New validator combines the existing validators such as required, minLength, maxLength, email, and pattern. Also, a new directive, compareWith, is introduced to compare options from a select control, as shown:

<select [compareWith]="byId"   [(ngModel)]="selectedBook">   
   <option *ngFor="let book of   books" [ngValue]="book">{{book.title}}</option>   
</select>   
byId(p1: BookModel, p2:   BookModel) {   
   return p1.id === p2.id;   
}