Download the production version of class.js (minified) and implement it in your html code.
For HTML5 use:
<script src="/path/class.js"></script>
For HTML and XHTML versions use:
<script type="text/javascript" src="/path/class.js"></script>
You will be able to call Class.version
within your preferred browsers console
if class.js is implemented or initialized correctly. Feel free to explore the source.