http://www.freecodecamp.com/fcc0208647c 's solution for Bonfire: Diff Two Arrays

bonfire-diff-two-arrays.js

// Bonfire: Diff Two Arrays
// Author: @fcc0208647c
// Challenge: http://www.freecodecamp.com/challenges/bonfire-diff-two-arrays
// Learn to Code at Free Code Camp (www.freecodecamp.com)

function diff(arr1, arr2) {
  arr3 = arr1.concat(arr2);

final = arr3.filter(function(val, index, arr){
    console.log(arr3.indexOf(val),arr3.lastIndexOf(val),val);
    return arr3.indexOf(val) === arr3.lastIndexOf(val);
    
    });

return final;

}

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