[skysurfer]

And here the Javascript implementation:

 /**
  * @param year   the year of which easter has to be calculated
  * @param option calculate other date than easter (offset in days)
  * @returns JD of Easter date
  */

function easter(year, option)
{
    var golden, solar, lunar, pfm, dom, tmp, easterday,d;

    /* the Golden number */
    golden = (year % 19) + 1;

    if ( year <= 1752 )
    {
        /* JULIAN CALENDAR */
        /* the "Dominical number" - finding a Sunday */
        dom = (year + Math.floor(year/4) + 5) % 7;
        if (dom < 0) dom += 7;

        /* uncorrected date of the Paschal full moon */
        pfm = (3 - (11*golden) - 7) % 30;
        if (pfm < 0) pfm += 30;
    }
    else
    {
        /* GREGORIAN CALENDAR */
        /* the "Dominical number" - finding a Sunday */
        dom = (year + Math.floor(year/4) - Math.floor(year/100) + Math.floor(year/400)) % 7;
        if (dom < 0) dom += 7;

        /* the solar and lunar corrections */
        solar = Math.floor((year-1600)/100) - Math.floor((year-1600)/400);
        lunar = Math.floor((Math.floor((year-1400) / 100) * 8) / 25);

        /* uncorrected date of the Paschal full moon */
        pfm = (3 - (11*golden) + solar - lunar) % 30;
        if (pfm < 0) pfm += 30;
    }

    /* corrected date of the Paschal full moon - days after 21st March */
    if ((pfm == 29) || (pfm == 28 && golden > 11))
      pfm--;

    tmp = (4-pfm-dom) % 7;
    if (tmp < 0) tmp += 7;

    /* easterday as the number of days after 21st March */
    easterday = pfm + tmp + 1;

//alert(year + ' ' + tmp + ' ' + easterday);

    if (easterday < 11)
        d = datetojd(new Array(year,3, easterday+21,12,0,0));
    else
        d = datetojd(new Array(year,4, easterday-10,12,0,0));
    if (arguments.count > 1)
      d += option;
    d = Math.floor(d);
    return d;
}


function datetojd(datestr)
{
  n = datestr;  // array assumed y-m-d-h-i-s
  var date = new Date(n[0],n[1]-1, n[2], n[3], n[4], n[5]);
   var jd = date.getTime()/86400000 + 2440588 - (date.getTimezoneOffset()/1440);
//alert(jd + ' ' + (date.getTime()/86400000 + 2440588));
   return jd;
}