The index read-only property of the ServiceWorkerRegistration interface returns a reference to the ContentIndex interface, which allows for indexing of offline content.

A ContentIndex object.

You can access the property from either your main script or the registered service worker.

Here is an example from the main script:

// reference registration
const registration = await navigator.serviceWorker.ready;

// feature detection
if ("index" in registration) {
  // Content Index API functionality
  const contentIndex = registration.index;
}

From the service worker:

// service worker script

const contentIndex = self.registration.index;

• Content Index API
• An introductory article on the Content Index API
• An app which uses the Content Index API to list and remove 'save for later' content