You can see demo at https://babel-service-demo.herokuapp.com. Make sure to use a modern browser with ServiceWorker support (Chrome, Chrome Canary, Opera). Firefox should work if you enable a flag, but I had problem running Babel JS inside Firefox. What you should see: once a page registers a babel-service ServiceWorker, it should reload itself. The ServiceWorker will intercept a file app.js that contains a ES6 source code that uses default parameters.