[webkit-dev] Lazy loading

Thomas Steiner tomac at google.com
Mon Oct 28 12:08:24 PDT 2019

On Mon 28. Oct 2019 at 20:02 Simon Fraser <simon.fraser at apple.com> wrote:

> > On Oct 28, 2019, at 11:39 AM, Rob Buis <rbuis at igalia.com> wrote:
> >
> > Hi,
> >
> > I made a lazy image loading prototype earlier this year (
> https://bugs.webkit.org/show_bug.cgi?id=196698) and have been splitting
> it up into reviewable patches. The main implementation part landed recently
> so I am wondering about the next steps.
> >
> > One thing left to do for sure is cleaning up/adding tests. For one there
> are tests in http/tests/lazyload which can just be WPT tests, so I'll work
> in this area for sure. As usual, while adding new tests bugs may show up
> and more patches will be needed.
> >
> > Another possible task is implementing metadata fetch, but it makes the
> code more complex and chromium has backtracked from it.
> >
> > Changing the behavior of loading=auto to make lazy loading the default
> seems risky and should possibly only be done when lazy image loading is
> deemed stable enough.
> Agreed. Is there any compat data from other browsers?
> >
> > Yet another possible task is making lazy loading work for CSS
> backgrounds, this is implemented in the prototype but I don't think there
> are many tests for it.
> >
> > A related task is implementing lazy loading for iframe's, I took a quick
> look and this looks like similar work to lazy image loading, but should be
> much easier to implement now the building blocks are there.
> I think this one has the highest potential to give big page loading gains,
> especially if we can get this one turned on by default (or maybe for
> cross-origin frames), so I suggest working on this.
> Do we have any data from other browsers to know whether enabling
> lazy-loading iframe by default breaks the web?

We on the Chrome team have rolled this out to Lite Mode users recently and,
as far as I can tell, haven’t seen any breakage:
You can contact the blog post authors for more background if need be.

> >
> > Finally there is the task of setting threshold viewport distance values
> for triggering deferred loads. I only have access to iOS simulator, so I
> wonder if that is something Apple could help with?
> I would be happy to help.
> >
> > I do not have a strong preference among these tasks. Thoughts?
> > Cheers,
> >
> > Rob.
> >
> > P.S: I intend to attend the WebKit Contributors meeting, so feel free to
> chat with me there about lazy loading.
> See you there!
> Simon
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Thomas Steiner, PhD—Developer Advocate (https://blog.tomayac.com,

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