Module 2: Express.js Framework

Learn Express.js framework for building robust web applications and REST APIs with Node.js.

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Express.js Framework

Learn Express.js framework for building robust web applications and REST APIs with Node.js.

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Express.js Basics

Set up Express.js applications and understand the basic structure and configuration

Content by: Sachin Patel

Node.js Developer

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Introduction to Express.js

Express.js is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications. It simplifies the process of building web applications and APIs by providing a clean, simple API for handling HTTP requests and responses.

Setting Up Express.js

Code Example
// Install Express.js
npm install express

// Basic Express.js server
const express = require('express');
const app = express();
const port = 3000;

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

// Middleware for parsing URL-encoded bodies
app.use(express.urlencoded({ extended: true }));

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

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

// Express.js with ES modules
import express from 'express';
const app = express();
const port = 3000;

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

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

  • •app.js - Main application file with server setup
  • •routes/ - Directory for route handlers
  • •middleware/ - Custom middleware functions
  • •controllers/ - Business logic handlers
  • •models/ - Data models and database schemas
  • •config/ - Configuration files
  • •public/ - Static files (CSS, JS, images)
  • •views/ - Template files for rendering

Express.js vs Other Frameworks

  • •vs Koa.js: Express is more mature with larger ecosystem, Koa uses async/await
  • •vs Fastify: Express is simpler to learn, Fastify is faster but more complex
  • •vs Hapi.js: Express is more lightweight, Hapi has built-in features but heavier
  • •vs NestJS: Express is more flexible, NestJS is opinionated with TypeScript
  • •vs Sails.js: Express is minimal, Sails provides more structure out of the box

Express.js Core Features

Code Example
// Express.js core features demonstration
const express = require('express');
const app = express();

// 1. Middleware support
app.use((req, res, next) => {
    console.log('Request received:', req.method, req.url);
    next(); // Pass control to next middleware
});

// 2. Route parameters
app.get('/users/:id', (req, res) => {
    res.json({ userId: req.params.id });
});

// 3. Query parameters
app.get('/search', (req, res) => {
    res.json({ query: req.query.q, page: req.query.page });
});

// 4. Request body parsing
app.post('/users', express.json(), (req, res) => {
    res.json({ message: 'User created', user: req.body });
});

// 5. Static file serving
app.use('/static', express.static('public'));

// 6. Template engine support
app.set('view engine', 'ejs');
app.get('/home', (req, res) => {
    res.render('home', { title: 'Home Page' });
});

// 7. Error handling
app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).json({ error: 'Something went wrong!' });
});

// 8. 404 handling
app.use((req, res) => {
    res.status(404).json({ error: 'Route not found' });
});
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Express.js Best Practices

  • •Use environment variables: Store configuration in .env files
  • •Implement proper error handling: Use try-catch and error middleware
  • •Use middleware for common tasks: Logging, authentication, validation
  • •Organize routes: Separate route files for better maintainability
  • •Use HTTPS in production: Secure your application with SSL certificates
  • •Implement rate limiting: Prevent abuse and DoS attacks
  • •Use helmet for security: Set security-related HTTP headers
  • •Validate input data: Always validate and sanitize user input

Mini-Project: Express.js Starter App

Code Example
// Complete Express.js starter application
const express = require('express');
const cors = require('cors');
const helmet = require('helmet');
const morgan = require('morgan');
const rateLimit = require('express-rate-limit');
require('dotenv').config();

const app = express();
const PORT = process.env.PORT || 3000;

// Security middleware
app.use(helmet());
app.use(cors());

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

// Logging middleware
app.use(morgan('combined'));

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

// Custom middleware for request timing
app.use((req, res, next) => {
    req.startTime = Date.now();
    next();
});

// Routes
app.get('/', (req, res) => {
    res.json({
        message: 'Welcome to Express.js Starter App',
        version: '1.0.0',
        timestamp: new Date().toISOString(),
        uptime: process.uptime()
    });
});

// Health check endpoint
app.get('/health', (req, res) => {
    res.json({
        status: 'healthy',
        timestamp: new Date().toISOString(),
        memory: process.memoryUsage(),
        uptime: process.uptime()
    });
});

// API routes
app.get('/api/users', (req, res) => {
    const users = [
        { id: 1, name: 'John Doe', email: 'john@example.com' },
        { id: 2, name: 'Jane Smith', email: 'jane@example.com' }
    ];
    res.json(users);
});

app.post('/api/users', (req, res) => {
    const { name, email } = req.body;
    
    if (!name || !email) {
        return res.status(400).json({ error: 'Name and email are required' });
    }
    
    const newUser = {
        id: Date.now(),
        name,
        email,
        createdAt: new Date().toISOString()
    };
    
    res.status(201).json(newUser);
});

// Error handling middleware
app.use((err, req, res, next) => {
    console.error('Error:', err);
    res.status(500).json({
        error: 'Internal Server Error',
        message: process.env.NODE_ENV === 'development' ? err.message : 'Something went wrong'
    });
});

// 404 handler
app.use((req, res) => {
    res.status(404).json({ error: 'Route not found' });
});

// Graceful shutdown
process.on('SIGTERM', () => {
    console.log('SIGTERM received, shutting down gracefully');
    process.exit(0);
});

process.on('SIGINT', () => {
    console.log('SIGINT received, shutting down gracefully');
    process.exit(0);
});

// Start server
app.listen(PORT, () => {
    console.log(`Server running on port ${PORT}`);
    console.log(`Environment: ${process.env.NODE_ENV || 'development'}`);
});

module.exports = app;
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🎯 Practice Exercise

Test your understanding of this topic:

Previous Module

Module 1: Node.js Fundamentals

Next Module

Module 3: Database Integration

Additional Resources

📚 Recommended Reading

  • •Express.js Official Documentation
  • •Express.js Routing Guide
  • •Middleware in Express.js

🌐 Online Resources

  • •Express.js Tutorial for Beginners
  • •REST API Design with Express.js
  • •Express.js Best Practices

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Continue to Module 3