Improved deep equality testing for node and the browser.
## What is Deep-Eql?
Deep Eql is a module which you can use to determine if two objects are "deeply" equal - that is, rather than having referential equality (`a === b`), this module checks an object's keys recursively, until it finds primitives to check for referential equality. For more on equality in JavaScript, read [the comparison operators article on mdn](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators).
As an example, take the following:
```js
1 === 1 // These are primitives, they hold the same reference - they are strictly equal
1 == '1' // These are two different primitives, through type coercion they hold the same value - they are loosely equal
{ a: 1 } !== { a: 1 } // These are two different objects, they hold different references and so are not strictly equal - even though they hold the same values inside
{ a: 1 } != { a: 1 } // They have the same type, meaning loose equality performs the same check as strict equality - they are still not equal.
var deepEql = require("deep-eql");
deepEql({ a: 1 }, { a: 1 }) === true // deepEql can determine that they share the same keys and those keys share the same values, therefore they are deeply equal!
```
## Installation
### Node.js
`deep-eql` is available on [npm](http://npmjs.org).
$ npm install deep-eql
## Usage
The primary export of `deep-eql` is function that can be given two objects to compare. It will always return a boolean which can be used to determine if two objects are deeply equal.
### Rules
- Strict equality for non-traversable nodes according to [`Object.is`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is):
- `eql(NaN, NaN).should.be.true;`
- `eql(-0, +0).should.be.false;`
- All own and inherited enumerable properties are considered:
- `eql(Object.create({ foo: { a: 1 } }), Object.create({ foo: { a: 1 } })).should.be.true;`
- `eql(Object.create({ foo: { a: 1 } }), Object.create({ foo: { a: 2 } })).should.be.false;`
- When comparing `Error` objects, only `name`, `message`, and `code` properties are considered, regardless of enumerability:
- `eql(Error('foo'), Error('foo')).should.be.true;`
- `eql(Error('foo'), Error('bar')).should.be.false;`
- `eql(Error('foo'), TypeError('foo')).should.be.false;`
- `eql(Object.assign(Error('foo'), { code: 42 }), Object.assign(Error('foo'), { code: 42 })).should.be.true;`
- `eql(Object.assign(Error('foo'), { code: 42 }), Object.assign(Error('foo'), { code: 13 })).should.be.false;`
- `eql(Object.assign(Error('foo'), { otherProp: 42 }), Object.assign(Error('foo'), { otherProp: 13 })).should.be.true;`
- Arguments are not Arrays:
- `eql([], arguments).should.be.false;`
- `eql([], Array.prototype.slice.call(arguments)).should.be.true;`