I am not sure if the above answer would work .. I think it does not ..
cause dayName[now.getDay()+8] would look for an item in array with index 8+ and there are just 7 days (indexes 0-6) so it would produce an error ..
you can rather use this simple code
Code:
<script>
// current date
var now = new Date();
// our new date
var newDate = new Date();
// let's move 3 days to past
newDate.setDate(now.getDate()-3);
// now let's add 5 hours
newDate.setHours(now.getHours()+5);
// we can add 2 months as well
newDate.setMonth(now.getMonth()+2);
</script>
I think you get the point ...