to get a single element from it:
```
$dir = (getpwnam("daemon"))[7];
```
###
Multi-dimensional array emulation
Multidimensional arrays may be emulated by subscripting a hash with a list. The elements of the list are joined with the subscript separator (see ["$;" in perlvar](perlvar#%24%3B)).
```
$foo{$x,$y,$z}
```
is equivalent to
```
$foo{join($;, $x, $y, $z)}
```
The default subscript separator is "\034", the same as SUBSEP in **awk**.
### Slices
A slice accesses several elements of a list, an array, or a hash simultaneously using a list of subscripts. It's more convenient than writing out the individual elements as a list of separate scalar values.
```
($him, $her) = @folks[0,-1]; # array slice
@them = @folks[0 .. 3]; # array slice
($who, $home) = @ENV{"USER", "HOME"}; # hash slice
($uid, $dir) = (getpwnam("daemon"))[2,7]; # list slice
```
Since you can assign to a list of variables, you can also assign to an array or hash slice.
```
@days[3..5] = qw/Wed Thu Fri/;
@colors{'red','blue','green'}
= (0xff0000, 0x0000ff, 0x00ff00);
@folks[0, -1] = @folks[-1, 0];
```
The previous assignments are exactly equivalent to
```
($days[3], $days[4], $days[5]) = qw/Wed Thu Fri/;
($colors{'red'}, $colors{'blue'}, $colors{'green'})
= (0xff0000, 0x0000ff, 0x00ff00);
($folks[0], $folks[-1]) = ($folks[-1], $folks[0]);
```
Since changing a slice changes the original array or hash that it's slicing, a `foreach` construct will alter some--or even all--of the values of the array or hash.
```
foreach (@array[ 4 .. 10 ]) { s/peter/paul/ }
foreach (@hash{qw[key1 key2]}) {
s/^\s+//; # trim leading whitespace
s/\s+$//; # trim trailing whitespace
s/\b(\w)(\w*)\b/\u$1\L$2/g; # "titlecase" words
}
```
As a special exception, when you slice a list (but not an array or a hash), if the list evaluates to empty, then taking a slice of that empty list will always yield the empty list in turn. Thus:
```
@a = ()[0,1]; # @a has no elements
@b = (@a)[0,1]; # @b has no elements
@c = (sub{}->())[0,1]; # @c has no elements
@d = ('a','b')[0,1]; # @d has two elements
@e = (@d)[0,1,8,9]; # @e has four elements
@f = (@d)[8,9]; # @f has two elements
```
This makes it easy to write loops that terminate when a null list is returned:
```
while ( ($home, $user) = (getpwent)[7,0] ) {
printf "%-8s %s\n", $user, $home;
}
```
As noted earlier in this document, the scalar sense of list assignment is the number of elements on the right-hand side of the assignment. The null list contains no elements, so when the password file is exhausted, the result is 0, not 2.
Slices in scalar context return the last item of the slice.
```
@a = qw/first second third/;
%h = (first => 'A', second => 'B');
$t = @a[0, 1]; # $t is now 'second'
$u = @h{'first', 'second'}; # $u is now 'B'
```
If you're confused about why you use an '@' there on a hash slice instead of a '%', think of it like this. The type of bracket (square or curly) governs whether it's an array or a hash being looked at. On the other hand, the leading symbol ('$' or '@') on the array or hash indicates whether you are getting back a singular value (a scalar) or a plural one (a list).
####
Key/Value Hash Slices
Starting in Perl 5.20, a hash slice operation with the % symbol is a variant of slice operation returning a list of key/value pairs rather than just values:
```
%h = (blonk => 2, foo => 3, squink => 5, bar => 8);
%subset = %h{'foo', 'bar'}; # key/value hash slice
# %subset is now (foo => 3, bar => 8)
%removed = delete %h{'foo', 'bar'};
# %removed is now (foo => 3, bar => 8)
# %h is now (blonk => 2, squink => 5)
```
However, the result of such a slice cannot be localized or assigned to. These are otherwise very much consistent with hash slices using the @ symbol.
####
Index/Value Array Slices
Similar to key/value hash slices (and also introduced in Perl 5.20), the % array slice syntax returns a list of index/value pairs:
```
@a = "a".."z";
@list = %a[3,4,6];
# @list is now (3, "d", 4, "e", 6, "g")
@removed = delete %a[3,4,6]
# @removed is now (3, "d", 4, "e", 6, "g")
# @list[3,4,6] are now undef
```
Note that calling [`delete`](perlfunc#delete-EXPR) on array values is strongly discouraged.
###
Typeglobs and Filehandles
Perl uses an internal type called a *typeglob* to hold an entire symbol table entry. The type prefix of a typeglob is a `*`, because it represents all types. This used to be the preferred way to pass arrays and hashes by reference into a function, but now that we have real references, this is seldom needed.
The main use of typeglobs in modern Perl is create symbol table aliases. This assignment:
```
*this = *that;
```
makes $this an alias for $that, @this an alias for @that, %this an alias for %that, &this an alias for &that, etc. Much safer is to use a reference. This:
```
local *Here::blue = \$There::green;
```
temporarily makes $Here::blue an alias for $There::green, but doesn't make @Here::blue an alias for @There::green, or %Here::blue an alias for %There::green, etc. See ["Symbol Tables" in perlmod](perlmod#Symbol-Tables) for more examples of this. Strange though this may seem, this is the basis for the whole module import/export system.
Another use for typeglobs is to pass filehandles into a function or to create new filehandles. If you need to use a typeglob to save away a filehandle, do it this way:
```
$fh = *STDOUT;
```
or perhaps as a real reference, like this:
```
$fh = \*STDOUT;
```
See <perlsub> for examples of using these as indirect filehandles in functions.
Typeglobs are also a way to create a local filehandle using the local() operator. These last until their block is exited, but may be passed back. For example:
```
sub newopen {
my $path = shift;
local *FH; # not my!
open (FH, $path) or return undef;
return *FH;
}
$fh = newopen('/etc/passwd');
```
Now that we have the `*foo{THING}` notation, typeglobs aren't used as much for filehandle manipulations, although they're still needed to pass brand new file and directory handles into or out of functions. That's because `*HANDLE{IO}` only works if HANDLE has already been used as a handle. In other words, `*FH` must be used to create new symbol table entries; `*foo{THING}` cannot. When in doubt, use `*FH`.
All functions that are capable of creating filehandles (open(), opendir(), pipe(), socketpair(), sysopen(), socket(), and accept()) automatically create an anonymous filehandle if the handle passed to them is an uninitialized scalar variable. This allows the constructs such as `open(my $fh, ...)` and `open(local $fh,...)` to be used to create filehandles that will conveniently be closed automatically when the scope ends, provided there are no other references to them. This largely eliminates the need for typeglobs when opening filehandles that must be passed around, as in the following example:
```
sub myopen {
open my $fh, "@_"
or die "Can't open '@_': $!";
return $fh;
}
{
my $f = myopen("</etc/motd");
print <$f>;
# $f implicitly closed here
}
```
Note that if an initialized scalar variable is used instead the result is different: `my $fh='zzz'; open($fh, ...)` is equivalent to `open( *{'zzz'}, ...)`. `use strict 'refs'` forbids such practice.
Another way to create anonymous filehandles is with the Symbol module or with the IO::Handle module and its ilk. These modules have the advantage of not hiding different types of the same name during the local(). See the bottom of ["open" in perlfunc](perlfunc#open) for an example.
