fix: correct timezone handling for date selection and display

src/date_utils.ts

@@ -439,19 +439,38 @@ export function formatDate(
  * Safely formats a date.
  *
  * @param date - The date.
- * @param options - An object containing the dateFormat and locale.
+ * @param options - An object containing the dateFormat, locale, and optional timeZone.
  * @returns - The formatted date or an empty string.
  */
 export function safeDateFormat(
   date: Date | null | undefined,
-  { dateFormat, locale }: { dateFormat: string | string[]; locale?: Locale },
+  {
+    dateFormat,
+    locale,
+    timeZone,
+  }: { dateFormat: string | string[]; locale?: Locale; timeZone?: TimeZone },
 ): string {
   const formatStr = (
     Array.isArray(dateFormat) && dateFormat.length > 0
       ? dateFormat[0]
       : dateFormat
   ) as string; // Cast to string because it's impossible to get `string | string[] | undefined` here and typescript doesn't know that
-  return (date && formatDate(date, formatStr, locale)) || "";
+
+  if (!date) {
+    return "";
+  }
+
+  // Use timezone-aware formatting if timeZone is specified
+  if (timeZone) {
+    // Resolve locale string to locale object for formatInTimeZone
+    // Cast to DateFnsLocale since LocaleObj is a compatible subset
+    const localeObj = (
+      locale ? getLocaleObject(locale) : getLocaleObject(getDefaultLocale())
+    ) as DateFnsLocale | undefined;
+    return formatInTimeZone(date, formatStr, timeZone, localeObj);
+  }
+
+  return formatDate(date, formatStr, locale) || "";
 }
 
 /**
@@ -474,6 +493,7 @@ export function safeDateRangeFormat(
     dateFormat: string | string[];
     locale?: Locale;
     rangeSeparator?: string;
+    timeZone?: TimeZone;
   },
 ): string {
   if (!startDate && !endDate) {
@@ -496,7 +516,11 @@ export function safeDateRangeFormat(
  */
 export function safeMultipleDatesFormat(
   dates: Date[],
-  props: { dateFormat: string | string[]; locale?: Locale },
+  props: {
+    dateFormat: string | string[];
+    locale?: Locale;
+    timeZone?: TimeZone;
+  },
 ): string {
   if (!dates?.length) {
     return "";

src/index.tsx

@@ -534,6 +534,7 @@ export class DatePicker extends Component<DatePickerProps, DatePickerState> {
       selectsRange,
       formatMultipleDates,
       value,
+      timeZone,
     } = this.props;
     const dateFormat =
       this.props.dateFormat ?? DatePicker.defaultProps.dateFormat;
@@ -549,21 +550,24 @@ export class DatePicker extends Component<DatePickerProps, DatePickerState> {
         dateFormat,
         locale,
         rangeSeparator,
+        timeZone,
       });
     } else if (selectsMultiple) {
       if (formatMultipleDates) {
         const formatDateFn = (date: Date) =>
-          safeDateFormat(date, { dateFormat, locale });
+          safeDateFormat(date, { dateFormat, locale, timeZone });
         return formatMultipleDates(selectedDates ?? [], formatDateFn);
       }
       return safeMultipleDatesFormat(selectedDates ?? [], {
         dateFormat,
         locale,
+        timeZone,
       });
     }
     return safeDateFormat(selected, {
       dateFormat,
       locale,
+      timeZone,
     });
   };
 
@@ -1730,6 +1734,23 @@ export class DatePicker extends Component<DatePickerProps, DatePickerState> {
     if (!this.props.inline && !this.isCalendarOpen()) {
       return null;
     }
+
+    const { timeZone, selected, startDate, endDate, selectedDates } =
+      this.props;
+
+    // Convert dates to zoned time for calendar display when timeZone is specified
+    // This ensures the calendar highlights the correct day in the target timezone
+    const zonedSelected =
+      selected && timeZone ? toZonedTime(selected, timeZone) : selected;
+    const zonedStartDate =
+      startDate && timeZone ? toZonedTime(startDate, timeZone) : startDate;
+    const zonedEndDate =
+      endDate && timeZone ? toZonedTime(endDate, timeZone) : endDate;
+    const zonedSelectedDates =
+      selectedDates && timeZone
+        ? selectedDates.map((date) => toZonedTime(date, timeZone))
+        : selectedDates;
+
     return (
       <Calendar
         showMonthYearDropdown={undefined}
@@ -1738,6 +1759,11 @@ export class DatePicker extends Component<DatePickerProps, DatePickerState> {
         }}
         {...this.props}
         {...this.state}
+        // Override date props with zoned time versions for correct display
+        selected={zonedSelected}
+        startDate={zonedStartDate}
+        endDate={zonedEndDate}
+        selectedDates={zonedSelectedDates}
         setOpen={this.setOpen}
         dateFormat={
           this.props.dateFormatCalendar ??

