Using nested async await function calls

Question

I have a very simple code I'm trying to debug. I have an async function:

async function updateResult(event){

  let result = db.fetchResult(event.ProcessId);
  return result;

}

And I'm calling this from another simple async function:

exports.processEvent = async (event) => {
  try {

    let promises = [];


    const controls = await db.fetchControls(event.EventCode);
    
    if (controls) {     
      
       promises = controls.map((control) => {
         console.log(control);
         control.map(x => this.updateResult(event));
        
       });
           
     }

    return Promise.allSettled(promises);
  }
  catch (err) {
    console.error(err);
  }
};

The problem is that in exports.processEvent, the content of db.fetchControls(event.EventCode) is executed to completion (a few logics and a db getItem call).

But the call to db.fetchResult(event.ProcessId) via this.updateResult(x.Id, x.Version, event) does NOT complete executing the fetchResult tasks (a few other logics a db GET call).

I feel like fetchResult returns prematurely. What am I doing wrong?

try Promise.all()

Abdullah Mohammad Motiullah
– Abdullah Mohammad Motiullah

2022-05-25 03:29:24 +00:00
Commented May 25, 2022 at 3:29 — Abdullah Mohammad Motiullah
– Abdullah Mohammad Motiullah, Commented May 25, 2022 at 3:29
is fetchResult itself an async or promise?

Ricky Mo
– Ricky Mo

2022-05-25 03:37:48 +00:00
Commented May 25, 2022 at 3:37 — Ricky Mo
– Ricky Mo, Commented May 25, 2022 at 3:37

jfriend00 · Accepted Answer · 2022-05-25 03:29:26Z

1

.map() is NOT promise-aware. It does not wait for any of the promises in your callback to complete. So, in this piece of code:

control.map(x => this.updateResult(x.Id, x.Version, event));

It just runs through the entire array ignoring all the promises that are returned and thus NOTHING waits for those promises.

You can fix that by returning those promises to the higher level .map() which you are then awaiting with Promise.all():

  promises = controls.map((control) => {
     console.log(control);
     return Promise.all(control.map(x => this.updateResult(x.Id, x.Version, event)));
  });

answered May 25, 2022 at 3:29

jfriend00

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1 Comment

Mohammad Najar Over a year ago

Thank you very much .. Being a noob here this solved the problem.

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