Web/JavaScript/Reference/Global objects/WeakMap/has

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

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Syntax

ws.has(key);

Parameters

key

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

Return value

Boolean

Returns true if an element with the specified key exists in the WeakMap object; otherwise false.

Examples

Using the has method

var wm = new WeakMap();
wm.set(window, 'foo');

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

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'WeakMap.prototype.has' in that specification.

Browser compatibility

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
has	Chrome Full support 36	Edge Full support 12	Firefox Full support 6 Notes' Full support 6 Notes' Notes' Prior to 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.	IE Full support 11	Opera Full support 23	Safari Full support 8	WebView Android Full support 37	Chrome Android Full support 36	Firefox Android Full support 6 Notes' Full support 6 Notes' Notes' Prior to 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.	Opera Android Full support 24	Safari iOS Full support 8	Samsung Internet Android Full support 3.0	nodejs Full support 0.12 Full support 0.12 Full support 0.10 Disabled' Disabled' From version 0.10: this feature is behind the --harmony runtime flag.

Legend

Full support  

Full support

See implementation notes.'

See implementation notes.

User must explicitly enable this feature.'

User must explicitly enable this feature.

See also

• WeakMap
• WeakMap.prototype.set()
• WeakMap.prototype.get()

WeakMap.prototype.has() by Mozilla Contributors is licensed under CC-BY-SA 2.5.