1.2. Bringing Richness to Web Applications
Years ago, having a Web presence was a distinguishing factor for companies. That is no longer the case. Now just having a Web presence is no longer enough. Companies are distinguishing themselves further through Web applications that react intuitively to customer actions and anticipate user input. This book shows you how ASP.NET AJAX addresses specific Web development challenges and paves the way for taking your Web site to another level of user experience.
The fundamental set of technologies used in the AJAX model that enable the next generation of Web applications is not entirely new. You will find that many people point to Google, Flickr, and several other services as prime examples of leveraging AJAX and its underlying technologies in unique ways. The applications have some unique features, but in reality, the underlying technologies have been around and in use for nearly a decade. Look at how Microsoft Exchange Server provided rich access to e-mail from a Web browser in the Outlook Web Access application, and the concept of ubiquitous access from a browser while leveraging a common set of browser features for a rich user experience has been around for years. In this case, users get a remarkably full-featured application with no local installation and are able to access e-mail from virtually any machine.
While the AJAX acronym is nice, it doesn't do much to explain what is actually happening. Instead of building a Web application to be just a series of page views and postbacks, developers are using JavaScript to communicate asynchronously with the Web server and update parts of the page dynamically. This means that the Web page can dynamically adapt its appearance as the user interacts with it, and it can even post or fetch data to or from the Web server in the background. Gone are the days of the ugly postback, which clears the user's screen and breaks his concentration! Instead, you need to post back now only if you want to change to a different Web page.
Even that rule can be bent. Some applications are pushing this boundary and completely changing the user's view, just as though they navigated to a new page, but they do so through an asynchronous post and by changing the page content without actually navigating to a new URL.
The AJAX acronym refers to XML as the data format being exchanged between client and server, but in reality, applications are being built that retrieve simple pieces of text, XML, and JSON (JavaScript Object Notation) (which is discussed in more detail in Chapter 4). Part of the AJAX appeal is not even covered by the acronym alone: In addition, to communicating with the server without blocking, developers are leveraging Dynamic HTML (DHTML) and Cascading Style Sheets (CSS) to create truly amazing user interfaces. JavaScript code running on the client communicates asynchronously with the server and then uses DHTML to dynamically modify the page, which supports rich animations, transitions, and updates to the content while the user continues interacting with the page. In many cases, end users will sometimes forget they are using a Web application!
Just remember that AJAX is not a single holistic entity but instead is a novel and creative way of using a combination of technologies such as the XMLHttpRequest object, HTML, XHTML, CSS, DOM, XML, JSON, XSLT, and JavaScript. You might be thinking of the difficulties of piecing this all together to get the Web applications you want to build. Be ready to be wowed, however, as the focus of this book is on showing you how to use the built-in technologies provided by ASP.NET 3.5 to give you this power in an easy to use manner.