Calculate Easter in JavaScript

easter.js

/**
* Calculates Easter in the Gregorian/Western (Catholic and Protestant) calendar 
* based on the algorithm by Oudin (1940) from http://www.tondering.dk/claus/cal/easter.php
* @returns {array} [int month, int day]
*/
function getEaster(year) {
	var f = Math.floor,
		// Golden Number - 1
		G = year % 19,
		C = f(year / 100),
		// related to Epact
		H = (C - f(C / 4) - f((8 * C + 13)/25) + 19 * G + 15) % 30,
		// number of days from 21 March to the Paschal full moon
		I = H - f(H/28) * (1 - f(29/(H + 1)) * f((21-G)/11)),
		// weekday for the Paschal full moon
		J = (year + f(year / 4) + I + 2 - C + f(C / 4)) % 7,
		// number of days from 21 March to the Sunday on or before the Paschal full moon
		L = I - J,
		month = 3 + f((L + 40)/44),
		day = L + 28 - 31 * f(month / 4);

	return [month,day];
}

Thanks @johndyer and @wysal 👍

This algorithm seems to fail for year 2022 returning 23.04 instead of 17.04. Works fine for any other year I tried. Any idea on why that might be? I'm really curious and couldn't find explanation.

I had the same issue and solved it by applying parseInt(myYear, 0) on the variable containing the year.

console.log(getEaster("2022")); //Returns [4, 23] => NOK
console.log(getEaster(2022)); //Returns [4, 17] => OK
console.log(getEaster(parseInt("2022", 0))); //Returns [4, 17] => OK

Thanks @johndyer!

Thanks seem to work!

Was wondering if it's possible to get the good Friday from this? Since it's the Friday before Easter.

So I guess day - 2 will do for most cases at least.

When using this, I was passing the year in from an form input and it seems as though, only odd numbered years, returned the correct date (being Easter Sunday). The answer was to ensure the value passed in was an integer so added a line at the top of the function.

year = parseInt(year)