What is Service Worker?

What is a Service Worker?

A service worker is a special JavaScript file that runs in the browser separately from the page’s main thread. It can respond to events even when the page is not open, intercept network requests, return cached responses, or receive push notifications.

Service workers require HTTPS because they control an important part of the page’s network behavior. Poor cache rules can show users an outdated interface or stale data.

Lifecycle

• Register: The page registers the service worker file with the browser.
• Install: Static assets can be added to cache during first setup.
• Activate: Old cache versions are cleaned and the new worker takes control.
• Fetch: Network requests are intercepted and handled with cache-first, network-first, or stale-while-revalidate strategies.
• Push and sync: Notifications or background synchronization events are processed.

Business Use

Service workers support resilient experiences for news sites, e-commerce catalogs, field applications, and users with unreliable connectivity. Product lists can open quickly from cache, order drafts can sync when the connection returns, and critical notifications can be delivered through the browser.

This technology is a core part of PWA architecture. It should not be shipped without an update strategy, cache versioning, and a rollback plan for faulty workers.