4 Simple Ways to Remove Duplicates From a JavaScript Array

Removing duplication is a common task when dealing with arrays in Javascript. In this tutorial, I will show you 4 dead simple ways to remove duplications in a JS array.

Now, let dive into it!

Sets

The Set object lets you store unique values of any type, whether primitive values or object references.

const cars = ['audi', 'ford', 'tesla', 'ford', 'toyota', 'audi'];

function removeDuplicates(cars) {
  return [...new Set(cars)];
}

console.log(removeDuplicates(cars));
// 👇🏽 See the output below

[ 'audi', 'ford', 'tesla', 'toyota', 'Bugatti' ]

Filter

The filter() method of Array instances creates a shallow copy* of a portion of a given array, filtered down to just the elements from the given array that pass the test implemented by the provided function.

const cars = ['audi', 'ford', 'tesla', 'ford', 'toyota', 'audi', 'Bugatti']

function removeDuplicates(cars) {
  return cars.filter((value, index) => cars.indexOf(value) === index)
}

console.log(removeDuplicates(cars))
// 👇🏽 See the output below

[ 'audi', 'ford', 'tesla', 'toyota', 'Bugatti' ]

Modifying Prototype

In JavaScript, the array prototype constructor allows you to add new properties and methods to the Array object. The Array prototype is also like a set of methods and properties that all arrays inherit. So we can create a new method that will return a new set of array items, and just call it to remove duplications in our previous array.

const cars = ['audi', 'ford', 'tesla', 'ford', 'toyota', 'audi', 'Bugatti']

Array.prototype.unique = function() {
  return Array.from(new Set(this));
}

function removeDuplicates(cars) {
  return cars.unique()
}

console.log(removeDuplicates(cars))
// 👇🏽 See the output below

[ 'audi', 'ford', 'tesla', 'toyota', 'Bugatti' ]

Lodash

_.uniq method of the lodash library produces a duplicate-free version of the array. We can also sort this array by passing the second parameter is true.

import { _ } from 'lodash' 

const cars = ['audi', 'ford', 'tesla', 'ford', 'toyota', 'audi', 'Bugatti']

function removeDuplicates(cars) {
  return _.uniq(cars)
}

console.log(removeDuplicates(cars))
// 👇🏽 See the output below

[ 'audi', 'ford', 'tesla', 'toyota', 'Bugatti' ]

🎒 More resources

Learn more about Set
Learn more about Filter
Lodash Documentation