But the reason Javascript isn't a functional language is because its built-in data structures are all mutable which encourages an imperative style, not because

But the reason Javascript isn't a functional language is because its built-in data structures are all mutable which encourages an imperative style, not because its functions are tupled or it lacks a function composition operator. I agree syntax is important, but your definition rules out languages like Clojure which most people would consider functional. Haskell programmers might disagree, but I would assume on the grounds of purity rather than the syntactic overhead of partial application.