Just because you use async/await doesn't mean you can't use Promise.all.

In fact, my immediate intuition with the await examples was to parallelize with Promise.all.

    await Promise.all([/* build promises */]);

Yeah they had that in the post.

> How would you handle two asynchronous saves which can happen in parallel without using a Promise.all?

This question doesn't make sense. Async/await is just a nicer syntax for interacting with promises. So my answer to your "gotcha" question is just:

  await Promise.all([..., ...])

There's nothing impure going on here. The majority of the time, async/await can make it much easier to see a code's control flow by getting rid of most of the Promise related cruft and callbacks.

I would call Promise.all a benefit here, as it makes it stand out where I'm doing something in parallel.

  const x = somethingAsync();
  const y = somethingAsyncToo();

  return  { foo: await x, bar: await y }

There is no point in returning one before the other because you need both?

I think you’re trying to recreate the semantics of Promise.all without using Promise.all.

You’re effectively saying that Promises are a better async programming paradigm than async/await…which is also what the author is saying in the article.

I'm not saying anything about promises vs async/await. The original comment said that you can't have 2 async things happen in parallel without Promise.all, my code snippet proves that you can.

But in JavaScript, these two awaits will not happen in parallel, you really need to await Promise.all() for that.

You've really missed the point spectacularly of that example.

Both those promises start, and both are waited for after both have started..

That is the same as promise.all... There's just an explicit order for the wait, rather than as they resolve, but the result is the same.

Now, promise.any.... You'd have a point...

This is correct, I wasn't paying attention.

In Javascript, a Promise is started as soon as it is created. In other words, this is not the `await` that starts the Promise.

If the first await is the slowest, the second one will return immediately (like calling .then on an already resolved promise).

+1 Notably, this is different in Python where promises (futures) are executed lazily, i.e. when you await them.

Pretty sure there can be unexpected behavior if you wait too long before you do those awaits at the end.

No, why would there be?

Node 16 will exit if an exception is thrown and not awaited for some finite period of time. So if your goal is to keep those promises in some cache and then resolve them later on at your leisure, you will find the entire node process will abort. There is a feature flag to restore the older behavior but it’s a pretty big gotcha.

There is no such finite period of time. You can call an async function and never await it.

Exception handling is something completely different. Yes, if you call an async function and do not catch the exception, Node will stop. But that is independent of having called await or not. Whether or not you await something async does not affect exception behavior.

Promises are also just syntactic sugar to make your code look more synchronous, you can do everything with plain callbacks. Which I find ironic with the article that he argues against that but still just stops at the next turtle, instead of following his own advice and actually learning how Javascript and it's runtime works.

Not really correct.

    const fooP = fetch(a)
    const bar = await fetch(b)
    const foo = await fooP

Wait, why don't do that? What's the point?

Yup - I prefer async/await but that was actually a good example on optimizing multiple promises I had not though of before.