SEE ALSO
---------
See <perlvar> for a description of Perl's built-in variables and a discussion of legal variable names. See <perlref>, <perlsub>, and ["Symbol Tables" in perlmod](perlmod#Symbol-Tables) for more discussion on typeglobs and the `*foo{THING}` syntax.
| programming_docs |
perl TAP::Base TAP::Base
=========
CONTENTS
--------
* [NAME](#NAME)
* [VERSION](#VERSION)
* [SYNOPSIS](#SYNOPSIS)
* [DESCRIPTION](#DESCRIPTION)
* [METHODS](#METHODS)
+ [Class Methods](#Class-Methods)
- [callback](#callback)
- [get\_time](#get_time)
- [time\_is\_hires](#time_is_hires)
- [get\_times](#get_times)
NAME
----
TAP::Base - Base class that provides common functionality to <TAP::Parser> and <TAP::Harness>
VERSION
-------
Version 3.44
SYNOPSIS
--------
```
package TAP::Whatever;
use base 'TAP::Base';
# ... later ...
my $thing = TAP::Whatever->new();
$thing->callback( event => sub {
# do something interesting
} );
```
DESCRIPTION
-----------
`TAP::Base` provides callback management.
METHODS
-------
###
Class Methods
#### `callback`
Install a callback for a named event.
#### `get_time`
Return the current time using Time::HiRes if available.
#### `time_is_hires`
Return true if the time returned by get\_time is high resolution (i.e. if Time::HiRes is available).
#### `get_times`
Return array reference of the four-element list of CPU seconds, as with ["times" in perlfunc](perlfunc#times).
perl Test2::EventFacet::Control Test2::EventFacet::Control
==========================
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
* [FIELDS](#FIELDS)
* [SOURCE](#SOURCE)
* [MAINTAINERS](#MAINTAINERS)
* [AUTHORS](#AUTHORS)
* [COPYRIGHT](#COPYRIGHT)
NAME
----
Test2::EventFacet::Control - Facet for hub actions and behaviors.
DESCRIPTION
-----------
This facet is used when the event needs to give instructions to the Test2 internals.
FIELDS
------
$string = $control->{details}
$string = $control->details() Human readable explanation for the special behavior.
$bool = $control->{global}
$bool = $control->global() True if the event is global in nature and should be seen by all hubs.
$exit = $control->{terminate}
$exit = $control->terminate() Defined if the test should immediately exit, the value is the exit code and may be `0`.
$bool = $control->{halt}
$bool = $control->halt() True if all testing should be halted immediately.
$bool = $control->{has\_callback}
$bool = $control->has\_callback() True if the `callback($hub)` method on the event should be called.
$encoding = $control->{encoding}
$encoding = $control->encoding() This can be used to change the encoding from this event onward.
$phase = $control->{phase}
$phase = $control->phase() Used to signal that a phase change has occurred. Currently only the perl END phase is signaled.
SOURCE
------
The source code repository for Test2 can be found at *http://github.com/Test-More/test-more/*.
MAINTAINERS
-----------
Chad Granum <[email protected]> AUTHORS
-------
Chad Granum <[email protected]> COPYRIGHT
---------
Copyright 2020 Chad Granum <[email protected]>.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
See *http://dev.perl.org/licenses/*
perl Encode::Byte Encode::Byte
============
CONTENTS
--------
* [NAME](#NAME)
* [SYNOPSIS](#SYNOPSIS)
* [ABSTRACT](#ABSTRACT)
* [DESCRIPTION](#DESCRIPTION)
* [SEE ALSO](#SEE-ALSO)
NAME
----
Encode::Byte - Single Byte Encodings
SYNOPSIS
--------
```
use Encode qw/encode decode/;
$greek = encode("iso-8859-7", $utf8); # loads Encode::Byte implicitly
$utf8 = decode("iso-8859-7", $greek); # ditto
```
ABSTRACT
--------
This module implements various single byte encodings. For most cases it uses \x80-\xff (upper half) to map non-ASCII characters. Encodings supported are as follows.
```
Canonical Alias Description
--------------------------------------------------------------------
# ISO 8859 series
(iso-8859-1 is in built-in)
iso-8859-2 latin2 [ISO]
iso-8859-3 latin3 [ISO]
iso-8859-4 latin4 [ISO]
iso-8859-5 [ISO]
iso-8859-6 [ISO]
iso-8859-7 [ISO]
iso-8859-8 [ISO]
iso-8859-9 latin5 [ISO]
iso-8859-10 latin6 [ISO]
iso-8859-11
(iso-8859-12 is nonexistent)
iso-8859-13 latin7 [ISO]
iso-8859-14 latin8 [ISO]
iso-8859-15 latin9 [ISO]
iso-8859-16 latin10 [ISO]
# Cyrillic
koi8-f
koi8-r cp878 [RFC1489]
koi8-u [RFC2319]
# Vietnamese
viscii
# all cp* are also available as ibm-*, ms-*, and windows-*
# also see L<http://msdn.microsoft.com/en-us/library/aa752010%28VS.85%29.aspx>
cp424
cp437
cp737
cp775
cp850
cp852
cp855
cp856
cp857
cp860
cp861
cp862
cp863
cp864
cp865
cp866
cp869
cp874
cp1006
cp1250 WinLatin2
cp1251 WinCyrillic
cp1252 WinLatin1
cp1253 WinGreek
cp1254 WinTurkish
cp1255 WinHebrew
cp1256 WinArabic
cp1257 WinBaltic
cp1258 WinVietnamese
# Macintosh
# Also see L<http://developer.apple.com/technotes/tn/tn1150.html>
MacArabic
MacCentralEurRoman
MacCroatian
MacCyrillic
MacFarsi
MacGreek
MacHebrew
MacIcelandic
MacRoman
MacRomanian
MacRumanian
MacSami
MacThai
MacTurkish
MacUkrainian
# More vendor encodings
AdobeStandardEncoding
nextstep
hp-roman8
```
DESCRIPTION
-----------
To find how to use this module in detail, see [Encode](encode).
SEE ALSO
---------
[Encode](encode)
perl perlxstut perlxstut
=========
CONTENTS
--------
* [NAME](#NAME)
* [DESCRIPTION](#DESCRIPTION)
* [SPECIAL NOTES](#SPECIAL-NOTES)
+ [make](#make)
+ [Version caveat](#Version-caveat)
+ [Dynamic Loading versus Static Loading](#Dynamic-Loading-versus-Static-Loading)
+ [Threads and PERL\_NO\_GET\_CONTEXT](#Threads-and-PERL_NO_GET_CONTEXT)
* [TUTORIAL](#TUTORIAL)
+ [EXAMPLE 1](#EXAMPLE-1)
+ [EXAMPLE 2](#EXAMPLE-2)
+ [What has gone on?](#What-has-gone-on?)
+ [Writing good test scripts](#Writing-good-test-scripts)
+ [EXAMPLE 3](#EXAMPLE-3)
+ [What's new here?](#What's-new-here?)
+ [Input and Output Parameters](#Input-and-Output-Parameters)
+ [The XSUBPP Program](#The-XSUBPP-Program)
+ [The TYPEMAP file](#The-TYPEMAP-file)
+ [Warning about Output Arguments](#Warning-about-Output-Arguments)
+ [EXAMPLE 4](#EXAMPLE-4)
+ [What has happened here?](#What-has-happened-here?)
