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 & Architecture
To reason about Node.js performance, you first have to understand the machinery underneath your code—the V8 engine that compiles your JavaScript, libuv that supplies the event loop and thread pool, and the single-threaded, event-driven model that ties them together. These concepts explain why Node excels at I/O-heavy workloads and why blocking the event loop is the cardinal sin. The last few rows cover the developer-facing surface—--watch, native TypeScript, and the REPL—that has made the modern runtime feel batteries-included.
| Concept | Example | Description |
|---|---|---|
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. | |
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. | |
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. | |
fs.readFile(path, callback) returns immediately | • Operations return control immediately • results are delivered via callbacks, promises, or async/await when ready. | |
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. |