iOS Safari Limitations

Safari on iOS supports Service Workers, Cache API, and IndexedDB — but with significant constraints that differ from desktop browsers. Understanding these is essential for production offline-first apps.

7-Day Eviction Policy

The most critical limitation: iOS Safari evicts all website data — IndexedDB, Cache API, and Service Worker registrations — after 7 days of no user engagement.

Mitigation

Encourage PWA installation — standalone mode is the only reliable protection. Detect eviction on startup:

async function detectEviction() {
  try {
    const db = await openDB();
    const tx = db.transaction("meta", "readonly");
    const store = tx.objectStore("meta");
    const marker = await new Promise((r) => {
      const req = store.get("app-initialized");
      req.onsuccess = () => r(req.result);
    });
    return !marker;
  } catch {
    return true;
  }
}

IndexedDB Storage Limit

iOS Safari imposes a ~50 MB soft limit on IndexedDB — significantly lower than desktop browsers (typically unlimited up to free disk space). Above 50 MB, QuotaExceededError is thrown on writes.

Monitoring

async function monitorStorage() {
  const estimate = await navigator.storage.estimate();
  const usageMB = estimate.usage / (1024 * 1024);
  const quotaMB = estimate.quota / (1024 * 1024);
  if (usageMB > 40) console.warn("Approaching iOS IndexedDB limit");
  return { usageMB, quotaMB };
}

Note: navigator.storage.estimate() on iOS often reports a very large quota (~500 MB+) but writes will still fail around 50 MB. Trim cached data aggressively and implement proactive cleanup.

No beforeinstallprompt

iOS Safari does not fire the beforeinstallprompt event. Use the Share menu "Add to Home Screen" flow instead:

function showInstallGuide() {
  if (window.navigator.standalone) return;
  const isIOS = /iphone|ipad|ipod/i.test(navigator.userAgent);
  if (isIOS && "serviceWorker" in navigator) {
    showIOSInstallInstructions(); // 1. Share → 2. Add to Home Screen
  }
}

Detect Standalone Mode

const standalone = {
  ios: window.navigator.standalone,
  standard: window.matchMedia("(display-mode: standalone)").matches,
};

WKWebView Constraints

Third-party browsers on iOS (Chrome, Firefox, Edge) are WKWebView wrappers around Safari's engine. They share Safari's limitations:

Push Notifications

Push notifications on iOS can only be tested on a physical device, not the simulator.

Private Browsing Mode

In Safari private browsing, IndexedDB and Cache API may throw errors or return empty databases. Data does not persist after the session ends.

async function isPrivateMode() {
  try {
    const db = indexedDB.open("__detect_private__");
    return new Promise((resolve) => {
      db.onerror = () => resolve(true);
      db.onsuccess = () => {
        indexedDB.deleteDatabase("__detect_private__");
        resolve(false);
      };
    });
  } catch {
    return true;
  }
}

Service Worker Lifecycle on iOS

iOS terminates service workers more aggressively than desktop:

Implications: Background sync does not exist on iOS — use the online event listener instead. Mutation queue processing must happen in the main thread, not the SW.

navigator.storage.persist() on iOS

On iOS, persistent storage requests are always denied. The only reliable prevention is standalone mode (Home Screen installation).

Compatibility Summary

Testing on iOS

Next Steps

• Storage Quota Management — quota limits and eviction
• Offline-First Architecture — build resilient for all platforms