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ChaiJS 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.

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!



deep-eql is available on npm.

$ npm install deep-eql


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.


  • Strict equality for non-traversable nodes according to
    • eql(NaN, NaN);
    • eql(-0, +0);
  • All own and inherited enumerable properties are considered:
    • eql(Object.create({ foo: { a: 1 } }), Object.create({ foo: { a: 1 } }));
    • eql(Object.create({ foo: { a: 1 } }), Object.create({ foo: { a: 2 } }));
  • Arguments are not Arrays:
    • eql([], arguments);
    • eql([],;
  • Error objects are compared by reference (see
    • eql(new Error('msg'), new Error('msg'));
    • var err = new Error('msg'); eql(err, err);