JavaScript's support has been moved to the reactiverse project. It's an incubation like project for projects that aren't fully 1.0.0 yet. In there you will find https://reactiverse.io/es4x/, the EcmaScript support For Vert.x. It's a new approach of using vert.x with GraalVM to provide modern ES language features such as ES12, instead of the old Nashorn ES5.1.

It also changes the development workflow from a maven-based project to a NPM-based project which should be more familiar to JavaScript developers.