title: Add a class in all the elements of selector get by class in angular2
body: <p>I am getting a element ref by below code and I want add a class and remove a class from all the elements which i get.</p>
  
  <p>app.component.html</p>
  
  <pre><code>&lt;ul&gt;
     &lt;li class="option-btn cm-grey" /&gt;option 1&lt;/li&gt;
     &lt;li class="option-btn cm-grey" /&gt;option 1&lt;/li&gt;
     &lt;li class="option-btn cm-grey" /&gt;option 1&lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>app.component.ts</p>
  
  <pre><code>var allbtn = document.querySelectorAll('.option-btn');
  allbtn.removeClass('cm-grey');
  allbtn.addClass('cm-blue');
  </code></pre>
  
  <p>Above code is not working.</p>