Set.prototype.add()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The add() method of Set instances inserts the specified value into this set, if it is not already present.

Try it

const set = new Set();

set.add(42);
set.add(42);
set.add(13);

for (const item of set) {
  console.log(item);
  // Expected output: 42
  // Expected output: 13
}

Syntax

add(value)

Parameters

value

The value to add to the Set object. Objects are compared by reference, not by value.

Return value

The Set object.

Examples

Using add()

js
const mySet = new Set();

mySet.add(1);
mySet.add(5).add("some text"); // chainable

console.log(mySet);
// Set [1, 5, "some text"]

Specifications

Specification

ECMAScript® 2027 Language Specification
# sec-set.prototype.add

Browser compatibility

Enable JavaScript to view this browser compatibility table.

Help improve MDN

Was this page helpful to you?

Yes No

Learn how to contribute

This page was last modified on Sep 22, 2025 by MDN contributors.

View this page on GitHub • Report a problem with this content

Standard built-in objects
Set
Constructor
1. Set()
Static properties
1. [Symbol.species]
Instance methods
Instance properties
1. size
Inheritance
Object/Function
Static methods
Static properties
Instance methods
Instance properties
1. __proto__
2. constructor