A quick javascript dateDiff function that returns results in terms of days, months and years taking into account variable month lengths and leap years

Javascript dateDiff function to calculate difference in terms of days, months and years

/*
 * Function to calculate the absolute difference in days, months and years between 2 days taking into account variable month lengths and leap years
 * It ignores any time component (ie hours, minutes and seconds)
 *
 */
function dateDiff(dt1, dt2)
{
    /*
     * setup 'empty' return object
     */
    var ret = {days:0, months:0, years:0};

    /*
     * If the dates are equal, return the 'empty' object
     */
    if (dt1 == dt2) return ret;

    /*
     * ensure dt2 > dt1
     */
    if (dt1 > dt2)
    {
        var dtmp = dt2;
        dt2 = dt1;
        dt1 = dtmp;
    }

    /*
     * First get the number of full years
     */

    var year1 = dt1.getFullYear();
    var year2 = dt2.getFullYear();

    var month1 = dt1.getMonth();
    var month2 = dt2.getMonth();

    var day1 = dt1.getDate();
    var day2 = dt2.getDate();

    /*
     * Set initial values bearing in mind the months or days may be negative
     */

    ret['years'] = year2 - year1;
    ret['months'] = month2 - month1;
    ret['days'] = day2 - day1;

    /*
     * Now we deal with the negatives
     */

    /*
     * First if the day difference is negative
     * eg dt2 = 13 oct, dt1 = 25 sept
     */
    if (ret['days'] < 0)
    {
        /*
         * Use temporary dates to get the number of days remaining in the month
         */
        var dtmp1 = new Date(dt1.getFullYear(), dt1.getMonth() + 1, 1, 0, 0, -1);

        var numDays = dtmp1.getDate();

        ret['months'] -= 1;
        ret['days'] += numDays;

    }

    /*
     * Now if the month difference is negative
     */
    if (ret['months'] < 0)
    {
        ret['months'] += 12;
        ret['years'] -= 1;
    }

    return ret;
}