Hmm will it work this way?

app.js

@@ -95,13 +95,16 @@ async function initialize() {
     });
   }
 
-  readConfigFromFile();
-  config.rooms.forEach(room => {
-    addRoomToList(room);
-  });
+  const configExists = fs.existsSync("./config.json");
+  if (configExists) {
+    readConfigFromFile();
+    config.rooms.forEach(room => {
+      addRoomToList(room);
+    });
+  }
 
   const registerDiv = document.querySelector('#register');
-  if (registerDiv && config.userName !== '') {
+  if (registerDiv && !configExists) {
     registerDiv.classList.remove('hidden');
   }