[webkit-dev] Replacing DOM Mutation Events

Adam Klein adamk at chromium.org
Thu Aug 18 09:41:42 PDT 2011

On Wed, Aug 17, 2011 at 5:39 PM, Dominic Cooney <dominicc at chromium.org> wrote:
> This looks awesome.
> Do you have a link to Jonas‘ latest proposal? Because the original one
> you linked to <http://lists.w3.org/Archives/Public/public-webapps/2011AprJun/1318.html>
> seems to be different to your patch (eg in API names, etc.) The
> asymmetry between addMutationListener, which can incrementally
> register for specific types, and removeMutationListener, which is a
> blunt instrument, is curious… I would like to read the specific
> proposal.

This is the proposal mine is based on (it's also linked from the
ChangeLog in my patch):


Note that I say "based on"; the biggest divergence is that I don't do
any coalescing of mutations, so:


will result in a MutationRecordList with three MutationRecords, one
for each of those called. This makes the implementation simpler than
it would be otherwise, and allows MutationRecords to be 1) immutable
and 2) shared by all MutationListeners.

> It would be nice if there was an open source test suite that is easily
> accessible to UA implementors to ensure implementations are
> consistent.

Agreed, though we'll want to move a little closer together before we
get there (discussion is still ongoing about details of the API).

- Adam

> Dominic
> On Wed, Aug 17, 2011 at 11:07 AM, Adam Klein <adamk at chromium.org> wrote:
>> Greetings webkit-dev,
>> It's generally agreed upon in the web community, and in WebKit
>> specifically, that DOM Mutation Events are a bad thing. See, e.g.,
>> discussion on https://bugs.webkit.org/show_bug.cgi?id=8191 (relating
>> to DOMAttrModified, and why WebKit does not wish to implement it) and
>> https://lists.webkit.org/pipermail/webkit-dev/2010-August/013805.html
>> (a discussion of replacing DOM mutations with something better, or
>> removing them entirely).
>> In late June, Jonas Sicking and Olli Pettay from Mozilla put forward
>> proposals on public-webapps
>> (http://lists.w3.org/Archives/Public/public-webapps/2011AprJun/1318.html)
>> to replace mutation events with a different API, one that avoids the
>> problems associated with the existing spec.
>> Rafael Weinstein has helpfully summarized the public-webapps thread
>> (which is now upwards of 200 messages long) in
>> http://lists.w3.org/Archives/Public/public-webapps/2011JulSep/0779.html,
>> and discussion is ongoing in
>> http://lists.w3.org/Archives/Public/public-webapps/2011JulSep/0780.html.
>> Any WebKit folks interested in the future of mutation events in the
>> DOM are invited to join that discussion, and their input would be much
>> appreciated.
>> I've also put together a partial implementation of Jonas' most recent
>> proposal and uploaded my
>> work-in-progress patch to
>> https://bugs.webkit.org/show_bug.cgi?id=66079. Note that this is very
>> early work, and if I were submitting it for review it would be in much
>> smaller chunks, but I welcome any comments or questions on the code
>> as-is.
>> - Adam
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