Node.js Cheat Sheet

Core Modules

fsFile system
pathPath utilities
http/httpsHTTP server
osOS information
eventsEvent emitter
cryptoCryptography
streamStream handling

npm Commands

npm initCreate package.json
npm installInstall deps
npm install -DDev dependency
npm updateUpdate packages
npm runRun script
npm outdatedCheck updates

Global Objects

__dirnameCurrent dir
__filenameCurrent file
processProcess info
consoleConsole output
BufferBinary data
moduleModule object

Process Object

process.envEnvironment vars
process.argvCLI arguments
process.cwd()Working dir
process.exit()Exit process
process.pidProcess ID

File System (fs/promises)

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

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

// Write file
await writeFile('./output.txt', 'Hello World');

// Create directory
await mkdir('./newdir', { recursive: true });

// Check if exists
import { access } from 'fs/promises';
try {
  await access('./file.txt');
} catch { /* doesn't exist */ }
          

HTTP Server

import http from 'http';

const server = http.createServer((req, res) => {
  if (req.url === '/' && req.method === 'GET') {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ message: 'Hello' }));
  }
});

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

Path Module

import path from 'path';

path.join('/foo', 'bar')
// /foo/bar

path.resolve('./file.txt')
// Absolute path

path.dirname('/foo/bar.txt')
// /foo

path.basename('/foo/bar.txt')
// bar.txt

path.extname('file.txt')
// .txt
          

Event Emitter

import { EventEmitter } from 'events';

const emitter = new EventEmitter();

// Listen for event
emitter.on('data', (msg) => {
  console.log(msg);
});

// Emit event
emitter.emit('data', 'Hello!');

// Once listener
emitter.once('connect', () => {});
          

Async Patterns

// Promises
const fetchData = () => {
  return new Promise((resolve, reject) => {
    setTimeout(() => resolve('data'), 1000);
  });
};

// Async/Await
async function main() {
  try {
    const data = await fetchData();
    const [a, b] = await Promise.all([task1(), task2()]);
  } catch (err) {
    console.error(err);
  }
}
          

Streams

import { createReadStream } from 'fs';
import { pipeline } from 'stream/promises';

const readable = createReadStream('input.txt');

readable.on('data', (chunk) => {
  console.log(chunk);
});

// Pipeline
await pipeline(
  readStream,
  transformStream,
  writeStream
);
          

ES Modules

// Named exports
export const add = (a, b) => a + b;
export { add, subtract };

// Default export
export default class App {}

// Import
import App from './app.js';
import { add } from './math.js';
import * as utils from './utils.js';
          

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