1301625 - Fire img "error" and "loadend" event off a single task

Status: NEW

(Core :: DOM: Core & HTML, defect, P3)

Description

[Edgar Chen [:edgar] (Parental leave until Oct. 09.)]

+++ This bug was initially created as a follow-up of Bug #599975 comment #31 +++

We're not following the spec for the case when we _do_ fire both error and loadend events: we're firing them off separate runnables, but the spec says to fire them off a single task [1].

[1] See step 11.4. of
https://html.spec.whatwg.org/multipage/embedded-content.html#update-the-image-data

Comment 1

[Ben Kelly [:bkelly, not reviewing]]

What do other browsers do here?  It seems in general we should be yielding the main thread more often, not less.

Comment 2

[Boris Zbarsky [:bzbarsky]]

It's hard to black-box test this.  In particular, telling the difference between a single task that fires two event and two back-to-back tasks that fire one event each is only possible if you can get some other task queue to interleave between the two tasks in the latter case...  I don't think there's any other way to tell them apart.

Comment 3

[Olli Pettay [:smaug][[e-mail]]]

The first event listener could do a postMessage to the current window and then onmessage would be called before the latter event, right?
(though, per spec those might go to different event queues)

Comment 4

[Boris Zbarsky [:bzbarsky]]

> (though, per spec those might go to different event queues)

Indeed.  Different task queues is in fact the only way that the onmessage could happen before the second event; if these tasks and the postMessage tasks used the same task queue then the onmessage would always happen after the second event.