Why is currying useful in JavaScript?

Transforming a function with multiple arguments into a sequence of single-argument functions: f(a, b, c) becomes f(a)(b)(c). Each call returns a function that takes the next argument.

Return a function that collects arguments. If enough arguments (args.length >= fn.length), call the original. Otherwise, return a new function that collects more. Use recursion.

Currying transforms into one-argument-at-a-time: f(a)(b)(c). Partial application presets some arguments and returns a function for the rest: f'(b, c) with a preset. Currying is one-at-a-time; partial is some-now.