Just reading through the first few chapters of the book on the `this` keyword (which, as an aside, is shocking to see that the feature is so confusing that it merits its own entire book), the code snippets could use some serious attention.

The variables are all `foo`, `bar`, `baz`, `a`, `obj`, etc. And the values are all just numbers. Sometimes they have a function that takes a value `a`, and they just do `this.a = a`. It requires a ton of cognitive strain to glean out what they're trying to show you in the examples because of this.

IMO the best books are those where they use silly (possibly contrived) "sample program" that the examples all build on. I mean, you could make your classes Cows and Animals, your functions moo's, your properties things like name and favoriteColor, and things can suddenly be a lot more readable when you want to do something like show lexical scoping rules. ("Oh no, that cow's name is steve, when you may have expected it to be bob because of the difference in what `this` refers to" is a lot easier in my mind than a big see of `foo`'s and `bar`'s.) Or maybe an example involving a bank and deposits and withdrawals.

It seems like a minor nitpick but it's things like these that I really use to judge whether a book is actually of good quality. I mean sure, any half-decent programming book exposes you the concepts that make you a better developer, but the good ones do so in a manner that makes it easy to understand.