How to properly chain rxjs 6 observables?

Question

Any suggestions, how this can be rewritten in more promise-chaining style?:

this.apiService.sendPutRequest('/api/users/activate', usrObj).pipe(
        map(() => {
            return this.apiService.sendGetRequest('/api/users/' + this.currentUserId).pipe(
                map(data => {
                    return this.setActiveUser(data).pipe(
                        map(() => {
                            return this.apiService.sendGetRequest('api/tasks/user/' + this.currentUserId).pipe(
                                map(tasks => {
                                    return this.taskService.setCurrentUserTasks(tasks);
                                })
                            );
                        })
                    );
                })
            );
        })
    );

Answer 1

You can use switchMap for handling observables and tap for side efects handling. And you need to subscribe because it's cold observable

For error handling use catchError for all requests

this.apiService.sendPutRequest('/api/users/activate', usrObj).pipe(
    catchError(err=> this.errorHandler(err)),
    switchMap(() => this.apiService.sendGetRequest('/api/users/' + this.currentUserId)
        .pipe(catchError(err=> this.errorHandler(err)))
    ),
    tap(data => this.setActiveUser(data)),
    switchMap(() => this.apiService.sendGetRequest('api/tasks/user/' + this.currentUserId)
        .pipe(catchError(err=> this.errorHandler(err)))
    ),
    tap(tasks => this.taskService.setCurrentUserTasks(tasks))
).subscribe()

Answer 2

use SwitchMap for that.

mainApiCall.pipe(
    switchMap(result=>secondApiCall(result)),
    switchMap(resultFromSecondApiCall=>thirdApiCall(resultFromSecond))
...
and so on
)