index.ts

import { of } from 'rxjs';
import { switchMap, map, catchError } from 'rxjs/operators';

of(1, 2, 3, 4, 5).pipe(
  switchMap(x => of(x)),
  map(x => {
    if (x != 3) {
      return `x: ${x}`
    }
    throw 'x is 3';
  }),
  catchError(error => of(error)),
).subscribe(console.log);

console.log();

of(1, 2, 3, 4, 5).pipe(
  switchMap(y => of(y).pipe(
    map(y => {
      if (y != 3) {
        return `y: ${y}`
      }
      throw 'y is 3';
    }),
    catchError(error => of(error)),
  )),
).subscribe(console.log);