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const copyProperty = (to, from, property, ignoreNonConfigurable) => {
// `Function#length` should reflect the parameters of `to` not `from` since we keep its body.
// `Function#prototype` is non-writable and non-configurable so can never be modified.
if (property === 'length' || property === 'prototype') {
return;
}
// `Function#arguments` and `Function#caller` should not be copied. They were reported to be present in `Reflect.ownKeys` for some devices in React Native (#41), so we explicitly ignore them here.
if (property === 'arguments' || property === 'caller') {
return;
}
const toDescriptor = Object.getOwnPropertyDescriptor(to, property);
const fromDescriptor = Object.getOwnPropertyDescriptor(from, property);
if (!canCopyProperty(toDescriptor, fromDescriptor) && ignoreNonConfigurable) {
return;
}
Object.defineProperty(to, property, fromDescriptor);
};
// `Object.defineProperty()` throws if the property exists, is not configurable and either:
// - one its descriptors is changed
// - it is non-writable and its value is changed
const canCopyProperty = function (toDescriptor, fromDescriptor) {
return toDescriptor === undefined || toDescriptor.configurable || (
toDescriptor.writable === fromDescriptor.writable &&
toDescriptor.enumerable === fromDescriptor.enumerable &&
toDescriptor.configurable === fromDescriptor.configurable &&
(toDescriptor.writable || toDescriptor.value === fromDescriptor.value)
);
};
const changePrototype = (to, from) => {
const fromPrototype = Object.getPrototypeOf(from);
if (fromPrototype === Object.getPrototypeOf(to)) {
return;
}
Object.setPrototypeOf(to, fromPrototype);
};
const wrappedToString = (withName, fromBody) => `/* Wrapped ${withName}*/\n${fromBody}`;
const toStringDescriptor = Object.getOwnPropertyDescriptor(Function.prototype, 'toString');
const toStringName = Object.getOwnPropertyDescriptor(Function.prototype.toString, 'name');
// We call `from.toString()` early (not lazily) to ensure `from` can be garbage collected.
// We use `bind()` instead of a closure for the same reason.
// Calling `from.toString()` early also allows caching it in case `to.toString()` is called several times.
const changeToString = (to, from, name) => {
const withName = name === '' ? '' : `with ${name.trim()}() `;
const newToString = wrappedToString.bind(null, withName, from.toString());
// Ensure `to.toString.toString` is non-enumerable and has the same `same`
Object.defineProperty(newToString, 'name', toStringName);
Object.defineProperty(to, 'toString', {...toStringDescriptor, value: newToString});
};
export default function mimicFunction(to, from, {ignoreNonConfigurable = false} = {}) {
const {name} = to;
for (const property of Reflect.ownKeys(from)) {
copyProperty(to, from, property, ignoreNonConfigurable);
}
changePrototype(to, from);
changeToString(to, from, name);
return to;
}
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