+ [Anatomy of .xs file](#Anatomy-of-.xs-file)
+ [Getting the fat out of XSUBs](#Getting-the-fat-out-of-XSUBs)
+ [More about XSUB arguments](#More-about-XSUB-arguments)
+ [The Argument Stack](#The-Argument-Stack)
+ [Extending your Extension](#Extending-your-Extension)
+ [Documenting your Extension](#Documenting-your-Extension)
+ [Installing your Extension](#Installing-your-Extension)
+ [EXAMPLE 5](#EXAMPLE-5)
+ [New Things in this Example](#New-Things-in-this-Example)
+ [EXAMPLE 6](#EXAMPLE-6)
+ [New Things in this Example](#New-Things-in-this-Example1)
+ [EXAMPLE 7 (Coming Soon)](#EXAMPLE-7-(Coming-Soon))
+ [EXAMPLE 8 (Coming Soon)](#EXAMPLE-8-(Coming-Soon))
+ [EXAMPLE 9 Passing open files to XSes](#EXAMPLE-9-Passing-open-files-to-XSes)
+ [Troubleshooting these Examples](#Troubleshooting-these-Examples)
* [See also](#See-also)
* [Author](#Author)
+ [Last Changed](#Last-Changed)
NAME
----
perlxstut - Tutorial for writing XSUBs
DESCRIPTION
-----------
This tutorial will educate the reader on the steps involved in creating a Perl extension. The reader is assumed to have access to <perlguts>, <perlapi> and <perlxs>.
This tutorial starts with very simple examples and becomes more complex, with each new example adding new features. Certain concepts may not be completely explained until later in the tutorial in order to slowly ease the reader into building extensions.
This tutorial was written from a Unix point of view. Where I know them to be otherwise different for other platforms (e.g. Win32), I will list them. If you find something that was missed, please let me know.
SPECIAL NOTES
--------------
### make
This tutorial assumes that the make program that Perl is configured to use is called `make`. Instead of running "make" in the examples that follow, you may have to substitute whatever make program Perl has been configured to use. Running **perl -V:make** should tell you what it is.
###
Version caveat
When writing a Perl extension for general consumption, one should expect that the extension will be used with versions of Perl different from the version available on your machine. Since you are reading this document, the version of Perl on your machine is probably 5.005 or later, but the users of your extension may have more ancient versions.
To understand what kinds of incompatibilities one may expect, and in the rare case that the version of Perl on your machine is older than this document, see the section on "Troubleshooting these Examples" for more information.
If your extension uses some features of Perl which are not available on older releases of Perl, your users would appreciate an early meaningful warning. You would probably put this information into the *README* file, but nowadays installation of extensions may be performed automatically, guided by *CPAN.pm* module or other tools.
In MakeMaker-based installations, *Makefile.PL* provides the earliest opportunity to perform version checks. One can put something like this in *Makefile.PL* for this purpose:
```
eval { require 5.007 }
or die <<EOD;
############
### This module uses frobnication framework which is not available
### before version 5.007 of Perl. Upgrade your Perl before
### installing Kara::Mba.
############
EOD
```
###
Dynamic Loading versus Static Loading
It is commonly thought that if a system does not have the capability to dynamically load a library, you cannot build XSUBs. This is incorrect. You *can* build them, but you must link the XSUBs subroutines with the rest of Perl, creating a new executable. This situation is similar to Perl 4.
This tutorial can still be used on such a system. The XSUB build mechanism will check the system and build a dynamically-loadable library if possible, or else a static library and then, optionally, a new statically-linked executable with that static library linked in.
Should you wish to build a statically-linked executable on a system which can dynamically load libraries, you may, in all the following examples, where the command "`make`" with no arguments is executed, run the command "`make perl`" instead.
If you have generated such a statically-linked executable by choice, then instead of saying "`make test`", you should say "`make test_static`". On systems that cannot build dynamically-loadable libraries at all, simply saying "`make test`" is sufficient.
###
Threads and PERL\_NO\_GET\_CONTEXT
For threaded builds, perl requires the context pointer for the current thread, without `PERL_NO_GET_CONTEXT`, perl will call a function to retrieve the context.
For improved performance, include:
```
#define PERL_NO_GET_CONTEXT
```
as shown below.
For more details, see [perlguts](perlguts#How-multiple-interpreters-and-concurrency-are-supported).
TUTORIAL
--------
Now let's go on with the show!
###
EXAMPLE 1
Our first extension will be very simple. When we call the routine in the extension, it will print out a well-known message and return.
Run "`h2xs -A -n Mytest`". This creates a directory named Mytest, possibly under ext/ if that directory exists in the current working directory. Several files will be created under the Mytest dir, including MANIFEST, Makefile.PL, lib/Mytest.pm, Mytest.xs, t/Mytest.t, and Changes.
The MANIFEST file contains the names of all the files just created in the Mytest directory.
The file Makefile.PL should look something like this:
```
use ExtUtils::MakeMaker;
# See lib/ExtUtils/MakeMaker.pm for details of how to influence
# the contents of the Makefile that is written.
WriteMakefile(
NAME => 'Mytest',
VERSION_FROM => 'Mytest.pm', # finds $VERSION
LIBS => [''], # e.g., '-lm'
DEFINE => '', # e.g., '-DHAVE_SOMETHING'
INC => '-I', # e.g., '-I. -I/usr/include/other'
);
```
The file Mytest.pm should start with something like this:
```
package Mytest;
use 5.008008;
use strict;
use warnings;
require Exporter;
our @ISA = qw(Exporter);
our %EXPORT_TAGS = ( 'all' => [ qw(
) ] );
our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );
our @EXPORT = qw(
);
our $VERSION = '0.01';
require XSLoader;
XSLoader::load('Mytest', $VERSION);
# Preloaded methods go here.
1;
__END__
# Below is the stub of documentation for your module. You better
# edit it!
```
The rest of the .pm file contains sample code for providing documentation for the extension.
Finally, the Mytest.xs file should look something like this:
```
#define PERL_NO_GET_CONTEXT
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "ppport.h"
MODULE = Mytest PACKAGE = Mytest
```
Let's edit the .xs file by adding this to the end of the file:
```
void
hello()
CODE:
printf("Hello, world!\n");
```
It is okay for the lines starting at the "CODE:" line to not be indented. However, for readability purposes, it is suggested that you indent CODE: one level and the lines following one more level.
Now we'll run "`perl Makefile.PL`". This will create a real Makefile, which make needs. Its output looks something like:
```
% perl Makefile.PL
Checking if your kit is complete...
Looks good
Writing Makefile for Mytest
%
```
Now, running make will produce output that looks something like this (some long lines have been shortened for clarity and some extraneous lines have been deleted):
```
% make
cp lib/Mytest.pm blib/lib/Mytest.pm
perl xsubpp -typemap typemap Mytest.xs > Mytest.xsc && \
mv Mytest.xsc Mytest.c
Please specify prototyping behavior for Mytest.xs (see perlxs manual)
cc -c Mytest.c
Running Mkbootstrap for Mytest ()
chmod 644 Mytest.bs
rm -f blib/arch/auto/Mytest/Mytest.so
cc -shared -L/usr/local/lib Mytest.o -o blib/arch/auto/Mytest/Mytest.so
chmod 755 blib/arch/auto/Mytest/Mytest.so
cp Mytest.bs blib/arch/auto/Mytest/Mytest.bs
chmod 644 blib/arch/auto/Mytest/Mytest.bs
Manifying blib/man3/Mytest.3pm
%
```
You can safely ignore the line about "prototyping behavior" - it is explained in ["The PROTOTYPES: Keyword" in perlxs](perlxs#The-PROTOTYPES%3A-Keyword).
Perl has its own special way of easily writing test scripts, but for this example only, we'll create our own test script. Create a file called hello that looks like this:
```
#! /opt/perl5/bin/perl
use ExtUtils::testlib;
use Mytest;
Mytest::hello();
```
Now we make the script executable (`chmod +x hello`), run the script and we should see the following output:
```
% ./hello
Hello, world!
