Progress bar with Vue and Axios

I'm making an image uploader, and I'd like to display a progress bar which starts incrementing once a file is selected.

I'm using Axios to access the backend, and have it setup like this:

const BASE_URL = 'http://localhost:3000';

function uploadImage(data, listingId) {
  const url = `${BASE_URL}/listings/${listingId}/images`;
  let config = {
    onUploadProgress(progressEvent) {
      var percentCompleted = Math.round((progressEvent.loaded * 100) /
        progressEvent.total);
      return percentCompleted;
    },
  };
  return axios.post(url, data, config).
      then(x => x.request.response).
      catch(error => error);
}

How can I access the percentCompleted from the Vue side below?

inputDidChange(e) {
  let inputData = e.target.files[0];
  var formData = new FormData();
  formData.append('image', inputData);
  uploadImage(formData, this.listingId).
    then((x) => {
      var xParsed = JSON.parse(x);
      this.newFile = xParsed.image.image.url;
      this.files.push(this.newFile);
      console.log('success');
  });
},