Dynamic amount of sequential HTTP requests in Angular

Question

This is my first question here, sorry if it isn't detailed enough.

I am looking to make a dynamic amount of requests sequentially (could be a lot) to get data,

I would need this data to be collected from each request and returned as a final observable at the end of the last request.

I have attempted to use forkJoin to combine the requests, although, this does not make each request sequentially and then also concat, which emits and observable after each request.

Hi, Please show some code to help us see what you've already tried — Skel
– Skel, Commented Mar 4, 2020 at 16:41
Do you know how many requests you'll need to make when you start, or is it possible that it might change while requests are being made? — Kurt Hamilton
– Kurt Hamilton, Commented Mar 4, 2020 at 16:42
@KurtHamilton Once you start, you will know how many requests you will need. — jay
– jay, Commented Mar 4, 2020 at 16:48

Kurt Hamilton · Accepted Answer · 2020-03-04 17:46:48Z

9

You want to:

Make an arbitrary number of sequential HTTP requests (based on some array, I assume)
Return an array of results

I would use concat in conjunction with toArray here. concat will run the requests sequentially, and toArray will emit an array when all responses are available.

// some dynamic array
const source = [ 1, 2, 3, 4, 5 ];

const observables = source.map(x => this.http.get('some url'));
concat(
  ...observables
).pipe(
  toArray()
).subscribe(responses => {
  console.log(responses);
  // array of results
});

DEMO: https://stackblitz.com/edit/angular-s1fdxj

edited Mar 4, 2020 at 17:46

answered Mar 4, 2020 at 16:54

Kurt Hamilton

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2 Comments

Eliseo Over a year ago

you can use also toArray: learnrxjs.io/learn-rxjs/operators/transformation/toarray

Kurt Hamilton Over a year ago

@Eliseo Thanks. I knew there would be a better implementation

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