reporting errors with Deferred

[Nick Santos]

When I run a unit test, I usually install a goog.testing.MockClock.

This causes problems for goog.async.Deferred. Deferred uses a
setTimeout to report errors "out-of-band", and the errors get eaten up
by the MockClock.

I can think of a few reasonable ways to fix this. One strawman is to
make a static/global "default" error-handler for Deferred, and make
sure MockClock overrides this method.

Does anybody have strong feelings about this?

Nick

[Nate]

Unlike twisted, it would be nice if deferreds erred back with the last exception as a value. like:

addErrback(function(err){

 if(err instanceof Error)...

});

OR...

addCatch/Exceptionback which would always call back with an exception (or list of) that occurred.. 

Nate

[Nick Santos]

@nate: closure-library does both of these things, but it's behind a setTimeout.

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[Nate Skulic]

Looking at http://closure-library.go if specifiedoglecode.com/svn/docs/closure_third_party_closure_goog_mochikit_async_deferred.js.source.html#line527 ... Seems like it does neither?  Errors are thrown outside the deferred chain, and there is no way to capture the list of exceptions that occurred in one callback.

What i was suggesting: instead of letting errors get thrown uncaptured; let them be handled by an errback or separate callback. If no errback (or exception callback) specified, simply throw out the exception.

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