ngOnInit(): void {
        firebase.init({
          persist: true,
          storageBucket: 'gs://**************/',
          onAuthStateChanged: (data: any) => {
            console.log(JSON.stringify(data))
            if (data.loggedIn) {
              BackendService.token = data.user.uid;
            }
            else {
              BackendService.token = "";
            }
          }
        }).then(
          function (instance) {
            console.log("firebase.init done");
          },
          function (error) {
            console.log("firebase.init error: " + error);
          }
          );
firebase.keepInSync(
        "/users", // which path in your Firebase needs to be kept in sync?
        true      // set to false to disable this feature again
    ).then(
        function () {
            console.log("firebase.keepInSync is ON for /users");
        },
        function (error) {
            console.log("firebase.keepInSync error: " + error);
        }
    );

login(user: User) {
return firebase.login({
  type: firebase.LoginType.PASSWORD,
  email: user.email,
  password: user.password
}).then((result: any) => {
      BackendService.token = result.uid;
      return JSON.stringify(result);
  }, (errorMessage: any) => {
    // alert(errorMessage);
    alert('Email address / Password is wrong!!!');
  });