Update app.js

app.js

@@ -98,7 +98,9 @@ wss.on('connection', ws => {
   ws.on('close', () => {
     if (currentRoom && rooms.has(currentRoom)) {
       rooms.get(currentRoom).delete(ws);
+      
     }
+    currentRoom = null;
     console.log("room close")
   });
 });