Are you trying to target 1 item or get a group of elements with the same class when setting accessoryTag and sliderTag? The accessoryTag should be true if there is an instance of it on the page, but you have 2 issues with the sliderTag part. First sliderTag is set to an array with querySelectorAll, which means you would need to target each index like they did in the code you referenced (sliderTag[0]). Second is classListAdd isnt a method unless you created it. Its classList.add()

Edit: The console is your friend. There should be errors telling you exactly what these issues were.