Should I throw an error or return a rejected promise inside an async function? [duplicate]

Answer 1

A throw within a Promise/Promise chain will automatically cause that Promise/Promise Chain to be rejected.

const myFunc = input => {
  return new Promise((resolve, reject) => {
    if (badInput) {
      throw new Error('failed')
    }

    return resolve(sns.createTopic(input).promise())
  })
}

return myFunc('some input')
  .then(result => { 
    // handle result
  })
  .catch(err => { console.log(err) }) // will log 'failed'

However, your myCustomFunction isn't wrapped in a Promise, it is using throw before the Promise is returned by sns.createTopic().promise(). To create and return a Promise already in a rejected state you would use Promise.reject(new Error('failed')) instead of throw.