Google sign-in in Firebase - Step-by-Step Execution

Process Flow - Google sign-in

User clicks 'Sign in with Google'

↓

Firebase triggers Google sign-in popup

↓

User selects Google account

↓

Firebase receives Google account info

↓

Firebase authenticates user

↓

User signed in, app updates UI

This flow shows how a user clicks the Google sign-in button, selects an account, and Firebase authenticates them, updating the app state.

Execution Sample

Firebase

const provider = new firebase.auth.GoogleAuthProvider();
firebase.auth().signInWithPopup(provider)
  .then(result => {
    console.log('User signed in:', result.user.email);
  })
  .catch(error => {
    console.error('Sign-in error:', error.message);
  });

This code triggers a Google sign-in popup and logs the signed-in user's email or an error.

Process Table

Step	Action	Firebase State	User Interaction	Result
1	User clicks 'Sign in with Google'	No user signed in	Click button	Popup opens
2	Firebase shows Google sign-in popup	Waiting for user	Select Google account	Account info sent
3	Firebase authenticates user	Authenticating	None	User credentials verified
4	Sign-in success	User signed in	None	User email available
5	App updates UI	User signed in	None	Welcome message shown
6	End	User signed in	None	Process complete

💡 User successfully signed in or error handled after popup interaction

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
firebase.auth().currentUser	null	null	null	{email: '[e-mail]'}	{email: '[e-mail]'}
signInWithPopup(provider) promise	pending	pending	resolved	resolved	resolved

Key Moments - 3 Insights

Why does the popup open only after clicking the sign-in button?

Because Firebase triggers the Google sign-in popup only when signInWithPopup(provider) is called, which happens after the user clicks the button (see execution_table step 1).

What happens if the user closes the popup without selecting an account?

The promise rejects with an error, so the catch block runs (not shown in table), and no user is signed in (firebase.auth().currentUser remains null).

When is the user information available in the app?

After Firebase successfully authenticates the user (step 4), the user info is available in firebase.auth().currentUser and can be used to update the UI.

Visual Quiz - 3 Questions

Look at the execution table, what is the Firebase state at Step 3?

A Waiting for user

B User signed in

C Authenticating

D No user signed in

💡 Hint

Check the 'Firebase State' column at Step 3 in the execution_table.

At which step does the user email become available?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Result' column where user email is mentioned in the execution_table.

If the user closes the popup without selecting an account, what happens to firebase.auth().currentUser?

A It remains null

B It becomes the selected account

C It becomes undefined

D It contains an error message

💡 Hint

Refer to key_moments about popup closure and variable_tracker for currentUser state.

Concept Snapshot

Google sign-in with Firebase:
1. Create GoogleAuthProvider instance.
2. Call signInWithPopup(provider) on user click.
3. User selects Google account in popup.
4. Firebase authenticates and returns user info.
5. Update app UI with signed-in user.
Always handle errors from popup rejection.

Full Transcript

This visual execution trace shows how Google sign-in works with Firebase. When the user clicks the sign-in button, Firebase opens a Google sign-in popup. The user selects their Google account, and Firebase authenticates them. After successful authentication, the user's email is available in firebase.auth().currentUser, and the app updates the UI to welcome the user. If the user closes the popup without signing in, no user is signed in and an error is handled. The trace follows each step, showing Firebase state changes and user interactions.

Practice

1. What is the main purpose of using Google sign-in with Firebase Authentication?

easy

A. To store user data in Google Drive

B. To let users log in easily using their Google accounts

C. To send emails through Gmail automatically

D. To create Google Cloud virtual machines

Solution

1. Step 1: Understand Firebase Authentication

   Firebase Authentication helps users sign in securely to apps.

2. Step 2: Identify Google sign-in role

   Google sign-in allows users to log in using their Google accounts easily.

