@Directive
decorator on a class and specifying a selector. For directives, the selector name must be camelCase and wrapped in square brackets to specify that it is an attribute binding. We're using the @HostListener
decorator to listen in on events on the component or element it's attached to. In this case we're watching the click
event and passing in the event details which are given by the special $event
keyword. Next, we want to attach this directive to the button we created earlier.window.confirm
call. To take advantage of this new input property, we add another binding to our button.