Observable Finally on Subscribe

According to this artcle, onComplete and onError function of the subscribe are mutually exclusive.

Meaning either onError or onComplete events will fire up in my subscribe.
I have a logic block which needs to be executed whether I receive an error, or I finish my steam of information successfully.

I looked up for something like finally in python, but all I found is finally which needs to be attached to the observable I create.

But I want to to do that logic only when I subscribe, and after the stream has ended, whether successfully or with an error.

Any ideas?

Solution 1:

The current "pipable" variant of this operator is called finalize() (since RxJS 6). The older and now deprecated "patch" operator was called finally() (until RxJS 5.5).

I think finalize() operator is actually correct. You say:

do that logic only when I subscribe, and after the stream has ended

which is not a problem I think. You can have a single source and use finalize() before subscribing to it if you want. This way you're not required to always use finalize():

let source = new Observable(observer => {
  observer.next(1);
  observer.error('error message');
  observer.next(3);
  observer.complete();
}).pipe(
  publish(),
);

source.pipe(
  finalize(() => console.log('Finally callback')),
).subscribe(
  value => console.log('#1 Next:', value),
  error => console.log('#1 Error:', error),
  () => console.log('#1 Complete')
);

source.subscribe(
  value => console.log('#2 Next:', value),
  error => console.log('#2 Error:', error),
  () => console.log('#2 Complete')
);

source.connect();

This prints to console:

#1 Next: 1
#2 Next: 1
#1 Error: error message
Finally callback
#2 Error: error message

Jan 2019: Updated for RxJS 6

Solution 2:

The only thing which worked for me is this

fetchData()
  .subscribe(
    (data) => {
       //Called when success
     },
    (error) => {
       //Called when error
    }
  ).add(() => {
       //Called when operation is complete (both success and error)
  });