What is Node.js?

Node.js is not a language, not a framework — it's a runtime environment that lets JavaScript run outside the browser.

The Architecture

Node.js is built on two core components that work together:

The Event Loop — Simplified

Node.js runs on a single thread. This sounds like a weakness, but it's actually its superpower — here's why:

Because Node hands I/O work to the OS and continues, a single Node process can handle thousands of simultaneous connections — all waiting for databases, files, or network responses — without spawning thousands of threads.

Node.js vs Other Runtimes

Your First Node.js Script

Open a terminal and try this — no framework, no npm packages:

// hello.js
const http = require('http');

const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({ message: 'Hello from Node.js!' }));
});

server.listen(3000, () => {
  console.log('Server running at http://localhost:3000');
});

# Run it
node hello.js

# In another terminal, test it
curl http://localhost:3000

This is a complete HTTP server in 8 lines. Express (which you'll learn next) just makes this pattern much more comfortable to work with at scale.

Node Version Management

Always use a version manager — never install Node.js directly. The two most popular:

• nvm (Node Version Manager) — the classic, shell-based
• fnm (Fast Node Manager) — newer, faster, Rust-based

# Install a specific version
nvm install 20

# Use it in the current project
nvm use 20

# Pin the version for a project (.nvmrc file)
echo "20" > .nvmrc

Go Deeper

Primary source: nodejs.org — Introduction to Node.js

Video: Fireship — Node.js Explained in 100 Seconds