WeakMap() constructor
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The WeakMap() constructor creates WeakMap objects.
Syntax
js
new WeakMap()
new WeakMap(iterable)
Parameters
iterable-
An
Arrayor other iterable 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.nullis treated asundefined.
Examples
Using WeakMap
js
const wm1 = new WeakMap();
const wm2 = new WeakMap();
const wm3 = new WeakMap();
const o1 = {};
const o2 = () => {};
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® 2026 Language Specification # sec-weakmap-constructor |
Browser compatibility
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