Firebase Cloud Messaging: Complete Guide for Node.js and Mobile

Why Firebase Cloud Messaging (FCM) is the Best Choice 

• Free and Scalable
  You can send millions of notifications without worrying about cost — FCM is completely free and handles large volumes easily. 

• Works on All Platforms
  Whether it’s Android, iOS, or Web — FCM supports all major platforms with just one integration. 

• Reliable Delivery
  Since it runs on Google’s powerful infrastructure, your messages are delivered quickly and consistently, even at scale. 

• Send More Than Just Notifications
  FCM allows you to send rich messages — not just titles and bodies, but also custom data (like IDs, URLs, Images) that your app can use to take actions. 

• Smart Targeting
  You can choose exactly who should receive the message — by device, user group, app version, or custom topics. 

• Built-in Analytics and Tracking
  FCM comes with delivery reports and integrates with Firebase Analytics, so you know how your messages are performing. 

FCM Architecture Overview 

• Device Registration:
  The mobile device registers with FCM (Android) or APNS (iOS) to obtain a Device Token used for uniquely identifying the app instance. 

• Developer Setup:
  The developer configures the Firebase project and uploads APNS certificates (for iOS) or uses FCM Server Key (for Android) to authorize message sending. 

• Token Sharing:
  The app sends the obtained Device Token to the Backend Server or Notification Provider, enabling them to send targeted messages. 

• Sending Notifications:
  The Backend or Notification Provider sends messages to FCM/APNS, which then delivers them to the appropriate devices using the token.

FCM Message Payload Structure 

FCM supports two types of messages: 

• Notification Messages (Handled automatically by OS if app is in background). 

• Data Messages (Requires app-side handling, useful for in-app updates). 

Sample JSON Payload: 

  { 
  "message": { 
    "token": "DEVICE_FCM_TOKEN", // FCM token of the target device 
    "notification": { 
      "title": "New Message!",   // Title shown in the notification 
      "body": "You have a new notification." //Body text shown in the notification 
    }, 
    "data": { 
      "action": "chat", // Custom key: Used to define app behavior (e.g., open chat screen) 
      "userId": "123"     // Custom key: Can be used to identify a specific user or context 
    } 
  } 
} 

Setting Up FCM in Android and iOS 

Android Setup: 

1. Add Firebase to Android Project 

• Go to Firebase Console. 
• Add your Android app (com.example.app) and download google-services.json. 
• Place it in app/ directory. 

2. Add Dependencies (app/build.gradle) 

implementation 'com.google.firebase:firebase-messaging:23.0.0' 

3.  Create a Service to Handle Messages 

class MyFirebaseMessagingService : FirebaseMessagingService() { 
    override fun onMessageReceived(message: RemoteMessage) { 
        // Handle notification/data payload here 
        Log.d("FCM", "Message: ${message.notification?.title}") 
    } 
} 

iOS Setup: 

1. Add Firebase to iOS Project 

• Register your iOS app in Firebase Console. 

• Download GoogleService-Info.plist and add it to Xcode.

2. Install Firebase SDK 

3. Configure AppDelegate for FCM 

Sending FCM Message from NodeJs 

1. Setup Firebase Project & Download Admin SDK 

• Go to Firebase Console 

• Create a new project (or use an existing one) 

• Navigate to: Project Settings → Service accounts 

• Click Generate new private key 

• Save the JSON file (this contains your Firebase credentials) 

• Install Firebase Admin SDK 

• npm install firebase-admin 

2. Initialize Firebase Admin 

const admin = require("firebase-admin"); 

const serviceAccount = require("./service-account-key.json"); 

admin.initializeApp({ 
  credential: admin.credential.cert(serviceAccount), 
}); 

// Send a notification 
const sendFCM = async (token, title, body, data = {}) => { 
  const message = { 
    token, 
    notification: { title, body }, 
    data, 
  }; 

  try { 
    await admin.messaging().send(message); 
    console.log("Message sent successfully!"); 
  } catch (err) { 
    console.error("FCM Error:", err); 
  } 
}; 

// Example usage 
sendFCM( 
  "DEVICE_TOKEN", 
  "Hello from Node.js!", 
  "This is a test FCM message.", 
  { action: "test" } 
); 

Testing and Sending Notifications 

You can test by calling your Node.js API with a valid device token. Use Postman to send a POST request to your backend with parameters like:

{ 
"token": "DEVICE_FCM_TOKEN", 
"title": "Hello", 
"body": "This is a test message." 
}

Common Issues and Fixes 

• Make sure the device token is correct. 
• Always handle errors (e.g., invalid tokens, network issues)
• Ensure Firebase is properly initialized in both frontend and backend.
• For iOS, ensure APNs certificates are uploaded in Firebase. 

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