Edit in JSFiddle

/// <summary>Class Module</summary>
/// <description>Module to implement Inheritance.</description>
/// <version>1.0</version>
/// <author>John DeVight</author>
/// <license>
/// Licensed under the MIT License (MIT)
/// You may obtain a copy of the License at
/// http://opensource.org/licenses/mit-license.html
/// </license>

var Class = function () {
  function _defineMethodsAndProperties (cls, def) {
    /// <summary>Identify the methods and properties.</summary>
	
    for (var key in def) {
      if (typeof def[key] === "function") {
        // This is a method.
        cls.prototype[key] = def[key];
      } else if (def[key] !== null && (typeof def[key].get === "function" || typeof def[key].set === "function")) {
        // This is a property.
        Object.defineProperty(cls.prototype, key, def[key]);
      } else if (def[key] === null) {
        // This is a member variable.
        Object.defineProperty(cls.prototype, key, {
          value: null,
          writable: true,
          configurable: true,
          enumerable: true
        });
      } else {
        // This is a constant.
        Object.defineProperty(cls.prototype, key, { value: def[key] });
      }
    }
  };
  
  function extend (parent, def) {
    /// <summary>Extend the object with additional methods and properties.</summary>
	
    var cls = null;
    
    if (def.constructor === Object) {
      // The class doesn't have a constructor, so create a constructor
      // that calls the parent constructor.
      cls = function () {
        parent.apply(this, arguments);
      };
    } else {
      // Use the class constructor.
      cls = def.constructor;
    }
    
    cls.prototype = Object.create(parent.prototype);
    cls.prototype.constructor = cls;

    _defineMethodsAndProperties(cls, def);

    return cls;
  };
  
  function define (def) {
    /// <summary>Define a new object.</summary>
	
    var cls = def.constructor || Object.create(Object.prototype);

    _defineMethodsAndProperties(cls, def);

    cls.extend = function (def) {
      return extend(cls, def);
    };
    
    // Return the class definition.
    return cls;
  }
  
  return {
    define: define,
    extend: extend
  }
}();


var $console = $("#console");
function log() { for (var idx = 0; idx < arguments.length; idx++) $console.append("<div><pre>" + arguments[idx].toString() + "</pre></div>") };


/*
 * Define Person Class
 */

var Person = Class.define({
  name: null,
  birthday: null,
 
  constructor: function (name, birthday) {
    this.name = name;
    this.birthday = birthday;
  },
 
  age: {
    get: function () {
      var ageDifMs = Date.now() - this.birthday.getTime();
      var ageDate = new Date(ageDifMs);
      return Math.abs(ageDate.getUTCFullYear() - 1970);
    }
  },
 
  sayHello: function () {
    return "Hello, my name is " + this.name;
  }
});


/*
 * Create instance of Person Class
 */

var p = new Person("John", new Date("1/1/1970"));
log("Create instance of Person Class",
	  "var p = new Person('John', new Date('1/1/1970'));",
    "p.age = " + p.age,
    "p.sayHello() = " + p.sayHello(),
    "<br/>");


/*
 * Define Employee Class
 */

var Employee = Person.extend({
  employer: null,
  constructor: function (name, birthday, employer) {
    Person.call(this, name, birthday);
    this.employer = employer;
  },
  sayHello: function () {
    // Call the parent class sayHello function.
    var greeting = Person.prototype.sayHello.call(this);
    greeting += ". I work for " + this.employer;
    return greeting;
  }
});


/*
 * Create instance of Employee Class
 */

var e = new Employee("John", new Date("1/1/1970"), "Acme Inc.");
log("Create instance of Employee Class",
	  "var e = new Employee('John', new Date('1/1/1970'), 'Acme Inc.');",
    "e.sayHello() = " + e.sayHello(),
    "<br/>");


/*
 * Define StringBuilder Class
 */

var StringBuilder = Class.extend(Array, {
  constructor: function (value) {
    if (typeof value !== "undefined") {
      this.push(value.toString());
    }
  },
  append: function (value) {
    this.push(value.toString());
  },
  appendLine: function (value) {
    this.push(value.toString() + "\r\n");
  },
  toString: function () {
    var result = "";
    for (var idx = 0; idx < this.length; idx++) {
      result += this[idx];
    }
    return result;
  }
});


/*
 * Create instance of StringBuilder Class
 */

var sb = new StringBuilder("Hello");
sb.appendLine(", my name is John.");
sb.append("Nice to meet you.");
log("Create instance of StringBuilder Class",
    "var sb = new StringBuilder('Hello');",
    "sb.appendLine(', my name is John.');",
    "sb.append('Nice to meet you.');",
    "sb.toString() = " + sb.toString());

<div id="console">

</div>

<div style="margin-top:20px;">
<span>Learn about this fiddle at:</span>
<a href="http://jsdev.wikidot.com/blog:2" target="_top">JavaScript Prototypical Inheritance simplified with a Class module</a>
</div>