RxJs mapping operators

01.ts

const http$ : Observable<Course[]> = this.http.get('/api/courses');

http$
    .pipe(
        tap(() => console.log('HTTP request executed')),
        map(res => Object.values(res['payload']))
    )
    .subscribe(
        courses => console.log("courses", courses)
    );

02.ts

this.form.valueChanges
    .subscribe(
       formValue => {
      
           const httpPost$ = 
                 this.http.put(`/api/course/${courseId}`, formValue);

           httpPost$.subscribe(
               res => ... handle successful save ...
               err => ... handle save error ...
           );

       }        
    );

03.ts

const series1$ = of('a', 'b');

const series2$ = of('x', 'y');

const result$ = concat(series1$, series2$);

result$.subscribe(console.log);

04.ts

this.form.valueChanges
    .pipe(
        concatMap(formValue => this.http.put(`/api/course/${courseId}`, 
                                             formValue))
    )
    .subscribe(
       saveResult =>  ... handle successful save ...,
        err => ... handle save error ...      
    );

05.ts

const series1$ = interval(1000).pipe(map(val => val*10));

const series2$ = interval(1000).pipe(map(val => val*100));

const result$ = merge(series1$, series2$);

result$.subscribe(console.log);

06.ts

this.form.valueChanges
    .pipe(
        mergeMap(formValue => 
                 this.http.put(`/api/course/${courseId}`, 
                               formValue))
    )
    .subscribe(
       saveResult =>  ... handle successful save ...,
        err => ... handle save error ...      
    );

07.ts

const searchText$: Observable<string> = 
      fromEvent<any>(this.input.nativeElement, 'keyup')
    .pipe(
        map(event => event.target.value),
        startWith('')
    )
    .subscribe(console.log);
  
  

08.ts

const searchText$: Observable<string> = 
      fromEvent<any>(this.input.nativeElement, 'keyup')
    .pipe(
        map(event => event.target.value),
        startWith(''),
        debounceTime(400)
    )
    .subscribe(console.log);

09.ts

const searchText$: Observable<string> = 
      fromEvent<any>(this.input.nativeElement, 'keyup')
    .pipe(
        map(event => event.target.value),
        startWith(''),
        debounceTime(400),
        distinctUntilChanged()
    ); 

const lessons$: Observable<Lesson[]> = searchText$
    .pipe(
        switchMap(search => this.loadLessons(search))        
    )
    .subscribe();

function loadLessons(search:string): Observable<Lesson[]> {
    
    const params = new HttpParams().set('search', search);
   
    return this.http.get(`/api/lessons/${coursesId}`, {params});
}

10.ts

fromEvent(this.saveButton.nativeElement, 'click')
    .pipe(
        concatMap(() => this.saveCourse(this.form.value))
    )
    .subscribe();

11.ts

fromEvent(this.saveButton.nativeElement, 'click')
    .pipe(
        exhaustMap(() => this.saveCourse(this.form.value))
    )
    .subscribe();

12.ts

@Component({
    selector: 'course-dialog',
    templateUrl: './course-dialog.component.html'
})
export class CourseDialogComponent implements AfterViewInit {

    form: FormGroup;
    course:Course;

    @ViewChild('saveButton') saveButton: ElementRef;

    constructor(
        private fb: FormBuilder,
        private dialogRef: MatDialogRef<CourseDialogComponent>,
        @Inject(MAT_DIALOG_DATA) course:Course) {

        this.course = course;

        this.form = fb.group({
            description: [course.description, 
                          Validators.required],
            category: [course.category, Validators.required],
            releasedAt: [moment(), Validators.required],
            longDescription: [course.longDescription,
                              Validators.required]
        });
    }
}
          
          

Shouldn't 07.ts, 08.ts and 09.ts be doing the subscribe as a separate statement? Now it seems like they're trying to assign a Subscription to a const typed as an Observable.
For example

const searchText$ :Observable<string> = ...pipe(...);
searchText$.subscribe(console.log);