progressive-web-app · secondsky — Claude Code skill: PWA and offline

---
name: progressive-web-app
description: Progressive Web Apps with service workers, web manifest, offline support, installation prompts. Use for installable web apps, offline functionality, push notifications, or encountering service worker registration, cache strategy, manifest configuration errors.
license: MIT
---

# Progressive Web App (PWA)

Build web applications that work like native apps with offline support and installability.

## Web App Manifest

```json
{
  "name": "My Application",
  "short_name": "MyApp",
  "start_url": "/",
  "display": "standalone",
  "background_color": "#ffffff",
  "theme_color": "#000000",
  "icons": [
    { "src": "/icon-192.png", "sizes": "192x192", "type": "image/png" },
    { "src": "/icon-512.png", "sizes": "512x512", "type": "image/png" }
  ]
}
```

## Service Worker

```javascript
const CACHE_NAME = 'app-v1';
const STATIC_ASSETS = ['/', '/index.html', '/styles.css', '/app.js'];

// Install
self.addEventListener('install', event => {
  event.waitUntil(
    caches.open(CACHE_NAME).then(cache => cache.addAll(STATIC_ASSETS))
  );
});

// Fetch with cache-first strategy
self.addEventListener('fetch', event => {
  event.respondWith(
    caches.match(event.request).then(cached => {
      if (cached) return cached;

      return fetch(event.request).then(response => {
        if (response.status === 200) {
          const clone = response.clone();
          caches.open(CACHE_NAME).then(cache => cache.put(event.request, clone));
        }
        return response;
      });
    })
  );
});
```

## Install Prompt

```javascript
let deferredPrompt;

window.addEventListener('beforeinstallprompt', e => {
  e.preventDefault();
  deferredPrompt = e;
  showInstallButton();
});

async function installApp() {
  if (!deferredPrompt) return;
  deferredPrompt.prompt();
  const { outcome } = await deferredPrompt.userChoice;
  console.log('Install outcome:', outcome);
  deferredPrompt = null;
}
```

## Push Notifications

```javascript
async function subscribeToPush() {
  const registration = await navigator.serviceWorker.ready;
  const subscription = await registration.pushManager.subscribe({
    userVisibleOnly: true,
    applicationServerKey: VAPID_PUBLIC_KEY
  });
  await sendSubscriptionToServer(subscription);
}
```

## PWA Checklist

- [ ] HTTPS enabled
- [ ] Web manifest configured
- [ ] Service worker registered
- [ ] Offline fallback page
- [ ] Responsive design
- [ ] Fast loading (<3s on 3G)
- [ ] Installable