Some of the examples use monadwidget, with mainwidget. While obelisk generated project expects you to use a frontend data type. I couldn't find a reference to this type in the guide, but how would you use monadwidget within the type?
You're supposed to use prerener or prerender_:
prerender_ blank $ bodyElement
Youll have to disable cors too: Disable same origin policy in Chrome
Source: https://github.com/obsidiansystems/obelisk/issues/320