Function returns promise object instead of value (async/await)

Question

I got this code using the async/await :

function _getSSID(){
   return new Promise((resolve, reject)=>{
      NetworkInfo.getSSID(ssid => resolve(ssid))
   })
}

async function getSSID(){
   let mySSID =  await _getSSID()
   if (mySSID == "error") {
     return 'The value I want to return'
   }
}

And getSSID() is equal to this :

Looks like the getSSID() function will always return a promise. How can I get "The value I want to return" in plain text ?

Any help is greatly appreciated.

`getSSID().then(value => { /* do something with value */ })` — Patrick Roberts, Feb 21 '18 at 14:54
You could call it inside another async function and await for the result. Asynchoronous effect is contagious. Once you have something async it makes async everything it touches. — Yury Tarabanko, Feb 21 '18 at 14:56
@YuryTarabanko that's not poisonous, that's just contagious ;) — Patrick Roberts, Feb 21 '18 at 14:57
@PatrickRoberts but what if I want to create a variable with the value of what I want to return ? I can't just put `getSSID().then(value => { return value })` — Lawris, Feb 21 '18 at 14:58
@Lawris please refer to the duplicate question, it explains everything. — Patrick Roberts, Feb 21 '18 at 14:58
@Lawris: you can have a variable: `var result = await getSSID()`. Just the context you call it from has to be `async`. — Wiktor Zychla, Feb 21 '18 at 14:59
@WiktorZychla Is there no way to create that variable without having it in an async context? — Aslan French, May 02 '19 at 17:00

samanime · Answer 1 · 2020-05-27T05:30:50.083

18

Declaring a function async means that it will return the Promise. To turn the Promise into a value, you have two options.

The "normal" option is to use then() on it:

getSSID().then(value => console.log(value));

You can also use await on the function:

const value = await getSSID();

The catch with using await is it too must be inside of an async function.

At some point, you'll have something at the top level, which can either use the first option, or can be a self-calling function like this:

((async () => {
    const value = await getSSID();
    console.log(value);
})()).catch(console.error):

If you go with that, be sure to have a catch() on that function to catch any otherwise uncaught exceptions.

You can't use await at the top-level.

edited May 27 '20 at 05:30

answered Feb 21 '18 at 14:59

samanime

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While I hope top-level `await` never makes the cut (see [top-level `await` is a footgun](https://gist.github.com/Rich-Harris/0b6f317657f5167663b493c722647221)), it is currently [a stage 1 proposal](https://github.com/MylesBorins/proposal-top-level-await). – Patrick Roberts Feb 21 '18 at 15:02
1

Indeed. I've read that, and I tend to agree with the gist you linked. That's why I like the anonymous self-calling async function to kick things off. Still mostly at the top level, with the benefits of not really being there. – samanime Feb 21 '18 at 15:03
3

It doesn't actually solve my problem, I want to create a variable that will be equal to the value I want to return with the promise. – Lawris Feb 21 '18 at 15:35
It should. If `mySSID === 'error'`, then the `value` in all of the examples above will equal `"The value I want to return"` – samanime Feb 21 '18 at 15:47

Function returns promise object instead of value (async/await)

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