What are the Computational/Time Complexity Guarantees for Keyed Collections in Javascript ES6?

Keyed Collections in Javascript ES6: Computational/Time Complexity

The ES6 specification provides Keyed Collections (Set, Map, WeakSet, and WeakMap) with specific computational/time complexity guarantees. These collections implement observable semantics that mandate sublinear access times on average, proportional to the number of elements in the collection.

While the specification does not mandate specific algorithms, it suggests that implementations use performant ones. Nevertheless, the spec does not explicitly require constant-time access (O(1)) for operations such as Set.prototype.has, add, and delete.

An important clarification comes from the specification itself, stating that the data structures used in the Keyed Collections specification are only meant to describe the required observable semantics, not a specific implementation model. This leaves open the possibility for implementations to employ hash tables or similar structures to achieve constant access.

In summary, while the ES6 specification does not strictly mandate O(1) time complexity for Keyed Collections, it strongly encourages implementations to use performant algorithms. As a result, most implementations are designed to provide constant access time on average.

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