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Re: [UndoManager] Re-introduce DOMTransaction interface?

From: Ryosuke Niwa <rniwa@webkit.org>
Date: Wed, 4 Jul 2012 17:39:43 -0700
Message-ID: <CABNRm61DC_vgtgce4QXJK9AF5wfbnFGgg91mAqU9SpK7vgz4yg@mail.gmail.com>
To: olli@pettay.fi
Cc: Erik Arvidsson <arv@chromium.org>, Jonas Sicking <jonas@sicking.cc>, Ehsan Akhgari <ehsan@mozilla.com>, Aryeh Gregor <ayg@aryeh.name>, Adam Barth <w3c@adambarth.com>, public-webapps <public-webapps@w3.org>, Ojan Vafai <ojan@chromium.org>, Sukolsak Sakshuwong <sukolsak@gmail.com>
On Jul 4, 2012 5:26 PM, "Olli Pettay" <Olli.Pettay@helsinki.fi> wrote:
>
> On 07/05/2012 03:11 AM, Ryosuke Niwa wrote:
>
>> On Wed, Jul 4, 2012 at 5:00 PM, Olli Pettay <Olli.Pettay@helsinki.fi<mailto:
Olli.Pettay@helsinki.fi>> wrote:
>>
>>     On 07/05/2012 01:38 AM, Ryosuke Niwa wrote:
>>
>>         Hi all,
>>
>>         Sukolsak has been implementing the Undo Manager API in WebKit
but the fact undoManager.transact() takes a pure JS object with callback
>>         functions is
>>         making it very challenging.  The problem is that this object
needs to be kept alive by either JS reference or DOM but doesn't have a
backing C++
>>         object.  Also, as far as we've looked, there are no other
specification that uses the same mechanism.
>>
>>
>>     I don't understand what is difficult.
>>     How is that any different to
>>     target.addEventListener("foo", { handleEvent: function() {}})
>>
>>
>> It will be very similar to that except this object is going to have 3
callbacks instead of one.
>>
>> The problem is that the event listener is a very special object in
WebKit for which we have a lot of custom binding code. We don't want to
implement a
>> similar behavior for the DOM transaction because it's very error prone.
>
>
> So, it is very much implementation detail.
> (And I still don't understand how a callback can be so hard in this case.
There are plenty of different kinds of callback objects.
>  new MutationObserver(some_callback_function_object) )

Yes. It's an implementation feedback. The mutation observer callback is
implemented as a special event handler in WebKit.

>>         Since I want to make the API consistent with the rest of the
platform and the implementation maintainable in WebKit, I propose the
following
>>         changes:
>>
>>            * Re-introduce DOMTransaction interface so that scripts can
instantiate new DOMTransaction().
>>            * Introduce AutomaticDOMTransaction that inherits from
DOMTransaction and has a constructor that takes two arguments: a function
and an
>>         optional label
>>
>>
>>         After this change, authors can write:
>>         scope.undoManager.transact(new
AutomaticDOMTransaction{__function () {
>>
>>               scope.appendChild("foo");
>>         }, 'append "foo"'));
>>
>>
>>     Looks somewhat odd. DOMTransaction would be just a container for a
callback?
>>
>>
>> Right. If we wanted, we can make DOMTransaction an event target and
implement execute, undo, & redo as event listeners to further simplify the
matter.
>
>
> That could make the code more consistent with rest of the platform, but
the API would become harder to use.

Why? What's harder in the new syntax?

- Ryosuke
Received on Thursday, 5 July 2012 00:40:11 GMT

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