Is there a way to get my result from promise assigned to outside variable?

Question

I want to set the value of the result to the promise variable, which is JSON file.

I tried returns, creating the variable like (result) => {var myVar = result}

async function getUpdate() {
  async function getFirstEvent() {
    //code returning a JSON
  }
  async function getSecondEvent() {
    //code returning a JSON
  }

  let firstPull = await getFirstEvent(); //unimportant
  var dataPull1 = await JSON.stringify(firstPull); //unimportant

  var promise = new Promise(async function(resolve, error) {
    let secondPull = await getSecondEvent();
    var dataPull2 = await JSON.stringify(secondPull);

    setTimeout(() => resolve(dataPull2), 3000);
  }).then((result) => {
    //return a value to promise ???
  });
}

getUpdate();
setInterval(getUpdate, 5000);

I've received undefined, but that's because of the variable didn't get any value assigned to.

[Never pass an `async function` as the executor to `new Promise`](https://stackoverflow.com/q/43036229/1048572)! — Bergi, Jul 30 '19 at 13:01
Where exactly did you try to get a `result` value but failed to do? — Bergi, Jul 30 '19 at 13:02

score 0 · Accepted Answer · answered Jul 30 '19 at 12:33

0

In future try to not mix async/await with Promise

function sleep(ms) {
 return new Promise((resolve) => setTimeout(resolve, ms));
}

async function getUpdate() {
 async function getFirstEvent() {
  //code returning a JSON
 }

 async function getSecondEvent() {
  //code returning a JSON
  return "result";
 }

 let firstPull = await getFirstEvent(); //unimportant
 var dataPull1 = await JSON.stringify(firstPull); //unimportant
 let secondPull = await getSecondEvent();
 var dataPull2 = await JSON.stringify(secondPull);
 await sleep(3000);
 console.log(dataPull2);
 return dataPull2;
}

getUpdate();
setInterval(getUpdate, 5000);

answered Jul 30 '19 at 12:33

ponury-kostek

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`In future try to not mix async/await with Promise` could you clarify this a bit? – Clarity Jul 30 '19 at 12:39
@Clarity mixing `async/await` with `Promise`, makes it harder to read and understand what is actually happening, also error handling could be more complicated – ponury-kostek Jul 30 '19 at 12:51

score 0 · Answer 2 · answered Jul 30 '19 at 12:36

You should not use async / await here, it makes writing a solution much harder, rather, you should use .then() to consume a promise. You can return the data from the function, and use that data with .then():

const getUpdate = () => {
  const getSecondEvent = () => new Promise((resolve, reject) => resolve([1,2,3]))
  return getSecondEvent().then(JSON.stringify)
}

getUpdate().then(console.log)

score -1 · Answer 3 · answered Jul 30 '19 at 12:32

Why would you create a promise at the "promise" variable if you actually want a value? Using your code, something like this should work:

var promise = await new Promise(async function(resolve, error) {
... // your function
resolve(data);
}

but that looks kinda nasty. For a better, cleaner code i'd take out the whole promise to an outside function which returns a promise, and then put var promise = await promiseFunc(), which looks much better.

Is there a way to get my result from promise assigned to outside variable?

3 Answers3