Authentication trigger functions in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Firebase Authentication trigger function?

Consider this Firebase Cloud Function that triggers when a user is created. What will be logged when a new user with email '[e-mail]' is created?

Firebase

exports.userCreated = functions.auth.user().onCreate((user) => {
  console.log(`New user created: ${user.email}`);
  return null;
});

A New user created: [e-mail]

B New user created: undefined

C Error: user.email is not defined

D No output is logged

💡 Hint

The user object passed to the trigger contains the user's email property.

The onCreate trigger receives a user object with properties including email. Logging user.email prints the new user's email.

🧠 Conceptual

intermediate

Which Firebase Authentication trigger runs when a user deletes their account?

Firebase Authentication provides triggers for user lifecycle events. Which trigger function runs when a user deletes their account?

A functions.auth.user().onDestroy()

B functions.auth.user().onRemove()

C functions.auth.user().onDelete()

D functions.auth.user().onExpire()

💡 Hint

The trigger name includes 'Delete' for account deletion.

The onDelete() trigger runs when a user account is deleted in Firebase Authentication.

📝 Syntax

advanced

Identify the syntax error in this Firebase Authentication trigger function

Which option contains the correct syntax for a Firebase Authentication onCreate trigger function?

Firebase

exports.newUser = functions.auth.user().onCreate((user) => {
  console.log('User created:', user.uid);
  return null;
});

A

exports.newUser = functions.auth.user().onCreate((user) => {
  console.log('User created:', user.uid);
  return null;
}

B

exports.newUser = functions.auth.user().onCreate((user) => {
  console.log('User created:', user.uid)
  return null;
});

C

exports.newUser = functions.auth.user().onCreate(user => {
  console.log('User created:', user.uid);
  return null;
});

D

exports.newUser = functions.auth.user().onCreate((user) => {
  console.log('User created:', user.uid);
  return null;
});

💡 Hint

Check for missing semicolons and balanced brackets.

Option D has correct arrow function syntax, balanced braces, and semicolons. Others have missing semicolon or brace.

❓ optimization

advanced

How to optimize a Firebase Authentication onCreate trigger to minimize cold start time?

You want your Firebase Authentication onCreate trigger to run quickly when a user signs up. Which practice helps reduce cold start delays?

A Use global imports and initialize heavy libraries outside the trigger function

B Import only necessary modules inside the trigger function, not globally

C Write all code inside the trigger function without external imports

D Avoid using async/await in the trigger function

💡 Hint

Cold start is affected by how much code loads before the function runs.

Initializing heavy libraries globally allows Firebase to reuse the instance, reducing cold start time.

🔧 Debug

expert

Why does this Firebase Authentication onDelete trigger fail to run?

Given this code, why does the onDelete trigger not execute when a user deletes their account? exports.userDeleted = functions.auth.user().onDelete((user) => { console.log('User deleted:', user.uid); return null; });

A The user parameter is undefined in onDelete triggers

B The function is not deployed to Firebase after code changes

C The trigger should be onRemove, not onDelete

D Firebase Authentication does not support onDelete triggers

💡 Hint

Check if the function is active in your Firebase project.

If the function is not deployed, it won't run even if the code is correct.