Google Local uses AJAX extensively.
This background downloading, using the XMLHttpRequest object, makes using Google
Local such a smooth and rewarding experience. Remember, nothing is new here; it??™s just
that having the XMLHttpRequest object built into the browser that can do this asynchronously
makes it possible to develop applications like this.
?– Note For full details on how to develop in AJAX, check out Foundations of AJAX(Apress, 2005).
CHAPTER 1 ?– INTRODUCING AJAX 9
You will be looking at AJAX from a high level in this book and delving more deeply
into how Microsoft ASP.NET AJAX will allow you to quickly and easily build AJAX-enabled
applications.
Using the XMLHttpRequest Object
As mentioned, the XMLHttpRequest object is the heart of AJAX. This object sends requests
to the server and processes the responses from it. In versions of Internet Explorer prior
to IE7, it is implemented using ActiveX, whereas in other browsers, such as Mozilla
Firefox, Safari, Opera, and Internet Explorer 7, it is a native JavaScript object. Unfortunately,
because of these differences, you need to write JavaScript code that inspects the
browser type and creates an instance of it using the correct technology.
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