You seem to be confusing server side code (your Perl script) with client side code (JavaScript) and what can be done in each context. Maybe you've just been unclear about which code is where?

I think what you are trying to achieve is to have a client side user facing list update as the user makes selections in another list. If that is the case then there are two quite distinct parts of the solution. The first part is to create on the server the master list (student id in this case) and a look up table indexed by master list entries. Use these two structures to populate the user facing student list and a hidden JavaScript look up table. I tend to wrap the table in a JS function that is generated for each page and use the function to return an appropriate list (exams in this case) in the OnClick handler call. Something like:

onClick="displayExams(examList(document.getElementById('STUDENT_NAME')
+.value));"
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