title: AngularJS, using ng-class to assign a class if variable = something
body: <p>I'm trying to assign a different class to an icon if its category is selected. I want to add class ìcon-pfeil_unten` if variable category == a number. I am trying with: </p>
  
  <pre><code>&lt;i class="icon-pfeil_oben" ng-class="{'icon-pfeil_unten': category.16}"&gt;&lt;/i&gt;
  </code></pre>
  
  <p>Where 16 is the category's ID. If category == 16, nothing happens. I guess I am writing the expression wrong. What's the correct way to test the value of a variable using ng-class ?</p>