Built-in Module Quick Reference¶

Node ships with over 40 built-in modules You don't need to memorize every API but you need to know what exists so you don't reinvent the wheel Here's every core module grouped by category with what it does and when to use it

I/O Modules¶

Module	Description	Key exports	When to use
fs	File system operations	readFile , writeFile , createReadStream , mkdir , stat , watch	Everything file-related
path	Path manipulation	join , resolve , basename , dirname , extname , parse	Always - never hardcode paths
stream	Streaming data API	Readable , Writable , Transform , Duplex , pipeline	Large data , piping between I/O
buffer	Binary data handling	Buffer , Buffer.alloc , Buffer.from , Buffer.concat	Binary data , network protocols
readline	Read line-by-line	createInterface	Process large text files line by line
string_decoder	Decode buffers to strings	StringDecoder	Proper multi-byte UTF-8 decoding
zlib	Compression/decompression	gzip , gunzip , deflate , inflate , brotliCompress	Compress HTTP responses , files
crypto	Cryptography	randomBytes , createHash , createHmac , createCipheriv , sign , verify	Hashing , encryption , token generation

Network Modules¶

Module	Description	Key exports	When to use
http	HTTP client and server	createServer , request , get	REST APIs , HTTP services
https	HTTPS client and server	createServer , request , get	Secure HTTP - always use in production
http2	HTTP/2 client and server	createServer , connect	gRPC , low-latency APIs
net	TCP client and server	createServer , connect	Raw TCP , custom protocols
dns	DNS resolution	lookup , resolve , resolve4 , resolve6 , reverse	Domain lookups , email validation
dgram	UDP communication	createSocket	DNS servers , real-time protocols , broadcasting
tls	TLS/SSL encryption	createServer , connect , TLSSocket	Secure TCP , certificate verification
url	URL parsing and formatting	URL , URLSearchParams , parse , format	Working with URLs (always use URL class)

System Modules¶

Module	Description	Key exports	When to use
os	Operating system info	cpus , totalmem , freemem , hostname , platform , homedir	Thread pool sizing , system info
process	Current process control	argv , env , exit , cpuUsage , memoryUsage , uptime	CLI apps , monitoring
child_process	Spawn child processes	spawn , exec , execFile , fork	Running external commands
cluster	Multi-process load balancing	fork , isMaster , isPrimary	Scaling HTTP across CPU cores
worker_threads	Thread-based parallelism	Worker , parentPort , workerData , SharedArrayBuffer	CPU-intensive work
perf_hooks	Performance measurement	performance , PerformanceObserver , createHistogram	Profiling , timing
v8	V8 engine access	getHeapStatistics , setFlagsFromString , serialize	Memory debugging , serialization
vm	Virtual machine context	createContext , runInContext , runInNewContext	Sandboxed code execution
wasi	WebAssembly System Interface	WASI	Rust/AssemblyScript in Node
tty	Terminal I/O	WriteStream , ReadStream , isatty	CLI tools - detect terminal , colors

Data Modules¶

Module	Description	Key exports	When to use
querystring	Query string parsing	parse , stringify , escape , unescape	Legacy query parsing (prefer URL)
punycode	Unicode encoding	encode , decode , toASCII , toUnicode	International domain names
util	General utilities	promisify , callbackify , types , inspect , inherits	Debugging , type checking
assert	Testing assertions	strict , ok , equal , deepEqual , throws , rejects	Writing tests
events	Event system	EventEmitter , once , getEventListeners	Custom event-driven code

Control Flow Modules¶

Module	Description	Key exports	When to use
timers	Delayed execution	setTimeout , setInterval , setImmediate , queueMicrotask	Throttling , debouncing , scheduling
async_hooks	Async resource tracking	createHook , executionAsyncId , triggerAsyncId	Advanced diagnostic , APM tools
diagnostics_channel	Pub/sub diagnostic channel	channel , subscribe , hasSubscribers	Cross-module observability

Debug and Tooling Modules¶

Module	Description	Key exports	When to use
report	Diagnostic report	writeReport , getReport , triggerReport	Crash diagnostics , memory analysis
inspector	Debugging protocol	open , close , url , Sessions	Custom debugging tools
trace_events	Trace event instrumentation	createTracing	Performance analysis
module	Module system internals	builtinModules , Module , createRequire , findSourceMap	Module loading customization
console	Debug output	log , error , warn , table , time , trace , dir	Everything debug

Security-Critical Modules¶

Module	Key Security Properties
crypto	Use for hashing (SHA-256+) , encryption (AES-256-GCM) , random bytes
tls	Always verify certificates , set rejectUnauthorized: true
https	Always use https over http in production
vm	NOT a security sandbox - code can escape the context
child_process	Command injection via shell - use spawn with arrays
fs	Path traversal - validate user-provided paths
net	No built-in encryption - use tls wrapper for sensitive data

Module Loading¶

// CommonJS (default in Node)
const fs = require('fs')

// ESM (ES Modules)
import fs from 'node:fs'
import { readFile } from 'node:fs/promises'

// Built-in modules use the 'node:' scheme (recommended in ESM)
import { createServer } from 'node:http'

The node: prefix is supported in Node 16+ and makes built-in imports explicit Required: node:fs , optional-style: fs (both work)

Quick Start Import Patterns¶

// Most commonly used imports
const fs = require('fs')
const fsPromises = require('fs/promises')
const path = require('path')
const { EventEmitter } = require('events')
const { spawn } = require('child_process')
const http = require('http')
const https = require('https')
const crypto = require('crypto')
const os = require('os')
const util = require('util')
const { pipeline } = require('stream/promises')
const { Worker } = require('worker_threads')

Prerequisites¶

ref_01_events_api.md - EventEmitter used by many core modules