pwa-development

PWA Development Skill

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Purpose: Build Progressive Web Apps that work offline, install like native apps, and deliver fast, reliable experiences across all devices.

---

Core PWA Requirements

┌─────────────────────────────────────────────────────────────────┐
│  THE THREE PILLARS OF PWA                                       │
│  ─────────────────────────────────────────────────────────────  │
│                                                                 │
│  1. HTTPS                                                       │
│     Required for service workers and security.                  │
│     localhost allowed for development.                          │
│                                                                 │
│  2. SERVICE WORKER                                              │
│     JavaScript that runs in background.                         │
│     Enables offline, caching, push notifications.               │
│                                                                 │
│  3. WEB APP MANIFEST                                            │
│     JSON file describing app metadata.                          │
│     Enables installation and app-like experience.               │
├─────────────────────────────────────────────────────────────────┤
│  INSTALLABILITY CRITERIA (Chrome)                               │
│  ─────────────────────────────────────────────────────────────  │
│  • HTTPS (or localhost)                                         │
│  • Service worker with fetch handler                            │
│  • Web app manifest with: name, icons (192px + 512px),          │
│    start_url, display: standalone/fullscreen/minimal-ui         │
└─────────────────────────────────────────────────────────────────┘

---

Web App Manifest

Required Fields

{
  "name": "My Progressive Web App",
  "short_name": "MyPWA",
  "description": "A description of what the app does",
  "start_url": "/",
  "display": "standalone",
  "background_color": "#ffffff",
  "theme_color": "#000000",
  "icons": [
    {
      "src": "/icons/icon-192.png",
      "sizes": "192x192",
      "type": "image/png"
    },
    {
      "src": "/icons/icon-512.png",
      "sizes": "512x512",
      "type": "image/png"
    },
    {
      "src": "/icons/icon-512-maskable.png",
      "sizes": "512x512",
      "type": "image/png",
      "purpose": "maskable"
    }
  ]
}

Enhanced Manifest (Full Features)

{
  "name": "My Progressive Web App",
  "short_name": "MyPWA",
  "description": "A full-featured PWA",
  "start_url": "/?source=pwa",
  "scope": "/",
  "display": "standalone",
  "orientation": "portrait-primary",
  "background_color": "#ffffff",
  "theme_color": "#3367D6",
  "dir": "ltr",
  "lang": "en",
  "categories": ["productivity", "utilities"],

  "icons": [
    { "src": "/icons/icon-72.png", "sizes": "72x72", "type": "image/png" },
    { "src": "/icons/icon-96.png", "sizes": "96x96", "type": "image/png" },
    { "src": "/icons/icon-128.png", "sizes": "128x128", "type": "image/png" },
    { "src": "/icons/icon-144.png", "sizes": "144x144", "type": "image/png" },
    { "src": "/icons/icon-152.png", "sizes": "152x152", "type": "image/png" },
    { "src": "/icons/icon-192.png", "sizes": "192x192", "type": "image/png" },
    { "src": "/icons/icon-384.png", "sizes": "384x384", "type": "image/png" },
    { "src": "/icons/icon-512.png", "sizes": "512x512", "type": "image/png" },
    { "src": "/icons/icon-maskable.png", "sizes": "512x512", "type": "image/png", "purpose": "maskable" }
  ],

  "screenshots": [
    {
      "src": "/screenshots/desktop.png",
      "sizes": "1280x720",
      "type": "image/png",
      "form_factor": "wide"
    },
    {
      "src": "/screenshots/mobile.png",
      "sizes": "750x1334",
      "type": "image/png",
      "form_factor": "narrow"
    }
  ],

  "shortcuts": [
    {
      "name": "New Item",
      "short_name": "New",
      "description": "Create a new item",
      "url": "/new?source=shortcut",
      "icons": [{ "src": "/icons/shortcut-new.png", "sizes": "192x192" }]
    }
  ],

  "share_target": {
    "action": "/share",
    "method": "POST",
    "enctype": "multipart/form-data",
    "params": {
      "title": "title",
      "text": "text",
      "url": "url",
      "files": [{ "name": "files", "accept": ["image/*"] }]
    }
  },

  "protocol_handlers": [
    {
      "protocol": "web+myapp",
      "url": "/handle?url=%s"
    }
  ],

  "file_handlers": [
    {
      "action": "/open-file",
      "accept": {
        "text/plain": [".txt"]
      }
    }
  ]
}

