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

Ryosuke Niwa rniwa at webkit.org
Mon Aug 8 23:22:40 PDT 2011

Hi everyone,

I have updated my document on http://rniwa.com/editing/undomanager.html to
address all responses I've got so far.  Most of it is about clarifying
details and adding some examples.

Now, I'd really like to get your opinions on what event(s) we should have
for this to work.  The minimum list I can think of is the following:

   - Undo
   - Redo
   - EditingAction
   - Transaction (or Transacted)

Undo, Undo, and EditingAction are synchronous, cancelable, bubbling events
that fire immediately before undo, redo, or user editing action or
execCommand is to be executed respectively.  Transaction (or Transacted or
whatever you'd like to call it) is an event that fires after new transaction
is inserted (not cancelable).

- Ryosuke

On Tue, Jul 26, 2011 at 11:34 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:

> Hi all,
> In the last couple of weeks, I've been working with developers of CKEditor,
> TinyMCE, and Google Docs to come up with *new API for undo and redo*.
> Why? Because* undo and redo are broken on the Web today*. Whenever Web
> apps try to add a custom editing operation without using execCommand or do a
> "fix up" after browser executes a user editing action, user agents get
> confused by DOM mutations made by the apps and won't be able to undo or redo
> user editing actions and execCommand. This forces Web apps to re-implement
> undo and redo themselves, and in fact, *many rich text editors store
> innerHTML of a contenteditable element* as a string in their internal undo
> transaction history (a.k.a undo stack).
> Also, there's no way for Web apps to add new undo item and populate undo
> and redo menus on user agent's native UI.  In addition, if an editor app has
> a widget with input/textarea, then the undo stack of the editor gets
> confused when the widget goes away because the undo transaction history
> exists only per document.
> In order to solve above and numerous other problems, we've come to a
> conclusion that we need to *add UndoManager and Transaction*.
> *UndoManager* is an interface for managing undo transaction history.  It
> exists on a document and an element with the *undoscope* content
> attribute.  UndoManager applies new transaction (i.e. make undoable DOM
> changes) and manage them.  The main purpose of UndoManager is to communicate
> the list of undoable items with the user agent so that the user agent can
> provide a native UI (e.g. populating menu items with them).
> A *transaction* is a collection of DOM mutations that can be applied,
> unapplied, or reapplied. UndoManager manages transactions and execute
> unapply and reapply upon undo and redo respectively.
> There are two types of DOM transactions:
>    - *Managed transaction* - the app supplies apply() and the user agent
>    automatically takes care of undo and redo. It is *compatible with user
>    editing actions and editing commands*, and allows Web apps to easily
>    add new editing operations or fix up DOM after user editing actions or
>    editing commands and still have the user agent manage the undo and redo.
>    - *Manual transaction* - the app supplies apply(), unapply(), and
>    reapply() and *the app takes the full control of undo and redo*.
>    However, it is NOT compatible with user editing actions, editing commands,
>    or managed transactions, meaning that, the user agents won't be able to undo
>    or redo them. This transaction is useful for apps such as a collaborative
>    editor that implements domain-specific undo or redo.
> You can see more concrete definitions of UndoManager and Transaction at:
> https://rniwa.com/editing/undomanager.html and see a list of uses cases
> at https://rniwa.com/editing/undomanager-usecases.html.  The documents are
> incomplete and I need your feedback in order to refine details.
> Best regards,
> Ryosuke Niwa
> Software Engineer
> Google Inc.

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