firebase

# Firebase Firebase gives you a complete backend in minutes - auth, database, storage, functions, hosting. But the ease of setup hides real complexity. Security rules are your last line of defense, and they're often wrong. Firestore queries are limited, and you learn this after you've designed your data model. This skill covers Firebase Authentication, Firestore, Realtime Database, Cloud Functions, Cloud Storage, and Firebase Hosting. Key insight: Firebase is optimized for read-heavy, denormalized data. If you're thinking relationally, you're thinking wrong. 2025 lesson: Firestore pricing can surprise you. Reads are cheap until they're not. A poorly designed listener can cost more than a dedicated database. Plan your data model for your query patterns, not your data relationships. ## Principles - Design data for queries, not relationships - Security rules are mandatory, not optional - Denormalize aggressively - duplication is cheap, joins are expensive - Batch writes and transactions for consistency - Use offline persistence wisely - it's not free - Cloud Functions for what clients shouldn't do - Environment-based config, never hardcode keys in client ## Capabilities - firebase-auth - firestore - firebase-realtime-database - firebase-cloud-functions - firebase-storage - firebase-hosting - firebase-security-rules - firebase-admin-sdk - firebase-emulators ## Scope - general-backend-architecture -> backend - payment-processing -> stripe - email-sending -> email - advanced-auth-flows -> authentication-oauth - kubernetes-deployment -> devops ## Tooling ### Core - firebase - When: Client-side SDK Note: Modular SDK - tree-shakeable - firebase-admin - When: Server-side / Cloud Functions Note: Full access, bypasses security rules - firebase-functions - When: Cloud Functions v2 Note: v2 functions are recommended ### Testing - @firebase/rules-unit-testing - When: Testing security rules Note: Essential - rules bugs are security bugs - firebase-tools - When: Emulator suite Note: Local development without hitting production ### Frameworks - reactfire - When: React + Firebase Note: Hooks-based, handles subscriptions - vuefire - When: Vue + Firebase Note: Vue-specific bindings - angularfire - When: Angular + Firebase Note: Official Angular bindings ## Patterns ### Modular SDK Import Import only what you need for smaller bundles **When to use**: Client-side Firebase usage # MODULAR IMPORTS: """ Firebase v9+ uses modular SDK. Import only what you need. This enables tree-shaking and smaller bundles. """ // WRONG: v8-compat style (larger bundle) import firebase from 'firebase/compat/app'; import 'firebase/compat/firestore'; const db = firebase.firestore(); // RIGHT: v9+ modular (tree-shakeable) import { initializeApp } from 'firebase/app'; import { getFirestore, collection, doc, getDoc } from 'firebase/firestore'; const app = initializeApp(firebaseConfig); const db = getFirestore(app); // Get a document const docRef = doc(db, 'users', 'userId'); const docSnap = await getDoc(docRef); if (docSnap.exists()) { console.log(docSnap.data()); } // Query with constraints import { query, where, orderBy, limit } from 'firebase/firestore'; const q = query( collection(db, 'posts'), where('published', '==', true), orderBy('createdAt', 'desc'), limit(10) ); ### Security Rules Design Secure your data with proper rules from day one **When to use**: Any Firestore database # FIRESTORE SECURITY RULES: """ Rules are your last line of defense. Every read and write goes through them. Get them wrong, and your data is exposed. """ rules_version = '2'; service cloud.firestore { match /databases/{database}/documents { // Helper functions function isSignedIn() { return request.auth != null; } function isOwner(userId) { return request.auth.uid == userId; } function isAdmin() { return request.auth.token.admin == true; } // Users collection match /users/{userId} { // Anyone can read public profile allow read: if true; // Only owner can write their own data allow write: if isOwner(userId); // Private subcollection match /private/{document=**} { allow read, write: if isOwner(userId); } } // Posts collection match /posts/{postId} { // Anyone can read published posts allow read: if resource.data.published == true || isOwner(resource.data.authorId); // Only authenticated users can create allow create: if isSignedIn() && request.resource.data.authorId == request.auth.uid; // Only author can update/delete allow update, delete: if isOwner(resource.data.authorId); } // Admin-only collection match /admin/{document=**} { allow read, write: if isAdmin(); } } } ### Data Modeling for Queries Design Firestore data structure around query patterns **When to use**: Designing Firestore schema # FIRESTORE DATA MODELING: """ Firestore is NOT relational. You can't JOIN. Design your data for how you'll QUERY it, not how it relates. """ // WRONG: Normalized (SQL thinking) // users/{userId} // posts/{postId} with authorId field // To get "posts by user" - need to query posts collection // RIGHT: Denormalized for queries // users/{userId}/posts/{postId} - subcollection // OR // posts/{postId} with embedded author data // Document structure for a post const post = { id: 'post123', title: 'My Post', content: '...', // Embed frequently-needed author data author: { id: 'user456', name: 'Jane Doe', avatarUrl: '...' }, // Arrays for IN queries (max 30 items for 'in') tags: ['javascript', 'firebase'], // Maps for compound queries stats: { likes: 42, comments: 7, views: 1000 }, // Timestamps createdAt: serverTimestamp(), updatedAt: serverTimestamp(), // Booleans for filtering published: true, featured: false }; // Query patterns this enables: // - Get post with author