First Firebase integration - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Firebase Initialization Behavior

What happens if you try to initialize Firebase twice in the same web app without checking if it is already initialized?

A Firebase throws an error indicating it is already initialized.

B Firebase silently re-initializes without any error.

C Firebase merges the new config with the old one and continues.

D Firebase resets all previous data and starts fresh.

💡 Hint

Think about how Firebase protects against multiple initializations in a single app instance.

Firebase SDK throws an error if you try to initialize it more than once without checking, to prevent conflicts.

❓ Configuration

intermediate

Correct Firebase Config Object

Which of the following is a valid Firebase configuration object for initializing Firebase in a web app?

A { api_key: "abc123", auth_domain: "myapp.firebaseapp.com", project_id: "myapp" }

B { key: "abc123", domain: "myapp.firebaseapp.com", id: "myapp" }

C { apiKey: "abc123", authDomain: "myapp.firebaseapp.com", projectId: "myapp" }

D { apiKey: "abc123", authDomain: "myapp.firebaseapp.com" }

💡 Hint

Look for the exact property names Firebase expects in its config.

Firebase requires specific keys like apiKey, authDomain, and projectId to initialize properly.

❓ Architecture

advanced

Firebase Hosting and Cloud Functions Integration

You want to serve a static website and also run backend code on Firebase. Which architecture correctly uses Firebase Hosting and Cloud Functions together?

A Host static files on Cloud Functions and use Firebase Hosting only for API calls.

B Host static files on Firebase Hosting and use Cloud Functions as API endpoints triggered by HTTPS requests.

C Use Firebase Hosting to run backend code and Cloud Functions only for database triggers.

D Deploy backend code inside Firebase Hosting and static files inside Cloud Functions.

💡 Hint

Think about which Firebase service is optimized for static content and which for backend logic.

Firebase Hosting is optimized for static content delivery, while Cloud Functions handle backend logic via HTTPS triggers.

❓ security

advanced

Firebase Security Rules for Firestore

Which Firestore security rule allows only authenticated users to read and write their own user document under 'users/{userId}'?

Firebase

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{userId} {
      allow read, write: if ________ ;
    }
  }
}

A request.auth.uid != null

B request.auth == null || request.auth.uid == userId

C request.auth != null && request.auth.token.email_verified == true

D request.auth != null && request.auth.uid == userId

💡 Hint

Users should only access their own documents and must be signed in.

The rule checks that the user is signed in and the document ID matches their user ID.

❓ service_behavior

expert

Firebase Realtime Database Offline Behavior

What happens when a Firebase Realtime Database client loses internet connection but continues to write data locally?

A Writes are queued locally and synchronized automatically when connection is restored.

B Writes are lost and not saved locally during offline periods.

C Writes fail immediately and throw an error until connection is back.

D Writes are saved locally but require manual sync calls to update the server.

💡 Hint

Consider Firebase's offline capabilities and automatic synchronization.

Firebase Realtime Database caches writes locally and syncs them automatically once online.