Backend & APIs

# Create project folder
mkdir my-api && cd my-api

# Initialize Node.js project
npm init -y

# Install Express
npm install express

# Install dev tools
npm install -D nodemon  # auto-restart on file changes

# Add to package.json scripts:
# "dev": "nodemon server.js"

# Start dev server
npm run dev

const express = require('express');
const app = express();

// Middleware: parse JSON bodies
app.use(express.json());

// CORS: allow frontend to call this API
app.use((req, res, next) => {
  res.header('Access-Control-Allow-Origin', '*');
  res.header('Access-Control-Allow-Headers', 'Content-Type, Authorization');
  next();
});

// In-memory "database" (use a real DB in production)
let posts = [
  { id: 1, title: 'Hello World', author: 'Alice' },
  { id: 2, title: 'My Second Post', author: 'Bob' },
];

// GET all posts
app.get('/api/posts', (req, res) => {
  res.json({ success: true, data: posts });
});

// GET single post by ID
app.get('/api/posts/:id', (req, res) => {
  const post = posts.find(p => p.id === +req.params.id);
  if (!post) return res.status(404).json({ error: 'Not found' });
  res.json({ success: true, data: post });
});

// POST create a post
app.post('/api/posts', (req, res) => {
  const { title, author } = req.body;
  if (!title || !author) {
    return res.status(400).json({ error: 'title and author required' });
  }
  const newPost = { id: posts.length + 1, title, author };
  posts.push(newPost);
  res.status(201).json({ success: true, data: newPost });
});

// PUT update a post
app.put('/api/posts/:id', (req, res) => {
  const idx = posts.findIndex(p => p.id === +req.params.id);
  if (idx === -1) return res.status(404).json({ error: 'Not found' });
  posts[idx] = { ...posts[idx], ...req.body };
  res.json({ success: true, data: posts[idx] });
});

// DELETE a post
app.delete('/api/posts/:id', (req, res) => {
  posts = posts.filter(p => p.id !== +req.params.id);
  res.json({ success: true, message: 'Deleted' });
});

// Start server
app.listen(3000, () =>
  console.log(' API running at http://localhost:3000')
);

// 1. Install Firebase SDK
// npm install firebase

import { initializeApp } from 'firebase/app';
import {
  getFirestore, collection, addDoc,
  getDocs, doc, updateDoc, deleteDoc,
  onSnapshot, query, where, orderBy
} from 'firebase/firestore';

// 2. Initialize (from Firebase Console → Project Settings)
const app = initializeApp({
  apiKey: process.env.VITE_FIREBASE_API_KEY,
  authDomain: 'your-app.firebaseapp.com',
  projectId: 'your-app-id',
});

const db = getFirestore(app);

// 3. Add a document
async function addPost(title, content) {
  const docRef = await addDoc(collection(db, 'posts'), {
    title,
    content,
    createdAt: new Date(),
    likes: 0
  });
  console.log('Added with ID:', docRef.id);
}

// 4. Get all documents
async function getPosts() {
  const snapshot = await getDocs(collection(db, 'posts'));
  return snapshot.docs.map(d => ({ id: d.id, ...d.data() }));
}

// 5. Real-time listener (auto-updates when data changes!)
onSnapshot(collection(db, 'posts'), (snapshot) => {
  const posts = snapshot.docs.map(d => ({ id: d.id, ...d.data() }));
  renderPosts(posts); // update your UI
});

// 6. Query with filters
const q = query(
  collection(db, 'posts'),
  where('likes', '>', 10),
  orderBy('createdAt', 'desc')
);

// 7. Update a document
await updateDoc(doc(db, 'posts', postId), { likes: 11 });

// 8. Delete a document
await deleteDoc(doc(db, 'posts', postId));

import {
  getAuth, signInWithPopup, GoogleAuthProvider,
  createUserWithEmailAndPassword,
  signInWithEmailAndPassword,
  signOut, onAuthStateChanged
} from 'firebase/auth';

const auth     = getAuth(app);
const provider = new GoogleAuthProvider();

// === Google Sign-In (one-click!) ===
async function signInWithGoogle() {
  const result = await signInWithPopup(auth, provider);
  const user = result.user;
  console.log('Signed in as:', user.displayName, user.email);
  // user.uid = unique user ID, use this in Firestore
}

// === Email + Password Sign Up ===
async function signUp(email, password) {
  const userCredential = await
    createUserWithEmailAndPassword(auth, email, password);
  return userCredential.user;
}

// === Email + Password Login ===
async function login(email, password) {
  const { user } = await
    signInWithEmailAndPassword(auth, email, password);
  return user;
}

// === Sign Out ===
const logout = () => signOut(auth);

// === Listen to auth state (runs on every page) ===
onAuthStateChanged(auth, (user) => {
  if (user) {
    // User is logged in
    console.log('Logged in:', user.uid);
    document.getElementById('user-name').textContent = user.displayName;
    document.getElementById('login-btn').style.display = 'none';
    document.getElementById('logout-btn').style.display = 'block';
  } else {
    // User is logged out
    document.getElementById('login-btn').style.display = 'block';
  }
});

// === Firestore Security Rules ===
// In Firebase Console → Firestore → Rules:
// rules_version = '2';
// service cloud.firestore {
//   match /databases/{db}/documents {
//     match /posts/{id} {
//       allow read: if true;         // anyone can read
//       allow write: if request.auth != null; // only logged-in users
//     }
//   }
// }

// File: /api/send-email.js (Vercel auto-routes this)

export default async function handler(req, res) {
  if (req.method !== 'POST') {
    return res.status(405).json({ error: 'Method not allowed' });
  }

  const { name, email, message } = req.body;

  // Send email with Resend.com (free 3000 emails/month)
  const response = await fetch('https://api.resend.com/emails', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${process.env.RESEND_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      from: 'noreply@yourdomain.com',
      to: 'you@yourdomain.com',
      subject: `New message from ${name}`,
      html: `<p><strong>From:</strong> ${email}</p><p>${message}</p>`
    })
  });

  if (!response.ok) {
    return res.status(500).json({ error: 'Email failed' });
  }

  res.json({ success: true, message: 'Email sent!' });
}

# File: .env  (NEVER commit this to git!)
# Add ".env" to your .gitignore file

FIREBASE_API_KEY=AIzaSy...
FIREBASE_PROJECT_ID=my-app-123
RESEND_API_KEY=re_abc123...
STRIPE_SECRET_KEY=sk_live_...
DATABASE_URL=postgresql://user:pass@host/db

# In Node.js, access via:
# process.env.FIREBASE_API_KEY

# In Vite (frontend), prefix with VITE_:
# VITE_FIREBASE_API_KEY=...  →  import.meta.env.VITE_FIREBASE_API_KEY

## .gitignore — protect your secrets ##
node_modules/
.env
.env.local
.env.production
dist/
.DS_Store