Book · 2015
You Don't Know JS
by Kyle Simpson
Kyle Simpson's free GitHub series that bootcamp grads keep crediting when they finally understand closures, this, and coercion.
What does Reddit think of You Don't Know JS?
Twenty mentions across seven years, almost all of them (16) in r/learnprogramming, the rest in r/cscareerquestions. The thread that matters isn't a single rave; it's the same shape of comment, repeated. Someone asks how to get past tutorial-level JavaScript and a high-upvoted reply points at YDKJS and tells them it dives into the idiosyncrasies the bootcamp skipped. The cscareerquestions post at ↑23 is the clean example: a 13-week bootcamp grad finished the curriculum in 4 weeks, spent the rest on YDKJS, and credited it for placing 2nd in their cohort. There is one piece of contested context. A ↑45 comment flags that author Kyle Simpson has a reputation for controversial tweets, while explicitly noting the books are free and well-regarded on their own. Mention volume peaks in 2019 (12) and trails off after — fewer recs, not fewer endorsements.
Community feedback & reader fit
Themes
- · the closures-this-coercion gap between bootcamp JS and real JS
- · free GitHub series as the standard r/learnprogramming next step
- · author reputation vs book reputation kept separate
- · post-fundamentals not for absolute beginners
- · the ydkjs-exercises.com companion built by readers
Common praise
- + The scope/closure book is what makes 'this' finally click for bootcamp grads.
- + Free on GitHub forever, which is why r/learnprogramming keeps linking it instead of paid courses.
- + A cscareerquestions commenter blew through their bootcamp in 4 weeks and used YDKJS for the other 9, then placed 2nd in their cohort.
- + Covers the language quirks (hoisting, coercion, prototypes) that interviewers actually ask about.
- + Community-built exercises at ydkjs-exercises.com let you check whether you actually learned it.
Common criticism
- − Not easy — a ↑57 comment in r/learnprogramming says outright that going through it is hard work.
- − If you don't already know JS fundamentals, the consensus reply is keep learning JS first and come back.
- − Kyle Simpson's Twitter has cost him some goodwill; a ↑45 thread flags it while still recommending the books.
- − Mention volume dropped from 12 in 2019 to 1 in 2023 — still cited, but the rec engine has moved on.
- − No mentions in r/javascript or r/webdev in the dataset, which is where the deeper-than-MDN crowd actually lives.
Who it's for
You finished a bootcamp or freeCodeCamp and can write a React component, but 'this', closures, and == still feel like magic you're working around. Read it then. If you've never touched JavaScript, the top-upvoted r/learnprogramming reply is blunt: keep learning JS first. Treat it as the post-fundamentals book, not the first one. And if the author's Twitter is a dealbreaker for you, that's a fair call — the books are free on GitHub and stand on their own.
Mentions over time
Top subreddits
Which Reddit comments matter for You Don't Know JS?
Top-upvoted quotes across the subreddits where this book is mentioned. Click through to read the full thread.
“Hey there. I'm going to touch on a few things in the following areas: skills, resume, and interviews. First, some background about me. I've been in web and front-end professionally for 10 years, and I'm currently an engineering director in NYC. I've interviewed and hired engineers as well as a numb…
“Here's my list of the classics: **General Computing** * But How Do It Know? - The Basic Principles of Computers for Everyone * The Elements of Computing Systems: Building a Modern Computer from First Principles * […
“Check out to test your knowledge! 25 open source developers and I created it
“React uses JS. You will have a difficult time using React if you don't know JS.
“Front-end development (JavaScript, HTML, CSS) is a safe bet in today's job market. Various companies build their applications on various back-end stacks, but almost all of them need competent front-end developers. General front-end skills to know: ## JavaScript * Knowledge of how JS works as a lan…
“$1 Tier CSS: The Definitive Guide: Visual Presentation for the Web Using SVG with CSS3 and HTML5 [Learning React: Functional Web De…
“There’s an error in the section about variable names. 11booth is not a valid name. Variables have to start with a letter or an underscore. With a project like this, you *really* need to have the details correct. YDKJS isn’t great because it gives a serviceable overview of basic JS, it’s great be…
“First of all, people are paying you to build a site. Clients don't 'eat' HTML or CSS code and unless they ask for it, they don't care how you do it as long it's done in a good way. Using 2014 technologies properly is perfectly fine today IF you are using them properly. Javascript is still Javascript…
Convinced? Pick up You Don't Know JS
What else does r/webdev read?
Other books mentioned in the same sub, ranked. Shared-sub overlap with this title breaks ties.
Clean Code
Robert C. Martin
The book 536 Reddit threads cite when arguing about naming variables — revered by beginners, argued over by seniors.
Eloquent JavaScript
Marijn Haverbeke
Marijn Haverbeke's free online JavaScript book — variables to async in one volume — by someone who said he wouldn't wish a game-programming career on anyone.
The Mythical Man-Month
Frederick P. Brooks Jr.
Fred Brooks spent the 1960s building IBM's OS/360 and wrote down everything that went wrong — in 1975, and it still lands.
Design Patterns
Erich Gamma
The 1994 Gang of Four catalog that named 23 object-oriented patterns, gave developers a shared vocabulary, and taught a generation to over-apply both.
The Pragmatic Programmer
Andy Hunt
Two veterans hand you a checklist for the craft: don't write code you don't need, own your tools, and fix the broken window before someone else does.
Code Complete
Steve McConnell
Steve McConnell's 900-page construction manual for software, ranked third on Reddit's canonical reading list and still cited 25 years after publication.
You Don't Know JS — frequently asked
Is You Don't Know JS still worth reading in 2026?+
Yes, with one caveat. The content is still accurate; it's just no longer the default rec.
Should I read YDKJS before or after a bootcamp?+
After. The strongest data point in the set is a ↑23 r/cscareerquestions post where a bootcamp grad used YDKJS during the back half of their program and placed 2nd in their cohort. A ↑57 r/learnprogramming reply calls it 'not easy at all' and recommends it once you're comfortable with fundamentals. Treat it as a second-pass book, not a first one.
Is YDKJS free or do I have to buy it?+
Free. Every recommendation in the dataset points at the GitHub repo at github.com/getify/You-Dont-Know-JS, and the ↑45 r/learnprogramming comment makes the point explicitly: 'YDKJS is always free.' Print editions exist if you want them, but no one on Reddit is telling you to buy them. There's also a community exercise site at ydkjs-exercises.com built by 25 open-source devs.
Does the Kyle Simpson Twitter controversy matter for the books?+
Depends on you. One ↑45 r/learnprogramming comment flags Simpson's 'controversial tweets' and singles out his takes on Nigerian developers, then immediately notes the books are free and recommended regardless. No other thread in the dataset brings it up. If author conduct affects whether you'll read something, you already know your answer; if it doesn't, the technical content is what every other thread is recommending.