Actionscript :: Bind Exists Property In It?

How can i do binding exists property in actionscript e.g. i want image still in middle aplication..in mxml i do this simple as <mx:Image source="image.jpg" x="{this.width/2}"/> ...i don't know how can i do this simple in actionscript without event handlers... i put this code to application_creationCompleteHandler..something like var image:Image = new Image();image.source="image.jpg";image.x=this.width/2; or have i put this to another function?