info: 1 read (no join needed) // - Posts by tag: where('tags', 'array-contains', 'javascript') // - Featured posts: where('featured', '==', true) // - Recent posts: orderBy('createdAt', 'desc') // When author updates their name, update all their posts // This is the tradeoff: writes are more complex, reads are fast ### Real-time Listeners Subscribe to data changes with proper cleanup **When to use**: Real-time features # REAL-TIME LISTENERS: """ onSnapshot creates a persistent connection. Always unsubscribe when component unmounts to prevent memory leaks and extra reads. """ // React hook for real-time document function useDocument(path) { const [data, setData] = useState(null); const [loading, setLoading] = useState(true); const [error, setError] = useState(null); useEffect(() => { const docRef = doc(db, path); // Subscribe to document const unsubscribe = onSnapshot( docRef, (snapshot) => { if (snapshot.exists()) { setData({ id: snapshot.id, ...snapshot.data() }); } else { setData(null); } setLoading(false); }, (err) => { setError(err); setLoading(false); } ); // Cleanup on unmount return () => unsubscribe(); }, [path]); return { data, loading, error }; } // Usage function UserProfile({ userId }) { const { data: user, loading } = useDocument(`users/${userId}`); if (loading) return <Spinner />; return <div>{user?.name}</div>; } // Collection with query function usePosts(limit = 10) { const [posts, setPosts] = useState([]); useEffect(() => { const q = query( collection(db, 'posts'), where('published', '==', true), orderBy('createdAt', 'desc'), limit(limit) ); const unsubscribe = onSnapshot(q, (snapshot) => { const results = snapshot.docs.map(doc => ({ id: doc.id, ...doc.data() })); setPosts(results); }); return () => unsubscribe(); }, [limit]); return posts; } ### Cloud Functions Patterns Server-side logic with Cloud Functions v2 **When to use**: Backend logic, triggers, scheduled tasks # CLOUD FUNCTIONS V2: """ Cloud Functions run server-side code triggered by events. V2 uses more standard Node.js patterns and better scaling. """ import { onRequest } from 'firebase-functions/v2/https'; import { onDocumentCreated } from 'firebase-functions/v2/firestore'; import { onSchedule } from 'firebase-functions/v2/scheduler'; import { getFirestore } from 'firebase-admin/firestore'; import { initializeApp } from 'firebase-admin/app'; initializeApp(); const db = getFirestore(); // HTTP function export const api = onRequest( { cors: true, region: 'us-central1' }, async (req, res) => { // Verify auth token const token = req.headers.authorization?.split('Bearer ')[1]; if (!token) { res.status(401).json({ error: 'Unauthorized' }); return; } try { const decoded = await getAuth().verifyIdToken(token); // Process request with decoded.uid res.json({ userId: decoded.uid }); } catch (error) { res.status(401).json({ error: 'Invalid token' }); } } ); // Firestore trigger - on document create export const onUserCreated = onDocumentCreated( 'users/{userId}', async (event) => { const snapshot = event.data; const userId = event.params.userId; if (!snapshot) return; const userData = snapshot.data(); // Send welcome email, create related documents, etc. await db.collection('notifications').add({ userId, type: 'welcome', message: `Welcome, ${userData.name}!`, createdAt: FieldValue.serverTimestamp() }); } ); // Scheduled function (every day at midnight) export const dailyCleanup = onSchedule( { schedule: '0 0 * * *', timeZone: 'UTC' }, async (event) => { const cutoff = new Date(); cutoff.setDate(cutoff.getDate() - 30); // Delete old documents const oldDocs = await db.collection('logs') .where('createdAt', '<', cutoff) .limit(500) .get(); const batch = db.batch(); oldDocs.docs.forEach(doc => batch.delete(doc.ref)); await batch.commit(); console.log(`Deleted ${oldDocs.size} old logs`); } ); ### Batch Operations Atomic writes and transactions for consistency **When to use**: Multiple document updates that must succeed together # BATCH WRITES AND TRANSACTIONS: """ Batches: Multiple writes that all succeed or all fail. Transactions: Read-then-write operations with consistency. Max 500 operations per batch/transaction. """ import { writeBatch, runTransaction, doc, getDoc, increment, serverTimestamp } from 'firebase/firestore'; // Batch write - no reads, just writes async function createPostWithTags(post, tags) { const batch = writeBatch(db); // Create post const postRef = doc(collection(db, 'posts')); batch.set(postRef, { ...post, createdAt: serverTimestamp() }); // Update tag counts for (const tag of tags) { const tagRef = doc(db, 'tags', tag); batch.set(tagRef, { count: increment(1), lastUsed: serverTimestamp() }, { merge: true }); } await batch.commit(); return postRef.id; } // Transaction - read and write atomically async function likePost(postId, userId) { return runTransaction(db, async (transaction) => { const postRef = doc(db, 'posts', postId); const likeRef = doc(db, 'posts', postId, 'likes', userId); const postSnap = await transaction.get(postRef); if (!postSnap.exists()) { throw new Error('Post not found'); } const likeSnap = await transaction.get(likeRef); if (likeSnap.exists()) { throw new Error('Already liked'); } // Increment like count and add like document transaction.update(postRef, { likeCount: increment(1) }); transaction.set(likeRef, { userId, createdAt: serverTimestamp() }); return postSnap.data().likeCount + 1; }); } ### Social Login (Google, GitHub, etc.) OAuth provider setup and authentication flows **When to use**: Social login implementation # SOCIAL LOGIN WITH FIREBASE AUTH import { getAuth, signInWithPopup, signInWithRedirect, GoogleAuthProvider, GithubAuthProvider, OAuthProvider } from "firebase/auth";