You-Dont-Know-JS

You Don't Know JS Yet is a series of books that go deep into how the JavaScript language actually works under the hood, written by Kyle Simpson. The repository is where the second edition is being written and shared, and it also keeps the finished first edition available on a separate branch. JavaScript is the language that runs in web browsers and powers most modern websites and many backend systems, and these books are aimed at developers who already use it but want to understand its core mechanisms properly rather than treating them as magic.

The series is organized as separate small books, each focused on one topic, intended to be read in this order: Get Started, Scope & Closures, Objects & Classes, Types & Grammar, Sync & Async, and ES.Next & Beyond. Together they walk through the language's foundations and progressively cover more advanced subjects like asynchronous behavior and modern features. The second edition is described as a work in progress.

You'd use this if you write JavaScript and want to genuinely understand things that other resources gloss over — like how scope and closures actually behave, how object and class semantics work, how synchronous and asynchronous execution interact, and what's coming in newer versions of the language. The books are available to read online for free directly from the repo, and the second edition is being self-published through GetiPub for sale as physical books. The repository itself is essentially the manuscript and supporting material for the book series, not a software project.