freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/arguments-optional.md

id	title	challengeType	forumTopicId	dashedName
a97fd23d9b809dac9921074f	Arguments Optional	5	14271	arguments-optional

--description--

Create a function that sums two arguments together. If only one argument is provided, then return a function that expects one argument and returns the sum.

For example, addTogether(2, 3) should return 5, and addTogether(2) should return a function.

Calling this returned function with a single argument will then return the sum:

var sumTwoAnd = addTogether(2);

sumTwoAnd(3) returns 5.

If either argument isn't a valid number, return undefined.

--hints--

addTogether(2, 3) should return 5.

assert.deepEqual(addTogether(2, 3), 5);

addTogether(23, 30) should return 53.

assert.deepEqual(addTogether(23, 30), 53);

addTogether(5)(7) should return 12.

assert.deepEqual(addTogether(5)(7), 12);

addTogether("http://bit.ly/IqT6zt") should return undefined.

assert.isUndefined(addTogether('http://bit.ly/IqT6zt'));

addTogether(2, "3") should return undefined.

assert.isUndefined(addTogether(2, '3'));

addTogether(2)([3]) should return undefined.

assert.isUndefined(addTogether(2)([3]));

--seed--

--seed-contents--

function addTogether() {
  return false;
}

addTogether(2,3);

--solutions--

function addTogether() {
  var a = arguments[0];
  if (toString.call(a) !== '[object Number]') return;
  if (arguments.length === 1) {
    return function(b) {
      if (toString.call(b) !== '[object Number]') return;
      return a + b;
    };
  }
  var b = arguments[1];
  if (toString.call(b) !== '[object Number]') return;
  return a + arguments[1];
}