src/test/timezone_test.test.tsx

@@ -688,6 +688,173 @@ describe("DatePicker with timeZone prop", () => {
     expect(changedStartDate).toBeInstanceOf(Date);
     expect(changedEndDate).toBeNull();
   });
+
+  // Test for issue #6193: Date selection with extreme timezone difference
+  it("should correctly select date when timezone differs significantly from browser timezone (issue #6193)", () => {
+    // Simulate: browser in UTC, timezone prop set to Pacific/Kiritimati (UTC+14)
+    // When user clicks Dec 26 in the calendar, onChange should receive Dec 26 in Kiritimati
+    // which is Dec 25 10:00 UTC - and the input should still display Dec 26
+
+    // Start with a date that represents Dec 26 00:00 in Kiritimati (= Dec 25 10:00 UTC)
+    const initialUtcDate = new Date("2025-12-25T10:00:00Z");
+    let selectedDate: Date | null = initialUtcDate;
+
+    const { container, rerender } = render(
+      <DatePicker
+        selected={selectedDate}
+        onChange={(date) => {
+          selectedDate = date;
+        }}
+        timeZone="Pacific/Kiritimati"
+        dateFormat="yyyy-MM-dd"
+      />,
+    );
+
+    // The input should display Dec 26 (the date in Kiritimati timezone)
+    const input = container.querySelector("input");
+    expect(input?.value).toBe("2025-12-26");
+
+    // Open the calendar
+    if (input) {
+      fireEvent.focus(input);
+    }
+
+    // Find and click Dec 26 in the calendar
+    const days = container.querySelectorAll(".react-datepicker__day");
+    const dayToClick = Array.from(days).find(
+      (day) =>
+        !day.classList.contains("react-datepicker__day--outside-month") &&
+        day.textContent === "26",
+    );
+    expect(dayToClick).toBeTruthy();
+
+    // The day 26 should be marked as selected before clicking
+    expect(
+      dayToClick?.classList.contains("react-datepicker__day--selected"),
+    ).toBe(true);
+
+    if (dayToClick) {
+      fireEvent.click(dayToClick);
+    }
+
+    // After clicking, re-render with the new selected date
+    rerender(
+      <DatePicker
+        selected={selectedDate}
+        onChange={(date) => {
+          selectedDate = date;
+        }}
+        timeZone="Pacific/Kiritimati"
+        dateFormat="yyyy-MM-dd"
+      />,
+    );
+
+    // The input should still display Dec 26 (same date user clicked)
+    expect(input?.value).toBe("2025-12-26");
+
+    // The onChange should have been called with a UTC date that represents Dec 26 in Kiritimati
+    // Dec 26 00:00 Kiritimati = Dec 25 10:00 UTC
+    expect(selectedDate).not.toBeNull();
+    expect(selectedDate?.getUTCFullYear()).toBe(2025);
+    expect(selectedDate?.getUTCMonth()).toBe(11); // December
+    expect(selectedDate?.getUTCDate()).toBe(25);
+    expect(selectedDate?.getUTCHours()).toBe(10);
+  });
+
+  // Test that clicking a different date works correctly with timezone
+  it("should correctly change date when clicking different day with timezone (issue #6193)", () => {
+    // Start with Dec 26 00:00 Kiritimati (= Dec 25 10:00 UTC)
+    const initialUtcDate = new Date("2025-12-25T10:00:00Z");
+    let selectedDate: Date | null = initialUtcDate;
+
+    const { container, rerender } = render(
+      <DatePicker
+        selected={selectedDate}
+        onChange={(date) => {
+          selectedDate = date;
+        }}
+        timeZone="Pacific/Kiritimati"
+        dateFormat="yyyy-MM-dd"
+      />,
+    );
+
+    const input = container.querySelector("input");
+    expect(input?.value).toBe("2025-12-26");
+
+    // Open the calendar
+    if (input) {
+      fireEvent.focus(input);
+    }
+
+    // Click Dec 27 instead
+    const days = container.querySelectorAll(".react-datepicker__day");
+    const dayToClick = Array.from(days).find(
+      (day) =>
+        !day.classList.contains("react-datepicker__day--outside-month") &&
+        day.textContent === "27",
+    );
+    expect(dayToClick).toBeTruthy();
+
+    if (dayToClick) {
+      fireEvent.click(dayToClick);
+    }
+
+    // Re-render with new selected date
+    rerender(
+      <DatePicker
+        selected={selectedDate}
+        onChange={(date) => {
+          selectedDate = date;
+        }}
+        timeZone="Pacific/Kiritimati"
+        dateFormat="yyyy-MM-dd"
+      />,
+    );
+
+    // The input should now display Dec 27
+    expect(input?.value).toBe("2025-12-27");
+
+    // The UTC date should represent Dec 27 00:00 Kiritimati = Dec 26 10:00 UTC
+    expect(selectedDate?.getUTCDate()).toBe(26);
+  });
+
+  // Test for selectsMultiple with timezone
+  it("should correctly display and select multiple dates with timezone", () => {
+    // Dec 26 00:00 Kiritimati = Dec 25 10:00 UTC
+    // Dec 27 00:00 Kiritimati = Dec 26 10:00 UTC
+    const initialDates = [
+      new Date("2025-12-25T10:00:00Z"),
+      new Date("2025-12-26T10:00:00Z"),
+    ];
+    let selectedDates: Date[] = initialDates;
+
+    const { container } = render(
+      <DatePicker
+        selectedDates={selectedDates}
+        selectsMultiple
+        onChange={(dates) => {
+          selectedDates = dates as Date[];
+        }}
+        timeZone="Pacific/Kiritimati"
+        dateFormat="yyyy-MM-dd"
+        inline
+        // Set openToDate to ensure calendar shows December 2025
+        openToDate={new Date("2025-12-25T10:00:00Z")}
+      />,
+    );
+
+    // Both Dec 26 and Dec 27 should be marked as selected in the calendar
+    // Filter to only days in current month (not outside-month days)
+    const selectedDays = container.querySelectorAll(
+      ".react-datepicker__day--selected:not(.react-datepicker__day--outside-month)",
+    );
+    expect(selectedDays.length).toBe(2);
+
+    // Check that the correct days are highlighted
+    const dayTexts = Array.from(selectedDays).map((d) => d.textContent);
+    expect(dayTexts).toContain("26");
+    expect(dayTexts).toContain("27");
+  });
 });
 
 describe("Timezone fallback behavior (when date-fns-tz is not installed)", () => {