Manifest Checklist

• name and short_name defined
• start_url set (use query param for analytics)
• display set to standalone or fullscreen
• Icons: 192x192 and 512x512 minimum
• Maskable icon included for Android adaptive icons
• theme_color matches app design
• background_color for splash screen
• Screenshots for richer install UI (optional)
• Shortcuts for quick actions (optional)

---

Service Worker Patterns

Basic Service Worker

// sw.js
const CACHE_NAME = 'app-cache-v1';
const STATIC_ASSETS = [
  '/',
  '/index.html',
  '/styles/main.css',
  '/scripts/app.js',
  '/offline.html'
];

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

// Activate: Clean old caches
self.addEventListener('activate', (event) => {
  event.waitUntil(
    caches.keys()
      .then((keys) => Promise.all(
        keys
          .filter((key) => key !== CACHE_NAME)
          .map((key) => caches.delete(key))
      ))
      .then(() => self.clients.claim())
  );
});

// Fetch: Serve from cache, fall back to network
self.addEventListener('fetch', (event) => {
  event.respondWith(
    caches.match(event.request)
      .then((cached) => cached || fetch(event.request))
      .catch(() => caches.match('/offline.html'))
  );
});

Registration

// main.js
if ('serviceWorker' in navigator) {
  window.addEventListener('load', async () => {
    try {
      const registration = await navigator.serviceWorker.register('/sw.js', {
        scope: '/'
      });
      console.log('SW registered:', registration.scope);
    } catch (error) {
      console.error('SW registration failed:', error);
    }
  });
}

---

Caching Strategies

Strategy Selection Guide

Strategy	Use Case	Description
Cache First	Static assets (CSS, JS, images)	Check cache, fall back to network
Network First	API responses, dynamic content	Try network, fall back to cache
Stale While Revalidate	Semi-static content (avatars, articles)	Serve cache immediately, update in background
Network Only	Non-cacheable requests (analytics)	Always use network
Cache Only	Offline-only assets	Only serve from cache

Cache First (Offline First)

// Best for: Static assets that rarely change
self.addEventListener('fetch', (event) => {
  if (event.request.destination === 'image' ||
      event.request.destination === 'style' ||
      event.request.destination === 'script') {
    event.respondWith(
      caches.match(event.request)
        .then((cached) => {
          if (cached) return cached;
          return fetch(event.request).then((response) => {
            const clone = response.clone();
            caches.open(CACHE_NAME).then((cache) => {
              cache.put(event.request, clone);
            });
            return response;
          });
        })
    );
  }
});

Network First (Fresh First)

// Best for: API data, frequently updated content
self.addEventListener('fetch', (event) => {
  if (event.request.url.includes('/api/')) {
    event.respondWith(
      fetch(event.request)
        .then((response) => {
          const clone = response.clone();
          caches.open(CACHE_NAME).then((cache) => {
            cache.put(event.request, clone);
          });
          return response;
        })
        .catch(() => caches.match(event.request))
    );
  }
});

Stale While Revalidate

// Best for: Content that's okay to be slightly outdated
self.addEventListener('fetch', (event) => {
  if (event.request.url.includes('/articles/')) {
    event.respondWith(
      caches.open(CACHE_NAME).then((cache) => {
        return cache.match(event.request).then((cached) => {
          const fetchPromise = fetch(event.request).then((response) => {
            cache.put(event.request, response.clone());
            return response;
          });
          return cached || fetchPromise;
        });
      })
    );
  }
});

---

Workbox (Recommended)

Why Workbox?

• Battle-tested caching strategies
• Precaching with revision management
• Background sync for offline forms
• Automatic cache cleanup
• TypeScript support

Installation

npm install workbox-webpack-plugin  # Webpack
npm install @vite-pwa/vite-plugin   # Vite

Workbox with Vite

// vite.config.js
import { VitePWA } from 'vite-plugin-pwa';

export default {
  plugins: [
    VitePWA({
      registerType: 'autoUpdate',
      includeAssets: ['favicon.ico', 'robots.txt', 'apple-touch-icon.png'],
      manifest: {
        name: 'My App',
        short_name: 'App',
        theme_color: '#ffffff',
        icons: [
          { src: 'pwa-192x192.png', sizes: '192x192', type: 'image/png' },
          { src: 'pwa-512x512.png', sizes: '512x512', type: 'image/png' }
        ]
      },
      workbox: {
        globPatterns: ['**/*.{js,css,html,ico,png,svg}'],
        runtimeCaching: [
          {
            urlPattern: /^https:\/\/api\.example\.com\/.*/i,
            handler: 'NetworkFirst',
            options: {
              cacheNam

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