There is a URL that returns a list of courses given a course group (as an XHTML snippet):

• courselist_partial?course_group=BIOL
• courselist_partial?course_group=CSCI

What's involved:

• Prototype Javascript library
• Server-side process to generate course list markup (courselist_partial which take a course_group query parameter)
• Custom Javascript function (getCourseList) to call server-side process
• Javascript to invokee the custom getCourseList function.

Javascript:

<script type="text/javascript" src="js/prototype.js"> <!--prototype library--> </script> <script type="text/javascript"> function getCourseList() { var cg = document.getElementById("course_group"); var i = cg.options[cg.selectedIndex].value; var p = "course_group=" + i ; aj = new Ajax.Updater('courselist', 'courselist_partial', {asynchronous:true, parameters: p , method: 'get'}); } </script>

Invoking the Javascript:

<select name="course_group" id="course_group" onchange="getCourseList()">