15 Firebase Interview Questions and Answers

Firebase is a comprehensive app development platform backed by Google, offering a suite of tools and services to help developers build high-quality apps quickly. It provides functionalities such as real-time databases, authentication, analytics, and cloud storage, making it a popular choice for both mobile and web applications. Firebase’s seamless integration with other Google services and its ability to scale effortlessly make it an invaluable resource for developers.

This article presents a curated selection of interview questions designed to test your knowledge and proficiency with Firebase. By familiarizing yourself with these questions and their answers, you will be better prepared to demonstrate your expertise and problem-solving abilities in a technical interview setting.

Firebase Interview Questions and Answers

1. How does Firebase Authentication work, and what methods does it support?

Firebase Authentication provides a secure way to authenticate users, supporting various methods like email/password, phone number, social media logins, anonymous access, and custom systems. The process involves verifying user credentials and issuing a token for session management.

2. Explain the concept of Firebase Cloud Functions and provide a use case where they would be beneficial.

Firebase Cloud Functions are JavaScript functions that run in a managed environment, triggered by Firebase events or HTTPS requests. They extend app functionality without server management. For instance, you can automate sending a welcome email to new users upon account creation.

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.sendWelcomeEmail = functions.auth.user().onCreate((user) => {
  const email = user.email;
  const displayName = user.displayName;
  console.log(`Sending welcome email to ${email} for user ${displayName}`);
});

3. Write a function to send a push notification using Firebase Cloud Messaging (FCM).

Firebase Cloud Messaging (FCM) allows sending notifications to user devices. Here’s a Python example for sending a push notification:

import requests
import json

def send_push_notification(token, title, body):
    url = 'https://fcm.googleapis.com/fcm/send'
    headers = {
        'Content-Type': 'application/json',
        'Authorization': 'key=YOUR_SERVER_KEY'
    }
    payload = {
        'to': token,
        'notification': {
            'title': title,
            'body': body
        }
    }
    response = requests.post(url, headers=headers, data=json.dumps(payload))
    return response.status_code, response.json()

# Example usage
token = 'DEVICE_REGISTRATION_TOKEN'
title = 'Hello'
body = 'This is a test notification'
status_code, response = send_push_notification(token, title, body)
print(status_code, response)

4. Explain the difference between Firebase Realtime Database and Firestore.

Firebase Realtime Database and Firestore are NoSQL databases with different architectures. The Realtime Database is a single JSON tree optimized for simple data and real-time sync, while Firestore uses a structured, hierarchical model for complex queries and scalability.

5. Write a function to listen for real-time updates in a specific Firestore document.

Real-time listeners in Firestore are useful for applications needing instant updates, like chat apps. Here’s how to set up a listener for a Firestore document using JavaScript:

import firebase from 'firebase/app';
import 'firebase/firestore';

const firebaseConfig = {
  apiKey: "YOUR_API_KEY",
  authDomain: "YOUR_AUTH_DOMAIN",
  projectId: "YOUR_PROJECT_ID",
  storageBucket: "YOUR_STORAGE_BUCKET",
  messagingSenderId: "YOUR_MESSAGING_SENDER_ID",
  appId: "YOUR_APP_ID"
};

firebase.initializeApp(firebaseConfig);
const db = firebase.firestore();

function listenForDocumentUpdates(docId) {
  db.collection('yourCollection').doc(docId)
    .onSnapshot((doc) => {
      if (doc.exists) {
        console.log('Current data: ', doc.data());
      } else {
        console.log('No such document!');
      }
    }, (error) => {
      console.error('Error getting document:', error);
    });
}

listenForDocumentUpdates('yourDocumentId');

6. Explain how Firebase Analytics can be used to track user behavior in an app.

Firebase Analytics tracks user behavior, providing insights for improving user experience. It automatically collects data on interactions and allows logging custom events. Key features include event tracking, user properties, audience segmentation, real-time analytics, and integration with other Firebase services.

