Hi Pedro,
I misunderstood, I though you were using the ListItem widget, which has the list-item class, but the same principle is valid.
The goal of the Javascript was to identifiy the first row, which was searching for the first element with the class list-item but it is failing because there is no element with that class.
What you can do is to enclose your artist block in a container:

And give it a class, let's say artist-list-item. Your Widget Tree should look like this in the end:
Now you have your "hook" on each element of the list, because now each element will be a container with the class artist-list-item.
You now just need to replace the part on your Javsacript where it is .list-item by .artist-list-item.
So your Javascript should be:
$parameters.WidgetId = document.getElementsByClassName("artist-list-item")[0];

Hope it helps.
Regards,
João