Express.js

Express is a minimal and flexible Node.js web application framework. It's the most popular Node.js framework and provides a thin layer of fundamental web application features without obscuring Node.js capabilities.

Key Features

• Minimal: Small core, extend with middleware
• Routing: Flexible route handling with parameters
• Middleware: Composable request processing pipeline
• Template engines: Support for Pug, EJS, Handlebars
• Static files: Built-in static file serving

Basic Example

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

// Middleware
app.use(express.json());

// Routes
app.get('/api/users', (req, res) => {
  res.json([{ id: 1, name: 'Alice' }]);
});

app.get('/api/users/:id', (req, res) => {
  res.json({ id: req.params.id, name: 'Alice' });
});

app.post('/api/users', (req, res) => {
  const user = req.body;
  res.status(201).json(user);
});

// Start server
app.listen(3000, () => {
  console.log('Server running on port 3000');
});

Middleware Pattern

// Logging middleware
const logger = (req, res, next) => {
  console.log(`${req.method} ${req.path}`);
  next();
};

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

// Error handling middleware
const errorHandler = (err, req, res, next) => {
  console.error(err);
  res.status(500).json({ error: 'Internal Server Error' });
};

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

Popular Middleware

Package	Purpose
cors	Cross-origin resource sharing
helmet	Security headers
compression	Gzip responses
morgan	HTTP request logging
express-validator	Input validation
passport	Authentication strategies

What We Like

• Simplicity: Easy to learn, quick to build
• Flexibility: No opinions, use what you want
• Ecosystem: Vast middleware and plugin options
• Documentation: Extensive guides and examples
• Community: Largest Node.js framework community

What We Don't Like

• Minimal: Requires many decisions and additions
• Callback-based: Original API not async/await native
• No structure: Easy to create messy codebases
• Maintenance: Slow release cycle (though stable)

Express vs Alternatives

Framework	Style	Best For
Express	Minimal	Flexibility, learning
Fastify	Performance	High-throughput APIs
NestJS	Opinionated	Enterprise, TypeScript
Koa	Modern	Cleaner async handling

When to Use Express

• Learning Node.js web development
• Simple APIs and microservices
• Projects needing maximum flexibility
• Teams comfortable with Node.js patterns

For TypeScript-first enterprise applications, consider NestJS. For performance-critical APIs, consider Fastify.