fullScr_btn.addEventListener(MouseEvent.CLICK, fullscr);

function fullscr (a:Event)
{
    if (stage.displayState == StageDisplayState.NORMAL)
    {
        ting.width = stage.stageWidth;
        ting.height = stage.stageHeight;
        ting.x = tong.x; ting.y = tong.y;
        stage.displayState = StageDisplayState.FULL_SCREEN;
    }
    else
    {
        ting.width = 640; ting.height = 360;
        ting.x = 300; ting.y = 200;
        stage.displayState = StageDisplayState.NORMAL;
    }
}