workboxbackgroundsync

Workbox Background Sync is a module within Google's Workbox library designed to simplify the use of background synchronization in progressive web apps. It provides a way to queue requests that fail while the user is offline or when the network is unreliable, and to replay them automatically when connectivity improves. The feature is particularly useful for state-changing requests such as form submissions or data updates that should not be lost.

The module works by intercepting network requests for a specified route and method and, if a request would fail due to network issues, storing the request details in a browser database (IndexedDB). The queued requests are then retried in the background when the service worker detects viable network connectivity, without requiring the user to resubmit. Each queue is given a name, and items have a retention period after which they are discarded.

Usage and integration with Workbox involve routing and strategies. A background sync plugin is created with a queue name and optional settings such as retention time, and attached to a route via a strategy that performs the actual network request, for example a NetworkOnly strategy with the plugin. This enables offline submissions to be captured and retried automatically when the user comes back online.

Limitations and compatibility include reliance on the browser’s Background Sync API and service workers. It is not supported in all browsers or on all devices, and some users may have restrictions that disable background synchronization. In such cases, requests may fail permanently unless alternative fallback mechanisms are provided.

See also: Workbox, service workers, background sync API.