If you're going to work with spark core and want to have an arduino for faster development in flaky wifi connections (or whatever reason), use the pin set as an object, so you can change everywhere at once, when switching devices.

hrdwr.js

var pins = {
  spark: {
    servo: 'D0',
    button: 'D7',
    red: 'A0',
    green: 'A1',
    blue: 'A4'
  },
  arduino: {
    servo: 10,
    button: 8,
    red: 3,
    green: 5,
    blue: 6
  }
};

// on spark core
var button = new five.Button(pins.spark.button);
var servo = new five.Servo(pins.spark.servo);

// on arduino
var button = new five.Button(pins.arduino.button);
var servo = new five.Servo(pins.arduino.servo);

// so this will always work on both hardwares
button.on('down', buttonDown);
servo.sweep();