Node.js Cheat Sheet

Covers CommonJS and ES module syntax, filesystem operations, async patterns, the built-in HTTP server, and core Node.js globals.

3 PagesIntermediateMar 2, 2026

CommonJS & ES Modules

The two module systems Node.js supports.

javascript

// CommonJS (default in .js unless package.json has "type": "module")const fs = require('fs');module.exports = { greet };function greet(name) { return `Hi ${name}`; }// ES Modules (package.json "type": "module", or .mjs extension)import fs from 'fs';export function greet(name) { return `Hi ${name}`; }export default greet;

Filesystem & Async Patterns

Reading files and working with streams and events.

javascript

const fs = require('fs/promises');async function readConfig() {  const data = await fs.readFile('config.json', 'utf8');  return JSON.parse(data);}// Streams for large filesconst { createReadStream, createWriteStream } = require('fs');createReadStream('input.txt').pipe(createWriteStream('output.txt'));// EventEmitter patternconst { EventEmitter } = require('events');const emitter = new EventEmitter();emitter.on('data', (chunk) => console.log(chunk));emitter.emit('data', 'hello');

Built-in HTTP Server

Creating a server without a framework.

javascript

const http = require('http');const server = http.createServer((req, res) => {  if (req.url === '/health' && req.method === 'GET') {    res.writeHead(200, { 'Content-Type': 'application/json' });    res.end(JSON.stringify({ status: 'ok' }));    return;  }  res.writeHead(404);  res.end('Not found');});server.listen(3000, () => console.log('Listening on 3000'));

Core Modules & Globals

Frequently used built-ins.

process.env- access environment variables
process.argv- command-line arguments passed to the script
__dirname / __filename- CommonJS-only globals for the current module's directory and file path
path.join() / path.resolve()- cross-platform path construction
Buffer- handles raw binary data
child_process.spawn() / exec()- run external commands from within Node
event loop phases- timers, pending callbacks, poll, check, and close callbacks, in that order

Pro Tip

Prefer the fs/promises API with async/await over callback-based fs methods: it composes cleanly with try/catch and avoids callback nesting, and Node has shipped it as stable since version 14.

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