Development Flash ActionScript

package {
    import flash.display.Sprite;
    import flash.events.MouseEvent;
    
    public class Main extends Sprite {
        private var _sprite:Sprite;
    
        public function Main(  ) {
            _sprite = new Sprite(  );
            addChild(_sprite);
            _sprite.graphics.beginFill(0xffffff);
            _sprite.graphics.drawRect(0, 0, 400, 400);
            _sprite.graphics.endFill(  );
            _sprite.addEventListener(MouseEvent.MOUSE_DOWN, onMouseDown);
            _sprite.addEventListener(MouseEvent.MOUSE_UP, onMouseUp);
        }
        private function onMouseDown(event:MouseEvent):void {
            _sprite.graphics.lineStyle(1, 0, 1);
            _sprite.graphics.moveTo(mouseX, mouseY);
            _sprite.addEventListener(MouseEvent.MOUSE_MOVE, onMouseMove);
        }
        
        private function onMouseUp(event:MouseEvent):void
        {
            _sprite.removeEventListener(MouseEvent.MOUSE_MOVE, onMouseMove);
        }
        private function onMouseMove(event:MouseEvent):void {
            _sprite.graphics.lineTo(mouseX, mouseY);
        }
    }
}