You didn't follow instructions! Page 2 of the link you posted says:

Remember to Load your Library
Remember to add a <script> tag to your HTML document to load the Core library
of functions (core.js) before the <script> tag that runs your program, as shown
in the code below. Otherwise, your program won’t be able to find
Core.getElementsByClass, and your browser will report a JavaScript error.

Code:

stripy_tables.html (excerpt) 
<script type="text/javascript" src="core.js"></script> 
<script type="text/javascript" src="stripy_tables.js"> 
</script>

Your HTML in the first post clearly doesn't load the Core library.