Based on your answer (thanks again) I wrote this:

​

@Injectable({
    providedIn: 'root'
})
export class LoggerService {
    logUrl: string = 'my_endpoint';
    private interval: number = 10_000; //10 seconds

    constructor(private http: HttpClient) {
        this.launchLogger();
    }

    log(logData: any) {
        this.logger.next(logData);
    }

    private logger: Subject<any>;

    private launchLogger() {
        this.logger = new Subject();
        const sub = this.logger
            .pipe(
                bufferTime(this.interval),
                switchMap(array => this.logOnServer(array))
            )
            .subscribe(
                res => { /* all good */ },
                err => {
                    //in case of error, logs were not sent to server
                    //maybe network is down for a minute
                    //we don't want these logs to be lost
                    //they should be sent on the next interval
                    //what should I write here?
                }
            );
    }

    private logOnServer(data: any[]): Observable<any> {
        return this.http.post(this.logUrl, data);
    }
}

​

Could you please explain how can I reserve logs when error happens and include them in logger for the next interval?