On Sep 17, 2009, at 3:35 PM, Brady Eidson wrote:
On Sep 17, 2009, at 2:17 PM, Ojan Vafai wrote:
On Thu, Sep 17, 2009 at 2:11 PM, John Abd-El-Malek <[email protected]>
wrote:
On Thu, Sep 17, 2009 at 2:09 PM, Darin Fisher <[email protected]>
wrote:
On Thu, Sep 17, 2009 at 12:52 PM, Maciej Stachowiak <[email protected]>
wrote:
Based on your comments below, I think the expedient thing to do is
to let Image loads (only) complete their I/O when initiated from
unload or pagehide.
Why exclude beforeunload? Some of the sites we found use the busy
loop hack in beforeunload.
These sites presumably did it to split the sleep calls across as
many handlers as possible to avoid hung script detectors. If they
rewrite their pages to use one clean method, it seems they only
need to do it in one place.
There a plenty of sites that only have a beforeunload handler and
have no reason to register an unload handler. If you're not
prompting the user to stay on the page, the two events are
essentially equivalent.
This is not true.
I couldn't test IE right now but for Safari, Opera, and Firefox, I
just independently verified that:
-unload handlers prevent a page from going into the page cache.
-beforeunload handlers do not
-beforeunload handlers are called before a page is navigated away
from, even when the page is going into the page cache.
So the key difference is that while an unload handler will *only*
ever run once, when a page is destroyed, a beforeunload handler
might run multiple times, each time the user navigates away from the
page after returning to it.
This might not be immediately relevant to the conversation, but they
are not the same and I'd rather the conversation not assume they are.
In practice, if an author uses beforeunload as their unload handler,
they are doing The Wrong Thing(tm)
Another obvious difference is that the beforeunload event is
dispatched earlier in the navigation process and its handlers may
cancel the navigation.
- Maciej
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