Futures

Dean Landolt dean at deanlandolt.com
Tue Apr 23 05:56:16 PDT 2013


On Tue, Apr 23, 2013 at 4:54 AM, David Bruant <bruant.d at gmail.com> wrote:

> Le 22/04/2013 19:32, Dean Landolt a écrit :
>
>  I was just saying there will be pressure to include support for thenables
>> (already in DOMFutures). If you believe otherwise don't let me dissuade you
>> -- I would absolutely love it if I were proven wrong!
>>
> I guess it would take making sure no content can be confused by the
> current steps 3-5 of the current resolve spec [1]. I believe browser
> vendors have tools to study this kind of things.
>
> CasperJS [2] create objects with a then method [3]. Interestingly, this
> doesn't run in the browser (until someone decides to re-implement it of top
> of a web browser or FirefoxOS. [4] ?). Potentially more interestingly,
> Casper objects could be promises subclasses (to be considered).
> It wouldn't be surprising if there were content on the web where the
> promise subclass trick couldn't work.
>


What do you mean by the promise subclass trick? If you mean that Casper
instances would subclass Promise I don't think that'd work out too well as
is. Promises/A (and I presume A+) intentionally specified `then` to return
a new promise, so Casper would have to change in a very breaking way to
pull this off.


In any case, considering that an object with a 'then' function is a promise
> is a recipe for confusion. Promise/A+ folks asked for and are happy about
> it. The rest of the webdevs who aren't aware of this subtle non-intuitive
> rule will have a very hard time when, for whatever reason, they have a
> 'then' function in a resolve value and their code really behaves in a way
> they don't understand.
>


I agree it's a recipe for confusion. But the weight of legacy code (growing
by the day) may be too much to bear. Hopefully not -- it's really very
simple for Promises/A+ libs to add `then` to the Promise prototype.


I don't think in the entire platform there is a precedent of doing this
> (maybe for a good reason?). We'll see what web browsers end up implementing.
>


IMHO __proto__ is one precedent -- and we know how that's going :P
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