Advanced Caching Techniques - Progressive Web Apps

1. Introduction

In this lesson, we will dive into advanced caching techniques for Progressive Web Apps (PWAs). Caching is crucial for enhancing performance, enabling offline access, and improving user experience.

2. Key Concepts

Service Workers: Scripts that run in the background and manage caching strategies.
Cache API: Allows you to store and retrieve network requests and responses.
Cache-Control: HTTP headers that dictate caching behavior for resources.

3. Caching Strategies

3.1. Cache First Strategy

This strategy serves cached content first and falls back to the network if the content is not available.


const CACHE_NAME = 'my-cache-v1';
const urlsToCache = [
    '/',
    '/index.html',
    '/styles/main.css',
];

self.addEventListener('install', event => {
    event.waitUntil(
        caches.open(CACHE_NAME)
            .then(cache => cache.addAll(urlsToCache))
    );
});

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

3.2. Network First Strategy

This strategy attempts to fetch the latest content from the network before falling back to the cache.


self.addEventListener('fetch', event => {
    event.respondWith(
        fetch(event.request)
            .then(response => {
                return caches.open(CACHE_NAME).then(cache => {
                    cache.put(event.request, response.clone());
                    return response;
                });
            })
            .catch(() => caches.match(event.request))
    );
});

3.3. Stale While Revalidate Strategy

This strategy serves cached content while revalidating in the background.


self.addEventListener('fetch', event => {
    event.respondWith(
        caches.match(event.request)
            .then(response => {
                const fetchPromise = fetch(event.request).then(networkResponse => {
                    return caches.open(CACHE_NAME).then(cache => {
                        cache.put(event.request, networkResponse.clone());
                        return networkResponse;
                    });
                });
                return response || fetchPromise;
            })
    );
});

4. Best Practices

Utilize versioning for cache names to prevent stale cache.
Use Cache-Control headers to control caching behavior.
Implement error handling for network requests.
Regularly update cache based on user interaction and content updates.

5. FAQ

What is a Service Worker?

A Service Worker is a script that runs in the background of a web application, separate from the main browser thread, to enable functionalities such as caching, push notifications, and background sync.

How can I debug Service Workers?

You can debug Service Workers using the Developer Tools in your browser (Chrome, Firefox) under the Application tab, where you can view the status, cache storage, and network requests.

What are Cache-Control headers?

Cache-Control headers are HTTP headers used to specify directives for caching mechanisms in both requests and responses, helping to manage how and when resources are cached.