title: In Angular, what ways can you auto-update a data binding that is bound to a method?
body: <p>Say you have an object with a method:</p>
  
  <pre><code>/*
  chat.author    ==  a String
  chat.message   ==  a String
  chat.timestamp ==  a Date 
  chat.timeago() ==  a method that returns a string, like "2 minutes ago"
  */
  </code></pre>
  
  <p>And your html looks something like:</p>
  
  <pre><code>&lt;div&gt;{{ chat.author    }}&lt;/div&gt;
  &lt;div&gt;{{ chat.message   }}&lt;/div&gt;
  &lt;div&gt;{{ chat.timeago() }}&lt;/div&gt;
  </code></pre>
  
  <p>The return value of chat.timeago() will change based on the elapsed time since chat.timestamp, so it may change from "just now", to "a few seconds ago", to "a minute ago", "2 hours ago", etc.</p>
  
  <p>What options exist to instruct Angular when to update the data that is bound to the method, and which option is the most elegant or traditional way in Angular?</p>