how to get the reference of one object's parent

Parent/child relationships pertain to display list only. When you instantiate ClassB in ClassA - it becomes a property of the scope where you instantiated it - NOT A CHILD. Note the word "scope" - variable may belong to class or function, etc.

Instance of a class is totally agnostic to who instantiated it unless you pass a reference of the class that made the instance. Nevertheless, of a class is a DisplayObject, once it is placed on display list - it knows who the parent is.

Instance can be either property or child or both proeprty and child.

class ClassB{

public function ClassB()

{

var classa:ClassA=new ClassA();

trace("my parent is"+classa.myVar.);

}

}

should work