Service Worker Strategy Builder

A Service Worker is a JavaScript file that runs separately from the main browser thread. It intercepts network requests, allowing you to cache assets locally, serve offline fallback pages, and handle background synchronization or push notifications. It is the core technology that makes a Progressive Web App (PWA) work offline.

Network First attempts to fetch the latest resource from the network. If the network request fails (e.g., the user is offline), it falls back to a previously cached version. This is highly recommended for HTML pages so users always see the most up-to-date content when connected.

This strategy instantly serves a resource from the cache for maximum speed, but simultaneously fires off a background network request to update the cache for the *next* time the user visits. It's perfect for CSS and JavaScript files.

Cache First looks for the resource in the cache and serves it immediately. It only goes to the network if the resource isn't cached yet. This saves a massive amount of bandwidth and is the ideal strategy for static assets like images and web fonts that rarely change.

Place the downloaded sw.js file in the root directory of your website. Then, paste this registration script into your main HTML file, right before the closing </body> tag: <script> if ('serviceWorker' in navigator) { window.addEventListener('load', () => { navigator.serviceWorker.register('/sw.js'); }); } </script>

Workbox is a set of libraries developed by Google that makes writing Service Workers incredibly easy. Writing vanilla Service Worker caching logic from scratch is prone to edge-case bugs. Workbox abstracts the hard parts (like cache expiration and routing) into clean, readable code.