Nodejs make an array and print it outside of loop

Question

I wanted to make an array based on query results from mongodb, after created the array I can not print this outside of for loop here is the code

    let results = await model.find({status: 'active'});
    let finalResult = [];

     results.forEach( async result=> {
      let fromDate = new Date(result.validFrom);
      query = {
       createdAt: {
        $gte: fromDate.getTime(),
        $lte: toDate.getTime(),
       }
      }

       results1 = await model1.find(query);
         results1.forEach(result1=> {
          finalResult.push(result1);
        })
      
   });

   console.log(finalResult);

I am getting an empty array for finalResult log. can you please help me for this?

Does this answer your question? [How to return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-to-return-the-response-from-an-asynchronous-call) — goto, May 29 '21 at 12:03
Use `for...of` and the question above to figure out how to return a value from an asynchronous call. — goto, May 29 '21 at 12:04

hoangdv · Accepted Answer · 2021-05-29T12:17:59.240

1

Use for...of instead of forEach. forEach recipes a callback function as a parameter, and it not support async function.

const results = await model.find({ status: 'active' });
const finalResult = [];

for (const result of results) {
  let fromDate = new Date(result.validFrom);
  query = {
     createdAt: {
        $gte: fromDate.getTime(),
        $lte: toDate.getTime(),
     }
  };
  const items = await model1.find(query);
  finalResult.push(...items);
}

console.log(finalResult);

edited May 29 '21 at 12:17

answered May 29 '21 at 12:06

hoangdv

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you not used the query variable, can you please use query variable as I used? – mdkamrul May 29 '21 at 12:09
@mdkamrul Updated. But why? – hoangdv May 29 '21 at 12:11
because I have used this var at other place – mdkamrul May 29 '21 at 12:12
how can I use results object at loop? – mdkamrul May 29 '21 at 12:15
Do you mean `results` 's element? just change `_` to what you want. – hoangdv May 29 '21 at 12:16
I have edited my question please check, so I want to use results object at loop – mdkamrul May 29 '21 at 12:16
yes its working fine now, thanks for you solution – mdkamrul May 29 '21 at 12:22
is there any solution to omit query in loop? this will harm performance – mdkamrul May 29 '21 at 12:23
Try to get minimum and maximum of `createdAt` and take one query. re-filter by js code. – hoangdv May 29 '21 at 12:39
can you please another solution for this? – mdkamrul May 29 '21 at 13:03

Naren · Answer 2 · 2021-05-29T12:31:35.187

forEach with async doesn't work as expected. forEach don't wait for asynchronous calls. Better use map or for...of loops.

Using for...of is serial, Using map & Promise.all is parallel,

const results = await model.find({ status: 'active' });

const resultMap = results.map(async result =>  await model1.find({
    createdAt: {
      $gte: fromDate.getTime(),
      $lte: toDate.getTime(),
    }
  })
)

Promise.all(resultMap).then((data) => {
  console.log(data); // You might need one more loop here for finalData
})

Nodejs make an array and print it outside of loop

2 Answers2