Factorio packages are Blueprints and Blueprint Books! And the equivalent of npmjs.com would be https://factorioprints.com .
https://wiki.factorio.com/Blueprint
https://wiki.factorio.com/Blueprint_book
https://www.reddit.com/r/factorio/comments/7vnkze/blueprint_...
One of the stages of evolution of a Factorio programmer is learning how to make scalable modular blueprints that you can stamp down one next to another, with their inputs and output routed so they all plug together easily and run in parallel, without having to be manually wired together.