package {
	import flash.display.Sprite;
	import flash.events.Event;

	public class ExampleApplication extends Sprite{
		
		public function ExampleApplication(){
			graphics.lineStyle(1,0,1);
			addEventListener(Event.ENTER_FRAME, onEnterFrame);
		}
		private function onEnterFrame(event:Event):void{
			graphics.lineTo(Math.random() * 400, Math.random() * 400);
		}
	}
}

Got this out of the o'reilly ActionScript 3.0 Cookbook

onEnterFrame Event using Actionscript 3

event

ActionScript 3