title: The AngularJS directive ngClass is not working?
body: <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;a href="#/main" class="bottom-nav-btn"&gt;
   &lt;img ng-src="dist/images/toolbar1.png" alt="首页" class="nav-img" /&gt;
   &lt;p class="nav-text" ng-class="{active: isActive==='main'}"&gt;首页&lt;/p&gt;
   &lt;p&gt;{{ isActive === 'main' }}&lt;/p&gt;
  &lt;/a&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>I am using this Angulars code.
  Finally I find the expression {{ isActive === 'main' }} is  true,but the className 'active' is not updated</p>