Intent to implement: ES6 destructuring binding and assignment

[Andy Wingo]

Implement ES6 destructuring binding and assignment.

The implementation will proceed in V8 under the --harmony-destructuring flag.

Owners: Andy Wingo (wi...@igalia.com), Dmitry Lomov (dsl...@chromium.org)

# TC39 acceptance

Destructuring binding and assignment have been in ES6 for a year or so
now, and have seen very few changes over the past months.

There was a minor change in the last meeting in which a ToObject call
was added to all binding right-hand-sides, so some things may yet
change, though all indications are that the spec is stable.

# Interest from other vendors

Firefox currently ships ES6 destructuring, and WebKit has an
implementation that has not shipped yet in release (that I am aware of).

Both Firefox and WebKit's implementations are incomplete and lag behind
the specification: they do not support default value initializers, they
do not correctly use the iterator protocol when destructuring to array
patterns, and they do not support rest patterns. Firefox is currently
working on fixing this
(https://bugzilla.mozilla.org/show_bug.cgi?id=1055984).

IE has not shipped, but has stated intent to implement.

# Technical considerations

Design document:

https://docs.google.com/document/d/1iJWvuakeKsPJOeA-RJ-4bM3Jha5iewQjxKsylgzHEB0

[Jonas Sicking]

On Wed, Aug 20, 2014 at 4:22 AM, Andy Wingo <wi...@igalia.com> wrote:
> Firefox is currently working on fixing this
> (https://bugzilla.mozilla.org/show_bug.cgi?id=1055984).

Please be a little more careful when speaking to what Firefox is or is
not doing. If you actually took the time to follow the above link,
you'd see that it's pretty clear that this isn't being worked on.

That said, my guess is that we're planning on implementing this stuff
per the latest ES6 spec eventually. But I can't speak with authority
on the subject since I'm not at all involved in this effort.

/ Jonas

[Andy Wingo]

On Thu 21 Aug 2014 00:53, Jonas Sicking <jo...@sicking.cc> writes:

> On Wed, Aug 20, 2014 at 4:22 AM, Andy Wingo <wi...@igalia.com> wrote:
>> Firefox is currently working on fixing this
>> (https://bugzilla.mozilla.org/show_bug.cgi?id=1055984).
>
> Please be a little more careful when speaking to what Firefox is or is
> not doing. If you actually took the time to follow the above link,
> you'd see that it's pretty clear that this isn't being worked on.

I'm happy to correct the statement if it's false!

For the record, *I* filed that bug after spending an hour researching
the status of things. (I am also a SpiderMonkey committer.) See the
dependent bugs, which have active recent work.

Andy

[Jonas Sicking]

You are right. There is a part of that which is being worked on, but
the majority of issues are not.

I think in this instance it's not terribly important, since I think
these features are fairly uncontroversial. But we've seen a lot strong
statements on this list about level of support from Mozilla for
various features, which hasn't always fully matched reality.

/ Jonas