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

Syntax

wm.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 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.
Draft  

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung InternetNode.js
Basic supportChrome Full support 36Edge Full support YesFirefox 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 11Opera Full support 23Safari Full support 8WebView Android Full support 37Chrome Android Full support 36Edge Mobile Full support YesFirefox 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 23Safari iOS Full support 8Samsung Internet Android Full support Yesnodejs 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

Document Tags and Contributors

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