arguments Optional

index.js

/*
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.
*/

function addTogether(num) {
  num = Array.prototype.slice.call(arguments);

  if (num.length > 1) {
    return twoNumbers(num[0], num[1]);
  } else {
    return oneNumber(num[0]);
  }

  function isnumber(num) {
    if (typeof num !== 'number' || typeof num === undefined) {
      return undefined;
    } else {
      return num;
    }
  }

  function twoNumbers(first, second) {
    first = isnumber(first);
    second = isnumber(second);
    if (first !== undefined && second !== undefined) {
      return first + second;
    }
    return undefined;
  }

  function oneNumber(num) {
    num = isnumber(num);
    if (num !== undefined) {
      return function(num2) {
        num2 = isnumber(num2);
        if (num2 !== undefined) {
          return num + num2;
        }
        return undefined;
      };
    }
    return undefined;
  }
}
addTogether(4)([3]);

/*
Test your code here
addTogether(2, 3) should return 5.
addTogether(2)(3) should return 5.
addTogether("http://bit.ly/IqT6zt") should return undefined.
addTogether(2, "3") should return undefined.
addTogether(2)([3]) should return undefined.
*/