import { of } from 'rxjs';
import { concatMap, timeout, catchError, delay } from 'rxjs/operators';
function makeRequest(timeToDelay) {
return of('Request Complete!').pipe(delay(timeToDelay));
makeRequest(duration).pipe(
catchError(error => of(`Request timed out after: ${duration}`))
* "Request timed out after: 4000"
* "Request timed out after: 3000"
.subscribe(val => console.log(val));