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Re: navigationStart and the actual start of the navigation

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Fri, 27 Jun 2014 11:53:58 -0400
Message-ID: <53AD9396.80105@mit.edu>
To: Przemysław Pietrzkiewicz <ppi@google.com>
CC: public-web-perf@w3.org
On 6/27/14, 11:31 AM, Przemysław Pietrzkiewicz wrote:
> I see, thanks for the explanation. In this case, maybe we could go for:
>
> "This attribute must return the time when the user agent determines that
> the navigation will happen. For navigations from documents other than
> the initial about:blank of the browsing context, this is the time when
> the user agent finishes prompting to unload the previous document."

Here's a question.

Say I click a link like this: <a target="foo" href="bar">Click me</a>.

The UA decides that a navigation will happen at the point when I click. 
  Then it has to go look for a named target (which might take a while, 
depending on how many frames are reachable from that document).  If it 
finds one it will prompt to unload that document; if not, it will open a 
tab/window/whatever.

Should the time needed to find the named target be considered when 
deciding when navigationStart is?  I guess it can't be if we want to 
exclude the time it takes to fire beforeunload handlers...

> Actually, the second sentence might be redundant - the time when the
> user agent determines that the navigation will happen in the presence of
> a document already loaded in the browsing context is the end of
> beforeunload.

OK...

But initial about:blank can also have beforeunload handlers, note, 
though not in the case when the UA is creating a new browsing context 
and then immediately navigating it.

I guess an important question is this: how is browsing context creation 
fundamentally different from beforeunload handler execution in terms of 
whether it should be included in the time taken to load?  It sounds like 
you want to include the former but exclude the latter, right?

-Boris

P.S. "when the user agent determines that the navigation will happen" is 
a non-testable requirement, fundamentally; UAs can do whatever the heck 
they want with it.
Received on Friday, 27 June 2014 15:54:26 UTC

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