Test inserted async script execution order

[domenic]

• Chromium passes these tests
• WebKit almost passes, but suffers from https://bugs.webkit.org/show_bug.cgi?id=272505: for some reason it fires the error event from script 2 before executing script 1
• Gecko fails these tests. It both executes script 1 and fires the error event from script 2 synchronously.

whatwg/html#9864 discusses the issue. whatwg/html#10272 matches what is tested here.

[foolip]

This is very nice and clear. I haven't reviewed the spec text to confirm this is the required behavior, as I assume that is not in question.

[domfarolino]

Chrome and Safari seem to run them async but not using microtask timing

I am assuming Chrome & Safari both run them async in a single posted task (not microtask)? Could you maybe modify the tests locally to see if instead of using queueMicrotask() here, if you used setTimeout() (or maybe postTask()?) the tests pass in those browsers?

If they do, then maybe the easiest thing to do is just align the spec to both of those implementations to at least match reality.

[annevk]

When you insert a script like this, is it essentially synchronous even though it says "async", except parsing/execution happens after a single microtask? What if they contain further import statements?

Because if we do actually go in parallel somewhere here I agree that we need a task.

[domenic]

I am assuming Chrome & Safari both run them async in a single posted task (not microtask)? Could you maybe modify the tests locally to see if instead of using queueMicrotask() here, if you used setTimeout() (or maybe postTask()?) the tests pass in those browsers?

When doing setTimeout(,0), it becomes a race condition, presumably because whatever task source they're using for scheduling the script execution (networking task source?) is not always faster than the timer task source. setTimeout(,10) works.

When you insert a script like this, is it essentially synchronous even though it says "async", except parsing/execution happens after a single microtask?

This question made me re-inspect the spec. It seems I got it slightly wrong. Let's discuss over in whatwg/html#9864.