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




Required. 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.


Using the has method

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

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


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'WeakMap.prototype.has' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'WeakMap.prototype.has' in that specification.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support36 Yes6111238
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support3636 Yes61238 ?

1. 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.

See also

Document Tags and Contributors

 Contributors to this page: wbamberg, fscholz, jameshkramer, nmve, kdex, realityking
 Last updated by: wbamberg,