Authentication trigger functions in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a Firebase Authentication trigger for user creation.

Firebase

exports.userCreated = functions.auth.user().[1]((user) => {
  console.log('User created:', user.uid);
});

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

AonWrite

BonDelete

ConCreate

DonUpdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using onDelete instead of onCreate triggers on user deletion.

Using onUpdate triggers on user data changes, not creation.

The onCreate method triggers the function when a new user is created.

2fill in blank

medium

Complete the code to define a Firebase Authentication trigger for user deletion.

Firebase

exports.userDeleted = functions.auth.user().[1]((user) => {
  console.log('User deleted:', user.uid);
});

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

AonDelete

BonCreate

ConUpdate

DonWrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using onCreate instead of onDelete triggers on user creation.

Using onUpdate triggers on user data changes, not deletion.

The onDelete method triggers the function when a user is deleted.

3fill in blank

hard

Fix the error in the code to correctly trigger on user creation.

Firebase

exports.newUser = functions.auth.user().[1]((user) => {
  console.log('New user ID:', user.uid);
});

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

AonCreate

BonUpdate

ConDelete

DonWrite

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing onCreate with onDelete or onUpdate triggers.

Using onWrite which is not a valid auth trigger.

The correct trigger for user creation is onCreate. Using onDelete or others will not trigger on creation.

4fill in blank

hard

Fill both blanks to log the user's email and UID when a user is deleted.

Firebase

exports.logDeletedUser = functions.auth.user().[1]((user) => {
  console.log('Deleted user email:', user.[2]);
});

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

AonDelete

BonCreate

Cemail

Duid

Attempts:

3 left

💡 Hint

Common Mistakes

Using onCreate instead of onDelete for deletion triggers.

Accessing user.uid instead of user.email when email is needed.

The trigger onDelete runs when a user is deleted. The user's email is accessed with user.email.

5fill in blank

hard

Fill all three blanks to create a trigger that logs the user's UID, email, and creation time when a user is created.

Firebase

exports.logNewUser = functions.auth.user().[1]((user) => {
  console.log('User ID:', user.[2]);
  console.log('Email:', user.[3]);
  console.log('Created at:', user.metadata.creationTime);
});

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

AonCreate

Buid

Cemail

DonDelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using onDelete instead of onCreate for creation triggers.

Mixing up user.uid and user.email properties.

The trigger onCreate runs when a user is created. The user's UID and email are accessed with user.uid and user.email.

Practice

1. What does the Firebase Authentication trigger function onCreate do?

easy

A. It sends a password reset email.

B. It deletes a user from the database.

C. It runs automatically when a new user signs up.

D. It updates user profile information.

Solution

1. Step 1: Understand the purpose of onCreate

   The onCreate trigger runs when a new user account is created in Firebase Authentication.

2. Step 2: Match the trigger to the correct action

   Since it runs on new user sign-up, it does not delete users or send emails directly.

3. Final Answer:

   It runs automatically when a new user signs up. -> Option C

4. Quick Check:

   onCreate = New user signup trigger [OK]

Hint: Remember: onCreate = new user signup trigger [OK]

Common Mistakes:

• Confusing onCreate with onDelete trigger
• Thinking onCreate sends emails automatically
• Assuming onCreate updates user data

2. Which of the following is the correct syntax to define a Firebase Authentication trigger function for user deletion in Node.js?

easy

A. functions.auth.user().onCreate((user) => { /* code */ });

B. exports.userDeleted = functions.auth.user().onDelete((user) => { /* code */ });

C. exports.userDeleted = functions.auth.user().onRemove((user) => { /* code */ });

D. functions.auth.user().delete((user) => { /* code */ });

Solution

1. Step 1: Identify the correct trigger for user deletion

   The correct trigger for user deletion is onDelete attached to functions.auth.user().

2. Step 2: Check the syntax for exporting the function

   The function should be exported using exports.functionName = ... syntax.

