WeakMap

Summary

Like a Map, but keys must be objects and are held weakly — meaning entries are automatically garbage-collected once the key object is no longer referenced elsewhere. Weak references make `WeakMap` useful for metadata and caches where entries should disappear when their associated objects become unreachable.

• 1Read why WeakMap is useful for attaching private metadata to objects. Then apply the idea in a small example so the theory becomes practical.
• 2Understand why WeakMaps aren't iterable — a direct consequence of weak references. Be able to explain the concept in your own words and identify where it appears in a real application.
• 3Compare a real use case: caching computed data per DOM node without leaking memory.