You can use this function to get a base64 encoded version of a File object for uploading to an API. Works with await, or in a promise chain.

getDataUrl.js

function getDataUrl(file) {
  return new Promise((resolve, reject) => {
    var reader = new FileReader();
    reader.readAsDataURL(file);
    reader.onload = () => resolve(reader.result);
    reader.onerror = err => reject(err);
  });
};