text: 
  export class Event_Emitter {
      constructor() {
          this._events = {};
      }
      
      on(evt, listener) {
          (this._events[evt] || (this._events[evt] = [])).push(listener);
          return this;
      }
      
      emit(evt, arg) {
          (this._events[evt] || []).slice().forEach(lsn => lsn(arg));
      }
      
      clean(){
          this._events = {};
      }
  }