Redirect on Complete

new MultipleUpload(document.getElementById('demo-redirect'), {
 uploadUrl: '/api/upload',
 multiple: true,
 onComplete: function(files) {
 var msg = document.getElementById('redirect-msg');
 msg.style.display = '';
 var seconds = 3;
 msg.textContent = files.length + ' file(s) uploaded! Redirecting in ' + seconds + 's...';

 var timer = setInterval(function() {
 seconds--;
 if (seconds <= 0) {
 clearInterval(timer);
 msg.textContent = 'Redirect cancelled (demo mode).';
 // In production: window.location.href = '/thank-you';
 } else {
 msg.textContent = files.length + ' file(s) uploaded! Redirecting in ' + seconds + 's...';
 }
 }, 1000);
 }
});

Moving on when the queue drains

onComplete is the natural place to advance: navigate to the record, close the dialog, refresh the list. It fires once everything in the queue has settled.

Settled includes failed

The queue completes when nothing is left in flight, which includes files that failed and exhausted their retries. Redirecting unconditionally takes the user away from the only screen that could have told them two attachments did not upload — check the state before navigating.