When doing a two way binding [(ngModel)]= to a piped value [(ngModel)]="camp.end_at | date:'yyyy-MM-dd'" you get the following error
Parser Error: Cannot have a pipe in an action expression
To correct, do one way binding and change the value via (ngModelChange) e.g.
<input type="date" name="eday" min="2018-08-01" class="form-control rounded" [(ngModel)]="camp.end_at | date:'yyyy-MM-dd'" (ngModelChange)="camp.end_at=$event">
source https://stackoverflow.com/questions/39642882/using-pipes-within-ngmodel-on-input-elements-in-angular