Recently, new features have been announced as part of the ASP.NET AJAX 4.0 release: The UpdatePanel is an ASP.NET server control that updates portions of a web page without reloading it.
The ASP.NET controls that have been specified as content in an UpdatePanel are able to cause either synchronous (traditional) or asynchronous postbacks, by means of triggers.
A trigger is an event coming from an ASP.NET control that causes an UpdatePanel to refresh its contents.
In the following code, only the content of the Update control (the span element that displays the current date and time) is re-rendered every time the button is clicked.
ASP.NET AJAX framework brings JSONserialization features to the ASP.NET web-services and allows calling web-services from client-side JavaScript, even using third-party JavaScript-libraries like jQuery.