Duck type

var Duck = function(){
    this.quack = function(){alert('Quaaaaaack!');};
    this.feathers = function(){alert('The duck has white and gray feathers.');};
    return this;
};
 
var Person = function(){
    this.quack = function(){alert('The person imitates a duck.');};
    this.feathers = function(){alert('The person takes a feather from the ground and shows it.');};
    this.name = function(){alert('John Smith');};
    return this;
};
 
var in_the_forest = function(duck){
    duck.quack();
    duck.feathers();
};
 
var game = function(){
    var donald = new Duck();
    var john = new Person();
    in_the_forest(donald);
    in_the_forest(john);
};
 
game();