Anonymous authentication in Firebase - Mini Project: Build & Apply

Anonymous Authentication with Firebase

📖 Scenario: You are building a simple app that lets users try it without signing up. This is called anonymous authentication. It helps users explore your app quickly.

🎯 Goal: Create a Firebase project setup that allows users to sign in anonymously. You will write code to initialize Firebase, enable anonymous sign-in, and handle the sign-in process.

📋 What You'll Learn

Initialize Firebase app with given config

Enable anonymous authentication in Firebase

Write code to sign in users anonymously

Handle sign-in success and failure

💡 Why This Matters

🌍 Real World

Anonymous authentication lets users try apps quickly without creating accounts. This improves user experience and can increase app engagement.

💼 Career

Understanding Firebase anonymous authentication is useful for frontend and backend developers working on user authentication and app onboarding.

1

Initialize Firebase App

Create a constant called firebaseConfig with the exact keys and values: apiKey: 'AIzaSyA-ExampleKey12345', authDomain: 'your-app.firebaseapp.com', projectId: 'your-app', storageBucket: 'your-app.appspot.com', messagingSenderId: '1234567890', appId: '1:1234567890:web:abcdef123456'. Then initialize Firebase app by calling initializeApp(firebaseConfig) and assign it to a constant called app.

Firebase

# Create firebaseConfig object and initialize Firebase app
# Your code here

Hint

Use const firebaseConfig = { ... } with the exact keys and values. Then call initializeApp(firebaseConfig) and assign it to app.

2

Import and Setup Firebase Auth

Import getAuth and signInAnonymously from 'firebase/auth'. Create a constant called auth by calling getAuth(app).

Firebase

import { initializeApp } from 'firebase/app';
// Import getAuth and signInAnonymously from 'firebase/auth'

const firebaseConfig = {
  apiKey: 'AIzaSyA-ExampleKey12345',
  authDomain: 'your-app.firebaseapp.com',
  projectId: 'your-app',
  storageBucket: 'your-app.appspot.com',
  messagingSenderId: '1234567890',
  appId: '1:1234567890:web:abcdef123456'
};

const app = initializeApp(firebaseConfig);

// Create auth constant by calling getAuth(app)
# Your code here

Hint

Import getAuth and signInAnonymously from 'firebase/auth'. Then create auth by calling getAuth(app).

3

Sign In Anonymously

Write a function called signInUserAnonymously that calls signInAnonymously(auth). Use .then() to handle success by receiving a userCredential parameter and accessing userCredential.user. Use .catch() to handle errors by receiving an error parameter.

Firebase

import { initializeApp } from 'firebase/app';
import { getAuth, signInAnonymously } from 'firebase/auth';

const firebaseConfig = {
  apiKey: 'AIzaSyA-ExampleKey12345',
  authDomain: 'your-app.firebaseapp.com',
  projectId: 'your-app',
  storageBucket: 'your-app.appspot.com',
  messagingSenderId: '1234567890',
  appId: '1:1234567890:web:abcdef123456'
};

const app = initializeApp(firebaseConfig);
const auth = getAuth(app);

// Write function signInUserAnonymously to sign in anonymously
# Your code here

Hint

Create a function signInUserAnonymously. Inside, call signInAnonymously(auth). Use .then() to get userCredential and access userCredential.user. Use .catch() to handle errors.

4

Call Anonymous Sign-In Function

Call the function signInUserAnonymously() to start the anonymous sign-in process.

Firebase

import { initializeApp } from 'firebase/app';
import { getAuth, signInAnonymously } from 'firebase/auth';

const firebaseConfig = {
  apiKey: 'AIzaSyA-ExampleKey12345',
  authDomain: 'your-app.firebaseapp.com',
  projectId: 'your-app',
  storageBucket: 'your-app.appspot.com',
  messagingSenderId: '1234567890',
  appId: '1:1234567890:web:abcdef123456'
};

const app = initializeApp(firebaseConfig);
const auth = getAuth(app);

function signInUserAnonymously() {
  signInAnonymously(auth)
    .then((userCredential) => {
      const user = userCredential.user;
      // User signed in anonymously
    })
    .catch((error) => {
      // Handle error
    });
}

// Call the signInUserAnonymously function
# Your code here

Hint

Simply call signInUserAnonymously() to start the anonymous sign-in.

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