function gregorian_to_jalali(gy, gm, gd) {
g_d_m = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334];
if (gy > 1600) {
jy = 979;
gy -= 1600;
} else {
jy = 0;
gy -= 621;
}
gy2 = (gm > 2) ? (gy + 1) : gy;
days = (365 * gy) + (parseInt((gy2 + 3) / 4)) - (parseInt((gy2 + 99) / 100)) + (parseInt((gy2 + 399) / 400)) - 80 + gd + g_d_m[gm - 1];
jy += 33 * (parseInt(days / 12053));
days %= 12053;
jy += 4 * (parseInt(days / 1461));
days %= 1461;
if (days > 365) {
jy += parseInt((days - 1) / 365);
days = (days - 1) % 365;
}
jm = (days < 186) ? 1 + parseInt(days / 31) : 7 + parseInt((days - 186) / 30);
jd = 1 + ((days < 186) ? (days % 31) : ((days - 186) % 30));
return [jy, jm, jd];
}
const dateElements = document.getElementsByClassName("date"); // get all elements with the class "date"
[...dateElements].forEach(function(dateElement) { // loop through each element, where dateElement is the current node
const year = Number(dateElement.dataset.year);
const month = Number(dateElement.dataset.month);
const day = Number(dateElement.dataset.day);
dateElement.textContent = gregorian_to_jalali(year, month, day).join('/');
})
<div class="date" data-year="2019" data-month="5" data-day="7"></div>
<br />
<div class="date" data-year="2019" data-month="2" data-day="7"></div>
<br />
<div class="date" data-year="2019" data-month="2" data-day="8"></div>
<br />
<div class="date" data-year="2019" data-month="2" data-day="9"></div>
<br />
<div class="date" data-year="2019" data-month="2" data-day="10"></div>
