JS in the JVM is used heavily in Mirth (https://www.nextgen.com/products-and-services/integration-en...) for scripting of channels and data transformations. It's kinda janky but runs a lot of healthcare systems. It's using Rhino, not Nashorn, FWIW.

User-defined scripting of a system written in Java. Everyone knows Javascript and it's easier to allow a user to submit text scripts and run them via the embedded engine than require users to run some kind of plugin build process.

We are. We use a library called rules.js to do some basic content validations that can run on either/both the client and server.

And now I look foolish for suggesting it (using Nashorn).

I know of one CMS that uses it extensively underneath to construct the pages.

I use it for server-rendering React in a Spring app