Is there a way to add/remove several classes in one single instruction with classList?

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

is equal

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

The new spread operator makes it even easier to apply multiple CSS classes as array:

const list = ['first', 'second', 'third'];
element.classList.add(...list);

The classList property ensures that duplicate classes are not unnecessarily added to the element. In order to keep this functionality, if you dislike the longhand versions or jQuery version, I'd suggest adding an addMany function and removeMany to DOMTokenList (the type of classList):

DOMTokenList.prototype.addMany = function(classes) {
    var array = classes.split(' ');
    for (var i = 0, length = array.length; i < length; i++) {
      this.add(array[i]);
    }
}

DOMTokenList.prototype.removeMany = function(classes) {
    var array = classes.split(' ');
    for (var i = 0, length = array.length; i < length; i++) {
      this.remove(array[i]);
    }
}

These would then be useable like so:

elem.classList.addMany("first second third");
elem.classList.removeMany("first third");

Update

As per your comments, if you wish to only write a custom method for these in the event they are not defined, try the following:

DOMTokenList.prototype.addMany = DOMTokenList.prototype.addMany || function(classes) {...}
DOMTokenList.prototype.removeMany = DOMTokenList.prototype.removeMany || function(classes) {...}