Node.js Introduction

What You’ll Learn

This page is a self-contained introduction to Node.js—JavaScript on the server. You will understand what Node.js is, how it differs from browser JavaScript, and build your first programs from the terminal and over HTTP.

🤔 What is Node.js?

Node.js is an open-source, cross-platform JavaScript runtime that lets developers run JavaScript on the server side of web applications—and on desktops, CLIs, and IoT devices—without a browser.

It uses an event-driven, non-blocking I/O model, which means Node.js can handle many concurrent connections efficiently without creating a new thread for every request. That design makes it a strong fit for APIs, real-time chat, streaming, and data-intensive apps.

Node.js ships with a huge ecosystem of packages through npm (Node Package Manager), the world’s largest software registry. You can install libraries for databases, authentication, testing, and more with a single command.

👴 Who Is the Creator of Node.js?

The creator of Node.js is Ryan Dahl. He first presented Node.js at the European JSConf in 2009 and continued leading the project until 2012, when he handed maintenance to the open-source community under the OpenJS Foundation.

Dahl wanted a way to build high-performance web servers without the overhead of creating a new thread per connection. By combining JavaScript with an event loop and non-blocking I/O, Node.js changed how developers think about back-end development.

📈 Is Node.js Scalable?

Yes, Node.js is generally considered a scalable technology. It is a lightweight, event-driven platform with a single-threaded, asynchronous programming model. That architecture lets one Node process handle thousands of simultaneous connections efficiently, which suits I/O-heavy workloads like APIs and real-time messaging.

You can scale Node.js horizontally by adding more server instances behind a load balancer, or vertically by giving a machine more CPU and memory. Tools like the built-in cluster module and process managers (PM2) help run multiple workers on one machine.

However, scalability depends on your whole system—application design, database choices, caching, networking, and how you handle CPU-bound tasks. Node.js is a good choice for building scalable applications, but it is not a guarantee of scalability on its own.

• Great for — JSON APIs, WebSockets, microservices, SSR, CLI tools
• Watch out for — heavy CPU work blocking the event loop (offload to worker threads or another service)
• Combine with — Redis caching, message queues, and horizontal scaling in production

✍️ What Language Is Node.js Written In?

Node.js itself is written primarily in C and C++, with JavaScript used for higher-level APIs and bindings. The JavaScript engine at its core is V8, originally developed by Google for the Chrome browser.

When you write server.js, your JavaScript source is parsed and compiled by V8 into fast machine code. Node adds native bindings (written in C++) for filesystem access, networking, cryptography, and other system-level features exposed through built-in modules like fs, http, and crypto.

💻 Install and Verify Node.js

Download the LTS (Long Term Support) build from nodejs.org, run the installer, then confirm everything works:

node -v
npm -v

• node -v — prints the Node.js version (e.g. v22.x)
• npm -v — prints npm version bundled with Node
• Create a folder, save a .js file, and run node filename.js
• Use npm init -y to create a package.json when starting a project

📄 Hello World in Node.js

Start with the simplest program—print text to the terminal:

console.log('Hello World');

$ node hello.js
Hello World

Hello World HTTP server

Here is a classic Node.js program that creates a web server using the built-in http module. When a client visits the URL, the server responds with Hello World:

const http = require('http');

const server = http.createServer((request, response) => {
  response.writeHead(200, { 'Content-Type': 'text/plain' });
  response.end('Hello World\n');
});

server.listen(8080, () => {
  console.log('Server running at http://127.0.0.1:8080/');
});

Server running at http://127.0.0.1:8080/

GET http://127.0.0.1:8080/
Response body: Hello World

Save as server.js, run node server.js, then open the URL in your browser. For larger apps, most teams use Express.js instead of raw http.

🤔 Where Is Node.js Used?

Some common use cases for Node.js include:

1. Web applications — fast, scalable backends, often with Express.js, Fastify, or NestJS
2. Real-time applications — chat apps, online games, live dashboards, and collaboration tools using WebSockets or Socket.IO
3. API development — REST and GraphQL services that expose data to web and mobile clients
4. Microservices — small, independent services that compose into larger systems
5. Command-line tools — scripts and CLIs that automate builds, migrations, and dev workflows
6. Serverless functions — short-lived handlers on AWS Lambda, Vercel, or Cloudflare Workers

🌐 Top 7 Sites That Use Node.js

Many global companies rely on Node.js for performance and developer productivity. Here are seven well-known examples:

1. Netflix — one of the world’s largest video streaming services
2. LinkedIn — the world’s largest professional networking platform
3. PayPal — a popular online payments system
4. Uber — a leading ride-hailing and delivery company
5. Walmart — one of the largest retailers in the world
6. Medium — a popular online publishing platform
7. Trello — a widely used project management tool

Node.js is also common at startups and enterprises building APIs, BFF (backend-for-frontend) layers, and JavaScript-first engineering teams.

🧰 Core Building Blocks

Examples Gallery

Five starter programs after installing Node.js. Save each file, run with node filename.js, and read the terminal output.

const message = 'Hello from Node.js!';
console.log(message);
console.log('Node version:', process.version);

Hello from Node.js!
Node version: v22.x.x

const http = require('http');

http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello World\n');
}).listen(3000, () => {
  console.log('Listening on http://localhost:3000');
});

Listening on http://localhost:3000

Browser shows: Hello World

const fs = require('fs');

const text = fs.readFileSync('hello.txt', 'utf8');
console.log(text);

Hi there

const path = require('path');

const file = path.join(__dirname, 'data', 'users.json');
console.log('Full path:', file);
console.log('Extension:', path.extname(file));

Full path: C:\projects\demo\data\users.json
Extension: .json

console.log('Start');

setTimeout(() => {
  console.log('Timer finished (async)');
}, 1000);

console.log('End (runs before timer)');

Start
End (runs before timer)
Timer finished (async)

Summary

• Node.js runs JavaScript on the server using the V8 engine and an event-driven model.
• Created by Ryan Dahl in 2009; maintained today by the open-source community.
• It scales well for I/O-heavy apps but still requires good architecture and infrastructure.
• Core pieces: modules, npm, built-in APIs (http, fs, path), and the event loop.
• Common uses: APIs, real-time apps, microservices, CLIs, and serverless functions.
• Next step: learn Express.js to build routes and middleware faster than raw http.

💡 Best Practices