Node.js Cheat Sheet

Updated 2026-04-29

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Node.js is a server-side JavaScript runtime built on Chrome's V8 engine, designed for building scalable network applications. It uses an event-driven, non-blocking I/O model that makes it lightweight and efficient, particularly well-suited for data-intensive real-time applications. As of Node.js 26 (released April 2026, the last release under the old even/odd LTS model), the runtime has reached a "batteries-included" maturity—with native TypeScript type stripping, a built-in Permission Model, native fetch() and WebSocket client, a built-in SQLite module, and a built-in test runner that eliminate many previously required npm dependencies. Understanding Node.js means understanding that most operations are asynchronous by default and that the event loop's single-threaded model shapes every architectural decision.

What This Cheat Sheet Covers

This topic spans 22 focused tables and 203 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.

Table 1: Runtime & ArchitectureTable 2: Asynchronous PatternsTable 3: Module SystemTable 4: Core Modules - File SystemTable 5: Core Modules - StreamsTable 6: Core Modules - HTTP & NetworkingTable 7: Built-in Web-Standard APIsTable 8: Core Modules - Process & EnvironmentTable 9: Core Modules - EventsTable 10: Core Modules - TimersTable 11: Core Modules - Path & URLTable 12: Core Modules - UtilitiesTable 13: Core Modules - Crypto & SecurityTable 14: Core Modules - Child Processes & ConcurrencyTable 15: npm & Package ManagementTable 16: package.json ConfigurationTable 17: Error HandlingTable 18: Performance & MonitoringTable 19: TestingTable 20: Debugging & CLI ToolsTable 21: OS & System InformationTable 22: Advanced Core Modules

Table 1: Runtime & Architecture

Concept	Example	Description
Event Loop	Processes callbacks from timers, I/O, and setImmediate queues in phases	• Core mechanism enabling non-blocking I/O • continuously cycles through six phases (timers, pending callbacks, idle, poll, check, close callbacks) executing queued callbacks without spawning new threads.
V8 Engine	Compiles JS to machine code using JIT compilation	• Google's open-source JavaScript engine that powers Node.js • handles memory allocation, garbage collection, and code optimization; Node.js 26 ships V8 14.3.
libuv	Cross-platform async I/O library underneath Node.js	Provides the event loop and thread pool for file system work while abstracting platform-specific async APIs across Windows, macOS, and Linux.
Non-blocking I/O	`fs.readFile(path, callback)` returns immediately	• Operations return control immediately • results are delivered via callbacks, promises, or async/await when ready.
Single-threaded	Main event loop runs on one thread	JavaScript execution stays on a single thread, while I/O operations are delegated to the kernel or thread pool.

Table 1: Runtime & Architecture

Concept	Example	Description
Event Loop	Processes callbacks from timers, I/O, and setImmediate queues in phases	• Core mechanism enabling non-blocking I/O • continuously cycles through six phases (timers, pending callbacks, idle, poll, check, close callbacks) executing queued callbacks without spawning new threads.
V8 Engine	Compiles JS to machine code using JIT compilation	• Google's open-source JavaScript engine that powers Node.js • handles memory allocation, garbage collection, and code optimization; Node.js 26 ships V8 14.3.
libuv	Cross-platform async I/O library underneath Node.js	Provides the event loop and thread pool for file system work while abstracting platform-specific async APIs across Windows, macOS, and Linux.
Non-blocking I/O	`fs.readFile(path, callback)` returns immediately	• Operations return control immediately • results are delivered via callbacks, promises, or async/await when ready.
Single-threaded	Main event loop runs on one thread	JavaScript execution stays on a single thread, while I/O operations are delegated to the kernel or thread pool.