proposal: Object Members

Jordan Harband ljharb at
Mon Jul 23 22:48:44 UTC 2018

When extending builtins, `super()` is the only way you can get the
appropriate internal slots applied to the instance. (Private fields work
the same way by providing a matching guarantee - that the only way someone
can subclass you successfully is using `class extends` and `super`)

On Mon, Jul 23, 2018 at 3:43 PM, Ben Wiley <therealbenwiley at>

> What exactly can be accomplished with super that can't be accomplished
> otherwise? I know the transpiled code is very verbose and unintuitive to
> read if you avoid explicitly naming the base class, but I wasn't aware of
> new capabilities that were previously impossible.
> Ben
> Le lun. 23 juill. 2018 18 h 06, Ranando King <kingmph at> a écrit :
>> Granted about `super()`. That's the one thing I can't easily reproduce.
>> However, barring those internal slots, I can reproduce the functionality of
>> `super` and the checks performed as a result of the internal slots, all in
>> ES6. As for built-ins, I can easily and properly extend builtins without
>> `class` since ES6 officially has `Object.setPrototypeOf()`. If you don't
>> think it's possible, you should take a close look at what I'm doing in the
>> link from my first post.
>> As for whether or not the sugary nature of `class` is a good thing, it
>> really is a matter of opinion. I just happen to be of the persuasion that
>> since there's literally no construct that `class` can produce that I cannot
>> reproduce by other means, then that means the `class` keyword (even in
>> light of `super`) is little more than syntactic sugar. As such, we
>> shouldn't be so hasty to turn an Object Oriented Prototype Based language
>> into an Object Oriented Class Based language. The only way to do that
>> reasonably is to ensure that whatever you can construct with `class` can
>> always be equivalently constructed without it.
>> Here's a more logical argument instead. Even if there are subtle
>> differences between `class` constructors and object factory functions,
>> providing an isolated path specific to `class` is likely to lead to
>> situations very similar to what happens when an open source package gets
>> forked. Eventually, the difference between the two paths may become so
>> great that one is eventually abandoned (by developers) in favor of the
>> other. This is only a valid argument because the power of ES is in it's
>> simplicity. It's like building a house with wood, nails, sheetrock, etc...
>> (JS) vs. building a house with pre-fabricated parts (class-based languages).
>> Don't get me wrong. The `class` keyword is a great thing. It simplifies
>> the production of creating object factories with prototypes. As I
>> understand it, that was the purpose. Let's not make the mistake of allowing
>> something to be done with `class` that cannot be reasonably reproduced
>> without it. The moment we do that, we're diverging from the intended
>> purpose of `class`.
>> On Mon, Jul 23, 2018 at 4:17 PM Jordan Harband <ljharb at> wrote:
>>> Extend builtins, in particular - ie, `super()` allows your subclass to
>>> obtain internal slots it can't otherwise get.
>>> Even if `class` were just sugar, I don't think I see the argument that
>>> that's a *good* thing to preserve.
>>> On Mon, Jul 23, 2018 at 2:05 PM, Ranando King <kingmph at> wrote:
>>>> ---------- Forwarded message ---------
>>>> From: Ranando King <kingmph at>
>>>> Date: Mon, Jul 23, 2018 at 4:04 PM
>>>> Subject: Re: proposal: Object Members
>>>> To: <ljharb at>
>>>> You've made that argument before. Exactly what is it in ES6 that you
>>>> **can** do with `class` that you cannot do without class? I'd like some
>>>> clarification on this.
>>>> On Mon, Jul 23, 2018 at 3:30 PM Jordan Harband <ljharb at>
>>>> wrote:
>>>>> `class` is already not just syntactic sugar, so that notion isn't
>>>>> correct, and shouldn't be maintained.
>>>>> On Mon, Jul 23, 2018 at 12:38 PM, Ranando King <kingmph at>
>>>>> wrote:
>>>>>> I've written up a new draft proposal based on my own work with ES5 &
>>>>>> ES6 compatible classes with fields. That can be found [here](
>>>>>> I'm already
>>>>>> aware of the class-members proposal, but I think it breaks far to many
>>>>>> things and doesn't do anything to maintain the notion that "`class` is just
>>>>>> syntactic sugar".
>>>>>> This proposal is specifically based on the code [here](
>>>>>> I've also got
>>>>>> a []( that
>>>>>> shows the same code running.
>>>>>> The idea behind the proposal is that instead of injecting a lot of
>>>>>> new logic into how `class` works, let's allow `class` to remain syntactic
>>>>>> sugar, and put that extra ability into object declarations instead. Then
>>>>>> simply allow `class` to do the same with it's own prototypes.
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