Book Review : You don't know JS yet

Book Review Apr 07, 2020

Though I have read the previous editions of the series. Here is a formal review of the Book "You don't know" JS by Kyle Simpson. This review is also present on the book page on

Start of review

Just finished reading Getting started from You Don't know JS 2nd Edition(online). In india US dollars are too expensive.

Just  to set the context, I have also read the previous series a few years  back and to be true, it helped me understand how everything works deep  inside(Or should I say deep-deep inside). That time I just started with  front end development and a lot of the things just went over my head.  But as suggested you need to read some of the text again once you get  hold of JS.

I started my career with Java and got a change to  work with JS some time back. I remember when I worked with JS and found  myself with so many questions even for a single line of code. You could  write JS program in a file, as inline, in script tag, as requirejs  modules, as event listener directly onto the element, as ES6 modules,  and in dev console directly etc. And to complicate it, all the methods  behave differently. Sometimes, the same code worked when written in a  file, but sometimes it doesn't if executed directly in the dev console.

80%  of the people with whom I started, felt frustrated and left front-end  dev and went back to Java. When you come from an object oriented mindset  like Java and told(read lied!) that JS is also same as Java with  similar syntax, similar rules and classes with objects; you are tricked.  After working for a few weeks you feel betrayed!

It took me 2  months to understand how closure works and almost a year to understand  why is it even required. In fact when I take interviews today, I ask  people why is closure there in JS at the first place instead of asking  what is a closure. And it seems almost every junior developer believes  that closure is there to create modules with private variables.

Javascript  indeed requires a separate getting started book. This book does cover  most of the things and sometimes even more than a getting started  should.

This book and possibly the rest of the books in the  series are NOT for beginners. If you are starting with front-end,  especially Javascript, I would suggest you to get some hands on  experience and maybe perhaps get interviewed for various JS dev  positions. Come back home, try to find out answers to all the weird  interview questions. Do some hands on again and then start with this  series. You will appreciate the books more.

This book is just a warning to you how much you don't know. It tells you about
How JS started,
How it was miss-named,
What is the diff between JS and browser apis. alert() is not JS. Its an api.
REPL tools behaves differently : Don't trust console executed scripts
What multi-paradigm means? Procedural? Object oriented? Functional? Yes JS can do all or is it?
What is Backward compatibilty and why is it required : The root of such a vast eco system of various JS features.
Hoisting : Although just a glimpse, but you will find answer to related ques: Is JS compiled or interpreted?
Coercion : Another JS concept that adds 10 tricky questions to the interview list
Prototypal Inheritance : He mentions that although nobody is writing  prototype based classes now a days but still its popular in interviews.  That's because if a person knows about prototype, it gives a hint that  he has studied on his own and is quite interested in Javascript  internals.

Of course you will find answers to all the questions  on the internet but believe me 90% of the time you will only get  incorrect examples which do work but are not completely true and will  frustrate you more when you encounter other trivial things.

Though  at times, the author gives his opinions where he does not agree with  the rest of the world but he mentions it clearly that its his  perspective and things might not be like this in future. For example I  feel that he supports the Object delegation(using Object.create) method  of inheritance but its not getting popular and people are more inclined  towards class based inheritance(With prototype earlier and now ES6  classes). I myself find classes too much complicated with tens of  different ways you can achieve them with JS but you can't help it. "You  either die as a hero or you live long enough to see yourself a villain"

Well  I am sure the rest of the books in the series do justify their previous  editions and helps us in understanding every bit of JS

Looking  forward for them. Although all the text is available online which is  like gold for people like us, I would suggest the author to consider the  pricing region wise. In india this book costs 57$ paperback and 20$  kindle edition which is way too expensive for professionals who are  getting 300$-500$ as monthly income on an average. Yes there are a few  who can spend but I am talking about the masses.



Developer. Artist. Human.