Edit in JSFiddle

//http://www.jermywells.com
//js polymorphism

var Person = function(){
    this.openDrawerMessage = 'sees clothes in dresser drawer';   
    this.openDrawer = function(){
        return this.openDrawerMessage;
    }
}

var BankTeller = function(){
    this.openDrawerMessage = 'sees cash in cash drawer. cha ching!'; 
}
BankTeller.prototype = new Person();
BankTeller.prototype.openDrawer = function(){
    return this.openDrawerMessage;
}

var StayAtHomeDad = function(){
    this.openDrawerMessage = 
        'sees kitchen knife [for cutting crusts off of a sammich].'
}
StayAtHomeDad.prototype = new Person();
StayAtHomeDad.prototype.openDrawer = function(){
    return this.openDrawerMessage;
}

//get an instance of each object
var person = new Person();
var teller = new BankTeller();
var stayAtHomeDad = new StayAtHomeDad();


document.body.innerHTML +=
    'A Person is a Person/an instanceof a Person: ' +
    '<b>' + (person instanceof Person) + '</b><br />' +
    'The Person\'s open drawer result is: ' + 
    '<b>' + person.openDrawer() + '</b><br /><br />';

document.body.innerHTML +=
    'A Bank Teller is a Person/an instanceof a Person: ' +
    '<b>' + (teller instanceof Person) + '</b><br />' +
    'The Bank Teller\'s open drawer result is: ' + 
    '<b>' + teller.openDrawer() + '</b><br /><br />';

document.body.innerHTML +=
    'A Stay-At-Home-Dad is a Person/an instanceof a Person: ' +
    '<b>' + (stayAtHomeDad instanceof Person) + '</b><br />' +
    'The Stay-At-Home-Dad\'s open drawer result is: ' + 
    '<b>' + stayAtHomeDad.openDrawer() + '</b><br /><br />';