// Without Express - parsing JSON body manually
const http = require('http');

http.createServer((req, res) => {
  if (req.method === 'POST' && req.url === '/users') {
    let body = '';
    req.on('data', chunk => { body += chunk; });
    req.on('end', () => {
      const user = JSON.parse(body);
      res.writeHead(201, { 'Content-Type': 'application/json' });
      res.end(JSON.stringify(user));
    });
  }
}).listen(3000);

npm install express

const express = require('express');
const app = express();
const PORT = 5000;

app.get('/', (req, res) => {
  res.send('Hello from Express!');
});

app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});

// GET request
app.get('/about', (req, res) => {
  res.send('About Page');
});

// POST request
app.post('/contact', (req, res) => {
  res.send('Contact Form Submitted');
});

// Dynamic Parameters
app.get('/users/:id', (req, res) => {
  res.send(`User ID: ${req.params.id}`);
});

const logger = (req, res, next) => {
  console.log(`${req.method} ${req.protocol}://${req.get('host')}${req.originalUrl}`);
  next(); // Call next middleware
};

// Initialize middleware
app.use(logger);

// Parse JSON bodies
app.use(express.json());

// Parse URL-encoded bodies (forms)
app.use(express.urlencoded({ extended: false }));

const path = require('path');

// Set 'public' folder as static folder
app.use(express.static(path.join(__dirname, 'public')));

const express = require('express');
const router = express.Router();

// All routes here are prefixed with /api/users
router.get('/', (req, res) => {
  res.json([{ id: 1, name: 'John' }]);
});

router.get('/:id', (req, res) => {
  res.json({ id: req.params.id, name: 'John' });
});

router.post('/', (req, res) => {
  res.status(201).json({ message: 'User created' });
});

module.exports = router;

const express = require('express');
const userRoutes = require('./routes/users');

const app = express();

app.use(express.json());
app.use('/api/users', userRoutes);

app.listen(3000);

// Custom error class
class AppError extends Error {
  constructor(message, statusCode) {
    super(message);
    this.statusCode = statusCode;
    this.isOperational = true;
  }
}

// Route that throws error
app.get('/error', (req, res, next) => {
  next(new AppError('Something went wrong', 500));
});

// Async error wrapper
const asyncHandler = (fn) => (req, res, next) =>
  Promise.resolve(fn(req, res, next)).catch(next);

// Usage with async routes
app.get('/users', asyncHandler(async (req, res) => {
  const users = await User.find(); // If this throws, error handler catches it
  res.json(users);
}));

// Error handling middleware (must be last)
app.use((err, req, res, next) => {
  console.error(err.stack);
  
  const statusCode = err.statusCode || 500;
  const message = err.isOperational ? err.message : 'Internal Server Error';
  
  res.status(statusCode).json({
    success: false,
    error: message,
    ...(process.env.NODE_ENV === 'development' && { stack: err.stack })
  });
});

app.post('/api/data', (req, res) => {
  // URL parameters (/users/:id)
  console.log(req.params.id);
  
  // Query string (/users?sort=name&order=desc)
  console.log(req.query.sort);    // 'name'
  console.log(req.query.order);   // 'desc'
  
  // Request body (POST/PUT data)
  console.log(req.body);
  
  // Headers
  console.log(req.headers['content-type']);
  console.log(req.get('Authorization'));
  
  // Cookies (requires cookie-parser)
  console.log(req.cookies.session);
  
  // Full URL info
  console.log(req.originalUrl);   // /api/data?sort=name
  console.log(req.path);          // /api/data
  console.log(req.hostname);      // localhost
  console.log(req.ip);            // Client IP
  console.log(req.protocol);      // http or https
  console.log(req.method);        // POST
});

app.get('/response-examples', (req, res) => {
  // Send string
  res.send('Hello World');
  
  // Send JSON
  res.json({ message: 'Hello' });
  
  // Send with status
  res.status(201).json({ created: true });
  
  // Redirect
  res.redirect('/other-route');
  res.redirect(301, '/permanent-redirect');
  
  // Render template (with template engine)
  res.render('index', { title: 'Home' });
  
  // Download file
  res.download('./file.pdf');
  
  // Send file
  res.sendFile('/absolute/path/to/file.html');
  
  // Set headers
  res.set('Content-Type', 'text/html');
  res.set({
    'X-Custom-Header': 'value',
    'Cache-Control': 'no-cache'
  });
  
  // Set cookie
  res.cookie('session', 'abc123', {
    httpOnly: true,
    secure: true,
    maxAge: 3600000
  });
  
  // Clear cookie
  res.clearCookie('session');
});

const express = require('express');
const helmet = require('helmet');       // Security headers
const cors = require('cors');           // Cross-origin requests
const morgan = require('morgan');       // Logging
const compression = require('compression'); // Gzip
const rateLimit = require('express-rate-limit'); // Rate limiting

const app = express();

// Security headers
app.use(helmet());

// CORS
app.use(cors({
  origin: 'https://example.com',
  methods: ['GET', 'POST'],
  credentials: true
}));

// Logging
app.use(morgan('dev'));  // or 'combined' for production

// Compression
app.use(compression());

// Rate limiting
const limiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100 // limit each IP to 100 requests per windowMs
});
app.use('/api', limiter);

// Body parsers
app.use(express.json({ limit: '10mb' }));
app.use(express.urlencoded({ extended: true }));

project/
├── src/
│   ├── config/
│   │   └── db.js
│   ├── controllers/
│   │   └── userController.js
│   ├── middleware/
│   │   ├── auth.js
│   │   └── errorHandler.js
│   ├── models/
│   │   └── User.js
│   ├── routes/
│   │   ├── index.js
│   │   └── userRoutes.js
│   ├── services/
│   │   └── userService.js
│   ├── utils/
│   │   └── helpers.js
│   └── app.js
├── tests/
├── .env
├── .gitignore
├── package.json
└── server.js