Recursive Http Calls. The RXJS way 😎

#rxjs #typescript #axios #recusivity

This article will show a quick example of achieving recursive http calls using RXJS for those who suffer from Promises.

Imagine that you want to collect all entries from an endpoint that only supports a paging API, means that you can't get all rows at once. So the idea is to keep calling the Api by page till the last page which is our stop condition.

I'll use an Endpoint to fetch Artists

While next is truthy we proceed to the next call with the new page.

Let's move to the fun stuffs 😎, To achieve that we will have a magic rxjs operator EXPAND.

import { from, EMPTY } from 'rxjs';
import { expand, tap, switchMap } from 'rxjs/operators';

let rows = []
const firstUrl = 'https://api.happi.dev/v1/artists?page=1'
const getArtists = (url: string) => from(fetch(url)).pipe(
    switchMap(response => response.json())
)

getArtists(firstUrl).pipe(
 tap(response => rows = rows.concat(response.result)), // on success we concat with the new coming rows
 expand((previousData) => previousData.next 
            ? getArtists(previousData.next)
            : EMPTY;
 )
).subscribe();