<div id="testWrapper" class="wrapper background fading"><div>
If we looking to modify each class name we will need to loop through all instances.
There are multiple approaches here. Firstly, we can split each class name by the blank space and convert the result to an Array:
const wrapperElement = document.getElementById('testWrapper') const classNames = wrapperElement.className.split(' ');
This will give us each class name in an array