title: Typescript and multiple classes
body: <p>I have a component class as <code>EventSchedulePage</code>.It extends  <code>HandleStorageService</code> <code>abstract</code> class as shown below.You can see that there is a method named <code>showInvalidTokenAlert()</code> on this subclass.I have to call this method each and every component(This method gives a token based error message to the user).So can you tell me how to implement or redesign my classes to cater this situation? 'cause I don't like to put <code>showInvalidTokenAlert()</code> on each and every component.I would like to keep that method's implementation on a single place.</p>
  
  <p><em>Subclass</em></p>
  
  <pre><code>    export class EventSchedulePage extends HandleStorageService {
  
      constructor() {
          super();
           }
  
       showInvalidTokenAlert() {
         //show alert
        }
    }
  </code></pre>
  
  <p><em>abstract class</em> </p>
  
  <pre><code>export abstract class HandleStorageService {
    result: string = '';
  
    constructor() {
    }
  }
  </code></pre>