Directives allow you to extend the existing HTML with your own elements or attributes and to add behavior to existing elements or attributes. There are many built-in directives we use as part of angular app. Similarly, we can create our own custom directives to define the reusable component.Directives allow you to extend the existing HTML with your own elements or attributes and to add behavior to existing elements or attributes. There are many built-in directives we use as part of angular app. Similarly, we can create our own custom directives to define the reusable component.