weakMap.has

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 2017 Draft (ECMA-262) The definition of 'WeakMap.prototype.has' in that specification.	Draft

Browser compatibility

Firefox-specific notes

• Prior to SpiderMonkey 38 (Firefox 38 / Thunderbird 38 / SeaMonkey 2.35), 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 ES2015 specification (bug 1127827).

See also

• WeakMap
• WeakMap.prototype.set()
• WeakMap.prototype.get()