It would be awesome if Intel replied to this! I have wondered how to use UART under Node myself.
As you can see in Re: intel edison python with uart, Arfoll (The Architect of libmraa & UPM) says that UART in MRAA is not available yet. All it does right now is enable the muxes for you and can return the correct tty device to use. Check MRAA: Uart Class Reference for more information about the UART class reference.
Thank you for the prompt response. I'll try to use MRAA to activate the Serial communication and then use a library like node-serialport to accomplish it.