> Hasn't Nashorn been superseded by GraalJS?

It depends, do you want support for your JVM? If so:

* Graal CE has no support

* Graal EE requires either running on Oracle Cloud or calling Oracle Sales for a custom quote. These are non-starters for many.

* JVMCI requires `-XX:+UnlockExperimentalVMOptions` which often voids support.

* I believe Mandrel is supported but requires RHEL