Alternative to nested promises

I'm trying to create a function that gets a presigned s3 url (call 1) and does a put to s3. The only way I'm able to figure it out in my head is using a nested promise which I understand to be an anti-pattern.

Writing it out in js/pseudocode

uploadfile(file){
  return new Promise((resolve, reject) => {
    axios.get(get-presigned-s3url).then((url) =>{ return axios.put(file)}
  })
}

let filePromises = files.forEach(file => uploadfile(file));
promises.all((filePromises) => notifyUpload(filePromises));

I need to return a promise from the uploadfile function to wait for all the promises to resolve. What's the right way to handle this scenario?

Solution

Since axios.get returns a Promise already, you don't need to construct another one around it with new Promise.

files.forEach won't work, because forEach returns undefined. Use .map instead, so you have an array of Promises.

const uploadFile = file => axios.get(url)
    .then((url) => { return axios.put(file); });

Promise.all(
  files.map(uploadFile)
)
  .then(notifyUpload)
  .catch(handleErrors);