Node.js Cheatsheet — Built-in Modules & Common Patterns

File System (fs)

import { readFile, writeFile, readdir, stat, mkdir } from 'fs/promises';

// Read file
const data = await readFile('file.txt', 'utf8');

// Write file
await writeFile('out.txt', 'hello');

// List directory
const files = await readdir('.', { withFileTypes: true });

// Check if exists
const info = await stat('file.txt').catch(() => null);

// Create directory
await mkdir('new-dir', { recursive: true });

Path Module

import path from 'path';

path.join('/users', 'docs', 'file.txt')  // /users/docs/file.txt
path.resolve('./src')                      // /absolute/path/src
path.extname('file.txt')                   // .txt
path.basename('/a/b/file.txt')             // file.txt
path.dirname('/a/b/file.txt')              // /a/b

HTTP Server

import http from 'http';

const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({ hello: 'world' }));
});

server.listen(3000);

Process & Environment

process.env.NODE_ENV           // Environment variable
process.cwd()                  // Current working directory
process.argv                   // CLI arguments
process.exit(1)                // Exit with code
process.on('uncaughtException', console.error);

Child Process

import { exec, execSync, spawn } from 'child_process';

// Quick command
const output = execSync('ls -la', { encoding: 'utf8' });

// Streaming output
const child = spawn('npm', ['test']);
child.stdout.on('data', chunk => process.stdout.write(chunk));