JavaScript - copy array

In this article, we would like to show you how to copy an array in JavaScript.

Quick solution:

const array = [1, 2, 3];
const copy = array.slice();  // <----- solution

Problem overview

In JavaScript, when the same object is assigned to different variable, reference is used. This way many variables may indicate the same object in the memory. So, making modification on one that varible we see changes on next one. That makes necessary to use some technique to make object copy, what was presented in next sections.

Problem example:

// ONLINE-RUNNER:browser;

const array1 = [1, 2, 3];
const array2 = array1;

array2[1] = 'value';

console.log(array1);  // [1, 'value', 3]  // array1 variable indicates to the same object like array2 variable
console.log(array2);  // [1, 'value', 3]

Possible solutions

1. Array slice() method

// ONLINE-RUNNER:browser;

const array = [1, 2, 3];
const copy = array.slice();  // <----- solution

console.log(copy);  // [1, 2, 3]

2. Spread operator example

// ONLINE-RUNNER:browser;

const array = [1, 2, 3];
const copy = [...array];  // <----- solution

console.log(copy);  // [1, 2, 3]

3. Array from() method

// ONLINE-RUNNER:browser;

const array = [1, 2, 3];
const copy = Array.from(array);  // <----- solution

console.log(copy);  // [1, 2, 3]

4. Array map() method

// ONLINE-RUNNER:browser;

const array = [1, 2, 3];
const copy = array.map(x => x);  // <----- solution

console.log(copy);  // [1, 2, 3]

5. Array concat() method

// ONLINE-RUNNER:browser;

const array = [1, 2, 3];
const copy = [].concat(array);  // <----- solution

console.log(copy);  // [1, 2, 3]