[whatwg] Fixing undo on the Web - UndoManager and Transaction

Jonas Sicking jonas at sicking.cc
Tue Aug 9 14:55:32 PDT 2011

On Tue, Aug 9, 2011 at 2:44 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:

> On Tue, Aug 9, 2011 at 1:59 PM, Jonas Sicking <jonas at sicking.cc> wrote:
>> On Tue, Aug 9, 2011 at 12:03 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:
>>> On Tue, Aug 9, 2011 at 1:17 AM, Jonas Sicking <jonas at sicking.cc> wrote:
>>>> On Tue, Aug 9, 2011 at 12:42 AM, Ryosuke Niwa <rniwa at webkit.org> wrote:
>>>> > On Tue, Aug 9, 2011 at 12:31 AM, Jonas Sicking <jonas at sicking.cc>
>>>> wrote:
>>>>  >> Likewise I still haven't heard of any examples where the
>>>> apply function
>>>> >> isn't simply init+reapply. So it still seems better to me to have a
>>>> >> init/apply/unapply split rather than a apply/reapply/unapply split.
>>>> >
>>>> > This is also pending for developer feedback.
>>> I've talked about this with Alex, and we both agreed that having
>>> apply/reapply split is cleaner because in many cases you'd like to know
>>> whether you're in redo or not.  i.e. more work is done in reapply than in
>>> apply.
>> Could you please provide examples. I feel like I'm fighting an elusive
>> shadow.
> For example, in editing apps, you have to restore selection on redo.
>  Presumably, the UA can auto-restore selection in managed transactions but
> restoring selection in manual selection is hard since DOM after redo might
> look completely different from the DOM after the first apply.
> (I've sent out a massive email to a bunch of Googlers who have worked on
> RTE, but unfortunately some of them are OOO until mid or late September so
> please be patient with me about developer feedbacks).
> On the other hand, what are use cases that are better addressed by your
> proposal?  Do you have specific examples in your mind?  Also, the following
> code will provide the same functionality as your proposal:
> apply: function () {init(); action();}
> unapply: unapply
> reapply: action

Selection restoration is indeed a important point, i'll have to think about

I don't think it's a matter of which use cases can or can't be solved with
either solution. It's pretty clear to me that all scenarios can be solved
with either API. It's just a matter of which pattern is more common and so
which one we should make more convenient. If almost everyone puts the same
code in apply and reapply then we're just creating more work for people.

Here's how you'd implement the apply/reapply/unapply syntax using simply

apply: function() { if (!this.applied) { action1(); this.applied = true; }
else { action2(); }
unapply: unapply

I like this! (except for the apply/reapply/unapply split, please do answer
>> the question above)
>> The example used in this thread would become something like (independent
>> of if we use init/apply/unapply or apply/reapply/unapply):
>> myEditor.undoManager.manualTransaction(
>>  { apply: function () {
>> this.nodeBefore.parentNode.insertBefore(this.text, this.nodeBefore); },
>>     unapply: function () { this.text.parentNode.removeChild(this.text); },
>>     text: document.createTextNode('hello'),
>>    nodeBefore: window.getSelection().anchorNode
>>   });
> Yeah, this looks much cleaner than the current syntax.  Let's make this
> change then (duck typed object).


/ Jonas

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