Remove duplicated array items in JavaScript

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Hello Coders! 👋 😊

In this short article, I would like to show you how to remove duplicated items from an array in JavaScript.

Quick solution

In this quick solution, I've used the built-in filter() function which has been added to improve functional programming.

If an index with the same value is found on another position, it won't be saved (in other words, it saves only those that occurred for the first time, it does not take into account the next ones).

Runnable example:

// ONLINE-RUNNER:browser;

const array = [1, 2, 3, 1, 1, 2, 2, 3, 3];
const result = array.filter((item, index, array) => array.indexOf(item) === index);

console.log(JSON.stringify(result)); // [1,2,3]

Iterative example

In this approach, I've used a blocker object that represents a map of elements that have already occurred. The for loop iterates only once over all elements adding to this map and if an element has already appeared, it won't add it again.

This solution is more optimal because it has lower computational complexity. 📉✅

Runnable example:

// ONLINE-RUNNER:browser;

const removeDuplicates = (array) => {
  	const result = [];
	const blocker = {}; // prevents against item duplication
  	for (const item of array) {
    	if (blocker.hasOwnProperty(item)) {
      	blocker[item] = true;
  	return result;

// Usage example:

const array = [1, 2, 3, 1, 1, 2, 2, 3, 3];
const uniqueItems = removeDuplicates(array);

console.log(JSON.stringify(uniqueItems)); // [1,2,3]

Set based example

By conversion from Array to Set and back we are able to remove duplicated items too.

// ONLINE-RUNNER:browser;

const array = [1, 2, 3, 1, 1, 2, 2, 3, 3];

const set = new Set(array);
const uniqueItems = Array.from(set);

console.log(JSON.stringify(uniqueItems)); // [1,2,3]


Thank you for your time! I hope you like the solutions. 😊

 See you in upcoming posts! 🔥🔜


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