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weakMap.has

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

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

Browser compatibilityUpdate compatibility data on GitHub

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

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap/has