相关疑难解决方法(0)

我有以下代码:

    class Animal
        constructor: (@name) -> 
        say: () -> console.log "Hello from animal called #{ @name }"

    class Dog extends Animal

        say: () ->
            super.say()
            console.log "Hello from dog called #{ @name }"

    a = new Animal('Bobby')
    a.say()

    d = new Dog("Duffy")
    d.say()            

结果不是

Hello from animal called Bobby
Hello from animal called Duffy
Hello from dog called Duffy

但是我收到以下错误:

Hello from animal called Bobby
Hello from animal called Duffy
Uncaught TypeError: Cannot call method 'say' of undefined

为什么超级未定义？如何调用父方法以扩展它？谢谢