fix: use dateLib for getting days/months/years from a Date

src/DayPicker.tsx

@@ -346,7 +346,7 @@ export function DayPicker(props: DayPickerProps) {
                           onChange={handleMonthChange(calendarMonth.date)}
                           options={dropdownMonths}
                           style={styles?.[UI.Dropdown]}
-                          value={calendarMonth.date.getMonth()}
+                          value={dateLib.getMonth(calendarMonth.date)}
                         />
                       ) : (
                         <span role="status" aria-live="polite">
@@ -367,7 +367,7 @@ export function DayPicker(props: DayPickerProps) {
                           onChange={handleYearChange(calendarMonth.date)}
                           options={dropdownYears}
                           style={styles?.[UI.Dropdown]}
-                          value={calendarMonth.date.getFullYear()}
+                          value={dateLib.getYear(calendarMonth.date)}
                         />
                       ) : (
                         <span role="status" aria-live="polite">

src/helpers/getBroadcastWeeksInMonth.ts

@@ -23,7 +23,7 @@ export function getBroadcastWeeksInMonth(month: Date, dateLib: DateLib): 4 | 5 {
     FIVE_WEEKS * 7 - 1
   );
   const numberOfWeeks =
-    month.getMonth() === lastDateOfLastWeek.getMonth()
+    dateLib.getMonth(month) === dateLib.getMonth(lastDateOfLastWeek)
       ? FIVE_WEEKS
       : FOUR_WEEKS;
 

src/helpers/getNavMonth.ts

@@ -1,5 +1,3 @@
-import { TZDate } from "@date-fns/tz";
-
 import type { DateLib } from "../classes/DateLib.js";
 import type { DayPickerProps } from "../types/index.js";
 
@@ -28,7 +26,9 @@ export function getNavMonths(
     startOfMonth,
     endOfMonth,
     addYears,
-    endOfYear
+    endOfYear,
+    newDate,
+    today
   } = dateLib;
 
   // Handle deprecated code
@@ -37,35 +37,29 @@ export function getNavMonths(
     startMonth = fromMonth;
   }
   if (!startMonth && fromYear) {
-    startMonth = new dateLib.Date(fromYear, 0, 1);
+    startMonth = dateLib.newDate(fromYear, 0, 1);
   }
   if (!endMonth && toMonth) {
     endMonth = toMonth;
   }
   if (!endMonth && toYear) {
-    endMonth = new dateLib.Date(toYear, 11, 31);
+    endMonth = newDate(toYear, 11, 31);
   }
 
   const hasDropdowns = props.captionLayout?.startsWith("dropdown");
   if (startMonth) {
     startMonth = startOfMonth(startMonth);
   } else if (fromYear) {
-    startMonth = new dateLib.Date(fromYear, 0, 1);
+    startMonth = newDate(fromYear, 0, 1);
   } else if (!startMonth && hasDropdowns) {
-    const today =
-      props.today ??
-      (props.timeZone ? TZDate.tz(props.timeZone) : new dateLib.Date());
-    startMonth = startOfYear(addYears(today, -100));
+    startMonth = startOfYear(addYears(props.today ?? today(), -100));
   }
   if (endMonth) {
     endMonth = endOfMonth(endMonth);
   } else if (toYear) {
-    endMonth = new dateLib.Date(toYear, 11, 31);
+    endMonth = newDate(toYear, 11, 31);
   } else if (!endMonth && hasDropdowns) {
-    const today =
-      props.today ??
-      (props.timeZone ? TZDate.tz(props.timeZone) : new dateLib.Date());
-    endMonth = endOfYear(today);
+    endMonth = endOfYear(props.today ?? today());
   }
   return [
     startMonth ? startOfDay(startMonth) : startMonth,

src/helpers/getWeekdays.ts

@@ -1,5 +1,3 @@
-import { TZDate } from "@date-fns/tz";
-
 import { DateLib } from "../classes/DateLib.js";
 
 /**
@@ -11,17 +9,16 @@ export function getWeekdays(
   dateLib: DateLib,
   /** Use ISOWeek instead of locale/ */
   ISOWeek?: boolean | undefined,
-  timeZone?: string | undefined,
   /** @since 9.4.0 */
   broadcastCalendar?: boolean | undefined
 ): Date[] {
-  const date = timeZone ? TZDate.tz(timeZone) : new dateLib.Date();
+  const today = dateLib.today();
 
   const start = broadcastCalendar
-    ? dateLib.startOfBroadcastWeek(date, dateLib)
+    ? dateLib.startOfBroadcastWeek(today, dateLib)
     : ISOWeek
-      ? dateLib.startOfISOWeek(date)
-      : dateLib.startOfWeek(date);
+      ? dateLib.startOfISOWeek(today)
+      : dateLib.startOfWeek(today);
 
   const days: Date[] = [];
   for (let i = 0; i < 7; i++) {