如何在rxjs中解包map中的可观察对象？

import { of } from 'rxjs';
import { mergeMap } from 'rxjs/operators';

of(1, 2, 3).pipe(
  mergeMap(val => of(`Value: ${val}`))
).subscribe(console.log);

// 输出:
// Value: 1
// Value: 2
// Value: 3

import { of } from 'rxjs';
import { concatMap } from 'rxjs/operators';

of(1, 2, 3).pipe(
  concatMap(val => of(`Value: ${val}`))
).subscribe(console.log);

// 输出:
// Value: 1
// Value: 2
// Value: 3

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

const input = document.querySelector('input');
const keyup$ = fromEvent(input, 'keyup');

keyup$.pipe(
  map(event => event.target.value),
  switchMap(searchTerm => fetch(`https://api.example.com/search?q=${searchTerm}`))
).subscribe(response => console.log(response));

import { interval, of } from 'rxjs';
import { exhaustMap } from 'rxjs/operators';

interval(1000).pipe(
  exhaustMap(() => of('Result'))
).subscribe(console.log);

// 输出:
// Result (每秒一次)

import { of } from 'rxjs';
import { mergeMap, tap, catchError } from 'rxjs/operators';

of(1, 2, 3).pipe(
  mergeMap(val => {
    if (val === 2) {
      throw new Error('Value 2 is not allowed');
    }
    return of(`Value: ${val}`);
  }),
  tap(console.log),
  catchError(error => of(`Caught error: ${error.message}`))
).subscribe();