I basically having hard times understanding why I cannot overwrite an object property when using inheritance from another object, it goes like this.

var Person = function(firstName, lastName) {

  this.firstName = firstName;

  this.lastName = lastName;

};



Object.defineProperties(Person.prototype, {

  sayHi : {

   value :function() {

     return Hi there;

   },

   enumerable : true,

   writable : true

  },

 fullName : {

   get : function() {

    return this.firstName +   + this.lastName;  

   },

   enumerable : true

  }                      

});





var createEmployee = function(firstName, lastName, ocupation) {

  var employee = new Person(firstName, lastName);

  employee.ocupation = ocupation;  



 Object.defineProperty(employee, sayHi, {

   sayHi : {

    value : function() {

     return Hey I am  + this.firstName;

    }

   }

 });



 return employee;

};



var janeDoe = createEmployee('Jane', 'Doe', 'Actress');

So, accoding to what I understand, I should overwrite the sayHi property on the employee object, however, I get it as undefined.

Could please some1 show me money?

here is the jsfiddle

Best Regards.