Typescript. Try call api again if got any errors

I have function that calls API and returns result based on response. But sometimes i could receive error or something else goes wrong. I want my code to try again until good response is received.

Example code:

for(let i = 0; i < someValues.length; i++) {
    await Test(someValues[i]);
}

async function Test(someValue: string): Promise<SomeObject | null> {
    try {
        const response: any = await someapi.call(someValue); // if got some error from api (connect etc.) then try again 
        if(response) {
            return response;
        }

        return null;
    }
    catch(err) {
        console.log(err);
        setTimeout(async () => {
            await Test(someValue);
        }, 100);
    }
}

Is this code will work? If first try will get api error, what would this loop above receive as response?

Also getting this error in Promise<SomeObject | null> :

Function lacks ending return statement and return type does not include 'undefined'

Solution

The problem is that you're not returning anything in your catch block, so the function is implicitly returning undefined. If you want a delay before retry (a good call) you'll need to manage it differently.

Something like this would work:

for(let i = 0; i < someValues.length; i++) {
    await Test(someValues[i]);
}

async function Test(someValue: string): Promise<SomeObject | null> {
    try {
        const response: any = await someapi.call(someValue); // if got some error from api (connect etc.) then try again 
        if(response) {
            return response;
        }

        return null;
    }
    catch(err) {
        console.log(err);
        return new Promise(resolve => setTimeout(async () => {
            resolve(await Test(someValue));
        }, 100));
    }
}

Alternatively, a slightly cleaner way you could do it is something like this in that block:

// Wait 100ms
await new Promise(resolve => setTimeout(resolve, 100));
// Retry
return await Test(someValue);

And a warning, if the call fails, you're going to infinitely recurse. You probably want to track some kind of count of attempts so you can abort at some point.