Логика: Как сохранить предыдущее значение изменяющейся переменной ?

[udaaff]

package
{
	import flash.display.Sprite;
	import flash.events.MouseEvent;
	import flash.text.TextField;
	import flash.text.TextFieldAutoSize;
 
	public class Main extends Sprite
	{
		public function Main()
		{
			super();
 
			createChilden();
		}
 
		private var textField:TextField;
 
		private var lastIndex:int;
 
		private function textField_mouseMoveHandler(event:MouseEvent):void
		{
			var currentIndex:int = textField.getCharIndexAtPoint(textField.mouseX, textField.mouseY);
 
			if (lastIndex != currentIndex)
			{
				lastIndex = currentIndex;
 
				trace(lastIndex);
			}
 
		}
 
		private function createChilden():void
		{
			textField = new TextField();
			textField.text = "some text asdfasdfasdfasdfasdfasdfasdfasdfasdf";
			textField.autoSize = TextFieldAutoSize.LEFT;
			textField.border = true;
			addChild(textField);
 
			textField.addEventListener(MouseEvent.MOUSE_MOVE, textField_mouseMoveHandler);
		}
	}
}