7. Write a function to delete a user from Firebase Authentication and their corresponding data from Firestore.

To delete a user from Firebase Authentication and their data from Firestore, use the Firebase Admin SDK:

import firebase_admin
from firebase_admin import auth, firestore

firebase_admin.initialize_app()

def delete_user_and_data(uid):
    auth.delete_user(uid)
    print(f'Successfully deleted user: {uid}')
    
    db = firestore.client()
    user_ref = db.collection('users').document(uid)
    user_ref.delete()
    print(f'Successfully deleted user data for: {uid}')

delete_user_and_data('user_uid')

8. Describe the process of setting up Firebase Hosting for a web application.

Setting up Firebase Hosting involves installing Firebase CLI, initializing Firebase in your project, deploying your application, and configuring hosting settings via the firebase.json file.

npm install -g firebase-tools
firebase init
firebase deploy

9. Write a function to schedule a Firebase Cloud Function to run daily at midnight.

To schedule a Firebase Cloud Function to run daily at midnight, use Google Cloud Scheduler:

const functions = require('firebase-functions');

exports.scheduledFunction = functions.pubsub.schedule('every 24 hours').onRun((context) => {
  console.log('This will be run every day at midnight!');
  return null;
});

Deploy the function with:

firebase deploy --only functions

Configure Cloud Scheduler:

gcloud scheduler jobs create pubsub daily-job --schedule "0 0 * * *" --time-zone "UTC" --topic "firebase-scheduled-function" --message-body "{}"

10. Describe how Firebase App Distribution can be used to distribute pre-release versions of an app.

Firebase App Distribution helps distribute pre-release app versions. Integrate the Firebase SDK, upload builds, invite testers, distribute builds, collect feedback, and track usage.

11. Write a function to implement custom claims in Firebase Authentication for role-based access control.

Custom claims in Firebase Authentication enable role-based access control. Set claims using Firebase Admin SDK and verify them in your app:

const admin = require('firebase-admin');
admin.initializeApp();

async function setCustomClaims(uid, claims) {
    await admin.auth().setCustomUserClaims(uid, claims);
    console.log(`Custom claims set for user ${uid}`);
}

setCustomClaims('user_uid', { role: 'admin' });

Verify claims:

firebase.auth().currentUser.getIdTokenResult()
    .then((idTokenResult) => {
        if (idTokenResult.claims.role === 'admin') {
            console.log('User is an admin');
        } else {
            console.log('User is not an admin');
        }
    })
    .catch((error) => {
        console.error('Error fetching ID token:', error);
    });

12. Explain how Firebase Performance Monitoring works and provide an example use case.

Firebase Performance Monitoring collects app data to identify performance issues. It uses traces to measure app performance and network requests. For example, in a mobile e-commerce app, it can track startup time and key interactions to optimize user experience.

13. Explain how Firebase Dynamic Links work and provide a scenario where they would be beneficial.

Firebase Dynamic Links are smart URLs that direct users to specific app locations, adjusting based on device and app installation status. They are useful in marketing campaigns, directing users to promotional content even if the app isn’t installed.

14. Discuss the advantages and disadvantages of using Firebase as a backend service compared to traditional server-based architectures.

Advantages of Firebase:

• Ease of Use: Comprehensive tools simplify backend setup.
• Real-Time Capabilities: Instant data sync is ideal for real-time apps.
• Scalability: Automatic scaling with user growth.
• Authentication: Built-in services simplify user management.
• Hosting: Easy deployment of web applications.

Disadvantages of Firebase:

• Vendor Lock-In: Ties you to Google’s ecosystem.
• Limited Querying: Real-time database has limited query capabilities.
• Cost: Costs can escalate with scale.
• Data Privacy: Concerns about third-party data storage.
• Flexibility: Less flexibility compared to traditional architectures.

15. Explain how Firebase ML Kit can be used in an application and provide an example use case.

Firebase ML Kit offers machine learning tasks like text recognition, face detection, and more. For example, text recognition can digitize documents or process receipts.

implementation 'com.google.firebase:firebase-ml-vision:24.0.3'

FirebaseVisionImage image = FirebaseVisionImage.fromBitmap(bitmap);
FirebaseVisionTextRecognizer detector = FirebaseVision.getInstance().getOnDeviceTextRecognizer();

detector.processImage(image)
    .addOnSuccessListener(new OnSuccessListener<FirebaseVisionText>() {
        @Override
        public void onSuccess(FirebaseVisionText firebaseVisionText) {
            String recognizedText = firebaseVisionText.getText();
        }
    })
    .addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
        }
    });