3. Final Answer:

   exports.userDeleted = functions.auth.user().onDelete((user) => { /* code */ }); -> Option B

4. Quick Check:

   onDelete trigger syntax = exports.userDeleted = functions.auth.user().onDelete((user) => { /* code */ }); [OK]

Hint: Use exports.functionName = functions.auth.user().onDelete(...) [OK]

Common Mistakes:

• Using onCreate instead of onDelete for deletion
• Using non-existent onRemove trigger
• Not exporting the function properly

3. Given the following Firebase Authentication trigger function, what will be logged when a user signs up?

exports.welcomeUser = functions.auth.user().onCreate((user) => {
  console.log(`Welcome, ${user.email}!`);
});

medium

A. Welcome, undefined!

B. Welcome, user.email!

C. No output, function does not run on sign-up.

D. Welcome, [e-mail]!

Solution

1. Step 1: Understand the onCreate trigger behavior

   The function runs automatically when a new user signs up, receiving the user object with an email property.

2. Step 2: Analyze the console.log statement

   The template string inserts the user's email, so it logs "Welcome, [e-mail]!" if the user's email is [e-mail].

3. Final Answer:

   Welcome, [e-mail]! -> Option D

4. Quick Check:

   onCreate logs user email correctly [OK]

Hint: onCreate passes user object with email property [OK]

Common Mistakes:

• Assuming user.email is undefined
• Thinking function does not run on sign-up
• Misreading template string syntax

4. Identify the error in this Firebase Authentication trigger function code:

exports.deleteUserData = functions.auth.user().onDelete(user => {
  const uid = user.uid;
  admin.database().ref(`/users/${uid}`).remove();
});

medium

A. admin is not initialized or imported.

B. Incorrect trigger function; should use onCreate instead of onDelete.

C. Missing return statement for the database operation.

D. The user parameter should be destructured as { uid }.

Solution

1. Step 1: Check for admin SDK initialization

   The code uses admin.database() but does not show admin being imported or initialized, which causes runtime errors.

2. Step 2: Verify other parts of the code

   The trigger and user parameter usage are correct; missing return is not mandatory but recommended.

3. Final Answer:

   admin is not initialized or imported. -> Option A

4. Quick Check:

   admin SDK must be initialized before use [OK]

Hint: Always import and initialize admin SDK before database calls [OK]

Common Mistakes:

• Confusing onDelete with onCreate trigger
• Ignoring admin SDK initialization
• Thinking return statement is mandatory

5. You want to send a welcome email only to users who sign up with an email ending in @example.com. Which code snippet correctly implements this using Firebase Authentication trigger functions?

hard

A. exports.sendWelcomeEmail = functions.auth.user().onCreate((user) => {
if (user.email.endsWith('@example.com')) {
sendEmail(user.email);
}
});

B. exports.sendWelcomeEmail = functions.auth.user().onDelete((user) => {
if (user.email.includes('@example.com')) {
sendEmail(user.email);
}
});

C. exports.sendWelcomeEmail = functions.auth.user().onCreate((user) => {
if (user.email === '@example.com') {
sendEmail(user.email);
}
});

D. exports.sendWelcomeEmail = functions.auth.user().onCreate((user) => {
if (user.email.indexOf('@example.com') === 0) {
sendEmail(user.email);
}
});

Solution

1. Step 1: Choose the correct trigger for new user sign-up

   Use onCreate to run code when a user signs up, not onDelete.

2. Step 2: Check the email condition for domain matching

   Use endsWith('@example.com') to check if the email ends with the domain. Using includes or equality check is incorrect here.

3. Final Answer:

   exports.sendWelcomeEmail = functions.auth.user().onCreate((user) => { if (user.email.endsWith('@example.com')) { sendEmail(user.email); } }); -> Option A

4. Quick Check:

   Use onCreate + endsWith() for domain check [OK]

Hint: Use onCreate and endsWith('@domain.com') to filter emails [OK]

Common Mistakes:

• Using onDelete instead of onCreate
• Checking email equality instead of endsWith
• Using indexOf === 0 instead of endsWith