This book is heavily concentrated on explaining why JavaScript is a functional programming language and how that can be used by the developer. The first half of the book is dedicated to JavaScript functions, there is everything you will need to know about JavaScript functions: anonymous functions, recursions, inline named function and so on.
The second half of the book explains everything that you will need to develop well structured JavaScript code.
The only remark I have for this book is about the ‘Regular Expressions’ chapter, in my opinion it is not written very clear and can be confusing, but it is fer to say that the authors are suggesting additional literature for getting familiar with regular expressions.
Big plus is that all the source code form the book examples is very well structured and packed in zip file that enables you to quickly try the examples on computer.
Its a good buy, and I highly recommend it.