Javascript Function IN or NOT IN

else if (item.get_text() == "SplitTaxes") {
            vdataItemIndex = $find("<%=grdAvailableForSale.MasterTableView.ClientID%>").get_selectedItems()[0];
            var afsSource = vdataItemIndex.get_cell("afsSource").innerHTML;
            var afsSourceDetail = vdataItemIndex.get_cell(afsSourceDetail).innerHTML;
            var mymessage = afsSource.substring(0, 2)
            if (mymessage == "LT")
            args.set_cancel(!confirm("Are you sure you want to split taxes?" + afsSource));
            selectedRows.clear;
            }
            else {
                alert("Tax Split on Lottery Deals Only!");
                selectedRows.clear;
            }
                              

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