Hi Mittal,
Firstly, I should point that this is not a general support forum for Share development, it is more specific to the Share Extras add-ons, so you may find that you get more help by posting on the Alfresco forums or on stackoverflow.
That said, your issue is that you are mixing up your web script JS with client-side JavaScript. Alfresco.util.Node is a client-side helper class and is therefore available to client-side JS running in the web browser, but not to your web script code which runs on the server.
If you are look at the source of alfresco-util.js, which you are including, you will see that there is a helper class there called AlfrescoUtil. I would suggest that you want to use the function AlfrescoUtil.getNodeDetails() from that class, but check the source to see which parameters are required. It seems to me you can pass in a nodeRef, plus an optional site name, plus some options if you wish.