Expo Starter: Progressive Web App (PWA)

Install Dependencies

% yarn add -D workbox-webpack-plugin \
							workbox-background-sync \
							workbox-broadcast-update \
							workbox-cacheable-response \
							workbox-core \
							workbox-expiration \
							workbox-navigation-preload \
							workbox-precaching \
							workbox-range-requests \
							workbox-routing \
							workbox-strategies \
							workbox-streams

Update Webpack Configuration

// webpack.config.js
...
const WorkboxWebpackPlugin = require('workbox-webpack-plugin');
...
module.exports = async (env, argv) => {
  const config = await createExpoWebpackConfigAsync(env, argv);

  if (env.mode === 'production') {
    config.plugins.push(
      // Generate a service worker script that will precache, and keep up to date,
      // the HTML & assets that are part of the webpack build.
      new WorkboxWebpackPlugin.InjectManifest({
        swSrc: path.resolve(__dirname, 'src/service-worker.js'),
        dontCacheBustURLsMatching: /\.[0-9a-f]{8}\./,
        exclude: [
          /\.map$/,
          /asset-manifest\.json$/,
          /LICENSE/,
          /\.js\.gz$/,
          // Exclude all apple touch and chrome images because they're cached locally after the PWA is added.
          /(apple-touch-startup-image|chrome-icon|apple-touch-icon).*\.png$/,
        ],
        // Bump up the default maximum size (2mb) that's precached,
        // to make lazy-loading failure scenarios less likely.
        // See https://github.com/cra-template/pwa/issues/13#issuecomment-722667270
        maximumFileSizeToCacheInBytes: 5 * 1024 * 1024,
      }),
    );
  }
  ...
  return config;
};

If you didn't already, you have to run expo customize:web and generate webpack.config.js.

Create ServiceWorker

// src/service-worker.js
/* eslint-disable no-restricted-globals */

// This service worker can be customized!
// See https://developers.google.com/web/tools/workbox/modules// for the list of available Workbox modules, or add any other
// code you'd like.
// You can also remove this file if you'd prefer not to use a
// service worker, and the Workbox build step will be skipped.

import { clientsClaim } from 'workbox-core';
import { ExpirationPlugin } from 'workbox-expiration';
import { precacheAndRoute, createHandlerBoundToURL } from 'workbox-precaching';
import { registerRoute } from 'workbox-routing';
import { StaleWhileRevalidate } from 'workbox-strategies';

clientsClaim();

// Precache all of the assets generated by your build process.
// Their URLs are injected into the manifest variable below.
// This variable must be present somewhere in your service worker file,
// even if you decide not to use precaching. See https://cra.link/PWA// eslint-disable-next-line no-underscore-dangle
precacheAndRoute(self.__WB_MANIFEST);

// Set up App Shell-style routing, so that all navigation requests
// are fulfilled with your index.html shell. Learn more at
// https://developers.google.com/web/fundamentals/architecture/app-shellconst fileExtensionRegexp = new RegExp('/[^/?]+\\.[^/]+$');
registerRoute(
  // Return false to exempt requests from being fulfilled by index.html.
  ({ request, url }) => {
    // If this isn't a navigation, skip.
    if (request.mode !== 'navigate') {
      return false;
    } // If this is a URL that starts with /_, skip.

    if (url.pathname.startsWith('/_')) {
      return false;
    } // If this looks like a URL for a resource, because it contains // a file extension, skip.

    if (url.pathname.match(fileExtensionRegexp)) {
      return false;
    } // Return true to signal that we want to use the handler.

    return true;
  },
  createHandlerBoundToURL(`${process.env.PUBLIC_URL || ''}/index.html`),
);

// An example runtime caching route for requests that aren't handled by the
// precache, in this case same-origin .png requests like those from in public/
registerRoute(
  // Add in any other file extensions or routing criteria as needed.
  ({ url }) => url.origin === self.location.origin && url.pathname.endsWith('.png'), // Customize this strategy as needed, e.g., by changing to CacheFirst.
  new StaleWhileRevalidate({
    cacheName: 'images',
    plugins: [
      // Ensure that once this runtime cache reaches a maximum size the
      // least-recently used images are removed.
      new ExpirationPlugin({ maxEntries: 50 }),
    ],
  }),
);

// This allows the web app to trigger skipWaiting via
// registration.waiting.postMessage({type: 'SKIP_WAITING'})
self.addEventListener('message', event => {
  if (event.data && event.data.type === 'SKIP_WAITING') {
    self.skipWaiting();
  }
});

// Any other custom service worker logic can go here.

