LunarMonthCalender.js

let LunarCalendarDay = 0;
const LunarCalendarTable = [
    0x04AE53, 0x0A5748, 0x5526BD, 0x0D2650, 0x0D9544, 0x46AAB9, 0x056A4D, 0x09AD42, 0x24AEB6, 0x04AE4A, 
    0x6A4DBE, 0x0A4D52, 0x0D2546, 0x5D52BA, 0x0B544E, 0x0D6A43, 0x296D37, 0x095B4B, 0x749BC1, 0x049754, 
    0x0A4B48, 0x5B25BC, 0x06A550, 0x06D445, 0x4ADAB8, 0x02B64D, 0x095742, 0x2497B7, 0x04974A, 0x664B3E, 
    0x0D4A51, 0x0EA546, 0x56D4BA, 0x05AD4E, 0x02B644, 0x393738, 0x092E4B, 0x7C96BF, 0x0C9553, 0x0D4A48, 
    0x6DA53B, 0x0B554F, 0x056A45, 0x4AADB9, 0x025D4D, 0x092D42, 0x2C95B6, 0x0A954A, 0x7B4ABD, 0x06CA51, 
    0x0B5546, 0x555ABB, 0x04DA4E, 0x0A5B43, 0x352BB8, 0x052B4C, 0x8A953F, 0x0E9552, 0x06AA48, 0x6AD53C, 
    0x0AB54F, 0x04B645, 0x4A5739, 0x0A574D, 0x052642, 0x3E9335, 0x0D9549, 0x75AABE, 0x056A51, 0x096D46, 
    0x54AEBB, 0x04AD4F, 0x0A4D43, 0x4D26B7, 0x0D254B, 0x8D52BF, 0x0B5452, 0x0B6A47, 0x696D3C, 0x095B50, 
    0x049B45, 0x4A4BB9, 0x0A4B4D, 0xAB25C2, 0x06A554, 0x06D449, 0x6ADA3D, 0x0AB651, 0x093746, 0x5497BB, 
    0x04974F, 0x064B44, 0x36A537, 0x0EA54A, 0x86B2BF, 0x05AC53, 0x0AB647, 0x5936BC, 0x092E50, 0x0C9645, 
    0x4D4AB8, 0x0D4A4C, 0x0DA541, 0x25AAB6, 0x056A49, 0x7AADBD, 0x025D52, 0x092D47, 0x5C95BA, 0x0A954E, 
    0x0B4A43, 0x4B5537, 0x0AD54A, 0x955ABF, 0x04BA53, 0x0A5B48, 0x652BBC, 0x052B50, 0x0A9345, 0x474AB9, 
    0x06AA4C, 0x0AD541, 0x24DAB6, 0x04B64A, 0x69573D, 0x0A4E51, 0x0D2646, 0x5E933A, 0x0D534D, 0x05AA43, 
    0x36B537, 0x096D4B, 0xB4AEBF, 0x04AD53, 0x0A4D48, 0x6D25BC, 0x0D254F, 0x0D5244, 0x5DAA38, 0x0B5A4C, 
    0x056D41, 0x24ADB6, 0x049B4A, 0x7A4BBE, 0x0A4B51, 0x0AA546, 0x5B52BA, 0x06D24E, 0x0ADA42, 0x355B37, 
    0x09374B, 0x8497C1, 0x049753, 0x064B48, 0x66A53C, 0x0EA54F, 0x06B244, 0x4AB638, 0x0AAE4C, 0x092E42, 
    0x3C9735, 0x0C9649, 0x7D4ABD, 0x0D4A51, 0x0DA545, 0x55AABA, 0x056A4E, 0x0A6D43, 0x452EB7, 0x052D4B, 
    0x8A95BF, 0x0A9553, 0x0B4A47, 0x6B553B, 0x0AD54F, 0x055A45, 0x4A5D38, 0x0A5B4C, 0x052B42, 0x3A93B6, 
    0x069349, 0x7729BD, 0x06AA51, 0x0AD546, 0x54DABA, 0x04B64E, 0x0A5743, 0x452738, 0x0D264A, 0x8E933E, 
    0x0D5252, 0x0DAA47, 0x66B53B, 0x056D4F, 0x04AE45, 0x4A4EB9, 0x0A4D4C, 0x0D1541, 0x2D92B5          
];
const MonthAdd = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334];

function LunarCalendar(year, month, day) {
    let Spring_NY = 0;
    let Sun_NY = 0;
    let StaticDayCount = 0;
    let index = 0;
    let flag = 0;

    if (((LunarCalendarTable[year - 1901] & 0x0060) >> 5) === 1) {
        Spring_NY = (LunarCalendarTable[year - 1901] & 0x001F) - 1;
    } else {
        Spring_NY = (LunarCalendarTable[year - 1901] & 0x001F) + 30;
    }

    Sun_NY = MonthAdd[month - 1] + day - 1;

    if ((year % 4 === 0) && (month > 2)) {
        Sun_NY += 1;
    }

    if (Sun_NY >= Spring_NY) {
        Sun_NY = Sun_NY - Spring_NY;
        month = 1;
        index = 1;
        flag = 0;

        if ((LunarCalendarTable[year - 1901] & (0x80000 >> (index - 1))) === 0) {
            StaticDayCount = 29;
        } else {
            StaticDayCount = 30;
        }

        while (Sun_NY >= StaticDayCount) {
            Sun_NY -= StaticDayCount;
            index += 1;

            if (month === ((LunarCalendarTable[year - 1901] & 0xF00000) >> 20)) {
                flag = ~flag;
                if (flag === 0) {
                    month += 1;
                }
            } else {
                month += 1;
            }

            if ((LunarCalendarTable[year - 1901] & (0x80000 >> (index - 1))) === 0) {
                StaticDayCount = 29;
            } else {
                StaticDayCount = 30;
            }
        }

        day = Sun_NY + 1;
    } else {
        Spring_NY -= Sun_NY;
        year -= 1;
        month = 12;

        if (((LunarCalendarTable[year - 1901] & 0xF00000) >> 20) === 0) {
            index = 12;
        } else {
            index = 13;
        }

        flag = 0;

        if ((LunarCalendarTable[year - 1901] & (0x80000 >> (index - 1))) === 0) {
            StaticDayCount = 29;
        } else {
            StaticDayCount = 30;
        }

        while (Spring_NY > StaticDayCount) {
            Spring_NY -= StaticDayCount;
            index -= 1;

            if (flag === 0) {
                month -= 1;
            }

            if (month === ((LunarCalendarTable[year - 1901] & 0xF00000) >> 20)) {
                flag = ~flag;
            }

            if ((LunarCalendarTable[year - 1901] & (0x800000 >> (index - 1))) === 0) {
                StaticDayCount = 29;
            } else {
                StaticDayCount = 30;
            }
        }

        day = StaticDayCount - Spring_NY + 1;
    }

    LunarCalendarDay |= day;
    LunarCalendarDay |= (month << 6);

    if (month === (LunarCalendarTable[year - 1901] & 0xF00000) >> 20) {
        return 1;
    } else {
        return 0;
    }
}

// Example
const y = 2008
const m = 8
const d = 16

console.log((LunarCalendar(y, m, d) === 1) ? "Leap" : "");
console.log(`${(LunarCalendarDay & 0x3C0) >> 6}/${LunarCalendarDay & 0x3F}`);