Node.js

Node.js is an open-source runtime built on Chrome's V8 engine that lets you run JavaScript on a server or your own computer. It uses an event-driven, non-blocking I/O model, which suits handling many concurrent network connections.

Why it matters

Node.js lets teams use one language across front end and back end, and it powers most modern build tooling, including bundlers and development servers. It excels at I/O-heavy work such as APIs and WebSockets, but a single CPU-heavy task can block the event loop and stall every request.

Example

const http = require('http');
http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('OK');
}).listen(3000);

Visiting http://localhost:3000 returns the text OK with status 200.

Common mistakes

• Running CPU-intensive work on the main thread, which freezes all other requests.
• Not handling uncaught exceptions, so the process exits and the site goes down until restarted.
• Running it without a process manager or restart policy in production.

Related

• npm
• Back End
• WebSocket
• Bundler
• Tool: Http status checker

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