Linking multiple providers in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize Firebase with the correct configuration object.

Firebase

const app = initializeApp([1]);

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

Asettings

BconfigObject

CfirebaseConfig

DappConfig

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that does not hold the Firebase config object.

Passing an empty object or undefined.

The initializeApp function requires the Firebase configuration object, which is usually named firebaseConfig.

2fill in blank

medium

Complete the code to link a Google provider to the current Firebase user.

Firebase

const provider = new GoogleAuthProvider();
const result = await linkWithPopup(auth.currentUser, [1]);

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

Aprovider

BtwitterProvider

CfacebookProvider

DgithubProvider

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a different provider variable that is not initialized.

Passing the provider class instead of an instance.

The linkWithPopup function requires the provider instance you want to link. Here, it is provider which is a GoogleAuthProvider instance.

3fill in blank

hard

Fix the error in the code to link a Facebook provider using a popup.

Firebase

const facebookProvider = new FacebookAuthProvider();
const user = auth.currentUser;
const linkedUser = await linkWithPopup([1], facebookProvider);

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

Auser

Bauth

Cauth.currentUser.uid

DfacebookProvider

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the auth object instead of the user.

Passing the user ID string instead of the user object.

The first argument to linkWithPopup must be the current user object, which is stored in user. Passing auth or other values causes errors.

4fill in blank

hard

Fill both blanks to link Twitter and GitHub providers to the current user.

Firebase

const twitterProvider = new TwitterAuthProvider();
const githubProvider = new GithubAuthProvider();
await linkWithPopup(auth.currentUser, [1]);
await linkWithPopup(auth.currentUser, [2]);

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

AtwitterProvider

BgithubProvider

CfacebookProvider

DgoogleProvider

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up provider variables.

Using providers not initialized in the code.

To link multiple providers, you call linkWithPopup with the current user and the provider instance. Here, the first call links twitterProvider, the second links githubProvider.

5fill in blank

hard

Fill all three blanks to handle linking Google, Facebook, and Twitter providers with error handling.

Firebase

try {
  await linkWithPopup(auth.currentUser, [1]);
  await linkWithPopup(auth.currentUser, [2]);
  await linkWithPopup(auth.currentUser, [3]);
} catch (error) {
  console.error('Error linking provider:', error);
}

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

AgoogleProvider

BfacebookProvider

CtwitterProvider

DgithubProvider

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong provider names.

Not wrapping calls in try-catch for error handling.

This code tries to link three providers: Google, Facebook, and Twitter. Each linkWithPopup call uses the current user and one provider instance. Errors are caught and logged.

Practice

1. What is the main purpose of linking multiple providers in Firebase Authentication?

easy

A. Encrypt user passwords for security

B. Allow users to sign in using different login methods for the same account

C. Automatically delete old user accounts

D. Create multiple accounts for one user

Solution

1. Step 1: Understand user account linking

   Linking multiple providers means connecting different login methods (like Google, Facebook) to one user account.

2. Step 2: Identify the purpose

   This allows users to sign in with any linked provider but access the same account.

3. Final Answer:

   Allow users to sign in using different login methods for the same account -> Option B

4. Quick Check:

   Linking providers = multiple logins one account [OK]

Hint: Linking means one account, many login ways [OK]

Common Mistakes:

• Thinking linking creates multiple accounts
• Confusing linking with password encryption
• Assuming linking deletes old accounts

2. Which Firebase method is used to link a new provider to an existing signed-in user using a popup?

easy

A. createUserWithEmailAndPassword

B. signInWithPopup

C. linkWithPopup

D. signOut

Solution

1. Step 1: Recall Firebase linking methods

   To link a new provider, Firebase offers methods like linkWithPopup and linkWithCredential.

2. Step 2: Identify the popup linking method

   linkWithPopup is specifically for linking using a popup window.

3. Final Answer:

   linkWithPopup -> Option C

4. Quick Check:

   Popup linking method = linkWithPopup [OK]

Hint: Popup linking always uses linkWithPopup [OK]

Common Mistakes:

• Using signInWithPopup instead of linkWithPopup
• Confusing createUserWithEmailAndPassword with linking
• Trying to link without a signed-in user

3. Consider this code snippet:

const user = firebase.auth().currentUser;
const credential = firebase.auth.GoogleAuthProvider.credential(idToken);

user.linkWithCredential(credential)
  .then(() => console.log('Linked!'))
  .catch(error => console.log(error.message));

What will happen if user is null?

medium

A. An error will occur because no user is signed in

B. The user will be linked successfully

C. The code will silently do nothing

D. A new user account will be created automatically

Solution

1. Step 1: Check currentUser value

   If user is null, it means no user is signed in currently.

2. Step 2: Understand linkWithCredential behavior

   linkWithCredential requires a signed-in user to link a new provider. Without a user, it throws an error.

3. Final Answer:

   An error will occur because no user is signed in -> Option A

4. Quick Check:

   Null user + linkWithCredential = error [OK]

Hint: Linking needs signed-in user; null means error [OK]

Common Mistakes:

• Assuming linking works without a signed-in user
• Expecting silent failure instead of error
• Thinking a new user is created automatically

4. You try to link a Facebook provider to a user but get an error: "auth/credential-already-in-use". What is the likely cause?

medium

A. The user is not signed in

B. The Firebase project is not configured for Facebook login

C. The Facebook SDK is not initialized

D. The Facebook account is already linked to another Firebase user

Solution

1. Step 1: Understand the error message

   "auth/credential-already-in-use" means the credential (Facebook account) is linked to a different Firebase user.

2. Step 2: Identify cause of error

   Trying to link a provider already linked to another user causes this error.

3. Final Answer:

   The Facebook account is already linked to another Firebase user -> Option D

4. Quick Check:

   Credential in use = linked to another user [OK]

Hint: Credential already linked means another user owns it [OK]

Common Mistakes:

• Assuming user not signed in causes this error
• Blaming SDK initialization instead of credential conflict
• Ignoring Firebase project configuration issues

5. You want to let users link Google and Facebook providers to one account. Which sequence correctly links both providers safely?

hard

A. Sign in user, link Google with linkWithPopup, then link Facebook with linkWithCredential

B. Link Google with linkWithPopup before sign-in, then sign in user, then link Facebook

C. Sign in user, link Facebook with linkWithPopup, then sign out and link Google

D. Create user with Facebook, then create user with Google, then merge accounts manually

Solution

1. Step 1: Ensure user is signed in before linking

   Linking requires a signed-in user, so sign in first.

2. Step 2: Link providers one by one

   Use linkWithPopup or linkWithCredential to link Google and Facebook safely after sign-in.

3. Step 3: Avoid signing out before linking all providers

   Signing out breaks the user session and prevents linking multiple providers to one account.

4. Final Answer:

   Sign in user, link Google with linkWithPopup, then link Facebook with linkWithCredential -> Option A

5. Quick Check:

   Sign in first, then link providers [OK]

Hint: Always sign in before linking multiple providers [OK]

Common Mistakes:

• Trying to link providers before signing in
• Signing out between linking providers
• Creating separate users instead of linking