This feature is experimental. It may be changed or removed in a future version without prior notice or deprecation.
Adds or removes the given class from the given element.
If you don't need IE11 support you may also use the built-in
Element#classList.toggle(className) to the same effect.
The element for which to add or remove the class.
A boolean value to determine whether the class should be added or removed.
If omitted, the class will be added if missing and removed if present.