code: function(event, callback) {
  //            if (this instanceof FSObject) {
  //                if (event === 'watcher') {
  //                    this.__watch_listeners = this.__watch_listeners || 0 + 1;
  //                    this.setWatcher();
  //                } else if (event === 'fileWatcher') {
  //                    this.__watch_file_listeners = this.__watch_file_listeners || 0 + 1;
  //                    this.setFileWatcher();
  //                }
  //            }
              var args = Array.prototype.slice.call(arguments);
              (this.emitter || (this.emitter = new emitter())).on.apply(this, args);
              return this;
          }
docs: Add event listener
  
  @param {string} event Event identifier.
  @param {function} callback Callback function to be called when the event is raised. Arguments of raise() will be passed to the callback.
  @returns {object} Component this.