- From: Boris Zbarsky <bzbarsky@MIT.EDU>
- Date: Wed, 20 Jul 2011 13:23:36 -0400
- To: Dave Raggett <dsr@w3.org>
- CC: public-webapps@w3.org
On 7/20/11 11:43 AM, Dave Raggett wrote:
> Perhaps we need to distinguish auto generated attributes from those that
> are set by markup or scripts.
I'm not sure what you mean.
> Could you please clarify for me the
> difference between the html "style" attribute and the one you are
> referring to?
There isn't one.
> My understanding is that the html style attribute is set
> via markup or scripts and *doesn't* reflect all of the computed style
> properties for this DOM node.
That's correct.
Let me give you a concrete testcase:
<!DOCTYPE html>
<body style="margin: 0;">
<script>
document.body.style.marginLeft = "5px";
document.body.style.marginRight = "5px";
document.body.style.top = "17px";
alert(document.body.getAttribute("style"));
</script>
This alerts "margin: 0pt 5px; top: 17px" in Gecko, "margin-top: 0px;
margin-bottom: 0px; margin-left: 5px; margin-right: 5px; top: 17px" in
WebKit and Presto. So the value of the style attribute changes when you
modify inline style via the CSS2Properties and CSSDeclaration
interfaces. Not only that, but what's stored are the longhand property
names and values, with shorthand generation happening at serialization
time in at least some UAs.
It's pretty common to have situations where lots (10-20) of properties
are set in inline style, especially in cases where the inline style is
being changed via CSS2Properties from script (think animations and the
like, where the objects being animated tend to have width, height,
various margin/border/padding/background properties, top, left, etc all
set). Those are precisely the cases that are most performance-sensitive
and where the overhead of serializing the style attribute on every
mutation is highest due to the large number of properties set.
-Boris
Received on Wednesday, 20 July 2011 17:24:20 UTC