data.chinahighlights.com/js/chinese-calendar-converter.js

var LC = {
  lunarInfo: new Array(0x04bd8, 0x04ae0, 0x0a570, 0x054d5, 0x0d260, 0x0d950, 0x16554, 0x056a0, 0x09ad0, 0x055d2, 0x04ae0, 0x0a5b6, 0x0a4d0, 0x0d250, 0x1d255, 0x0b540, 0x0d6a0, 0x0ada2, 0x095b0, 0x14977, 0x04970, 0x0a4b0, 0x0b4b5, 0x06a50, 0x06d40, 0x1ab54, 0x02b60, 0x09570, 0x052f2, 0x04970, 0x06566, 0x0d4a0, 0x0ea50, 0x06e95, 0x05ad0, 0x02b60, 0x186e3, 0x092e0, 0x1c8d7, 0x0c950, 0x0d4a0, 0x1d8a6, 0x0b550, 0x056a0, 0x1a5b4, 0x025d0, 0x092d0, 0x0d2b2, 0x0a950, 0x0b557, 0x06ca0, 0x0b550, 0x15355, 0x04da0, 0x0a5d0, 0x14573, 0x052d0, 0x0a9a8, 0x0e950, 0x06aa0, 0x0aea6, 0x0ab50, 0x04b60, 0x0aae4, 0x0a570, 0x05260, 0x0f263, 0x0d950, 0x05b57, 0x056a0, 0x096d0, 0x04dd5, 0x04ad0, 0x0a4d0, 0x0d4d4, 0x0d250, 0x0d558, 0x0b540, 0x0b5a0, 0x195a6, 0x095b0, 0x049b0, 0x0a974, 0x0a4b0, 0x0b27a, 0x06a50, 0x06d40, 0x0af46, 0x0ab60, 0x09570, 0x04af5, 0x04970, 0x064b0, 0x074a3, 0x0ea50, 0x06b58, 0x055c0, 0x0ab60, 0x096d5, 0x092e0, 0x0c960, 0x0d954, 0x0d4a0, 0x0da50, 0x07552, 0x056a0, 0x0abb7, 0x025d0, 0x092d0, 0x0cab5, 0x0a950, 0x0b4a0, 0x0baa4, 0x0ad50, 0x055d9, 0x04ba0, 0x0a5b0, 0x15176, 0x052b0, 0x0a930, 0x07954, 0x06aa0, 0x0ad50, 0x05b52, 0x04b60, 0x0a6e6, 0x0a4e0, 0x0d260, 0x0ea65, 0x0d530, 0x05aa0, 0x076a3, 0x096d0, 0x04bd7, 0x04ad0, 0x0a4d0, 0x1d0b6, 0x0d250, 0x0d520, 0x0dd45, 0x0b5a0, 0x056d0, 0x055b2, 0x049b0, 0x0a577, 0x0a4b0, 0x0aa50, 0x1b255, 0x06d20, 0x0ada0),
  Animals: new Array("Rat", "Ox", "Tiger", "Rabbit", "Dragon", "Snake", "Horse", "Goat", "Monkey", "Rooster", "Dog", "Pig"),
  Gan: new Array("Jia", "Yi", "Bing", "Ding", "Wu", "Ji", "Geng", "Xin", "Ren", "Gui"),
  Zhi: new Array("Zi", "Chou", "Yin", "Mao", "Chen", "Si", "Wu", "Wei", "Shen", "You", "Xu", "Hai"),
  weekDayNames: ["", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"],
  monthName: new Array("January", "February", "March", "April", "May ", "June", "July", "August", "September", "October", "November", "December"),
  lYearDays: function(y) {
      var i, sum = 348
      for (i = 0x8000; i > 0x8; i >>= 1) sum += (LC.lunarInfo[y - 1900] & i) ? 1 : 0
      return (sum + LC.leapDays(y))
  },
  leapDays: function(y) {
      if (this.leapMonth(y)) return ((LC.lunarInfo[y - 1900] & 0x10000) ? 30 : 29)
      else return (0)
  },
  leapMonth: function(y) {
      return (LC.lunarInfo[y - 1900] & 0xf);
  },
  monthDays: function(y, m) {
      return ((LC.lunarInfo[y - 1900] & (0x10000 >> m)) ? 30 : 29);
  },
  newf: function(y, m) {
      return ((LC.lunarInfo[y - 1900] & (0x10000 >> m)) ? 30 : 29);
  },
  lunar: function(objDate) {
      var i, leap = 0,
          temp = 0
      var baseDate = new Date(1900, 0, 31)
      var offset = (objDate - baseDate) / 86400000
      this.dayCyl = offset + 40
      this.monCyl = 14
      for (i = 1900; i < 2050 && offset > 0; i++) {
          temp = LC.lYearDays(i)
          offset -= temp
          this.monCyl += 12
      }
      if (offset < 0) {
          offset += temp;
          i--;
          this.monCyl -= 12
      }
      this.year = i
      this.yearCyl = i - 1864
      leap = LC.leapMonth(i)
      this.isLeap = false
      for (i = 1; i < 13 && offset > 0; i++) {
          if (leap > 0 && i == (leap + 1) && this.isLeap == false) {
              --i;
              this.isLeap = true;
              temp = LC.leapDays(this.year);
          } else {
              temp = LC.monthDays(this.year, i);
          }
          if (this.isLeap == true && i == (leap + 1)) this.isLeap = false
          offset -= temp
          if (this.isLeap == false) this.monCyl++
      }
      if (offset == 0 && leap > 0 && i == leap + 1)
          if (this.isLeap) {
              this.isLeap = false;
          } else {
              this.isLeap = true;
              --i;
              --this.monCyl;
          }
      if (offset < 0) {
          offset += temp;
          --i;
          --this.monCyl;
      }
      this.month = i
      this.day = offset + 1
  },
  get_ganzhi: function(year) {
      var num = year - 1900 + 36;
      return (LC.Gan[num % 10] + " " + LC.Zhi[num % 12]);
  },
  get_animal: function(year) {
      return LC.Animals[(year - 4) % 12];
  },
  get_ganzhiMonth: function(year, month) {
      var num = year - 1900 + 36;
      var gan = ((num % 10) % 5 + 1) * 2;
      gan = gan == 10 ? 0 : gan;
      gan = gan + month;
      gan = gan >= 10 ? gan - 10 : gan;
      var zhi = month + 2;
      zhi = zhi >= 12 ? zhi - 12 : zhi;
      return (LC.Gan[gan] + " " + LC.Zhi[zhi]);
  },
  get_ganzhiDay: function(curDate) {
      var year = curDate.getFullYear();
      var p = [0, 1, 0, 1, 1, 2, 2, 3, 4, 4, 5, 5];
      var y = year >= 2000 ? (100 + year - 2000) : year - 1900;
      var d1 = (y * 5) % 60;
      var d2 = Math.floor(y / 4);
      var m = (curDate.getMonth() + 1) % 2 == 0 ? 30 : 0;
      var d = d1 + d2 + 9 + curDate.getDate() + p[curDate.getMonth()] - m;
      d = d > 60 ? (d - 60) : d;
      var gan = (d % 10 == 0 ? 10 : d % 10) - 1;
      var zhi = (d % 12 == 0 ? 12 : d % 12) - 1;
      if (year % 4 != 0 && curDate.getMonth() < 2) {
          gan = (gan == 9 ? 0 : gan + 1);
          zhi = (zhi == 11 ? 0 : zhi + 1);
      }
      return (LC.Gan[gan] + " " + LC.Zhi[zhi]);
  },
  get_season: function(month) {
      if (month < 6 && month > 2) return "Spring";
      else if (month < 9 && month > 5) return "Summer";
      else if (month < 12 && month > 8) return "Autumn";
      else return "Winter";
  }
}

