WeakMap() constructor
The WeakMap() constructor creates WeakMap objects.
Syntax
Parameters
iterable-
An
Arrayor 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 aWeakMapkey 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
js
const wm1 = new WeakMap();
const wm2 = new WeakMap();
const wm3 = new WeakMap();
const o1 = {};
const o2 = function () {};
const 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
| Specification |
|---|
| ECMAScript Language Specification # sec-weakmap-constructor |
Browser compatibility
| desktop | mobile | server | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
WeakMap() constructor | |||||||||||||
new WeakMap(iterable) | |||||||||||||
new WeakMap(null) | |||||||||||||