Rxjs how to make two http requests in sequence?

Question

JavaScript

There is a stream for receiving data and deleting data.
It is necessary to sequentially delete the data, first the first data, and only then the second. But first you need to make sure they are.
Here's what I wrote, but I think it's wrong

let params1 = 1;
let params2 = 2;

service.getData(): Observable
service.deleteData() : Observable

service.getData(params1).subscribe(res => {
  if(res) {
     service.deleteData(params1).subscribe(res => {
       service.getData(params2).subscribe(res => {
           if(res) {
             service.deleteData(params2).subscribe();
           }
     });
  } else {
     service.getData(params2).subscribe(res => {
        if(res) {
           service.deleteData(params2).subscribe();
        }
  }
});

Answer 1

In general, I found the answer myself, maybe it will be useful to someone

// последовательно

let someStream$ = service.getData().flatMap(res => {
  return service.deleteData(res)
})

someStream$.subscribe(res => {
   // res - результат последнего 
})

// параллельно
let getData$ = service.getData();
let deleteData$ = service.deleteData();

Observable.forkJoin([getData$, deleteData$]).subscribe(results => {
      // results[0] дата из getData$
      // results[1] дата из deleteData$
      this.a = results[1];
      this.b = results[0];
    });