customClassList

This property is not yet available to all users.

You can use this property to manipulate the custom CSS classes of an element. For example, you can add a custom class to an element or replace an existing class with a new custom class.

Custom classes are those that you create on your site, not the predefined global classes that are provided for each element.

Note: For more information, see Styling Elements with CSS and the MDN CSS reference docs.