Device token management in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

How does Firebase Cloud Messaging handle device tokens when a user reinstalls the app?

When a user uninstalls and then reinstalls your app, what happens to the device token used for push notifications?

A A new device token is generated after reinstalling the app.

B The device token remains the same as before the uninstall.

C The old token is reused only if the user logs in with the same account.

D The device token is deleted permanently and cannot be regenerated.

💡 Hint

Think about how Firebase ensures messages reach the correct device after app reinstall.

Firebase generates a new device token after the app is reinstalled to ensure secure and accurate message delivery.

❓ security

intermediate

What is the best practice to secure device tokens in your backend?

Which method best protects device tokens stored on your server to prevent unauthorized access?

A Store device tokens in plain text in a public database.

B Encrypt device tokens before storing them and restrict database access.

C Send device tokens only over unsecured HTTP connections.

D Share device tokens openly with third-party services without restrictions.

💡 Hint

Consider how sensitive data should be handled to avoid leaks.

Encrypting device tokens and restricting access helps protect user privacy and prevents misuse of tokens.

❓ Architecture

advanced

Designing a scalable system for device token updates

You have millions of users whose device tokens can change frequently. Which architecture best handles real-time token updates efficiently?

A Implement a distributed cache layer with asynchronous token update propagation.

B Use a single centralized database with synchronous writes for all token updates.

C Store tokens only on the client side and never update the server.

D Manually update tokens once a month via batch processing.

💡 Hint

Think about how to reduce latency and avoid bottlenecks in large-scale systems.

A distributed cache with asynchronous updates reduces load on the database and improves scalability for frequent token changes.

❓ Configuration

advanced

Firebase Cloud Messaging token refresh handling

Which Firebase method should you implement to handle device token refresh events correctly in your app?

Firebase

firebase.messaging().onTokenRefresh(callback)

A Delete the old token from Firebase console when a token refresh occurs.

B Ignore token refresh events; tokens never change after initial generation.

C Manually generate new tokens on the client without Firebase methods.

D Use firebase.messaging().onTokenRefresh(callback) to update the token on your server.

💡 Hint

Firebase provides a built-in way to detect token changes.

Using onTokenRefresh ensures your app updates the backend with the latest token to maintain message delivery.

✅ Best Practice

expert

Handling invalid device tokens in Firebase Cloud Messaging

When sending push notifications, some device tokens become invalid. What is the best practice to handle these invalid tokens?

A Keep sending notifications to all tokens regardless of errors.

B Manually reset tokens on the client device without server involvement.

C Remove tokens from your database when Firebase returns a 'NotRegistered' error.

D Ignore errors and retry sending notifications indefinitely.

💡 Hint

Consider how to keep your token list clean and efficient.

Removing tokens flagged as 'NotRegistered' prevents wasted resources and improves notification delivery success.