JavaScript · Collections, storage and utilities

WeakMap / WeakSet

Collections with weak keys that can be garbage-collected. They are not iterable and are used for private metadata.

javascriptRunnable example javascript course

Syntax

new WeakMap()

Example

Try it

const meta = new WeakMap();
const key = {};
meta.set(key, { seen: true });
console.log(meta.get(key).seen);

Reference pages are the quick answer. The course explains the why, shows the full example and ends with a challenge.