Level 5: Async and functions · Exercise 72 of 76 · Free

Curry a function

A JavaScript exercise from Scriptdrill. Solve it with a code editor in your browser that runs your function against example and hidden tests, and it is checked the moment you submit.

The task

`fn` takes a fixed number of parameters, available as `fn.length`. Return a curried version: it accepts the arguments in any grouping, `c(1)(2)(3)`, `c(1, 2)(3)` or `c(1, 2, 3)`, and calls `fn` once it has received at least `fn.length` arguments, returning `fn`'s result. Extra arguments are passed along. A function with 0 or 1 parameters runs on the first call. Partial applications are independent and reusable: with `const add1 = c(1)`, both `add1(2)` and `add1(3)` work and give 3 and 4.

What this exercise teaches

Each partial application closes over its own copy of the arguments so far, so reusing one never leaks arguments into another. Comparing with >= rather than === is what lets extra arguments through instead of returning yet another function.

A hint if you get stuck

Write an inner `curried(...args)`: if `args.length >= fn.length` return `fn(...args)`; otherwise return `(...more) => curried(...args, ...more)`. Spreading into a new array each time is what keeps partial applications independent.