ES6 Collections: Is Linear Time Complexity Mandatory?

The ES6 specification introduces keyed collections such as Set, Map, WeakSet, and WeakMap. These collections provide efficient ways to store and retrieve data based on keys. However, the question arises: does the specification mandate a linear time complexity for the operations on these collections?

Linear Time Complexity or Algo Choice Left Open

Despite expectations of widely accepted performant algorithms like O(1) access for the Set and Map prototypes, the ES6 specification surprisingly leaves the door open for linear time algorithms.

The specification states that "Set objects must be implemented using [mechanisms] that, on average, provide access times that are sublinear." This language can be interpreted to include linear time algorithms. However, it does not explicitly mandate them.

Similarly, the specification does not rule out more performant algorithms like hash tables or balanced trees, which provide logarithmic time complexity.

Absence of Explicit Performance Mandates

The absence of explicit performance mandates in the specification has raised eyebrows among developers who expected the spec to prioritize fast algorithms.

However, it is important to note that the specification focuses on observable semantics, such as predictable iteration order. While an efficient hash-based implementation is widely expected, the specification allows for alternative data structures like trees, which offer logarithmic time complexity.

Conclusion

The ES6 specification does not explicitly mandate linear time complexity for operations on keyed collections. While linear time algorithms may be observable in some implementations, the specification leaves room for more performant implementations. Developers should consult the specific browser or runtime documentation to understand the actual time complexity of these collection operations in different contexts.