javascript - Array reduce function with async await

I'm trying to skip one object from an array objects based on a async operator. I've tried following cases, but getting a Type error.

Tried Method 1

newObjectArray = await Promise.all(objectAray.reduce(async (result, el) => {
  const asyncResult = await someAsyncTask(el);
  if (asyncResult) {
      result.push(newSavedFile);
  }
  return result;
}, []));

Tried Method 2

newObjectArray = await Promise.all(objectAray.reduce(async (prevPromise, el) => {
  const collection = await prevPromise;
  const asyncResult = await someAsyncTask(el);
  if (asyncResult) {
      prevPromise.push(newSavedFile);
  }

  collection.push(newSavedFile);
  return collection;
}, Promise.resolve([])));

Error

'TypeError: #<Promise> is not iterable',
'    at Function.all (<anonymous>)',

I'm trying to skip one object from an array objects based on a async operator. I've tried following cases, but getting a Type error.

Tried Method 1

newObjectArray = await Promise.all(objectAray.reduce(async (result, el) => {
  const asyncResult = await someAsyncTask(el);
  if (asyncResult) {
      result.push(newSavedFile);
  }
  return result;
}, []));

Tried Method 2

newObjectArray = await Promise.all(objectAray.reduce(async (prevPromise, el) => {
  const collection = await prevPromise;
  const asyncResult = await someAsyncTask(el);
  if (asyncResult) {
      prevPromise.push(newSavedFile);
  }

  collection.push(newSavedFile);
  return collection;
}, Promise.resolve([])));

Error

'TypeError: #<Promise> is not iterable',
'    at Function.all (<anonymous>)',

Share Improve this question asked Oct 5, 2018 at 22:36 Ankit Balyan 1,32919 silver badges33 bronze badges

Could you please explain what is the desired output? – gr4viton Commented Oct 5, 2018 at 22:39

Add a ment |

1 Answer 1

Sorted by: Reset to default 15

In your first try, result is a promise as all async functions evaluate to a promise when called, so you have to await result before you can push to the array, and then you don't need the Promise.all:

 newObjectArray = await objectAray.reduce(async (result, el) => {
  const asyncResult = await someAsyncTask(el);
  if (asyncResult) {
    (await result).push(newSavedFile);
  }
  return result;
}, []);

But I'd guess that it is way faster to just filter afterwards:

 newObjectArray = (await Promise.all(objArray.map(someAsyncTask))).filter(el => el);

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