Intermediate Algorithm Scripting: Diff Two Arrays

Hello there,

I’ve been stuck for some hours with this challenge, and even though I’ve come to a solution, the code still shows as invalid.
I’ve tried it outside of the course’s console and it seems to work fine, so I was wondering if I did something wrong.

function diffArray(arr1, arr2) {
  var newArr = [];
  // Same, same; but different.
  var sortArr = arr1.concat(arr2).sort();
  var counts = {};
  for (var i = 0; i < sortArr.length; i++){
    var num = sortArr[i];
    counts[num] = counts[num] ? counts[num] + 1 : 1;
  for(var item in counts){
    if (counts[item] == 1){
  return newArr;

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

Getting the following errors:
[1, 2, 3, 5], [1, 2, 3, 4, 5] should return [4] .
[1, "calf", 3, "piglet"], [1, "calf", 3, 4] should return ["piglet", 4] .
[1, "calf", 3, "piglet"], [7, "filly"] should return [1, "calf", 3, "piglet", 7, "filly"]

My first guess was that the tutorial was being picky for not returning the array in the same order, but straight from the exercise notes it reads: You can return the array with its elements in any order.

Any input is welcome.


Just looking at this first test, I see that you are returning ['4'] instead of [4].

Thanks for the reply Ariel.

While I finally used .filter() instead, I’ll dig into that code to see why numbers are being passed as strings to the array.

When you use for in, the variable declared for the key will be a string.

for(var item in counts){ // item will be a string, because keys in objects are strings.

Technically, arrays in JavaScript are special objects. The indices are the keys.