There are situations where having a REPL or shell can be useful. ES4X provides such a feature out of the box by running the command:

> npm run shell


And you are now able to REPL. For example:

js:> require('./index.js');
Server listening at: http://localhost:8080/


The shell can also be run without the need of npm using a packaged runnable jar.

java -jar your-package.jar run "js:>"

A bootstrapped shell will be available to run your code with all the components available in your classpath.