Cloudflare Worker Example

const PRERENDER_TOKEN = 'your_prerender_token';
const PRERENDER_URL = 'https://service.prerender.io/';

async function handleRequest(request) {
  const url = new URL(request.url);

  if (shouldPrerender(request)) {
    const prerenderUrl = PRERENDER_URL + url.href + '?token=' + PRERENDER_TOKEN;
    const prerenderResponse = await fetch(prerenderUrl);
    return new Response(prerenderResponse.body, {
      status: prerenderResponse.status,
      statusText: prerenderResponse.statusText,
      headers: prerenderResponse.headers,
    });
  } else {
    return fetch(request);
  }
}

function shouldPrerender(request) {
  const userAgent = request.headers.get('User-Agent') || '';
  const isCrawler = /bot|googlebot|crawler|spider|robot|crawling/i.test(userAgent);
  return isCrawler;
}

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