Why thenables?

Mark S. Miller erights at google.com
Thu Oct 10 16:19:38 PDT 2013

On Thu, Oct 10, 2013 at 3:39 PM, Rick Waldron <waldron.rick at gmail.com>wrote:

> On Thu, Oct 10, 2013 at 6:26 PM, David Bruant <bruant.d at gmail.com> wrote:
>> Hi,
>> The question of thenables came back on Mozilla's Bugzilla [1] (see
>> comment 29 & 30) with a decent share of skepticism that I share too.
>> I'm sorry I didn't go through all the promises discussions, but what's
>> the rationale of supporting thenables? I fear this feature won't be
>> necessary 2 or 3 years after native promises ship. For sure, it's of no use
>> to those who only use native promises.
>> I read from the meeting notes that it was pretty much the only point of
>> debate and a long one.
> There was no long debate about thenables, only two requests for
> clarification of their meaning and one request for explanation of their
> backing store mechanism, all with immediate responses. The notes reflect
> exactly that.


> I can't speak for Anne, with regard to comment#30, but I don't recall him
> sharing any kind of skepticism during the conversation. Hopefully he will
> clarify for us.

Anne can correct me if I'm wrong, but I don't see any skepticism expressed
in comment 30 <https://bugzilla.mozilla.org/show_bug.cgi?id=879245#c30>.
It's a reply to Jonas' 29. Interleaving the two:

Jonas:  So the spec ended up with support for thenables after all? Rather
> than just doing branding :(
> Anne: Yes
> Jonas: I take it in order to be compatible with currently existing
> libraries?
> Anne: yes
> Jonas: I guess if that's what TC39 decided on then that's what we should
> do. But I'm definitely saddened by it. Like you say, the past is shorter
> than the future.
> Anne: agreed.

I would have given Jonas the same answers. We agreed to thenable
assimilation for reasons that have been endlessly discussed. During the
process, everyone deeply involved always wished thenable assimilation
wasn't needed. But it is what we agreed to. We declared an official TC39
consensus. There are now several implementation efforts already proceeding
based on that consensus -- probably many more than we know of. This is not
skepticism. It is agreeing that "that's what we should do" while sharing
Jonas' sadness.

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