Any Scenario(s) that RXJS Observable Subscribe wont trigger either success and error

Question

This is more like question than resolve a problem.
I would like to know if there any scenario that both "Success" and Error" is not triggered.

The post call to "/logout" will result Http status return code 200 with empty respond body which is expected

import { httpClient } from angular/common/http;
private http: HttpClient;

this.http.post<any>('/logout', {})
      .subscribe(
      () => {
        console.log("Logout");
      }, error => {
        console.log(error);
      },
      () => {
        console.log("Finally");
      });

It will output "Finally" 100% of time. That means success and error is not triggered at all.

Is there possibilities that either success and error not trigger. And clearly the http status code response is 200 OK.

Update: The answer that @meriton provided work great.

Answer 1

Observable, in general, are not required to complete or error. They may remain live, and continue to emit values, forever.

However, Observable returned by HttpClient are guaranteed to terminate with either success or error (though the error may take a few minutes in case of a timeout) according to the HTTP status of the response. The presence of absence of a body does not affect this. If the request is successful, the observable will emit exactly one value: the response body (or null if the response body is absent).

I can not reproduce your claim that "success or error is not triggered at all". May you have misunderstood what the callbacks mean? When you provide three callbacks to subscribe, they are, in order:

• the next callback, which receives emitted values
• the error callback, which notifies that the Observable has aborted due to an error
• the complete callback, which notifies that the Observable has completed successfully

The danger of mixing up callbacks is one reason why the RXJS team has deprecated passing several callbacks as separate arguments to subscribe in RXJS 8. The future proof way to write your code would be:

this.http.post<any>('/logout', {}).subscribe({
  complete: () => {
    console.log("Logout successful")
  },
  error: (error) => {
    console.log(error);
  }
});

BTW, none of these callbacks mean "finally", as in the finally clause of a try-statement, which is executed both in case of success and error. If you want to do something irrespective of whether the Observable completed successfully or failed with an error, you could use the finalize operator.