;function onMonthChange(selmonth, selday, selyear) {
  var selDay = document.getElementById(selday);
  var selMonth = document.getElementById(selmonth);
  var selYear = document.getElementById(selyear);
  var v = selMonth.value;
  if (selDay.options[29 - 1] == null) {
      var varItem = new Option(29, 29);
      selDay.options.add(varItem);
  }
  if (selDay.options[30 - 1] == null) {
      var varItem = new Option(30, 30);
      selDay.options.add(varItem);
  }
  if (v == 1 || v == 3 || v == 5 || v == 7 || v == 8 || v == 10 || v == 12) {
      if (selDay.options[31 - 1] == null) {
          var varItem = new Option(31, 31);
          selDay.options.add(varItem);
      }
  } else if (v == 4 || v == 6 || v == 9 || v == 11) {
      if (selDay.options[31 - 1] != null) {
          selDay.options[31 - 1] = null;
      }
  } else if (v == 2) {
      if (selDay.options[31 - 1] != null) {
          selDay.options[31 - 1] = null;
      }
      if (selDay.options[30 - 1] != null) {
          selDay.options[30 - 1] = null;
      }
      if (selDay.options[29 - 1] != null) {
          vv = selYear.value;
          if ((vv % 4 == 0 && vv % 100 != 0) || vv % 400 == 0) {} else {
              selDay.options[29 - 1] = null;
          }
      }
  }
}

