jQuery <=> rails.js <=> Rails

UJS Investigation

TL;DR: jQuery <=> rails.js <=> Rails is a strange beast. 

Breakdown:
Rails expects a format to translate a request into a response. This could be
HTML, JSON, Script (js request), etc. Usually a straight GET/POST/etc. translates
to HTML. Ajax requests translate to a Script request. An odd thing starts happening
when you start playing with the request type params (or acceptance headers). Rails 
has some behind-the-scenes defaults of how it translates requests to response formats
when not specified or if the specified does not exists. This gets confusing the more
response handlers you add. 

The process is a bit more complicated because jQuery has its own set of acceptance/request
type header setters/handlers, Rails has a script that handles remote forms that does
some magic for parsing/handling/responding to request types, and Rails expects its
own formats to be matched. Somewhere in between, wires get crossed funny and I haven't
untangled it all yet.

The basic problem we had/have is TJ needed a json response. He added a format.json 
response handler. Unknowingly, I was using the JS handler (ancient code) that was actually 
requesting json. Rails will translate JSON requests => script requests if the controller
lacks an explicit JSON handler, probably because it is still an Ajax request. So when 
TJ added the EXPLICIT JSON handler, the in-meeting registry pages suddenly had a JSON
response, but it was not what was expected.

The fix for now is that the JSON responder will now check for what kind of request we
are handling (registration from the new landing pages or in-meeting request). 

The proper fix is to split all of these conditions for registering and where from into
something much more organized and stable.

Rails: Web Development That Doesn't Hurt.