Background Sync Failed — Service Worker Offline Data Sync Errors

Overview

Fix Background Sync API failures where offline actions queued by Service Workers fail to sync when the browser regains network connectivity.

Key Details

• Background Sync allows Service Workers to defer actions until the user has stable network connectivity
• The sync event fires in the Service Worker when the browser detects a stable network connection
• If the sync handler fails, the browser retries with exponential backoff
• After a maximum number of retries (browser-dependent), the sync is abandoned
• Background Sync requires a registered Service Worker and user has visited the site recently

Common Causes

• Service Worker sync event handler throwing an error or rejecting the promise
• Network connection detected but the target API server is unreachable
• Sync data stored in IndexedDB was deleted or corrupted before the sync could complete
• Browser killed the Service Worker before the sync event could complete (battery saver, memory pressure)

Steps

1. 1Check Service Worker logs: DevTools > Application > Service Workers > check for sync event errors
2. 2Verify IndexedDB data: DevTools > Application > IndexedDB > check if queued data is intact
3. 3Test sync handler manually: in Service Worker DevTools, simulate the sync event
4. 4Implement proper error handling: catch errors in the sync handler and re-queue failed operations
5. 5Notify the user if sync fails permanently so they can retry the action manually

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