Where do the service workers sit?

I'm looking for this index.js: https://github.com/johnkmzhou/cordova-create-react-app/blob/master/src/index.js

It seems there is not a single line in the whole create-react-app-redux generated project containing something that suggests the existence of a serviceWorker. Even after ejecting the project.

What gives? Is it wrapped into some third party component or something?

Thanks a lot.