xhr-with-progress.js

const formData = new FormData();
const URL = '/path-to-something';
var req = new XMLHttpRequest();

formData.append('file', /* a file */);

req.upload.addEventListener('progress', (e) => {
    if (!e.lengthComputable) return;
    console.log(`${(Math.round((e.loaded/e.total)*100))}% done`);
});
req.onload = () => console.log('all done');
req.onerror = () => console.log('an error happened');
                                
req.open('POST', URL, true);
req.send(formData);