How can you listen on port 80 with Node?
Trick question! You should not try to listen with Node on port 80 (in Unix-like systems) - to do so you would need superuser rights, but it is not a good idea to run your application with it.
Still, if you want to have your Node.js application listen on port 80, here is what you can do. Run the application on any port above 1024, then put a reverse proxy like nginx in front of it.