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.
TheWeakMap() constructor createsWeakMap objects.
Syntax
js
new WeakMap()new WeakMap(iterable)Parameters
iterableAn
Arrayor otheriterable 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 functionwm2.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 wm2wm2.get(o3); // undefined, because that is the set valuewm1.has(o2); // truewm2.has(o2); // falsewm2.has(o3); // true (even if the value itself is 'undefined')wm3.set(o1, 37);wm3.get(o1); // 37wm1.has(o1); // truewm1.delete(o1);wm1.has(o1); // falseSpecifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-weakmap-constructor |