app.js

if ('serviceWorker' in navigator) {

  // attach event listener  on page l aod
  window.addEventListener('load', () => {

    // register serviceWorker withthe [sw.js] file
    navigator.serviceWorker.register('/sw.js').then(registration => {

      console.log('ServiceWorker registration successful with scope: ', registration.scope);

    }, function(err) {
      // registration failed :(
      console.log('ServiceWorker registration failed: ', err);
    });

  });
}