Frontend Development › JavaScript & TypeScript

Node.js

A JavaScript runtime for servers and tooling.

Also known as: Node, Node.js, nodejs, server-side JavaScript

Node.js is a runtime that lets JavaScript run outside the browser: on servers, in command-line tools and in build scripts. It uses Chrome’s V8 engine, plus APIs for files, networking and processes that browsers don’t offer.

import { readFile } from "node:fs/promises";
import http from "node:http";

http.createServer(async (req, res) => {
  const page = await readFile("index.html", "utf8");
  res.setHeader("Content-Type", "text/html");
  res.end(page);
}).listen(3000);

node server.js
node --version

What it’s used for

• Web servers and APIs (with Express, Fastify, NestJS and others).
• Tooling: bundlers, test runners, linters. Most frontend build tools run on Node.
• Scripts and CLIs.
• Server-side rendering for frameworks like Next.js.

How it works

Node is single-threaded for your JavaScript, with a non-blocking event loop. I/O (network, disk) is handed off and your code continues, which makes it good at handling many concurrent connections that mostly wait.

Things to know

• CPU-heavy work blocks everything. A long loop stops all requests. Use worker threads or another service.
• Never block with synchronous calls (readFileSync) inside a request handler.
• Packages come from npm (npm). Many dependencies means supply-chain risk, so lock versions and audit.
• Two module systems: CommonJS (require) and ES modules (import) (JS modules).
• Use an LTS version in production, and pin it (.nvmrc, engines).
• Handle uncaught errors and unhandled promise rejections, since they can crash the process.
• Alternatives: Deno and Bun are newer runtimes.

Node’s APIs (fs, path, process) don’t exist in the browser, and the browser’s (window, document) don’t exist in Node.