Alice Feng

Beautiful! You could add tooltips (with .append("title")), so hovering a circle displays the note.
And if you want to allow people to open their own MusicXML or MIDI files here, take a look at this: https://observablehq.com/@fheyen/parsing-midi-and-musicxml (sorry for the ad;) )

Thanks for taking a look and for the comments! It would be cool to let people be able to import their own pieces, but my code to generate the dataset of note counts currently uses a Python library. It looks like you're doing really useful work building out a JS-based library for musical analysis, it'd definitely be great to be able to do all of this in one language rather than switching between tools.