Clone/Copy an Array in JavaScript and Node.js

You’re naturally in the needs of handy utilities when working with JavaScript handling arrays. Modern JavaScript frameworks —especially the frontend frameworks— abstract most of the DOM interaction. You’re focusing on the actual logic and implement the data handling.

When implementing the logic, a handy utility related to JavaScript arrays is the ability to clone arrays. This tutorial shows you two ways using native array methods:

  • Array#slice
  • Array#concat

Node.js Series Overview

  1. Get Number of Seconds Since Epoch in JavaScript
  2. Get Tomorrow’s Date in JavaScript (Coming soon)
  3. Increase a Date in JavaScript by One Week (Coming soon)

Clone an Array in JavaScript

You don’t need to iterate over the original array and push each item into another array. Cloning arrays in JavaScript is as straightforward as slice or concat.

Calling .slice on the original array clones the array:

const original = [1, 2, 3]  
const clone = original.slice()  

Please notice, slice creates a shallow clone, not a deep clone.

If you only want to clone a slice of the original array, you may pass the starting index as an argument to slice:

const original = [1, 2, 3]  
const clone = original.slice(1)

// clone = [2, 3]

You may also use the Array#concat method for cloning:

const original = [1, 2, 3]  
const clone = [].concat(original)  

concat combines the two arrays and creates a new one.

Which One Should You Use?

Personally, I prefer concat over slice because my brain quickly understands what the method call does. When I see slice in my code, I need to stop for a second and remember what this method does. For me, concat is more intuitive. Choose what you like best 😃

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