How can I calculate the date of Chinese New year In JavaScript?

Question

I need the start date of the Year in Chinese Calendar given the Year that we use on Occident (Gregorian Calendar).

How can I achieve this in code, most usefull JS but any approach will do, or if not does somebody has a list of them that i can put on a DB?

Thanks

Welcome to SO, Please provide the code you tried so far and what's not working to improve the quality of your question — Tamir Klein, Mar 06 '19 at 12:54

score 1 · Answer 1 · answered Mar 06 '19 at 12:45

1

How about using this JS library : https://github.com/commenthol/date-chinese ?

answered Mar 06 '19 at 12:45

vijayakm

43
4

Cees Timmerman · Answer 2 · 2023-01-22T15:18:50.993

If you don't want an entire library, use this snippet i made today:

function get_new_moons(date) {
    const LUNAR_MONTH = 29.5305888531  // https://en.wikipedia.org/wiki/Lunar_month
    let y = date.getFullYear()
    let m = date.getMonth() + 1  // https://stackoverflow.com/questions/15799514/why-does-javascript-getmonth-count-from-0-and-getdate-count-from-1
    let d = date.getDate()
    // https://www.subsystems.us/uploads/9/8/9/4/98948044/moonphase.pdf
    if (m <= 2) {
        y -= 1
        m += 12
    }
    a = Math.floor(y / 100)
    b = Math.floor(a / 4)
    c = 2 - a + b
    e = Math.floor(365.25 * (y + 4716))
    f = Math.floor(30.6001 * (m + 1))
    julian_day = c + d + e + f - 1524.5
    days_since_last_new_moon = julian_day - 2451549.5
    new_moons = days_since_last_new_moon / LUNAR_MONTH
    days_into_cycle = (new_moons % 1) * LUNAR_MONTH
    return new_moons
}

function in_chinese_new_year(date) {
    /* The date is decided by the Chinese Lunar Calendar, which is based on the
    cycles of the moon and sun and is generally 21–51 days behind the Gregorian
    (internationally-used) calendar. The date of Chinese New Year changes every
    year, but it always falls between January 21st and February 20th. */
    return Math.floor(get_new_moons(date)) > Math.floor(get_new_moons(new Date(date.getFullYear(), 0, 20))) ? 1 : 0
}

function get_chinese_new_year(gregorian_year) {
    // Does not quite line up with https://www.travelchinaguide.com/essential/holidays/new-year/dates.htm
    for (let i = 0; i <= 30; ++i) {
        let start = new Date(gregorian_year, 0, 1)
        start.setDate(21 + i)
        if(in_chinese_new_year(start)) return start
    }
}

Usage:

>>> get_chinese_new_year(2023)
Sun Jan 22 2023 00:00:00 GMT+0100 (Midden-Europese standaardtijd)

How can I calculate the date of Chinese New year In JavaScript?

2 Answers2