WeakSet

WeakSet is a built-in collection in JavaScript that stores object references with weak memory semantics. It is designed to track object presence without preventing garbage collection. Only objects can be added to a WeakSet; attempting to add a non-object value results in a TypeError. The set itself does not expose its elements, and elements are not enumerable.

The core operations of a WeakSet are add, has, and delete. However, it has important limitations: there is no size property, no clear method, and the contents cannot be iterated or directly inspected. Because the references are weak, the JavaScript engine may garbage collect an object that is only contained in the WeakSet, and such objects disappear from the set without any observable notification. This behavior means WeakSet is not suitable for scenarios that require enumeration or lifetime guarantees.

In practice, WeakSet is often used to track metadata or associations for objects without preventing their disposal. A common use case is marking DOM nodes or other objects to indicate a special status or to prevent repeated processing, while allowing the objects themselves to be garbage collected when no longer referenced elsewhere.

Relation to other structures: a WeakSet stores only object references and does not offer iteration, unlike Set which stores values with strong references and supports iteration. It is also distinct from WeakMap, which stores key-value pairs with weak keys. WeakSet emphasizes membership information about objects without owning them, enabling memory-efficient patterns in certain caching or cleanup tasks.