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javascriptoperatorsrxjsreactive-programming
bbop99
bbop99

Reputation: 1685

RxJs V4 Operator that combines forkJoin and map

I am trying to find an operator that lets me handle the operations performed by forkJoin and map in one step instead of two.

My input is an array of observables with varying lengths and I would like to wait until all of them have completed and then create a computed result from the observable outputs that I can subscribe to.

I haven't come across one that allows for those requirements and takes an array as input.

Below an example of a use case:

const observable1 = Rx.Observable.create(
  (observer) => {
    observer.onNext([1, 2, 3, 4]);
    observer.complete();
  }
);

const observable2 = Rx.Observable.create(
  (observer) => {
    observer.onNext([5, 6, 7, 8]);
    observer.complete();
  }
);

Rx.Observable.magigOperator([observable1, observable2])
   .subscribe(
     (result) => console.log
   );

Now the result I am trying to get is an output of [1,2,3,4,5,6,7,8]; I can achieve it by using forkJoin and map and running a flatten function, but I was wondering whether there is a single operator that allows me to do this in one go.

Thanks.

Upvotes: 0

Views: 1788

Answers (3)

Lievno
Lievno

Reputation: 1041

By the way you can create your observables like this (cold observable are automatically completed when values are emitted):

const observable1 = Rx.Observable.of([1,2,3,4]);
const observable2 = Rx.Observable.of([5,6,7,8]);

Observable.forkJoin(observable1, observable2, (...args)=> [].concat(...args));

Thanks kit for you answer.

Upvotes: 0

Sergey Karavaev
Sergey Karavaev

Reputation: 1761

You don't have to use map, you can just pass a result selector function as a last argument of forkJoin, e.g.:

Rx.Observable.forkJoin([observable1, observable2], _.concat)

Also note that observable1 and observable2 in your example do not complete which prevents forkJoin from emitting the result.

Upvotes: 2

kit
kit

Reputation: 4920

last argument of forkJoin is a function that can manipulate the results from observables. try something like this:

const observable1 = Rx.Observable.create(
    (observer) => {
        observer.next([1, 2, 3, 4]);
        observer.complete();
    }
);

const observable2 = Rx.Observable.create(
    (observer) => {
        observer.next([5, 6, 7, 8]);
        observer.complete();
    }
);

Rx.Observable.forkJoin([observable1, observable2], (res1, res2) => [...res1, ...res2]).subscribe((res) => {
    console.log(res);
});

notice that observer has next no onNext method. Also if you want to you forkJoin the observer has to complete.

Upvotes: 0

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