Fallback Strategies for Offline Mode

1. Introduction

Progressive Web Apps (PWAs) provide a reliable experience to users, even in offline scenarios. Implementing fallback strategies is crucial to ensure that users can still interact with your application when internet connectivity is lost. This lesson covers key concepts, definitions, and practical examples of fallback strategies.

2. Key Concepts

3. Fallback Strategies

Implementing fallback strategies involves the following steps:

1. Define the resources to be cached.
2. Create a service worker to handle caching and requests.
3. Implement offline fallback content.
4. Register the service worker in your application.

3.1 Step-by-Step Process

Step 1: Define Resources to Cache

Identify the static assets and API endpoints you want to cache for offline use.

Step 2: Create a Service Worker

self.addEventListener('install', event => {
    event.waitUntil(
        caches.open('my-cache').then(cache => {
            return cache.addAll([
                '/',
                '/index.html',
                '/styles.css',
                '/script.js',
                '/offline.html' // Fallback page
            ]);
        })
    );
});
            

Step 3: Implement Offline Fallback Content

self.addEventListener('fetch', event => {
    event.respondWith(
        fetch(event.request).catch(() => {
            return caches.match('/offline.html');
        })
    );
});
            

Step 4: Register the Service Worker

if ('serviceWorker' in navigator) {
    navigator.serviceWorker.register('/service-worker.js')
    .then(() => {
        console.log('Service Worker registered.');
    });
}
            

4. Code Examples

Below is a sample service worker code that demonstrates caching strategies and fallback handling:

const CACHE_NAME = 'my-cache-v1';

self.addEventListener('install', event => {
    event.waitUntil(
        caches.open(CACHE_NAME).then(cache => {
            return cache.addAll([
                '/',
                '/index.html',
                '/styles.css',
                '/script.js',
                '/offline.html'
            ]);
        })
    );
});

self.addEventListener('fetch', event => {
    event.respondWith(
        caches.match(event.request).then(response => {
            return response || fetch(event.request).catch(() => {
                return caches.match('/offline.html');
            });
        })
    );
});
            

5. Best Practices

• Keep your cache size limited to avoid excessive storage use.
• Implement cache versioning for easy updates.
• Test your service worker thoroughly to ensure fallbacks work as expected.
• Provide a user-friendly offline experience with clear messaging and navigation.

6. FAQ