Look at this

sample.html

<form (ngSubmit)="save()" #projectForm="ngForm">
  <div>
    <input [(ngModel)]="project.name"
           required
           name="name"
           #name="ngModel">
  </div>
  <div [hidden]="name.valid || name.pristine" class="alert">
      Name is required
  </div>
  <div>
    <button [disabled]="!projectForm.valid" type="submit">Save</button>
  </div>
</form>