When is Set a better choice than an Array, and how does Set determine uniqueness?

A Set stores each value at most once and preserves insertion order for iteration. It is often a clearer semantic choice when the operation is “is this value a member?” rather than “what value is at index i?”

• Primitive duplicates collapse as expected; NaN is treated as the same Set value as NaN, and positive/negative zero are not distinct Set members.
• Objects are unique by identity, so two different {} objects remain two Set entries even if they have the same visible properties.
• Arrays are better when duplicates matter, numeric indexing matters, or array transformation APIs and positional semantics dominate.
• Converting [...new Set(array)] is convenient for primitive/reference-identity deduplication but is not deep deduplication of structurally equal objects.