add service worker for offline access

lib/index.js

@@ -14,6 +14,7 @@ const app = express()
 app.set('view engine', 'ejs')
 app.set('views', path.join(__dirname, 'views'))
 
+app.use(express.static(path.join(__dirname, 'public')))
 app.use(favicon(path.join(__dirname, 'views', 'favicon.ico')))
 app.use(bodyParser())
 

lib/public/service-worker.js

@@ -0,0 +1,19 @@
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open('fb-to-ical').then((cache) => {
+      return cache.addAll([
+        '/',
+        '/favicon.ico',
+      ])
+    })
+  )
+})
+
+self.addEventListener('fetch', (event) => {
+  event.respondWith(
+    caches.match(event.request)
+      .then((response) => {
+        return response || fetch(event.request)
+      })
+  )
+})

lib/views/index.ejs

@@ -72,6 +72,8 @@
         </div>
         <div class="status-item" id="error">
         </div>
+        <div class="status-item" id="service-worker">
+        </div>
       </div>
     </div>
 
@@ -112,6 +114,10 @@
         }
 
         const getStorage = () => {
+          if (!useStorage) {
+            return null
+          }
+
           const storage = localStorage.getItem('fb-to-ical-events')
 
           if (!storage) {
@@ -249,6 +255,13 @@
           error.classList.add('show')
         }
 
+        const setServiceWorkerStatus = (status) => {
+          clearStatuses()
+          const sw = document.querySelector('#service-worker')
+          sw.innerText = status
+          status ? sw.classList.add('show') : sw.classList.remove('show')
+        }
+
         const pendingRequest = () => {
           input.disabled = true
           submitButton.disabled = true
@@ -292,8 +305,43 @@
         const link = document.querySelector("#current-download")
         const table = document.querySelector('#list')
         const tableBody = table.querySelector('tbody')
+        const noJScheckbox = document.querySelector('#nojs')
 
+        const loadNoJS = () => {
+          if (!useStorage) {
+            return
+          }
+          const value = localStorage.getItem('fb-to-ical-nojs')
+          noJScheckbox.checked = value ? JSON.parse(value) : false
+        }
+
+        loadNoJS()
+
+        if (window.navigator && window.navigator.serviceWorker && !noJS()) {
+          const serviceWorker = window.navigator.serviceWorker
+          serviceWorker.register('service-worker.js', {
+            scope: './',
+          }).then((registration) => {
+            setServiceWorkerStatus(`Service worker registered with scope ${registration.scope}`)
+            setTimeout(() => {
+              setServiceWorkerStatus('')
+            }, 4500)
+          }).catch((err) => {
+            setServiceWorkerStatus(`Service worker error: ${err.toString()}`)
+          })
+        }
+
+        if (!noJS()) {
           hydrateList()
+        }
+
+        noJScheckbox.addEventListener('click', (event) => {
+          if (!useStorage) {
+            return
+          }
+
+          localStorage.setItem('fb-to-ical-nojs', event.target.checked)
+        })
 
         submitButton.addEventListener('click', (event) => {
           if (noJS()) {