Coding Practice: Implement Currying

Question #

Please design a currying function to achieve the following effects:

function join(a, b, c) {
  return `${a}_${b}_${c}`
}

const curriedJoin = curry(join)
console.log(curriedJoin(1, 2, 3)) // '1_2_3'
console.log(curriedJoin(1)(2, 3)) // '1_2_3'
console.log(curriedJoin(1, 2)(3)) // '1_2_3'
console.log(curriedJoin(1)(2)(3)) // '1_2_3'

Solution #

function curry(fn) {
  const context = this
  return function curried(...args) {
    if (args.length >= fn.length) {
      return fn.apply(context, args)
    }
    return function (...restArgs) {
      return curried.apply(context, args.concat(restArgs))
    }
  }
}

function join(a, b, c) {
  return `${a}_${b}_${c}`
}

const curriedJoin = curry(join)
console.log(curriedJoin(1, 2, 3)) // '1_2_3'
console.log(curriedJoin(1)(2, 3)) // '1_2_3'
console.log(curriedJoin(1, 2)(3)) // '1_2_3'
console.log(curriedJoin(1)(2)(3)) // '1_2_3'

Or, we can use the bind method to achieve the same effect:

function curry(fn) {
  const context = this
  return function curried(...args) {
    if (args.length >= fn.length) {
      return fn.apply(context, args)
    }
    return curried.bind(context, ...args)
  }
}

Or, we can use arrow function to achieve the same effect:

function curry(fn) {
  const curried = (...args) => {
    if (args.length >= fn.length) {
      return fn(...args)
    }
    return (...restArgs) => curried(...args, ...restArgs)
  }
  return curried
}