Angular 9.0(blog.angular.io)

    public user$: BehaviorSubject<any[]>;

    constructor(
        public selectionService: SelectionService
    ) {
        this.userSubscription$ = selectionService.user$.subscribe(user => this.drawUserInCanvas(user));
    }

    <ng-template [ngIf]="lessons" [ngIfElse]="loading">
       <div class="lessons-list">
         ... 
       </div>
    </ng-template>

    <ng-template #loading>
        <div>Loading...</div>
    </ng-template>

    @Component({
      selector: 'app-root',
      template: `      
    <ng-template #estimateTemplate let-lessonsCounter="estimate">
        <div> Approximately {{lessonsCounter}} lessons ...</div>
    </ng-template>
    <ng-container 
       *ngTemplateOutlet="estimateTemplate;context:ctx">
    </ng-container>
    `})
    export class AppComponent {

        totalEstimate = 10;
        ctx = {estimate: this.totalEstimate};

    }