title: Run document.ready only if jquery is loaded
body: <p>I have this code in a global JS file.</p>
  
  <pre><code>$(document).ready(function() {
         DoStuff();
   });
  </code></pre>
  
  <p>Unfortunately there are pages that include this file but doesn't include the jquery file. So I get errors:</p>
  
  <pre><code>Message: The value of the property '$' is null or undefined, 
  not a Function object
  </code></pre>
  
  <p>How do I run <code>document.ready()</code> only if JQuery file is loaded.</p>