Error: No Firebase App '[DEFAULT]' has been created - call Firebase App.initializeApp()

Question

You are probably invoking firebase before the app is initialized. All calls to firebase must come after .initializeApp();

firebase.initializeApp(config);
var db = firebase.firestore();

Complete tutorial source link

Use initializeApp before @NgModule

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { RouteReuseStrategy } from '@angular/router';

import { IonicModule, IonicRouteStrategy } from '@ionic/angular';
import { SplashScreen } from '@ionic-native/splash-screen/ngx';
import { StatusBar } from '@ionic-native/status-bar/ngx';

import { AppComponent } from './app.component';
import { AppRoutingModule } from './app-routing.module';
import { environment } from 'src/environments/environment';
import { AuthenticateService } from './services/authentication.service';
import { AngularFireAuthModule } from '@angular/fire/auth';

import * as firebase from 'firebase';

firebase.initializeApp(environment.firebase);

@NgModule({
  declarations: [AppComponent],
  entryComponents: [],
  imports: [
    BrowserModule, 
    IonicModule.forRoot(), 
    AppRoutingModule,
    AngularFireAuthModule
  ],
  providers: [
    StatusBar,
    SplashScreen,
    AuthenticateService,
    { provide: RouteReuseStrategy, useClass: IonicRouteStrategy }
  ],
  bootstrap: [AppComponent]
})
export class AppModule {}

If you using Dart and Flutter

1. add firebase_core dependency to pubspac.ymal.
2. go to main.dart
3. import 'package:firebase_core/firebase_core.dart';

4.add async in main()

follow my code

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  var fsconnect = FirebaseFirestore.instance;

  myget() async {
    var d = await fsconnect.collection("students").get();
    // print(d.docs[0].data());

    for (var i in d.docs) {
      print(i.data());
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: Scaffold(
      appBar: AppBar(
        title: Text('Firebase Firestore App'),
      ),
      body: Column(
        children: <Widget>[
          RaisedButton(
            child: Text('send data'),
            onPressed: () {
              fsconnect.collection("students").add({
                'name': 'sarah',
                'title': 'xyz',
                'email': '[email protected]',
              });
              print("send ..");
            },
          ),
          RaisedButton(
            child: Text('get data'),
            onPressed: () {
              myget();
              print("get data ...");
            },
          )
        ],
      ),
    ));
  }
}

My problem was because I added a second parameter:

AngularFireModule.initializeApp(firebaseConfig, 'reservas')

if I remove the second parameter it works fine:

AngularFireModule.initializeApp(firebaseConfig)

I had a similar issue following Firebase's online guide found here.

The section heading "Initialize multiple apps" is misleading as the first example under this heading actually demonstrates how to initialize a single, default app. Here's said example:

// Initialize the default app
var defaultApp = admin.initializeApp(defaultAppConfig);

console.log(defaultApp.name);  // "[DEFAULT]"

// Retrieve services via the defaultApp variable...
var defaultAuth = defaultApp.auth();
var defaultDatabase = defaultApp.database();

// ... or use the equivalent shorthand notation
defaultAuth = admin.auth();
defaultDatabase = admin.database();

If you are migrating from the previous 2.x SDK you will have to update the way you access the database as shown above, or you will get the, No Firebase App '[DEFAULT]' error.

Google has better documentation at the following:

1. INITIALIZE: https://firebase.google.com/docs/database/admin/start

2. SAVE: https://firebase.google.com/docs/database/admin/save-data

3. RETRIEVE: https://firebase.google.com/docs/database/admin/retrieve-data

This may not be best answer but, I had to initialize app with admin and firebase like below. I use admin for it's own purposes and firebase as well.

const firebase = require("firebase");
const admin = require("firebase-admin");

admin.initializeApp(functions.config().firebase);
firebase.initializeApp(functions.config().firebase);
// Get the Auth service for the default app
var authService = firebase.auth();

 function createUserWithEmailAndPassword(request, response) {
        const email = request.query.email;
        const password = request.query.password;
        if (!email) {
            response.send("query.email is required.");
            return;
        }
        if (!password) {
            response.send("query.password is required.");
            return;
        }
        return authService.createUserWithEmailAndPassword(email, password)
            .then(success => {
                let responseJson = JSON.stringify(success);
                console.log("createUserWithEmailAndPassword.responseJson", responseJson);
                response.send(responseJson);
            })
            .catch(error => {
                let errorJson = JSON.stringify(error);
                console.log("createUserWithEmailAndPassword.errorJson", errorJson);
                response.send(errorJson);
            });
    }

Flutter web

For me the error occurred when I run my application in "release" mode

flutter run -d chrome --release

and when I deployed the application on the Firebase hosting

firebase deploy

Solution

Since I initialized Firebase in the index.html, I had to change the implementation order of firebase and main.dart.js

<script>
  var firebaseConfig = {
  apiKey: "xxxxxxxxxxxxxxxxxxxxxx",
  authDomain: "xxxxxxxxxxx.firebaseapp.com",
  databaseURL: "https://xxxxxxxxxx.firebaseio.com",
  projectId: "xxxxxxxxxxx",
  storageBucket: "xxxxxxxx.appspot.com",
  messagingSenderId: "xxxxxxxxxxx",
  appId: "1:xxxxxxxxxx:web:xxxxxxxxxxxxx",
  measurementId: "G-xxxxxxxxx"
  };
  // Initialize Firebase
  firebase.initializeApp(firebaseConfig);
  firebase.analytics();
</script>

//moved below firebase init
<script src="main.dart.js" type="application/javascript"></script>