Extension of location object to get the site name (of SLD, second level domain) of either the document's URL or from a given URL.

gistfile1.js

/*************
* Custom siteName functionality
*    window.location.siteName reduces a either the documents url or a
*    given url to the top most site name.
*    i.e. photography.nataionalgeographic.com would return nationalgeographic.com,
*    mysubdomain.mywebsite.co.uk would return mywebsite.co.uk.
***********/
if (typeof window.location.siteName === 'undefined') {
    window.location.siteName = function (url) {
        var hostName = url || window.location.hostname,
            hostNamePosFromEnd;
        //Don't want any http:// or similar stuff.
        hostName = hostName.replace(/^\w+?:\d*?\/\//, '');
       
        //Drop any path info from url.
        hostName = hostName.split('/')[0];
        hostName = hostName.split('.');
        hostNamePosFromEnd = (hostName.length >= 2) ? ((hostName[hostName.length - 2].length === 2) ? 3 : 2) : 1;
        while (hostName.length > hostNamePosFromEnd) {
            hostName.shift();
        }
        return hostName.join('.');
    };
}