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103 Early Hints

Allow a client to request static assets while waiting for the HTML response.

To ensure Early Hints are enabled:

  1. Log in to the Cloudflare Dashboard and select your account and website.
  2. Go to Speed -> Optimization.
  3. Enable the Early Hints toggle to on.
const CSS = `body { color: red; }`;

const HTML = `
<!doctype html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>Early Hints test</title>
    <link rel="stylesheet" href="/test.css">
</head>
<body>
    <h1>Early Hints test page</h1>
</body>
</html>
`;



async function handleRequest(request) {
  // If request is for test.css, serve the raw CSS
  if (/test\.css$/.test(request.url)) {
    return new Response(CSS, {
      headers: {
        'content-type': 'text/css',
      },
    });
  } else {
    // Serve raw HTML using Early Hints for the CSS file
    return new Response(HTML, {
      headers: {
        'content-type': 'text/html',
        'Link': '</test.css>; rel=preload; as=style',
      },
    });
  }

}



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

});