"mute iframe load" flag doesn't seem to accurately capture what UAs do

[bzbarsky]

I don't quite know how to reconcile this with #4291 but...

Consider the following testcase:

<script>
function doIt() {
  log.textContent += "called";
  var doc = frames[0].document;
  doc.open();
  doc.defaultView.addEventListener("load", () => console.log('load'));
  doc.write("testing");
  doc.close();
}
</script>
<div id=log></div>
<iframe onload="doIt()"> </iframe>

Per spec as written, it should log "load" at some point, but it does not. The spec's "mute iframe load" flag prevents doIt being called a second time, but what UAs are doing is more than that: they're not firing the load event at all on the window in the iframe in this case after the close() call, as far as I can see. And that's even true if I add an <img src> to that DOM...

I haven't tested what happens if I call doIt from the load event firing on the window in the subframe instead of from the load event firing on the iframe element, by the way. At least in Gecko I expect that to also suppress the load event for the written document.

[bzbarsky]

@TimothyGu @domenic @annevk

[bzbarsky]

Hmm. Actually, looking at the spec again I guess the "iframe load in progress" flag is set when doIt is called, so open() sets the mute iframe load flag, and hence "load" should not get logged per spec?

[annevk]

Yeah, that seems to be the case. It's very strange however that this is only a flag for iframe elements, despite embed, object, and frame likely having similar problems.

[bzbarsky]

Yeah, in Gecko I'm flagging this on the document itself, not the iframe element...

[domenic]

Preivously: https://www.w3.org/Bugs/Public/show_bug.cgi?id=28773