Urutan RXJS dari panggilan API

firstPOSTCallToAPI('url', data).pipe(
    concatMap(result1 => secondPOSTCallToAPI('url', result1))
      concatMap( result2 => thirdPOSTCallToAPI('url', result2))
       concatMap(result3 => fourthPOSTCallToAPI('url', result3))
    ....
).subscribe(
    success => { /* display success msg */ },
    errorData => { /* display error msg */ }
);
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