JQuery :: DatePicker - Determine Number Of Days Between Two Dates

I have searched Datepicker, the forums and the internet in general to find the way to determine the number of days between two dates using Datepicker. My inputs are named: Starts, Ends, Days. I found the code below, but cannot get it to work.

// calculates reservation duration
function resDuration(#Starts, #Ends) {
var date1 = new Date(#Starts.value);
var date2 = new Date(#Ends.value);
var minutes = 1000*60;
var hours = minutes*60;
var days = hours*24;
var diff = Math.abs(date2.getTime() - date1.getTime());
return round(diff / days);
}
/* put that value in elapsed days field */
$('#Days').val(diff);
I will then do validation on the result - input field "Days".