Node.js Cheat Sheet

# Check version
node --version
npm --version
 
# Run JavaScript file
node index.js
 
# Start REPL (interactive shell)
node
 
# Run with flags
node --inspect index.js      # Enable debugger
node

// Export
module.exports = { add, multiply };
module.exports.add = add;
exports.add = add;         // Shorthand
 
// Import
const math = require('./math');

// package.json
{
 "type": "module"
}
 
// or use .mjs extension
 
// Export
export function add(a, b) { return a + b; }
export const PI

const fs = require('fs');
 
// Read file (callback)
fs.readFile('file.txt', 'utf8', (err, data) 

const path = require('path');
 
// Join paths
path.join('/home', 'user', 'file.txt'

const http = require('http');
 
// Create server
const server = http.createServer((req, res) =>

const os = require('os');
 
os.platform()           // 'linux', 'darwin', 'win32'
os.arch()             // 'x64', 'arm'
os.cpus()             // Array of CPU info

// Current directory
process.cwd()           // Current working directory
process.chdir('/new/path')    // Change directory
 
// Environment

const util = require('util');
 
// Promisify callback-based functions
const fs = require('fs');
const readFile = util.promisify(fs.readFile);

const EventEmitter = require('events');
 
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
 
// Listen to events
myEmitter.

// Create buffer
const buf1 = Buffer.from('Hello');
const buf2 = Buffer.from([72, 101, 108, 

const fs = require('fs');
 
// Readable stream
const readable = fs.createReadStream('input.txt');
readable.on('data'

fs.readFile('file.txt', 'utf8', (err, data) => {
 if (err) {
  console.error(err);
  return;
 }
 console.log(data);
});

const fs = require('fs').promises;
 
fs.readFile('file.txt', 'utf8')
 .then(data => console.log(data))

async function readFiles() {
 try {
  const data1 = await fs.readFile('file1.txt', 'utf8');
  const data2 = await fs.readFile(

# Initialize project
npm init
npm init -y             # Skip prompts
 
# Install packages

{
 "scripts": {
  "start": "node index.js",
  "dev": "nodemon index.js",
  "build": "webpack",
  "test": "jest",
  "lint": "eslint .",
  "format": "prettier --write ."

// .env file
// PORT=3000
// DB_HOST=localhost
// API_KEY=secret123
 
// Install dotenv: npm install dotenv
require('dotenv').config();
 
const port = process.env.PORT || 3000;
const dbHost =

// Try/catch with async/await
async function getUser(id) {
 try {
  const user = await db.findUser(id);
  return user;

const express = require('express');
const app = express();
 
// Middleware
app.use(express.json());
app.use

const fs = require('fs').promises;
const path = require('path');
 
async function saveFile(filename, data) {
 const uploadDir = path.

const fs = require('fs').promises;
 
// Read & parse JSON
async function readJSON(filepath) {
 const data = await fs.readFile(filepath, 'utf8');
 return JSON

async function fetchWithRetry(url, options = {}, maxRetries = 3) {
 for (let i = 0; i < maxRetries; i++) {
  try {

// console methods
console.log('Log message');
console.error('Error message');
console.warn('Warning');
console.table([{ name: 'John', age: 30 }]);
console.

// Use async APIs (don't block event loop)
const data = await fs.readFile('file.txt');  // Good
// const data = fs.readFileSync('file.txt');  // Bad
 
// Stream large files
fs.createReadStream('large-file.txt'

__dirname             // Current directory path
__filename            // Current file path
__filename            // Current file path
global              // Global object
console              // Console object
process              // Process object
Buffer              // Buffer class
setTimeout()           // Set timeout
setInterval()           

# Web frameworks
npm install express        # Minimal web framework
npm install fastify        # Fast web framework
npm install koa          # Modern framework
 
# Database
npm install mongoose