[Moo] jsonp catching bad request response (400) and such?

[Rolf -nl]

Working with some api that can return a bad request code 400 error
with the error message as a response in json. Is there a way I can use
it? Because the response contains useful information about wrongly
used params? There's a failure event, but that works with the timeout
and I that's not really usable or the same.