How to handle error in async/await function?

Question

I have a function like this:

async getPatient(patientId: string): Promise<PatientDTO> {
    const patient = await PatientDAO.getPatients({ id: patientId })

    if (patient.length === 0) {
        throw new NotFoundError("Patient Not Found!")
    }

    return patient[0]
}

But I got an error UnhandledPromiseRejectionWarning: Error: Patient Not Found!

This happened cause I have used async function. How can I make this code running properly?

Does this answer your question? [How to properly implement error handling in async/await case](https://stackoverflow.com/questions/48685872/how-to-properly-implement-error-handling-in-async-await-case) — Roy, Jul 08 '21 at 07:02
@ManuelSpigolon just for getting data from server using fetch — Fahri Bullseye, Jul 08 '21 at 07:27
@roy for my case, PatientDAO not trowed any error, I was used custom error if the function return empty array — Fahri Bullseye, Jul 08 '21 at 07:36

score 1 · Answer 1 · answered Jul 08 '21 at 07:02

In order to manage errors in an async function, you have to use a try/catch block:

async getPatient(patientId: string): Promise<PatientDTO> {
    try {
      const patient = await PatientDAO.getPatients({ id: patientId })

      return patient[0]
    } catch (error) {
        // Do whatever you may want with error
        throw error;
    }
    
}

I should mention, that if you simply want to throw the error thats received from getPatients theres no need for a try/catch block at all. Its only needed if you wish to modify the error or perform an extra action according to the error that was thrown.

It's just return null – Fahri Bullseye Jul 08 '21 at 07:34 — Fahri Bullseye, Jul 08 '21 at 07:34

score 0 · Answer 2 · answered Jul 08 '21 at 07:07

0

You have 2 options: First one is try/catch block with await keyword. Please notice that await has to be used in async function.

try {
    const patient = await getPatient(foo);
    // handle your data here
} catch(e) {
    // error handling here
}

Second one is catch function

getPatient(foo)
    .then(patient => {
        // handle your data here
    }).catch(error => {
        // error handling here
    });

answered Jul 08 '21 at 07:07

Piotr Duperas

26
3

In this case I want to check if patient exist in my database, I throw the Error if function return empty array. I tried for the first code but not working. – Fahri Bullseye Jul 08 '21 at 07:30

How to handle error in async/await function?

2 Answers2