server: listen to port 80 && extract subdomain from req

deno.json

···
 {
   "tasks": {
-    "dev": "deno run --watch --allow-net --allow-env=HOSTNAME,PORT main.ts"
+    "dev": "PORT=8000 deno run --watch --allow-net --allow-env=HOSTNAME,PORT main.ts"
   },
   "imports": {}
 }

main.ts

···
 const ROOT_DOMAIN = Deno.env.get("HOSTNAME") || "localhost";
+const PORT = Number(Deno.env.get("PORT")) || 80;
+
 const SUBDOMAIN_REGEX = new RegExp(`.+(?=\\.${ROOT_DOMAIN}$)`, "gm");
 
-Deno.serve(
-  { port: parseInt("" + Deno.env.get("PORT")) || 8000, hostname: ROOT_DOMAIN },
-  (req) => {
-    const reqUrl = new URL(req.url);
-    const subdomain = reqUrl.hostname.match(SUBDOMAIN_REGEX)?.at(0);
+Deno.serve({ port: PORT, hostname: ROOT_DOMAIN }, (req) => {
+  const reqUrl = new URL(req.url);
+  const subdomain = reqUrl.hostname.match(SUBDOMAIN_REGEX)?.at(0)?.split(".");
 
-    return new Response(
-      `Could not resolve domain "${subdomain ?? ""}${subdomain ? "." : ""}${ROOT_DOMAIN}"`,
-      {
-        status: 404,
-      }
-    );
-  }
-);
+  return new Response(
+    `Could not resolve domain "${subdomain.join(".")}.${ROOT_DOMAIN}"`,
+    {
+      status: 404,
+    }
+  );
+});