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<h1 align=center> |
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<a href="http://chaijs.com" title="Chai Documentation"> |
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<img alt="deep-eql" src="https://raw.githubusercontent.com/chaijs/deep-eql/main/deep-eql-logo.svg"/> |
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</a> |
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</h1> |
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<p align=center> |
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Improved deep equality testing for <a href="http://nodejs.org/">node</a> and the browser. |
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</p> |
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<a href="https://github.com/chaijs/deep-eql/actions"> |
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alt="build:?" |
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src="https://github.com/chaijs/deep-eql/workflows/Build/badge.svg" |
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src="https://img.shields.io/coveralls/chaijs/deep-eql/master.svg?style=flat-square" |
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alt="Join the Slack chat" |
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</p> |
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## What is Deep-Eql? |
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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). |
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As an example, take the following: |
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```js |
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1 === 1 // These are primitives, they hold the same reference - they are strictly equal |
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1 == '1' // These are two different primitives, through type coercion they hold the same value - they are loosely equal |
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{ 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 |
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{ a: 1 } != { a: 1 } // They have the same type, meaning loose equality performs the same check as strict equality - they are still not equal. |
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var deepEql = require("deep-eql"); |
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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! |
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``` |
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## Installation |
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### Node.js |
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`deep-eql` is available on [npm](http://npmjs.org). |
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$ npm install deep-eql |
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## Usage |
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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. |
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### Rules |
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- Strict equality for non-traversable nodes according to [`Object.is`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is): |
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- `eql(NaN, NaN).should.be.true;` |
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- `eql(-0, +0).should.be.false;` |
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- All own and inherited enumerable properties are considered: |
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- `eql(Object.create({ foo: { a: 1 } }), Object.create({ foo: { a: 1 } })).should.be.true;` |
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- `eql(Object.create({ foo: { a: 1 } }), Object.create({ foo: { a: 2 } })).should.be.false;` |
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- When comparing `Error` objects, only `name`, `message`, and `code` properties are considered, regardless of enumerability: |
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- `eql(Error('foo'), Error('foo')).should.be.true;` |
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- `eql(Error('foo'), Error('bar')).should.be.false;` |
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- `eql(Error('foo'), TypeError('foo')).should.be.false;` |
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- `eql(Object.assign(Error('foo'), { code: 42 }), Object.assign(Error('foo'), { code: 42 })).should.be.true;` |
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- `eql(Object.assign(Error('foo'), { code: 42 }), Object.assign(Error('foo'), { code: 13 })).should.be.false;` |
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- `eql(Object.assign(Error('foo'), { otherProp: 42 }), Object.assign(Error('foo'), { otherProp: 13 })).should.be.true;` |
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- Arguments are not Arrays: |
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- `eql([], arguments).should.be.false;` |
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- `eql([], Array.prototype.slice.call(arguments)).should.be.true;` |
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