Wait on async method in while loop

Question

I have a while loop that loops from one date to the other date. And I want to submit some data to the firebase realtime database.

I want to submit, and wait till the result is back. And then go to the next iteration.

var loop = moment(startDate, 'MM-DD-YYYY').toDate();
var end = moment(endDate, 'MM-DD-YYYY').toDate();

while(loop <= end){

   firebaseAdmin.database().ref('test/data').set({}).then(function(){

   }).catch(function(error) {                 

   });

   const newDate = loop.setDate(loop.getDate() + 1);
   loop = new Date(newDate);  

}

The firebase database uses promises. How can I use them to go further in the loop when the insert is done. And how do I know that everything is done so I can return?

Fals · Accepted Answer · 2018-02-26 16:35:21Z

2

You can do this recursively, given that you want to continue only if your current request succeeded, like this:

var loop = moment(startDate, 'MM-DD-YYYY').toDate();
var end = moment(endDate, 'MM-DD-YYYY').toDate();

function fetchDataRec(loop, end)
{
  if(loop <= end) return;

  firebaseAdmin.database().ref('test/data').set({}).then(function(){
      if(/*check if you want to continue*/) {
         const newDate = loop.setDate(loop.getDate() + 1);
         loop = new Date(newDate);
         fetchDataRec(loop, end);// loop while refactored to recursion
      }
   }).catch(function(error) {                 

   });
}
fetchDataRec(loop, end);

https://www.sitepoint.com/recursion-functional-javascript/

edited Feb 26, 2018 at 16:35

answered Feb 26, 2018 at 16:27

Fals

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Madara's Ghost · Accepted Answer · 2018-02-26 16:30:18Z

0

There are several ways (you could use .reduce() to create a chain of promises for example)

But the best way these days is to use an async function:

async function insertMany(startDate, endDate) {
  var loop = moment(startDate, 'MM-DD-YYYY').toDate();
  var end = moment(endDate, 'MM-DD-YYYY').toDate();

  while(loop <= end){
    try {
      await firebaseAdmin.database().ref('test/data').set({});
      // bla bla
    } catch (e) {
      // bla bla
    }
    const newDate = loop.setDate(loop.getDate() + 1);
    loop = new Date(newDate);  
  }

  return 'all done!';
}

Or something similar to that, I didn't run it.

answered Feb 26, 2018 at 16:30

Madara's Ghost

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1 Comment

Fals Over a year ago

Does async/await work everywhere? Isn't it just for node v6+?

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