curryify

curry.js

function curry(fn) {
  // fn(1,2,3) => fn(1)(2,3) => fn(1,2)(3)
  // so it return a function which:
  //  1. if enough param, just run it
  //  2. if not enough param, return another function with param prefilled
  return function curried(...args) {
    if (args.length >= fn.length) {
      return fn.apply(null, args)
    } else {
      return curried.bind(null, ...args)
    }
  }
}