Implement curry()

[cheatsheet1999]

Currying is a useful technique used in JavaScript applications.

Please implement a curry() function, which accepts a function and return a curried one.

Here is an example

const join = (a, b, c) => {
   return `${a}_${b}_${c}`
}

const curriedJoin = curry(join)

curriedJoin(1, 2, 3) // '1_2_3'

curriedJoin(1)(2, 3) // '1_2_3'

curriedJoin(1, 2)(3) // '1_2_3'

---

Regular function

function curry(fn) {
    return function curried(...args) {
        // 1. if enough args, call func
        // 2. if not enough, bind the args and wait for new one

        if (args.length >= fn.length) {
            // 'this' is pointing to Window, apply is used to call the function fn
            //console.log(this)
            return fn.apply(this, args)
        } else {
            // 'this' is pointing to Window
            //console.log(this)
            return curried.bind(this, ...args)

        }
    }
}

Using arrow function, this is no need to apply or bind, since 'this' in arrow function inherited from the parent scope

function curry(fn) {
  return function curried(...args) {
    if (args.length >= fn.length) {
         return fn(...args);
       } else {
         return (...args2) => curried(...args, ...args2);
       }
    }
}