How to Send Notifications Using Firebase Functions

Use Firebase Cloud Functions to trigger events and send notifications via Firebase Cloud Messaging (FCM). Write a function that listens to database or authentication events, then call admin.messaging().send() with the notification payload to deliver messages to devices.

Syntax

The basic syntax involves creating a Firebase Cloud Function that triggers on an event, then using the Firebase Admin SDK to send a notification message.

• functions.firestore.document('path').onCreate((snap, context) => { ... }): Trigger on Firestore document creation.
• admin.messaging().send(message): Sends a notification message.
• message: Object containing token or topic and notification details.

javascript

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.sendNotification = functions.firestore.document('messages/{messageId}').onCreate((snap, context) => {
  const messageData = snap.data();
  const payload = {
    notification: {
      title: messageData.title,
      body: messageData.body
    },
    token: messageData.token
  };
  return admin.messaging().send(payload);
});

Example

This example shows a Firebase Cloud Function that sends a notification when a new Firestore document is created in the messages collection. The notification includes a title and body, and is sent to a specific device token.

javascript

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.notifyNewMessage = functions.firestore.document('messages/{messageId}').onCreate(async (snap, context) => {
  const message = snap.data();

  const payload = {
    notification: {
      title: message.title || 'New Message',
      body: message.body || 'You have a new message.'
    },
    token: message.token
  };

  try {
    const response = await admin.messaging().send(payload);
    console.log('Notification sent successfully:', response);
    return null;
  } catch (error) {
    console.error('Error sending notification:', error);
    return null;
  }
});

Output

Notification sent successfully: projects/your-project-id/messages/1234567890

Common Pitfalls

• Missing device token: Notifications require a valid device token; ensure it is stored and passed correctly.
• Not initializing admin SDK: Always call admin.initializeApp() before using messaging.
• Incorrect payload format: The message object must have correct keys like notification and token or topic.
• Not handling async properly: Use async/await or return promises to avoid function timeout.

javascript

/* Wrong: Missing admin.initializeApp() */
const functions = require('firebase-functions');
const admin = require('firebase-admin');

exports.badFunction = functions.firestore.document('messages/{id}').onCreate((snap) => {
  const message = snap.data();
  const payload = { notification: { title: 'Hi' }, token: message.token };
  return admin.messaging().send(payload); // Error: admin not initialized
});

/* Right: Initialize admin SDK */
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.goodFunction = functions.firestore.document('messages/{id}').onCreate(async (snap) => {
  const message = snap.data();
  const payload = { notification: { title: 'Hi' }, token: message.token };
  return await admin.messaging().send(payload);
});

Quick Reference

Remember these key points when sending notifications with Firebase Functions:

• Initialize Firebase Admin SDK once per function file.
• Use triggers like Firestore, Realtime Database, or Authentication events.
• Prepare a message object with notification and token or topic.
• Return or await the admin.messaging().send() promise to complete the function.

Key Takeaways

Initialize Firebase Admin SDK before sending notifications in Cloud Functions.

Use event triggers like Firestore document creation to send notifications automatically.

Send notifications by calling admin.messaging().send() with a proper message payload.

Always handle asynchronous calls with async/await or return promises to avoid errors.

Ensure device tokens are valid and included in the notification payload.