On 11/10/06, nrlz <[EMAIL PROTECTED]> wrote:
>
> I've been using Mochikit's Deferred object for a while now and there
> are some characteristics which I don't like about it. My most disliked
> one being that exceptions thrown in the callback will cause the errback
> to run:
>
> var async = doNetworkRequestAndReturnDeferred();
>
> async.addCallback(function() {
> alert("Success!");
> doSuccessStuff();
> doOtherStuff();
> });
>
> async.addErrback(function() {
> alert("Failure!");
> revertChanges();
> });
>
> In the above code, if my callback is buggy and throws an exception (or
> an external library that I'm using throws an exception), then errback
> will be called and the user will see "Success!" and then "Failure!".
> But the failure had nothing to do with the async request, which is what
> errback is only for. In my opinion, when the async request logic has
> finished, either the request was successful and callback should be
> called, or it wasn't unsuccessful and errback should be called. It
> should never call both callback and errback. In other words, callback
> should *only* handle the case that the async request was successful and
> errback should *only* handle the case that the async request failed.
Well, no. If things worked the way you think they should, then you
wouldn't be able to chain Deferreds together, which is very important.
Anyway, the behavior you want is easy to obtain. Use addCallbacks to
add both at the same depth in the chain instead of addCallback then
addErrback which puts them in subsequent depths.
Another option is that you could put the addErrback first and make
sure it returns or throws an error, which would then ensure that the
success callback does not run. You could put a second errback after
that to catch programming errors.
-bob
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