This page is a self-contained introduction to Express.js—the most popular web framework for Node.js. You will understand what Express does, install it, and build your first HTTP server with routes and middleware.
What Express adds.
Middleware & routes.
Why teams pick it.
npm & listen.
Hello API.
Pros & cons.
Express.js, commonly known as Express, is a minimal and flexible Node.js web application framework that provides a robust set of features to develop web and mobile backends.
It simplifies building scalable, maintainable server applications by offering clean routing, middleware hooks, and helpers for HTTP requests and responses. Instead of wiring low-level http modules by hand, Express gives you a small API that scales from a one-file demo to production APIs.
Install Node.js first, then run npm install express in a project folder. Start with a single app.get('/') route before adding databases or authentication.
Express is known for its middleware support, which lets you extend the application with functions that receive req, res, and next. Use middleware for logging, authentication, parsing JSON bodies, and centralized error handling.
const express = require('express');
const app = express();
const customMiddleware = (req, res, next) => {
console.log('This middleware runs before the route handler.');
next();
};
app.use(customMiddleware);
app.get('/', (req, res) => {
res.send('Hello, Express!');
});
const port = 3000;
app.listen(port, () => {
console.log(`Server is running on http://localhost:${port}`);
});Express provides a simple routing system based on HTTP methods and URL patterns. Define app.get, app.post, app.put, and app.delete handlers to keep code organized as your API grows.
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send('Hello, Express!');
});
app.get('/about', (req, res) => {
res.send('This is the About page.');
});
app.listen(3000, () => {
console.log('Server is running on http://localhost:3000');
});Express supports template engines such as EJS, Pug, and Handlebars for server-side HTML rendering. Set view engine, place templates in a views folder, and call res.render() to separate presentation from route logic.
const express = require('express');
const app = express();
app.set('view engine', 'ejs');
app.get('/', (req, res) => {
res.render('index', {
title: 'Express.js Example',
message: 'Hello, Express!'
});
});
app.listen(3000, () => {
console.log('Server is running on http://localhost:3000');
});Express makes request and response handling straightforward. Built-in middleware parses JSON and URL-encoded bodies; response helpers send JSON, set headers, redirect, and stream files.
const express = require('express');
const app = express();
app.use(express.json());
app.post('/api/user', (req, res) => {
const { username, email } = req.body;
res.json({ username, email });
});
app.listen(3000, () => {
console.log('Server is running on http://localhost:3000');
});Express runs on Node.js. Create a project, install the package, write a server file, and start it with node.
mkdir my-express-app
cd my-express-app
npm init -y
npm install express
node app.jsnpm init -y — creates package.json with default settings.npm install express — adds Express to node_modules and records it in dependencies.node app.js — runs your server; visit the URL printed in the console.nodemon app.js during development to auto-restart on file changes.| Concept | What it does |
|---|---|
Application (app) | Main Express instance; registers routes and middleware |
| Router | Modular mini-app for grouping related routes |
| Middleware | Functions that run in order for each request |
| Route handlers | Callbacks that send responses for specific URLs and methods |
req object | Incoming HTTP request (params, query, body, headers) |
res object | Outgoing response (send, json, status, render) |
app.listen() | Starts the HTTP server on a port |
| Task | Code snippet |
|---|---|
| Create app | const app = express(); |
| GET route | app.get('/path', (req, res) => { ... }); |
| Parse JSON body | app.use(express.json()); |
| Send text | res.send('Hello'); |
| Send JSON | res.json({ ok: true }); |
| Start server | app.listen(3000, () => console.log('Ready')); |
Five starter servers you can copy into app.js after running npm install express. Save the file, run node app.js, and test routes in a browser or with curl.
The smallest useful server: one GET route and app.listen.
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send('Hello, Express!');
});
const port = 3000;
app.listen(port, () => {
console.log(`Server is running on http://localhost:${port}`);
});const express = require('express');
const app = express();
app.use((req, res, next) => {
console.log(`${req.method} ${req.url}`);
next();
});
app.get('/', (req, res) => {
res.send('Logged request!');
});
app.listen(3000, () => {
console.log('Server is running on http://localhost:3000');
});const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send('Home page');
});
app.get('/about', (req, res) => {
res.send('This is the About page.');
});
app.listen(3000, () => {
console.log('Server is running on http://localhost:3000');
});const express = require('express');
const app = express();
app.use(express.json());
app.post('/api/user', (req, res) => {
const { username, email } = req.body;
res.json({ username, email });
});
app.listen(3000, () => {
console.log('Server is running on http://localhost:3000');
});const express = require('express');
const app = express();
app.get('/users/:id', (req, res) => {
res.json({ userId: req.params.id });
});
app.listen(3000, () => {
console.log('Server is running on http://localhost:3000');
});Dynamic segments like :id appear in req.params—essential for REST APIs.
| Framework | Style | Best for beginners when… |
|---|---|---|
| Express | Minimal, middleware-centric | You want the largest ecosystem and most tutorials |
| Fastify | Performance-focused, schema validation | You need high throughput APIs with built-in logging |
| Koa | Async middleware (from Express creators) | You prefer modern async/await middleware patterns |
| Node http | Built-in, no framework | You want to understand HTTP at the lowest level first |
Browser or API client hits a URL like GET /api/user.
Logging, JSON parsing, and auth middleware execute in registration order.
Express finds the handler for the method and path, then runs your callback.
res.send, res.json, or res.render returns data to the client.
express.json() before routes that read JSON bodiesres.status(404), etc.)helmet and cors middleware in production APIsres.send twice in the same request handlernext() in middleware that should pass control forwardprocess.env.PORTreq.body dataExpress has been the de facto Node.js web framework since 2010. Major platforms—including many tutorial sites and production APIs—use Express with EJS templates, static file serving, and middleware like Helmet for security. The CodeToFun website itself is built with Express and EJS.
Create a folder, run npm install express, paste Example 1 into app.js, and start building.
12 people found this page helpful