You Don't Know JS — open source GitHub project

You Don't Know JS is Kyle Simpson’s book series about understanding JavaScript deeply and reading the language beyond surface syntax.

What You Don’t Know JS is

You-Dont-Know-JS is Kyle Simpson’s book-series repository about JavaScript. The current README points to the second edition, You Don’t Know JS Yet, which dives into language mechanisms rather than surface recipes.

The series became notable because it treated JavaScript as a language worth understanding deeply. Scope, closures, objects, classes, types, and grammar are explained as engineering mechanisms.

What is inside

The README lists Get Started and Scope & Closures, plus The Unbooks with Objects & Classes and Types & Grammar. It links to the first edition branch and notes that the second edition series is complete and no longer open to contributions.

Reading order

The repository acts as a map from language entry points to deeper mechanisms.

Language: Markdown

- Get Started
- Scope & Closures
- Objects & Classes
- Types & Grammar
- First edition archive

Why it is useful

It works as a free open bookshelf for JavaScript fundamentals. It is best when you want to understand why code behaves the way it does: scope creation, closures, object behavior, and types.

Limits

It is a book series, not a constantly updated reference for every browser or Node.js API. For day-to-day work you still need MDN, runtime docs, framework guides, and real projects.