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Javascript OOP encapsulation trouble

Hi,

I am trying to prove some concepts in OO javascript, with the help of the following code;

[code]

function catClass(){
this.sound = "miau";
this.makeSound = function(){
alert(this.sound);
}
}

var cat = new catClass();

[/code]

This code is held inside the <head> part of the HTML document.

If I call the function cat.makeSound(); then the correct alert will show ("miau").

But if I use this command:

window.onload = cat.makeSound;

Then it shows [undefined] as alert message! That means it loses its reference, I know, and I would like to know how to prevent that.

Thanks in advance!

it works if you do this:

<body onload="cat.makeSound();">

or this:

window.onload = function(){cat.makeSound();};

even (oddly) this:

window.onload = cat.makeSound();

??

oh no, i was getting confused, it just got called at that point, sorry...

THis definitely works:

window.onload = new Function("cat.makeSound();");

so in summary, these definitely work:

window.onload = new Function("cat.makeSound();");

OR

<body onload="cat.makeSound();">

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Put in the onload attribute will works also:
<BODY onload="cat.makeSound.apply(cat);">