Diff Two Arrays

function diff(arr1, arr2) {
  var newArr = [];
  // Same, same; but different.
  var a = arr1.filter(function(e){
    return arr2.indexOf(e) < 0;
  });
  var b = arr2.filter(function(e){
    return arr1.indexOf(e) < 0;
  });
  newArr = a.concat(b);
  return newArr;
}

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