Date Validation

First convert the date parts to a UTC representation
 
firstDate = Date.UTC(year, month, day, hours, minutes, seconds);
secondDate = Date.UTC(year, month, day, hours, minutes, seconds);
 
now, if(firstDate < secondDate)
 
then firstDate is an earlier date. The Date.UTC method converts the date to a timestamp, 
the number of seconds since midnight of January 1, 1970 according to universal time. So you can do standard math comparisions.
 
 
To calculate the difference between the 2 dates in days.
 
day = 60*60*24; //60 seconds, times 60 minutes, times 24 hours.
 
differenceInDays = Math.abs(secondDate - firstDate) / day;
 
The subtraction will return the difference between the 2 dates in seconds. It will then take the absolute value of that, 
and divide it by the number of seconds in a day, resulting in the number of days between the 2 dates.