var DateUtil = function() {

  /**

   * 获取旧历几月几日

   * d : date对象

   * showYear: 是否显示农历年

   */
  this.getLunarDay = function(d, showYear) {
    var CalendarData = new Array(100);
    var madd = new Array(12);
    var tgString = "甲乙丙丁戊己庚辛壬癸";
    var dzString = "子丑寅卯辰巳午未申酉戌亥";
    var numString = "一二三四五六七八九十";
    var monString = "正二三四五六七八九十冬腊";
    var sx = "鼠牛虎兔龙蛇马羊猴鸡狗猪";
    var cYear, cMonth, cDay, TheDate;
    CalendarData = new Array(0xA4B, 0x5164B, 0x6A5, 0x6D4, 0x415B5, 0x2B6, 0x957, 0x2092F, 0x497, 0x60C96, 0xD4A, 0xEA5, 0x50DA9, 0x5AD, 0x2B6, 0x3126E, 0x92E, 0x7192D, 0xC95, 0xD4A, 0x61B4A, 0xB55, 0x56A, 0x4155B, 0x25D, 0x92D, 0x2192B, 0xA95, 0x71695, 0x6CA, 0xB55, 0x50AB5, 0x4DA, 0xA5B, 0x30A57, 0x52B, 0x8152A, 0xE95, 0x6AA, 0x615AA, 0xAB5, 0x4B6, 0x414AE, 0xA57, 0x526, 0x31D26, 0xD95, 0x70B55, 0x56A, 0x96D, 0x5095D, 0x4AD, 0xA4D, 0x41A4D, 0xD25, 0x81AA5, 0xB54, 0xB6A, 0x612DA, 0x95B,
      0x49B, 0x41497, 0xA4B, 0xA164B, 0x6A5, 0x6D4, 0x615B4, 0xAB6, 0x957, 0x5092F,
      0x497, 0x64B, 0x30D4A, 0xEA5, 0x80D65, 0x5AC, 0xAB6, 0x5126D, 0x92E, 0xC96, 0x41A95, 0xD4A, 0xDA5, 0x20B55, 0x56A, 0x7155B, 0x25D, 0x92D, 0x5192B, 0xA95, 0xB4A, 0x416AA, 0xAD5, 0x90AB5, 0x4BA, 0xA5B, 0x60A57, 0x52B, 0xA93, 0x40E95);
    madd[0] = 0;
    madd[1] = 31;
    madd[2] = 59;
    madd[3] = 90;
    madd[4] = 120;
    madd[5] = 151;
    madd[6] = 181;
    madd[7] = 212;
    madd[8] = 243;
    madd[9] = 273;
    madd[10] = 304;
    madd[11] = 334;

    function GetBit(m, n) {
      return (m >> n) & 1;
    }

    function e2c() {
      TheDate = (arguments.length != 3) ? new Date() : new Date(arguments[0], arguments[1], arguments[2]);
      var total, m, n, k;
      var isEnd = false;
      var tmp = TheDate.getFullYear();
      total = (tmp - 1921) * 365 + Math.floor((tmp - 1921) / 4) + madd[TheDate.getMonth()] + TheDate.getDate() - 38;
      if (TheDate.getYear() % 4 == 0 && TheDate.getMonth() > 1) {
        total++;
      }
      for (m = 0;; m++) {
        k = (CalendarData[m] < 0xfff) ? 11 : 12;
        for (n = k; n >= 0; n--) {
          if (total < = 29 + GetBit(CalendarData[m], n)) {
            isEnd = true;
            break;
          }
          total = total - 29 - GetBit(CalendarData[m], n);
        }
        if (isEnd) break;
      }
      cYear = 1921 + m;
      cMonth = k - n + 1;
      cDay = total;
      if (k == 12) {
        if (cMonth == Math.floor(CalendarData[m] / 0x10000) + 1) {
          cMonth = 1 - cMonth;
        }
        if (cMonth > Math.floor(CalendarData[m] / 0x10000) + 1) {
          cMonth--;
        }
      }
    }

    function GetcDateString(showYear) {
      var tmp = "";
      if (showYear) {
        tmp += tgString.charAt((cYear - 4) % 10);
        tmp += dzString.charAt((cYear - 4) % 12);
        tmp += "年 ";
      }

      if (cMonth < 1) {
        tmp += "(闰)";
        tmp += monString.charAt(-cMonth - 1);
      } else {
        tmp += monString.charAt(cMonth - 1);
      }
      tmp += "月";
      tmp += (cDay < 11) ? "初" : ((cDay < 20) ? "十" : ((cDay < 30) ? "廿" : "三十"));
      if (cDay % 10 != 0 || cDay == 10) {
        tmp += numString.charAt((cDay - 1) % 10);
      }
      return tmp;
    }

    function GetLunarDay(solarYear, solarMonth, solarDay) {
      if (solarYear < 1921 || solarYear > 2020) {
        return "";
      } else {
        solarMonth = (parseInt(solarMonth) > 0) ? (solarMonth - 1) : 11;
        e2c(solarYear, solarMonth, solarDay);
        return GetcDateString(showYear);
      }
    }

    if (!d) {
      var d = new Date();
    }
    return GetLunarDay(d.getFullYear(), d.getMonth() + 1, d.getDate());
  }

  return this;
}();

//alert(DateUtil.getLunarDay(null)) //当天的农历日期

//alert(DateUtil.getLunarDay(new Date("1988-02-06"))) //腊月十九

//alert(DateUtil.getLunarDay(new Date("1988-02-06"), true)) //丁卯年 腊月十九

原址:gitcode