An injection token that allows you to provide one or more initialization functions. These function are injected at application startup and executed during app initialization. If any of these functions returns a Promise, initialization does not complete until the Promise is resolved.
const APP_INITIALIZER: InjectionToken<(() => void)>;
You can, for example, create a factory function that loads language data or an external configuration, and provide that function to the
APP_INITIALIZER token. That way, the function is executed during the application bootstrap process, and the needed data is available on startup.