Question

This is for a system that essentially allows you to set the first date for a given event, then to set the recurrence period.

Eg. I set a date for a week from now, 19/07/2012, so I know that I have to put the cat out with the milk. I also set it to be a weekly notification, so in future weeks I want to be notified of the same.

That original date sits in my database, which is fine for week 1, but in week 2 I need to return the date as the original plus 1 week.

On the face of it, that may seem straightforward, but I need to make sure I can account for leap years and different recurrence frequencies (fortnightly, monthly, yearly, whatever).

I’d like to keep this as a javascript implementation – because it’s quicker and I feel probably would require less code than updating dates in the database. Maybe it’s not achievable, any pointers would be excellent.

I think these may be a starting point:

Given a start date , how to calculate number of years till current date in javascript

Given a date, how can I efficiently calculate the next date in a given sequence (weekly, monthly, annually)?

Update, I’ve written the below to return the amount of time to add in each different case, from there I can just use the answer below:

var strDate = $(this).find('.next').text();
            var frequency = $(this).find('.occurs').text();
            var frmDate = getDateObject(strDate);
            var toDate = new Date();

            var days = parseInt(Math.floor((frmDate - toDate) / 86400000));

            if(days < 0) {
                // find out how many WHOLE 'frequencies' have passed
                var weeks = Math.ceil(0 - (days / 7));
                var months = Math.ceil(0 - (monthDiff(toDate,frmDate)));
                var years = Math.ceil(months / 12);
                //alert(days + '/' + weeks + '/' + fortnights + '/' + months + '/' + quarters + '/' + years);

                if(frequency == 'Weekly') { frmDate.add(weeks).weeks(); }
                if(frequency == 'Fortnightly') { frmDate.add(weeks*2).weeks(); }
                if(frequency == 'Monthly') { frmDate.add(months).months(); }
                if(frequency == 'Quarterly') { frmDate.add(months*3).months(); }
                if(frequency == 'Annually') { frmDate.add(years).years(); }

                var newdate = frmDate.toString("dd/MM/yyyy");
                //alert(newdate);

                $(this).find('.next').text(newdate);
            }

Answer 1

Also, the SQL implementation for this would be using DATEADD:

http://sql-plsql.blogspot.com/2010/07/dateadd.html

You don’t have to worry about special dates like leap year and so forth, because most Date functions take care of that.

Alternatively, you can use the getDate(), getMonth() as the other user suggested.
var today = new Date();
today.setDate(today.getDate() + numberOfDaysToAdd);