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.
new WeakMap([iterable])
iterable
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
Desktop | ||||||
---|---|---|---|---|---|---|
WeakMap() constructor |
36 | 12 | 6 | 11 | 23 | 8 |
new WeakMap(iterable) |
38 | 12 | 36 | No | 25 | 9 |
WeakMap() without new throws |
36 | 12 | 42 | 11 | 23 | 9 |
new WeakMap(null) |
36 | 12 | 37 | 11 | 23 | 8 |
Mobile | ||||||
---|---|---|---|---|---|---|
WeakMap() constructor |
37 | 36 | 6 | 24 | 8 | 3.0 |
new WeakMap(iterable) |
38 | 38 | 36 | 25 | 9 | 3.0 |
WeakMap() without new throws |
37 | 36 | 42 | 24 | 9 | 3.0 |
new WeakMap(null) |
37 | 36 | 37 | 24 | 8 | 3.0 |
Server | |
---|---|
WeakMap() constructor |
0.12
|
new WeakMap(iterable) |
0.12 |
WeakMap() without new throws |
0.12 |
new WeakMap(null) |
0.12
|
WeakMap
in the JavaScript guideMap
Set
WeakSet
© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap/WeakMap