extensions required: live server that's all.
I am going to assume that you already have previous programming knowledge and that you have tried to use socket.io and for any reason it has not worked for you, so I will share you the code that I used to make my first socket and that it worked especially for the problem of cors.
else it'll deny you access and will throw cors error
now that it works you have the basic to begin on websockets, finally you have to search more and better info to make upgrade your code
feel free to feedback
and there you go, my first basic beginners socket.io post