I want to recommend a book by Jeremy Keith, called ”Bulletproof Ajax”. I recommend it for several reasons. First of all, the book is an excellent introduction to Ajax programming in general and everybody starting to write JavaScript code to do Ajax should read it before touching any of the libraries out there.
Secondly the book is especially suited to anybody who is interested in writing Ajax powered apps on mobile devices and constrained browsers. After all the book is all about making JavaScript code bulletproof and that’s exactly what you need to do if you are facing browser constraints, flaky implementations of JavaScript engines and a hugely fragment environment overall.

Jeremy’s book is suited for the beginner, but also for the seasoned developer, since it makes it clear what it all comes down to: writing clean code that gracefully degrades (Jeremy calls his method to do this Hijax) if the application runs in a less-than-ideal environment. There are many best practices and useful code snippets contained and topics such as JSON, web services and accessibility.

The book is not entirely new but nevertheless a must-buy, it was published New Riders Press in February 2007 and I urge everybody interested in Ajax to grab a copy, e.g. at Amazon.