WeakMap.prototype.has()
The has()
method returns a boolean indicating whether an element with the specified key exists in the WeakMap
object or not.
Syntax
JavaScript
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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 theWeakMap
object; otherwisefalse
.
Examples
Using the has
method
JavaScript
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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 2017 Draft (ECMA-262) The definition of 'WeakMap.prototype.has' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 36 | 6.0 (6.0) | 11 | 23 | 7.1 |
Feature | Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|
Basic support | No support | 6.0 (6.0) | No support | No support | 8 |
Firefox-specific notes
- Prior to SpiderMonkey 38 (Firefox 38 / Thunderbird 38 / SeaMonkey 2.35), this method threw a
TypeError
when thekey
parameter was not an object. This has been fixed in version 38 and later to returnfalse
as per latest ES6 standard (bug 1127827).
See also
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/javascript/reference/global_objects/weakmap/has