Express.js

What is Express.js?

Express.js is a fast, unopinionated, and minimalist web framework for Node.js. It provides a robust set of features for web and mobile applications, making it easier to build APIs and web applications. Express.js is the most popular Node.js framework and serves as the foundation for many other frameworks and applications in the Node.js ecosystem.

Key Features

• Minimalist Framework: Lightweight with essential features for web development
• Middleware Support: Extensible through middleware functions
• Routing: Powerful routing system for handling different HTTP methods and URLs
• Template Engines: Support for various template engines like EJS, Pug, Handlebars
• Static File Serving: Built-in support for serving static files
• Error Handling: Comprehensive error handling mechanisms

Basic Express.js Application

                        
const express = require('express');
const app = express();
const port = 3000;

// Middleware for parsing JSON
app.use(express.json());

// Basic route
app.get('/', (req, res) => {
    res.send('Hello World!');
});

// API route with parameters
app.get('/users/:id', (req, res) => {
    const userId = req.params.id;
    res.json({ 
        message: `User ID: ${userId}`,
        user: { id: userId, name: 'John Doe' }
    });
});

// POST route
app.post('/users', (req, res) => {
    const { name, email } = req.body;
    res.status(201).json({
        message: 'User created successfully',
        user: { name, email }
    });
});

app.listen(port, () => {
    console.log(`Server running at http://localhost:${port}`);
});
                        
                    

Middleware in Express.js

Middleware functions are functions that have access to the request object, response object, and the next middleware function in the application's request-response cycle.

                        
// Custom middleware
const logger = (req, res, next) => {
    console.log(`${req.method} ${req.url} - ${new Date().toISOString()}`);
    next(); // Call next() to proceed to the next middleware
};

// Use middleware
app.use(logger);

// Built-in middleware
app.use(express.static('public')); // Serve static files
app.use(express.urlencoded({ extended: true })); // Parse URL-encoded bodies

// Third-party middleware
const cors = require('cors');
app.use(cors()); // Enable CORS
                        
                    

Popular Express.js Middleware

• body-parser: Parse incoming request bodies (now built into Express)
• cors: Enable Cross-Origin Resource Sharing
• helmet: Set security-related HTTP headers
• morgan: HTTP request logger middleware
• compression: Compress response bodies
• express-rate-limit: Rate limiting middleware

Express.js vs Other Frameworks

• Express.js: Minimalist, flexible, large ecosystem
• Koa.js: Next-generation framework by Express team, uses async/await
• Fastify: High-performance alternative with built-in JSON schema validation
• NestJS: TypeScript-first framework with decorators and dependency injection

Best Practices

• Use Environment Variables: Store configuration in environment variables
• Error Handling: Implement proper error handling middleware
• Security: Use security middleware like Helmet
• Validation: Validate input data using libraries like Joi or express-validator
• Logging: Implement comprehensive logging for debugging and monitoring
• Testing: Write unit and integration tests using Jest or Mocha

Learning Path

1. Learn Node.js fundamentals and npm package management
2. Understand HTTP methods, status codes, and REST API principles
3. Practice building basic Express.js applications with routing
4. Learn middleware concepts and implement custom middleware
5. Integrate databases (MongoDB, PostgreSQL) with Express.js
6. Implement authentication and authorization
7. Build and deploy full-stack applications using Express.js