nodejs服务器应用程序有类型错误，如path.join

As i am running my server.js ,it starts of pretty well with the main staring page being loaded up but there i have to enter a nickname to enter any room. As i enter the name and click on the Create chat room button it shows this type of error. Since i am new to building node.js apps ,please help me to solve this issue..The server code is provided below..As i am running my server.js ,it starts of pret