When to use asObservable() in rxjs?

Question

I am wondering what is the use of asObservable:

As per docs:

An observable sequence that hides the identity of the source sequence.

But why would you need to hide the sequence?

Answer 1

When you don't want to leak the "observer-side" of a Subject out of your API. (Basically to prevent leaky abstraction).

var myAPI = {
  getData: () => {
    var subject = new Subject();
    var source = new SomeWeirdDataSource();
    source.onMessage = (data) => subject.next({ type: 'message', data });
    source.onOtherMessage = (data) => subject.next({ type: 'othermessage', data });
    return subject.asObservable();
  }
};

Now when someone gets the observable result from myAPI.getData() they can't next values in to the result:

var result = myAPI.getData();
result.next('LOL hax!'); // throws an error because `next` doesn't exist