Notify new application version with browser service workers - polymer

Question

I build an html/js application (a progressive web app) with Polymer and polymer-cli and the well generated service-worker for caching and offline.
I wonder how to notify the user when a new version of the application is available and invite him to restart browser.
any ideas ?
Edit
a talk at IO2016 where Eric Bidel talk about service worker and notify user about new version of an application :
https://youtu.be/__KvYxcIIm8?list=PLOU2XLYxmsILe6_eGvDN3GyiodoV3qNSC&t=1510
Need to check the google IO Web source code

Answer 1

References:
https://developers.google.com/web/fundamentals/instant-and-offline/service-worker/lifecycle
https://classroom.udacity.com/courses/ud899
// page script
document.addEventListener('DOMContentLoaded', function(){
if ('serviceWorker' in navigator) {
navigator.serviceWorker
.register('/sw.js')
.then(function(registration) {
console.info('ServiceWorker registration successful with scope:', registration.scope);
// if there's no controller, this page wasn't loaded
// via a service worker, so they're looking at the latest version.
// In that case, exit early
if (!navigator.serviceWorker.controller) return;
// if there's an updated worker already waiting, update
if (registration.waiting) {
console.info('show toast and upon click update...');
registration.waiting.postMessage({ updateSw: true });
return;
}
// if there's an updated worker installing, track its
// progress. If it becomes "installed", update
if (registration.installing) {
registration.addEventListener('statechange', function(){
if (registration.installing.state == 'installed'){
console.info('show toast and upon click update...');
registration.installing.postMessage({ updateSw: true });
return;
}
});
}
// otherwise, listen for new installing workers arriving.
// If one arrives, track its progress.
// If it becomes "installed", update
registration.addEventListener('updatefound', function(){
let newServiceWorker = registration.installing;
newServiceWorker.addEventListener('statechange', function() {
if (newServiceWorker.state == 'installed') {
console.info('show toast and upon click update...');
newServiceWorker.postMessage({ updateSw: true });
}
});
});
})
.catch(function(error) {
console.info('ServiceWorker registration failed:', error);
});
navigator.serviceWorker.addEventListener('controllerchange', function() {
window.location.reload();
});
}
});
// sw script
self.addEventListener('message', function(e) {
if (e.data.updateSw){
self.skipWaiting();
}
});

Answer 2

Thanks to IO team .. we need to check if the current service-worker becomes redundant
// Check to see if the service worker controlling the page at initial load
// has become redundant, since this implies there's a new service worker with fresh content.
if (navigator.serviceWorker && navigator.serviceWorker.controller) {
navigator.serviceWorker.controller.onstatechange = function(event) {
if (event.target.state === 'redundant') {
// Define a handler that will be used for the next io-toast tap, at which point it
// be automatically removed.
const tapHandler = function() {
window.location.reload();
};
if (IOWA.Elements && IOWA.Elements.Toast &&
IOWA.Elements.Toast.showMessage) {
IOWA.Elements.Toast.showMessage(
'A new version of this app is available.', tapHandler, 'Refresh',
null, 0); // duration 0 indications shows the toast indefinitely.
} else {
tapHandler(); // Force reload if user never was shown the toast.
}
}
};
}