var Person = Class.create();
Person.prototype = {
  initialize: function(name, age) {
    this.name = name;
    this.age = age;
  },  
  toJSON: function() {
    return ('My name is ' + this.name + 
      ' and I am ' + this.age + ' years old.').toJSON();
  }
};
var john = new Person('John', 49);
Object.toJSON(john);
//-> '"My name is John and I am 49 years old."'