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Bug 18630 - [Shadow]: It's unclear where a 'load' event is fired for replaced elements which has an author shadow root.
Summary: [Shadow]: It's unclear where a 'load' event is fired for replaced elements wh...
Status: RESOLVED WONTFIX
Alias: None
Product: WebAppsWG
Classification: Unclassified
Component: HISTORICAL - Component Model (show other bugs)
Version: unspecified
Hardware: PC All
: P2 normal
Target Milestone: ---
Assignee: Dimitri Glazkov
QA Contact: public-webapps-bugzilla
URL:
Whiteboard:
Keywords:
Depends on:
Blocks: 14978
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Reported: 2012-08-20 23:01 UTC by Hayato Ito
Modified: 2012-08-20 23:22 UTC (History)
1 user (show)

See Also:

Attachments

Description Hayato Ito 2012-08-20 23:01:02 UTC 
The spec says:
http://dvcs.w3.org/hg/webcomponents/raw-file/tip/spec/shadow/index.html#html-elements
> all HTML elements must have an equivalent of a shadow DOM subtree that is created and populated at the time of element instantiation.

According to the spec, <img> element should have a shadow DOM subtree like:

<img id=A src='a.png'>
   -#shadow-root
      <real-image-implementation>

Next, we attach an author shadow root (and its children) to an image element like:

<img src='a.png'>
   -#shadow-root
      <real-image-implementation>
   -#author-shadow-root
     - <div id=B>
        - <shadow>

So a composed shadow tree would become:

 <img id=A src='a.png'>
    <div id=B>
        <real-image-implementation>

My question is:
- Where a 'load' event should be fired after 'a.png' is loaded?

Option A) On an <img id=A> element directly.
Option B) On a <real-image-implementation> so that <div id=B> can receive an load event.

If we adopt option B, we must not stop the 'load' event at shadow boundary of <img>.

That means:
- We should not stop a load event if it is fired on real-image-implementation at the shadow boundary between <img> and <real-image-implementation>.
- We should stop other load events at the shadow boundary.
Comment 1 Hayato Ito 2012-08-20 23:03:52 UTC 
My preference is option B.
Comment 2 Dimitri Glazkov 2012-08-20 23:06:27 UTC 
(In reply to comment #1)
> My preference is option B.

Can you explain why?
Comment 3 Hayato Ito 2012-08-20 23:09:09 UTC 
I don't have a strong technical reason, but it looks natural for me at first glance.

(In reply to comment #2)
> (In reply to comment #1)
> > My preference is option B.
> 
> Can you explain why?
Comment 4 Dimitri Glazkov 2012-08-20 23:17:35 UTC 
(In reply to comment #3)
> I don't have a strong technical reason, but it looks natural for me at first
> glance.

Here's why I think we should stay with option A (which is what is in HTML spec right now):

1) No additional work necessary. The HTML spec clearly states that the event is dispatched on HTMLImageElement.

2)  Logically, there's a clear separation of responsibilities. The <real-image-implementation> is just a pixel surface. The loading machinery lives in HTMLImageElement, where it should be. In a way, the <real-image-implementation> could be just a canvas tag. It has no loading/error plumbing whatsoever.
Comment 5 Hayato Ito 2012-08-20 23:22:50 UTC 
Okay. Thank you. I don't have strong opinion on this because we don't have a strong use case that requires option B. Let's close the bug.

Shinya, please feel free to reopen this if you encounter a use case which requires option B.

(In reply to comment #4)
> (In reply to comment #3)
> > I don't have a strong technical reason, but it looks natural for me at first
> > glance.
> 
> Here's why I think we should stay with option A (which is what is in HTML spec
> right now):
> 
> 1) No additional work necessary. The HTML spec clearly states that the event is
> dispatched on HTMLImageElement.
> 
> 2)  Logically, there's a clear separation of responsibilities. The
> <real-image-implementation> is just a pixel surface. The loading machinery
> lives in HTMLImageElement, where it should be. In a way, the
> <real-image-implementation> could be just a canvas tag. It has no loading/error
> plumbing whatsoever.