Node.js Cheat Sheet

Core Modules

File System (fs)

const fs = require('fs');

// Read file (async)
fs.readFile('file.txt', 'utf8', (err, data) => {
  if (err) throw err;
  console.log(data);
});

// Read file (sync)
const data = fs.readFileSync('file.txt', 'utf8');

// Write file
fs.writeFile('output.txt', 'Hello', (err) => {
  if (err) throw err;
});

// Promises API (modern)
const fs = require('fs').promises;
const data = await fs.readFile('file.txt', 'utf8');

HTTP Server

const http = require('http');

const server = http.createServer((req, res) => {
  // Set response headers
  res.writeHead(200, { 'Content-Type': 'text/html' });

  // Routing
  if (req.url === '/') {
    res.end('<h1>Home</h1>');
  } else if (req.url === '/api') {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ message: 'API response' }));
  } else {
    res.writeHead(404);
    res.end('Not Found');
  }
});

server.listen(3000, () => {
  console.log('Server running on port 3000');
});

NPM Commands

Environment Variables

// Access environment variables
const port = process.env.PORT || 3000;
const dbUrl = process.env.DATABASE_URL;

// Using dotenv package
require('dotenv').config();
const apiKey = process.env.API_KEY;

// .env file format:
// PORT=3000
// DATABASE_URL=mongodb://localhost/mydb
// API_KEY=your_key_here