How can I call the built-in swfs function from Javascript?

I have a swf which is a preloader for another swf (game). I need to respond to a swf game from Javascript but can't figure out how to do it. I can call back to the preloader by registering the callback with ExternalInterface.

I tried document.getElementById("preloader")

which returns an object. preloader

has a public property called GameObj

that returns a reference to the game object that was loaded by the preloader.

Problem: document.getElementById("preloader").GameObj

always null

.

Is it possible to do this or do I need a shell call in the preloader?