Ajax framework

I am working on php/mysql application and the client wants it to be fully ajax based with no refresh at all.

can anyone suggest a robust ajax framework to be used and secondly what are the disadvantges if i directly use XmlHttRequest object and work on it.

use JQuery :

I would also strongly recommend jQuery.

Also have a look at http://www.prototypejs.org/ and http://developer.yahoo.com/yui/

There are a handful of Ajax functions in jQuery and I can assure you that they will cover MOST of your needs. Most of them are simply wrapper functions.