fetchProductTypeForCategory(event) {
  let category = event.srcElement.attributes.value || event.currentTarget.value;
  this.productTypeSrv.fetchProductTypesParam(category)
    .subscribe(res => {
      this.productTypes = res;
    }, err => {
      console.log(err);
    })
}

<select class="form-control" [formControl]="subCategoryForm.controls['l1category']" (change)="fetchProductTypeForCategory($event)">
  <option *ngFor="let item of categorys" [value]="item.id">{{item.name}}</option>
  <!-- <option *ngFor="let item of categorys" [value]="item.slug">{{item.name}}</option> -->  // need this in order to submit the form
</select>