title: Angular 4 | "Notify" component to perform an action
body: <p>I have a navbar component which I inject into my app using the <code>"&lt; app-navbar &gt;"</code> brackets, so it is loaded at all times, even when there is a route change. </p>
  
  <p>I have a login system where the user gets redirected from my backend server to my frontend server together with some URL parameters. A component (<code>localhost:4200/auth/steam</code>) takes care of saving these parameters in my local storage and redirects the user to my frontend homepage (<code>localhost:4200/</code>) on success. Now that the user is logged in I want to display his username in my navbar. </p>
  
  <p>The problem is that I don't have a clue on how to "notify" my navbar component to get the username from local storage so it can be displayed. </p>
  
  <p>What is an elegant way of doing this?</p>
  
  <p>BTW: Sorry if this question is a bit hard to understand, I just don't know how to explain it better.</p>
  
  <p>BTW2: I don't think that a code example is necessary since this is rather a general question. If you need some comment below</p>