AWS Lambda nodejs - problem with return values from await async function

Question

This is AWS Lambda function awaiting on async function. I can not get returned value. I need to do fetch data in loop as long as there are still some values on the server to be retrieved:

let do_search = true;
while (do_search) {
        const url = 'xxx';
        await fetchData(url)
            .then(response => {
                console.log("fetchData result:", response);
                if (response) {
                    console.log("Stop searching, no more data");
                    do_search = false;
                }
            })
.....

while my fetchData returns false value when there is still more data to be processed. fetchData function:

async function fetchData(url) {
...
console.log("Returning false");
return false;

The problem is even my fetchData returns false, my log are always:

Returning false
fetchData result: true

I have also tried to use other approach with:

 const createModelBInstance = async () => {
            let response = await fetchData(url)
            console.log("fetchData result:", response);
            if (response){
                do_search=false;
            }
           }

           await createModelBInstance();

Based on some examples on this forum. But exactly same problem, my fetchData returns false while "fetchData result: true".

Any working example? That Promise values returned are causing simple code to be very complicated:(

Answer 1

You shouldn't write hard loops in JavaScript. It's single-threaded.

Here's an example of a fetchData method that sleeps for 1 second, then indicates whether or not data is available (available with 10% likelihood, not available 90% likelihood). This is purely to simulate your asynchronous URL fetcher.

const getRandom = (low, count) => {
  return Math.floor((Math.random() * count) + low)
}

const fetchData = () => {
  const promise = new Promise((resolve, reject) => {
    setTimeout(() => {
      const rand = getRandom(1, 10);
      if (rand % 7) {
        resolve({ rand });
      } else {
        resolve({ data: 'Here is the data', rand });
      }
    }, 1000);
  });

  return promise;
}

Here's an example of calling this code on an interval, every 2 seconds, until data becomes available.

const interval = setInterval(() => {
  fetchData().then(rc => {
    console.log(rc);
    if (rc.data) {
      // do something with rc.data
      clearInterval(interval);
    }
  });
}, 2000);

An example of the output:

{ rand: 2 }
{ rand: 10 }
{ rand: 1 }
{ data: 'Here is the data', rand: 7 }