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Comments about lazyload & postpone

From: Podjarny, Guy <gpodjarn@akamai.com>
Date: Fri, 6 Sep 2013 09:04:58 -0500
To: "public-web-perf@w3.org" <public-web-perf@w3.org>
Message-ID: <CE4F5926.39C67%gpodjarn@akamai.com>
All,

I recently read through the "Resource Priorities" draft (https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourcePriorities/Overview.html).
I really like it, and feel like it captures the vast majority of what I'd like to see in such a capability.

I do have a few comments/thoughts on it, though:

 1.  I assume lazyload on a link tag won't block rendering either, but it's not explicitly stated.
 2.  If a page holds multiple link tags to stylesheets, and some of them have the lazyload attribute, what's the cascading order? Is it in the order of appearance in the DOM, or the order in which they were processed (I.e. The lazy loaded ones are last). Also, what's the cascading order between multiple lazy loaded stylesheets? This seems to be addressed for links, since as soon as ordering is needed, lazyload is ignored.
 3.  I assume postpone and lazyload objects don't delay DOMContentLoaded either? Is there a requirement to not download a lazy-loaded resource until DOMContentLoaded has been fired?
 4.  What effect can (inline or not lazy-loaded) scripts in a page can have on lazy loaded resources? I.e. Can a script interrupt a lazy loaded or postponed download, for instance by hiding it? Would that abort the request? What's the effect of a script removing the lazyload or postpone attribute? The answer to some of these may be fairly obvious (to me, at least), but I think it'll be good to define these behaviors in the spec.
 5.  I assume this replaces the img defer attribute? (http://lists.w3.org/Archives/Public/public-web-perf/2013Apr/0063.html)

Cheers,
Guypo

--
Guy Podjarny | CTO, Web Experience, Akamai
Received on Friday, 6 September 2013 17:00:30 UTC

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