// Compare two arrays and return a new array with any items only found 
// in one of the two given arrays, but not both. In other words, return 
// the symmetric difference of the two arrays.

function diffArray(arr1, arr2) {
    return arr1
      .concat(arr2)
      .filter(item => !arr1.includes(item) || !arr2.includes(item));
}
console.log(diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]));