feat: throw error on unknown locale (#1071)

src/faker.ts

@@ -45,8 +45,34 @@ const metadataKeys: ReadonlyArray<keyof LocaleDefinition> = [
 
 export class Faker {
   locales: UsedLocales;
-  locale: UsableLocale;
-  localeFallback: UsableLocale;
+  private _locale: UsableLocale;
+  private _localeFallback: UsableLocale;
+
+  get locale(): UsableLocale {
+    return this._locale;
+  }
+
+  set locale(locale: UsableLocale) {
+    if (!this.locales[locale]) {
+      throw new FakerError(
+        `Locale ${locale} is not supported. You might want to add the requested locale first to \`faker.locales\`.`
+      );
+    }
+    this._locale = locale;
+  }
+
+  get localeFallback(): UsableLocale {
+    return this._localeFallback;
+  }
+
+  set localeFallback(localeFallback: UsableLocale) {
+    if (!this.locales[localeFallback]) {
+      throw new FakerError(
+        `Locale ${localeFallback} is not supported. You might want to add the requested locale first to \`faker.locales\`.`
+      );
+    }
+    this._localeFallback = localeFallback;
+  }
 
   readonly definitions: LocaleDefinition = this.initDefinitions();
 

test/faker.spec.ts

@@ -32,6 +32,24 @@ describe('faker', () => {
     );
   });
 
+  it('should throw error if locale is not known', () => {
+    const instance = new Faker({ locales: { en: { title: 'English' } } });
+    expect(() => (instance.locale = 'unknown')).toThrow(
+      new FakerError(
+        'Locale unknown is not supported. You might want to add the requested locale first to `faker.locales`.'
+      )
+    );
+  });
+
+  it('should throw error if localeFallback is not known', () => {
+    const instance = new Faker({ locales: { en: { title: 'English' } } });
+    expect(() => (instance.localeFallback = 'unknown')).toThrow(
+      new FakerError(
+        'Locale unknown is not supported. You might want to add the requested locale first to `faker.locales`.'
+      )
+    );
+  });
+
   it('should not log anything on startup', () => {
     const spies: Array<SpyInstance> = Object.keys(console)
       .filter((key) => typeof console[key] === 'function')