code: def do(self, callback, *userdata):
          
          if hasattr(self.event_method_bound, '_js_code'):
              self.event_source_instance.attributes[self.event_name] = self.event_method_bound._js_code%{
                  'emitter_identifier':self.event_source_instance.identifier, 'event_name':self.event_name}
          self.callback = callback
          self.userdata = userdata
docs: The callback and userdata gets stored, and if there is some javascript to add
              the js code is appended as attribute for the event source