New Built-in Classes: WeakSet and WeakMap

WeakSet and WeakMap

Suppose you added an object as a value to a Set or as a key to a Map. If that object is no longer needed in your application, it can’t be garbage collected. The Set or the Map that holds on to the object will prevent it from being cleaned up. This is not very gentle on memory usage and may be an issue in some applications that use a large amount of data. WeakSet, a counterpart of Set, and WeakMap, a counterpart of Map, can be used to solve this issue since both have a minimal impact on memory usage.

The word weak refers to coupling, as in weak coupling. A Set, for example, tightly holds onto the data that is added. However, a WeakSet will hold only weakly and will not prevent the object from being released. Let’s discuss why we may need a weak collection before looking at the built-in weak collections in JavaScript.

An analogy

Suppose you have an application where information about various vehicles based on vehicle identification number (VIN) is obtained from a database.