fix: Cannot redefine property: __original https://github.com/i18next/react-i18next/issues/1863\#issuecomment-3528319023

Author: adrai

CHANGELOG.md

@@ -1,3 +1,7 @@
+### 16.3.2
+
+- fix: avoid "Uncaught TypeError: Cannot redefine property: \_\_original"
+
 ### 16.3.1
 
 - revert fix: Incosistent behaviour of Trans and t. Trans set defaultValue when t call doesn't set the field. [1876](https://github.com/i18next/react-i18next/issues/1876) [f22d478](https://github.com/i18next/react-i18next/commit/f22d4787187e6cfc54d57f5fbede1c816ea19565)

react-i18next.js

@@ -3499,13 +3499,17 @@
     }, [i18n, props.lng, namespaces, ready, useSuspense, loadCount]);
     const finalI18n = i18n || {};
     const ret = React.useMemo(() => {
-      const i18nWrapper = Object.create(Object.getPrototypeOf(finalI18n), Object.getOwnPropertyDescriptors(finalI18n));
-      Object.defineProperty(i18nWrapper, '__original', {
-        value: finalI18n,
-        writable: false,
-        enumerable: false,
-        configurable: false
-      });
+      const descriptors = Object.getOwnPropertyDescriptors(finalI18n);
+      if (descriptors.__original) delete descriptors.__original;
+      const i18nWrapper = Object.create(Object.getPrototypeOf(finalI18n), descriptors);
+      if (!Object.prototype.hasOwnProperty.call(i18nWrapper, '__original')) {
+        Object.defineProperty(i18nWrapper, '__original', {
+          value: finalI18n,
+          writable: false,
+          enumerable: false,
+          configurable: false
+        });
+      }
       const arr = [t, i18nWrapper, ready];
       arr.t = t;
       arr.i18n = i18nWrapper;

react-i18next.min.js

@@ -129,18 +129,20 @@ export const useTranslation = (ns, props = {}) => {
   const finalI18n = i18n || {};
 
   const ret = useMemo(() => {
-    const i18nWrapper = Object.create(
-      Object.getPrototypeOf(finalI18n),
-      Object.getOwnPropertyDescriptors(finalI18n),
-    );
-
-    // Store reference to the original instance for tests/debugging
-    Object.defineProperty(i18nWrapper, '__original', {
-      value: finalI18n,
-      writable: false,
-      enumerable: false,
-      configurable: false,
-    });
+    // Copy descriptors but avoid carrying over any existing "__original"
+    const descriptors = Object.getOwnPropertyDescriptors(finalI18n);
+    if (descriptors.__original) delete descriptors.__original;
+    const i18nWrapper = Object.create(Object.getPrototypeOf(finalI18n), descriptors);
+
+    // Store reference to the original instance for tests/debugging if absent
+    if (!Object.prototype.hasOwnProperty.call(i18nWrapper, '__original')) {
+      Object.defineProperty(i18nWrapper, '__original', {
+        value: finalI18n,
+        writable: false,
+        enumerable: false,
+        configurable: false,
+      });
+    }
 
     const arr = [t, i18nWrapper, ready];
     arr.t = t;

src/useTranslation.js

@@ -254,4 +254,29 @@ describe('useTranslation', () => {
       expect(container.textContent).toBeTruthy();
     });
   });
+
+  describe('useTranslation __original safety', () => {
+    it('does not throw when the source i18n has a non-configurable __original property', async () => {
+      const mockI18n = createInstance();
+      await mockI18n.init({
+        lng: 'en',
+        resources: { en: { translation: { key1: 'test' } } },
+        react: { useSuspense: false },
+      });
+
+      // Simulate a non-configurable __original on the source instance
+      Object.defineProperty(mockI18n, '__original', {
+        value: 'existing',
+        writable: false,
+        enumerable: false,
+        configurable: false,
+      });
+
+      // Should not throw; wrapper creation should handle the existing non-configurable descriptor
+      const { result } = renderHook(() => useTranslation('translation', { i18n: mockI18n }));
+
+      // The returned wrapper should expose __original pointing to the original instance
+      expect(result.current.i18n.__original).toBe(mockI18n);
+    });
+  });
 });