HTTP2 server push

Push static assets to a client's browser without waiting for HTML to render.
const CSS = `body { color: red; }`;
const HTML = `
<!doctype html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>Server push test</title>
    <link rel="stylesheet" href="http2_push/h2p/test.css">
</head>
<body>
    <h1>Server push 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 HTTP/2 for the CSS file
    return new Response(HTML, {
      headers: {
        'content-type': 'text/html',
        'Link': '</http2_push/h2p/test.css>; rel=preload; as=style',
      },
    });
  }
}

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