npm install git://github.com/malinkie/node-mac.git

//Get it!
var mac = require('node-mac');

//Use it

//MAC attempts to find hosts MAC address based on commands in config.js set for the returned value of process.platform
//stdout from this command is searched though for corrosponding reg ex pattern and the first match is returned.
mac.MAC(function(err, res){
    console.log(res); // response will be string representation of mac address.
});

//isMAC returns true if given string is a valid representatio of a MAC Address
//false otherwise
var isThisStringAMacAddress = mac.isMAC("12:34:56:78:90:AB")