using ActiveX

I try to use an activeX with javascript. There are some methods are
implemented in interface xxx from this activeX. How do I refer it with
queryInterface(). the activex document says:

interface xxx: Iunknown{

HRESULT _stdcall zzzz(...)
....

}

My javascript is as following:

var my = new ActiveXObject("AAA.yyy");
my.LoadFromFile("Simple");
//above is ok
my.zzzz(....);
//this doesn't work