prefetch-with-csp.html

Enable keyboard shortcuts

<!DOCTYPE html>

  <html>

    <head>

      <script>

        let link = document.createElement("link");

        link.rel = "prefetch";

        const bc = new BroadcastChannel(new URLSearchParams(location.search).get("uid"));

        link.addEventListener("error", e => bc.postMessage(false));

        link.href = "pass.png";

        document.head.appendChild(link);

        const observer = new PerformanceObserver(entries => {

          const found = entries.getEntriesByName(new URL("pass.png", location.href).href);

          if (found.length)

            bc.postMessage(found[0].encodedBodySize > 0);

});

        observer.observe({entryTypes: ["resource"]});

      </script>

    </head>

  </html>