在while循环内使用await是否是个坏习惯

Question

Is it a bad practice to use a await inside a while loop?

I have the following code:

// this is inside a async function
try {
  let res = await api.resource.create(...args) // create resource
  do {
    let res = await api.resource.show(res.body.id)
    if (res.body.status === 'COMPLETED')
      return res.body
  } while(1)
} catch (err) {
  errorHandler(err)
}

I have a couple of questions here:

1. Is it ok to use two res variables?
2. Am I going to use performance because I'm using a await inside a while loop?
3. Is there a better solutin?

Thank you in advance.

Answer 1

Is it ok to use two res variables?

No. The way you are using the inner one, the access in the arguments is always in the temporal dead zone and you will always get an exception.

Am I going to use performance because I'm using a await inside a while loop?

There's nothing wrong with using await in loops, as long as you expect them to run sequentially and not all iterations concurrently.

Is there a better solution?

try {
  let res = await api.resource.create(...args) // create resource
  do {
    res = await api.resource.show(res.body.id)
  } while (res.body.status !== 'COMPLETED')
  return res.body
} catch (err) {
  errorHandler(err)
}

Notice also that if errorHandler comes from a callback parameter, you should drop the entire try / catch and just use .catch(errorHandler) on the promise returned by the call.

Also, while I don't know what api.resource.show does, it looks like you are polling for a result. It would be better if the method would just return a promise that fulfills at the right time. If that is not possible and you need to poll, I would recommend at least some delay between the calls.