Last updated on 16th Jun 2025| 9688
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- Introduction to Express.js
- Setting Up Express
- Routing in Express
- Middleware Functions
- RESTful API with Express
- Error Handling
- Integrating with MongoDB
- Template Engines(e.g.,EJS,Pug)
- Security Best Practices
- Comparison with Other Frameworks
- Conclusion
Introduction to Express.js
Express.js, commonly known as Express, is a minimal and flexible Node.js web application framework that provides a robust set of features for building web and mobile applications. It simplifies the process of writing server-side code with Node.js, offering utilities to handle routing, middleware, HTTP requests, and responses in an efficient and scalable manner. Developed by TJ Holowaychuk and first released in 2010, Express quickly became one of the most popular backend frameworks in the JavaScript ecosystem, powering many enterprise and startup web applications. Express serves as the de facto standard for building server-side applications in Node.js, due to its lightweight architecture and rich middleware ecosystem. Express supports building RESTful APIs, web apps, and single-page applications (SPAs) by enabling easy HTTP method routing, middleware chaining, and integration with templating engines. Getting started with Express is straightforward. Since Express is a Node.js framework, you need Node.js installed on your system. Follow these basic steps to set up an Express application.
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Setting Up Expres
Initialize a Node.js project:- const express = require(‘express’);
- const app = express();
- const PORT = process.env.PORT || 3000;
- app.get(‘/’, (req, res) => {
- res.send(‘Hello, Express!’);
- });
- app.listen(PORT, () => {
- console.log(`Server is running on port ${PORT}`);
- });
Create an index.js file:
Run the app using:
Routing in Express
Routing is how an application responds to client requests to specific endpoints, defined by a URL and an HTTP method (GET, POST, etc.). Express provides a straightforward way to define routes.
Basic Routing
Routes in Express are defined using methods that correspond to HTTP methods:
- app.get(‘/users’, (req, res) => {
- res.send(‘Get all users’);
- });
- app.post(‘/users’, (req, res) => {
- res.send(‘Create a user’);
- });
- app.put(‘/users/:id’, (req, res) => {
- res.send(`Update user with ID ${req.params.id}`);
- });
- app.delete(‘/users/:id’, (req, res) => {
- res.send(`Delete user with ID ${req.params.id}`);
- });
Route parameters allow you to capture values from the URL:
- app.get(‘/users/:userId/books/:bookId’, (req, res) => {
- res.send(req.params);
- });
You can chain route handlers for the same path:
- app.route(‘/users’)
- .get((req, res) => { res.send(‘Get all users’);
- })
- .post((req, res) => { res.send(‘Create user’);
- });
Express supports modular routing by creating instances of express.Router() to handle route groups:
- const userRouter = express.Router();
- userRouter.get(‘/’, (req, res) => {
- res.send(‘User List’);
- });
- userRouter.get(‘/:id’, (req, res) => {
- res.send(`User ${req.params.id}`);
- });
- app.use(‘/users’, userRouter);
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Middleware Functions
Middleware functions are functions that have access to the request (req) and response (res) objects and the next middleware function in the application’s request-response cycle. Middleware can perform tasks like logging, parsing request bodies, authentication, and error handling.
Types of Middleware
Middleware can be applied globally or to specific routes:
-
// Global middleware
- app.use(express.json()); // Parses JSON bodies // Route-specific middleware
- app.get(‘/admin’, checkAuth, (req, res) => {
- res.send(‘Welcome Admin’);
- });
- function checkAuth(req, res, next) { // Authorization logic
- if (req.user && req.user.isAdmin) {
- next();
- } else {
- res.status(403).send(‘Forbidden’);
- }
- }
Query parameters:
- app.get(‘/search’, (req, res) => {
- const term = req.query.term;
- res.send(`Searching for ${term}`);
- });
Headers and Cookies:
- const userAgent = req.get(‘User-Agent’);
- const cookies = req.cookies;
Sending Responses
- res.send() for sending strings or JSON.
- res.json() for sending JSON specifically.
- res.status() to set HTTP status code.
- res.redirect() for redirection.
- res.render() to render templates (when using a view engine). Example:
- res.status(201). json({ message: ‘Created’ });
Express supports various response methods:
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Weekday / Weekend BatchesSee Batch DetailsRESTful API with Express
Express is ideal for building RESTful APIs, which follow REST principles: resources databases are accessed via URLs, use HTTP methods to perform CRUD operations, and use stateless communication.
Example of a Simple REST API
- const express = require(‘express’);
- const app = express();
- app.use(express.json());
- let users = [
- { id: 1, name: ‘Alice’ },
- { id: 2, name: ‘Bob’ }
- ];
- app.get(‘/users’, (req, res) => {
- res.json(users);
- });
- app.get(‘/users/:id’, (req, res) => {
- const user = users.find(u => u.id === parseInt(req.params.id));
- if (!user) return res.status(404). send(‘User not found’);
- res.json(user);
- });
- app.post(‘/users’, (req, res) => {
- const user = { id: users.length + 1, name: req.body.name };
- users.push(user);
- res.status(201).json(user);
- });
- app.put(‘/users/:id’, (req, res) => {
- const user = users.find(u => u.id === parseInt(req.params.id));
- if (!user) return res.status(404). send(‘User not found’);
- user.name = req.body.name;
- res.json(user);
- });
- app.delete(‘/users/:id’, (req, res) => {
- users = users.filter(u => u.id !== parseInt(req.params.id));
- res.status(204).send();
- });
- app.listen(3000, () => console.log(‘API running on port 3000’));
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Error Handling
Proper error handling is essential for robust applications. Express has built-in support for error-handling middleware, which has four arguments: (err, req, res, next).
