Example of optionally exporting a module

optionally-export-module.js

const SomeDependency = require('some-dependency')

class TopLevelProcess {
  constructor (someDependency) { ... }
  start () { ... }
}

const isNodeProcess = require.main === module
if (isNodeProcess) {
  new TopLevelProcess(new SomeDependency()).start()
} else {
  module.exports = { TopLevelProcess }
}