MissingTranslationHandler API

Use a MissingTranslationHandler to customize what happens when a translation key cannot be resolved.

The fallbackLang configuration is consulted first: if a fallback language is set, ngx-translate tries the key there before invoking the handler. With no fallback, the handler is called immediately.

The matching provider helper is provideMissingTranslationHandler(). See Configuration → Provider helpers.

API

export interface MissingTranslationHandlerParams {
  key: string;
  translateService: TranslateService;
  interpolateParams?: object;
}

export abstract class MissingTranslationHandler {
  abstract handle(
    params: MissingTranslationHandlerParams,
  ): StrictTranslation | Observable<StrictTranslation>;
}

API Description

handle() is called once per missing translation with the following:

• key: the translation ID that was not found.
• translateService: the TranslateService instance making the lookup.
• interpolateParams: the parameters passed by the caller (if any).

The default handler returns the key itself.

Return value handling:

• If the handler returns a value, that value is used.
• If it returns an Observable, the value emitted by the observable is used, except when the lookup was via instant(), which is synchronous and cannot wait for an observable.
• If it returns undefined, the key is used as the value.

Registering a Custom Handler

app.config.ts

import {
  provideTranslateService,
  provideMissingTranslationHandler,
} from '@ngx-translate/core';

export const appConfig: ApplicationConfig = {
  providers: [
    provideTranslateService({
      missingTranslationHandler: provideMissingTranslationHandler(MyHandler),
    }),
  ],
};

Factory form:

provideTranslateService({
  missingTranslationHandler: provideMissingTranslationHandler(
    () => new MyHandler({ reportTo: '/missing-keys' }),
  ),
})

How to Build a Custom Handler

For a step-by-step example see How to handle missing translations.