Angular load file content once on startup

Question

I am using Angular 5 & need some configuration data from a .json file before Angular startup. I tried using APP_INITIALIZER as below in app.module.ts

const appConfigLoader = (appConfig: AppConfig) => {
    return () => {
        return appConfig.loadAppConfig();
    };
};
@NgModule({
    providers: [
        {
            provide: APP_INITIALIZER,
            useFactory: appConfigLoader,
            multi: true,
            deps: [AppConfig]
        }
    ]
})

My loadAppConfig function

loadAppConfig() {
    const http = this.injector.get(HttpClient);
    const configPath = DEBUG_INFO_ENABLED ? 'config/application-dev.json' : 'config/application-prod.json';
    return http.get(configPath)
        .toPromise()
        .then((data) => {
            AppConfig.API_URL = data['API_URL'];
        });
}

Currently it works well but when I update content of application-dev.json/application-prod.json, Angular also update it to use new content. So I wonder is there any solution if I want it to load only once on startup and doesn't update when I update file content?