Frankly speaking, I had to sleep a night over before typing this review.
And even now it is not an easy, straight-forward task to write this recension. I'm not sure whether I'm the right kind of audience this title is actually addressed to. It clearly states that this book is for web developers which are very familiar with jQuery library but would like to extend their knowledge to vanilla JavaScript. Not being part of this particular group it felt strange to go through the various chapters after all. This title is clearly addressed to experienced jQuery users and developers especially while looking for improvements in performance and better ways of optimisations. Sometimes just to simplify the existing jQuery code in order to avoid the heavy load of the complete jQuery library and sometimes for the better understanding of JavaScript and its syntax.
Callum's style of writing is clear and the numerous code samples used to emphasize the various techniques are good ones and easy to understand. Quite interestingly, it put a light smile on my face when I compared his sample code of sending an AJAX request to some code in one of my own blog articles I wrote back in 2006 (in German language). JavaScript is clearly a mature language and certain requirements are simply done this way. And Callum explains the nuts and bolts of JavaScript very well.
Personally, I gained most out of this book from chapter 5 - JavaScript Conventions. The paragraphs and code snippets on Optimizations and Common Antipatterns gave me a better understanding on various aspects of JavaScript development, and I definitely have to revise a couple of code fragments I have written in the past.
Overall the book provides solid information on JavaScript for jQuery developers and is worth the money spent. Just be sure that you're part of the targeted audience.