Here’s a link to installing a specific version of Node.js with nvm:
When I checked the Node.js version used with Volumio earlier this summer, it was 8.11.1. Perhaps the newest Volumio release uses something else. Check with node --version to be sure.
I also installed jshint and its VS Code extension.
Yes, that has happened to me as well. What seems to work for me is to copy the new files (or all of them) to /data/plugins/music_service/iheartrad/ in your case and execute volumio vrestart. If you have a fairly recent Pi (I use a 3B+), the restart is pretty quick, maybe 20 seconds or so. I just wrote a quick shell script, something like:
#!/bin/bash
cp -R ~/yourplugindevelopmentdir/* /data/plugins/music_service/iheartrad/
volumio vrestart
mpc clear # clears songs still playing in mpc
journalctl -f # watch the logs fly by for errors, etc.
Then just chmod +x that thing and fire it when you have changes.