title: How to show and hide DIV in angular
body: <p>I have two div(s)</p>
  
  <pre><code>&lt;div id = 'a'&gt;
  &lt;/div&gt;
  &lt;div id = 'b'&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>click on "add" button i want to hide div a and show div b</p>