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Introduction to AJAX Technologies

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It's important that you take some time and understand where AJAX fits into the big picture of web development. This section helps bring you up to speed with AJAX’s place in your web development toolbox.
This chapter is from the book

This chapter is from the book


  • AJAX and Web 2.0
  • Why Use AJAX?
  • AJAX: An Example
  • Using the AJAX Library

If you’ve purchased this book, you probably are interested in AJAX technologies. If you are not familiar with the technology or are new to AJAX, it is important that you take some time and understand where AJAX fits into the big picture of web development. This section helps bring you up to speed with AJAX’s place in your web development toolbox.

One problem with the design of web pages (especially ASP.NET web pages) is that to refresh the data on the page, it must postback to the server. This causes the page to flicker while the page is posting, and then the page is reloaded in the browser with the results of the post. You can view the amount of data with tools such as IEHTTPHeaders and HTTPWatch. You will quickly notice that the amount of information getting posted is quite sizeable because ASP.NET applications not only postback the controls, but also post the page’s ViewState. Although the technique of a postback works, it creates a lot of traffic over the wire and inherently reduces the overall scalability of your application.

Asynchronous JavaScript and XML (AJAX) is a development pattern that you can use to provide your users with a much richer user experience in your web applications. Simply stated, AJAX allows you to asynchronously load data into pieces of a page on demand instead of loading the whole page each time data is requested.

An example of where a user experience can be enhanced by AJAX is a web page that contains related dropdown boxes. For example, say that you have a web page that supplies information on cars in which a user must select the year, make, and model of his car from dropdown boxes on the page. When a user selects a year, she populates all makes for a selected year in the make dropdown box. Additionally, when a user selects a make of car, the models dropdown is populated with models for a given year and make.

If you use traditional ASP.NET without AJAX, you will probably set the AutoPostBack property of your dropdowns to true and the page will postback (and flicker) when your user makes selections on the page.

Conversely, if you use AJAX, data can be loaded asynchronously into the list boxes as the user makes selections on the page. This is much more efficient because only the data being requested will travel in the request to the server, which could be as simple as a query string appended to the end of a page request. Also, the page will not flicker as the user makes selections in the dropdowns because the post actually is happening in the background.

AJAX and Web 2.0

Web 2.0 is a term (or rather buzzword) that you often hear when describing most “modern” web sites; however, it shouldn’t be a new concept to web developers. Web 2.0 is actually a consolidation of many existing technologies that allows you to provide a rich interactive user experience over the web. Examples of Web 2.0 technologies include, but aren’t limited to, the following areas:

  • Rich Internet Applications (RIAs), which include AJAX, Adobe Flash, Silverlight, and Moonlight
  • Web services
  • Blogs
  • Wikis
  • Social networking
  • Social bookmarking
  • RSS/Atom

Before the Web 2.0 movement began on the Internet, web pages often focused solely on providing the user with data. The user would simply request a page, view the page, request another page, view that page, and so on.

In contrast, the patterns and techniques behind Web 2.0 are all about the user experience with the web: AJAX and web services for rich, efficient user experiences, blogs, wikis, social networking, and social bookmarking for collaboration, and RSS/Atom so that users can “subscribe” to data.

As technologies such as AJAX evolve and are adopted in large scale on the web, Web 2.0 techniques are quickly becoming the expected user experience for the web. Mainstream examples of AJAX include the Google-based applications, such as Google’s Maps, Docs, and Calendar, as well as Microsoft-based applications, such as Hotmail, and Windows Live-based applications. As users start utilizing these types of applications in their everyday lives, they will come to expect the same type of functionality in the applications you develop.

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