Here is the simple code for AS3 preloader, slightly different from AS2:
this.addEventListener(Event.ENTER_FRAME, loadProgress);
function loadProgress(event:Event):void {
var bytes_loaded:int = this.root.loaderInfo.bytesLoaded;
var bytes_total:int = this.root.loaderInfo.bytesTotal;
var bytes_percent:int = Math.round((bytes_loaded/bytes_total)*100);
trace(bytes_percent + “% is loaded”);
if (bytes_loaded >= bytes_total) {
trace(”This movie is loaded”);
removeEventListener(Event.ENTER_FRAME, loadProgress);
}
};