问如何检查多个订阅是否到达onComplete()？

EN

import { Component } from '@angular/core';
import { forkJoin, Observable } from 'rxjs'

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ]
})
export class AppComponent  {
  name = 'Angular';

 constructor(){
   forkJoin([this.observableTest(2000), this.observableTest(3000)])
   .subscribe(data => {
     this.runMeAfter(data)
   })
 }

  runMeAfter(data){
    alert('yeahhh done with data, check your console for data')
    console.log(data)
  }

  observableTest(delay){
    return Observable.create(observer => {
      setTimeout(() => {
        observer.next("data to send can be object or anything");
        console.log("am done");
        observer.complete(); // to show we are done with our processing 
      }, delay);
    })
  }
}

const stream1$ = of (1,2,3);
    const stream2$ = of (4,5,6);
    const result$ = merge(stream1$, stream2$);
    result$.subscribe(
// value
      (val) => {console.log(val) },
// error
    (err) => { console.log(err) },
//on complete
    ()=>{console.log('completed') });