[whatwg] Link.onload; defer on style, depends

Ian Hickson ian at hixie.ch
Mon Apr 27 23:50:37 PDT 2009

On Mon, 27 Apr 2009, Boris Zbarsky wrote:
> Ian Hickson wrote:
> > The spec requires the page 'load' event to be fired asynchronously. 
> > (There's no black-box way to distinguish this from the case of waiting 
> > for the other 'load' events to have fired, as far as I can tell.)
> Phrased that way, yes.  But maybe I wasn't clear on the exact behavior 
> Gecko has here.  For image load events, not only does the async event 
> prevent the page load from firing until after it has fired, but it also 
> prevents _checking_ whether the page load should fire until after it has 
> fired.  So if the image load event has a listener that starts new 
> network requests, the page load would not fire until after those 
> requests complete.  In your proposed model above, whether it does or not 
> depends on the precise order in which the image's async load event races 
> with other network access.  If it fires before all other network access 
> is complete (and therefore before your proposed async page load event 
> has been posted), the page load event will wait for the load started 
> from the onload handler.  If not, then it won't.
> There are pros and cons to both setups, I guess; the race above is no 
> worse than a network request whose completion would trigger onload 
> racing against a timeout that starts a network request...

On Mon, 27 Apr 2009, Boris Zbarsky wrote:
> Or did I misunderstand and by "fired asynchronously" you mean 
> "asynchronously check again whether all network activity is done"?  (I 
> expect not, but just checking.)

As far as I can tell, as specced, there isn't a race condition (other 
than the inherent network race condition).


In this case:

   <body onload="2">
    <img onload="1; image = new Image(); image.src = 'test'; image.onload = 3">

The main 'load' event is queued as soon as there is nothing left that 
depends on it -- which happens as soon as the <img> load event was queued 
up, but before it runs. So the handlers run in the order given (1, 2, 3).

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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