Anonymous authentication in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to sign in a user anonymously using Firebase Authentication.

Firebase

firebase.auth().[1]()

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

AsignInAnonymously

BsignOut

CcreateUserWithEmailAndPassword

DsignInWithEmailAndPassword

Attempts:

3 left

💡 Hint

Common Mistakes

Using signInWithEmailAndPassword instead of signInAnonymously.

Trying to create a user with email and password for anonymous sign-in.

The signInAnonymously() method allows users to sign in without providing credentials.

2fill in blank

medium

Complete the code to check if the current user is signed in anonymously.

Firebase

const user = firebase.auth().currentUser;
if (user && user.[1]) {
  console.log('User is anonymous');
}

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

AisSignedIn

BisAnonymous

Canonymous

DisGuest

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent property like isSignedIn or isGuest.

Checking user.anonymous instead of user.isAnonymous.

The isAnonymous property is true if the user signed in anonymously.

3fill in blank

hard

Fix the error in the code to handle anonymous sign-in errors correctly.

Firebase

firebase.auth().signInAnonymously()
  .then(() => {
    console.log('Signed in anonymously');
  })
  .catch(error => {
    console.error('Error code:', [1]);
  });

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

Aerror.message

Berror.status

Cerror.code

Derror.reason

Attempts:

3 left

💡 Hint

Common Mistakes

Using error.message instead of error.code for error codes.

Using non-existent properties like error.status or error.reason.

The error.code property contains the error code string from Firebase Authentication.

4fill in blank

hard

Fill both blanks to link an anonymous user to an email/password account.

Firebase

const credential = firebase.auth.EmailAuthProvider.[1](email, password);
firebase.auth().currentUser.[2](credential)
  .then(() => console.log('Account linked'))
  .catch(error => console.error(error));

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

Acredential

BlinkWithCredential

CsignInWithCredential

DcreateCredential

Attempts:

3 left

💡 Hint

Common Mistakes

Using signInWithCredential instead of linkWithCredential for linking accounts.

Using createCredential which is not a Firebase method.

The EmailAuthProvider.credential() creates a credential object, and linkWithCredential() links it to the current user.

5fill in blank

hard

Fill both blanks to sign out the current user and then sign in anonymously again.

Firebase

firebase.auth().[1]()
  .then(() => firebase.auth().[2]())
  .then(() => console.log('Signed out and signed in anonymously'))
  .catch(error => console.error(error));

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

AsignOut

BsignInAnonymously

CsignInWithEmailAndPassword

DcreateUserWithEmailAndPassword

Attempts:

3 left

💡 Hint

Common Mistakes

Using signInWithEmailAndPassword instead of signInAnonymously for anonymous sign-in.

Not signing out before signing in anonymously again.

First, signOut() signs out the current user, then signInAnonymously() signs in anonymously again.

Practice

1. What is the main purpose of Firebase anonymous authentication?

easy

A. Store user data permanently without authentication

B. Require users to verify their email before using the app

C. Allow users to use the app without creating an account

D. Force users to sign in with Google or Facebook

Solution

1. Step 1: Understand anonymous authentication concept

   Anonymous authentication lets users access the app without signing up or providing credentials.

2. Step 2: Identify the purpose

   This reduces signup friction and improves user experience by creating a temporary user ID.

3. Final Answer:

   Allow users to use the app without creating an account -> Option C

4. Quick Check:

   Anonymous authentication = Allow use without account [OK]

Hint: Anonymous means no signup needed to start [OK]

Common Mistakes:

• Thinking anonymous auth requires email verification
• Confusing anonymous auth with social login
• Assuming anonymous users have permanent accounts

2. Which Firebase method is used to sign in anonymously in JavaScript?

easy

A. firebase.auth().signInWithEmailAndPassword()

B. firebase.auth().signOut()

C. firebase.auth().createUserWithEmailAndPassword()

D. firebase.auth().signInAnonymously()

Solution

1. Step 1: Recall Firebase anonymous sign-in method

   The correct method to sign in anonymously is signInAnonymously().

2. Step 2: Eliminate other methods

   Other methods are for email/password sign-in or sign-out, not anonymous sign-in.

3. Final Answer:

   firebase.auth().signInAnonymously() -> Option D

4. Quick Check:

   Anonymous sign-in method = signInAnonymously() [OK]

Hint: Anonymous sign-in uses signInAnonymously() method [OK]

Common Mistakes:

• Using email/password sign-in methods for anonymous login
• Confusing createUserWithEmailAndPassword with anonymous sign-in
• Trying to sign out instead of sign in

3. What will the following JavaScript code output if anonymous sign-in succeeds?

firebase.auth().signInAnonymously()
  .then(() => console.log('User ID:', firebase.auth().currentUser.uid))
  .catch(error => console.log('Error:', error.message))

medium

A. User ID: undefined

B. User ID: a unique temporary ID string

C. Error: User not signed in

D. User ID: null

Solution

1. Step 1: Understand signInAnonymously success behavior

   On success, Firebase creates a temporary user with a unique ID accessible via currentUser.uid.

2. Step 2: Analyze console.log output

   The code logs 'User ID:' followed by the unique temporary ID string.

3. Final Answer:

   User ID: a unique temporary ID string -> Option B

4. Quick Check:

   Anonymous sign-in returns unique temp ID [OK]

Hint: Success logs unique temporary user ID [OK]

Common Mistakes:

• Expecting undefined or null user ID after sign-in
• Assuming error message on success
• Confusing currentUser.uid with email or password

4. Identify the error in this Firebase anonymous sign-in code snippet:

firebase.auth().signInAnonymously
  .then(() => console.log('Signed in anonymously'))
  .catch(error => console.log(error))

medium

A. Missing parentheses after signInAnonymously

B. Incorrect use of .then() method

C. No catch block for errors

D. Using console.log inside then block

Solution

1. Step 1: Check method call syntax

   The method signInAnonymously must be called with parentheses ().

2. Step 2: Identify missing parentheses

   The code uses signInAnonymously without parentheses, so it does not invoke the function.

3. Final Answer:

   Missing parentheses after signInAnonymously -> Option A

4. Quick Check:

   Method calls need () to execute [OK]

Hint: Always add () to call functions [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Misplacing .then() or .catch() chaining
• Assuming console.log causes errors

5. You want to let users start anonymously but later upgrade to email/password without losing data. Which Firebase feature helps achieve this?

hard

A. Linking anonymous user to email/password credential

B. Deleting anonymous user and creating new account

C. Signing out anonymous user before email sign-up

D. Using separate Firebase projects for anonymous and email users

Solution

1. Step 1: Understand user upgrade process

   Firebase allows linking an anonymous user to an email/password credential to keep the same user ID and data.

2. Step 2: Evaluate options

   Deleting or signing out loses data; separate projects complicate management.

3. Final Answer:

   Linking anonymous user to email/password credential -> Option A

4. Quick Check:

   Link anonymous to email to keep data [OK]

Hint: Link accounts to upgrade without losing data [OK]

Common Mistakes:

• Deleting anonymous user before upgrade
• Signing out instead of linking accounts
• Using multiple projects unnecessarily