%
```
###
EXAMPLE 2
Now let's add to our extension a subroutine that will take a single numeric argument as input and return 1 if the number is even or 0 if the number is odd.
Add the following to the end of Mytest.xs:
```
int
is_even(input)
int input
CODE:
RETVAL = (input % 2 == 0);
OUTPUT:
RETVAL
```
There does not need to be whitespace at the start of the "`int input`" line, but it is useful for improving readability. Placing a semi-colon at the end of that line is also optional. Any amount and kind of whitespace may be placed between the "`int`" and "`input`".
Now re-run make to rebuild our new shared library.
Now perform the same steps as before, generating a Makefile from the Makefile.PL file, and running make.
In order to test that our extension works, we now need to look at the file Mytest.t. This file is set up to imitate the same kind of testing structure that Perl itself has. Within the test script, you perform a number of tests to confirm the behavior of the extension, printing "ok" when the test is correct, "not ok" when it is not.
```
use Test::More tests => 4;
BEGIN { use_ok('Mytest') };
#########################
# Insert your test code below, the Test::More module is use()ed here
# so read its man page ( perldoc Test::More ) for help writing this
# test script.
is( Mytest::is_even(0), 1 );
is( Mytest::is_even(1), 0 );
is( Mytest::is_even(2), 1 );
```
We will be calling the test script through the command "`make test`". You should see output that looks something like this:
```
%make test
PERL_DL_NONLAZY=1 /usr/bin/perl "-MExtUtils::Command::MM" "-e"
"test_harness(0, 'blib/lib', 'blib/arch')" t/*.t
t/Mytest....ok
All tests successful.
Files=1, Tests=4, 0 wallclock secs ( 0.03 cusr + 0.00 csys = 0.03 CPU)
%
```
###
What has gone on?
The program h2xs is the starting point for creating extensions. In later examples we'll see how we can use h2xs to read header files and generate templates to connect to C routines.
h2xs creates a number of files in the extension directory. The file Makefile.PL is a perl script which will generate a true Makefile to build the extension. We'll take a closer look at it later.
The .pm and .xs files contain the meat of the extension. The .xs file holds the C routines that make up the extension. The .pm file contains routines that tell Perl how to load your extension.
Generating the Makefile and running `make` created a directory called blib (which stands for "build library") in the current working directory. This directory will contain the shared library that we will build. Once we have tested it, we can install it into its final location.
Invoking the test script via "`make test`" did something very important. It invoked perl with all those `-I` arguments so that it could find the various files that are part of the extension. It is *very* important that while you are still testing extensions that you use "`make test`". If you try to run the test script all by itself, you will get a fatal error. Another reason it is important to use "`make test`" to run your test script is that if you are testing an upgrade to an already-existing version, using "`make test`" ensures that you will test your new extension, not the already-existing version.
When Perl sees a `use extension;`, it searches for a file with the same name as the `use`'d extension that has a .pm suffix. If that file cannot be found, Perl dies with a fatal error. The default search path is contained in the `@INC` array.
In our case, Mytest.pm tells perl that it will need the Exporter and Dynamic Loader extensions. It then sets the `@ISA` and `@EXPORT` arrays and the `$VERSION` scalar; finally it tells perl to bootstrap the module. Perl will call its dynamic loader routine (if there is one) and load the shared library.
The two arrays `@ISA` and `@EXPORT` are very important. The `@ISA` array contains a list of other packages in which to search for methods (or subroutines) that do not exist in the current package. This is usually only important for object-oriented extensions (which we will talk about much later), and so usually doesn't need to be modified.
The `@EXPORT` array tells Perl which of the extension's variables and subroutines should be placed into the calling package's namespace. Because you don't know if the user has already used your variable and subroutine names, it's vitally important to carefully select what to export. Do *not* export method or variable names *by default* without a good reason.
As a general rule, if the module is trying to be object-oriented then don't export anything. If it's just a collection of functions and variables, then you can export them via another array, called `@EXPORT_OK`. This array does not automatically place its subroutine and variable names into the namespace unless the user specifically requests that this be done.
See <perlmod> for more information.
The `$VERSION` variable is used to ensure that the .pm file and the shared library are "in sync" with each other. Any time you make changes to the .pm or .xs files, you should increment the value of this variable.
###
Writing good test scripts
The importance of writing good test scripts cannot be over-emphasized. You should closely follow the "ok/not ok" style that Perl itself uses, so that it is very easy and unambiguous to determine the outcome of each test case. When you find and fix a bug, make sure you add a test case for it.
By running "`make test`", you ensure that your Mytest.t script runs and uses the correct version of your extension. If you have many test cases, save your test files in the "t" directory and use the suffix ".t". When you run "`make test`", all of these test files will be executed.
###
EXAMPLE 3
Our third extension will take one argument as its input, round off that value, and set the *argument* to the rounded value.
Add the following to the end of Mytest.xs:
```
void
round(arg)
double arg
CODE:
if (arg > 0.0) {
arg = floor(arg + 0.5);
} else if (arg < 0.0) {
arg = ceil(arg - 0.5);
} else {
arg = 0.0;
}
OUTPUT:
arg
```
Edit the Makefile.PL file so that the corresponding line looks like this:
```
LIBS => ['-lm'], # e.g., '-lm'
```
Generate the Makefile and run make. Change the test number in Mytest.t to "9" and add the following tests:
```
my $i;
$i = -1.5;
Mytest::round($i);
is( $i, -2.0, 'Rounding -1.5 to -2.0' );
$i = -1.1;
Mytest::round($i);
is( $i, -1.0, 'Rounding -1.1 to -1.0' );
$i = 0.0;
Mytest::round($i);
is( $i, 0.0, 'Rounding 0.0 to 0.0' );
$i = 0.5;
Mytest::round($i);
is( $i, 1.0, 'Rounding 0.5 to 1.0' );
$i = 1.2;
Mytest::round($i);
is( $i, 1.0, 'Rounding 1.2 to 1.0' );
```
Running "`make test`" should now print out that all nine tests are okay.
Notice that in these new test cases, the argument passed to round was a scalar variable. You might be wondering if you can round a constant or literal. To see what happens, temporarily add the following line to Mytest.t:
```
Mytest::round(3);
```
Run "`make test`" and notice that Perl dies with a fatal error. Perl won't let you change the value of constants!
###
What's new here?
* We've made some changes to Makefile.PL. In this case, we've specified an extra library to be linked into the extension's shared library, the math library libm in this case. We'll talk later about how to write XSUBs that can call every routine in a library.
* The value of the function is not being passed back as the function's return value, but by changing the value of the variable that was passed into the function. You might have guessed that when you saw that the return value of round is of type "void".
###
Input and Output Parameters
You specify the parameters that will be passed into the XSUB on the line(s) after you declare the function's return value and name. Each input parameter line starts with optional whitespace, and may have an optional terminating semicolon.
The list of output parameters occurs at the very end of the function, just after the OUTPUT: directive. The use of RETVAL tells Perl that you wish to send this value back as the return value of the XSUB function. In Example 3, we wanted the "return value" placed in the original variable which we passed in, so we listed it (and not RETVAL) in the OUTPUT: section.
###
The XSUBPP Program
The **xsubpp** program takes the XS code in the .xs file and translates it into C code, placing it in a file whose suffix is .c. The C code created makes heavy use of the C functions within Perl.
