JavaScript: The Definitive Guide

JavaScript: The Definitive Guide has been frequently revised for new versions of JavaScript and therefore has multiple editions. This review is of the seventh edition, first published in May of 2020.

Reviews of programming language books are challenging since people learn languages in different ways. A short calibration for my preferences may therefore be useful.

I'm both an experienced programmer in multiple languages (C, Perl, Python, and some Java and Ruby professionally; Rust, some PHP, and a few minor languages as a hobby) and I specialized in software theory in college. I therefore like to learn languages comparatively and am comfortable with a lot of up-front syntax and discussion of the unique properties of the language. Introductory programs and practical exercises doesn't matter as much to me; I'm happy to hold the syntax in my head until enough of the language has been introduced to write simple programs.

For me, this book is excellent. It's one of the best language manuals that I've read, and that requires some work because JavaScript is a sprawling mess with odd corners, deprecated features, and alternate implementations of core constructs. Flanagan takes the syntax-first, comprehensive approach that I prefer, working methodically through the language (defining your own functions aren't introduced until chapter eight) and discussing all of the quirks as he goes. I felt like I thoroughly understood each portion of the language before moving on.

And this book is tight. Some comprehensive language introductions sprawl, but the benefit of seven editions of iteration is a book that has been honed to the most direct and effective explanation of each concept. The section on type conversions with operators, for example, was so good that I was able to immediately understand the unintuitive result of [1] + 2 (the string '12'), despite this being one of the most confusing parts of the language. The sections on JavaScript's prototype-based object type system and its three concurrency models (callbacks, promises, and async/await) were equally good. I came away feeling like I not only understood promises and callback chains but had a feel for how the same code would look when written in the different systems.

The drawback in this approach is that if you instead want a language reference that only tells you the parts of the language that you should use and leaves out the legacy weirdness and obscure corners for later (or never), this may not be the book for you. Flanagan labels the obsolete constructs, but he's meticulous about explaining the entire language, including such things as new Boolean or var variables that no one should use. This is what I wanted; I prefer to have a thorough grounding in language primitives so that it doesn't surprise me. But it can be a lot to juggle and prune in your head.

JavaScript is a language used in some very different domains. The approach Flanagan takes to that is to spend as long as possible on the core language that's usable both in the browser and on the server (while marking the pieces, such as the module system, that are markedly different between Node and browsers). He then puts two monster chapters at the back of the book that cover JavaScript in web browsers and JavaScript as implemented by Node. Both are more of overviews than orientations, since a comprehensive manual for either is probably as long again as this book, but they were more than adequate for my purposes. (I bogged down a bit in the web browser chapter, in part because I didn't have an immediate use for most of the material.) Flanagan wisely defers to MDN as the reference manual for the JavaScript APIs available in web browsers.

I thought Flanagan also hit the right balance of explanation to examples, and did a good job controlling the length of the examples. Most of the code excerpts are short and to the point. The longer ones have a high level of explanatory power per line, since Flanagan uses them to pull together multiple concepts and show how they interact. I was particularly impressed with the example that closes the chapter on web browsers, which uses <canvas>, ImageData, generators, promises, web workers, and other areas of the language Flanagan previously explained to implement a Mandelbrot set explorer in eleven pages of code. I think that's the longest example in the book, and it's well worth it.

This sort of introduction will always have limitations. Flanagan provides a brief orientation to the ecosystem surrounding JavaScript in the last chapter, but most JavaScript programmers will be working with packaging tools and frameworks that could themselves be the topic of another book and that he doesn't have room to cover. JavaScript, even more than most languages, is commonly used via a heavy layer of supporting libraries and abstractions, so you will probably not be able to tackle a practical JavaScript project using solely the material in this book. But if you're the sort of programmer who wants to start with a solid syntactical and conceptual understanding of the language core before starting on more applied topics, I've rarely seen it done better than this book.

If you want a quick-start guide that will get you writing code quickly and is opinionated about what parts of the language you should learn, this may not be the book for you. But if you're comfortable with comprehensive detail in your language guides, this was exactly what I was looking for. Recommended.

Rating: 9 out of 10

Reviewed: 2021-03-28