welcome

JavaScript is everywhere—browsers, servers, embedded systems, edge computing—yet most developers treat the language as a black box. They write code without fully understanding what the runtime actually does with it. This gap between what developers write and what machines execute causes real problems: memory leaks that crash production servers, performance cliffs that appear without warning, and optimization strategies based on outdated folklore rather than current reality.

This book pulls back the curtain on JavaScript itself, the engines that implement it, and runtimes like Node.js to understand what is happening under the hood. You'll learn how JavaScript's seemingly simple features create complex runtime behaviors, why certain patterns destroy performance while similar ones run blazingly fast, and how the evolution of both the language and the implementation of it have invalidated much of the "common wisdom" about JavaScript optimization that has persisted through the years.

The first four chapters establish a foundation: