Transparant redirect for jquery ajax requests in rails with status code 278

There is no perfect backwards compatible solution out there afaik, but this is getting me pretty close to where I want it to be.

• instead of redirecting set a empty 278 response (made up status code) for xhr requests
• tell jquery to redirect when receiving a 278 response
• the success handlers are still executed / there is no way to stop them, but they can either just insert the blank reply or do a != '' check

// application.js
// when we get a fake redirect response, go there
// this will still execute success handlers, but hopefully the fail or are not ugly ...
$.ajaxSetup({
  statusCode: {
    278: function(_,_,response){
      // using turbolinks to not lose back functionality
      Turbolinks.visit(response.getResponseHeader('X-278-redirect'));
    }
  }
})

# some controller
redirect_to_with_xhr signup_path

# application_controller.rb
# ajax requests follow all redirects, so we have to improvise with a
# special code and header to not get placeholders replaced with full pages.
def redirect_to_with_xhr(path)
  if request.xhr?
    response.headers["X-278-redirect"] = path
    head 278
  else
    redirect_to path
  end
end

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