http://www.freecodecamp.com/tylerl-uxai 's solution for Bonfire: Diff Two Arrays

bonfire-diff-two-arrays.js

// Bonfire: Diff Two Arrays
// Author: @tylerl-uxai
// Challenge: http://www.freecodecamp.com/challenges/bonfire-diff-two-arrays
// Learn to Code at Free Code Camp (www.freecodecamp.com)

function diff(arr1, arr2) {
  // Same, same; but different.

  return arr1.concat(arr2).filter(function(val){
    return !(arr1.indexOf(val)>=0 && arr2.indexOf(val) >=0);
    
  });
}

diff([1, 2, 3, 5], [1, 2, 3, 4, 5]);