Datasheet

ASP.NET needs to add this functionality. The question becomes, how does one add client-side function-
ality to a development methodology that is mostly a server-side technology?
From a network standpoint, these applications are more efficient because they communicate back only
the necessary pieces of information and get back only the necessary updates from the server. From a web
server standpoint, these applications tend to use less CPU on the server. As a result, these types of appli-
cations are highly desirable.
What Is AJAX?
So into this development environment comes a set of technologies that are collectively referred to as AJAX.
If you are an “old guy” developer like me, then AJAX represents a similar concept to the client-server
development mentioned earlier in the chapter. With client-server development, the amount of data trans-
ferred is minimized over a terminal application by transferring only the necessary data back and forth.
Similarly, with AJAX, only the necessary data is transferred back and forth between the client and the web
server. This minimizes the network utilization and processing on the client.
Advantages of AJAX
The advantages of AJAX over classical web-based applications include:
❑ Asynchronous calls — AJAX allows for the ability to make asynchronous calls to a web server.
This allows the client browser to avoid waiting for all data to arrive before allowing the user to
act once more.
❑ Minimal data transfer — By not performing a full postback and sending all form data to the
server, network utilization is minimized and quicker operations occur. In sites and locations
with restricted pipes for data transfer, this can greatly improve network performance.
❑ Limited processing on the server — Along with the fact that only the necessary data is sent to
the server, the server is not required to process all form elements. By sending only the necessary
data, there is limited processing on the server. There is no need to process all form elements,
process the
ViewState, send images back to the client, or send a full page back to the client.
❑ Responsiveness — Because AJAX applications are asynchronous on the client, they are perceived
to be very responsive.
❑ Context — With a full postback, users may lose the context of where they are. Users may be at
the bottom of a page, hit the Submit button, and be redirected back to the top of the page. With
AJAX there is no full postback. Clicking the Submit button in an application that uses AJAX will
allow users to maintain their location. The user state is maintained, and the users are no longer
required to scroll down to the location they were at before clicking Submit.
History of AJAX
For all its perceived newness and sexiness, the technologies that make up AJAX are really not new. The abil-
ity to communicate back to the server through a hidden frame without posting the main page back to the
server has been around for a long time. Communication between client and server has been available —
back to the release of Internet Explorer’s ability to script ActiveX controls on the client browser and to the
MSXML component, both of which date back into the late 1990s. Personally, I saw the first formal usage of
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Chapter 1: Introduction to ASP.NET AJAX
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