RxJS BehaviorSubject with custom create logic

Question

Because BehaviorSubject extends Subject and Subject extends Observable, all of those three have static .create(observer) method to create them using custom values emission logic.
I' able to use with good result Observable.create(observer), for instance:

a = Rx.Observable.create(obs => {
    setInterval(() => {
        obs.next('tick');
    }, 500)
})
s = a.subscribe(v => console.log(v))

Gives me expected output (tick every 500ms)

But when I replace Observable with Subject/BehaviorSubject, it's not so willing to get up and running:

a = Rx.Subject.create(obs => {
    setInterval(() => {
        obs.next('tick');
    }, 500)
})
s = a.subscribe(v => console.log(v)); // Nothing
a.next(5); // Still nothing

Basically, subject seems to work as intended to only if they are created via new operator like below:

a = new Rx.Subject();
s = a.subscribe(v => {console.log(v)});
a.next(5) // Ok, got value here

Even if I try to use non-parametrized create method, which invocation shall boil down to same result as using new:

a = Rx.Subject.create();

I'm still unable to force it to emit values.

I'm aware that subjects are designed to receive values from outside world (not to generate them internally as Observables), thus subject shall be triggered by external code with subject.next('value'), but I was just curios that if they are strictly related to Observables, logic behind create and further behavior shall be same...

Can anyone explain, why usage of create on Subject (even if they are not designed to work this way, but still it shall be possible) does not work as supposed to?

RxJS BehaviorSubject with custom create logic

0 Answers