Hacker News Reader

HNHacker News

Top New Best Ask Show Jobs

Comment by aGHz | Hacker News Reader

Parent Full thread

aGHz·

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

View on HN

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.

Reply on news.ycombinator.com