如何使用rxjs取消嵌套请求

import { from, Observable, Subject } from 'rxjs';
import { mergeMap, takeUntil } from 'rxjs/operators';

const cancelRequest$ = new Subject();

function nestedRequest(url: string): Observable<any> {
  return from(fetch(url)).pipe(
    mergeMap(response => response.json())
  );
}

function mainFunction() {
  nestedRequest('https://api.example.com/endpoint1')
    .pipe(takeUntil(cancelRequest$))
    .subscribe(response1 => {
      // 处理第一个嵌套请求的响应数据

      nestedRequest('https://api.example.com/endpoint2')
        .pipe(takeUntil(cancelRequest$))
        .subscribe(response2 => {
          // 处理第二个嵌套请求的响应数据
        });
    });

  // 当需要取消嵌套请求时
  cancelRequest$.next();
}