How do I display errors in a component view with Angular 2?
In Angular 1, the ng-messages modules are used to help us to display error messages and validation to our forms.
In Angular 2, the ngModel provides error objects for each of the built-in input validators. You can access these errors from a reference to the ngModel itself then build useful messaging around them to display to your users.
//The Validator Services.
Stayed Informed - Angular 2 forms validation