function lunchstr() {
  var reval =
      "<div class=\"yycalbox\">" +
      "<div class=\"yycal_info\">" +
      "<span class=\"yycal_title\">Gregorian</span>" +
      "<span class=\"yycal_title_s\">- Chinese Calendar Converter</span>" +
      "</div>" +
      "<form class=\"form-inline yycal_searchbar\" name=\"yycal\" id=\"yycal\">" +
      "<p><select name=\"themonth\" id=\"themonth\"></select></p>" +
      "<p><select name=\"theday\" id=\"theday\"></select></p>" +
      "<p><select name=\"theyear\" id=\"theyear\"></select></p>" +
      "<input type=\"button\" value=\"Search\" id=\"btnsearch\" name=\"btnsearch\" class=\"sendButton\">" +
      "</form>" +
      "<div id=\"yycal_result\" class=\"yycal_resultbox\">" +
      "<p><span class=\"yycal_stitle\">Gregorian date: </span> <span id=\"searchinfo\"></span></p>" +
      "<p><span class=\"yycal_stitle\">Chinese lunar calendar date: </span> <span id=\"resultinfo\"></span></p>" +
      "<p><span class=\"yycal_stitle\">Chinese zodiac sign: </span>  <span id=\"yycal_zodiac\"></span></p>" +
      "</div>" +
      "</div>";
  return reval;
}
$(function() {
  if (typeof citsLoad != 'undefined') {
      try {
          citsLoad.css(['//data.chinahighlights.com/css/lunarcalendar.css']);
          citsLoad.js(['//data.chinahighlights.com/js/Lunarcalendar.js']);
      } catch (e) {

      }
  }
  var str_LC = lunchstr();
  $('#thelcbox').append(str_LC);
  var myDate = new Date();
  var dayoption = '';
  for (var i = 1; i <= 31; i++) {
      dayoption += '<option value="' + i + '"';
      if (i == myDate.getDate()) {
          dayoption += ' selected';
      }
      dayoption += '>' + i + '</option>';
  }
  $('#theday').html(dayoption);
  var monoption = '';
  var en_month = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
  for (var i = 0; i < 12; i++) {
      monoption += '<option value="' + (i + 1) + '"';
      if (i == myDate.getMonth()) {
          monoption += ' selected';
      }
      monoption += '>' + en_month[i] + '</option>';
  }
  $('#themonth').html(monoption);
  var yearoption = '';
  for (var i = 1930; i < 2023; i++) {
      yearoption += '<option value="' + i + '"';
      if (i == myDate.getFullYear()) {
          yearoption += ' selected';
      }
      yearoption += '>' + i + '</option>';
  }
  $('#theyear').html(yearoption);

  onMonthChange('themonth', 'theday', 'theyear');

  $('#themonth').change(function() {
      onMonthChange('themonth', 'theday', 'theyear');
  });
  $('#theyear').change(function() {
      onMonthChange('themonth', 'theday', 'theyear');
  });
  $('#btnsearch').click(function() {
      var d = document.getElementById("theday").value;
      var m = document.getElementById("themonth").value;
      var y = document.getElementById("theyear").value;
      var curDate = new Date(y, parseInt(m - 1), d);
      var ht = [];
      var lc = new LC.lunar(curDate);
      var txt_searchinfo = LC.monthName[parseInt(m - 1)] + ' ' + d + ', ' + y;
      $('#searchinfo').html(txt_searchinfo);
      var txt_season = LC.get_season(parseInt(m));
      var txt_resultinfo = txt_season + ' (month ' + lc.month + '), date ' + parseInt(lc.day) + ', ' + lc.year + '';
      $('#resultinfo').html(txt_resultinfo);
      var txt_zodiac = '<a target="_blank" href="http:' + '//www.chinahighlights.com/travelguide/chinese-zodiac/' + LC.get_animal(lc.year).toLowerCase() + '.htm">' + LC.get_animal(lc.year) + '</a>';
      $('#yycal_zodiac').html(txt_zodiac);
      //$('#yycal_season').html(txt_season);
      $('#yycal_result').show();
  });
});