WeakSet.prototype.has()

Baseline Widely available

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

The has() method of WeakSet instances returns a boolean indicating whether an object exists in this WeakSet or not.

Try it

const weakset1 = new WeakSet();
const object1 = {};
const object2 = {};
weakset1.add(object1);
console.log(weakset1.has(object1));
// Expected output: true
console.log(weakset1.has(object2));
// Expected output: false

Syntax

js
has(value)

Parameters

value

The value to test for presence in the WeakSet.

Return value

Returns true if an element with the specified value exists in the WeakSet object; otherwise false. Always returns false if value is not an object or a non-registered symbol.

Examples

Using the has() method

js
const ws = new WeakSet();
const obj = {};
ws.add(window);
ws.has(window); // returns true
ws.has(obj); // returns false
// Storing a non-registered symbol
const sym = Symbol("foo");
ws.add(sym);
ws.add(Symbol.iterator);

Specifications

Specification
ECMAScript® 2026 Language Specification
# sec-weakset.prototype.has

Browser compatibility

See also