[whatwg] events when navigating away before page load?

Mike Wilson mikewse at hotmail.com
Fri Dec 14 14:28:50 PST 2012

Ian Hickson wrote on 14 december 2012 21:11:
> As a general rule, the intent of the spec is that you 
> get a "load" when all your scripts (and other resources) 
> have loaded, and you get an "unload" when the page is 
> going away. Thus if the page goes away before the page 
> has finished loading, you just get an "unload".

Yes, when I think about this a bit more it makes a lot of
sense. Initially I did expect a behaviour more like
abort/stop - skipping all outstanding i/o and "fast-
forwarding" to the firing of the load event(s). 
But as you say, as we are leaving the page anyway, there 
shouldn't be a big need to do page load initializations.
And a smart page can actually detect it's being rushed
through by looking for unload without load.

Note to self and to other page authors: make sure unload 
handlers don't break if related code in load handlers 
weren't executed.

> We additionally also suggest firing a "load" and so forth 
> when the user aborts the page, on the assumption that you 
> probably have all the scripts you need and are only 
> missing minor things like ads or analytics

Makes sense too - the user probably stopped the page
when it seemed complete enough to him, so he should get
event handlers and all other UI stuff set up that's
normally in load handlers.

I did a few more tests and found even more differences.
Chrome has different behaviour depending on if the 
navigation is initiated while parsing <head> or <body>,
and for the latter it fires the same events as Firefox
although in a different order:

FF17       Chr23      Chr23      IE9        spec
nav head   nav head   nav body   nav head   nav head
or body                          or body    or body
---------- ---------- ---------- ---------- ----------
beforeunld domload    domload    beforeunld beforeunld
domload    unload     beforeunld            unload
unload                unload

Interesting stuff indeed :-)

Best regards

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