Progressive Web Apps (PWA)

Also Known As

TL;DR

Explanation

A PWA requires three things: HTTPS (required for service workers), a web app manifest (JSON describing the app for installation), and a service worker (JavaScript that intercepts network requests and manages caching). Capabilities: install to home screen (A2HS), offline functionality, push notifications, background sync, and access to some device APIs. PWAs are progressively enhanced — they work as normal websites for browsers without service worker support. For PHP-rendered apps, PWA techniques add mobile app qualities without a native app.

Diagram

flowchart TD
    subgraph PWA_Requirements
        HTTPS[HTTPS required]
        MANIFEST[Web App Manifest<br/>name icons theme]
        SW[Service Worker<br/>offline caching]
    end
    HTTPS & MANIFEST & SW --> PWA[Progressive Web App]
    PWA --> INSTALL[Install to home screen]
    PWA --> OFFLINE[Works offline]
    PWA --> PUSH[Push notifications]
    subgraph Cache_Strategy
        SW -->|static assets| CACHE_FIRST[Cache first]
        SW -->|API calls| NET_FIRST[Network first<br/>fallback to cache]
    end
style PWA fill:#6e40c9,color:#fff
style INSTALL fill:#238636,color:#fff
style OFFLINE fill:#238636,color:#fff
style CACHE_FIRST fill:#1f6feb,color:#fff
style NET_FIRST fill:#d29922,color:#fff

Common Misconception

Why It Matters

Common Mistakes

• Service worker that caches everything including API responses without expiry — stale data shown indefinitely.
• Not providing a fallback offline page — a blank screen is worse than a 'You are offline' message.
• Manifest without all required icons — installation prompts fail silently without the required icon sizes.
• Registering the service worker without scoping it correctly — it may intercept requests it should not.

Code Examples

// Service worker caches everything forever — stale data:
self.addEventListener('fetch', event => {
    event.respondWith(
        caches.match(event.request).then(cached => {
            return cached || fetch(event.request).then(response => {
                caches.open('v1').then(cache => cache.put(event.request, response.clone()));
                return response;
            });
        })
    );
    // API responses cached indefinitely — user sees week-old data
});

// Cache-first for assets, network-first for API:
self.addEventListener('fetch', event => {
    const url = new URL(event.request.url);
    if (url.pathname.startsWith('/api/')) {
        // Network-first for API — fresh data, fallback to cache:
        event.respondWith(fetch(event.request).catch(() => caches.match(event.request)));
    } else {
        // Cache-first for static assets:
        event.respondWith(caches.match(event.request).then(c => c || fetch(event.request)));
    }
});

Tags

🧠 Logic Engine

References

• https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps