How to add/subtract dates with JavaScript?

I want to let users easily add and subtract dates using JavaScript in order to browse their entries by date.

The dates are in the format: “mm/dd/yyyy”. I want them to be able to click a “Next” button, and if the date is: ” 06/01/2012″ then on clicking next, it should become: “06/02/2012”. If they click the ‘prev’ button then it should become, “05/31/2012”.

It needs to keep track of leap years, number of days in the month, etc.

Any ideas?

P.S using AJAX to get the date from the server isn’t an option, its a bit laggy and not the experience for the user that the client wants.

Answer

Code:

var date = new Date('2011', '01', '02');
alert('the original date is ' + date);
var newdate = new Date(date);

newdate.setDate(newdate.getDate() - 7); // minus the date

var nd = new Date(newdate);
alert('the new date is ' + nd);

Using Datepicker:

$("#in").datepicker({
    minDate: 0,
    onSelect: function(dateText, inst) {
       var actualDate = new Date(dateText);
       var newDate = new Date(actualDate.getFullYear(), actualDate.getMonth(), actualDate.getDate()+1);
        $('#out').datepicker('option', 'minDate', newDate );
    }
});

$("#out").datepicker();​

JSFiddle Demo

Extra stuff that might come handy:

getDate()   Returns the day of the month (from 1-31)
getDay()    Returns the day of the week (from 0-6)
getFullYear()   Returns the year (four digits)
getHours()  Returns the hour (from 0-23)
getMilliseconds()   Returns the milliseconds (from 0-999)
getMinutes()    Returns the minutes (from 0-59)
getMonth()  Returns the month (from 0-11)
getSeconds()    Returns the seconds (from 0-59)

Good link: MDN Date