The read-only id property of the ContentIndexEvent interface is a String which identifies the deleted content index via its id.

A String representation of the deleted content index id.

This example listens for the contentdelete event and logs the removed content index id.

The ContentIndexEvent is only available to the global scope of a ServiceWorker.

self.addEventListener("contentdelete", (event) => {
  console.log(event.id);

  // logs content index id, which can then be used to determine what content to delete from your cache
});

• An introductory article on the Content Index API
• An app which uses the Content Index API to list and remove 'save for later' content
• Service Worker API, along with information about Cache and CacheStorage