How to reject in async/await syntax?

0 votes

How can I reject a promise that returned by an async/await function?

e.g. Originally

foo(id: string): Promise<A> {
  return new Promise((resolve, reject) => {
    someAsyncPromise().then((value)=>resolve(200)).catch((err)=>reject(400))
  });
}

Translate into async/await

async foo(id: string): Promise<A> {
  try{
    await someAsyncPromise();
    return 200;
  } catch(error) {//here goes if someAsyncPromise() rejected}
    return 400; //this will result in a resolved promise.
  });
}

So, how could I properly reject this promise in this case?

Sep 23 in Java-Script by kartik
• 30,630 points
25 views

1 answer to this question.

0 votes

Hello @kartik,

 throw an Error wrapping the value, which results in a rejected promise with an Error wrapping the value:

} catch (error) {
    throw new Error(400);
}

You can also just throw the value, but then there's no stack trace information:

} catch (error) {
    throw 400;
}

Alternately, return a rejected promise with an Error wrapping the value, but it's not idiomatic:

} catch (error) {
    return Promise.reject(new Error(400));
}

Hope it helps!!

ThanK you!!

answered Sep 23 by Niroj
• 66,420 points

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