JavaScript Set is a collection of items that are unique, meaning no element can be repeated. Elements of the set can be iterated in the insertion order. A Set can store any type of value, whether primitive or objects.

Syntax

new Set()

Example: This example will show the use of Set() constructor.

const mySet = new Set();

mySet.add("California");
mySet.add("India");
mySet.add("California");
mySet.add(10);
mySet.add(10);

const myObject = { a: 1, a: 5 };

mySet.add(myObject);

console.log(mySet);

Output:

Set(4) { 'California', 'India', 10, { a: 5 } }

The complete list of JavaScript Set has listed below:

JavaScript Set Constructor

A constructor is called when an object is created using the new keyword.

JavaScript Set Properties

 A JavaScript property is a member of an object that associates a key with a value.

Instance Property

An instance property is a property that has a new copy for every new instance of the class.

JavaScript Set Methods

Methods are actions that can be performed on objects.

Instance Method

If the method is called on an instance of a Set then it is called an instance method.

Comparison with JavaScript Arrays

• Uniqueness: Sets ensure all values are unique, whereas arrays can have duplicate values.
• Performance: Sets provide better performance for membership testing and uniqueness checks.

Examples and Use Cases

1. Creating a Set

Creating a Set and adding elements to the set.

const set1 = new Set(['apple', 'banana', 'cherry']);
console.log(set1);

Set(3) { 'apple', 'banana', 'cherry' }

2. Adding and Deleting Elements

Adding new elements and Deleting the elements.

const set2 = new Set();
set2.add(1);
set2.add(5);
set2.add(5); // Duplicate element will not be added
set2.add('Hello');
console.log(set2); 
set2.delete(5);
console.log(set2);

Set(3) { 1, 5, 'Hello' }
Set(2) { 1, 'Hello' }

3. Checking for Element Existence

Checking for already existing elements.

const set3 = new Set(['a', 'b', 'c']);
console.log(set3.has('a'));
console.log(set3.has('z'));

true
false

4. Iterating Over a Set

Iterating over the set and printing one by one.

const set4 = new Set([1, 2, 3, 4]);
for (let item of set4) {
  console.log(item);
}

1
2
3
4

5. Removing Duplicates

Removing the duplicate elements from the array using set.

const numbers = [1, 2, 2, 3, 4, 4, 5];
const uniqueNumbers = [...new Set(numbers)];
console.log(uniqueNumbers);