1. Couch doesn't emit errors. It just returns 0 rows (or the map results, if only the reduce function errored.)
2. Couch *can't*, because the errors happen in the background (e.g. post a _design doc, then call stale=update_after).
3. This is not a runtime error that the user needs to catch and handle; it will only happen at devlopment time, unless the users are crazy and passing dynamically evaled javascript functions, which they shouldn't do.

It sucks to rely on console.log, but I couldn't really think of any other way while remaining Couch API compliant.