How to Create a Set in JavaScript: Syntax and Examples

In JavaScript, you create a set using the Set constructor like new Set(). A set stores unique values, so duplicates are automatically removed.

Syntax

The basic syntax to create a set is using the Set constructor. You can create an empty set or initialize it with an array of values.

• new Set(): creates an empty set.
• new Set(iterable): creates a set with unique values from the iterable (like an array).

javascript

const emptySet = new Set();
const numberSet = new Set([1, 2, 3, 2]);

Example

This example shows how to create a set, add values, and see that duplicates are removed automatically.

javascript

const fruits = new Set(['apple', 'banana', 'apple', 'orange']);
console.log(fruits);
console.log(fruits.has('banana'));
fruits.add('grape');
console.log([...fruits]);

Output

Set(3) { 'apple', 'banana', 'orange' }
true
[ 'apple', 'banana', 'orange', 'grape' ]

Common Pitfalls

Common mistakes include trying to create a set without new, or expecting sets to keep duplicate values.

Also, sets compare objects by reference, so two different objects with the same content are treated as different.

javascript

/* Wrong: missing 'new' keyword */
// const mySet = Set([1, 2, 3]); // This throws an error

/* Right: use 'new' */
const mySet = new Set([1, 2, 3]);

/* Objects in sets */
const obj1 = {a: 1};
const obj2 = {a: 1};
const objSet = new Set([obj1, obj2]);
console.log(objSet.size); // 2 because obj1 and obj2 are different objects

Output

2

Quick Reference

• Create empty set: new Set()
• Create set with values: new Set([values])
• Add value: set.add(value)
• Check value: set.has(value)
• Remove value: set.delete(value)
• Clear all: set.clear()

Key Takeaways

Use new Set() to create a set in JavaScript.

Sets store only unique values; duplicates are automatically removed.

Always use the new keyword when creating a set.

Sets compare objects by reference, not by content.

Use add, has, and delete methods to manage set items.