checking for object code variables loaded before proceeding

I have some variables that get passed to my AS3 flash movie through the object code: (myMovie.swf?myVariable=xxx). My Flash movie is a single page of actionscript (package, constructor etc) single-frame movie. I recall in AS2 and before these sorts of variables often did not load right away and I traditionally had to setup a loop to check for the existence of variable values, and then allow the movie to proceed once the variables finally loaded.

How do I do this sort of thing in my new AS3 format. Do I need to concern myself with the load time for these variables? Is there a specific way to access variables that have been passed to flash through the object code?

I need to make sure the values for those variables exist before my code proceeds and I'm not sure exactly how to do that in this new structure.

Any help is appreciated.