# Set.prototype.difference()

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The difference() method of Set instances takes a set and returns a new set containing elements in this set but not in the given set.

## Syntax

js

difference(other)


### Return value

A new Set object containing elements in this set but not in the other set.

## Description

In mathematical notation, difference is defined as:

$A ∖ B = { x ∊ A ∣ x ∉ B } A\setminus B = {x\in A\mid x\notin B}$

And using Venn diagram: difference() accepts set-like objects as the other parameter. It requires this to be an actual Set instance, because it directly retrieves the underlying data stored in this without invoking any user code. Then, its behavior depends on the sizes of this and other:

• If there are more elements in this than other.size, then it iterates over other by calling its keys() method, and constructs a new set with all elements in this that are not seen in other.
• Otherwise, it iterates over the elements in this, and constructs a new set with all elements e in this that cause other.has(e) to return a falsy value.

The order of elements in the returned set is the same as in this.

## Examples

### Using difference()

The following example computes the difference between the set of odd numbers (<10) and the set of perfect squares (<10). The result is the set of odd numbers that are not perfect squares.

js

const odds = new Set([1, 3, 5, 7, 9]);
const squares = new Set([1, 4, 9]);
console.log(odds.difference(squares)); // Set(3) { 3, 5, 7 }


## Specifications

Specification
Set methods
# sec-set.prototype.difference

## Browser compatibility

BCD tables only load in the browser