[onion2k]

Sure, but as the README.md states "adds notes to the margin with the text provided in HTML attributes" it's presumably left up to the user how else they display the data if they want it to be visible for people who disable JS. This library is a progressive enhancement. It's very much the right way to do web dev in my opinion.

[NoGravitas]

It's almost the right way -- somewhat better would be to do what one of the above comments say, to add the notes as footnotes using POSH. Then the javascript can rewrite the footnotes into hide/show marginal notes with the same appearance and user interface as this library.