Advanced Node.js

Chapter 8: Advanced Express Patterns

8.1 Middleware Patterns

Middleware functions have access to request, response, and next. They can execute code, modify request/response, and call the next middleware.

// Custom middleware
function logger(req, res, next) {
    console.log(`${req.method} ${req.path} - ${new Date()}`);
    next();
}

function authenticate(req, res, next) {
    const token = req.headers.authorization;
    if (!token) {
        return res.status(401).json({ error: 'Unauthorized' });
    }
    // Verify token
    req.user = decodeToken(token);
    next();
}

// Error handling middleware
function errorHandler(err, req, res, next) {
    console.error(err.stack);
    res.status(500).json({ error: 'Something went wrong!' });
}

app.use(logger);
app.use('/api', authenticate);
app.use(errorHandler);

8.2 Route Middleware

// Route-specific middleware
app.get('/profile', authenticate, (req, res) => {
    res.json({ user: req.user });
});

// Multiple middleware
app.post('/posts', authenticate, validatePost, createPost);

// Middleware array
const middleware = [authenticate, validateInput, rateLimit];
app.put('/users/:id', middleware, updateUser);

8.3 Async Middleware

// Wrapper for async middleware
const asyncHandler = (fn) => (req, res, next) => {
    Promise.resolve(fn(req, res, next)).catch(next);
};

// Usage
app.get('/users/:id', asyncHandler(async (req, res) => {
    const user = await User.findById(req.params.id);
    res.json(user);
}));

8.4 Router Organization

// routes/users.js
const express = require('express');
const router = express.Router();

router.get('/', getUsers);
router.get('/:id', getUser);
router.post('/', createUser);
router.put('/:id', updateUser);
router.delete('/:id', deleteUser);

module.exports = router;

// app.js
const userRoutes = require('./routes/users');
app.use('/api/users', userRoutes);