Book · 2015
You Don't Know JS
by Kyle Simpson
A front-end director tells a career-change hopeful to stop skimming tutorials and actually learn how JavaScript works underneath React.
What does Reddit think of You Don't Know JS?
The most direct case for this book on Reddit isn't a review, it's a syllogism: "React uses JS. You will have a difficult time using React if you don't know JS" (r/webdev, ↑134). That's the whole pitch in two sentences. A career-advice thread from a hiring engineering director recommends it as part of a broader skills path (↑350), and r/learnprogramming built a companion exercise site around it, 25 contributors deep (↑163). But the fiercest excerpt here is critical, not promotional: r/Python's top comment argues the project built from the book has an actual error, a variable name that isn't valid JS, and concludes the series "isn't great because it gives a serviceable overview" rather than something more (↑69). So the disagreement isn't about whether fundamentals matter. It's whether this particular text nails them. Mention volume has dropped sharply since 2019, from 22 that year to a handful since.
Community feedback & reader fit
Themes
- · JavaScript fundamentals underneath frameworks like React
- · Scope, closures, and "this" as recurring trouble spots
- · Learning JS deeply versus learning a framework fast
- · Community-built exercises extending the book's material
Common praise
- + One hiring manager includes it in career-advice recommendations for people breaking into front-end (↑350).
- + 25 developers built a free exercise site off the book's content, which only happens if people are actually working through it (↑163).
- + The React-needs-JS argument for reading it shows up as a one-line consensus, not a hedge (↑134).
- + Gets grouped with front-end fundamentals like CSS and SVG on curated learning lists (↑70).
Common criticism
- − r/Python catches an actual code error in the sample project and calls out the sloppiness directly (↑69).
- − The same critical commenter says it only delivers a "serviceable overview," not depth, undercutting the book's whole premise.
- − None of the top-voted excerpts describe finishing the whole series, only recommending pieces of it in passing.
Who it's for
Coming from bootcamp React tutorials with no idea what closures or hoisting actually do? This is aimed at exactly that blind spot. Don't expect polish — check your own code against the samples rather than trusting them line for line, since even a Python-sub commenter caught a naming error in the project code. If you're already comfortable explaining prototypal inheritance from memory, you've outgrown it. Front-end hopefuls assembling a self-study stack tend to slot this in next to CSS references and SVG guides rather than treat it as a standalone curriculum.
Mentions over time
Top subreddits
Which Reddit comments matter for You Don't Know JS?
The most relevant excerpts across the subreddits where this book is mentioned — opinionated, argued takes first, then top-upvoted mentions. 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 * […
“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…
“That's awesome. I remember having the same feeling when I went through that book. It's a great book. Not easy at all. If JS interests you, I highly recommend the ydkjs series once you feel comfortable with fundamentals. It dives deep into core JS knowledge needed in the real world.
“EloquentJS & YDKJS. Excellent books for JavaScript. Read them in that order. You will be able to build interesting things locally without learning build tools etc that you'll need the internet to download. Either way wi…
“Just an FYI, this guy has quite a reputation for posting... controversial tweets we’ll say. YDKJS is always free and so is Elegant JavaScript. Lots of great free stuff that is written by folks with great reputations. Edit: look specifically to his take on Nigerian developers.
“I know that I'm really enjoying reading You Don't Know JS, but you can also read it free on github.
“Eric Meyer's CSS books are definitive and excellent (and do cover modern topics such as flex and grid). You Don't Know JS is also really great for understanding the finer bits of JavaScript (the parts that people complain about because they don't understand them), though [it's available for free as…
“I went to a 13 week bootcamp in Jan 2018. I was putting in tons of extra after hours effort and blew through the curriculum in 4 weeks those following 9 weeks I spent diving deeper with YDKJS and starting to learn Python. When I graduated with my cohort of 24 (started at 30) I was easily the 2nd bes…
“ydkjs
“'You Don't know JS' helped a lot to understand a lot of basic and important concepts in JavaScript. It mentions a lot of idiosyncrasies in the language as well. This will help for sure.
“Start with YDKJS, eloquent gets buck wild after chapter 5.
“I would say get really comfortable with html, css and JavaScript first before jumping into a framework. Especially JavaScript. Follow along a book like 'eloquent JavaScript' or 'you don't know JS' because it will make things easier once you start using frameworks. All those tools you mentioned wil…
“From this, Node is really a good choice. For database, SQLite is the best, no need to install a server for database, it's just a file. I'm thankfully for Kyle Simpson, the author of You Don't Know JS series. I watched his talk which covers the stuff in the books, it help me so much, like I can u…
“Take a look at the "you don't know JS" series by Kyle Simpson. It really upped my JS knowledge!
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.
You Don't Know JS — frequently asked
Do I need You Don't Know JS if I'm just trying to learn React?+
Reddit's answer leans yes. The r/webdev argument is blunt: "React uses JS. You will have a difficult time using React if you don't know JS" (↑134). A separate career-advice thread from a hiring engineering director includes it in a broader front-end skills recommendation (↑350), treating JS fundamentals as a prerequisite rather than optional background reading.
Is You Don't Know JS accurate enough to trust its code examples?+
r/Python's top comment on it flags a real bug in the accompanying project — an invalid variable name — and argues the book "gives a serviceable overview" rather than something rigorous (↑69). Nobody else in the displayed excerpts disputes the fundamentals-first premise, but that one critique is specific and unresolved.
Is there a community resource to practice what You Don't Know JS teaches?+
Yes. r/learnprogramming surfaces ydkjs-exercises.com, built by 25 open source developers specifically to test the book's material (↑163). That kind of unpaid follow-through is a stronger signal of engagement than any star rating.
Who still recommends You Don't Know JS given how old some of the mentions are?+
Mostly r/webdev and r/learnprogramming, and mostly in the context of front-end job prep rather than general programming literacy. Mentions were heaviest in 2019 and have thinned since, but the r/webdev framing — JS fundamentals as a React prerequisite — hasn't been contradicted in later threads.