Calculate week day from UTC date

Thanks to Scott Ventura for reporting this issue! I hope it solves it.

package.json

@@ -1,6 +1,6 @@
 {
     "name": "doomsday",
-    "version": "1.3.16",
+    "version": "1.3.17",
     "description": "Test your mastery of Conway's Doomsday rule.",
     "author": "F.W. Dekker",
     "browser": "dist/bundle.js",
@@ -16,15 +16,15 @@
         "deploy": "grunt deploy"
     },
     "devDependencies": {
-        "grunt": "^1.4.0",
-        "grunt-cli": "^1.4.2",
+        "grunt": "^1.4.1",
+        "grunt-cli": "^1.4.3",
         "grunt-contrib-clean": "^2.0.0",
         "grunt-contrib-copy": "^1.0.0",
         "grunt-contrib-watch": "^1.1.0",
         "grunt-focus": "^1.0.0",
         "grunt-text-replace": "^0.4.0",
-        "grunt-webpack": "^4.0.3",
-        "webpack": "^5.36.0",
-        "webpack-cli": "^4.6.0"
+        "grunt-webpack": "^5.0.0",
+        "webpack": "^5.64.0",
+        "webpack-cli": "^4.9.1"
     }
 }

src/main/js/main.js

@@ -227,7 +227,7 @@ class ToggleableSection {
 /**
  * A wrapper around the good ol' `Date` class that provides a bunch of useful Doomsday-specific methods.
  *
- * @property {Date} the underlying date
+ * @property {Date} date the underlying date
  */
 class DoomsdayDate {
     /**
@@ -256,7 +256,7 @@ class DoomsdayDate {
      */
     getCenturyAnchorString() {
         const centuryAnchorNumber = (5 * (this.getCentury() % 4)) % 7 + 2;
-        return DoomsdayDate.dayNumberToString(centuryAnchorNumber);
+        return DoomsdayDate.getWeekDayOf(centuryAnchorNumber);
     };
 
     /**
@@ -268,7 +268,7 @@ class DoomsdayDate {
         const anchorDate = new Date(this.date);
         anchorDate.setDate(4); // 4th
         anchorDate.setMonth(3); // April
-        return DoomsdayDate.dayNumberToString(anchorDate.getDay());
+        return DoomsdayDate.getWeekDayOf(anchorDate);
     };
 
     /**
@@ -277,32 +277,36 @@ class DoomsdayDate {
      * @return {string} the day of the week of this `DoomsdayDate`
      */
     getWeekdayString() {
-        return DoomsdayDate.dayNumberToString(this.date.getDay());
+        return DoomsdayDate.getWeekDayOf(this.date);
     };
 
 
     /**
-     * Returns the name of the day given its 0-based index, where 0 is `Sunday`.
+     * Returns the week day of [date].
      *
-     * @param dayNumber {number} the number of the day, as returned by `Date`'s `#getDay` function.
-     * @return {string} the name of the day given its 0-based index, where 0 is `Sunday`
+     * @param date {Date|number} the date to get the week day of; if it is a `number`, then 0 corresponds to Sunday
+     * @return {string} the name of the week day corresponding to [date]
      */
-    static dayNumberToString(dayNumber) {
-        switch (dayNumber % 7) {
-            case 0:
-                return "Sunday";
-            case 1:
-                return "Monday";
-            case 2:
-                return "Tuesday";
-            case 3:
-                return "Wednesday";
-            case 4:
-                return "Thursday";
-            case 5:
-                return "Friday";
-            case 6:
-                return "Saturday";
+    static getWeekDayOf(date) {
+        if (date instanceof Date) {
+            return date.toLocaleString("en-US", {timeZone: "GMT", weekday: "long"});
+        } else {
+            switch (date % 7) {
+                case 0:
+                    return "Sunday";
+                case 1:
+                    return "Monday";
+                case 2:
+                    return "Tuesday";
+                case 3:
+                    return "Wednesday";
+                case 4:
+                    return "Thursday";
+                case 5:
+                    return "Friday";
+                case 6:
+                    return "Saturday";
+            }
         }
     };
 
@@ -341,7 +345,7 @@ class DoomsdayDate {
      * @return {DoomsdayDate} a random date
      */
     static random() {
-        // TODO Give custom dates to this method
+        // TODO Give custom date range to this method
         const minDate = new Date("0001-01-01").getTime() / 86400000;
         const maxDate = new Date("9999-12-31").getTime() / 86400000;
         return new DoomsdayDate(new Date(generateRandom(minDate, maxDate) * 86400000));
@@ -475,6 +479,7 @@ doAfterLoad(() => {
         quizDate = DoomsdayDate.random();
         console.log("# Reset");
         console.log(`New date:  ${quizDate.date.toISOString().substr(0, 10)}`);
+        console.log(`           ${quizDate.date}`);
         console.log(`Century#:  ${quizDate.getCentury()}`);
         console.log(`Century:   ${quizDate.getCenturyAnchorString()}`);
         console.log(`Year:      ${quizDate.getYearAnchorString()}`);