servicework

Service workers are a type of web worker, a JavaScript script that runs in the background of a web browser, separate from the main browser thread. They are a core technology of Progressive Web Apps (PWAs) and enable features like offline functionality, push notifications, and background synchronization.

A service worker acts as a proxy between the browser and the network. It intercepts network requests from the web page, allowing developers to programmatically control how requests are handled. This interception capability is key to enabling offline experiences, as a service worker can cache responses and serve them directly from the cache when the network is unavailable.

The service worker lifecycle involves installation, activation, and idle states. During installation, the service worker fetches and caches essential resources. Once installed, it waits to be activated, which typically happens when no other service worker is controlling the page. After activation, it can intercept fetch events.

Key functionalities include offline support through caching strategies, push notifications that can wake up the app and display messages even when the browser is closed, and background synchronization for updating content when the network is stable. Service workers are registered by a JavaScript file on the web page and have access to the Cache API and other background sync APIs. They do not have direct access to the DOM.