Cloud Functions setup in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Cloud Function Trigger Behavior

You deploy a Firebase Cloud Function triggered by Firestore document creation in the 'orders' collection. What happens when a new document is added to 'orders'?

A The function runs continuously as long as there is at least one document in 'orders'.

B The function runs once for every update to any document in 'orders'.

C The function runs only once when the first document is added to 'orders'.

D The function runs once for each new document added to 'orders'.

💡 Hint

Think about what triggers a Firestore onCreate function.

The Cloud Function triggers every time a new document is created in the specified collection. It does not trigger on updates or deletions.

❓ Configuration

intermediate

Correct Firebase Function Initialization

Which code snippet correctly initializes a Firebase Cloud Function to respond to HTTP requests?

A

const functions = require('firebase-functions');
exports.myFunc = functions.https.onRequest((req, res) => { res.send('Hello'); });

B

const functions = require('firebase-functions');
exports.myFunc = functions.firestore.document('path').onWrite((change, context) => { /* ... */ });

C

const functions = require('firebase-functions');
exports.myFunc = functions.database.ref('path').onWrite((change, context) => { /* ... */ });

D

const functions = require('firebase-functions');
exports.myFunc = functions.storage.object().onFinalize((object) => { /* ... */ });

💡 Hint

Check which Firebase function type supports HTTP triggers.

Only functions.https.onRequest creates an HTTP-triggered function. Others are for database or storage triggers.

❓ Architecture

advanced

Designing Scalable Cloud Functions

You want to design a Firebase Cloud Function that processes image uploads to Cloud Storage and scales efficiently under heavy load. Which approach is best?

A Use a Cloud Function triggered on image upload that places a message in a Pub/Sub queue for asynchronous processing.

B Use a single Cloud Function triggered on every image upload that processes the image synchronously.

C Use a Cloud Function triggered on HTTP requests to process images uploaded manually by users.

D Use a Cloud Function triggered on Firestore writes to track image uploads and process images in the function.

💡 Hint

Think about decoupling processing from upload to handle spikes.

Using Pub/Sub decouples upload from processing, allowing the system to scale and retry processing without blocking uploads.

❓ security

advanced

Securing Firebase Cloud Functions

Which practice best secures a Firebase Cloud Function that handles sensitive user data via HTTP requests?

A Use HTTP Basic Authentication with hardcoded credentials in the function.

B Allow all requests and rely on Firestore security rules to protect data.

C Require Firebase Authentication tokens and verify them inside the function before processing.

D Make the function public and encrypt data only after processing.

💡 Hint

Think about verifying the identity of the caller before processing sensitive data.

Verifying Firebase Authentication tokens ensures only authorized users access the function, protecting sensitive data.

✅ Best Practice

expert

Optimizing Cold Start Times in Cloud Functions

You notice your Firebase Cloud Functions have high cold start latency. Which option is the best way to reduce cold start times?

A Increase the memory allocation to the maximum allowed for all functions.

B Keep function code minimal and avoid importing large libraries unless needed.

C Deploy all functions in a single file to reduce deployment size.

D Use synchronous blocking code to ensure all initialization completes before handling requests.

💡 Hint

Think about what affects the time it takes to start a function instance.

Smaller code and fewer imports reduce initialization time, lowering cold start latency.

Practice

1. What is the first command you run to start setting up Cloud Functions in a Firebase project?

easy

A. firebase init functions

B. firebase deploy --only functions

C. firebase start functions

D. firebase create functions

Solution

1. Step 1: Understand Firebase setup commands

   The command firebase init functions initializes Cloud Functions in your project by creating necessary files and folders.

2. Step 2: Differentiate from deploy command

   firebase deploy --only functions is used after setup to upload your functions to Firebase, not to start setup.

3. Final Answer:

   firebase init functions -> Option A

4. Quick Check:

   Setup starts with firebase init functions [OK]

Hint: Setup always begins with 'firebase init functions' command [OK]

Common Mistakes:

• Confusing deploy command as setup
• Using non-existent commands like 'firebase start functions'
• Skipping initialization step

2. Which of the following is the correct way to deploy only Cloud Functions after writing your code?

easy

A. firebase deploy --only database

B. firebase deploy --only hosting

C. firebase deploy --only functions

D. firebase deploy --only storage

Solution

1. Step 1: Identify deployment targets

   Firebase allows deploying specific parts like hosting, functions, database, or storage using the --only flag.

