WeakMap() constructor
The WeakMap()
creates WeakMap
objects which are a collections of key/value pairs in which the keys are weakly referenced. The keys must be objects and the values can be arbitrary values.
You can learn more about WeakMap
s in the section WeakMap object in Keyed collections.
Syntax
new WeakMap() new WeakMap(iterable)
Parameters
iterable
-
Iterable is an Array or other iterable object whose elements are key-value pairs (2-element Arrays). Each key-value pair will be added to the new WeakMap. null is treated as undefined.
Examples
Using WeakMap
const wm1 = new WeakMap(), wm2 = new WeakMap(), wm3 = new WeakMap(); const o1 = {}, o2 = function() {}, o3 = window; wm1.set(o1, 37); wm1.set(o2, 'azerty'); wm2.set(o1, o2); // a value can be anything, including an object or a function wm2.set(o3, undefined); wm2.set(wm1, wm2); // keys and values can be any objects. Even WeakMaps! wm1.get(o2); // "azerty" wm2.get(o2); // undefined, because there is no key for o2 on wm2 wm2.get(o3); // undefined, because that is the set value wm1.has(o2); // true wm2.has(o2); // false wm2.has(o3); // true (even if the value itself is 'undefined') wm3.set(o1, 37); wm3.get(o1); // 37 wm1.has(o1); // true wm1.delete(o1); wm1.has(o1); // false
Specifications
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
WeakMap |
36 |
12 |
6 |
11 |
23 |
8 |
37 |
36 |
6 |
24 |
8 |
3.0 |
iterable_allowed |
38 |
12 |
36 |
No |
25 |
9 |
38 |
38 |
36 |
25 |
9 |
3.0 |
new_required |
36 |
12 |
42 |
11 |
23 |
9 |
37 |
36 |
42 |
24 |
9 |
3.0 |
null_allowed |
36 |
12 |
37 |
11 |
23 |
8 |
37 |
36 |
37 |
24 |
8 |
3.0 |
See also
- A polyfill of
WeakMap
is available incore-js
WeakMap
in the JavaScript guide- Hiding Implementation Details with ECMAScript 6 WeakMaps
Map
Set
WeakSet
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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/WeakMap