hwta is .classlist.add code example

Example 1: add multiple class list at once in js

elem.classList.add("first");
elem.classList.add("second");
elem.classList.add("third");

is equal to :

elem.classList.add("first","second","third");

Example 2: classList has class

if (document.body.classList.contains('thatClass')) {
    // do some stuff
}