Ajax Patterns and Best Practices enables you to just pick up the book
and then write applications that work properly. This book is not just
about the technical, low-level details of the API's, but is about making
something happen on both the client and server. For example, the Ajax
Widgets chapter outlines a number of canned widgets that perform some
functionality. The book explains the widget implementation so you can
not only understand what is happening, but copy and paste if necessary.