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 element with the specified key exists in this WeakMap or not.

Try it

Syntax

js
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

js
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

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desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
has

Legend

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Full support
Full support
See implementation notes.

See also