📝 Commit Details:

backend/node_modules/date-fns/differenceInCalendarISOWeeks.js

@@ -0,0 +1,56 @@
+import { getTimezoneOffsetInMilliseconds } from "./_lib/getTimezoneOffsetInMilliseconds.js";
+import { normalizeDates } from "./_lib/normalizeDates.js";
+import { millisecondsInWeek } from "./constants.js";
+import { startOfISOWeek } from "./startOfISOWeek.js";
+
+/**
+ * The {@link differenceInCalendarISOWeeks} function options.
+ */
+
+/**
+ * @name differenceInCalendarISOWeeks
+ * @category ISO Week Helpers
+ * @summary Get the number of calendar ISO weeks between the given dates.
+ *
+ * @description
+ * Get the number of calendar ISO weeks between the given dates.
+ *
+ * ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
+ *
+ * @param laterDate - The later date
+ * @param earlierDate - The earlier date
+ * @param options - An object with options
+ *
+ * @returns The number of calendar ISO weeks
+ *
+ * @example
+ * // How many calendar ISO weeks are between 6 July 2014 and 21 July 2014?
+ * const result = differenceInCalendarISOWeeks(
+ *   new Date(2014, 6, 21),
+ *   new Date(2014, 6, 6),
+ * );
+ * //=> 3
+ */
+export function differenceInCalendarISOWeeks(laterDate, earlierDate, options) {
+  const [laterDate_, earlierDate_] = normalizeDates(
+    options?.in,
+    laterDate,
+    earlierDate,
+  );
+
+  const startOfISOWeekLeft = startOfISOWeek(laterDate_);
+  const startOfISOWeekRight = startOfISOWeek(earlierDate_);
+
+  const timestampLeft =
+    +startOfISOWeekLeft - getTimezoneOffsetInMilliseconds(startOfISOWeekLeft);
+  const timestampRight =
+    +startOfISOWeekRight - getTimezoneOffsetInMilliseconds(startOfISOWeekRight);
+
+  // Round the number of weeks to the nearest integer because the number of
+  // milliseconds in a week is not constant (e.g. it's different in the week of
+  // the daylight saving time clock shift).
+  return Math.round((timestampLeft - timestampRight) / millisecondsInWeek);
+}
+
+// Fallback for modularized imports:
+export default differenceInCalendarISOWeeks;