Instruct: Classify a review into positive or negative sentiment.
Query: Essential book on the topic

I have spent a lot of time thoroughly going through this excellent book - an almost complete reference on the subject. The only weakness in the book is the lack of discussion regarding the appropriate place to use it. Otherwise, this book covers all aspects of AJAX concerns: AJAX's weaknesses and strengths, refactoring code for maintainability, how it impacts user performance, security, graceful error recovery, and best of all, working example code - lots of it. The practical examples are significantly meatier than most books 'hello world' versions of technology normally presented.A must read for anyone considering doing much more than just a couple of AJAX calls.