testbed-deckarts-workers-dev

addEventListener("fetch", (event) => {
  event.respondWith(
    handleRequest(event.request).catch(
      (err) => new Response(err.stack, { status: 500 })
    )
  );
});

const addPreloadAfter = (href) => ({
  element: (el) => {
    el.after(`
<!--testbed-->
<link rel="preload" href="${href}" />
<!--/testbed-->`, { html: true });
  }
});

const addImportanceHigh = () => ({
  element: (el) => {
    el.setAttribute("importance", "high");
  }
});

async function handleRequest(request) {
  const url = new URL(request.url);
  const host = request.headers.get('x-host');
  const bypassTransform = request.headers.get('x-bypass-transform') || false;
  const acceptHeader = request.headers.get('accept');
  const { searchParams } = new URL(request.url);
  let lcpHref = searchParams.get("lcp");

  if (!lcpHref) {
    return new Response(
`
<h1>SEO for Developers Testbed</h1>
<form action="https://testbed.deckart.workers.dev/" method="get">
  <label for="lcp">Path to LCP:</label>
  <input style="min-width: 350px;" type="text" name="lcp" id="lcp" value="path">
  <button>Test</button><br>
  <input type="checkbox" id="importance" name="importance" value="high" disabled>
  <label for="importance">Add Importance High? </label>
</form>
`, {
    headers: {
      "content-type": "text/html;charset=UTF-8",
    }});
  }

  const counter = parseInt(await KV.get('counter') || 0);

  if (!host || counter > 1000) {
    return new Response('hit limit exceeded or x-host missing', {status: 403});
  } else {
    await KV.put("counter", counter + 1);
  }

  url.hostname = host

  if ((acceptHeader
    && acceptHeader.indexOf('text/html') >= 0)
    && (!bypassTransform
    || (bypassTransform
    && bypassTransform.indexOf('true') === -1))) {

    const response = await fetch(url.toString(), request);
    const newResponse = new Response(response.body, response);

    return new HTMLRewriter()
      .on('link', {
        element: el => {
          const link_href = el.getAttribute('href');
          const link_rel = el.getAttribute('rel');
          const link_as = el.getAttribute('as');
          if (link_href && link_href.startsWith('/')) {
            el.setAttribute('href', 'https://' + host + link_href);
          }
        }
      })
      .on('script', {
        element: el => {
          const script_src = el.getAttribute('src');
           if (script_src && script_src.startsWith('/')) {
             el.setAttribute('src', 'https://' + host + script_src);
           }
        }
      })
      .on('img', {
        element: el => {
          const img_src = el.getAttribute('src');
          if (img_src && img_src.startsWith('/')) {
            el.setAttribute('src', 'https://' + host + img_src);
          }
        }
      })
      .on('title', addPreloadAfter('https://testbed.deckart.workers.dev' + lcpHref))
      // .on('article:first-of-type.stream-article > div.article-image > a > img.image', addImportanceHigh())
      .transform(newResponse);
  }

  return fetch(url, request);
}