The tag read-only property of the PeriodicSyncEvent interface returns the developer-defined identifier for the PeriodicSyncEvent. This is specified when calling the PeriodicSyncManager.register() method of the PeriodicSyncManager interface. Multiple tags can be used by the web app to run different periodic tasks at different frequencies.

Returns a String of the defined identifier.

The following example demonstrates listening for a periodic sync event in the service worker, and accessing the tag property.

self.addEventListener("periodicsync", (event) => {
  console.log(event.tag); // logs the events tag
});

• Richer offline experiences with the Periodic Background Sync API
• A Periodic Background Sync demo app