How to add a bootstrap toast message when internet is not connected

constructor(private connectionService: ConnectionService) {
    this.connectionService.monitor().subscribe((isConnected) => {
      this.isConnected = isConnected.hasInternetAccess;
      if (!this.isConnected) {
        this.status = 'The web-app is offline';
        alert(this.status);
      }
    });
}