Assistance with date calculation for newbie, please?

// using parts of a date// adjust sName for field and sDateFmt for format of date// input field namevar sName = "Date0";// number of days to addvar nAdd = 3;// date format for input and displayed datevar sDateFmt = 'mm/dd/yyyy';// do not change below this line// get inputted date stringvar sDate = this.getField(sName).value;// convert date string to date objectvar oDate = util.scand(sDateFmt, sDate); // get parts of the datevar nFullYear = oDate.getFullYear(); // full yearvar nMonth = oDate.getMonth(); // zero based monthvar nDate = oDate.getDate(); // date of month// add nAdd days to datenNewDate = nAdd + nDate; // convert to new date objectvar oNewDate = new Date(nFullYear, nMonth, nNewDate);// make date stringvar sNewDate = util.printd(sDateFmt, oNewDate);// set field valueevent.value = sNewDate;

// using date object and milliseconds// adjust sName for field and sDateFmt for format of date// input field namevar sName = "Date0";// number of days to addvar nAdd = 3;// date format for input and displayed datevar sDateFmt = 'mm/dd/yyyy'; // do not change below this line// get inputted date stringvar sDate = this.getField(sName).value;// convert date string to date objectvar oDate = util.scand(sDateFmt, sDate); // define some date constantsvar nSec = 1000; // milliseconds in one secondvar nMin = 60 * nSec; // seconds in one minutevar nHr = 60 * nMin; // minutes in one hourvar nDay = 24 * nHr; // hours in one day // get number of milliseconds from date objectvar nDate = oDate.getTime();// add nAdd days days to datenNewDate = nAdd * nDay + nDate; // convert to new date objectvar oNewDate = new Date(nNewDate);// make date stringvar sNewDate = util.printd(sDateFmt, oNewDate); // set field valueevent.value = sNewDate;