For my projects that require a distinct unit of functionality, I typically reach for a JS library that I can include as a payload (no npm, no deps, just a JS file). SortableJS is a good example, so is MarkdownJS if I want the browser to handle MD rendering.
This only goes so far, though. At some point, an app developer might want to integrate these distinct units of functionality, and I'm not sure how I would go about that. I haven't gotten to that point.
