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Re: Should MutationObservers be able to observe work done by the HTML parser?

From: Ryosuke Niwa <rniwa@webkit.org>
Date: Sun, 17 Jun 2012 12:24:14 -0700
Message-ID: <CABNRm63+ydrU8fbncy4sWttNgA+Bv-YNPrzoZQGuqjWNB=dcvg@mail.gmail.com>
To: Adam Klein <adamk@chromium.org>
Cc: WebApps WG <public-webapps@w3.org>, Olli@pettay.fi, Rafael Weinstein <rafaelw@chromium.org>
On Fri, Jun 15, 2012 at 4:36 PM, Adam Klein <adamk@chromium.org> wrote:
> On Fri, Jun 15, 2012 at 4:35 PM, Adam Klein <adamk@google.com> wrote:
>> This code alerts in Firefox but not in Chrome:
>> <!DOCTYPE html>
>> <body>
>>   <script>
>>     var observer = new MutationObserver(function(r) {
>>       alert(r);
>>     });
>>     observer.observe(document.body, {childList: true, subtree: true});
>>   </script>
>>   <p>Hello, World</p>
>> </body>
>> In WebKit's implementation, we had assumed that MutationObservers were
>> meant to observe changes after page load (and I personally thought that
>> we'd specced it that way, by putting it in DOM4, not HTML). But it seems
>> the Mozilla implementors made a different assumption. But what should
>> happen?
>> IMHO, it may not be worth the gain may not be worth the possible
>> performance degradation. If script wants to find out what the parser put on
>> the page, it should wait for DOMContentLoaded. But I can imagine a use case
>> where script might want to find out about the parser's work during load.
If script authors want to ignore DOM mutations made by the parser, then
they can wait until DOMContentLoaded (or even load) fires to attach
mutation observers.

- Ryosuke
Received on Sunday, 17 June 2012 19:25:03 UTC

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