[whatwg] should async scripts block the document's load event?

Nicholas Zakas nzakas at yahoo-inc.com
Fri Feb 12 10:10:47 PST 2010

To me "asynchronous" fundamentally means "doesn't block other things
from happening," so if async currently does block the load event from
firing then that seems very wrong to me.





Commander Lock: "Damnit Morpheus, not everyone believes what you

Morpheus: "My beliefs do not require them to."


From: whatwg-bounces at lists.whatwg.org
[mailto:whatwg-bounces at lists.whatwg.org] On Behalf Of Brian Kuhn
Sent: Friday, February 12, 2010 8:03 AM
To: Jonas Sicking
Cc: Steve Souders; WHAT Working Group
Subject: Re: [whatwg] should async scripts block the document's load


Right.  Async scripts aren't really asynchronous if they block all the
user-visible functionality that sites currently tie to window.onload.


I don't know if we need another attribute, or if we just need to change
the behavior for all async scripts.  But I think the best time to fix
this is now; before too many UAs implement async.







On Thu, Feb 11, 2010 at 10:41 PM, Jonas Sicking <jonas at sicking.cc>

Though what we want here is a DONTDELAYLOAD attribute. I.e. we want
load to start asap, but we don't want the load to hold up the load
event if all other resources finish loading before this one.

/ Jonas

On Thu, Feb 11, 2010 at 10:23 PM, Steve Souders <whatwg at souders.org>
> I just sent email last week proposing a POSTONLOAD attribute for
> -Steve
> On 2/10/2010 5:18 PM, Jonas Sicking wrote:
>> On Fri, Nov 6, 2009 at 4:22 PM, Brian Kuhn<bnkuhn at gmail.com>  wrote:
>>> No one has any thoughts on this?
>>> It seems to me that the purpose of async scripts is to get out of
the way
>>> of
>>> user-visible functionality.  Many sites currently attach
>>> functionality to window.onload, so it would be great if async
scripts at
>>> least had a way to not block that event.  It would help minimize the
>>> affect
>>> that secondary-functionality like ads and web analytics have on the
>>> experience.
>>> -Brian
>> I'm concerned that this is too big of a departure from how people are
>> used to<script>s behaving.
>> If we do want to do something like this, one possibility would be to
>> create a generic attribute that can go on things like<img>,<link
>> rel=stylesheet>,<script>  etc that make the resource not block the
>> 'load' event.
>> / Jonas


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