rxjs - Angular observables - Do I need unsubscribe if no subscription?

Question

I am using latest angular 8 and am new to the concept of observables. Question I have if I am directly calling an observable and not apply it to a subscription variable, do I still need to unsubscribe. Below are the scenarios I would like to know if I need to unsubscribe on? Many thanks in advance

Scenario 1 - Calling a httpService from a component:

Service - httpService

     getContactsHttp(){
         let headers: any = new HttpHeaders(this.authService.getHeadersClient());
         return this.httpClient.get('/contacts', {headers: headers})
          .pipe(timeout(this.authService.getTimeoutLimit('normal')));
        }

Component - Calling getContactsHttp and sorting response

getContacts() {
 this.httpService.getContactsHttp().subscribe((data:any[])=>{
  this.records = this.sortData(data)
 })
}

Scenario 2 - on an observable susbcribed in a component

contacts$: new Subject<any[]>;

ngOnInit() {
  this.getContacts();
  this.contacts$.subscribe((data:any[])=>{
    this.records = this.sortData(data);
  })
}

getContacts() {
    this.httpService.getContactsHttp().subscribe((data:ContactSearch[])=>{      
      this.contacts$.next(data);
    })
  }

Service - httpService

     getContactsHttp(){
         let headers: any = new HttpHeaders(this.authService.getHeadersClient());
         return this.httpClient.get('/contacts', {headers: headers})
          .pipe(timeout(this.authService.getTimeoutLimit('normal')));
        }

Answer 1

Short answer, yes, you still unsubscribe to your observables in your component to avoid subscription leaks. One of my preferred ways of doing so would be to make use of the takeUntil() operator.

This is how you can use it in your component.

private unsubscribe: Subject<void> = new Subject();

ngOnDestroy() {
  this.unsubscribe.next();
  this.unsubscribe.complete();
}

getContacts() {
  this.httpService.getContactsHttp()
    .pipe(
      takeUntil(this.unsubscribe),
    ).subscribe((data:ContactSearch[])=>{      
      this.contacts$.next(data);
    });
 }

As explained by Brian Love,

• First, we import the takeUntil() operator as well as the Subject class.
• Next, we define a private instance property named unsubscribe, which is a Subject.
• We also create a new instance of Subject, defining the generic type as void. We use the takeUntil() operator in the pipe() method before invoking subscribe(), providing the unsubscribe observable.
• In the ngOnDestroy() lifecycle method we emit a next() notification, and then complete() the unsubscribe observable. The subscription is now complete, and we have immediately unsubscribed when the ngOnDestroy() method is invoked during the lifecycle of our component.