WeakMap.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 July 2015.

The has() method of WeakMap instances returns a boolean indicating whether an entry with the specified key exists in this WeakMap or not.

Try it

const weakmap = new WeakMap();
const object1 = {};
const object2 = {};

weakmap.set(object1, "foo");

console.log(weakmap.has(object1));
// Expected output: true

console.log(weakmap.has(object2));
// Expected output: false

Syntax

has(key)

Parameters

key: The key of the entry to test for presence in the WeakMap object. Object keys are compared by reference, not by value.

Return value

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

Examples

Using has()

const wm = new WeakMap();
wm.set(window, "foo");

wm.has(window); // returns true
wm.has("baz"); // returns false

Specifications

Specification
ECMAScript® 2027 Language Specification # sec-weakmap.prototype.has

Browser compatibility

	Desktop					Mobile							Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on iOS	Samsung Internet	WebView Android	WebView on iOS	Bun	Deno	Node.js
`has`	36	12	6 Before Firefox 38, this method threw a `TypeError` when the key parameter was not an object. This has been fixed in version 38 and later to return `false` as per the ES2015 standard.	23	8	36	6 Before Firefox for Android 38, this method threw a `TypeError` when the key parameter was not an object. This has been fixed in version 38 and later to return `false` as per the ES2015 standard.	24	8	3.0	37	8	1.0.0	1.0	0.12.0