← flaviocopes.com

How to remove duplicates from a JavaScript array

Published Mar 12 2020

Psssst! The 2023 WEB DEVELOPMENT BOOTCAMP is starting on FEBRUARY 01, 2023! SIGNUPS ARE NOW OPEN to this 10-weeks cohort course. Learn the fundamentals, HTML, CSS, JS, Tailwind, React, Next.js and much more! ✨

Let’s say you have an array containing a series of primitive values, for example numbers or strings.

Some of those elements are repeated.

Like in this example:

const list = [1, 2, 3, 4, 4, 3]

We can generare a new array containing the same values, without the duplicates, in this way:

const uniqueList = [...new Set(list)]

uniqueList will now be a new array with the values [1, 2, 3, 4] in it.

How does this work?

Set is a new data structure, introduced in ES6 in 2015, and its main characteristic is to be a container for data that can’t be repeated in the same set. See my full guide on Set here.

By initializing a Set with a destructured array (see the ... operator before new Set()), we pass values and Set automatically removes the duplicates. Then we convert it to an array by wrapping it into square brackets [].

This method works with anything that’s not an object: numbers, strings, booleans, symbols.

I write books for developers 👇🏼

© 2023 Flavio Copes Flavio Copes made in Italy 🇮🇹 using Notion to Site Notion to Site