notify

gistfile1.js

var data = 42;
var object = {
  get x() {
    return data;
  },
  set x(v) {
    notifier.notify({
      type: 'updated',
      name: 'x',
      oldValue: data
    }); 
    data = v;
  }  
};
var notifier = Object.getNotifier(object);