Progressive Web Apps (PWAs) use modern web capabilities to deliver app-like experiences. They are installable, work offline, receive push notifications, and load instantly. All through the web, no app store required.
Core PWA requirements: HTTPS (security), web app manifest (installability metadata), and service worker (offline support and caching). Meeting these requirements enables the browser install prompt.
Web app manifest: a JSON file defining app name, icons, start URL, display mode (standalone for app-like experience), theme color, and background color. This metadata controls how the PWA appears when installed.
Service workers: JavaScript files running in a separate thread that intercept network requests, manage caches, and enable offline functionality. Service workers are the core technology enabling PWA capabilities.
Caching strategies: cache-first (fast, may serve stale content), network-first (fresh content, slower), stale-while-revalidate (fast with background updates). Choose strategy per resource type.
Offline support: cache critical app shell resources during service worker installation. Provide meaningful offline fallback pages. Show cached content when offline and sync when connectivity returns.
Push notifications: engage users outside the browser. Request notification permission thoughtfully (not on first visit). Send relevant, timely notifications. Excessive notifications drive users to disable them.
App installability: PWAs can be installed on mobile and desktop without app stores. The install prompt appears when PWA criteria are met. Installed PWAs launch from the home screen with no browser chrome.
Performance advantages: service worker caching enables instant repeat loads. App shell architecture loads the UI immediately and fills content asynchronously. PWAs consistently achieve 90+ Lighthouse performance scores.
PWA limitations: limited iOS support (no push notifications until iOS 16.4, limited background processing), no access to some native APIs (NFC, Bluetooth on some platforms), and app store discoverability requires separate PWA wrapper.
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