pwa-offline-first-expert

PWA & Offline-First Expert (2026 Edition)

English | Bahasa Indonesia

---

English

Description

Expert guide for building enterprise-grade Local-First and Progressive Web Applications (PWA). Eliminates loading spinners by reading and writing to local databases (OPFS SQLite, RxDB, IndexedDB) first, replicating seamlessly in the background with zero conflict (CRDTs, ElectricSQL, PowerSync), and packaging to native stores via PWABuilder.

Trigger Conditions

• Applications requiring full offline functionality (field operations, mobile dashboards, transit apps).
• User experience demands 0ms local read/write latency without loading spinners.
• Multi-device sync architecture with automatic conflict resolution.
• Packaging web apps for distribution on Google Play Store, iOS Safari PWA, or Microsoft Store.

---

1. The Local-First Principles (2026 Standard)

1. No Spinners for Local Data: UI reads and writes to local storage (OPFS / IndexedDB) synchronously. Latency is always 0ms.
2. Multi-Device Conflict-Free Replication: Changes replicate in the background using CRDTs or central event logs (ElectricSQL / PowerSync).
3. Network is an Enhancement: App is 100% functional on an airplane or subway without internet.
4. User Owns Their Data: Data persists on client hardware first; cloud server is a backup/sync relay.

---

2. Production Recipe: Service Worker Caching (Workbox v7 / Native SW)

// sw.ts - Production Service Worker with Stale-While-Revalidate
/// <reference lib="webworker" />
declare const self: ServiceWorkerGlobalScope;

const CACHE_NAME = 'app-v2.11.0-cache';
const STATIC_ASSETS = [
  '/',
  '/index.html',
  '/manifest.json',
  '/styles/global.css',
  '/icons/icon-512x512.png',
];

// 1. Install & Pre-cache critical application shell
self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME).then((cache) => cache.addAll(STATIC_ASSETS))
  );
  self.skipWaiting();
});

// 2. Activate & Clean stale caches
self.addEventListener('activate', (event) => {
  event.waitUntil(
    caches.keys().then((keys) =>
      Promise.all(
        keys.filter((k) => k !== CACHE_NAME).map((k) => caches.delete(k))
      )
    )
  );
  self.clients.claim();
});

// 3. Stale-While-Revalidate Strategy for Navigation & API GETs
self.addEventListener('fetch', (event) => {
  const { request } = event;

  // Ignore POST/PUT/DELETE mutations (handled by offline sync queues)
  if (request.method !== 'GET') return;

  event.respondWith(
    caches.open(CACHE_NAME).then(async (cache) => {
      const cachedResponse = await cache.match(request);
      
      const fetchPromise = fetch(request)
        .then((networkResponse) => {
          if (networkResponse.status === 200) {
            cache.put(request, networkResponse.clone());
          }
          return networkResponse;
        })
        .catch(() => cachedResponse || Response.error());

      return cachedResponse || fetchPromise;
    })
  );
});

// 4. Background Sync for offline mutations
self.addEventListener('sync', (event: any) => {
  if (event.tag === 'sync-mutations') {
    event.waitUntil(flushOfflineMutationQueue());
  }
});

async function flushOfflineMutationQueue() {
  // Read pending mutations from IndexedDB and POST to backend
}