Data commit

Task/Holidays-related-to-Easter/JavaScript/holidays-related-to-easter-1.js

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+const Пасха = год => {
+	let дата = (год % 19 * 19 + 15) % 30;
+	дата += (год % 4 * 2 + год % 7 * 4 + 6 * дата + 6) % 7;
+	if (год >= 1918) дата += (год / 100 | 0) - (год / 400 | 0) - 2;
+	return new Date(год, 2, 22 + дата);
+};
+
+for (let год = 400; год <= 2100; год += год < 2000 ? 100 : год >= 2020 ? 80 : год < 2010 ? 10 : 1) {
+	const дата_Пасхи = Пасха(год);
+	document.write(
+		год + ": " +
+		[ ["Easter", 1], ["Ascension", 40], ["Trinity (Pentecost)", 50], ["All Saints' Sunday", 57] ].map(праздник => {
+			let дата = new Date(дата_Пасхи);
+			дата.setDate(дата.getDate() + праздник[1] - 1);
+			return праздник[0] + ": " + new Intl.DateTimeFormat("ru", { month: "numeric", day: "numeric" }).format(дата);
+		}).join("; ") + ".<br />"
+	);
+}

Task/Holidays-related-to-Easter/JavaScript/holidays-related-to-easter-2.js

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+const Easter = year => {
+    let date = (year % 19 * 19 + 15) % 30;
+    date += (year % 4 * 2 + year % 7 * 4 + 6 * date + 6) % 7;
+    if (year >= 1918) date += (year / 100 | 0) - (year / 400 | 0) - 2;
+    return new Date(year, 2, 22 + date);
+};
+
+for (let year = 400; year <= 2100; year += year < 2000 ? 100 : year >= 2020 ? 80 : year < 2010 ? 10 : 1) {
+    const Easter_Date = Easter(year);
+    document.write(
+        year + ": " +
+        [ ["Easter", 1], ["Ascension", 40], ["Trinity (Pentecost)", 50], ["All Saints' Sunday", 57] ].map(holiday => {
+            let date = new Date(Easter_Date);
+            date.setDate(date.getDate() + holiday[1] - 1);
+            return holiday[0] + ": " + new Intl.DateTimeFormat("ru", { month: "numeric", day: "numeric" }).format(date);
+        }).join("; ") + ".<br />"
+    );
+}

Task/Holidays-related-to-Easter/JavaScript/holidays-related-to-easter-3.js

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+function getEasterDate(year = new Date().getFullYear(), church = 1, calendar = year < 1918 ? 1 : 2) {
+/*	year: a number of the year (from 325 CE);
+	church: an algorithm of the computus,
+		for Orthodox = 1; for Catholic = 2;
+	calendar: a calendar of the output date,
+		Julian = 1; Gregorian = 2. */
+
+	if (church == 1) {
+		let d = (year % 19 * 19 + 15) % 30;
+		d += (year % 4 * 2 + year % 7 * 4 + 6 * d + 6) % 7;
+		if (calendar == 1)
+			return d > 9 ? [d - 9, 4] : [22 + d, 3];
+		else if (calendar == 2) {
+			const c = (year / 100 | 0) - (year / 400 | 0) - 2;
+			return d > 39 - c ? [d - 39 + c, 5] : [d - 9 + c, 4];
+		}
+	}
+
+	else if (church == 2) {
+		const
+			a = year % 19, b = year / 100 | 0, c = year % 100,
+			d = (19 * a + b - (b / 4 | 0) - ((b - ((b + 8) / 25 | 0) + 1) / 3 | 0) + 15) % 30,
+			e = (32 + 2 * (b % 4) + 2 * (c / 4 | 0) - d - c % 4) % 7,
+			f = d + e - 7 * ((a + 11 * d + 22 * e) / 451 | 0) + 114;
+		if (calendar == 1) {
+			const
+				g = f % 31 + 1,
+				h = (year / 100 | 0) - (year / 400 | 0) - 2;
+			return g <= h ? [31 + g - h, 3] : [g - h, f / 31 | 0];
+		}
+		else if (calendar == 2)
+			return [f % 31 + 1, f / 31 | 0];
+	}
+}
+
+const
+	OrthodoxHolidays = [["Easter", 1], ["Ascension", 40], ["Trinity (Pentecost)", 50], ["All Saints' Sunday", 57]],
+	CatholicHolidays = [["Easter", 1], ["Ascension", 40], ["Pentecost", 50], ["Trinity Sunday", 57], ["Corpus Christi", 61]];
+
+const firstYearOfNewStyle = 1918;
+
+function getHolidaysDates(year = new Date().getFullYear(), church = 1) {
+	const
+		Easter = getEasterDate(year, church, year < firstYearOfNewStyle ? 1 : 2),
+		holidays = church == 1 ? OrthodoxHolidays : CatholicHolidays;
+	return year + ": " +
+		holidays.map(h => {
+			const d = new Date(year, Easter[1] - 1, Easter[0]);
+			d.setDate(d.getDate() + h[1] - 1);
+			return h[0] + ": " + new Intl.DateTimeFormat("ru", { month: "numeric", day: "numeric" }).format(d);
+		}).join("; ") + ".";
+}
+
+for (let year = 400; year <= 2100; year += year < 2000 ? 100 : year >= 2021 ? 80 : year < 2010 ? 10 : 1)
+	document.write(getHolidaysDates(year, 1) + " <br />");