如何正确使用try / catch，promise catch和async功能？

Question

This is how my upload function looks like at the moment. I'm using apollo mutation in that to upload a file.

I do not understand how to use try/catch and catch of the promise (which client.mutate() is) correctly. Also I declared the upload function as async .

So I guess I'm mixing some things up :-(

How do I catch errors correctly?

Do I need both catches? Shouldn't I replace try/catch if I'm using a async function?

export default async function upload (client) {
  try {
    return client.mutate({
      mutation: uploadsMutation
    }).catch(err => {
      console.error(err)
    })
  } catch (error) {
    Alert.alert('Error', 'Could not upload files')
  }
}

Answer 1

async and await have to be used hand in hand - meaning nothing is automatically 'awaited' without using the await keyword. In your example you're just returning the Promise returned from client.mutate .

export default async function upload (client) {
  try {
    return await client.mutate({
      mutation: uploadsMutation
    });
  } catch (error) {
    Alert.alert('Error', 'Could not upload files')
  }
}

Bear in mind your upload function is also returning a Promise by being async . So calling code should handle it appropriately.