This function is intended to find the even number in an array where all the other numbers are odd, or the odd number in an array where all the other numbers are even.

```
function findOutlier(integers){
let oddOne = integers.filter((item) => item % 2 === 1);
let odderOne = integers.filter((item) => item % 2 === 0)
if (oddOne.length === 1) {
return oddOne[0];
}
else {
return odderOne[0];
}
}
```

It works for most types of arrays, but will sometimes give me ‘undefined’ or if the value at 0 is negative, it will just return that number.

Is there some kind of basic JavaScript rule I’m missing out on? I can’t work out how to get it to work for those ones.