Why JohnDoe.whoAreYou() does return undefined ?:

```
<html>
<head>
</head>

<body>
  <script>
    var JohnDoe = {
        //public property
        firstName: "John",
        lastName: "Doe",

        //public method
        whoAreYou: function() {
          alert( "I am literal object and my name is " + this.toString());
        },
        whatIsYourAge: function() {
          alert("My age is " + this.Age);
        }               
    };    
  </script>

  <script>
    JohnDoe.Age = 10;
    JohnDoe.toString = function() {this.firstName + " " + this.lastName};
    JohnDoe.whoAreYou();    
    JohnDoe.whatIsYourAge();
  </script>

</body>
</html>

```