Re: element.onresize

But what if we can get notification only for some of elements (not all) 
via setting some properties or methods. This not solve performance isue?

Something like this:
el.resized = true
el.resized(true|false)
etc.
and only el will generate resize event.

Or fire resize only for elements that changedviauser interactions, or 
elements that matched to the resize property:
http://dev.w3.org/csswg/css-ui-3/#resize

New HTML firing resize event for <video> element (when video has been 
fetched or whenever the intrinsic width or intrinsic height of the video 
changes) so adding that possibility only for some element should not be 
performance problem.