Hmmm. Maybe URLs aren't part of json/rpc ? So you need to wrap a http lib (request) around the json-rpc ?
I mean it is remote procedure call.. Nothing there really suggests a URL. All the code I am working on with that has the same approach.
BTW, if you ever think nodejs seems like a good all purpose language to write regular code with nested loops... Think long and hard before you go down that path. I have been using nodejs on a project and it is great for servers, but then we started using it for tools and oh Lord what a headache.