code: function on(element, ev, cb, context) {
              for (var _len = arguments.length, args = Array(_len > 4 ? _len - 4 : 0), _key = 4; _key < _len; _key++) {
                  args[_key - 4] = arguments[_key];
              }
  
              var _this = this;
  
              var el = element.el,
                  events = ev.split(' '),
                  fn = function fn(e) {
                  cb.apply(context || _this, [e, element].concat(args));
              };
  
              events.forEach(function (event) {
                  el.addEventListener(event, fn);
              });
              var evt = {
                  remove: function remove() {
                      events.forEach(function (event) {
                          return el.removeEventListener(event, fn);
                      });
                      var evts = element._events;
                      evts.splice(evts.indexOf(evt), 1);
                  }
              };
              element._events.push(evt);
              return evt;
          }
docs: Adding DOM Event in to Element  @method on @param {dom.Element} element @param {String} ev @param {Function} cb @param {Object} context @return {Object} { remove() }