Node.js Introduction

What Is Node.js?

Node.js is an open-source JavaScript runtime that runs on servers and desktops—not in a browser. It uses Google’s V8 engine and an event-driven, non-blocking I/O model built for APIs, real-time apps, and tools.

JavaScript  =  the language
Node.js     =  the runtime outside the browser

Stack pieces:
  V8 engine  →  runs your JS
  libuv      →  async I/O & event loop
  npm        →  packages & scripts

Ryan Dahl created Node.js in 2009 so developers could use one language on both the client and the server. Today it powers backends, CLIs, build tools, and full-stack frameworks.

Why Use Node.js?

Browsers already run JavaScript. Node lets the same language handle files, networks, and processes on the server.

How Node.js Handles Work

Requests and I/O go through the event loop instead of blocking one thread per connection:

Install, Hello World & First Server

Download the LTS build from nodejs.org, then verify:

node -v
npm -v
node hello.js

console.log('Hello World');

$ node hello.js
Hello World

Hello World HTTP server

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/');
});

Terminal:
Server running at http://127.0.0.1:8080/

Browser (http://127.0.0.1:8080/):
Hello World

How It Works

1. Module. require('http') loads Node’s built-in HTTP module.

2. Create. createServer registers a callback for each request.

3. Listen. listen(8080) starts the server; open the URL in a browser.

Next, build apps faster with Express.

Node.js vs Browser JavaScript

Same language, different environment and APIs:

When to use which

Core Building Blocks

These pieces show up in almost every Node project:

Where Is Node.js Used?

Node shows up across modern JavaScript stacks:

Key Takeaways