Memory leaks, WeakMap, and WeakSet

Leaks happen when data stays reachable after it is no longer useful. Common frontend causes: forgotten event listeners, intervals, global caches, detached DOM nodes, and closures holding large graphs.

`WeakMap` keys must be objects; keys are weakly held and not enumerable — good for object-associated metadata without preventing collection. `WeakSet` tracks object membership weakly.

Weak collections do not fix leaks if the value closes over the key or another strong reference remains.

On interviews, explain the concept with a concrete example and name the runtime behavior interviewers probe.

Common pitfalls include mixing similar APIs and forgetting edge cases during live coding.

The trade-off is often clarity versus performance or safety versus convenience.

Checklist:

• Clean lifecycle resources.
• Bound cache size for strong Maps.
• Use WeakMap for per-object metadata.