JavaScript prototype template

ClassPrototype.js

var Person = (function() {
  // private statics
  var greetHeader = "Welcome,";
  var greetFooter = "! Have a nice day!";
  
  // constructor -- define instance specific stuff
  function Person(isMale, firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
    
    // modifiable public field
    this.userData = null;
	
    // instance private fields
    Object.defineProperty(this, "_gender", {
      enumerable: false,
      configurable: false,
      writable: false,
      value: (isMale ? "Mr" : "Ms")
    });
    
    // prevent extension of instance 
    Object.seal(this);
  }
  
  // public final class statics (accessed via Person.serialVersionUID)
  Person.serialVersionUID = "AA2q9AalA729L";
  // freeze class 
  Object.freeze(Person);
  
  
  // instance public methods
  Person.prototype.constructor = Person;
  Person.prototype.toString = function() {
    return greetHeader + " " + this._gender + " " + this.firstName + " " + 
      this.lastName + " " + greetFooter;
  }
  // instance public fields (getters & setters)
  var fields = ['firstName','lastName'];
  fields.forEach(function(fieldName) {
    Object.defineProperty (Person.prototype, fieldName, {
      configurable: false,
      enumarable: true,
      get: function () { return this["_"+fieldName]; },
      set: function (value) { this["_"+fieldName] = value; }
    });
  });
  // public final instance statics (accessed via personInstance.serialVersionUID)
  Person.prototype.serialVersionUID = "AA2q9AalA729L";
  // freeze prototype
  Object.freeze(Person.prototype);
  
  return Person;
})();

var max = new Person(true, "Max", "Payne");
var sarah = new Person(false, "Sarah", "Connor");
console.log(max.toString());
console.log(max);
console.log(sarah.toString());
console.log(sarah);
console.log();

console.log(Person.serialVersionUID);
console.log(max.serialVersionUID);
console.log();

sarah.lastName = max.lastName;
console.log(max.toString());
console.log(sarah.toString());
console.log();

max.toString = function() { return ""};
console.log(max.toString());
max.gender = "Ms";
console.log(max.toString());
console.log();

sarah.foo = "bar";
console.log(sarah.foo);
Person.foo = "bar";
console.log(Person.foo);
console.log();

console.log(sarah.userData);
sarah.userData = "I fight Skynet!";
console.log(sarah.userData);
console.log();