###
The TYPEMAP file
The **xsubpp** program uses rules to convert from Perl's data types (scalar, array, etc.) to C's data types (int, char, etc.). These rules are stored in the typemap file ($PERLLIB/ExtUtils/typemap). There's a brief discussion below, but all the nitty-gritty details can be found in <perlxstypemap>. If you have a new-enough version of perl (5.16 and up) or an upgraded XS compiler (`ExtUtils::ParseXS` 3.13\_01 or better), then you can inline typemaps in your XS instead of writing separate files. Either way, this typemap thing is split into three parts:
The first section maps various C data types to a name, which corresponds somewhat with the various Perl types. The second section contains C code which **xsubpp** uses to handle input parameters. The third section contains C code which **xsubpp** uses to handle output parameters.
Let's take a look at a portion of the .c file created for our extension. The file name is Mytest.c:
```
XS(XS_Mytest_round)
{
dXSARGS;
if (items != 1)
Perl_croak(aTHX_ "Usage: Mytest::round(arg)");
PERL_UNUSED_VAR(cv); /* -W */
{
double arg = (double)SvNV(ST(0)); /* XXXXX */
if (arg > 0.0) {
arg = floor(arg + 0.5);
} else if (arg < 0.0) {
arg = ceil(arg - 0.5);
} else {
arg = 0.0;
}
sv_setnv(ST(0), (double)arg); /* XXXXX */
SvSETMAGIC(ST(0));
}
XSRETURN_EMPTY;
}
```
Notice the two lines commented with "XXXXX". If you check the first part of the typemap file (or section), you'll see that doubles are of type T\_DOUBLE. In the INPUT part of the typemap, an argument that is T\_DOUBLE is assigned to the variable arg by calling the routine SvNV on something, then casting it to double, then assigned to the variable arg. Similarly, in the OUTPUT section, once arg has its final value, it is passed to the sv\_setnv function to be passed back to the calling subroutine. These two functions are explained in <perlguts>; we'll talk more later about what that "ST(0)" means in the section on the argument stack.
###
Warning about Output Arguments
In general, it's not a good idea to write extensions that modify their input parameters, as in Example 3. Instead, you should probably return multiple values in an array and let the caller handle them (we'll do this in a later example). However, in order to better accommodate calling pre-existing C routines, which often do modify their input parameters, this behavior is tolerated.
###
EXAMPLE 4
In this example, we'll now begin to write XSUBs that will interact with pre-defined C libraries. To begin with, we will build a small library of our own, then let h2xs write our .pm and .xs files for us.
Create a new directory called Mytest2 at the same level as the directory Mytest. In the Mytest2 directory, create another directory called mylib, and cd into that directory.
Here we'll create some files that will generate a test library. These will include a C source file and a header file. We'll also create a Makefile.PL in this directory. Then we'll make sure that running make at the Mytest2 level will automatically run this Makefile.PL file and the resulting Makefile.
In the mylib directory, create a file mylib.h that looks like this:
```
#define TESTVAL 4
extern double foo(int, long, const char*);
```
Also create a file mylib.c that looks like this:
```
#include <stdlib.h>
#include "mylib.h"
double
foo(int a, long b, const char *c)
{
return (a + b + atof(c) + TESTVAL);
}
```
And finally create a file Makefile.PL that looks like this:
```
use ExtUtils::MakeMaker;
$Verbose = 1;
WriteMakefile(
NAME => 'Mytest2::mylib',
SKIP => [qw(all static static_lib dynamic dynamic_lib)],
clean => {'FILES' => 'libmylib$(LIB_EXT)'},
);
sub MY::top_targets {
'
all :: static
pure_all :: static
static :: libmylib$(LIB_EXT)
libmylib$(LIB_EXT): $(O_FILES)
$(AR) cr libmylib$(LIB_EXT) $(O_FILES)
$(RANLIB) libmylib$(LIB_EXT)
';
}
```
Make sure you use a tab and not spaces on the lines beginning with "$(AR)" and "$(RANLIB)". Make will not function properly if you use spaces. It has also been reported that the "cr" argument to $(AR) is unnecessary on Win32 systems.
We will now create the main top-level Mytest2 files. Change to the directory above Mytest2 and run the following command:
```
% h2xs -O -n Mytest2 Mytest2/mylib/mylib.h
```
This will print out a warning about overwriting Mytest2, but that's okay. Our files are stored in Mytest2/mylib, and will be untouched.
The normal Makefile.PL that h2xs generates doesn't know about the mylib directory. We need to tell it that there is a subdirectory and that we will be generating a library in it. Let's add the argument MYEXTLIB to the WriteMakefile call so that it looks like this:
```
WriteMakefile(
NAME => 'Mytest2',
VERSION_FROM => 'Mytest2.pm', # finds $VERSION
LIBS => [''], # e.g., '-lm'
DEFINE => '', # e.g., '-DHAVE_SOMETHING'
INC => '', # e.g., '-I/usr/include/other'
MYEXTLIB => 'mylib/libmylib$(LIB_EXT)',
);
```
and then at the end add a subroutine (which will override the pre-existing subroutine). Remember to use a tab character to indent the line beginning with "cd"!
```
sub MY::postamble {
'
$(MYEXTLIB): mylib/Makefile
cd mylib && $(MAKE) $(PASSTHRU)
';
}
```
Let's also fix the MANIFEST file by appending the following three lines:
```
mylib/Makefile.PL
mylib/mylib.c
mylib/mylib.h
```
To keep our namespace nice and unpolluted, edit the .pm file and change the variable `@EXPORT` to `@EXPORT_OK`. Finally, in the .xs file, edit the #include line to read:
```
#include "mylib/mylib.h"
```
And also add the following function definition to the end of the .xs file:
```
double
foo(a,b,c)
int a
long b
const char * c
OUTPUT:
RETVAL
```
Now we also need to create a typemap because the default Perl doesn't currently support the `const char *` type. Include a new TYPEMAP section in your XS code before the above function:
```
TYPEMAP: <<END
const char * T_PV
END
```
Now run perl on the top-level Makefile.PL. Notice that it also created a Makefile in the mylib directory. Run make and watch that it does cd into the mylib directory and run make in there as well.
Now edit the Mytest2.t script and change the number of tests to "5", and add the following lines to the end of the script:
```
is( Mytest2::foo( 1, 2, "Hello, world!" ), 7 );
is( Mytest2::foo( 1, 2, "0.0" ), 7 );
ok( abs( Mytest2::foo( 0, 0, "-3.4" ) - 0.6 ) <= 0.01 );
```
(When dealing with floating-point comparisons, it is best to not check for equality, but rather that the difference between the expected and actual result is below a certain amount (called epsilon) which is 0.01 in this case)
Run "`make test`" and all should be well. There are some warnings on missing tests for the Mytest2::mylib extension, but you can ignore them.
###
What has happened here?
Unlike previous examples, we've now run h2xs on a real include file. This has caused some extra goodies to appear in both the .pm and .xs files.
* In the .xs file, there's now a #include directive with the absolute path to the mylib.h header file. We changed this to a relative path so that we could move the extension directory if we wanted to.
* There's now some new C code that's been added to the .xs file. The purpose of the `constant` routine is to make the values that are #define'd in the header file accessible by the Perl script (by calling either `TESTVAL` or `&Mytest2::TESTVAL`). There's also some XS code to allow calls to the `constant` routine.
* The .pm file originally exported the name `TESTVAL` in the `@EXPORT` array. This could lead to name clashes. A good rule of thumb is that if the #define is only going to be used by the C routines themselves, and not by the user, they should be removed from the `@EXPORT` array. Alternately, if you don't mind using the "fully qualified name" of a variable, you could move most or all of the items from the `@EXPORT` array into the `@EXPORT_OK` array.
* If our include file had contained #include directives, these would not have been processed by h2xs. There is no good solution to this right now.
