Step-by-step articles on Node.js, part of our Backend collection.
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If you learned Node.js a few years ago, you probably install packages for things the runtime now does itself. Here's a tour of built-ins in current LTS versions. fetch, WebSocket and Web APIs const res = await fetch('https://api.github.com/repos/nodejs/node');...
Node.js ships a full test runner. For many backends and libraries it replaces Jest or Mocha entirely, with zero dependencies. Writing tests // test/cart.test.js import { describe, it, beforeEach } from 'node:test'; import assert from 'node:assert/strict'; impo...
Node.js supports two module systems: the original CommonJS ( require ) and standard ES modules ( import ). New projects should use ESM, but you'll meet both. Turning on ESM // package.json { "type": "module" } With "type": "module" , .js files are ESM. Without...
Configuration such as database URLs and API keys belongs in environment variables, not in code. Node.js can now load .env files itself. Loading from the command line # .env DATABASE_URL=postgres://localhost:5432/app PORT=3000 node --env-file=.env src/server.js...
Reading a 5 GB log file with fs.readFile loads all 5 GB into memory. Streams process data in small chunks, so memory use stays flat no matter how big the input is. The four stream types Readable - a source (file, HTTP request, database cursor). Writable - a de...
Node.js runs your JavaScript on a single thread. That's fine for I/O, but a CPU-heavy task (resizing images, parsing a huge file, heavy maths) blocks the event loop, and every other request waits. Spot the problem app.get('/report', (req, res) => { const resul...
Express 5 finally handles async route handlers properly: if an async handler throws or returns a rejected promise, the error goes to your error middleware. No more express-async-errors or wrapping every route in try/catch. Async handlers just work app.get('/us...
Most API breaches come from a few well-known mistakes. Work through this checklist for every Node.js service you deploy. 1. Validate every input import { z } from 'zod'; const CreateOrder = z.object({ productId: z.uuid(), quantity: z.number().int().min(1).max(...
Containers and process managers stop your app by sending SIGTERM . If you exit immediately, requests in progress fail and database transactions are cut off. A graceful shutdown finishes the current work first. The steps Stop accepting new connections. Let in-f...
A memory leak shows up as memory that keeps climbing until the process is killed or restarts. The fix starts with proving where the memory goes. 1. Confirm the leak setInterval(() => { const { heapUsed, rss } = process.memoryUsage(); console.log(`heap ${(heapU...
