Progressive Web Apps (PWAs) combine the reach of the web with the smooth feel of native apps, offering offline support, install prompts, and push notifications.

What defines a PWA?

• Site served over HTTPS
• Web App Manifest for install metadata
• Service Worker controlling requests and caching assets
• Optional Push Notifications for re‑engagement
• Good performance scores in tools like Lighthouse

---

1 – Create a manifest

manifest.json

{
  "name": "Todo PWA",
  "short_name": "Todo",
  "start_url": "/index.html",
  "display": "standalone",
  "background_color": "#ffffff",
  "theme_color": "#1976d2",
  "icons": [
    { "src": "/icons/icon-192.png", "sizes": "192x192", "type": "image/png" },
    { "src": "/icons/icon-512.png", "sizes": "512x512", "type": "image/png" }
  ]
}

Add in your HTML head:

<link rel="manifest" href="/manifest.json" />

---

2 – Register a service worker

if ('serviceWorker' in navigator) {
  window.addEventListener('load', () => {
    navigator.serviceWorker.register('/sw.js');
  });
}

---

3 – Cache assets

sw.js

const CACHE = 'v1';
const ASSETS = [
  '/',
  '/index.html',
  '/styles.css',
  '/app.js'
];

self.addEventListener('install', event => {
  event.waitUntil(
    caches.open(CACHE).then(cache => cache.addAll(ASSETS))
  );
});

self.addEventListener('fetch', event => {
  event.respondWith(
    caches.match(event.request).then(resp => resp || fetch(event.request))
  );
});

---

4 – Add push notifications (optional)

1. Ask permission with Notification.requestPermission().
2. Subscribe using registration.pushManager.subscribe().
3. Send messages from your server with Web Push.

---

5 – Test your PWA

• Run Lighthouse with the PWA preset.
• Switch Chrome DevTools to Offline and reload; content should still display.
• Visit twice, then look for an Install option in the browser’s menu.

---

PWAs shine in areas with spotty connectivity and on sites that want repeat engagement without forcing app‑store installs.