On 07/05/2012 03:11 AM, Ryosuke Niwa wrote:
On Wed, Jul 4, 2012 at 5:00 PM, Olli Pettay <olli.pet...@helsinki.fi
<mailto:olli.pet...@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) )
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.
- Ryosuke
