title: How can I add a new class style to an input field if it is valid (in Angular 4)
body: <p>I'm a newbie to Angular, I was working on Reactive Forms and I also included Bootstrap in the project, if an input text is valid and has class "ng-valid",
  I need to add the class "has-success" to the parent div, so it will become green and takes the styles of Bootstrap.</p>