Christian Wenz was writing about AJAX before AJAX was invented...er, coined, so he knows a lot about JavaScript. He can succinctly differentiate the marketing of DHTML from the usability of DOM as an object model and API. He has expertise in both the Microsoft and Open Source realms. And, Wenz helped create the Phrasebook series. This is not a book for "Dummies," this is the real thing.
Lots of web sites are using AJAX libraries today, and way too many web designers have called upon JavaScript with client-side tricks downloaded over the years. What a typical developer needs are clear methods for tweaking AJAX, fixing buggy tricks, and just for making the quick hack on the client to solve a problem.
While a book this small can't begin to cover everything, it has an intelligent outline that does cover many common code techniques. Best of all, the Phrasebook format has the right balance of explanation to code. It's tighter than an O'Reilly Nutshell edition, while handier than a Pocket Guide. Let's face it, a selection from the latter series does fit in your pocket, but at the expense of no explanations nor examples.
Here's an example of a handy hack easily solved with the JavaScript Phrasebook, one that might not be so obvious to a JavaScript novice. You've got a dynamic iframe element inside of a static web page, and you want to pass a parameter from the static URL. Huh, aren't query strings for dynamic pages? Sure, but what's the hack? Wenz provides a short item on "Retrieving GET Parameters" in Chapter 2 on "Common Phrases" along with "Using Iframes" in Chapter 9 on Windows and Frames.
So, if you are a developer in need of such essentials on the fly, you'll find the JavaScript Phrasebook to be handy. Oh yeah, it does fit in a pocket.