title: how to add new class to Angular JS ng-class with dollar sign?
body: <p>I've recently joined a team, and they are using AngularJS. Their codes is:</p>
  
  <p>html:</p>
  
  <pre><code>&lt;div ng-class="$ctrl.styles.className"&gt;I need to add one new class here&lt;/div&gt;
  </code></pre>
  
  <p>If I want to put more classes into one div, I can easily make the classes in to an array, like this: </p>
  
  <pre><code>&lt;div ng-class="[$ctrl.styles.classNameOne,$ctrl.styles.classNameTwo]"&gt; But how to add the third new class into the array??&lt;/div&gt;
  </code></pre>
  
  <p>CSS:</p>
  
  <pre><code>.classNameOne {
      position: fixed;       
  }
  .classNameTwo{
      color:red;
  }
  </code></pre>
  
  <p>But how to add more new classes into the array of <code>div</code> ? 
  I tried many ways, but I don't know how to add new classes into the array of the
      <code>&lt;div&gt;</code>, because the class must with the dollar sign: 
      <code>$ctrl.styles.className</code>.</p>
  
  <p>Could anyone tell me how to add new classes with dollar signs?</p>