[PageVisibility] Are visibility change events synchronous?

• From: Boris Zbarsky <bzbarsky@MIT.EDU>
• Date: Wed, 28 Sep 2011 22:25:07 -0400
• To: public-web-perf@w3.org
• Message-ID: <4E83D703.5030302@mit.edu>

If there is a visibility change, is the visibility change event fired 
synchronously?

Note that this is sort of page-observable: a page could poll the 
visibilityState and see whether it matches the previous state without 
having seen an event.  Then again, it's hard to tell that situation 
apart from one where some other script called stopImmediatePropagation 
on the event and then dispatched a new event...

My personal preference would be to allow or require asynchronous firing; 
the alternative involves, e.g. a tab switch triggering synchronous JS 
execution before it completes, which is not great for users navigating 
across tabs using the keyboard.

-Boris

Received on Thursday, 29 September 2011 02:25:45 UTC