<!DOCTYPE html>
<body>
<script>
(async () => {
  const sxg_path = 'sxg/sxg-subresource.sxg';
  const scipt_sxg_path = 'sxg/sxg-subresource-script.sxg';
  const scipt_path = 'sxg-subresource-script.js';
  const wait_for_prefetch = new Promise((resolve) => {
    new PerformanceObserver((list) => {
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        if (e.name.endsWith(scipt_sxg_path)) {
          resolve();
        } else if (e.name.endsWith(scipt_path)) {
          window.parent.postMessage(
            scipt_path + ' should not be prefetched', '*');
        }
      }
    }).observe({ entryTypes: ['resource'] });
  });

  const link = document.createElement('link');
  link.rel = 'prefetch';
  link.href = sxg_path;
  document.body.appendChild(link);
  await wait_for_prefetch;
  location.href = sxg_path;
})()
</script>
</body>
