change code structure

src/registerServiceWorker.js

@@ -0,0 +1,44 @@
+let refresh = false
+
+function invokeServiceWorkerUpdateFlow (registration) {
+  const agree = confirm('New version of the app is available. Refresh now?')
+  if (agree) {
+    if (registration.waiting) {
+      // let waiting Service Worker know it should became active
+      refresh = true
+      registration.waiting.postMessage({ type: 'SKIP_WAITING' })
+    }
+  }
+}
+
+if ('serviceWorker' in navigator) {
+  window.addEventListener('load', async () => {
+    const registration = await navigator.serviceWorker.register('service-worker.js')
+    // ensure the case when the updatefound event was missed is also handled
+    // by re-invoking the prompt when there's a waiting Service Worker
+    if (registration.waiting) {
+      invokeServiceWorkerUpdateFlow(registration)
+    }
+
+    // detect Service Worker update available and wait for it to become installed
+    registration.addEventListener('updatefound', () => {
+      const newRegestration = registration.installing
+      if (newRegestration) {
+        // wait until the new Service worker is actually installed (ready to take over)
+        newRegestration.addEventListener('statechange', () => {
+          if (registration.waiting && navigator.serviceWorker.controller) {
+            invokeServiceWorkerUpdateFlow(registration)
+          }
+        })
+      }
+    })
+
+    // detect controller change and refresh the page
+    navigator.serviceWorker.addEventListener('controllerchange', () => {
+      if (refresh) {
+        window.location.reload()
+        refresh = false
+      }
+    })
+  })
+}