1120: Access of undefined property loader.

Answer 1

private function load() : void {
  var loader:URLLoader = new URLLoader();
  loader.addEventListener(Event.COMPLETE, onComplete);
  loader.load(new URLRequest("external.txt")); 
}

private function onComplete(e:Event):void {
  text1.text = URLLoader(e.target).data; 
}

this should work.

Answer 2

You are not using it right. Your code should look like:

loader.contentLoaderInfo.addEventListener(Event.COMPLETE, onComplete);