currying.babel.js

"use strict";

var currying = function currying(fn) {
  var fun = function fun() {
    for (var _len = arguments.length, orig = Array(_len), _key = 0; _key < _len; _key++) {
      orig[_key] = arguments[_key];
    }

    var inner = function inner() {
      for (var _len2 = arguments.length, val = Array(_len2), _key2 = 0; _key2 < _len2; _key2++) {
        val[_key2] = arguments[_key2];
      }
      return fun.apply(undefined, orig.concat(val));
    };
    
    inner.valueOf = function () {
      return fn.apply(undefined, orig).valueOf();
    };
    
    return inner;
  };
  return fun;
};

currying.js

var currying = function (fn) {
  var fun = function (...orig) {
    var inner = (...val) => fun(...orig, ...val);
    inner.valueOf = () => fn(...orig).valueOf();
    return inner;
  };
  return fun;
};

test.js

var a = (a1, a2, a3, a4) => a1 + a2 + a3 + a4;

var currying_a = currying(a);

console.log(currying_a(1)(2)(3)(4) == a(1, 2, 3, 4));
console.log(currying_a(1)(2, 3, 4) == a(1, 2, 3, 4));
console.log(currying_a(1, 2)(3, 4) == a(1, 2, 3, 4));
console.log(currying_a(1, 2, 3)(4) == a(1, 2, 3, 4));
console.log(currying_a(1, 2, 3, 4) == a(1, 2, 3, 4));

var currying_a_2_3 = currying_a(2, 3);

console.log(currying_a_2_3(4)(5) == a(2, 3, 4, 5));
console.log(currying_a_2_3(5, 6) == a(2, 3, 5, 6));

var currying_currying_a = currying(currying_a)

console.log(currying_currying_a(1)(2)(3)(4) == a(1, 2, 3, 4));
console.log(currying_currying_a(1)(2, 3, 4) == a(1, 2, 3, 4));
console.log(currying_currying_a(1, 2)(3, 4) == a(1, 2, 3, 4));
console.log(currying_currying_a(1, 2, 3)(4) == a(1, 2, 3, 4));
console.log(currying_currying_a(1, 2, 3, 4) == a(1, 2, 3, 4));

var currying_currying_currying_a_2_3 = currying(currying_currying_a(2, 3))
console.log(currying_currying_currying_a_2_3(4)(5) == a(2, 3, 4, 5));
console.log(currying_currying_currying_a_2_3(5, 6) == a(2, 3, 5, 6));