You Don't Know JS Yet: JavaScript Book Series
/You-Dont-Know-JS
You Don't Know JS Yet is Kyle Simpson's book series on the JavaScript language, now in its second edition with Get Started and Scope & Closures finished. Read it for a chapter-by-chapter explanation of scope, closures, and prototypes instead of a syntax reference; skip it if you need coverage of async patterns or newer ES.Next features, since the README marks those two planned titles canceled.
Visit โUnderstanding the You Don't Know JS Yet Series
The You Don't Know JS Yet series is a set of books by Kyle Simpson that walks through JavaScript's internal mechanics instead of treating the language as a black box. Per the README, the second edition's order starts with Get Started, then Scope & Closures, then an ebook called The Unbooks bundling draft chapters on Objects & Classes and Types & Grammar. The books are readable at no cost right in this repository.
Core JavaScript Concepts Explored
- โGet Started lays the groundwork before the deeper books, per the README's recommended reading order.
- โScope & Closures is the second title in that order, covering how JavaScript resolves variables and forms closures.
- โThe Unbooks ebook bundles Objects & Classes, marked "draft stable" in the README, covering object behavior and class mechanics.
- โThe Unbooks also bundles Types & Grammar, marked "rough draft," covering type coercion and JS's grammar rules.
- โRepo topics span closures, prototypes, and es2015/es6 concepts, reflecting the scope both editions cover.
- โTwo more titles, Sync & Async and ES.Next & Beyond, were planned for the second edition but the README marks both canceled.
Who Benefits from This Series?
Pick this up if you already write JavaScript but want to understand why closures capture variables the way they do, or how prototypal inheritance actually resolves property lookups, instead of pattern-matching from memory. It suits developers moving from tutorial-level JS toward interview-level or library-author-level understanding. It's a poor fit if you're looking for a first introduction to programming, or for coverage of newer async patterns and ES.Next syntax, since those two chapters were canceled.
Strengths
- โTwo of the second edition's core titles, Get Started and Scope & Closures, are finished and lead the README's recommended reading order.
- โThe text sits directly in the repository, so there's no signup or paywall between a reader and the content.
- โCoverage stays narrow and mechanism-focused (scope, closures, prototypes, type coercion) rather than a broad syntax tour, matching the repo's own topic tags.
- โFrontend Masters sponsors the first two second-edition books, per the README, and also sells related video training if you'd rather learn in that format.
- โThe first edition is still available on a separate branch for readers who prefer it or already started there.
Current Status and Series Scope
- โณThe README describes the series as finished and closed to new outside contributions, so pull requests proposing additional chapters won't be merged.
- โณTwo planned second-edition titles, Sync & Async and ES.Next & Beyond, are marked canceled, so this edition has no updated chapters on promises, async/await, or newer ES.Next syntax.
- โณObjects & Classes carries a "draft stable" label and Types & Grammar a "rough draft" label in the README, meaning part of the second edition isn't in finished form yet.
- โณThe content's license, Creative Commons Attribution-NonCommercial-NoDerivs 4.0, blocks commercial reuse and redistributing a modified version.
- โณGitHub's own license metadata fields for the repo weren't populated at the time these facts were pulled, so licensing terms come only from the README's copyright notice.
Other Resources for Advanced JavaScript
Common Questions About YDKJS Yet
You Don't Know JS Yet is free to read online in this GitHub repository, since the README promises readers can always get the books here at no charge. The second edition is also self-published through GetiPub, so a purchased copy is available from retailers like Leanpub and Amazon for anyone who wants one.
You Don't Know JS Yet covers JavaScript's core mechanisms: scope and closures, prototypal behavior through Objects & Classes, and type coercion and grammar through Types & Grammar, plus a Get Started volume on the language's fundamentals, matching the repo's own topic tags of closures, prototypes, es2015, and es6.
The second edition lists three main titles in the README's recommended order: Get Started, Scope & Closures, and an ebook called The Unbooks that itself bundles draft chapters on Objects & Classes and Types & Grammar. Two further titles, Sync & Async and ES.Next & Beyond, were planned but the README marks both canceled.
You Don't Know JS Yet isn't accepting new outside contributions anymore. The README calls the series finished and thanks everyone who took part over what it describes as an 11 years journey, so a pull request proposing new chapters wouldn't be merged at this point.
You Don't Know JS Yet's text is released under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 Unported License, per the README's copyright notice covering the materials under Kyle Simpson's copyright, dated 2019-2025. That license allows reading and sharing but blocks commercial use and modified redistributions.
Kyle Simpson wrote the You Don't Know JS Yet series. The README's copyright notice credits the materials to him and links to workshops he teaches through Frontend Masters under his own name.
Best use cases
- โขPreparing for a JavaScript interview that probes closures, scope, or prototypal inheritance instead of framework trivia.
- โขFilling gaps a bootcamp or tutorial course left behind by teaching JS syntax without explaining scope resolution or type coercion.
- โขReading Scope & Closures specifically before working in a codebase that leans on closures for private state or memoization.
- โขChecking Objects & Classes or Types & Grammar while they're still in draft, for an early look at how the second edition frames those topics.
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