Nodejs Synchronous for loop

Question

Can some one help me to run the below loop in a synchronous manner? As the below code is getting executed asynchronously,value of arra is always returning null.

var arra=[];
//Query doctors collection and get necessary details           
for (i = 0; i <arr.length; i++) {
    var docregistrationnumber = arr[i].docregistrationnumber
    var registrationAuthority = arr[i].docregistrationauthority                
    doctorData.getDoctorByRegNumber(docregistrationnumber,registrationAuthority,function(data){
        console.log(JSON.stringify(data))  
        arra.push(data)                
    })
} 
console.log(arra)

No, it's not possible to run an asynchronous function synchronously. You can time the calls sequentially, though. Use a recursive approach. — Bergi
– Bergi, Commented May 1, 2018 at 15:46

Taki · Accepted Answer · 2018-05-01 16:00:41Z

5

you can try async/await

var arra = [];
//Query doctors collection and get necessary details    

async function getData() {
  for (i = 0; i < arr.length; i++) {
    var docregistrationnumber = arr[i].docregistrationnumber
    var registrationAuthority = arr[i].docregistrationauthority
    var data = await doctorData.getDoctorByRegNumber(docregistrationnumber, registrationAuthority);

    arra.push(data);   
  }

  return arra;
}  

getData().then( data => console.log(data) );

answered May 1, 2018 at 16:00

Taki

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2 Comments

Sona Shetty Over a year ago

Which npm package shud i install to work with async/await library

Ben West Over a year ago

It's not a library, it's a language feature. You need to use Node 7.6 or newer. getDoctorByRegNumber also must return a Promise for this to work.

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