fix: resolve webpack warning for optional date-fns-tz dependency

src/date_utils.ts

@@ -99,6 +99,10 @@ export function __setDateFnsTzNull(): void {
   dateFnsTzLoadAttempted = true;
 }
 
+// Declare webpack's special require function that bypasses bundling
+// This is used to avoid webpack warnings for optional dependencies
+declare const __non_webpack_require__: typeof require | undefined;
+
 /**
  * Attempts to load date-fns-tz module.
  * Returns null if the module is not installed.
@@ -111,13 +115,25 @@ function getDateFnsTz(): DateFnsTz | null {
   dateFnsTzLoadAttempted = true;
 
   try {
-    // Dynamic require for date-fns-tz
-    // Use a variable to prevent webpack from statically analyzing the require
-    // and showing warnings when the optional dependency is not installed
-    // See: https://github.com/Hacker0x01/react-datepicker/issues/6154
-    const dateFnsTzModuleName = "date-fns-tz";
+    // Use __non_webpack_require__ to tell webpack to use native require
+    // and avoid bundling warnings for this optional dependency
+    // See: https://github.com/Hacker0x01/react-datepicker/issues/6181
+    //
+    // For Vite and other ESM-only bundlers, require is not available.
+    // In those environments, users need to configure their bundler to
+    // pre-bundle date-fns-tz or use the optimizeDeps option.
+    // See: https://github.com/Hacker0x01/react-datepicker/issues/6204
     // eslint-disable-next-line @typescript-eslint/no-require-imports
-    dateFnsTz = require(dateFnsTzModuleName) as DateFnsTz;
+    const requireFn =
+      typeof __non_webpack_require__ !== "undefined"
+        ? __non_webpack_require__
+        : typeof require !== "undefined"
+          ? require
+          : /* istanbul ignore next - only executes in ESM-only environments like Vite */ null;
+
+    if (requireFn) {
+      dateFnsTz = requireFn("date-fns-tz") as DateFnsTz;
+    }
   } catch {
     /* istanbul ignore next - only executes when date-fns-tz is not installed */
     dateFnsTz = null;

src/test/timezone_test.test.tsx

@@ -761,3 +761,36 @@ describe("Timezone fallback behavior (when date-fns-tz is not installed)", () =>
     consoleSpy.mockRestore();
   });
 });
+
+describe("Webpack __non_webpack_require__ support", () => {
+  beforeEach(() => {
+    __resetDateFnsTzCache();
+  });
+
+  afterEach(() => {
+    // Clean up the global
+    // @ts-expect-error - cleaning up test global
+    delete globalThis.__non_webpack_require__;
+    __resetDateFnsTzCache();
+  });
+
+  it("should use __non_webpack_require__ when available in webpack environment", () => {
+    const testDate = new Date("2024-06-15T12:00:00Z");
+
+    // Simulate webpack environment by defining __non_webpack_require__
+    // @ts-expect-error - simulating webpack global
+    globalThis.__non_webpack_require__ = require;
+
+    // This should use __non_webpack_require__ and successfully load date-fns-tz
+    const result = toZonedTime(testDate, "America/New_York");
+
+    // Should convert the date (not return original), proving date-fns-tz loaded
+    expect(result).toBeInstanceOf(Date);
+    expect(result.getHours()).toBe(8); // 12:00 UTC = 08:00 EDT
+  });
+});
+
+// Note: The Vite ESM environment case (where require is not available) cannot be
+// tested in Jest because require is always available in Node.js module scope.
+// The code path is covered by an istanbul ignore comment and verified manually
+// in actual Vite environments. See: https://github.com/Hacker0x01/react-datepicker/issues/6204