sort-descending.pipe.ts

@Pipe({
    name: "sortDescending"
})
export class SortDescendingPipe implements PipeTransform {

    transform(list: any[], ...args: any[]): any[] {
      return list.slice().sort((elem1, elem2) => elem2.rollNo - elem1.rollNo);
    }
}

// use it in your template like this:
{{ todo | sortDescending }} to display it or like <div *ngFor="let singleTodo of todo | sortDescending">…</div> to iterate over the descending array