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

id	title	challengeType	forumTopicId
a97fd23d9b809dac9921074f	Arguments Optional	5	14271

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.

Instructions

Tests

tests:
  - text: <code>addTogether(2, 3)</code> should return 5.
    testString: assert.deepEqual(addTogether(2, 3), 5);
  - text: <code>addTogether(23, 30)</code> should return 53.
    testString: assert.deepEqual(addTogether(23, 30), 53);
  - text: <code>addTogether(5)(7)</code> should return 12.
    testString: assert.deepEqual(addTogether(5)(7), 12);
  - text: <code>addTogether("http://bit.ly/IqT6zt")</code> should return undefined.
    testString: assert.isUndefined(addTogether("http://bit.ly/IqT6zt"));
  - text: <code>addTogether(2, "3")</code> should return undefined.
    testString: assert.isUndefined(addTogether(2, "3"));
  - text: <code>addTogether(2)([3])</code> should return undefined.
    testString: assert.isUndefined(addTogether(2)([3]));

Challenge Seed

function addTogether() {
  return false;
}

addTogether(2,3);

Solution

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];
}