Oops. You are right, I beg your pardon. Here's a working example.

HTML

  <span class="a b c"></span>

JS

  function getClassList(el) {
    let ele = document.querySelector(el);
    let list = ele.classList;

    return {
      add: function (c) {
        list.add(c);
        return this;
      },
      toggle: function (c) {
        list.toggle(c);
        return this;
      },
      remove: function (c) {
        list.remove(c);
        return this;
      },
    }
  }
  getClassList('span').remove('b').add('e').toggle('a');
  console.log(document.querySelector('span').classList);