Add Computus in Javascript and Typescript

Author: hugo-s29

contents/computus/code/javascript/gauss_easter.js

@@ -0,0 +1,82 @@
+/**
+ * In this code, the modulus operator is used.
+ * However, this operator in javascript/typescript doesn't support negative numbers.
+ * So, where there may be negative numbers, the function mod is used.
+ * This function gives the modulo of any relative number a
+ */
+
+/**
+ * @param {number} a
+ * @param {number} b
+ * @returns {number}
+ */
+function mod(a, b) {
+  if (a < 0) return mod(a + b, b);
+  else return a % b;
+}
+
+/**
+ * @param {number} year
+ * @param {boolean} [servois=false]
+ * @returns {string}
+ */
+function computus(year, servois = false) {
+  // Year's position in metonic cycle
+  const a = year % 19;
+
+  // Century index
+  const k = Math.floor(year / 100);
+
+  // Shift of metonic cycle, add a day offset every 300 years
+  const p = Math.floor((13 + 8 * k) / 25);
+
+  // Correction for non-observed leap days
+  const q = Math.floor(k / 4);
+
+  // Correction to starting point of calculation each century
+  const M = mod(15 - p + k - q, 30);
+
+  // Number of days from March 21st until the full moon
+  const d = (19 * a + M) % 30;
+
+  // Returning if user wants value for Servois' table
+  if (servois) return ((21 + d) % 31).toString();
+
+  // Finding the next Sunday
+  // Century-based offset in weekly calculation
+  const N = mod(4 + k - q, 7);
+
+  // Correction for leap days
+  const b = year % 4;
+  const c = year % 7;
+
+  // Days from d to next Sunday
+  let e = (2 * b + 4 * c + 6 * d + N) % 7;
+
+  // Historical corrections for April 26 and 25
+  if (e === 6) if (d === 29 || (d === 28 && a > 10)) e = -1;
+
+  // Determination of the correct month for Easter
+  if (22 + d + e > 31) return `April ${d + e - 9}`;
+  else return `March ${22 + d + e}`;
+}
+
+console.log(
+  "The following are the dates of the Paschal full moon (using Servois " +
+    "notation) and the date of Easter for 2020-2030 AD:"
+);
+
+const values = [];
+
+for (let year = 2020; year <= 2030; year++) {
+  const servoisNumber = computus(year, true);
+  const easterDate = computus(year);
+
+  // Creation of an object to be displayed as a line in the output table
+  values[year] = {
+    "servois number": +servoisNumber,
+    easter: easterDate,
+  };
+}
+
+console.table(values);

contents/computus/code/typescript/gauss_easter.ts

@@ -0,0 +1,80 @@
+/**
+ * In this code, the modulus operator is used.
+ * However, this operator in javascript/typescript doesn't support negative numbers.
+ * So, where there may be negative numbers, the function mod is used.
+ * This function gives the modulo of any relative number a
+ */
+
+function mod(a: number, b: number): number {
+  if (a < 0) return mod(a + b, b);
+  else return a % b;
+}
+
+function computus(year: number, servois: boolean = false): string {
+  // Year's position in metonic cycle
+  const a = year % 19;
+
+  // Century index
+  const k = Math.floor(year / 100);
+
+  // Shift of metonic cycle, add a day offset every 300 years
+  const p = Math.floor((13 + 8 * k) / 25);
+
+  // Correction for non-observed leap days
+  const q = Math.floor(k / 4);
+
+  // Correction to starting point of calculation each century
+  const M = mod(15 - p + k - q, 30);
+
+  // Number of days from March 21st until the full moon
+  const d = (19 * a + M) % 30;
+
+  // Returning if user wants value for Servois' table
+  if (servois) return ((21 + d) % 31).toString();
+
+  // Finding the next Sunday
+  // Century-based offset in weekly calculation
+  const N = mod(4 + k - q, 7);
+
+  // Correction for leap days
+  const b = year % 4;
+  const c = year % 7;
+
+  // Days from d to next Sunday
+  let e = (2 * b + 4 * c + 6 * d + N) % 7;
+
+  // Historical corrections for April 26 and 25
+  if (e === 6) if (d === 29 || (d === 28 && a > 10)) e = -1;
+
+  // Determination of the correct month for Easter
+  if (22 + d + e > 31) return `April ${d + e - 9}`;
+  else return `March ${22 + d + e}`;
+}
+
+console.log(
+  "The following are the dates of the Paschal full moon (using Servois " +
+    "notation) and the date of Easter for 2020-2030 AD:"
+);
+
+// Type of a line in the output table
+interface IOutputLine {
+  "servois number": number;
+  easter: string;
+}
+
+const values: IOutputLine[] = [];
+
+for (let year = 2020; year <= 2030; year++) {
+  const servoisNumber = computus(year, true);
+  const easterDate = computus(year);
+
+  // Creation of an object to be displayed as a line in the output table
+  const line: IOutputLine = {
+    "servois number": +servoisNumber,
+    easter: easterDate,
+  };
+
+  values[year] = line;
+}
+
+console.table(values);

contents/computus/computus.md

@@ -320,6 +320,10 @@ For now, we have the code outputting a tuple of $$d$$ and $$e$$, so users can us
 [import, lang:"lisp"](code/clisp/gauss-easter.lisp)
 {% sample lang="nim" %}
 [import, lang:"nim"](code/nim/gauss_easter.nim)
+{% sample lang="javascript" %}
+[import, lang:"nim"](code/javascript/gauss_easter.js)
+{% sample lang="typescript" %}
+[import, lang:"nim"](code/typescript/gauss_easter.ts)
 {% endmethod %}