feat($build): Added the support for PWA

Added SWPrecacheWebpackPlugin and a service worker to serve assets from local cache

Author: halfzebra

config/webpack.config.prod.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const autoprefixer = require('autoprefixer');
+const SWPrecacheWebpackPlugin = require('sw-precache-webpack-plugin');
 const DefinePlugin = require('webpack/lib/DefinePlugin');
 const UglifyJsPlugin = require('webpack/lib/optimize/UglifyJsPlugin');
 const HtmlWebpackPlugin = require('html-webpack-plugin');
@@ -195,6 +196,37 @@ module.exports = {
     // Note: this won't work without ExtractTextPlugin.extract(..) in `loaders`.
     new ExtractTextPlugin({
       filename: cssFilename
-    })
+    }),
+
+    // Generate a service worker script that will precache, and keep up to date,
+    // the HTML & assets that are part of the Webpack build.
+    new SWPrecacheWebpackPlugin({
+      // By default, a cache-busting query parameter is appended to requests
+      // used to populate the caches, to ensure the responses are fresh.
+      // If a URL is already hashed by Webpack, then there is no concern
+      // about it being stale, and the cache-busting can be skipped.
+      dontCacheBustUrlsMatching: /\.\w{8}\./,
+      filename: 'service-worker.js',
+      logger(message) {
+        if (message.indexOf('Total precache size is') === 0) {
+          // This message occurs for every build and is a bit too noisy.
+          return;
+        }
+        if (message.indexOf('Skipping static resource') === 0) {
+          // This message obscures real errors so we ignore it.
+          // https://github.com/facebookincubator/create-react-app/issues/2612
+          return;
+        }
+        console.log(message);
+      },
+      minify: true,
+      // For unknown URLs, fallback to the index page
+      navigateFallback: publicUrl + '/index.html',
+      // Ignores URLs starting from /__ (useful for Firebase):
+      // https://github.com/facebookincubator/create-react-app/issues/2237#issuecomment-302693219
+      navigateFallbackWhitelist: [/^(?!\/__).*/],
+      // Don't precache sourcemaps (they're large) and build asset manifest:
+      staticFileGlobsIgnorePatterns: [/\.map$/, /asset-manifest\.json$/],
+    }),
   ]
 };

package.json

@@ -48,6 +48,7 @@
     "react-error-overlay": "^1.0.10",
     "string-replace-loader": "^1.3.0",
     "style-loader": "^0.18.1",
+    "sw-precache-webpack-plugin": "^0.11.4",
     "url-loader": "^0.5.9",
     "webpack": "^3.5.5",
     "webpack-dev-server": "^2.7.1"

template/public/index.html

@@ -4,6 +4,12 @@
     <meta charset="utf-8">
     <meta http-equiv="x-ua-compatible" content="ie=edge">
     <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+    <meta name="theme-color" content="#000000">
+    <!--
+      manifest.json provides metadata used when your web app is added to the
+      homescreen on Android. See https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/
+    -->
+    <link rel="manifest" href="%PUBLIC_URL%/manifest.json">
     <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
     <title>Elm App</title>
 </head>

template/public/manifest.json

@@ -0,0 +1,15 @@
+{
+  "short_name": "Elm App",
+  "name": "Create Elm App Sample",
+  "icons": [
+    {
+      "src": "favicon.ico",
+      "sizes": "192x192",
+      "type": "image/png"
+    }
+  ],
+  "start_url": "./index.html",
+  "display": "standalone",
+  "theme_color": "#000000",
+  "background_color": "#ffffff"
+}

template/src/index.js

@@ -1,4 +1,7 @@
 import './main.css';
 import { Main } from './Main.elm';
+import registerServiceWorker from './registerServiceWorker';
 
 Main.embed(document.getElementById('root'));
+
+registerServiceWorker();

template/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();
+    });
+  }
+}