A more detailed overview will be drafted sometime soon.
Velt is one of the best plugins for running JS code on Spigot. Velt tries to give you as many utilities for running Spigot code as possible, but it doesn't provide unnecessary modules that aren't useful for creating concise and simple scripts. As Velt provides you almost the same modules as NodeJS does, many of your same npm scripts should be able to run using Velt, and you can install npm modules on Velt.
Guide: https://velt.js.org