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Re: document.register and ES6

From: Erik Arvidsson <arv@chromium.org>
Date: Thu, 7 Feb 2013 22:16:44 -0500
Message-ID: <CAJ8+Goh+u85Sk70b9gmjb+Es+V4564i1HYJz89Tjqsz1jHHDag@mail.gmail.com>
To: Scott Miles <sjmiles@google.com>
Cc: public-webapps <public-webapps@w3.org>, daniel <daniel@mozilla.com>, Boris Zbarsky <bzbarsky@mit.edu>, Dimitri Glazkov <dglazkov@google.com>
Actually, that reminds me. How is a polyfill supposed to be able to create
an element with the tag name my-button and still have the instance be an
HTMLButtonElement? That does not seem possible. I guess a polyfill just
need to limit the base to HTMLUnknownElement.
On Feb 7, 2013 8:44 PM, "Scott Miles" <sjmiles@google.com> wrote:

> In my excitement for getting something that worked on the Big Three
> (webkit, IE, FF), I inadvertently cheated by adding an extra parameter to
> 'document.register'.
>
> TL;DR version:
>
> Solutions to the extra parameter problem:
>
> 1. go ahead and have an (optional) extra parameter to document.register
>
>    MyButton = function() { ... };
>    MyButton.prototype = { ... };
>    MyButton = document.register('x-button', MyButton, 'button');
>
> 2. require user to chain prototypes himself and infer the tagName from the
> prototype
>
>    MyButton = function() { ... };
>    // making prototype requires icky DefineProperty syntax
>    // on IE the only purpose of chaining the prototype is for tagName
> inference
>    MyButton.prototype = Object.create(HTMLButtonElement.prototype, { });
>    MyButton = document.register('x-button', MyButton);
>
> 3. introduce an intermediate method to build the 'class':
>
>   MyButton = function() { ... };
>   MyButton.prototype = { ... };
>   MyButton = document.extendElement('button', MyButton);
>   document.register('x-button', MyButton);
>
> Right now I'm preferring (3). WDTY?
>
> ===
>
> Long version:
>
> Recall that the goal is to support the simple notion of: make class,
> register to tag. So,
>
>   class MyButton extends HTMLButtonElement...
>   document.register('x-button', MyButton);
>
> My last proposed non-ES6 version had syntax like this:
>
>    MyButton = function() { ... };
>    MyButton.prototype = { ... };
>    MyButton = document.register('x-button', MyButton, 'button');
>
> The third parameter serves two purposes: (1) allows register to chain the
> correct prototype (HTMLButtonElement.prototype) to MyButton.prototype and
> (2) allows register to generate an appropriate constructor (i.e. one the
> instantiates a 'button' element).
>
> Trying to remove the third parameter created some new quandries.
>
> One avenue is to suggest the developer set up the inheritance chain
> outside of register. This is immediately appealing because it's very close
> to the 'goal syntax'. IOW,
>
>    MyButton = function() { ... };
>    MyButton.prototype = Object.create(HTMLButtonElement.prototype, { });
>    MyButton = document.register('x-button', MyButton);
>
> Btw: this form requires inferring the tag name 'button' from
> HTMLButtonElement.prototype, which AFAIK, is not as easy as it sounds.
>
> There are two potential downsides (1) adding properties to
> MyButton.prototype requires property descriptors (or some helper function
> the user must write), (2) on IE we aren't using the chained prototype
> anyway.
>
> An alternative would be to introduce another method, something like
> 'document.extendElement'. Usage would be like so:
>
>   MyButton = function() { ... };
>   MyButton.prototype = { ... };
>   MyButton = document.extendElement('button', MyButton);
>   document.register('x-button', MyButton);
>
> Scott
>
>
> On Thu, Feb 7, 2013 at 3:15 PM, Dimitri Glazkov <dglazkov@google.com>wrote:
>
>>
>>
>>
>> On Wed, Feb 6, 2013 at 10:01 AM, Boris Zbarsky <bzbarsky@mit.edu> wrote:
>>
>>> On 2/6/13 5:07 PM, Erik Arvidsson wrote:
>>>
>>>> This refactoring is needed for ES6 anyway so it might be worth looking
>>>> into no matter what.
>>>>
>>>
>>> Well, yes, but it's a matter of timeframes.  It's incredibly unlikely
>>> that a complete refactoring of how functions are implemented (which is what
>>> I was given to understand would be required here) could be done in the next
>>> several months to a year....  I doubt we want to wait that long to do
>>> document.register.
>>
>>
>> This is a valid and important concern. Boris, in your opinion, what is
>> the most compatible way to proceed here? I see a couple of options, but
>> don't know how difficult they will be implementation-wise:
>>
>> 1) Expose the ability to override [[Construct]]. Arv tells me that he
>> spoke with V8 peeps and they think they can do this fairly easily. How's
>> the SpiderMonkey story looking here?
>>
>> 2) Until ES6 is here, return a generated constructor from
>> document.register, which is the approach that Scott/Arv/Daniel came up with
>> for polyfills. Effectively, this generated constructor will serve as the
>> surrogate [[Construct]] override.
>>
>> 3) ...
>>
>> 4) PROFIT
>>
>> :DG<
>>
>
>
Received on Friday, 8 February 2013 03:17:13 GMT

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