add simple toJSON function to fix uncontrolled serialization

fixes: i18next/react-i18next#1322

CHANGELOG.md

@@ -1,3 +1,7 @@
+### 20.3.0
+
+- add simple toJSON function to fix uncontrolled serialization, fixes [1322](https://github.com/i18next/react-i18next/issues/1322)
+
 ### 20.2.4
 
 - fix types for LanguageDetector detect function

i18next.js

@@ -2468,6 +2468,16 @@
         };
         return clone;
       }
+    }, {
+      key: "toJSON",
+      value: function toJSON() {
+        return {
+          options: this.options,
+          store: this.store,
+          language: this.language,
+          languages: this.languages
+        };
+      }
     }]);
 
     return I18n;

src/i18next.js

@@ -529,6 +529,15 @@ class I18n extends EventEmitter {
 
     return clone;
   }
+
+  toJSON() {
+    return {
+      options: this.options,
+      store: this.store,
+      language: this.language,
+      languages: this.languages
+    };
+  }
 }
 
 export default new I18n();

test/i18next.spec.js

@@ -1,4 +1,5 @@
 import i18next from '../src/i18next.js';
+import { get as getDefaults } from '../src/defaults';
 
 describe('i18next', () => {
   before(() => {
@@ -131,4 +132,49 @@ describe('i18next', () => {
       });
     });
   });
+
+  describe('#JSON.stringify', () => {
+    let newInstance;
+    before(() => {
+      newInstance = i18next.createInstance({ some: 'options' });
+    });
+
+    it('it should JSON.stringify non-initialized without errors', () => {
+      expect(JSON.stringify(newInstance)).to.equal(
+        JSON.stringify({
+          options: { some: 'options' },
+        }),
+      );
+    });
+
+    it('it should JSON.stringify initialized without errors', done => {
+      newInstance.init({ other: 'opts' }, err => {
+        if (err) return done(err);
+
+        newInstance.addResourceBundle('en', 'translation', { key: 'value' });
+        newInstance.changeLanguage('en');
+
+        expect(JSON.stringify(newInstance)).to.equal(
+          JSON.stringify({
+            options: {
+              ...getDefaults(),
+              some: 'options',
+              other: 'opts',
+              ignoreJSONStructure: true,
+            },
+            store: {
+              en: {
+                translation: {
+                  key: 'value',
+                },
+              },
+            },
+            language: 'en',
+            languages: ['en', 'dev'],
+          }),
+        );
+        done();
+      });
+    });
+  });
 });