XML.com: Converting Between XML and JSON
More and more web service providers seem to be interested in offering JSON APIs beneath their XML APIs. One considerable advantage of using a JSON API is its ability to provide cross-domain requests while bypassing the restrictive same domain policy of the XmlHttpRequest object. On the client-side, JSON comes with a native language-compliant data structure, with which it performs much better than corresponding DOM calls required for XML processing. So if you’re working in this space, you probably need to convert an existing XML document to a JSON structure