Service Worker
A browser-resident script that sits between your site and the network, enabling offline support, caching strategies and push notifications.
· Reviewed by senior engineers
A Service Worker is a script the browser keeps alive in the background, separate from any open page, and which can intercept network requests from your site. That interception is what makes Progressive Web Apps possible: cache assets and API responses for offline use, serve stale-while-revalidate, queue background sync, receive push notifications.
The power is also the danger. A service worker that caches the wrong things can pin a broken version of your site in front of every returning user, and the only escape is a kill-switch the engineer remembered to ship. Versioning, skipWaiting behaviour and a clear cache-busting strategy are non-negotiable.
Libraries like Workbox handle the boilerplate and the gotchas. They give you well-tested caching strategies (cache-first, network-first, stale-while-revalidate), precaching with manifests, and routing rules that match Express's familiar shape.
Devinsta builds service workers only when offline support or push notifications genuinely move the needle for a client, and always with an explicit kill switch and staged rollout. They are powerful, but a fast site without one beats a clever one that ships stale HTML for a week.