_.once has the problem that if you call the once'd function while it is
still in progress (re-entrantly or in another Fiber), it returns
undefined immediately. That's bad for uniload! uniload already has a
cache, so just use that. (In the future, perhaps detect an attempt to
uniload something that's currently in the process of being uniloaded in
another fiber and block until the other fiber is ready.)
Using instanceof with things you've uniloaded is a little sketchy: maybe
two different uniload calls will end up with two different copies of
Package.meteor.Meteor.Error, and it seems kind of hairy to ensure you're
not mixing and matching copies. However, Meteor.Errors are all tagged
with a string errorType, which fills me with much less fear,
uncertainty, and doubt than instanceof.
08a6fa99fd