I USING THE XMLHTTPREQUEST OBJECT in Font

Create Data Matrix 2d barcode in Font I USING THE XMLHTTPREQUEST OBJECT

Load and Save will provide Web developers with a common API to access and modify the DOM in a language- and platform-independent way. In other words, it won t matter if you re on Windows or Linux, and it won t matter if you re developing in VBScript or JavaScript. You will also be able to save a DOM tree as an XML document or take an XML document and load it into the DOM. The specification also provides support for XML 1.1, XML Schema 1.0, and SOAP 1.2. Once available, it is expected to be widely used by developers.

We keep talking about the DOM, and if you haven t done a lot of work on the client side, you might not know what the DOM is. The DOM is a W3C specification for a platform- and languageindependent way of accessing and modifying the content and structure of a document. In other words, it s a common way to represent and manipulate an HTML or XML document. It s important to note that the design of the DOM is based on specifications from the Object Management Group, which allows it to be used with any programming language. It was originally conceived as a way of making JavaScript portable across browsers, though it has expanded beyond that limited application. The DOM really is an object model in the object-oriented sense. The DOM defines the objects needed to represent and modify documents, the behavior and attributes of these objects, and the relationship between these objects. You can think of the DOM as a tree representation of the data and structure on a page, though of course it may not actually be implemented that way. Say you have a Web page that looks something like Listing 2-5. Listing 2-5. Simple Table <table> <tbody> <tr> <td>Foo</td> <td>Bar</td> </tr> </tbody> </table> You can picture the DOM of this simple table as something like Figure 2-6. The beauty of the DOM specification is that it gives you a standard way to interact with your documents. Without the DOM, the most interesting aspects of Ajax wouldn t be possible. Since the DOM allows you to not only traverse but also edit the content, you can make highly dynamic pages.

Summary

While Ajaxesque techniques have been used for many years, the recent adoption of the XMLHttpRequest object by modern browsers has ushered in a new era of developing rich Web applications. In this chapter, we established the basics of working with the heart of Ajax, the XMLHttpRequest object. At this point, you know the methods and properties of the XMLHttpRequest object, and we ve shown you some simple examples of their use. As you can see, the object is pretty straightforward and hides much of its complexity from you. Combined with a healthy dose of JavaScript and some basic DOM manipulation, Ajax allows for a level of interactivity previously unmatched on the Web. As mentioned in 1, with XMLHttpRequest you are no longer limited to complete page refreshes and synchronous conversations with your server. In the upcoming chapters, we ll show you how to combine your existing expertise of server-side technologies with the unique capabilities of XMLHttpRequest to provide highly interactive Web applications.

ow the real fun begins! It s time to put your newfound knowledge of the XMLHttpRequest object to work. By showing some simple examples, we ll demonstrate how the XMLHttpRequest object sends requests to the server and how to process the server response with JavaScript.

I Note The examples in this chapter do not use a dynamic server to process the response and provide

a real-time response. Instead, the examples use simple text files to mimic the server s response. Doing so removes complexity, allowing you to focus on what s happening in the browser.