Promise.all not waiting to complete the requests

Question

await Promise.all(
  endpoints.map((endpoint) =>
    this.httpService.get(endpoint).pipe(
      map((response) => {
        return response.data['result'];
      }),
    ),
  ),
).then(
  axios.spread((...allData) => {
    allData.forEach((res) =>
      res.subscribe((res) => {
        apiFeedBack.push(res);
        console.log(apiFeedBack);
      }),
    );
  }),
);

While debugging it is skipping promise.all execution and directly returns undefined as response. What am i missing here

I don't think so you should be using observables and promises at the same time. — Ali Hussnain - alichampion, Mar 09 '22 at 05:28
If you want to use `Promise.all` you will have to convert observable into promise and return it from your `array.map` — Ali Hussnain - alichampion, Mar 09 '22 at 05:30
@AliHussnain I am new to nestjs, Could you provide the code snippet for conversion of observable to promise for above code — qwerty, Mar 09 '22 at 05:47
Whatsup with the `map` function *inside* the `pipe` function? Are you receiving an array as a result from `httpService.get`? — Emiel Zuurbier, Mar 09 '22 at 06:43

Apoorva Chikara · Answer 1 · 2022-03-09T06:47:36.623

0

First of all, when you are using await don't use then. This is how it be like:

const promiseAll = async () => {
try {
  const res = await Promise.all(promises);
  return res;
} catch (e) {
 console.error(e);
}
}

Now, we need to get the values from the promises using await, Also, it would be clean if you write it this way:

const endpoints_Promises = endPoints.map(endPoint => {
 return new Promise((resolve, reject) => {
  this.httpService.get(endpoint).pipe(
    map((response) => {
      resolve(response.data['result']);
    })
   ) 
 })
})
try {
const responses = await Promise.all(endpoints_Promises);
responses.forEach(data =>  console.log(data));
} catch (e) {
   console.error(`Error occured: ${e}`);
}

edited Mar 09 '22 at 06:47

answered Mar 09 '22 at 06:34

Apoorva Chikara

8,277
3
20
35

From where is resolve function coming up? – Ali Hussnain - alichampion Mar 09 '22 at 06:38
You can check [this](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) link. – Apoorva Chikara Mar 09 '22 at 07:03

Ali Hussnain - alichampion · Answer 2 · 2022-03-09T07:04:16.237

folks as you may know that @nestjs/axios in NestJS returns observable rather then promise however this is not the case of axios.

So in case you need to make observable asynchronous you will need to convert it to promise, although it's not a recommended way and .toPromise() is deprecated in the latest version of @nestjs/axios.

Promise.all(
  return endpoints.map((endpoint) =>
    this.httpService.get(endpoint).toPromise(),
  ),
).then((responses)=> {
   // here you get the resolved promises responses array
})

Check this out to learn more about Promise.all fulfillment.

Check this out for more information if you should be using observable async/await Is it a good practice using Observable with async/await?

`toPromise` will be deprecated soon. Also, You can't use await and then together. This is anti-pattern. — Apoorva Chikara, Mar 09 '22 at 07:02

score -1 · Answer 3 · answered Mar 09 '22 at 05:24

-1

You need to return the array of promises received from the map function as below:

await Promise.all(
  return endpoints.map((endpoint) =>
    this.httpService.get(endpoint).pipe(
      map((response) => {
        return response.data['result'];
      }),
    ),
  ),
).then(
  axios.spread((...allData) => {
    allData.forEach((res) =>
      res.subscribe((res) => {
        apiFeedBack.push(res);
        console.log(apiFeedBack);
      }),
    );
  }),
)

answered Mar 09 '22 at 05:24

Siddharth Seth

643
5
18

1

This will cause a `SyntaxError` as the `Promise.all` function expects an expression and not a `return` keyword. The problem lies in that there are no promises returned *inside* the `map` function. – Emiel Zuurbier Mar 09 '22 at 06:34

Promise.all not waiting to complete the requests

3 Answers3