This is a question about AS3.0 split

I wrote the code as below, but the list is not separated and saved in the array sm.
What's wrong with my code?
Any help would be appreciated.

var sm:Array = [];

var request:URLRequest = new URLRequest("http://.............../Text/soundList.txt");
// txt file : "a,b,c,d,.........."
var loader:URLLoader = new URLLoader();
loader.load(request);
loader.addEventListener(Event.COMPLETE, completeHandler);

function completeHandler(event:Event):void {
	var str:String = event.target.data;
	//trace(str);  // "a,b,c,d,..............."
	sm = str.split(",");  // comma
	//trace(sm);  // "a,b,c,d,..............."
}
trace(sm.length); // result => 0