Rails 2.1 breaks prototype’s responseJSON
It appears that a render of json:
-
render :json => {:blah => "hi"}.to_json
Is responding with a mime type of text/json instead of the previous application/json
The latest version of prototype (and previous versions) specifically looks for application/json in order to fill the responseJSON property of the response object.

Registering a mimetype will fix it:
Mime::Type.register “application/json”, :json