Conditional response

const handler: ExportedHandler = {
  async fetch(request) {
    const BLOCKED_HOSTNAMES = ["nope.mywebsite.com", "bye.website.com"];
    // Return a new Response based on a URL's hostname
    const url = new URL(request.url);
    if (BLOCKED_HOSTNAMES.includes(url.hostname)) {
      return new Response("Blocked Host", { status: 403 });
    }
    // Block paths ending in .doc or .xml based on the URL's file extension
    const forbiddenExtRegExp = new RegExp(/\.(doc|xml)$/);
    if (forbiddenExtRegExp.test(url.pathname)) {
      return new Response("Blocked Extension", { status: 403 });
    }
    // On HTTP method
    if (request.method === "POST") {
      return new Response("Response for POST");
    }
    // On User Agent
    const userAgent = request.headers.get("User-Agent") || "";
    if (userAgent.includes("bot")) {
      return new Response("Block User Agent containing bot", { status: 403 });
    }
    // On Client's IP address
    const clientIP = request.headers.get("CF-Connecting-IP");
    if (clientIP === "1.2.3.4") {
      return new Response("Block the IP 1.2.3.4", { status: 403 });
    }
    // On ASN
    if (request.cf && request.cf.asn == 64512) {
      return new Response("Block the ASN 64512 response");
    }
    // On Device Type
    // Requires Enterprise "CF-Device-Type Header" zone setting or
    // Page Rule with "Cache By Device Type" setting applied.
    const device = request.headers.get("CF-Device-Type");
    if (device === "mobile") {
      return Response.redirect("https://mobile.example.com");
    }
    console.error(
      "Getting Client's IP address, device type, and ASN are not supported in playground. Must test on a live worker"
    );
    return fetch(request);
  },
};

export default handler;