FCM setup in Firebase - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Firebase Cloud Messaging (FCM)?

FCM is a service that lets you send notifications and messages to users' devices for free, helping apps stay connected and updated.

beginner

What is the first step to set up FCM in a mobile app?

Create a Firebase project in the Firebase console and add your app to that project.

beginner

Why do you need to download the configuration file (GoogleService-Info.plist or google-services.json)?

This file contains keys and settings that connect your app to Firebase services, including FCM.

intermediate

What role does the Firebase SDK play in FCM setup?

The Firebase SDK helps your app receive messages and notifications by handling communication with Firebase servers.

beginner

How do you send a test notification after setting up FCM?

Use the Firebase console's Cloud Messaging tab to compose and send a test message to your app or device.

What is the main purpose of Firebase Cloud Messaging?

A Host app backend servers

B Store user data securely

C Analyze app usage statistics

D Send notifications and messages to user devices

FCM is designed to send notifications and messages to devices.

Which file must you add to your app to connect it with Firebase services?

A firebase-config.json

B config.xml

C GoogleService-Info.plist or google-services.json

D appsettings.json

This file contains the necessary Firebase project settings for your app.

Where do you create a Firebase project for FCM setup?

A Firebase Console

B Xcode

C Android Studio

D Google Cloud Console

Firebase Console is where you create and manage Firebase projects.

What is required to receive messages in your app using FCM?

A Firebase SDK integrated in the app

B A web server

C A database connection

D An email account

The Firebase SDK handles receiving messages from FCM.

How can you test sending a notification after FCM setup?

A Send an email to Firebase support

B Use Firebase Console's Cloud Messaging tab

C Restart the app multiple times

D Use Android Studio's emulator only

Firebase Console provides a simple interface to send test messages.

Describe the main steps to set up Firebase Cloud Messaging in a mobile app.

Think about what you do from Firebase console to your app code.

Explain why the Firebase configuration file is important for FCM setup.

Consider what would happen if the app had no connection info.

Practice

1. What is the main purpose of Firebase Cloud Messaging (FCM)?

easy

A. To host web applications

B. To store user data securely in the cloud

C. To create user authentication systems

D. To send notifications and messages to users' devices

Solution

1. Step 1: Understand FCM's role

   FCM is designed to send notifications and messages to devices.

2. Step 2: Compare with other Firebase features

   Other options describe different Firebase services, not FCM.

3. Final Answer:

   To send notifications and messages to users' devices -> Option D

4. Quick Check:

   FCM = Messaging service [OK]

Hint: FCM = Firebase messaging to devices [OK]

Common Mistakes:

• Confusing FCM with data storage
• Thinking FCM handles authentication
• Assuming FCM hosts websites

2. Which Firebase method is used to request permission for notifications in a web app?

easy

A. Notification.requestPermission()

B. firebase.messaging().getToken()

C. firebase.initializeApp()

D. firebase.auth().signIn()

Solution

1. Step 1: Identify permission request method

   Web notifications require calling Notification.requestPermission() to ask user consent.

2. Step 2: Differentiate from other Firebase methods

   getToken() retrieves the token after permission; initializeApp() sets up Firebase; signIn() is for authentication.

3. Final Answer:

   Notification.requestPermission() -> Option A

4. Quick Check:

   Permission request = Notification.requestPermission() [OK]

Hint: Permission uses browser Notification API, not Firebase method [OK]

Common Mistakes:

• Using getToken() to request permission
• Confusing initializeApp() with permission request
• Thinking signIn() handles notifications

3. Given this code snippet, what will console.log(token) output if permission is granted and token is retrieved successfully?

const messaging = firebase.messaging();
Notification.requestPermission().then(() => {
  return messaging.getToken();
}).then(token => {
  console.log(token);
}).catch(err => {
  console.error('Error:', err);
});

medium

A. undefined

B. A string token representing the device registration

C. An error message

D. null

Solution

1. Step 1: Analyze permission and token retrieval

   If permission is granted, messaging.getToken() returns a string token.

2. Step 2: Understand console.log output

   console.log(token) prints the token string, not undefined or null.

3. Final Answer:

   A string token representing the device registration -> Option B

4. Quick Check:

   Successful getToken() = string token [OK]

Hint: getToken() returns string token on success [OK]

Common Mistakes:

• Expecting undefined or null instead of token
• Assuming error logs on success
• Confusing token with permission status

4. You wrote this code to get an FCM token but always get an error. What is the likely mistake?

const messaging = firebase.messaging();
const token = messaging.getToken();
console.log(token);

medium

A. Missing permission request before calling getToken()

B. firebase.messaging() is not initialized

C. getToken() returns a promise, not a direct value

D. console.log() cannot print tokens

Solution

1. Step 1: Verify permission requirement

   The code calls getToken() without first requesting notification permission using Notification.requestPermission().

2. Step 2: Consequence of missing permission

   Without granted permission, messaging.getToken() rejects the promise with an error, leading to an unhandled promise rejection error.

3. Final Answer:

   Missing permission request before calling getToken() -> Option A

4. Quick Check:

   Permission before getToken() [OK]

Hint: Request permission with Notification.requestPermission() before getToken() [OK]

Common Mistakes:

• Not using .then() or await with getToken()
• Forgetting to initialize Firebase
• Thinking console.log() cannot print tokens

5. You want to ensure your app always sends notifications to the correct device even if the FCM token changes. What is the best practice to handle token updates?

hard

A. Generate a new token manually every time the app starts

B. Store the token once and never update it

C. Listen for token refresh events and update your server with the new token

D. Ignore token changes because they rarely happen

Solution

1. Step 1: Understand token lifecycle

   FCM tokens can change, so apps must detect and handle updates.

2. Step 2: Use token refresh listener

   Listening for token refresh events lets the app send new tokens to the server to keep messaging accurate.

3. Final Answer:

   Listen for token refresh events and update your server with the new token -> Option C

4. Quick Check:

   Handle token refresh = update server [OK]

Hint: Always update server on token refresh events [OK]

Common Mistakes:

• Storing token once without updates
• Manually generating tokens incorrectly
• Ignoring token changes