This property returns the index of the last row that is currently visible.
var selBox = scene.getBoxById("myListBox");
if (selBox)
{
for (var i = selBox.firstVisibleRowIndex; i < selBox.lastVisibleRowIndex; i++)
{
var bx = selBox.getBoxAtRow(i);
if (bx)
{
bx.setAttribute("label", "Updating...");
}
}
}