jQuery XS AJAX Plugin

Description

It is well known that with the help of a dynamically generated DOM node corresponding to a XHTML <script> element, one can achieve a portable cross-site (XS) variation of an AJAX-style client-server communication as the <script> element is not staying under the "same-origin security policy" which restricts all the regular AJAX methods. This allows one to asynchronously load JavaScript code from a third-party URL.

The JavaScript code in jquery.xsajax.js is a jQuery plugin, providing an abstraction layer for this functionality by resembling the standard AJAX-based jQuery.getScript(url, callback) function with a companion jQuery.getScriptXS(url, callback) function.

Hints

Notice 1: the point of this plugin is not the bare dynamic generation of the <script>. The point is that a callback function is executed once the script was loaded and executed by the browser and that the generated <script> is automatically garbage collected from the DOM again afterwards.

Notice 2: the possibility to load a JavaScript file from a sibling but third-party URL is also of great interest when one wishes to set cookies for the third-party URLs. Suppose you have three websites www.example.com, www.example.net and www.example.org and on www.example.com/login you have your customer login form. Once the customer was authenticated, a cookie containing a "certificate" should be set. Setting this for ".example.com" is trivial, but how do you at the same time set it for all three domains?

The solution is this: www.example.com/login uses jQuery.getScriptXS() to send the issued "certificate" via a query string to both www.example.net/reflector and www.example.org/reflector. Behind those URLs a small CGI just converts the "certificate" in the query string into a corresponding HTTP response cookie (now for its own domain!) and returns even a possibly empty JavaScript script. Once www.example.com/login has received the two final notification (via the callback function) that both scripts were loaded, it knows that the two third-party cookies were set and can proceed by forwarding to the next page in sequence. Last hint: keep P3P in mind for MSIE when setting the cookie in the HTTP response ;-)

Example

http://www.example.com/test.html:

<script type="text/javascript">
   jQuery.$foo = "bar";
   alert("jQuery.$foo="+jQuery.$foo);
   jQuery.getScriptXS(
       "http://www.example.net/test.js",
       function () { alert("jQuery.$foo="+jQuery.$foo); }
   );
</script>

http://www.example.net/test.js
```
jQuery.$foo = "quux";
            
```