* We've also told Perl about the library that we built in the mylib subdirectory. That required only the addition of the `MYEXTLIB` variable to the WriteMakefile call and the replacement of the postamble subroutine to cd into the subdirectory and run make. The Makefile.PL for the library is a bit more complicated, but not excessively so. Again we replaced the postamble subroutine to insert our own code. This code simply specified that the library to be created here was a static archive library (as opposed to a dynamically loadable library) and provided the commands to build it.
###
Anatomy of .xs file
The .xs file of ["EXAMPLE 4"](#EXAMPLE-4) contained some new elements. To understand the meaning of these elements, pay attention to the line which reads
```
MODULE = Mytest2 PACKAGE = Mytest2
```
Anything before this line is plain C code which describes which headers to include, and defines some convenience functions. No translations are performed on this part, apart from having embedded POD documentation skipped over (see <perlpod>) it goes into the generated output C file as is.
Anything after this line is the description of XSUB functions. These descriptions are translated by **xsubpp** into C code which implements these functions using Perl calling conventions, and which makes these functions visible from Perl interpreter.
Pay a special attention to the function `constant`. This name appears twice in the generated .xs file: once in the first part, as a static C function, then another time in the second part, when an XSUB interface to this static C function is defined.
This is quite typical for .xs files: usually the .xs file provides an interface to an existing C function. Then this C function is defined somewhere (either in an external library, or in the first part of .xs file), and a Perl interface to this function (i.e. "Perl glue") is described in the second part of .xs file. The situation in ["EXAMPLE 1"](#EXAMPLE-1), ["EXAMPLE 2"](#EXAMPLE-2), and ["EXAMPLE 3"](#EXAMPLE-3), when all the work is done inside the "Perl glue", is somewhat of an exception rather than the rule.
###
Getting the fat out of XSUBs
In ["EXAMPLE 4"](#EXAMPLE-4) the second part of .xs file contained the following description of an XSUB:
```
double
foo(a,b,c)
int a
long b
const char * c
OUTPUT:
RETVAL
```
Note that in contrast with ["EXAMPLE 1"](#EXAMPLE-1), ["EXAMPLE 2"](#EXAMPLE-2) and ["EXAMPLE 3"](#EXAMPLE-3), this description does not contain the actual *code* for what is done during a call to Perl function foo(). To understand what is going on here, one can add a CODE section to this XSUB:
```
double
foo(a,b,c)
int a
long b
const char * c
CODE:
RETVAL = foo(a,b,c);
OUTPUT:
RETVAL
```
However, these two XSUBs provide almost identical generated C code: **xsubpp** compiler is smart enough to figure out the `CODE:` section from the first two lines of the description of XSUB. What about `OUTPUT:` section? In fact, that is absolutely the same! The `OUTPUT:` section can be removed as well, *as far as `CODE:` section or `PPCODE:` section* is not specified: **xsubpp** can see that it needs to generate a function call section, and will autogenerate the OUTPUT section too. Thus one can shortcut the XSUB to become:
```
double
foo(a,b,c)
int a
long b
const char * c
```
Can we do the same with an XSUB
```
int
is_even(input)
int input
CODE:
RETVAL = (input % 2 == 0);
OUTPUT:
RETVAL
```
of ["EXAMPLE 2"](#EXAMPLE-2)? To do this, one needs to define a C function `int is_even(int input)`. As we saw in ["Anatomy of .xs file"](#Anatomy-of-.xs-file), a proper place for this definition is in the first part of .xs file. In fact a C function
```
int
is_even(int arg)
{
return (arg % 2 == 0);
}
```
is probably overkill for this. Something as simple as a `#define` will do too:
```
#define is_even(arg) ((arg) % 2 == 0)
```
After having this in the first part of .xs file, the "Perl glue" part becomes as simple as
```
int
is_even(input)
int input
```
This technique of separation of the glue part from the workhorse part has obvious tradeoffs: if you want to change a Perl interface, you need to change two places in your code. However, it removes a lot of clutter, and makes the workhorse part independent from idiosyncrasies of Perl calling convention. (In fact, there is nothing Perl-specific in the above description, a different version of **xsubpp** might have translated this to TCL glue or Python glue as well.)
###
More about XSUB arguments
With the completion of Example 4, we now have an easy way to simulate some real-life libraries whose interfaces may not be the cleanest in the world. We shall now continue with a discussion of the arguments passed to the **xsubpp** compiler.
When you specify arguments to routines in the .xs file, you are really passing three pieces of information for each argument listed. The first piece is the order of that argument relative to the others (first, second, etc). The second is the type of argument, and consists of the type declaration of the argument (e.g., int, char\*, etc). The third piece is the calling convention for the argument in the call to the library function.
While Perl passes arguments to functions by reference, C passes arguments by value; to implement a C function which modifies data of one of the "arguments", the actual argument of this C function would be a pointer to the data. Thus two C functions with declarations
```
int string_length(char *s);
int upper_case_char(char *cp);
```
may have completely different semantics: the first one may inspect an array of chars pointed by s, and the second one may immediately dereference `cp` and manipulate `*cp` only (using the return value as, say, a success indicator). From Perl one would use these functions in a completely different manner.
One conveys this info to **xsubpp** by replacing `*` before the argument by `&`. `&` means that the argument should be passed to a library function by its address. The above two function may be XSUB-ified as
```
int
string_length(s)
char * s
int
upper_case_char(cp)
char &cp
```
For example, consider:
```
int
foo(a,b)
char &a
char * b
```
The first Perl argument to this function would be treated as a char and assigned to the variable a, and its address would be passed into the function foo. The second Perl argument would be treated as a string pointer and assigned to the variable b. The *value* of b would be passed into the function foo. The actual call to the function foo that **xsubpp** generates would look like this:
```
foo(&a, b);
```
**xsubpp** will parse the following function argument lists identically:
```
char &a
char&a
char & a
```
However, to help ease understanding, it is suggested that you place a "&" next to the variable name and away from the variable type), and place a "\*" near the variable type, but away from the variable name (as in the call to foo above). By doing so, it is easy to understand exactly what will be passed to the C function; it will be whatever is in the "last column".
You should take great pains to try to pass the function the type of variable it wants, when possible. It will save you a lot of trouble in the long run.
###
The Argument Stack
If we look at any of the C code generated by any of the examples except example 1, you will notice a number of references to ST(n), where n is usually 0. "ST" is actually a macro that points to the n'th argument on the argument stack. ST(0) is thus the first argument on the stack and therefore the first argument passed to the XSUB, ST(1) is the second argument, and so on.
When you list the arguments to the XSUB in the .xs file, that tells **xsubpp** which argument corresponds to which of the argument stack (i.e., the first one listed is the first argument, and so on). You invite disaster if you do not list them in the same order as the function expects them.
The actual values on the argument stack are pointers to the values passed in. When an argument is listed as being an OUTPUT value, its corresponding value on the stack (i.e., ST(0) if it was the first argument) is changed. You can verify this by looking at the C code generated for Example 3. The code for the round() XSUB routine contains lines that look like this:
```
double arg = (double)SvNV(ST(0));
/* Round the contents of the variable arg */
sv_setnv(ST(0), (double)arg);
```
The arg variable is initially set by taking the value from ST(0), then is stored back into ST(0) at the end of the routine.
XSUBs are also allowed to return lists, not just scalars. This must be done by manipulating stack values ST(0), ST(1), etc, in a subtly different way. See <perlxs> for details.
XSUBs are also allowed to avoid automatic conversion of Perl function arguments to C function arguments. See <perlxs> for details. Some people prefer manual conversion by inspecting `ST(i)` even in the cases when automatic conversion will do, arguing that this makes the logic of an XSUB call clearer. Compare with ["Getting the fat out of XSUBs"](#Getting-the-fat-out-of-XSUBs) for a similar tradeoff of a complete separation of "Perl glue" and "workhorse" parts of an XSUB.