2. Step 2: Match the correct target for Cloud Functions

   To deploy Cloud Functions only, use firebase deploy --only functions.

3. Final Answer:

   firebase deploy --only functions -> Option C

4. Quick Check:

   Deploy functions with --only functions [OK]

Hint: Use '--only functions' to deploy just Cloud Functions [OK]

Common Mistakes:

• Using wrong target like hosting or database
• Omitting '--only' and deploying everything
• Typing incorrect command syntax

3. Given this Cloud Function code snippet, what will happen when an HTTP request is made to it?

const functions = require('firebase-functions');
exports.helloWorld = functions.https.onRequest((request, response) => {
  response.send('Hello from Firebase!');
});

medium

A. The function does nothing and times out.

B. The function returns 'Hello from Firebase!' as the HTTP response.

C. The function throws an error because of missing return statement.

D. The function returns a JSON object with message 'Hello from Firebase!'.

Solution

1. Step 1: Understand the function trigger type

   This function uses functions.https.onRequest, which handles HTTP requests and sends responses.

2. Step 2: Analyze the response sent

   The function calls response.send('Hello from Firebase!'), which sends a plain text response with that message.

3. Final Answer:

   The function returns 'Hello from Firebase!' as the HTTP response. -> Option B

4. Quick Check:

   HTTP function sends plain text response [OK]

Hint: HTTP functions respond with response.send() text [OK]

Common Mistakes:

• Thinking response.send requires return
• Expecting JSON without using response.json()
• Assuming function times out without response

4. You wrote this Cloud Function but get an error when deploying:

exports.myFunction = functions.https.onRequest((req, res) => {
  res.send('Hi');
}

What is the problem?

medium

A. Missing closing parenthesis and semicolon after the function definition.

B. Using 'req' and 'res' instead of 'request' and 'response'.

C. The function name 'myFunction' is invalid.

D. Cloud Functions cannot handle HTTP requests.

Solution

1. Step 1: Check function syntax carefully

   The code snippet is missing a closing parenthesis ')' and semicolon ';' after the arrow function.

2. Step 2: Validate other parts

   Using 'req' and 'res' is valid parameter naming. Function name is valid. Cloud Functions support HTTP triggers.

3. Final Answer:

   Missing closing parenthesis and semicolon after the function definition. -> Option A

4. Quick Check:

   Syntax errors cause deployment failure [OK]

Hint: Check for missing brackets and semicolons in function code [OK]

Common Mistakes:

• Ignoring syntax errors like missing parentheses
• Thinking parameter names must be 'request' and 'response'
• Assuming Cloud Functions don't support HTTP

5. You want to create a Cloud Function that triggers when a new user is added to Firebase Authentication and logs their email. Which setup is correct?

hard

A. exports.logNewUser = functions.database.ref('/users/{userId}').onCreate((snapshot) => {
console.log('New user:', snapshot.val().email);
});

B. exports.logNewUser = functions.storage.object().onFinalize((object) => {
console.log('New user:', object.email);
});

C. exports.logNewUser = functions.https.onRequest((req, res) => {
console.log('New user:', req.body.email);
res.send('Logged');
});

D. exports.logNewUser = functions.auth.user().onCreate((user) => {
console.log('New user:', user.email);
});

Solution

1. Step 1: Identify the correct trigger for new Firebase Authentication users

   The trigger functions.auth.user().onCreate runs when a new user is created in Firebase Authentication.

2. Step 2: Confirm the logging of user email

   The callback receives a user object with an email property, which can be logged directly.

3. Step 3: Differentiate from other triggers

   Database triggers listen to database changes, HTTP triggers respond to requests, and storage triggers respond to file changes, so they are incorrect here.

4. Final Answer:

   Use auth user onCreate trigger to log new user email. -> Option D

5. Quick Check:

   Auth user onCreate triggers new user events [OK]

Hint: Use auth.user().onCreate for new Firebase Authentication users [OK]

Common Mistakes:

• Using database triggers for auth events
• Using HTTP triggers to detect user creation
• Confusing storage triggers with auth triggers