title: Apply ng-class based on length of Input
body: <p>I have a input box where I can count characters. This input box is called ng-model="social.text". I can get that thing's length by going social.text.length.</p>
  
  <p>Now, I want to subtract input.text.length from 280, so I have {{280-social.text.length}}</p>
  
  <p>All this works without a hitch.</p>
  
  <p>However! In the counter that I want to set up, I want to change its background color to yellow, if the math returns something under 100, and to red if it goes below 50.</p>
  
  <p>So I have css classes set up that apply a background-color. </p>
  
  <p>Now, I need to somehow apply these classes based on the length of the string. </p>
  
  <pre><code>&lt;div class="chip" id="socialCounter"&gt;
      {{280-social.text.length}}
  &lt;/div&gt; 
  </code></pre>
  
  <p>So how do I apply ng-class to that? I'm quite lost here, so I'm sorry if I seem a bit incoherent.</p>