refactor: use 'String#startsWith' & replace if-then-else (#5501)

Author: noritaka1166

lib/Server.js

@@ -3130,7 +3130,7 @@ class Server {
 
         // support "." as a subdomain wildcard
         // e.g. ".example.com" will allow "example.com", "www.example.com", "subdomain.example.com", etc
-        if (allowedHost[0] === ".") {
+        if (allowedHost.startsWith(".")) {
           // "example.com"  (value === allowedHost.substring(1))
           // "*.example.com"  (value.endsWith(allowedHost))
           if (
@@ -3217,12 +3217,7 @@ class Server {
       hostname.endsWith(".localhost") ||
       hostname === this.options.host;
 
-    if (isValidHostname) {
-      return true;
-    }
-
-    // disallow
-    return false;
+    return isValidHostname;
   }
 
   /**