Save confirm Javascript

Hi, I'm not wery well in Java.. I've do this code, when I set a Date in 'DataVendita' I want to get a Save Confirm, but it don't works..
var TS = Runner.getControl(pageid, 'Targa');

var DV = Runner.getControl(pageid, 'DataVendita');

TS.addCSS('highlight');

TS.addStyle('font-size: 12px;font-weight:bold; color: red;');

TS.addStyle('text-transform: uppercase;');
DV.on('change', function(e){

if (this.getValue() !=null)

{

this.on('beforeSave', function(formObj, fieldControlsArr, pageObj)

{

if (confirm('Sei sicuro di voler inserire la data di vendita?'))

return true;

else

return false;

}

)}

});