Actionscript 3.0 - Eventlistener

button_btn.addEventListener(MouseEvent.MOUSE_OVER, buttonGrow);
button_btn.addEventListener(MouseEvent.MOUSE_OUT, buttonShrink);

function buttonGrow(event:MouseEvent):void
{
button_btn.scaleX = button_btn.scaleY = 1.1;
}

function buttonShrink(event:MouseEvent):void
{
button_btn.scaleX = button_btn.scaleY = 1;
}