Illustrator Scripting :: Simple / Direct Method To Identify Index Of Selected Item In List Box

I can't seem to figure out a simple/direct method to identify the index of the selected item in a list box.

I feel like I'm missing something, but I can't seem to figure which (if any) property returns an index number if you use it with the .onChange callback for a ListBox.

The following code accomplishes what I need but isn't particularly efficient or elegant and can get muddled if you introduce multiple lists to check.

Any way to duplicate this same behavior with better code
 
var res = "palette {text: 'Example List', properties:{resizeable:true}
pnl: Panel{orientation: 'row',preferredSize: [400,600],
list1: ListBox{preferredSize: [400,550], properties:{multiselect:true,numberOfColumns:2, showHeaders:true,columnTitles: ['List 1', 'Subitem 0']}},
}}"

[Code]...