Basic Error Handler Example- app.use((err, req, res, next) => {
- console.error(err.stack);
- res.status(500).send(‘Something broke!’);
- });
Throwing Errors in Routes
- app.get(‘/error’, (req, res, next) => {
- try {
- throw new Error(‘Deliberate error’);
- } catch (err) {
- next(err);
- }
- });
Using Async/Await and Error Handling
Express doesn’t catch errors in asynchronous code automatically, so use wrapper functions:
- const asyncHandler = fn => (req, res, next) => {
- Promise.resolve(fn(req, res, next)).catch(next);
- };
- app.get(‘/async’, asyncHandler(async (req, res) => {
- const data = await someAsyncOperation();
- res.send(data);
- }));
Integrating with MongoDB
Express is commonly used alongside MongoDB, a NoSQL database, to build full-stack applications.
Setup with MongooseMongoose is an ODM (Object Data Modeling) library for MongoDB and Node.js.
npm install mongoose
Example integration:
- const mongoose = require(‘mongoose’);
- mongoose.connect(‘mongodb://localhost/testdb’, {
- useNewUrlParser: true,
- useUnifiedTopology: true
- });
- const UserSchema = new mongoose.Schema({
- name: String,
- email: String,
- createdAt: { type: Date, default: Date.now }
- });
- const User = mongoose.model(‘User’, UserSchema);
- app.post(‘/users’, async (req, res) => {
- const user = new User(req.body);
- await user.save();
- res.status(201).json(user);
- });
- app.get(‘/users’, async (req, res) => {
- const users = await User.find();
- res.json(users);
- });
This shows how Express works smoothly with MongoDB to handle data persistence.
Template Engines (e.g., EJS, Pug)
Express supports various template engines to dynamically render HTML pages on the server side.
Using EJS (Embedded JavaScript)Install EJS:
npm install ejsSetup in Express:
- app.set(‘view engine’, ‘ejs’);
- app.get(‘/’, (req, res) => {
- res.render(‘index’, { title: ‘Home Page’ });
- });
npm install pug
Setup:
- app.set(‘view engine’, ‘pug’);
- app.get(‘/’, (req, res) => {
- res.render(‘index’, { title: ‘Home Page’ });Using Pug (formerly Jade)
Setup:
- app.set(‘view engine’, ‘pug’);
- app.get(‘/’, (req, res) => {
- res.render(‘index’, { title: ‘Home Page’ });
- });
Template engines let you create reusable components and inject dynamic data into views.
Security Best Practices
Security is critical in Express apps. Here are some best practices:
Use HelmetHelmet helps secure Express apps by setting HTTP headers:
npm install helmet
- const helmet = require(‘helmet’);
- app.use(helmet());
Use libraries like express-validator or sanitize inputs to prevent injection attacks.
Enable CORS Properly
Use the cors package to control cross-origin requests:
npm install cors
- const cors = require(‘cors’);
- app.use(cors({ origin: ‘https://example.com’ }));
Prevent brute-force attacks by limiting request rates using express-rate-limit.
- Avoid Information Leakage:Hide stack traces in production and handle errors gracefully.
- Use HTTPS:Serve your app over HTTPS to encrypt data in transit.
- Secure Cookies and Sessions:Set flags like HttpOnly, Secure, and SameSite on cookies.
- Koa is developed by the same team but is more modern and lightweight.
- Uses async functions by default, while Express supports middleware with callback or async.
- Koa has no bundled middleware; Express includes many built-in helpers. Express vs Hapi
- Hapi emphasizes configuration over code and has built-in validation and authentication.
- Express is more minimalistic and flexible but requires external plugins. Express vs Fastify
- Fastify is newer, focused on performance and low overhead.
- Fastify provides built-in schema-based validation and logging.
- Express has a larger ecosystem and community. Express vs Django/Flask (Python)
- Express is JavaScript-based, ideal for full-stack JS developers.
- Django is full-featured with an ORM and admin interface.
- Express offers more flexibility but requires assembling middleware.
Comparison with Other Frameworks
-
Express vs Koa
Conclusion
Express.js is a versatile, minimalistic, and highly extensible framework that empowers developers to build scalable web applications and RESTful APIs with Node.js. Its robust routing, middleware support, integration capabilities, and vast ecosystem make it the backbone of many modern web services. From simple websites to complex backend authentication systems, Express adapts to project needs, promoting rapid development while allowing fine-grained control over the request-response cycle. Mastering Express.js is essential for any Node.js developer aiming to build efficient, maintainable, and secure server-side applications.
