TC39 Delegates on 2025-09-20

00:56	<Mathieu Hofman>	Something is confusing me about AsyncGeneratorStart / AsyncGeneratorCompleteStep. Is the return value of an async generator not awaited? Does that mean the final iterator result may have a promise as its `value` ? From my testing that doesn't seem to be the case, but I don't see how that's happening in the spec. `(async function * () { return Promise.resolve(42); })().next().then(x => console.log(x)); // { value: 42, done: true }`
01:21	<bakkot>	awaiting of `return` values actually happens as part of the evaluation of the `return` itself
01:22	<bakkot>	https://tc39.es/ecma262/multipage/ecmascript-language-statements-and-declarations.html#sec-return-statement-runtime-semantics-evaluation
01:24	<Mathieu Hofman>	Oh that is wild!
01:32	<bakkot>	This way it triggers finally statements
01:32	<bakkot>	Which, also kinda weird
02:59	<Mathieu Hofman>	I'm not sure I understand, `finally` always executes if a `return` is in a `try`. Internally awaiting the return expression shouldn't change that. And if there was a `catch` it shouldn't trigger it, in the same way `yield`ing a rejected promise only triggers a `catch` if the consumer of the iterator called `throw`. (I might have gotten myself confused again with generator behaviors and afk so can't easily double check)
04:08	<bakkot>	sorry, I meant `catch` not `finally`
04:08	<bakkot>	and it doe trigger a `catch`
04:08	<bakkot>	`(async function*(){ try { return Promise.reject('hi'); } catch (e) { console.log('caught', e); } })().next() // caught hi`
04:09	<bakkot>	this is in contrast to async functions `(async function(){ try { return Promise.reject('hi'); } catch (e) { console.log('caught', e); } })().catch(e => console.log('did not catch', e)) // did not catch hi`
04:09	<bakkot>	yielding a rejected promise does also trigger a `catch` incidentally
04:10	<bakkot>	which I am pretty sure is why `return` works that way in async generators
07:20	<Mathieu Hofman>	Well at least it's consistent. And now that you mention it, I think I knew that and just forgot about that oddity.