Difference to Static Date

script

//Set this variable to your initial date to measure time from
let dtOne = new Date("January 1, 1999");

//Date diff function sourced from https://gist.github.com/clecuona/2945438
/*
 * 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;
}

//Set second date as now
let dtTwo = new Date();

//Get the difference from the specified date to now
let dtDiff = dateDiff(dtOne, dtTwo);

//Insert the date period as text at the current cursor position
editor.setSelectedText(dtDiff['years'] + " years, " + dtDiff['months'] + " months, and " + dtDiff['days'] + " days");
//Jump to the end of the text we just inserted
editor.setSelectedRange(editor.getSelectedRange()[0] + editor.getSelectedRange()[1],0);
//Reactivate the editor
editor.activate();