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? — goto
– goto, Commented May 29, 2021 at 12:03
Use for...of and the question above to figure out how to return a value from an asynchronous call. — goto
– goto, Commented May 29, 2021 at 12:04

hoangdv · Accepted Answer · 2021-05-29 12:17:59Z

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, 2021 at 12:17

answered May 29, 2021 at 12:06

hoangdv

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10 Comments

mdkamrul Over a year ago

you not used the query variable, can you please use query variable as I used?

hoangdv Over a year ago

@mdkamrul Updated. But why?

mdkamrul Over a year ago

because I have used this var at other place

mdkamrul Over a year ago

how can I use results object at loop?

hoangdv Over a year ago

Do you mean results 's element? just change _ to what you want.

|

Naren · Accepted Answer · 2021-05-29 12:31:35Z

0

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
})

edited May 29, 2021 at 12:31

answered May 29, 2021 at 12:17

Naren

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