gistfile1.js

var person = SC.Object.create({
  firstName: 'John',
  lastName: 'Smith',
  fullName: function () {
    var first = this.get('firstName');
    var last = this.get('lastName');
    return '%@ %@'.fmt(first,last);
  }.property('firstName','lastName').cacheable()
});
person.get('firstName'); // 'John'
person.get('lastName'); // 'Smith'
person.get('fullName'); // 'John Smith'

person.set('firstName','Dan'); // 'Dan'
person.get('fullName'); // 'Dan Smith'