Bug 395853

Description Mark Macdonald 2012-12-05 14:22:02 EST

There are two different ways Deferred.all can be invoked:

1)
> Deferred.all(promises)
Returns a promise that resolves once all promises have resolved, or rejects as soon as a single promise has rejected (fail fast).

2)
> Deferred.all(promises, optOnError)
Returns a promise that resolves once all promises have been fulfilled (i.e. rejected or resolved). The returned promise always resolves; rejections are delegated to the optOnError function.

Here the optOnError parameter does double duty as both:
 i) A handler to intercept individual rejections (and optionally transform them into another value in the final results array)
ii) A flag to disable the fail-fast behavior of .all() and guarantee that every promise is fulfilled.

Sometimes you only want (ii) and don't care about (i). In these cases, it would be convenient to call

> Deferred.all(promises, true)

... which would be equivalent to writing this under the current behavior:

> Deferred.all(promises, function(e) {return e;})