using while loop with async function and setTimeout. Nodejs

Question

I'm trying to create a test, to verify that I've put an item in a dynamoDB table. In order to do so, right after I make a call that should put an Item (vehicle) in the database, I am trying to get the vehicle from the DB.

In my test I want to have a maximum number of retries (5). I want this while loop to be block the thread until my query has resolved to give a vehicle, or tried 5 times. Inside my test I have:

    let count = 0
    let car
    while (!car || count < 5) {
        setTimeout(async () => {
            car = await findVehicle(greenCar.vehicleInfo)
        }, 3000)
        count++
    }

And findVehicle is an asynchronous function that does a get from the dynamoDB table

setTimeout does not return a Promise, await setTimeout does not make sense — CertainPerformance
– CertainPerformance, Commented Dec 7, 2018 at 18:12
Well, you are incrementing count in setTimeout.. You should increment it below it. — Alex G
– Alex G, Commented Dec 7, 2018 at 18:21

Alex G · Accepted Answer · 2018-12-07 18:47:45Z

1

If you want to wait on each iteration you can do this:

let count = 0;
let car;

while (!car || count < 5) {

    await new Promise((resolve) =>
        setTimeout(async () => {
            car = await findVehicle(greenCar.vehicleInfo);
            resolve();
        }, 3000));

    count++
}

So you are resolving the promise you are awaiting after you get your data. Also your function must be async in order to use await. Hope this helps.

answered Dec 7, 2018 at 18:47

Alex G

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