Custom SW config

package.json

@@ -5,7 +5,8 @@
   "devDependencies": {
     "react-scripts": "^1.0.10",
     "snazzy": "^7.0.0",
-    "standard": "^10.0.2"
+    "standard": "^10.0.2",
+    "sw-precache": "^5.2.0"
   },
   "dependencies": {
     "polished": "^1.2.1",
@@ -19,7 +20,8 @@
   },
   "scripts": {
     "start": "react-scripts start",
-    "build": "react-scripts build && react-snapshot",
+    "build": "react-scripts build && react-snapshot && npm run sw",
+    "sw": "sw-precache --config='sw-precache-config.js'",
     "test": "standard | snazzy && react-scripts test --env=jsdom",
     "eject": "react-scripts eject"
   },

src/index.js

@@ -1,6 +1,7 @@
 import React from 'react'
 import { render } from 'react-snapshot'
 import App from './App'
+import registerServiceWorker from './registerServiceWorker'
 
 const rootEl = document.getElementById('root')
 render(<App />, rootEl)
@@ -11,3 +12,5 @@ if (module.hot) {
     render(<NextApp />, rootEl)
   })
 }
+
+registerServiceWorker()

src/registerServiceWorker.js

@@ -0,0 +1,108 @@
+// In production, we register a service worker to serve assets from local cache.
+
+// This lets the app load faster on subsequent visits in production, and gives
+// it offline capabilities. However, it also means that developers (and users)
+// will only see deployed updates on the "N+1" visit to a page, since previously
+// cached resources are updated in the background.
+
+// To learn more about the benefits of this model, read https://goo.gl/KwvDNy.
+// This link also includes instructions on opting out of this behavior.
+
+const isLocalhost = Boolean(
+  window.location.hostname === 'localhost' ||
+    // [::1] is the IPv6 localhost address.
+    window.location.hostname === '[::1]' ||
+    // 127.0.0.1/8 is considered localhost for IPv4.
+    window.location.hostname.match(
+      /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/
+    )
+)
+
+export default function register () {
+  if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
+    // The URL constructor is available in all browsers that support SW.
+    const publicUrl = new URL(process.env.PUBLIC_URL, window.location)
+    if (publicUrl.origin !== window.location.origin) {
+      // Our service worker won't work if PUBLIC_URL is on a different origin
+      // from what our page is served on. This might happen if a CDN is used to
+      // serve assets see https://github.com/facebookincubator/create-react-app/issues/2374
+      return
+    }
+
+    window.addEventListener('load', () => {
+      const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`
+
+      if (!isLocalhost) {
+        // Is not local host. Just register service worker
+        registerValidSW(swUrl)
+      } else {
+        // This is running on localhost. Lets check if a service worker still exists or not.
+        checkValidServiceWorker(swUrl)
+      }
+    })
+  }
+}
+
+function registerValidSW (swUrl) {
+  navigator.serviceWorker
+    .register(swUrl)
+    .then(registration => {
+      registration.onupdatefound = () => {
+        const installingWorker = registration.installing
+        installingWorker.onstatechange = () => {
+          if (installingWorker.state === 'installed') {
+            if (navigator.serviceWorker.controller) {
+              // At this point, the old content will have been purged and
+              // the fresh content will have been added to the cache.
+              // It's the perfect time to display a "New content is
+              // available please refresh." message in your web app.
+              console.log('New content is available; please refresh.')
+            } else {
+              // At this point, everything has been precached.
+              // It's the perfect time to display a
+              // "Content is cached for offline use." message.
+              console.log('Content is cached for offline use.')
+            }
+          }
+        }
+      }
+    })
+    .catch(error => {
+      console.error('Error during service worker registration:', error)
+    })
+}
+
+function checkValidServiceWorker (swUrl) {
+  // Check if the service worker can be found. If it can't reload the page.
+  fetch(swUrl)
+    .then(response => {
+      // Ensure service worker exists, and that we really are getting a JS file.
+      if (
+        response.status === 404 ||
+        response.headers.get('content-type').indexOf('javascript') === -1
+      ) {
+        // No service worker found. Probably a different app. Reload the page.
+        navigator.serviceWorker.ready.then(registration => {
+          registration.unregister().then(() => {
+            window.location.reload()
+          })
+        })
+      } else {
+        // Service worker found. Proceed as normal.
+        registerValidSW(swUrl)
+      }
+    })
+    .catch(() => {
+      console.log(
+        'No internet connection found. App is running in offline mode.'
+      )
+    })
+}
+
+export function unregister () {
+  if ('serviceWorker' in navigator) {
+    navigator.serviceWorker.ready.then(registration => {
+      registration.unregister()
+    })
+  }
+}

sw-precache-config.js

@@ -0,0 +1,23 @@
+// we overwrite the default service worker config to enable runtimeCaching
+module.exports = {
+  stripPrefix: 'build/',
+  staticFileGlobs: [
+    'build/**/*.html',
+    'build/*.svg',
+    'build/*.jpg',
+    'build/*.png',
+    'build/*.ico',
+    'build/*.json',
+    'build/static/**/!(*map*)',
+    'build/manifest.json'
+  ],
+  dontCacheBustUrlsMatching: /\.\w{8}\./,
+  swFilePath: 'build/service-worker.js',
+  // any external urls you wish to cache (e.g. CDN)
+  runtimeCaching: [
+    {
+      urlPattern: /^https?:\/\/.*example-cdn.com/,
+      handler: 'cacheFirst'
+    }
+  ]
+}

yarn.lock

@@ -6189,7 +6189,7 @@ sw-precache-webpack-plugin@0.11.3:
     sw-precache "^5.1.1"
     uglify-js "^3.0.13"
 
-sw-precache@^5.1.1:
+sw-precache@^5.1.1, sw-precache@^5.2.0:
   version "5.2.0"
   resolved "https://registry.yarnpkg.com/sw-precache/-/sw-precache-5.2.0.tgz#eb6225ce580ceaae148194578a0ad01ab7ea199c"
   dependencies: