Angular Material DataTable Pagination undefined

Question

Why mt pagination is not working

export class AppComponent implements OnInit {
  title = 'app';
  displayedColumns: string[] = ['position', 'name', 'weight', 'symbol'];
  dataSource = new MatTableDataSource<PeriodicElement>(ELEMENT_DATA);
  @ViewChild(MatPaginator) paginator: MatPaginator;

  ngOnInit() {
     this.dataSource.paginator = this.paginator;
  }

This is the same exaple which I copied from https://material.angular.io/components/table/overview