The WeakMap()
creates a WeakMap
object, optionally based on a provided Array
or other iterable object.
WeakMap() constructor
Syntax
new WeakMap() new WeakMap(iterable)
Parameters
-
iterable
-
An
Array
or other iterable object that implements an @@iterator method that returns an iterator object that produces a two-element array-like object whose first element is a value that will be used as aWeakMap
key and whose second element is the value to associate with that key. Each key-value pair will be added to the newWeakMap
. 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 | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | Deno | Node.js | |
WeakMap |
36
|
12
|
6
|
11
|
23
|
8
|
37
|
36
|
6
|
24
|
8
|
3.0
|
1.0
|
0.12.0
0.10.0
|
iterable_allowed |
38
|
12
|
36
|
No
|
25
|
9
|
38
|
38
|
36
|
25
|
9
|
3.0
|
1.0
|
0.12.0
|
new_required |
36
|
12
|
42
|
11
|
23
|
9
|
37
|
36
|
42
|
24
|
9
|
3.0
|
1.0
|
0.12.0
|
null_allowed |
36
|
12
|
37
|
11
|
23
|
8
|
37
|
36
|
37
|
24
|
8
|
3.0
|
1.0
|
0.12.0
0.10.0
|
See also
© 2005–2022 MDN 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/WeakMap