NodeJS find query inside for loop results after the loops end

Question

var user_id = '98-XXXXXXXX'

Contact.find({user_id: user_id})
.exec(function (err, results) {
  if (err) { 
    return next(err); 
  }
    var finalArray = [];
    for(var i = 0; i< results[0].Total; i++) {

      if(results[0].Contacts[i].name != "SPAM") {

       for(var j = 0; j < results[0].Contacts[i].phoneNumbers.length; j++){

           var number = results[0].Contacts[i].phoneNumbers[j].number
           number = number.replace(/ /g,'');
            var user_id = number.substr(number.length - 10); 

                Login.find({user_id:user_id})
                .exec(function(err,results) {
                if(err) {
                return next(err); }

                    var intCount = results.length;
                        if (intCount > 0)
                        {
                            console.log('called')
                            finalArray.push(results[0])
                            console.log(finalArray)
                        } 
               });

            }
         }

        //console.log(i,results[0].Total - 1);
        //if(i == results[0].Total - 1)



    } 
                    console.log('Ended Here',finalArray)
                    var responseTosend = {"message":finalArray,"user_id":user_id}
                    return  res.send(responseTosend);

});

EndedHere[] this is coming up first empty, after that i got the result of login.find query which is correct. Any ideas how to get the finalArray after all the calculation. Thanks in advance

abskmj · Accepted Answer · 2018-12-19 10:14:36Z

1

Since the functions are returning promises within the loops, the code execution has to wait till all those promises are resolved. Consider using Promise.all or Promise.map to wait. Reference

answered Dec 19, 2018 at 10:14

abskmj

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1 Comment

Nivesh Over a year ago

I am new to nodeJS can you please give a snippet of code for a reference how it really works

BenSower · Accepted Answer · 2018-12-19 12:05:23Z

As already mentioned, a structure like this, will not return the results, but the intermediate functions or objects before they are finished, since nodejs does not know it should await the results first.

const x = [1,2,3]
let results = []

for (let i = 0; i < x.length; i++){
  results.push(someAsyncJobLikeADatabaseCall(x[i]))
}

// this will not return the results, but the intermediate async objects/functions
console.log(results)

Here is a better version using promises and the .map function. Notice, how we replaced the for loop with .map() (which you could see as a shorthand for .forEach + push() or for() + push(). Mongoose returns Promises if configured right, so you don't even have to manually define them and we can directly return them in .map.

const x = [1,2,3]
let results = []

async function getAsyncResults(array){
  // map returns an array, this time, an array of promises
  const promises = x.map(number => someAsyncJobLikeADatabaseCall(number))
  // Promise.all resolves, if all promises in the array have been resolved
  return Promise.all(promises)
}

try {
  let results = await getAsyncResults(x)
  // this will return the results you expect.
  console.log(results)
} catch (err) {
  console.log('Some error', err)
}

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