Feature: key prefix option (#1644)

* add keyPrefix argument to getFixedT

* add typescript types

* add unit tests

* fix formatting

* improve tests

* code review changes: ts signature

index.d.ts

@@ -947,9 +947,15 @@ export interface i18n {
    * Returns a t function that defaults to given language or namespace.
    * Both params could be arrays of languages or namespaces and will be treated as fallbacks in that case.
    * On the returned function you can like in the t function override the languages or namespaces by passing them in options or by prepending namespace.
+   *
+   * Accepts optional keyPrefix that will be automatically applied to returned t function.
    */
-  getFixedT(lng: string | readonly string[], ns?: string | readonly string[]): TFunction;
-  getFixedT(lng: null, ns: string | readonly string[]): TFunction;
+  getFixedT(
+    lng: string | readonly string[],
+    ns?: string | readonly string[],
+    keyPrefix?: string,
+  ): TFunction;
+  getFixedT(lng: null, ns: string | readonly string[] | null, keyPrefix?: string): TFunction;
 
   /**
    * Changes the language. The callback will be called as soon translations were loaded or an error occurs while loading.

src/i18next.js

@@ -310,7 +310,7 @@ class I18n extends EventEmitter {
     return deferred;
   }
 
-  getFixedT(lng, ns) {
+  getFixedT(lng, ns, keyPrefix) {
     const fixedT = (key, opts, ...rest) => {
       let options;
       if (typeof opts !== 'object') {
@@ -322,14 +322,18 @@ class I18n extends EventEmitter {
       options.lng = options.lng || fixedT.lng;
       options.lngs = options.lngs || fixedT.lngs;
       options.ns = options.ns || fixedT.ns;
-      return this.t(key, options);
+
+      const keySeparator = this.options.keySeparator || '.';
+      const resultKey = keyPrefix ? `${keyPrefix}${keySeparator}${key}` : key;
+      return this.t(resultKey, options);
     };
     if (typeof lng === 'string') {
       fixedT.lng = lng;
     } else {
       fixedT.lngs = lng;
     }
     fixedT.ns = ns;
+    fixedT.keyPrefix = keyPrefix;
     return fixedT;
   }
 

test/i18next.spec.js

@@ -88,6 +88,12 @@ describe('i18next', () => {
         expect(translatedKey).to.equal('default');
         expect(translatedSecondKey).to.equal('default');
       });
+      it('should apply keyPrefix', () => {
+        i18next.addResource('fr', 'translation', 'deeply.nested.key', 'ici!');
+        const t = i18next.getFixedT('fr', null, 'deeply.nested');
+        expect(t('key')).to.equal('ici!');
+        expect(t.keyPrefix).to.equal('deeply.nested');
+      });
     });
   });