HTTP trigger functions in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an HTTP trigger function named 'helloWorld'.

Firebase

exports.helloWorld = functions.https.[1]((req, res) => {
  res.send('Hello from Firebase!');
});

Drag options to blanks, or click blank then click option'

AonRequest

BonCall

ConEvent

DonTrigger

Attempts:

3 left

💡 Hint

Common Mistakes

Using onCall instead of onRequest for HTTP triggers.

Using onEvent which is not a valid method here.

The correct method to create an HTTP trigger function in Firebase is onRequest. It listens for HTTP requests.

2fill in blank

medium

Complete the code to send a JSON response with a message in the HTTP function.

Firebase

exports.sendJson = functions.https.onRequest((req, res) => {
  res.[1]({ message: 'Hello JSON!' });
});

Drag options to blanks, or click blank then click option'

Ajson

BsendStatus

CsendFile

DsendText

Attempts:

3 left

💡 Hint

Common Mistakes

Using sendText which is not a valid method.

Using sendFile which is for sending files.

Use res.json() to send a JSON response in an HTTP function.

3fill in blank

hard

Fix the error in the HTTP function to correctly access query parameters.

Firebase

exports.queryParam = functions.https.onRequest((req, res) => {
  const name = req.[1].name;
  res.send(`Hello, ${name}!`);
});

Drag options to blanks, or click blank then click option'

Abody

Bparams

Cheaders

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.body which is for POST data.

Using req.params which is for URL path parameters.

Query parameters in HTTP requests are accessed via req.query.

4fill in blank

hard

Fill both blanks to create an HTTP function that responds with status 200 and a JSON message.

Firebase

exports.statusJson = functions.https.onRequest((req, res) => {
  res.status([1]).[2]({ message: 'Success' });
});

Drag options to blanks, or click blank then click option'

A200

Bjson

Csend

D404

Attempts:

3 left

💡 Hint

Common Mistakes

Using status 404 which means not found.

Using send instead of json for JSON responses.

Use res.status(200) to set HTTP status OK, then res.json() to send JSON.

5fill in blank

hard

Fill all three blanks to create an HTTP function that reads a POST JSON body field 'name' and responds with a greeting.

Firebase

exports.greetPost = functions.https.onRequest((req, res) => {
  const name = req.[1].[2];
  res.[3]({ greeting: `Hello, ${name}!` });
});

Drag options to blanks, or click blank then click option'

Abody

Bname

Cjson

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to get POST data from req.query.

Using res.send instead of res.json for JSON response.

POST JSON data is accessed via req.body. The field is name. Use res.json() to send JSON response.

Practice

1. What does an HTTP trigger function in Firebase do?

easy

A. Automatically updates the database without user input

B. Runs code when a specific web URL is visited

C. Sends emails to users without any request

D. Creates a new Firebase project

Solution

1. Step 1: Understand HTTP trigger functions

   HTTP trigger functions run when someone visits a specific web address (URL).

2. Step 2: Compare options with this behavior

   Only Runs code when a specific web URL is visited describes running code on visiting a URL, matching the definition.

3. Final Answer:

   Runs code when a specific web URL is visited -> Option B

4. Quick Check:

   HTTP trigger = run code on URL visit [OK]

Hint: HTTP trigger = runs code on web URL visit [OK]

Common Mistakes:

• Confusing HTTP triggers with database triggers
• Thinking HTTP triggers run automatically without requests
• Assuming HTTP triggers send emails by default

2. Which of the following is the correct way to define an HTTP trigger function in Firebase using Node.js?

easy

A. exports.myFunc = functions.storage.object().onFinalize((object) => { });

B. exports.myFunc = functions.database.onWrite((change, context) => { });

C. exports.myFunc = functions.https.onRequest((req, res) => { res.send('Hello'); });

D. exports.myFunc = functions.auth.user().onCreate((user) => { });

Solution

1. Step 1: Identify HTTP trigger syntax

   HTTP triggers use functions.https.onRequest with (req, res) parameters.

2. Step 2: Match options to this syntax

   Only exports.myFunc = functions.https.onRequest((req, res) => { res.send('Hello'); }); uses functions.https.onRequest correctly; others are for database, auth, or storage triggers.