Add ServiceWorker Registration

// src/serviceWorkerRegistration.js

// This optional code is used to register a service worker.
// register() is not called by default.

// 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 subsequent visits to a page, after all the
// existing tabs open on the page have been closed, since previously cached
// resources are updated in the background.

// To learn more about the benefits of this model and instructions on how to
// opt-in, read https://cra.link/PWAconst isLocalhost = Boolean(
  window.location.hostname === 'localhost' ||
    // [::1] is the IPv6 localhost address.
    window.location.hostname === '[::1]' ||
    // 127.0.0.0/8 are considered localhost for IPv4.
    window.location.hostname.match(/^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/),
);

export function register(config) {
  const isEnvProduction = process.env.NODE_ENV === 'production';
  if (isEnvProduction && 'serviceWorker' in navigator) {
    // The URL constructor is available in all browsers that support SW.
    const publicUrl = new URL(process.env.PUBLIC_URL || '', window.location.href);
    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/facebook/create-react-app/issues/2374return;
    }

    window.addEventListener('load', () => {
      const swUrl = `${process.env.PUBLIC_URL || ''}/service-worker.js`;

      if (isLocalhost) {
        // This is running on localhost. Let's check if a service worker still exists or not.
        checkValidServiceWorker(swUrl, config);

        // Add some additional logging to localhost, pointing developers to the
        // service worker/PWA documentation.
        navigator.serviceWorker.ready.then(() => {
          console.log(
            'This web app is being served cache-first by a service ' +
              'worker. To learn more, visit https://cra.link/PWA',
          );
        });
      } else {
        // Is not localhost. Just register service worker
        registerValidSW(swUrl, config);
      }
    });
  }
}

function registerValidSW(swUrl, config) {
  navigator.serviceWorker
    .register(swUrl)
    .then(registration => {
      // eslint-disable-next-line no-param-reassign
      registration.onupdatefound = () => {
        const installingWorker = registration.installing;
        if (installingWorker == null) {
          return;
        }
        installingWorker.onstatechange = () => {
          if (installingWorker.state === 'installed') {
            if (navigator.serviceWorker.controller) {
              // At this point, the updated precached content has been fetched,
              // but the previous service worker will still serve the older
              // content until all client tabs are closed.
              console.log(
                'New content is available and will be used when all ' +
                  'tabs for this page are closed. See https://cra.link/PWA.',
              );

              // Execute callback
              if (config && config.onUpdate) {
                config.onUpdate(registration);
              }
            } 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.');

              // Execute callback
              if (config && config.onSuccess) {
                config.onSuccess(registration);
              }
            }
          }
        };
      };
    })
    .catch(error => {
      console.error('Error during service worker registration:', error);
    });
}

function checkValidServiceWorker(swUrl, config) {
  // Check if the service worker can be found. If it can't reload the page.
  fetch(swUrl, {
    headers: { 'Service-Worker': 'script' },
  })
    .then(response => {
      // Ensure service worker exists, and that we really are getting a JS file.
      const contentType = response.headers.get('content-type');
      if (response.status === 404 || (contentType != null && contentType.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, config);
      }
    })
    .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();
      })
      .catch(error => {
        console.error(error.message);
      });
  }
}

Register ServiceWorker in App.tsx

...
import * as serviceWorkerRegistration from './serviceWorkerRegistration';
...
// If you want your app to work offline and load faster, you can change
// unregister() to register() below. Note this comes with some pitfalls.
// Learn more about service workers: https://cra.link/PWA
serviceWorkerRegistration.register();

Test the PWA

{
	...
	"scripts": {
      ...
      "web:mobile": "expo start:web --https --ios --android",
      "web:ios": "expo start:web --https --ios",
      "web:android": "expo start:web --https --android",
      "build:web": "expo build:web && npx serve web-build",
      ...
	}
	...
}

Normal refreshing won't affect the ServiceWorker so you can hard reset the service workers with ⌘+shift+R.