Re: [UndoManager] Re-introduce DOMTransaction interface?

On Wed, Jul 4, 2012 at 5:00 PM, Olli Pettay <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.

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.

- Ryosuke