Intro to Node.js

Node.js changed everything: JavaScript, once confined to the browser, could now run on the server. Here's how to get started.

What is Node.js?

Node.js is a JavaScript runtime built on Chrome's V8 engine. It allows you to:

• Build web servers and APIs
• Create command-line tools
• Run build scripts and automation
• Power real-time applications (chat, gaming, etc.)

Your first server

const http = require('http')

const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' })
  res.end('Hello, Node.js!')
})

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

Save this as server.js, run node server.js, and visit http://localhost:3000.

npm — the package ecosystem

Node.js comes with npm, the world's largest package registry:

npm init -y          # create a package.json
npm install express  # add a dependency
npm install -g nodemon  # install globally

Key built-in modules

| Module | Purpose | |---|---| | fs | File system operations | | path | Path handling across OS | | http | HTTP server and client | | events | Event-driven programming | | stream | Handling streaming data |

The event loop

Node.js is single-threaded but non-blocking. The event loop handles asynchronous operations — I/O, timers, network requests — without blocking the main thread. This is what makes it fast and scalable.

// Non-blocking — the callback runs after the file is read
fs.readFile('data.txt', 'utf-8', (err, data) => {
  if (err) throw err
  console.log(data)
})
console.log('This runs first!')

Node.js is the foundation of modern JavaScript development. Mastering it opens doors to full-stack engineering, CLI tooling, and beyond.