With org-mode and org-export it’s very easy to embed HTML, CSS, and JavaScript into your content. All that you need to do is use the begin_export block and declare it to be html. Now anything you put within that box will be added to the HTML document. For example the following:

#+begin_export html
<div><p><u>This</u> is a <emp style="color: red;">test</emp></p></div>
#+end_export

Will product this:

This will work with JavaScript as well, so long as you export html and then use <script> tags: