<!DOCTYPE html>
<body>
<script>
let channel = new MessageChannel();
channel.port1.onmessage = event => {
    if (event.data === 'intercepted') {
        const iframe = document.querySelector('iframe');
        iframe.sandbox = '';
        navigator.serviceWorker.controller.postMessage({ type: 'ack' });
    }
};
navigator.serviceWorker.controller.postMessage({ type: 'register', port: channel.port2 }, [channel.port2]);
</script>
<iframe src='inner'></iframe>
</body>
