WeakMap() constructor
The WeakMap()
constructor 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.
Syntax
new WeakMap([iterable])
Parameters
iterable
- Iterable is an Array or other iterable object whose elements are key-value pairs (2-element Arrays). Each key-value pair will be added to the new WeakMap. 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
BCD tables only load in the browser