I've been away from any kind of JavaScript development long enough to leave me completely at a loss about how to use modern JS tooling. So, for example, while the instructions at https://github.com/PencilCode/pencilcode-site/blob/master/README.md are great at explaining how to build and test changes to the main IDE, I'm less sure how I might make and test my first change here.
David, if you can point me in a general direction, I'd be happy to write up what I find as breadcrumbs to those to come after.