Errors show up as timeouts

[aquach]

Because this project uses JSONP to receive HTTP responses, it can't receive any responses sent with HTTP 400/500 because the browser won't try to load them as actual scripts. To reproduce this, try converting a client ID that isn't a part of an experiment: you'll get a request timed out error because the callback is never executed, which is because the browser is not evaluating the response body that would look like sixpack.callback1({ "status": "failed", "message": "not in experiment" }) or something similar.

One way to fix this is to not use HTTP status codes and always return 200. Another solution is to avoid JSONP and use CORS and standard HTTP requests.