title: What does the "locals" argument to $controller do?
body: <p>In Angular, <code>$controller</code> takes two arguments - <code>constructor</code> and <code>locals</code>.</p>
  
  <p><a href="https://docs.angularjs.org/api/ng/service/$controller" rel="noreferrer">Documentation</a></p>
  
  <p>The documentation basically just says that:</p>
  
  <ol>
  <li><code>locals</code> is an object.</li>
  <li>"Injection locals for Controller."</li>
  </ol>
  
  <p>But I still don't understand what it does. Can anyone elaborate and explain?</p>