implementing redo undo in flex

See more:

Flex

private var currentIndex:int = 0;

private function txtTemplate_change():void
{
   arrChanges.push(txtTemplate.htmlText);
   currentDataIndex = arrChanges.length - 1;
}

/** Undo changes **/
private function btnUndo_click():void
{
   if(currentDataIndex >= -1)
   {
      txtTemplate.htmlText = arrChanges[currentDataIndex];
      currentDataIndex--;
   }
}

/** Redo Changes **/
private function btnRedo_click():void
{
   if(currentDataIndex+1 < arrChanges.length)
      {
         currentDataIndex++;
         txtTemplate.htmlText = arrChanges[currentDataIndex];
      }
}

i pasted these code in my app i am getting so many errors please provide detailed code for me iam new to this flex