While experts may argue about these idioms, a novice to Perl guts may prefer a way which is as little Perl-guts-specific as possible, meaning automatic conversion and automatic call generation, as in ["Getting the fat out of XSUBs"](#Getting-the-fat-out-of-XSUBs). This approach has the additional benefit of protecting the XSUB writer from future changes to the Perl API.
###
Extending your Extension
Sometimes you might want to provide some extra methods or subroutines to assist in making the interface between Perl and your extension simpler or easier to understand. These routines should live in the .pm file. Whether they are automatically loaded when the extension itself is loaded or only loaded when called depends on where in the .pm file the subroutine definition is placed. You can also consult [AutoLoader](autoloader) for an alternate way to store and load your extra subroutines.
###
Documenting your Extension
There is absolutely no excuse for not documenting your extension. Documentation belongs in the .pm file. This file will be fed to pod2man, and the embedded documentation will be converted to the manpage format, then placed in the blib directory. It will be copied to Perl's manpage directory when the extension is installed.
You may intersperse documentation and Perl code within the .pm file. In fact, if you want to use method autoloading, you must do this, as the comment inside the .pm file explains.
See <perlpod> for more information about the pod format.
###
Installing your Extension
Once your extension is complete and passes all its tests, installing it is quite simple: you simply run "make install". You will either need to have write permission into the directories where Perl is installed, or ask your system administrator to run the make for you.
Alternately, you can specify the exact directory to place the extension's files by placing a "PREFIX=/destination/directory" after the make install (or in between the make and install if you have a brain-dead version of make). This can be very useful if you are building an extension that will eventually be distributed to multiple systems. You can then just archive the files in the destination directory and distribute them to your destination systems.
###
EXAMPLE 5
In this example, we'll do some more work with the argument stack. The previous examples have all returned only a single value. We'll now create an extension that returns an array.
This extension is very Unix-oriented (struct statfs and the statfs system call). If you are not running on a Unix system, you can substitute for statfs any other function that returns multiple values, you can hard-code values to be returned to the caller (although this will be a bit harder to test the error case), or you can simply not do this example. If you change the XSUB, be sure to fix the test cases to match the changes.
Return to the Mytest directory and add the following code to the end of Mytest.xs:
```
void
statfs(path)
char * path
INIT:
int i;
struct statfs buf;
PPCODE:
i = statfs(path, &buf);
if (i == 0) {
XPUSHs(sv_2mortal(newSVnv(buf.f_bavail)));
XPUSHs(sv_2mortal(newSVnv(buf.f_bfree)));
XPUSHs(sv_2mortal(newSVnv(buf.f_blocks)));
XPUSHs(sv_2mortal(newSVnv(buf.f_bsize)));
XPUSHs(sv_2mortal(newSVnv(buf.f_ffree)));
XPUSHs(sv_2mortal(newSVnv(buf.f_files)));
XPUSHs(sv_2mortal(newSVnv(buf.f_type)));
} else {
XPUSHs(sv_2mortal(newSVnv(errno)));
}
```
You'll also need to add the following code to the top of the .xs file, just after the include of "XSUB.h":
```
#include <sys/vfs.h>
```
Also add the following code segment to Mytest.t while incrementing the "9" tests to "11":
```
my @a;
@a = Mytest::statfs("/blech");
ok( scalar(@a) == 1 && $a[0] == 2 );
@a = Mytest::statfs("/");
is( scalar(@a), 7 );
```
###
New Things in this Example
This example added quite a few new concepts. We'll take them one at a time.
* The INIT: directive contains code that will be placed immediately after the argument stack is decoded. C does not allow variable declarations at arbitrary locations inside a function, so this is usually the best way to declare local variables needed by the XSUB. (Alternatively, one could put the whole `PPCODE:` section into braces, and put these declarations on top.)
* This routine also returns a different number of arguments depending on the success or failure of the call to statfs. If there is an error, the error number is returned as a single-element array. If the call is successful, then a 7-element array is returned. Since only one argument is passed into this function, we need room on the stack to hold the 7 values which may be returned.
We do this by using the PPCODE: directive, rather than the CODE: directive. This tells **xsubpp** that we will be managing the return values that will be put on the argument stack by ourselves.
* When we want to place values to be returned to the caller onto the stack, we use the series of macros that begin with "XPUSH". There are five different versions, for placing integers, unsigned integers, doubles, strings, and Perl scalars on the stack. In our example, we placed a Perl scalar onto the stack. (In fact this is the only macro which can be used to return multiple values.)
The XPUSH\* macros will automatically extend the return stack to prevent it from being overrun. You push values onto the stack in the order you want them seen by the calling program.
* The values pushed onto the return stack of the XSUB are actually mortal SV's. They are made mortal so that once the values are copied by the calling program, the SV's that held the returned values can be deallocated. If they were not mortal, then they would continue to exist after the XSUB routine returned, but would not be accessible. This is a memory leak.
* If we were interested in performance, not in code compactness, in the success branch we would not use `XPUSHs` macros, but `PUSHs` macros, and would pre-extend the stack before pushing the return values:
```
EXTEND(SP, 7);
```
The tradeoff is that one needs to calculate the number of return values in advance (though overextending the stack will not typically hurt anything but memory consumption).
Similarly, in the failure branch we could use `PUSHs` *without* extending the stack: the Perl function reference comes to an XSUB on the stack, thus the stack is *always* large enough to take one return value.
###
EXAMPLE 6
In this example, we will accept a reference to an array as an input parameter, and return a reference to an array of hashes. This will demonstrate manipulation of complex Perl data types from an XSUB.
This extension is somewhat contrived. It is based on the code in the previous example. It calls the statfs function multiple times, accepting a reference to an array of filenames as input, and returning a reference to an array of hashes containing the data for each of the filesystems.
Return to the Mytest directory and add the following code to the end of Mytest.xs:
```
SV *
multi_statfs(paths)
SV * paths
INIT:
AV * results;
SSize_t numpaths = 0, n;
int i;
struct statfs buf;
SvGETMAGIC(paths);
if ((!SvROK(paths))
|| (SvTYPE(SvRV(paths)) != SVt_PVAV)
|| ((numpaths = av_top_index((AV *)SvRV(paths))) < 0))
{
XSRETURN_UNDEF;
}
results = (AV *)sv_2mortal((SV *)newAV());
CODE:
for (n = 0; n <= numpaths; n++) {
HV * rh;
STRLEN l;
SV * path = *av_fetch((AV *)SvRV(paths), n, 0);
char * fn = SvPVbyte(path, l);
i = statfs(fn, &buf);
if (i != 0) {
av_push(results, newSVnv(errno));
continue;
}
rh = (HV *)sv_2mortal((SV *)newHV());
hv_store(rh, "f_bavail", 8, newSVnv(buf.f_bavail), 0);
hv_store(rh, "f_bfree", 7, newSVnv(buf.f_bfree), 0);
hv_store(rh, "f_blocks", 8, newSVnv(buf.f_blocks), 0);
hv_store(rh, "f_bsize", 7, newSVnv(buf.f_bsize), 0);
hv_store(rh, "f_ffree", 7, newSVnv(buf.f_ffree), 0);
hv_store(rh, "f_files", 7, newSVnv(buf.f_files), 0);
hv_store(rh, "f_type", 6, newSVnv(buf.f_type), 0);
av_push(results, newRV_inc((SV *)rh));
}
RETVAL = newRV_inc((SV *)results);
OUTPUT:
RETVAL
```
And add the following code to Mytest.t, while incrementing the "11" tests to "13":
```
my $results = Mytest::multi_statfs([ '/', '/blech' ]);
ok( ref $results->[0] );
ok( ! ref $results->[1] );
```
###
New Things in this Example
There are a number of new concepts introduced here, described below:
* This function does not use a typemap. Instead, we declare it as accepting one SV\* (scalar) parameter, and returning an SV\* value, and we take care of populating these scalars within the code. Because we are only returning one value, we don't need a `PPCODE:` directive - instead, we use `CODE:` and `OUTPUT:` directives.
