🐛 Refactor DatePicker component to handle null startDate date range selection properly

src/date_utils.ts

@@ -245,11 +245,11 @@ export function safeDateRangeFormat(
     rangeSeparator?: string;
   },
 ): string {
-  if (!startDate) {
+  if (!startDate && !endDate) {
     return "";
   }
 
-  const formattedStartDate = safeDateFormat(startDate, props);
+  const formattedStartDate = startDate ? safeDateFormat(startDate, props) : "";
   const formattedEndDate = endDate ? safeDateFormat(endDate, props) : "";
   const dateRangeSeparator = props.rangeSeparator || DATE_RANGE_SEPARATOR;
 

src/index.tsx

@@ -670,12 +670,14 @@ export class DatePicker extends Component<DatePickerProps, DatePickerState> {
         this.props.locale,
         strictParsing,
       );
-      const endDateNew = parseDate(
-        valueEnd ?? "",
-        dateFormat,
-        this.props.locale,
-        strictParsing,
-      );
+      const endDateNew = startDateNew
+        ? parseDate(
+            valueEnd ?? "",
+            dateFormat,
+            this.props.locale,
+            strictParsing,
+          )
+        : null;
       const startChanged = startDate?.getTime() !== startDateNew?.getTime();
       const endChanged = endDate?.getTime() !== endDateNew?.getTime();
 
@@ -832,6 +834,7 @@ export class DatePicker extends Component<DatePickerProps, DatePickerState> {
       if (selectsRange) {
         const noRanges = !startDate && !endDate;
         const hasStartRange = startDate && !endDate;
+        const hasOnlyEndRange = !startDate && !!endDate;
         const isRangeFilled = startDate && endDate;
         if (noRanges) {
           onChange?.([changedDate, null], event);
@@ -847,6 +850,12 @@ export class DatePicker extends Component<DatePickerProps, DatePickerState> {
           } else {
             onChange?.([startDate, changedDate], event);
           }
+        } else if (hasOnlyEndRange) {
+          if (changedDate && isDateBefore(changedDate, endDate)) {
+            onChange?.([changedDate, endDate], event);
+          } else {
+            onChange?.([changedDate, null], event);
+          }
         }
         if (isRangeFilled) {
           onChange?.([changedDate, null], event);

src/test/date_utils_test.test.ts

@@ -1264,6 +1264,14 @@ describe("date_utils", () => {
       );
     });
 
+    it("should return a formatted endDate prefixed by a dash when startDate is null", () => {
+      const startDate = null;
+      const endDate = new Date("2021-04-20 00:00:00");
+      expect(safeDateRangeFormat(startDate, endDate, props)).toBe(
+        " - 04/20/2021",
+      );
+    });
+
     it("should return a formatted startDate followed by a dash followed by a formatted endDate when startDate and endDate both have values", () => {
       const startDate = new Date("2021-04-20 00:00:00");
       const endDate = new Date("2021-04-28 00:00:00");

src/test/datepicker_test.test.tsx

@@ -4531,4 +4531,115 @@ describe("DatePicker", () => {
       expect(input?.value).toBe("07/17/2025");
     });
   });
+
+  describe("Date Range - Handle null start date", () => {
+    it("should display the endDate when the startDate is not available", () => {
+      const endDateLabel = "2025-11-22";
+      const { container } = render(
+        <DatePicker
+          selectsRange
+          startDate={null}
+          endDate={newDate(endDateLabel)}
+          dateFormat="yyyy-MM-dd"
+          onChange={() => {}}
+          isClearable
+        />,
+      );
+      const input = safeQuerySelector<HTMLInputElement>(container, "input");
+      expect(input.value).toBe(` - ${endDateLabel}`);
+    });
+
+    it("should clear the input when the startDate alone is cleared while the endDate is still available", () => {
+      const startDateLabel = "2025-11-17";
+      const endDateLabel = "2025-11-22";
+      const onChangeSpy = jest.fn();
+
+      const { container } = render(
+        <DatePicker
+          selectsRange
+          startDate={newDate(startDateLabel)}
+          endDate={newDate(endDateLabel)}
+          dateFormat="yyyy-MM-dd"
+          onChange={onChangeSpy}
+          isClearable
+        />,
+      );
+      const input = safeQuerySelector<HTMLInputElement>(container, "input");
+      expect(input.value).toBe(`${startDateLabel} - ${endDateLabel}`);
+
+      fireEvent.change(input, { target: { value: ` - ${endDateLabel}` } });
+      expect(onChangeSpy).toHaveBeenCalledTimes(1);
+      expect(onChangeSpy).toHaveBeenCalledWith([null, null], expect.anything());
+    });
+
+    it("should clear the endDate and set the startDate when the endDate is alone available and the newly selected startDate is greater than the endDate", () => {
+      const endDateLabel = "2025-11-20";
+      const onChangeSpy = jest.fn();
+      const { container } = render(
+        <DatePicker
+          selectsRange
+          startDate={null}
+          selected={newDate(endDateLabel)}
+          endDate={newDate(endDateLabel)}
+          dateFormat="yyyy-MM-dd"
+          onChange={onChangeSpy}
+          isClearable
+        />,
+      );
+      const input = safeQuerySelector<HTMLInputElement>(container, "input");
+      fireEvent.focus(input);
+
+      expect(container.querySelector(".react-datepicker")).toBeTruthy();
+      const newStartDateEl = safeQuerySelector(
+        container,
+        ".react-datepicker__day--021",
+      );
+      fireEvent.click(newStartDateEl);
+
+      expect(onChangeSpy).toHaveBeenCalledTimes(1);
+      const changedDateRange = onChangeSpy.mock.calls[0][0];
+      const [changedStartDate, changedEndDate] = changedDateRange;
+
+      expect(changedEndDate).toBe(null);
+      expect(changedStartDate.toISOString()).toBe(
+        newDate("2025-11-21").toISOString(),
+      );
+    });
+
+    it("should set the startDate when the endDate is alone available and the newly selected startDate is less than the endDate", () => {
+      const endDateLabel = "2025-11-20";
+      const onChangeSpy = jest.fn();
+      const { container } = render(
+        <DatePicker
+          selectsRange
+          startDate={null}
+          selected={newDate(endDateLabel)}
+          endDate={newDate(endDateLabel)}
+          dateFormat="yyyy-MM-dd"
+          onChange={onChangeSpy}
+          isClearable
+        />,
+      );
+      const input = safeQuerySelector<HTMLInputElement>(container, "input");
+      fireEvent.focus(input);
+
+      expect(container.querySelector(".react-datepicker")).toBeTruthy();
+      const newStartDateEl = safeQuerySelector(
+        container,
+        ".react-datepicker__day--019",
+      );
+      fireEvent.click(newStartDateEl);
+
+      expect(onChangeSpy).toHaveBeenCalledTimes(1);
+      const changedDateRange = onChangeSpy.mock.calls[0][0];
+      const [changedStartDate, changedEndDate] = changedDateRange;
+
+      expect(changedEndDate.toISOString()).toBe(
+        newDate(endDateLabel).toISOString(),
+      );
+      expect(changedStartDate.toISOString()).toBe(
+        newDate("2025-11-19").toISOString(),
+      );
+    });
+  });
 });