Did i can make one unified script file using node.js?

I have some trouble using node.js i want to build an application using node.js which can performs / handling login, register, and chat (for context i tried to build chat apps).
I get some trouble how do i put my code in app.js i assume that app.js are my main form (i comfortable develop desktop apps) which i think it will mess with another code for login and register...
Any suggestion ? any help are appreciated :) github