[RxJS] Creation operator: create()

We have been using Observable.create() a lot in previous lessons, so let‘s take a closer look how does it work.

The create function:

var foo = Rx.Observable.create( function(observer){
  observer.next(42);
  observer.next(100);
  observer.next(200);
  observer.complete();
})  ;

foo.subscribe(
  (x)=>{console.log(‘next ‘ + x);},
  (err)=>{console.log(‘err ‘ + err);},
  ()=>{console.log(‘done‘);},
)

In deep, create() function equal to new Rx.Observable():

var foo = new Rx.Observable( function(observer){
  observer.next(42);
  observer.next(100);
  observer.next(200);
  observer.complete();
})  ;

And this also equal to:

function subscribe(observer){
  observer.next(42);
  observer.next(100);
  observer.next(200);
  observer.complete();
}

var foo = new Rx.Observable( subscribe );

So, if we get rid of RxJS, then we can create the create() function like:

function subscribe(observer){
  observer.next(42);
  observer.next(100);
  observer.next(200);
  observer.complete();
}

var observer = {
  next: (x)=>{console.log(‘next ‘ + x);},
  error: (err)=>{console.log(‘err ‘ + err);},
  complete: ()=>{console.log(‘done‘);}
}

subscribe(observer);

Of course, it‘s useful to have the observable type because then it has all those nice operators that we saw and that we are also seeing new operators coming next. If you paid attention, then you‘re going to remember that in the subscribe, we had previously three functions here as argument. Instead of an object, as we have now, we had just these three functions.

Also, the observable type, it converts these three functions into an observer object. Before it calls this, it will actually take these three functions and put labels in front of them like that, to create the observer object. It‘s normalizing it.