What are Firebase Cloud Functions?

Firebase Cloud Functions

Firebase Cloud Functions is a serverless backend for your Firebase app that allows you to run backend logic in response to events triggered by Firebase services and HTTPS requests.

How It Works

You write JavaScript/TypeScript functions.
These functions run in a Node.js environment on Google Cloud.
Functions execute when specific triggers occur (e.g., database changes, user sign-ups, HTTP requests).
No need to manage servers—Google scales automatically.

Key Features

* Event-driven execution – Respond to Firebase & Google Cloud events.
* Serverless – No need to manage infrastructure.
* Scalable – Automatically scales based on demand.
* Secure – Runs in an isolated cloud environment.
* Integrates with Firebase & external APIs – Can interact with Firestore, FCM, Auth, and more.

Common Use Cases

* Authentication Triggers – Send welcome emails when users sign up.
* Firestore Triggers – Validate or modify data when added/updated.
* FCM Triggers – Send push notifications on specific events.
* Scheduled Tasks – Run periodic jobs (e.g., cleanup inactive users).
* Custom APIs – Expose REST API endpoints for web & mobile apps.

How to Set Up Firebase Cloud Functions

1. Install Firebase CLI

npm install -g firebase-tools

2. Initialize Cloud Functions

firebase init functions

Select JavaScript or TypeScript.
Choose the Firebase project.
Install dependencies.

3. Writing a Simple Function

Open functions/index.js and add:

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

// Simple HTTP function
exports.helloWorld = functions.https.onRequest((req, res) => {
    res.send("Hello from Firebase Cloud Functions!");
});

4. Deploy Your Function

firebase deploy --only functions

5. Triggering the Function

Once deployed, Firebase provides a URL:

https://us-central1-YOUR_PROJECT.cloudfunctions.net/helloWorld

Open it in a browser or call it from a mobile app.

Example: Firestore Trigger

Send a push notification when a new document is added to Firestore.

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

admin.initializeApp();

exports.sendNotification = functions.firestore
    .document("messages/{messageId}")
    .onCreate(async (snap, context) => {
        const messageData = snap.data();
        
        const payload = {
            notification: {
                title: "New Message!",
                body: messageData.text,
                click_action: "FLUTTER_NOTIFICATION_CLICK"
            }
        };

        return admin.messaging().sendToTopic("messages", payload);
    });

Cloud Function Triggers

Trigger	Description
HTTPS Requests	Expose REST APIs (`onRequest`)
Firestore	Listen for document changes (`onCreate`, `onUpdate`, `onDelete`)
Authentication	React to user sign-ups or deletions (`onCreate`, `onDelete`)
Firebase Storage	Run functions on file uploads (`onFinalize`, `onDelete`)
Firebase Messaging (FCM)	Process push notifications (`onMessagePublished`)
Scheduled Functions	Run tasks on a cron schedule (`pubsub.schedule`)

Advanced Features

Environment Variables: Store API keys securely.
Logging & Monitoring: Use Firebase Logs (firebase functions:log).
Cloud Functions with Express.js: Build complex APIs.