Beginning Web Development, Silverlight, and ASP.NET AJAX

254
CHAPTER 11 ■ AJAX APPLICATIONS AND EMPOWERING THE WEB USER EXPERIENCE
Figure 11-1. MSN MoneyCentral
This web site is a pretty typical one, presenting a portal of information to customers.
There are many information panes on this portal, three of which can be seen in the
screenshot (Video on MSN Money, Quote watchlist, and The Basics). Some of these information
panes provide user interaction—for example, the Quote watchlist allows you to
enter the stocks that you are interested in monitoring. It uses a simple HTML form where
you enter the ticker of the stock you are interested in and click Add.
The typical web site will refresh the entire page once you click the Add button, causing
a lag for the user, and the expense of traffic for the web site administrator. If you were
to use a technique that allows for a partial refresh, then only the information pane that
you want to change (i.e., the Quote watchlist) would be changed.
It was with use cases like this in mind that browser developers started adding new
features long before the term Ajax was coined. The first attempt at allowing something
like this was the IFrame, introduced in Internet Explorer 3 in 1996. This allowed you to
use something similar to a frameset, but to have a frame showing a different set of content
to be embedded within a page. Thus, in an application such as MoneyCentral, you
would have one master page, and one complete subpage for each of the information
panes. These pages would then be rendered on the master page using an IFrame. This
technology still works and is useful today, but it makes for more complex management of
a portal such as MoneyCentral, as many independent pages need to be maintained. The
IFrame, and other new elements such as and , when grouped together with
JavaScript, evolved into the generic term DHTML (Dynamic HTML), with the intent
being that developers could produce pages that rewrite their own HTML in response to