* When dealing with references, it is important to handle them with caution. The `INIT:` block first calls SvGETMAGIC(paths), in case paths is a tied variable. Then it checks that `SvROK` returns true, which indicates that paths is a valid reference. (Simply checking `SvROK` won't trigger FETCH on a tied variable.) It then verifies that the object referenced by paths is an array, using `SvRV` to dereference paths, and `SvTYPE` to discover its type. As an added test, it checks that the array referenced by paths is non-empty, using the `av_top_index` function (which returns -1 if the array is empty). The XSRETURN\_UNDEF macro is used to abort the XSUB and return the undefined value whenever all three of these conditions are not met.
* We manipulate several arrays in this XSUB. Note that an array is represented internally by an AV\* pointer. The functions and macros for manipulating arrays are similar to the functions in Perl: `av_top_index` returns the highest index in an AV\*, much like $#array; `av_fetch` fetches a single scalar value from an array, given its index; `av_push` pushes a scalar value onto the end of the array, automatically extending the array as necessary.
Specifically, we read pathnames one at a time from the input array, and store the results in an output array (results) in the same order. If statfs fails, the element pushed onto the return array is the value of errno after the failure. If statfs succeeds, though, the value pushed onto the return array is a reference to a hash containing some of the information in the statfs structure.
As with the return stack, it would be possible (and a small performance win) to pre-extend the return array before pushing data into it, since we know how many elements we will return:
```
av_extend(results, numpaths);
```
* We are performing only one hash operation in this function, which is storing a new scalar under a key using `hv_store`. A hash is represented by an HV\* pointer. Like arrays, the functions for manipulating hashes from an XSUB mirror the functionality available from Perl. See <perlguts> and <perlapi> for details.
* To create a reference, we use the `newRV_inc` function. Note that you can cast an AV\* or an HV\* to type SV\* in this case (and many others). This allows you to take references to arrays, hashes and scalars with the same function. Conversely, the `SvRV` function always returns an SV\*, which may need to be cast to the appropriate type if it is something other than a scalar (check with `SvTYPE`).
* At this point, xsubpp is doing very little work - the differences between Mytest.xs and Mytest.c are minimal.
###
EXAMPLE 7 (Coming Soon)
XPUSH args AND set RETVAL AND assign return value to array
###
EXAMPLE 8 (Coming Soon)
Setting $!
###
EXAMPLE 9 Passing open files to XSes
You would think passing files to an XS is difficult, with all the typeglobs and stuff. Well, it isn't.
Suppose that for some strange reason we need a wrapper around the standard C library function `fputs()`. This is all we need:
```
#define PERLIO_NOT_STDIO 0 /* For co-existence with stdio only */
#define PERL_NO_GET_CONTEXT /* This is more efficient */
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include <stdio.h>
int
fputs(s, stream)
char * s
FILE * stream
```
The real work is done in the standard typemap.
For more details, see ["Co-existence with stdio" in perlapio](perlapio#Co-existence-with-stdio).
**But** you lose all the fine stuff done by the perlio layers. This calls the stdio function `fputs()`, which knows nothing about them.
The standard typemap offers three variants of PerlIO \*: `InputStream` (T\_IN), `InOutStream` (T\_INOUT) and `OutputStream` (T\_OUT). A bare `PerlIO *` is considered a T\_INOUT. If it matters in your code (see below for why it might) #define or typedef one of the specific names and use that as the argument or result type in your XS file.
The standard typemap does not contain PerlIO \* before perl 5.7, but it has the three stream variants. Using a PerlIO \* directly is not backwards compatible unless you provide your own typemap.
For streams coming *from* perl the main difference is that `OutputStream` will get the output PerlIO \* - which may make a difference on a socket. Like in our example...
For streams being handed *to* perl a new file handle is created (i.e. a reference to a new glob) and associated with the PerlIO \* provided. If the read/write state of the PerlIO \* is not correct then you may get errors or warnings from when the file handle is used. So if you opened the PerlIO \* as "w" it should really be an `OutputStream` if open as "r" it should be an `InputStream`.
Now, suppose you want to use perlio layers in your XS. We'll use the perlio `PerlIO_puts()` function as an example.
In the C part of the XS file (above the first MODULE line) you have
```
#define OutputStream PerlIO *
or
typedef PerlIO * OutputStream;
```
And this is the XS code:
```
int
perlioputs(s, stream)
char * s
OutputStream stream
CODE:
RETVAL = PerlIO_puts(stream, s);
OUTPUT:
RETVAL
```
We have to use a `CODE` section because `PerlIO_puts()` has the arguments reversed compared to `fputs()`, and we want to keep the arguments the same.
Wanting to explore this thoroughly, we want to use the stdio `fputs()` on a PerlIO \*. This means we have to ask the perlio system for a stdio `FILE *`:
```
int
perliofputs(s, stream)
char * s
OutputStream stream
PREINIT:
FILE *fp = PerlIO_findFILE(stream);
CODE:
if (fp != (FILE*) 0) {
RETVAL = fputs(s, fp);
} else {
RETVAL = -1;
}
OUTPUT:
RETVAL
```
Note: `PerlIO_findFILE()` will search the layers for a stdio layer. If it can't find one, it will call `PerlIO_exportFILE()` to generate a new stdio `FILE`. Please only call `PerlIO_exportFILE()` if you want a *new* `FILE`. It will generate one on each call and push a new stdio layer. So don't call it repeatedly on the same file. `PerlIO_findFILE()` will retrieve the stdio layer once it has been generated by `PerlIO_exportFILE()`.
This applies to the perlio system only. For versions before 5.7, `PerlIO_exportFILE()` is equivalent to `PerlIO_findFILE()`.
###
Troubleshooting these Examples
As mentioned at the top of this document, if you are having problems with these example extensions, you might see if any of these help you.
* In versions of 5.002 prior to the gamma version, the test script in Example 1 will not function properly. You need to change the "use lib" line to read:
```
use lib './blib';
```
* In versions of 5.002 prior to version 5.002b1h, the test.pl file was not automatically created by h2xs. This means that you cannot say "make test" to run the test script. You will need to add the following line before the "use extension" statement:
```
use lib './blib';
```
* In versions 5.000 and 5.001, instead of using the above line, you will need to use the following line:
```
BEGIN { unshift(@INC, "./blib") }
```
* This document assumes that the executable named "perl" is Perl version 5. Some systems may have installed Perl version 5 as "perl5".
See also
---------
For more information, consult <perlguts>, <perlapi>, <perlxs>, <perlmod>, <perlapio>, and <perlpod>
Author
------
Jeff Okamoto <*[email protected]*>
Reviewed and assisted by Dean Roehrich, Ilya Zakharevich, Andreas Koenig, and Tim Bunce.
PerlIO material contributed by Lupe Christoph, with some clarification by Nick Ing-Simmons.
Changes for h2xs as of Perl 5.8.x by Renee Baecker
This document is now maintained as part of Perl itself.
###
Last Changed
2020-10-05
| programming_docs |
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