Input timestamp into last cell

I work on a script to input timestamp in the lastcell when all previus cells are modified. The following is not working.

function timestamp() {  var archivo =SpreadsheetApp.getActiveSpreadsheet();  var ss = archivo.getSheetByName("No Contact");  var activa = ss.getActiveCell();  var valor =activa.getValue();  var filaActiva = activa.getRow();  var colActiva =activa.getColumn();  var lastcell =ss.getLastColumn();  if(filaActiva>=2 && (colActiva>=2) && archivo.getActiveSheet()){    if(activa.getLastCell().getValue()){      }else{    lastcell.setValue(new Date()).setNumberFormat("MM/dd-HH:mm");    }  }}function onEdit(){  timestamp()}