Finding the diff of two arrays

arraydiff.js

function diffArray(arr1, arr2) {
  var newArr = [];
  newArr = arr1.concat(arr2);
  var filteredArray = newArr.filter(function(val) {
    return (arr1.indexOf(val) < 0 || arr2.indexOf(val) < 0);
  });
  return filteredArray;
}

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