const robotsTxtContent = "User-agent: BadBot\nDisallow: /\n";

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

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

  if (url.pathname === "/robots.txt") {
    return new Response(robotsTxtContent, {
      status: 200,
      headers: new Headers({
        "content-type": "text/plain"
      })
    });
  }
  return new Response("Not found", { status: 404 });
}