deep-eql

What is deep-eql?

The deep-eql package is a deep equality testing library that allows developers to compare two values for structural equality, rather than just reference equality. It is useful for testing and assertions when you need to ensure that two complex objects, arrays, or other nested structures are equivalent in content.

What are deep-eql's main functionalities?

Deep Equality Check

This feature allows you to check if two objects are deeply equal, meaning their structure and nested values are equivalent.

const deepEql = require('deep-eql');
const obj1 = { a: 1, b: { c: 2 } };
const obj2 = { a: 1, b: { c: 2 } };
console.log(deepEql(obj1, obj2)); // true

Custom Type Comparisons

This feature allows you to provide a custom comparator function to define equality for specific types or instances.

const deepEql = require('deep-eql');
class Person {
  constructor(name) {
    this.name = name;
  }
}
const person1 = new Person('Alice');
const person2 = new Person('Alice');
console.log(deepEql(person1, person2, { comparator: (a, b) => a.name === b.name })); // true

Other packages similar to deep-eql

lodash.isequal

Lodash's isEqual function performs a deep comparison between two values to determine if they are equivalent. It is similar to deep-eql but is part of the larger Lodash utility library, which offers a wide range of functions for manipulating and comparing data.

chai

Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any javascript testing framework. It includes a deep equality assertion, similar to deep-eql, as part of its extensive assertion library.

deep-equal

This package provides a function for deep equality checks, similar to deep-eql. It is a standalone library that focuses solely on deep equality without additional dependencies or utilities.

README

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.

As an example, take the following:

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.

$ 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:
  • 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;