In case anyone wants to see a Java (well, Scala) app that uses Nashorn:

https://insightful.demo.talkyard.io/-17/i-can-no-longer-work...

Is uses Nashorn for server side rendering a React.js Single Page App, calling from Scala to Nashorn running React.js code in the same JVM. (I'm developing it. Hmm I should clean up that demo forum.)