the default code when you create a new Cloudflare Worker

Cloudflare-new-worker-default.js

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

/**
 * Many more examples available at:
 *   https://developers.cloudflare.com/workers/examples
 * @param {Request} request
 * @returns {Promise<Response>}
 */
async function handleRequest(request) {
  const { pathname } = new URL(request.url);

  if (pathname.startsWith("/api")) {
    return new Response(JSON.stringify({ pathname }), {
      headers: { "Content-Type": "application/json" },
    });
  }

  if (pathname.startsWith("/status")) {
    const httpStatusCode = Number(pathname.split("/")[2]);
    const nocat= new Response("That's not a valid HTTP status code.");
    if(!Number.isInteger(httpStatusCode)) return nocat;

    const cat= await fetch("https://http.cat/" + httpStatusCode);
    return cat.status ===200 ? cat : nocat;
  }

  return fetch("https://welcome.developers.workers.dev");
}