anchor.diff:              "seq": this._sequence
             });
           }
  -        this._heartbeatInterval =
  -            new Duration(milliseconds: json['d']['heartbeat_interval']);
  -        new Timer.periodic(_heartbeatInterval, (Timer t) => this._heartbeat());
  +
  +        this._heartbeatTimer = new Timer.periodic(
  +            new Duration(milliseconds: json['d']['heartbeat_interval']),
  +            (Timer t) => this._heartbeat());
           break;
   
         case _OPCodes.invalidSession:
  
positive.code:   }
  
    void _heartbeat() {
      this.send("HEARTBEAT", _sequence);
    }
  
  
negative.code:   }
  
    void _handleErr() {
      this._heartbeatTimer.cancel();
  
      switch (this._socket.closeCode) {
        case 1005:
          return;
  