3. Final Answer:

   To let users log in easily using their Google accounts -> Option B

4. Quick Check:

   Google sign-in = Easy user login [OK]

Hint: Google sign-in means easy login with Google accounts [OK]

Common Mistakes:

• Confusing sign-in with data storage
• Thinking it sends emails automatically
• Assuming it manages cloud machines

2. Which Firebase Authentication code snippet correctly initializes Google sign-in in JavaScript?

easy

A. const provider = new firebase.auth.TwitterAuthProvider();

B. const provider = new firebase.auth.EmailAuthProvider();

C. const provider = new firebase.auth.FacebookAuthProvider();

D. const provider = new firebase.auth.GoogleAuthProvider();

Solution

1. Step 1: Identify correct provider for Google sign-in

   Google sign-in uses GoogleAuthProvider in Firebase Authentication.

2. Step 2: Match code snippet

   The snippet with new firebase.auth.GoogleAuthProvider() is correct.

3. Final Answer:

   const provider = new firebase.auth.GoogleAuthProvider(); -> Option D

4. Quick Check:

   GoogleAuthProvider = Google sign-in [OK]

Hint: Google sign-in uses GoogleAuthProvider class [OK]

Common Mistakes:

• Using EmailAuthProvider for Google sign-in
• Confusing with Twitter or Facebook providers
• Missing 'new' keyword in initialization

3. Given this JavaScript code snippet for Google sign-in, what will be logged if the user successfully signs in?

const provider = new firebase.auth.GoogleAuthProvider();
firebase.auth().signInWithPopup(provider)
  .then((result) => {
    console.log(result.user.email);
  })
  .catch((error) => {
    console.log(error.message);
  });

medium

A. The user's Google email address

B. An error message about sign-in failure

C. The user's Google profile photo URL

D. The user's Google display name

Solution

1. Step 1: Analyze the success callback

   On success, result.user.email is logged.

2. Step 2: Understand what result.user.email contains

   It contains the signed-in user's Google email address.

3. Final Answer:

   The user's Google email address -> Option A

4. Quick Check:

   result.user.email = user email [OK]

Hint: signInWithPopup success logs user email [OK]

Common Mistakes:

• Confusing email with display name or photo URL
• Assuming error message logs on success
• Ignoring the promise success path

4. You wrote this code to sign in with Google but get an error: firebase.auth().signInWithPopup(provider) is not a function. What is the likely cause?

medium

A. The user canceled the sign-in popup

B. Google sign-in is disabled in Firebase console

C. Firebase Authentication SDK is not imported or initialized properly

D. The provider variable is not declared

Solution

1. Step 1: Understand the error message

   The error says signInWithPopup is not a function, meaning Firebase Auth is missing or not loaded.

2. Step 2: Identify common causes

   Not importing or initializing Firebase Authentication SDK causes this error.

3. Final Answer:

   Firebase Authentication SDK is not imported or initialized properly -> Option C

4. Quick Check:

   Missing SDK causes method undefined error [OK]

Hint: Check Firebase Auth SDK import if signInWithPopup missing [OK]

Common Mistakes:

• Assuming Google sign-in disabled causes method error
• Ignoring SDK import errors
• Confusing user cancel with missing function error

5. You want to allow users to sign in with Google and then save their display name and email in Firestore. Which sequence of steps is correct?

hard

A. Enable Google sign-in in Firebase console, sign in with GoogleAuthProvider, then write user info to Firestore

B. Sign in with GoogleAuthProvider, then enable Google sign-in in Firebase console, then write user info

C. Write user info to Firestore first, then enable Google sign-in, then sign in

D. Enable Google sign-in in Firebase console, write user info to Firestore, then sign in

Solution

1. Step 1: Enable Google sign-in in Firebase console

   This step is required before users can sign in with Google.

2. Step 2: Sign in users using GoogleAuthProvider

   After enabling, use Firebase code to sign in users.

3. Step 3: Save user display name and email to Firestore

   Once signed in, write user info to Firestore database.

4. Final Answer:

   Enable Google sign-in in Firebase console, sign in with GoogleAuthProvider, then write user info to Firestore -> Option A

5. Quick Check:

   Enable -> Sign in -> Save data [OK]

Hint: Enable sign-in first, then sign in, then save user data [OK]

Common Mistakes:

• Trying to sign in before enabling Google sign-in
• Saving user data before sign-in
• Changing order of steps incorrectly