Using an await in function parameter

Question

Is it possible to use await with a parameter? for example:

const run = async () => {
  getStudentDetails(await getStudentId());
}

Even if it is, it seems like it might not be the best idea. Anyone done this before?

Thats the best idea ever, I'm doing that all the time, thats what `await` is good for! — Jonas Wilms, Oct 04 '18 at 20:20
i've done it: `var pw=this.parseHex(await this.derive(password));` — dandavis, Oct 04 '18 at 20:22
`const run = async () => { try{getStudentDetails(await getStudentId());}catch(e){ //Do something when getSTudentId() fails} }` — Cody Ｇ, Oct 04 '18 at 20:23
the proposed `do` block will allow inline handling of errors... — dandavis, Oct 04 '18 at 20:24
Hmmm. New question: what happens when you call something like `foo(await bar1(), await bar2())` ? I assume `bar2` waits until `bar1` but I'm too lazy to try and have never used that syntax — Cody Ｇ, Oct 04 '18 at 20:25
Yeah never used that syntax either. Honestly the more I think about it is probably kinda dangerous. As there is not an easy way to handle errors, and hard to read. Probably better to define it before running function. — Justin, Oct 04 '18 at 20:28
@CodyＧfoo(await bar1(), await bar2()) will not work in parallel. I wrote an answer how to do in a best way — Kirill Reznikov, Jun 26 '19 at 17:31
Refer https://stackoverflow.com/questions/42964102/syntax-for-async-arrow-function — shamila, Jan 31 '20 at 11:09

Bergi · Accepted Answer · 2018-10-04T20:22:59.287

15

Yes, you can use await expressions in every arbitrary context (where it parses) inside the async function, including as arguments to function calls. There's nothing wrong with it.

It's equivalent to

const run = async () => {
  const studentId = await getStudentId();
  getStudentDetails(studentId);
}

edited Oct 04 '18 at 20:22

answered Oct 04 '18 at 20:19

Bergi

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1

And as long as you are in the same calling context as the async function, e.g. this doesn't work: `async () => fnTakingCb(() => await getStudentId());` – Explosion Pills Oct 04 '18 at 20:21
@ExplosionPills Yes, that's not in the async function, that's in the arrow function callback. – Bergi Oct 04 '18 at 20:22

score 5 · Answer 2 · answered Jun 26 '19 at 17:15

I do it all the time. However in case if you want to pass more than one parameter to function they will be resolved sequentially. To fight that problem I wrote an util function which looks like that:

async function call(func, ...args) {
    return func(...await Promise.all(args));
}

(async function() {
        console.log(await call(functionToCall, delay(2000), delay(2000)));
})();

With that syntax functionToCall will be called in 2 seconds instead of 4

score 2 · Answer 3 · answered Oct 04 '18 at 20:20

Yes, this will work, as you can use the await keyword everywhere where you can use an expression.

However, I'd prefer a slightly updated version of your code for better readability (and for better debugability, too):

const run = async () => {
  const studentId = await getStudentId();

  getStudentDetails(studentId);
}

I hope this helps

Using an await in function parameter

3 Answers3

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