Is there any way to respond to a single GET request with both the requested document and a JSON object from the http.Server request callback?
If you're wanting to give two different HTTP Content-Types from the same page, that is not possible due to limitations in the protocol. You could however, create another iFrame on the page, and have the main frame serve one type, and the iFrame serve the other.
If you want two different types in a single response, I think that a Multi-Part MIME response is your best bet.