Awaiting a .then() statement

Question

If I have this return statement

return await foo1().then(() => foo2());

and both foo1 and foo2 are async, would the code wait for the resolution of foo2 or only foo1 ?

thanks.

If a promise returns a promise, it becomes part of the chain, so it will wait for both. But saying that if your using await, i would drop the then. — Keith, Jul 29 '18 at 17:12
I was just wondering about the behavior of using both in the same line. Thanks — Étienne Boutet, Jul 29 '18 at 17:15
You can use them both, but I use promises constantly now and very rarely use then. But it does still come in handy, for example creating a kind of program fork.. — Keith, Jul 29 '18 at 17:22

score 2 · Accepted Answer · answered Jul 29 '18 at 17:21

await awaits for the entire expression foo1().then(...), regardless of what ... is. The same applies to a chain of then-s (you asked it in a comment).
Also, you do not really need await here, you could simply return the Promise created by then (or a chain of them), see Difference between `return await promise` and `return promise` for explanation.

score 1 · Answer 2 · answered Jul 29 '18 at 17:23

1

return await somePromise(); is an anti-pattern since await wraps the result of somePromise(), which is itself a Promise, in a newly created Promise.

return somePromise(); is the correct form.

answered Jul 29 '18 at 17:23

Rob Raisch

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score 0 · Answer 3 · answered Jul 29 '18 at 17:16

0

Yes it will wait because the await operator has lower precedence than the . operator.

However, your code fails to take advantage of await which provides superior readability.

Prefer

await foo1();
const result = await foo2();
return result;

answered Jul 29 '18 at 17:16

Aluan Haddad

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Awaiting a .then() statement

3 Answers3