WeakMap & WeakSet

To improve performance
To implement caching
To track object relationships while allowing garbage collection
Combining WeakMap and WeakSet is useful for: 1) Tracking complex object relationships without preventing garbage collection, 2) Implementing bi-directional relationships between objects, 3) Maintaining object graphs that can be partially garbage collected, 4) Creating sophisticated object tracking systems, 5) Implementing memory-efficient object relationship patterns, 6) Allowing natural cleanup of related object groups, 7) Managing complex data structures without memory leaks, 8) Building advanced object lifecycle management systems.
To create thread-safe collections