deep-eql

Improved deep equality testing for node and the browser.

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## 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;`