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Get the corresponding day of week for a date. Algorithm provided by Claus Tøndering - http://www.tondering.dk/claus/cal/chrweek.php#calcdow.
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| /* | |
| * Given a Date, Month and Year | |
| * Return DAY_OF_WEEK. | |
| * | |
| * @param {Number} [D] Date in the following format: d | |
| * @param {Number} [M] Month in the following format: m | |
| * @param {Number} [Y] Year in the following format: yyyy | |
| * @param {Boolean} [J=false] Defaults to the Gregorian calendar, when J is omitted or set to false. When set to true, the Day Of Week in the Julian calendar is returned. | |
| * @return {String} The Day of Week, UPPERCASED. | |
| */ | |
| function DayOfDate(D, M, Y, J) { | |
| var L = ~~ ((14 - M) / 12); | |
| Y -= L; | |
| return "SUN MON TUES WEDNES THURS FRI SATUR".split(" ")[((J ? 5 : (~~(Y / 400) - ~~(Y / 100))) + D + Y + ~~(Y / 4) + ~~(31 * (M + 12 * L - 2) / 12)) % 7] | |
| + "DAY" | |
| }; |
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Algorithm used in the first revision was provided by Scott Flansburg, the Human Calculator in his talk - http://youtu.be/hesKQ_y1P7k?t=40m0s
Amazing talk! Unfortunately the single lookup table for months wasn't enough to get the Day of Week for all centuries.
Rev. 2 also provides the Day of Week in the Julian Calendar, not that it's used by that many people, but the functionality was added by no more than a ternary and the substitution of two formulas with the number 5.