onValChange(event: Date) {
    const datePipe = new DatePipe('en-US');
    const val = datePipe.transform(event, 'MM/dd/yyyy');
    this.writeValue(moment(event));
  }

<input class="form-control form-control-sm requiredV" [(ngModel)]="dateValue"
             placeholder="mm/dd/yyyy" name="dateField" id="dateField" ngbDatepicker
             #dateFieldngb="ngbDatepicker" [required]="isRequired"
             [ngClass]="{'isUntouched':formName.submitted}" (ngModelChange)="onValChange($event)"
             (keypress)="allow_only_numbers($event)" (click)="dateFieldngb.toggle()" />