How to Deep Copy an Array in JavaScript

Jun 23, 2021

When you copy an object in JavaScript, you can either create a deep copy or a shallow copy. The benefit of a deep copy is that it copies nested objects, so you can modify the cloned array without affecting the original array. The only problem is that you either need a library like Lodash, or will need to use a combination of JSON.stringify() and JSON.parse().


Lodash's cloneDeep(value) function will deep copy the array for you.

const objects = [{ 'a': 1 }, { 'b': 2 }];

const deep = _.cloneDeep(objects);
deep[0] === objects[0]; // returns false

deep[0].a = 2;
objects[0].a; // 1, didn't change

Lodash's cloneDeep() does a good job of handling edge cases, like cloning dates:

const objects = [{ createdAt: new Date('2017-06-01') }];

const deep = _.cloneDeep(objects);

deep[0].createdAt === objects[0].createdAt; // false
deep[0].createdAt instanceof Date; // true
objects[0].createdAt instanceof Date; // true

JSON.stringify() and JSON.parse()

This combination of functions does get the job done but is not perfect.

const obj = { name: { first: 'Jean-Luc', last: 'Picard' } };
const copy = JSON.parse(JSON.stringify(obj)); = 'Johnny';; // Jean-Luc

Note: This approach only works on objects containing the following JavaScript primitives:

If the object you want to copy contains a date, for example, it could lead to some problems later on:

const obj = { date: new Date() };
const copy = JSON.parse(JSON.stringify(obj)); instanceof Date; // true Date; // false, date is now a string

More Fundamentals Tutorials