code: function scrollTop() {
      var assign;
  
      var args = [], len = arguments.length;
      while ( len-- ) args[ len ] = arguments[ len ];
      var top = args[0];
      var duration = args[1];
      var easing = args[2];
      var callback = args[3];
      if (args.length === 3 && typeof easing === 'function') {
        (assign = args, top = assign[0], duration = assign[1], callback = assign[2], easing = assign[3]);
      }
      var dom = this;
      if (typeof top === 'undefined') {
        if (dom.length > 0) { return dom[0].scrollTop; }
        return null;
      }
      return dom.scrollTo(undefined, top, duration, easing, callback);
    }
docs: scrollTop(top, duration, easing, callback) {