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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.
Syntax
wm.has(key);Parameters
- key
- Required. The key of the element to test for presence in the
WeakMapobject.
Return value
- Boolean
- Returns
trueif an element with the specified key exists in theWeakMapobject; otherwisefalse.
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 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
TypeErrorwhen thekeyparameter was not an object. This has been fixed in version 38 and later to returnfalseas per latest ES6 standard (bug 1127827).