title: two way data binding in angular 2
body: <p>I am quiet recent to angular 2 and was bumping my head around two way data binding. Here is the confusion:</p>
  
  <pre><code>  &lt;input  (input)="username = $event.target.value" id="testing"&gt;
    &lt;p&gt;{{username}}&lt;/p&gt;
  </code></pre>
  
  <p>This serves the purpose well. It already seems to be two way data binded. I can access username inside the component and the value property of the input element is updated as well. Why do i need [ ] at all then? What is the two way binding here? what goes inside the component and what comes out of the component.</p>
  
  <p>Disclaimer: I know it's a very naive and seemingly stupid question :|</p>