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JavaScript·Advanced·Coding·1 min read

What problems do default and rest parameters cause for generic curry helpers?

Short interview answer

Function.length stops before the first default parameter and excludes rest parameters, so it may not represent the intended arity. Production helpers often require explicit arity or define clear limitations.

Example

JavaScript
((a, b, c) => 0).length;      // 3((a, b = 1, c) => 0).length; // 1 — stops at the first default((...xs) => 0).length;       // 0 — rest params don't count

Key takeaway

Explain the underlying mental model clearly, then support it with a concrete example and its trade-offs.

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