What Is Set Data Structure in JavaScript?


Larry Thompson

In JavaScript, the Set data structure is a built-in object that allows you to store unique values of any type. It was introduced in ECMAScript 2015 (ES6) and provides a simple and efficient way to manage collections of data without any duplicates. Sets can be used to solve various problems and are particularly useful when dealing with lists or arrays that need to maintain uniqueness.

Creating a Set

To create a new Set object, you can use the new Set() constructor. You can pass an iterable object such as an array or a string as an argument to the constructor, or create an empty Set.

// Creating an empty set
const mySet = new Set();

// Creating a set from an array
const myArray = ['apple', 'banana', 'orange', 'apple'];
const mySet = new Set(myArray);

// Creating a set from a string
const myString = 'hello';
const mySet = new Set(myString);

Adding and Removing Elements

You can add elements to a Set using the add() method:

// Adding elements to the set

The add() method returns the updated Set, allowing you to chain multiple add() calls together.

To remove elements from a Set, you can use the delete() method:

// Removing an element from the set

The delete() method returns true if the element existed in the Set and has been successfully removed, and false otherwise.

Checking for the Existence of Elements

You can use the has() method to check if an element exists in a Set:

// Checking if an element exists
mySet.has('apple'); // Returns true
mySet.has('kiwi'); // Returns false

Getting the Size of a Set

The size property returns the number of elements in a Set:

// Getting the size of a set
mySet.size; // Returns 3

Iterating Over a Set

You can use various methods to iterate over the elements of a Set, such as:

  • forEach(): Invokes a callback function for each element in insertion order.
  • for..of: Allows you to loop over the values in insertion order.
  • entries(): Returns an iterator object that contains arrays of [value, value] pairs for each element.
// Using forEach() to iterate over a set
mySet.forEach((value) => {

// Using for.of to iterate over a set
for (const value of mySet) {

// Using entries() to iterate over a set and get [value, value] pairs
for (const entry of mySet.entries()) {
  console.log(entry[0], entry[1]);

Converting a Set to an Array

If you need to convert a Set to an array, you can use the Array.from() method or the spread operator:

// Converting a set to an array using Array.from()
const myArray = Array.from(mySet);

// Converting a set to an array using the spread operator
const myArray = [.mySet];

This allows you to take advantage of array methods and perform operations that are not available on Sets.


The Set data structure in JavaScript provides an efficient way to store unique values. It offers methods for adding, removing, and checking for the existence of elements.

Additionally, Sets can be easily converted to arrays when needed. Understanding how Sets work can greatly enhance your ability to manage collections of data effectively in JavaScript.

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