一个帮助你理解prototype中Class.create()方法的例子

var Animal = Class.create();
Animal.prototype = {
initialize: function(name, sound) {
this.name  = name;
this.sound = sound;
},
speak: function() {
alert(name + " says: " + sound + "!");
}
};
var snake = new Animal("Ringneck", "hissssssssss");
snake.speak();
// -> alerts "Ringneck says: hissssssssss!"
var Dog = Class.create();
Dog.prototype = Object.extend(new Animal(), {
initialize: function(name) {
this.name  = name;
this.sound = "woof";
}
});

var fido = new Dog("Fido");
fido.speak();

// -> alerts "Fido says: woof!"