Node.js

Core Modules

const fs = require('fs')—File system module

const path = require('path')—Path utilities

const http = require('http')—HTTP server/client

const os = require('os')—OS information

const events = require('events')—Event emitter

const crypto = require('crypto')—Cryptography

const url = require('url')—URL parsing

const util = require('util')—Utility functions

File System (fs)

fs.readFileSync(path, "utf8")—Read file sync

fs.writeFileSync(path, data)—Write file sync

fs.promises.readFile(path)—Read file async

fs.promises.writeFile(path, d)—Write file async

fs.existsSync(path)—Check file exists

fs.mkdirSync(dir, {recursive})—Create directory

fs.readdirSync(dir)—List directory contents

fs.unlinkSync(path)—Delete file

fs.statSync(path).isFile()—Check if file

fs.createReadStream(path)—Streaming file read

Path Module

path.join(a, b)—Join paths safely

path.resolve(rel)—Absolute path

path.basename(p)—File name

path.dirname(p)—Directory name

path.extname(p)—File extension

path.parse(p)—Parse path parts

__dirname—Current dir (CJS)

__filename—Current file (CJS)

npm & Package Management

npm init -y—Create package.json

npm install pkg—Install dependency

npm install -D pkg—Install dev dependency

npm install -g pkg—Install globally

npm uninstall pkg—Remove package

npm update—Update packages

npm run script—Run package script

npx command—Execute package binary

npm list—List installed packages

npm audit—Check vulnerabilities

HTTP Server

http.createServer((req, res) => {})—Create server

server.listen(3000)—Listen on port

req.method—HTTP method (GET, POST)

req.url—Request URL path

req.headers—Request headers object

res.writeHead(200, headers)—Set status & headers

res.end(body)—Send response

res.setHeader("key", "val")—Set response header

Process & Environment

process.env.VAR—Environment variable

process.argv—CLI arguments array

process.cwd()—Working directory

process.exit(0)—Exit process

process.pid—Process ID

process.platform—OS platform name

process.stdin / stdout—Standard I/O streams

process.on("uncaughtException")—Global error handler

Async Patterns

callback(err, result)—Node callback pattern

util.promisify(fn)—Convert callback to promise

EventEmitter—Event-driven pattern

emitter.on("event", fn)—Listen for event

emitter.emit("event", data)—Fire event

setImmediate(fn)—Next event loop tick

setTimeout(fn, ms)—Delayed execution

Promise.allSettled()—Wait for all (no fail)

ES Modules in Node

"type": "module"—Enable ESM in package.json

import x from "mod"—Default import

import { x } from "mod"—Named import

import.meta.url—Current file URL (ESM)

import { fileURLToPath }—Convert URL to path

await import("mod")—Dynamic import

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