My approach is to use the content metadata to instruct my footer template to load extra js files. The JS is not part of the content (that’s a presentation concern), so don’t try to marry them in your markdown if you can avoid it.

Example content metadata:

+++
js = ["chart", "dropdown/latest.min"]
+++
At the bottom of the footer template, I have this:

{{- range .Params.js }}
<script src="/js/{{ . }}.js"></script>
{{- end }}