Prerender New Worker

prerender.worker.js

// User agents handled by Prerender
const BOT_AGENTS = [
  // Search Engines
  "googlebot",
  "adsbot-google",
  "apis-google",
  "mediapartners-google",
  "google-safety",
  "feedfetcher-google",
  "googleproducer",
  "google-site-verification",
  "bingbot",
  "yandexbot",
  "yabrowser",
  "yahoo",
  "baiduspider",
  "naver",
  "seznambot",
  "sznprohlizec",
  "qwantbot",
  "ecosia",
  "duckduckbot",
  "duckassistbot",
  "applebot",
  // Social Media
  "facebookexternalhit",
  "facebookcatalog",
  "facebookbot",
  "meta-externalagent",
  "twitterbot",
  "linkedinbot",
  "whatsapp",
  "slackbot",
  "pinterest",
  "pinterestbot",
  "tiktok",
  "tiktokspider",
  "bytespider",
  "discordbot",
  // SEO Tools
  "semrushbot",
  "ahrefsbot",
  "chrome-lighthouse",
  "screaming-frog",
  "oncrawlbot",
  "botifybot",
  "deepcrawl",
  "lumar",
  "rogerbot",
  "dotbot",
  // AI Bots
  "gptbot",
  "chatgpt",
  "oai-searchbot",
  "chatgpt-user",
  "claudebot",
  "google-extended",
  "perplexitybot",
  "perplexity-user",
  "youbot",
  "amazonbot",
  "anthropic-ai",
  "claude-web",
  "ccbot",
  "mistralai-user",
  // Other Known Bots & Crawlers
  "embedly",
  "quora link preview",
  "showyoubot",
  "outbrain",
  "pinterest/0.",
  "developers.google.com/+/web/snippet",
  "vkshare",
  "w3c_validator",
  "redditbot",
  "flipboard",
  "tumblr",
  "bitlybot",
  "skypeuripreview",
  "nuzzel",
  "google page speed",
  "qwantify",
  "bitrix link preview",
  "xing-contenttabreceiver",
  "google-inspectiontool",
  "telegrambot",
  // Testing
  "integration-test"
];

// These are the extensions that the worker will skip prerendering
// even if any other conditions pass.
const IGNORE_EXTENSIONS = [
  ".js",
  ".css",
  ".xml",
  ".less",
  ".png",
  ".jpg",
  ".jpeg",
  ".gif",
  ".pdf",
  ".doc",
  ".txt",
  ".ico",
  ".rss",
  ".zip",
  ".mp3",
  ".rar",
  ".exe",
  ".wmv",
  ".doc",
  ".avi",
  ".ppt",
  ".mpg",
  ".mpeg",
  ".tif",
  ".wav",
  ".mov",
  ".psd",
  ".ai",
  ".xls",
  ".mp4",
  ".m4a",
  ".swf",
  ".dat",
  ".dmg",
  ".iso",
  ".flv",
  ".m4v",
  ".torrent",
  ".woff",
  ".ttf",
  ".svg",
  ".webmanifest",
];

export default {
  /**
   * Hooks into the request, and changes origin if needed
   */
  async fetch(request, env) {
    return await handleRequest(request, env).catch(
      (err) => new Response(err.stack, { status: 500 })
    );
  },
};

/**
 * @param {Request} request
 * @param {any} env
 * @returns {Promise<Response>}
 */
async function handleRequest(request, env) {
  const url = new URL(request.url);
  const userAgent = request.headers.get("User-Agent")?.toLowerCase() || "";
  const isPrerender = request.headers.get("X-Prerender");
  const pathName = url.pathname.toLowerCase();
  const lastDot = pathName.lastIndexOf(".");
  const extension = lastDot > -1 ? pathName.substring(lastDot).toLowerCase() : "";

  // Prerender loop protection
  // Non robot user agent
  // Ignore extensions
  if (
    isPrerender ||
    !BOT_AGENTS.some((bot) => userAgent.includes(bot.toLowerCase())) ||
    (extension.length && IGNORE_EXTENSIONS.includes(extension))
  ) {
    return fetch(request);
  }

  // Build Prerender request
  const newURL = `https://service.prerender.io/${request.url}`;
  const newHeaders = new Headers(request.headers);

  newHeaders.set("X-Prerender-Token", env.PRERENDER_TOKEN);
  newHeaders.set("X-Prerender-Int-Type", "CloudFlare");

  return fetch(new Request(newURL, {
    headers: newHeaders,
    redirect: "manual",
  }));
}

return fetch(new Request(newURL, {
  headers: newHeaders,
  redirect: "manual",
}));

is perfectly fine if the request always succeeds.

But when service.prerender.io returns an error (for example, rate-limited, timeout, or a 5xx),
Cloudflare will raise “Error: No response!” if the fetch promise rejects

Good to wrap the fetch in a try/catch and provide a fallback:

try {
  const prerenderResp = await fetch(new Request(newURL, {
    headers: newHeaders,
    redirect: "manual",
  }));

  if (prerenderResp.ok) return prerenderResp;
  return fetch(request); // fallback to normal site
} catch (err) {
  console.error("Prerender fetch failed:", err);
  return fetch(request);
}

Without this fallback, any Prerender downtime causes “No response!” from your Worker.

Unfortunately this didnt work despite following all the steps supplied here: https://docs.prerender.io/docs/cloudflare-integration-v2
We ended up asking Lovable for step by step instructions on how to do this and got a working version from there. When I put the code above through a code checker it highlighted a number of issues found, hence why it wouldnt deploy and work for us.