实现柯里化

柯里化(Currying) 在JavaScript是一个常用的技巧。

请实现一个curry()方法，接受一个function然后返回一个柯里化过后的function。

For 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'

Answer

function curry(fn, ...args) {
  return fn.length > args.length
    ? (..._args) => curry(fn, ...args, ..._args)
    : fn(...args);
}

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

const curriedJoin = curry(join);
console.log(curriedJoin(1, 2, 3, 4));
console.log(curriedJoin(1)(2, 3));
console.log(curriedJoin(1, 2)(3));

基于上面的要求,请实现带占位符号的柯里化

For Example

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

const curriedJoin = curry(join)
const _ = curry.placeholder

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

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

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