Detect Browser Compatibility with the Request Object - Using a Function for Checking Compatibility
(Page 2 of 4 )
Wrap the compatibility check inside a JavaScript function, then call this function before you make any HTTP requests using the object. For example, in Mozilla-based browsers such as Netscape 7.1 and Firefox 1.5 (as well as in Safari 2.0 and Opera 8.5), the request object is available as a property of the top-levelwindowobject. The reference to this object in JavaScript code iswindow.XMLHttpRequest. The compatibility check for these browser types looks like this:
if(window.XMLHttpRequest){
request = new XMLHttpRequest();
request.onreadystatechange=handleResponse;
request.open("GET",theURL,true);
request.send(null);
}
The JavaScript variablerequest is to a top-level variable that will refer to the request object.
As an alternative model, the open-source library Prototype uses object-oriented JavaScript to wrap the request object into its own object, as in the object Ajax.Request (see Chapter 6).
If the browser supportsXMLHttpRequest, then:
if(window.XMLHttpRequest)returnstruebecause theXMLHttpRequestis notnullorundefined.
- The object will be instantiated with thenew keyword.
- Itsonreadystatechangeevent listener (see the section “XMLHttpRequest” earlier in this chapter) will be defined as a function namedhandleResponse().
- The code calls the request object’sopen()andsend()methods.
What about Internet Explorer users?
Microsoft Internet Explorer–related blogs mentioned, at the time this book went to publication, that IE 7 would support a native XMLHttpRequest object.
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 This article is excerpted from the book Ajax Hacks, written by Bruce W. Perry (O'Reilly; ISBN: 0596101694). Check it out today at your favorite bookstore. Buy this book now.
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