Factory function for creating a real service or a mock service

app.module.ts

export function locationsServiceFactory() {
    return (http: HttpClient, configService: AppConfigService, logging: LoggingService): LocationsService => {
        if (configService.useFakeData) {
            logging.logInfo('use mock service');
            return new LocationsServiceMock();
        } else {
            logging.logInfo('use real service');
            return new LocationsServiceImpl(http, configService);
        }
    };
}