3. Final Answer:

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

4. Quick Check:

   HTTP trigger uses functions.https.onRequest [OK]

Hint: HTTP triggers use functions.https.onRequest syntax [OK]

Common Mistakes:

• Using database or auth triggers instead of HTTP triggers
• Missing (req, res) parameters in function
• Confusing storage triggers with HTTP triggers

3. What will be the output when visiting the URL of this Firebase HTTP function?

exports.greet = functions.https.onRequest((req, res) => { const name = req.query.name || 'Guest'; res.send(`Hello, ${name}!`); });

URL visited: https://us-central1-project.cloudfunctions.net/greet?name=Alice

medium

A. Hello, Alice!

B. Hello, Guest!

C. Hello, undefined!

D. Error: name not found

Solution

1. Step 1: Understand query parameter usage

   The function reads the 'name' from the URL query string; if missing, it uses 'Guest'.

2. Step 2: Check the URL query

   The URL has '?name=Alice', so name = 'Alice'. The response is 'Hello, Alice!'.

3. Final Answer:

   Hello, Alice! -> Option A

4. Quick Check:

   Query name=Alice -> Hello, Alice! [OK]

Hint: Query params fill variables; missing uses default [OK]

Common Mistakes:

• Ignoring query parameters and using default always
• Assuming undefined if parameter missing
• Expecting error instead of default value

4. Identify the error in this Firebase HTTP trigger function:

exports.testFunc = functions.https.onRequest((request, response) => { response.send('Test'); response.send('Done'); });

medium

A. Incorrect parameter names for the function

B. Missing return statement after response.send()

C. No error, function works fine

D. Calling response.send() twice causes an error

Solution

1. Step 1: Check response.send() usage

   response.send() ends the HTTP response. Calling it twice causes an error.

2. Step 2: Analyze the code flow

   The function calls response.send('Test') then immediately calls response.send('Done'), which is invalid.

3. Final Answer:

   Calling response.send() twice causes an error -> Option D

4. Quick Check:

   Only one response.send() allowed per request [OK]

Hint: Use response.send() only once per HTTP request [OK]

Common Mistakes:

• Calling response.send() multiple times
• Thinking parameter names must be req, res exactly
• Ignoring that response ends after send

5. You want to create an HTTP trigger function that accepts a JSON body with a field age and responds with {"canVote": true} if age is 18 or more, otherwise {"canVote": false}. Which code snippet correctly implements this?

hard

A. exports.checkVote = functions.https.onRequest((req, res) => { const age = req.body.age; if(age >= 18) { res.json({canVote: true}); } else { res.json({canVote: false}); } });

B. exports.checkVote = functions.https.onRequest((req, res) => { const age = req.query.age; if(age > 18) { res.send({canVote: true}); } else { res.send({canVote: false}); } });

C. exports.checkVote = functions.https.onRequest((req, res) => { const age = req.body.age; if(age > 18) { res.send('{"canVote": true}'); } else { res.send('{"canVote": false}'); } });

D. exports.checkVote = functions.https.onRequest((req, res) => { const age = req.body.age; if(age > 18) { res.send({canVote: true}); } else { res.send({canVote: false}); } });

Solution

1. Step 1: Identify correct data source and response method

   The age is sent in JSON body, so use req.body.age. To send JSON response, use res.json().

2. Step 2: Check conditions and response format

   exports.checkVote = functions.https.onRequest((req, res) => { const age = req.body.age; if(age >= 18) { res.json({canVote: true}); } else { res.json({canVote: false}); } }); correctly checks age >= 18 and sends JSON object with canVote true or false using res.json().

3. Final Answer:

   exports.checkVote = functions.https.onRequest((req, res) => { const age = req.body.age; if(age >= 18) { res.json({canVote: true}); } else { res.json({canVote: false}); } }); -> Option A

4. Quick Check:

   Use req.body and res.json() for JSON input/output [OK]

Hint: Use req.body for JSON input and res.json() to respond [OK]

Common Mistakes:

• Using req.query instead of req.body for JSON data
• Sending JSON as string instead of object
• Using res.send() with object without res.json()