Using classList.remove() method. W3Schools offers free online tutorials, references and exercises in all the major languages of the web. Covering popular subjects like HTML, CSS, JavaScript, Python, SQL, Java, and many, many more. classList.add for adding; classList.remove for removing; Using the spread operator to add multiple classes in an array; Using the plus operator to add to the current class list; ClassList. Heres how form validation works with Bootstrap: HTML form validation is applied via CSSs two pseudo-classes, :invalid and :valid.It applies to ,