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WeakMap.prototype.has()

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

Try it

Syntax

has(key)

Parameters

key: The key of the element to test for presence in the WeakMap object.

Return value

Returns true if an element 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 the has method

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

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

Specifications

Specification
ECMAScript 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	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 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	1.0	0.12.0