CODEWITHSUNDEEP
rxjs
Ant Kutschera
Ant Kutschera

Reputation: 6588

Merging a new rxjs observable into existing subscribed observable

I have an rxjs observable which is already subscribed to:

const o = new rxjs.Subject();
o.subscribe( (v) => console.log("value: " + v);

Due to some unrelated event, e.g. a user clicking on a button, I need to go and fetch data from the server, and put that data into the existing observable o. Using axios, I have something like this:

const aPromise = axios.get("someurl...")

I then do the following:

const secondObservable = rxjs.of(aPromise)
                             .subscribe( (response) => o.next(response.data) )

My question is whether there is a better way to put the response data into the existing already subscribed to observable, perhaps using operators?

Upvotes: 3

Views: 1594

Answers (2)

kos
kos

Reputation: 5374

If you know that you need data from your original stream and might get updates from a button click — then we'll need to create a stream of button clicks, e.g.

const btnClick$ = new rxjs.Subject();

onClick(){
  this.btnClick$.next(void 0);
}

Then we'll turn this btnClick$ stream into a http-get request stream, using switchMap:

const request$ = btnClick$.pipe(
  // each click will be turned into a http-get
  switchMap(() => rxjs.of(axios.get("someurl...")))
)

And we're ready to consume results from both streams, original and a stream of possible data updates from server on button click:

// we'll take results both from original stream
// and our new possible source of data
merge(original$, request$).subscribe(data => {
  console.log(data);
})

Heres a little app using mocks:

const { fromEvent, of, merge } = rxjs;
const { map, delay, switchMap } = rxjs.operators;

// create a stream of btn clicks
const theButton = document.getElementById('the-btn');
const btnClicks$ = fromEvent(theButton, 'click');

console.log('Processing...');

// clicks turned into http-gets
const request$ = btnClicks$.pipe(
  switchMap(() => makeRequest())
);

// original source of data
const original$ = of('Please, click the button!').pipe(delay(500));

merge(original$, request$)
  .subscribe(data => {
    console.log(data);
  });

// mock for requests
function makeRequest(){
  return of(Date.now()).pipe(delay(500))
}
<script src="https://unpkg.com/[email protected]/bundles/rxjs.umd.min.js"></script>

<button
  id="the-btn"
  >Click me!</button>

Hope this helps

Upvotes: 1

Adrian Brand
Adrian Brand

Reputation: 21658

You can just pass the result of the call directly to your observable.

const axios = {
  get: url => Promise.resolve('some value')
};

const o = new rxjs.Subject();
o.subscribe(v => { console.log("value: " + v); });

axios.get('url').then(data => { o.next(data); });
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/6.4.0/rxjs.umd.min.js"></script>

Upvotes: 1

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