This book by Charles Wyke-Smith
The author assumes no previous JavaScript experience and goes through the basics of JavaScript covering variables, if statements, loops, arrays and how objects/classes work. Then the author goes into explaining the DOM works in modifying and referencing HTML elements of a web page as well as modifying CSS styles of elements (and child elements) of a page. This of course is the foundation of how to use AJAX properly and explained very nicely by the author will great examples to get anybody up and running easily.
The author then goes into explaining JavaScript events inrelation to how they affect an HTML page with window and mouse and keyboard events. The author also covers the Event object in talking about event delegation and working with the DOM in creating some complex JavaScript examples.
Then various JavaScript libraries such as jQuery, Adobe Spry, Prototype are explained with some really cool examples of using multiple libraries together which is very unique for most JavaScript books.
Finally, the author very nicely explains how the objects that work with AJAX work and how to create some really useful AJAX web pages with PHP.
Lots of good stuff to learn from this book and the author does a fabulous job doing it a relatively short book (300 pages).
A great book and worth buying