ghl404

addEventListener("fetch", event => {
  event.respondWith(handleRequest(event.request));
});

async function fetchAndStreamNotFoundPage(resp) {
  const { status, statusText } = resp;
  const { readable, writable } = new TransformStream();

  const response = await fetch("https://yourwebsite.com/404");
  const { headers } = response;

  response.body.pipeTo(writable);

  return new Response(readable, {
    status,
    statusText,
    headers
  });
}

function isHTMLContentTypeAccepted(request) {
  const acceptHeader = request.headers.get("Accept");
  return (
    typeof acceptHeader === "string" && acceptHeader.indexOf("text/html") >= 0
  );
}

async function handleRequest(request) {
  const response = await fetch(request);

  if (response.status === 404 && isHTMLContentTypeAccepted(request)) {
    return fetchAndStreamNotFoundPage(response);
  }

  return response;
}